Expression and regulation of glucose transporter 8 in rat Leydig cells

Basal and LH/human chorionic gonadotropin (hCG)stimulated testosterone formation by Leydig cells is dependent on ambient glucose levels. Inhibition of glucose uptake is associated with decreased testosterone formation. Recently. glucose transporter 8 (GLUTS) has been shown to be highly expressed in the testis. In the present study, we have investigated the expression and regulation of the GLUTS gene in rat Leydig cells. Primers were designed by using sequences that are not conserved in GLUT1 to GLUTS and that contain the glycosylation region of GLUTS. This yielded an amplicon of 186 bp. The tissue-specific expression experiments in adult rat (55- to 65-day-old) tissues revealed that GLUTS is expressed predominantly in the testis, in smaller amounts in heart and kidney, and in negligible amounts in liver and spleen. Furthermore. GLUTS mRNA was found to be highly expressed in crude interstitial cells, Leydig cells and testicular and epididymal genii cells. In prepubertal rat (20-day-old) tissues,. GLUTS expression was comparatively much lower than in the adult rat tissues. By comparative RT-PCR, hCG caused dose- and time-dependent increases of GLUTS mRNA levels. hCG and IGF-1 had synergistic effects on GLUTS mRNA and protein expression. GLUT1 and GLUT3 were also found to be expressed in Leydig cells. However, neither GLUT 1 nor GLUT3 were affected by treatments with hCG, IGF-I or hCG and IGF-1 combined. The addition of murine interleukin-1alpha (m1L-1alpha; 10 ng/ml), murine tumor necrosis factor-alpha (mTNF-alpha; 10 ng/ml), murine interferon-gamma (mIFN-gamma; 500 U/ml) separately or in combination decreased hCG-induced GLUT8 mRNA levels significantly. In conclusion, GLUTS mRNA in Leydig cells was positively regulated by hCG and IGF-I and down-regulated by cytokines, mIL-1alpha, mTNF-alpha and mIFN-gamma. These results indicate that hCG, growth factors and cytokines affect Leydig cell steroidogenesis by modulating GLUTS expression.