RESUMO
The I148M variant of PNPLA3 is closely associated with hepatic steatosis. Recent evidence indicates that the I148M mutant functions as an inhibitor of PNPLA2/ATGL-mediated lipolysis, leaving the role of wild-type PNPLA3 undefined. Despite showing a triglyceride hydrolase activity in vitro, PNPLA3 has yet to be established as a lipase in vivo. Here, we show that PNPLA3 preferentially hydrolyzes polyunsaturated triglycerides, mobilizing polyunsaturated fatty acids for phospholipid desaturation and enhancing hepatic secretion of triglyceride-rich lipoproteins. Under lipogenic conditions, mice with liver-specific knockout or acute knockdown of PNPLA3 exhibit aggravated liver steatosis and reduced plasma VLDL-triglyceride levels. Similarly, I148M-knockin mice show decreased hepatic triglyceride secretion during lipogenic stimulation. Our results highlight a specific context whereby the wild-type PNPLA3 facilitates the balance between hepatic triglyceride storage and secretion, and suggest the potential contribution of a loss-of-function by the I148M variant to the development of fatty liver disease in humans.
Assuntos
Ácidos Graxos Insaturados , Lipase , Lipoproteínas VLDL , Fígado , Camundongos Knockout , Triglicerídeos , Animais , Lipase/metabolismo , Lipase/genética , Fígado/metabolismo , Triglicerídeos/metabolismo , Camundongos , Lipoproteínas VLDL/metabolismo , Humanos , Ácidos Graxos Insaturados/metabolismo , Masculino , Fígado Gorduroso/metabolismo , Fígado Gorduroso/genética , Camundongos Endogâmicos C57BL , Lipólise , Proteínas de Membrana/metabolismo , Proteínas de Membrana/genética , Aciltransferases , Fosfolipases A2 Independentes de CálcioRESUMO
This study aimed to determine whether obese men with nonalcoholic fatty liver disease (NAFLD) display differences between those with simple steatosis versus steatohepatitis (NASH) in splanchnic and hepatic FFA and VLDL-triglycerides (VLDL-TG) balances. The study involved 17 obese men with biopsy-proven NAFLD (9 with NASH and 8 with simple steatosis). We used hepatic vein catheterization in combination with [3H]palmitate and [14C]VLDL-TG tracers to measure splanchnic palmitate and VLDL-TG uptake and release rates during basal and hyperinsulinemic conditions. Indocyanine green was used to measure splanchnic plasma flow. Splanchnic palmitate uptake was similar in the two groups and significantly reduced during hyperinsulinemia (NASH: 62 (48-77) versus 38 (18-58) µmol/min; simple steatosis: 62 (46-78) versus 45 (25-65) µmol/min, mean (95% CI), basal versus clamp periods, respectively, P = 0.02 time-effect). Splanchnic palmitate release was also comparable between groups and nonsignificantly diminished during hyperinsulinemia. The percent palmitate delivered to the liver originating from visceral adipose tissue lipolysis was similar and unchanged by hyperinsulinemia. Splanchnic uptake and release of VLDL-TG were similar between groups. Hyperinsulinemia suppressed VLDL-TG release (P <0.05 time-effect) in both groups. Insulin-mediated glucose disposal was similar in the two groups (P = 0.54). Obese men with NASH and simple steatosis have similar splanchnic uptake and release of FFA and VLDL-TG and a similar proportion of FFA from visceral adipose tissue lipolysis delivered to the liver. These results demonstrate that the splanchnic balances of FFA and VLDL-TG do not differ between obese men with NASH and those with simple steatosis.
Assuntos
Insulina , Lipoproteínas VLDL , Hepatopatia Gordurosa não Alcoólica , Triglicerídeos , Humanos , Masculino , Lipoproteínas VLDL/metabolismo , Hepatopatia Gordurosa não Alcoólica/metabolismo , Hepatopatia Gordurosa não Alcoólica/patologia , Pessoa de Meia-Idade , Triglicerídeos/metabolismo , Triglicerídeos/sangue , Insulina/metabolismo , Ácidos Graxos não Esterificados/metabolismo , Ácidos Graxos não Esterificados/sangue , Adulto , Fígado Gorduroso/metabolismo , Fígado Gorduroso/patologia , Fígado/metabolismo , Obesidade/metabolismo , Obesidade/complicaçõesRESUMO
BACKGROUND: Pathogenic variants in PLIN1-encoding PLIN1 (perilipin-1) are responsible for an autosomal dominant form of familial partial lipodystrophy (FPL) associated with severe insulin resistance, hepatic steatosis, and important hypertriglyceridemia. This study aims to decipher the mechanisms of hypertriglyceridemia associated with PLIN1-related FPL. METHODS: We performed an in vivo lipoprotein kinetic study in 6 affected patients compared with 13 healthy controls and 8 patients with type 2 diabetes. Glucose and lipid parameters, including plasma LPL (lipoprotein lipase) mass, were measured. LPL mRNA and protein expression were evaluated in abdominal subcutaneous adipose tissue from patients with 5 PLIN1-mutated FPL and 3 controls. RESULTS: Patients with PLIN1-mutated FPL presented with decreased fat mass, insulin resistance, and diabetes (glycated hemoglobin A1c, 6.68±0.70% versus 7.48±1.63% in patients with type 2 diabetes; mean±SD; P=0.27). Their plasma triglycerides were higher (5.96±3.08 mmol/L) than in controls (0.76±0.27 mmol/L; P<0.0001) and patients with type 2 diabetes (2.94±1.46 mmol/L, P=0.006). Compared with controls, patients with PLIN1-related FPL had a significant reduction of the indirect fractional catabolic rate of VLDL (very-low-density lipoprotein)-apoB100 toward IDL (intermediate-density lipoprotein)/LDL (low-density lipoprotein; 1.79±1.38 versus 5.34±2.45 pool/d; P=0.003) and the indirect fractional catabolic rate of IDL-apoB100 toward LDL (2.14±1.44 versus 7.51±4.07 pool/d; P=0.005). VLDL-apoB100 production was not different between patients with PLIN1-related FPL and controls. Compared with patients with type 2 diabetes, patients with PLIN1-related FPL also showed a significant reduction of the catabolism of both VLDL-apoB100 (P=0.031) and IDL-apoB100 (P=0.031). Plasma LPL mass was significantly lower in patients with PLIN1-related FPL than in controls (21.03±10.08 versus 55.76±13.10 ng/mL; P<0.0001), although the LPL protein expression in adipose tissue was similar. VLDL-apoB100 and IDL-apoB100 indirect fractional catabolic rates were negatively correlated with plasma triglycerides and positively correlated with LPL mass. CONCLUSIONS: We show that hypertriglyceridemia associated with PLIN1-related FPL results from a marked decrease in the catabolism of triglyceride-rich lipoproteins (VLDL and IDL). This could be due to a pronounced reduction in LPL availability, related to the decreased adipose tissue mass.
