Liang He

Osteoarthritis (OA) is among the most prevalent chronic diseases worldwide. However, currently employed pharmacological therapies for OA are associated with various reported side effects. Exercise therapy represents a potentially safer and more effective strategy for OA treatment, although its underlying mechanism remains unclear. Here, we demonstrate that compared with high-intensity continuous training, moderate-intensity continuous training (MICT) has greater therapeutic potential for OA. Notably, these beneficial effects of MICT were abrogated following gut microbiota depletion. Moreover, transplantation of the gut microbiota from MICT-treated mice inhibited OA progression. Akkermansia was identified as the most significantly altered microbiota in response to MICT, and supplementation with Akkermansia in destabilization of the medial meniscus mice also alleviated OA. Mechanistically, MICT protects against OA by reducing plasma lactate levels. Production of high levels of lactate by numerous microbiotas was identified as a risk factor induced by destabilization of the medial meniscus. Consistent with these findings, our genetic data revealed that both the knockout of the lactate receptor Gpr81 and the knockdown of Gpr81 in articular cartilage with adeno-associated virus 2 mitigated OA progression by increasing anabolic metabolism and suppressing catabolic metabolism. The Gαi-CREB/NF-κB axis was further identified as the primary downstream pathway mediating the biological effects of Gpr81 in chondrocytes. Clinically, we validated a negative correlation between Akkermansia abundance and both synovial fluid lactate levels and GPR81 expression in the articular cartilage of OA patients. Collectively, the results of this study not only reveal the mechanism underlying the protective effects of exercise against OA but also identify a novel therapeutic target for OA treatment.

G protein‐coupled receptor 81 (GPR81) is a hydroxycarboxylic acid receptor that has been identified in recent years to be widely expressed in cells of a variety of tissues. It has been demonstrated that lactate (LA) is the sole endogenous, natural ligand for GPR81 under physiological conditions. However, the precise function of GPR81 in the regulation of arterial function remains to be elucidated. The present study constructed a mouse model of impaired arterial function by subjecting C57/BL6J female mice to a high‐fat diet (HFD) and ovariectomy (OVX). The results demonstrated that mice with OVX and obesity exhibited increased arterial stiffness, accompanied by lipid metabolism disorder. Furthermore, a substantial quantity of oxidized low‐density lipoprotein (ox‐LDL) was observed in the aortic sinus region, which is a critical factor in the development of atherosclerosis. However, the 8‐week aerobic exercise intervention was found to be capable of effectively reversing these adverse effects. Concurrently, in ovariectomized obese mice, serum LA levels exhibited a significant increase following exercise, as did the expression levels of aortic GPR81. Furthermore, an increase in cAMP‐response element‐binding protein 1 (CREB) phosphorylation was observed, which resulted in an enhancement of endothelial nitric oxide synthase (eNOS) expression. Finally, the study confirmed that exercise did not restore arterial function‐related indices in ovariectomized obese Gpr81 knockout mice. Thus, it was determined that exercise may enhance arterial function through the LA/GPR81/p‐CREB/CREB/eNOS signaling pathway.

Adhesion G protein–coupled receptors (GPCRs) play crucial roles in numerous physiological and pathological conditions. However, the functions of adhesion GPCRs remain poorly understood because of the lack of effective modulators. Here, we used the adhesion GPCR D1 (ADGRD1/GPR133) as a model to unveil a strategy for finding exogenous agonists that target adhesion GPCRs while revealing previously unidentified functions of ADGRD1. We identified the small molecule GL64 as a selective agonist of ADGRD1. GL64 activates ADGRD1 by mimicking the stachel sequence. Using GL64 as a chemical tool, we demonstrated that ADGRD1 negatively regulates bone loss by inhibiting osteoclastogenesis. The cAMP-PKA-NFATC1 pathway was identified as the downstream signaling pathway of ADGRD1 in osteoclasts. Furthermore, administering GL64 prevented bone loss and suppressed osteoclast activity in the osteoporosis mouse model induced by ovariectomy. Our findings provide mechanistic insights into the activation of adhesion GPCRs by exogenous agonists and underscore the therapeutic potential of targeting ADGRD1 in osteoclast-related diseases.

Background/Objectives: Mesenchymal stem cells (MSCs) possess the remarkable ability to differentiate into various cell types, including osteoblasts. Understanding the molecular mechanisms governing MSC osteogenic differentiation is crucial for advancing clinical applications and our comprehension of complex disease processes. However, the key biological molecules regulating this process remain incompletely understood. Methods: In this study, we conducted systematic re-analyses of published high-throughput transcriptomic datasets to identify and validate key biological molecules that dynamically regulate MSC osteogenic differentiation. Our approach involved a comprehensive analysis of gene expression patterns across human tissues, followed by the rigorous experimental validation of the identified candidates. Results: Through integrated analytical and experimental approaches, we utilized high-throughput transcriptomics to identify four critical regulators of MSC osteogenic differentiation: PTBP1, H2AFZ, BCL6, and TTPAL (C20ORF121). Among these, PTBP1 and H2AFZ functioned as positive regulators, while BCL6 and TTPAL acted as negative regulators in osteogenesis. The regulatory roles of these genes in osteogenesis were further validated via overexpression experiments. Conclusions: Our findings advance our understanding of MSC differentiation fate determination and open new therapeutic possibilities for bone-related disorders. The identification of these regulators provides a foundation for developing targeted interventions in regenerative medicine.

