The molecular mechanism of how hepatocytes maintain cholesterol homeostasis has become much more transparent with the discovery of sterol regulatory element binding proteins (SREBPs) in recent years. These membrane pr...The molecular mechanism of how hepatocytes maintain cholesterol homeostasis has become much more transparent with the discovery of sterol regulatory element binding proteins (SREBPs) in recent years. These membrane proteins aremembers of the basic helix-loop-helix-leucine zipper (bHLHZip) family of transcription factors. They activate the expression of at least 30 genes involved in the synthesis of cholesterol and lipids. SREBPs are synthesized as precursor proteins in the endoplasmic reticulum (ER), where they form a complex with another protein, SREBP cleavage activating protein (SCAP). The SCAP molecule contains a sterol sensory domain. In the presence of high cellular sterol concentrations SCAP confines SREBP to the ER. With low cellular concentrations, SCAP escorts SREBP to activation in the Golgi. There, SREBP undergoes two proteolytic cleavage steps to release the mature, biologically active transcription factor, nuclear SREBP (nSREBP). nSREBP translocates to the nucleus and binds to sterol response elements (SRE) in the promoter/enhancer regions of target genes. Additional transcription factors are required to activate transcription of these genes. Three different SREBPs are known, SREBPs-1a, -1c and -2. SREBP-1a and -1c are isoforms produced from a single gene by alternate splicing. SREBP-2 is encoded by a different gene and does not display any isoforms. It appears that SREBPs alone, in the sequence described above, can exert complete control over cholesterol synthesis, whereas many additional factors (hormones, cytokines, etc.) are required for complete control of lipid metabolism. Medicinal manipulation of the SREBP/SCAP system is expected to prove highly beneficial in the management of cholesterol-related disease.展开更多
Fuzhuan brick-tea(FZT)has long been consumed for its supposed weight loss and lipid-lowering benefi ts.In this study,we show that the regulation of fat storage in Caenorhabditis elegans from a water extract of FZT was...Fuzhuan brick-tea(FZT)has long been consumed for its supposed weight loss and lipid-lowering benefi ts.In this study,we show that the regulation of fat storage in Caenorhabditis elegans from a water extract of FZT was affected by cholesterol levels.We found that FZT signifi cantly decreased fat storage under normal cholesterol levels or in a cholesterol-free diet,while lipid accumulation was increased for a high cholesterol diet.Moreover,this mechanism may involve the conserved sterol regulatory element-binding protein(SREBP)/mediator-15(MDT-15)signaling pathway and the nuclear hormone receptor NHR-80.In addition,lipid synthesis-related genes inhibited by FZT were partially affected by a cholesterol-free diet.Thus,our fi ndings suggested that the potential lipid-lowering effects of FZT may depend on the cholesterol level,which may help to improve the consumption of FZT.展开更多
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...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.展开更多
Plasma cholesterol level is determined by a complex dynamics that involves transport lipoproteins which levels are tightly dependent on how the liver and the intestine regulate cholesterol and biliary acid metabolism....Plasma cholesterol level is determined by a complex dynamics that involves transport lipoproteins which levels are tightly dependent on how the liver and the intestine regulate cholesterol and biliary acid metabolism. Regulation of cholesterol and biliary acids by the liver and the intestine is in turn coupled to a large array of enzymes and transporters that largely influence the inflow and the outflow of cholesterol and biliary acids through these organs. The activity of the key regulators of cholesterol and biliary acids may be influenced by several external factors such as pharmacological drugs and the nutritional status. In recent years, more information has been gathered about the impact of estrogens on regulation of cholesterol in the body. Exposure to high levels of estrogens has been reported to promote cholesterol gallstone formation and women are twice as likely as men to develop cholesterol gallstones. The impact of estrogen withdrawal, such as experienced by menopausal women, is therefore of importance and more information on how the absence of estrogens influence cholesterol regulation is started to come out, especially through the use of animal models. An interesting alternative to metabolic deterioration due to estrogen deficiency is exercise training. The present review is intended to summarize the present information that links key regulators of cholesterol and biliary acid pathways in liver and intestine to the absence of estrogens in an animal model and to discuss the potential role of exercise training as an alternative.展开更多
