Mechanogenetics: An Integrated Approach to Aging in Muscle Dysfunction

Project Summary Cardiomyocytes in the Drosophila melanogaster heart tube undergo progressive loss of their intercalated disc proteins and increased expression of extracellular matrix with age, resulting in reduced sarcomere lattice crystallinity and thus power stroke inefficiency; maintaining inter-myofilament spacing–by upregulating cardiac- specific expression of vinculin or downregulating matrix proteins–preserved heart wall velocity and extended life- and health-span in a mechanism conserved in non-human primates. Recently, we also showed that nuclei stiffen in aged hearts, reducing the amount of chromatin accessibility in key muscle transcription factors and leading to reduced cardiac output; when expression of the nucleoskeletal protein Lamin C–which decreases with age–is restored in aged cardiomyocytes, nuclei soften and become deformable again, prolong cardiac function, and maintain transcription factor expression, i.e., mechanogenetics. Most importantly in aged cardiomyocytes, we found that restoration of transcription factors alone was sufficient to maintain cardiac identity. While our prior studies have examined these structures separately, in this grant renewal application, we propose two further aims to investigate mechanical links between age-associated remodeling of sarcomere and nuclei. For aim 1, we will investigate age-associated changes in the structural connections between sarcomeres and nuclei, e.g., the Linker of Nucleoskeleton and Cytoskeleton (LINC) complex. Preliminary data suggests that significant age-associated transcriptional and chromatin accessibility reductions in LINC genes MSP300 and Klar–which physically connect these structures–could underlie the maintenance of deformable nuclei, Lamin C and transcription factor expression with age, and the extension of lifespan. For a second aim, we have developed new engineering methods to ask a critical question of aging, namely: can “exercising” the sarcomeres restore transcription factor expression in aged hearts? Using mechanical and pharmacological perturbations, we will challenge aged hearts to maintain force transduction, which we hypothesize will maintain soft, deformable nuclei that will in turn preserve the chromatin accessibility of key muscle transcription factors. In light of the challenges that mechanical forces play on gene expression, we believe that this on-going work will continue to improve our understanding of how forces are required to maintain cardiac identity and ensure appropriate cardiac output in the aged heart.