Huntington's disease (HD) is a fatal, dominantly inherited disorder caused by polyglutamine repeat expansion in the huntingtin (htt) gene. Here, we observe that HD mice develop hypothermia associated with impaired activation of brown adipose tissue (BAT). Although sympathetic stimulation of PPARgamma coactivator 1alpha (PGC-1alpha) was intact in BAT of HD mice, uncoupling protein 1 (UCP-1) induction was blunted. In cultured cells, expression of mutant htt suppressed UCP-1 promoter activity; this was reversed by PGC-1alpha expression. HD mice showed reduced food intake and increased energy expenditure, with dysfunctional BAT mitochondria. PGC-1alpha is a known regulator of mitochondrial function; here, we document reduced expression of PGC-1alpha target genes in HD patient and mouse striatum. Mitochondria of HD mouse brain show reduced oxygen consumption rates. Finally, HD striatal neurons expressing exogenous PGC-1alpha were resistant to 3-nitropropionic acid treatment. Altered PGC-1alpha function may thus link transcription dysregulation and mitochondrial dysfunction in HD.

Here we report multiple lines of evidence for a comprehensive model of energy metabolism in the vertebrate eye. Metabolic flux, locations of key enzymes, and our finding that glucose enters mouse and zebrafish retinas mostly through photoreceptors support a conceptually new model for retinal metabolism. In this model, glucose from the choroidal blood passes through the retinal pigment epithelium to the retina where photoreceptors convert it to lactate. Photoreceptors then export the lactate as fuel for the retinal pigment epithelium and for neighboring Müller glial cells. We used human retinal epithelial cells to show that lactate can suppress consumption of glucose by the retinal pigment epithelium. Suppression of glucose consumption in the retinal pigment epithelium can increase the amount of glucose that reaches the retina. This framework for understanding metabolic relationships in the vertebrate retina provides new insights into the underlying causes of retinal disease and age-related vision loss.

A kinetics database of wild-type and 20 mutants of glucokinase was developed. Many kinetic differences were found for the mutants. The mathematical model to calculate the threshold for glucose-stimulated insulin release predicts fasting blood glucose between 3 and 7 mmol/l in subjects with glucokinase gene mutations. [Diabetologia 42: 1175-1186]

(T2DM) is increasing, creating a need for T2DM animal models for the study of disease pathogenesis, prevention, and treatment. The purpose of this project was to develop a rat model of T2DM that more closely models the pathophysiology of T2DM in humans. The model was created by crossing obese Sprague-Dawley rats with insulin resistance resulting from polygenic adult-onset obesity with Zucker diabetic fatty-lean rats that have a defect in pancreatic ␤-cell function but normal leptin signaling. We have characterized the model with respect to diabetes incidence; age of onset; longitudinal measurements of glucose, insulin, and lipids; and glucose tolerance. Longitudinal fasting glucose and insulin data demonstrated progressive hyperglycemia (with fasting and fed glucose concentrations Ͼ250 and Ͼ450 mg/dl, respectively) after onset along with hyperinsulinemia resulting from insulin resistance at onset followed by a progressive decline in circulating insulin concentrations, indicative of ␤-cell decompensation. The incidence of diabetes in male and female rats was 92 and 43%, respectively, with an average age of onset of 6 mo in males and 9.5 mo in females. Results from intravenous glucose tolerance tests, pancreas immunohistochemistry, and islet insulin content further support a role for ␤-cell dysfunction in the pathophysiology of T2DM in this model. Diabetic animals also exhibit glycosuria, polyuria, and hyperphagia. Thus diabetes in the UC Davis-T2DM rat is more similar to clinical T2DM in humans than in other existing rat models and provides a useful model for future studies of the pathophysiology, treatment, and prevention of T2DM. diabetic rodent model; hyperglycemia; insulin; ␤-cell TYPE 2 DIABETES MELLITUS (T2DM) is a devastating metabolic disease presently affecting at least 16 million people in the United States alone (33, 49). The prevalence of T2DM is also increasing in children and adolescents (42). With the increasing incidence of T2DM, the identification of preventative measures has become crucial, necessitating the development of effective preclinical models for studying approaches for both diabetes prevention and treatment.The most commonly used rodent models of T2DM include the Zucker diabetic fatty (ZDF) rat, the Otsuka Long Evans Tokushima fatty (OLETF) rat, and the db/db mouse, all of which exhibit obesity-associated insulin resistance and impaired ␤-cell function, resulting in diabetes (5, 25, 38). While these animal models have contributed substantially to understanding the pathophysiology and treatment of T2DM and its complications, the basic mechanisms underlying the pathogenesis of diabetes in these models do not correspond with what occurs in most human patients with T2DM. These differences in etiology are likely to hinder effective translational research.Obesity and insulin resistance in most animal models of T2DM result from monogenic mutations that are rare in human and animal populations and present multiple problems in terms of applying these models to clinical T2DM. For example, mutat...

