Molecular Mechanisms Governing Vascular Cell Function and Phenotype in Health and Disease

PROJECT SUMMARY/ABSTRACT
Endothelial dysfunction resulting from chronic inflammation and elevated circulating cholesterol promotes the
formation of plaques in the sub-endothelium of major arteries causing coronary heart disease—a leading
cause of morbidity and mortality worldwide. Repair of the injured endothelium holds great promise to treat
heart disease; however, endogenous endothelial cell (EC) regeneration is an inefficient process. The ability to
restore patency of the arterial endothelium would provide a significant therapeutic advancement. Because
vascular smooth muscle cells (VSMCs) constitute the majority of cells in the arterial wall and are capable of
phenotypic plasticity in response to pathophysiological stimuli, these cells represent an appealing source of
functional endothelial cells. Unraveling the molecular mechanisms and signaling pathways that govern trans-
differentiation of VSMCs into ECs to mend the injured endothelium would establish a novel treatment paradigm
for coronary heart disease. Our long-term goal is to discover new molecules and signaling pathways that
facilitate VSMC-to-endothelial transition (MEndoT). Our laboratory has identified and characterized a family of
evolutionarily-conserved endocytic adaptor proteins called epsins, which have crucial roles in coordinating
endocytosis and signal transduction. Our studies show that loss of epsins 1 and 2 in ECs and myeloid cells
reduces vascular inflammation and prevents plaque initiation and progression. To further assess the
therapeutic effects of targeting epsins in cells that drive lesion progression as well as plaque composition and
stability, we will use recently created disease-specific mice harboring VSMC-specific deficiency of these
epsins. We propose to interrogate the function of VSMC epsin proteins in these processes and establish that
therapeutic targeting of these proteins will promote beneficial VSMC phenotype switching. So far, our
preliminary studies indicate that ApoE-/- mice with a deficiency in VSMC epsins have a significant reduction in
plaque size, enhanced plaque stability (including an increase in fibrous cap area and ACTA2+ cells within the
cap), a reduction in the number of infiltrating cells (CD45+ immune and inflammatory cells and CD68+ foam
cells), and a prominent decrease in vascular stiffness and calcification. In addition, RNA-seq analyses show
that Klf4, the pluripotent transcriptional factor controlling phenotypic switching of VSMCs, is downregulated by
epsin loss, as is oxLDL-triggered Runx2 ubiquitination and degradation. In light of these findings, we will
investigate the following Specific Aims using unique mutant mice, in vitro models, and novel reagents: 1) To
determine the molecular mechanisms by which epsins regulate phenotype switching and mesenchymal-to-
endothelial differentiation, 2) To determine the molecular mechanisms by which epsins regulate VSMC
osteogenesis and promote arterial stiffness, and 3) To determine the therapeutic potential of targeting epsins
for atheroma formation and resolution. If fruitful, the proposed study will complement our prior work and
strengthen the concept that epsin proteins may serve as a potent therapeutic target for coronary heart disease.

Grant Number: 5R01HL158097-04
NIH Institute/Center: NIH
Principal Investigator: Hong Chen