Androgen Receptor-Mediated Genomic Androgen Action Augments Ischemia-Induced Neovascularization

Increasing evidence indicates that androgens regulate ischemia-induced neovascularization. However, the role of genomic androgen action mediated by androgen receptor (AR), a ligand-activated nuclear transcription factor, remains poorly understood. Using an AR knockout (KO) mouse strain that contains a transcriptionally inactive AR (AR^Δex3KO), we examined the role of AR genomic function in modulating androgen-mediated augmentation of ischemia-induced neovascularization. Castrated wild-type (AR^WT) and AR^Δex3KO mice were implanted with 5α-dihydrotestosterone (DHT) or placebo pellets after hindlimb ischemia (HLI). DHT modulation of angiogenesis and vasculogenesis, key processes for vascular repair and regeneration, was examined. Laser Doppler perfusion imaging revealed that DHT enhanced blood flow recovery in AR^WT mice post-HLI. In AR^WT mice, DHT enhanced angiogenesis by down-regulating prolyl hydroxylase 2 and augmenting hypoxia-inducible factor-1α (HIF-1α) levels in the ischemic tissues post-HLI. DHT also enhanced the production and mobilization of Sca1+/CXCR4+ progenitor cells in the bone marrow (BM) and circulating blood, respectively, in AR^WT mice. By contrast, DHT-mediated enhancement of blood flow recovery was abrogated in AR^Δex3KO mice. DHT modulation of HIF-1α expression was attenuated in AR^Δex3KO mice. DHT-induced HIF-1α transcriptional activity and DHT-augmented paracrine-mediated endothelial cell tubule formation were attenuated in fibroblasts isolated from AR^Δex3KO mice in vitro. Furthermore, DHT-induced augmentation of Sca1+/CXCR4+ progenitor cell production and mobilization was absent in AR^Δex3KO mice post-HLI. BM transplantation revealed that ischemia-induced mobilization of circulating progenitor cells was abolished in recipients of AR^Δex3KO BM. Together, these results indicate that androgen-mediated augmentation of ischemia-induced neovascularization is dependent on genomic AR transcriptional activation.