Abstract 5600: GTP Cyclohydrolase/BH4 Pathway Protects EPC Function via Suppressing Oxidative Stress and Thrombospondin-1 in Salt-Sensitive Hypertension

Abstract

Background: Endothelial progenitor cells (EPC) are both reduced and dysfunctional in hypertension that correlates inversely with its mortality, but the mechanisms are poorly understood. eNOS critically regulates EPC mobilization and function, but is uncoupled in DOCA-salt hypertension due to reduced essential cofactor tetrahydrobiopterin (BH4). We tested the hypothesis that GTP cyclohydrolase I (GTPCH), the rate-limiting enzyme of BH4 synthesis, protects EPC function in DOCA-salt mice. Methods and Results: EPCs were isolated from peripheral blood and bone marrow of wild-type (WT), WT DOCA-salt, endothelial-specific GTPCH transgenic (Tg-GCH), DOCA-salt treated Tg-GCH, and BH4 deficient hph-1 mice. Both EPC adhesion and angiogenic functions were impaired in WT DOCA (58 and 38%, respectively, n=5– 8, p<0.01) and hph-1 mice (40 and 31%, respectively, n=5–8, p<0.01, vs. WT), which were rescued in DOCA Tg-GCH mice (93 and 92%, respectively, n=6–7). Superoxide (O 2 − , DHE-) and NO (DAF-FM flow cytometry) levels in EPCs were elevated and reduced, respectively, in WT DOCA (220% and 53%, respectively, n=5–12, p<0.01) and hph-1 mice (280% and 41%, respectively, n=6–12, p<0.05, vs. WT), which were blunted in DOCA Tg-GCH mice (137% and 96%, respectively, n=6–7). Thrombospondin-1 (TSP-1), a secreted potent anti-angiogenic protein, was elevated in EPCs of WT DOCA and hph-1 mice (290 and 280%, respectively, n=8–12, p<0.01 vs. WT), but not in DOCA Tg-GCH mice (160%, n=9–12, p>0.05). In vitro treatment of EPCs from WT DOCA mice with BH4, PEG-SOD, or L-NNA significantly reduced TSP-1 (51, 42 and 53%, respectively, n=5–12, p<0.01) and O 2 − levels (58, 67 and 69%, respectively, n=5– 6, p<0.01 vs. WT-DOCA). NO level in EPCs of WT DOCA mice was rescued by BH4 and PEG-SOD (144 and 165%, respectively, n=4–7, p<0.05 vs. control), but not L-NNA. Crossing eNOS KO and Tg-GCH mice resulted in preserved circulating EPC number (88%, n=4–15, p>0.05 vs. WT), reduced EPC O 2 − level (64%, n=4 – 8, p<0.05 vs. WT-DOCA), and improved EPC adhesion and angiogenic functions (160 and 158%, respectively, n=4 –12, p<0.05 vs. WT-DOCA). Conclusion: We demonstrate for the first time that GTPCH/BH4 pathway protects EPC function via suppressing oxidative stress and TSP-1 level in salt-sensitive hypertension. This research has received full or partial funding support from the American Heart Association, Midwest Affiliate (Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, South Dakota & Wisconsin).