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Leydig and Sertoli cells are both targets of androgen action in the testis. Androgen exerts contrasting effects on the two cell types partially inhibiting steroidogenesis in adult Leydig cell and stimulating adult Sertoli cell functions required to support spermatogenesis. The developmental changes in the messenger RNA (mRNA) levels of androgen receptor (AR) also differ between Leydig and Sertoli cells, with Leydig cell AR mRNA being highest on day 35 postpartum, whereas Sertoli cell AR mRNA levels are highest on day 90. The purpose of the present study was to determine if the concentrations of AR in Leydig and Sertoli cells are differentially regulated during development using quantitative immunostaining. AR protein levels were measured in rat testes after hormonal treatments at three developmental stages: on days 21, 35, and 90 postpartum. At each age, five groups of animals were treated for 4 days with: 1) vehicle; 2) LHRH antagonist (NalGlu, 0.3 mg/kg BW.day) to suppress endogenous levels of androgen that accompany inhibition of LH and FSH secretion; 3) NalGlu + LH (0.2 mg/kg BW.day); 4) NalGlu + testosterone (T, at 7.5 mg/kg BW.day); and 5) NalGlu + MENT (a potent synthetic androgen, 7 alpha-methyl-19-nortestosterone, 0.7 mg/kg BW.day). AR protein was visualized by immunohistochemistry and measured by computer-assisted image analysis in Leydig and Sertoli cells using frozen sections of tests. After NalGlu treatment, AR levels in Leydig cells declined sharply to 42% and 31% of vehicle control (P < 0.01) in the 21 and 35 days postpartum age groups, respectively, but in 90-day-old rats there was no change. AR levels were partially maintained by exogenous LH, and completely maintained by exogenous androgen treatments in Leydig cells from 21- and 35-day-old rats, whereas in Leydig cells from 90-day-old rats, AR levels were unaffected in all treatment groups. In contrast, after NalGlu treatment, the AR concentration in Sertoli cells from 90-day-old rats were reduced to 32% of control (P < 0.01). Moreover, in Sertoli cells from 90-day-old rats, AR levels were partially maintained by LH and completely maintained by androgens. A similar trend was observed on day 35. On day 21, however, AR levels in immature Sertoli cells were unaffected in all treatment groups. These results indicate that androgen maximally stimulates AR levels in immature Leydig cells but is without significant effect in adult Leydig cells. In contrast, AR levels in Sertoli cells are more sensitive to androgen regulation in adult compared with immature animals. These findings indicate that there are distinct mechanisms controlling AR concentrations in Leydig and Sertoli cells during the development of the testis.

Testosterone produced by Leydig cells is critical for the maintenance of spermatogenesis by Sertoli cells throughout adulthood in the rat. However, the presence of androgen receptors (AR) in Leydig cells in prepubertal rats suggests additional roles for androgen in early Leydig cell function and differentiation. In the present study, AR messenger RNA (mRNA) was directly measured by in situ hybridization in sections of rat testes at three developmental stages: on day 21 postpartum, when Leydig cells exist as mesenchymal-like progenitors; on day 35, when they are still immature, producing low amounts of testosterone; and on day 90, when they are fully functional in the sexually mature animal. Testicular AR mRNA was detected in Leydig cells, pericytes, peritubular myoid cells, and Sertoli cells. On day 90, AR mRNA levels in Sertoli cells varied with the cycle of the seminiferous epithelium, achieving peak intensity at stages VII-VIII. Measurements were made by image analysis and expressed as integrated signal intensities per unit labeled area (mean +/- SEM; n = 3 rats at each age). The results showed that levels of Leydig cell and Sertoli cell AR mRNA change significantly during development (P < 0.05). Leydig cell AR mRNA was intermediate on day 21 (at 17.3 +/- 0.7), highest on day 35 (at 26.9 +/- 1.6), and lowest on day 90 (at 11.8 +/- 1.1). The trend for isolated Leydig cells from these three ages was identical. In contrast, Sertoli cell AR mRNA was lowest on day 21 (at 19.3 +/- 1.0), intermediate on day 35 (at 24.5 +/- 1.4), and highest on day 90 (at 36.9 +/- 0.5). In Leydig cells, the highest level of AR mRNA was present during puberty, whereas the greatest amount of AR mRNA in Sertoli cells was present on day 90. This indicates that Leydig cells and Sertoli cells use different mechanisms to maintain AR levels. We infer from these data that Leydig cells are maximally sensitive to androgen during puberty, which is consistent with our hypothesis that androgens facilitate their differentiation.

