Elevation Of Mitochondrial Ca2 Research Articles

Abstract 9601: Sarcolipin Reduction Prevents Mitochondrial Dysfunction in Dystrophic Myocardium

Rationale & Hypothesis: Sarcolipin (SLN), an inhibitor of sarco/endoplasmic reticulum Ca 2+ ATPase (SERCA) is abnormally high and enriched in the mitochondrial associated membrane (MAM) fractions of dystrophic hearts. We, therefore, hypothesized that in the dystrophic cardiomyocytes, SLN upregulation causes abnormal elevation of intracellular Ca 2+ (Ca 2+ i ) including Ca 2+ mishandling in the MAM region, resulting in sustained elevation of mitochondrial Ca 2+ (Ca 2+ m ), which in turn affects mitochondrial structure and function. Approach: We chose dystrophin mutant and utrophin deficient, mdx:utr -/- mice for our studies and generated SLN haploinsufficient mdx:utr -/- (mdx:utr -/- :sln +/- ) mice. Single-cell Ca 2+ transients and Ca 2+ m efflux were measured in isolated cardiomyocytes (CM's) to determine Ca 2+ i handling and Ca 2+ m content, respectively. Mitochondrial membrane potential was assessed with membrane-permeant dyes in isolated CM's followed by confocal imaging. Mitochondrial respiration was measured using Complex activity assays and Seahorse metabolic profiling in ventricular tissue lysates and isolated mitochondria respectively. Mitochondrial structure, number, and area were evaluated using electron micrographs (EM). Results: Heterozygous deletion of the SLN gene normalized SLN expression and improved Ca 2+ i cycling and prevented Ca 2+ m overload in dystrophic CM's. Furthermore, reducing SLN expression prevents loss of membrane potential and improves mitochondrial respiration in the dystrophic cardiac myocytes. TEM analyses of the dystrophic heart revealed significant cristae loss in the mitochondria globally as well as in the MAM-associated mitochondria. On the other hand, the reduction in SLN expression prevents these changes. Conclusions: In conclusion, reduction in SLN expression preserves the SR-mitochondrial interface and restores the mitochondrial function by mitigating the Ca 2+ overload, membrane potential loss, and structural damage. These changes improve cardiac function and prevent the development of cardiomyopathy in mdx:utr -/- mice. Our findings suggest that SLN reduction could be a potential therapeutic strategy for the treatment of Duchenne muscular dystrophy and associated cardiomyopathy.

Abstract P385: Sarcolipin Reduction Prevents Mitochondrial Dysfunction In Dystrophic Myocardium

Rationale & Hypothesis: Sarcolipin (SLN), an inhibitor of sarco/endoplasmic reticulum Ca 2+ ATPase (SERCA) is abnormally high and enriched in the mitochondrial associated membrane (MAM) fractions of dystrophic hearts. We, therefore, hypothesized that in the dystrophic cardiomyocytes, SLN upregulation causes abnormal elevation of intracellular Ca 2+ (Ca 2+ i ) including Ca 2+ mishandling in the MAM region, resulting in sustained elevation of mitochondrial Ca 2+ (Ca 2+ m ) , which in turn affects mitochondrial structure and function. Approach: We chose dystrophin mutant and utrophin deficient, mdx:utr -/- mice for our studies and generated SLN haploinsufficient mdx:utr -/- (mdx:utr -/- :sln +/- ) mice. Single-cell Ca 2+ transients and Ca 2+ m efflux were measured in isolated cardiomyocytes to determine Ca 2+ i handling and Ca 2+ m content, respectively. Mitochondrial membrane potential was assessed with membrane-permeant dyes in isolated cardiomyocytes followed by confocal imaging. Mitochondrial respiration was measured using Complex activity assays and Seahorse metabolic profiling in ventricular tissue lysates and isolated mitochondria respectively. Mitochondrial structure, number, and area were evaluated using electron micrographs. Results: Heterozygous deletion of the SLN gene normalized SLN expression and improved Ca 2+ i cycling and prevented Ca 2+ m overload in dystrophic cardiac myocytes. Furthermore, reducing SLN expression prevents loss of membrane potential and improves mitochondrial respiration in the dystrophic cardiac myocytes. Transmission electron microscopic analyses of the dystrophic heart revealed significant cristae loss in the mitochondria globally as well as in the MAM-associated mitochondria. On the other hand, the reduction in SLN expression prevents these changes. Conclusions: In conclusion, reduction in SLN expression preserves the SR-mitochondrial interface and restores the mitochondrial function by mitigating the Ca 2+ overload, membrane potential loss, and structural damage. These changes improve cardiac function and prevent the development of cardiomyopathy in mdx:utr -/- mice. Our findings suggest that SLN reduction could be a potential therapeutic strategy for the treatment of Duchenne muscular dystrophy and associated cardiomyopathy.

