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Approximately 45% of the human genome is comprised of transposable elements (TEs), also known as mobile genetic elements. However, their biological function remains largely unknown. Among them, retrotransposons are particularly abundant, and some of the copies are still capable of mobilization within the genome through RNA intermediates. This review focuses on the life cycle of human retrotransposons and summarizes their regulatory mechanisms and impacts on cellular processes. Retrotransposons are generally epigenetically silenced in somatic cells, but are transcriptionally reactivated under certain conditions, such as tumorigenesis, development, stress, and ageing, potentially leading to genetic instability. We explored the dual nature of retrotransposons as genomic parasites and regulatory elements, focusing on their roles in genetic diversity and innate immunity. Furthermore, we discuss how host factors regulate retrotransposon RNA and cDNA intermediates through their binding, modification, and degradation. The interplay between retrotransposons and the host machinery provides insight into the complex regulation of retrotransposons and the potential for retrotransposon dysregulation to cause aberrant responses leading to inflammation and autoimmune diseases.

Human endogenous retroviruses (HERVs) are genomic fragments integrated into human DNA from germline infections by exogenous retroviruses that threatened primates early in their evolution and are inherited vertically in the germline. So far, HERVs have been studied in the context of extensive immunopathogenic, neuropathogenic and even oncogenic effects within their host. In particular, in our paper, we elaborate on the aspects related to the possible correlation of transposable HERV elements' activation and SARS-CoV-2 spike protein's presence in cells of COVID-19 patients or upon COVID-19 vaccination with implications for natural and adaptive immunity. In particular, the release of cytokines TNF-α, IL-1β and IL-6 occurs in such cases and plays a notable role in sustaining chronic inflammation. Moreover, well-known interindividual variations of HERVs might partially account for the interpersonal variability of COVID-19 symptoms or unwanted events post-vaccination. Accordingly, further studies are required to clarify the SARS-CoV-2 spike protein's role in triggering HERVs. [ABSTRACT FROM AUTHOR]

Papillary thyroid cancer (PTC) is one of the fastest-growing cancers worldwide, lacking established causal factors or validated early diagnostics. Human endogenous retroviruses (HERVs), comprising 8% of human genomes, have potential as PTC biomarkers due to their comparably high baseline expression in healthy thyroid tissues, indicating homeostatic roles. However, HERV regions are often overlooked in genome-wide association studies because of their highly repetitive nature, low sequence coverage, and decreased sequencing quality. Using targeted whole-genome sequence analysis in conjunction with high sequencing depth to overcome methodological limitations, we identified associations of specific HERV variants with PTC. Analyzing WGS data from 138 patients with PTC generated through The Cancer Genome Atlas project and 2015 control samples from the 1000 Genomes Project, we examined the mutational variation in HERVs within a 20 kb radius of known cancer predisposition genes (CPGs) differentially expressed in PTC. We discovered 15 common and 13 rare germline HERV variants near or within 20 CPGs that distinguish patients with PTC from healthy controls. We identified intragenic–intronic HERV variants within RYR2, LRP1B, FN1, MET, TCRVB, UNC5D, TRPM3, CNTN5, CD70, RYR1, RUNX1, CRLF2, and PCDH1X, and three variants downstream of SERPINA1 and RUNX1T1. Sanger sequencing analyses of 20 thyroid and 5 non-thyroid cancer cell lines confirmed associations with PTC, particularly for MSTA HERV-L variant rs200077102 within the FN1 gene and HERV-L MLT1A LTR variant rs78588384 within the CNTN5 gene. Variant rs78588384, in particular, was shown in our analyses to be located within a POL2 binding site regulating an alternative transcript of CNTN5. In addition, we identified 16 variants that modified the poly(A) region in Alu elements, potentially altering the potential to retrotranspose. In conclusion, this study serves as a proof-of-concept for targeted variant analysis of HERV regions and establishes a basis for further exploration of HERVs in thyroid cancer development. [ABSTRACT FROM AUTHOR]

Abstract Background Decoding human genomic sequences requires comprehensive analysis of DNA sequence functionality. Through computational and experimental approaches, researchers have studied the genotype-phenotype relationship and generate important datasets that help unravel complicated genetic blueprints. Thus, the recently developed artificial intelligence methods can be used to interpret the functions of those DNA sequences. Methods This study explores the use of deep learning, particularly pre-trained genomic models like DNA_bert_6 and human_gpt2-v1, in interpreting and representing human genome sequences. Initially, we meticulously constructed multiple datasets linking genotypes and phenotypes to fine-tune those models for precise DNA sequence classification. Additionally, we evaluate the influence of sequence length on classification results and analyze the impact of feature extraction in the hidden layers of our model using the HERV dataset. To enhance our understanding of phenotype-specific patterns recognized by the model, we perform enrichment, pathogenicity and conservation analyzes of specific motifs in the human endogenous retrovirus (HERV) sequence with high average local representation weight (ALRW) scores. Results We have constructed multiple genotype-phenotype datasets displaying commendable classification performance in comparison with random genomic sequences, particularly in the HERV dataset, which achieved binary and multi-classification accuracies and F1 values exceeding 0.935 and 0.888, respectively. Notably, the fine-tuning of the HERV dataset not only improved our ability to identify and distinguish diverse information types within DNA sequences but also successfully identified specific motifs associated with neurological disorders and cancers in regions with high ALRW scores. Subsequent analysis of these motifs shed light on the adaptive responses of species to environmental pressures and their co-evolution with pathogens. Conclusions These findings highlight the potential of pre-trained genomic models in learning DNA sequence representations, particularly when utilizing the HERV dataset, and provide valuable insights for future research endeavors. This study represents an innovative strategy that combines pre-trained genomic model representations with classical methods for analyzing the functionality of genome sequences, thereby promoting cross-fertilization between genomics and artificial intelligence.

Background: Decoding human genomic sequences requires comprehensive analysis of DNA sequence functionality. Through computational and experimental approaches, researchers have studied the genotype-phenotype relationship and generate important datasets that help unravel complicated genetic blueprints. Thus, the recently developed artificial intelligence methods can be used to interpret the functions of those DNA sequences. Methods: This study explores the use of deep learning, particularly pre-trained genomic models like DNA_bert_6 and human_gpt2-v1, in interpreting and representing human genome sequences. Initially, we meticulously constructed multiple datasets linking genotypes and phenotypes to fine-tune those models for precise DNA sequence classification. Additionally, we evaluate the influence of sequence length on classification results and analyze the impact of feature extraction in the hidden layers of our model using the HERV dataset. To enhance our understanding of phenotype-specific patterns recognized by the model, we perform enrichment, pathogenicity and conservation analyzes of specific motifs in the human endogenous retrovirus (HERV) sequence with high average local representation weight (ALRW) scores. Results: We have constructed multiple genotype-phenotype datasets displaying commendable classification performance in comparison with random genomic sequences, particularly in the HERV dataset, which achieved binary and multi-classification accuracies and F1 values exceeding 0.935 and 0.888, respectively. Notably, the fine-tuning of the HERV dataset not only improved our ability to identify and distinguish diverse information types within DNA sequences but also successfully identified specific motifs associated with neurological disorders and cancers in regions with high ALRW scores. Subsequent analysis of these motifs shed light on the adaptive responses of species to environmental pressures and their co-evolution with pathogens. Conclusions: These findings highlight the potential of pre-trained genomic models in learning DNA sequence representations, particularly when utilizing the HERV dataset, and provide valuable insights for future research endeavors. This study represents an innovative strategy that combines pre-trained genomic model representations with classical methods for analyzing the functionality of genome sequences, thereby promoting cross-fertilization between genomics and artificial intelligence. [ABSTRACT FROM AUTHOR]

