Contributions of mouse genetic strain background to age-related phenotypes in physically active HET3 mice.

We assessed aging hallmarks in skin, muscle, and adipose in the genetically diverse HET3 mouse, and generated a broad dataset comparing these to individual animal diagnostic SNPs from the 4 founding inbred strains of the HET3 line. For middle- and old-aged HET3 mice, we provided running wheel exercise to ensure our observations were not purely representative of sedentary animals, but age-related phenotypes were not improved with running wheel activity. Adipose tissue fibrosis, peripheral neuropathy, and loss of neuromuscular junction integrity were consistent phenotypes in older-aged HET3 mice regardless of physical activity, but aspects of these phenotypes were moderated by the SNP% contributions of the founding strains for the HET3 line. Taken together, the genetic contribution of founder strain SNPs moderated age-related phenotypes in skin and muscle innervation and were dependent on biological sex and chronological age. However, there was not a single founder strain (BALB/cJ, C57BL/6J, C3H/HeJ, DBA/2J) that appeared to drive more protection or disease-risk across aging in this mouse line, but genetic diversity in general was more protective.

Lifespan effects in male UM-HET3 mice treated with sodium thiosulfate, 16-hydroxyestriol, and late-start canagliflozin.

Genetically heterogeneous UM-HET3 mice born in 2020 were used to test possible lifespan effects of alpha-ketoglutarate (AKG), 2,4-dinitrophenol (DNP), hydralazine (HYD), nebivolol (NEBI), 16α-hydroxyestriol (OH_Est), and sodium thiosulfate (THIO), and to evaluate the effects of canagliflozin (Cana) when started at 16 months of age. OH_Est produced a 15% increase (p = 0.0001) in median lifespan in males but led to a significant (7%) decline in female lifespan. Cana, started at 16 months, also led to a significant increase (14%, p = 0.004) in males and a significant decline (6%, p = 0.03) in females. Cana given to mice at 6 months led, as in our previous study, to an increase in male lifespan without any change in female lifespan, suggesting that this agent may lead to female-specific late-life harm. We found that blood levels of Cana were approximately 20-fold higher in aged females than in young males, suggesting a possible mechanism for the sex-specific disparities in its effects. NEBI was also found to produce a female-specific decline (4%, p = 0.03) in lifespan. None of the other tested drugs provided a lifespan benefit in either sex. These data bring to 7 the list of ITP-tested drugs that induce at least a 10% lifespan increase in one or both sexes, add a fourth drug with demonstrated mid-life benefits on lifespan, and provide a testable hypothesis that might explain the sexual dimorphism in lifespan effects of the SGLT2 inhibitor Cana.

Testing the role of P2X7 receptors in the development of type 1 diabetes in nonobese diabetic mice.

Although P2rx7 has been proposed as a type 1 diabetes (T1D) susceptibility gene in NOD mice, its potential pathogenic role has not been directly determined. To test this possibility, we generated a new NOD stock deficient in P2X(7) receptors. T1D development was not altered by P2X(7) ablation. Previous studies found CD38 knockout (KO) NOD mice developed accelerated T1D partly because of a loss of CD4(+) invariant NKT (iNKT) cells and Foxp3(+) regulatory T cells (Tregs). These immunoregulatory T cell populations are highly sensitive to NAD-induced cell death activated by ADP ribosyltransferase-2 (ART2)-mediated ADP ribosylation of P2X(7) receptors. Therefore, we asked whether T1D acceleration was suppressed in a double-KO NOD stock lacking both P2X(7) and CD38 by rescuing CD4(+) iNKT cells and Tregs from NAD-induced cell death. We demonstrated that P2X(7) was required for T1D acceleration induced by CD38 deficiency. The CD38 KO-induced defects in homeostasis of CD4(+) iNKT cells and Tregs were corrected by coablation of P2X(7). T1D acceleration in CD38-deficient NOD mice also requires ART2 expression. If increased ADP ribosylation of P2X(7) in CD38-deficient NOD mice underlies disease acceleration, then a comparable T1D incidence should be induced by coablation of both CD38 and ART2, or CD38 and P2X(7). However, a previously established NOD stock deficient in both CD38 and ART2 expression is T1D resistant. This study demonstrated the presence of a T1D resistance gene closely linked to the ablated Cd38 allele in the previously reported NOD stock also lacking ART2, but not in the newly generated CD38/P2X(7) double-KO line.

