Acid-sensing Ion Channel 1a Expression Research Articles

Identification and analgesic activity study of analgesic protein Ⅶ-2 from Naja naja atra venom.

Acid-sensing ion channel 1a (ASIC1a) plays a critical role in physiological and pathological processes. To further elucidate the biological functions of ASICs and their relationships with disease occurrence and development, it is advantageous to investigate and develop additional regulatory factors for ASICs. In this study, cation exchange chromatography was used to separate seven chromatographic components from Naja naja atra venom. Capillary electrophoresis was employed to detect that Ⅶ peak component containing a main protein Ⅶ-2, which could bind to ASIC1a. The analgesic effects of Ⅶ-2 protein were determined using hot plate methods, and ASIC1a expression in spinal cord tissue from rats with inflammatory pain was detected using western blot. The purified Ⅶ-2 protein named Naja naja atra venom-Ⅶ-2 (NNAV-Ⅶ-2) was obtained by Sephadex G-50 gel filtration, which exhibited a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with a molecular weight of 6.7 kD. Remarkably, the NNAV-Ⅶ-2 protein demonstrated a significant analgesic effect and downregulated ASIC1a expression in the spinal cord tissue of rats with inflammatory pain. The analgesic mechanism of the NNAV-Ⅶ-2 protein may be associated with its binding to ASIC1a, consequently downregulating ASIC1a expression in neural tissues.

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

AbstractNesfatin-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.

Regulation of gliomagenesis and stemness through acid sensor ASIC1a.

Glioblastoma multiforme (GBM) is the most prevalent and aggressive type of adult gliomas. Despite intensive therapy including surgery, radiation, and chemotherapy, invariable tumor recurrence occurs, which suggests that glioblastoma stem cells (GSCs) render these tumors persistent. Recently, the induction of GSC differentiation has emerged as an alternative method to treat GBM, and most of the current studies aim to convert GSCs to neurons by a combination of transcriptional factors. As the tumor microenvironment is typically acidic due to increased glycolysis and consequently leads to an increased production of lactic acid in tumor cells, in the present study, the role of acid-sensing ion channel 1a (ASIC1a), an acid sensor, was explored as a tumor suppressor in gliomagenesis and stemness. The bioinformatics data from The Cancer Genome Atlas revealed that ASIC1 expression levels in GBM tumor tissues were lower than those in normal brain, and glioma patients with high ASIC1 expression had longer survival than those with low ASIC1 expression. Our immunohistochemistry data from tissue microarray revealed that ASIC1a expression was negatively associated with glioma grading. Functional studies revealed that the downregulation of ASIC1a promoted glioma cell proliferation and invasion, while upregulation of ASIC1a inhibited their proliferation and invasion. Furthermore, ASIC1a suppressed growth and proliferation of glioma cells through G1/S arrest and apoptosis induction. Mechanistically, ASIC1a negatively modulated glioma stemness via inhibition of the Notch signaling pathway and GSC markers CD133 and aldehyde dehydrogenase 1. ASIC1a is a tumor suppressor in gliomagenesis and stemness and may serve as a promising prognostic biomarker and target for GBM patients.

OTME-19. Regula Regulation of Gliomagenesis and Stemness Through Acid Sensor ASIC1a