Despite remarkable progress, a cure for HIV-1 infection remains elusive. Rebound competent latent and transcriptionally active reservoir cells persevere despite antiretroviral therapy and rekindle infection due to inefficient proviral silencing. We propose a novel "block-lock-stop" approach, entailing long term durable silencing of viral expression towards an irreversible transcriptionally inactive latent provirus to achieve long term antiretroviral free control of the virus. A graded transformation of remnant HIV-1 in PLWH from persistent into silent to permanently defective proviruses is proposed, emulating and accelerating the natural path that human endogenous retroviruses (HERVs) take over millions of years. This hypothesis was based on research into delineating the mechanisms of HIV-1 latency, lessons from latency reversing agents and advances of Tat inhibitors, as well as expertise in the biology of HERVs. Insights from elite controllers and the availability of advanced genome engineering technologies for the direct excision of remnant virus set the stage for a rapid path to an HIV-1 cure.

Papillary thyroid cancer (PTC) is one of the fastest-growing cancers worldwide, lacking established causal factors or validated early diagnostics. Human endogenous retroviruses (HERVs), comprising 8% of human genomes, have potential as PTC biomarkers due to their comparably high baseline expression in healthy thyroid tissues, indicating homeostatic roles. However, HERV regions are often overlooked in genome-wide association studies because of their highly repetitive nature, low sequence coverage, and decreased sequencing quality. Using targeted whole-genome sequence analysis in conjunction with high sequencing depth to overcome methodological limitations, we identified associations of specific HERV variants with PTC. Analyzing WGS data from 138 patients with PTC generated through The Cancer Genome Atlas project and 2015 control samples from the 1000 Genomes Project, we examined the mutational variation in HERVs within a 20 kb radius of known cancer predisposition genes (CPGs) differentially expressed in PTC. We discovered 15 common and 13 rare germline HERV variants near or within 20 CPGs that distinguish patients with PTC from healthy controls. We identified intragenic–intronic HERV variants within RYR2, LRP1B, FN1, MET, TCRVB, UNC5D, TRPM3, CNTN5, CD70, RYR1, RUNX1, CRLF2, and PCDH1X, and three variants downstream of SERPINA1 and RUNX1T1. Sanger sequencing analyses of 20 thyroid and 5 non-thyroid cancer cell lines confirmed associations with PTC, particularly for MSTA HERV-L variant rs200077102 within the FN1 gene and HERV-L MLT1A LTR variant rs78588384 within the CNTN5 gene. Variant rs78588384, in particular, was shown in our analyses to be located within a POL2 binding site regulating an alternative transcript of CNTN5. In addition, we identified 16 variants that modified the poly(A) region in Alu elements, potentially altering the potential to retrotranspose. In conclusion, this study serves as a proof-of-concept for targeted variant analysis of HERV regions and establishes a basis for further exploration of HERVs in thyroid cancer development.

Male infertility is a multifactorial heterogeneous reproductive disorder in which genetic, epigenetic, and environmental factors play a role in the development of disease. Recent studies have shown that retrotransposon expression alterations may be related to impairment of spermatogenesis. Therefore, in this pilot study, we aimed to investigate whether HERV-K6 and HERV-K11 insertional variations have a role in idiopathic infertility among normozoospermic men. Genomic DNA isolated from the blood samples of 41 infertile normozoospermic and 45 fertile normozoospermic men were analyzed by inter-retrotransposon polymorphism polymerase chain reaction. HERV-K6 variation rates in the infertile and the fertile group were 0–58.3% and 0–53.4%, respectively. The variation rates of HERV-K11 were 0–75.0% in infertile and 0–77.8% in fertile men. The HERV-K6 and HERV-K11 insertion rates of the fertile group were higher than the infertile group (P < 0.0001 and P = 0.007, respectively). The findings of the study suggest that HERV-K6 and HERV-K11 retrotransposon insertion show variation among individuals, and their insertions might be associated with male infertility. [ABSTRACT FROM AUTHOR]

Approximately 45% of the human genome is comprised of transposable elements (TEs), also known as mobile genetic elements. However, their biological function remains largely unknown. Among them, retrotransposons are particularly abundant, and some of the copies are still capable of mobilization within the genome through RNA intermediates. This review focuses on the life cycle of human retrotransposons and summarizes their regulatory mechanisms and impacts on cellular processes. Retrotransposons are generally epigenetically silenced in somatic cells, but are transcriptionally reactivated under certain conditions, such as tumorigenesis, development, stress, and ageing, potentially leading to genetic instability. We explored the dual nature of retrotransposons as genomic parasites and regulatory elements, focusing on their roles in genetic diversity and innate immunity. Furthermore, we discuss how host factors regulate retrotransposon RNA and cDNA intermediates through their binding, modification, and degradation. The interplay between retrotransposons and the host machinery provides insight into the complex regulation of retrotransposons and the potential for retrotransposon dysregulation to cause aberrant responses leading to inflammation and autoimmune diseases. [ABSTRACT FROM AUTHOR]

While studies demonstrating the expression of repetitive elements (REs) in psoriatic skin using RNA-seq have been published before, not many studies have focused on the genome-wide expression patterns using larger cohorts. This study investigated the transcriptional landscape of differentially expressed REs in lesional and non-lesional skin from two previously published large datasets. We observed significant differential expression of REs in lesional psoriatic skin as well as the skin of healthy controls. Significant downregulation of several ERVs, HERVs (including HERV-K) and LINEs was observed in lesional psoriatic skin from both datasets. The upregulation of a small subset of HERV-Ks and Alus in lesional psoriatic skin was also reported. An interesting finding from this expression data was the significant upregulation and overlapping of tRNA repetitive elements in lesional and non-lesional psoriatic skin. The data from this study indicate the potential role of REs in the immunopathogenesis of psoriasis. The expression data from the two independent large study cohorts are powerful enough to confidently verify the differential expression of REs in relation to psoriatic skin pathology. Further studies are warranted to understand the functional impact of these repetitive elements in psoriasis pathogenesis, thereby expanding their significance as a potential targeting pathway for the disease treatment of psoriasis and other inflammatory diseases. [ABSTRACT FROM AUTHOR]

Interspersed repetitive sequence (IRS) consists of various classes. IRS methylation possesses different levels in cell type, cell condition, and pathogenesis of the disease. The current study aimed to evaluate IRS methylation in HIV-1 infected T lymphocytes in patients living with human immunodeficiency virus (HIV) (PLWH). We examined HERV-E LTR2C, HERV-K LTR5Hs, LINE-1, and Alu methylation status in CD4+ T cells and non-CD4+ T cells such as CD8+ T cells of people living with HIV (PLWH) in comparison with healthy donors. Later, we infected peripheral blood mononuclear cells (PBMCs) from healthy donors with HIV-1 and observed methylation level changes of HERV-K and HERV-E for up to 14 days. We found that the methylation of LINE-1 and Alu did not change significantly in either CD4+ or CD8+ T cells. Interestingly, we observed a significant increase in HERV-K methylation and a significant reduction in HERV-E methylation in both cell types. In the HIV-1 infected T lymphocytes experiment, after 4 days, we noticed a reduction in HERV-K methylation and an induction of HERV-E methylation. Nevertheless, there are trends of increased HERV-K methylation and decreased HERV-E methylation on days 7, 10, and 14. The IRS methylation changes were not associated with the HIV-1 quantity. In summary, IRS methylation level was cell type specific. HERV elements methylation had a different pattern in PLWH. The present study provided fundamental knowledge of IRS methylation in T cells of PLWH. The mechanisms and consequences of these virus-associated epigenetic changes should be further investigated. [ABSTRACT FROM AUTHOR]

