Molecular basis of arrhythmic substrate in ageing murine peroxisome proliferator-activated receptor γ co-activator deficient hearts modelling mitochondrial dysfunction

Abstract

Introduction: Ageing and chronic metabolic disorders are associated with mitochondrial dysfunction and cardiac pro-arrhythmic phenotypes which were recently attributed to slowed atrial and ventricular action potential (AP) conduction in peroxisome proliferator-activated receptor γ co-activator deficient (Pgc-1β−/−) mice. Methods: We compared expression levels of voltage-gated Na+ channel (NaV1.5) and gap junction channels, Connexins 40 and 43 (Cx40 and Cx43) in the hearts of young and old, and wild-type (WT) and Pgc-1β−/− mice. This employed Western blotting (WB) for NaV1.5, Cx40 and Cx43 in atrial/ventricular tissue lysates, and immunofluorescence (IF) from Cx43 was explored in tissue sections. Results were analysed using two-way analysis of variance (ANOVA) for independent/interacting effects of age and genotype. Results: In atria, increased age and Pgc-1β−/− genotype each independently decreased both Cx40 and Cx43 expression without interacting effects. In IF experiments, both age and Pgc-1β deletion independently reduced Cx43 expression. In ventricles, age and genotype exerted interacting effects in WB studies of NaV1.5 expression. Young Pgc-1β−/− then showed greater NaV1.5 expression than young WT ventricles. However, neither age nor Pgc-1β deletion affected Cx43 expression, independently or through interacting effects in both WB and IF studies. Conclusion: Similar pro-arrhythmic atrial/ventricular phenotypes arise in aged/Pgc-1β−/− from differing contributions of altered protein expression and functional effects that may arise from multiple acute mechanisms.

Protein expression profiles in murine ventricles modeling catecholaminergic polymorphic ventricular tachycardia: effects of genotype and sex

“…7,8 CPVT is associated with mutations in the cardiac RyR2 Ca 2+ release channel, [20][21][22] SR Ca 2+ -binding CASQ2, [23][24][25][26][27] Murine homozygotic RyR S/S atrial and ventricular cardiomyocytes thus demonstrated associated elevations in cytosolic Ca 2+ , reflecting altered balances between the action of the underlying RyR2, CASQ2, FKBP12, Ca V 1.2, NCX1, and SERCA2a, and proarrhythmic DAD events. [28][29][30][31]35 Additionally, there were compromised AP generation and CV, 32,[37][38][39][40][41] particularly following adrenergic challenge. 32,39,40,42,43 These functions depend on Na V 1.5 and Cx43 expression and function, 39,44,45 Cx43 phosphorylation levels, 46 and any alterations in cardiomyocyte capacitance or coupling following TGF-β-induced, often age-related, fibrotic change.…”

“…Protein extraction and BCA assay preparation were performed as previously described 41,53,54 . Protein quantification was performed using Image Studio™ software (LI‐COR Biosciences, EU).…”

“…31,36 First, the expression and function of any of the Ca 2+ homeostasis proteins RyR2, CASQ2, FK506binding protein 12 (FKBP12, termed FKBP1A, or calstabin1), voltage-dependent L-type Ca 2+ channels (Ca V 1.2), cardiac Na + /Ca 2+ exchanger 1 (NCX1), and the cardiac SR Ca 2+ -ATPase 2a (SERCA2a) could modify cytosolic Ca 2+ , thereby altering proarrhythmic DAD generation. Second, recently reported proarrhythmic reductions in RyR2-P2328S ventricular action potential (AP) conduction velocities (CV), 32,[37][38][39][40][41] particularly following adrenergic challenge, 32,39,40,42,43 were suggested to reflect altered Na V 1.5 expression and/or function; Na V 1.5 mediates fast Na + currents (I Na ), driving AP upstroke and conduction. Alternatively, connexins, including connexin (Cx)-43, in intercalated disks separating atrial and ventricular myocytes, 44 determine axial resistances (r a ) to cell-cell coupling, 38,45 with r a increased by Cx phosphorylation.…”

Mitochondrial Dysfunction Increases Arrhythmic Triggers and Substrates; Potential Anti-arrhythmic Pharmacological Targets

“…A clear link exists between aging and mitochondrial dysfunction, occurring through various mechanism which include mitochondrial DNA damage, clonal expansion of deleterious mutations in mitochondrial DNA and deficiencies in the enzymes of the mitochondrial respiratory chain, such as cytochrome-c-oxidase ( 32 – 36 ). This phenomenon of aging driving mitochondrial genetic instability has thus been observed not just in humans but several other mammalian species, including in mice, rats, and rhesus monkeys ( 37 – 39 ).…”

“…However, this effect was blocked by application of mitoTEMPO a specific scavenger of mitochondrial superoxide ( 69 , 70 ). In murine hearts modeling mitochondrial dysfunction, increased age and Pgc-1β-/- genotype interacted to decrease atrial Na V 1.5 channel expression ( 36 ). Furthermore, the A280V mutation in glycerol-3-phosphate dehydrogenase 1-like (GPD1-L) protein, which causes Brugada syndrome, reduces I Na via increasing cytosolic NADH and mitochondrial ROS levels ( 73 , 74 ).…”