Synergistically regulated spontaneous calcium signaling is attributed to cartilaginous extracellular matrix metabolism

CA²⁺ has been recognized as a key molecule for chondrocytes, however, the role and mechanism of spontaneous [CA ²⁺ ] _i signaling in cartilaginous extracellular matrix (ECM) metabolism regulation are unclear. Here we found that spontaneous CA ²⁺ signal of in-situ porcine chondrocytes was [CA ²⁺ ] _o dependent, and mediated by [CA ²⁺ ] _i store release. T-type voltage-dependent Calcium Channel (T-VDCC) mediated [CA ²⁺ ] _o influx was associated with decreased cell viability and expression levels of ECM deposition genes. Further analysis revealed that chondrocytes expressed both inositol 1,4,5-trisphosphate receptor (InsP3R) and Orai isoforms. Inhibition of endoplasmic reticulum (ER) CA ²⁺ release and store-operated calcium entry significantly abolished spontaneous [CA ²⁺ ] _i signaling of in-situ chondrocytes. Moreover, blocking ER CA ²⁺ release with InsP3R inhibitors significantly upregulated ECM degradation Enzymes production, and was accompanied by decreased proteoglycan and collagen type II intensity. Taken together, our data provided evidence that spontaneous [CA ²⁺ ] _i signaling of in-situ porcine chondrocytes was tightly regulated by [CA ²⁺ ] _o influx, InsP3Rs mediated [CA ²⁺ ] _i store release, and Orais mediated calcium release-activated calcium channels activation. Both T-VDCC mediated [CA ²⁺ ] _o influx and InsP3Rs mediated ER CA ²⁺ release were found crucial to cartilaginous ECM metabolism through distinct regulatory mechanisms.