Altered mTOR and Beclin-1 mediated autophagic activation during right ventricular remodeling in monocrotaline-induced pulmonary hypertension

Abstract

BackgroundRight ventricular structure and function is a major predictor of outcomes in pulmonary hypertension (PH), yet the underlying mechanisms remain poorly understood. Growing evidence suggests the importance of autophagy in cardiac remodeling; however, its dynamics in the process of right ventricle(RV) remodeling in PH has not been fully explored. We sought to study the time course of cardiomyocyte autophagy in the RV in PH and determine whether mammalian target of rapamycin (mTOR) and Beclin-1 hypoxia-related pro-autophagic pathways are underlying mechanisms.MethodsRats were studied at 2, 4, and 6 weeks after subcutaneous injection of 60 mg/kg monocrotaline (MCT) (MCT-2 W, 4 W, 6 W) or vehicle (CON-2 W, 4 W, 6 W). Cardiac hemodynamics and RV function were assessed in rats. Autophagy structures and markers were assessed using transmission electron microscope, RT-qPCR, immunohistochemistry staining, and western blot analyses. Western blot was also used to quantify the expression of mTOR and Beclin-1 mediated pro-autophagy signalings in the RV.ResultsTwo weeks after MCT injection, pulmonary artery systolic pressure increased and mild RV hypertrophy without RV dilation was observed. RV enlargement presented at 4 weeks with moderately decreased function, whereas typical characteristics of RV decompensation and failure occurred at 6 weeks thus demonstrating the progression of RV remodeling in the MCT model. A higher LC3 (microtubule- associated protein light chain 3) II/I ratio, upregulated LC3 mRNA and protein levels, as well as accumulation of autophagosomes in RV of MCT rats indicated autophagy induction. Autophagy activation was coincident with increased pulmonary artery systolic pressure. Pro-autophagy signaling pathways were activated in a RV remodeling stage-dependent manner since phospho-AMPK (adenosine monophosphate-activated protein kinase)-α were primarily upregulated and phospho-mTOR suppressed in the RV at 2 and 4 weeks post-MCT injection, whearas, BNIP3 (Bcl2-interacting protein 3) and beclin-1 expression were relatively low during these stages, they were significantly upregulated after 6 weeks in this model.ConclusionsOur findings provide evidence of sustained activation of autophagy in RV remodeling of MCT induced PH model, while pro-autophagic signaling pathways varied depending on the phase.

Downregulation of miR-26b-5p, miR-204-5p, and miR-497-3p Expression Facilitates Exercise-Induced Physiological Cardiac Hypertrophy by Augmenting Autophagy in Rats

“…Thus, decreased miR-26b, miR-204 and miR-497 were associated with the increased autophagy and cardiac hypertrophy. Previous studies also demonstrated that ULK1 and LC3B were activated during cardiac hypertrophy, and Beclin1 mediated autophagy was also enhanced during right ventricular remodeling (Huang et al, 2015;Deng et al, 2017;Zhang et al, 2019), supporting our finding that ULK1, LC3B, and Beclin1 were up-regulated in physiological LVH. Given LVH in response to endurance exercise is protective, the miRNA changes in physiological LVH is supposed to be adaptive and to promote moderate autophagy which is essential for physiological LVH.…”

Lower Body Weight in Rats Under Hypobaric Hypoxia Exposure Would Lead to Reduced Right Ventricular Hypertrophy and Increased AMPK Activation

“…Conversely, in the AL group exposed to CH, increased mTOR activation and decreased AMPK activation showed an inverse regulation between the two kinases. Further support for our findings comes from reports demonstrating that the inhibition of mTOR under chronic hypobaric hypoxic conditions resulted in the prevention of RVH in an animal model (Paddenberg et al, 2007) and that increased AMPK activity and decreased mTOR activity attenuated RVH in pulmonary-artery-hypertensioninduced rats (Deng et al, 2017).…”

Renal denervation attenuates pressure overload‐induced cardiac remodelling in rats with biphasic regulation of autophagy

“…Indeed, mice with cardiac‐specific deletion of Ttg5 developed severe LV dilatation and cardiac dysfunction, with accumulation of misfolded proteins at the early stage after TAC and without cardiac functional compensation . Similarly, Deng et al found that induced autophagy was protective for the right ventricle in the compensatory phase after pulmonary hypertension. Hence, the presence of basal and even moderate autophagy at this early stage of cardiac remodelling is beneficial for retaining a normal myocardial structure.…”

“…Another interesting finding from this study was that during the decompensatory period, the excessive activation of autophagy was accompanied by the increased expression of HIF‐α, BNIP3 and beclin 1, which was barely seen in the early stage. Prior studies have suggested that the different roles of autophagy depend on the activation of different signalling pathways . Beclin 1 and BNIP3 serve as cross‐talk molecules between the autophagic and apoptotic pathways, which may contribute to the autophagy‐originated cardiac damage during this period.…”