The C57BL/6J (B6J) strain is the most widely used mouse strain in metabolic research. B6J mice produce a truncated form of nicotinamide nucleotide transhydrogenase (NNT), an enzyme that pumps protons across the inner mitochondrial membrane. It has been proposed that this results in B6J mice having reduced insulin secretion and glucose intolerance compared with other strains of mice (e.g. C3H/HeH and DBA/2) that have a full-length NNT. The aim of this study was to determine whether truncated NNT was associated with reduced insulin secretion and glucose intolerance, comparing B6 substrains that differ in having a truncated NNT. C57BL/6N (B6N) mice have wild-type Nnt. We compared Nnt expression and activity levels as well as in vivo insulin secretion and glucose tolerance between these mice and B6J. Body weights and specific fat-pad depot masses were alike and Nnt expression and activity levels were similar between B6N and B6J mice. Glucose-mediated insulin secretion and insulin sensitivity were comparable between the two groups of mice, as were plasma glucose and insulin levels during the oral glucose tolerance test. The presence of a truncated Nnt did not affect insulin secretion or glucose tolerance on the C57BL/6 background. We suggest that low or normal levels of NNT (regardless of truncation) have little effect on insulin secretion. Rather, it is the increase in expression of Nnt that regulates and enhances insulin secretion. Our data confirm that B6J is a reasonable control strain for diabetes research; this is especially important considering that it is the strain commonly used to generate genetically modified animals.

Aims/hypothesis Insulin hypersecretion may be an independent predictor of progression to type 2 diabetes. Identifying genes affecting insulin hypersecretion are important in understanding disease progression. We have previously shown that diabetes-susceptible DBA/2 mice congenitally display high insulin secretion. We studied this model to map and identify the gene(s) responsible for this trait. Methods Intravenous glucose tolerance tests followed by a genome-wide scan were performed on 171 (C57BL/6 × DBA/2) × C57BL/6 backcross mice. Results A quantitative trait locus, designated hyperinsulin production-1 (Hip1), was mapped with a logarithm of odds score of 7.7 to a region on chromosome 13. Production of congenic mice confirmed that Hip1 influenced the insulin hypersecretion trait. By studying appropriate recombinant inbred mouse strains, the Hip1 locus was further localised to a 2 Mb interval, which contained only nine genes. Expression analysis showed that the only gene differentially expressed in islets isolated from the parental strains was Nnt, which encodes the mitochondrial proton pump, nicotinamide nucleotide transhydrogenase (NNT). We also found in five mouse strains a positive correlation (r 2 =0.90, p<0.01) between NNT activity and first-phase insulin secretion, emphasising the importance of this enzyme in beta cell function. Furthermore, of these five strains, only those with high NNT activity are known to exhibit severe diabetes after becoming obese. Conclusions/interpretation Insulin hypersecretion is associated with increased Nnt expression. We suggest that NNT must play an important role in beta cell function and that its effect on the high insulin secretory capacity of the DBA/2 mouse may predispose beta cells of these mice to failure.

Obesity is a chronic low-grade inflammatory disease caused by increased energy intake and reduced energy expenditure. Studies using animal models with deletion of inflammatory cytokines have produced conflicting results with some showing increased weight gain and others showing no effect or even reduced body weights. Clearly, more work is necessary to understand the role of cytokines on body weight control. The aim of this study was to determine the effect of interferon-γ deletion (IFNγ(-/-)) on body weight regulation and glucose metabolism. Male IFNγ(-/-) and wild-type C57BL/6 mice were fed a low-fat chow diet, and body weight, food intake, and energy expenditure were monitored over 20 wk. At the end of the study, ip glucose tolerance test, insulin tolerance test, basal glucose turnover, and hyperinsulinemic/euglycemic clamps were performed. Expression levels of arcuate nucleus neuropeptide Y, Agouti-related peptide, and proopiomelanocortin mRNA as well as circulating leptin levels were also determined. IFNγ(-/-) mice had improved glucose tolerance with reduced rate of glucose appearance and increased insulin sensitivity due to greater suppression of endogenous glucose output, which was associated with decreased hepatic glucose-6-phosphatase activity. In addition, we also observed reduced body weight associated with decreased food intake and increased physical activity. Neuropeptide Y and Agouti-related peptide mRNA expression was reduced, whereas proopiomelanocortin mRNA expression was increased, as were plasma leptin levels. Global deletion of IFNγ in mice resulted in reduced body weight associated with negative energy balance, improved glucose tolerance, and hepatic insulin sensitivity. Our findings demonstrate that IFNγ plays a critical role in the regulation of body weight and glucose metabolism.

