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KMID : 1025520090510060493
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Journal of Animal Science and Technology
2009 Volume.51 No. 6 p.493 ~ p.502
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Expressional Comparison of Glucose Cotransporter Isoforms in the Rat Epididymis During Postnatal Development.
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Lee Dong-Mok
Son Chan-Wok
Seo Hee-Jung
Lee Yong-Ho
Choi In-Ho
Chun Tae-Hoon
Lee Ki-Ho
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Abstract
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Glucose is a major source of metabolic fuel and lipid and protein syntheses. Transport of glucose into the cell is regulated by an action of glucose transport‐associated transporters, especially solute carriers 2A(Slc2a, protein symbol GLUT). The present study was focused on examination of mRNA expression of various Slc2a isoforms in the epididymis during postnatal development. Total RNAs isolated from different epididymal segments(caput, corpus, and caudal epididymis) were utilized for real-time polymerase chain reaction analyses. Results showed that Slc2a 1, 3, 4, 5, and 8 were expressed in the entire epididymal regions. In addition, the abundance of these Slc2a isoforms’ transcripts was different within each epididymal regions. Moreover, the present study showed differential expression of these Slc2a isoforms among different epididymal segments according to postnatal ages. The current study suggests that glucose transport in the epididymis via various Slc2a isoforms would be necessary for maintenance of the epididymal functions.
The epididymis is a part of the excurrent duct of the male reproductive tract and is divided into three regions, head (caput), body(corpus), and tail(cauda), based on their morphological features and physiological functions(Cornwall, 2009; Cosentino and Cockett, 1986). The epididymis is a coiled tubular structure which has a lumen inside surrounded by a single layer of epithelium(Cornwall, 2009; Cosentino and Cockett, 1986). The primary cell type of the epithelium is the principle cell which is responsible for secretion of various proteins into the lumen(Cornwall, 2009). However, other cell types also participate in regulation and maintenance of epididymal functions(Kujala et al., 2007; Pietrement et al., 2006; Seiler et al., 1999). The main function of the epididymis is maturation of spermatozoa produced from the testis(Cornwall, 2009). Moving throughout the epididymis leads to acquirement of fertilizing capacity of spermatozoa(Cornwall, 2009). In addition, the epididymis plays other important functional roles, including storage of spermatozoa, reabsorption of luminal fluid, and acidification of luminal compartment for sperm quiescence(Cornwall, 2009). Hence, it is important to understand how the epididymis maintains its functions for male fertility.
Glucose is a major substance utilized commonly by most of mammalian cells to generate energy in the form of ATP and to synthesize protein and lipid (Zhao and Keating, 2007). Because blood glucose levels in mammals must be maintained within a narrow range, movement of glucose into the cell should be precisely controlled by homeostatic mechanisms(Zhao and Keating, 2007). Generally, transport of extracellular glucose into the cell is regulated by a passive and/or active transport processes (Widdas, 1988; Zhoa and Keating, 2007). A passive, facilitative transport of glucose is simply driven by gradient differences of glucose concentration across the plasma membrane(Widdas, 1988). Active transport of glucose is primarily used by a secondary active transport mechanism which absorbs glucose against its electrochemical gradient(Zhao and Keating, 2007). This active glucose transport uses Na+ concentration gradient established by Na+‐K+ ATPase and is chiefly occurred in the epithelial cell brush border of the small intestine and in the proximal convoluted tubules of the kidney(Zhao and Keating, 2007). Thus, the regulation of glucose transport across cell membrane is chiefly governed by complex but coordinated actions of a number of glucose transport‐associated transporters.
The passive glucose transport process is mediated by the family of facilitative glucose transporters, solute carriers 2A(Slc2a, protein symbol GLUT), while Na+‐dependent glucose transport is achieved by the family of Na+/glucose cotransporters, solute carriers 5A(Slc5a, protein symbol SGLT). Until now, there are 13 members of Slc2a family and 6 members of Slc5a family identified in mammalian(Wright and Turk, 2004; Zhao and Keating, 2007). Even though members of Slc2a genes are structurally related each other, most of GLUT proteins have different kinetics and efficiencies for glucose and hexose transport (Zhao and Keating, 2007). For example, Slc2a4 has a high affinity for glucose, while Slc2a5 has a high affinity for fructose and a very low affinity for glucose(Wood and Trayhurn, 2003; Zhao and Keating, 2007). In addition, each Slc2a isoforms has a tissue‐ and/or cell‐specific distribution, even one or more isoforms are expressed in the same tissue at different developmental time points(Zhao and Keating, 2007). For example, there are 7 different Slc2a isoforms present in the skeletal muscle and 4 different Slc2a isoforms expressed in the kidney, at least(Wood and Trayhurn, 2003). In the testis of the male reproductive tract, predominant expression of Slc2a8 has been demonstrated by Chen et al.(2003) and Zhao et al.(2004). Others have also shown that Slc2a1, Slc2a5, and Slc2a7 are localized in the testis(Burant et al., 1992; Davidson et al., 1992; Li et al., 2004; Ulisse et al., 1992). Even though Schürmann et al.(2002) have shown the presence of GLUT8 at the acrosomal region of mature spermatozoa within the epididymis, the expression of other Slc2a isoforms in the epididymis has not been determined in detail.
Our preliminary study showed the expression of five Slc2a transcripts, Slc2a1, 3, 4, 5, and 8, of 13 Slc2a isoforms in the caput epididymis at 1 month of age(data not shown here). Based on these findings, in the present study, we attempted to detect expression of these Slc2a isoforms in the epididymal segments of the male reproductive tract using real‐time PCR analysis. In addition, we tried to determine expression pattern of Slc2a isoforms in the epididymis during postnatal development.
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KEYWORD
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Epididymis, Glucose cotransporter, Male reproduction, Postnatal development, Gene expression
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