DGAT1
Diacylglycerol O-acyltransferase 1 (EC 2.3.1.20) (ACAT-related gene product 1) (Acyl-CoA retinol O-fatty-acyltransferase) (EC 2.3.1.76) (ARAT) (Retinol O-fatty-acyltransferase) (Diglyceride acyltransferase) [AGRP1] [DGAT]
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Nonalcoholic fatty liver disease (NAFLD) is the most common liver disease worldwide. NAFLD usually begins as low-grade hepatic steatosis which further progresses in an age-dependent manner to nonalcoholic steatohepatitis (NASH), fibrosis, cirrhosis, and hepatocellular carcinoma in some patients. Ghrelin is a hormone known to promote adiposity in rodents and humans, but its potential role in hepatic steatosis is unknown. We hypothesized that genetic ghrelin deletion will protect against the development of age-related hepatic steatosis. To examine this hypothesis, we utilized ghrelin knockout (KO) mice. Although no different in young animals (3 months old), we found that at 20 months of age, ghrelin KO mice have significantly reduced hepatic steatosis compared to aged-matched wild-type (WT) mice. Examination of molecular pathways by which deletion of ghrelin reduces steatosis showed that the increase in expression of diacylglycerol O-acyltransferase-1 (DGAT1), one of the key enzymes of triglyceride (TG) synthesis, seen with age in WT mice, is not present in KO mice. This was due to the lack of activation of CCAAT/enhancer binding protein-alpha (C/EBPα) protein and subsequent reduction of C/EBPα-p300 complexes. These complexes were abundant in livers of old WT mice and were bound to and activated the DGAT1 promoter. However, the C/EBPα-p300 complexes were not detected on the DGAT1 promoter in livers of old KO mice resulting in lower levels of the enzyme. In conclusion, these studies demonstrate the mechanism by which ghrelin deletion prevents age-associated hepatic steatosis and suggest that targeting this pathway may offer therapeutic benefit for NAFLD.
MeSH Terms
- Age Factors
- Animals
- Diacylglycerol O-Acyltransferase
- Down-Regulation
- Fatty Liver
- Ghrelin
- Male
- Mice, Inbred C57BL
- Mice, Knockout
- Triglycerides
Keywords
- C/EBP proteins
- aging
- ghrelin
- liver
- p300
- steatosis
Female fertility in Holstein cattle can decline when intense genetic selection is placed on milk production. One approach to improving fertility is to identify the genomic regions and variants affecting fertility traits and then incorporate this knowledge into selection decisions. The objectives of this study were to identify or refine the positions of the genomic regions associated with lactation persistency, female fertility traits (age at first service, cow first service to conception, heifer and cow nonreturn rates), longevity traits (herd life, indirect herd life, and direct herd life), and lifetime profit index in the North American Holstein dairy cattle population. A genome-wide association study was performed for each trait, using a single SNP (single nucleotide polymorphism) regression mixed linear model and imputed high-density panel (777k) genotypes. No associations were identified for fertility traits. Several peak regions were detected for lifetime profit index, lactation persistency, and longevity. The results overlap with previous findings and identify some novel regions for lactation persistency. Previously proposed causative and candidate genes supported by this work include DGAT1, GRINA, and CPSF1, whereas new candidate genes are SLC2A4RG and THRB. Thus, the chromosomal regions identified in this study not only confirm several previous findings but also highlight new regions that may contribute to genetic variation in lactation persistency and longevity-associated traits in dairy cattle.
MeSH Terms
- Animals
- Cattle
- Female
- Fertility
- Genome-Wide Association Study
- Lactation
- Longevity
- Phenotype
Keywords
- fertility
- genome-wide association study
- lifetime profit index
- longevity
Diacylglycerol acyltransferase 1 (DGAT1) catalyzes the final step in triglyceride synthesis, the conversion of diacylglycerol (DAG) to triglyceride. Dgat1(-/-) mice exhibit a number of beneficial metabolic effects including reduced obesity and improved insulin sensitivity and no known cardiac dysfunction. In contrast, failing human hearts have severely reduced DGAT1 expression associated with accumulation of DAGs and ceramides. To test whether DGAT1 loss alone affects heart function, we created cardiomyocyte-specific DGAT1 knock-out (hDgat1(-/-)) mice. hDgat1(-/-) mouse hearts had 95% increased DAG and 85% increased ceramides compared with floxed controls. 50% of these mice died by 9 months of age. The heart failure marker brain natriuretic peptide increased 5-fold in hDgat1(-/-) hearts, and fractional shortening (FS) was reduced. This was associated with increased expression of peroxisome proliferator-activated receptor α and cluster of differentiation 36. We crossed hDgat1(-/-) mice with previously described enterocyte-specific Dgat1 knock-out mice (hiDgat1(-/-)). This corrected the early mortality, improved FS, and reduced cardiac ceramide and DAG content. Treatment of hDgat1(-/-) mice with the glucagon-like peptide 1 receptor agonist exenatide also improved FS and reduced heart DAG and ceramide content. Increased fatty acid uptake into hDgat1(-/-) hearts was normalized by exenatide. Reduced activation of protein kinase Cα (PKCα), which is increased by DAG and ceramides, paralleled the reductions in these lipids. Our mouse studies show that loss of DGAT1 reproduces the lipid abnormalities seen in severe human heart failure.
