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Glutamine synthetase: a key enzyme for intestinal epithelial differentiation?
M D Weiss1, V DeMarco, D M Strauss
1Department of Pediatrics, University of Florida, Gainesville 32610, USA.
Background:
We have previously shown that glutamine synthetase protein and mRNA are concentrated in the crypt region of the rat small intestine and that 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 active enterocyte differentiation. This led to our current hypothesis that glutamine synthetase is important in the differentiation of enterocytes.
Methods:
To test our hypothesis, we treated Caco-2 cells with physiologic (0.6 mM) glutamine concentrations in cell culture medium. The experimental group was treated with methionine sulfoximine, an irreversible glutamine synthetase inhibitor, and the control group with phosphate buffered saline. Three standard and well-defined markers of intestinal differentiation-sucrase-isomaltase activity, microvillus formation, and electrical impedance in transwell plates-were compared between the two groups.
Results:
The methionine-sulfoximine-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 was found to be less differentiated by all three markers of differentiation. Therefore, glutamine synthetase is important for Caco-2 cell differentiation.