Background: Excess nutrients induce adipose inflammation. Results: Excess glucose and palmitate generate ROS via NOX4 by a mechanism that involves the PPP and translocation of NOX4 into LRs, rather than by mitochondrial oxidation. Conclusion: NOX4 activates monocyte chemotactic factor expression. Significance: Understanding the source of ROS generation may lead to the development of new therapeutic targets for adipose tissue inflammation.

Summary Here, we demonstrate that the fractalkine(FKN)/CX3CR1 system represents a previously undescribed regulatory mechanism for pancreatic islet beta cell function and insulin secretion. CX3CR1 KO mice exhibited a marked defect in glucose and GLP1-stimulated insulin secretion, and this defect was also observed in vitro in isolated islets from CX3CR1 KO mice. In vivo administration of FKN improved glucose tolerance with an increase in insulin secretion. In vitro treatment of islets with FKN increased intracellular Ca2+ and potentiated insulin secretion in both mouse and human islets. The KO islets exhibited reduced expression of a set of genes necessary for the fully functional, differentiated beta cell state, whereas, treatment of WT islets with FKN led to increased expression of these genes. Lastly, expression of FKN in islets was decreased by aging and HFD/obesity, suggesting that decreased fractalkine/CX3CR1 signaling could be a mechanism underlying beta cell dysfunction in type 2 diabetes.

In comparison with UW organ preservation, exposure of pancreata to the TLM result in greater islet yields and extended preservation times.

ATP and ADP levels are critical regulators of glucosestimulated insulin secretion. In many aerobic cell types, the phosphorylation potential (ATP/ADP/P i ) is controlled by sensing mechanisms inherent in mitochondrial metabolism that feed back and induce compensatory changes in electron transport. To determine whether such regulation may contribute to stimulus-secretion coupling in islet cells, we used a recently developed flow culture system to continuously and noninvasively measure cytochrome c redox state and oxygen consumption as indexes of electron transport in perifused isolated rat islets. Increasing substrate availability by increasing glucose increased cytochrome c reduction and oxygen consumption, whereas increasing metabolic demand with glibenclamide increased oxygen consumption but not cytochrome c reduction. The data were analyzed using a kinetic model of the dual control of electron transport and oxygen consumption by substrate availability and energy demand, and ATP/ADP/P i was estimated as a function of time. ATP/ADP/P i increased in response to glucose and decreased in response to glibenclamide, consistent with what is known about the effects of these agents on energy state. Therefore, a simple model representing the hypothesized role of mitochondrial coupling in governing phosphorylation potential correctly predicted the directional changes in ATP/ADP/P i . Thus, the data support the notion that mitochondrial-coupling mechanisms, by virtue of their role in establishing ATP and ADP levels, may play a role in mediating nutrient-stimulated insulin secretion. Our results also offer a new method for continuous noninvasive measures of islet cell phosphorylation potential, a critical metabolic variable that controls insulin secretion by ATP-sensitive K ؉ -dependent and -independent mechanisms. Diabetes 53: [401][402][403][404][405][406][407][408][409] 2004 F ree ATP and ADP levels are understood to couple glucose metabolism with the closing of ATPsensitive K ϩ (K ATP ) channels and the ionic events leading to the exocytosis of insulin (1,2). Furthermore, the phosphorylation potential (ATP/ADP/P i ) may augment insulin secretion beyond that mediated by K ATP channels (3). Although it is well established that the critical ATP and ADP levels depend on islet substrate metabolism and mitochondrial electron transport (4 -6), it is less broadly appreciated that ADP stimulates electron transport and ATP production (7,8) as a feedback regulator of ATP/ADP/P i (9,10). Thus, mitochondrial ATP production, the ATP/ADP/P i , and ultimately the insulin secretory rate depend dually on both substrate supply as well as energy demand.Although the mechanisms by which mitochondria sense ADP levels and control ATP/ADP/P i are not fully established, a likely candidate is cytochrome c oxidase, the rate-limiting step in the electron transport chain (11). Wilson et al. (11,12) validated a mathematical model correlating substrate supply and energy demand (i.e., as phosphorylation potential) to the redox state and oxygen cons...