Cell fusion in the placenta is tightly regulated. Suppressyn is a human placental endogenous retroviral protein that inhibits the profusogenic activities of another well-described endogenous retroviral protein, syncytin-1. In this study, we aimed to elucidate the mechanisms underlying suppressyn's placenta-specific expression. We identified the promoter region and a novel enhancer region for the gene encoding suppressyn, ERVH48-1, and examined their regulation via DNA methylation and their responses to changes in the oxygen concentration. Like other endogenous retroviral genes, the ERVH48-1 promoter sequence is found within a characteristic retroviral 5′ LTR sequence. The novel enhancer sequence we describe here is downstream of this LTR sequence (designated EIEs: ERV internal enhancer sequence) and governs placental expression. The placenta-specific expression of ERVH48-1 is tightly controlled by DNA methylation and further regulated by oxygen concentration-dependent, hypoxia-induced transcription factors (HIF1α and HIF2α). Our findings highlight the involvement of (1) tissue specificity through DNA methylation, (2) expression specificity through placenta-specific enhancer regions, and (3) the regulation of suppressyn expression in differing oxygen conditions by HIF1α and HIF2α. We suggest that these regulatory mechanisms are central to normal and abnormal placental development, including the development of disorders of pregnancy involving altered oxygenation, such as preeclampsia, pregnancy-induced hypertension, and fetal growth restriction. [ABSTRACT FROM AUTHOR]

ABSTRACT Human endogenous retroviruses (HERVs) integrated into the human genome millions of years ago, and their expression has been described both in healthy tissues and in pathology. In the present study, we study the differential expression of multiple HERV families in the presence of human immunodeficiency virus (HIV) infection in the peripheral blood mononuclear cells (PBMCs) of HIV-positive individuals, in HIV-infected cell lines, and in vitro HIV-infected macrophages/monocytes of healthy donors, utilizing publicly available data sets for secondary analysis using a pipeline appropriate for HERV transcription detection and comparison. We recognized significantly decreased expression of HERV-H in treatment-naïve HIV patients with viremia and increased expression of multiple HERV families in the PBMCs of HIV-infected individuals under combination antiretroviral therapy compared to healthy donors, in in vitro HIV-infected Stanford University pediatric T (SUP-T1) cells at 24 hours after HIV infection compared to non-infected SUP-T1 cells, and in in vitro HIV-infected MT4 T cells at 3 days after HIV infection compared to non-infected MT4 T cells. We recognized significantly increased expression of HERV-W, after HIV infection in monocyte-derived macrophage cell culture; no difference was found in HERV expression after HIV infection of monocyte cultures. We found a significantly decreased expression of HERV-K (HML-6) in donor-derived macrophage cultures at 36 hours after HIV infection, which does not persist at 6 days after infection. HIV infection modifies the expression of multiple HERV families in the PBMCs of HIV patients and in T cell-derived cultures, while the effect of HIV infection on HERV expression appears to be more restricted in cells of monocytic origin. IMPORTANCE In this work, we demonstrated that human immunodeficiency virus (HIV) infection leads to the modification of the human endogenous retrovirus (HERV) expression. Differential expression of multiple HERVs was found in peripheral blood mononuclear cells derived from HIV-infected patients compared to healthy donors and HIV-infected T cell cultures compared to non-infected. The effect of HIV presence on HERV expression appears to be more restricted in cells of monocytic origin, as only deregulation of HERV-W and HERV-K (HML-6) was found in these cell cultures after their infection with HIV. Multiple factors contribute to this aberrant HERV expression, and its levels appear to be modified in a time-dependent manner. Further studies and the development of optimized in vitro protocols are warranted to elucidate the interactions between HIV and HERVs in detail.

Introduction: Human endogenous retroviruses (HERVs) are transcriptionally-active remnants of ancient retroviral infections that may play a role in Alzheimer's disease. Methods: We combined two, publicly available RNA-Seq datasets with a third, novel dataset for a total cohort of 103 patients with Alzheimer's disease and 45 healthy controls. We use telescope to perform HERV quantification for these samples and simultaneously perform gene expression analysis. Results: We identify differentially expressed genes and differentially expressed HERVs in Alzheimer's disease patients. Differentially expressed HERVs are scattered throughout the genome; many of them are members of the HERVK superfamily. A number of HERVs are correlated with the expression of dysregulated genes in Alzheimer's and are physically proximal to genes which drive disease pathways. Discussion: Dysregulated expression of ancient retroviral insertions in the human genome are present in Alzheimer's disease and show localization patterns that may explain how these elements drive pathogenic gene expression. [ABSTRACT FROM AUTHOR]

IntroductionHuman endogenous retroviruses (HERVs) are transcriptionally-active remnants of ancient retroviral infections that may play a role in Alzheimer’s disease.MethodsWe combined two, publicly available RNA-Seq datasets with a third, novel dataset for a total cohort of 103 patients with Alzheimer’s disease and 45 healthy controls. We use telescope to perform HERV quantification for these samples and simultaneously perform gene expression analysis.ResultsWe identify differentially expressed genes and differentially expressed HERVs in Alzheimer’s disease patients. Differentially expressed HERVs are scattered throughout the genome; many of them are members of the HERV-K superfamily. A number of HERVs are correlated with the expression of dysregulated genes in Alzheimer’s and are physically proximal to genes which drive disease pathways.DiscussionDysregulated expression of ancient retroviral insertions in the human genome are present in Alzheimer’s disease and show localization patterns that may explain how these elements drive pathogenic gene expression.

Introduction: Our research group and others demonstrated the implication of the human endogenous retroviruses (HERVs) in SARS-CoV-2 infection and their association with disease progression, suggesting HERVs as contributing factors in COVID-19 immunopathology. To identify early predictive biomarkers of the COVID-19 severity, we analyzed the expression of HERVs and inflammatory mediators in SARS-CoV-2-positive and -negative nasopharyngeal/oropharyngeal swabs with respect to biochemical parameters and clinical outcome. Methods: Residuals of swab samples (20 SARS-CoV-2-negative and 43 SARSCoV-2-positive) were collected during the first wave of the pandemic and expression levels of HERVs and inflammatory mediators were analyzed by qRTReal time PCR. Results: The results obtained show that infection with SARS-CoV-2 resulted in a general increase in the expression of HERVs and mediators of the immune response. In particular, SARS-CoV-2 infection is associated with increased expression of HERV-K and HERV-W, IL-1ß, IL-6, IL-17, TNF-α, MCP-1, INF-γ, TLR-3, and TLR-7, while lower levels of IL-10, IFN-α, IFN-ß, and TLR-4 were found in individuals who underwent hospitalization. Moreover, higher expression of HERV-W, IL-1ß, IL-6, IFN-α, and IFN-ß reflected the respiratory outcome of patients during hospitalization. Interestingly, a machine learning model was able to classify hospitalized vs not hospitalized patients with good accuracy based on the expression levels of HERV-K, HERV-W, IL-6, TNF-a, TLR-3, TLR-7, and the N gene of SARS-CoV-2. These latest biomarkers also correlated with parameters of coagulation and inflammation. Discussion: Overall, the present results suggest HERVs as contributing elements in COVID-19 and early genomic biomarkers to predict COVID-19 severity and disease outcome. [ABSTRACT FROM AUTHOR]

Transposable Elements (TE) are mobile DNA elements that can replicate and insert themselves into different locations within the host genome. Their propensity to self-propagate has a myriad of consequences and yet their biological significance is not well-understood. Indeed, retrotransposons have evaded evolutionary attempts at repression and may contribute to somatic mosaicism. Retrotransposons are emerging as potent regulatory elements within the human genome. In the diseased state, there is mounting evidence that endogenous retroelements play a role in etiopathogenesis of inflammatory diseases, with a disposition for both autoimmune and neurological disorders. We postulate that active mobile genetic elements contribute more to human disease pathogenesis than previously thought.

