Effects of fructosamine-3-kinase deficiency on function and survival of mouse pancreatic islets after prolonged culture in high glucose or ribose concentrations

Pascal, Séverine [UCL] Veiga da Cunha, Maria [UCL] Gilon, Patrick [UCL] Van Schaftingen, Emile [UCL] Jonas, Jean-Christophe [UCL]

Pascal SM, Veiga-da-Cunha M, Gilon P, Van Schaftingen E, Jonas JC. Effects of fructosamine-3-kinase deficiency on function and survival of mouse pancreatic islets after prolonged culture in high glucose or ribose concentrations. Am J Physiol Endocrinol Metab 298: E586-E596, 2010. First published December 15, 2009; doi:10.1152/ajpendo.00503.2009.-Due to their high glucose permeability, insulin-secreting pancreatic beta-cells likely undergo strong intracellular protein glycation at high glucose concentrations. They may, however, be partly protected from the glucotoxic alterations of their survival and function by fructosamine-3-kinase (FN3K), a ubiquitous enzyme that initiates deglycation of intracellular proteins. To test that hypothesis, we cultured pancreatic islets from Fn3k-knockout (Fn3k(-/-)) mice and their wild-type (WT) littermates for 1-3 wk in the presence of 10 or 30 mmol/l glucose (G10 or G30, respectively) and measured protein glycation, apoptosis, preproinsulin gene expression, and Ca2+ and insulin secretory responses to acute glucose stimulation. The more potent glycating agent D-ribose (25 mmol/l) was used as positive control for protein glycation. In WT islets, a 1-wk culture in G30 significantly increased the amount of soluble intracellular protein-bound fructose-epsilon-lysines and the glucose sensitivity of beta-cells for changes in Ca2+ and insulin secretion, whereas it decreased the islet insulin content. After 3 wk, culture in G30 also strongly decreased beta-cell glucose responsiveness and preproinsulin mRNA levels, whereas it increased islet cell apoptosis. Although protein-bound fructose-epsilon-lysines were more abundant in Fn3k(-/-) vs. WT islets, islet cell survival and function and their glucotoxic alterations were almost identical in both types of islets, except for a lower level of apoptosis in Fn3k(-/-) islets cultured for 3 wk in G30. In comparison, D-ribose (1 wk) similarly decreased preproinsulin expression and beta-cell glucose responsiveness in both types of islets, whereas it increased apoptosis to a larger extent in Fn3k(-/-) vs. WT islets. We conclude that, despite its ability to reduce the glycation of intracellular islet proteins, FN3K is neither required for the maintenance of beta-cell survival and function under control conditions nor involved in protection against beta-cell glucotoxicity. The latter, therefore, occurs independently from the associated increase in the level of intracellular fructose-epsilon-lysines.