Bo Xu1, Runlin Xing2, Zhengquan Huang2, Songjiang Yin2, Xiaochen Li2, Li Zhang2, Liang Ding2, Peimin Wang3. 1. Affiliated Hospital of Nanjing University of Chinese Medicine, Nanjing 210029, China; Jiangsu Province Hospital of Chinese Medicine, Nanjing 210029, China; Key Laboratory for Metabolic Diseases in Chinese Medicine, First College of Clinical Medicine, Nanjing University of Chinese Medicine, Nanjing 210023, China. 2. Affiliated Hospital of Nanjing University of Chinese Medicine, Nanjing 210029, China; Jiangsu Province Hospital of Chinese Medicine, Nanjing 210029, China. 3. Affiliated Hospital of Nanjing University of Chinese Medicine, Nanjing 210029, China; Jiangsu Province Hospital of Chinese Medicine, Nanjing 210029, China. Electronic address: 15298384532@163.com.
Abstract
AIMS: Chondrocyte apoptosis is the most common pathological feature of cartilage in osteoarthritis (OA). Excessive mechanical stress can induce chondrocyte apoptosis and destroy cartilage tissue. Transient receptor potential channel vanilloid 4 (TRPV4) is a mechanosensitive ion channel that mediates chondrocyte response to mechanical stress. Here, we investigated the potential role of TRPV4 in chondrocyte apoptosis induced by excessive mechanical stress. MAIN METHODS: Using a rat OA anterior cruciate-ligament transection (ALCT) model, we detected immunolocalization of calmodulin protein and mRNA and protein levels of TRPV4, calmodulin, and cleaved caspase-8 in articular cartilage. Primary chondrocytes were isolated and cultured in vitro, and Fluo-4AM staining was used to assess intracellular Ca2+ levels in order to evaluate TRPV4-mediated Ca2+ influx. Flow cytometry and western blot were performed to detect apoptosis and apoptosis-related protein levels in chondrocytes, respectively. KEY FINDINGS: TRPV4 was upregulated in ALCT-induced OA articular cartilage, and we found that administration of a TRPV4 inhibitor attenuated cartilage degeneration. Additionally, TRPV4 specifically mediated extracellular Ca2+ influx, leading to chondrocyte apoptosis in vitro, which was inhibited by transfection of TRPV4 small-interfering RNA or administration of a TRPV4 inhibitor. Moreover, increased Ca2+ influx triggered apoptosis by upregulating FAS-associated protein with death domain and cleaved caspase-3, -6, -7, and -8 levels, with these effects abolished by TRPV4 knockdown or TRPV4 inhibition. SIGNIFICANCE: These results indicated that TRPV4 was upregulated in OA articular cartilage, and that excessive mechanical stress might induce chondrocyte apoptosis via TRPV4-mediated Ca2+ influx, suggesting TRPV4 as a potential drug target in OA.
AIMS: Chondrocyte apoptosis is the most common pathological feature of cartilage in osteoarthritis (OA). Excessive mechanical stress can induce chondrocyte apoptosis and destroy cartilage tissue. Transient receptor potential channel vanilloid 4 (TRPV4) is a mechanosensitive ion channel that mediates chondrocyte response to mechanical stress. Here, we investigated the potential role of TRPV4 in chondrocyte apoptosis induced by excessive mechanical stress. MAIN METHODS: Using a rat OA anterior cruciate-ligament transection (ALCT) model, we detected immunolocalization of calmodulin protein and mRNA and protein levels of TRPV4, calmodulin, and cleaved caspase-8 in articular cartilage. Primary chondrocytes were isolated and cultured in vitro, and Fluo-4AM staining was used to assess intracellular Ca2+ levels in order to evaluate TRPV4-mediated Ca2+ influx. Flow cytometry and western blot were performed to detect apoptosis and apoptosis-related protein levels in chondrocytes, respectively. KEY FINDINGS:TRPV4 was upregulated in ALCT-induced OA articular cartilage, and we found that administration of a TRPV4 inhibitor attenuated cartilage degeneration. Additionally, TRPV4 specifically mediated extracellular Ca2+ influx, leading to chondrocyte apoptosis in vitro, which was inhibited by transfection of TRPV4 small-interfering RNA or administration of a TRPV4 inhibitor. Moreover, increased Ca2+ influx triggered apoptosis by upregulating FAS-associated protein with death domain and cleaved caspase-3, -6, -7, and -8 levels, with these effects abolished by TRPV4 knockdown or TRPV4 inhibition. SIGNIFICANCE: These results indicated that TRPV4 was upregulated in OA articular cartilage, and that excessive mechanical stress might induce chondrocyte apoptosis via TRPV4-mediated Ca2+ influx, suggesting TRPV4 as a potential drug target in OA.