PARP1Induced Abnormalities In Triglyceride Metabolism By Suppressing Hepatic Fatty Acid Oxidation Through Impairing PPARα Sensing In High Fat Diet Fed Mice

Part I Critical role of PARP1in high saturated fat diet induced abnormalities in triglyceride metabolism in miceAims:To explore the role of poly(ADP-ribose) polymerase1(PARP1) in the high saturated fat diet (HSFD)-induced abnormalities in triglyceride metabolism.Methods:8-10weeks old male129S1/SvImJ mice (Wild Type, WT) and PARP1gene knockout mice (PARPl-/-,129S-Parpltmlzqw/J, PKO) were chosed. The mice were randomly divided into four groups:(1) standard chow diet (SCD)(WT) group;(2) high saturated fat diet (HSFD)(WT) group;(3) SCD (PKO) group;(4) HSFD (PKO) group. Mice were suffered to glucose tolerance test and intraperitoneal injection of insulin tolerance test respectively to evaluate the insulin resistant state. Lipids in plasma or liver were quantified using commercial kits. Pathologic examination of liver slices were employed to observe hepatic steatosis. Real-time RT-PCR and Western blot analysis were used to detect the transcriptional levels of triglyceride metabolism-related genes in liver tissue.Results:HSFD feeding promoted PARP1activation in liver, which in turn suppressed peroxisome proliferator-activated receptor a (PPARa) sensing through poly(ADP-ribosyl)ation. Pharmacological inhibition or genetic deletion of PARP1restored the lipid sensing of PPARa, and thus inhibited the HFD induced NHS. Further study revealed that PPARa was a substrate of PARP1mediated poly(ADP-ribosyl)ation. Poly(ADP-ribosyl)ation prevented binding of PPARa to its target promoter, and thus suppressed transcription.Conclusions:Activation of PARP1contributes crucially to the HSFD induced abnormalities in triglyceride metabolism through impairment of PPARa signaling pathway. Part Ⅱ The effects of different types of fatty acid on the activity of poly(ADP-ribos) polymerase1in hepatocytesAims:Given that the over-activation of poly(ADP-ribos) polymerase1(PARP1) played a crucial role in many complex pathophysiological processes, three types of fetty acid were employed to explore their influence on the activity of PARP1.Methods:The hepatocytes of liver from wild-type mice were cultured with monounsaturated fatty acids (MUFA), polyunsaturated fatty acids (PUFA) and saturated fatty acids (SFA) at the same concentration. Then the activity of PARP1in the hepatocyts was detected. The poly(ADP-ribosyl)ation levels of PPARa were also determined by the IP assay in the hepatocytes. Furthermore, the mRNA levels of gene involved in the triglyceride metabolism were measured in the WT or PKO hepatocytes.Results:PARP activity assay showed that administration of SFA significantly increased PARP activity, while PUFA and MUFA did not. IP assay demonstrated that treatment with SFA, but not PUFA or MUFA, enhanced the poly(ADP-ribosyl)ation of PPARa through activation of PARP1. Moreover, SFA increased the target gene expression of PPARain PKO-hepatocytes but not in the WT-hepatocytes.Conclusions:These data illustrated that SFA promoted PARP1activation and PARP1suppressed the stimulatory effects of SFA on PPARa transactivation. PartⅢ PARP activity is positively correlated with hepatic triglyceride accumulation in human subjectsAims:To investigate a possible connection between PARP activity and hepatic triglyceride accumulation in human subjects.Methods:A total of72histologically normal liver tissue specimens (all were surgically resected) were obtained from the Tissue Bank of Huazhong University of Science and Technology. Triglyceride and non-esterified fatty acids (NEFA) in the liver tissue were quantified using commercial kits. Person correlation analysis was conducted to examine the association. Oil Red O staining were used to examine the influences of PARP1inhibition on triglyceride accumulation in human hepatoma HepG2cells.Results:The results showed the hepatic PARP activity positively correlated with hepatic levels of triglyceride (r=0.509, p<0.001), and NEFA (r=0.454, p=0.002). Treatment with H2O2significantly increased the intracellular triglyceride accumulation and the stimulatory effects of H2O2was effectively reversed by PARP1knockdown or administration of3AB or PJ34.Conclusions:All these finding demonstrated that PARP activity is positively correlated with hepatic triglyceride accumulation in human subjects.