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The prevalence of Alzheimer's disease is greater in women, but the underlying mechanisms remain to be elucidated. We herein demonstrated that α-secretase ADAM10 was downregulated and ADAM10 inhibitor sFRP1 was upregulated in 5xFAD mice. While there were no sex effects on ADAM10 protein and sFRP1 mRNA levels, female 5xFAD and age-matched non-transgenic mice exhibited higher levels of sFRP1 protein than corresponding male mice. Importantly, female 5xFAD mice accumulated more Aβ than males, and sFRP1 protein levels were positively associated with Aβ42 levels in 5xFAD mice. Our study suggests that sFRP1 is associated with amyloid pathology in a sex-dependent manner.

Neurotoxic amyloid β-peptides are thought to be a causative agent of Alzheimer's disease in humans. The production of amyloid β-peptides from amyloid precursor protein (APP) could be diminished by enhancing α-processing; however, the physical interactions between APP and α-secretases are not well understood. In this study, we employed super-resolution light microscopy to examine in cell-free plasma membranes the abundance and association of APP and α-secretases ADAM10 (a disintegrin and metalloproteinase) and ADAM17. We found that both secretase molecules localize similarly closely to APP (within ≤50 nm). However, when cross-linking APP with antibodies directed against the GFP tag of APP, in confocal microscopy, we observed that only ADAM10 coaggregated with APP. Furthermore, we mapped the involved protein domain by using APP variants with an exchanged transmembrane segment or lacking cytoplasmic/extracellular domains. We identified that the transmembrane domain of APP is required for association with α-secretases and, as analyzed by Western blot, for α-processing. We propose that the transmembrane domain of APP interacts either directly or indirectly with ADAM10, but not with ADAM17, explaining the dominant role of ADAM10 in α-processing of APP. Further understanding of this interaction may facilitate the development of a therapeutic strategy based on promoting APP cleavage by α-secretases., Competing Interests: Conflict of interest The authors declare that they have no conflicts of interest with the contents of this article., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

MicroRNAs are small non-coding RNAs regulating mRNA translation. They play a crucial role in regulating homeostasis in neurons, especially in regulating local and stimulation dependent protein synthesis. Since activity-mediated protein synthesis in neurons is critical for memory and cognition, microRNAs have become key players in modulating these processes. Dementia is a broad term used for symptoms involving decline of memory and cognition. Several studies have implicated the dysregulation of microRNAs in many brain diseases like neurodegenerative diseases, neurodevelopmental disorders, brain injuries and dementia. In this review, we give an overview of microRNA-mediated regulation of proteins and cellular processes affected in dementia pathology, hence illustrating the importance of microRNAs in normal functioning. We also focus on a relatively less explored area in dementia pathology-the importance of activity-mediated protein synthesis at the synapse and the role of microRNAs in modulating this. Overall, this review will be helpful in looking at the significance of microRNAs in dementia from the perspective of defective regulation of protein synthesis and synaptic dysfunction., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Background: Amyloid precursor protein (APP), best known for its association with Alzheimer disease, has recently been implicated in breast cancer progression. However, the precise mechanism involved remains unclear. Here, we investigated the role of APP proteolytic cleavage in breast cancer functions., Methods: The presence of APP proteolytic cleavage products was examined in breast cancer cell lines. The functional roles of APP in breast cancer were studied in vitro and tumor xenograft model using siRNA. The effects of full length APP and the α-secretase cleaved ectodomain fragment, soluble APPα (sAPPα) were further investigated for their overexpression in breast cancers. The α-secretase involved was identified. The α-secretase expression together with APP was examined in clinical breast cancers., Results: We showed that APP underwent proteolytic cleavage in breast cancer cells to generate sAPPα. The sAPPα and full length protein mediated breast cancer migration and proliferation, but in different functional extent. This proteolytic cleavage was mediated by ADAM10. Downregulation of APP and ADAM10 brought about similar functional effects. Overexpression of sAPPα reversed the effects of ADAM10 downregulation. Interestingly, in patients with non-luminal breast cancers, APP and ADAM10 expression correlated with each other and their co-expression was associated with the worst outcome., Conclusions: These results demonstrated the contributory role of APP cleavage on its oncogenic roles in breast cancer. ADAM10 was the key α-secretase. APP and ADAM10 co-expression was associated with worse survival in non-luminal breast cancers. Targeting of APP or its processing by ADAM10 might be a promising treatment option in these cancers., (Copyright © 2018 The Authors. Published by Elsevier B.V. All rights reserved.)

