Potentiation of TRPM5 with Stevioside in the Beta Cells Stimulates Insulin Secretion

The calcium-activated monovalent cation channel TRPM5 is expressed in human and murine beta cells. Members of the TRP ion channel family can be activated by a plethora of different stimuli as temperature, voltage, and ligands, including natural compounds. Studies have shown that TrpM5-knockout mice have increased blood glucose levels and an impaired insulin secretion. Mutations in TRPM5 are more prevalent in patients with diabetes or metabolic syndrome. Stevioside is a sweet tasting organic molecule isolated from the leaves of the scrub plant Stevia rebaudiana, it is widely used in consumer foods and beverages. Despite its wide use, the molecular interactions of stevioside in the body remained elusive. Here we show that stevioside potentiates TRPM5 channel activity. This leads to increased calcium dynamics in both human and mouse islets, which relates to increased insulin secretion. We show that the steviol core of stevioside is responsible for the TRPM5-potentiating effect. When mice on a high fat diet are given stevioside, we observe an attenuation of the development of hyperglycemia in a TRPM5-dependent manner. With this work, we elucidate the molecular mechanism of action of stevioside. Furthermore, we provide a deeper insight in the regulation of insulin secretion from the beta-cells and identify TRPM5 as an important part of a healthy secretion pathway. TRPM5 constitutes a novel possible drug target in the battle against type 2 diabetes.