Abstract B19: Neurofibromin 2 regulates metabolism in the heart

Introduction: Neurofibromin 2 (NF2) is a tumor suppressor that can engage the Hippo signaling pathway and modulate cell proliferation and survival. We previously demonstrated that NF2 mediates cardiomyocyte apoptosis and injury caused by acute myocardial infarction (MI) through inhibition of the Hippo target YAP. However, the function of NF2 in the heart remains largely uncharacterized. Our current study sought to determine whether NF2 contributes to cardiac remodeling, dysfunction, and heart failure due to chronic stress. Methods and Results: We used a transverse aortic constriction (TAC) model in WT C57BL/6J mice to generate chronic pressure overload (PO) stress, which elicits cardiac hypertrophy, remodeling, and eventually heart failure. We found that NF2 is transiently upregulated in mouse myocardium in response to PO stress. To investigate if increased NF2 contributes to pathology, we used cardiomyocyte-specific NF2 knockout (cKO) mice. At baseline, adult NF2 cKO mice had normal cardiac morphology and function. However, following TAC, NF2 cKO hearts unexpectedly showed worsened cardiac function, assessed by echocardiography and hemodynamic analysis, compared to littermate controls. Interestingly, no differences in the extent of TAC-induced cardiac hypertrophy or cardiomyocyte apoptosis were observed between NF2 cKO and control mice. To investigate the mechanism underlying the NF2 cKO phenotype, we performed RNAseq. Our analysis indicated downregulation of several metabolic pathways including oxidative phosphorylation (OXPHOS) and fatty acid oxidation (FAO) in unstressed NF2 cKO hearts, which was confirmed by qPCR. We also determined that ATP content in NF2 cKO hearts was significantly reduced at baseline compared to control mice. Estrogen-related receptors (ERRs) are important regulators of mitochondrial biogenesis and metabolic function. RNAseq revealed the downregulation of ERRβ and ERRγ in NF2 cKO hearts, which was confirmed by qPCR. Experiments in neonatal cardiomyocytes confirmed that regulation of ERRβ and ERRγ expression by NF2 is cell autonomous. Luciferase reporter assays demonstrated that modulation of NF2 regulates ERR function in cardiomyocytes. We also found that YAP activation is enhanced in NF2 cKO hearts and cardiomyocytes deficient for NF2. Co-IP analysis indicated that YAP associates with components of the nucleosome remodeling and deacetylase (NuRD) complex in cardiomyocytes, which may mediate targeted gene suppression. Conclusion: Myocardial NF2 expression is upregulated and may be compensatory during PO stress through preservation of metabolic gene expression and energy content in the heart. Citation Format: Yu Zhang, Wataru Mizushima, Shinichi Oka, Peiyong Zhai, Dominic Del Re. Neurofibromin 2 regulates metabolism in the heart [abstract]. In: Proceedings of the AACR Special Conference on the Hippo Pathway: Signaling, Cancer, and Beyond; 2019 May 8-11; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(8_Suppl):Abstract nr B19.