Aims: Alterations in calcium homeostasis in the intracellular endo/sarcoplasmic reticulum (ER/SR) and mitochondria of cardiomyocytes cause cell death via the SR a

/pdf/role-of-the-calcium-sensing-receptor-in-cardiomyocyte-4ctcm3kqf6.pdf

Role of the Calcium-Sensing Receptor in Cardiomyocyte Apoptosis via the Sarcoplasmic Reticulum and Mitochondrial Death Pathway in Cardiac Hypertrophy and Heart Failure

In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis updated guidelines for monitoring autophagy in different organisms. Despite numerous reviews, there continues to be confusion regarding acceptable methods to evaluate autophagy, especially in multicellular eukaryotes. Here, we present a set of guidelines for investigators to select and interpret methods to examine autophagy and related processes, and for reviewers to provide realistic and reasonable critiques of reports that are focused on these processes. These guidelines are not meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being asked and the system being used. Moreover, no individual assay is perfect for every situation, calling for the use of multiple techniques to properly monitor autophagy in each experimental setting. Finally, several core components of the autophagy machinery have been implicated in distinct autophagic processes (canonical and noncanonical autophagy), implying that genetic approaches to block autophagy should rely on targeting two or more autophagy-related genes that ideally participate in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for bona fide autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation in the field.

Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition)

Reperfusion may induce additional cell death in patients with acute myocardial infarction receiving primary angioplasty or thrombolysis. Altered intracellular Ca 2+ handling was initially considered an essential mechanism of reperfusion-induced cardiomyocyte death. However, more recent studies have demonstrated the importance of Ca 2+ -independent mechanisms that converge on mitochondrial permeability transition (MPT) and are shared by cardiomyocytes and other cell types. This article analyses the importance of Ca 2+ -dependent cell death in light of these new observations. Altered Ca 2+ handling includes increased cytosolic Ca 2+ levels, leading to activation of calpainmediated proteolysis and sarcoplasmic reticulum-driven oscillations; this can induce hypercontracture, but also MPT due to the privileged Ca 2+ transfer between sarcoplasmic reticulum and mitochondria through cytosolic Ca 2+ microdomains. In the opposite direction, permeability transition can worsen altered Ca 2+ handling and favour hypercontracture. Ca 2+ appears to play an important role in cell death during the initial minutes of reperfusion, particularly after brief periods of ischaemia. Developing effective and safe treatments to prevent Ca 2+ -mediated cardiomyocyte death in patients with transient ischaemia, by targeting Ca 2+ influx, intracellular Ca 2+ handling, or Ca 2+ -induced cell death effectors, is an unmet challenge with important therapeutic implications and large potential clinical impact.

/pdf/calcium-mediated-cell-death-during-myocardial-reperfusion-rnhqm9204l.pdf

Calcium-mediated cell death during myocardial reperfusion

Since the discovery of the calcium-sensing receptor, studies reveal that it can detect not only calcium but a host of extracellular signals and that besides its key role in calcium homeostasis the receptor is involved in a myriad of unrelated biological processes. This review provides a comprehensive exploration of the receptor, including its structure, stimuli, signaling pathways, interacting protein partners and tissue expression patterns, and relates the impact of these different aspects of the calcium-sensing receptor to its functionality from a molecular perspective.

The Calcium-Sensing Receptor: A Molecular Perspective

H2S belongs to the class of molecules known as gasotransmitters, which also includes nitric oxide (NO) and carbon monoxide (CO). Three enzymes are recognized as endogenous sources of H2S in various cells and tissues: cystathionine g-lyase (CSE), cystathionine β-synthase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST). The current article reviews the regulation of these enzymes as well as the pathways of their enzymatic and non-enzymatic degradation and elimination. The multiple interactions of H2S with other labile endogenous molecules (e.g. NO) and reactive oxygen species are also outlined. The various biological targets and signaling pathways are discussed, with special reference to H2S and oxidative posttranscriptional modification of proteins, the effect of H2S on channels and intracellular second messenger pathways, the regulation of gene transcription and translation and the regulation of cellular bioenergetics and metabolism. The pharmacological and molecular tools currently available to study H2S physiology are also reviewed, including their utility and limitations. In subsequent sections, the role of H2S in the regulation of various physiological and cellular functions is reviewed. The physiological role of H2S in various cell types and organ systems are overviewed. Finally, the role of H2S in the regulation of various organ functions is discussed as well as the characteristic bell-shaped biphasic effects of H2S. In addition, key pathophysiological aspects, debated areas, and future research and translational areas are identified A wide array of significant roles of H2S in the physiological regulation of all organ functions emerges from this review.

