Testosterone dependent androgen receptor stabilization and activation of cell proliferation in primary human myometrial microvascular endothelial cells: Testosterone induces HMMEC proliferation

OBJECTIVE: To clarify, whether uterine endothelial proliferation could be regulated via an autocrine estrogen producing mechanism or direct actions of testosterone. DESIGN: In vitro study. SETTING: Tertiary care facility. PATIENT(S): Human myometrial tissue obtained from 40 women undergoing hysterectomy without further intrauterine pathology. INTERVENTION(S): Cell culture, proliferation assay and CYP19 activity assay on human myometrial endothelial cells treated with testosterone, estradiol, letrozole, flutamide, PD98059, MG-132 alone or in combination. MAIN OUTCOME MEASURE(S): We analyzed whether aromatase is expressed in human myometrial microvascular endothelial cells (HMMECs) and whether it affects proliferation and converts androgens to estrogens. In addition, we aimed to define whether or not T could have a direct capability to affect HMMEC proliferation. RESULT(S): Using quantitative real-time PCR and Western analysis, primary passage four HMMECs were shown to express low levels of aromatase mRNA and protein, respectively. However, HMMECs were unable to convert radioactively labeled 3∗H-1β-androstenedione to estrogen. Pharmacologic doses of T (10(-6) and 10(-4) M) increased HMMEC proliferation, assessed through a bromodeoxyuridine ELISA. This effect of T on proliferation could not be blocked after pretreatment of cells with the aromatase inhibitor letrozole. In addition, HMMECs were found to express androgen receptors (ARs), and the AR antagonist flutamide abolished T-dependent proliferation. T was shown to increase AR protein levels, which was due to T-dependent receptor stabilization and not activation of gene transcription. CONCLUSION(S): We conclude that myometrial endothelial proliferation is not regulated through myometrial endothelial estrogen production. However, pharmacologic doses of T increase myometrial endothelial proliferation through a receptor-dependent and -stabilizing mechanism.