Glucose Tolerance in Mice is Linked to the Dose of the p53 Transactivation Domain

Abstract

Aim: To test the transactivation domain-mediated control of glucose homeostasis by the tumor suppressor p53.

Background: The tumor suppressor p53 has a critical role in maintenance of glucose homeostasis. Phosphorylation of Ser18 in the transaction domain of p53 controls the expression of Zpf385a, a zinc finger protein that regulates adipogenesis and adipose function. This results suggest that the transactivation domain of p53 is essential to the control of glucose homeostasis.

Materials and methods: Mice with mutations in the p53 transactivation domain were examined for glucose homeostasis as well as various metabolic parameters. Glucose tolerance and insulin tolerance tests were performed on age matched wild type and mutant animals. In addition, mice expressing increased dosage of p53 were also examined.

Results: Mice with a mutation in p53Ser18 exhibit reduced Zpf385a expression in adipose tissue, adipose tissue-specific insulin resistance, and glucose intolerance. Mice with relative deficits in the transactivation domain of p53 exhibit similar defects in glucose homeostasis, while "Super p53" mice with an increased dosage of p53 exhibit improved glucose tolerance.

Conclusion: These data support the role of an ATM-p53 cellular stress axis that helps combat glucose intolerance and insulin resistance and regulates glucose homeostasis.

Keywords: Glucose intolerance; Mouse genetics; p53.

Fig. 1. Zfp385a is decreased specifically in WAT of p53^S18A(B6) mice

(A–B) The expression of Sesn 1/2, Zfp385a, p53, and Gapdh mRNA was measured by quantitative real time PCR analysis in 6 month old wildtype mice compared to p53^S18A mice in white adipose tissue (WAT) (A) and liver (B). The amount of Gapdh mRNA in each sample was used to calculate relative mRNA expression (mean ± S.E.M.; n = 3, done in triplicate). Statistically significant differences between WT and p53^S18A mice are indicated (*, P < 0.05).

Fig. 2. p53^S18A(B6) mice exhibit decreased glucose sensitivity with increased insulin levels

Wildtype (WT) and p53^S18A (S18A) mice were maintained on a standard chow diet. Experiments were performed on 6–7 months old animals. (A) Glucose tolerance test (GTT). Mice fasted overnight were treated with glucose (1g/kg) by intraperitoneal injection. Blood glucose concentration was measured at the indicated times (mean ± S.E.M.; n = 15). (B) Body weight was measured at 6 months (mean ± S.E.M.; n = 15). (C) Insulin measurement in mice fasted overnight (mean ± S.E.M.; n = 9). (D–E) WT and p53^S18A mice were fasted overnight and the blood concentration of IL-6 (D) and TNFα(E) was measured (mean ± S.E.M.; n = 12). (A – E) Statistically significant differences between WT and p53^S18A mice are indicated (*, P < 0.05).

Fig. 3. p53^S18A(B6) mice mice exhibit adipose tissue insulin resistance and dysfunction

Wildtype (WT) and p53^S18A (S18A) mice were maintained on a standard chow diet. Experiments were performed on 6–7 month old animals. (A) Adipose tissue insulin resistance. Hyperinsulinemia-euglycemic clamp analysis (means ± S.E.M.; n = 5). (B) Representative histological sections from epididymal fat pads from WT and p53^S18A mice. (C –E) WT and p53^S18A mice were fasted overnight and the blood concentration of leptin (C), adiponectin (D), and resistin (E) were measured (mean ± S.E.M.; n = 6). Statistically significant differences are indicated (*, P < 0.05).

Fig. 4. p44Tg mice exhibit decreased glucose sensitivity and defects in adipose tissue

Wildtype (WT) and p44Tg mice were maintained on a standard chow diet. Experiments were performed on 3 – 4 month old animals. (A) Glucose tolerance test (GTT). Mice fasted overnight were treated with glucose (1g/kg) by intraperitoneal injection. Blood glucose concentration was measured at the indicated times (mean ± S.E.M.; n = 5 – 20). (B) Insulin Tolerance Test (ITT). Mice fed ad libitum were treated with insulin (0.75 U/kg) by intraperitoneal injection. Blood glucose was measured at the indicated times (mean ± S.E.M.; n = 5 – 20). Statistically significant differences are indicated (*, P < 0.05). (C) Triglyceride levels under fed or fasted conditions for times indicated. (D) Gene expression in WAT from 3 month old male determined by qPCR.

Fig. 5. Super p53 mice exhibit increased glucose sensitivity

Wildtype (WT) and p53^super/+ mice were maintained on a standard chow diet. Experiments were performed on 4 months old animals. (A) Glucose tolerance test (GTT). Mice fasted overnight were treated with glucose (1g/kg) by intraperitoneal injection. Blood glucose concentration was measured at the indicated times (mean ± S.E.M.; n = 10). (B) Insulin Tolerance Test (ITT). Mice fed ad libitum were treated with insulin (0.75 U/kg) by intraperitoneal injection. Blood glucose was measured at the indicated times (mean ± S.E.M.; n = 10). The mice were fasted overnight and treated without or with insulin (1.5 U/kg body mass) by intraperitoneal injection (30 mins). Statistically significant differences are indicated (*, P < 0.05).