Loss of p53 Sensitizes Cells to Palmitic Acid-Induced Apoptosis by Reactive Oxygen Species Accumulation.

Guowu Yu,Yubi Huang,Yangping Li,Yinghong Liu,Yufeng Hu,Na Zhang,Yi Tang,Junjie Zhang,Hanmei Liu,Yongbin Wang,Hongwei Luo,Huanhuan Huang

doi:10.3390/ijms20246268

Abstract

Palmitic acid, the most common saturated free fatty acid, can lead to lipotoxicity and apoptosis when overloaded in non-fat cells. Palmitic acid accumulation can induce pancreatic β-cell dysfunction and cardiac myocyte apoptosis. Under various cellular stresses, the activation of p53 signaling can lead to cell cycle arrest, DNA repair, senescence, or apoptosis, depending on the severity/type of stress. Nonetheless, the precise role of p53 in lipotoxicity induced by palmitic acid is not clear. Here, our results show that palmitic acid induces p53 activation in a dose- and time-dependent manner. Furthermore, loss of p53 makes cells sensitive to palmitic acid-induced apoptosis. These results were demonstrated in human colon carcinoma cells (HCT116) and primary mouse embryo fibroblasts (MEF) through analysis of DNA fragmentation, flow cytometry, colony formation, and Western blots. In the HCT116 p53−/− cell line, palmitic acid induced greater reactive oxygen species formation compared to the p53+/+ cell line. The reactive oxygen species (ROS) scavengers N-acetyl cysteine (NAC) and reduced glutathione (GSH) partially attenuated apoptosis in the HCT116 p53−/− cell line but had no obvious effect on the p53+/+ cell line. Furthermore, p53 induced the expression of its downstream target genes, p21 and Sesn2, in response to ROS induced by palmitic acid. Loss of p21 also leads to more palmitic acid-induced cell apoptosis in the HCT116 cell line compared with HCT116 p53+/+ and HCT116 p53−/−. In a mouse model of obesity, glucose tolerance test assays showed higher glucose levels in p53−/− mice that received a high fat diet compared to wild type mice that received the same diet. There were no obvious differences between p53−/− and p53+/+ mice that received a regular diet. We conclude that p53 may provide some protection against palmitic acid- induced apoptosis in cells by targeting its downstream genes in response to this stress.

Highlights

Palmitic acid, a long chain saturated fatty acid, is widely distributed in plants, including palm fruit [1,2], maize grain [3], and other cereal seeds [4,5]
Our results suggest that p53 can potentially protect cells from apoptosis induced by PA treatment
We identified differences in PA-induced apoptosis between p53+/+ and p53−/− cell lines. p53 potentially protects cells from PA-induced apoptosis though induction of its target genes, p21 and Sesn2. p21 induces cell cycle arrest, and Sesn2 functions as an antioxidant factor in response to reactive oxygen species induced by PA in p53 wild type cell lines

Summary

Introduction

A long chain saturated fatty acid, is widely distributed in plants, including palm fruit [1,2], maize grain [3], and other cereal seeds [4,5]. There is increasing evidence that palmitic acid induces cellular apoptosis in Chinese hamster ovary (CHO) cells [1,8,9], pancreatic β-cells [10,11], breast cancer cell lines [12], cardiac myocytes [13], vascular smooth muscle cell [14], hepatic cells [15], and neural stem cells [16]. P53 is a multi-functional protein that plays many roles in determining cell fate in response to cellular stress [20,21,22]. P53 is activated to induce cell cycle arrest, DNA repair, senescence, or apoptosis, which have been previously shown to contribute to tumor suppression [22,23]. Under stress-free or low stress conditions, p53 increases transcription of multiple downstream target genes (i.e., p21, BcL2, Sesn, and Sesn2), engaging anti-apoptosis pathways by counteracting apoptosis in cells [22,23,24,25,26]

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Discussion

Conclusion