Physiological roles of hydrogen sulfide in mammalian cells, tissues and organs.

Hydrogen sulfide (H2S), an important gasotransmitter, regulates cardiovascular functions. Mitochondrial damage induced by the overproduction of reactive oxygen species (ROS) results in myocardial injury with a diabetic state. The purpose of this study was to investigate the effects of exogenous H2S on mitophagy formation in diabetic cardiomyopathy. In this study, we found that exogenous H2S could improve cardiac functions, reduce mitochondrial fragments and ROS levels, enhance mitochondrial respiration chain activities and inhibit mitochondrial apoptosis in the hearts of db/db mice. Our results showed that exogenous H2S facilitated parkin translocation into mitochondria and promoted mitophagy formation in the hearts of db/db mice. Our studies further revealed that the ubiquitination level of cytosolic parkin was increased and the expression of USP8, a deubiquitinating enzyme, was decreased in db/db cardiac tissues. S-sulfhydration is a novel posttranslational modification of specific cysteine residues on target proteins by H2S. Our results showed that the S-sulfhydration level of USP8 was obviously decreased in vivo and in vitro under hyperglycemia and hyperlipidemia, however, exogenous H2S could reverse this effect and promote USP8/parkin interaction. Dithiothreitol, a reducing agent that reverses sulfhydration-mediated covalent modification, increased the ubiquitylation level of parkin, abolished the effects of exogenous H2S on USP8 deubiquitylation and suppressed the interaction of USP8 with parkin in neonatal rat cardiomyocytes treated with high glucose, oleate and palmitate. Our findings suggested that H2S promoted mitophagy formation by increasing S-sulfhydration of USP8, which enhanced deubiquitination of parkin through the recruitment of parkin in mitochondria.

Exogenous H2S Promoted USP8 Sulfhydration to Regulate Mitophagy in the Hearts of db/db Mice.

The intracellular Ca2+ concentration ([Ca2+]i) is increased during cardiac ischemia/reperfusion injury (IRI), leading to endo(sarco)plasmic reticulum (ER) stress. Persistent ER stress, such as with the accumulation of [Ca2+]i, results in apoptosis. Ischemic post-conditioning (PC) can protect cardiomyocytes from IRI by reducing the [Ca2+]i via protein kinase C (PKC). The calcium-sensing receptor (CaR), a G protein-coupled receptor, causes the production of inositol phosphate (IP3) to increase the release of intracellular Ca2+ from the ER. This process can be negatively regulated by PKC through the phosphorylation of Thr-888 of the CaR. This study tested the hypothesis that PC prevents cardiomyocyte apoptosis by reducing the [Ca2+]i through an interaction of PKC with CaR to alleviate [Ca2+]ER depletion and [Ca2+]m elevation by the ER-mitochondrial associated membrane (MAM). Cardiomyocytes were post-conditioned after 3 h of ischemia by three cycles of 5 min of reperfusion and 5 min of re-ischemia before 6 h of reperfusion. During PC, PKCe translocated to the cell membrane and interacted with CaR. While PC led to a significant decrease in [Ca2+]i, the [Ca2+]ER was not reduced and [Ca2+]m was not increased in the PC and GdCl3–PC groups. Furthermore, there was no evident ∆ψm collapse during PC compared with ischemia/reperfusion (I/R) or PKC inhibitor groups, as evaluated by laser confocal scanning microscopy. The apoptotic rates detected by TUNEL and Hoechst33342 were lower in PC and GdCl3–PC groups than those in I/R and PKC inhibitor groups. Apoptotic proteins, including m-calpain, BAP31, and caspase-12, were significantly increased in the I/R and PKC inhibitor groups. These results suggested that PKCe interacting with CaR protected post-conditioned cardiomyocytes from programmed cell death by inhibiting disruption of the mitochondria by the ER as well as preventing calcium-induced signaling of the apoptotic pathway.

