Potentiatie van TRPM5 ionenkanaalactiviteit is een nieuwe onthult een nieuwe weg voor de ontwikkeling van antidiabetes medicatie

In this thesis we explored the therapeutic potential of modulating TRPM5 ion channel activity in the context of high fat diet-induced diabetes in mice. TRPM5 is a monovalent selective cation channel that is activated by increases in intracellular calcium. The channel is functionally expressed in the type II taste receptor cells in the taste buds, where it is essential for the transduction of sweet, bitter and umami taste. TRPM5 expression was also shown in pancreatic beta-cells. Trpm5-/- mice have impaired insulin secretion and a prediabetic glucose metabolism. Therefore potentiation of TRPM5 might lead to increased taste perception and increased insulin secretion. At the start of this project no compounds were available that could accomplish this. In a first part of this study, we developed a thallium-based fluorescence screening method to detect TRPM5 modulating molecules in a high throughput. We found that ketoconazole and robustic acid (amongst others) are potent inhibitors of TRPM5 and confirmed their inhibiting effect with patch clamp experiments. We identified and describe the first known TRPM5 potentiators chloro-acetoxy-quinoline and exemestane. More interesting was the observation that glimepiride, an oral antidiabetic, was a potentiator of TRPM5 activity. This shows that TRPM5 is already a target in the treatment of diabetes, albeit unknown. A second part of the study focused on the interaction between steviol glycosides and TRPM5. We identified steviol glycosides, the sweet molecules in the stevia rebaudiana plant, as selective TRPM5 potentiators. We analyzed in detail the effects of stevioside and steviol on TRPM5. We showed that the overwhelming sweet taste of steviol glycosides can be explained by a potentiation of TRPM5 in the taste receptor cells. Furthermore, steviol on its own does not taste sweet, but it increases taste perception for sweet, bitter and umami compounds in a TRPM5-dependent way. We measured potentiation of TRPM5 currents in an overexpression system and in pancreatic beta-cells. We observed increased calcium oscillations upon application of stevioside in WT but not on Trpm5-/- mice. We finally analyzed the effect of stevioside administration in a high-fat diet induced diabetic mouse model. We found that stevioside increased the insulin secretion due to potentiation of TRPM5 in the beta-cells of the pancreas. This led to the prevention of severe hyperglycemia in these mice and effectively delayed the onset of diabetes. The effects of stevioside are mediated through TRPM5, as no e ects were observed in knockout animals. Taken together, i) our data con rm the essential role of TRPM5 in taste perception and insulin secretion, which was previously suggested from studies with knockout mice. ii) We show that TRPM5 is essential for the biological action of steviol and steviol glycosides iii) We show that potentiation of TRPM5 channel activity is an efficient strategy to prevent the development of type 2 diabetes, at least in mice and possibly also in humans.status: publishe