Liquiritin from Radix Glycyrrhizae Protects Cardiac Mitochondria from Hypoxia/Reoxygenation Damage.

Aims The purpose of this study was to evaluate the protective effect of liquiritin (LIQ) from Radix Glycyrrhizae on cardiac mitochondria against hypoxia/reoxygenation (HR) injury. Methods H9C2 cells were subject to the HR model. LIQ purified from Radix Glycyrrhizae (purity > 95%) was administrated to reoxygenation period. Cell viability, mitochondrial mass, mitochondrial membrane potential, reactive oxygen species, and mitochondrial Ca2⁺ level were then assessed by using Cell Counting kit-8 and suitable fluorescence probe kits. Results LIQ administration remarkably reduced the rate of HR damage via increasing H9C2 cell viability level and preserving mitochondria after HR. Particularly, 60 μM of LIQ posthypoxic treatment markedly reduced cell death in HR-subjected H9C2 cell groups (p < 0.05). Interestingly, posthypoxic treatment of LIQ significantly prevented the loss of mitochondrial membrane potential, the decrease in mitochondrial mass, the increase in reactive oxygen species production, and the elevation of mitochondrial Ca2⁺ level in HR-treated H9C2 cells. Conclusion The present study provides for the first time the cardioprotective of LIQ posthypoxic treatment via reducing H9C2 cell death and protecting cardiac mitochondria against HR damage.

α-Synuclein-Dependent Calcium Entry Underlies Differential Sensitivity of Cultured SN and VTA Dopaminergic Neurons to a Parkinsonian Neurotoxin.

Parkinson’s disease (PD) is a debilitating neurodegenerative disease characterized by a loss of dopaminergic neurons in the substantia nigra (SN). Although mitochondrial dysfunction and dysregulated α-synuclein (aSyn) expression are postulated to play a role in PD pathogenesis, it is still debated why neurons of the SN are targeted while neighboring dopaminergic neurons of the ventral tegmental area (VTA) are spared. Using electrochemical and imaging approaches, we investigated metabolic changes in cultured primary mouse midbrain dopaminergic neurons exposed to a parkinsonian neurotoxin, 1-methyl-4-phenylpyridinium (MPP+). We demonstrate that the higher level of neurotoxicity in SN than VTA neurons was due to SN neuron-specific toxin-induced increase in cytosolic dopamine (DA) and Ca2+, followed by an elevation of mitochondrial Ca2+, activation of nitric oxide synthase (NOS), and mitochondrial oxidation. The increase in cytosolic Ca2+ was not caused by MPP+-induced oxidative stress, but rather depended on the activity of both L-type calcium channels and aSyn expression, suggesting that these two established pathogenic factors in PD act in concert.

Fluorescence Analysis of the Mitochondrial Effect of a Plasmalemmal Na+/Ca2+ Exchanger Inhibitor, SEA0400, in Permeabilized H9c2 Cardiomyocytes.

We investigated the effect on mitochondrial Ca2+ of SEA0400, an inhibitor of the Na+/Ca2+ exchanger (NCX) which reduces mitochondrial Ca2+ overload during myocardial ischemia, in digitonin-permeabilized H9c2 cells expressing the mitochondrial-targeted Ca2+ indicator, yellow cameleon 3.1. The elevation of mitochondrial Ca2+ concentration caused by an increase in extramitochondrial Ca2+ concentration was inhibited by carbonyl cyanide p-(trifluoromethoxy) phenylhydrazone (FCCP) or ruthenium red, but enhanced by CGP-37157, a mitochondrial NCX inhibitor. SEA0400 had no effect on mitochondrial Ca2+ under normal and ischemic conditions. Thus, the mitochondria-protective effects of SEA0400 could be explained by inhibition of plasmalemmal NCX but not mitochondrial NCX.

The role of mitochondrial permeability transition pore in regulating the shedding of the platelet GPIbα ectodomain

Agonists induce platelet activation or apoptosis with concomitant shedding of the platelet receptor glycoprotein Ibα (GPIbα) ectodomain in a disintegrin and metalloproteinase 17 (ADAM17)-dependent mechanism. Mitochondrial permeability transition pore (MPTP) plays a pivotal role in platelet activation or apoptosis. However, its impact on ADAM17-mediated GPIbα ectodomain shedding remains unclear. Here, we aimed to test the hypothesis that MPTP regulates ADAM17-dependent GPIbα ectodomain shedding. We showed that calcium ionophore A23187- or thrombin plus collagen-induced GPIbα ectodomain shedding was partially inhibited by a MPTP inhibitor, and a MPTP potentiator promoted A23187-induced GPIbα cleavage. Furthermore, A23187-induced elevation of mitochondrial Ca2+ levels was blocked by the mitochondrial calcium uniporter (MCU) inhibitor Ru360 or treatment with the membrane-permeable Ca2+ chelator BAPTA-AM. We also demonstrated that an increase in mitochondrial Ca2+ levels triggered MPTP opening, as revealed by the examination of mitochondrial inner transmembrane potential depolarization. In addition, A23187 induced-mitochondrial reactive oxygen species (ROS) generation was blocked by the MPTP inhibitor or by treatment with the mitochondria-targeted ROS scavenger. Lastly, A23187-induced GPIbα shedding was partially blocked by inhibitors of either ROS or calpain, and was completely inhibited when platelets were exposed to both inhibitors. Therefore, these observations indicate that MPTP opening triggered mitochondrial ROS production, which plays an important role in regulating ADAM17-mediated shedding of the GPIbα ectodomain in A23187-treated platelets.

