Disruption of Z-Disc Function Promotes Mechanical Dysfunction in Human Myocardium: Evidence for a Dual Myofilament Modulatory Role by Alpha-Actinin 2

Abstract

The ACTN2 gene encodes α-actinin 2, located in the Z-disc of the sarcomeres in striated muscle. In this study, we sought to investigate the effects of an ACTN2 missense variant of unknown significance (p.A868T) on cardiac muscle structure and function. Left ventricular free wall samples were obtained at the time of cardiac transplantation from a heart failure patient with the ACTN2 A868T heterozygous variant. This variant is in the EF 3–4 domain known to interact with titin and α-actinin. At the ultrastructural level, ACTN2 A868T cardiac samples presented small structural changes in cardiomyocytes when compared to healthy donor samples. However, contractile mechanics of permeabilized ACTN2 A868T variant cardiac tissue displayed higher myofilament Ca2+ sensitivity of isometric force, reduced sinusoidal stiffness, and faster rates of tension redevelopment at all Ca2+ levels. Small-angle X-ray diffraction indicated increased separation between thick and thin filaments, possibly contributing to changes in muscle kinetics. Molecular dynamics simulations indicated that while the mutation does not significantly impact the structure of α-actinin on its own, it likely alters the conformation associated with titin binding. Our results can be explained by two Z-disc mediated communication pathways: one pathway that involves α-actinin’s interaction with actin, affecting thin filament regulation, and the other pathway that involves α-actinin’s interaction with titin, affecting thick filament activation. This work establishes the role of α-actinin 2 in modulating cross-bridge kinetics and force development in the human myocardium as well as how it can be involved in the development of cardiac disease.

Signatures of cysteine oxidation on muscle structural and contractile proteins are associated with physical performance and muscle function in older adults: Study of Muscle, Mobility and Aging (SOMMA)

“…Alpha‐actinin EF‐hand domains interact with titin, where we saw oxidation of Cys788 and Cys869 (Young & Gautel, 2000 ) (calmodulin‐like domain; Figure 4c ). Disruption of this interaction impacts myofilament lattice spacing and cross‐bridge kinetics (Rodriguez Garcia et al., 2023 ). Additionally, Cys868 of ACTN3 (Cys869 in human) was identified as redox‐sensitive in an aging mouse study (McDonagh et al., 2014 ) (Figure 4a ), supporting the notion that ACTN3 may be a redox‐regulated protein.…”

Ryanodine receptor‐associated myopathies: What's myosin got to do with it?

“…MD has been widely used to examine molecular processes that are challenging, if not impossible to assess in muscle with current experimental approaches. 11,[15][16][17][18][19] Dynamic simulations of portions of MYH7 rod suggest that phosphorylation could negatively impact structural dynamics of the rod-and by implication the thick filament backbone and interaction with IHM-in myopathy patients.…”