Androgen receptor-mediated genomic androgen action augments ischemia-induced neovascularization

Abstract

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 (ARΔex3KO), we examined the role of AR genomic function in modulating androgen-mediated augmentation of ischemia-induced neovascularization. Castrated wild-type (ARWT) and ARΔex3KO 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 ARWT mice post-HLI. In ARWT 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 ARWT mice. By contrast, DHT-mediated enhancement of blood flow recovery was abrogated in ARΔex3KO mice. DHT modulation of HIF-1α expression was attenuated in ARΔex3KO mice. DHT-induced HIF-1α transcriptional activity and DHT-augmented paracrine-mediated endothelial cell tubule formation were attenuated in fibroblasts isolated from ARΔex3KO mice in vitro. Furthermore, DHT-induced augmentation of Sca1+/CXCR4+ progenitor cell production and mobilization was absent in ARΔex3KO mice post-HLI. BM transplantation revealed that ischemia-induced mobilization of circulating progenitor cells was abolished in recipients of ARΔex3KO BM. Together, these results indicate that androgen-mediated augmentation of ischemia-induced neovascularization is dependent on genomic AR transcriptional activation.