Abstract 11: The Role of Human Osteopontin Isoforms in Post-Ischemic Neovascularization
Coronary and peripheral artery diseases lead to ischemia, initiating processes that promote neovascularization to restore blood flow and preserve tissue function. We demonstrated previously 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. To assess how human OPN isoforms affect neovascularization, OPN -/- mice underwent hind limb ischemia surgery. At the time of surgery, 1.5x10 6 lentivirus particles expressing human OPNa, OPNb or OPNc were delivered by intramuscular injection. While OPNa improved limb perfusion 30.4%±0.8 in OPN -/- mice, OPNc improved perfusion by 70.9%±6.3 (d14; p<0.001 vs. LVGFP), as measured by laser Doppler perfusion imaging. Importantly, both OPNa and OPNc isoforms significantly rescued neovascularization better than OPNb (n=6, p<0.05). Isoform effects on vascular volume, density, connectivity and diameter were further assessed using Micro-CT angiograms. OPNa and OPNc rescued limb function compared to control and OPNb treated animals (61.1%±8.2; 76.2%±9.7; p<0.05), as assessed by voluntary running wheel use. To verify the differences in neovascularization were due to divergent effects on receptor binding and/or signaling and not variations in isoform expression, we confirmed similar OPN isoform expression levels by ELISA (n=6, p=ns) and immunofluorescence. OPN isoforms a and c both increased macrophage infiltration 2.5 fold, as assessed by mRNA (d7; p<0.05) and histology, leading to increases in vascular smooth muscle cell (VSMC) infiltration (d7; p<0.05). Several pro-arteriogenic factors were also significantly increased at the mRNA level. Finally, we confirmed in vitro that OPNa and OPNc significantly increased VSMC migration compared to OPN b and control (49.8%±3.1; 75.2%±6.3; p<0.05). In conclusion, human OPN isoforms may exhert divergent effects on neovascularization through varried effects on macrophage and VSMC recruitment. Human OPN isoforms may represent potential new therapeutic targets to promote neovascularization and preserve function in patients with peripheral artery disease.