Paternal-maternal effects on phenotypic characteristics in spontaneously diabetic Nagoya-Shibata-Yasuda mice

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.

Analysis of the expression of candidate genes for type 1 diabetes susceptibility in T cells

Type 1 diabetes is characterized by T-cell-mediated autoimmune destruction of pancreatic β-cells. Currently, approximately 50 type 1 diabetes susceptibility genes or chromosomal regions have been identified. However, the functions of type 1 diabetes susceptibility genes in T cells are elusive. In this study, we evaluated the correlation between type 1 diabetes susceptibility genes and T-cell signaling. The expression levels of 22 candidate type 1 diabetes susceptibility genes in T cells from nonobese diabetic (NOD), control C57BL/6 (B6), and NOD-control F1 hybrid mice were analyzed in response to 2 key immunoregulatory cytokines: interleukin-2 (IL-2) and transforming growth factor β (TGF-β). Exogenous gene expression studies were also performed in EL4 and Jurkat E6.1 T-cell lines. Significant differences in the expression of Clec16a, Dlk1, Il2, Ptpn22, Rnls, and Zac1 (also known as Plagl1) were observed in T cells derived from the 3 strains of mice, and TGF-β differentially influenced the expression of Ctla4, Foxp3, Il2, Ptpn22, Sh2b3, and Zac1. We found that TGF-β induced Zac1 expression in both primary T cells and EL4 cells and that exogenous expression of Zac1 and ZAC1 in T-cell lines altered the expression of Il2 and DLK1, respectively. The results of our study indicate the possibility that additional genetic pathways underlying type 1 diabetes susceptibility, including those involving Clec16a, Dlk1, Rnls, Sh2b3, and Zac1 under IL-2 and TGF-β signaling in T cells, may be shared between human and NOD mice.

Analysis of hepatic gene expression profile in a spontaneous mouse model of type 2 diabetes under a high sucrose diet

Both genetic factors and diabetogenic environmental factors, such as a high-sucrose diet (HSD), are involved in the development of type 2 diabetes. In this study, the Nagoya-Shibata-Yasuda (NSY) mouse, an animal model of type 2 diabetes and C3H mice used as controls, were fed a HSD, a high-fat diet (HFD) or a regular diet (RD) from weaning. In C3H mice, HFD significantly increased body weight gain, but maintained glucose tolerance. In contrast, in NSY mice, HSD resulted in increased body weight gain and liver steatosis and increased glucose intolerance to a greater extent than HFD. Furthermore, we performed DNA microarray analysis to detect differences in hepatic gene expression levels in both strains under HSD. We then performed RT-PCR analysis on selected genes to evaluate basal expression level under RD and changes under HSD conditions. HSD-fed NSY, but not C3H mice, exhibited increased hepatic expression levels of Pparg2, an isoform of Pparg as well as G0s2, a target of Pparg, which are known to be adipocyte-specific genes. Compared to RD-fed C3H mice, hepatic expression levels of Kat2b (transcriptional regulation), Hsd3b5 (steroid hormone metabolism) and Cyp7b1 (bile acid metabolism) were initially lower in RD-fed NSY mice, and were further decreased in HSD-fed NSY mice. Expression of Metallothionein (Mt1) and Metallothionein 2 (Mt2) was significantly lower in NSY mice compared to C3H mice, irrespective of dietary condition. These data suggest that elucidation of this heterogeneity in response to HSD might contribute to further understanding of the gene-environment interactions leading to diabetes in humans.

Dose effect and mode of inheritance of diabetogenic gene on mouse chromosome 11

The quantitative trait locus (QTL) mapping in segregating crosses of NSY (Nagoya-Shibata-Yasuda) mice, an animal model of type 2 diabetes, with nondiabetic strain C3H/He mice has identified diabetogenic QTLs on multiple chromosomes. The QTL on chromosome 11 (Chr11) (Nidd1n) showing the largest effect on hyperglycemia was confirmed by our previous studies with homozygous consomic mice, C3H-11(NSY), in which the NSY-derived whole Chr11 was introgressed onto control C3H background genes. C3H-11(NSY) mice also showed a streptozotocin (STZ) sensitivity. In the present study, we constructed heterozygous C3H-11(NSY) mice and the phenotypes were analyzed in detail in comparison with those of homozygous C3H-11(NSY) and C3H mice. Heterozygous C3H-11(NSY) mice had significantly higher blood glucose levels and STZ sensitivity than those in C3H mice. Hyperglycemia and STZ sensitivity in heterozygous C3H-11(NSY) mice, however, were not as severe as in homozygous C3H-11(NSY) mice. The body weight and fat pad weight in heterozygous C3H-11(NSY) mice were similar to those in C3H and homozygous C3H-11(NSY) mice. These data indicated that the introgression of Chr11 of the diabetes-susceptible NSY strain onto diabetes-resistant C3H caused marked changes in the glucose tolerance and STZ susceptibility even in a heterozygous state, and suggested that the mode of inheritance of a gene or genes on Chr11 for hyperglycemia and STZ sensitivity is additive.

