Epigenetic control of smooth muscle cell phenotype during microvascular remodeling

PROJECT SUMMARY Peripheral Artery Disease (PAD) is an occlusive disease of the lower extremity arteries leading to debilitating complications (e.g., claudication, amputation) due to defects in proper vascularization and efficient vascular remodeling. Recent attempts to promote therapeutic angiogenesis by VEGF therapies in patients with PAD have failed, perhaps because these strategies have only not targeted smooth muscle cells (SMC). These cells are essential for remodeling capillaries and terminal arterioles (i.e., arteriogenesis). Arteriogenesis relies on the ability of SMC to be plastic and undergo a reversible phenotypic switching where they transiently downregulate their contractile apparatus, participate in micro-vessel investment, and then re-differentiate back to the contractile state. However, the understanding of the mechanisms controlling SMC ability to re-differentiate and the retention of their lineage memory in vivo is limited. During the original funding cycle of this project, we demonstrated that the histone post-translational modification H3K4 di-methylation (H3K4me2) governs SMC lineage identity and transcriptional memory on the SMC gene repertoire. Mechanistically, H3K4me2 is essential for recruiting the methylcytosine dioxygenase and SMC master regulator, TET2, on the SMC genes. Our preliminary data suggest that loss of TET2 expression is associated with defective migration in SMC and lack of participation in microvascular remodeling during hindlimb ischemia. We found that hypoxia caused a concomitant increase in TET2 expression and a reduction in TET2 dioxygenase activity. These data support a major shift in the current paradigm in that TET2 might display functions beyond the pro-contractility role previously reported but may be involved in both contractility and migration in a context-dependent and dioxygenase-dependent manner. Studies in this proposal will test the central hypothesis that TET2 mediates hypoxia-induced SMC migration and adaptive vascular remodeling through non-canonical non-dioxygenase function. Aim 1 will determine whether TET2 controls SMC migration through dioxygenase-independent function in hypoxia-mediated angiogenesis and arteriogenesis in a series of in vitro and in vivo studies. Aim 2 will delineate the epigenetic mechanisms by which TET2 regulates SMC gene expression in hypoxia. Finally, Aim 3 will determine whether TET2 deficiency in SMC leads to defective adaptive vascular remodeling, decreased tissue perfusion, and SMC dysfunction in hindlimb ischemia (HLI). We expect the completion of these studies will lead to the identification of novel mechanisms controlling smooth muscle cell plasticity, migration, and participation in beneficial microvascular arterialization and maturation. These results could serve to develop new strategies for enhancing therapeutic vascularization in patients with PAD.