The PNPLA3-I148M variant increases polyunsaturated triglycerides in human adipose tissue.

BACKGROUND & AIMS: The I148M variant in PNPLA3 is the major genetic risk factor for non-alcoholic fatty liver disease (NAFLD). The liver is enriched with polyunsaturated triglycerides (PUFA-TGs) in PNPLA3-I148M carriers. Gene expression data indicate that PNPLA3 is liver-specific in humans, but whether it functions in adipose tissue (AT) is unknown. We investigated whether PNPLA3-I148M modifies AT metabolism in human NAFLD. METHODS: Profiling of the AT lipidome and fasting serum non-esterified fatty acid (NEFA) composition was conducted in 125 volunteers (PNPLA3148MM/MI , n = 63; PNPLA3148II , n = 62). AT fatty acid composition was determined in 50 volunteers homozygous for the variant (PNPLA3148MM , n = 25) or lacking the variant (PNPLA3148II , n = 25). Whole-body insulin sensitivity of lipolysis was determined using [2 H5 ]glycerol, and PNPLA3 mRNA and protein levels were measured in subcutaneous AT and liver biopsies in a subset of the volunteers. RESULTS: PUFA-TGs were significantly increased in AT in carriers versus non-carriers of PNPLA3-I148M. The variant did not alter the rate of lipolysis or the composition of fasting serum NEFAs. PNPLA3 mRNA was 33-fold higher in the liver than in AT (P < .0001). In contrast, PNPLA3 protein levels per tissue protein were three-fold higher in AT than the liver (P < .0001) and nine-fold higher when related to whole-body AT and liver tissue masses (P < .0001). CONCLUSIONS: Contrary to previous assumptions, PNPLA3 is highly abundant in AT. PNPLA3-I148M locally remodels AT TGs to become polyunsaturated as it does in the liver, without affecting lipolysis or composition of serum NEFAs. Changes in AT metabolism do not contribute to NAFLD in PNPLA3-I148M carriers.

USF1 deficiency alleviates inflammation, enhances cholesterol efflux and prevents cholesterol accumulation in macrophages.

BACKGROUND: The focus of studies on high-density lipoproteins (HDL) has shifted from HDL-cholesterol (HDL-C) to HDL function. We recently demonstrated that low USF1 expression in mice and humans associates with high plasma HDL-C and low triglyceride levels, as well as protection against obesity, insulin resistance, and atherosclerosis. Here, we studied the impact of USF1 deficiency on HDL functional capacity and macrophage atherogenic functions, including inflammation, cholesterol efflux, and cholesterol accumulation. METHODS: We used a congenic Usf1 deficient mice in C57Bl/6JRccHsd background and blood samples were collected to isolate HDL for structural and functional studies. Lentiviral preparations containing the USF1 silencing shRNA expression vector were used to silence USF1 in human THP-1 and Huh-7 cells. Cholesterol efflux from acetyl-LDL loaded THP-1 macrophages was measured using HDL and plasma as acceptors. Gene expression analysis from USF1 silenced peritoneal macrophages was carried out using Affymetrix protocols. RESULTS: We show that Usf1 deficiency not only increases HDL-C levels in vivo, consistent with elevated ABCA1 protein expression in hepatic cell lines, but also improves the functional capacity of HDL particles. HDL particles derived from Usf1 deficient mice remove cholesterol more efficiently from macrophages, attributed to their higher contents of phospholipids. Furthermore, silencing of USF1 in macrophages enhanced the cholesterol efflux capacity of these cells. These findings are consistent with reduced inflammatory burden of USF1 deficient macrophages, manifested by reduced secretion of pro-inflammatory cytokines MCP-1 and IL-1ß and protection against inflammation-induced macrophage cholesterol accumulation in a cell-autonomous manner. CONCLUSIONS: Our findings identify USF1 as a novel factor regulating HDL functionality, showing that USF1 inactivation boosts cholesterol efflux, reduces macrophage inflammation and attenuates macrophage cholesterol accumulation, linking improved macrophage cholesterol metabolism and inflammatory pathways to the antiatherogenic function of USF1 deficiency.

PNPLA3 mediates hepatocyte triacylglycerol remodeling.

