Impact of 9 Days of Bed Rest on Hepatic and Peripheral Insulin Action, Insulin Secretion, and Whole-Body Lipolysis in Healthy Young Male Offspring of Patients With Type 2 Diabetes

The goal of this review is to develop the hypothesis, and review the evidence, that protein restriction, through synergistic effects on multiple organ systems predisposes to loss of normal regulation of fuel homeostasis that plays the central role in the development of type 2 (non-insulin-dependent) diabetes mellitus. The ability of insulin to regulate glucose production and disposal varies between individuals. These differences, together with the various compensatory mechanisms that are invoked to attempt to normalize fuel homeostasis, are of fundamental importance in the development and clinical course of type 2 diabetes mellitus. Protein deprivation impacts on both insulin secretion and insulin action. These effects may persist even when a diet containing adequate protein is presented subsequently. Data are presented that suggest that protein restriction results in an impaired ability of pancreatic β-cells to compensate adequately for the defect in insulin action in insulin-resistant individuals. This persistent impairment of insulin secretion resulting from protein restriction predisposes to loss of glucoregulatory control and impaired insulin action after the subsequent imposition of a diabetogenic challenge. This inability to maintain the degree of compensatory hyperinsulinaemia necessary to prevent loss of glucose tolerance may have relevance to the increased incidence of diabetes on changing from a nutritionally-poor diet to a Western diet, and to the hypothesis that some cases of type 2 diabetes in adulthood may be related to poor early nutrition.

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Exocytosis mechanisms underlying insulin release and glucose uptake: conserved roles for Munc18c and syntaxin 4

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00597.2009 ◽

2010 ◽

Vol 298 (3) ◽

pp. R517-R531 ◽

Cited By ~ 72

Author(s):

Jenna L. Jewell ◽

Eunjin Oh ◽

Debbie C. Thurmond

Keyword(s):

Type 2 Diabetes ◽

Insulin Secretion ◽

Glucose Uptake ◽

Pancreatic Beta Cells ◽

Insulin Action ◽

Molecular Mechanisms ◽

Receptor Protein ◽

Peripheral Tissues ◽

Syntaxin 4

Type 2 diabetes has been coined “a two-hit disease,” as it involves specific defects of glucose-stimulated insulin secretion from the pancreatic beta cells in addition to defects in peripheral tissue insulin action required for glucose uptake. Both of these processes, insulin secretion and glucose uptake, are mediated by SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) protein core complexes composed of syntaxin, SNAP-23/25, and VAMP proteins. The SNARE core complex is regulated by the Sec1/Munc18 (SM) family of proteins, which selectively bind to their cognate syntaxin isoforms with high affinity. The process of insulin secretion uses multiple Munc18-syntaxin isoform pairs, whereas insulin action in the peripheral tissues appears to use only the Munc18c-syntaxin 4 pair. Importantly, recent reports have linked obesity and Type 2 diabetes in humans with changes in protein levels and single nucleotide polymorphisms (SNPs) of Munc18 and syntaxin isoforms relevant to these exocytotic processes, although the molecular mechanisms underlying the observed phenotypes remain incomplete ( 5 , 104 , 144 ). Given the conservation of these proteins in two seemingly disparate processes and the need to design and implement novel and more effective clinical interventions, it will be vitally important to delineate the mechanisms governing these conserved SNARE-mediated exocytosis events. Thus, we provide here an up-to-date historical review of advancements in defining the roles and molecular mechanisms of Munc18-syntaxin complexes in the pathophysiology of Type 2 diabetes.

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