Human endogenous retroviruses represent approximately 8% of our genome. Most of these sequences are defective except for a few genes such as the ancestral retroviral HEMO envelope gene (Human Endogenous MER34 ORF), recently characterized by our group. In this study, we characterized transcriptional activation of HEMO in primary tumors from The Cancer Genome Atlas (TCGA) and in metastatic tumors from a Gustave Roussy cohort. Pan‐cancer detection of the HEMO protein in a series of patient samples validated these results. Differential gene expression analysis in various TCGA datasets revealed a link between HEMO expression and activation of Wnt/β‐catenin signaling, in particular in endometrial cancer. Studies on cell models led us to propose that the Wnt/β‐catenin pathway could act as an upstream regulator of this retroviral endogenous sequence in tumor condition. Characterization of transcriptomic profiles of both HEMOLow and HEMOHigh tumors suggested that activation of HEMO is negatively associated with immune response signatures. Taken together, these results highlight that HEMO, as an endogenous retroviral envelope protein specifically expressed in tumors, represents a promising tumor biomarker and therapeutic target.

IntroductionOur research group and others demonstrated the implication of the human endogenous retroviruses (HERVs) in SARS-CoV-2 infection and their association with disease progression, suggesting HERVs as contributing factors in COVID-19 immunopathology. To identify early predictive biomarkers of the COVID-19 severity, we analyzed the expression of HERVs and inflammatory mediators in SARS-CoV-2-positive and -negative nasopharyngeal/oropharyngeal swabs with respect to biochemical parameters and clinical outcome.MethodsResiduals of swab samples (20 SARS-CoV-2-negative and 43 SARS-CoV-2-positive) were collected during the first wave of the pandemic and expression levels of HERVs and inflammatory mediators were analyzed by qRT-Real time PCR.ResultsThe results obtained show that infection with SARS-CoV-2 resulted in a general increase in the expression of HERVs and mediators of the immune response. In particular, SARS-CoV-2 infection is associated with increased expression of HERV-K and HERV-W, IL-1β, IL-6, IL-17, TNF-α, MCP-1, INF-γ, TLR-3, and TLR-7, while lower levels of IL-10, IFN-α, IFN-β, and TLR-4 were found in individuals who underwent hospitalization. Moreover, higher expression of HERV-W, IL-1β, IL-6, IFN-α, and IFN-β reflected the respiratory outcome of patients during hospitalization. Interestingly, a machine learning model was able to classify hospitalized vs not hospitalized patients with good accuracy based on the expression levels of HERV-K, HERV-W, IL-6, TNF-a, TLR-3, TLR-7, and the N gene of SARS-CoV-2. These latest biomarkers also correlated with parameters of coagulation and inflammation.DiscussionOverall, the present results suggest HERVs as contributing elements in COVID-19 and early genomic biomarkers to predict COVID-19 severity and disease outcome.

Human endogenous retroviruses (HERVs) are proviral relics of infections that affected primates' germ line. Many HERV elements retain a residual capacity to encode transcripts and proteins that have been occasionally domesticated for the host physiology. In addition, HERV transcriptional modulation is of great interest to clarify the etiology of complex disorders such as cancer, even if a few studies assessed the specific HERV loci modulated in tumor tissues. In the present work, we used a transcriptomic approach to investigate the specific expression of ~3300 HERV loci in paired tumor and normal tissues of 7 colorectal cancer (CRC) patients. A total of 102 HERVs were significantly modulated in CRC, with a general tendency towards downregulation. Of note, among the 42 upregulated HERVs 23 belonged to the HERV-H group, that is the most investigated in CRC. De novo transcriptome reconstruction and qPCR validation allowed to identify a transcript from a HERV-H locus on chromosome Xp22.3 with high specific expression in CRC samples, potentially encoding for a partial Pol protein. These results provide a detailed description of HERV transcriptional variations in CRC and its interindividual variability, identifying a HERV-H transcript that deserves further investigation for its possible impact on tumor progression., (© 2025 The Author(s). Journal of Medical Virology published by Wiley Periodicals LLC.)

Lentivirus (LV) vectors offer permanent delivery of therapeutic genes to the host through an RNA intermediate genome. They are one of the most commonly used vectors for clinical gene therapy of inherited disorders such as immune deficiencies and cancer immunotherapy. One of the most difficult challenges facing their widespread application to patients is the large-scale production of highly pure vector stocks. To improve vector production and downstream purification, there has been a recent investment in the United Kingdom to establish good manufacturing process (GMP)-licensed centers for manufacture and quality control. Other requirements for these vectors include their target cell specificity and tropism, how to regulate gene expression of the therapeutic payload and their potential side effects. Comprehensive detail on the full nucleic acid content of LV is unknown, even though they have entered clinical trials. With potential adverse effects in mind, it is important to identify these contents to assess their safety and purity. In this study, we used highly sensitive PacBio long-distance, next-generation sequencing of reverse-transcribed vector component RNA to investigate the nucleic acid composition of recombinant HIV-1 particles generated by human 293T packaging cells. In this article, we describe our findings of nucleic acids other than the recombinant vector genome that exist, which could potentially be delivered during gene transfer, and suggest that removal of these unwanted components be considered before clinical LV application.

ABSTRACT SARS-CoV-2 infection is known to trigger an important inflammatory response, which has a major role in COVID-19 pathogenesis. In infectious and inflammatory contexts, the modulation of human endogenous retroviruses (HERV) has been broadly reported, being able to further sustain innate immune responses due to the expression of immunogenic viral transcripts, including double-stranded DNA (dsRNA), and eventually, immunogenic proteins. To gain insights on this poorly characterized interplay, we performed a high-throughput expression analysis of ~3,300 specific HERV loci in the peripheral blood mononuclear cells (PBMCs) of 10 healthy controls and 16 individuals being either convalescent after the infection (6) or retesting positive after convalescence (10) (Gene Expression Onmibus [GEO] data set GSE166253). Results showed that the exposure to SARS-CoV-2 infection modulates HERV expression according to the disease stage and reflecting COVID-19 immune signatures. The differential expression analysis between healthy control (HC) and COVID-19 patients allowed us to identify a total of 282 differentially expressed HERV loci (deHERV) in the individuals exposed to SARS-CoV-2 infection, independently from the clinical form. In addition, 278 and 60 deHERV loci that were specifically modulated in individuals convalescent after COVID19 infection (C) and patients that retested positive to SARS-CoV-2 after convalescence (RTP) as individually compared to HC, respectively, as well as 164 deHERV loci between C and RTP patients were identified. The identified HERV loci belonged to 36 different HERV groups, including members of all three classes. The present study provides an exhaustive picture of the HERV transcriptome in PBMCs and its dynamic variation in the presence of COVID-19, revealing specific modulation patterns according to the infection stage that can be relevant to the disease clinical manifestation and outcome. IMPORTANCE We report here the first high-throughput analysis of HERV loci expression along SARS-CoV-2 infection, as performed with peripheral blood mononuclear cells (PBMCs). Such cells are not directly infected by the virus but have a crucial role in the plethora of inflammatory and immune events that constitute a major hallmark of COVID-19 pathogenesis. Results provide a novel and exhaustive picture of HERV expression in PBMCs, revealing specific modulation patterns according to the disease condition and the concomitant immune activation. To our knowledge, this is the first set of deHERVs whose expression is dynamically modulated across COVID-19 stages, confirming a tight interplay between HERV and cellular immunity and revealing specific transcriptional signatures that can have an impact on the disease clinical manifestation and outcome.

