Understanding the Cardiac Benefits of Exercise at the Cellular and Molecular Level

Project Summary/Abstract Heart failure (HF) is a growing cause of morbidity and mortality. Despite the best available treatments, prognosis remains poor for many HF patients underscoring the unmet clinical need for new HF therapies. This Outstanding Investigator Award application is inspired by the observation that exercise protects the

heart, promoting cardiomyocyte (CM) survival and proliferation while reducing fibrosis and inflammation. Yet we understand little of the responsible mechanisms and whether they can be exploited therapeutically. Here, I plan to leverage the longer-term support and scientific flexibility afforded by the NHLBI R35 Outstanding

Investigator Award to illuminate the cellular and molecular basis of the cardiac benefits of exercise and to validate potential new therapeutic targets in preclinical models. We discovered that although exercise and pathological stress both induce cardiac hypertrophy, the mechanisms underlying exercise-induced

hypertrophy are largely distinct and, rather than leading to adverse sequelae, paradoxically protect the heart (Cell, 2010). We also found that exercise dramatically enhances endogenous cardiomyogenesis in the adult mammalian heart (Nature Comm., 2018). In some cases, mimicking the changes seen in exercise not only

prevents but can reverse established HF (Science Transl. Med., 2019). Here we propose a broad program to delineate the cellular and molecular effects of exercise, define the mechanistic pathways mediating cardiomyogenesis and other benefits of exercise, and explore the translational potential of these pathways

in preclinical models. To describe the heart’s adaptive response to exercise in cardiomyocytes and non- cardiomyocytes, a range of unbiased discovery tools will be employed including single nucleus RNA- sequencing (snRNA-seq), bulk RNA-seq, and Assay for Transposase-Accessible Chromatin (ATAC-seq).

snRNA-seq will provide insight into cell lineage-specific changes in gene expression in response to exercise over time, and this approach will be combined with lineage-specific gain- and loss-of-function models to help define crosstalk between cell types. Several labeling tools will be used to facilitate identification of dividing

CMs in snRNA-seq studies to profile this dynamic process and test the hypotheses that specific subpopulations of CMs and/or permissive environments are required for cardiomyogenesis. Statistically robust candidates will be screened for protective and cardiomyogenic effects using relevant in vitro cell

culture and in vivo zebrafish models. The most promising will be studied in preclinical murine and porcine models to uncover new biological pathways and develop new therapeutic approaches. The R35 mechanism uniquely provides the flexibility and timeframe required to support the proposed unbiased discovery and

bioinformatic analyses and the generation of unique animal models. Successful completion of this program will advance our understanding of cardiomyogenesis and the beneficial effects of exercise in the heart, while delineating pathways with the potential to mitigate heart failure, thus meeting a pressing clinical need.