Calcium dysregulation, mitochondrial pathology and protein aggregation in a culture model of amyotrophic lateral sclerosis: Mechanistic relationship and differential sensitivity to intervention

The combination of Ca2+ influx during neurotransmission and low cytosolic Ca2+ buffering contributes to the preferential vulnerability of motor neurons in amyotrophic lateral sclerosis (ALS). This study investigated the relationship among Ca2+ accumulation in intracellular compartments, mitochondrial abnormalities, and protein aggregation in a model of familial ALS (fALS1). Human SOD1, wild type (SOD1WT) or with the ALS-causing mutation G93A (SOD1G93A), was expressed in motor neurons of dissociated murine spinal cord–dorsal root ganglia (DRG) cultures. Elevation of mitochondrial Ca2+ ([Ca2+]m), decreased mitochondrial membrane potential (Δψ) and rounding of mitochondria occurred early, followed by increased endoplasmic reticular Ca2+ ([Ca2+]ER), elevated cytosolic Ca2+ ([Ca2+]c), and subsequent appearance of SOD1G93A inclusions (a consequence of protein aggregation). [Ca2+]c was elevated to a greater extent in neurons with inclusions than in those with diffusely distributed SOD1G93A and promoted aggregation of mutant protein, not vice versa: both [Ca2+]c and the percentage of neurons with SOD1G93A inclusions were reduced by co-expressing the cytosolic Ca2+-buffering protein, calbindin D-28K; treatment with the heat shock protein inducer, geldanamycin, prevented inclusions but not the increase in [Ca2+]c, [Ca2+]m or loss of Δψ, and inhibiting proteasome activity with epoxomicin, known to promote aggregation of disease-causing mutant proteins including SOD1G93A, had no effect on Ca2+ levels. Both expression of SOD1G93A and epoxomicin-induced inhibition of proteasome activity caused mitochondrial rounding, independent of Ca2+ dysregulation and reduced Δψ. That geldanamycin prevented inclusions and mitochondrial rounding, but not Ca2+ dysregulation or loss of Δψ indicates that chaperone-based therapies to prevent protein aggregation may require co-therapy to address these other underlying mechanisms of toxicity.

Mitochondrial activation directly triggers the exocytosis of insulin in permeabilized pancreatic beta-cells.

In the pancreatic beta-cell, insulin secretion is stimulated by glucose metabolism resulting in membrane potential-dependent elevation of cytosolic Ca2+ ([Ca2+]c). This cascade involves the mitochondrial membrane potential (delta psi[m]) hyperpolarization and elevation of mitochondrial Ca2+ ([Ca2+]m) which activates the Ca(2+)-sensitive NADH-generating dehydrogenases. Metabolism-secretion coupling requires unidentified signals, other than [Ca2+]c, possibly generated by the mitochondria through the rise in [Ca2+]m. To test this paradigm, we have established an alpha-toxin permeabilized cell preparation permitting the simultaneous monitoring of [Ca2+] with mitochondrially targeted aequorin and insulin secretion under conditions of saturating [ATP] (10 mM) and of clamped [Ca2+]c at substimulatory levels (500 nM). The tricarboxylic acid (TCA) cycle intermediate succinate hyperpolarized delta psi(m), raised [Ca2+]m up to 1.5 microM and stimulated insulin secretion 20-fold, without changing [Ca2+]c. Blockade of the uniporter-mediated Ca2+ influx into the mitochondria abolished the secretory response. Moreover, glycerophosphate, which raises [Ca2+]m by hyperpolarizing delta psi(m) without supplying carbons to the TCA cycle, failed to stimulate exocytosis. Activation of the TCA cycle with citrate evoked secretion only when combined with glycerophosphate. Thus, mitochondrially driven insulin secretion at permissive [Ca2+]c requires both a substrate for the TCA cycle and a rise in [Ca2+]m. Therefore, mitochondrial metabolism generates factors distinct from Ca2+ and ATP capable of inducing insulin exocytosis.