Elimination of Age-Associated Hepatic Steatosis and Correction of Aging Phenotype by Inhibition of cdk4-C/EBPα-p300 Axis.
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ABSTRACT:
SUBMITTER: Nguyen P
PROVIDER: S-EPMC8209958 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description: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.
| S-EPMC5771394 | biostudies-literature
Project description:Non-alcoholic fatty liver disease (NAFLD), characterized by an increase in hepatic triglyceride (TG) content, is the most common liver disease worldwide. Aging has been shown to increase susceptibility to NAFLD; however, the underlying molecular mechanism remains poorly understood. In the present study, we examined hepatic TG content and gene expression profiles in body weight-matched young (3 months old), middle-aged (10 months old), and old (20 months old) C57BL/6 mice and found that TGs were markedly accumulated while mitochondrial β-oxidation-related genes, including PPARα, were downregulated in the liver of old mice. In addition, advanced glycation end product receptor (RAGE), a key regulator of glucose metabolism, was upregulated in the old mice. Mechanistically, suppression of RAGE upregulated PPARα and its downstream target genes, which in turn led to reduced TG retention. Finally, we found that hepatic RAGE expression was increased in aging patients, a finding that correlated with decreased PPARα levels. Taken together, our findings demonstrate that the upregulation of RAGE may play a critical role in aging-associated liver steatosis.
| S-EPMC7576254 | biostudies-literature
Project description:GPR109A agonists have been used for the treatment of obesity however, the role of GPR109A in regulating aging-associated alterations in lipid metabolism is unknown. In this study we used Gpr109a-/- mice to investigate the effect of aging in the regulation of lipid accumulation. We observed that in mouse and human livers, in addition to Kupffer cells, GPR109A is expressed in hepatocytes. Over 12 months, compared to wild type (WT), Gpr109a-/- mice gained significantly more weight. Food intake and levels of serum lipids were similar among both groups. Compared to age-matched WT mice, 12-months old Gpr109a-/- mice had significantly increased liver weight, hepatic steatosis and serum markers of liver injury. The fatty liver phenotype in Gpr109a-/- mice was associated with increased hepatic expression of lipogenesis genes and decreased expression of lipolysis genes. Gpr109a-/- mice had significantly increased fat tissues, which was associated with significant increase in adipocyte diameter and surface area. Adipose tissue from Gpr109a-/- mice had increased expression of lipogenesis genes; however, expression of lipolytic genes was similar in both groups. Collectively, these results indicate that during aging, GPR109A modulates de novo lipid accumulation in liver and adipose tissue, and its dysregulation can lead to age-associated obesity and hepatic steatosis.
| S-EPMC6366969 | biostudies-literature
Project description:Purpose: to identify the impact of cdk4 inhibition on genes and pathways involved in age-associated liver disorders using next generation sequencing on young and control- or PD0332991-treated aged mice. Methods: RNA was isolated from livers of young (2 month old) and old (20-22 month old) C57Bl6 mice. Old mice were either either control-aged mice or PD-0332991 treated aged mice (450mg/dk for 2 weeks). The three conditions were represented in triplicate. Raw reads passing quality filtration were aligned to the mm10 mouse genome using UCSC annotations by pseudoalignment in Kallisto. All reasonably expressed transcripts were submitted for statistical analysis to identify age-altered transcripts corrected by cdk4 inhibition. Results: We mapped a minimum of 20 million reads per sample, which corresponded to a total of 25,240 transcripts. Of these, 12,551 were considered reasonably expressed and were included in analysis comparing control-aged v young and PD0332991-treated-aged v young. Conclusion: Inhibition of cdk4 in ages wildtype mice by cdk4 inhibitor PD-0332991 reduces CEBPa-p300 and reduced aged-related alterations of hepatic structure and function.
