Effect of Daxx on cholesterol accumulation in hepatic cells

AIM： To study the effect of Daxx on cholesterol accumulation in hepatic cells. METHODS： Sprague Dawley （SD） rats were fed a normal or high fat diet for 6 wk, and serum lipids and Daxx expression of hepatic tissues were measured by immunoblot assays. HepG2 cells were transfected with the pEGFP-C1/Daxx or pEGFP-C1 plasmid. Cells stably transfected with Daxx were identified by RTPCR analysis. Total cholesterol levels were determined by high performance liquid chromatography. Activated- SREBP and caveolin-1 were assayed by western blotting. RESULTS： Hepatic Daxx protein was higher in normal rats than in high fat diet-fed rats. Noticeable negative correlations were seen between Daxx and LDL-C （γ=-7.56, ρ=0.018）, and between Daxx and TC （γ=-9.07, ρ= 0.01）, respectively. The total cholesterol of HepG2/GFP-Daxx cells was lower than that of control cells or HepG2/GFP cells （9.28±0.19 vs 14.36± 4.45 or 13.94±2.62, both P 〈 0.05）. Furthermore, in HepG2/GFP cells, the expression of activated SREBP was lower than that of control cells, whereas caveolin-1 expression was higher. CONCLUSION： Overexpression of Daxx in HepG2 cells decreased intracellular cholesterol accumulation, which might be associated with inhibition of SREBP activity and an increase in caveolin-1 expression.

PPARα activator irbesartan suppresses the proliferation of endometrial carcinoma cells via SREBP1 and ARID1A

Endometrial carcinoma(EMC)is associated with obesity;however,the underlying mechanisms have not yet been elucidated.Peroxisome proliferator-activated receptor alpha(PPARα)is a nuclear receptor that is involved in lipid,glucose,and energy metabolism.PPARαreportedly functions as a tumor suppressor through its effects on lipid metabolism;however,the involvement of PPARαin the development of EMC remains unclear.The present study demonstrated that the immunohistochemical expression of nuclear PPARαwas lower in EMC than in normal endometrial tissues,suggesting the tumor suppressive nature of PPARα.A treatment with the PPARαactivator,irbesartan,inhibited the EMC cell lines,Ishikawa and HEC1A,by down-regulating sterol regulatory element-binding protein 1(SREBP1)and fatty acid synthase(FAS)and up-regulating the tumor suppressor genes p21 and p27,antioxidant enzymes,and AT-rich interaction domain 1A(ARID1A).These results indicate the potential of the activation of PPARαas a novel therapeutic approach against EMC.

Pathophysiology of insulin resistance and steatosis in patients with chronic viral hepatitis

Chronic hepatitis due to any cause leads to cirrhosis and end-stage liver disease.A growing body of literature has also shown that fatty liver due to overweight or obesity is a leading cause of cirrhosis.Due to the obesity epidemic,fatty liver is now a significant problem in clinical practice.Steatosis has an impact on the acceleration of liver damage in patients with chronic hepatitis due to other causes.An association between hepatitis C virus (HCV) infection,steatosis and the onset of insulin resistance has been reported.Insulin resistance is one of the leading factors for severe fibrosis in chronic HCV infections.Moreover,hyperinsulinemia has a deleterious effect on the management of chronic HCV.Response to therapy is increased by decreasing insulin resistance by weight loss or the use of thiazolidenediones or metformin.The underlying mechanisms of this complex interaction are not fully understood.A direct cytopathic effect of HCV has been suggested.The genomic structure of HCV (suggesting that some viral sequences are involved in the intracellular accumulation of triglycerides),lipid metabolism,the molecular links between the HCV core protein and lipid droplets (the core protein of HCV and its transcriptional regulatory function which induce a triglyceride accumulation in hepatocytes) and increased neolipogenesis and inhibited fatty acid degradation in mitochondria have been investigated.

Resveratrol and fenofibrate ameliorate fructose-induced nonalcoholic steatohepatitis by modulation of genes expression

