Understanding Genetic Heterogeneity in Type 2 Diabetes by Delineating Physiological Phenotypes: SIRT1 and its Gene Network in Impaired Insulin Secretion

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Abstract
The Review of Diabetic Studies,2016,13,1,17-34.
Published:May 2016
Type:Review Article
Authors:
Author(s) affiliations:

Shafat Ali1, Shazia Nafis1, Ponnusamy Kalaiarasan1, Ekta Rai2, Swarkar Sharma2, and Rameshwar N. Bamezai1

1National Centre of Applied Human Genetics, School of Life Sciences, Jawaharlal Nehru University, New Delhi, INDIA.

2Human Genetics Research Group, Department of Biotechnology, Shri Mata Vaishno Devi University, Katra, INDIA.

Abstract:

Type 2 diabetes (T2D) is a chronic metabolic disease which shows an exponential increase in all parts of the world. However, the disease is controllable by early detection and modified lifestyle. A series of factors have been associated with the pathogenesis of diabetes, and genes are considered to play a critical role. The individual risk of developing T2D is determined by an altered genetic background of the enzymes involved in several metabolism-related biological mechanisms, including glucose homeostasis, insulin metabolism, the glucose and ion transporters involved in glucose uptake, transcription factors, signaling intermediates of insulin signaling pathways, insulin production and secretion, pancreatic tissue development, and apoptosis. However, many candidate genes have shown heterogeneity of associations with the disease in different populations. A possible approach to resolving this complexity and understanding genetic heterogeneity is to delineate the physiological phenotypes one by one as studying them in combination may cause discrepancies in association studies. A systems biology approach involving regulatory proteins, transcription factors, and microRNAs is one way to understand and identify key factors in complex diseases such as T2D. Our earlier studies have screened more than 100 single nucleotide polymorphisms (SNPs) belonging to more than 60 globally known T2D candidate genes in the Indian population. We observed that genes invariably involved in the activity of pancreatic β-cells provide susceptibility to type 2 diabetes (T2D). Encouraged by these results, we attempted to delineate in this review one of the commonest physiological phenotypes in T2D, namely impaired insulin secretion, as the cause of hyperglycemia. This review is also intended to explain the genetic basis of the pathophysiology of insulin secretion in the context of variations in the SIRT1 gene, a major switch that modulates insulin secretion, and a set of other genes such as HHEX, PGC-α, TCF7L2, UCP2, and ND3 which were found to be in association with T2D. The review aims to look at the genotypic and transcriptional regulatory relationships with the disease phenotype.