Transportation of vitamin C [also called ascorbic acid (AA)], an important water-soluble antioxidant and cofactor in testis, requires glucose transporter family (GLUTs) and sodium/vitamin C cotransporter family (SVCT1 and SVCT2). There is so far scant information vis-à-vis the functional roles of SVCTs in testis, although they possess higher affinity for transportation of AA compared to GLUTs. To analyze the biological effects of SVCT2 in testis, we assessed testicular expression of SVCT2 in different experimental settings and the effect of SVCT2 ablation on spermatogenesis. Persistent expression of SVCT2 was shown in the mouse testis at different stages of postnatal development, demonstrated on day 14 of testicular development in mice consistent with appearance of pachytene spermatocytes during the first wave of spermatogenesis. Testicular expression of SVCT2 was enriched in the cytoplasm of murine Sertoli cells (SCs). We then showed that in vivo inhibition of SVCT2 in mouse testis significantly impaired male fertility by causing oligozoospermia and asthenospermia, which mainly stemmed from a deficiency in lactate production. By generating the TM4SVCT2-/- cells and by profiling TM4SVCT2-/- cells with a constitutively activated HIF-1α mutant, we demonstrated that SVCT2 deficiency led to impaired lactate synthesis and reduced expression of Ldha mRNA in SCs. Mechanistically, ablation of SVCT2 resulted in ubiquitination and subsequent degradation of HIF-1α protein in the FSH-stimulated SCs. Collectively, our data document a novel testicular site of action of SVCT2 in the control of lactate synthesis by SCs, probably via ubiquitination-dependent regulation of HIF-1α stability.
Guozheng Gao, Yong Zhao, Ke Wang, and Fang Wang
Leping Zhao, Yong Pan, Kesong Peng, Zhe Wang, Jieli Li, Dan Li, Chao Tong, Yi Wang, and Guang Liang
11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) controls the production of active glucocorticoid (GC) and has been proposed as a new target for the treatment of type 2 diabetes. We have previously reported that a natural product, curcumin, exhibited moderate inhibition and selectivity on 11β-HSD1. By analyzing the models of protein, microsome, cells and GCs-induced mice in vitro and in vivo, this study presented a novel curcumin analog, LG13, as a potent selective 11β-HSD1 inhibitor. In vivo, Type 2 diabetic mice were treated with LG13 for 42 days to assess the pharmacological benefits of 11β-HSD1 inhibitor on hepatic glucose metabolism. In vitro studies revealed that LG13 selectively inhibited 11β-HSD1 with IC50 values at nanomolar level and high selectivity over 11β-HSD2. Targeting 11β-HSD1, LG13 could inhibit prednisone-induced adverse changes in mice, but had no effects on dexamethasone-induced ones. Further, the 11β-HSD1 inhibitors also suppressed 11β-HSD1 and GR expression, indicating a possible positive feedback system in the 11β-HSD1/GR cycle. In type 2 diabetic mice induced by high fat diet plus low-dosage STZ injection, oral administration with LG13 for 6 weeks significantly decreased fasting blood glucose, hepatic glucose metabolism, structural disorders, and lipid deposits. LG13 exhibited better pharmacological effects in vivo than insulin sensitizer pioglitazone and potential 11β-HSD1 inhibitor PF-915275. These pharmacological and mechanistic insights on LG13 also provide us novel agents, leading structures, and strategy for the development of 11β-HSD1 inhibitors treating metabolic syndromes.