Genetic control of non obese diabetic mice susceptibility to high-dose streptozotocin-induced diabetes

Hepatic conversion of acetyl-CoA to acetate plays crucial roles in energy stress

Accumulating evidence indicates that acetate is increased under energy stress conditions such as those that occur in diabetes mellitus and prolonged starvation. However, how and where acetate is produced and the nature of its biological significance are largely unknown. We observed overproduction of acetate to concentrations comparable to those of ketone bodies in patients and mice with diabetes or starvation. Mechanistically, ACOT12 and ACOT8 are dramatically upregulated in the liver to convert free fatty acid-derived acetyl-CoA to acetate and CoA. This conversion not only provides a large amount of acetate, which preferentially fuels the brain rather than muscle, but also recycles CoA, which is required for sustained fatty acid oxidation and ketogenesis. We suggest that acetate is an emerging novel 'ketone body' that may be used as a parameter to evaluate the progression of energy stress.

The Therapeutic Effect of Coriolus versicolor Fruiting Body on STZ-Induced ICR Diabetic Mice

Coriolus versicolor is a natural drugs which has many pharmacological effects such as antitumor and enhanced immune activity. This paper studies the therapeutic effect of Coriolus versicolor fruiting body (CVFB) on streptozotocin (STZ)-induced Institute of Cancer Research (ICR) diabetic mice, the STZ solution was administered intraperitoneally at a dose of 150 mg/kg after fasting the mice, and ICR mice with fasting blood glucose >16.7 mmol/l were selected for research. Metformin was the positive control, and the dose of CVFB powder (1000 mg/kg, 2000 mg/kg, and 4000 mg/kg) for 28 consecutive days by gavage. The serum and liver of mice were collected for relevant index content testing. The results showed that CVFB can control or reduce the fasting blood glucose of mice and accelerate the rate of glucose metabolism, can reduce the levels of total cholesterol (T-CHO), triglyceride (TG), and high-density lipoprotein cholesterol (HDL-C) in mice, and regulate the abnormal symptoms of blood lipid metabolism commonly found in diabetes. It can increase the activity of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) antioxidant enzymes and enhance the ability of antioxidative stress in diabetic mice. In the H&E staining and apoptosis experiments of pancreatic tissue, CVFB can greatly reduce the inflammatory factors present in islets, increase the islet cells, and reduce the apoptotic rate caused by diabetes. All data confirmed the therapeutic effect of CVFB on diabetic ICR mice. The present study provides a scientific basis for the development of drugs for the prevention and treatment of diabetes, it is of great significance to the in-depth study of Coriolus versicolor.

β-Cell failure in diabetes: Common susceptibility and mechanisms shared between type 1 and type 2 diabetes

Diabetes mellitus is etiologically classified into type 1, type 2 and other types of diabetes. Despite distinct etiologies and pathogenesis of these subtypes, many studies have suggested the presence of shared susceptibilities and underlying mechanisms in β-cell failure among different types of diabetes. Understanding these susceptibilities and mechanisms can help in the development of therapeutic strategies regardless of the diabetes subtype. In this review, we discuss recent evidence indicating the shared genetic susceptibilities and common molecular mechanisms between type 1, type 2 and other types of diabetes, and highlight the future prospects as well.

Selectively Bred Diabetes Models: GK Rats, NSY Mice, and ON Mice

The polygenic background of selectively bred diabetes models mimics the etiology of type 2 diabetes. So far, three different rodent models (Goto-Kakizaki rats, Nagoya-Shibata-Yasuda mice, and Oikawa-Nagao mice) have been established in the diabetes research field by continuous selective breeding for glucose tolerance from outbred rodent stocks. The origin of hyperglycemia in these rodents is mainly insulin secretion deficiency from the pancreatic β-cells and mild insulin resistance in insulin target organs. In this chapter, we summarize backgrounds and phenotypes of these rodent models to highlight their importance in diabetes research. Then, we introduce experimental methodologies to evaluate β-cell exocytosis as a putative common defect observed in these rodent models.