Assuntos
Diabetes Mellitus Tipo 2 , Hipertrigliceridemia , Resistência à Insulina , Lipodistrofia Parcial Familiar , Lipase Lipoproteica , Lipoproteínas , Perilipina-1 , Triglicerídeos , Humanos , Masculino , Perilipina-1/genética , Perilipina-1/metabolismo , Perilipina-1/sangue , Triglicerídeos/sangue , Hipertrigliceridemia/sangue , Hipertrigliceridemia/genética , Feminino , Adulto , Pessoa de Meia-Idade , Estudos de Casos e Controles , Diabetes Mellitus Tipo 2/sangue , Diabetes Mellitus Tipo 2/genética , Diabetes Mellitus Tipo 2/complicações , Lipoproteínas/sangue , Lipase Lipoproteica/sangue , Lipase Lipoproteica/metabolismo , Lipase Lipoproteica/genética , Lipodistrofia Parcial Familiar/genética , Lipodistrofia Parcial Familiar/sangue , Lipodistrofia Parcial Familiar/metabolismo , Mutação , Glicemia/metabolismo , Lipoproteínas VLDL/sangue , Lipoproteínas VLDL/metabolismo , Biomarcadores/sangue , Fenótipo , Predisposição Genética para Doença , Lipólise , RNA Mensageiro/metabolismo , RNA Mensageiro/genéticaRESUMO
Recent advances in human genetics, together with a substantial body of epidemiological, preclinical and clinical trial evidence, strongly support a causal relationship between triglyceride-rich lipoproteins (TRLs) and atherosclerotic cardiovascular disease. Consequently, the secretion and metabolism of TRLs have a significant impact on cardiovascular health. This knowledge underscores the importance of understanding the molecular mechanisms and regulation of very-low-density lipoprotein (VLDL) and chylomicron biogenesis. Fortunately, there has been a resurgence of interest in the intracellular assembly, trafficking, degradation, and secretion of VLDL, leading to many ground-breaking molecular insights. Furthermore, the identification of molecular control mechanisms related to triglyceride metabolism has greatly advanced our understanding of the complex metabolism of TRLs. In this review, we explore recent advances in the assembly, secretion, and metabolism of TRLs. We also discuss available treatment strategies for hypertriglyceridemia.
Assuntos
Lipoproteínas VLDL , Triglicerídeos , Humanos , Triglicerídeos/metabolismo , Lipoproteínas VLDL/metabolismo , Hipertrigliceridemia/metabolismo , Lipoproteínas/metabolismo , Animais , Apolipoproteínas B/metabolismo , Quilomícrons/metabolismo , Aterosclerose/metabolismoRESUMO
PURPOSE OF REVIEW: Transmembrane 6 superfamily member 2 ( TM6SF2 ) gene was identified through exome-wide studies in 2014. A genetic variant from glutamic acid to lysine substitution at amino acid position 167 (NM_001001524.3:c.499G> A) (p.Gln167Lys/p.E167K, rs58542926) was discovered (p.E167K) to be highly associated with increased hepatic fat content and reduced levels of plasma triglycerides and LDL cholesterol. In this review, we focus on the discovery of TM6SF2 and its role in VLDL secretion pathways. Human data suggest TM6SF2 is linked to hepatic steatosis and cardiovascular disease (CVD), hence understanding its metabolic pathways is of high scientific interest. RECENT FINDINGS: Since its discovery, completed research studies in cell, rodent and human models have defined the role of TM6SF2 and its links to human disease. TM6SF2 resides in the endoplasmic reticulum (ER) and the ER-Golgi interface and helps with the lipidation of nascent VLDL, the main carrier of triglycerides from the liver to the periphery. Consistent results from cells and rodents indicated that the secretion of triglycerides is reduced in carriers of the p.E167K variant or when hepatic TM6SF2 is deleted. However, data for secretion of APOB, the main protein of VLDL particles responsible for triglycerides transport, are inconsistent. SUMMARY: The identification of genetic variants that are highly associated with human disease presentation should be followed by the validation and investigation into the pathways that regulate disease mechanisms. In this review, we highlight the role of TM6SF2 and its role in processing of liver triglycerides.
