Enhanced cell-volume regulation in cyclosporin A cardioprotection

Chloride ions in health and disease

Chloride is a key anion involved in cellular physiology by regulating its homeostasis and rheostatic processes. Changes in cellular Cl- concentration result in differential regulation of cellular functions such as transcription and translation, post-translation modifications, cell cycle and proliferation, cell volume, and pH levels. In intracellular compartments, Cl- modulates the function of lysosomes, mitochondria, endosomes, phagosomes, the nucleus, and the endoplasmic reticulum. In extracellular fluid (ECF), Cl- is present in blood/plasma and interstitial fluid compartments. A reduction in Cl- levels in ECF can result in cell volume contraction. Cl- is the key physiological anion and is a principal compensatory ion for the movement of the major cations such as Na+, K+, and Ca2+. Over the past 25 years, we have increased our understanding of cellular signaling mediated by Cl-, which has helped in understanding the molecular and metabolic changes observed in pathologies with altered Cl- levels. Here, we review the concentration of Cl- in various organs and cellular compartments, ion channels responsible for its transportation, and recent information on its physiological roles.

Chloride Homeostasis Regulates cGAS-STING Signaling

The cGAS-STING signaling pathway has emerged as a key mediator of inflammation. However, the roles of chloride homeostasis on this pathway are unclear. Here, we uncovered a correlation between chloride homeostasis and cGAS-STING signaling. We found that dysregulation of chloride homeostasis attenuates cGAS-STING signaling in a lysosome-independent manner. Treating immune cells with chloride channel inhibitors attenuated 2'3'-cGAMP production by cGAS and also suppressed STING polymerization, leading to reduced cytokine production. We also demonstrate that non-selective chloride channel blockers can suppress the NPC1 deficiency-induced, hyper-activated STING signaling in skin fibroblasts derived from Niemann Pick disease type C (NPC) patients. Our findings reveal that chloride homeostasis majorly affects cGAS-STING pathway and suggest a provocative strategy to dampen STING-mediated inflammation via targeting chloride channels.

CLIC4 localizes to mitochondrial-associated membranes and mediates cardioprotection

Mitochondrial-associated membranes (MAMs) are known to modulate organellar and cellular functions and can subsequently affect pathophysiology including myocardial ischemia-reperfusion (IR) injury. Thus, identifying molecular targets in MAMs that regulate the outcome of IR injury will hold a key to efficient therapeutics. Here, we found chloride intracellular channel protein (CLIC4) presence in MAMs of cardiomyocytes and demonstrate its role in modulating ER and mitochondrial calcium homeostasis under physiological and pathological conditions. In a murine model, loss of CLIC4 increased myocardial infarction and substantially reduced cardiac function after IR injury. CLIC4 null cardiomyocytes showed increased apoptosis and mitochondrial dysfunction upon hypoxia-reoxygenation injury in comparison to wild-type cardiomyocytes. Overall, our results indicate that MAM-CLIC4 is a key mediator of cellular response to IR injury and therefore may have a potential implication on other pathophysiological processes.

Focus on the Role of the NLRP3 Inflammasome in Multiple Sclerosis: Pathogenesis, Diagnosis, and Therapeutics

Neuroinflammation is initiated with an aberrant innate immune response in the central nervous system (CNS) and is involved in many neurological diseases. Inflammasomes are intracellular multiprotein complexes that can be used as platforms to induce the maturation and secretion of proinflammatory cytokines and pyroptosis, thus playing a pivotal role in neuroinflammation. Among the inflammasomes, the nucleotide-binding oligomerization domain-, leucine-rich repeat- and pyrin domain-containing 3 (NLRP3) inflammasome is well-characterized and contributes to many neurological diseases, such as multiple sclerosis (MS), Alzheimer's disease (AD), and ischemic stroke. MS is a chronic autoimmune disease of the CNS, and its hallmarks include chronic inflammation, demyelination, and neurodegeneration. Studies have demonstrated a relationship between MS and the NLRP3 inflammasome. To date, the pathogenesis of MS is not fully understood, and clinical studies on novel therapies are still underway. Here, we review the activation mechanism of the NLRP3 inflammasome, its role in MS, and therapies targeting related molecules, which may be beneficial in MS.

