Mechanisms of Amplified Arteriogenesis in Collateral Artery Segments Exposed to Flow Direction Reversal

Objective— Collateral arteriogenesis, the growth of existing arterial vessels to a larger diameter, is a fundamental adaptive response that is often critical for the perfusion and survival of tissues downstream of chronic arterial occlusion(s). Shear stress regulates arteriogenesis; however, the arteriogenic significance of flow direction reversal, occurring in numerous collateral artery segments after femoral artery ligation, is unknown. Our objective was to determine if flow direction reversal in collateral artery segments differentially regulates endothelial cell signaling and arteriogenesis. Approach and Results— Collateral segments experiencing flow reversal after femoral artery ligation in C57BL/6 mice exhibit increased pericollateral macrophage recruitment, amplified arteriogenesis (30% diameter and 2.8-fold conductance increases), and remarkably permanent (12 weeks post femoral artery ligation) remodeling. Genome-wide transcriptional analyses on human umbilical vein endothelial cells exposed to flow reversal conditions mimicking those occurring in vivo yielded 10-fold more significantly regulated transcripts, as well as enhanced activation of upstream regulators (nuclear factor κB [NFκB], vascular endothelial growth factor, FGF2, and transforming growth factor-β) and arteriogenic canonical pathways (PKA, PDE, and mitogen-activated protein kinase). Augmented expression of key proarteriogenic molecules (Kruppel-like factor 2 [KLF2], intercellular adhesion molecule 1, and endothelial nitric oxide synthase) was also verified by quantitative real-time polymerase chain reaction, leading us to test whether intercellular adhesion molecule 1 or endothelial nitric oxide synthase regulate amplified arteriogenesis in flow-reversed collateral segments in vivo. Interestingly, enhanced pericollateral macrophage recruitment and amplified arteriogenesis was attenuated in flow-reversed collateral segments after femoral artery ligation in intercellular adhesion molecule 1 −/− mice; however, endothelial nitric oxide synthase −/− mice showed no such differences. Conclusions— Flow reversal leads to a broad amplification of proarteriogenic endothelial signaling and a sustained intercellular adhesion molecule 1–dependent augmentation of arteriogenesis. Further investigation of the endothelial mechanotransduction pathways activated by flow reversal may lead to more effective and durable therapeutic options for arterial occlusive diseases.