Age-related changes to adipose tissue and peripheral neuropathy in genetically diverse HET3 mice differ by sex and are not mitigated by rapamycin longevity treatment.

Neural communication between the brain and adipose tissues regulates energy expenditure and metabolism through modulation of adipose tissue functions. We have recently demonstrated that under pathophysiological conditions (obesity, diabetes, and aging), total subcutaneous white adipose tissue (scWAT) innervation is decreased ('adipose neuropathy'). With advanced age in the C57BL/6J mouse, small fiber peripheral nerve endings in adipose tissue die back, resulting in reduced contact with adipose-resident blood vessels and other cells. This vascular neuropathy and parenchymal neuropathy together likely pose a physiological challenge for tissue function. In the current work, we used the genetically diverse HET3 mouse model to investigate the incidence of peripheral neuropathy and adipose tissue dysregulation across several ages in both male and female mice. We also investigated the anti-aging treatment rapamycin, an mTOR inhibitor, as a means to prevent or reduce adipose neuropathy. We found that HET3 mice displayed a reduced neuropathy phenotype compared to inbred C56BL/6 J mice, indicating genetic contributions to this aging phenotype. Compared to female HET3 mice, male HET3 mice had worse neuropathic phenotypes by 62 weeks of age. Female HET3 mice appeared to have increased protection from neuropathy until advanced age (126 weeks), after reproductive senescence. We found that rapamycin overall had little impact on neuropathy measures, and actually worsened adipose tissue inflammation and fibrosis. Despite its success as a longevity treatment in mice, higher doses and longer delivery paradigms for rapamycin may lead to a disconnect between life span and beneficial health outcomes.

Rapamycin/metformin co-treatment normalizes insulin sensitivity and reduces complications of metabolic syndrome in type 2 diabetic mice.

Rapamycin treatment has positive and negative effects on progression of type 2 diabetes (T2D) in a recombinant inbred polygenic mouse model, male NONcNZO10/LtJ (NcZ10). Here, we show that combination treatment with metformin ameliorates negative effects of rapamycin while maintaining its benefits. From 12 to 30 weeks of age, NcZ10 males were fed a control diet or diets supplemented with rapamycin, metformin, or a combination of both. Rapamycin alone reduced weight gain, adiposity, HOMA-IR, and inflammation, and prevented hyperinsulinemia and pre-steatotic hepatic lipidosis, but exacerbated hyperglycemia, hypertriglyceridemia, and pancreatic islet degranulation. Metformin alone reduced hyperinsulinemia and circulating c-reactive protein, but exacerbated nephropathy. Combination treatment retained the benefits of both while preventing many of the deleterious effects. Importantly, the combination treatment reversed effects of rapamycin on markers of hepatic insulin resistance and normalized systemic insulin sensitivity in this inherently insulin-resistant model. In adipose tissue, rapamycin attenuated the expression of genes associated with adipose tissue expansion (Mest, Gpam), inflammation (Itgam, Itgax, Hmox1, Lbp), and cell senescence (Serpine1). In liver, the addition of metformin counteracted rapamycin-induced alterations of G6pc, Ppara, and Ldlr expressions that promote hyperglycemia and hypertriglyceridemia. Both rapamycin and metformin treatment reduced hepatic Fasn expression, potentially preventing lipidosis. These results delineate a state of "insulin signaling restriction" that withdraws endocrine support for further adipogenesis, progression of the metabolic syndrome, and the development of its comorbidities. Our results are relevant for the treatment of T2D, the optimization of current rapamycin-based treatments for posttransplant rejection and various cancers, and for the development of treatments for healthy aging.

Differential Effects of Rapamycin on Glucose Metabolism in Nine Inbred Strains.

