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Testis |
a Unitat de Recerca Biomedica, Hospital Materno-Infantil Vall d'Hebron, Barcelona, Spain
b Department of Biochemistry & Molecular Biology
c Department of Cell Biology, Georgetown University Medical School, Washington, District of Columbia 20007
Chemical agents can disrupt the balance between survival and apoptosis during spermatogenesis and thus give rise to reduced counts of spermatozoa (oligospermia). One such agent that produces significant germ cell apoptosis at specific stages of the cycle of the seminiferous epithelium is methoxy acetic acid (MAA), the active metabolite of a commonly used solvent, methoxyethanol. Although MAA gives rise to apoptosis of pachytene spermatocytes, it is not known whether MAA exerts a direct effect on germ cells or whether it also affects other testicular cell types such as the Sertoli cells. In the present investigation, we tested the hypothesis that MAA has direct effects on Sertoli cells in vivo. In MAA-treated rats, stage-specific expression of androgen receptor (AR) protein in Sertoli cells was significantly altered, as determined by AR immunohistochemistry. In MAA-treated animals, high AR expression was found in Sertoli cells coincident with the MAA-induced apoptosis of late-stage pachytene spermatocytes. The altered expression of AR in MAA-treated animals was also seen in seminiferous tubules harvested by laser capture microdissection. In addition to effects on AR expression, androgen-binding protein (ABP) mRNA levels were also altered in a stage-specific manner. Using a different system for mouse Sertoli cell lines TM4 and MSC-1, positive for either AR or ABP, respectively, we found a direct effect of MAA on ABP protein and mRNA expression in the MSC-1 cell but did not detect an effect on AR protein or mRNA expression in TM4 cells. Mouse fibroblasts that express endogenous AR were stably transfected with two AR promoter/reporter systems (MMTV-CAT and probasin-luciferase, respectively). We used these fibroblasts to examine the ability of MAA to potentiate dihydrotestosterone (DHT) activation of AR. Although MAA did not activate AR directly, it did potentiate DHT activation of the AR by 2- to 4-fold. MAA altered the expression level of AR and ABP in vivo and increased AR transcriptional activity in tissue culture cells. The abnormal spermatogenesis generated by MAA is at least partly due to direct effects on Sertoli cells. It is still unclear whether MAA elicits a proapoptotic signal from Sertoli cells or diminishes a prosurvival signal required by germ cells downstream to altering AR and ABP expression in a stage-specific fashion.
2 Correspondence: Carlos A. Suárez-Quian, Department of Cell Biology, Georgetown University Medical School, 3900 Reservoir Rd., N.W., Washington, DC 20007. FAX: 202 687 1823; suarezc{at}georgetown.edu
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