ABSTRACT
@#Liver cholesterol metabolism disorder plays an important role in the development of non-alcoholic fatty liver disease (NAFLD).In order to reveal the molecular mechanism of cholesterol homeostasis imbalance induced by saturated fatty acids, HepG2 cells were stimulated with palmitic acid (PA).Lipids accumulation was analyzed by Oil Red O staining, intracellular triglyceride and cholesterol quantification.The level of genes and proteins related to cholesterol homeostasis was measured by RT-qPCR and western blotting.Additionally, intracellular bile acids and mitochondrial oxysterols were detected by LC-MS/MS.The results demonstrated that intracellular lipids such as TG and TC were significantly increased in the model with PA stimulation.Although no significant difference was detected in genes related to cholesterol synthesis and uptake, the protein expression of ABCG5 and LXRα were significantly down-regulated, indicating a decrease in cholesterol efflux.Meanwhile, the gene expression of STARD1 and CYP7B1, which are responsible for bile acid alternative synthesis, were markedly enhanced, along with a significant increase of cholesterol and 27-OHC in mitochondria and CDCA in cells.These results suggested that PA overload may disrupt cholesterol homeostasis by inhibiting cholesterol efflux and promoting bile acids synthesis.
ABSTRACT
Objective To detect steroidogenic acute regulatory protein (StAR) expression in apolipoprotein E-deficient mice at different ages and serum lipid levels. Methods Nighty-six C57BL/6J and apoE-/- mice were enrolled, which were divided into 16 groups with 6 mice per group according to age (1 day, 1, 3, 5 months), sex and genotype (C57BL/6J and apoE-/-). The serum lipid levels in C57BL/6J and apoE-/- mice were detected by commercial kits. StAR mRNA and protein expressions in liver were detected by Real-time PCR and Western blot respectively. Results ApoE-/- mice had higher LDL-cholesterol and lower HDL-cholesterol compared with C57BL/6J mice of the same age and sex. StAR mRNA and protein expressions were decreased following with aging in C57BL/6J mice. However, in apoE-/- mice with higher lipid levels, StAR mRNA and protein expressions were changed with the lipid levels other than ages. StAR mRNA and protein increased in the early stage, and then decreased with the increasement of lipids levels. Conclusions StAR could affect lipids levels and may be an effective regulator for atherosclerosis and other cardiovascular diseases.
ABSTRACT
Oxysterols are 27-carbon atom molecules resulting from autoxidation or enzymatic oxidation of cholesterol. They are present in numerous foodstuffs and have been demonstrated to be present at increased levels in the plasma of patients with cardiovascular diseases and in atherosclerotic lesions. Thus, their role in lipid disorders is widely suspected, and they might also be involved in important degenerative diseases such as Alzheimer's disease, osteoporosis, and age-related macular degeneration. Since atherosclerosis is associated with the presence of apoptotic cells and with oxidative and inflammatory processes, the ability of some oxysterols, especially 7-ketocholesterol and 7beta-hydroxycholesterol, to trigger cell death, activate inflammation, and modulate lipid homeostasis is being extensively studied, especially in vitro. Thus, since there are a number of essential considerations regarding the physiological/pathophysiological functions and activities of the different oxysterols, it is important to determine their biological activities and identify their signaling pathways, when they are used either alone or as mixtures. Oxysterols may have cytotoxic, oxidative, and/or inflammatory effects, or none whatsoever. Moreover, a substantial accumulation of polar lipids in cytoplasmic multilamellar structures has been observed with cytotoxic oxysterols, suggesting that cytotoxic oxysterols are potent inducers of phospholipidosis. This basic knowledge about oxysterols contributes to a better understanding of the associated pathologies and may lead to new treatments and new drugs. Since oxysterols have a number of biological activities, and as oxysterol-induced cell death is assumed to take part in degenerative pathologies, the present review will focus on the cytotoxic activities of these compounds, the corresponding cell death signaling pathways, and associated events (oxidation, inflammation, and phospholipidosis).
Subject(s)
Animals , Humans , Apoptosis/drug effects , Hydroxycholesterols/toxicity , Inflammation/chemically induced , Lipidoses/chemically induced , Phospholipids/metabolism , Oxidation-ReductionABSTRACT
BACKGROUND: Formation of cholesterol oxidation products is a suggested mechanism of neurodegenerative disorders. Neuronal cell death is mediated by an increased release of excitotoxic glutamate from the presynaptic nerve endings. Tyrosine-specific protein kinases modulate neurotransmitter release at the nerve terminals. Tyrphostin AG126 has anti-inflammatory and cytoprotective effects. However, it remains uncertain whether tyrphostin AG126 has a preventive effect on the alteration of nerve terminal function induced by cholesterol oxidation products. METHODS: The present study was performed to assess the effect of cholesterol oxidation products against nerve terminal function using synaptosomes isolated from rat cerebrum. We determined the preventive effect of tyrphostin AG126 against oxysterol toxicity by measuring the effects on the glutamate release, depolarization of the membrane potential, changes in Ca2+ levels, and Na+/K+-ATPase activity. RESULTS: Synaptosomes treated with 7-ketocholesterol or 25-hydroxycholesterol exhibited a sustained release of glutamate, depolarization of membrane potential, early rapid increase in cellular Ca2+ levels and decrease in Na+/K+-ATPase activity. Those responses were concentration-dependent. Treatment of tyrphostin AG126 interfered with alteration of synaptosomal functions and decrease in Na+/K+-ATPase activity induced by 7-ketocholesterol or 25-hydroxycholesterol. CONCLUSIONS: The results show that 7-ketocholesterol and 25-hydroxycholesterol seem to cause the release of glutamate by inducing depolarization of the membrane potential and early rapid increase in cellular Ca2+ levels and by inactivating Na+/K+-ATPase in the cerebral synaptosomes. Treatment of tyrphostin AG126 may prevent the oxysterol-induced nerve terminal dysfunction.