Studies in mice suggest that rapamycin has a negative impact on glucose homeostasis by inducing insulin resistance. However, results have been inconsistent and difficult to assess because the strains, methods of treatment, and analysis vary among studies. Using a consistent protocol, we surveyed nine inbred strains of mice for the effect of rapamycin on various aspects of glucose metabolism. Across all strains, rapamycin significantly delayed glucose clearance after challenge. However, rapamycin showed no main effect on systemic insulin sensitivity. Analysis of individual strains shows that rapamycin induced higher glucose values at 15 minutes post-challenge in 7/9 strains. However, only three strains show rapamycin-induced reduction in glucose clearance from 15 to 120 minutes. Although pancreatic insulin content was reduced by rapamycin in seven strains, none showed reduced serum insulin values. Although one strain showed no effects of rapamycin on glucose metabolism (129), another showed increased systemic insulin sensitivity (B6). We suggest that rapamycin likely inhibits insulin production and secretion in most strains while having strain-specific effects on glucose clearance without altering systemic insulin sensitivity. This strain survey indicates that genetic differences greatly influence the metabolic response to rapamycin.

Cardioprotective effects of dietary rapamycin on adult female C57BLKS/J-Leprdb mice.

Rapamycin (RAPA), an inhibitor of mTORC signaling, has been shown to extend life span in mice and other organisms. Recently, animal and human studies have suggested that inhibition of mTORC signaling can alleviate or prevent the development of cardiomyopathy. In view of this, we used a murine model of type 2 diabetes (T2D), BKS-Leprdb , to determine whether RAPA treatment can mitigate the development of T2D-induced cardiomyopathy in adult mice. Female BKS-Leprdb mice fed diet supplemented with RAPA from 11 to 27 weeks of age showed reduced weight gain and significant reductions of fat and lean mass compared with untreated mice. No differences in plasma glucose or insulin levels were observed between groups; however, RAPA-treated mice were more insulin sensitive (P < 0.01) than untreated mice. Urine albumin/creatinine ratio was lower in RAPA-treated mice, suggesting reduced diabetic nephropathy and improved kidney function. Echocardiography showed significantly reduced left ventricular wall thickness in mice treated with RAPA compared with untreated mice (P = 0.02) that was consistent with reduced heart weight/tibia length ratios, reduced myocyte size and cardiac fibrosis measured by histomorphology, and reduced mRNA expression of Col1a1, a marker for cardiomyopathy. Our results suggest that inhibition of mTORC signaling is a plausible strategy for ameliorating complications of obesity and T2D, including cardiomyopathy.

Novel leptin receptor mutation in NOD/LtJ mice suppresses type 1 diabetes progression: II. Immunologic analysis.

Recently, we identified in normally type 1 diabetes-prone NOD/LtJ mice a spontaneous new leptin receptor (LEPR) mutation (designated Lepr(db-5J)) producing juvenile obesity, hyperglycemia, hyperinsulinemia, and hyperleptinemia. This early type 2 diabetes syndrome suppressed intra-islet insulitis and permitted spontaneous diabetes remission. No significant differences in plasma corticosterone, splenic CD4(+) or CD8(+) T-cell percentages, or functions of CD3(+) T-cells in vitro distinguished NOD wild-type from mutant mice. Yet splenocytes from hyperglycemic mutant donors failed to transfer type 1 diabetes into NOD.Rag1(-/-) recipients over a 13-week period, whereas wild-type donor cells did so. This correlated with significantly reduced (P < 0.01) frequencies of insulin and islet-specific glucose-6-phosphatase catalytic subunit-related protein-reactive CD8(+) T-effector clonotypes in mutant mice. Intra-islet insulitis was also significantly suppressed in lethally irradiated NOD-Lepr(db-5J)/Lt recipients reconstituted with wild-type bone marrow (P < 0.001). In contrast, type 1 diabetes eventually developed when mutant marrow was transplanted into irradiated wild-type recipients. Mitogen-induced T-cell blastogenesis was significantly suppressed when splenic T-cells from both NOD/Lt and NOD-Lepr(db-5J)/Lt donors were incubated with irradiated mutant peritoneal exudate cells (P < 0.005). In conclusion, metabolic disturbances elicited by a type 2 diabetes syndrome (insulin and/or leptin resistance, but not hypercorticism) appear to suppress type 1 diabetes development in NOD-Lepr(db-5J)/Lt by inhibiting activation of T-effector cells.

