a-method-for-mouse-pancreatic-islet-isolation-intracellular-camp

A Method for Mouse Pancreatic Islet Isolation and Intracellular cAMP Determination

Uncontrolled glycemia is a hallmark of diabetes mellitus and promotes morbidities like neuropathy, nephropathy, and retinopathy. With the increasing ...

University of Wisconsin-Madison

BTBR mice develop severe diabetes in response to genetically induced obesity due to a failure of the β-cells to compensate for peripheral insulin resistance. In analyzing BTBR islet gene expression patterns, we observed that Pgter3, the gene for the prostaglandin E receptor 3 (EP3), was upregulated with diabetes. The EP3 receptor is stimulated by prostaglandin E2 (PGE2) and couples to G-proteins of the Gi subfamily to decrease intracellular cAMP, blunting glucose-stimulated insulin secretion (GSIS). Also upregulated were several genes involved in the synthesis of PGE2. We hypothesized that increased signaling through EP3 might be coincident with the development of diabetes and contribute to β-cell dysfunction. We confirmed that the PGE2-to-EP3 signaling pathway was active in islets from confirmed diabetic BTBR mice and human cadaveric donors, with increased EP3 expression, PGE2 production, and function of EP3 agonists and antagonists to modulate cAMP production and GSIS. We also analyzed the impact of EP3 receptor activation on signaling through the glucagon-like peptide (GLP)-1 receptor. We demonstrated that EP3 agonists antagonize GLP-1 signaling, decreasing the maximal effect that GLP-1 can elicit on cAMP production and GSIS. Taken together, our results identify EP3 as a new therapeutic target for β-cell dysfunction in T2D.

Prostaglandin E2 receptor, EP3, is induced in diabetic islets and negatively regulates glucose- and hormone-stimulated insulin secretion.

Hyperhomocysteinemia is a condition that results from altered methyl group metabolism and is associated with numerous pathological conditions. A number of nutritional and hormonal factors have been shown to influence circulating homocysteine concentrations; however, the impact of exercise on homocysteine and methyl group balance is not well understood. Our hypothesis was that exercise represents an effective means to prevent hyperhomocysteinemia in a folate-independent manner. The purpose of this study was to determine the influence of exercise on homocysteine metabolism in a dietary folate-restricted mouse model characterized by moderate hyperhomocysteinemia. Female outbred mice (12 weeks old) were assigned to either a sedentary or free-access wheel exercise group. Following a 4-week acclimation period, half of the mice in each group were provided a folate-restricted diet for 7-weeks prior to euthanasia and tissue collection. As expected, folate-restricted sedentary mice exhibited a 2-fold increase in plasma total homocysteine concentrations; however, exercise completely prevented the increase in circulating homocysteine concentrations. Moreover, exercise reduced plasma homocysteine concentrations 36% within the group fed only the control diet. The prevention of hyperhomocysteinemia by exercise appears, at least in part, to be the result of increased folate-independent homocysteine remethylation owing to a 2-fold increase in renal betaine homocysteine S-methyltransferase. To our knowledge, this is the first report demonstrating the prevention of hyperhomocysteinemia by exercise in a dietary folate-restriction model. Future research will be directed at determining if exercise can have a positive impact on other nutritional, hormonal, and genetic models of hyperhomocysteinemia relevant to humans.

Exercise prevents hyperhomocysteinemia in a dietary folate-restricted mouse model.

The worldwide prevalence of obesity is steadily increasing, nearly doubling between 1980 and 2008. Obesity is often associated with insulin resistance, a major risk factor for type 2 diabetes mellitus (T2DM): a costly chronic disease and serious public health problem. The underlying cause of T2DM is a failure of the beta cells of the pancreas to continue to produce enough insulin to counteract insulin resistance. Most current T2DM therapeutics do not prevent continued loss of insulin secretion capacity, and those that do have the potential to preserve beta cell mass and function are not effective in all patients. Therefore, developing new methods for preventing and treating obesity and T2DM is very timely and of great significance. There is now considerable literature demonstrating a link between inhibitory guanine nucleotide-binding protein (G protein) and G protein-coupled receptor (GPCR) signaling in insulin-responsive tissues and the pathogenesis of obesity and T2DM. These studies are suggesting new and emerging therapeutic targets for these conditions. In this review, we will discuss inhibitory G proteins and GPCRs that have primary actions in the beta cell and other peripheral sites as therapeutic targets for obesity and T2DM, improving satiety, insulin resistance and/or beta cell biology.

Article	Year
Prostaglandin E2 receptor, EP3, is induced in diabetic islets and negatively regulates glucose- and hormone-stimulated insulin secretion. Diabetes\| PubMed ID: 23349487	2013
Exercise prevents hyperhomocysteinemia in a dietary folate-restricted mouse model. Nutrition research (New York, N.Y.)\| PubMed ID: 23746565	2013
Inhibitory G proteins and their receptors: emerging therapeutic targets for obesity and diabetes. Experimental & molecular medicine\| PubMed ID: 24946790	2014

Joshua C. Neuman

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