Effect of hyperglycemia on insulin receptor signaling in the cultured retinal Müller glial cells.
Hyperglycemia and impaired insulin signaling are considered as major factors in the retinal pathology in diabetic retinopathy (DR). Numerous reports support that these two factors damage retinal glial as well as neuronal cells early in diabetes. However, it is not known whether diabetic induced hyperglycemia causes a depression to the insulin signaling. In this study we utilized a well characterized cultured Muller cells (TR-MUL) where we found a high expression of insulin receptor molecules. TR-MUL Cells were treated with high glucose, glutamate and hydrogen peroxide, and activated with insulin. Following treatments, cell lysates were analyzed by immunoblotting experiments for insulin receptor (IRβ) and insulin receptor substrate (IRS1). In addition, cell lysates were immunoprecipitated using antibodies against insulin receptor proteins to analyze tyrosine phosphorylation and serine phosphorylation of insulin receptor proteins. Results indicate that hyperglycemia did not affect the expression of insulin receptor proteins in cultured TR-MUL cells. Although, hyperglycemia seems to inhibit the interaction between IRS1 and IRβ. Hydrogen peroxide increased the tyrosine phosphorylation of insulin receptor proteins but excess glutamate could not affect the insulin receptor proteins indicating that glutamate may not cause oxidative stress in TR-MUL cells. Hyperglycemia lowered serine phosphorylation of IRS(ser632) and IRS(ser1101) however, IRS(ser307) was not affected. Thus, hyperglycemia may not affect insulin signaling through tyrosine phosphorylation of insulin receptor proteins but may inhibit the interactions between insulin receptor proteins. Hyperglycemia induced phosphorylation of various serine residues of IRS1 and their influence on insulin signaling needs further investigation in TR-MUL cells.
Department of Biochemistry, College of Science, King Saud University, Riyadh, Saudi Arabia. Electronic address: mola@ksu.edu.sa.
Mohammad Shamsul
MS
Ola
D000818:Animals; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D005947:Glucose / Q000494:pharmacology*; D018698:Glutamic Acid / Q000494:pharmacology; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007004:Hypoglycemic Agents / Q000494:pharmacology; D015151:Immunoblotting; D007328:Insulin / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins / Q000378:metabolism; D009457:Neuroglia / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D016877:Oxidants / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding; D051381:Rats; D011972:Receptor, Insulin / Q000378:metabolism*; D012160:Retina / Q000166:cytology; D015398:Signal Transduction / Q000187:drug effects*; D014443:Tyrosine / Q000378:metabolism
D007004:Hypoglycemic Agents; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526296:Irs1 protein, rat; D016877:Oxidants; D018698:Glutamic Acid; D014443:Tyrosine; D006861:Hydrogen Peroxide; D011972:Receptor, Insulin; D005947:Glucose
Hyperglycemia; Insulin; Muller cells; Neurodegeneration; Retina