Post-conditioning protects cardiomyocytes from apoptosis via PKCε-interacting with calcium-sensing receptors to inhibit endo(sarco)plasmic reticulum-mitochondria crosstalk

Hydrogen sulfide (H2S) is involved in diverse physiological functions, such as anti-hypertension, anti-proliferation, regulating ATP synthesis, and reactive oxygen species production. Sirtuin 3 (SIRT3) is a NAD
 +
 -dependent deacetylase that regulates mitochondrial energy metabolism. The role of H2S in energy metabolism in diabetic cardiomyopathy (DCM) may be related to regulate SIRT3 expression; however, this role remains to be elucidated. We hypothesized that exogenous H2S could switch cardiac energy metabolic substrate preference by lysine acetylation through promoting the expression of SIRT3 in cardiac tissue of db/db mice. Db/db mice, neonatal rat cardiomyocytes, and H9c2 cell line with the treatment of high glucose, oleate, and palmitate were used as animal and cellular models of type 2 diabetes. Using LC-MS/MS, we identified 76 proteins that increased acetylation, including 8 enzymes related to fatty acid β-oxidation and 7 enzymes of the tricarboxylic acid (TCA) cycle in the db/db mice hearts compared to those with the treatment of NaHS. Exogenous H2S restored the expression of NAMPT and the ratio of NAD+/NADH enhanced the expression and activity of SIRT3. As a result of activation of SIRT3, the acetylation level and activity of fatty acid β-oxidation enzyme LCAD and the acetylation of glucose oxidation enzymes PDH, IDH2, and CS were reduced which resulted in activation of PDH, IDH2, and CS. Our finding suggested that H2S induced a switch in cardiac energy substrate utilization from fatty acid β-oxidation to glucose oxidation in DCM through regulating SIRT3 pathway.

Exogenous H2S switches cardiac energy substrate metabolism by regulating SIRT3 expression in db/db mice

The calcium-sensing receptor (CaR) is a G protein-coupled receptor. The CaR stimulation elicits phospholipase C-mediated inositol triphosphate formation, leading to an elevation in the level of intracellular calcium released from endoplasmic reticulum (ER). Depletion of ER Ca(2+) leads to ER stress, which is thought to induce apoptosis. Intracellular calcium overload-induced apoptosis in cardiac myocytes during hypoxia-reoxygenation (H/Re) has been demonstrated. However, the links between CaR, ER stress and apoptosis during H/Re are unclear. This study hypothesized that the CaR could induce apoptosis in neonatal rat cardiomyocytes during H/Re via the ER stress pathway. Neonatal rat cardiomyocytes were subjected to 3 hr of hypoxia, followed by 6 hr of reoxygenation. CaR expression was elevated and the number of apoptotic cells was significantly increased, as shown by transferase-mediated dUTP nick end-labelling, with exposure to CaCl(2), a CaR activator, during H/Re. The intracellular calcium concentration was significantly elevated and the Ca(2+) concentration in the ER was dramatically decreased during H/Re with CaCl(2); both intracellular and ER calcium concentrations were detected by laser confocal microscopy. Expression of GRP78 (glucose-regulated protein 78), the cleavage products of ATF6 (activating transcription factor 6), phospho-PERK [pancreatic ER kinase (PKR)-like ER kinase], the activated fragments of caspase-12, and phospho-JNK (c-Jun NH(2)-terminal kinase) were increased following exposure to CaCl(2) during H/Re. Our results confirmed that the activated CaR can induce cardiomyocyte apoptosis via ER stress-associated apoptotic pathways during H/Re.

Calcium‐Sensing Receptors Induce Apoptosis in Rat Cardiomyocytes via the Endo(sarco)plasmic Reticulum Pathway during Hypoxia/Reoxygenation

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Exogenous H2S Promoted USP8 Sulfhydration to Regulate Mitophagy in the Hearts of db/db Mice.

Post-conditioning protects cardiomyocytes from apoptosis via PKCε-interacting with calcium-sensing receptors to inhibit endo(sarco)plasmic reticulum-mitochondria crosstalk

Exogenous H2S switches cardiac energy substrate metabolism by regulating SIRT3 expression in db/db mice

Calcium‐Sensing Receptors Induce Apoptosis in Rat Cardiomyocytes via the Endo(sarco)plasmic Reticulum Pathway during Hypoxia/Reoxygenation