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Previous reports have showed that
Previous reports have showed that the expression and localization of GLUT8 in mouse (Gómez et al., 2006; Kim and Moley, 2007), rat (Ibberson et al., 2002) and human (Schürmann et al., 2002). In this study, GLUT8 protein mainly localized in the spermatocytes, elongated and round spermatids in the adult boar seminiferous tubules. Our results are in general agreement with prior reports by Kim and Moley (2007), Gómez et al., 2009, Gómez et al., 2006, Schürmann et al. (2002) and Ibberson et al. (2002). In the GLUT family, GLUT8 has a high activity for transporting glucose (Doege et al., 2000, Ibberson et al., 2000). The spermatids have a great dependency on glucose utilization for maintaining their morphological integrity and extent of protein synthesis, which seems to be a reason for the higher expression of GLUT8 in elongated and round spermatids in boar.
The tight junctions of the blood-testis barrier divided seminiferous epithelium into two compartments: basal compartment and adluminal compartment (Dym and Fawcett, 1970). Spermatogonia located in basal compartment, the later stage of germ cell differentiation (spermatocytes and spermatids) located in adluminal compartment. The blood-testis barrier provides an immunologically privileged microenvironment for the later stage of germ cell differentiation. In the present study, GLUT8 expression was detected in all germ Lisinopril dihydrate except spermatogonia in boar. These results suggested that GLUT8 may mainly provide glucose for the later stage of germ cell differentiation in adluminal compartment in adult boar testes. It is possible that there are other different mechanisms of glucose uptake in the germ cells of basal compartment and adluminal compartment. This may be one of the reasons why GLUT8 was expressed in later stage of germ cell differentiation in adluminal compartment.
A report showed that GLUT8 knockout results in reduced mitochondrial potential of spermatozoa and sperm motility in the mouse (Gawlik et al., 2008). Wyman et al. (2003) demonstrated that GLUT8 expression decrease or translocation would decline glucose transport rates. And glucose is necessary for normal spermatogenesis (Grootegoed et al., 1984). In this study, GLUT8 expression persists during eight stages of boar spermatogenesis. Therefore, GLUT8 is important for the normal spermatogenesis in the testes.
Acknowledgment
This research was supported by the National Natural Science Foundation of China (NSFC) (Grant No.31470124).
Introduction
Glucose is the primary energy source for life on earth. Maintenance of an optimum concentration of blood glucose is important because both hyper and hypoglycemia have deleterious effects. Hyperglycemia plays a key role in the pathogenesis of diabetic complications such as nephropathy, retinopathy, and peripheral neuropathy (Danaei et al., 2006). Hypoglycemia can be a risk factor for both abnormal electrical activity in the heart and arrhythmias (Marques et al., 1997, Pistrosch et al., 2015). Three families of glucose transporters have been identified: facilitative diffusion of glucose transporter family (GLUT), sodium–glucose transporter family (SGLT), and sugars will eventually be exported transporter family (SWEET) (Wright and Turk, 2004, Zehendner et al., 2013, Zhang et al., 2009). GLUT is ubiquitously expressed in all tissues (Mueckler and Thorens, 2013) with 14 isoforms identified in humans (Mueckler et al., 1985). Using the sodium ion concentration gradient, SGLT transports glucose into the cell with sodium ions (Burdakov et al., 2005, Matsuoka et al., 1998). SWEET, identified as a novel glucose transporter family in plants, is not found in mammals yet (Chandran, 2015, Chen et al., 2010). Among these, GLUT and SGLT, as glucose transporters, are being studied as potential targets for the treatment of dysglycemic-relevant diseases. However, currently no therapeutic agents targeting GLUT are present.hyperglycemic conditions
SGLT was identified as the first cotransporter protein in 1984 (Huang et al., 2011). There are six isoforms distributed throughout the human body (Andrea Scheepers et al., 2004a, Scheepers et al., 2004b; Wright and Turk, 2004). SGLT-1, found in enterocytes within the small intestine and renal proximal tubule cells, plays a role in glucose uptake (Turk et al., 1991). SGLT-2 is mainly distributed in the renal cortex and is a key player in glucose reabsorption (Wright et al., 2011). Unlike the other SGLT isoforms, SGLT-3 does not transport glucose, but is involved in glucose sensing in the small intestine and skeletal muscle (Freeman et al., 2006). SGLT-4 and −5 exhibit higher affinity for mannose than glucose (Grempler et al., 2012, Tazawa et al., 2005), while SGLT-6 is the most highly expressed SGLT isoform in the brain, and it transports inositol rather than glucose (Lin et al., 2009).