Glioblastoma multiforme (GBM) is the most prevalent and aggressive type of adult gliomas. Despite intensive therapy including surgery, radiation, and chemotherapy, invariable tumor recurrence occurs, which suggests that glioblastoma stem cells (GSC) render these tumors persistent. Recently, GSC differentiation has emerged as an alternative method to treat GBM, and most of current studies aim to convert GSC to neurons by a combination of transcriptional factors. As the tumor microenvironment is typically acidic due to increased glycolysis in tumor cells, here, we explored the role of acid-sensing ion channel 1a (ASIC1a), an acid sensor, as a tumor suppressor in gliomagenesis and stemness. The bioinformatics data from TCGA shows that ASIC1 expression levels in GBM tumor tissues were lower than those in normal brain, and glioma patients with elevated ASIC1 expression have longer survival than those with lowered ASIC1 expression. Our immunohistochemistry data from tissue microarray shows that ASIC1a expression is negatively correlated with glioma grading. Functional studies reveal that the downregulation of ASIC1a promotes glioma cell proliferation and invasion, while upregulation of ASIC1a inhibits their proliferation and invasion. Furthermore, ASIC1a suppresses glioma cells’ growth and proliferation through G1/S arrest and apoptosis induction. Mechanistically, ASIC1a negatively modulates glioma stemness via inhibition of the Notch signaling pathway and GSC markers CD133 and ALDH1. Our findings indicate that ASIC1a is a tumor suppressor in gliomagenesis and stemness and may serve as a promising prognostic biomarker and target for GBM patients.

Estrogen Protects Articular Cartilage by Downregulating ASIC1a in Rheumatoid Arthritis.

PurposeThe severity of rheumatoid arthritis (RA) in women is generally lower than that in men. RA is mediated, at least in part, by the protective effects of estradiol. However, the mechanisms underlying the protective effect of estradiol on RA are still unclear. Recent studies have demonstrated that activation of acid-sensing ion channel 1a (ASIC1a) by tissue acidosis plays an important role in the injury of cartilage in RA. Here, we assessed the effects of estradiol on acid-mediated cartilage injury both in vitro and in vivo and explored the involvement of ASIC1a in RA and its underlying mechanism.MethodsCultured primary articular chondrocytes were subjected to acidosis-mediated injury in vitro. Beclin1, LC3, p62, GPER1, and ASIC1a expression was detected through Western blotting, quantitative real-time PCR, and immunofluorescence analysis. Adjuvant arthritis (AA) was induced in rats through intradermal immunization by injecting 0.25 mL heat-killed mycobacteria (10 mg/mL) suspended in complete Freund’s adjuvant into the left hind metatarsal footpad. The levels of estrogen and related inflammatory factors in the serum were measured using enzyme-linked immunosorbent assay. The expression of ASIC1a and autophagy-related proteins was detected through immunohistochemical analysis and Western blot.ResultsTreatment of primary articular chondrocytes with estradiol decreased the expression of ASIC1a and autophagy level. The symptoms of cartilage damage and levels of inflammatory cytokines in the serum were reduced after estradiol treatment in the rats with AA. In addition, estradiol treatment reduced ASIC1a expression via the PI3K-AKT-mTOR pathway, among which G-protein coupled estradiol receptor 1 (GPER1) plays a regulatory role. Finally, the level of autophagy in chondrocytes was decreased by the selective ASIC1a blocker psalmotoxin-1 (PCTX-1).ConclusionEstradiol can protect the cartilage of rats with AA against acidosis-mediated damage and autophagy by suppressing ASIC1a expression through GPER1.

Evidence for role of acid-sensing ion channel 1a in chronic rhinosinusitis with nasal polyps.

A variety of inflammatory cells are infiltrated histologically in sinonasal mucosa of chronic rhinosinusitis with nasal polyps (CRSwNP), especially CRSwNP with asthma. Acid-sensing ion channel 1a (ASIC1a) is essential in the process of sensing acidification and triggering inflammation. Whereas, its role and mechanism in CRSwNP remain uncertain. The present study aimed to explore the roles and mechanism of ASIC1a in the pathogenesis of CRSwNP. Nasal secretions from control subjects, patients with CRSwNP with or without asthma were collected for measuring pH values. Western blotting, real-time PCR and immunohistochemistry (IHC) were employed to assess ASIC1a expression in nasal tissue samples from included subjects. The co-localization of ASIC1a with inflammatory cells was evaluated by immunofluorescence staining. Then, dispersed nasal polyp cells (DNPCs) were cultured under acidified condition (pH 6.0), with or without ASIC1a inhibitor amiloride. Western blotting, real-time PCR, LDH activity kit, and ELISA were performed to assess the effects and mechanisms of stimulators on the cells. The pH values were significantly lower in the nasal secretions from patients with CRSwNP with asthma. Significant upregulation of ASIC1a protein, mRNA levels, and positive cells was found in CRSwNP with asthma. ASIC1a was detected in a variety of inflammatory cells. In cultured DNPCs, significant alterations of ASIC1a levels, LDH activity, HIF-1α levels, and inflammatory cytokines were found under acidified condition (pH 6.0), but were prevented by amiloride. Upregulation of ASIC1a might be essential in the process of sensing acidification and triggering inflammatory response via enhancing HIF-1α expression and LDH activity to activate inflammatory cells in the pathogenesis of CRSwNP, especially in CRSwNP with asthma.