Differential endocrine responses to rosiglitazone therapy in new mouse models of type 2 diabetes.

Polygenic mouse models for obesity-induced type 2 diabetes (T2D) more accurately reflect the most common manifestations of the human disease. Two inbred mouse strains (NON/Lt and NZO/HlLt) separately contributed T2D susceptibility- conferring quantitative trait loci to F1 males. Although chronic administration of rosiglitazone (Rosi) in diet (50 mg/kg) effectively suppressed F1 diabetes, hepatosteatosis was an undesired side effect. Three recombinant congenic strains (designated RCS1, -2, and -10) developed on the NON/Lt background carry variable numbers of these quantitative trait loci that elicit differential weight gain and male glucose intolerance syndromes of variable severity. We previously showed that RCS1 and -2 mice responded to chronic Rosi therapy without severe steatosis, whereas RCS10 males were moderately sensitive. In contrast, another recombinant congenic strain, RCS8, responded to Rosi therapy with the extreme hepatosteatosis observed in the F1. Longitudinal changes in multiple plasma analytes, including insulin, the adipokines leptin, resistin, and adiponectin, and plasminogen activator inhibitor-1 (PAI-1) allowed profiling of the differential Rosi responses in steatosis-exacerbated F1 and RCS8 males vs. the resistant RCS1 and RCS2 or moderately sensitive RCS10. Of these biomarkers, PAI-1 most effectively predicted adverse drug responses. Unexpectedly, mean resistin concentrations were higher in Rosi-treated RCS8 and RCS10. In summary, longitudinal profiling of multiple plasma analytes identified PAI-1 as a useful biomarker to monitor for differential pharmacogenetic responses to Rosi in these new mouse models of T2D.

Novel leptin receptor mutation in NOD/LtJ mice suppresses type 1 diabetes progression: I. Pathophysiological analysis.

A spontaneous single-base mutation in the leptin receptor of type 1 diabetes-prone NOD/LtJ mice (designated as Lepr(db-5J)) produced a glycine640valine transversion in the extracellular domain. All mutant mice became obese and hyperinsulinemic at weaning, with 70-80% developing early-onset hyperglycemia. However, these obese diabetic mice continued to gain weight without insulin therapy. Spontaneous diabetes remission was observed in all obese females and a subset of obese males. Insulitis was largely limited to islet perimeters, with intraislet insulitis infrequently observed. In 17 obese males (age 39 weeks), we observed phenotypic heterogeneity, including full remission from hyperglycemia (24%), intermediate hyperglycemia with elevated body weight (41%), and severe hyperglycemia and weight loss (35%). The remitting normoglycemic and intermediate hyperglycemic phenotypes were associated with extensive beta-cell hyperplasia. Unlike the extensive intraislet insulitis present in diabetic lean NOD/Lt mice, the severe obese diabetic phenotype was associated with islet atrophy without extensive intraislet insulitis. These results indicated that the manipulation of the leptin/leptin receptor axis may provide a novel means of downregulating autoimmunity in type 1 diabetes and confirmed a role for leptin as a mediator in the development of this disease in NOD mice.

Rapamycin treatment benefits glucose metabolism in mouse models of type 2 diabetes.

Numerous studies suggest that rapamycin treatment promotes insulin resistance, implying that rapamycin could have negative effects on patients with, or at risk for, type 2 diabetes (T2D). New evidence, however, indicates that rapamycin treatment produces some benefits to energy metabolism, even in the context of T2D. Here, we survey 5 mouse models of T2D (KK, KK-Ay, NONcNZO10, BKS-db/db, TALLYHO) to quantify effects of rapamycin on well-recognized markers of glucose homeostasis within a wide range of T2D environments. Interestingly, dietary rapamycin treatment did not exacerbate impaired glucose or insulin tolerance, or elevate circulating lipids as T2D progressed. In fact, rapamycin increased insulin sensitivity and reduced weight gain in 3 models, and decreased hyperinsulinemia in 2 models. A key covariate of this genetically-based, differential response was pancreatic insulin content (PIC): Models with low PIC exhibited more beneficial effects than models with high PIC. However, a minimal PIC threshold may exist, below which hypoinsulinemic hyperglycemia develops, as it did in TALLYHO. Our results, along with other studies, indicate that beneficial or detrimental metabolic effects of rapamycin treatment, in a diabetic or pre-diabetic context, are driven by the interaction of rapamycin with the individual model's pancreatic physiology.