Background/Objectives: Mesenchymal Stem Cells (MSCs) possess the remarkable ability to dif-ferentiate into various cell types, including osteoblasts. Understanding the molecular mecha-nisms governing MSC osteogenic differentiation is crucial for advancing clinical applications and our comprehension of complex disease processes. However, the key biological molecules regu-lating this process remain incompletely understood, necessitating further investigation. Methods: In this study, we employed high-throughput transcriptomic sequencing to identify and validate key biological molecules that dynamically regulate MSC osteogenic differentiation. Our approach involved comprehensive analysis of gene expression patterns across human tissues, followed by rigorous experimental validation of identified candidates. Results: Through our integrated analytical and experimental approach, we pinpointed four critical regulators of MSC osteogenic differentiation: PTBP1, H2AFZ, BCL6, and TTPAL (C20ORF121). Notably, this study represents the first instance of utilizing high-throughput transcriptomics to uncover regulatory factors involved in MSC osteogenesis, marking a significant advancement in the field. Conclusions: Our findings substantially enhance our understanding of the molecular mechanisms determining MSC differentiation fate. This research holds significant implications for clinical ap-plications involving MSCs and provides valuable insights into complex disease processes. The identification of these key regulators opens new avenues for targeted interventions and therapies in bone-related disorders and regenerative medicine. Furthermore, this study establishes a robust framework for future investigations in stem cell biology, potentially leading to innovative ap-proaches in regenerative medicine.

Inflammatory diseases decrease the extracellular environmental pH. However, whether proton-activated G protein-coupled receptors (GPCRs) can regulate the development of osteoarthritis (OA) is largely unknown. In this study, we report that proton-activated GPR4 is essential for OA development. We found a marked increase in expression of the proton-activated GPR4 in human and mouse OA cartilage. Lentivirus-mediated overexpression of GPR4 in mouse joints accelerated the development of OA, including promotion of articular cartilage damage, synovial hyperplasia, and osteophyte formation, while Gpr4 knockout effectively attenuated the development of posttraumatic and aging-associated OA in mice. We also found that inhibition of GPR4 with the antagonist NE52-QQ57 ameliorated OA progression in mice, promoted extracellular matrix (ECM) production, and protected cartilage from degradation in human articular cartilage explants. Moreover, GPR4 overexpression upregulated matrix-degrading enzymes’ expression and inflammation factors under pro-inflammatory and slightly acidic conditions. Mechanistically, GPR4 suppressed chondrocyte differentiation and upregulated cartilage homeostasis through NF-κB/MAPK signaling activation by regulating CXCR7/CXCL12 expression. Together, our results take the lead to illustrate that proton-activated GPCR acts as a key regulator for OA pathogenesis in vivo, and support that GPR4 could be a promising therapeutic target for OA treatment.

Therapeutics targeting osteoclasts are commonly used treatments for bone metastasis; however, whether and how osteoclasts regulate premetastatic niche and bone tropism are largely unknown. In this study, we report that osteoclast precursors (OPs) can function as a premetastatic niche component that facilitates breast cancer (BCa) bone metastasis at early stages. At the molecular level, unbiased GPCR ligand/agonist screening in BCa cells suggested that R-spondin 2 (RSPO2) and RANKL, through interaction with their receptor LGR4, promoted osteoclastic premetastatic niche formation and enhanced BCa bone metastasis. This was achieved by RSPO2/RANKL-LGR4 signal modulating the WNT inhibitor DKK1 through Gα_q and β-catenin signaling. DKK1 directly facilitated OP recruitment through suppression of its receptor LDL receptor–related protein 5 (LRP5) but not LRP6, upregulating Rnasek expression via inhibition of canonical WNT signaling. In clinical samples, RSPO2, LGR4, and DKK1 expression showed a positive correlation with BCa bone metastasis. Furthermore, soluble LGR4 extracellular domain (ECD) protein, acting as a decoy receptor for RSPO2 and RANKL, significantly alleviated bone metastasis and osteolytic lesions in a mouse bone metastasis model. These findings provide unique insights into the functional role of OPs as key components of the premetastatic niche for BCa bone metastasis and identify RSPO2/RANKL-LGR4 signaling as a promising target for inhibiting BCa bone metastasis.

Adhesion GPCR Gpr126/Adgrg6 regulates mouse body length and bone mass by controlling osteoblast differentiation.