Upregulation of acid sensing ion channel 1a (ASIC1a) by hydrogen peroxide through the JNK pathway.

Oxidative stress is intimately tied to neurodegenerative diseases, including Parkinson's disease and amyotrophic lateral sclerosis, and acute injuries, such as ischemic stroke and traumatic brain injury. Acid sensing ion channel 1a (ASIC1a), a proton-gated ion channel, has been shown to be involved in the pathogenesis of these diseases. However, whether oxidative stress affects the expression of ASIC1a remains elusive. In the current study, we examined the effect of hydrogen peroxide (H2O2), a major reactive oxygen species (ROS), on ASIC1a protein expression and channel function in NS20Y cells and primary cultured mouse cortical neurons. We found that treatment of the cells with H2O2 (20 µM) for 6 h or longer increased ASIC1a protein expression and ASIC currents without causing significant cell injury. H2O2 incubation activated mitogen-activated protein kinases (MAPKs) pathways, including the extracellular signal-regulated kinase1/2 (ERK1/2), c-Jun N-terminal kinase (JNK), and p38 pathways. We found that neither inhibition of the MEK/ERK pathway by U0126 nor inhibition of the p38 pathway by SB203580 affected H2O2-induced ASIC1a expression, whereas inhibition of the JNK pathway by SP600125 potently decreased ASIC1a expression and abolished the H2O2-mediated increase in ASIC1a expression and ASIC currents. Furthermore, we found that H2O2 pretreatment increased the sensitivity of ASIC currents to the ASIC1a inhibitor PcTx1, providing additional evidence that H2O2 increases the expression of functional ASIC1a channels. Together, our data demonstrate that H2O2 increases ASIC1a expression/activation through the JNK signaling pathway, which may provide insight into the pathogenesis of neurological disorders that involve both ROS and activation of ASIC1a.

ASIC1a activation induces calcium-dependent apoptosis of BMSCs under conditions that mimic the acidic microenvironment of the degenerated intervertebral disc.

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.

β-Estradiol Protects Against Acidosis-Mediated and Ischemic Neuronal Injury by Promoting ASIC1a (Acid-Sensing Ion Channel 1a) Protein Degradation.

Background and Purpose- Sex differences in the incidence and outcome of stroke have been well documented. The severity of stroke in women is, in general, significantly lower than that in men, which is mediated, at least in part, by the protective effects of β-estradiol. However, the detailed mechanisms underlying the neuroprotection by β-estradiol are still elusive. Recent studies have demonstrated that activation of ASIC1a (acid-sensing ion channel 1a) by tissue acidosis, a common feature of brain ischemia, plays an important role in ischemic brain injury. In the present study, we assessed the effects of β-estradiol on acidosis-mediated and ischemic neuronal injury both in vitro and in vivo and explored the involvement of ASIC1a and underlying mechanism. Methods- Cultured neurons and NS20Y cells were subjected to acidosis-mediated injury in vitro. Cell viability and cytotoxicity were measured by methylthiazolyldiphenyl-tetrazolium bromide and lactate dehydrogenase assays, respectively. Transient (60 minutes) focal ischemia in mice was induced by suture occlusion of the middle cerebral artery in vivo. ASIC currents were recorded using whole-cell patch-clamp technique while intracellular Ca2+ concentration was measured with fluorescence imaging using Fura-2. ASIC1a expression was detected by Western blotting and quantitative real-time polymerase chain reaction. Results- Treatment of neuronal cells with β-estradiol decreased acidosis-induced cytotoxicity. ASIC currents and acid-induced elevation of intracellular Ca2+ were all attenuated by β-estradiol treatment. In addition, we showed that β-estradiol treatment reduced ASIC1a protein expression, which was mediated by increased protein degradation, and that estrogen receptor α was involved. Finally, we showed that the level of ASIC1a protein expression in brain tissues and the degree of neuroprotection by ASIC1a blockade were lower in female mice, which could be attenuated by ovariectomy. Conclusions- β-estradiol can protect neurons against acidosis-mediated neurotoxicity and ischemic brain injury by suppressing ASIC1a protein expression and channel function. Visual Overview- An online visual overview is available for this article.

