Cholesterol Metabolism In Hepatocytes Research Articles

The role of STAT3/VAV3 in glucolipid metabolism during the development of HFD-induced MAFLD.

Metabolic-associated fatty liver disease (MAFLD) is a globally prevalent chronic hepatic disease. Previous studies have indicated that the activation of the signal transducer and activator of transcription3 (STAT3) plays a vital role in MAFLD progression at the very beginning. However, the specific association between STAT3 and abnormal hepatic metabolism remains unclear. In this study, activated inflammation was observed to induce abnormal glucolipid metabolic disorders in the hepatic tissues of high-fat diet (HFD)-fed ApoE-/- mice. Furthermore, we found that the activation of STAT3 induced by HFD might function as a transcriptional factor to suppress the expression of VAV3, which might participate in intracellular glucolipid metabolism and the regulation of glucose transporter 4 (GLUT4) storage vesicle traffic in the development of MAFLD both in vitro and in vivo. We verified that VAV3 deficiency could retard the GLUT4 membrane translocation and impair the glucose homeostasis. Additionally, VAV3 participates in cholesterol metabolism in hepatocytes, eventually resulting in the accumulation of intracellular cholesterol. Moreover, rAAV8-TBG-VAV3 was conducted to restore the expression of VAV3 in HFD-fed ApoE-/- mice. VAV3 overexpression was observed to improve glucose homeostasis as well as attenuate hepatic cholesterol accumulation in vivo. In conclusion, the STAT3/VAV3 signaling pathway might play a significant role in MAFLD by regulating glucose and cholesterol metabolism, and VAV3 might be a potential therapeutic strategy which could consequently ameliorate MAFLD.

Role of sortilin 1 (SORT1) on fatty acid-mediated cholesterol metabolism in primary calf hepatocytes.

Ketosis is a common metabolic disorder in peripartal dairy cows that is caused by excessive mobilization of fat and incomplete hepatic metabolism of fatty acids (FFA). Recent data in nonruminant models revealed that sortilin 1 (SORT1) is involved in a variety of lipid metabolism-related diseases. It plays important roles in the regulation of triglyceride (TAG) and total cholesterol (TC) levels. In this study, we first used liver biopsies from healthy cows (serum β-hydroxybutyrate concentration <0.6 mM) and cows diagnosed with clinical ketosis (serum β-hydroxybutyrate concentration >3.0 mM) to assess alterations in cholesterol synthesis, transport, and excretion. Then, to assess mechanistic links between SORT1 and fatty acid-mediated cholesterol metabolism, hepatocytes isolated from 4 healthy female calves (1 d old, 35-45 kg) were challenged with or without a mixture of free fatty acids (FFA; 1.2 mM) to induce metabolic stress. Hepatocytes were then treated with empty adenovirus vectors (with green fluorescent protein; Ad-GFP) or with SORT1-overexpressing adenovirus (Ad-SORT1) for 6 h or with SORT1 inhibitor (SORT1i) for 2 h, followed by a challenge with (Ad-GFP+FFA, Ad-SORT1+FFA, or SORT1i+FFA) or without (Ad-GFP, Ad-SORT1, or SORT1i) 1.2 mM FFA mixture for 12 h. Data analysis of calf hepatocyte treatment comparisons were assessed by 2-way ANOVA, and multiplicity for each experiment was adjusted using the Bonferroni procedure. Expression levels of factors related to cholesterol synthesis, transport, and excretion in liver tissue of cows with ketosis was lower. Hepatocytes challenged with FFA had lower concentrations of TC and mRNA and protein abundances of sterol regulatory element-binding protein 2 (SREBF2), acetyl acyl coenzyme A-cholesterol acyltransferase 2 (ACAT2), ATP-binding cassette transporter A1 (ABCA1), ABC subfamily G member 5 (ABCG5), and ABC subfamily G member 8 (ABCG8). Compared with FFA challenge alone, SORT1i + FFA led to greater protein abundance of 3-hydroxy-3-methyl-glutaryl coenzyme A reductase (HMGCR), ACAT2, and ABCG5, and greater mRNA abundance of ABCG5. Compared with FFA challenge alone, SORT1 overexpression led to lower protein abundance of SREBF2. In contrast, protein abundance of ABCA1 was greater. Overall, our data suggested that exogenous FFA induced abnormal cholesterol metabolism in hepatocytes, whereas a high abundance of SORT1 affected cholesterol esterification and potentially influx into bile. Thus, downregulation of hepatic SORT1 might be a cholesterol-regulated protective mechanism in the presence of a marked increase in FFA.

TRPV1 Protect against Hyperglycemia and Hyperlipidemia Induced Liver Injury via OPA1 in Diabetes.

