Abstract Body: Background:
Myocardial infarction (MI) results in the significant loss of myocardial and vascular tissue, which impairs cardiac function and blood flow. Employing transcriptomics, we discovered 56 secreted ligand genes expressed by epicardium-derived cells that regulate coronary angiogenesis and specification during development. In particular, collagen, type XVIII, alpha 1 (Col18a1), was highly expressed in surface epicardial cells, but its function in the heart has not been previously studied.

Objective:
This study aims to elucidate the function of vascular regulatory factors during embryonic angiogenesis, which may be utilized to promote neovascularization in the adult heart after MI.

Methods:
C57BL/6 mice were used to investigate the expression of Col18a1 in the heart during embryonic (E) stages and neonatal development using fluorescence in situ hybridization, immunohistochemistry, and gene expression studies. To determine whether COL18A1 influences endothelial cell (EC) angiogenesis and artery-vein specification, we performed adenoviral-mediated overexpression of COL18A1 in the E12.5 epicardium.

Results:
Col18a1 increased in Wt1+ epicardial cells during coronary vasculature formation, peaking at E16.5 and maintaining stable expression during early postnatal periods. COL18A1 overexpression in the developing epicardium altered EC positioning. Gene expression analysis confirmed a dysregulation in EC differentiation noted by the downregulation of the arterial marker Nrp1 and an upregulation of the vein identity markers Apln and Nr2f2 associated with cells of the coronary sinus venosus. Additionally, overexpression of COL18A1 led to increased epithelial-to-mesenchymal transition (EMT), suggesting that COL18A1 may also play a role in regulating functions beyond those of ECs.

Conclusions:
Our data indicate that Col18a1 levels increase during vasculature maturation, which helps to limit coronary angiogenesis and promote the stability of the blood vessels. Additionally, we found that overexpressing COL18A1 in the epicardium altered EC migration and artery-vein specification while also increasing the expression of genes associated with EMT. To further establish the significance of Col18a1 in coronary angiogenesis, we plan to use a Col18a1 knockout mouse model.