2018-04-01 | GSE104395 | GEO
Project description:Adipose tissue lipolysis produces glycerol and nonesterified fatty acids (NEFA) that serve as energy sources during nutrient scarcity. Adipose tissue lipolysis is tightly regulated and excessive lipolysis causes hepatic steatosis, as NEFA released from adipose tissue constitutes a major source of TG in the liver of patients with nonalcoholic fatty liver diseases. Here we show that the liver-enriched transcription factor CREBH is activated by TG accumulation and induces FGF21, which suppresses adipose tissue lipolysis, ameliorating hepatic steatosis. CREBH-deficient mice developed severe hepatic steatosis due to increased adipose tissue lipolysis, when fasted or fed a high-fat low-carbohydrate ketogenic diet. FGF21 production was impaired in CREBH-deficient mice, and adenoviral overexpression of FGF21 suppressed adipose tissue lipolysis and improved hepatic steatosis in these mice. Thus, our results uncover a negative feedback loop in which CREBH regulates NEFA flux from adipose tissue to the liver via FGF21.
| S-EPMC4908383 | biostudies-literature
Project description:Nonalcoholic fatty liver disease (NAFLD) is increasing in worldwide prevalence, closely tracking the obesity epidemic, but specific pharmaceutical treatments for NAFLD are lacking. Defining the key molecular pathways underlying the pathogenesis of NAFLD is essential for developing new drugs. Here we demonstrate that inhibition of gut-derived serotonin synthesis ameliorates hepatic steatosis through a reduction in liver serotonin receptor 2A (HTR2A) signaling. Local serotonin concentrations in the portal blood, which can directly travel to and affect the liver, are selectively increased by high-fat diet (HFD) feeding in mice. Both gut-specific Tph1 knockout mice and liver-specific Htr2a knockout mice are resistant to HFD-induced hepatic steatosis, without affecting systemic energy homeostasis. Moreover, selective HTR2A antagonist treatment prevents HFD-induced hepatic steatosis. Thus, the gut TPH1-liver HTR2A axis shows promise as a drug target to ameliorate NAFLD with minimal systemic metabolic effects.
| S-EPMC6240035 | biostudies-literature
Project description:Background and aimsRAS protein activator like 2 (RASAL2) is a newly discovered metabolic regulator involved in energy homeostasis and adipogenesis. However, whether RASAL2 is involved in hepatic lipid metabolism remains undetermined. This study explored the function of RASAL2 and elucidated its potential mechanisms in nonalcoholic fatty liver disease (NAFLD).MethodsNAFLD models were established either by feeding mice a high-fat diet or by incubation of hepatocytes with 1 mM free fatty acids (oleic acid:palmitic acid=2:1). Pathological changes were observed by hematoxylin and eosin staining. Lipid accumulation was assessed by Oil Red O staining, BODIPY493/503 staining, and triglyceride quantification. The in vivo secretion rate of very low-density lipoprotein was determined by intravenous injection of tyloxapol. Gene regulation was analyzed by chromatin immunoprecipitation assays and hydroxymethylated DNA immunoprecipitation combined with real-time polymerase chain reaction.ResultsRASAL2 deficiency ameliorated hepatic steatosis both in vivo and in vitro. Mechanistically, RASAL2 deficiency upregulated hepatic TET1 expression by activating the AKT signaling pathway and thereby promoted MTTP expression by DNA hydroxymethylation, leading to increased production and secretion of very low-density lipoprotein, which is the major carrier of triglycerides exported from the liver to distal tissues.ConclusionsOur study reports the first evidence that RASAL2 deficiency ameliorates hepatic steatosis by regulating lipid metabolism through the AKT/TET1/MTTP axis. These findings will help understand the pathogenesis of NAFLD and highlight the potency of RASAL2 as a new molecular target for NAFLD.
