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

Nesfatin-1 exerts protective effects on acidosis-stimulated chondrocytes and rats with adjuvant-induced arthritis by inhibiting ASIC1a expression

Nesfatin-1, a newly identified energy-regulating peptide, has been reported to possess antioxidant, anti-inflammatory, and antiapoptotic properties; however, to date, its effect on rheumatoid arthritis (RA) has not been previously explored in detail. We previously showed that activation of acid-sensing ion channel 1a (ASIC1a) by acidosis plays an important role in RA pathogenesis. Therefore, in this study, we evaluated the effects of nesfatin-1 on acidosis-stimulated chondrocyte injury in vitro and in vivo and examined the involvement of ASIC1a and the mechanism underlying the effects of nesfatin-1 on RA. Acid-stimulated articular chondrocytes were used to examine one of the several possible mechanisms underlying RA pathogenesis in vitro. The mRNA expression profile of acid-induced chondrocytes treated or not treated with nesfatin-1 was investigated by RNA sequencing. The effects of nesfatin-1 on oxidative stress, inflammation, and apoptosis in acid-induced chondrocytes were measured. The mechanistic effect of nesfatin-1 on ASIC1a expression and intracellular Ca²⁺ in acid-stimulated chondrocytes was studied. Rats with adjuvant-induced arthritis (AA) were used for in vivo analysis of RA pathophysiology. Cartilage degradation and ASIC1a expression in chondrocytes were detected in rats with AA after intraarticular nesfatin-1 injection. The in vitro experiments showed that nesfatin-1 decreased acidosis-induced cytotoxicity and elevation of intracellular Ca²⁺ levels in chondrocytes. Moreover, it attenuated acid-induced oxidative stress, inflammation, and apoptosis in chondrocytes. Nesfatin-1 decreased ASIC1a protein levels in acid-stimulated chondrocytes via the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) and nuclear factor kappa-B (NF-κB) signaling pathways. In vivo analysis showed that nesfatin-1 ameliorated cartilage degradation and decreased ASIC1a expression in the chondrocytes of rats with AA. Collectively, nesfatin-1 suppressed acidosis-induced oxidative stress, inflammation, and apoptosis in acid-stimulated chondrocytes and alleviated arthritis symptoms in rats with AA, and its mechanism may be related to its ability to decrease ASIC1a protein levels via the MAPK/ERK and NF-κB pathways.

ASIC1α up-regulates MMP-2/9 expression to enhance mobility and proliferation of liver cancer cells via the PI3K/AKT/mTOR pathway

A major challenge in the treatment of liver cancer is that a large proportion of patients fail to achieve long-term disease control, with death from liver cancer cell migration and invasion. Acid-sensitive ion channel 1α (ASIC1α) is involved in the migration, invasion, and proliferation of liver cancer cells. Therefore, we explored the mechanism of ASIC1α-mediated liver cancer cell migration and invasion. We determined the levels of ASIC1α by western blotting and immunofluorescence in HepG2 and SK-Hep1 cells cultured in various acidic conditions. In addition, wound healing assay, transwell invasion assay, and MTT assay were conducted to assess the migration, invasion, and proliferation abilities of liver cancer cells. Western blotting was conducted to determine the levels of MMP2, MMP9, ASIC1α, p-PI3Kp85, t-PI3Kp85, p-AKT(Ser473), t-AKT, p-mTOR (Ser2448), t-mTOR. We first found that the levels of ASIC1α in the HepG2 and SK-Hep1 cells in acidic conditions (pH 6.5) were significantly increased. Inhibition and knockdown of ASIC1α down-regulated MMP-2/9 expression and inhibited the migration, invasion, and proliferation of HepG2 and SK-Hep1 cells; overexpression of ASIC1α had the opposite effect. We further demonstrated that ASIC1α up-regulates MMP-2/9 via activation of the PI3K/AKT/mTOR pathway, thereby promoting migration, invasion, and proliferation of liver cancer cells. Overexpression of MMP-2/9 and activation of AKT reversed these effects on liver cancer cells caused by inhibition of ASIC1α. We conclude that ASIC1α can regulate migration, invasion, and proliferation of liver cancer cells through the MMP-2/9/PI3K/AKT/mTOR pathway. These observations may provide a new reference for liver cancer chemotherapy.