Direct evidence for susceptibility genes for type 2 diabetes on mouse chromosomes 11 and 14

AIMS/HYPOTHESIS

Diabetogenic loci for type 2 diabetes have been mapped to mouse chromosome (Chr) 11 and 14 in the Nagoya-Shibata-Yasuda (NSY) mouse, an animal model of type 2 diabetes. We aimed to obtain direct evidence of these genes on each chromosome and to clarify their function and interaction in conferring susceptibility to type 2 diabetes.

METHODS

We established three consomic strains homozygous for diabetogenic NSY-Chr11, NSY-Chr14 or both on the control C3H background (C3H-11(NSY), C3H-14(NSY) and C3H-11(NSY)14(NSY), respectively), and monitored diabetes-related phenotypes longitudinally. The glucokinase gene was sequenced as a positional candidate gene on Chr11.

RESULTS

C3H-11(NSY) mice showed hyperglycaemia associated with impaired insulin secretion and age-dependent insulin resistance without obesity. C3H-14(NSY) mice exhibited hyperglycaemia mainly due to insulin resistance, with a slight increase in percentage body fat. C3H-11(NSY)14(NSY) double consomic mice showed marked hyperglycaemia and obesity, which was not observed in single consomic strains. Sequences of the glucokinase gene were allelically variant between NSY and C3H mice.

CONCLUSIONS/INTERPRETATION

These data provide direct evidence that Chr11 and Chr14 harbour major susceptibility genes for type 2 diabetes. These two chromosomes interact to cause more severe hyperglycaemia and obesity, which was not observed with the presence of either single chromosome, indicating different modes of gene-gene interaction depending on the phenotype. Marked changes in the phenotypes retained in the consomic strains will facilitate fine mapping and the identification of the responsible genes and their interaction with each other, other genes and environmental factors.

Fatty liver and obesity: phenotypically correlated but genetically distinct traits in a mouse model of type 2 diabetes

AIMS/HYPOTHESIS

Obesity and fatty liver are commonly associated with type 2 diabetes, but the genetic and functional bases linking fatty liver with obesity and diabetes are largely unknown. Our aim was to investigate the association of fatty liver with obesity and other diabetes-related phenotypes and to define the genetic control of obesity and fatty liver.

MATERIALS AND METHODS

We established 306 F2 mice by crossing Nagoya-Shibata-Yasuda (NSY) mice, an animal model of type 2 diabetes, with control C3H mice, and analysed their phenotypes. Whole-genome screening of F2 mice was performed to identify the loci responsible for fatty liver and obesity.

RESULTS

A strong association of fatty liver with obesity, hyperinsulinaemia and hyperglycaemia was observed in F2 mice. Using whole-genome screening in 306 F2 mice, we mapped a new locus for fatty liver (Fl1n) on chromosome 6 (maximum logarithm of odds score [MLS] 10.0) and one for body weight (Bw1n) on chromosome 7 (MLS 5.1). Fl1n was linked to epididymal fat weight as well as fatty liver, but its effects were opposite in the two tissues in that the NSY allele increased liver fat but decreased epididymal fat, suggesting a role of Fl1n in partitioning of fat mass. The sequence of peroxisome proliferator-activated receptor gamma (Pparg), a candidate for Fl1n, showed allelic variation between NSY and C3H mice.

CONCLUSIONS/INTERPRETATION

These data suggest that fatty liver and obesity are phenotypically related but genetically independent. Loci homologous to Fl1n and Bw1n are good candidate genes for susceptibility to fatty liver and obesity in humans.

Prevention and treatment of obesity, insulin resistance, and diabetes by bile acid-binding resin

Bile acid-binding resins, such as cholestyramine and colestimide, have been clinically used as cholesterol-lowering agents. These agents bind bile acids in the intestine and reduce enterohepatic circulation of bile acids, leading to accelerated conversion of cholesterol to bile acids. A significant improvement in glycemic control was reported in patients with type 2 diabetes whose hyperlipidemia was treated with bile acid-binding resins. To confirm the effect of such drugs on glucose metabolism and to investigate the underlying mechanisms, an animal model of type 2 diabetes was given a high-fat diet with and without colestimide. Diet-induced obesity and fatty liver were markedly ameliorated by colestimide without decreasing the food intake. Hyperglycemia, insulin resistance, and insulin response to glucose, as well as dyslipidemia, were markedly and significantly ameliorated by the treatment. Gene expression of the liver indicated reduced expression of small heterodimer partner, a pleiotropic regulator of diverse metabolic pathways, as well as genes for both fatty acid synthesis and gluconeogenesis, by treatment with colestimide. This study provides a molecular basis for a link between bile acids and glucose metabolism and suggests the bile acid metabolism pathway as a novel therapeutic target for the treatment of obesity, insulin resistance, and type 2 diabetes.

