Effect of Hyperglycemia on Syntaxin - 1 and Mint - 1 Mediated Insulin Exocytosis

Abstract

Insulin plays an important function in glucose metabolism and in homeostasis. Deformities in insulin secretion or the mechanism of insulin secretion might lead to chronic hyperglycaemic conditions, which ultimately culminates into diabetes. Diabetic is characterized by reduced islet population, diminished meagre insulin production and yet more diminished secretion. In the current study, we attempted at counting the alpha as well as beta cells population, in a pancreatic islet. During Diabetes We also attempted to quantitate beta-cells by using dithizone staining. We observed a remarkable decrease in the quantification of beta cells along with an increase in the quantification of alpha cells during diabetes. Insulin hormone exocytosis is activated by a cascade of molecular events, which gets activated upon an elevation in the circulating glycaemic levels, followed by a calcium mediated exocytosis. During the priming stage, the insulin granules mature in the later stage i.e. fusion. The SNARE complex plays a functional role in initiation and coordination of insulin exocytosis. Hence, Syntaxin1 a target SNARE, forms a core protein of the SNARE complex that is involved in a crucial function through exocytotic machinery. Syntaxin1, stays in a closed confirmation as it is bound to Munc-18Mint, a Munc binding protein, binds to Munc18 and dislocates it from Syntaxin, bringing about a conformational change in the Syntaxin, activating it, thereby resulting in SNARE complex activation. SNARE activation results in cell membrane and vesicular fusion by formation of fusion pore which causes the vesicular content to be released out of the cell. Previous studies suggest Syntaxin-1 and Mint1 to be down-regulated during diabetes. In the current study, we carried out the effect of over-expression of Syntaxin-1 and Mint-1 on insulin secretion. This was carried out using a cloning technique. Syntaxin containing vector peGFP(N1), was transfected in Min6 cells, and the resultant gene expression levels and insulin secretion was assessed Syntaxin-1gene expression was found to be upregulated in transfected MIN 6 cells, along with an increase in insulin secretion. Mint-1 gene cloning was also attempted in a pcDNA3.1 vector, however, the cloning could not not be achieved successfully. However, based on expression levels of Syntaxin-1 in transfected Min6 cells and the resultant insulin secretion, it can be concluded that Syntaxin-1 has a functionally regulatory role on insulin secretion.