The Studies of Effects of Vitamin A Status on Type 2 Diabetes in Zucker Diabetic Fatty Rats and Retinoic Acid on Glucose Transporter 4 Expression in L6 Cells

The epidemic of metabolic diseases such as diabetes has become a public health concern. Previous research data from our lab have shown that vitamin A (VA) status and retinoic acid (RA), a metabolite of VA, contribute to the glucose and lipid metabolism in the body and cells. As the skeletal muscle contributes to metabolic homeostasis, the effects of VA signaling system on its glucose metabolism are worth to be investigated. Here in this dissertation, the following two projects were carried out to study the VA’s role in the control of metabolism. (1) The effects of VA status on the development of type 2 diabetes mellitus (T2DM) were studied in Zucker diabetic fatty (ZDF) rats fed a VA deficient (VAD), VA marginal (VAM) or VA sufficient (VAS) diet with basal fat (BF) or high fat (HF) content for 8 weeks. Zucker lean (ZL) rats fed the same diets were used as controls. We found that VA statuses affect body mass gain in ZL/ZDF rats in BF/HF diets. The mRNA and protein levels of lipogenic genes were reduced when the dietary VA dropped in ZL/ZDF rats fed the BF diets. Interestingly, the effects of VA status on lipogenesis in ZDF rats were masked in the presence of HF diets. Therefore, controlling VA intake and its metabolism may help to prevent obesity and T2DM in ZDF rats. (2) The effects of insulin and RA on the glucose transporter 4 (GLUT4) expression in L6 cells were studied. To determine the specificity of commercially available antibodies, we constructed a recombinant adenovirus overexpressing GLUT4 protein (Ad-mGLUT4), and successfully used it to determine a functional and workable antibody for the detection of GLUT4 in L6 cells. The rats L6 muscle cells were treated with or without 10 nM insulin in the absence or presence of 1μM RA for 4 or 6 days and fractionated to prepare different lysates. We found that RA alone and in combination with insulin induced the translocation of GLUT4 on the membrane of differentiated L6 muscle cells. RA + insulin induced the GLUT4 expression in total lysate of L6 cells on day 4.