Abstract
Purpose: In the degenerated intervertebral disc (IVD), matrix acidity challenges transplanted bone marrow mesenchymal stem cells (BMSCs). The Ca2+-permeable acid-sensing ion channel 1a (ASIC1a) is responsible for acidosis-mediated tissue injury. The aim of our study was to confirm whether ASIC1a activation induces BMSC apoptosis under conditions that mimic the acidic microenvironment of the degenerated IVD.Methods: ASIC1a expression in rat BMSCs was investigated by real time-PCR, Western blot (WB) and immunofluorescence. The proliferation and apoptosis of BMSCs under acidic conditions were analyzed by MTT and TUNEL assays. Ca2+-imaging was used to assess the acid-induced increase in the intracellular Ca2+ concentration ([Ca2+]i). The activation of calpain and calcineurin was analyzed using specific kits, and WB analysis was performed to detect apoptosis-related proteins. Ultrastructural changes in BMSCs were observed using transmission electron microscopy (TEM).Results: Acid exposure led to the activation of ASIC1a and increased BMSC apoptosis. The Ca2+ imaging assay showed a significant increase in the [Ca2+]i in response to a solution at pH 6.0. However, BMSC apoptosis and [Ca2+]i elevation were alleviated in the presence of an ASIC1a inhibitor. Moreover, ASIC1a mediated the Ca2+ influx-induced activation of calpain and calcineurin in BMSCs. WB analysis and TEM revealed mitochondrial apoptosis, which was inhibited by an ASIC1a inhibitor, in BMSCs under acidic conditions.Conclusions: The mimical acidic microenvironment of the degenerated IVD can induce BMSC apoptosis by activating Ca2+-permeable ASIC1a. An acid-induced elevation of [Ca2+]i in BMSCs leads to the subsequent activation of calpain and calcineurin, further resulting in increased mitochondrial permeability and mitochondrial-mediated apoptosis.
Highlights
Low back pain (LBP) is considered the most debilitating condition worldwide, and it results in substantial healthcare and socioeconomic consequences [1]
We found that the acid-induced elevation of the [Ca2+]i in bone marrow mesenchymal stem cell (BMSC) leads to the subsequent activation of calpain and calcineurin
BMSC transplantation can promote the regeneration of degenerative discs, the vitality of BMSCs is relatively limited in the harsh microenvironment of degenerative discs
Summary
Low back pain (LBP) is considered the most debilitating condition worldwide, and it results in substantial healthcare and socioeconomic consequences [1]. It has been reported that approximately 20% of annual healthcare costs caused in the U.S.A. are related to LBP [4,5]. One of the most common etiologies of LBP is intervertebral disc degeneration (IVDD) [6]. The intervertebral disc (IVD) consist mainly of three cell types: annulus fibrosus cells (AFCs) in the outer region; nucleus pulposus cells (NPCs) in the inner region; and endplate chondrocytes in the cephalic. The annulus fibrosus (AF) comprises 15–25 concentric rings of highly organized collagen fibers and surrounds the nucleus pulposus (NP) region, providing shape and mechanical tensile strength to the IVD [11,12,13]. The loss in number and decline in function of NPCs contributes to IVDD
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