Retinoic acid signaling biomarkers after treatment with retinoic acid and retinoic acid receptor alpha antagonist (Ro 41-5253) in canine testis: an in vitro organ culture study.

Retinoic acid (RA) is an essential component for development and maintenance of the male genital tract and for spermatogenesis. Aldehyde dehydrogenase (ALDH)1, cytochrome P450 (CYP)26b1, RA receptor (RAR)α, cellular RA-binding protein (CRAB)II, and stimulated by RA gene (STRA)8 are involved in synthesis, metabolism signaling pathways, and as downstream effectors of RA. The objective was to elucidate the effects of exogenous RA and a RARα antagonist on gene expression of ALDH1, CYP26b1, RARα, cellular RA-binding protein II, and STRA8 in an in vitro organ culture model of canine testis. Testicular tissues from medium-sized mixed breed dogs (N = 5; age 8 ± 0.17 mo) were subjected to exogenous all trans-RA (final concentrations of 1, 2, and 10 μM, and DMSO as control) for 24 h. Similarly, testicular tissues were treated with Ro 41-5253 (RARα antagonist), at 1, 10, and 50 μM final concentrations (DMSO as control) for 24 h. Exogenous RA or the RARα antagonist decreased (P < 0.05) mRNA abundance of ALDH1 in a dose-dependent manner compared with control. The CRABII mRNA abundance was greater after RA treatment compared with control (P < 0.01), but only 50 μM Ro 41-5253 effectively decreased CRABII mRNA abundance compared with control (P < 0.01). Although RA did not affect RARα mRNA abundance, the RARα antagonist treatment lowered RARα mRNA abundance compared with control (P < 0.05). Abundance of CYP26b1and STRA8 mRNA were greater (P < 0.05) after RA treatment, but lower (P < 0.05) after RARα antagonist treatment compared with control. In conclusion, exogenous RA decreased mRNA abundance of ALDH1 and increased mRNA abundance of RA signaling molecules and its downstream effectors (CYP26b1, CRABII, and STRA8), whereas treatment with a RARα antagonist effectively decreased RARα and RA metabolism molecules and its downstream effectors in canine testis. Perhaps pharmacological intervention via the RA pathway would enable canine male contraception or treatment of testicular pathology.