MeSH Terms
- Aging
- Animals
- Blood Glucose
- Cholesterol
- Diacylglycerol O-Acyltransferase
- Enzyme Inhibitors
- Exenatide
- Fatty Acids
- Gene Deletion
- Gene Expression Regulation
- Heart Failure
- Humans
- Intestines
- Lipids
- Male
- Mice, Inbred C57BL
- Mice, Knockout
- Myocardium
- Myocytes, Cardiac
- Organ Specificity
- Peptides
- Phenotype
- Protein Kinase C
- Triglycerides
- Venoms
Keywords
- Animal Model
- Cardiac Metabolism
- Ceramide
- Diacylglycerol
- Heart Failure
- Lipid
- Lipotoxicity
- Metabolism
- Signal Transduction
Calorie restriction results in leanness, which is linked to metabolic conditions that favor longevity. We show here that deficiency of the triglyceride synthesis enzyme acyl CoA:diacylglycerol acyltransferase 1 (DGAT1), which promotes leanness, also extends longevity without limiting food intake. Female DGAT1-deficient mice were protected from age-related increases in body fat, tissue triglycerides, and inflammation in white adipose tissue. This protection was accompanied by increased mean and maximal life spans of ~25% and ~10%, respectively. Middle-agedDgat1-/- mice exhibited several features associated with longevity, including decreased levels of circulating insulin growth factor 1 (IGF1) and reduced fecundity. Thus, deletion of DGAT1 in mice provides a model of leanness and extended lifespan that is independent of calorie restriction.
MeSH Terms
- Adipose Tissue
- Aging
- Animals
- Body Composition
- Bone Density
- Caloric Restriction
- Diacylglycerol O-Acyltransferase
- Energy Metabolism
- Female
- Fertility
- Gene Expression Profiling
- Gene Expression Regulation
- Genotype
- Litter Size
- Longevity
- Mice
- Mice, Knockout
- Thinness
Recent publications indicate genetic variation in milk production traits on proximal BTA14, which cannot be explained solely with genetic variation in the DGAT1 gene. To elucidate these QTL effects, animals from a German Holstein granddaughter design (18 families, 1,291 sons) were genotyped for CYP11B1 (V30A) and DGAT1 (K232A) polymorphisms. Frequencies of alleles of maternal descent were estimated for CYP11B1(V) (0.776) and DGAT1(K) (0.549). Allele substitution effects (alpha/2) were first calculated for both alleles in separate models and then in a joint model. From the joint analysis, CYP11B1(V) effects on fat content ( 0.04%) and protein content ( 0.01%) were positive. Effects on milk yield (-82 kg), fat yield (-0.5 kg), and protein yield (-1.9 kg) were negative. Compared with the individual analysis, DGAT1(K) effects on fat content ( 0.28%), protein content ( 0.06%), and milk yield (-258 kg) were reduced; fat yield ( 10.8 kg) was enhanced; and protein yield (-3.8 kg) was reduced. In the joint analysis, allele substitution effects of CYP11B1(V) and DGAT1(K) together explained more of the variation in milk production traits than DGAT1(K) alone. Further significant effects were found for CYP11B1(V) and DGAT1(K) among 6 reproduction traits and 14 conformational traits. These observations indicate a possible negative influence of DGAT1(K) on maternal nonreturn rate, and thus, on length of productive life.
MeSH Terms
- Animals
- Breeding
- Cattle
- Chromosome Mapping
- Diacylglycerol O-Acyltransferase
- Female
- Genetic Linkage
- Genetic Markers
- Genetic Variation
- Genotype
- Longevity
- Male
- Milk
- Quantitative Trait Loci
- Reproduction
- Steroid 11-beta-Hydroxylase
Aged male rats show a decrease in liver PPARalpha. We aimed to determine if the sexual dimorphism in lipid metabolism observed in the PPARalpha-/- mouse is also present in senescent rats. Eighteen-month old rats were obese and presented high plasma NEFA concentrations. Old male rats were more hypercholesterolemic and hyperleptinemic than females, presenting a higher content in hepatic triglycerides and cholesteryl esters, while 18-month old females were more hypertriglyceridemic than males. Although PPARalpha expression and binding activity was reduced in liver from old male and female rats, the mRNA for a PPARalpha target gene, such as CPT-I, was reduced in old males (-56%), while increased by 286% in old females. LXRalpha protein was increased, and its binding activity was decreased in livers of old males, while livers of old females showed an increase in DGAT1 (2.6-fold) and DGAT2 (4.9-fold) mRNA, with respect to 3-month old animals. The increases in DGAT1 and DGAT2 mRNAs matched in old females those of plasma (3.1-fold) and liver triglycerides (5.0-fold). These features disclose a marked sexual dimorphism in lipid metabolism associated to old age in rats that can be partially attributed not only to an age-related decrease in liver PPARalpha expression, but also to changes in other hepatic transcription factors and enzymes, such as liver X receptor alpha (LXRalpha) and diacylglycerol acyltransferases (DGAT).
MeSH Terms
- Acyltransferases
- Aging
- Animals
- Diacylglycerol O-Acyltransferase
- Electrophoretic Mobility Shift Assay
- Female
- Gene Expression Regulation, Enzymologic
- Hormones
- Lipid Metabolism
- Liver
- Male
- PPAR alpha
- Phenotype
- Rats
- Rats, Sprague-Dawley
- Sex Characteristics