Abstract 1326: HIF Pathway is Associated with Progression and Neovascularization of Human Atherosclerosis
Atherosclerotic plaque growth and instability are associated with plaque neovascularization. As hypoxia-inducible transcription factors (HIF) are upstream regulators of neovascularization, HIF and its target genes may also be expressed in atherosclerotic plaques and associated with plaque progression and neovascularization. The mRNA and protein expression of HIF1α, 2α and HIF target genes, vascular endothelial growth factor (VEGF), glucose transporter (GLUT) 1, -3, hexokinase (HK) 1, - 2, and carbonic anhydrase (CA) IX was determined in human veins, non-diseased and atherosclerotic carotid arteries using microarray, realtime PCR, in situ hybridization and immunohistochemistry. A possible association with microvessel density and proliferating endothelial cells (KiEC) was studied with CD31/CD34 and Ki67 immunohistochemistry. Microarray analysis showed upregulation of HIF1α (1.5 fold), VEGF (1.7 fold), GLUT1 (1.2 fold), GLUT3 (2.3 fold) and HK2 (2.2 fold) between early (n=9) and stable carotid lesions (n=8). Realtime PCR demonstrated only significantly different mRNA levels for VEGF, 4.6 fold increased between early (n=5) and stable carotid lesions (n=5), and HK1, 1.8 fold decreased between stable and thrombus-containing (n=5) lesions. In situ hybridization (n=6) and immunohistochemistry (n=62) showed strong expression of HIF1α, 2α and their target genes in intimal macrophages, and modest expression in smooth muscle and endothelial cells. Protein expression of HIF1α, 2α and their target genes was absent in non-diseased vasculature and increased with atherosclerotic progression. This increase coincided with the increase in microvessel density from 0/mm2 in early to 2.2/mm2 in both types of advanced lesions. KiEC were only present in 2.2% of microvessels in thrombus-containing lesions, showing that plaque microvessel EC were not actively proliferating. In conclusion, HIF1α, 2α and their target genes were expressed in human atherosclerosis, principally in macrophage-rich regions, and associated with lesion progression and microvessel density.