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Objective: We earlier identified that the histone methyltransferase Disruptor of telomeric silencing 1-like (DOT1L) is as a master protector of cartilage health via limiting excessive activation of the Wnt pathway. However, cartilage-specific homozygous Dot1l knockout mice exhibited a severe growth phenotype and perinatal death, which hampered their use in induced or ageing models of osteoarthritis (OA). The aim of this study was to generate and examine haploinsufficient and inducible conditional Dot1l-deficient mouse models to evaluate the importance of DOT1L during post-traumatic or ageing-associated OA onset and progression.Method: We used cartilage-specific heterozygous and postnatal tamoxifen-inducible Dot1l knockout mice and performed destabilization of the medial meniscus (DMM) and ageing as OA models. Mice were examined histologically using X-rays and micro-computed tomography (μCT), and cartilage damage and osteophyte formation were assessed based on OARSI guidelines. Immunohistochemistry of DOT1L, H3K79me2, TCF1 and COLX was performed.Results: Both Dot1l-deficient strains exhibit a phenotype characterized by joint remodeling with extensive osteophyte formation and ectopic ossification upon ageing, indicating accelerated development of spontaneous osteoarthritis. In the DMM-induced OA mouse model, absence of Dot1l resulted in increased cartilage damage. Wnt signalling hyper-activation and ectopic chondrocyte hypertrophy were observed in the articular cartilage of both Dot1l-deficient mice.Conclusions: This study demonstrated the functional relevance of DOT1L in vivo during the development of OA using genetically modified mice. Thus, maintaining or enhancing DOT1L activity during ageing or after trauma might prevent OA onset and progression. [ABSTRACT FROM AUTHOR]

Objectives: Osteoarthritis (OA) is linked to disrupted lipid metabolism. We aimed to profile the lipid composition of human articular cartilage, investigate OA-associated lipidome changes, and explore biological effects., Methods: Lipidomic profiling and computational analyses were performed on human articular chondrocytes (hACs) from non-OA (n = 13) and OA (n = 14) hips. Lipid changes were confirmed in the destabilisation of the medial meniscus (DMM) mouse model. The effect of specific lipids was evaluated by in vitro supplementation and gene silencing., Results: We identified 573 lipid species covering 11 lipid classes in hACs. OA and non-OA hACs showed distinct lipid profiles. Most ceramides and dihydroceramides were increased, while cholesteryl esters, diacylglycerols, triacylglycerols, sphingomyelins, hexosylceramides, and lactosylceramides were predominantly decreased in OA chondrocytes. Most upregulated lipids in OA contained C18:1, C20:4, or C22:4 side chains. Many downregulated lipids contained C18:2 or odd-chain C17:0. Lipid profiling of articular cartilage from the DMM mouse model paralleled changes in OA hACs, including odd-chain C17:0 reduction. Further analysis showed that deficiency in enzyme 2-hydroxyacyl-CoA lyase 1 (HACL1), responsible for odd-chain fatty acid synthesis, leads to accumulation of 2-hydroxy C18:0, precursor of C17:0, which results in a shift in hACs from an anabolic to a catabolic state., Conclusions: Our study maps the hAC lipid composition and highlights changes in lipid profiles associated with OA. Dysregulation of certain lipids, especially odd-chain fatty acids, linked to a deficiency in the enzyme HACL1, leads to pathological changes. This understanding opens potential avenues for therapies aimed at targeting lipid imbalances to slow down or treat OA., Competing Interests: Competing interests Leuven Research and Development, the technology transfer office of KU Leuven, has received consultancy and speaker fees and research grants on behalf of RJL from AbbVie, Amgen (formerly Celgene), Biocon, Biosplice Therapeutics (formerly Samumed), Eli Lilly, Galapagos, Fresenius Kabi, Janssen, Novartis, Pfizer, and UCB. The other authors declare that they have no competing interests., (Copyright © 2025. Published by Elsevier B.V.)

Osteoarthritis is the most common joint disease and a global leading cause of pain and disability. Current treatment is limited to symptom relief, yet there is no disease-modifying therapy. Its multifactorial etiology includes excessive activation of Wnt signaling, but how Wnt causes joint destruction remains poorly understood. Here, we identify that Wnt signaling promotes the transcription of insulin-like growth factor 1 (IGF1) in articular chondrocytes and that IGF1 is a major driver of Wnt-induced joint damage. Male mice with cartilage-specific Igf1 deficiency are protected from Wnt-triggered joint disease. Mechanistically, Wnt-induced IGF1 transcription depends on β-catenin and binding of Wnt transcription factor TCF4 to the IGF1 gene promoter. In a clinically relevant mouse model of post-traumatic osteoarthritis, cartilage-specific deletion of Igf1 protects against the disease in male mice. IGF1 silencing in chondrocytes from patients with osteoarthritis restores a healthy molecular profile. Our findings reveal that reducing Wnt-induced IGF1 is a potential therapeutic strategy for osteoarthritis., (© 2024. The Author(s).)

