Abstract 627: Human Osteopontin Isoforms Differentially Promote Neovascularization in Response to Ischemia via Macrophage Recruitment and Survival

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Background: Coronary and peripheral artery diseases result in vessel occlusion and ischemia, initiating neovascularization to restore blood flow and preserve function. We previously established that osteopontin (OPN), a matricellular cytokine, is critical to ischemia-induced neovascularization. Unlike rodents, humans express 3 OPN isoforms (a, b, and c); however, the roles of these isoforms in neovascularization and cell migration remain undefined. Methods and Results: Using a murine model of hindlimb ischemia in OPN -/- mice and 1.5x10 6 lentivirus particles expressing OPNa, OPNb or OPNc delivered IM, we found that OPN isoforms have different effects on functional perfusion recovery in vivo . OPNa increased limb perfusion 30.4%±0.8 and OPNc by 70.9%±6.3, as measured by laser Doppler perfusion imaging (d14; p<0.001 vs. LVGFP). Increases in perfusion translated to significant increases in functional limb use in OPNa and OPNc treated animals (61.1%±8.2; 76.2%±9.7; p<0.05), as assessed by voluntary running wheel use, and was not due to isoform expression differences (ELISA, n=6, p=ns). While OPN isoforms did not differentially affect angiogenesis, OPNa and OPNc significantly increased arteriogenesis (enlargement of arterioles), as measured by the increase in SM α-actin positive vessels in the small (200 - 700 μm 2 ; 47.2%±6.1; 55.9%±6.7) and large artery (1000 - 2500 μm 2 ; 54.2%±6.1; 76.5%±10.9) ranges in vivo (n=9; p<0.001 vs. OPNb). We hypothesized that OPN isoform-dependent effects on arteriogenesis are due to differential effects on macrophage function. OPN isoforms did not differentially affect macrophage polarization and all 3 isoforms increased macrophage survival (64.9%±1.1 - 78.6%±1.9 vs. control; p<0.0001). However, OPNa and OPNc both increased macrophage migration, where OPNc was the more potent migratory stimulus (n=4, p<0.001 vs. no trx, OPNa, OPNb). Conclusion: In conclusion, human OPN isoforms exert divergent effects on neovascularization through differential effects on arteriogenesis and macrophage migration and survival. Altogether, these data support that human OPN isoforms may represent novel therapeutic targets to improve neovascualrization and preserve tissue function in obstructive artery disease patients.