Impaired angiogenesis and mobilization of circulating angiogenic cells in HIF-1α heterozygous-null mice after burn wounding

Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that controls vascular responses to hypoxia and ischemia. In this study, mice that were heterozygous (HET) for a null allele at the locus encoding the HIF-1α subunit (HET mice) and their wild-type (WT) littermates were subjected to a thermal injury involving 10% of the body surface area. HIF-1α protein levels were increased in burn wounds of WT but not of HET mice on day 2. The serum levels of stromal-derived factor 1α, which binds to CXCR4, were increased on day 2 in WT but not in HET mice. Circulating angiogenic cells were also increased on day 2 in WT but not in HET mice and included CXCR4 ⁺Sca1⁺ cells. Laser Doppler perfusion imaging demonstrated increased blood flow in burn wounds of WT but not HET mice on day 7. Immunohistochemistry on day 7 revealed a reduced number of CD31⁺ vessels at the healing margin of burn wounds in HET as compared with WT mice. Vessel maturation was also impaired in wounds of HET mice as determined by the number of α-smooth muscle actin-positive vessels on day 21. The remaining wound area on day 14 was significantly increased in HET mice compared with WT littermates. The percentage of healed wounds on day 14 was significantly decreased in HET mice. These data delineate a signaling pathway by which HIF-1 promotes angiogenesis during burn wound healing.