MicroRNA-155 exerts anti-angiogenic but pro-arteriogenic effects in the regulation of adaptive neovascularization in mice by cell specific regulation of divergent target genes

Abstract

Background: MicroRNAs (miRNAs) are small non-coding RNAs, which regulate mRNAs by inhibition of translation or degradation. The adaptive growth of blood vessels is known to be modulated by miRNAs and includes both the sprouting of new endothelial capillaries (angiogenesis) as well as the enlargement of pre-existing arteriolar and arterial anastomoses to functional collateral arteries (arteriogenesis) after occlusion or narrowing of a major artery. We now aimed to identify new regulatory miRNAs involved in regulation of neovascularization in a murine model of femoral artery occlusion. Methods and results: We explored the expression profile of miRNAs after occlusion of the femoral artery in mice using miRNA-transcriptome analysis and identified miR-155 as one of the top down-regulated miRNAs. Following this, we examined the angiogenic properties of miR-155 in human umbilical endothelial cells (HUVECS) and found an inhibitory function of miR-155 on proliferation and angiogenic tube formation by suppression of the direct miR-155 target angiotensin II receptor type one (AGTR1). Surprisingly, miR-155 deficient mice showed an unexpected phenotype in vivo, with an impaired blood flow recovery after femoral artery ligation, due to a reduction of pro-arteriogenic cytokine expression, a reduction of infiltrating monocytes/macrophages and an attenuation of collateral artery growth (arteriogenesis). Based on this, we examined leukocyte-endothelial interaction and migration capacity of circulating cells in this mouse strain. Intravital imaging of mesenteric venules after systemic TNF-alpha treatment revealed a lower number of rolling and adherent cells on the endothelium compared to wildtype mice. In addition, we observed a significantly reduced migration capacity of miR-155 deficient bone marrow derived macrophages (BMDM) compared to wildtype cells and in a model of sterile induced peritonitis miR-155 deficiency led to a significant reduction of leukocytes in peritoneal lavage. Subsequently, we examined the cytokine expression profile in BMDM and found a decreased expression of pro-arteriogenic cytokines in cells lacking miR-155, which was partly mediated by the direct miR-155 target SOCS-1. Conclusion: Our data demonstrate that miR-155 exerts a cell-specific anti-angiogenic but pro-arteriogenic function in the regulation of neovascularization by targeting divergent genes and that its expression in bone marrow derived cells is essential for arteriogenesis in response to hindlimb ischemia in mice. MiRNAs could represent attractive target molecules for modulation of blood vessel growth.