NO in the dPAG modulates panic-like responses and ASIC1a expression in the prefrontal cortex and hippocampus in mice

Panic disorder (PD) is a multifactorial neuropsychiatric disorder. Our previous study has demonstrated that the nitric oxide (NO) pathway and the acid-sensing ion channel 1a (ASIC1a) level in the dorsal midbrain periaqueductal gray (dPAG) are involved in the modulation of panic-like responses. In addition, the prefrontal cortex (PFC) and the hippocampus also play a role in panic-like responses. However, no studies have investigated the protein level of ASIC1a in the PFC and hippocampus in a mouse model of panic-like disorders after alteration of the NO pathway in the dPAG. We investigated the production of a panic attack with intra-dPAG injections of SNAP, an NO donor, and 7-NI, an nNOS inhibitor. Moreover, we measured ASIC1a protein levels in the PFC and hippocampus. The rat exposure test (RET) is frequently used as an animal model of panic. In our study, C57BL/6 mice received an intra-dPAG injection of SNAP or 7-NI before RET; neurobehavioral tests were then conducted, followed by mechanistic evaluation through western blot analysis in the PFC and hippocampus. An intra-dPAG infusion of SNAP significantly increased the panic-like effect, whereas treatment with 7-NI decreased fear behavior. Mice treated with SNAP/7-NI showed significantly increased/decreased ASIC1a expression in the PFC, and a decreasing/increasing trend in the hippocampus. The present study suggests that the NO pathway in the dPAG plays a key role in panic-like responses in mice confronted by a rat, further, NO intra-dPAG injection also modulates the ASIC1a expression levels in the PFC and hippocampus.

Abstract TP140: Intra-Arterial Mesenchymal Stem Cell Therapy Modulates Expression of NLRP1 Inflammasome in Animal Model of Ischemic Stroke

Background: Stroke is one of the leading causes of long-term disability worldwide. Ischemia, followed by acidosis, worsens the pathology by activating the acid sensing ion channel 1a (ASIC1a). This activated ASIC1a increases the expression of NLRP1 inflammasome in a pH dependent manner that further activates the inflammatory cascade. ASIC1a once activated triggers the influx of Ca 2+ ions and its overload contributes to neuronal injury and death in ischemic stroke. Cell based therapy with mesenchymal stem cells (MSCs) is promising for clinical translation and reported to improve neurological outcome in rodent model. We aim to test if intra-arterial (IA) MSCs can inhibit the production of inflammasome by attenuating ASIC1a expression to render neuroprotection. Methods: Middle-aged Sprague Dawley rodents were infused with IA MSCs at 6 hours post middle cerebral artery occlusion (MCAo) followed by 24 hours of reperfusion. Rats were evaluated for neurodeficit and motor functions. Brains were harvested for infarct size estimation, biochemical analysis and western blot experiments. Results: IA MSCs when given at a dose of 1x10 5 cells at 6 hours following ischemia confer neuroprotection as evident by reduction in infarct volume, improvement in neurodeficit scores and motor function. Increase in GSH levels and reduction in elevated nitrite and MDA levels were observed in the IA MSCs treated animals. IA MSCs infusion also attenuated the expression of ASIC1a, NLRP1, NLRP3, ASC1, IL1β and caspase-1 in the cortical brain regions following ischemia. Conclusion: IA MSCs confers neuroprotection by attenuating acidosis by modulating NLRP1 mediated ASIC1a expression. Keywords: Ischemic Stroke, Mesenchymal stem cell, Inflammasome, Interleukin-1β, Peri-infarct area

