Osteoarthritis (OA) is one of the most common degenerative joint diseases in the elderly, increasing in prevalence and posing a substantial socioeconomic challenge, while no disease-modifying treatments available. Better understanding of the early molecular events will benefit the early-stage diagnosis and clinical therapy. Here, we observed the nucleus accumulation of ZBTB20, a member of ZBTB-protein family, in the chondrocytes of early-stage OA. Chondrocytes-specific depletion of Zbtb20 in adult mice attenuated DMM-induced OA progress, restored the balance of extracellular matrix anabolism and catabolism. The NF-κB signaling mediated disturbance of ECM maintenance by ZBTB20 requires its suppression of Pten and consequent PI3K-Akt signaling activation. Furthermore, the subcellular localization of ZBTB20 was modulated by the kinase LATS1. Independent approaches to modulating ZBTB20 via utilizing TRULI and DAPA can restore ECM homeostasis, improving the abnormal behavior and moderating cartilage degeneration. The compounds TRULI and DAPA modulating ZBTB20 may serve as anti-OA drugs.

The circadian clock maintains homeostasis in peripheral tissues, including articular cartilage. Cartilage as a highly mechanical loaded tissue experiences diurnal rhythmic mechanical loading activity/rest cycle patterns, which gives external time cue on chondrocytes. Given the cartilage clock driven by loading patterns, we hypothesize that abnormal mechanical loading, a major risk factor for osteoarthritis (OA), can disrupt the cartilage clock, further contributing to OA progression. We used both noninvasive in vivo mechanical loading system and PER2Luc reporter mice for ex vivo bioluminescence recording. RNA sequencing was performed in mouse primary chondrocytes treated with 1.0 MPa static compression, and identified core clock molecule REV-ERBα, which was confirmed in human and murine OA cartilage samples. Chondrocytes were treated with Rev-erbα small interfering RNA (si-Rev-erbα), and adeno-associated virus carrying Rev-erbα-specific short hairpin RNA (AAV-shRev-erbα) was injected intra-articularly in mice to knock down Rev-erbα. Relevant signaling pathways regulating REV-ERBα were analyzed by RNA sequencing data. Intraperitoneal injection of SR8278, a specific REV-ERBα antagonist, was performed in mice after mechanical overloading for OA treatment. Excessive mechanical loading disrupted the circadian rhythm of articular cartilage. The core clock molecule REV-ERBα was increased in OA cartilage and knockdown of Rev-erbαalleviated compression-induced chondrocyte dysfunction. Inhibition of MAPK-MYC pathway by U0126 or SB203580 attenuated compression-induced REV-ERBα up-regulation and cartilage clock disruption. Finally, pharmacological inhibition of REV-ERBα expression by SR8278 restored cartilage clock upon abnormal loading and mitigated OA progression. REV-ERBα is a key factor in the association between mechanical overloading-induced circadian disruption and OA pathology. This study illustrates the essential mechanism of impaired circadian rhythm under overloading and provides a possibly impactful therapeutic approach for the treatment of OA. Inhibition REV-ERBα expression by clock-based therapeutic drug SR8278 or MAPK-MYC pathway inhibitors could ameliorate mechanical overloading-induced circadian disruption of cartilage and OA degeneration, indicating a clinical conversion potential for OA treatment.

The Drosophila ovary is recognized as a powerful model to study stem cell self-renewal and differentiation. Decapentaplegic (Dpp) is secreted from the germline stem cell (GSC) niche to activate Bone Morphogenic Protein (BMP) signaling in GSCs for their self-renewal and is restricted in the differentiation niche for daughter cell differentiation. Here, we report that Switch/sucrose non-fermentable (SWI/SNF) component Osa depletion in escort cells (ECs) results in a blockage of GSC progeny differentiation. Further molecular and genetic analyses suggest that the defective germline differentiation is partially attributed to the elevated dpp transcription in ECs. Moreover, ectopic Engrailed (En) expression in osa-depleted ECs partially contributes to upregulated dpp transcription. Furthermore, we show that Osa regulates germline differentiation in a Brahma (Brm)-associated protein (BAP)-complex-dependent manner. Additionally, the loss of EC long cellular processes upon osa depletion may also partly contribute to the germline differentiation defect. Taken together, these data suggest that the epigenetic factor Osa plays an important role in controlling EC characteristics and germline lineage differentiation.

Articular cartilage, a highly specialized avascular connective tissue, forms a smooth, load-bearing surface on articulating bone ends to facilitate frictionless joint movement. While cell-derived small extracellular vesicles (sEVs) have emerged as promising therapeutic biomaterials for cartilage regeneration, two major limitations impede their clinical translation: the scarcity of autologous donor cells, and suboptimal functional efficacy of conventional sEVs preparations. We established an induced pluripotent stem cell (iPSC)-based approach by differentiating iPSCs into chondrocytes (designated iChondrocytes). After characterizing the derived iChondrocytes, we isolated their secreted sEVs (iChondrocyte-sEVs) and systematically evaluated their therapeutic effects and underlying mechanisms in cartilage regeneration through in vitro and in vivo experiments. Functional assays revealed that iChondrocyte-sEVs significantly enhanced chondrogenic differentiation, stimulated extracellular matrix (ECM) deposition, and maintained chondrocyte homeostasis. In murine osteoarthritis (OA) models, intra-articularly administered iChondrocyte-sEVs efficiently penetrated deep cartilage layers, alleviated OA-associated pathological changes, and restored cartilage microstructure and biomechanical properties to near-normal levels. Furthermore, therapeutic intervention with iChondrocyte-sEVs resulted in significant improvements in joint mobility and motor function in OA-affected mice. Proteomic profiling identified serine racemase (SRR) as a key upregulated protein in iChondrocyte-sEVs. Mechanistic studies suggested that SRR may contribute to cartilage regeneration by suppressing the P38/ERK signaling pathway. This study highlights the significant therapeutic potential of iChondrocyte-sEVs, demonstrating their ability to promote both structural and functional regeneration of articular cartilage. These findings suggest a promising novel strategy for OA treatment. This study highlights the therapeutic potential of iChondrocyte-sEVs, demonstrating their ability to promote both structural and functional regeneration of articular cartilage. These findings indicate a clinical conversion potential for OA treatment.