Glutamine synthetase: A key enzyme for intestinal epithelial differentiation?

Background: We have previously shown that glutamine synthetase protein and mRNA are concentrated in the crypt region of the rat small intestine and th at the activity of this enzyme is highest around the time of weaning. This anatomical location and time of peak activity are sites and periods of acti ve enterocyte differentiation. This led to our current hypothesis that glut amine synthetase is important in the differentiation of enterocytes. Method s: To test our hypothesis, we treated Caco-2 cells with physiologic (0.6 mM ) glutamine concentrations in cell culture medium. The experimental group w as treated with methionine sulfoximine, an irreversible glutamine synthetas e inhibitor, and the control group with phosphate buffered saline. Three st andard and well-defined markers of intestinal differentiation-sucrase-isoma ltase activity, microvillus formation, and electrical impedance in transwel l plates-were compared between the two groups. Results: The methionine-sulf oximine-inhibited group was found to have lower sucrase-isomaltase activity , a lower density of microvilli, and lower electrical impedance values over time compared with the control group. Conclusion: The experimental group w as found to be less differentiated by all three markers of differentiation. Therefore, glutamine synthetase is important for Caco-2 cell differentiati on.