Differential levels of diabetogenic stress in two new mouse models of obesity and type 2 diabetes.

The genetic basis for the more common forms of human obesity predisposing to insulin resistance and development of type 2 diabetes is multigenic rather than monogenic in origin. New mouse "diabesity" models have been created by combining independent diabetes risk-conferring quantitative trait loci from two unrelated parental strains: New Zealand Obese (NZO/HlLt) and Nonobese Nondiabetic (NON/Lt). F1 hybrid males, heterozygous at all polymorphic autosomal loci distinguishing the two parental strains, are driven to obesity-induced diabetes (diabesity) at high frequencies. This review focuses on two new recombinant congenic strains (RCSs) developed by introgressing multiple NZO/HlLt chromosomal segments into the nominally diabesity-resistant NON/Lt strain background. Both RCSs gain more weight than NON animals. Although exhibiting comparable weight gain and adiposity, only one of the two RCSs develops diabetes. Hence, these two RCSs will be instructive in elucidating genetic and pathophysiological differences underlying uncomplicated obesity syndromes versus diabetogenic obesity (diabesity) syndromes. Unlike mice with null mutations in a single gene producing morbid obesity, the new models develop a more moderate obesity produced by the interaction of numerous genes with relatively small effects. These RCSs are differentially sensitive to adverse side effects of thiazolidinediones and thus should be particularly useful for pharmacogenetic analyses.

Deconstructing and reconstructing obesity-induced diabetes (diabesity) in mice.

Obesity-driven type 2 diabetes (diabesity) involves complex genetic and environmental interactions to trigger disease. Here, we combine variable numbers of known quantitative trait loci (QTL) for obesity and diabetes contributed by New Zealand Obese (NZO/HlLt) and Nonobese Nondiabetic (NON/Lt) strains in the form of 10 interval-directed recombinant congenic strains (RCS), with NON/Lt as the background strain, to dissect the genetic interactions involved. All 10 RCS gain significantly more weight than the NON parental strain, but none are as obese as the parental, diabetes-prone NZO. Diabetes development in these RCS at F12 ranges between 0 and 100%, depending on genetic constitution. RCS-2, -1, and -10 represent a step-wise increase in numbers of specific diabetogenic QTL, resulting in a step-wise increase in diabetes incidence. RCS-10 recreates the 100% incidence seen in (NZOxNON)F1 males, but with less weight gain. Similarly, RCS-6, -7, -8, and -9 represent diabetes-prone strains with different combinations of diabetogenic QTL. RCS-3, -4, and -5 represent obese strains that do not transit to diabetes. Because these obesity and diabetes syndromes reflect different collections of QTL, rather than null mutations in the leptin or leptin receptor genes, they are extremely relevant as models for the polygenic obesity/diabesity syndromes in humans.

Caspase-1 is not required for type 1 diabetes in the NOD mouse.

Interleukin (IL)-1 beta and IL-18 are two cytokines associated with the immunopathogenesis of diabetes in NOD mice. Both of these cytokines are cleaved by caspase-1 to their biologically active forms. IL-1 is a proinflammatory cytokine linked to beta-cell damage, and IL-18 stimulates production of interferon (IFN)gamma in synergy with IL-12. To examine the effects produced by caspase-1 deficiency on diabetes development in NOD/Lt mice, a disrupted Casp1 gene was introduced by a speed congenic technique. Casp1(-/-) bone marrow-derived macrophages stimulated with lipopolysaccharide produced no detectable IL-18, fourfold lower IL-1 beta, and 20-30% less IL-1 alpha than macrophages from wild-type Casp1(+/+) or Casp1(+/-) controls. Unexpectedly, despite reduced IL-1 and IL-18, there was no change in the rate of diabetes or in total incidence as compared with that in wild-type NOD mice. IL-1 reportedly makes an important pathological contribution in the multidose streptozotocin model of diabetes; however, there was no difference in sensitivity to streptozotocin between NOD mice and NOD.Casp1(-/-) mice at 40 mg/kg body wt or at 25 mg/kg body wt dosage levels. These findings show that caspase-1 processing of IL-1 beta and IL-18 is not absolutely required for mediation of spontaneous or chemically induced diabetes pathogenesis in the NOD mouse.