ASIC1a promotes the proliferation of synovial fibroblasts via the ERK/MAPK pathway

Synovial hyperplasia, a profound alteration in the structure of synovial tissue, is the basis for cumulative joint destruction in rheumatoid arthritis (RA). It is generally accepted that controlling synovial hyperplasia can delay the progression of RA. As one of the most intensively studied isoforms of acid-sensing ion channels (ASICs), ASIC1a contributes to various physiopathologic conditions, including RA, due to its unique property of being permeable to Ca2+. However, the role and the regulatory mechanisms of ASIC1a in synovial hyperplasia are poorly understood. Here, rats induced with adjuvant arthritis (AA) and human primary synovial fibroblasts were used in vivo and in vitro to investigate the role of ASIC1a in the proliferation of RA synovial fibroblasts (RASFs). The results show that the expression of ASIC1a was significantly increased in synovial tissues and RASFs obtained from patients with RA as well as in the synovium of rats with AA. Moreover, extracellular acidification improved the ability of RASFs colony formation and increased the expression of proliferation cell nuclear antigen (PCNA) and Ki67, which was abrogated by the specific ASIC1a inhibitor psalmotoxin-1 (PcTX-1) or ASIC1a-short hairpin RNA (ASIC1a-shRNA), suggesting that extracellular acidification promotes the proliferation of RASFs by activating ASIC1a. In addition, the activation of c-Raf and extracellular signal-regulated protein kinases (ERKs) signaling was blocked with PcTX-1 or ASIC1a-shRNA and the proliferation of RASFs was further inhibited by the ERK inhibitor (U0126), indicating that ERK/MAPK signaling contributes to the proliferation process of RASFs promoted by the activation of ASIC1a. These findings gave us an insight into the role of ASIC1a in the proliferation of RASFs, which may provide solid foundation for ASIC1a as a potential target in the treatment of RA.

Acid-Sensing Ion Channel-1a in Articular Chondrocytes and Synovial Fibroblasts: A Novel Therapeutic Target for Rheumatoid Arthritis

Acid-sensing ion channel 1a (ASIC1a) is a member of the extracellular H⁺-activated cation channel family. Emerging evidence has suggested that ASIC1a plays a crucial role in the pathogenesis of rheumatoid arthritis (RA). Specifically, ASIC1a could promote inflammation, synovial hyperplasia, articular cartilage, and bone destruction; these lead to the progression of RA, a chronic autoimmune disease characterized by chronic synovial inflammation and extra-articular lesions. In this review, we provided a brief overview of the molecular properties of ASIC1a, including the basic biological characteristics, tissue and cell distribution, channel blocker, and factors influencing the expression and function, and focused on the potential therapeutic targets of ASIC1a in RA and possible mechanisms of blocking ASIC1a to improve RA symptoms, such as regulation of apoptosis, autophagy, pyroptosis, and necroptosis of articular cartilage, and synovial inflammation and invasion of fibroblast-like cells in synovial tissue.

Metabolome-Driven Regulation of Adenovirus-Induced Cell Death

A viral infection that involves virus invasion, protein synthesis, and virion assembly is typically accompanied by sharp fluctuations in the intracellular levels of metabolites. Under certain conditions, dramatic metabolic shifts can result in various types of cell death. Here, we review different types of adenovirus-induced cell death associated with changes in metabolic profiles of the infected cells. As evidenced by experimental data, in most cases changes in the metabolome precede cell death rather than represent its consequence. In our previous study, the induction of autophagic cell death was observed following adenovirus-mediated lactate production, acetyl-CoA accumulation, and ATP release, while apoptosis was demonstrated to be modulated by alterations in acetate and asparagine metabolism. On the other hand, adenovirus-induced ROS production and ATP depletion were demonstrated to play a significant role in the process of necrotic cell death. Interestingly, the accumulation of ceramide compounds was found to contribute to the induction of all the three types of cell death mentioned above. Eventually, the characterization of metabolite analysis could help in uncovering the molecular mechanism of adenovirus-mediated cell death induction and contribute to the development of efficacious oncolytic adenoviral vectors.

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

Acid-sensing ion channels (ASICs) are members of the degenerin/epithelial sodium channel superfamily. They are extracellular pH sensors that are activated by protons. Among all ASICs, ASIC1a is one of the most intensively studied isoforms because of its unique ability to be permeable to Ca²⁺. In addition, it is considered to contribute to various pathophysiological conditions. As a membrane proton receptor, the number of ASIC1a present on the cell surface determines its physiological and pathological functions, and this number partially depends on protein synthesis, degradation, and membrane trafficking processes. Recently, several studies have shown that various factors affect these processes. Therefore, this review elucidated the major factors and underlying molecular mechanisms affecting ASIC1a protein expression and membrane trafficking.