Abstract Body: Background: Cardiovascular disease is uniformly associated with structural and functional changes that lead to pathological cardiac remodeling, characterized in part by fibrosis. Conversely, exercise leads to cardioprotective structural and functional changes to the heart through physiological remodeling without the development of fibrosis. The mechanisms through which the benefits of exercise are conferred remain undefined. We previously found that the Nrf2-dependent antioxidant gene program is induced in cardiac fibroblasts (CFs) by exercise and suppressed in disease. Nrf2 is a transcription factor that is typically targeted for proteasomal degradation via an interaction with Keap1. However, oxidant overabundance disrupts the Keap1 - Nrf2 interaction, allowing Nrf2 to translocate into the nucleus where it activates the expression of genes encoding antioxidant proteins.

Hypothesis: We hypothesize that exercise provides a cardioprotective oxidative challenge in CFs, increasing chromatin accessibility at Nrf2-dependent antioxidant genes and suppressing cardiac fibrosis.

Methods/Results: Using acute treadmill running in mice, we found that Nrf2 protein is transiently increased after exercise before returning to baseline. Similarly, we modeled repetitive oxidative stress in cultured fibroblasts, identifying a physiological dose that suppresses profibrotic genes. Using siRNA-mediated gene knockdown and pharmacological approaches in fibroblasts, we found that Nrf2-dependent antioxidant gene induction correlates with the suppression of profibrotic genes. Importantly, Angiotensin II-dependent interstitial cardiac fibrosis was significantly increased when Nrf2 was genetically ablated in cardiac fibroblasts compared to wildtype littermate control mice. To investigate the cardioprotective mechanism of exercise, we performed single nucleus RNA/ATAC-sequencing to define the Nrf2-dependent genomic and transcriptomic changes that correlate with reduced fibrosis.

Conclusions: We have shown that Nrf2 stimulation in fibroblasts by exercise prevents fibrosis and identified this pathway as a potential therapeutic target for cardiovascular disease.