NOD mice have distinct metabolic and immunologic profiles when compared with genetically similar MHC-matched ICR mice

Abstract

Nonobese diabetic (NOD) mice are the most commonly used rodent model to study mechanisms relevant to the autoimmunity and immunology of type 1 diabetes. Although many different strains of mice have been used as controls for studies comparing nondiabetic lines to the NOD strain, we hypothesized that the parental strain that gave rise to the NOD line might be one of the best options. Therefore, we compared female ICR and NOD mice, which are matched at key major histocompatibility complex (MHC) loci, to understand their metabolic and immunologic similarities and differences. Several novel observations emerged: 1) NOD mice have greater circulating proinsulin when compared with ICR mice. 2) NOD mice display CD3+ and IBA1+ cell infiltration into and near pancreatic islets before hyperglycemia. 3) NOD mice show increased expression of the Il1b and Cxcl11 genes in islets when compared with islets from age-matched ICR mice. 4) NOD mice have a greater abundance of STAT1 and ICAM-1 protein in islets when compared with ICR mice. These data show that ICR mice, which are genetically similar to NOD mice, do not retain the same immunologic outcomes. Thus, ICR mice are an excellent choice as a genetically similar and MHC-matched control for NOD mice in studies designed to understand mechanisms relevant to autoimmune-mediated diabetes onset as well as novel therapeutic interventions.NEW & NOTEWORTHY Nonobese diabetic (NOD) mice have more proinsulin in circulation and STAT1 protein in islets compared with the major histocompatibility complex (MHC)-matched ICR line. NOD mice also display greater expression of cytokines and chemokines in pancreatic islets consistent with immune cell infiltration before hyperglycemia when compared with age-matched ICR mice. Thus, ICR mice represent an excellent control for autoimmunity and inflammation studies using the NOD line of mice.

Keywords: autoimmunity; islet; mice.

Graphical abstract

Figure 1.

Body composition and insulin sensitivity are similar in MHC-matched female NOD and ICR mice. Body mass (A), fat mass (B), lean mass (C), and fluid mass (D) were measured weekly in age-matched female NOD and ICR mice. n = 16–20/group. Blood glucose was measured twice weekly (E), and values were used to calculate the % of animals that remained diabetes free (F). n = 28–34 mice at baseline. A GTT was performed at 12 wk of age (n = 18; G) and an ITT was performed at 16 wk of age (n = 10–11; H) in NOD compared with ICR mice. *P < 0.05. Data are represented as means ± SE with multiple t test analysis. GTT, glucose tolerance test; ITT, insulin tolerance test; MHC, major histocompatibility complex; NOD, nonobese diabetic.

Figure 2.

Energy expenditure is similar between NOD and ICR mice. A: mean energy expenditure (EE; kcal/h) across 7 days in 12-wk-old female NOD and ICR mice. Gray bars represent lights off, and white bars represent lights on. Quantification of light cycle data (B) and quantification of mean data (C) across 7 days as shown in A. D: mean respiratory quotient (RQ) across 7 days in NOD and ICR mice. Quantification of light cycle data shown in D (E), and quantification of mean data across 7 days (F). Mean food intake (G), mean water intake (H), and mean sleep time (I) for each light cycle over a 7 day period in NOD vs. ICR mice. n = 8/group. *P < 0.05, ***P < 0.001, ****P < 0.0001. Data are represented as means ± SE with analysis by one-way ANOVA. NOD, nonobese diabetic.

Figure 3.

Spontaneous and voluntary physical activity is greater in NOD relative to ICR mice. A: mean activity (measured by X and Y bream breaks) across 7 days in 12-wk-old female NOD and ICR mice. Gray bars represent lights off, and white bars represent lights on. B: quantification of light cycle data shown in A. C: mean RPM (measuring voluntary wheel running) across 7 days in 12-wk-old female NOD and ICR mice. Quantification of light cycle data shown in C (D) and calculation of total RPM run over 7 days (E). F: grip strength measured using a BIO-GS3 force sensor. n = 8/group. *P < 0.05, ***P < 0.001, ****P < 0.0001. Data are represented as means ± SE. Data in A–E analyzed by one-way ANOVA and data in F by Welch’s t test. NOD, nonobese diabetic; ns, not significant.

Figure 4.

Glucose-stimulated insulin secretion is similar between NOD and ICR, but NOD mice have more circulating proinsulin. A: insulin secretion at 5.6 mM (baseline) and 16.7 mM glucose (stimulated) and insulin secretion in response to 20 mM KCl. B: insulin content measured from islets isolated from 12-wk-old female NOD and ICR mice (n = 4). Serum insulin at 8 (n = 4), 12 (n = 4), 14 (n = 10), and 18-wk old (n = 24; C) and serum proinsulin (n = 10) in 14-wk-old (D) female NOD and ICR mice. *P < 0.05, **P < 0.01, ***P < 0.001. Results are plotted as means ± SE with data in A–C analyzed by one-way ANOVA and data in D analyzed by Welch’s t test. NOD, nonobese diabetic.

Figure 5.

Beta cell area, insulin gene expression, and Nkx6.1 nuclear expression are similar between NOD and ICR mice. Insulin positive area (A) and islet fraction (B) at 8 (n = 4), 12 (n = 4), 14 (n = 5), and 18-wk-old (n = 8) female NOD and ICR mice. Ins1 (C) and Ins2 (D) gene expression in islets isolated from 12-wk-old female ICR and NOD mice (n = 4 for ICR; n = 12 pooled islets for NOD). E: Nkx6.1 colocalization with insulin in islets from normoglycemic 18-wk-old female nondiabetic NOD and ICR mice. Data are represented as means ± SE with results in C and D analyzed by Welch’s t test. NOD, nonobese diabetic. *P < 0.05.

Figure 6.

NOD mice display robust elevations in inflammatory gene expression, ICAM-1 protein abundance, and immune cell infiltration relative to the ICR control strain. Il1b (A) and Cxcl11 (B) gene expression in islets isolated from 12-wk-old female ICR and NOD mice (n = 4 for ICR; n = 12 pooled islets for NOD). Insulin and ICAM-1 (C) and IBA1+ and CD3+ cell (D) colocalization with insulin in islets from 12-wk-old female nondiabetic NOD and ICR mice. *P < 0.05. Data are represented as means ± SE with results in A and B analyzed by Welch’s t test. NOD, nonobese diabetic.

Figure 7.

Increased presence of STAT1 in the islets of NOD mice. Staining of FFPE pancreatic sections from 12-wk-old female ICR compared with 12-wk-old female NOD mice. Pancreatic tissue from two separate mice per strain are shown. Scale bar = 100 µm. FFPE, formalin-fixed paraffin-embedded; NOD, nonobese diabetic.