Purinergic signalling is required for calcium oscillations in migratory chondrogenic progenitor cells

Osteoarthritis (OA) is the most common form of chronic musculoskeletal disorders. A migratory stem cell population termed chondrogenic progenitor cells (CPC) with in vitro chondrogenic potential was previously isolated from OA cartilage. Since intracellular Ca 2+ signalling is an important regulator of chondrogenesis, we aimed to provide a detailed understanding of the Ca 2+ homeostasis of CPCs. In this work, CPCs immortalised by lentiviral administration of the human telomerase reverse transcriptase (hTERT) and grown in monolayer cultures were studied. Expressions of all three IP 3 Rs were confirmed, but no RyR subtypes were detected. Ca 2+ oscillations observed in CPCs were predominantly dependent on Ca 2+ release and store replenishment via store-operated Ca 2+ entry; CPCs express both STIM1 and Orai1 proteins. Expressions of adenosine receptor mRNAs were verified, and adenosine elicited Ca 2+ transients. Various P2 receptor subtypes were identified; P2Y 1 can bind ADP; P2Y 4 is targeted by UTP; and ATP may evoke Ca 2+ transients via detected P2X subtypes, as well as P2Y 1 and P2Y 2 . Enzymatic breakdown of extracellular nucleotides by apyrase completely abrogated Ca 2+ oscillations, suggesting that an autocrine/paracrine purinergic mechanism may drive Ca 2+ oscillations in these cells. As CPCs possess a broad spectrum of functional molecular elements of Ca 2+ signalling, Ca 2+ -dependent regulatory mechanisms can be supposed to influence their differentiation potential.