IntroductionNight shift (NS) work has been associated with an increased risk of different conditions characterized by altered inflammatory and immune responses, such as cardio-metabolic and infectious diseases, cancer, and obesity. Epigenetic modifications, such as DNA methylation, might mirror alterations in biological processes that are influenced by NS work.MethodsThe present study was conducted on 94 healthy female workers with different working schedules and aimed at identifying whether NS was associated with plasmatic concentrations of the inflammatory proteins NLRP3 and TNF-alpha, as well as with DNA methylation levels of ten human endogenous retroviral (HERV) sequences, and nine genes selected for their role in immune and inflammatory processes. We also explored the possible role of the body mass index (BMI) as an additional susceptibility factor that might influence the effects of NS work on the tested epigenetic modifications.Results and discussionWe observed a positive association between NS and NLRP3 levels (p-value 0.0379). Moreover, NS workers retained different methylation levels for ERVFRD-1 (p-value = 0.0274), HERV-L (p-value = 0.0377), and HERV-P (p-value = 0.0140) elements, and for BIRC2 (p-value = 0.0460), FLRT3 (p-value = 0.0422), MIG6 (p-value = 0.0085), and SIRT1 (p-value = 0.0497) genes. We also observed that the BMI modified the relationship between NS and the methylation of ERVE, HERV-L, and ERVW-1 elements. Overall, our results suggest that HERV methylation could pose as a promising biomolecular sensor to monitor not only the effect of NS work but also the cumulative effect of multiple stressors.

Background: Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a chronic disease considered to be triggered by viral infections in a majority of cases. Symptoms overlap largely with those of post-acute sequelae of COVID-19/long-COVID implying common pathogenetic mechanisms. SARS-CoV-2 infection is risk factor for sustained latent virus reactivation that may account for the symptoms of post-viral fatigue syndromes. The aim of this study was first to investigate whether patients with ME/CFS and healthy donors (HDs) differed in their antibody response to mild/asymptomatic SARS-CoV-2 infection. Secondly, to analyze whether COVID-19 imposes latent virus reactivation in the cohorts. Methods: Anti-SARS-CoV-2 antibodies were analyzed in plasma and saliva from non-vaccinated ME/CFS (n=95) and HDs (n=110) using soluble multiplex immunoassay. Reactivation of human herpesviruses 1-6 (HSV1, HSV2, VZV, EBV, CMV, HHV6), and human endogenous retrovirus K (HERV-K) was detected by anti-viral antibody fingerprints in saliva. Results: At 3-6 months after mild/asymptomatic SARS-CoV-2 infection, virus-specific antibodies in saliva were substantially induced signifying a strong reactivation of latent viruses (EBV, HHV6 and HERV-K) in both cohorts. In patients with ME/CFS, antibody responses were significantly stronger, in particular EBV-encoded nuclear antigen-1 (EBNA1) IgG were elevated in patients with ME/CFS, but not in HDs. EBV-VCA IgG was also elevated at baseline prior to SARS-infection in patients compared to HDs. Conclusion: Our results denote an altered and chronically aroused anti-viral profile against latent viruses in ME/CFS. SARS-CoV-2 infection even in its mild/asymptomatic form is a potent trigger for reactivation of latent herpesviruses (EBV, HHV6) and endogenous retroviruses (HERV-K), as detected by antibody fingerprints locally in the oral mucosa (saliva samples). This has not been shown before because the antibody elevation is not detected systemically in the circulation/plasma. asymptomatic form is a potent trigger for reactivation of latent herpesviruses (EBV, HHV6) and endogenous retroviruses (HERV-K), as detected by antibody fingerprints locally in the oral mucosa (saliva samples). This has not been shown before because the antibody elevation is not detected systemically in the circulation/plasma. [ABSTRACT FROM AUTHOR]

The expression of genes is altered in various diseases and is responsible for the disease's initiation, progression and pathology. Several other genes, predominantly inactivated, may become activated in a given condition and contribute to the initiation and progression of the disease. Similarly, human endogenous viruses (HERVs) are an incomplete, non-productive and inactive viral sequence present in the heterochromatin of the human genome, and are often referred to as junk DNA. HERVs were inserted into the host genome millions of years ago. However, they were silenced due to multiple mutations and recombination that occurred over time. However, their expression is increased in cancers due to either epigenetic or transcriptional dysregulation. Some of the HERVs having intact open reading frames have been reported to express virus-like particles, functional peptides and proteins involved in tumorigenesis. To summarize, there is involvement of different HERVs in the initiation and progression of several cancers. The present review aims to provide concise information on HERV and its involvement in the initiation and progression of multiple types of cancer. [ABSTRACT FROM AUTHOR]

Human endogenous retroviruses (HERVs) are ‘fossil viruses’ that resulted from stable integrations of exogenous retroviruses throughout evolution. HERVs are defective and do not produce infectious viral particles. However, some HERVs retain a limited coding capacity and produce retroviral transcripts and proteins, which function in human developmental process and various pathologies, including many cancers and neurological diseases. Recently, it has been reported that HERVs are differently expressed in COVID-19 disease caused by infection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In this review, we discuss the molecular structure and function of HERV ENV proteins, particularly syncytins, and their conventional roles in human development and diseases, and potential involvement in COVID-19 regarding the newly reported mental symptoms. We also address COVID-19 vaccine-related infertility concerns arising from the similarity of syncytin with the spike protein of SARS-CoV-2, which have been proved invalid.

Abstract Zhang et al. (Proc Natl Acad Sci 118:e2105968118, 2021) recently reported that SARS-CoV-2 RNA can be retrotranscribed and integrated into the DNA of human cells by the L1 retrotransposon machinery. This phenomenon could cause persistence of viral sequences in patients and may explain the prolonged PCR-positivity of SARS-CoV-2 infected patients, even long after the phase of active virus replication has ended. This commentary does critically review the available data on this topic and discusses them in the context of findings made for other exogenous viruses and ancestral endogenous retroviral elements.