Acute Ethanol Exposure Promotes Autophagy-Lysosome Pathway-Dependent ASIC1a Protein Degradation and Protects Against Acidosis-Induced Neurotoxicity.

Tissue acidosis is a common feature of brain ischemia which causes neuronal injury. Activation of acid-sensing ion channel 1a (ASIC1a) plays an important role in acidosis-mediated neurotoxicity. Acute ethanol administration has been shown to provide neuroprotective effects during ischemic stroke, but the precise mechanisms have yet to be determined. In this study, we investigated the effect of ethanol on the activity/expression of ASIC1a channels and acidosis-induced neurotoxicity. We showed that acute treatment of neuronal cells with ethanol for more than 3h could reduce ASIC1a protein expression, ASIC currents, and acid-induced [Ca2+]i elevation. We further demonstrated that ethanol-induced reduction of ASIC1a expression is mediated by autophagy-lysosome pathway (ALP)-dependent protein degradation. Finally, we showed that ethanol protected neuronal cells against acidosis-induced cytotoxicity, which effect was mimicked by autophagy activator rapamycin and abolished by autophagy inhibitor CQ. Together, these results indicate that moderate acute ethanol exposure can promote autophagy-lysosome pathway-dependent ASIC1a protein degradation and protect against acidosis-induced neurotoxicity.

Mechanism of nitric oxide and acid-sensing ion channel 1a modulation of panic-like behaviour in the dorsal periaqueductal grey of the mouse

Predators induce defensive responses and fear behaviours in prey. The rat exposure test (RET) is frequently used as an animal model of panic. Nitric oxide (NO) which has been reported to be activated by the NMDA receptor, in turn mediates calcium/calmodulin-dependent protein kinase II (CaMKII) signalling pathways in defensive responses. ACCN2, the orthologous human gene of acid-sensing ion channel 1a (ASIC1a), is also associated with panic disorder; however, few studies have focused on the role of ASIC1a in the modulation of panic and calcium/CaMKII signalling by NO. In the present study, NG-nitro-L-arginine-methyl-ester (L-NAME; non-selective NOS inhibitor), S-nitroso-N-acetyl-D,L-penicillamine (SNAP; NO donor), and psalmotoxin (PcTx-1; selective ASIC1a blocker) were administered to the dorsal periaqueductal grey (dPAG) before the predator stimulus, and the roles of NO in the expression of ASIC1a, phosphorylation of CaMKIIα (p-CaMKIIα) and expression of calmodulin (CaM) were investigated. The effects of ASIC1a, p-CaMKIIα and CaM regulation were also examined. Our results showed that intra-dPAG infusion of L-NAME weakened panic-like behaviour and decreased ASIC1a, p-CaMKIIα and CaM expression levels, whereas intra-dPAG infusion of SNAP enhanced panic-like behaviour and increased ASIC1a, p-CaMKIIα and CaM levels. Intra-dPAG infusion of PcTx-1 also weakened panic-like behaviour and decreased p-CaMKIIα expression level. Taken together, these results indicate that NO and ASIC1a are involved in the modulation of RET-induced panic-like behaviour in the dPAG. NO regulates the calcium/CaMKII signalling pathways, and ASIC1a participates in this regulation.

Involvement of acid-sensing ion channel 1a in gastric carcinoma cell migration and invasion.

