Abstract 14395: Abnormal Regulation of P53-mTOR Pathway by MRNA-binding Protein ZFP36L2 in Peri-partum Cardiomyopathy

Introduction: A loss of function mutation in the mRNA binding protein ZFP36L2 has been associated with congenital heart diseases in humans, although the mechanism remains unclear. Objectives: We sought to elucidate the role of ZFP36L2 in the heart using mice with cardiac-specific ZFP36L2 deletion. Results: Cardiac-specific Zfp36l2 knockout (cs-L2KO) female mice exhibit a dramatic phenotype in which the majority of mice die after repeated pregnancies due to heart failure. We performed RNA-seq in H9c2 cells with ZFP36L2 KD, and found the expression of multiple mTOR pathway genes were altered, including marked repression of Redd1 and Sesn2 . Consistent with the RNA-seq data, the activity of mTORC1 was increased in cs-L2KO mouse hearts and in ZFP36L2 KD H9c2 cells. Loss of TSC2 mitigated mTORC1 hyperactivity in ZFP36L2 KD cells, indicating that ZFP36L2 regulates mTORC1 activity through the TSC2 complex. Overexpression of REDD1 rescued increased mTORC1 activity with ZFP36L2 KD, suggesting that ZFP36L2 regulates mTORC1, in-part through REDD1. Under total amino acid starvation, we observed higher p-S6K T389 levels in ZFP36L2 KD cells, and SESN2 overexpression mitigated p-S6K T389 , indicating loss of ZFP36L2 also regulates mTORC1 through amino acid sensing. p53 is a transcriptional activator of both REDD1 and SESN2, and we found that ZFP36L2 was required to maintain p53 levels by directly destabilizing MDM2 mRNA. Accordingly, administration of Nutlin3, an MDM2 inhibitor, reversed the reduction in p53, REDD1 and SESN2 protein levels, and prevented the increase in S6K phosphorylation in response to ZFP36L2 KD. Next, we treated pregnant mice with rapamycin, and cs-L2KO mice treated with rapamycin displayed significantly improved cardiac function after delivery. Finally, we analyzed human heart samples from patients with peri-partum cardiomyopathy and found ZFP36L2 protein to be significantly decreased and p-S6K T389 levels increased, compared to healthy controls. Conclusions: Our studies demonstrate that ZFP36L2 regulates mTORC1 activity through modifying p53 stability, and that the disruption of this pathway induces peri-partum cardiomyopathy. Inhibition of mTORC1 hyperactivity with rapamycin can be a potential therapy for this disease.