Figure 10: β-cell-specific ablation of p53 alleviates palmitic acid-induced impairment of mitochondrial metabolism and GSIS.

(a) MIN6 β-cells were treated with palmitic acid (PA, 500 μM) for 24 h, followed by immunoblotting with an antibody against MDM2, p53, PC or β-actin as indicated. The right panel is the densitometric analysis for the relative abundance of MDM2, p53 and PC normalized with β-actin (n=4). (b–e) Pancreatic islets were isolated from 14-week-old male β-cell-specific p53 KO mice and its WT controls, followed by treatment with PA (500 μM) for 24 h. (b) mRNA level of PC and p53 in the treated islets (n=3). (c,d) Intracellular levels of ATP (c) and OAA (d) in the islets with glucose stimulation (20 mM) for 10 and 30 min, respectively. (c) The value is normalized with their respective vehicle-treated control with glucose stimulation (n=4). (d) The value is normalized with WT-vehicle with glucose stimulation (n=4). (e) Static GSIS assay measured at 30 min after glucose stimulation (n=5). *P<0.05 (Student’s t-test (a,b,c,e), one-way analysis of variance with Bonferroni correction for multiple comparisons (e)). All data are represented as the mean±s.e.m. Note that insulin content of the isolated islets was comparable between different treatment groups. (f) Proposed model for the role of MDM2–p53–PC signalling axis in GSIS. Sustained elevation of p53 or dysregulation of the MDM2–p53 signalling axis elicited by a wide variety of chronic stress signals directly represses expression of PC by binding to the promoter region of PC via the p53 RE. Reduction of PC impairs TCA cycle, leading to decreased production of ATP, OAA and amplifying factors (such as NADPH), resulting in defective GSIS.