Sestrin2 is involved in the Nrf2-regulated antioxidative signaling pathway in luteolin-induced prevention of the diabetic rat heart from ischemia/reperfusion injury

Luteolin attenuates myocardial ischemia/reperfusion (I/R) injury in diabetes through activating the nuclear factor erythroid 2-related factor 2 (Nrf2)-related antioxidative response. Though sestrin2, a highly conserved stress-inducible protein, is regarded as a modulator of Nrf2 and reduces I/R injury, the effect of sestrin2 on luteolin-induced prevention of the diabetic heart from I/R injury remains unclear. We hypothesized that luteolin could relieve myocardial I/R injury in diabetes by activating the sestrin2-modulated Nrf2 antioxidative response. Diabetes was induced in rats using a single dose of streptozotocin (65 mg kg^-1, i.p.) for 6 weeks, and then luteolin (100 mg kg^-1 d^-1, i.g.), Nrf2 inhibitor brusatol, or sestrin2 blocker leucine was administered for 2 consecutive weeks. After that, the hearts were isolated and exposed to global I/R (30 min/120 min). Luteolin markedly improved cardiac function, myocardial viability and expressions of Nrf2-regulated antioxidative genes, and reduced lactate dehydrogenase release, malondialdehyde, and 8-hydroxydeoxyguanosine in the diabetic I/R hearts. Ca²⁺-induced mitochondrial permeability transition and membrane potential disruption were markedly inhibited in luteolin-treated diabetic ventricular myocytes. All these effects of luteolin were significantly reversed by Nrf2 inhibitor brusatol or sestrin2 inhibitor leucine. Luteolin-induced diminished Keap1 and augmented nuclear translocation and ARE binding activity of Nrf2 were hampered by leucine in the diabetic I/R heart. In addition, luteolin-induced augmented transcription of sestrin2 was markedly blocked by brusatol in the diabetic I/R heart. These data suggest that sestrin2 and Nrf2 positively interact to promote antioxidative actions and attenuate mitochondrial damage, by which luteolin relieves diabetic myocardial I/R injury.

Intracellular Chloride Channels: Novel Biomarkers in Diseases

Ion channels are integral membrane proteins present on the plasma membrane as well as intracellular membranes. In the human genome, there are more than 400 known genes encoding ion channel proteins. Ion channels are known to regulate several cellular, organellar, and physiological processes. Any mutation or disruption in their function can result in pathological disorders, both common or rare. Ion channels present on the plasma membrane are widely acknowledged for their role in various biological processes, but in recent years, several studies have pointed out the importance of ion channels located in intracellular organelles. However, ion channels located in intracellular organelles are not well-understood in the context of physiological conditions, such as the generation of cellular excitability and ionic homeostasis. Due to the lack of information regarding their molecular identity and technical limitations of studying them, intracellular organelle ion channels have thus far been overlooked as potential therapeutic targets. In this review, we focus on a novel class of intracellular organelle ion channels, Chloride Intracellular Ion Channels (CLICs), mainly documented for their role in cardiovascular, neurophysiology, and tumor biology. CLICs have a single transmembrane domain, and in cells, they exist in cytosolic as well as membranous forms. They are predominantly present in intracellular organelles and have recently been shown to be localized to cardiomyocyte mitochondria as well as exosomes. In fact, a member of this family, CLIC5, is the first mitochondrial chloride channel to be identified on the molecular level in the inner mitochondrial membrane, while another member, CLIC4, is located predominantly in the outer mitochondrial membrane. In this review, we discuss this unique class of intracellular chloride channels, their role in pathologies, such as cardiovascular, cancer, and neurodegenerative diseases, and the recent developments concerning their usage as theraputic targets.

Chloride channel blocker IAA-94 increases myocardial infarction by reducing calcium retention capacity of the cardiac mitochondria

Indanyloxyacetic acid-94 (IAA-94), an intracellular chloride channel blocker, is shown to ablate cardioprotection rendered by ischemic preconditioning (IPC), N (6)-2-(4-aminophenyl) ethyladenosine or the PKC activator phorbol 12-myristate 13-acetate and cyclosporin A (CsA) in both ex-vivo and in-vivo ischemia-reperfusion (IR) injury. Thus signifying the role of the IAA-94 sensitive chloride channels in mediating cardio-protection upon IR injury. Although IAA-94 sensitive chloride currents are recorded in cardiac mitoplast, there is still a lack of understanding of the mechanism by which IAA-94 increases myocardial infarction (MI) by IR injury. Mitochondria are the key arbitrators of cell life and death pathways. Both oxidative stress and calcium overload in the mitochondria, elicit pathways resulting in the opening of mitochondrial permeability transition pore (mPTP) leading to cell death. Therefore, in this study we explored the role of IAA-94 in MI and in maintaining calcium retention capacity (CRC) of cardiac mitochondria after IR. IAA-94 inhibited the CRC of the isolated cardiac mitochondria in a concentration-dependent manner as measured spectrofluorimetrically using calcium green-5 N. Interestingly, IAA-94 did not change the mitochondrial membrane potential. Further, CsA a blocker of mPTP opening could not override the effect of IAA-94. We also showed for the first time that IAA-94 perfusion after ischemic event augments MI by reducing the CRC of mitochondria. To conclude, our results demonstrate that the mechanism of IAA-94 mediated cardio-deleterious effects is via modulating the mitochondria CRC, thereby playing a role in mPTP opening. These findings highlight new pharmacological targets, which can mediate cardioprotection from IR injury.

