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Genetic variation at rs4240624 on chromosome 8 is associated with an attenuated signal on hepatic computerized tomography, which has been attributed to changes in hepatic fat. The closest coding gene to rs4240624, PPP1R3B, encodes a protein that promotes hepatic glycogen synthesis. Here, we performed studies to determine whether the x-ray attenuation associated with rs4240624 is due to differences in hepatic glycogen or hepatic triglyceride content (HTGC). A sequence variant in complete linkage disequilibrium with rs4240624, rs4841132, was genotyped in the Dallas Heart Study (DHS), the Dallas Liver Study, and the Copenhagen Cohort (n = 112,428) of whom 1,539 had nonviral liver disease. The minor A-allele of rs4841132 was associated with increased hepatic x-ray attenuation (n = 1,572; P = 4 × 10-5 ), but not with HTGC (n = 2,674; P = 0.58). Rs4841132-A was associated with modest, but significant, elevations in serum alanine aminotransferase (ALT) in the Copenhagen Cohort (P = 3 × 10-4 ) and the DHS (P = 0.004), and with odds ratios for liver disease of 1.13 (95% CI, 0.97-1.31) and 1.23 (1.01-1.51), respectively. Mice lacking protein phosphatase 1 regulatory subunit 3B (PPP1R3B) were deficient in hepatic glycogen, whereas HTGC was unchanged. Hepatic overexpression of PPP1R3B caused accumulation of hepatic glycogen and elevated plasma levels of ALT, but did not change HTGC.ConclusionThese observations are consistent with the notion that the minor allele of rs4841132 promotes a mild form of hepatic glycogenosis that is associated with hepatic injury. (Hepatology 2018;67:2182-2195).

The X-ray structure of human ABCG5/ABCG8 heterodimer in a nucleotide-free state, being the first atomic model of an ABC sterol transporter. Human ABCG5/ABCG8 sterol transporter Cholesterol is an essential component of vertebrate cell membranes. Animals maintain sterol balance by limiting dietary sterol uptake from the gut and promoting sterol secretion from hepatocytes into bile. These physiological processes are mediated by ABCG5/ABCG8, a heterodimeric ABC transporter. These authors have solved the X-ray crystal structure of the human ABCG5/ABCG8 heterodimer in a nucleotide-free state. As well as being the first atomic model of an ABC sterol transporter, the structure provides mechanistic insights into sterol transport and establishes a framework for understanding mutations responsible for sitosterolaemia, a human disease characterized by premature atherosclerosis. ATP binding cassette (ABC) transporters play critical roles in maintaining sterol balance in higher eukaryotes. The ABCG5/ABCG8 heterodimer (G5G8) mediates excretion of neutral sterols in liver and intestines.sup.1,2,3,4,5. Mutations disrupting G5G8 cause sitosterolaemia, a disorder characterized by sterol accumulation and premature atherosclerosis. Here we use crystallization in lipid bilayers to determine the X-ray structure of human G5G8 in a nucleotide-free state at 3.9 Å resolution, generating the first atomic model of an ABC sterol transporter. The structure reveals a new transmembrane fold that is present in a large and functionally diverse superfamily of ABC transporters. The transmembrane domains are coupled to the nucleotide-binding sites by networks of interactions that differ between the active and inactive ATPases, reflecting the catalytic asymmetry of the transporter. The G5G8 structure provides a mechanistic framework for understanding sterol transport and the disruptive effects of mutations causing sitosterolaemia., Author(s): Jyh-Yeuan Lee [sup.1] , Lisa N. Kinch [sup.2] [sup.3] [sup.4] , Dominika M. Borek [sup.2] [sup.3] , Jin Wang [sup.1] , Junmei Wang [sup.5] , Ina L. Urbatsch [sup.6] [...]

A genetic variant in PNPLA3 [(PNPLA3.sup.I148M]), a triacylglycerol (TAG) hydrolase, is a major risk factor for non-alcoholic fatty liver disease (NAFLD); however, the mechanism underlying this association is not known. To develop an animal model of PNPLA3-induced fatty liver disease, we generated transgenic mice that overexpress similar amounts of wild-type PNPLA3 [(PNPLA3.sup.WT]) or mutant PNPLA3 [(PNPLA3.sup.I148M]) either in liver or adipose tissue. Overexpression of the transgenes in adipose tissue did not affect liver fat content. Expression of [PNPLA3.sup.I148M], but not [PNPLA3.sup.WT], in liver recapitulated the fatty liver phenotype as well as other metabolic features associated with this allele in humans. Metabolic studies provided evidence for 3 distinct alterations in hepatic TAG metabolism in [PNPLA3.sup.I148M] transgenic mice: increased formation of fatty acids and TAG, impaired hydrolysis of TAG, and relative depletion of TAG long-chain polyunsaturated fatty acids. These findings suggest that PNPLA3 plays a role in remodeling TAG in lipid droplets, as they accumulate in response to food intake, and that the increase in hepatic TAG levels associated with the I148M substitution results from multiple changes in hepatic TAG metabolism. The development of an animal model that recapitulates the metabolic phenotype of the allele in humans provides a new platform in which to elucidate the role of [PNLPA3.sup.I148M] in NAFLD., Introduction Higher organisms stockpile triacylglycerol (TAG) in adipose tissue as a buffer against fluctuations in food availability and energy demands. TAG is usually maintained at much lower concentrations in other [...]

