Enhanced Mitochondria-SR Tethering Triggers Adaptive Cardiac Muscle Remodeling.

Background: Cardiac contractile function requires high energy from mitochondria, and Ca from the sarcoplasmic reticulum (SR). Via local Ca transfer at close mitochondria-SR contacts, cardiac excitation feedforward regulates mitochondrial ATP production to match surges in demand (excitation-bioenergetics coupling). However, pathological stresses may cause mitochondrial Ca overload, excessive reactive oxygen species production and permeability transition, risking homeostatic collapse and myocyte loss.

Defective dimerization of FoF1-ATP synthase secondary to glycation favors mitochondrial energy deficiency in cardiomyocytes during aging.

Aged cardiomyocytes develop a mismatch between energy demand and supply, the severity of which determines the onset of heart failure, and become prone to undergo cell death. The FoF1-ATP synthase is the molecular machine that provides >90% of the ATP consumed by healthy cardiomyocytes and is proposed to form the mitochondrial permeability transition pore (mPTP), an energy-dissipating channel involved in cell death. We investigated whether aging alters FoF1-ATP synthase self-assembly, a fundamental biological process involved in mitochondrial cristae morphology and energy efficiency, and the functional consequences this may have.

A Primeval Mechanism of Tolerance to Desiccation Based on Glycolic Acid Saves Neurons in Mammals from Ischemia by Reducing Intracellular Calcium-Mediated Excitotoxicity.

Stroke is the second leading cause of death and disability worldwide. Current treatments, such as pharmacological thrombolysis or mechanical thrombectomy, reopen occluded arteries but do not protect against ischemia-induced damage that occurs before reperfusion or neuronal damage induced by ischemia/reperfusion. It has been shown that disrupting the conversion of glyoxal to glycolic acid (GA) results in a decreased tolerance to anhydrobiosis in Caenorhabditis elegans dauer larva and that GA itself can rescue this phenotype.

Mitochondrial Ca concentrations in live cells: quantification methods and discrepancies.

Intracellular Ca signaling controls numerous cellular functions. Mitochondria respond to cytosolic Ca changes by adapting mitochondrial functions and, in some cell types, shaping the spatiotemporal properties of the cytosolic Ca signal. Numerous methods have been developed to specifically and quantitatively measure the mitochondrial-free Ca concentrations ([Ca ] ), but there are still significant discrepancies in the calculated absolute values of [Ca ] in stimulated live cells.

Spatial Separation of Mitochondrial Calcium Uptake and Extrusion for Energy-Efficient Mitochondrial Calcium Signaling in the Heart.

Mitochondrial Ca elevations enhance ATP production, but uptake must be balanced by efflux to avoid overload. Uptake is mediated by the mitochondrial Ca uniporter channel complex (MCUC), and extrusion is controlled largely by the Na/Ca exchanger (NCLX), both driven electrogenically by the inner membrane potential (ΔΨ). MCUC forms hotspots at the cardiac mitochondria-junctional SR (jSR) association to locally receive Ca signals; however, the distribution of NCLX is unknown.

Why don't mice lacking the mitochondrial Ca uniporter experience an energy crisis?

Current dogma holds that the heart balances energy demand and supply effectively and sustainably by sequestering enough Ca into mitochondria during heartbeats to stimulate metabolic enzymes in the tricarboxylic acid (TCA) cycle and electron transport chain (ETC). This process is called excitation-contraction-bioenergetics (ECB) coupling. Recent breakthroughs in identifying the mitochondrial Ca uniporter (MCU) and its associated proteins have opened up new windows for interrogating the molecular mechanisms of mitochondrial Ca homeostasis regulation and its role in ECB coupling.

Regulation of mitochondrial bioenergetics by the non-canonical roles of mitochondrial dynamics proteins in the heart.

Recent advancement in mitochondrial research has significantly extended our knowledge on the role and regulation of mitochondria in health and disease. One important breakthrough is the delineation of how mitochondrial morphological changes, termed mitochondrial dynamics, are coupled to the bioenergetics and signaling functions of mitochondria. In general, it is believed that fusion leads to an increased mitochondrial respiration efficiency and resistance to stress-induced dysfunction while fission does the contrary.

Strategic Positioning and Biased Activity of the Mitochondrial Calcium Uniporter in Cardiac Muscle.

Control of myocardial energetics by Ca signal propagation to the mitochondrial matrix includes local Ca delivery from sarcoplasmic reticulum (SR) ryanodine receptors (RyR2) to the inner mitochondrial membrane (IMM) Ca uniporter (mtCU). mtCU activity in cardiac mitochondria is relatively low, whereas the IMM surface is large, due to extensive cristae folding. Hence, stochastically distributed mtCU may not suffice to support local Ca transfer.

Lifeguard Inhibits Fas Ligand-mediated Endoplasmic Reticulum-Calcium Release Mandatory for Apoptosis in Type II Apoptotic Cells.

