Ischemic postconditioning protects against ischemic brain injury by up-regulation of acid-sensing ion channel 2a

Ischemic postconditioning for stroke treatment: current experimental advances and future directions

Ischemic postconditioning (IPostC) protects against brain injury induced by stroke and is a potential strategy for ischemic stroke treatment. Understanding its underlying mechanisms and potential hurdles is essential for clinical translation. In this review article, we will summarize the current advances in IPostC for stroke treatment and the underlying protective mechanisms. Strong evidence suggests that IPostC reduces brain infarct size, attenuates blood-brain barrier (BBB) damage and brain edema, and improves neurological outcomes. IPostC also promotes neurogenesis and angiogenesis at the recovery phase of ischemic stroke. The protective mechanisms involve its effects on anti-oxidative stress, anti-inflammation, and anti-apoptosis. In addition, it regulates neurotransmitter receptors, ion channels, heat shock proteins (HSP) 40/70, as well as growth factors such as BDNF and VEGF. Furthermore, IPostC modulates several cell signaling pathways, including the PI3K/Akt, MAPK, NF-κB, and the Gluk2/PSD95/MLK3/MKK7/JNK3 pathways. We also discuss the potential hurdles for IPostC's clinical translation, including insufficient IPostC algorithm studies, such as therapeutic time windows and ischemia-reperfusion periods and cycles, as well as its long-term protection. In addition, future studies should address confounding factors such as age, sex, and pre-existing conditions such as hypertension and hyperglycemia before stroke onset. At last, the combination of IPostC with other treatments, such as tissue plasminogen activator (t-PA), merits further exploration.

Acid-sensing ion channels: Linking extracellular acidification with atherosclerosis

Extracellular acidification in atherosclerosis-prone regions of arterial walls is considered pro-atherosclerotic by exerting detrimental effect on macrophages, endothelial cells (ECs) and vascular smooth muscle cells (VSMCs). Acid-sensing ion channels (ASICs), a family of extracellular H⁺ (proton)-gated cation channels, are present extensively in the nervous system and other tissues, implying physiologic as well as pathophysiologic importance. Aberrant activation of ASICs is thought to be associated in EC dysfunction, macrophage phenotypic switch, and VSMC migration and proliferation. Although in vitro evidence acknowledges the contribution of ASIC activation in atherosclerosis, no direct evidence confirms their pro-atherosclerotic roles in vivo. In this review, the effect of extracellular acidity on three major contributors, ECs, macrophages, and VSMCs, is discussed focusing on the potential roles of ASICs in atherosclerotic development and underlying pathology. A more comprehensive understanding of ASICs in these processes may provide promising new therapeutic targets for treatment and prevention of atherosclerotic diseases.

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.

Ischemic Tolerance of the Brain and Spinal Cord: A Review

Ischemic tolerance is an endogenous neuroprotective phenomenon induced by sublethal ischemia. Ischemic preconditioning (IPC), the first discovered form of ischemic tolerance, is widely seen in many species and in various organs including the brain and the spinal cord. Ischemic tolerance of the spinal cord is less familiar among neurosurgeons, although it has been reported from the viewpoint of preventing ischemic spinal cord injury during aortic surgery. It is important for neurosurgeons to have opportunities to see patients with spinal cord ischemia, and to understand ischemic tolerance of the spinal cord as well as the brain. IPC has a strong neuroprotective effect in animal models of ischemia; however, clinical application of IPC for ischemic brain and spinal diseases is difficult because they cannot be predicted. In addition, one drawback of preconditioning stimuli is that they are also capable of producing injury with only minor changes to their intensity or duration. Numerous methods to induce ischemic tolerance have been discovered that vary in their timing and the site at which short-term ischemia occurs. These methods include ischemic postconditioning (IPoC), remote ischemic preconditioning (RIPC), remote ischemic perconditioning (RIPerC) and remote ischemic postconditioning (RIPoC), which has had a great impact on clinical approaches to treatment of ischemic brain and spinal cord injury. Especially RIPerC and RIPoC to induce spinal cord tolerance are considered clinically useful, however the evidence supporting these methods is currently insufficient; further experimental or clinical research in this area is thus necessary.

A Review on Potential Involvement of TRPV1 Channels in Ischemia–Reperfusion Injury

Besides functioning as thermosensors, transient receptor potential vanilloid 1 (TRPV1) channels play a pivotal role in ischemia–reperfusion injury. Transient receptor potential vanilloid 1 channel activation attenuates ischemia–reperfusion-induced injury in various organs including the heart, lungs, kidneys, and the brain. Transient receptor potential vanilloid 1 channels are expressed on the sensory neurons innervating the myocardium, ventricles of the heart, epicardial surface of the heart, endothelial cells, and the vascular smooth muscle cells. During ischemic conditions, activation of TRPV1 channels on the perivascular nerves stimulates the release of calcitonin gene-related peptide and substance P to produce cardioprotection. Furthermore, TRPV1 channel activation reduces the generation of free radicals and inflammatory cytokines, inhibits neutrophil infiltration, and enhances the production of anti-inflammatory cytokines to reduce ischemia–reperfusion-induced tissue injury. The present review describes the potential involvement of TRPV1 channels and the signaling cascade in attenuating ischemia–reperfusion injury in various organs.

Cerebral ischemic post‑conditioning induces autophagy inhibition and a HMGB1 secretion attenuation feedback loop to protect against ischemia reperfusion injury in an oxygen glucose deprivation cellular model

Cerebral ischemic postconditioning (IPOC) has been demonstrated to be neuroprotective against cerebral ischemia reperfusion injury. The present study aimed to determine whether IPOC could inhibit autophagy and high mobility group box 1 (HMGB1) release in a PC12 cell oxygen glucose deprivation/reperfusion (OGD/R) model. An 8 h OGD and 24 h reperfusion cellular model was developed to mimic cerebral ischemia reperfusion injury, with 3 cycles of 10 min OGD/5 min reperfusion treatment to imitate IPOC. Cell viability was determined to demonstrate the efficiency of OGD/R, IPOC and autophagy activator, rapamycin (RAP), treatment. Transmission electron microscopy was performed to observe the formation of autophagosomes, and immunofluorescence, western blot and co‑immunoprecipitation were used to examine the expression of autophagy‑associated proteins and HMGB1. Enzyme‑linked immunosorbent assay analysis was conducted to examine the level of HMGB1 in cell supernatants. Additionally, PC12 cells were treated with RAP to examine the effect of autophagy on HMGB1 release, and the effect of recombinant human HMGB1 and Beclin1 small interfering RNA on autophagy was investigated. The present study confirmed that IPOC inhibited autophagy and HMGB1 secretion, autophagy inhibition induced a decrease in HMGB1 secretion, and HMGB1 secretion attenuation caused autophagy inhibition in return, as demonstrated by immunofluorescence and western blot analyses. Autophagy inhibition and HMGB1 secretion attenuation were, therefore, demonstrated to form a feedback loop under IPOC. These mechanisms illustrated the protective effects of IPOC and may accelerate the clinical use of IPOC.