Mitochondrial dysfunction is implicated in the pathological mechanism of Alzheimer's disease (AD). Amyloid β-protein (Aβ), which plays a central role in AD pathogenesis, is reported to accumulate within mitochondria. However, a question remains as to whether Aβ is generated locally from amyloid precursor protein (APP) within mitochondria. We investigated this issue by analyzing the expression patterns of APP, APP-processing secretases, and APP metabolites in mitochondria separated from human neuroblastoma SH-SY5Y cells and those expressing Swedish mutant APP. APP, BACE1, and PEN-2 protein levels were significantly lower in crude mitochondria than microsome fractions while those of ADAM10 and the other γ-secretase complex components (presenilin 1, nicastrin, and APH-1) were comparable between fractions. The crude mitochondrial fraction containing substantial levels of cathepsin D, a lysosomal marker, was further separated via iodixanol gradient centrifugation to obtain mitochondria- and lysosome-enriched fractions. Mature APP, BACE1, and all γ-secretase complex components (in particular, presenilin 1 and PEN-2) were scarcely present in the mitochondria-enriched fraction, compared to the lysosome-enriched fraction. Moreover, expression of the β-C-terminal fragment (β-CTF) of APP was markedly low in the mitochondria-enriched fraction. Additionally, immunocytochemical analysis showed very little co-localization between presenilin 1 and Tom20, a marker protein of mitochondria. In view of the particularly low expression levels of BACE1, γ-secretase complex proteins, and β-CTF in mitochondria, we propose that it is unlikely that Aβ generation from APP occurs locally within this organelle., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Alzheimer's disease (AD) is characterized by the deposition of β-amyloid (Aβ) peptide in the brain, which is produced by the proteolysis of β-amyloid precursor protein (APP). Recently, the mitochondrial transcription factor 4 (MTERF4), a member of the MTERF family, was implicated in regulating mitochondrial DNA transcription and directly in controlling mitochondrial ribosomal translation. The present study identified a novel role for MTERF4 in shifting APP processing toward the amyloidogenic pathway. The levels of MTERF4 protein were significantly increased in the hippocampus of APP/PS1 mice. In addition, the overexpression of MTERF4 induced a significant increase in the levels of APP protein and secreted Aβ42 in HEK293-APPswe cells compared with control cells. Further, MTERF4 overexpression shifted APP processing from α-to β-cleavage, as indicated by decreased C83 levels and elevated C99 levels. Finally, the MTERF4 overexpression suppressed a disintegrin and metalloproteinase 10 (ADAM10) expression via a transcriptional mechanism. Taken together, these results suggest that MTERF4 promotes the amyloidogenic processing of APP by inhibiting ADAM10 in HEK293-APPswe cells; therefore, MTERF4 may play an important role in the pathogenesis of AD., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Despite existing knowledge about the role of the A Disintegrin and Metalloproteinase 10 (ADAM10) as the α-secretase involved in the non-amyloidogenic processing of the amyloid precursor protein (APP) and Notch signalling we have only limited information about its regulation. In this study, we have identified ADAM10 interactors using a split ubiquitin yeast two hybrid approach. Tetraspanin 3 (Tspan3), which is highly expressed in the murine brain and elevated in brains of Alzheimer´s disease (AD) patients, was identified and confirmed to bind ADAM10 by co-immunoprecipitation experiments in mammalian cells in complex with APP and the γ-secretase protease presenilin. Tspan3 expression increased the cell surface levels of its interacting partners and was mainly localized in early and late endosomes. In contrast to the previously described ADAM10-binding tetraspanins, Tspan3 did not affect the endoplasmic reticulum to plasma membrane transport of ADAM10. Heterologous Tspan3 expression significantly increased the appearance of carboxy-terminal cleavage products of ADAM10 and APP, whereas N-cadherin ectodomain shedding appeared unaffected. Inhibiting the endocytosis of Tspan3 by mutating a critical cytoplasmic tyrosine-based internalization motif led to increased surface expression of APP and ADAM10. After its downregulation in neuroblastoma cells and in brains of Tspan3-deficient mice, ADAM10 and APP levels appeared unaltered possibly due to a compensatory increase in the expression of Tspans 5 and 7, respectively. In conclusion, our data suggest that Tspan3 acts in concert with other tetraspanins as a stabilizing factor of active ADAM10, APP and the γ-secretase complex at the plasma membrane and within the endocytic pathway., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Background: Plant secondary metabolites may induce adaptive cellular stress-responses in a variety of cells including neurons at the sub-toxic doses ingested by humans. Such 'neurohormesis' phenomenon, activated by flavonoids such as quercetin or rutin, may involve cell responses driven by modulation of signaling pathways which are responsible for its neuroprotective effects., Purpose: We attempt to explore the molecular mechanisms involved in the neurohormetic responses to quercetin and rutin exposure, in a SH-SY5Y cell line which stably overexpresses the amyloid precursor protein (APP) Swedish mutation, based on a biphasic concentration-response relationship for cell viability., Methods: We examined the impact of both natural compounds, at concentrations in its hormetic range on the following cell parameters: chymotrypsin-like activity of the proteasome system; PARP-1 protein levels and expression and caspase activation; APP processing; and the main endogenous antioxidant enzymes., Results: Proteasome activities following quercetin or rutin treatment were significantly augmented in comparison with non-treated cells. Activity of caspase-3 was significantly attenuated by treatment with quercetin or rutin. Modest increased levels of PARP-1 protein and mRNA transcripts were observed in relation to the mild increase of proteasome activity. Significant reductions of the full-length APP and sAPP protein and APP mRNA levels were related to significant enhancements of α-secretase ADAM-10 protein and mRNA transcripts and significant increases of BACE processing in cells exposed to rutin. Furthermore, quercetin or rutin treatment displayed an overall increase of the four antioxidant enzymes., Conclusions: The upregulation of the proteasome activity observed upon quercetin or rutin treatment could be afforded by a mild increased of PARP-1. Consequently, targeting the proteasome by quercetin or rutin to enhance its activity in a mild manner could avoid caspase activation. Moreover, it is likely that APP processing of cells upon rutin treatment is mostly driven by the non-amyloidogenic pathway leading to a putative reduction of βA production. Overall induction of endogenous antioxidant enzymes under quercetin or rutin treatments of APPswe cells might modulate its proteasome activity. We might conclude that quercetin and rutin might exert a neurohormetic cell response affecting various signaling pathways and molecular networks associated with modulation of proteasome function., (Copyright © 2016 Elsevier GmbH. All rights reserved.)