In a recent characterization of the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) variability present in 30 diagnostic samples from patients of the first COVID-19 pandemic wave, 41 amino acid substitutions were documented in the RNA-dependent RNA polymerase (RdRp) nsp12. Eight substitutions were selected in this work to determine whether they had an impact on the RdRp activity of the SARS-CoV-2 nsp12-nsp8-nsp7 replication complex. Three of these substitutions were found around the polymerase central cavity, in the template entry channel (D499G and M668V), and within the motif B (V560A), and they showed polymerization rates similar to the wild type RdRp. The remaining five mutations (P323L, L372F, L372P, V373A, and L527H) were placed near the nsp12-nsp8 F contact surface; residues L372, V373, and L527 participated in a large hydrophobic cluster involving contacts between two helices in the nsp12 fingers and the long α-helix of nsp8 F . The presence of any of these five amino acid substitutions resulted in important alterations in the RNA polymerization activity. Comparative primer elongation assays showed different behavior depending on the hydrophobicity of their side chains. The substitution of L by the bulkier F side chain at position 372 slightly promoted RdRp activity. However, this activity was dramatically reduced with the L372P, and L527H mutations, and to a lesser extent with V373A, all of which weaken the hydrophobic interactions within the cluster. Additional mutations, specifically designed to disrupt the nsp12-nsp8 F interactions (nsp12-V330S, nsp12-V341S, and nsp8-R111A/D112A), also resulted in an impaired RdRp activity, further illustrating the importance of this contact interface in the regulation of RNA synthesis., Competing Interests: Competing interests statement:The authors declare no competing interest.

Since its introduction in the human population, SARS-CoV-2 has evolved into multiple clades, but the events in its intrahost diversification are not well understood. Here, we compare three-dimensional (3D) self-organized neural haplotype maps (SOMs) of SARS-CoV-2 from thirty individual nasopharyngeal diagnostic samples obtained within a 19-day interval in Madrid (Spain), at the time of transition between clades 19 and 20. SOMs have been trained with the haplotype repertoire present in the mutant spectra of the nsp12- and spike (S)-coding regions. Each SOM consisted of a dominant neuron (displaying the maximum frequency), surrounded by a low-frequency neuron cloud. The sequence of the master (dominant) neuron was either identical to that of the reference Wuhan-Hu-1 genome or differed from it at one nucleotide position. Six different deviant haplotype sequences were identified among the master neurons. Some of the substitutions in the neural clouds affected critical sites of the nsp12-nsp8-nsp7 polymerase complex and resulted in altered kinetics of RNA synthesis in an in vitro primer extension assay. Thus, the analysis has identified mutations that are relevant to modification of viral RNA synthesis, present in the mutant clouds of SARS-CoV-2 quasispecies. These mutations most likely occurred during intrahost diversification in several COVID-19 patients, during an initial stage of the pandemic, and within a brief time period., Competing Interests: Competing interests statement:The authors declare no competing interest.

Objectives: As more has become known of the pathophysiology of osteoarthritis (OA), evidence that inflammation plays a critical role in its development and progression has accumulated. Here, we aim to review current knowledge of the complex inflammatory network in the OA joint., Design: This narrative review is presented in three main sections: local inflammation, systemic inflammation, and therapeutic implications. We focused on inflammatory mediators and their link to OA structural changes in the joint., Results: OA is characterized by chronic and low-grade inflammation mediated mostly by the innate immune system, which results in cartilage degradation, bone remodeling and synovial changes. Synovitis is regarded as an OA characteristic and associated with increased severity of symptoms and joint dysfunction. However, the articular cartilage and the subchondral bone also produce several pro-inflammatory mediators thus establishing a complex interplay between the different tissues of the joint. In addition, systemic low-grade inflammation induced by aging, obesity and metabolic syndrome can contribute to OA development and progression. The main inflammatory mediators associated with OA include cytokines, chemokines, growth factors, adipokines, and neuropeptides., Conclusions: Future research is needed to deeper understand the molecular pathways mediating the inflammation in OA to provide new therapeutics that target these pathways, or to repurpose existing drugs., Competing Interests: Conflict of interest Leuven Research and Development, the technology transfer office of KU Leuven, has received consultancy and speaker fees and research grants on behalf of R.J.L. from Abbvie, Boehringer-Ingelheim, Amgen (formerly Celgene), Eli-Lilly, Galapagos, Janssen, Fresenius Kabi, MSD, Novartis, Pfizer, Biosplice Therapeutics (formerly Samumed) and UCB. The other authors declare that they have no competing financial interests., (Copyright © 2023 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.)