Repetitive sequences represent about half of the human genome. They are actively transcribed and play a role during development and in epigenetic regulation. The altered activity of repetitive sequences can lead to genomic instability and they can contribute to the establishment or the progression of degenerative diseases and cancer transformation. In this work, we analyzed the expression profiles of DNA repetitive sequences in the breast cancer specimens of the HMUCC cohort. Satellite expression is generally upregulated in breast cancers, with specific families upregulated per histotype: in HER2-enriched cancers, they are the human satellite II (HSATII), in luminal A and B, they are part of the ALR family and in triple-negative, they are part of SAR and GSAT families, together with a perturbation in the transcription from endogenous retroviruses and their LTR sequences. We report that the background expression of repetitive sequences in healthy tissues of cancer patients differs from the tissues of non-cancerous controls. To conclude, peculiar patterns of expression of repetitive sequences are reported in each specimen, especially in the case of transcripts arising from satellite repeats. [ABSTRACT FROM AUTHOR]

Skin inflammation and photosensitivity are common in lupus erythematosus (LE) patients, and ultraviolet (UV) light is a known trigger of skin and possibly systemic inflammation in systemic lupus erythematosus (SLE) and discoid lupus erythematosus (DLE) patients. Type I interferons (IFN) are upregulated in LE skin after UV exposure; however, the mechanisms to explain UVB‐induced inflammation remain unclear. Here, we demonstrated that UVB irradiation‐induced activation of human endogenous retroviruses (HERVs) plays a major role in the immune response. UVB‐induced HERV‐associated dsRNA transcription and subsequent activation of the innate antiviral RIG‐I/MDA5/IRF7 pathway led to downstream transcription of interferon‐stimulated genes, which promotes UVB‐induced apoptosis and proliferation inhibition in keratinocytes through RIG‐I and MDA5 pathways. Our findings indicate that UVB irradiation induces HERV‐dsRNA overexpression, and the dsRNA‐sensing innate immunity pathway promotes type I IFN production, which may be a potential mechanism of skin inflammatory response and skin lesion of SLE/DLE. [ABSTRACT FROM AUTHOR]

Many drugs have been evaluated to reactivate HIV-1 from cellular reservoirs, but the off-target effects of these latency reversal agents (LRA) remain poorly defined. Transposable elements (TEs) are reactivated during HIV-1 infection, but studies of potential off-target drug effects on TE expression have been limited. We analyzed the differential expression of TEs induced by canonical and non-canonical NF-κB signaling. We evaluated the effect of PKC agonists (Bryostatin and Ingenol B) on the expression of TEs in memory CD4+ T cells. Ingenol B induced 38 differentially expressed TEs (17 HERV (45%) and 21 L1 (55%)). Interestingly, TE expression in effector memory CD4+ T cells was more affected by Bryostatin compared to other memory T-cell subsets, with 121 (107 upregulated and 14 downregulated) differentially expressed (DE) TEs. Of these, 31% (n = 37) were HERVs, and 69% (n = 84) were LINE-1 (L1). AZD5582 induced 753 DE TEs (406 HERV (54%) and 347 L1 (46%)). Together, our findings show that canonical and non-canonical NF-κB signaling activation leads to retroelement expressions as an off-target effect. Furthermore, our data highlights the importance of exploring the interaction between LRAs and the expression of retroelements in the context of HIV-1 eradication strategies. [ABSTRACT FROM AUTHOR]

ABSTRACT The long terminal repeats (LTRs) of human endogenous retroviruses (HERVs) are distributed throughout the human genome and provide favorable conditions to regulate the expression of their adjacent genes. HML-2 is the most biologically active subgroup of the HERV-K family, and expression of its members has been associated with many cancer types. The LTRs of HML-2 have been classified into three subgroups (LTR5A, LTR5B, and LTR5Hs) based on phylogenetic analyses. The current study aimed to explore the LTR transcriptional activity differences among the three subtypes and further explore the underlying factors. A total of 43 LTR5A elements, 62 LTR5B elements, and 194 LTR5Hs elements were selected. A phylogenetic tree showed that the LTR5Hs group was clearly separated from the LTR5A and LTR5B groups. A luciferase reporter assay indicated that LTR5Hs had the strongest promoter activity, followed by LTR5A and LTR5B. To investigate the underlying factors, LTR5Hs was divided into 4 sections, and the homologous fragments in LTR5B were replaced successively. Replacement of the third section (−263 to 0) significantly increased LTR5B activity. Subsequent mutation experiments revealed that the increased transcriptional activity was induced by the TATA box and the two p53 binding sites within the section. Further interference with TP53 significantly decreased LTR5Hs transcriptional activity. Chromatin immunoprecipitation (ChIP) and CUT&Tag experiments finally confirmed the direct binding of the p53 protein with the two LTR5Hs p53 binding sites. Overall, the two p53 binding sites in the third section (−263 to 0) of LTR5Hs were revealed to play critical roles in the difference in transcriptional activity among the three subtypes. IMPORTANCE Human endogenous retroviruses (HERVs) were integrated into the human genome in ancient times and have been coevolving with the host. Since the Human Genome Project, HERVs have attracted increasing attention. Many studies have focused on their characterization, evolution, and biological function. In particular, the expression of HERV-K has been associated with many diseases, such as germ cell tumors, neurotoxicity, ovarian cancer, prostate cancer, and melanoma. Indeed, two HML-2-produced proteins, Np9 and Rec, are associated with certain cancers. However, their roles in these disease associations remain unclear. The current work focused on subgroup HML-2 of HERV-K, which is recognized as the most biologically active subgroup, and aimed to explore the mechanistic basis of transcriptional activity. The results revealed that p53 deeply determined the activity of HML-2 LTR5Hs. p53 is a rather important tumor suppressor protein. It can regulate the expression of genes related to cell cycle arrest, organic processes, and apoptosis in response to cellular stress and is critical for the control of homeostasis. Previous ChIP and expression studies of individual genes suggested that p53 sites in HERV LTRs may be part of the p53 transcription program and directly regulate p53 target genes in a species-specific manner. However, the exact function of p53 in the regulation of HERV LTR expression is largely elusive. Our results clearly demonstrated the interaction between LTR5Hs of HML-2 and p53. They are of great significance for the future comprehensive study of the physiological and pathological functions of LTRs of HERVs.

Human endogenous retroviruses (HERVs) occupy approximately 8% of the human genome. HERVs, transcribed in early embryos, are epigenetically silenced in somatic cells, except under pathological conditions. HERV-K is thought to protect embryos from exogenous viral infection. However, uncontrolled HERV-K expression in somatic cells has been implicated in several diseases. Here, we show that SOX2, which plays a key role in maintaining the pluripotency of stem cells, is critical for HERV-K LTR5Hs. HERV-K undergoes retrotransposition within producer cells in the absence of Env expression. Furthermore, we identified new HERV-K integration sites in long-term culture of induced pluripotent stem cells that express SOX2. These results suggest that the strict dependence of HERV-K on SOX2 has allowed HERV-K to protect early embryos during evolution while limiting the potentially harmful effects of HERV-K retrotransposition on host genome integrity in these early embryos. [ABSTRACT FROM AUTHOR]

Human endogenous retroviruses represent approximately 8% of our genome. Most of these sequences are defective except for a few genes such as the ancestral retroviral HEMO envelope gene (Human Endogenous MER34 ORF), recently characterized by our group. In this study, we characterized transcriptional activation of HEMO in primary tumors from The Cancer Genome Atlas (TCGA) and in metastatic tumors from a Gustave Roussy cohort. Pan-cancer detection of the HEMO protein in a series of patient samples validated these results. Differential gene expression analysis in various TCGA datasets revealed a link between HEMO expression and activation of Wnt/b-catenin signaling, in particular in endometrial cancer. Studies on cell models led us to propose that the Wnt/b-catenin pathway could act as an upstream regulator of this retroviral endogenous sequence in tumor condition. Characterization of transcriptomic profiles of both HEMOLow and HEMOHigh tumors suggested that activation of HEMO is negatively associated with immune response signatures. Taken together, these results highlight that HEMO, as an endogenous retroviral envelope protein specifically expressed in tumors, represents a promising tumor biomarker and therapeutic target. [ABSTRACT FROM AUTHOR]

