Genetic And Pharmacological Inhibition Of Rheb1-mTORC1-S6k Signaling Exerts Cardio-protection Against Adverse Cardiac Remodeling In Mice

Congestive heart failure (CHF) is a leading cause of morbidity and mortalityworldwide. CHF is commonly caused by pathological cardiac remodeling followinga wide spectrum of cardiovascular diseases, such as hypertension and myocardialinfarction (MI). Although myocardial remodeling is compensatory initially, it canbecome maladaptive and eventually lead to CHF if left untreated. Recently, despitethe widespread use of beta-blockers and inhibitors of renin-angiotensin-aldosteronesystem clinically, the incidence of CHF still remains high, highlighting the need foradditional understanding of remodeling events. The purpose of this experiment wasto observe whether genetic and pharmacological inhibition of this signalingimproved pathological ventricular remodeling in mice through Rheb1/mTORC1/S6ksignaling pathway, and this provided a strategy for the clinical treatment of CHF.Our group induced pathological ventricular remodeling of mice by myocardialinfarction (MI) and tranverse aotic constriction (TAC) surgeries, and found that S6and4EBP1(two important targets of mTORC1signaling pathway) phosphorylationlevels were significantly higher, suggesting that this pathway activation may play agreat role in pathological ventricular remodeling. Previous study indicated thatRheb1is required for mTORC1in the brain. However, the function of Rheb1in theheart is still elusive. Thus, we deleted Rheb1specifically in cardiomyocytes andfound that3weeks and3days after mice with MI surgery, heart weight/body weightratio was significantly reduced, cardiac systolic and diastolic functions were notablyimproved, and the fibrosis area of the infarcted area, cardiomyocytes size, apoptotic cells, and infarcted area and neutrophil infiltration in infarct border zone weremarkedly reduced. Meanwhile, it was found that3weeks after mice with TACsurgery, heart weight/body weight ratio, collagen deposition among myocardialfibers and cardiomyocytes size were significantly decreased. Western blottinganalysis showed that loss of Rheb protein can significantly repressed augment of S6and4EBP1phosphorylation levels and did not affect the level of Akts473, p38andERK phosphorylation. These results suggest that Rheb1is also essential for themTORC1signaling activation in the myocardium and genetic inhibition ofRheb1-mTORC1signaling pathway can ameliorate pathological ventricularremodeling in mice with MI and TAC surgeries.Rapamycin is a potent inhibitor against mTOR signaling and is used clinicallyfor many years. However, if rapamycin is long-term applicated in treating CHF, ittend to bring more adverse effects. Therefore, it is critical clinical significance tosearch for some new drugs with mild side effects. Our research group have foundthat Astragaloside IV (As-IV), a monomeric compound isolated from Astragalusmembranaceus Bge, can inhibit S6and4EBP1phosphorylation in vitro and mousetoxic test showed that As-IV has no effect on body weight and cardiac function.Furthermore, in vivo we found that As-IV can improve heart dysfunction andpathological ventricular remodeling in mice after MI and TAC surgeries throughspecific inhibition of S6k, S6and4EBP1phosphorylation, and the levels of Akts473,p38and ERK phosphorylation were not changed. In view of the research finding onthe critical role of S6k activation in pathological ventricular remodeling after MI, weassumed that S6k inhibition can ameliorate pathological ventricular remodeling afterMI, and it tend to reduce side effects when drug targeting mTORC1downstreamwith few targets was chose. Therefore, we firstly used PF-4708671as specific S6k inhibitor to treat MI mice, and found that heart dysfunction were improved andfibrosis of infarcted zone and cardiomyocytes size were notably reduced.In summary, the above-mentioned results show that the genetic inhibition ofRheb1expression and pharmacological inhibition of mTORC1and S6k activitiesrender a protective effect on pathological ventricular remodeling after mice with MIand TAC surgeries, and this provides the theoretical basis for the clinical applicationof astragaloside IV and specific S6k inhibitor PF-4708671on treating congestiveheart failure.