Congenic mapping and candidate gene analysis for streptozotocin-induced diabetes susceptibility locus on mouse chromosome 11

Streptozotocin (STZ) has been widely used to induce diabetes in rodents. Strain-dependent variation in susceptibility to STZ has been reported; however, the gene(s) responsible for STZ susceptibility has not been identified. Here, we utilized the A/J-11^SM consomic strain and a set of chromosome 11 (Chr. 11) congenic strains developed from A/J-11^SM to identify a candidate STZ-induced diabetes susceptibility gene. The A/J strain exhibited significantly higher susceptibility to STZ-induced diabetes than the A/J-11^SM strain, confirming the existence of a susceptibility locus on Chr. 11. We named this locus Stzds1 (STZ-induced diabetes susceptibility 1). Congenic mapping using the Chr. 11 congenic strains indicated that the Stzds1 locus was located between D11Mit163 (27.72 Mb) and D11Mit51 (36.39 Mb). The Mpg gene, which encodes N-methylpurine DNA glycosylase (MPG), a ubiquitous DNA repair enzyme responsible for the removal of alkylated base lesions in DNA, is located within the Stzds1 region. There is a close relationship between DNA alkylation at an early stage of STZ action and the function of MPG. A Sanger sequence analysis of the Mpg gene revealed five polymorphic sites in the A/J genome. One variant, p.Ala132Ser, was located in a highly conserved region among rodent species and in the minimal region for retained enzyme activity of MPG. It is likely that structural alteration of MPG caused by the p.Ala132Ser mutation elicits increased recognition and excision of alkylated base lesions in DNA by STZ.

Verification That Mouse Chromosome 14 Is Responsible for Susceptibility to Streptozotocin in NSY Mice

INTRODUCTION

Streptozotocin- (STZ-) induced diabetes is under polygenic control, and the genetic loci for STZ susceptibility are mapped to chromosome (Chr) 11 in Nagoya-Shibata-Yasuda (NSY) mice. In addition to Chr11, other genes on different chromosomes may contribute to STZ susceptibility in NSY mice. The aim of this study was to determine whether NSY-Chr14 contributes to STZ susceptibility and contains the STZ-susceptible region.

MATERIALS AND METHODS

A consomic C3H-14^NSY strain (R0: homozygous for NSY-derived whole Chr14 on the control C3H background), two congenic strains (R1: the region retained proximal and middle segments of NSY-Chr14 and R2: the region retained a proximal segment of NSY-Chr14), and parental NSY and C3H mice were intraperitoneally injected with a single injection of STZ at a dose of 175 mg/kg body weight at 12 weeks of age. Blood glucose levels and body weights were measured at days 0, 1, 2, 4, 5, 7, 8, and 14 after STZ injection. At day 14 after STZ injection, pancreata were dissected and fixed.

RESULTS

After STZ injection, blood glucose levels were significantly higher in R0 mice than in C3H mice. However, blood glucose levels in R0 mice were not as severely affected as those in NSY mice. In R1 and R2 mice, blood glucose levels were similar to those in C3H mice and were significantly lower than those in R0 mice. Body weights were decreased in NSY and R0 mice; however, this change was not observed in R1, R2, and C3H mice. Although islet tissues in all strains exhibited degeneration and cellular infiltration, histological changes in NSY and R0 mice were more severe than those in R1, R2, and C3H mice.

CONCLUSIONS

These data demonstrated that NSY-Chr14 was a STZ-susceptible chromosome and that STZ susceptibility was mapped to the distal segment of NSY-Chr14.

Diabetes provides an unfavorable environment for muscle mass and function after muscle injury in mice

It is of common knowledge that diabetes decreases skeletal muscle contractility and induces atrophy. However, how hyperglycemia and insulin deficiency modify muscle mass and neuromuscular recovery after muscle injury is not well known. We have analyzed two models of diabetes: streptozotocin (STZ)-treated Swiss mice and Akita mice that spontaneously develop diabetes. A fast muscle, the tibialis anterior, was injured following injection of a myotoxic agent (cardiotoxin). Neuromuscular function was evaluated by examining in situ isometric contractile properties of regenerating muscles in response to nerve stimulation 14, 28 and 56 days after myotoxic injury. We found that STZ-induced diabetes reduces muscle weight and absolute maximal tetanic force in both regenerating and uninjured muscles (p = 0.0001). Moreover, it increases specific maximal tetanic force and tetanic fusion in regenerating and uninjured muscles (p = 0.04). In the Akita mice, diabetes decreases muscle weight and absolute maximal tetanic force, and increases tetanic fusion in both regenerating and uninjured muscles (p < or = 0.003). Interestingly, STZ-induced diabetes exerts more marked effects than diabetes of genetic origin, in particular on muscle weight. This reduction in muscle mass was not due to an increased expression of the atrogenes MuRF1 and atrogin-1 during STZ-induced diabetes. The present study in mice demonstrates that both models of diabetes impair regenerating muscles as well as uninjured muscles. Regenerating fast muscles are weaker, lighter and slower in diabetic compared with nondiabetic mice.

