Regression of Post-Prandial Cardiac Hypertrophy in Burmese Pythons is Mediated by FoxO1
As ambush-hunting predators that consume large prey after long intervals of fasting, Burmese pythons evolved with unique adaptations for regulating organ structure and function. Among these is cardiac hypertrophy that develops within three days following a meal (1, 2), which we previously showed was initiated by circulating growth factors (3). Post-prandial cardiac hypertrophy in pythons also rapidly regresses with subsequent fasting (2); however, the molecular mechanisms that regulate the dynamic cardiac remodeling in pythons during digestion are largely unknown. In this study, we employed a multi-omics approach coupled with targeted molecular analyses to examine remodeling of the python ventricular transcriptome and proteome throughout digestion. We found that forkhead box protein O1 (FoxO1) signaling was suppressed prior to hypertrophy development and then activated with regression, which coincided with decreased and then increased expression, respectively, of FoxO1 transcriptional targets involved in protein degradation. To define the molecular mechanistic role of FoxO1 in hypertrophy regression, we used cultured mammalian cardiomyocytes treated with post-fed python plasma. Hypertrophy regression both in pythons and in vitro coincided with activation of FoxO1-dependent autophagy; however, introduction of a FoxO1-specific inhibitor prevented both regression of cell size and autophagy activation. Finally, to determine if FoxO1 activation could induce regression, we generated an adenovirus expressing a constitutively active FoxO1. FoxO1 activation was sufficient to prevent and reverse post-fed plasma-induced hypertrophy, which was partially prevented by autophagy inhibition. Our results indicate that modulation of FoxO1 activity contributes to the dynamic ventricular remodeling in post-prandial Burmese pythons. Overall design: To identify factors associated with the regression of cardiac mass in Burmese pythons, we performed bulk RNA sequencing on poly-A-enriched left ventricle tissue samples from fasted, 1-day post-fed (DPF), 4DPF, and 6DPF python ventricles. Snakes were fasted for 28 days and then fed pythons received rodent meals equivalent to 25% of their body mass. 1DPF represents an actively hypertrophing timepoint, 4DPF represents an early regression timepoint, while 6DPF represents a later regression timepoint. We then performed differential gene expression and pathway enrichment analysis to genes and pathways changing between group and across the postprandial resposne.