GTP cyclohydrolase I prevents diabetic-impaired endothelial progenitor cells and wound healing by suppressing oxidative stress/thrombospondin-1
Tie L., Chen L-Y., Chen D-D., Xie H-H., Channon KM., Chen AF.
<jats:p> Endothelial progenitor cell (EPC) dysfunction is a key contributor to diabetic refractory wounds. Endothelial nitric oxide synthase (eNOS), which critically regulates the mobilization and function of EPCs, is uncoupled in diabetes due to decreased cofactor tetrahydrobiopterin (BH<jats:sub>4</jats:sub>). We tested whether GTP cyclohydrolase I (GTPCH I), the rate-limiting enzyme of BH<jats:sub>4</jats:sub> synthesis, preserves EPC function in type 1 diabetic mice. Type 1 diabetes was induced in wild-type (WT) and GTPCH I transgenic (Tg-GCH) mice by intraperitoneal injection of streptozotocin (STZ). EPCs were isolated from the peripheral blood and bone marrow of WT, Tg-GCH, and GTPCH I-deficient hph-1 mice. The number of EPCs was significantly lower in STZ-WT mice and hph-1 mice and was rescued in STZ Tg-GCH mice. Furthermore, GTPCH I overexpression improved impaired diabetic EPC migration and tube formation. EPCs from WT, Tg-GCH, and STZ-Tg-GCH mice were administered to diabetic excisional wounds and accelerated wound healing significantly, with a concomitant augmentation of angiogenesis. Flow cytometry measurements showed that intracellular nitric oxide (NO) levels were reduced significantly in STZ-WT and hph-1 mice, paralleled by increased superoxide anion levels; both were rescued in STZ-Tg-GCH mice. Western blot analysis revealed that thrombospondin-1 (TSP-1) was significantly upregulated in the EPCs of STZ-WT mice and hph-1 mice and suppressed in STZ-treated Tg-GCH mice. Our results demonstrate that the GTPCH I/BH<jats:sub>4</jats:sub> pathway is critical to preserve EPC quantity, function, and regenerative capacity during wound healing in type 1 diabetic mice at least partly through the attenuation of superoxide and TSP-1 levels and augmentation of NO level. </jats:p>