Endothelial Cell Sprouting in Coronary Collateral Growth

Abstract

Rationale– Coronary collateral growth is a natural bypass for ischemic heart diseases. It offers tremendous therapeutic benefit, but the process of coronary collateral growth is incompletely understood due to limited preclinical murine models that would enable interrogation of its mechanisms and processes via genetic modification and lineage tracing. Understanding the processes by which coronary collaterals develop can unlock new therapeutic strategies for ischemic heart disease.Objective– To develop a murine model of coronary collateral growth by repetitive ischemia (RI) and investigate the process of coronary collateral growth in adult hearts by lineage tracing.Methods and Results– A murine model of coronary collateral growth was developed using short episodes of repetitive ischemia. Repetitive ischemia resulted in robust collateral growth in adult mouse hearts, validated by high‐resolution micro‐computed tomography. ROSA mT/mG reporter mice with Apln‐CreERT2 transgene were used for lineage tracing of sprouting endothelial cells to determine cellular contributions to coronary collateral growth. Two‐photon and confocal microscopy imaging revealed RI‐induced coronary collateral growth initiated from sprouting Apelin+GFP+endothelial cells. Newly formed capillaries in the collateral‐dependent zone expanded in diameter upon RI stimulation and arterialized with smooth muscle cell recruitment to form mature coronary collateral arteries. Notably, pre‐existing coronary arteries and arterioles were not Apelin+ GFP+, and all Apelin+endothelial cells arose from sprouting capillaries. HIF1α, VEGFR2, CXCR4, MCP‐1, and JAG1 signaling in the collateral‐dependent zone were also upregulated during coronary collateral growth.Conclusions– We developed a murine model of RI‐induced coronary collateral growth, and our data show sprouting EC contribute to coronary collateral growth in adult hearts. Sprouting angiogenesis is shown for the first time to arterialize into mature blood vessels of larger diameter in response to repetitive ischemia in adult hearts.