Chronic stress aggravates glucose intolerance in leptin receptor-deficient (db/db) mice

Genetic predisposition and environmental challenges interact to determine individual vulnerability to obesity and type 2 diabetes. We previously established a mouse model of chronic subordination stress-induced hyperphagia, obesity, metabolic like-syndrome and insulin resistance in the presence of a high-fat diet. However, it remains to be established if social stress could also aggravate glucose intolerance in subjects genetically predisposed to develop obesity and type 2 diabetes. To answer this question, we subjected genetically obese mice due to deficiency of the leptin receptor (db/db strain) to chronic subordination stress. Over five weeks, subordination stress in db/db mice led to persistent hyperphagia, hyperglycemia and exacerbated glucose intolerance altogether suggestive of an aggravated disorder when compared to controls. On the contrary, body weight and fat mass were similarly affected in stressed and control mice likely due to the hyperactivity shown by subordinate mice. Stressed db/db mice also showed increased plasma inflammatory markers. Altogether our results suggest that chronic stress can aggravate glucose intolerance but not obesity in genetically predisposed subjects on the basis of a disrupted leptin circuitry.     

Genetic Regulation of Plasma Corticosterone Concentration and its Response to Castration and Allogeneic Tumour Growth in the Mouse

EXCESS fat deposition after castration is thought to be a response to hyperinsulinism induced by an increased level of adrenal glucocorticoids¹. Two mutant alleles, lethal yellow (A^y) and viable yellow (A^vy), at the agouti locus in the mouse induce excess fat deposition; the A^y allele has also been found to induce insulin resistance². Katsh³ concluded that in adrenalectomized KL strain mice a considerable portion of the high insulin tolerance depended on normal adrenal function. In the inbred YS/Wf and VY/Wf strains, both yellow pheno-types modulate serum insulin concentration⁴. Castration of inbred YS strain males causes a large decrease in serum insulin⁴, suggesting a possible relationship¹ to the concentration of adrenal glucocorticoids. Growth of allogeneic tumour cells has different effects on the serum insulin concentrations of YS and VY strain mice⁴.     

Anti-Insulin Receptor Autoantibodies Are Not Required for Type 2 Diabetes Pathogenesis in NZL/Lt Mice,a New Zealand Obese (NZO)-Derived Mouse Strain

The New Zealand obese (NZO) mouse strain shares with the related New Zealand black (NZB) strain a number of immunophenotypic traits. Among these is a high proportion of B-1 B lymphocytes, a subset associated with autoantibody production. Approximately 50% of NZO/HlLt males develop a chronic insulin-resistant type 2 diabetes syndrome associated with 2 unusual features: the presence of B lymphocyte–enriched peri-insular infiltrates and the development of anti-insulin receptor autoantibodies (AIRAs). To establish the potential pathogenic contributions ofBlymphocytes and AIRAs in this model, a disrupted immunoglobulin heavy chain gene (Igh-6) congenic on the NZB/BlJ background was backcrossed 4 generations into the NZO/HlLt background and was then intercrossed to produce mice that initially segregated for wild-type versus the mutant Igh-6 allele and thus permitted comparison of syndrome development. A new flow cytometric assay (AIRA binding to transfected Chinese hamster ovary cells stably expressing mouse insulin receptor) showed IgM and IgG subclass AIRAs in serum from Igh-6 intact males, but not in Igh6^null male serum. However, the absence of B lymphocytes and antibodies distinguishing mutant from wild-type males failed to significantly affect diabetes-free survival. The Igh6^nullmales gained weight less rapidly than wild-type males, probably accounting for a retardation, but not prevention, of hyperglycemia. Thus, AIRA and the Blymphocyte component of the peri-insulitis in chronic diabetics were not essential either to development of insulin resistance or to eventual pancreatic beta cell failure and loss. A new substrain, designated NZL, was generated by inbreeding Igh-6 wild-type segregants. Currently at the F10 generation, NZL mice exhibit the same juvenile-onset obesity as NZO/HlLt males, but develop type 2 diabetes at a higher frequency (> 80%). Also, unlike NZO/HlLt mice that are difficult to breed, the NZL/Lt strain breeds well and thus offers clear advantages to obesity/diabetes researchers.     