To further assess the hormonal response capabilities of Leydig cell progenitors (PLC) from 21-day-old rats, their levels of LH and androgen receptors (LH-R and AR) were measured and compared to those of isolated immature (ILC) and adult Leydig cells (ALC) from 35- and 90-day-old rats, respectively. Levels of LH receptor were estimated by Scatchard analysis of binding to [125I]hCG, and levels of LH receptor mRNA were determined by Northern blot analysis using a rat LH receptor antisense RNA probe. The numbers of LH receptors per cell measured by the binding study were 2,623 +/- 1,110 in PLC, 9,024 +/- 1,992 in ILC, and 39,896 +/- 15,234 in ALC (mean +/- SEM of four replicate experiments; ALC significantly greater than either PLC or ILC at P less than 0.05). The Northern blotting revealed three major bands [6.7, 2.6, and 2.3 kilobases (kb)] that were present in Leydig cells at all three ages and were not detected in HepG2 cells. When the steady state levels of the predominant 6.7-kb species were normalized to actin mRNA, PLC were 6.3-fold lower than ILC and 1.7-fold lower than ALC (n = 3 replicate isolations of poly(A) RNA). The 2.6- and 2.3-kb species exhibited similar trends. Levels of AR were estimated by immunoblotting using a polyclonal antibody against a synthetic peptide of the receptor (residues 14-32) that detected a 110-kilodalton AR protein. Levels of AR mRNA were estimated by Northern blot analysis, using a rat AR antisense RNA probe that detected a single 10-kb AR mRNA. The relative levels of AR protein were 1.0, 1.5, and 0.5 in PLC, ILC, and ALC, respectively (n = 3). Similar trends were observed for AR mRNA (n = 3). The observation that both LH and AR levels were lower in PLC compared to ILC is consistent with the hypothesis that the former are progenitors of Leydig cells.

A full-length rat androgen receptor cDNA was used to produce a recombinant baculovirus (AcrAR) by homologous recombination. Spodoptera frugiperda (Sf9) cells infected with this virus expressed a 110-kDa polypeptide that amounted up to about one-third of total cell protein. Studies with AR antibodies confirmed that this protein was indeed rAR. Only a minor portion of the recombinant AR was soluble in buffers without ionic detergents, but its complete solubilization was achieved in 6 M guanidine HCl (GdnHCl). Electron microscopy of cell pellets revealed that AR was localized to electron-dense cytoplasmic aggregates. The soluble cytosolic receptor was biologically active, in that it bound [3H]mibolerone with high affinity and specificity and interacted with an androgen-responsive element. The functions of the GdnHCl-solubilized AR were partially restored by a 20-50-fold dilution. The solubilized receptor was purified to an apparent homogeneity in a single step by gel filtration on a Sephacryl S-400 column in the presence of 6 M GdnHCl. The homogeneous AR protein could be renatured to bind [3H]mibolerone, interact specifically with a DNA element, and be recognized by receptor antibodies. Receptor-DNA interaction was stabilized by an antibody directed against the N-terminal part and abolished by an antibody against the hinge region of the receptor Zn2+ ions were essential for the purified receptor to refold into a specific DNA-binding form during the renaturation, with the optimal ZnCl2 concentration being 50-100 microM depending on the buffer conditions. Cd2+ ions were also capable of restoring the receptor's DNA-binding activity and did so at concentrations 10-fold lower than those of the Zn2+ ions.

The effects of androgen withdrawal and replacement on the concentrations of androgen receptor (AR) protein and AR mRNA were investigated in rat ventral prostate and seminal vesicles and in cultured human hepatoma (HepG2) cells. AR mRNA concentrations were determined by Northern blotting with single stranded AR cRNA as the hybridization probe, whereas antibodies raised against two synthetic 17-amino acid long peptides corresponding to the N-terminal and steroid-binding regions of the AR were employed in immunological receptor assays. AR mRNA levels in both prostate and seminal vesicles increased about 2-fold within 24 h after castration and continued to rise within the next 48 h to values that were 9- to 11-fold higher than those in intact controls. Administration of pharmacological doses of testosterone (400 micrograms steroid/day) to 1-day castrated animals for 24-48 h brought about a decrease in AR mRNA levels in accessory sex organs to levels in intact controls. Similar results were obtained in cultured HepG2 cells where a switch to serum- and steroid-free medium elicited a rapid increase (approximately 4-fold in 10 h) in the AR mRNA level, which was prevented by inclusion of 10(-7) M testosterone in culture medium. Similar, but quantitatively less marked, changes occurred in the AR protein concentration in prostate, seminal vesicles, and HepG2 cells, as determined by immunoblotting using antibodies against AR peptides. In addition, immunohistochemical studies showed that AR is a nuclear protein of the prostatic epithelial cells in both intact and castrated rats, and suggested that short term castration increases the concentration of nuclear AR in the prostate. Taken together, these data indicate that androgens down-regulate the concentration of AR protein and AR mRNA in a variety of target tissues.