The overarching goal of these studies is to understand the role of retinoid signaling in the regulation of spermatogenesis and to exploit the inhibition of its essential function as a new and novel approach to male contraception. All trans retinoic acid (ATRA) is an active metabolite of vitamin A and exerts its function at least in part by binding to nuclear receptors of the steroid hormone superfamily, the retinoic acid receptors (RARs). The importance of ATRA signaling via the RARa receptor in particular has been demonstrated by gene targeting in mice: RARa-deficient male mice are sterile with defects in spermatogenesis similar to those seen in vitamin A-deficient (VAD) animals. Following up on previous observations of 'testicular toxicity'in animals treated with the pan-RAR antagonist BMS-189453, we have now shown that indeed, spermatogenesis is inhibited, and further, that this induced sterility is reversible. This suggested that BMS-189453 had potential as a novel, non-steroid hormone-based approach to male contraception. The present proposal focuses specifically on the use of the RAR pan-antagonist BMS-189453 to inhibit spermatogenesis in vivo in the mouse model. Three integrated Aims are proposed, which range in scope from addressing very applied questions with regard to levels and length of dosing to maximize efficacy to elucidating the cellular and molecular targets of the drug's action. The first Specific Aim will i) extend the duration of treatment to determine the maximum period of inhibition of spermatogenesis after which normal spermatogenesis can be restored;ii) assess whether even lower doses of the drug than used in our preliminary experiments can be effective in inhibiting spermatogenesis;iii) determine the range above and below the optimal dose that is still effective in order to standardize the dosing regimen;and iv) examine the progeny that result after the restoration of fertility for their normal growth. VAD, treatment with the pan-antagonist BMS-189453, and lack of the RARa receptor specifically all result in defects in spermatid alignment and spermiation.
Specific Aim 2 will determine the cellular targets of retinoid signaling and how are they disrupted in its absence to result in these characteristic abnormalities. Finally, Aim 3 will test the hypothesis that at least some of the effects of BMS-189453 are mediated at the transcriptional level by identifying those genes whose expression is altered by inhibition of all three RARs, as compared to the changes seen in testes lacking only RARa and to normal mice, using microarray analysis.
The proposed studies will provide critical information on the potential use of retinoid antagonists as a new and novel approach to male contraception. The experiments will provide data on dosing regimens to maximize efficacy while minimizing compound exposure, all the while ensuring reversibility. Non-hormonal strategies for male contraception would provide health benefits to couples desiring alternative family planning approaches and to over-populated countries world-wide.
