Altered gene and protein expression of glucose transporter1 underlies dexamethasone inhibition of insulin-stimulated glucose uptake in chicken muscles1

Abstract

A study was performed to characterize the effects of dexamethasone (DEX) and insulin administration on gene expression of glucose transporters (GLUT) in chicken (Gallus gallus domesticus) skeletal muscles and in cultured embryonic myoblasts. Three groups of 1-wk-old male chickens were randomly subjected to one of the following treatments for 7 d: DEX (a subcutaneous injection of 1 mg/kg BW, twice daily at 0800 h and 2000 h), controls (injected with saline), and pair-fed controls (restricted to the same feed intake as for the DEX treatment). Expressions of GLUT-1, GLUT-3, GLUT-8, and 18S rRNA mRNA were determined by quantitative reverse transcription PCR in the pectoralis major (PM) and biceps femoris (BF) muscles. Using chicken embryonic myoblasts (CEM), the interaction between DEX (200 nM) and insulin (100 nM) administration was evaluated on GLUT gene and GLUT-1 protein expressions and 2-deoxy-D-[1, 2-(3)H]-glucose (2-DG) uptake. Myoblasts were incubated with serum-free medium for 3 h in the presence or absence of insulin (0, 0.02, 0.1, 0.5, and 2.5 μM). Although GLUT-1 is not considered an insulin-responsive GLUT in mammals, this study shows that insulin stimulated 2-DG uptake and GLUT-1 mRNA and protein expression in CEM (P < 0.0001), suggesting that both are regulated in chicken skeletal muscle. Dexamethasone inhibited insulin-stimulated glucose uptake in CEM (P < 0.0001), likely accounting for insulin resistance in skeletal muscles. The results of the present study indicate that the altered GLUT-1 gene and protein expression may contribute to the insulin resistance induced by DEX treatment in chicken muscles.

Differential regulation of the expression of lipid metabolism-related genes with skeletal muscle type in growing chickens

“…Plasma insulin concentrations were also significantly decreased by fasting (Table 2). Zhao et al (2012) reported that GLUT1 mRNA levels were decreased by food restriction in the pectoralis major muscle and that insulin significantly increased the expression of GLUT1 in an in vitro study using chicken embryonic myoblasts. Therefore, these findings suggest that GLUT1 expression may be regulated by insulin in glycolytic type IIB fibers in chickens.…”

“…For example, GLUT1, GLUT3, and GLUT8 are expressed in chicken skeletal muscle, whereas the GLUT4 gene is absent in chicken genome (Kono et al, 2005;Seki et al, 2003). GLUT1 mRNA levels, but not those of GLUT3 and GLUT8, were previously reported to be decreased in the pectoralis major muscle by restricted feeding (Zhao et al, 2012). PFK-M and PFK-L (liver type) are expressed in the skeletal muscle of chickens (Seki et al, 2006).…”

Avian and Mammalian Facilitative Glucose Transporters

“…Chicken GLUT1 shares 80% amino acid residues with humans [17]. Chicken GLUT1 has ubiquitous expression, with abundant expression in the hypothalamus, and has demonstrated response to insulin and dexamethasone [18]. According to NCBI Gene Database, GLUT1/SLC2A1 orthologs are conserved in 124 organisms including human, chicken, chimpanzee, cow, mouse, rat, Rhesus monkey, zebrafish and Eremothecium gossypii (fungus).…”

“…Chicken GLUT3 shares 70% sequence similarity with the human's [25,2] and is known to be a neuronal glucose transporter [25]. The neuronal functions of GLUT1 and GLUT3 are similar across chickens and mammals [17,18]. In chickens, the upregulation of GLUT1 and GLUT3 is associated with the formation of tight junctions in the blood-retinal barrier [26].…”

“…For chicken studies, GLUT1 has been analyzed across various chicken tissues [19] and embryonic myoblasts [18] and fibroblasts [62]. GLUT2 was cloned by screening a chicken liver cDNA library [20] and examined for expression in various chicken tissues [34,1].…”