Inhibition of acid‑sensing ion channel�1a attenuates acid‑induced activation of autophagy via a calcium signaling pathway in articular chondrocytes

Abstract

Acid-sensing ion channel 1a (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 ASIC1a 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 3II, Beclin1 and uncoordinated-51 like kinase1. Suppression of ASIC1a 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 ([Ca2+]i) was analyzed using a Ca2+-imaging method. Additionally, protein expression levels of the Ca2+/calmodulin-dependent protein kinase kinase β (CaMKKβ)/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 ASIC1a significantly decreased the expression levels of autophagy makers, accompanied by abrogation of the acid-induced [Ca2+]i increase. Furthermore, silencing of ASIC1a downregulated the levels of CaMKKβ/β-actin and phosphorylated (p-) AMPK/AMPK, and upregulated the levels of p-mTOR/mTOR. These results indicated that ASIC1a is a potent regulator of autophagy in chondrocytes, which may be associated with decreased Ca2+ influx and the CaMKKβ/AMPK/mTOR pathway.

Factors and Molecular Mechanisms Influencing the Protein Synthesis, Degradation and Membrane Trafficking of ASIC1a

“…PcTx1, the peptide toxin obtained from spiders, is a gating modifier of ASIC1a and has been widely used to explore the functions of ASIC1a (Leng and Xiong, 2013). Our previous studies have confirmed that PcTx1 reversed the enhancing effect of extracellular acidification on ASIC1a protein and mRNA expression in articular chondrocytes (Gao et al, 2019;Wu et al, 2019). Similarly, the increased expression and membrane trafficking of ASIC1a induced by PDGF stimulation were inhibited by PcTx1 (Zuo et al, 2019).…”

“…ASIC1a has been characterized as a potent proton sensor for detecting extracellular acidification in the peripheral tissues and brain (Cheng et al, 2018). Our previous studies have indicated that extracellular acidosis increases protein expression of ASIC1a in a pH-and time-dependent manner in rat articular chondrocytes (Dai et al, 2017;Gao et al, 2019;Zu et al, 2020). Moreover, it has been reported that ASIC1a expression is significantly increased in the articular cartilage of adjuvant arthritis (AA) rats (Zhou et al, 2015), the articular synovial fluid of which showed a low pH value compared to that of the non-arthritic rat synovial fluid (Zhou et al, 2018).…”

“…Moreover, it has been reported that ASIC1a expression is significantly increased in the articular cartilage of adjuvant arthritis (AA) rats (Zhou et al, 2015), the articular synovial fluid of which showed a low pH value compared to that of the non-arthritic rat synovial fluid (Zhou et al, 2018). Furthermore, blocking ASIC1a expression through pretreatment with the ASIC1a-specific blocker such as psalmotoxinf (PcTx1) or ASIC1a RNA interference (RNAi) reversed the promoting effect of extracellular acidification on the protein and mRNA expression levels of ASIC1a and decreased cell death induced by extracellular acidosis (Gao et al, 2019). Similarly, after PcTx1 treatment, both the severity of disease in AA rats and the protein expression of ASIC1a in the synovial tissue decreased in vivo (Qian et al, 2020).…”

Acid‐sensing ion channel 1a mediates acid‐induced pyroptosis through calpain‐2/calcineurin pathway in rat articular chondrocytes

“…In the past 2 years, our research team has shown that activated ASIC1a induces autophagy, synovial invasion, and synovial inflammation by mediating calcium influx (Gao, Xu, Ge, & Chen, 2019; Niu et al, 2020; Zhang et al, 2020). Calpains are ubiquitous calcium‐activated cysteine proteases.…”

Metabolome-Driven Regulation of Adenovirus-Induced Cell Death

“…Perhaps, it is related to the development of acidosis due to the lactic acid accumulation caused by the adenovirus-mediated stimulation of glycolysis [28]. While intracellular pH decreases, acid-sensing ion channels become activated and induce calcium influx [70,71]. Another possible mechanism of intracellular calcium accumulation is calcium flow through tiny pores in the membrane and lysosomal exocytosis induced by adenoviral E4 protein [20].…”