The I148M substitution in patatin-like phospholipase domain containing 3 (PNPLA3(I148M)) determines a genetic form of nonalcoholic fatty liver disease. To elucidate the mode of PNPLA3 action in human hepatocytes, we studied effects of WT PNPLA3 (PNPLA3(WT)) and PNPLA3(I148M) on HuH7 cell lipidome after [(13)C]glycerol labeling, cellular turnover of oleic acid labeled with 17 deuterium atoms ([D17]oleic acid) in triacylglycerols (TAGs), and subcellular distribution of the protein variants. PNPLA3(I148M) induced a net accumulation of unlabeled TAGs, but not newly synthesized total [(13)C]TAGs. Principal component analysis (PCA) revealed that both PNPLA3(WT) and PNPLA3(I148M) induced a relative enrichment of TAGs with saturated FAs or MUFAs, with concurrent enrichment of polyunsaturated phosphatidylcholines. PNPLA3(WT) associated in PCA with newly synthesized [(13)C]TAGs, particularly 52:1 and 50:1, while PNPLA3(I148M) associated with similar preexisting TAGs. PNPLA3(WT) overexpression resulted in increased [D17]oleic acid labeling of TAGs during 24 h, and after longer incubations their turnover was accelerated, effects not detected with PNPLA3(I148M). PNPLA3(I148M) localized more extensively to lipid droplets (LDs) than PNPLA3(WT), suggesting that the substitution alters distribution of PNPLA3 between LDs and endoplasmic reticulum/cytosol. This study reveals a function of PNPLA3 in FA-selective TAG remodeling, resulting in increased TAG saturation. A defect in TAG remodeling activity likely contributes to the TAG accumulation observed in cells expressing PNPLA3(I148M).

ORP10, a cholesterol binding protein associated with microtubules, regulates apolipoprotein B-100 secretion.

ORP10/OSBPL10 is a member of the oxysterol-binding protein family, and genetic variation in OSBPL10 is associated with dyslipidemias and peripheral artery disease. In this study we investigated the ligand binding properties of ORP10 in vitro as well as its localization and function in human HuH7 hepatocytes. The pleckstrin homology (PH) domain of ORP10 selectively interacts with phosphatidylinositol-4-phosphate, while the C-terminal ligand binding domain binds cholesterol and several acidic phospholipids. Full-length ORP10 decorates microtubules (MT), while the ORP10 N-terminal fragment (aa 1-318) localizes at Golgi membranes. Removal of the C-terminal aa 712-764 of ORP10 containing a predicted coiled-coil segment abolishes the MT association, but allows partial Golgi targeting. A PH domain-GFP fusion protein is distributed mainly in the cytosol and the plasma membrane, indicating that the Golgi affinity of ORP10 involves other determinants in addition to the PH domain. HuH7 cells expressing ORP10-specific shRNA display increased accumulation of apolipoprotein B-100 (apoB-100), but not of albumin, in culture medium, and contain reduced levels of intracellular apoB-100. Pulse-chase analysis of cellular [(35)S]apoB-100 demonstrates enhanced apoB-100 secretion by cells expressing ORP10-specific shRNA. The apoB-100 secretion phenotype is replicated in HepG2 cells transduced with the ORP10 shRNA lentiviruses. As a conclusion, the present study dissects the determinants of ORP10 association with MT and the Golgi complex and provides evidence for a specific role of this protein in ß-lipoprotein secretion by human hepatocytes.

Early secretory pathway localization and lack of processing for hepatitis E virus replication protein pORF1.

Hepatitis E virus (HEV) is a positive-strand RNA virus and a major causative agent of acute sporadic and epidemic hepatitis. HEV replication protein is encoded by ORF1 and contains the predicted domains of methyltransferase (MT), protease, macro domain, helicase (HEL) and polymerase (POL). In this study, the full-length protein pORF1 (1693 aa) and six truncated variants were expressed by in vitro translation and in human HeLa and hepatic Huh-7 cells by using several vector systems. The proteins were visualized by three specific antisera directed against the MT, HEL and POL domains. In vitro translation of full-length pORF1 yielded smaller quantities of two fragments. However, these fragments were not observed after pORF1 expression and pulse-chase studies in human cells, and their production was not dependent on the predicted protease domain in pORF1. The weight of evidence supports the proposition that pORF1 is not subjected to specific proteolytic processing, which is unusual among animal positive-strand RNA viruses but common for plant viruses. pORF1 was membrane associated in cells and localized to a perinuclear region, where it partially overlapped with localization of the endoplasmic reticulum (ER) marker BAP31 and was closely interspersed with staining of the ER-Golgi intermediate compartment marker protein ERGIC-53. Co-localization with BAP31 was enhanced by treatment with brefeldin A. Therefore, HEV may utilize modified early secretory pathway membranes for replication.

