Ligand-Dependent Regulation of Retinoic Acid Receptor α in Rat Testis: In Vivo Response to Depletion and Repletion of Vitamin A

Abstract

Male animals are sterile due to testicular degeneration in the absence of retinoic acid (RA) or functional retinoic acid receptor-alpha (RAR alpha). This degeneration can be reversed by injecting retinol, a precursor of RA, into vitamin A-deficient (VAD) rats. To determine the relationship between this ligand-dependent testicular degeneration and regeneration and the expression levels of RAR alpha messenger RNA and protein, testes were depleted and then replenished with retinol in vivo. Results showed that RAR alpha messenger RNA and protein levels declined to VAD amounts after 7 weeks on a VAD diet. This decline was due to decreased RAR alpha levels in early meiotic spermatocytes and the loss of advanced germ cells. Interestingly, the advanced germ cells still contained RAR alpha, but the protein was primarily cytoplasmic instead of nuclear, indicating inactivity as a transcription factor. In VAD testis, RAR alpha levels were low and then increased primarily in Sertoli cells after retinol replenishment. TUNEL analyses showed that most germ cells at the basal aspect of seminiferous tubules were undergoing apoptosis during degeneration. These results indicate that RAR alpha is either down-regulated or inactivated in RA-deficient testis and coincident with that, testes degenerate by apoptosis or selective loss of germ cells.

Follicle-stimulating Hormone Inhibits All-trans-retinoic Acid-induced Retinoic Acid Receptor α Nuclear Localization and Transcriptional Activation in Mouse Sertoli Cell Lines

“…In this report, we demonstrate that the ligand, tRA, increases the nuclear translocalization of RAR␣ within 30 min in mouse Sertoli cell lines (MSC-1 and MSC-1F) and that this localization is independent of new protein synthesis. This regulation of nuclear localization by ligand is consistent with the previous finding in the vitamin A-deficient rat model in which the RAR␣ subcellular localization in germ cells changed from primarily nuclear to more cytoplasmic following retinol depletion (33). These results clearly demonstrate the importance of ligand in the regulation of RAR␣ receptor subcellular localization.…”

“…Specifically, RAR␣ expression is induced in a time-dependent manner by tRA treatment, increasing significantly by 1 h, reaching a maximum of 2.5-fold within 3 h, and then declining by 24 h. This increase requires new protein synthesis and is probably due to the RAR␣ serving as an endogenous RARE-containing reporter gene because an RARE has previously been located within the promoter region of RAR␣ 2 (32). The pattern of increase in the expression of RAR␣ protein by tRA treatment in mouse Sertoli cell lines parallels the retinol-induced effect on RAR␣ protein expression previously observed in vivo in the testis of vitamin A-deficient rats (33). Following an injection of retinol into a vitamin A-deficient rat, the RAR␣ protein level reached a maximum level at 4 h and then decreased to a basal level within 24 h. At the mRNA level, there was nearly a 3-fold increase of RAR␣ mRNA as early as 2 h post-injection of retinol, followed by a subsequent decrease by 12 h (33).…”

A Novel Cytoplasmic Adaptor for Retinoic Acid Receptor (RAR) and Thyroid Receptor Functions as a Derepressor of RAR in the Absence of Retinoic Acid*

“…However, some studies have demonstrated that RAR and TR are retained in the cytoplasm and move to the nucleus when ligands are supplied (13)(14)(15)(16). In particular, we also found that RAR␣ shuttles between the cytoplasm and the nucleus in the Sertoli cell line TM4 in response to AtRA (Fig.…”

“…Cells-It has been reported that apoRAR␣ is cytoplasmic and holo-RAR␣ is nuclear in mouse testis Sertoli cell lines (15,16). These findings led us to investigate the role of CART1 in the intracellular distribution of RAR␣ in Sertoli cells.…”

“…A few reports have suggested that TRs (TR␣1 and TR␤1) actively shuttle between the nucleus and cytoplasm and that the ligand promotes cytoplasm-to-nucleus shuttling (13,14). In some Sertoli cell lines derived from mouse testis, RAR␣ is ordinarily located in the cytoplasm and rapidly moves to the nucleus in response to its ligand RA (15,16). In both cases, ligands are required for the promotion of nuclear translocation.…”