Acidic microenvironment, particularly acid-sensing ion channel 1a (ASIC1a), has been reported to promote carcinoma cell proliferation as well as migration. In this study, we explored the effect of ASIC1a on migration and invasion of gastric carcinoma (GC). ASIC1a expression levels were examined in paired GC and adjacent normal tissues from 16 patients by immunohistochemistry. Reverse transcription real-time PCR and immunoblotting were conducted to assess the ASIC1a expression levels in the GC cell line AGS after transfection with ASIC1a small hairpin RNA (shRNA). Wound healing and transwell invasion assays were utilized to detect metastasis and invasion following ASIC1a silencing. Tumor formation was used to detect the role of ASIC1a in tumorigenicity in vivo. It was found that ASIC1a expression level was significantly higher in GC tissues showing postoperative metastasis compared with non-metastasis and non-tumor tissues. Moreover, silencing of ASIC1a with shRNA significantly down-regulated ASIC1a expression and reduced GC cell migration and invasion. A moderately acidic extracellular environment inhibited GC cell viability. Furthermore, ASIC1a shRNA caused inhibition of tumorigenicity in vivo. Our study is the first report of attenuating the malignant phenotype of GC in vitro and in vivo by suppressing ASIC1a, and suggests a novel approach to study the relationship between ASICs and GC cell migration and invasion.

Acid-Sensing Ion Channel 1a Regulates Fate of Rat Nucleus Pulposus Cells in Acid Stimulus Through Endoplasmic Reticulum Stress.

Acid-sensing ion channel 1a (ASIC1a) participates in human intervertebral disc degeneration (IVDD) and regulates the destiny of nucleus pulposus cells (NPCs) in acid stimulus. However, the mechanism of ASIC1a activation and its downstream pathway remain unclear. Endoplasmic reticulum (ER) stress also participates in the acid-induced apoptosis of NPCs. The main purpose of this study was to investigate whether there is any connection between ASIC1a and ER stress in an acid-induced nucleus pulposus degeneration model. The IVDs of Sprague-Dawley rats were stained by immunohistochemical staining to evaluate the expression of ASIC1a in normal and degenerated rat nucleus pulposus. ASIC1a expression was also quantified by quantitative real-time-polymerase chain reaction and Western blotting analysis. NPCs were exposed to the culture media with acidity at pH 7.2 and 6.5 for 24 h, with or without 4-phenylbutyrate (4-PBA, a blocker of the ER stress pathway). Cell apoptosis was examined by Annexin V/Propidium Iodide (PI) staining and was quantified using flow cytometry analysis. ASIC1a-mediated intracellular calcium was determined by Ca2+ imaging using Fura-2-AM. Acidity-induced changes in ER stress markers were studied using Western blotting analysis. In vivo, ASIC1a expression was upregulated in natural degeneration. In vitro, acid stimulus increased intracellular calcium levels, but this effect was blocked by knockdown of ASIC1a, and this reversal was partly inhibited by 4-PBA. In addition, blockade of ASIC1a reduced expression of ER stress markers, especially the proapoptotic markers. ASIC1a partly regulates ER stress and promotes apoptosis of NPCs under acid stimulus and may be a novel therapeutic target in IVDD.

ASIC2a overexpression enhances the protective effect of PcTx1 and APETx2 against acidosis-induced articular chondrocyte apoptosis and cytotoxicity