PNPLA3 is regulated by glucose in human hepatocytes, and its I148M mutant slows down triglyceride hydrolysis.

Liver fat is increased in carriers of the minor G allele in rs738409 (I148M amino acid substitution) in patatin-like phospholipase domain-containing 3 (PNPLA3)/adiponutrin. We studied transcriptional regulation of PNPLA3 in immortalized human hepatocytes (IHH) and human hepatoma cells (HuH7) and the impact of PNPLA3 I148M mutant on hepatocyte triglyceride metabolism. Studies in IHH showed that silencing of the carbohydrate response element-binding protein (ChREBP) abolished induction of PNPLA3 mRNA by glucose. Glucose-dependent binding of ChREBP to a newly identified carbohydrate response element in the PNPLA3 promoter was demonstrated by chromatin immunoprecipitation. Adenoviral overexpression of mouse ChREBP in IHH failed to induce PNPLA3 mRNA. [(3)H]acetate or [(3)H]oleate incorporation with 1-h pulse labeling or 18-h [(3)H]oleate labeling in HuH7 cells showed no effect of PNPLA3 I148M on triglyceride (TG) synthesis in the absence of free fatty acid (FFA) loading. Increased [(3)H]oleate accumulation into triglycerides in I148M-expressing cells was observed after 18 h of labeling in the presence of 200 µM FFA-albumin complexes. This was accompanied by increased PNPLA3 protein levels. The rate of hydrolysis of [(3)H]TG during lipid depletion was decreased significantly by PNPLA3 I148M. Our results suggest that PNPLA3 is regulated in human hepatocytes by glucose via ChREBP. PNPLA3 I148M enhances cellular accumulation of [(3)H]TG in the presence of excess FFA, which is known to stabilize PNPLA3 protein. These data do not exclude an effect of PNPLA3 I148M on hepatocyte lipogenesis but show that the mutant increases the stability of triglycerides.

Cardiovascular event rate and death in high-risk secondary prevention patient cohort in Finland: A registry study.

BACKGROUND: A large number of patients are living with atherosclerotic cardiovascular (CV) disease and thus are at risk of life-threatening CV events. HYPOTHESIS: This study evaluated the risk for a recurrent CV event or death in Finnish real-world data. METHODS: Patients with an incident atherosclerotic CV event between 2012 and 2016 were included in this retrospective registry study and followed for recurrent CV events or death. The risk and risk factors of recurrent CV events or death and time from the first CV event to recurrence were assessed. RESULTS: A total of 48,405 patients were followed from their first CV event. The event rate was 14.34 events per 100 patient-years. Multistate models suggested that at 5 years post index CV event, 41.5% of the patients had died or suffered a recurrent CV event. Death was the most common type of subsequent event (61.5%). After the first CV event, there were rapid increases both in recurrent CV events and deaths during the next 6 months. The subsequent CV event was usually of the same type as the first, which was of the cardiac or cerebrovascular cluster. CONCLUSIONS: The incidence of recurrent CV events and all-cause mortality was high in patients suffering from their first CV event, particularly during the first 6 months after the index event. Death was the most common subsequent event. The event rate accelerated after each additional CV event. This suggests that the acute treatment of the index event should be followed by prompt secondary prevention measures to achieve guideline-recommended goals as soon as possible.

Splanchnic balance of free fatty acids, endocannabinoids, and lipids in subjects with nonalcoholic fatty liver disease.