文摘The molecular mechanism of how hepatocytes maintain cholesterol homeostasis has become much more transparent with the discovery of sterol regulatory element binding proteins (SREBPs) in recent years. These membrane proteins aremembers of the basic helix-loop-helix-leucine zipper (bHLHZip) family of transcription factors. They activate the expression of at least 30 genes involved in the synthesis of cholesterol and lipids. SREBPs are synthesized as precursor proteins in the endoplasmic reticulum (ER), where they form a complex with another protein, SREBP cleavage activating protein (SCAP). The SCAP molecule contains a sterol sensory domain. In the presence of high cellular sterol concentrations SCAP confines SREBP to the ER. With low cellular concentrations, SCAP escorts SREBP to activation in the Golgi. There, SREBP undergoes two proteolytic cleavage steps to release the mature, biologically active transcription factor, nuclear SREBP (nSREBP). nSREBP translocates to the nucleus and binds to sterol response elements (SRE) in the promoter/enhancer regions of target genes. Additional transcription factors are required to activate transcription of these genes. Three different SREBPs are known, SREBPs-1a, -1c and -2. SREBP-1a and -1c are isoforms produced from a single gene by alternate splicing. SREBP-2 is encoded by a different gene and does not display any isoforms. It appears that SREBPs alone, in the sequence described above, can exert complete control over cholesterol synthesis, whereas many additional factors (hormones, cytokines, etc.) are required for complete control of lipid metabolism. Medicinal manipulation of the SREBP/SCAP system is expected to prove highly beneficial in the management of cholesterol-related disease.
基金supported by the National Natural Science Foundation of China(31801547)Some C.elegans strains were provided by CGC,which is funded by the NIH Office of Research Infrastructure Programs.
文摘Fuzhuan brick-tea(FZT)has long been consumed for its supposed weight loss and lipid-lowering benefi ts.In this study,we show that the regulation of fat storage in Caenorhabditis elegans from a water extract of FZT was affected by cholesterol levels.We found that FZT signifi cantly decreased fat storage under normal cholesterol levels or in a cholesterol-free diet,while lipid accumulation was increased for a high cholesterol diet.Moreover,this mechanism may involve the conserved sterol regulatory element-binding protein(SREBP)/mediator-15(MDT-15)signaling pathway and the nuclear hormone receptor NHR-80.In addition,lipid synthesis-related genes inhibited by FZT were partially affected by a cholesterol-free diet.Thus,our fi ndings suggested that the potential lipid-lowering effects of FZT may depend on the cholesterol level,which may help to improve the consumption of FZT.
基金The National Natural Science Foundation of China, No. 30470719 and 30600249The National Major Basic Research Program of China (973), No. 2006CB503808The Sanitarian Research Foundation of Hunan province, No. B2004-078
文摘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.
基金Supported by The Natural Sciences and Engineering Research Council of Canada,No.NSERC 7594
文摘Plasma cholesterol level is determined by a complex dynamics that involves transport lipoproteins which levels are tightly dependent on how the liver and the intestine regulate cholesterol and biliary acid metabolism. Regulation of cholesterol and biliary acids by the liver and the intestine is in turn coupled to a large array of enzymes and transporters that largely influence the inflow and the outflow of cholesterol and biliary acids through these organs. The activity of the key regulators of cholesterol and biliary acids may be influenced by several external factors such as pharmacological drugs and the nutritional status. In recent years, more information has been gathered about the impact of estrogens on regulation of cholesterol in the body. Exposure to high levels of estrogens has been reported to promote cholesterol gallstone formation and women are twice as likely as men to develop cholesterol gallstones. The impact of estrogen withdrawal, such as experienced by menopausal women, is therefore of importance and more information on how the absence of estrogens influence cholesterol regulation is started to come out, especially through the use of animal models. An interesting alternative to metabolic deterioration due to estrogen deficiency is exercise training. The present review is intended to summarize the present information that links key regulators of cholesterol and biliary acid pathways in liver and intestine to the absence of estrogens in an animal model and to discuss the potential role of exercise training as an alternative.
基金This work was supported by grants from the National Natural Science Foundation of China （ No. 81173047 and No. 31371161 ） and the Natural Science Foundation of Hunan （No. 12JJ5068）.