Amyloid-β (Aβ), the major component of neuritic plaques in Alzheimer's disease (AD), is derived from sequential proteolytic cleavage of amyloid protein precursor (APP) by secretases. In this study, we found that cystatin C (CysC), a natural cysteine protease inhibitor, is able to reduce Aβ40 secretion in human brain microvascular endothelial cells (HBMEC). The CysC-induced Aβ40 reduction was caused by degradation of β-secretase BACE1 through the ubiquitin/proteasome pathway. In contrast, we found that CysC promoted secretion of soluble APPα indicating the activated non-amyloidogenic processing of APP in HBMEC. Further results revealed that α-secretase ADAM10, which was transcriptionally upregulated in response to CysC, was required for the CysC-induced sAPPα secretion. Knockdown of SIRT1 abolished CysC-triggered ADAM10 upregulation and sAPPα production. Taken together, our results demonstrated that exogenously applied CysC can direct amyloidogenic APP processing to non-amyloidgenic pathway in brain endothelial cells, mediated by proteasomal degradation of BACE1 and SIRT1-mediated ADAM10 upregulation. Our study unveils previously unrecognized protective role of CysC in APP processing.

Excessive accumulation of amyloid-β (Aβ) caused by cleavage of amyloid precursor protein (APP) is thought to be the primary cause of Alzheimer's disease (AD). Two key enzymes ADAM10 and BACE1 are involved in the initial cleavage of APP, resulting in the onset of two pathways, the amyloidogenic pathway and the non-amyloidogenic pathway, respectively. Altering APP metabolism towards the non-amyloidogenic pathway is thought to reduce Aβ production. It has been reported that, in vivo, exogenous neurotrophic factors make APP apt to entering the non-amyloidogenic pathway. Since astrocytes secrete a battery of neurotrophic factors, we investigated the role of astrocyte-derived factors in the dynamics of Aβ generation in neural cells. Results show that C6 glioma cell-conditioned medium (GCM), obtained from cultured astrocyte-derived C6 glioma cells, inhibit Aβ1-42 production and shift APP processing towards the non-amyloidogenic pathway in APPswe-HEK293 cells. Such effect is attributed to two key APP cleavage enzymes, ADAM10 and BACE1. Two neurotrophic factors in the GCM, nerve growth factor and fibroblast growth factor 2, are responsible for the up-regulation of ADAM10 and down-regulation of BACE1, respectively. Our findings enhance our understanding of the relationship between astrocytes and Aβ generation, indicating that stimulation of astrocytic neurotrophic factors could slow AD progression.

Retinoic acid, the bioactive metabolite of beta-carotene or vitamin A, plays a pleiotropic, multifunctional role in vertebrate development. Studies in rodents revealed that a diet deficient in vitamin A results in a complex neonatal syndrome (the VAD syndrome), manifested in many organs. In humans, the function of retinoic acid (RA) extends into adulthood, where it has important roles in fertility, vision, and suppression of neoplastic growth. In recent years, it has also been suggested that retinoic acid might potentially act as a therapeutically relevant drug in attenuating or even preventing neurodegenerative diseases such as Alzheimer's disease (AD). Here, we report that VAD leads to an increase in A-beta peptide levels while only minor effects were observed on expression levels of the amyloid precursor protein (APP) processing proteinases in wild type mice. In line with these findings, rescue of hypovitaminosis reduced A-beta amount to baseline and induced sApp-alpha secretion in combination with an increase of alpha-secretase Adam10. By comparing retinoic acid treatment starting from a full nutrition status and a "VAD" situation in human neuroblastoma cells, we show that while intensities of differential gene expression were higher in replenished cells, a large overlap in AD-related, regulated genes was observed. Our data suggest that hypovitaminosis A can contribute to onset or progression of AD by increasing synthesis of A-beta peptides and that several AD-related genes such as ADAM10 or BDNF are regulated by retinoic acid. We suggest that dietary supplementation with retinoic acid derivatives is likely to have a beneficial effect on AD-pathology in individuals with hypovitaminosis and patients with normal vitamin A status.