Assuntos
Lipoproteínas VLDL , Proteínas de Membrana , Humanos , Animais , Proteínas de Membrana/metabolismo , Proteínas de Membrana/genética , Lipoproteínas VLDL/metabolismo , Pesquisa Translacional BiomédicaRESUMO
Genetic polymorphisms that impair very low-density lipoprotein (VLDL) secretion are linked to hepatic steatosis, fibrosis, and hepatocellular cancer. Liver-specific deletion of microsomal triglyceride transfer protein (Mttp-LKO) impairs VLDL assembly, promoting hepatic steatosis and fibrosis, which are attenuated in Mttp-LKO X Fabp1-null [Fabp1/Mttp double knockout (DKO)] mice. The current study examined the impact of impaired VLDL secretion in Mttp-LKO mice on hepatocellular cancer incidence and progression in comparison to Fabp1/Mttp DKO mice. Diethylnitrosamine-treated Mttp-LKO mice exhibited steatosis with increased tumor burden compared with flox controls, whereas diethylnitrosamine-treated Fabp1/Mttp DKO mice exhibited a paradoxical increase in tumor burden and >50% mortality by 50 weeks. Serum high-density lipoprotein cholesterol was elevated in both Mttp-LKO and Fabp1/Mttp DKO mice, with increased intratumoral expression of apolipoprotein A1 and apolipoprotein E. Lipidomic surveys revealed progressive enrichment in distinct triglyceride species in livers from Mttp-LKO mice with further enrichment in Fabp1/Mttp DKO mice. RNA sequencing revealed mRNA changes suggesting altered monocarboxylic acid use and increased aerobic glycolysis, whereas hepatocytes from Fabp1/Mttp DKO mice exhibited increased capacity to use glucose and glutamine. These metabolic shifts were accompanied by reduced expression of HNF1 homeobox A (HNF1a), which correlated with tumor burden. Taken together, these findings demonstrate that hepatic tumorigenesis is increased in mice with impaired VLDL secretion and further accelerated via pathways including altered fatty acid compartmentalization and shifts in hepatic energy use.
Assuntos
Carcinogênese , Proteínas de Ligação a Ácido Graxo , Lipoproteínas VLDL , Neoplasias Hepáticas , Animais , Camundongos , Carcinogênese/genética , Carcinogênese/patologia , Carcinogênese/metabolismo , Carcinoma Hepatocelular/patologia , Carcinoma Hepatocelular/genética , Carcinoma Hepatocelular/metabolismo , Proteínas de Transporte/metabolismo , Proteínas de Transporte/genética , Proteínas de Ligação a Ácido Graxo/genética , Proteínas de Ligação a Ácido Graxo/metabolismo , Fígado Gorduroso/metabolismo , Fígado Gorduroso/patologia , Fígado Gorduroso/genética , Deleção de Genes , Lipoproteínas VLDL/metabolismo , Fígado/metabolismo , Fígado/patologia , Neoplasias Hepáticas/genética , Neoplasias Hepáticas/metabolismo , Neoplasias Hepáticas/patologia , Camundongos KnockoutRESUMO
BACKGROUND AND STUDY AIMS: Ghrelin is an appetite hormone-containing 28-amino acid and has 4 different forms in the body. Ghrelin forms have different physiological functions in the body. This study aims to analyze the effect of acyl and desacyl ghrelin hormone on hepatic steatosis and biochemical findings in 36 male Wistar rats. MATERIALS AND METHODS: Rats were split into 6 equal groups, consisting of control, acyl ghrelin, desacyl ghrelin, acyl/desacyl 3:1, acyl/desacyl 1:1, and acyl/desacyl 1:3 groups, and administered placebo or 200 ng/kg hormone subcutaneous twice a day for 14 days. Oral Glucose Tolerance Test (OGTT) was performed on Day 15, Insulin Tolerance Test (ITT) on Day 16, and scarification procedure on Day 17. Certain biochemical data and liver diacylglycerol (DAG), glycogen, protein kinase C and PPAR-γ levels were detected in the blood. Histological analyses were also conducted on the liver tissues. RESULTS: The highest plasma total cholesterol and VLDL-K levels were found in the acyl/desacyl 1:3 group, and lower insulin, and HOMA-IR levels were found in groups where acyl and desacyl were administered together (p < 0.05). PPAR-γ gene expression level increased in acyl ghrelin and acyl/desacyl 1:3 groups compared to the control group. Protein kinase C gene expression was highest in the acyl/desacyl 1:3 group. The most severe degenerative findings compliant with steatosis in the liver were observed in the acyl ghrelin group (p < 0.05). CONCLUSION: It was determined that administering rats acyl alone and acyl/desacyl by 1:3 caused the highest PPAR-γ gene expression, serum total cholesterol, HDL-K, and VLDL-K levels in the body. Besides, it is shown that desacyl ghrelin effectively regulates the blood glucose level when administered alone.