‘Sensing’ autoimmunity in type 1 diabetes

Type 1 diabetes (T1D) results from autoimmune-mediated loss of insulin-producing beta-cells. Recent findings suggest that the events controlling T1D development are not only immunological, but also neuronal in nature. In the non-obese diabetic (NOD) mouse model of T1D, a mutant sensory neuron channel, TRPV1, initiates chronic, progressive beta-cell stress, inducing islet cell inflammation. This novel mechanism of organ-specific damage requires a permissive, autoimmune-prone host, but ascribes tissue specificity to the local secretory dysfunction of sensory afferent neurons. In NOD mice, normalizing this neuronal function by administration of the neurotransmitter substance P clears islet cell inflammation, reduces insulin resistance and restores normoglycemia. Here, we discuss this neuro-immuno-endocrine model, its implications and the involvement of sensory neurons in other autoimmune disorders. These developments might provide novel neuronal-based therapeutic interventions, particularly in diabetes.

The genetic landscape of type 2 diabetes in mice

Inbred mouse strains provide genetic diversity comparable to that of the human population. Like humans, mice have a wide range of diabetes-related phenotypes. The inbred mouse strains differ in the response of their critical physiological functions, such as insulin sensitivity, insulin secretion, beta-cell proliferation and survival, and fuel partitioning, to diet and obesity. Most of the critical genes underlying these differences have not been identified, although many loci have been mapped. The dramatic improvements in genomic and bioinformatics resources are accelerating the pace of gene discovery. This review describes how mouse genetics can be used to discover diabetes-related genes, summarizes how the mouse strains differ in their diabetes-related phenotypes, and describes several examples of how loci identified in the mouse may directly relate to human diabetes.

Effects of experimental type 1 diabetes and exercise training on angiogenic gene expression and capillarization in skeletal muscle

Diabetes alters microvascular structure and function and is a major risk factor for cardiovascular diseases. In diabetic skeletal muscle, impaired angiogenesis and reduced VEGF-A expression have been observed, whereas in healthy muscle exercise is known to have opposite effects. We studied the effects of type 1 diabetes and combined exercise training on angiogenic mRNA expression and capillarization in mouse skeletal muscle. Microarray and real-time PCR analyses showed that diabetes altered the expression of several genes involved in angiogenesis. For example, levels of proangiogenic VEGF-A, VEGF-B, neuropilin-1, VEGFR-1, and VEGFR-2 were reduced and the levels of antiangiogenic thrombospondin-1 and retinoblastoma like-2 were increased. Exercise training alleviated some of these changes, but could not completely restore them. VEGF-A protein content was also reduced in diabetic muscles. In line with the reduced levels of VEGF-A and other angiogenic factors, and increased levels of angiogenesis inhibitors, capillary-to-muscle fiber ratio was lower in diabetic mice compared to healthy controls. Exercise training could not restore capillarization in diabetic mice. In conclusion, these data illustrate that type 1 diabetes is associated with reduced skeletal muscle capillarization and the dysregulation of complex angiogenesis pathways.

Susceptibility to streptozotocin-induced diabetes is mapped to mouse chromosome 11

To study the contribution of beta-cell vulnerability to susceptibility to diabetes, we studied beta-cell vulnerability to a single high dose of streptozotocin (STZ) in an animal model of type 2 diabetes, the NSY mouse, a sister strain of the STZ-sensitive NOD mouse, in comparison with the STZ-resistant C3H mouse. NSY mice were found to be extremely sensitive to STZ. Introgression of a single Chr 11, where STZ-sensitivity was mapped in the NOD mouse, from NSY mice converted STZ-resistant C3H mice to STZ-sensitive. Two nucleotide substitutions were identified in the nucleoredoxin gene, a positional and functional candidate gene for STZ-induced diabetes on Chr 11. These data, together with the co-localization of type 1 (Idd4) and type 2 (Nidd1n) susceptibility genes on Chr 11, suggest that the intrinsic vulnerability of pancreatic beta cells is determined by a gene or genes on Chr 11, which may also contribute to susceptibility to spontaneous diabetes.

Genetic background determines the size and structure of the endocrine pancreas

Key parameters of the endocrine pancreas, such as islet number, islet mass, beta-cell mass, and alpha-cell mass, were studied in different strains of inbred mice to investigate the impact of genetic background on the size and structure of the endocrine pancreas. Six mice from each of seven different strains of inbred mice were included in the study. For all parameters investigated, there was a pronounced interstrain variation. ANCOVA showed that only mouse strain was statistically significant as an explanatory parameter for the number of islets. Mouse strain, body weight, and pancreas mass reached statistical significance as explanatory parameters for the islet mass, with mouse strain as the most significant predictor. These data show that genetic background is the most important predictor of both the number of islets and total islet volume. We also conclude that inbred mice could be a valuable resource to identify the genes responsible for the size and structure of the endocrine pancreas.