Influence of Maternal Phenotype on Metabolic Differentiation of Agouti Locus Mutants in the Mouse

The results of extensive breeding experiments indicate that the phenotypic differentiation of embryos carrying the viable yellow, A ^vy, or mottled, a^m, mutations is influenced to a major extent by the agouti locus genotype and the strain genome of the dam. The A^vy/a and a^m/a genotypes are each expressed in a spectrum of coat color phenotypes. These can be grouped into two classes, mottled and pseudoagouti.—In a reciprocal cross of C57BL/6JNIcrWf and AM/Wf-a^m/a^m mice, 29.5% of the offspring of C57BL/6 dams were of the pseudoagouti phenotype, whereas no pseudoagouti offspring were produced by AM strain dams.—Mottled yellow A^vy/a mice become obese and tumor formation is enhanced in these mice in comparison with the lean pseudoagouti A^vy/a siblings.—In two different reciprocal crosses using four different inbred strains, the proportion of pseudoagouti A^vy/a offspring differed according to the strain of the dam. Regardless of strain, mottled yellow A ^vy/a dams produced significantly fewer pseudoagouti A ^vy/a offspring than did black a/a dams.—The data suggest that metabolic differentiation of A^vy/a zygotes into phenotypic classes with different susceptibilities to obesity and tumor formation is influenced to a considerable degree by the metabolic characteristics of the oviductal and uterine environment of the dam.     

Tyrosinase Activity (TH,DO, PAGE-Defined Isozymes) and Melanin Production in Regenerating Hairbulb Melanocytes of Lethal Yellow (Ay/a), Black (a/a), Agouti (AwJ/AwJ) and Albino (a/a/c2J/c2J) Mice (C57BL/6J)

We compared tyrosinase activity (TH, DO, and native PAGE-defined isozymes) and melanin production in participate and soluble fractions of hairbulb melanocytes of lethal yellow (A^y/a C/C), nonagouti black (a/a C/C), and albino (a/a c^2J/c^2J) of 3-, 6-, 9-, and 12-day regenerating hairbulbs. With respect to tyrosine hydroxylase (TH) and dopa oxidase (DO) activities, A^y/a melanocytes possessed only 25-35% of the activity of a/a; there were no genotype differences in either the subcellular distribution of activity in soluble and particulate fractions or in the relative increases of activity over the 12-day developmental period. TH data on wild-type agouti (A^wJ/A^wJ) mice over the 3-11 day regeneration interval showed an activity intermediate between that of a/a and A^y/a; the rate of TH increase reflected black and yellow phases of the agouti hair cycle. Analyses of the number and densities of dopa-sensitive bands following native PAGE of 3-, 6-, 9-, and 12-day hairbulb fractions of a/a and A^y/a mice suggested stage-dependent patterns. A comparison of rates and amounts of melanin production in 3-, 6-, 9-, and 12-day fractions showed consistent melanin production in A^y/a to be 10-20% that of a/a; however, fold increases in melanin production over the four stages were similar between genotypes. Overall, tyrosinase activity data support the notion that agouti locus modification of tyrosinase activity is a graded or quantitative rather than a qualitative phenomenon.     

Agouti Alleles Influence Thiol Concentrations in Hair Follicles and Extrafollicular Tissues of Mice (Ay/a,AwJ/AwJ,a/a)

Agouti protein (AP) expression in the wild-type agouti mouse (A^wJ/A^wJ) coincides with a switch in hair follicle melanogenesis from black (eumelanin) to yellow (pheomelanin). Ectopic overexpression of AP in the lethal yellow (A^y/a) mouse cause a pure yellow coat and the lethal yellow syndrome. Thiol concentrations may control the conversion of dopaquinone to pheomelanin in hair follicle melanocytes. Glutathione (GSH) also plays important roles in cellular health and protection. Using HPLC, cysteine and GSH were measured in 1) hair follicles, liver and serum of A^y/a, A^wJ/A^wJ, and a/a (black) mice, and 2) adipose and spleen tissues of A^y/a and a/a mice on day 9 of regenerating hair growth (late pheomelanin phase). Agouti locus alleles influence thiol metabolism in hair follicles and in other systemic tissues. A^y/a hair follicles and serum showed highest cysteine and lowest GSH levels. A^wJ/A^wJ mice showed intermediate levels, while a/a hair follicles and serum had lowest cysteine and highest GSH concentrations. In the hair follicle, cysteine (likely derived from enzymatic degradation of GSH) appears to be the primary pheomelanogenic thiol. Agouti locus alleles may also directly or indirectly affect thiol concentrations in systemic tissues like liver and spleen. Cysteine in spleen extracts showed A^y/a > a/a (P > 0.01). An A^y-induced imbalance of thiol metabolism (altering GSH concentrations in multiple tissues) may contribute to the pleiotropic defects of the lethal yellow syndrome.     