Death receptors are members of the tumor necrosis factor receptor superfamily involved in the extrinsic apoptotic pathway. Lifeguard (LFG) is a death receptor antagonist mainly expressed in the nervous system that specifically blocks Fas ligand (FasL)-induced apoptosis. To investigate its mechanism of action, we studied its subcellular localization and its interaction with members of the Bcl-2 family proteins.

Altered FoF1 ATP synthase and susceptibility to mitochondrial permeability transition pore during ischaemia and reperfusion in aging cardiomyocytes.

Aging is a major determinant of the incidence and severity of ischaemic heart disease. Preclinical information suggests the existence of intrinsic cellular alterations that contribute to ischaemic susceptibility in senescent myocardium, by mechanisms not well established. We investigated the role of altered mitochondrial function in the adverse effect of aging.

Microtubule stabilization with paclitaxel does not protect against infarction in isolated rat hearts.

What is the central question of this study? The microtubule network is disrupted during myocardial ischaemia-reperfusion injury. It was suggested that prevention of microtubule disruption with paclitaxel might reduce cardiac infarct size; however, the effects on infarction have not been studied. What is the main finding and its importance? Paclitaxel caused a reduction in microtubule disruption and cardiomyocyte hypercontracture during ischaemia-reperfusion.

Ischemic preconditioning protects cardiomyocyte mitochondria through mechanisms independent of cytosol.

Mitochondria play a central role in the protection conferred by ischemic preconditioning (IP) by not fully elucidated mechanisms. We investigated whether IP protects mitochondria against ischemia-reperfusion (IR) injury through mechanisms independent of cytosolic signaling. In isolated rat hearts, sublethal IR increased superoxide production and reduced complex-I- and II-mediated respiration in subsarcolemmal (SS), but not interfibrillar (IF) mitochondria.

Activation of RISK and SAFE pathways is not involved in the effects of Cx43 deficiency on tolerance to ischemia-reperfusion injury and preconditioning protection.

Connexin 43 (Cx43) deficiency increases myocardial tolerance to ischemia-reperfusion injury and abolishes preconditioning protection. It is not known whether modifications in baseline signaling through protective RISK or SAFE pathways or in response to preconditioning may contribute to these effects. To answer this question we used Cx43(Cre-ER(T)/fl) mice, in which Cx43 expression is abolished after 4-hydroxytamoxifen (4-OHT) administration.

Mitochondrial connexin 43 impacts on respiratory complex I activity and mitochondrial oxygen consumption.

Connexin 43 (Cx43) is present at the sarcolemma and the inner membrane of cardiomyocyte subsarcolemmal mitochondria (SSM). Lack or inhibition of mitochondrial Cx43 is associated with reduced mitochondrial potassium influx, which might affect mitochondrial respiration. Therefore, we analysed the importance of mitochondrial Cx43 for oxygen consumption.

The role of mitochondrial permeability transition in reperfusion-induced cardiomyocyte death depends on the duration of ischemia.

Mitochondrial permeability transition (MPT) is critical in cardiomyocyte death during reperfusion but it is not the only mechanism responsible for cell injury. The objectives of the study is to investigate the role of the duration of myocardial ischemia on mitochondrial integrity and cardiomyocyte death. Mitochondrial membrane potential (ΔΨm, JC-1) and MPT (calcein) were studied in cardiomyocytes from wild-type and cyclophilin D (CyD) KO mice refractory to MPT, submitted to simulated ischemia and 10 min reperfusion.

Effects of a reduction in the number of gap junction channels or in their conductance on ischemia-reperfusion arrhythmias in isolated mouse hearts.

A transient reduction of cell coupling during reperfusion limits myocardial necrosis, but little is known about its arrhythmogenic effects during ischemia-reperfusion. Thus, we analyzed the effect of an extreme reduction in the number of gap junction channels or in their unitary conductance on ventricular arrhythmias during myocardial ischemia-reperfusion. Available gap junction uncouplers have electrophysiological effects independent from their uncoupling actions.

Connexin and pannexin as modulators of myocardial injury.

Multicellular organisms have developed a variety of mechanisms that allow communication between their cells. Whereas some of these systems, as neurotransmission or hormones, make possible communication between remote areas, direct cell-to-cell communication through specific membrane channels keep in contact neighboring cells. Direct communication between the cytoplasm of adjacent cells is achieved in vertebrates by membrane channels formed by connexins.

The SR-mitochondria interaction: a new player in cardiac pathophysiology.

Mitochondria are essential for energy supply and cell signalling and may be triggers and effectors of cell death. Mitochondrial respiration is tightly controlled by the matrix Ca(2+) concentration, which is beat-to-beat regulated by uptake and release mainly through the mitochondrial Ca(2+) uniporter and Na(+)/Ca(2+) exchanger, respectively. Recent studies demonstrate that mitochondrial Ca(2+) uptake is more dependent on anatomo-functional microdomains established with the sarcoplasmic reticulum (SR) than on cytosolic Ca(2+).