BACKGROUND & AIMS: Animal studies suggest that endocannabinoids could contribute to the development of nonalcoholic fatty liver disease (NAFLD). In addition, NAFLD has been shown to be associated with multiple changes in lipid concentrations in liver biopsies. There are no data on splanchnic free fatty acid (FFA), glycerol, ketone body, endocannabinoid, and lipid fluxes in vivo in subjects with NAFLD. METHODS: We performed hepatic venous catheterization studies in combination with [(2)H(2)]palmitate infusion in the fasting state and during a low-dose insulin infusion in 9 subjects with various degrees of hepatic steatosis as determined using liver biopsy. Splanchnic balance of endocannabinoids and individual lipids was determined using ultra performance liquid chromatography coupled to mass spectrometry. RESULTS: Concentrations of the endocannabinoid 2-arachidonoylglycerol were higher in arterialized (91 ± 33 µg/L basally) than in hepatic venous (51 ± 19 µg/L; P < .05) plasma. Fasting arterial (r = 0.72; P = .031) and hepatic venous (r = 0.70; P = .037) concentrations of 2-arachidonoylglycerol were related positively to liver fat content. Analysis of fluxes of 85 different triglycerides showed that the fatty liver overproduces saturated triglycerides. In the plasma FFA fraction in the basal state, the relative amounts of palmitoleate and linoleate were lower and those of stearate and oleate were higher in the hepatic vein than in the artery. Absolute concentrations of all nontriglyceride lipids were comparable in arterialized venous plasma and the hepatic vein both in the basal and insulin-stimulated states. CONCLUSIONS: The human fatty liver takes up 2-arachidonoylglycerol and overproduces triacylglycerols containing saturated fatty acids, which might reflect increased de novo lipogenesis.

Cardiovascular event rates increase after each recurrence and associate with poor statin adherence.

AIMS: The study evaluated the quality of cardiovascular prevention in real-world clinical practice. The recurrence of up to five cardiovascular events was assessed, as data on recurrence beyond the first event and interindividual variations in event rates past the second event have been sparse. Low-density lipoprotein cholesterol concentrations and lipid-lowering therapy use were investigated. METHODS: This retrospective register-based study included adult patients with an incident cardiovascular event between 2004 and 2016 treated in the hospital district of southwest Finland. Patients were followed for consecutive cardiovascular events or cardiovascular death, low-density lipoprotein cholesterol and statin purchases. The timing of event recurrence was evaluated, and predictive factors were assessed. RESULTS: A wide interindividual variation in cardiovascular event recurrence was observed, each additional event caused an increased risk, the median time of recurrence decreased from 7 to one year for the second and fifth event. Event rates increased correspondingly from 12 to 43/100 patient-years and were most pronounced in the first years following the previous event. The low-density lipoprotein cholesterol goal (<1.8 mmol/l) was reached by 18% in the year after the event and statin underuse was associated with an increased risk of recurrence. Six months after the index event high intensity statins were used by only 22% of the cohort. CONCLUSION: The study provides new perspectives on individual risk assessment showing that event rates are not stable for all patients but increase 1.2-1.9-fold per consecutive event. The underuse of statins and poor adherence support the identification of these patients for intensified multifactorial preventive measures.

Novel hepatic microRNAs upregulated in human nonalcoholic fatty liver disease.

MicroRNAs (miRNAs) control gene expression by reducing mRNA stability and translation. We aimed to identify alterations in human liver miRNA expression/function in nonalcoholic fatty liver disease (NAFLD). Subjects with the highest (median liver fat 30%, n = 15) and lowest (0%, n = 15) liver fat content were selected from >100 obese patients for miRNA profiling of liver biopsies on microarrays carrying probes for 1438 human miRNAs (a cross-sectional study). Target mRNAs and pathways were predicted for the miRNAs most significantly upregulated in NAFLD, their cell-type-specific expression was investigated by quantitative PCR (qPCR), and the transcriptome of immortalized human hepatocytes (IHH) transfected with the miRNA with the highest number of predicted targets, miR-576-5p, was studied. The screen revealed 42 miRNAs up- and two downregulated in the NAFLD as compared to non-NAFLD liver. The miRNAs differing most significantly between the groups, miR-103a-2*, miR-106b, miR-576-5p, miRPlus-I137*, miR-892a, miR-1282, miR-3663-5p, and miR-3924, were all upregulated in NAFLD liver. Target pathways predicted for these miRNAs included ones involved in cancer, metabolic regulation, insulin signaling, and inflammation. Consistent transcriptome changes were observed in IHH transfected with miR-576-5p, and western analysis revealed a marked reduction of the RAC1 protein belonging to several miR-576-5p target pathways. To conclude, we identified 44 miRNAs differentially expressed in NAFLD versus non-NAFLD liver, 42 of these being novel in the context of NAFLD. The study demonstrates that by applying a novel study set-up and a broad-coverage array platform one can reveal a wealth of previously undiscovered miRNA dysregulation in metabolic disease.

