Testicular Glucose and Its Transporter GLUT 8 as a Marker of Age-Dependent Variation and Its Role in Steroidogenesis in Mice

The present study evaluates the hypothesis, that glucose is essential for steroidogenesis and inadequate supply of glucose to the testis may be responsible for decline in steroidogenesis in mice during aging. Mice of different age groups (birth, weaning, puberty, reproductively active, and senescence) were utilized for this study. The changes in glucose, glucose transporter (GLUT), and insulin receptor (IR) level in the testis were evaluated and compared with the testicular steroidogenic parameters such as steroidogenic acute regulatory protein (StAR), 3-hydroxy steroid dehydrogenase (3-HSD) and circulating testosterone levels. The result showed significant correlation between changes in GLUT 8 and glucose levels with changes in StAR level in the testis and circulating testosterone level in the mice from birth to senescence. Immunohistochemical analysis showed intense immunostaining of GLUT 8 and IR in the interstitial cells, most likely Leydig cells, in testis of pubertal and reproductively active mice suggesting their relevance in steroidogenesis. The in vitro study showed a significant positive correlation between luteinizing hormone (LH)-induced increase in GLUT 8 and StAR (r=0.82; P<0.05) proteins level in the testes with increase in testosterone (r=0.97; P<0.05) synthesis of reproductively active mice. This study also showed increased release of lactate with increased uptake of glucose by the testis. Further, intra-testicular treatment of 2-deoxy glucose, to reproductively active mice caused a significant decrease in 3-HSD enzyme activity in the testis. Based on these findings, it may be concluded that the changes in glucose level either directly or indirectly lead to changes in testicular steroidogenesis during aging. J. Exp. Zool. 321A: 490-502, 2014. (c) 2014 Wiley Periodicals, Inc.