Abstract P3096: Cardiac-specific Hadc3 Loss Induces Reorganization Of Peripheral Heterochromatin And Promotes Diet-induced Heart Failure

The nuclear periphery, including the nuclear lamina, serves as an important three-dimensional organizer of the genome. Together, with a subset of tethering proteins, nuclear lamina serves as a platform to anchor transcriptionally silent heterochromatin to the nuclear periphery. Peripheral heterochromatin, marked by the H3K9me2 histone modification, interacts with lamina proteins and is organized into lamina-associated domains (LADs). Our previous studies demonstrated that histone deacetylase 3 (HDAC3) is a scaffold for a nuclear lamina tethering complex and plays an important, non-enzymatic role in establishing cell identity in murine cardiac progenitor cells by reorganizing the LADs and releasing cardiac lineage-specific genes from the nuclear periphery during differentiation. This reorganization is critical as it makes specific genomic regions that are released from the nuclear periphery more accessible for transcriptional activation. Surprisingly, Hdac3 deficiency in murine cardiomyocytes did not lead to any observable phenotype in adult animals. However, when the mice were maintained on a high-fat diet, this resulted in a severe disruption of fat metabolism and lead to heart failure within months. In the present study, we seek to determine if Hdac3 deletion is sufficient to re-organize LADs, release the genes normally found there, and make them more accessible for transcriptional activation as the mechanism leading to cardiac dysfunction. Since H3K9me2 marks peripherally localized genomic regions, we performed H3K9me2 CUT&RUN assay on cardiomyocytes derived from WT and Hdac3 KO mice, fed with normal and high-fat diet, to compare the positioning of chromatin genome-wide. From these data, we identified a list of genes and enhancers found in those regions that vary significantly in H3K9me2 enrichment depending on genotype and condition. We then performed Gene Ontology (GO) Analysis. A significant finding is that numerous enhancers with relatively reduced H3K9me2 in Hdac3 KO cardiomyocytes are regulators of neuronal genes. Loss of H3K9me2 is generally associated with increased gene transcription. We predict that disruption of the peripheral heterochromatin organization upon Hdac3 deletion may result in loss of identity in cardiomyocytes by activating non-cardiomyocyte program-specific genes, such as those of neuronal cell fate, which are normally found at the nuclear periphery and silent in cardiac cells. The results of this work will help to gain insight into the function of nuclear lamina scaffolding proteins, and open new avenues to design therapies to replace lost scaffolding proteins in patients predisposed to heart disease.