USF1 deficiency activates brown adipose tissue and improves cardiometabolic health.

USF1 (upstream stimulatory factor 1) is a transcription factor associated with familial combined hyperlipidemia and coronary artery disease in humans. However, whether USF1 is beneficial or detrimental to cardiometabolic health has not been addressed. By inactivating USF1 in mice, we demonstrate protection against diet-induced dyslipidemia, obesity, insulin resistance, hepatic steatosis, and atherosclerosis. The favorable plasma lipid profile, including increased high-density lipoprotein cholesterol and decreased triglycerides, was coupled with increased energy expenditure due to activation of brown adipose tissue (BAT). Usf1 inactivation directs triglycerides from the circulation to BAT for combustion via a lipoprotein lipase-dependent mechanism, thus enhancing plasma triglyceride clearance. Mice lacking Usf1 displayed increased BAT-facilitated, diet-induced thermogenesis with up-regulation of mitochondrial respiratory chain complexes, as well as increased BAT activity even at thermoneutrality and after BAT sympathectomy. A direct effect of USF1 on BAT activation was demonstrated by an amplified adrenergic response in brown adipocytes after Usf1 silencing, and by augmented norepinephrine-induced thermogenesis in mice lacking Usf1. In humans, individuals carrying SNP (single-nucleotide polymorphism) alleles that reduced USF1 mRNA expression also displayed a beneficial cardiometabolic profile, featuring improved insulin sensitivity, a favorable lipid profile, and reduced atherosclerosis. Our findings identify a new molecular link between lipid metabolism and energy expenditure, and point to the potential of USF1 as a therapeutic target for cardiometabolic disease.

Regulation of Angiopoietin-Like Proteins (ANGPTLs) 3 and 8 by Insulin.

OBJECTIVE: Circulating ANGPTL8 has recently been used as a marker of insulin action. We studied expression and insulin regulation of ANGPTL8 and ANGPTL3 in vivo and in vitro. DESIGN AND METHODS: Expression of ANGPTL8 and ANGPTL3 was studied in 34 paired samples of human liver and adipose tissue. Effects of insulin on 1) plasma concentrations and adipose tissue expression of ANGPTL8 and ANGPTL3 (in vivo 6-h euglycemic hyperinsulinemia; n = 18), and 2) ANGPTL8 and ANGPTL3 gene and protein expression in immortalized human hepatocytes (IHH) and adipocytes were measured. Effect of ANGPTL3 on secretion of ANGPTL8 in cells stably overexpressing ANGPTL3, -8, or both was determined. RESULTS: ANGPTL3 was only expressed in the liver, whereas ANGPTL8 was expressed in both tissues. In vivo hyperinsulinemia significantly decreased both plasma ANGPTL8 and ANGPTL3 at 3 and 6 hours. Insulin increased ANGPTL8 expression in human adipose tissue 14- and 18-fold at 3 and 6 hours and ANGPTL8 was the most insulin-responsive transcript on microarray. Insulin also increased ANPGTL8 in cultured adipocytes and IHH but the protein mainly remained intracellular. In vitro in IHH, insulin decreased ANGPTL3 gene expression and secretion of ANGPTL3 into growth medium. Overexpression of ANGPTL8 in CHO cells did not result in its release into culture medium while abundant secretion occurred in cells co-expressing ANGPTL3 and -8. CONCLUSIONS: Insulin decreases plasma ANGPTL3 by decreasing ANGPTL3 expression in the liver. Insulin markedly increases ANGPTL8 in adipose tissue and the liver but not in plasma. These data show that measurement of plasma ANGPTL3 but not -8 reflects insulin action in target tissues.

OSBP-related protein 8 (ORP8) regulates plasma and liver tissue lipid levels and interacts with the nucleoporin Nup62.

