Absence of a gestational diabetes phenotype in the LepRdb/+ mouse is independent of control strain, diet, misty allele, or parity

Abstract

Treatment options for gestational diabetes (GDM) are limited. In order to better understand mechanisms and improve treatments, appropriate animal models of GDM are crucial. Heterozygous db mice (db/+) present with glucose intolerance, insulin resistance, and increased weight gain during, but not prior to, pregnancy. This makes them an ideal model for GDM. However, several recent studies have reported an absence of GDM phenotype in their colony. We investigated several hypotheses for why the phenotype may be absent, with the aim of re-establishing it and preventing further resources being wasted on an ineffective model. Experiments were carried out across two laboratories in two countries (New Zealand and China), and were designed to assess type of control strain, diet, presence of the misty allele, and parity as potential contributors to the lost phenotype. While hyperleptinemia and pre-pregnancy weight gain were present in all db/+mice across the four studies, we found no consistent evidence of glucose intolerance or insulin resistance during pregnancy. In conclusion, we were unable to acquire the GDM phenotype in any of our experiments, and we recommend researchers do not use the db/+ mouse as a model of GDM unless they are certain the phenotype remains in their colony.

Figure 1. There were no consistent differences in glucose tolerance between db/+ mice and either type of control strain both prior to, or during, pregnancy.

(A) OGTT results prior to the onset of pregnancy (12 weeks old). An asterix (*) indicates a significant difference between db/+ and C57BL/6J mice. A pound sign (^#) indicates a significant difference between WT and C57BL/6J mice (*p < 0.05. ^##p < 0.01). db/+ mice had significantly higher blood glucose at time = 90, and time = 120 of the glucose tolerance test, compared to C57BL/6J mice. WT mice had significantly higher blood glucose than C57BL/6J mice at every time point apart from fasting (time = 0). There were no significant differences between WT and db/+ mice. (B) AUC of OGTT prior to onset of pregnancy (12 weeks old). WT mice had significantly higher area under the curve than C57BL/6J mice, prior to pregnancy (^##p < 0.01). (C) OGTT results at GD16.5. db/+ mice had significantly higher blood glucose at time = 120 (*p < 0.05). (D) AUC of OGTT at GD16.5.

Figure 2. db/+ mice showed marked fasting hyperleptinemia, but no difference in glucose or insulin.

(A) Fasting blood glucose at GD18.5. (B) Fasting insulin concentrations at GD18.5. (C) HOMA-IR score at GD18.5. (D) Fasting leptin concentration at GD18.5. db/+ mice had significantly higher fasting plasma leptin than both WT (^^p < 0.01) and C57BL/6J mice (****p < 0.0001). WT mice also had significantly higher plasma leptin than C57BL/6J mice (^##p < 0.01).

Figure 3. db/+ mice had a significantly larger area under the OGTT curve than WT mice in Study 2.

(A) OGTT results at GD16.5. (B) AUC of OGTT at GD16.5. The asterix (*) indicates a significant difference between db/+ and WT mice in area under the curve (p < 0.05).

Figure 4. db/+ mice showed increased fasting blood glucose, insulin, HOMA-IR, and leptin compared to WT mice in Study 2.

(A) Fasting blood glucose at GD18.5. (B) Fasting insulin concentrations at GD18.5. There was a significant difference between db/+ mice and WT mice in insulin concentration (**p < 0.01) (C) HOMA-IR score at GD18.5. There was a significant difference between db/+ and WT mice in HOMA-IR (*p < 0.05) (D) Fasting leptin concentration at GD18.5. There was a significant difference between db/+ and WT mice in fasting leptin concentration (***p < 0.001).

Figure 5. There were no differences in glucose tolerance between misty db/+ mice and either type of control in Study 3.

(A) OGTT results at GD16.5. (B) AUC of OGTT at GD16.5.

Figure 6. There were no differences in fasting glucose or insulin between db/+ mice and control mice in Study 3, and there was only a slight difference in leptin.

(A) Fasting blood glucose at GD18.5. (B) Fasting insulin concentrations at GD18.5. (C) HOMA-IR score at GD18.5. (D) Fasting leptin concentration at GD18.5. There was almost a significant difference between db/+ and C57BL/6J mice in fasting leptin concentration (p = 0.051).

Figure 7. There were no differences in glucose tolerance between multiparous db/+ mice and controls in Study 4.

(A) OGTT results at GD16.5 of a second pregnancy. (B) AUC of OGTT at GD16.5 of a second pregnancy.