All protein-coding regions of the genome (the 'exome') are sequenced in two family members with combined hypolipidemia, marked by extremely low plasma levels of low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol and triglycerides. The analysis of ANGPTL3 (the angiopoietinlike 3 protein) mutations has highlighted a role for the gene in LDL cholesterol metabolism in humans and has displayed the usefulness of exome sequencing for identification of novel genetic causes of inherited disorders.

The relative activity of lipoprotein lipase (LPL) in different tissues controls the partitioning of lipoproteinderived fatty acids between sites of fat storage (adipose tissue) and oxidation (heart and skeletal muscle). Here we used a reverse genetic strategy to test the hypothesis that 4 angiopoietin-like proteins (ANGPTL3, -4, -5, and -6) play key roles in triglyceride (TG) metabolism in humans. We re-sequenced the coding regions of the genes encoding these proteins and identified multiple rare nonsynonymous (NS) sequence variations that were associated with low plasma TG levels but not with other metabolic phenotypes. Functional studies revealed that all mutant alleles of ANGPTL3 and ANGPTL4 that were associated with low plasma TG levels interfered either with the synthesis or secretion of the protein or with the ability of the ANGPTL protein to inhibit LPL. A total of 1% of the Dallas Heart Study population and 4% of those participants with a plasma TG in the lowest quartile had a rare loss-of-function mutation in ANGPTL3, ANGPTL4, or ANGPTL5. Thus, ANGPTL3, ANGPTL4, and ANGPTL5, but not ANGPTL6, play nonredundant roles in TG metabolism, and multiple alleles at these loci cumulatively contribute to variability in plasma TG levels in humans., Introduction In individuals consuming Western diets, more than 100 grams of triglycerides (TGs) are transported each day from the liver and small intestines to peripheral tissues. The partitioning of TG [...]

Proprotein convertase subtilisin-like kexin type 9 (PCSK9) is a newly discovered serine protease that destroys low density lipoprotein (LDL) receptors in liver and thereby controls the level of LDL in plasma. Mutations that increase PCSK9 activity cause hypercholesterolemia and coronary heart disease (CHD), mutations that inactivate PCSK9 have the opposite effect, lowering LDL levels and reducing CHD. Although the mechanism of PCSK9 action is not yet clear, the protease provides a new therapeutic target to lower plasma levels of LDL and prevent CHD.

Genetic defects in LDL clearance result in severe hypercholesterolemia and premature atherosclerosis. Mutations in the LDL receptor (LDLR) cause familial hypercholesterolemia (FH), the most severe form of genetic hypercholesterolemia. A [...]

The effect of loss-of-function mutations on the synthesis and secretion of proprotein convertase subtilisin/kexin type 9 (PCSK9) was examined. It predicted that circulating levels of PCSK9 was lower in individuals with loss-of-function mutations and serine protease is present in the circulation and identified the first known compound heterozygote with two inactivating mutations in PCSK9.

The incidence of coronary heart disease was compared over a 15-year interval in a study according to the presence or absence of sequence variants in the proprotein convertase substilisin/kexin type 9 serine protease gene (PCSK9) that are associated with reduced plasma levels of low density lipoprotein (LDL) cholesterol. The data indicate that moderate lifelong reduction in the plasma level of LDL cholesterol is associated with a substantial reduction in the incidence of coronary events even in populations with a high prevalence of non-lipid-related cardiovascular factors.

The structural features of sterols required to support mammalian cell growth have not been fully defined. Here, we use mutant CHO cells that synthesize only small amounts of cholesterol to test the capacity of various sterols to support growth. Sterols with minor modifications of the side chain (e.g., campesterol, [beta]-sitosterol, and desmosterol) supported long-term growth of mutant cells, but sterols with more complex modifications of the side chain, the sterol nucleus, or the 3-hydroxy group did not. After 60 days in culture, the exogenous sterol comprised >90% of cellular sterols. Inactivation of residual endogenous synthesis with the squalene epoxidase inhibitor NB-598 prevented growth in [beta]-sitosterol and greatly reduced growth in campesterol. Growth of ceils cultured in [beta]-sitosterol and NB-598 was restored by adding small amounts of cholesterol to the medium. Surprisingly, enantiomeric cholesterol also supported cell growth, even in the presence of NB-598. Thus, sterols fulfill two roles in mammalian cells: (i) a bulk membrane requirement in which phytosterols can substitute for cholesterol and (ii) other processes that specifically require small amounts of cholesterol but are not enantioselective. ent-cholesterol | phytosterols | NB-598