We earlier identified OSBP-related protein 8 (ORP8) as an endoplasmic reticulum oxysterol-binding protein implicated in cellular lipid homeostasis. We now investigated its action in hepatic cells in vivo and in vitro. Adenoviral overexpression of ORP8 in mouse liver induced a decrease of cholesterol, phospholipids, and triglycerides in serum (-34%, -26%, -37%, respectively) and liver tissue (-40%, -12%, -24%), coinciding with reduction of nuclear (n)SREBP-1 and -2 and mRNA levels of their target genes. Consistently, excess ORP8 reduced nSREBPs in HuH7 cells, and ORP8 overexpression or silencing by RNA interference moderately suppressed or induced the expression of SREBP-1 and SREBP-2 target genes, respectively. In accordance, cholesterol biosynthesis was reduced by ORP8 overexpression and enhanced by ORP8 silencing in [(3)H]acetate pulse-labeling experiments. ORP8, previously shown to bind 25-hydroxycholesterol, was now shown to bind also cholesterol in vitro. Yeast two-hybrid, bimolecular fluorescence complementation (BiFC), and co-immunoprecipitation analyses revealed the nuclear pore component Nup62 as an interaction partner of ORP8. Co-localization of ORP8 and Nup62 at the nuclear envelope was demonstrated by BiFC and confocal immunofluorescence microscopy. Furthermore, the impact of overexpressed ORP8 on nSREBPs and their target mRNAs was inhibited in cells depleted of Nup62. Our results reveal that ORP8 has the capacity to modulate lipid homeostasis and SREBP activity, probably through an indirect mechanism, and provide clues of an entirely new mode of ORP action.

Comparison of dorsocervical with abdominal subcutaneous adipose tissue in patients with and without antiretroviral therapy-associated lipodystrophy.

OBJECTIVE: Combination antiretroviral therapy (cART) is associated with lipodystrophy, i.e., loss of subcutaneous adipose tissue in the abdomen, limbs, and face and its accumulation intra-abdominally. No fat is lost dorsocervically and it can even accumulate in this region (buffalo hump). It is unknown how preserved dorsocervical fat differs from abdominal subcutaneous fat in HIV-1-infected cART-treated patients with (cART+LD+) and without (cART+LD-) lipodystrophy. RESEARCH DESIGN AND METHODS: We used histology, microarray, PCR, and magnetic resonance imaging to compare dorsocervical and abdominal subcutaneous adipose tissue in cART+LD+ (n=21) and cART+LD- (n=11). RESULTS: Albeit dorsocervical adipose tissue in cART+LD+ seems spared from lipoatrophy, its mitochondrial DNA (mtDNA; copies/cell) content was significantly lower (by 62%) than that of the corresponding tissue in cART+LD-. Expression of CD68 mRNA, a marker of macrophages, and numerous inflammatory genes in microarray were significantly lower in dorsocervical versus abdominal subcutaneous adipose tissue. Genes with the greatest difference in expression between the two depots were those involved in regulation of transcription and regionalization (homeobox genes), irrespective of lipodystrophy status. There was negligible mRNA expression of uncoupling protein 1, a gene characteristic of brown adipose tissue, in either depot. CONCLUSIONS: Because mtDNA is depleted even in the nonatrophic dorsocervical adipose tissue, it is unlikely that the cause of lipoatrophy is loss of mtDNA. Dorsocervical adipose tissue is less inflamed than lipoatrophic adipose tissue. It does not resemble brown adipose tissue. The greatest difference in gene expression between dorsocervical and abdominal subcutaneous adipose tissue is in expression of homeobox genes.

Genetic variation in PNPLA3 (adiponutrin) confers sensitivity to weight loss-induced decrease in liver fat in humans.