Food hardness as environmental factor in development of type 2 diabetes

The effect of hardness of the diet as an environmental factor on the development of diabetes was investigated in a mouse model of type 2 diabetes. NSY and control C3H/He mice were fed several types of dietary chow from 4 weeks of age. Autoclaved CRF-1, whose major components are almost the same as those of the MF diet except for increased pellet hardness, resulted in a significant reduction in body weight in both NSY (p<0.05) and C3H (p<0.001) mice at 16 weeks of age. The prevalence of diabetes in NSY mice fed autoclaved CRF-1 was significantly lower than that in those fed MF at 36 weeks of age (p<0.05), which was associated with a significant decrease in body weight (p<0.0001). At 16 weeks of age, NSY mice fed with a hard diet (autoclaved CRF-1) showed a significantly lower body weight (32.1+/-0.3g) and blood glucose levels during ipGTT than those with fed a normal (gamma-irradiated CRF-1) (35.6+/-1.3g, p<0.05 and <0.01, respectively) or soft (powdered CRF-1) (p<0.05 and <0.05, respectively) diet. Switching from normal (gamma-irradiated) to hard (autoclaved) chow, even after the development diabetes at 36 weeks of age, markedly improved glucose intolerance after 4 weeks in NSY mice despite the small change in body weight. These results indicate the importance of food hardness as an environmental factor in the development of type 2 diabetes.

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.

Mouse Models of Type 1 and Type 2 Diabetes Derived from the Same Closed Colony: Genetic Susceptibility Shared Between Two Types of Diabetes

Except for rare subtypes of diabetes, both type 1 and type 2 diabetes are multifactorial diseases in which genetic factors consisting of multiple susceptibility genes and environmental factors contribute to the disease development. Due to complex interaction among multiple susceptibility genes and between genetic and environmental factors, genetic analysis of multifactorial diseases is difficult in humans. Inbred animal models, in which the genetic background is homogeneous and environmental factors can be controlled, are therefore valuable in genetic dissection of multifactorial diseases. We are fortunate to have excellent animal models for both type 1 and type 2 diabetes--the nonobese diabetic (NOD) mouse and the Nagoya-Shibata-Yasuda (NSY) mouse, respectively. Congenic mapping of susceptibility genes for type 1 diabetes in the NOD mouse has revealed that susceptibility initially mapped as a single locus often consists of multiple components on the same chromosome, indicating the importance of congenic mapping in defining genes responsible for polygenic diseases. The NSY mouse is an inbred animal model of type 2 diabetes established from Jcl:ICR, from which the NOD mouse was also derived. We have recently mapped three major loci contributing to type 2 diabetes in the NSY mouse. Interestingly, support intervals where type 2 diabetes susceptibility genes were mapped in the NSY mouse overlapped the regions where type 1 diabetes susceptibility genes have been mapped in the NOD mouse. Although additional evidence is needed, it may be possible that some of the genes predisposing to diabetes are derived from a common ancestor contained in the original closed colony, contributing to type 1 diabetes in the NOD mouse and type 2 diabetes in the NSY mouse. Such genes, if they exist, will provide valuable information on etiological pathways common to both forms of diabetes, for the establishment of effective methods for prediction, prevention, and intervention in both type 1 and type 2 diabetes.

Mapping and promoter sequencing of HNF-1beta gene in diabetes-prone and -resistant mice

By using a novel single nucleotide polymorphism (SNP) in the coding sequence, the chromosomal location of Tcf2, encoding hepatic nuclear factor (HNF)-1beta, was determined in F2 intercrosses between Nagoya-Shibata-Yasuda (NSY) mice, an animal model of type 2 diabetes, and control C3H/He mice. The promoter region of Tcf2 gene was sequenced in NSY, non-obese diabetic (NOD) and control C3H/He mice. Tcf2 was mapped between genetic markers D11MIT320 and D11MIT195 with the following distances: D11MIT320-(7.3 cM)-Tcf2-(0.5 cM)-D11MIT195. A variant with insertion of C between -205 and -204 in the promoter region of Tcf2 was identified in NSY mice, but not NOD and C3H/He mice.