Identification of the Differential Role of Fructose Transporter (GLUT5) in Diet Induced Diabetes and Male Fertility

Abstract

Diets high in fructose have been reported to lead to type 2 diabetic complications in animal models (Rats). Dietary fructose is absorbed into the intestine via a specific saturable, facilitative glucose transporter GLUT5. GLUT-5 is expressed at high levels in the small intestine and at lower levels in kidney, brain, muscle, adipose tissue, testes, and sperm. Diabetes profoundly affects GLUT5 expression in the small intestine. Duodenal GLUT5 mRNA and protein levels increase three- to fourfold in type 2 diabetic subjects. Several studies in animal models have shown that diabetic male rats have diminished body and reproductive organ weight, lower testicular and epididymal sperm content, and lower sperm motility. The present study was carried out to identify the differential role of GLUT5 in diabetes and male fertility. The study was divided into two parts: Part 1 included induction of type II diabetes in adult male Wistar rats by feeding high fructose diet for a study period of 75 days. Diabetes induction was confirmed by estimation of triglyceride levels and by Oral Glucose Tolerance Test (OGTT). Total RNA was successfully isolated from all the required tissues using the TRIzol reagent (Sigma–Aldrich) according to the manufacturer‘s instructions and reverse transcribed (58). The semen characteristics and seminal plasma biochemistry were also studied. GLUT5 gene expression was performed in intestine, epididymal sperm, testis, seminal vesicle and prostate of high fructose fed male wistar rats and the control rat models, using specific primer. Diabetes was induced at the 45th day of diet feeding and was confirmed by analyzing the triglyceride (TG) levels and oral glucose tolerance test (OGTT). Parameters of Semen analysis and seminal plasma biochemistry also showed a marked difference. Decrease in sperm count, motility, viability and normal morphology was observed in fructose fed animal models as compared to control animals. An increase in seminal plasma enzymatic activities (Neutral alpha glucosidase, Lactate dehydrogenase, Acid phosphatase) was observed in fructose fed models as compared to control animals. Seminal plasma levels of Fructose, L-carnitine and Glycerophosphocholine also increased in fructose fed models as compared to control animals. An increase in GLUT5 expression in intestine (distal ileum and proximal colon) and sperm was observed in fructose fed animal models as compared to control animals. No expression was observed in testis, seminal vesicle and prostate of control and diabetic models. We concluded that GLUT5 expression is higher in diabetic models since the 11 level of fructose remains elevated in these models as compared to controls. Hence it can be said that GLUT5 serves as a marker of infertility in diet induced diabetic models. Part 2 included studies on semenological analysis and GLUT5 expression in ejaculated sperm of fertile men in age ranging from 26-40 years and correlating the same with the progression of age. Semen samples obtained were divided into three age groups of 26-30, 31-35, and 36-40 years. Semen analysis (count, motility, viability, morphology) and seminal plasma biochemistry was carried out. Effect of oxidative stress on fertility and its level with increase in age of individual was also studied. No specific trend was observed in semen characteristics with the progression in age. All the Seminal plasma enzymatic markers showed a marked variation with the increase in age. To assess the extent of oxidative stress, lipid peroxidation assay was done. Malondialdehyde (MDA) level was measured and was seen to be increasing with increase in age. Levels of antioxidants superoxide dismutase (SOD), catalase and reduced glutathione (GSH) were measured and a decrease in their levels was seen as per increase in age of individual. Total RNA was isolated from sperm by using TRI- Reagent and reverse transcribed. However GLUT5 expression was not observed in human ejaculated sperm. Decreasing trend in levels of the following organelle markers: α-glucosidase, L-carnitine, Fructose, LDH, Calcium and antioxidant levels (SOD and CAT) was observed suggesting a decreased reproductive functioning in higher age groups and thereby leading to impaired fertility with progression in age.