Conclusion
Loss or impairment of SGLT1 results in abnormal pancreatic islet (cyto)morphology and disturbed islet function regarding the insulin or glucagon release capacity from β- or α-cells, respectively. Consequently, our findings propose a new, additional role for SGLT1 maintaining proper islet structure and function.
Methods
Effects associated with the loss of SGLT1 on pancreatic islet (cyto) morphology and function were investigated by analyzing islets of a SGLT1 knockout mouse model, that were fed a glucose-deficient, fat-enriched diet (SGLT1-/--GDFE) to circumvent the glucose-galactose malabsorption syndrome. To distinguish diet- and Sglt1-/--dependent effects, wildtype mice on either standard chow (WT-SC) or the glucose-free, fat-enriched diet (WT-GDFE) were used as controls. Feeding a glucose-deficient, fat-enriched diet further required the analysis of intestinal SGLT1 expression and function under diet-conditions.
Results
Consistent with literature, our data provide evidence that small intestinal SGLT1 mRNA expression and function is regulated by nutrition. In contrast, pancreatic SGLT1 mRNA levels were not affected by the applied diet, suggesting different regulatory mechanisms for SGLT1 in diverse tissues. Morphological changes such as increased islet sizes and cell numbers associated with changes in proliferation and apoptosis and alterations of the β- and α-cell population are specifically observed for pancreatic islets of SGLT1-/--GDFE mice. Glucose stimulation revealed no insulin response in SGLT1-/--GDFE mice while WT-GDFE mice displayed only a minor increase of blood insulin. Irregular glucagon responses were observed for both, SGLT1-/--GDFE and WT-GDFE mice. Further, both animal groups showed a sustained release of GLP-1 compared to WT-SC controls.