Hepatocyte-Specific Inactivation Of Sirt1 Protects Against TNF-Induced Apoptosis And Liver Injury By Acetylating And Activating NF-?B

Acute liver failure(ALF) is a severe clinical syndrome that is characterized by massive apoptosis and necrosis of liver cells resulting from various hepatic diseases, leading to multi-organ failure. Although the incidence of ALF is low, the associated mortality is extremely high and is really a threat to the life of the patients.SIRT1, an NAD+-dependent protein deacetylase, as one of the members of the family of Sirtuins, is closely related to the cell proliferation, differentiation, and metabolism. The NF-?B is a dimmer protein, generally consists of two functional subunits(P65 and P50), in many cell types, NF- ?B combined with its inhibitory proteins forming unactive compounds and stady in cytoplasm. When tumor necrosis factor etc, acting on the corresponding receptors, this system can be triggered by the second messenger Cer. But virus infection, lipopolysaccharide, reactive oxygen intermediates, Buddha wave ester, double-stranded RNA, and the information transmission way of activation and PkA RKC waalwijk can directly activated NF � ?B. Activation process of NF- ?B is through phosphorylation inhibitory of proteins to change its conformation and make them fall off from the NF- ?B. Activated NF- ?B get into the nucleus, contact with DNA, and start or prevent the transcription of related genes. Nuclear factor ?B(NF- ?B) system mainly involves in the body's defense reactions, tissue damage and stress, cell differentiation and apoptosis and inhibit tumor growth in the process of information transmission. The NF-?B(RelA/p65) in liver cell damage caused by TNF alpha plays a protective role. Sirt1 can make the NF-?B(RelA/p65) acetylation on the 310- bit of lysine residues,thus inhibiting the NF-?B transcriptional activity, reducing its downstream gene expression to promote cell apoptosis. At the same time, the Sirt1 can also make the p53 deacetylation to inhibit the activity of p53 and resistance to apoptosis. he role of Sirt1 in liver cell apoptosis is still no definite conclusion. To this end, we conducted the following experiments:(1) through the cre- loxp system we set up the mice liver specificity knockout SIRT1 gene. To established the acute liver failure model, endotoxin(LPS) 10 mu g/Kg and D- amino galactosamine(D- Galn) 700 mg/Kg were injected to the Sirt1+/+ and Sirt1-/-. The survival rates of two groups and aminotransferase levels were observed. We observed 72 hours after the forming the mold, Sirt1+ / + mice with a 100% mortality rate, 6 h aminotransferase levels increased significantly. But the Sirt1-/- mortality rate is 0, and with a decreased aminotransferase levels compared to the Sirt1+/+ group.(2) On the cellular level, we extract Sirt1+/+ and Sirt1-/- primary liver cells respectively to culture. ACTD 20 ng/ml and TNF alpha 20 ng/ml were used to set up the damage model, finding that the Sirt1-/- cell apoptosis less than Sirt1+/+. But when with the NF-?B SiRNA interference,we found that the protection of SIRT1 on it disappeared.(3) We use a Sirt1 inhibitors, nicotinamide, to handle the cells before acute liver failure model established. Resulting show that the nicotinamide has obvious protective effect on acute liver failure. Nicotinamide pretreatment obviously improve the survival rate of mice, and reduce histopathologic damage significantly. Sirt1 significantly increased the acetylation level of NF-?B and improve the combination capacibility of NF-?B with DNA.Therefore, we conclude that Sirt1 deactivation increase the acetylation level of NF-?B after stimulated by TNF-?to protect liver cells.