Maternal environment and genotype interact to establish diabesity in mice

Abstract

Obesity, a major risk factor for type II diabetes, is becoming more prevalent in Western populations consuming high calorie diets while expending less energy both at the workplace and at home. Most human obesity, and probably most type II diabetes as well, reflects polygenic rather than monogenic inheritance. We have genetically dissected a polygenic mouse model of obesity-driven type II diabetes by outcrossing the obese, diabetes-prone, NZO (New Zealand Obese)/HlLt strain to the relatively lean NON (Nonobese Nondiabetic)/Lt strain, and then reciprocally backcrossing obese F1 mice to the lean NON/Lt parental strain. A continuous distribution of body weights was observed in a population of 203 first backcross males. The 22% of first backcross males developing overt diabetes showed highest peripubertal weight gains and earliest development of hyperinsulinemia. We report a complex diabetes-predisposing ("diabesity") QTL (Quantitative Trait Loci) on chromosome 1 contributing significant main effects to increases in body weight, plasma insulin, and plasma glucose. NZO contributed QTL with significant main effects on adiposity parameters on chromosomes 12 and 5. A NON QTL on chromosome 14 interacted epistatically with the NZO obesity QTL on chromosome 12 to increase adiposity. Although the main effect of the diabetogenic QTL on chromosome 1 was on rapid growth rather than adiposity, it interacted epistatically with the obesity QTL on chromosome 12 to increase plasma glucose levels. Additional complex epistatic interactions eliciting significant increases in body weight and/or plasma glucose were found between the NZO-contributed QTL on chromosome 1 and other NZO-contributed QTL on chromosomes 15 and 17, as well as with an NON-contributed QTL on chromosome 2. We further show that certain of these intergenic interactions are predicated on, or enhanced by, the maternal postparturitional environment. We show by cross-fostering experiments that the maternal environmental influence in part is because of the presence of early obesity-inducing factors in the milk of obese F1 dams. We also discuss a strategy for using recombinant congenic strains to separate and reassemble interacting QTL for future study.

Figure 1

Phenotypic relationships between body weight (BW), plasma insulin, and plasma glucose (PG). (A) Markedly different BW distributions distinguish the NZO/HlLt and NON/Lt parentals, whereas the BC1 males show a continuous BW distribution between these two extremes. (B) Relationship between BW and PG in this BC1 male population at 24 weeks showing that a BW threshold exists for diabesity development, with virtually all of the diabetic males having attained a BW ≥50 g. (C) Diabetes development in mice higher than the BW threshold is associated with extreme hyperinsulinemia. Males with BW >50 g but with a normal insulin level (<6 ng/mL) or even a high insulin level (6–24 ng/m) had normal mean PGs (216 + 33, 216 + 11mg/dl respectively) whereas those with an extremely high insulin level (>24 ng/mL) had a high mean PG (360 + 16mg/dl) (P < 0.0001). (D) Relationship between early development of hyperinsulinemia with rapid prematurational rate of weight gain. Males showing hyperinsulinemia by 16 weeks of age also showed the highest rate of weight gain and the highest rate of diabetes, accounting for the majority of the diabetics in the cross by termination. In Figure 1D, 12 mice were left out of the correlation because of oscillating phenotype and 16 because of missing data at one or more time points. Standard errors in D were so small that they could not be depicted in the figure.

Figure 2

Complexity of QTL (Quantitative Trait Loci) on chromosomes 1 and 15. (A) The peak of the QTL for BW (Body Weight) and PG (Plasma Glucose) on chromosome 1 spans a 14-cM region that probably consists of two separate but equal peaks marked by D1Mit411 and D1Mit76. For plasma insulin, the peak is much stronger for D1Mit411, although there is a distinct shoulder marked by D1Mit76. (B) Three separate loci on chromosome 15 show a suggestive effect on BW at progressive time points. The locus marked by D15Mit13 is only associated with early BW and thus probably a growth modifier. The locus marked by D15Mit26, 20 cM distal, is associated with later BW, gain, body mass index, and leptin, suggesting that it could be an adipocyte growth modifier. The third locus, another 20 cM distal, and marked by D15Mit159, is suggestively associated with late BW gain and significantly associated with PG. (LOD) logarithm of odds; (*) threshold for suggestive QTL; (**) threshold for significant QTL.

Figure 3

Maternal lactational effects on early weight gain. F1 and NON pups fostered on different lactational environments (obese F1 dam vs. lean NON dam) are significantly larger at postnatal day 18 if suckled on the obese F1 dam (P < 0.0001). Genotypic difference between F1 pups and NON pups is indicated by the fact that F1 pups will become significantly larger on the same lean NON lactational environment (P < 0.0001). Litter size was standardized to five to eight pups (mixed genders). Numbers of pups tested are shown in the bars. (BW) Body weight; (NON) nonobese nondiabetic.

Figure 4

Pairwise interactions between unlinked QTL. (A) The BW-increasing interaction between the homozygous NON allele marked by D6Mit275 with the distal NZO-derived locus identified on chromosome 17 and marked by D17Mit240. Both alleles failed to show a main effect QTL because their effect is dependent on the presence of the other locus which, in a backcross, would only happen in ∼25% of the population. (B) The BW-increasing interaction between the “diabesity” QTL from NZO on chromosome 1 (here marked by D1Mit46) and the NZO-derived allele marked by D15Mit26. (C) The NON-derived effect at D2Mit182 elevating PG is only apparent when a NON-derived modifier at D15Mit26 is present in homozygous state. (D) The elevation in PG attributable to the interaction between the F1 maternal environment with the NZO-derived allele marked by D17Mit61. (E,F) Homozygosity for the NON-derived allele on chromosome 14 marked by D14Mit212 epistatically enhances the ability of the strong NZO-derived QTL on chromosome 12 marked by D12Mit231 to increase AI and BMI. (BW) body weight, (NON) nonobese nondiabetic, (PG) plasma glucose, (AI) adiposity index, (BMI) body mass index.

Figure 5

Three-way interactions with maternal environment. (A) The interaction between the F1 maternal environment, the NZO-derived allele marked by D1Mit76, and the homozygous NON-derived allele marked by D2Mit109. The interaction is only discernible at the very earliest time point (4 weeks) suggesting that it is particularly age dependent. (B) The increase in BW because of the interaction of the NZO-derived alleles marked by D1Mit123 and D17Mit61 with the F1 maternal environment. In the presence of the NON maternal environment, there is no significant effect of either locus. (C–G) The effects on PG of interactions between the F1 maternal environment and five separate pairs of NZO-derived alleles on chromosomes 1 × 12, 1 × 17, 1 × 15, 12 × 15, and 17 × 15. All five show a similar pattern of dramatically increased mean PG into the diabetic range only when all three diabetogenic parameters are present. (B) body weight; (NON) nonobese nondiabetic; (PG) plasma glucose.