Abstract 12031: Novel Regulation of mTORC1 Through mRNA Binding Protein ZFP36L2 is Required for Normal Cardiac Function

IntroductionZFP36L2 is an mRNA binding protein that has been shown to regulate cell proliferation in blood cells, and global deletion of ZFP36L2 in mice results in lethal pancytopenia. In a recent study, a missense mutation in a zinc finger domain of ZFP36L2 gene was associated with human congenital heart diseases. Here, we sought to elucidate a role of ZFP36L2 in the heart using mice with cardiac-specific ZFP36L2 deletion.ResultsCardiac-specific ZFP36L2 knockout (cs-L2KO) male mice developed spontaneous systolic dysfunction by 8 weeks of age. Although female cs-L2KO mice showed only a subtle decrease in cardiac function at baseline, they exhibited a dramatically poor prognosis after repeated pregnancies due to heart failure. ZFP36L2 displayed an antioxidant effect in cardiomyocytes and a screening for antioxidant gene expression showed the involvement of mTOR pathway in this process. Additionally, the activity of mTORC1, as assessed by phosphorylation of ribosomal protein S6 kinase at Thr389, was aberrantly increased in the heart of cs-L2KO mice with a decrease in phosphorylation of AKT at Ser473. ZFP36L2 knockdown in H9c2 cells or mouse embryonic fibroblasts (MEF) recapitulated mTORC1 activation with attenuated response of phospho-Ser473-AKT upon insulin stimulation. This was restored by pretreatment with rapamycin, indicating that hyperactivation of mTORC1 by loss of ZFP36L2 induces negative feedback regulation on AKT. In TSC2 knockout MEF, the effect of ZFP36L2 deletion on mTORC1 activity was abolished, suggesting that ZFP36L2 negatively regulates mTORC1 upstream of TSC1/2 complex. Among TSC1/2 complex activators, we found that ZFP36L2 was required for p53 stabilization through directly regulating MDM2 mRNA and for Redd1 expression, a stress-induced negative mTORC1 regulator. Finally, treatment with rapamycin in cs-L2KO mice mitigated spontaneous and postpartum cardiac dysfunction in male and female mice, respectively.ConclusionsOur studies show that ZFP36L2-mediated fine-tuning of mTORC1 is required for cardiac homeostasis under physiological stress, and that the disruption of this pathway induces down-regulation of pro-survival AKT signaling. p53 and Redd1 are also involved in ZFP36L2-mediated mTORC1 regulation.