Assuntos
Diglicerídeos , Grelina , Insulina , Fígado , PPAR gama , Ratos Wistar , Transdução de Sinais , Grelina/metabolismo , Animais , Masculino , PPAR gama/metabolismo , Ratos , Fígado/metabolismo , Fígado/patologia , Insulina/metabolismo , Insulina/sangue , Diglicerídeos/metabolismo , Colesterol/sangue , Colesterol/metabolismo , Teste de Tolerância a Glucose , Proteína Quinase C/metabolismo , Fígado Gorduroso/metabolismo , Glicogênio/metabolismo , Resistência à Insulina , Glicemia/metabolismo , Lipoproteínas VLDL/metabolismo , Lipoproteínas VLDL/sangueRESUMO
N-Nitrosodiethylamine (NDEA), a carcinogen in some foods and medications, is linked to liver damage similar to non-alcoholic fatty liver disease (NAFLD). This study explores how NDEA disrupts liver lipid metabolism. Sprague-Dawley rats were given two doses of NDEA (100 mg/kg) orally, 24 h apart. Liver response was assessed through tissue staining, blood tests, and biochemical markers, including fatty acids, lipid peroxidation, and serum very-low density lipoprotein (VLDL) levels. Additionally, lipidomic analysis of liver tissues and serum was performed. The results indicated significant hepatic steatosis (fat accumulation in the liver) following NDEA exposure. Blood analysis showed signs of inflammation and liver damage. Biochemical tests revealed decreased liver protein synthesis and specific enzyme alterations, suggesting liver cell injury but maintaining mitochondrial function. Increased fatty acid levels without a rise in lipid peroxidation were observed, indicating fat accumulation. Lipidomic analysis showed increased polyunsaturated triglycerides in the liver and decreased serum VLDL, implicating impaired VLDL transport in liver dysfunction. In conclusion, NDEA exposure disrupts liver lipid metabolism, primarily through the accumulation of polyunsaturated triglycerides and impaired fat transport. These findings provide insight into the mechanisms of NDEA-induced liver injury and its progression to hepatic steatosis.
Assuntos
Dietilnitrosamina , Hepatopatia Gordurosa não Alcoólica , Ratos , Animais , Triglicerídeos/metabolismo , Dietilnitrosamina/toxicidade , Lipoproteínas VLDL/metabolismo , Ratos Sprague-Dawley , Fígado/metabolismo , Hepatopatia Gordurosa não Alcoólica/induzido quimicamente , Hepatopatia Gordurosa não Alcoólica/metabolismo , Metabolismo dos Lipídeos , Lipoproteínas LDL/metabolismo , Dieta HiperlipídicaRESUMO
OBJECTIVES: The assembly and secretion of hepatic very low-density lipoprotein (VLDL) plays pivotal roles in hepatic and plasma lipid homeostasis. Protein disulfide isomerase A1 (PDIA1/P4HB) is a molecular chaperone whose functions are essential for protein folding in the endoplasmic reticulum. Here we investigated the physiological requirement in vivo for PDIA1 in maintaining VLDL assembly and secretion. METHODS: Pdia1/P4hb was conditionally deleted in adult mouse hepatocytes and the phenotypes characterized. Mechanistic analyses in primary hepatocytes determined how PDIA1 ablation alters MTTP synthesis and degradation as well as altering synthesis and secretion of Apolipoprotein B (APOB), along with complementary expression of intact PDIA1 vs a catalytically inactivated PDIA1 mutant. RESULTS: Hepatocyte-specific deletion of Pdia1/P4hb inhibited hepatic MTTP expression and dramatically reduced VLDL production, leading to severe hepatic steatosis and hypolipidemia. Pdia1-deletion did not affect mRNA expression or protein stability of MTTP but rather prevented Mttp mRNA translation. We demonstrate an essential role for PDIA1 in MTTP synthesis and function and show that PDIA1 interacts with APOB in an MTTP-independent manner via its molecular chaperone function to support APOB folding and secretion. CONCLUSIONS: PDIA1 plays indispensable roles in APOB folding, MTTP synthesis and activity to support VLDL assembly. Thus, like APOB and MTTP, PDIA1 is an obligatory component of hepatic VLDL production.
Assuntos
Hepatócitos , Lipoproteínas VLDL , Nucleotídeos de Timina , Animais , Camundongos , Apolipoproteínas B/genética , Apolipoproteínas B/metabolismo , Hepatócitos/metabolismo , Lipoproteínas VLDL/metabolismo , Chaperonas Moleculares/genética , Chaperonas Moleculares/metabolismo , Triglicerídeos/metabolismoRESUMO
The poem Ode on the Odyssey of lipoproteins describes the structure, functions and metabolism of lipoproteins namely Chylomicrons, LDL, VLDL and HDL. This poem is a triolet with eight lines in each stanza. Odyssey is the travel experience of an adventurous journey when someone travels far and wide. This poem describes the transport adventures of Lipids when they travel in the form of lipoproteins. The poetic form of describing the metabolism of lipoproteins was intended to kindle the interest of the learners and to gain an imaginary experience in the metabolism of lipoproteins.
