OR09-03 Brain Aromatase Is Essential for Regulation of Sexual Activity in Male Mice

Abstract

Introduction: The biologically active form of estrogen, estradiol (E2), has important organizational roles in brain development and activational roles in adult brain physiology and behavior. It has been proposed that E2 formation in the brain might regulate sexual activity in various species. The mechanisms that link estrogen formation in the brain and sexual behavior, however, remain unclear. Aromatase is the key enzyme that catalyzes the conversion of testosterone (T) to E2 in the testis and brain of male mice. To determine the role of brain aromatase in male sexual activity, we generated a brain-specific aromatase knockout (bArKO) mouse model. Additionally, a newly generated total aromatase knockout (tArKO) mouse model served as a positive control. Methods: We generated the floxed aromatase mice (Aromfl/fl), which flanked the transcription and translation start sites and the common splice acceptor site for the upstream brain promoter I.f of the aromatase gene. We then crossed Nestin-Cre mice with Aromfl/fl mice to generate bArKO mice. Using the same Aromfl/fl mice, we bred tArKO via crossing with ZP3-Cre mice. Circulating and tissue (brain and testis) E2 levels were measured using liquid chromatography-tandem mass spectrometry. We assessed sexual activity in 12-14 week-old bArKO, tArKO and littermate control males over two 30-minute trials. The interactions were monitored and videotaped, and the videotape was scored for the sexual activity. To investigate whether the lack of estrogen production in the brain was causative for altered sexual behavior, 20 bArKO and 20 control mice were castrated at ~nine weeks of age and supplemented with exogenous sex hormone via 60-day time release pellet implantation. Results: E2 levels are significantly decreased in the brain but not the testis of bArKO mice as compared to control mice (P < 0.05, n=6-12). As expected, E2 levels in the brain and testis are significantly lower in tArKO mice compared with their WT littermates (n=6-9). Furthermore, we demonstrate that local aromatase expression and estrogen production in the brain is required for male sexual behavior and sex hormone homeostasis. Male bArKO mice exhibited significantly decreased sexual activity in the presence of strikingly elevated circulating T (n=5). In castrated adult bArKO mice, administration of E2 together with T restored maximum sexual behavior (n=5). Thus, aromatase in the brain is necessary for T-dependent male sexual activity. We also found that brain aromatase is required for negative feedback regulation of circulating T of testicular origin. Conclusion: Our findings suggest T activates male sexual behavior in part via conversion to E2 in the brain and provide the foundation for inhibition or enhancement of brain aromatase enzyme activity and/or utilization of selective estrogen receptor modulators in modifying sexual behavior. DCB and HZ contributed equally to this work.

Brain Aromatase and the Regulation of Sexual Activity in Male Mice

“…However, 100% of tArKO mice were infertile (more details in Supplemental Fig. 1, available in an online data repository ( 47) ). Body weight was assessed weekly for bArKO, tArKO, and age-matched heterozygous control male mice from 3 to 48 weeks of age.…”

“…Body weight was similar between control and bArKO mice but significantly increased in tArKO mice starting from 20 weeks of age compared with control mice (more details in Supplemental Fig. 2, available in an online data repository ( 47) ).…”

“…T and A4 levels in the brain and testis were significantly higher in tArKO mice compared with WT mice (more details in Supplemental Fig. 4, available in an online data repository ( 47) ).…”

“…Overall, intact bArKO mice spent less total time engaged in sexual behaviors such as mounting or intromission ( Fig. 2D and more details in Supplemental Movies 1 and 2, available in an online data repository ( 47) ). Taken together, these data suggest that while there was no difference in the qualitative acts associated with sexual behavior in intact bArKO and control mice, intact bArKO mice initiated these behaviors significantly less frequently.…”

“…By comparison, the disruption of sexual behavior was more severe in intact tArKO than in intact bArKO mice, with intact tArKO mice exhibiting no sexual activity ( Fig. 2E-2H and more details in Supplemental Movies 3-5, available in an online data repository ( 47) ). Mount and intromission behaviors were not observed in 5 intact tArKO mice analyzed across a total of 10 trials ( Fig.…”