Purinergic signalling is required for calcium oscillations 5 in migratory chondrogenic progenitor cells

14 Abstract Osteoarthritis (OA) is the most common form of 15 chronic musculoskeletal disorders. A migratory stem cell pop16 ulation termed chondrogenic progenitor cells (CPC) with 17 in vitro chondrogenic potential was previously isolated from 18 OA cartilage. Since intracellular Ca signalling is an impor19 tant regulator of chondrogenesis, we aimed to provide a 20 detailed understanding of the Ca homeostasis of CPCs. In 21 this work, CPCs immortalised by lentiviral administration of 22 the human telomerase reverse transcriptase (hTERT) and 23 grown in monolayer cultures were studied. Expressions of 24 all three IP3Rs were confirmed, but no RyR subtypes were 25 detected. Ca oscillations observed in CPCs were predomi26 nantly dependent on Ca release and store replenishment via 27 store-operated Ca entry; CPCs express both STIM1 and 28 Orai1 proteins. Expressions of adenosine receptor mRNAs 29 were verified, and adenosine elicited Ca transients. Various 30 P2 receptor subtypes were identified; P2Y1 can bind ADP; 31 P2Y4 is targeted by UTP; and ATP may evoke Ca 2+ transients 32 via detected P2X subtypes, as well as P2Y1 and P2Y2. Enzy33 matic breakdown of extracellular nucleotides by apyrase 34 completely abrogated Ca oscillations, suggesting that an 35 autocrine/paracrine purinergic mechanism may drive Ca 36 oscillations in these cells. As CPCs possess a broad spectrum 37 of functional molecular elements of Ca signalling, Ca38 dependent regulatory mechanisms can be supposed to influ39 ence their differentiation potential.