Assuntos
Lipoproteínas HDL , Lipoproteínas LDL , Lipoproteínas HDL/metabolismo , Lipoproteínas LDL/metabolismo , Lipoproteínas VLDL/metabolismo , Lipoproteínas/química , Lipoproteínas/metabolismo , Quilomícrons/metabolismoRESUMO
An acylated flavonol glycoside, trans-tiliroside (1), is found in certain parts of different herbs, including the seeds of Rosa canina (Rosaceae). Previous studies on compound 1 have focused on triglyceride (TG) metabolism, including its anti-obesity and intracellular TG reduction effects. In the present study, the effects of compound 1 on cholesterol (CHO) metabolism were investigated using human hepatocellular carcinoma-derived HepG2 cells and mice. Compound 1 decreased CHO secretion in HepG2 cells, which was enhanced by mevalonate in a concentration-dependent manner and decreased the secretion of apoprotein B (apoB)-100, a marker of very low-density lipoprotein (VLDL). Compound 1 also inhibited the activity of microsomal triglyceride transfer proteins, which mediate VLDL formation from cholesterol and triglycerides in the liver. In vivo, compound 1 inhibited the accumulation of Triton WR-1339-induced TG in the blood of fasted mice and maintained low levels of apoB-100. These results suggest that compound 1 inhibits the secretion of CHO as VLDL from the liver and has the potential for use for the prevention of dyslipidemia.
Assuntos
Lipoproteínas VLDL , Neoplasias Hepáticas , Camundongos , Humanos , Animais , Lipoproteínas VLDL/metabolismo , Lipoproteínas VLDL/farmacologia , Apolipoproteínas B/metabolismo , Células Hep G2 , Fígado/metabolismo , Triglicerídeos , Colesterol , Lipoproteínas LDL/metabolismoRESUMO
Hepatic lipidosis in dairy cows is the result of a disturbed balance between the uptake of non-esterified fatty acids (NEFA), their metabolism in the hepatocytes, and the limited efflux of TG as very-low-density lipoprotein (VLDL). Lipidosis and the associated risk for ketosis represents a consequence of selecting dairy cows primarily for milk production without considering the basic physiological mechanisms of this trait. The overall risk for lipidosis and ketosis possesses a genetic background and the recently released new breeding value of the German Holstein Friesian cows now sets the path for correction of this risk and in that confirms the assumed genetic threat. Ectopic fat deposition in the liver is the result of various steps including lipolysis, uptake of fat by the liver cell, its metabolism, and finally release as very-low-density lipoprotein (VLDL). These reactions may be modulated directly or indirectly and hence, serve as basis for prophylactic measures. The pertaining methods are described in order to support an improved understanding of the pathogenesis of lipidosis and ketosis. They consist of feeding a glucogenic diet, restricted feeding during the close-up time as well as supplementation with choline, niacin, carnitine, or the reduction of milking frequency. Prophylactic measures for the prevention of ketosis are also included in this discussion.
Assuntos
Doenças dos Bovinos , Cetose , Lipidoses , Feminino , Bovinos , Animais , Lactação/fisiologia , Predisposição Genética para Doença , Fígado/metabolismo , Ácidos Graxos não Esterificados , Leite/metabolismo , Lipidoses/genética , Lipidoses/prevenção & controle , Lipidoses/veterinária , Cetose/veterinária , Lipoproteínas VLDL/metabolismo , Doenças dos Bovinos/genética , Doenças dos Bovinos/prevenção & controleRESUMO
Avoiding hepatic steatosis is crucial for preventing liver dysfunction, and one mechanism by which this is accomplished is through synchronization of the rate of very low density lipoprotein (VLDL) synthesis with its secretion. Endoplasmic reticulum (ER)-to-Golgi transport of nascent VLDL is the rate-limiting step in its secretion and is mediated by the VLDL transport vesicle (VTV). Recent in vivo studies have indicated that α-tocopherol (α-T) supplementation can reverse steatosis in nonalcoholic fatty liver disease, but its effects on hepatic lipoprotein metabolism are poorly understood. Here, we investigated the impact of α-T on hepatic VLDL synthesis, secretion, and intracellular ER-to-Golgi VLDL trafficking using an in vitro model. Pulse-chase assays using [3H]-oleic acid and 100 µmol/L α-T demonstrated a disruption of early VLDL synthesis, resulting in enhanced apolipoprotein B-100 expression, decreased expression in markers for VTV budding, ER-to-Golgi VLDL transport, and reduced VLDL secretion. Additionally, an in vitro VTV budding assay indicated a significant decrease in VTV production and VTV-Golgi fusion. Confocal imaging of lipid droplet (LD) localization revealed a decrease in overall LD retention, diminished presence of ER-associated LDs, and an increase in Golgi-level LD retention. We conclude that α-T disrupts ER-to-Golgi VLDL transport by modulating the expression of specific proteins and thus reduces VLDL secretion.
