Background: Androgens enhance ischaemia-mediated neovascularisation, which requires both angiogenesis and vasculogenesis. However, the mechanisms underpinning androgen-mediated neovascularisation are poorly understood. In this study, we examined the effects of androgens on the transcription factor hypoxia-inducible factor-1α (HIF-1α) and endothelial progenitor cell mobilisation.

Methods: Male C57Bl/6J mice were castrated two weeks prior to the induction of unilateral hindlimb ischaemia (HLI) and implanted with a dihydrotestosterone (DHT) or placebo implant. Laser Doppler Perfusion Imaging (LDPI) assessed blood flow recovery following the ischaemic injury. Protein and mRNA was collected from the adductor muscle of ischemic and non-ischemic limbs and analysed by western blotting and qPCR. The level of Sca1+CXCR4+ endothelial progenitor cells (EPCs) was quantified in blood, bone marrow and spleen by flow cytometry.

Results: Mice treated with DHT displayed enhanced neovascularisation following ischaemic injury which was associated with increased HIF-1α mRNA and protein expression (p<0.001). Furthermore, DHT-treated mice had a marked reduction in the level of prolyl hydroxylase-2 (PHD-2) but not PHD-1 or PHD-3 (p<0.05) enzymes which regulate HIF-1α protein degradation. We therefore postulate that DHT induced reduction of PHD-2 levels led to increased HIF-1α expression and subsequent downstream HIF-1a regulated genes. Furthermore, DHT treatment increased EPC levels in the bone marrow and blood on day 3 after ischaemia (p<0.01) compared to placebo-treated mice, indicating that DHT treatment up-regulated EPC mobilisation.    

Conclusion: Androgen enhanced ischaemia-mediated neovascularisation is involved in both angiogenesis and vasculogenesis. DHT enhanced angiogenesis is associated with an increase in HIF-1α expression by reducing the level of its degradative enzyme PHD-2. On the other hand, DHT improves vasculogenesis by increasing the proliferation and mobilisation of EPCs.