AIM: To evaluate the effect of resveratrol, alone and in combination with fenofibrate, on fructose-induced metabolic genes abnormalities in rats.METHODS: Giving a fructose-enriched diet (FED) to rats for 12 wk was used as a model for inducing hepatic dyslipidemia and insulin resistance. Adult male albino rats (150-200 g) were divided into a control group and a FED group which was subdivided into 4 groups, a control FED, fenofibrate (FENO) (100 mg/kg), resveratrol (RES) (70 mg/kg) and combined treatment (FENO + RES) (half the doses). All treatments were given orally from the 9th week till the end of experimental period. Body weight, oral glucose tolerance test (OGTT), liver index, glucose, insulin, insulin resistance (HOMA), serum and liver triglycerides (TGs), oxidative stress (liver MDA, GSH and SOD), serum AST, ALT, AST/ALT ratio and tumor necrosis factor-α (TNF-α) were measured. Additionally, hepatic gene expression of suppressor of cytokine signaling-3 (SOCS-3), sterol regulatory element binding protein-1c (SREBP-1c), fatty acid synthase (FAS), malonyl CoA decarboxylase (MCD), transforming growth factor-β1 (TGF-β1) and adipose tissue genes expression of leptin and adiponectin were investigated. Liver sections were taken for histopathological examination and steatosis area were determined.RESULTS: Rats fed FED showed damaged liver, impairment of glucose tolerance, insulin resistance, oxidative stress and dyslipidemia. As for gene expression, there was a change in favor of dyslipidemia and nonalcoholic steatohepatitis (NASH) development. All treatment regimens showed some benefit in reversing the described deviations. Fructose caused deterioration in hepatic gene expression of SOCS-3, SREBP-1c, FAS, MDA and TGF-β1 and in adipose tissue gene expression of leptin and adiponectin. Fructose showed also an increase in body weight, insulin resistance (OGTT, HOMA), serum and liver TGs, hepatic MDA, serum AST, AST/ALT ratio and TNF-α compared to control. All treatments improved SOCS-3, FAS, MCD, TGF-β1 and leptin genes expression while only RES and FENO + RES groups showed an improvement in SREBP-1c expression. Adiponectin gene expression was improved only by RES. A decrease in body weight, HOMA, liver TGs, AST/ALT ratio and TNF-α were observed in all treatment groups. Liver index was increased in FENO and FENO + RES groups. Serum TGs was improved only by FENO treatment. Liver MDA was improved by RES and FENO + RES treatments. FENO + RES group showed an increase in liver GSH content.CONCLUSION: When resveratrol was given with half the dose of fenofibrate it improved NASH-related fructose-induced disturbances in gene expression similar to a full dose of fenofibrate.

Sodium acetate promotes fat synthesis by suppressing TATA element modulatory factor 1 in bovine mammary epithelial cells

Short-chain fatty acids are important nutrients that regulate milk fat synthesis.They regulate milk syn-thesis via the sterol regulatory element binding protein 1(SREBP1)pathway;however,the details are still unknown.Here,the regulation and mechanism of sodium acetate(SA)in milk fat synthesis in bovine mammary epithelial cells(BMECs)were assessed.BMECs were treated with SA supplementation(SAþ)or without SA supplementation(SA-),and milk fat synthesis and activation of the SREBP1 pathway were increased(P=0.0045;P=0.0042)by SAþand decreased(P=0.0068;P=0.0031)by SA-,respectively.Overexpression or inhibition of SREBP1 demonstrated that SA promoted milk fat synthesis(P=0.0045)via the SREBP1 pathway.Overexpression or inhibition of TATA element modulatory factor 1(TMF1)demon-strated that TMF1 suppressed activation of the SREBP1 pathway(P=0.0001)and milk fat synthesis(P=0.0022)activated by SAþ.Overexpression or inhibition of TMF1 and SREBP1 showed that TMF1 suppressed milk fat synthesis(P=0.0073)through the SREBP1 pathway.Coimmunoprecipitation analysis revealed that TMF1 interacted with SREBP1 in the cytoplasm and suppressed the nuclear localization of SREBP1(P=0.0066).The absence or presence of SA demonstrated that SA inhibited the expression of TMF1(P=0.0002)and the interaction between TMF1 and SREBP1(P=0.0001).Collectively,our research sug-gested that TMF1 was a new negative regulator of milk fat synthesis.In BMECs,SA promoted the SREBP1 pathway and milk fat synthesis by suppressing TMF1.This study enhances the current understanding of the regulation of milk fat synthesis and provides new scientific data for the regulation of milk fat synthesis.

MRCKα is a novel regulator of prolactin-induced lactogenesis in bovine mammary epithelial cells

Myotonic dystrophy-related Cdc42-binding kinase alpha(MRCKα)is an integral component of signaling pathways controlling vital cellular processes,including cytoskeletal reorganization,cell proliferation and cell survival.In this study,we investigated the physiological role of MRCKα in milk protein and fat production in dairy cows,which requires a dynamic and strict organization of the cytoskeletal network in bovine mammary epithelial cells(BMEC).Within a selection of 9 Holstein cows,we found that both mRNA and protein expression of MRCKα in the mammary gland were upregulated during lactation and correlated positively(r>0.89)with the mRNA and protein levels of b-casein.Similar positive correlations(r>0.79)were found in a primary culture of BMEC stimulated with prolactin for 24 h.In these cells,silencing of MRCKα decreased basal b-casein,sterol-regulatory element binding protein(SREBP)-1 and cyclin D1 protein level,phosphorylation of mTOR,triglyceride secretion,cell number and viabilitydwhile overexpression of MRCKα displayed the reversed effect.Notably,silencing of MRCKα completely prevented the stimulatory action of prolactin on the same parameters.These data demonstrate that MRCKα is a critical mediator of prolactin-induced lactogenesis via stimulation of the mTOR/SREBP1/cyclin D1 signaling pathway.