Agouti-Related Maturation and Tissue Distribution of oc-Melanocyte Stimulating Hormone in Wild-Type (AwJ/AwJ) and Mutant (Ay/a,a/a) Mice

Because of ectopic overproduction of agouti protein, yellow alleles (A^y and A^vy) of the murine agouti gene may secondarily modulate the synthesis, maturation (i.e., acetylation), and/or tissue deployment of α-Melanocyte Stimulating Hormone (MSH). We used HPLC to test the hypothesis that A^y/a mice exhibit altered concentrations of desacetyl-, monoacetyl-, and diacetyl-α-MSH in pituitaries, sera, and telogen hair bulbs when compared to black (a/a) mice. We also used RIA to measure total MSH in those same tissues of A^y/a, a/a, and white-bellied agouti (A^wJ/A^wJ) mice (Strain C57BL/6J). We found no evidence that A^y/a mice possessed an imbalance of des-, mono-, and diacetylated α-MSH species. However, radioimmunoassay (RIA) analyses of total MSH suggest that wild-type agouti mice (A^wJ/A^wJ) exhibited significantly decreased (P < 0.05) tissue levels of total α-MSH in pituitaries, sera, and regenerating hair bulbs when compared to those of mutant A^y/a and a/a mice.     

Fluorescence spectrophotometric analysis of melanins in the house mouse

We extracted the yellow melanin (phaeomelanin), black melanin (eumelanin), and mixed type of melanin from dorsal hair of dominant yellow (A ^y /a), non-agouti (a/a), and agouti (A/A) mice, respectively. Spectrophotometric and fluorescence spectrophotometric analysis demonstrated that the yellow melanin was qualitatively distinct from the black melanin and that the agouti hair contained both types of pigment.This work was supported by Grant 244004 from the Ministry of Education. Part of this work was presented at the X International Pigment Cell Conference.     

Inheritance of colour and coat in the Belgian Shepherd dog

The several colours and coats of the Belgian Shepherd dog are shown to be due primary to combinations of the following genes: dominant black (A ^s ), dominant yellow (A ^y ), chinchilla (ch), long hair (l) and wire hair (Wh). The gene for black and tan (a ^t ) is or has been present in the breed. All of the dominant yellow dogs exhibit a black facial mask and extensive suffusion of black guard hairs on the body.     

Dermal-epidermal interactions and the action of alleles at the agouti locus in the mouse

In the mouse, alleles at the agouti locus determine eumelanin or pheomelanin synthesis by the follicular melanocytes. Previous studies have identified the dermis as the site of action of these alleles. However, a recent investigation utilizing the yellow (A^y) allele suggested a possible role of the epidermis in the expression of agouti locus alleles. Using dermal-epidermal recombinations of embryonic skin of various agouti genotypes, the present investigation supports the role of both the dermis and epidermis. If nonagouti ($\text{a}\text{a}$) dermis is recombined with agouti ($\text{A}\text{A}$) epidermis, the resulting hairs are pigmented in the nonagouti pattern. The reciprocal recombination of agouti dermis and nonagouti epidermis results in hairs pigmented in the agouti pattern. The recombinations of yellow ($\text{A}{}^{\mathrm{y}}\text{a}$) dermis and agouti or extreme nonagouti ($\text{a}{}^{\mathrm{e}}\text{a}{}^{\mathrm{e}}$) epidermis result in hairs completely pigmented in the yellow pattern (pheomelanin). However, when extreme nonagouti or agouti dermis is recombined with yellow epidermis, the resulting hairs are completely pigmented with pheomelanin. Similar results occur in recombinations of “young” yellow epidermis (13 days) and “old” dermis (17 days) even though dermal papillae are present. The role of dermal-epidermal interactions in the expression of agouti alleles as well as possible explanations for the unique action of the yellow allele are discussed.     

Genetics of obesity in KK mouse and effects of A y allele on quantitative regulation

