Testis

Intratesticular Androgen Levels, Androgen Receptor Localization, and Androgen Receptor Expression in Adult Rat Sertoli Cells

Abstract
In the rat, quantitatively normal spermatogenesis is maintained only when intratesticular testosterone (ITT) levels greatly exceed the peripheral T concentration. When ITT concentrations fall below a threshold, germ cells are lost at specific stages of the seminiferous cycle. Germ cells can be restored by high doses of T that binds to androgen receptors (AR) in Sertoli cells. However, the relationships between germ cell dynamics, AR-mediated molecular events and ITT concentrations are not established. ITT levels may regulate germ cell life and death through an affect on AR localization and AR mRNA or protein levels within Sertoli cells at specific stages of the cycle. We determined AR localization and mRNA and protein expression in adult rat Sertoli cells in relation to reduced and then restored ITT concentrations in vivo. ITT levels were reduced by implanting rats with T- and estradiol (E)-filled capsules for 7-28 days, and subsequently restored with large T-filled capsules. AR is normally localized within Sertoli cell nuclei at stages VII-VIII of the seminiferous epithelium. After T/E treatment, AR immunostaining in Sertoli cell nuclei became non-detectable by 14-28 days, but was restored 6h following T restoration. The loss of Sertoli cell nuclear AR localization correlated with increasing numbers of apoptotic germ cells. AR mRNA levels in isolated Sertoli cells did not change through 14 days of T/E treatment, increased significantly by day 28, and remained elevated 24h after T restoration. AR mRNA levels in microdissected tubules at stages II-IV, VI-VIII and IX-XII did not decrease through 14 days of T/E treatment. In contrast, AR protein levels were reduced in seminiferous tubules by day 14 and in testes at day 28 post-T/E treatment, but were restored within 24h by T repletion. Therefore, the reduction of ITT concentration results in a time-dependent redistribution of AR and reduced AR protein, but not AR mRNA levels in Sertoli cells. Repletion of T restored AR protein and it relocated to Sertoli cell nuclei. By an unknown mechanism T regulates AR localization within Sertoli cells to determine germ cell life or death.

Key words: Testis • Androgen receptor • Apoptosis • Spermatogenesis • Testosterone

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