| S-EPMC9817063 | biostudies-literature
Project description:Background and Aims. Angiotensin converting enzyme 2 (ACE2) is an important component of the renin-angiotensin system. Since angiotensin peptides have been shown to be involved in hepatic steatosis, we aimed to evaluate the hepatic lipid profile in ACE2-deficient (ACE2-/y) mice. Methods. Male C57BL/6 and ACE2-/y mice were analyzed at the age of 3 and 6 months for alterations in the lipid profiles of plasma, faeces, and liver and for hepatic steatosis. Results. ACE2-/y mice showed lower body weight and white adipose tissue at all ages investigated. Moreover, these mice had lower levels of cholesterol, triglycerides, and nonesterified fatty acids in plasma. Strikingly, ACE2-/y mice showed high deposition of lipids in the liver. Expression of CD36, a protein involved in the uptake of triglycerides in liver, was increased in ACE2-/y mice. Concurrently, these mice exhibited an increase in hepatic oxidative stress, evidenced by increased lipid peroxidation and expression of uncoupling protein 2, and downregulation of sirtuin 1. ACE2-/y mice also showed impairments in glucose metabolism and insulin signaling in the liver. Conclusions. Deletion of ACE2 causes CD36/sirtuin 1 axis impairment and thereby interferes with lipid homeostasis, leading to lipodystrophy and steatosis.
| S-EPMC5215286 | biostudies-literature
Project description:The importance of epigenetic changes in etiology and pathogenesis of disease has been increasingly recognized. However, the role of epigenetic alterations in the genesis of hepatic steatosis and cause of individual susceptibilities to this pathological state are largely unknown.Male inbred C57BL/6J and DBA/2J mice were fed a lipogenic methyl-deficient diet (MDD) that causes liver injury similar to human non-alcoholic steatohepatitis (NASH) for 6, 12, or 18 weeks, and the status of global and repetitive elements cytosine methylation, histone modifications, and expression of proteins responsible for those epigenetic modifications in livers was determined.The development of hepatic steatosis in inbred C57BL/6J and DBA/2J mice was accompanied by prominent epigenetic abnormalities. This was evidenced by pronounced loss of genomic and repetitive sequences cytosine methylation, especially at major and minor satellites, accompanied by increased levels of repeat-associated transcripts, aberrant histone modifications, and alterations in expression of the maintenance DNA methyltransferase 1 (DNMT1) and de novo DNMT3A proteins in the livers of both mouse strains. However, the DBA/2J mice, which were characterized by an initially lower degree of methylation of repetitive elements and lower extent of histone H3 lysine 9 (H3K9) and H3 lysine 27 (H3K27) trimethylation in the normal livers, as compared to those in the C57BL/6J mice, developed more prominent NASH-specific pathomorphological changes.These results mechanistically link epigenetic alterations to the pathogenesis of hepatic steatosis and strongly suggest that differences in the cellular epigenetic status may be a predetermining factor to individual susceptibilities to hepatic steatosis.
| S-EPMC2773516 | biostudies-literature
Project description:Obesity and type 2 diabetes are associated with increased lipogenesis in the liver. This results in fat accumulation in hepatocytes, a condition known as hepatic steatosis, which is a form of nonalcoholic fatty liver disease (NAFLD), the most common cause of liver dysfunction in the United States. Carbohydrate-responsive element-binding protein (ChREBP), a transcriptional activator of glycolytic and lipogenic genes, has emerged as a major player in the development of hepatic steatosis in mice. However, the molecular mechanisms enhancing its transcriptional activity remain largely unknown. In this study, we have identified the histone acetyltransferase (HAT) coactivator p300 and serine/threonine kinase salt-inducible kinase 2 (SIK2) as key upstream regulators of ChREBP activity. In cultured mouse hepatocytes, we showed that glucose-activated p300 acetylated ChREBP on Lys672 and increased its transcriptional activity by enhancing its recruitment to its target gene promoters. SIK2 inhibited p300 HAT activity by direct phosphorylation on Ser89, which in turn decreased ChREBP-mediated lipogenesis in hepatocytes and mice overexpressing SIK2. Moreover, both liver-specific SIK2 knockdown and p300 overexpression resulted in hepatic steatosis, insulin resistance, and inflammation, phenotypes reversed by SIK2/p300 co-overexpression. Finally, in mouse models of type 2 diabetes and obesity, low SIK2 activity was associated with increased p300 HAT activity, ChREBP hyperacetylation, and hepatic steatosis. Our findings suggest that inhibition of hepatic p300 activity may be beneficial for treating hepatic steatosis in obesity and type 2 diabetes and identify SIK2 activators and specific p300 inhibitors as potential targets for pharmaceutical intervention.
| S-EPMC2993582 | biostudies-literature