KK mouse is known as a polygenic model for non-insulin-dependent diabetes mellitus with moderate obesity. To identify the quantitative trait loci (QTLs) responsible for the body weight in KK, linkage analysis with 97 microsatellite markers was carried out into 192 F₂ progeny, comprising 93 mice with a/a genotype at agouti locus and 99 mice with A ^y /a genotype, of a cross between C57BL/6J female and KK-A^y (A^y congenic) male, thereby the influence of A ^y allele on the quantitative regulation of body weight was also examined. In F₂ a/a mice, we identified a QTL on Chromosome (Chr) 4, and two loci with suggestive linkage on Chrs 15 and 18. In F₂ A ^y /a mice, a QTL was identified on Chr 6, and two loci with suggestive linkage were identified on Chrs 4 and 16. That the QTL on Chr 4 was held in common between F₂ a/a and F₂ A ^y /a progenies implies that this locus may be a primary component regulating body weight in KK and KK-A^y. These results suggest that the body weight in KK is controlled by multiple genes, and the different combination of loci is involved in the presence of A ^y allele. The QTL on Chr 6 seemed to determine the body weight by controlling fat deposition, because the linkage was identified on body weight and adiposity, and is suggested to be a component involved in the metabolic pathway in obesity caused by the A ^y allele. Received: 16 December 1997 / Accepted: 16 March 1998     

Dermal-epidermal interactions and the site of action of the yellow (Ay) and nonagouti (a) coat color genes in the mouse

The alleles at the agouti locus in mice determine whether eumelanin or pheomelanin is synthesized by the follicular melanocytes. Previous studies have indicated the dermis as the site of action of the agouti alleles, while implying that the epidermis plays only a passive role. Using methods of dermal-epidermal recombinations of embryonic yellow (A^y) and nonagouti (a) mouse skin, the study reported here indicates that the epidermis, as well as the dermis, plays a role in the action of the agouti alleles. When yellow dermis is recombined with nonagouti epidermis, the hairs produced contain only pheomelanin, thus substantiating the role of the dermis. However, the reciprocal combination of nonagouti dermis and yellow epidermis also produces hairs containing pheomelanin, indicating a more important role for the epidermis. The role of the dermal-epidermal interactions in the action of the alleles at the agouti locus is discussed.     

Inheritance of coat colour in the German Pinscher dog

The two primary colour varieties of the German Pinscher breed are the red and the black and tan. Respectively, these are produced by the dominant yellow allele A ^y and the black and tan allele a ^t of the agouti locus. The dilute gene d is present in the breed at a low frequency and produces the rarer isabella and blue and tan colours, with the genotypes A ^y -dd and a ^t dd, respectively.     

High fat diet induced insulin resistance and glucose intolerance are gender-specific in IGF-1R heterozygous mice

Interactions between genes and environment play a critical role in the pathogenesis of type 2 diabetes. Low birth weight, due to genetic and environmental variables affecting fetal growth, is associated with increased susceptibility to the development of type 2 diabetes and metabolic disorders in adulthood. Clinical studies have shown that polymorphisms in the Insulin-like growth factor 1 (IGF-1) gene or heterozygous mutations in IGF-1 and IGF-1 receptor (IGF-1R) genes, resulting in reduced IGF-1 action, are associated with low birth weight and post-natal growth. Mice lacking one of the IGF-1R alleles (Igf1r^+/−) exhibit a 10% reduction in post-natal growth, and develop glucose intolerance (males) and insulin resistance (males and females) as they age. To investigate whether adverse environmental factors could accelerate the onset of the metabolic syndrome, we conducted a short duration intervention of high fat diet (HFD) feeding in male and female Igf1r^+/− and wild-type (WT) control mice. The HFD resulted in insulin resistance, hyperglycemia, and impaired glucose tolerance in males of both genotypes whereas in females exacerbated diabetes was observed only in the Igf1r^+/− genotype, thus suggesting a sexual dimorphism in the influence of obesity on the genetic predisposition to diabetes caused by reduced IGF-1 action.     

Beneficial effect of oral administration of Lactobacillus casei strain Shirota on insulin resistance in diet-induced obesity mice

Aims: This study aimed at determining whether oral administration of a probiotic strain, Lactobacillus casei strain Shirota (LcS), can improve insulin resistance, which is the underlying cause of obesity‐associated metabolic abnormalities, in diet‐induced obesity (DIO) mice. Methods and Results: DIO mice were fed a high‐fat diet without or with 0·05% LcS for 4 weeks and then subjected to an insulin tolerance test (ITT) or oral glucose tolerance test (OGTT). Oral administration of LcS not only accelerated the reduction in plasma glucose levels during the ITT, but also reduced the elevation of plasma glucose levels during the OGTT. In addition, plasma levels of lipopolysaccharide‐binding protein (LBP), which is a marker of endotoxaemia, were augmented in the murine models of obese DIO, ob/ob, db/db and KK‐A^y and compared to those of lean mice. LcS treatment suppressed the elevation of plasma LBP levels in DIO mice, but did not affect intra‐abdominal fat weight. Conclusions: LcS improves insulin resistance and glucose intolerance in DIO mice. The reduction in endotoxaemia, but not intra‐abdominal fat, may contribute to the beneficial effects of LcS. Significance and Impact of the Study: This study suggests that LcS has the potential to prevent obesity‐associated metabolic abnormalities by improving insulin resistance.     

