Type 2 diabetes mellitus (NIDDM) is a complex metabolic disease that occurs when insulin secretion can no longer compensate insulin resistance in peripheral tissues. At the molecular level, insulin resistance correlates with impaired insulin signaling. This review provides new insights into the molecular mechanisms of insulin action and resistance in brown adipose tissue (BAT) and pinpoints the role of BAT in the control of glucose homeostasis.
"The physiologic consequence of this function is an unrestrained oxidation by drawing lipids and carbohydrates from outside the cell . BAT has also been found to be important in understanding the mechanism of insulin resistance , reducing adiposity, and improving type 2 diabetes  which make it a valuable target to study the pathogenicity of obesity and diabetes. "
[Show abstract][Hide abstract] ABSTRACT: Brown adipose tissue [BAT] metabolism in vivo is vital for the development of novel strategies in combating obesity and diabetes. Currently, BAT is activated at low temperatures and measured using 2-deoxy-2-18F-fluoro-D-glucose [18F-FDG] positron-emission tomography [PET]. We report the use of β3-adrenergic receptor-mediated activation of BAT at ambient temperatures using (R, R)-5-[2-[2,3-(3-chlorphenyl)-2-hydroxyethyl-amino]propyl]-1,3-benzodioxole-2,2-dicarboxylate, disodium salt [CL316,243] (a selective β3-adrenoceptor agonist) and measured by 18F-FDG PET/computed tomography [CT].
Control and CL316,243-treated (2 mg/kg) male Sprague-Dawley rats were administered with 18F-FDG for PET/CT studies and were compared to animals at cold temperatures. Receptor-blocking experiments were carried out using propranolol (5 mg/kg). Dose effects of CL316,243 were studied by injecting 0.1 to 1 mg/kg 30 min prior to 18F-FDG administration. Imaging results were confirmed by autoradiography, and histology was done to confirm BAT activation.
CL316,243-activated interscapular BAT [IBAT], cervical, periaortic, and intercostal BATs were clearly visualized by PET. 18F-FDG uptake of IBAT was increased 12-fold by CL316,243 vs. 1.1-fold by cold exposure when compared to controls. 18F-FDG uptake of the CL-activated IBAT was reduced by 96.0% using intraperitoneal administration of propranolol. Average 18F-FDG uptake of IBAT increased 3.6-, 3.5-, and 7.6-fold by doses of 0.1, 0.5, and 1 mg/kg CL, respectively. Ex vivo 18F-FDG autoradiography and histology of transverse sections of IBAT confirmed intense uptake in the CL-activated group and activated IBAT visualized by PET.
Our study indicated that BAT metabolic activity could be evaluated by 18F-FDG PET using CL316,243 at ambient temperature in the rodent model. This provides a feasible and reliable method to study BAT metabolism.
EJNMMI Research 12/2011; 1(1):30. DOI:10.1186/2191-219X-1-30
"BAT-dependent non-shivering thermogenesis significantly affects the body's energy balance. In addition to its energy storage function, the fat tissues also secrete a number of hormones and cytokines, and are involved in the control of body metabolism and energy balance at multiple sites , . BAT is of particular importance in neonates, small mammals (such as mice) in cold environments, and animals that hibernate, because its major physiological function is to dissipate stored energy as heat. "
[Show abstract][Hide abstract] ABSTRACT: Ovarian cancer G protein-coupled receptor 1 (OGR1) has been shown to be a proton sensing receptor in vitro. We have shown that OGR1 functions as a tumor metastasis suppressor gene when it is over-expressed in human prostate cancer cells in vivo. To examine the physiological functions of OGR1, we generated conditional OGR1 deficient mice by homologous recombination. OGR1 deficient mice were viable and upon gross-inspection appeared normal. Consistent with in vitro studies showing that OGR1 is involved in osteoclastogenesis, reduced osteoclasts were detected in OGR1 deficient mice. A pH-dependent osteoclasts survival effect was also observed. However, overall abnormality in the bones of these animals was not observed. In addition, melanoma cell tumorigenesis was significantly inhibited in OGR1 deficient mice. OGR1 deficient mice in the mixed background produced significantly less peritoneal macrophages when stimulated with thioglycolate. These macrophages also showed altered extracellular signal-regulated kinases (ERK) activation and nitric oxide (NO) production in response to lipopolysaccharide. OGR1-dependent pH responses assessed by cAMP production and cell survival in macrophages or brown fat cells were not observed, presumably due to the presence of other proton sensing receptors in these cells. Our results indicate that OGR1's role in osteoclastogenesis is not strong enough to affect overall bone development and its role in tumorigenesis warrants further investigation. The mice generated can be potentially used for several disease models, including cancers or osteoclast-related diseases.
PLoS ONE 02/2009; 4(5):e5705. DOI:10.1371/journal.pone.0005705 · 3.23 Impact Factor
"Co-immunoprecipitation experiments of IRS-1 and -2 were done in triplicates. Regardless of the fact that the authors has done the insulin injection once and then repeated the immunoblotting experiment three times on the harvested liver and hindlimbs of Dahl rats, it is documented that within 1 minute of acute insulin stimulation, enhancement of the insulin signaling pathway and augmentation of IRS content and tyrosyl phosphorylation together with PI3K activation occur [92,93]. On the contrary, chronic effects of insulin have been shown to enhance IRS-1 serine phosphorylation preventing its subsequent tyrosine phosphorylation . "
[Show abstract][Hide abstract] 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".
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