Assuntos
Fígado Gorduroso , Lipoproteínas VLDL , Humanos , Lipoproteínas VLDL/metabolismo , alfa-Tocoferol/farmacologia , alfa-Tocoferol/metabolismo , Fígado/metabolismo , Vesículas Transportadoras/metabolismo , Fígado Gorduroso/metabolismo , Retículo Endoplasmático/metabolismo , Triglicerídeos/metabolismoRESUMO
Ketosis is a metabolic disease that often occurs in dairy cows postpartum and is a result of disordered lipid metabolism. Acetyl-coenzyme A (CoA) acetyltransferase 2 (ACAT2) is important for balancing cholesterol and triglyceride (TG) metabolism; however, its role in subclinical ketotic dairy cows is unclear. This study aimed to explore the potential correlation between ACAT2 and lipid metabolism disorders in subclinical ketotic cows through in vitro and in vivo experiments. In the in vivo experiment, liver tissue and blood samples were collected from healthy cows (CON, n = 6, ß-hydroxybutyric acid [BHBA] concentration <1.0 mM) and subclinical ketotic cows (subclinical ketosis [SCK], n = 6, BHBA concentration = 1.2-3.0 mM) to explore the effect of ACAT2 on lipid metabolism disorders in SCK cows. For the in vitro experiment, bovine hepatocytes (BHEC) were used as the model. The effects of BHBA on ACAT2 and lipid metabolism were investigated via BHBA concentration gradient experiments. Subsequently, the relation between ACAT2 and lipid metabolism disorder was explored by transfection with siRNA of ACAT2. Transcriptomics showed an upregulation of differentially expression genes during lipid metabolism and significantly lower ACAT2 mRNA levels in the SCK group. Compared with the CON group in vivo, the SCK group showed significantly higher expression levels of peroxisome proliferator-activated receptor γ (PPARγ) and sterol regulator element binding protein 1c (SREBP1c) and significantly lower expression levels of peroxisome proliferator-activated receptor α (PPARα), carnitine palmitoyl-transferase 1A (CPT1A), sterol regulatory element binding transcription factor 2 (SREBP2), and 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR). Moreover, the SCK group had a significantly higher liver TG content and significantly lower plasma total cholesterol (TC) and free cholesterol content. These results were indicative of TG and cholesterol metabolism disorders in the liver of dairy cows with SCK. Additionally, the SCK group showed an increased expression of perilipin-2 (PLIN2), decreased expression of apolipoprotein B, and decreased plasma concentration of very low-density lipoproteins (VLDL) and low-density lipoproteins cholesterol (LDL-C) by downregulating ACAT2, which indicated an accumulation of TG in liver. In vitro experiments showed that BHBA induced an increase in the TG content of BHEC, decreased content TC, increased expression of PPARγ and SREBP1c, and decreased expression of PPARα, CPT1A, SREBP2, and HMGCR. Additionally, BHBA increased the expression of PLIN2 in BHEC, decreased the expression and fluorescence intensity of ACAT2, and decreased the VLDL and LDL-C contents. Furthermore, silencing ACAT2 expression increased the TG content; decreased the TC, VLDL, and LDL-C contents; decreased the expression of HMGCR and SREBP2; and increased the expression of SREBP1c; but had no effect on the expression of PLIN2. These results suggest that ACAT2 downregulation in BHEC promotes TG accumulation and inhibits cholesterol synthesis, leading to TG and cholesterol metabolic disorders. In conclusion, ACAT2 downregulation in the SCK group inhibited cholesterol synthesis, increased TG synthesis, and reduced the contents of VLDL and LDL-C, eventually leading to disordered TG and cholesterol metabolism.
Assuntos
Doenças dos Bovinos , Cetose , Transtornos do Metabolismo dos Lipídeos , Feminino , Bovinos , Animais , Metabolismo dos Lipídeos/fisiologia , LDL-Colesterol , PPAR alfa/genética , PPAR gama/metabolismo , Doenças dos Bovinos/metabolismo , Transtornos do Metabolismo dos Lipídeos/veterinária , Proteínas de Transporte/metabolismo , Lipoproteínas VLDL/metabolismo , Cetose/veterinária , Coenzima A/metabolismo , Ácido 3-HidroxibutíricoRESUMO
AIMS/HYPOTHESIS: This study explored the hypothesis that significant abnormalities in the metabolism of intestinally derived lipoproteins are present in individuals with type 2 diabetes on statin therapy. These abnormalities may contribute to residual CVD risk. METHODS: To investigate the kinetics of ApoB-48- and ApoB-100-containing lipoproteins, we performed a secondary analysis of 11 overweight/obese individuals with type 2 diabetes who were treated with lifestyle counselling and on a stable dose of metformin who were from an earlier clinical study, and compared these with 11 control participants frequency-matched for age, BMI and sex. Participants in both groups were on a similar statin regimen during the study. Stable isotope tracers were used to determine the kinetics of the following in response to a standard fat-rich meal: (1) apolipoprotein (Apo)B-48 in chylomicrons and VLDL; (2) ApoB-100 in VLDL, intermediate-density lipoprotein (IDL) and LDL; and (3) triglyceride (TG) in VLDL. RESULTS: The fasting lipid profile did not differ significantly between the two groups. Compared with control participants, in individuals with type 2 diabetes, chylomicron TG and ApoB-48 levels exhibited an approximately twofold higher response to the fat-rich meal, and a twofold higher increment was observed in ApoB-48 particles in the VLDL1 and VLDL2 density ranges (all p < 0.05). Again comparing control participants with individuals with type 2 diabetes, in the latter, total ApoB-48 production was 25% higher (556 ± 57 vs 446 ± 57 mg/day; p < 0.001), conversion (fractional transfer rate) of chylomicrons to VLDL was around 40% lower (35 ± 25 vs 82 ± 58 pools/day; p=0.034) and direct clearance of chylomicrons was 5.6-fold higher (5.6 ± 2.2 vs 1.0 ± 1.8 pools/day; p < 0.001). During the postprandial period, ApoB-48 particles accounted for a higher proportion of total VLDL in individuals with type 2 diabetes (44%) compared with control participants (25%), and these ApoB-48 VLDL particles exhibited a fivefold longer residence time in the circulation (p < 0.01). No between-group differences were seen in the kinetics of ApoB-100 and TG in VLDL, or in LDL ApoB-100 production, pool size and clearance rate. As compared with control participants, the IDL ApoB-100 pool in individuals with type 2 diabetes was higher due to increased conversion from VLDL2. CONCLUSIONS/INTERPRETATION: Abnormalities in the metabolism of intestinally derived ApoB-48-containing lipoproteins in individuals with type 2 diabetes on statins may help to explain the residual risk of CVD and may be suitable targets for interventions. TRIAL REGISTRATION: ClinicalTrials.gov NCT02948777.