Acid hydrarthrosis is another important pathological character in rheumatoid arthritis (RA), and acid-sensing ion channel 1a (ASIC1a) plays a destructive role in acidosis-induced articular chondrocyte cytotoxicity. Recently, ASIC2a has been reported to possess neuroprotective effect on acidosis-induced injury of neuronal cells. However, whether ASIC2a has an enhanced effect on the protective effect of blocking ASIC1a and ASIC3 against acid-induced chondrocyte apoptosis is still unclear. The aim of present study was to investigate the chondroprotective effect of ASIC2a with PcTx1 (ASIC1a specific blocker) and APETx2 (ASIC3 specific blocker) on acidosis-induced chondrocyte apoptosis. Our results revealed that acid (pH 6.0) decreased the cell viability and induced apoptosis of articular chondrocytes. PcTx1 and APETx2 combination significantly attenuated acidosis-induced chondrocyte cytotoxicity due to inhibit apoptosis, and this role could be enhanced by ASIC2a overexpression compared with the PcTx1 and APETx2 combination alone group. Moreover, both the [Ca2+]i levels and the levels of phosphorylated ERK1/2 as well as p38 were further reduced in acidosis-induced chondrocytes after ASIC2a overexpression in the presence of PcTx1 and APETx2. Furthermore, ASIC2a overexpression also reduced acid-induced the expression of ASIC1a. In addition, ASIC2a overexpression further promoted the PcTx1 and APETx2-increased levels of type II collagen in acidosis-induced chondrocytes. Taken together, the current data suggested that ASIC2a overexpression might enhance the anti-apoptotic and protective role of PcTx1 and APETx2 against acid-induced rat articular chondrocyte apoptosis by regulating ASIC1a expression and the [Ca2+]i levels and at least in part, suppressing p38 and ERK1/2 MAPK signaling pathways.

Interleukin-1β and tumor necrosis factor-α augment acidosis-induced rat articular chondrocyte apoptosis via nuclear factor-kappaB-dependent upregulation of ASIC1a channel

The acute-phase proinflammatory cytokines interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) demonstrate high-level expression and pleiotropic biological effects, and contribute to the progression and persistence of rheumatoid arthritis (RA). Acid hydrarthrosis is also an important pathological characteristic of RA, and the acid-sensing ion channel 1a (ASIC1a) plays a critical role in acidosis-induced chondrocyte cytotoxicity. However, the roles of IL-1β and TNF-α in acid-induced apoptosis of chondrocytes remain unclear. Rat adjuvant arthritis and primary articular chondrocytes were used as in vivo and in vitro model systems, respectively. ASIC1a expression in articular cartilage was increased and highly colocalized with nuclear factor (NF)-κB expression in vivo. IL-1β and TNF-α could upregulate ASIC1a expression. These cytokines activated mitogen-activated protein kinase and NF-κB pathways in chondrocytes, while the respective inhibitors of these signaling pathways could partially reverse the ASIC1a upregulation induced by IL-1β and TNF-α. Dual luciferase and gel-shift assays and chromatin immunoprecipitation-polymerase chain reaction demonstrated that IL-1β and TNF-α enhanced ASIC1a promoter activity in chondrocytes by increasing NF-κB DNA-binding activities, which was in turn prevented by the NF-κB inhibitor ammonium pyrrolidinedithiocarbamate. IL-1β and TNF-α also decreased cell viability but enhanced LDH release, intracellular Ca2+ concentration elevation, loss of mitochondrial membrane potential, cleaved PARP and cleaved caspase-3/9 expression, and apoptosis in acid-stimulated chondrocytes, which effects could be abrogated by the specific ASIC1a inhibitor psalmotoxin-1 (PcTX-1), ASIC1a-short hairpin RNA or calcium chelating agent BAPTA-AM. These results indicate that IL-1β and TNF-α can augment acidosis-induced cytotoxicity through NF-κB-dependent up-regulation of ASIC1a channel expression in primary articular chondrocytes.

Interleukin-6 enhances acid-induced apoptosis via upregulating acid-sensing ion channel 1a expression and function in rat articular chondrocytes

