Regression from pathological hypertrophy in mice is sexually dimorphic and stimulus specific.

Pathological cardiac hypertrophy is associated with increased morbidity and mortality. Understanding the mechanisms whereby pathological cardiac growth can be reversed could be of therapeutic value. Here, we show that pathways leading to regression of pathological cardiac hypertrophy are strongly dependent on the hypertrophic trigger and are significantly modified by sex. Two pathological stimuli causing hypertrophy via distinct pathways were administered to male and female mice: angiotensin II (ANG II) or isoproterenol (Iso). Stimuli were removed after 7 days of treatment, and left ventricles (LVs) were studied at 1, 4, and 7 days. ANG II-treated females did not show regression after stimulus removal. Iso-treated males showed rapid LV hypertrophy regression. Somewhat surprisingly, RNAseq analysis at after removal of triggers revealed only 45 differentially regulated genes in common among all the groups, demonstrating distinct responses. Ingenuity pathway analysis predicted strong downregulation of the TGFβ1 pathway in all groups except for ANG II-treated females. Consistently, we found significant downregulation of Smad signaling after stimulus removal including in ANG II-treated females. In addition, the ERK1/2 pathway was significantly reduced in the groups showing regression. Finally, protein degradation pathways were significantly activated only in Iso-treated males 1 day after stimulus removal. Our data indicate that TGFβ1 downregulation may play a role in the regression of pathological cardiac hypertrophy via downregulation of the ERK1/2 pathway and activation of autophagy and proteasome activity in Iso-treated males. This work highlights that the reversal of pathological hypertrophy does not use universal signaling pathways and that sex potently modifies this process. Pathological cardiac hypertrophy is a major risk factor for mortality and is thought to be largely irreversible in many individuals. Although cardiac hypertrophy itself has been studied extensively, very little is understood about its regression. It is important that we have a better understanding of mechanisms leading to regression, why this process is not reversible in some individuals and that sex differences need to be considered when contemplating therapies.