BACKGROUND: The rs738409 C→G single nucleotide polymorphism in the patatin-like phospholipase domain-containing 3 (PNPLA3; adiponutrin) leads to a missense mutation (I148M), which is associated with increased liver fat but not insulin resistance. The I148M mutation impedes triglyceride hydrolysis in vitro, and its carriers have an increased risk of developing severe liver disease. OBJECTIVE: We explored whether the rs738409 PNPLA3 G allele influences the ability of weight loss to decrease liver fat or change insulin sensitivity. DESIGN: We recruited 8 subjects who were homozygous for the rs738409 PNPLA3 G allele (PNPLA3-148MM) and 10 who were homozygous for the rs738409 PNPLA3 C allele (PNPLA3-148II). To allow comparison of changes in liver fat, the groups were matched with respect to baseline age, sex, body mass index, and liver fat. The subjects were placed on a hypocaloric low-carbohydrate diet for 6 d. Liver fat content (proton magnetic resonance spectroscopy), whole-body insulin sensitivity of glucose metabolism (euglycemic clamp technique), and lipolysis ([(2)H(5)]glycerol infusion) were measured before and after the diet. RESULTS: At baseline, fasting serum insulin and C-peptide concentrations were significantly lower in the PNPLA3-148MM group than in the PNPLA3-148II group, as predicted by study design. Weight loss was not significantly different between groups (PNPLA3-148MM: -3.1 ± 0.5 kg; PNPLA3-148II: -3.1 ± 0.4 kg). Liver fat decreased by 45% in the PNPLA3-148MM group (P < 0.001) and by 18% in the PNPLA3-148II group (P < 0.01). CONCLUSION: Weight loss is effective in decreasing liver fat in subjects who are homozygous for the rs738409 PNPLA3 G or C allele. This trial was registered at www.hus.fi as 233775.

OSBPL10, a novel candidate gene for high triglyceride trait in dyslipidemic Finnish subjects, regulates cellular lipid metabolism.

Analysis of variants in three genes encoding oxysterol-binding protein (OSBP) homologues (OSBPL2, OSBPL9, OSBPL10) in Finnish families with familial low high-density lipoprotein (HDL) levels (N = 426) or familial combined hyperlipidemia (N = 684) revealed suggestive linkage of OSBPL10 single-nucleotide polymorphisms (SNPs) with extreme end high triglyceride (TG; >90th percentile) trait. Prompted by this initial finding, we carried out association analysis in a metabolic syndrome subcohort (Genmets) of Health2000 examination survey (N = 2,138), revealing association of multiple OSBPL10 SNPs with high serum TG levels (>95th percentile). To investigate whether OSBPL10 could be the gene underlying the observed linkage and association, we carried out functional experiments in the human hepatoma cell line Huh7. Silencing of OSBPL10 increased the incorporation of [(3)H]acetate into cholesterol and both [(3)H]acetate and [(3)H]oleate into triglycerides and enhanced the accumulation of secreted apolipoprotein B100 in growth medium, suggesting that the encoded protein ORP10 suppresses hepatic lipogenesis and very-low-density lipoprotein production. ORP10 was shown to associate dynamically with microtubules, consistent with its involvement in intracellular transport or organelle positioning. The data introduces OSBPL10 as a gene whose variation may contribute to high triglyceride levels in dyslipidemic Finnish subjects and provides evidence for ORP10 as a regulator of cellular lipid metabolism.

OSBP-related protein 8 (ORP8) suppresses ABCA1 expression and cholesterol efflux from macrophages.

ORP8 is a previously unexplored member of the family of oxysterol-binding protein-related proteins (ORP). We now report the expression pattern, the subcellular distribution, and data on the ligand binding properties and the physiological function of ORP8. ORP8 is localized in the endoplasmic reticulum (ER) via its C-terminal transmembrane span and binds 25-hydroxycholesterol, identifying it as a new ER oxysterol-binding protein. ORP8 is expressed at highest levels in macrophages, liver, spleen, kidney, and brain. Immunohistochemical analysis revealed ORP8 in the shoulder regions of human coronary atherosclerotic lesions, where it is present in CD68(+) macrophages. In advanced lesions the ORP8 mRNA was up-regulated 2.7-fold as compared with healthy coronary artery wall. Silencing of ORP8 by RNA interference in THP-1 macrophages increased the expression of ATP binding cassette transporter A1 (ABCA1) and concomitantly cholesterol efflux to lipid-free apolipoprotein A-I but had no significant effect on ABCG1 expression or cholesterol efflux to spherical high density lipoprotein HDL(2). Experiments employing an ABCA1 promoter-luciferase reporter confirmed that ORP8 silencing enhances ABCA1 transcription. The silencing effect was partially attenuated by mutation of the DR4 element in the ABCA1 promoter and synergized with that of the liver X receptor agonist T0901317. Furthermore, inactivation of the E-box in the promoter synergized with ORP8 silencing, suggesting that the suppressive effect of ORP8 involves both the liver X receptor and the E-box functions. Our data identify ORP8 as a negative regulator of ABCA1 expression and macrophage cholesterol efflux. ORP8 may, thus, modulate the development of atherosclerosis.