Assuntos
Doenças Cardiovasculares , Diabetes Mellitus Tipo 2 , Inibidores de Hidroximetilglutaril-CoA Redutases , Humanos , Apolipoproteína B-100/uso terapêutico , Inibidores de Hidroximetilglutaril-CoA Redutases/uso terapêutico , Apolipoproteína B-48 , Diabetes Mellitus Tipo 2/tratamento farmacológico , Diabetes Mellitus Tipo 2/complicações , Doenças Cardiovasculares/tratamento farmacológico , Doenças Cardiovasculares/complicações , Lipoproteínas VLDL/metabolismo , Apolipoproteínas B/metabolismo , Apolipoproteínas B/uso terapêutico , Lipoproteínas , Triglicerídeos , Lipoproteínas IDL , QuilomícronsRESUMO
BACKGROUND AND AIMS: The worldwide prevalence of Non-alcoholic Fatty Liver Disease (NAFLD) raises concerns about associated risk factors, such as obesity and type 2 Diabetes Mellitus, for leading causes of disability and death. Besides Magnetic Resonance Imaging (MRI) and Spectroscopy (MRS), functional imaging with Positron Emission Tomography (PET) could contribute to a deeper understanding of the pathophysiology of NAFLD. Here we describe a novel approach using the PET tracer [18F]FTHA, which is an analog of long-chain free fatty acids (FFA) and is taken up by tissues to enter mitochondria or to be incorporated into complex lipids for further export as very-low-density lipoprotein (VLDL). METHODS: Male Sprague Dawley rats, after 6 weeks on a high-fat diet (HFD), were used as a model of diet induced NAFLD, while a standard diet (SD) served as a control group. Liver fat was estimated by MR spectroscopy at a 9.4 T system for phenotyping. To measure hepatic FFA uptake, rats underwent 60 min dynamic [18F]FTHA-PET scans after unrestricted access to food (HFD: n = 6; SD: n = 6) or overnight (≤16h) fasting (HFD: n = 6; SD: n = 5). FFA removal was assessed from incorporated 18F-residual in de novo synthesized VLDL out of plasma. RESULTS: MRS of the liver confirmed the presence of NAFLD (>5.6% fat). Under non-fasting conditions, hepatic [18F]FTHA uptake was significantly increased in NAFLD: SUVmean (p = 0.03) within [0; 60] min interval, SUVmean (p = 0.01) and SUVmax (p = 0.03) within [30; 60] min interval. SUVs for hepatic uptake under fasting conditions were not significantly different between the groups. Analysis of FFA removal demonstrated elevated values of 18F-residue in the VLDL plasma fraction of the healthy group compared to the NAFLD (p = 0.0569). CONCLUSION: Our novel approach for assessing FFA metabolism using [18F]FTHA demonstrated differences in the hepatic FFA uptake and FFA incorporation into VLDL between healthy and NAFLD rats. [18F]FTHA-PET could be used to study metabolic disturbances involved in the progression of NAFLD.
Assuntos
Diabetes Mellitus Tipo 2 , Hepatopatia Gordurosa não Alcoólica , Ratos , Masculino , Animais , Hepatopatia Gordurosa não Alcoólica/diagnóstico por imagem , Hepatopatia Gordurosa não Alcoólica/metabolismo , Ácidos Graxos não Esterificados , Lipoproteínas VLDL/metabolismo , Diabetes Mellitus Tipo 2/metabolismo , Tomografia Computadorizada por Raios X , Ratos Sprague-Dawley , Tomografia por Emissão de Pósitrons , Fígado/diagnóstico por imagem , Fígado/metabolismo , Dieta Hiperlipídica/efeitos adversosRESUMO
Apolipoprotein B (apoB)-lipoproteins initiate and promote atherosclerotic cardiovascular disease. Plasma tissue plasminogen activator (tPA) activity is negatively associated with atherogenic apoB-lipoprotein cholesterol levels in humans, but the mechanisms are unknown. We found that tPA, partially through the lysine-binding site on its Kringle 2 domain, binds to the N terminus of apoB, blocking the interaction between apoB and microsomal triglyceride transfer protein (MTP) in hepatocytes, thereby reducing very-low-density lipoprotein (VLDL) assembly and plasma apoB-lipoprotein cholesterol levels. Plasminogen activator inhibitor 1 (PAI-1) sequesters tPA away from apoB and increases VLDL assembly. Humans with PAI-1 deficiency have smaller VLDL particles and lower plasma levels of apoB-lipoprotein cholesterol. These results suggest a mechanism that fine-tunes VLDL assembly by intracellular interactions among tPA, PAI-1, and apoB in hepatocytes.
