Analyzing Vessel Regression and Endothelial Apoptosis as a Component of Angiogenic Vessel Remodeling

Angiogenic vessel remodeling is a critical step in establishing a hierarchical vessel network. Vessel networks rapidly expand through angiogenesis in response to pro-angiogenic factors. This leads to an initially dense vessel network that requires selective regression of vessel branches to establish a hierarchical conduit for blood flow, a process known as pruning. This involves migration of endothelial cells from low-flow vessels to adjacent high-flow vessels and generally occurs independently of cell death. Vessels may also regress in response to other stimuli, including reduced metabolic demand, redundancy, and pathological stimuli. In these contexts, widespread vessel regression typically occurs and involves loss of endothelial cells by apoptotic cell death. Thus, vessel remodeling occurs via both apoptosis independent and dependent vessel regression. In this chapter, we outline a semi-automated method for quantifying vessel regression using the neonatal model of angiogenesis. We further provide instruction on analyzing endothelial apoptosis in this model.