Lin, S.-C. J. | Search bioRxiv

bioRxiv2026

Deletion of cytoplasmic β/γ-actin in the mouse heart protects from disease by augmenting sarcolemma stability

The actin cytoskeleton of the cardiomyocyte is organized into two structurally and functionally distinct filament networks. The sarcomeric thin filaments, built primarily from cardiac -actin (CA), generate contractile force, whereas a separate subsarcolemmal cytoplasmic network, built from {beta}-actin (Actb gene) and {gamma}-actin (Actg1 gene), lies beneath the sarcolemma and is comparatively understudied in the mature heart. We hypothesized that this cytoplasmic actin network is required for sarcolemmal membrane integrity, signal transduction, and mechanosensing in the adult cardiomyocyte, and we generated cardiomyocyte-specific Actb and Actg1 double-gene deleted mice, using loxP (fl)-targeted Actbfl/fl and Actg1fl/fl alleles combined with an MHC (Myh6) promoter-driven Cre-recombinase transgene, to test this directly. Deletion of cytoplasmic {beta}-actin and {gamma}-actin from cardiomyocytes (Actb/g1fl/fl-Myh6-Cre mice) drove compensatory upregulation of a {gamma}-interferon like stress response with compensatory upregulation of skeletal -actin (SKA) and smooth muscle -actin (SMA) protein in adult cardiomyocytes, without altering baseline cardiac structure or function. To test if lost {beta}-actin and {gamma}-actin in the mouse heart impacts sarcolemmal stability, we crossed Actb/g1fl/fl-Myh6-Cremice onto the dystrophin-deficient mdx background, which is characterized by a fragile sarcolemma. Unexpectedly, hearts from Actb/g1fl/fl-Myh6- Cre; mdx mice showed greater membrane stability than mdx hearts alone with intact Actb/Actg1. We also observed that Actb/g1fl/fl-Myh6-Cremice subjected to chronic pressure overload by transverse aortic constriction (TAC) were protected and developed less cardiac hypertrophy, had better preserved systolic function, and improved survival. Together, these data indicate induction of the cytoplasmic {beta}-actin/{gamma}-actin network in the heart during disease stimulation is maladaptive and weakens the sarcolemma, and 2 downstream mechanisms are considered that could mediate this effect.

cell biology↗

bioRxiv2025

Atad3 is Essential for Mitochondrial Permeability Transition Pore Opening and Cardiac Ischemia Reperfusion Injury.

The molecular identity of the mitochondrial permeability transition pore (mPTP) has remained elusive since the discovery of its existence over 75 years ago. Despite the numerous candidate proteins proposed, none have withstood genetic ablation, leaving them relegated to auxiliary regulatory roles. To date, no essential mPTP component has been identified. Here, we establish ATAD3 as the first essential component of the mPTP. Genetic deletion of Atad3 in cardiomyocytes and hepatocytes renders heart and liver mitochondria incapable of undergoing Ca2+-induced mPTP-dependent swelling. Moreover, these mitochondria exhibit the highest Ca2+ retention capacity ever reported following genetic perturbation of the mPTP. Furthermore, patch-clamp recordings of recombinant ATAD3a in liposomes reveal intrinsic channel activity. Given the established role of mPTP-dependent necrosis in driving ischemia/reperfusion (I/R) injury, we show that cardiac-specific Atad3 deletion markedly reduces infarct size following I/R, with no additive protection from cyclosporine A. Together, these findings establish ATAD3 as an core, putative pore-forming component essential for mPTP opening and mPTP-dependent necrosis, resolving a long-standing mystery in mitochondrial biology.

cell biology↗