Contributions of dysregulated energy metabolism to type 2 diabetes development in NZO/H1Lt mice with polygenic obesity.

New Zealand Obese (NZO) male mice develop a polygenic juvenile-onset obesity and maturity-onset hyperinsulinemia and hyperglycemia (diabesity). Here we report on metabolic and molecular changes associated with the antidiabesity action of CL316,243 (CL), a beta(3)-adrenergic receptor agonist. Dietary CL treatment initiated at weaning reduced the peripubertal rise in body weight and adiposity while promoting growth without suppressing hyperphagia. The changes in adiposity, in turn, suppressed development of hyperinsulinemia, hyperleptinemia, hyperlipidemia, and hyperglycemia. These CL-induced alterations were reflected by decreased adipose tissue mass, increased expression of transcripts for uncoupling protein-1 (UCP-1), peroxisome proliferator-activated receptor alpha (PPARalpha), peroxisome proliferater-activated receptor coactivator-1 (PGC-1), and robust development of brown adipocyte function in white fat. Increased drug-mediated energy dissipation elicited a 1.5 degrees C increase in whole body temperature under conditions of increased food intake but with no change in physical activity. Indirect calorimetry of mice treated with CL showed both increased energy expenditure and a restoration of a prominent diurnal pattern in the respiratory exchange ratio suggesting improved nutrient sensing. Our data suggest that CL promotes increased energy dissipation in white and brown fat depots by augmenting thermogenesis and by metabolic re-partitioning of energy in a diabesity-protective fashion. This is the first report demonstrating the effects of dietary beta(3)-agonist in preventing the onset of diabesity in a polygenic rodent model of type 2 diabetes.

Rapamycin ameliorates nephropathy despite elevating hyperglycemia in a polygenic mouse model of type 2 diabetes, NONcNZO10/LtJ.

While rapamycin treatment has been reported to have a putatively negative effect on glucose homeostasis in mammals, it has not been tested in polygenic models of type 2 diabetes. One such mouse model, NONcNZO10/LtJ, was treated chronically with rapamycin (14 ppm encapsulated in diet) and monitored for the development of diabetes. As expected, rapamycin treatment accelerated the onset and severity of hyperglycemia. However, development of nephropathy was ameliorated, as both glomerulonephritis and IgG deposition in the subendothelial tuft were markedly reduced. Insulin production and secretion appeared to be inhibited, suppressing the developing hyperinsulinemia present in untreated controls. Rapamycin treatment also reduced body weight gain. Thus, rapamycin reduced some of the complications of diabetes despite elevating hyperglycemia. These results suggest that multiple factors must be evaluated when assessing the benefit vs. hazard of rapamycin treatment in patients that have overt, or are at risk for, type 2 diabetes. Testing of rapamycin in combination with insulin sensitizers is warranted, as such compounds may ameliorate the putative negative effects of rapamycin in the type 2 diabetes environment.

Comparison of Two New Mouse Models of Polygenic Type 2 Diabetes at the Jackson Laboratory, NONcNZO10Lt/J and TALLYHO/JngJ.

This review compares two novel polygenic mouse models of type 2 diabetes (T2D), TALLYHO/JngJ and NONcNZO10/LtJ, and contrasts both with the well-known C57BLKS/J-Lepr(db) (db/db) monogenic diabesity model. We posit that the new polygenic models are more representative of the "garden variety" obesity underlying human T2D in terms of their polygenetic rather than monogenic etiology. Moreover, the clinical phenotypes in these new models are less extreme, for example, more moderated development of obesity coupled with less extreme endocrine disturbances. The more progressive development of obesity produces a maturity-onset development of hyperglycemia in contrast to the juvenile-onset diabetes observed in the morbidly obese db/db model. Unlike the leptin receptor-deficient db/db models with central leptin resistance, the new models develop a progressive peripheral leptin resistance and are able to maintain reproductive function. Although the T2D pathophysiology in both TALLYHO/JngJ and NONcNZO10/LtJ is remarkably similar, their genetic etiologies are clearly different, underscoring the genetic heterogeneity underlying T2D in humans.

