Ca²⁺ overload and mitochondrial permeability transition pore activation in living δ-sarcoglycan-deficient cardiomyocytes

Abstract

Muscular dystrophies are often associated with significant cardiac disease that can be the prominent feature associated with gene mutations in sarcoglycan. Cardiac cell death is a main feature of cardiomyopathy in sarcoglycan deficiency and may arise as a cardiomyocyte intrinsic process that remains unclear. Deficiency of delta-sarcoglycan (delta-SG) induces disruption of the dystrophin-associated glycoprotein complex, a known cause of membrane instability that may explain cardiomyocytes cytosolic Ca2+ increase. In this study we assessed the hypothesis that cytosolic Ca2+ increase triggers cardiomyocyte death through mitochondrial Ca2+ overload and dysfunction in the delta-SG-deficient CHF147 hamster. We showed that virtually all isolated CHF147 ventricular myocytes exhibited elevated cytosolic and mitochondrial Ca2+ levels by the use of the Fura-2 and Rhod-2 fluorescent probes. Observation of living cells with Mito-Tracker red lead to the conclusion that approximately 15% of isolated CHF147 cardiomyocytes had disorganized mitochondria. Transmission electron microscope imaging showed mitochondrial swelling associated with crest and membrane disruption. Analysis of the mitochondrial permeability transition pore (MPTP) activity using calcein revealed that mitochondria of CHF147 ventricular cells were twofold leakier than wild types, whereas reactive oxygen species production was unchanged. Bax, Bcl-2, and LC3 expression analysis by Western blot indicated that the intrinsic apoptosis and the cell death associated to autophagy pathways were not significantly activated in CHF147 hearts. Our results lead to conclusion that cardiomyocytes death in delta-SG-deficient animals is an intrinsic phenomenon, likely related to Ca2+-induced necrosis. In this process Ca2+ overload-induced MPTP activation and mitochondrial disorganization may have an important role.

SERCA2a Gene Therapy Can Improve Symptomatic Heart Failure in δ-Sarcoglycan-Deficient Animals

“…Disruption of membrane stability by the loss of d-SG may lead to increased intracellular Ca 2 + levels that seem to be responsible for cell death (Fraysse et al, 2010). Previously, we have demonstrated that d-SG deficiency triggers a cascade of molecular modification in the myocardium.…”

“…The precise pathophysiology of the cardiomyopathy remains largely unknown, but disruption of the DGC, due to a d-SG mutation, is the leading molecular event, which triggers the disease as it induces weakening of the mechanical connection between the contractile apparatus and the cell membrane. However, the membrane instability also allows increased entry of calcium via nonspecific channels and mitochondrial disorganization (Fraysse et al, 2010). Ample evidence suggests that abnormal elevation of cytosolic calcium may play a central role in the pathogenesis of heart disease (Dunn and Radda, 1991;Alloatti et al, 1995;Williams and Allen, 2007;Fauconnier et al, 2010;Sarma et al, 2010).…”

Mitochondrial Alterations and Oxidative Stress in an Acute Transient Mouse Model of Muscle Degeneration

“…Elevated cytosolic Ca 2ϩ , abnormal activity of the mitochondrial permeability transition pore, and necrosis is observed in ␦-sarcoglycan-deficient hamster cardiomyocytes (76). Analysis of Facio scapulo humeral dystrophy revealed decreased cytochrome c oxidase activity and reduced ATP synthesis (46) and altered mitochondrial permeability transition pore and apoptosis (77).…”

Humanin rescues cultured rat cortical neurons from NMDA-induced toxicity through the alleviation of mitochondrial dysfunction

“…In the matrix, calcium upregulates the activity of Ca 2+ -sensitive dehydrogenases of the Krebs cycle and the F 1 F 0 -ATP synthase and thereby controls the rate of ATP production 5,6. A pathological aspect of this process is linked with the mitochondrial Ca 2+ overload, which might trigger the activation of the mitochondrial permeability transmission pore, which in turn releases apoptotic and necrotic signal factors, leading to cell death 7,8. Neuronal energy supplies are, meanwhile, entirely based on mitochondrial oxidative phosphorylation, making them especially vulnerable to mitochondrial dysfunction 4…”