Molecular identity of cardiac mitochondrial chloride intracellular channel proteins

Emerging evidences demonstrate significance of chloride channels in cardiac function and cardioprotection from ischemia-reperfusion (IR) injury. Unlike mitochondrial potassium channels sensitive to calcium (BKCa) and ATP (KATP), molecular identity of majority of cardiac mitochondrial chloride channels located at the inner membrane is not known. In this study, we report the presence of unique dimorphic chloride intracellular channel (CLIC) proteins namely CLIC1, CLIC4 and CLIC5 as abundant CLICs in the rodent heart. Further, CLIC4, CLIC5, and an ortholog present in Drosophila (DmCLIC) localize to adult cardiac mitochondria. We found that CLIC4 is enriched in the outer mitochondrial membrane, whereas CLIC5 is present in the inner mitochondrial membrane. Also, CLIC5 plays a direct role in regulating mitochondrial reactive oxygen species (ROS) generation. Our study highlights that CLIC5 is localized to the cardiac mitochondria and directly modulates mitochondrial function.

Combined Salvianolic Acid B and Ginsenoside Rg1 Exerts Cardioprotection against Ischemia/Reperfusion Injury in Rats

Lack of pharmacological strategies in clinics restricts the patient prognosis with myocardial ischemia/reperfusion (I/R) injury. The aim of this study was to evaluate the cardioprotection of combined salvianolic acid B (SalB) and ginsenoside Rg1 (Rg1) against myocardial I/R injury and further investigate the underlying mechanism. I/R injury was induced by coronary artery ligation for Wistar male rats and hypoxia/reoxygenation injury was induced on H9c2 cells. Firstly, the best ratio between SalB and Rg1was set as 2:5 based on their effects on heart function detected by hemodynamic measurement. Then SalB-Rg1 (2:5) was found to maintain mitochondrial membrane potential and resist apoptosis and necrosis in H9c2 cell with hypoxia/reoxygenation injury. Companying with same dose of SalB or Rg1 only, SalB-Rg1 showed more significant effects on down-regulation of myocardial infarct size, maintenance of myocardium structure, improvement on cardiac function, decrease of cytokine secretion including TNF-α, IL-1β, RANTES and sVCAM-1. Finally, the SalB-Rg1 improved the viability of cardiac myocytes other than cardiac fibroblasts in rats with I/R injury using flow cytometry. Our results revealed that SalB-Rg1 was a promising strategy to prevent myocardial I/R injury.

Cyclosporine A reduces microvascular obstruction and preserves left ventricular function deterioration following myocardial ischemia and reperfusion

Postconditioning and cyclosporine A prevent mitochondrial permeability transition pore opening providing cardioprotection during ischemia/reperfusion. Whether microvascular obstruction is affected by these interventions is largely unknown. Pigs subjected to coronary occlusion for 1 h followed by 3 h of reperfusion were assigned to control (n = 8), postconditioning (n = 9) or cyclosporine A intravenous infusion 10–15 min before the end of ischemia (n = 8). Postconditioning was induced by 8 cycles of repeated 30-s balloon inflation and deflation. After 3 h of reperfusion magnetic resonance imaging, triphenyltetrazolium chloride/Evans blue staining and histopathology were performed. Microvascular obstruction (MVO, percentage of gadolinium-hyperenhanced area) was measured early (3 min) and late (12 min) after contrast injection. Infarct size with double staining was smaller in cyclosporine (46.2 ± 3.1 %, P = 0.016) and postconditioning pigs (47.6 ± 3.9 %, P = 0.008) versus controls (53.8 ± 4.1 %). Late MVO was significantly reduced by cyclosporine (13.9 ± 9.6 %, P = 0.047) but not postconditioning (23.6 ± 11.7 %, P = 0.66) when compared with controls (32.0 ± 16.9 %). Myocardial blood flow in the late MVO was improved with cyclosporine versus controls (0.30 ± 0.06 vs 0.21 ± 0.03 ml/g/min, P = 0.002) and was inversely correlated with late-MVO extent (R² = 0.93, P < 0.0001). Deterioration of left ventricular ejection fraction (LVEF) between baseline and 3 h of reperfusion was smaller with cyclosporine (−7.9 ± 2.4 %, P = 0.008) but not postconditioning (−12.0 ± 5.5 %, P = 0.22) when compared with controls (−16.4 ± 5.5 %). In the three groups, infarct size (β = −0.69, P < 0.001) and late MVO (β = −0.33, P = 0.02) were independent predictors of LVEF deterioration following ischemia/reperfusion (R² = 0.73, P < 0.001). Despite both cyclosporine A and postconditioning reduce infarct size, only cyclosporine A infusion had a beneficial effect on microvascular damage and was associated with better preserved LV function when compared with controls.