Assuntos
Apolipoproteínas B , Aterosclerose , Hepatócitos , Lipoproteínas VLDL , Inibidor 1 de Ativador de Plasminogênio , Ativador de Plasminogênio Tecidual , Humanos , Apolipoproteínas B/sangue , Aterosclerose/sangue , Aterosclerose/metabolismo , Hepatócitos/metabolismo , Lipoproteínas VLDL/metabolismo , Inibidor 1 de Ativador de Plasminogênio/sangue , Inibidor 1 de Ativador de Plasminogênio/metabolismo , Ativador de Plasminogênio Tecidual/metabolismo , Animais , Camundongos , Camundongos Endogâmicos C57BLRESUMO
Dyslipidemia in obesity results from excessive production and impaired clearance of triglyceride-rich (TG-rich) lipoproteins, which are particularly pronounced in the postprandial state. Here, we investigated the impact of Roux-en-Y gastric bypass (RYGB) surgery on postprandial VLDL1 and VLDL2 apoB and TG kinetics and their relationship with insulin-responsiveness indices. Morbidly obese patients without diabetes who were scheduled for RYGB surgery (n = 24) underwent a lipoprotein kinetics study during a mixed-meal test and a hyperinsulinemic-euglycemic clamp study before the surgery and 1 year later. A physiologically based computational model was developed to investigate the impact of RYGB surgery and plasma insulin on postprandial VLDL kinetics. After the surgery, VLDL1 apoB and TG production rates were significantly decreased, whereas VLDL2 apoB and TG production rates remained unchanged. The TG catabolic rate was increased in both VLDL1 and VLDL2 fractions, but only the VLDL2 apoB catabolic rate tended to increase. Furthermore, postsurgery VLDL1 apoB and TG production rates, but not those of VLDL2, were positively correlated with insulin resistance. Insulin-mediated stimulation of peripheral lipoprotein lipolysis was also improved after the surgery. In summary, RYGB resulted in reduced hepatic VLDL1 production that correlated with reduced insulin resistance, elevated VLDL2 clearance, and improved insulin sensitivity in lipoprotein lipolysis pathways.
Assuntos
Cirurgia Bariátrica , Resistência à Insulina , Obesidade Mórbida , Humanos , Insulina , Lipoproteínas VLDL/metabolismo , Cinética , Obesidade Mórbida/cirurgia , Lipoproteínas/metabolismo , Apolipoproteínas B/metabolismoRESUMO
The association between serum levels of endothelial lipase (EL) and the serum levels and composition of apolipoprotein B (apoB)-containing lipoproteins in healthy subjects and patients with metabolic syndrome (MS) remained unexplored. Therefore, in the present study, we determined the serum levels and lipid content of apoB-containing lipoproteins using nuclear magnetic resonance (NMR) spectroscopy and examined their association with EL serum levels in healthy volunteers (HVs) and MS patients. EL was significantly negatively correlated with the serum levels of cholesterol in large very low-density lipoprotein (VLDL) particles, as well as with total-cholesterol-, free-cholesterol-, triglyceride-, and phospholipid-contents of VLDL and intermediate-density lipoprotein particles in MS patients but not in HVs. In contrast, EL serum levels were significantly positively correlated with the serum levels of apoB, triglycerides, and phospholipids in large low-density lipoprotein particles in HVs but not in MS patients. EL serum levels as well as the serum levels and lipid content of the majority of apoB-containing lipoprotein subclasses were markedly different in MS patients compared with HVs. We conclude that EL serum levels are associated with the serum levels and lipid content of apoB-containing lipoproteins and that these associations are markedly affected by MS.
Assuntos
Síndrome Metabólica , Humanos , Voluntários Saudáveis , Lipoproteínas/metabolismo , Colesterol , Triglicerídeos , Lipoproteínas VLDL/metabolismo , Lipase , Apolipoproteínas B/metabolismo , Fosfolipídeos , Lipoproteínas LDL/metabolismoRESUMO
AIMS: Apolipoprotein C-II (ApoC-II) is thought to activate lipoprotein lipase (LPL) and is therefore a possible target for treating hypertriglyceridemia. Its relationship with cardiovascular risk has not been investigated in large-scale epidemiologic studies, particularly allowing for apolipoprotein C-III (ApoC-III), an LPL antagonist. Furthermore, the exact mechanism of ApoC-II-mediated LPL activation is unclear. METHODS AND RESULTS: ApoC-II was measured in 3141 LURIC participants of which 590 died from cardiovascular diseases during a median (inter-quartile range) follow-up of 9.9 (8.7-10.7) years. Apolipoprotein C-II-mediated activation of the glycosylphosphatidylinositol high-density lipoprotein binding protein 1 (GPIHBP1)-LPL complex was studied using enzymatic activity assays with fluorometric lipase and very low-density lipoprotein (VLDL) substrates. The mean ApoC-II concentration was 4.5 (2.4) mg/dL. The relationship of ApoC-II quintiles with cardiovascular mortality exhibited a trend toward an inverse J-shape, with the highest risk in the first (lowest) quintile and lowest risk in the middle quintile. Compared with the first quintile, all other quintiles were associated with decreased cardiovascular mortality after multivariate adjustments including ApoC-III as a covariate (all P < 0.05). In experiments using fluorometric substrate-based lipase assays, there was a bell-shaped relationship for the effect of ApoC-II on GPIHBP1-LPL activity when exogenous ApoC-II was added. In ApoC-II-containing VLDL substrate-based lipase assays, GPIHBP1-LPL enzymatic activity was almost completely blocked by a neutralizing anti-ApoC-II antibody. CONCLUSION: The present epidemiologic data suggest that increasing low circulating ApoC-II levels may reduce cardiovascular risk. This conclusion is supported by the observation that optimal ApoC-II concentrations are required for maximal GPIHBP1-LPL enzymatic activity.