The human genome comprises 8 % of endogenous retroviruses (HERVs). Though HERVS contribute to physiological functions, copies retained pathogenic potential. The HERV-W ENV protein was shown expressed in patients with worse COVID-19 symptoms and post-COVID syndrome. A significant detection of the mRNA encoding HERV-W ENV from patients with COVID-19 in B cells from RNAseq reads obtained from peripheral blond mononuclear cells. This data stratified with increased COVID-19 symptoms or with post-acute sequelae of COVID-19 (long COVID) after 3 months. The HERV-W ENV-U3R RNA was confirmed to display the best alignment with chromosome X ERVWE2 locus. However, a stop codon precluding its translation was re-addressed after recent understandings of ribosome readthrough mechanisms. Experimental results evidenced that this HERV gene can effectively express a full-length protein in the presence of molecules allowing translation via a readthrough mechanism at the ribosome level. Results not only confirm HERV-W ENV RNA origin in these patients but show for the first time how a defective HERV copy can be translated into a complete protein when specific factors make it possible at the ribosome level. The present proof of concept now requires further studies to identify the factors involved in this newly understood mechanism, following SARS-CoV-2 exposure., (Copyright © 2024 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved.)

Human endogenous retroviruses (HERVs) are 'fossil viruses' that resulted from stable integrations of exogenous retroviruses throughout evolution. HERVs are defective and do not produce infectious viral particles. However, some HERVs retain a limited coding capacity and produce retroviral transcripts and proteins, which function in human developmental process and various pathologies, including many cancers and neurological diseases. Recently, it has been reported that HERVs are differently expressed in COVID-19 disease caused by infection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In this review, we discuss the molecular structure and function of HERV ENV proteins, particularly syncytins, and their conventional roles in human development and diseases, and potential involvement in COVID-19 regarding the newly reported mental symptoms. We also address COVID-19 vaccine-related infertility concerns arising from the similarity of syncytin with the spike protein of SARS-CoV-2, which have been proved invalid. [ABSTRACT FROM AUTHOR]

BackgroundHuman Endogenous Retroviruses (HERVs) comprise about 8% of the human genome and have lost their ability to replicate or to produce infectious particles after having accumulated mutations over time. We assessed the kinetics of expression of HERV-K (HML-2) Envelope mRNA transcript and surface unit (SU) and transmembrane (TM) subunit proteins during HIV-1 infection. We also mapped the specificity of the humoral response to HERV-K (HML-2) Envelope protein in HIV-1 infected subjects at different stages of disease, and correlated the response with plasma viral load.ResultsWe found that HIV-1 modified HERV-K (HML-2) Env mRNA expression, resulting in the expression of a fully N-glycosylated HERV-K (HML-2) envelope protein on the cell surface. Serological mapping of HERV-K (HML-2) envelope protein linear epitopes revealed two major immunogenic domains, one on SU and another on the ectodomain of TM. The titers of HERV-K (HML-2) TM antibodies were dramatically increased in HIV-1 infected subjects (p

Pediatric T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive malignancy resulting from overproduction of immature T-cells in the thymus and is typified by widespread alterations in DNA methylation. As survival rates for relapsed T-ALL remain dismal (10 to 25%), development of targeted therapies to prevent relapse is key to improving prognosis. Whereas mutations in the DNA demethylating enzyme TET2 are frequent in adult T-cell malignancies, TET2 mutations in T-ALL are rare. Here, we analyzed RNA-sequencing data of 321 primary T-ALLs, 20 T-ALL cell lines, and 25 normal human tissues, revealing that TET2 is transcriptionally repressed or silenced in 71% and 17% of T-ALL, respectively. Furthermore, we show that TET2 silencing is often associated with hypermethylation of the TET2 promoter in primary T-ALL. Importantly, treatment with the DNA demethylating agent, 5-azacytidine (5-aza), was significantly more toxic to TET2-silenced T-ALL cells and resulted in stable re-expression of the TET2 gene. Additionally, 5-aza led to up-regulation of methylated genes and human endogenous retroviruses (HERVs), which was further enhanced by the addition of physiological levels of vitamin C, a potent enhancer of TET activity. Together, our results clearly identify 5-aza as a potential targeted therapy for TET2-silenced T-ALL. [ABSTRACT FROM AUTHOR]

Background: Human endogenous retroviruses (HERVs), remnants of ancestral infections, represent 8% of the human genome. HERVs are co-opted for important physiological functions during embryogenesis; however, little is known about their expression in human gametes. We evaluated the transcriptional levels of several retroviral sequences in human spermatozoa. Methods and results: We assessed, through a Real-Time PCR assay, the transcription levels of the pol genes of HERV-H, -K and -W families and of env genes of syncytin (Syn)1 and Syn2 in the spermatozoa from 8 normospermic subjects. The entity and distribution of their expressions were compared to values found in white blood cells (WBCs) from 16 healthy volunteers. The level of HERV transcripts was significantly lower in spermatozoa than in WBCs for HERV-H-pol, HERV-K-pol, HERV-W-pol, and Syn2.In contrast, the level of expression of Syn1 in the sperm was similar to that found in WBCs and it was significantly higher than the mRNA concentrations of other HERV genes in spermatozoa. Conclusions: Our findings show, for the first time, the presence of several retroviral mRNAs in the sperm, although in low amounts. The higher concentration of Syn1 suggests that it could play a key role in the fusion process between gametes during fertilization and, perhaps, be involved in embryo development. Further studies could clarify whether aberrant HERV expressions, in particular of Syn1, negatively affect fertilization and embryo growth and whether sperm manipulation procedures, such as cryopreservation, may potentially influence HERV transcription in the human male gamete. [ABSTRACT FROM AUTHOR]

Comprising ~40% of the human genome, retroelements are mobile genetic elements which are transcribed into RNA, then reverse-transcribed into DNA and inserted into a new site in the genome. Retroelements are referred to as "genetic parasites", residing among host genes and relying on host machinery for transcription and evolutionary propagation. The healthy brain has the highest expression of retroelement-derived sequences compared to other somatic tissue, which leads to the question: how does retroelement-derived RNA influence human traits and cellular states? While the functional importance of upregulating retroelement expression in the brain is an active area of research, RNA species derived from retroelements influence both self- and host gene expression by contributing to chromatin remodeling, alternative splicing, somatic mosaicism and translational repression. Here, we review the emerging evidence that the functional importance of RNA derived from retroelements is multifaceted. Retroelements can influence organismal states through the seeding of epigenetic states in chromatin, the production of structured RNA and even catalytically active ribozymes, the generation of cytoplasmic ssDNA and RNA/DNA hybrids, the production of viral-like proteins, and the generation of somatic mutations. Comparative sequencing suggests that retroelements can contribute to intraspecies variation through these mechanisms to alter transcript identity and abundance. In humans, an increasing number of neurodevelopmental and neurodegenerative conditions are associated with dysregulated retroelements, including Aicardi-Goutieres syndrome (AGS), Rett syndrome (RTT), Amyotrophic Lateral Sclerosis (ALS), Alzheimer's disease (AD), multiple sclerosis (MS), schizophrenia (SZ), and aging. Taken together, these concepts suggest a larger functional role for RNA derived from retroelements. This review aims to define retroelement-derived RNA, discuss how it impacts the mammalian genome, as well as summarize data supporting phenotypic consequences of this unique RNA subset in the brain. [ABSTRACT FROM AUTHOR]