Type 2 diabetes mellitus (T2DM)-associated mitochondrial impairment may a key factor leading to liver injury. Transient receptor potential receptor vanilloid 1 (TRPV1) regulates the energy expenditure and cholesterol metabolism in hepatocytes and protects against oxidative toxicity. Optic atrophy 1 (OPA1) is involved in the protection of TRPV1 on cardiac microvascular and lung injury. The aim of this study is to identify the role of TRPV1 in redox signals and liver protection via OPA1. TRPV1 knockout (TRPV1-/-) mice were used. And T2DM associated liver injury was induced by high glucose and high fatty acid (HG/HF) treatment. Mechanisms were studied by TUNEL staining, transmission electron microscope (TEM) analysis, reverse transcription polymerase chain reaction (RT-PCR) and Western blotting in vivo and in vitro. We determined that HG/HF treatment increased TRPV1 expression in liver tissues and AML12 cells. The knockout of TRPV1 increased the apoptotic hepatocytes rate. The inhibition of TRPV1 by 5'-iRTX in HG/HF group elevated the reactive oxygen species (ROS) levels, whereas TRPV1 agonist capsaicin reduced ROS. Our studies also showed that the OPA1 expression was lower in livers from HG/HF treated mice than the control, and genetic ablation of TRPV1 decreased OPA1 expression to a greater extent than the HG/HF mice. The protective effects of TRPV1 on mitochondrial were blocked by OPA1 siRNA. In conclusion, our study showed that the identified regulation of TRPV1 to OPA1 has important implication to the pathogenesis of T2DM-associated liver injury. Targeting the action of TRPV1 and OPA1 presents a potential therapeutic intervention.

Hepatocyte sortilin 1 knockout and treatment with a sortilin 1 inhibitor reduced plasma cholesterol in Western diet-fed mice

Sortilin 1 (Sort1) is a member of the Vps10p domain intracellular trafficking receptor family. Genetic variations of the SORT1 gene are strongly associated with plasma cholesterol levels in humans. Recent studies have linked Sort1 to regulation of cholesterol metabolism in hepatocytes and pro-inflammatory response in macrophages, but the tissue-specific roles of Sort1 in lipid metabolism have not been well defined. We developed Sort1 floxed mice and investigated the development of Western diet (WD)-induced steatosis, hepatic inflammatory response, and hyperlipidemia in hepatocyte Sort1 KO mice and myeloid cell Sort1 KO mice. Our findings suggest that hepatocyte Sort1 deficiency attenuated diet-induced hepatic steatosis and hypercholesterolemia in mice. In contrast, myeloid Sort1 deficiency did not reduce hepatic cytokine expression or plasma cholesterol levels, but exacerbated hepatic triglyceride accumulation in WD-fed mice. Finally, we showed that treating WD-fed mice with an orally bioavailable Sort1 inhibitor, AF38469, decreased plasma cholesterol and hepatic cytokine expression. AF38469 treatment did not affect diet-induced obesity or insulin resistance, but was associated with reduced hepatic VLDL secretion and higher hepatic cholesterol 7α-hydrolase expression in WD-fed mice. In conclusion, findings from this study suggest that Sort1 loss-of-function in hepatocytes contributes to lower plasma cholesterol, and pharmacological inhibition of Sort1 attenuates diet-induced hypercholesterolemia in mice.

Modulation of Amyloidogenesis Controlled by the C-Terminal Domain of Islet Amyloid Polypeptide Shows New Functions on Hepatocyte Cholesterol Metabolism.

The islet amyloid polypeptide (IAPP) or amylin maintains a key role in metabolism. This 37-residues-peptide could form pancreatic amyloids, which are a characteristic feature of diabetes mellitus type 2. However, some species do not form amyloid fibril structures. By employing a biomimetic approach, we generated an extensive panel of optimized sequences of IAPP, which could drastically reduce aggregation propensity. A structural and cellular characterization analysis was performed on the C-terminal domain with the highest aggregation propensity. This allowed the observation of an aggregative phenomenon dependent of the lipid environment. Evaluation of the new F23R variant demonstrated inhibition of β-sheet structure and, therefore, amyloid formation on the native C-terminal, phenomenon that was associated with functional optimization in calcium and cholesterol management coupled with the optimization of insulin secretion by beta cells. When F23R variant was evaluated in microglia cells, a model of amyloidosis, cytotoxic conditions were not registered. In addition, it was found that C-terminal sequences of IAPP could modulate cholesterol metabolism in hepatocytes through regulation of SREBP-2, apoA-1, ABCA1, and LDLR, mechanism that may represent a new function of IAPP on the metabolism of cholesterol, increasing the LDL endocytosis in hepatocytes. Optimized sequences with only one residue modification in the C-terminal core aggregation could diminish β-sheet formation and represent a novel strategy adaptable to other pharmacological targets. Our data suggest a new IAPP function associated with rearrangements on metabolism of cholesterol in hepatocytes.

Epigallocatechin gallate changes mRNA expression level of genes involved in cholesterol metabolism in hepatocytes

Catechins, compounds derived from green tea, have been shown to improve cholesterol metabolism in animal studies, but the molecular mechanisms underlying this function have not been fully understood. We performed DNA microarray analysis in order to clarify the effects of epigallocatechin gallate (EGCG), the dominant catechin in green tea, on cholesterol metabolism in HepG2 hepatocytes. This revealed that the expression levels of several genes related to cholesterol metabolism, including the LDL receptor, were changed by EGCG treatment. Using a real-time PCR technique, we confirmed that EGCG treatment up-regulated mRNA expression level of the LDL receptor. Moreover, EGCG decreased extracellular apoB levels. These findings indicated that EGCG improves cholesterol metabolism through the up-regulation of LDL receptor and also reduces extracellular apoB levels.

Role of Scavenger Receptor CD36 in Cholesterol Metabolism in Hepatocytes.

Role of Scavenger Receptor CD36 in Cholesterol Metabolism in Hepatocytes.