p53 Activation in Adipocytes of Obese Mice

Abstract

The tumor suppressor p53 is a transcription factor that activates or represses its target genes after various genotoxic stresses. We have previously shown that sterol regulatory element-binding protein-1 (SREBP-1), a key transcriptional regulator of triglyceride synthesis, and the lipogenic enzymes under its control are markedly suppressed in adipocytes from genetically obese ob/ob mice. Here we demonstrate that p53 and its target genes are highly induced in adipocytes of ob/ob mice in a fed state, leading to the negative regulation of SREBP-1 and thereby lipogenic genes. In fact, disruption of p53 in ob/ob mice completely suppressed the p53-regulated genes to wild-type levels and partially restored expression of lipogenic enzymes. Consistently, reporter gene analysis showed that p53 overexpression suppressed the promoter activity of the SREBP-1c gene and its downstream genes. Thus, the activation of p53 might constitute a negative feedback loop against excess fat accumulation in adipocytes. In conclusion, we discovered a novel role of p53 in the pathophysiology of obesity.Obesity is a major health problem in industrialized societies, affecting ϳ20 -40% of adults (1). The genetically obese ob/ob mice develop obesity, insulin resistance, and glucose intolerance owing to an inherited deficiency of the appetite-suppressing hormone, leptin (2-6). The absence of leptin presents the most severe obesity known in both rodents and humans (7), and provides a good model of obesity and its related syndromes, including insulin resistance. Although the underlying mechanisms that link obesity and defective insulin signaling are as yet undefined, hypertrophied adipocyte-derived cytokines such as tumor necrosis factor (TNF) 1 -␣ have been reported to be mediators of insulin resistance in obesity (8,9).In the insulin signaling pathways, a transcription factor sterol regulatory element-binding protein-1 (SREBP-1) has recently been established to be a key molecule for the transcriptional regulation of triglyceride synthesis (10). SREBPs are members of the basic helix-loop-helix leucine zipper family of transcription factors that regulate fatty acid and cholesterol synthesis (reviewed in Refs. 11-13). Whereas SREBP-2 plays a crucial role in regulation of cholesterol synthesis, SREBP-1 controls the transcription and expression of lipogenic enzymes such as fatty acid synthase (FAS) (reviewed in Refs. 14 -17). In fact, SREBP-1 and its downstream lipogenic enzymes are drastically induced when fasted animals are refed (18). These lipogenic genes belong to the group of genes that are induced most strongly by glucose/insulin 2 and can be regarded as indicators of insulin signaling.We have recently reported that the refeeding responses of SREBP-1 and its downstream lipogenic enzymes are markedly suppressed in adipocytes of ob/ob mice, which is presumably associated with impaired insulin signaling (19). Although the precise role of this down-regulation is currently undefined, it could be a negative feedback mechanism to prevent excess fat ac...

Increased serum concentrations of macrophage inhibitory cytokine-1 in patients with obesity and type 2 diabetes mellitus: the influence of very low calorie diet

“…For example, increased circulating MIC-1 levels may reflect p53 pathway activation (24). This pathway may, among other important functions, play a role in the pathophysiology of obesity (25). Furthermore, MIC-1 expression is one of genes responsible for initiating the process of stimulus-induced adaptive changes (26).…”

Obesity and related consequences to ageing

“…Yahagi et al (2003) demonstrated that p53 and its target genes are highly induced in adipocytes of ob/ob mice in a fed state, leading to the negative regulation of lipogenic genes (Yahagi et al 2003). Moreover, disruption of p53 in ob/ ob mice fully suppressed the p53-regulated genes to the levels of wild-type subjects and partially restored expression of lipogenic enzymes.…”

“…Moreover, disruption of p53 in ob/ ob mice fully suppressed the p53-regulated genes to the levels of wild-type subjects and partially restored expression of lipogenic enzymes. The authors suggested that the activation of the p53 gene might develop a negative feedback loop against abnormal fat accumulation in adipocyte cells (Yahagi et al 2003). Another study on rodents showed that p53 expression in AT is a key component in the development of insulin resistance, which underlies age-related cardiovascular and metabolic disorders (Minamino et al 2009).…”

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