Design,synthesis, and effects of novel phenylpyrimidines as glucagon receptor antagonists

The hormone glucagon increases blood glucose levels through increasing hepatic glucose output. In diabetic patients, dysregulation of glucagon secretion contributes to hyperglycemia. Thus, the inhibition of glucagon receptor is one target for the treatment of hyperglycemia in type 2 diabetes. Here we designed and synthesized a series of small molecules based on phenylpyrimidine. Of these, the compound (R)-7a most significantly decreased the glucagon-induced cAMP production and glucagon-induced glucose production during in vitro and in vivo assays. In addition, (R)-7a showed good efficacy in glucagon challenge tests and lowered blood glucose levels in diabetic db/db mice. Our results suggest that the compound (R)-7a could be a potential glucose-lowering agent for treating type 2 diabetes.     

Ethnic disparity in hemoglobin A1c levels among normoglycemic offspring of parents with type 2 diabetes mellitus

ObjectiveTo investigate the racial/ethnic disparities in hemoglobin A_1c levels among nondiabetic persons with similar parental history of type 2 diabetes mellitus.MethodsWe studied a community-based sample of adult offspring of parents with type 2 diabetes mellitus. Measurements included anthropometry, hematology assessments, serial fasting plasma glucose, oral glucose tolerance testing, plasma insulin, hemoglobin A_1c, insulin sensitivity, and b-cell function, using a homeostasis model assessment.ResultsThe study included 302 participants (135 white, 167 black). Compared with white participants, black participants had lower fasting plasma glucose levels (91.9 ± 0.51 mg/dL vs 93.6 ± 0.50 mg/dL, P = .015), lower area under the curve of plasma glucose during oral glucose tolerance testing (P = <.001), higher body mass index (31.1 ± 0.61 kg/m² vs 28.5 ± 0.57 kg/m², P = <.001), and similar insulin sensitivity and b-cell function. Hemoglobin A_1c was higher in black participants than in white participants (5.68 ± 0.033% vs 5.45 ± 0.028%, P <.001). The absolute black-white difference in hemoglobin A_1c level of approximately 0.22% persisted after adjusting for age, hemoglobin, hematocrit, body mass index, waist circumference, fasting plasma glucose, glucose area under the curve, and other covariates.ConclusionsAmong healthy offspring of parents with type 2 diabetes mellitus in this study, African American participants had higher hemoglobin A_1c levels than white participants after adjusting for age, adiposity, blood glucose, and known variables. Thus, plasma glucose level is more valid than hemoglobin A_1c for diagnosing prediabetes or diabetes in black persons. (Endocr Pract. 2012; 18:356-362)     

Inheritance of coat colour in the Anatolian Shepherd dog

The predominant colour of the Anatolian Shepherd dog varies from a dark fawn to light red, with a variable black muzzle and face (mask). Evidence is presented that the colour is due to the dominant yellow allele (A ^y) of the agouti locus. Two other frequent colours are white spotting, due to the piebald allele (s ^p), and the chinchilla allele (ch). Two rarer colours are the agouti wolf-grey wild type (A ⁺) and a light fawn with a blue facial mask, due to the dilution allele (d).     

Stearoyl-CoA desaturase-1 deficiency attenuates obesity and insulin resistance in leptin-resistant obese mice

Obesity and adiposity greatly increase the risk for secondary conditions such as insulin resistance. Mice deficient in the enzyme stearoyl-CoA desaturase-1 (SCD1) are lean and protected from diet-induced obesity and insulin resistance. In order to determine the effect of SCD1 deficiency on various mouse models of obesity, we introduced a global deletion of the Scd1 gene into leptin-deficient ob/ob mice, leptin-resistant Agouti (A^y/a) mice, and high-fat diet-fed obese (DIO) mice. SCD1 deficiency lowered body weight, adiposity, hepatic lipid accumulation, and hepatic lipogenic gene expression in all three mouse models. However, glucose tolerance, insulin, and leptin sensitivity were improved by SCD1 deficiency only in A^y/a and DIO mice, but not ob/ob mice. These data uncouple the effects of SCD1 deficiency on weight loss from those on insulin sensitivity and suggest a beneficial effect of SCD1 inhibition on insulin sensitivity in obese mice that express a functional leptin gene.