Abstract
Despite the marked advances in research on insulin resistance (IR) in humans and animal models of insulin resistance, the mechanisms underlying high salt-induced insulin resistance remain unclear. Insulin resistance is a multifactorial disease with both genetic and environmental factors (such as high salt) involved in its pathogenesis. High salt triggers insulin resistance in genetically susceptible patients and animal models of insulin resistance. One of the mechanisms by which high salt might precipitate insulin resistance is through its ability to enhance an oxidative stress-induced inflammatory response that disrupts the insulin signaling pathway. The aim of this hypothesis is to discuss two complementary approaches to find out how high salt might interact with genetic defects along the insulin signaling and inflammatory pathways to predispose to insulin resistance in a genetically susceptible model of insulin resistance. The first approach will consist of examining variations in genes involved in the insulin signaling pathway in the Dahl S rat (an animal model of insulin resistance and salt-sensitivity) and the Dahl R rat (an animal model of insulin sensitivity and salt-resistance), and the putative cellular mechanisms responsible for the development of insulin resistance. The second approach will consist of studying the over-expressed genes along the inflammatory pathway whose respective activation might be predictive of high salt-induced insulin resistance in Dahl S rats.Variations in genes encoding the insulin receptor substrates -1 and/or -2 (IRS-1, -2) and/or genes encoding the glucose transporter (GLUTs) proteins have been found in patients with insulin resistance. To better understand the combined contribution of excessive salt and genetic defects to the etiology of the disease, it is essential to investigate the following question:Question 1: Do variations in genes encoding the IRS -1 and -2 and/or genes encoding the GLUTs proteins predict high salt-induced insulin resistance in Dahl S rats?A significant amount of evidence suggested that salt-induced oxidative stress might predict an inflammatory response that upregulates mediators of inflammation such as the nuclear factor- kappa B (NF-kappa B), the tumor necrosis factor-alpha (TNF-α) and the c-Jun Terminal Kinase (JNK). These inflammatory mediators disrupt the insulin signaling pathway and predispose to insulin resistance. Therefore, the following question will be thoroughly investigated:Question 2: Do variations in genes encoding the NF-kappa B, the TNF-α and the JNK, independently or in synergy, predict an enhanced inflammatory response and subsequent insulin resistance in Dahl S rats in excessive salt environment?Finally, to better understand the combined role of these variations on glucose metabolism, the following question will be addressed:Question 3: What are the functional consequences of gene variations on the rate of glucose delivery, the rate of glucose transport and the rate of glucose phosphorylation in Dahl S rats?The general hypothesis is that "high-salt diet in combination with defects in candidate genes along the insulin signaling and inflammatory pathways predicts susceptibility to high salt-induced insulin resistance in Dahl S rats".
Highlights
Insulin Resistance Insulin resistance is defined as an impaired responsiveness to both endogenous and exogenous insulin resulting in high blood glucose levels and compensatory hyperinsulinemia [1]
The long-term goal is to establish a subset of single nucleotide polymorphisms (SNPs) that are predictive of insulin resistance in excessive salt environments
Mechanisms underlying the contribution of Insulin receptor substrate 1 (IRS-1) and/or -2 variants to insulin resistance include [37] (Figure 3): i) altering IRS-1 and/or-2 expression and function, ii) reduced IRS-1 and/or -2 binding to the insulin receptor, iii) a defect in binding of IRS-1 and/or -2 variant (s) to the p85 regulatory subunit of the PI3-kinase and a decrease in PI3-kinase activity. This in turn leads to either a decreased GLUT4 translocation to the plasma membrane, further reducing glucose transport and glycogen synthesis, or a significant IRS-1 and/or -2 -induced decrease in phosphorylation of glycogen synthase kinase3 (GSK-3), an enzyme that is important in glycogen synthesis, causing reduced glycogen synthesis, iv) reduced IRS-1 content that is not compensated by a constitutive increase in the Insulin receptor substrate 2 (IRS-2) protein content
Summary
Insulin Resistance Insulin resistance is defined as an impaired responsiveness to both endogenous and exogenous insulin resulting in high blood glucose levels and compensatory hyperinsulinemia [1]. Mechanisms by which IRS-1 and/or -2 variants contribute to insulin resistance include: 1) altering IRS-1 and/or-2 expression and function, 2) reduced IRS-1 and/or -2 binding to the insulin receptor, 3) a defect in binding of IRS-1 and/or -2 variant (s) to the p85 regulatory subunit of the PI3-kinase and a decrease in PI3-kinase activity The latter leads to either a decreased GLUT4 translocation to the plasma membrane, further reducing glucose transport and glycogen synthesis, or a significant IRS-1 and/or -2 -induced decrease in phosphorylation of glycogen synthase kinase-3 (GSK-3), an enzyme that is important in glycogen synthesis, causing reduced glycogen synthesis, 4) reduced IRS-1 content that is not compensated by a constitutive increase in the IRS-2 protein content.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
