Title : Type II diabetes and related models of impaired glucose metabolism differentially regulate glucose transporters at the proximal tubule brush border

Objective: SGLT2 inhibitors are now in clinical use to reduce hyperglycemia in type II diabetes. However, renal glucose reabsorption across the brush border membrane (BBM) is not completely understood in diabetes. Increased consumption of a Western diet is strongly linked to type II diabetes. This study aimed to investigate the adaptations that occur in renal glucose transporters in response to experimental models of diet-induced insulin resistance. Research Design and Methods: The study used Goto-Kakizaki type II diabetic rats and normal rats rendered insulin resistant using junk-food or high-fat (HFD) diets. Levels of PKC-βI, GLUT2, SGLT1 and 2 were determined by western blotting of purified renal BBM. GLUTand SGLT-mediated [3H]-glucose uptake by BBM vesicles was measured in the presence and absence of the SGLT inhibitor phlorizin. Results: GLUTand SGLTmediated glucose transport were elevated in type II diabetic rats, accompanied by increased expression of GLUT2, its upstream regulator PKC-βI, and SGLT1 protein. Disclaimer: This is a confidential document. Junk-food and HFD feeding also caused higher membrane expression of GLUT2 and its upstream regulator PKC-βI. However, the junk-food diet also increased SGLT1 and 2 levels at the proximal tubule BBM. Conclusions: Glucose reabsorption across the proximal tubule BBM, via GLUT2, SGLT1 and 2, is not solely dependent on glycemic status, but is also influenced by diet-induced changes in glucose metabolism. We conclude that different metabolic disturbances result in complex adaptation in renal glucose transporter protein levels and function. New Findings: While SGLT2 inhibitors represent a promising treatment for patients suffering from diabetic nephropathy, the role of metabolic disruption on the expression and function of glucose transporters is largely unknown. In vivo models of metabolic disruption (type II rat and junk-food diet) demonstrate increased expression of SGLT1, SGLT2 and GLUT2 in the proximal tubule brush-border. In the type II model, this is accompanied by increased SGLTand GLUT-mediated glucose uptake. A fasted model of metabolic disruption (high-fat diet) demonstrated increased GLUT2 expression only. The differential alterations in glucose transporters in response to varying metabolic stress offer insight into therapeutic values of inhibitors. Dual Publication: No Funding: Diabetes UK: Kaila Srai, E S Debnam, BDA 06/0003308 Disclaimer: This is a confidential document. 1 Experimental type II diabetes and related models of impaired glucose metabolism differentially regulate glucose transporters at the proximal tubule brush border membrane Havovi Chichger, Mark E. Cleasby, Surjit K. Srai, Robert J. Unwin, Edward S. Debnam and Joanne Marks Biomedical Research Group, Department of Biomedical and Forensic Sciences, Anglia Ruskin University, Cambridge, UK, Department of Veterinary Basic Sciences, Royal Veterinary College, London, UK, Institute of Structural and Molecular Biology, University College London, London, UK. 4 London Epithelial Group, Department of Neuroscience, Physiology & Pharmacology, University College London, London, UK, Centre for Nephrology, University College London, London, UK. Corresponding author’s current address: Dr Havovi Chichger Biomedical Research Group Biomedical and Forensic Sciences Department Faculty of Science and Technology Anglia Ruskin University OPT 024, East Road Cambridge CB1 1PT, UK Email: Havovi.Chichger@Anglia.ac. uk Short title: GLUT2, SGLT1 and SGLT2 in diabetes-related disease