Androgen Receptor Promotes Sex-Independent Angiogenesis in Response to Ischemia and Is Required for Activation of Vascular Endothelial Growth Factor Receptor Signaling

Abstract

Background Hypoandrogenemia is associated with an increased risk of ischemic diseases. Since actions of androgens are exerted through androgen receptor (AR) activation, we studied hind limb ischemia in AR knockout (KO) mice to elucidate the role of AR in response to ischemia. Methods and Results Both male and female ARKO mice exhibited impaired blood flow recovery, more cellular apoptosis and a higher incidence of autoamputation after ischemia. In ex vivo and in vivo angiogenesis studies, AR-deficient vascular endothelial cells showed reduced angiogenic capability. In ischemic limbs of ARKO mice, reductions in the phosphorylation of the Akt protein kinase and endothelial nitric oxide synthase (eNOS) were observed despite a robust increase in hypoxia-inducible factor 1α and vascular endothelial cell growth factor (VEGF) gene expression. In in vitro studies, siRNA-mediated ablation of AR in vascular endothelial cells blunted VEGF-stimulated phosphorylation of Akt and eNOS. Immunoprecipitation experiments documented an association between AR and kinase insert domain protein receptor (KDR) that promoted the recruitment of downstream signaling components. Conclusion These results document a physiological role of AR in gender-independent angiogenic potency and provide evidence for a novel cross-talk between androgen/AR signaling and VEGF/KDR signaling pathways.

Roles of the Androgen – Androgen Receptor System in Vascular Angiogenesis

“…In addition, DHT, through activation of the AR, promoted in vitro angiogenic processes such as EC migration, proliferation, and tubulogenesis via VEGF-related mechanisms in ECs derived from male donors 74,75) . In contrast, we demonstrated that both male and female AR knockout mice showed impaired revascularization after ischemia despite a robust increase of VEGF expression 36) . Moreover, endothelial cells from AR knockout mice had attenuated angiogenic potency.…”

“…Sieveking et al reported that DHT induced dose-dependent increases in the mRNA expression of KDR, a major VEGF receptor, in male HUVECs 75) . We also demonstrated that AR activation is required for the compensatory up-regulation of KDR gene expression in response to ischemia, at least in male mice 36) . Previous studies revealed that a ternary complex formed among AR, PI3Kp85, and Src is essential for the androgen-stimulated activation of PI3K/Akt and mitogen-activated protein kinase 88,89) and that KDR is activated by the recruitment and activation of Src and PI3K 90) .…”

“…Although we showed that AR deficiency impaired ischemic-induced angiogenesis also occurs in females, pathophysiological roles of the AR in females are largely unknown. In female AR knockout mice, serum concentrations of androgens and estrogens were the same as female wildtype mice in our experiment 36) . Thus, we speculate that unliganded AR also plays a role in angiogenesis after ischemia regardless of sex.…”

“…Thus, depletion and/or dysfunction of EPCs are pathogenic events that contribute to the inability to maintain an intact endothelium and to promote angiogenesis 93) . Human EPCs express ARs, and androgens increase EPC mobilization from bone ylation was blunted by AR deficiency in vivo and in vitro 36) . Because the ischemic muscle of AR-deficient mice showed the attenuation of Akt-eNOS phosphorylation and the reduced activation of Akt and eNOS attenuated angiogenesis in the animal model, the AR is required for promoting angiogenesis partly through activation of the PI3K/Akt-eNOS signaling pathway in response to ischemic stress (Fig.…”

“…Animal models using castration or pharmacological interventions (except for non-aromatizable DHT) include the response of ER and AR dependent mechanism. To elucidate the physiological function of the androgen -AR system in cardiovascular organs in vivo, we used the AR knockout mice [25][26][27]36) .…”