Inhibition of acid-sensing ion channel la attenuates acid-induced activation of autophagy via a calcium signaling pathway in articular chondrocytes

Acid-sensing ion channel la (ASIC1a), member of the degenerin/epithelial sodium channel protein superfamily, serves a critical role in various physiological and pathological processes. The aim of the present study was to examine the role of ASICla in the autophagy of rat articular chondrocytes. Autophagy was induced by acidic stimulation in rat articular chondrocytes and the extent of autophagy was evaluated via the expression levels of microtubule-associated protein 1 light chain 311, Beclinl and uncoordinated-51 like kinasel. Suppression of ASICla was achieved using small interfering RNA technology and/or inhibitor psalmotoxin-1. The expression levels of autophagy markers were measured by western blot analysis and reverse transcription-quantitative polymerase chain reaction methods. Intracellular calcium ([[[Ca.sup.2+]].sub.i]) was analyzed using a [Ca.sup.2+]-imaging method. Additionally, protein expression levels of the [Ca.sup.2+]/calmodulin-dependent protein kinase kinase [beta] (CaMKKp)/5'-monophosphate-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) pathway were measured by western blot analysis. The results showed that autophagy was increased in a pH- and time-dependent manner with exposure to an acidic environment. In addition, silencing ASICla significantly decreased the expression levels of autophagy makers, accompanied by abrogation of the acid-induced [[[Ca.sup.2+]].sub.i] increase. Furthermore, silencing of ASICla downregulated the levels of CaMKK[beta]/[beta]-actin and phosphorylated (p-) AMPK/AMPK, and upregulated the levels of p-mTOR/mTOR. These results indicated that ASICla is a potent regulator of autophagy in chondrocytes, which may be associated with decreased [Ca.sup.2+] influx and the CaMKK[beta]/AMPK/mTOR pathway.