Human endogenous retroviruses (HERVs) are remnants of ancient retroviral germline infections. Most HERV sequences are silenced in somatic cells, but interest is emerging on the involvement of HERV derived transcripts and proteins in human physiology and disease. A HERV‐W encoded protein, syncytin‐1, has been co‐opted into fetal physiology, where it plays a role in trophoblast formation. Altered HERV transcription and expression of HERV derived proteins are associated with various cancer types and neurological diseases such as multiple sclerosis (MS). The implication of HERVs as potential mediators of both health and disease suggests important roles of regulatory mechanisms and alterations of these in physiological and pathological processes. The regulation of HERV sequences is mediated by a wide variety of mechanisms, and the focus of this review is on selected aspects of these, including epigenetic mechanisms such as CpG methylation and histone modifications of the HP1‐H3K9me axis, viral transactivation events, and regulatory perspectives of transient stimuli in the microenvironment. Increasing knowledge of the regulation of HERV sequences will not only contribute to the understanding of complex pathogeneses, but also may pinpoint potential targets for better diagnosis and treatment in complex diseases as MS. [ABSTRACT FROM AUTHOR]

Molecular diagnostics is a rapidly growing branch of the clinical laboratory and has accelerated the advance of personalized medicine in the fields of pharmacogenomics, pharmacogenetics, and nutrigenomics. The versatility of molecular biology allows it to be effective in several medical fields that include reproduction, immunogenetics, and virology. Implementation of molecular and sequencing technology in reproductive medicine can add another layer of understanding to better define the causes behind infertility and recurrent reproductive loss. In the following, we examine current molecular methods for probing factors behind reproductive pregnancy loss including reverse transcription polymerase chain reaction and next generation sequencing (NGS). We review several current and potential genetic (DNA) and transcriptional (RNA)‐based parameters in women with infertility that can be significant in diagnosis and treatment. These molecular factors can be inferred either from genomic DNA or RNA locally within the endometrium. Furthermore, we consider infection‐based abnormalities such as human herpesvirus‐6 and severe acute respiratory syndrome coronavirus‐2 (SARS‐CoV‐2). Finally, we present future directions as well as data demonstrating the potential role of human endogenous retroviruses in pregnancy loss. We hope these discussions will assist the clinician in delineating some of the intricate molecular factors that can contribute to infertility and recurrent reproductive failures. [ABSTRACT FROM AUTHOR]

Many neurodegenerative diseases are associated with chronic inflammation in the brain and periphery giving rise to a continuous imbalance of immune processes. Next to inflammation markers, activation of transposable elements, including long intrespersed nuclear elements (LINE) elements and endogenous retroviruses (ERVs), has been identified during neurodegenerative disease progression and even correlated with the clinical severity of the disease. ERVs are remnants of viral infections in the human genome acquired during evolution. Upon activation, they produce transcripts and the phylogenetically youngest ones are still able to produce viral-like particles. In addition, ERVs can bind transcription factors and modulate immune response. Being between own and foreign, ERVs are reviewed in the context of viral infections of the central nervous system, in aging and neurodegenerative diseases. Moreover, this review tests the hypothesis that viral infection may be a trigger at the onset of neuroinflammation and that ERVs sustain the inflammatory imbalance by summarizing existing data of neurodegenerative diseases associated with viruses and/or ERVs.

Many neurodegenerative diseases are associated with chronic inflammation in the brain and periphery giving rise to a continuous imbalance of immune processes. Next to inflammation markers, activation of transposable elements, including long intrespersed nuclear elements (LINE) elements and endogenous retroviruses (ERVs), has been identified during neurodegenerative disease progression and even correlated with the clinical severity of the disease. ERVs are remnants of viral infections in the human genome acquired during evolution. Upon activation, they produce transcripts and the phylogenetically youngest ones are still able to produce viral-like particles. In addition, ERVs can bind transcription factors and modulate immune response. Being between own and foreign, ERVs are reviewed in the context of viral infections of the central nervous system, in aging and neurodegenerative diseases. Moreover, this review tests the hypothesis that viral infection may be a trigger at the onset of neuroinflammation and that ERVs sustain the inflammatory imbalance by summarizing existing data of neurodegenerative diseases associated with viruses and/or ERVs. [ABSTRACT FROM AUTHOR]

Human endogenous retroviruses (HERVs) and mammalian apparent long terminal repeat (LTR) retrotransposons (MaLRs) are retroviral sequences that integrated into germ line cells millions of years ago. Transcripts of these LTR retrotransposons are present in several tissues, and their expression is modulated in pathological conditions, although their function remains often far from being understood. Here, we focused on the HERV/MaLR expression and modulation in a scenario of immune system activation. We used a public data set of human peripheral blood mononuclear cells (PBMCs) RNA-Seq from 15 healthy participants to a clinical trial before and after exposure to lipopolysaccharide (LPS), for which we established an RNA-Seq workflow for the identification of expressed and modulated cellular genes and LTR retrotransposon elements. [ABSTRACT FROM AUTHOR]

• CD5 is a pan T cell marker and regulate its development, function, and activation. • Expression of an alternative exon(E1B) directly downregulated its surface expression. • This study reports a poly aromatic hydrocarbon (BaP) induced and AHR mediated upregulation of E1B expression. • This increase in E1B expression could play an essential role in regulation of TCR activity thus contributing towards functional anomalies. • CD5 is a crucial surface receptor of T cells, whose expression majorly affects its development, function, and overall biology. • Expression of a Human Endogenous Retrovirus (HERV) originated exon (E1B) directly downregulates the surface expression of CD5. • This study reports a polycyclic aromatic hydrocarbon i.e. BaP, induced upregulation of E1B expression in an AHR dependent manner, leads to the reduction of CD5 surface expression. • This mechanism improves our understanding of an environmental pollutant induced deregulation of t cell activity in humans. The function of CD5 protein in T cells is well documented, but regulation of its surface-level expression has yet to be fully understood. However, variation in its surface expression is associated with various immunopathological conditions and haematological malignancies. Briefly, expression of an alternate exon E1B of a human endogenous retroviruses (HERV) origin directly downregulates the conventional transcript variant (E1A), as its expression leads to the retention of the resultant protein at the intracellular level (cCD5). A separate promoter governs the expression of E1B and may be influenced by different transcription factors. Hence, we performed in silico transcription factor binding site (TFBS) analysis of the 3 kb upstream region from TSS of exon E1B and found five putative DREs (Dioxin Response elements) with good similarity scores. Further, we observed the upregulation in E1B expression after the exposure of BaP (a dioxin) and the reduction of E1A expression and their respective protein, i.e. sCD5 and cCD5. The binding of AHR at the predicted DRE sites was confirmed by ChIP qPCR and AHR specific inhibitor and gene silencing studies suggested the involvement of AHR in exonal switch. This study indicates that the polycyclic aromatic hydrocarbon decreases the sCD5 expression by upregulating alternative exon expression, which may adversely affect the overall T cell functions. [ABSTRACT FROM AUTHOR]