The inflammatory cytokine interleukin-6 (IL-6) is a causative agent of rheumatoid arthritis (RA), a chronic inflammatory disease complicated with degenerative arthritic cartilage. However, the precise mechanism of IL-6 on chondrocyte apoptosis is largely unclear. Acid-sensing ion channels (ASICs), a family of extracellular H+-activated cation channels, can be transiently activated by extracellular acid and play a pivotal role in acid-induced cell injury. In the present study, to investigate the role of IL-6 in regulating acid-induced articular chondrocyte apoptosis, primary rat articular chondrocytes were subjected to different treatments with or without IL-6 in the presence of acid. The results showed that the mRNA and protein expressions of ASIC1a were significantly increased in articular cartilage and chondrocytes of adjuvant arthritis (AA) rats. IL-6 could dramatically upregulate the level of ASIC1a in a time- and dose-dependent manner, and induce the activation of JAK2, STAT3, ERK, JNK and NF-κB in articular chondrocytes. Moreover, both the respective inhibitors of these signaling pathways and the specific antibody against IL-6 receptor (tocilizumab) could partially abrogate the ASIC1a upregulation induced by IL-6. Furthermore, IL-6 inhibited the cell viability and enhanced LDH release, [Ca2+]i elevation, and apoptosis in acid-induced articular chondrocytes, and these changes could be reversed by using psalmotoxin 1(PcTX1), which is the specific antagonist of ASIC1a. In addition, pretreatment with PcTX1 could inhibit the downregulated expression of Bcl-2 and the upregulated expression of Bax induced by IL-6 in acid-induced articular chondrocytes. Taken together, these results indicated that IL-6 could enhance acid-induced articular chondrocyte apoptosis, the mechanism of which might partially be involved with its ability of regulating the activation of ASIC1a-dependent JAK2/STAT3 and MAPK/NF-κB signaling pathways.

A comparative study of gelatin sponge scaffolds and PLGA scaffolds transplanted to completely transected spinal cord of rat

This study sought to investigate whether gelatin sponge (GS) scaffold would produce less acidic medium in injured spinal cord, as compared with poly(lactic-co-glycolic acid) (PLGA) scaffold, to determine which of the two scaffolds as the biomaterial is more suitable for transplantation into spinal cord. GS scaffold or PLGA scaffold was transplanted into a transected spinal cord in this study. Two months after transplantation of scaffolds, acid sensing ion channel 1a (ASIC1a) positive cells expressing microtubule associated protein 2 (Map2) were observed as well as expressing adenomatous polyposis coli (APC) in spinal cord. GFAP positive cells were distributed at the rostral and caudal of the injury/graft area in the GS and PLGA groups. Western blot showed ASIC1a and GFAP expression of injured spinal cord was downregulated in the GS group. The number of CD68 positive cells was fewer and NF nerve fibers were more in the GS group. Nissl staining and cell counting showed that the number of survival neurons was comparable between the GS and PLGA groups in the pyramidal layer of sensorimotor cortex and the red nucleus of midbrain. However, in the Clarke's nucleus at L1 spinal segment, the surviving neurons in the GS group were more numerous than that in the PLGA group. H&E staining showed that the tissue cavities in the GS group were smaller in size than that in the PLGA group. The results suggest that GS scaffold is more suitable for transplantation to promote the recovery of spinal cord injury compared with PLGA scaffold.

Effect of Acid-sensing ion channel 1a in cultural human retinal pigment epithelial cells during oxidative stress

Objective To investigated whether Acid-sensing ion channel 1 a (ASIC1a) is expressed in the retinal pigment epithelium (RPE) cells and whether it is involved in the function of these cells.Methods Real time revere transcription-polymerase chain reaction (RT-PCR) and Western blotting were used to analyze the ASIC1a expression in ARPE-19 cells during oxidative stress induced by hydrogen peroxide (H2O2 ).Furthermore,blockage or overexpression of ASIC1a in RPE cells were obtained using inhibitors (amiloride and PCTxl ) or by the transfection of cDNA encoding hASIC1a.Cell viability was determined using the methyl thiazol tetrazolium (MTT) assay.Results The RT-PCR and Western blot results showed that both the mRNA and the protein of ASIC1a are expressed in RPE.Blockade of ASICs by amiloride in normal RPE cells resulted in cell death,indicating that ASICs play an important physiological role in RPE cells.Furthermore,overexpression of ASIC1a in RPE increased cell survival after oxidative stress induced by H2O2.Conclusion ASIC1a is functionally expressed in RPE cells and may play an important role in the physiological function of RPE cells in protecting them from oxidative stress. Key words: Acid-sensing ion channel 1a; Retinal pigment epithelium; Oxidative stress