Antiangiogenic VEGF₁₆₅b Regulates Macrophage Polarization via S100A8/S100A9 in Peripheral Artery Disease

Background: Atherosclerotic occlusions decrease blood flow to the lower limbs, causing ischemia and tissue loss in patients with peripheral artery disease (PAD). No effective medical therapies are currently available to induce angiogenesis and promote perfusion recovery in patients with severe PAD. Clinical trials aimed at inducing vascular endothelial growth factor (VEGF)-A levels, a potent proangiogenic growth factor to induce angiogenesis, and perfusion recovery were not successful. Alternate splicing in the exon-8 of VEGF-A results in the formation of VEGFxxxa (VEGF₁₆₅a) and VEGFxxxb (VEGF₁₆₅b) isoforms with existing literature focusing on VEGF₁₆₅b's role in inhibiting vascular endothelial growth factor receptor 2-dependent angiogenesis. However, we have recently shown that VEGF₁₆₅b blocks VEGF-A-induced endothelial vascular endothelial growth factor receptor 1 (VEGFR1) activation in ischemic muscle to impair perfusion recovery. Because macrophage-secreted VEGF₁₆₅b has been shown to decrease angiogenesis in peripheral artery disease, and macrophages were well known to play important roles in regulating ischemic muscle vascular remodeling, we examined the role of VEGF₁₆₅b in regulating macrophage function in PAD. Methods: Femoral artery ligation and resection were used as an in vivo preclinical PAD model, and hypoxia serum starvation was used as an in vitro model for PAD. Experiments including laser-Doppler perfusion imaging, adoptive cell transfer to ischemic muscle, immunoblot analysis, ELISAs, immunostainings, flow cytometry, quantitative polymerase chain reaction analysis, and RNA sequencing were performed to determine a role of VEGF₁₆₅b in regulating macrophage phenotype and function in PAD. Results: First, we found increased VEGF₁₆₅b expression with increased M1-like macrophages in PAD versus non-PAD (controls) muscle biopsies. Next, using in vitro hypoxia serum starvation, in vivo preclinical PAD models, and adoptive transfer of VEGF₁₆₅b-expressing bone marrow-derived macrophages or VEGFR1^+/- bone marrow-derived macrophages (M1-like phenotype), we demonstrate that VEGF₁₆₅b inhibits VEGFR1 activation to induce an M1-like phenotype that impairs ischemic muscle neovascularization. Subsequently, we found S100A8/S100A9 as VEGFR1 downstream regulators of macrophage polarization by RNA-Seq analysis of hypoxia serum starvation-VEGFR1^+/+ versus hypoxia serum starvation-VEGFR1^+/- bone marrow-derived macrophages. Conclusions: In our current study, we demonstrate that increased VEGF₁₆₅b expression in macrophages induces an antiangiogenic M1-like phenotype that directly impairs angiogenesis. VEGFR1 inhibition by VEGF₁₆₅b results in S100A8/S100A9-mediated calcium influx to induce an M1-like phenotype that impairs ischemic muscle revascularization and perfusion recovery.