Acid-sensing ion channel 1a regulates the survival of nucleus pulposus cells in the acidic environment of degenerated intervertebral discs

Objectives: Activation of acid-sensing ion channel 1a (ASIC1a) is responsible for tissue injury caused by acidosis in nervous systems. But its physiological and pathological roles in nucleus pulposus cells (NPCs) are unclear. The aim of this study is to investigate whether ASIC1a regulates the survival of NPCs in the acidic environment of degenerated discs.

Materials and methods: NPCs were isolated and cultured followed by immunofluorescent staining and Western-blot analysis for ASIC1a. Intracellular calcium ([CA²⁺]_i) was determined by CA²⁺-imaging using Fura-2-AM. Cell necrosis, Apoptosis, and senescence following acid exposure were determined using Lactate Dehydrogenase (LDH) release assay, annexin V-fluorescein isothiocyanate/propidium iodide dual-staining and cell cycle analysis, respectively, followed by Western-blot analysis for apoptosis-related proteins (Bax, Bcl-2, and Caspase-3) and senescence-related proteins (p53, p21, and p16). Effects of treatment with psalmotoxin-1 (PcTX1, blocker of ASIC1a) on [CA²⁺]_i and cell survival were investigated.

Results: ASIC1a was detected in healthy NPCs, and its expression was significantly higher in degenerated cells. When NPCs were treated with PcTX1, acid-induced increases in [CA²⁺]_i were significantly inhibited. PcTX1 treatment also resulted in decreased LDH release, cell Apoptosis and cell cycle arrest in acid condition. Acid exposure decreased the expression of Bcl-2 and increased the expression of Bax, cleaved Caspase-3 and senescence-related proteins (p53, p21, and p16), which was inhibited by PcTX1.

Conclusion: The present findings suggest that further understanding of ASIC1a functionality may provide not only a novel insight into intervertebral disc biology but also a novel therapeutic target for intervertebral disc degeneration.