OBJECTIVE-Fructose-1,6-bisphosphatase (FBPase) is a gluconeogenic enzyme that is upregulated in islets or pancreatic ␤-cell lines exposed to high fat. However, whether specific ␤-cell upregulation of FBPase can impair insulin secretory function is not known. The objective of this study therefore is to determine whether a specific increase in islet ␤-cell FBPase can result in reduced glucose-mediated insulin secretion. RESEARCH DESIGN AND METHODS-To test this hypothesis, we have generated three transgenic mouse lines overexpressing the human FBPase (huFBPase) gene specifically in pancreatic islet ␤-cells. In addition, to investigate the biochemical mechanism by which elevated FBPase affects insulin secretion, we made two pancreatic ␤-cell lines (MIN6) stably overexpressing huFBPase.RESULTS-FBPase transgenic mice showed reduced insulin secretion in response to an intravenous glucose bolus. Compared with the untransfected parental MIN6, FBPase-overexpressing cells showed a decreased cell proliferation rate and significantly depressed glucose-induced insulin secretion. These defects were associated with a decrease in the rate of glucose utilization, resulting in reduced cellular ATP levels.CONCLUSIONS-Taken together, these results suggest that upregulation of FBPase in pancreatic islet ␤-cells, as occurs in states of lipid oversupply and type 2 diabetes, contributes to insulin secretory dysfunction.

Duchenne muscular dystrophy (DMD) is a life-threatening neuromuscular disease caused by the lack of dystrophin, resulting in progressive muscle wasting and locomotor dysfunctions. By adulthood, almost all patients also develop cardiomyopathy, which is the primary cause of death in DMD. Although there has been extensive effort in creating animal models to study treatment strategies for DMD, most fail to recapitulate the complete skeletal and cardiac disease manifestations that are presented in affected patients. Here, we generated a mouse model mirroring a patient deletion mutation of exons 52-54 (Dmd Δ52-54). The Dmd Δ52-54 mutation led to the absence of dystrophin, resulting in progressive muscle deterioration with weakened muscle strength. Moreover, Dmd Δ52-54 mice present with early-onset hypertrophic cardiomyopathy, which is absent in current pre-clinical dystrophin-deficient mouse models. Therefore, Dmd Δ52-54 presents itself as an excellent pre-clinical model to evaluate the impact on skeletal and cardiac muscles for both mutation-dependent and -independent approaches.

We conclude that Herpud1 regulates insulin secretion via control of Nnt expression.

The importance of Glucagon like peptide 1 (GLP-1) for metabolic control and insulin release sparked the evolution of genes mimicking GLP-1 action in venomous species (e.g. Exendin-4 in Heloderma suspectum (gila monster)). We discovered that platypus and echidna express a single GLP-1 peptide in both intestine and venom. Specific changes in GLP-1 of monotreme mammals result in resistance to DPP-4 cleavage which is also observed in the GLP-1 like Exendin-4 expressed in Heloderma venom. Remarkably we discovered that monotremes evolved an alternative mechanism to degrade GLP-1. We also show that monotreme GLP-1 stimulates insulin release in cultured rodent islets, but surprisingly shows low receptor affinity and bias toward Erk signaling. We propose that these changes in monotreme GLP-1 are the result of conflicting function of this peptide in metabolic control and venom. This evolutionary path is fundamentally different from the generally accepted idea that conflicting functions in a single gene favour duplication and diversification, as is the case for Exendin-4 in gila monster. This provides novel insight into the remarkably different metabolic control mechanism and venom function in monotremes and an unique example of how different selective pressures act upon a single gene in the absence of gene duplication.

Glucose-controlled insulin secretion is a key component of its regulation. Here, we examined whether liver cell secretion of insulin derived from an engineered construct can be regulated by glucose. Adenovirus constructs were designed to express proinsulin or mature insulin containing the conditional binding domain (CBD). This motif binds GRP78 (HSPA5), an endoplasmic reticulum (ER) protein that enables the chimeric hormone to enter into and stay within the ER until glucose regulates its release from the organelle. Infected HepG2 cells expressed proinsulin mRNA and the protein containing the CBD. Immunocytochemistry studies suggested that GRP78 and proinsulin appeared together in the ER of the cell. The amount of hormone released from infected cells varied directly with the ambient concentration of glucose in the media. Glucose-regulated release of the hormone from infected cells was rapid and sustained. Removal of glucose from the cells decreased release of the hormone. In streptozotocin-induced diabetic mice, when infected with adenovirus expressing mature insulin, glucose levels declined. Our data show that glucose regulates release of exogenously expressed insulin from the ER of liver cells. This approach may be useful in devising new ways to treat diabetes mellitus.