Bechara, L. R. | Search bioRxiv

bioRxiv2026

Caloric Restriction Promotes Ischemia/Reperfusion Cardioprotection Through Increased Mitochondrial Na+/Ca2+ Exchange

Caloric restriction (CR) protects against cardiac ischemia/reperfusion (I/R) injury, but the underlying mechanisms remain incompletely understood. Since mitochondrial Ca2+ overload and redox imbalance is a major driver of cardiac damage during reperfusion, we investigated if enhanced mitochondrial Ca2+ efflux contributes toward CR-induced cardioprotection. Rats were subjected to 16 weeks of ad libitum (AL) feeding or 40% caloric restriction. CR significantly increased mitochondrial Ca2+ retention capacity when Na+ ions were present, reduced H2O2 release, and increased the expression of proteins related to mitochondrial Ca2+ extrusion. In cardiomyocytes exposed to serum from CR rats, Ca2+ retention capacity also markedly increased, as well as Ca2+ efflux and the expression of extrusion proteins NCLX and TMEM65. Following I/R, CR hearts exhibited improved functional recovery accompanied by enhanced retention and increased mitochondrial Ca2+ efflux activity, as well as reduced H2O2 release compared to AL controls. Inhibition of mitochondrial Na+/Ca2+ exchange abolished the mitochondrial adaptive effects of CR, eliminating its protection against damage in cardiomyocytes and perfused hearts. These findings demonstrate that CR protects the heart from I/R injury by enhancing CGP-sensitive Na+-dependent mitochondrial Ca2+ efflux, preserving mitochondrial function, limiting redox imbalance, and improving post-ischemic cardiac recovery.

biochemistry↗

bioRxiv2023

Cardiac Troponin I Directly Binds and Inhibits Mitochondrial ATP Synthase: a Noncanonical Role in the Post-Ischemic Heart

Cardiac troponin I (cTnI) is a sarcomeric protein critical to myocyte contraction. Unexpectedly, we found that some cTnI localized to the mitochondrial matrix in the heart, inhibited mitochondrial functions when stably expressed in non-cardiac cells and increased opening of the mitochondrial permeability transition pore under oxidative stress. Direct, specific, and saturable binding of cTnI to ATP synthase was demonstrated in vitro, using immune-captured ATP synthase, and in cells using proximity ligation assay. cTnI binding doubled F1F0 ATPase activity, whereas skeletal troponin I and several human mutant cTnI variants associated with familial hypertrophic cardiomyopathy did not. A rationally-designed ten amino acid peptide, P888, inhibited cTnI binding to ATP synthase, inhibited cTnI-induced increase in ATPase activity in vitro, and reduced cardiac injury following transient ischemia in vivo. We therefore suggest that mitochondria-associated cTnI may inhibit cardiac ATP synthase under basal conditions; pharmacological agents that release this inactivating effect of cTnI and thus preventing ATP hydrolysis during cardiac ischemia may increase the reservoir of functional mitochondria to reduce cardiac injury. Significance StatementCardiac troponin I (cTnI) is a key sarcomeric protein involved in the regulation of myocardial contractility. We found that some cTnI is present in the mitochondrial matrix where it binds to ATP synthase, disrupting mitochondrial function; inhibition of the cTnI-ATP synthase interaction with a selective peptide inhibitor reduces cardiac dysfunction following ischemia and reperfusion injury. Several pathogenic cTnI mutations associated with hypertrophic cardiomyopathy do not affect ATP synthase activity, suggesting a potential mechanism that contributes to the diverse pathologies associated with these mutations.

cell biology↗