Diet-induced obesity in two C57BL/6 substrains with intact or mutant nicotinamide nucleotide transhydrogenase (Nnt) gene.

The C57BL/6J (B6/J) male mouse represents a standard for diet-induced obesity (DIO) and is unique in expressing a loss-of-function nicotinamide nucleotide transhydrogenase (Nnt) gene. This mutation was associated with a marked reduction in glucose-stimulated insulin secretion from B6/J islets in vitro and moderately impaired glucose clearance in vivo. To assess the contribution of this Nnt mutation, we compared DIO responsiveness of Nnt-mutant B6/J males to Nnt wild-type C57BL/6NJ (B6/NJ) males over a 14-week period of feeding a high-fat (60% of calories) diet. Initial mean body weights at 6 weeks did not distinguish the substrains and both substrains were DIO-sensitive. However, B6/J males outgained the B6/NJ males, with a significant 3 g higher mean body weight at 20 weeks accompanied by significant increases in both lean and fat mass. Mean nonfasting serum glucose over time was also significantly higher in B6/J males, as was impairment of glucose tolerance assessed at 8 and 20 weeks of age. Serum leptin, but not insulin, was significantly higher in B6/J males over time. Potential contributions of the wild-type Nnt gene were demonstrable on a lower fat diet (10% of calories) where a significantly greater weight gain over time by B6/NJ males was correlated with a significantly higher serum insulin. In conclusion, DIO developed in response to 60% fat feeding regardless of Nnt allele status. Contribution of the B6/J-unique Nnt mutation was most evident in response to 10% fat feeding that resulted in reduced serum insulin and weight gain compared to B6/NJ males.

NOD x 129.H2(g7) backcross delineates 129S1/SvImJ-derived genomic regions modulating type 1 diabetes development in mice.

OBJECTIVE: Introduction of genes targeted in 129/Sv embryonic stem (ES) cells into NOD mice brings about linked genes that may modulate type 1 diabetes. Our objective was to identify 129S1/SvJ non-MHC regions contributing type 1 diabetes resistance or susceptibility in backcross to NOD/LtJ. RESEARCH DESIGN AND METHODS: After congenic transfer of the NOD H2(g7) haplotype onto 129S1/Sv, 310 females were produced by NOD x (NOD x 129.H2(g7))F1 backcross (N2). A genome scan for quantitative trait locus (QTL) affecting clinical diabetes, age of diabetes onset, and insulitis severity was performed using subphenotype characteristics to improve power and resolution for detection of diabetes susceptibility loci. RESULTS: Thirty-six of 310 (11.6%) N2 females developed type 1 diabetes between 14 and 40 weeks. Significant evidence of linkage for only a single previously reported Idd complex locus (Idd10/17/18, chromosome [Chr] 3) was indicated for clinical diabetes. The quantitative traits of insulitis either alone or combined with age at type 1 diabetes onset were significantly linked to known Idd regions on Chr 1 (Idd5 region), Chr 4 (Idd9 region), Chr 8 (Idd22), Chr 11 (Idd4.3), and proximal Chr 17 (Idd16 region). Significant 129S1/Sv resistance contributions were identified on Chr 1, 15 (two loci), and 19, with suggestive evidence for additional novel 129/Sv resistance QTL on Chr 5 and 17 and susceptibility on Chr 2. CONCLUSIONS: The 129S1/SvJ genome harbors collections of both known and potentially novel non-MHC Idd loci. Investigators targeting 129/Sv genes mapping within chromosomal regions reported herein or elsewhere in the genome need to exclude potential contributions from linked Idd loci by generating a NOD.129 control strain expressing the nontargeted allele.