The DNA damage checkpoint protein ATM promotes hepatocellular apoptosis and fibrosis in a mouse model of non-alcoholic fatty liver disease

Steatoapoptosis is a hallmark of non-alcoholic fatty liver disease (NAFLD) and is an important factor in liver disease progression. We hypothesized that increased reactive oxygen species resulting from excess dietary fat contribute to liver disease by causing DNA damage and apoptotic cell death, and tested this by investigating the effects of feeding mice high fat or standard diets for 8 weeks. High fat diet feeding resulted in increased hepatic H2O2, superoxide production, and expression of oxidative stress response genes, confirming that the high fat diet induced hepatic oxidative stress. High fat diet feeding also increased hepatic steatosis, hepatitis and DNA damage as exemplified by an increase in the percentage of 8-hydroxyguanosine (8-OHG) positive hepatocytes in high fat diet fed mice. Consistent with reports that the DNA damage checkpoint kinase Ataxia Telangiectasia Mutated (ATM) is activated by oxidative stress, ATM phosphorylation was induced in the livers of wild type mice following high fat diet feeding. We therefore examined the effects of high fat diet feeding in Atm-deficient mice. The prevalence of apoptosis and expression of the pro-apoptotic factor PUMA were significantly reduced in Atm-deficient mice fed the high fat diet when compared with wild type controls. Furthermore, high fat diet fed Atm−/− mice had significantly less hepatic fibrosis than Atm+/+ or Atm+/− mice fed the same diet. Together, these data demonstrate a prominent role for the ATM pathway in the response to hepatic fat accumulation and link ATM activation to fatty liver-induced steatoapoptosis and fibrosis, key features of NAFLD progression

The Dna Damage Checkpoint Protein Atm Promotes Hepatocellular Apoptosis And Fibrosis In A Mouse Model Of Non-Alcoholic Fatty Liver Disease

Steatoapoptosis is a hallmark of non-alcoholic fatty liver disease (NAFLD) and is an important factor in liver disease progression. We hypothesized that increased reactive oxygen species resulting from excess dietary fat contribute to liver disease by causing DNA damage and apoptotic cell death, and tested this by investigating the effects of feeding mice a high fat or standard diets for 8 weeks. High fat diet feeding resulted in increased hepatic H2O2, superoxide production, and expression of oxidative stress response genes, confirming that the high fat diet induced hepatic oxidative stress. High fat diet feeding also increased hepatic steatosis, hepatitis, and DNA damage as exemplified by an increase in the percentage of 8-hydroxyguanosine (8OHG) positive hepatocytes in high fat diet fed mice. Consistent with reports that the DNA damage checkpoint kinase Ataxia Telangiectasia Mutated (ATM) is activated by oxidative stress, ATM phosphorylation was induced in the livers of wild-type mice following high fat diet feeding. We therefore examined the effects of high fat diet feeding in Atm-deficient mice. The prevalence of apoptosis and expression of the pro-apoptotic factor Puma were significantly reduced in Atm-deficient mice fed the high fat diet when compared to wild-type controls. Furthermore, high fat diet fed Atm-/- mice had significantly less hepatic fibrosis than Atm+/+ or Atm+/- mice fed the same diet. Together, these data demonstrate a prominent role for the ATM pathway in the response to hepatic fat accumulation and link ATM activation to fatty liverinduced steatoapoptosis and fibrosis, key features of NAFLD progression

Sex-specific hepatic lipid and bile acid metabolism alterations in Fancd2-deficient mice following dietary challenge.

Defects in the Fanconi anemia (FA) DNA damage-response pathway result in genomic instability, developmental defects, hematopoietic failure, cancer predisposition, and metabolic disorders. The endogenous sources of damage contributing to FA phenotypes and the links between FA and metabolic disease remain poorly understood. Here, using mice lacking the Fancd2 gene, encoding a central FA pathway component, we investigated whether the FA pathway protects against metabolic challenges. Fancd2-/- and wildtype (WT) mice were fed a standard diet (SD), a diet enriched in fat, cholesterol, and cholic acid (Paigen diet), or a diet enriched in lipid alone (high-fat diet (HFD)). Fancd2-/- mice developed hepatobiliary disease and exhibited decreased survival when fed a Paigen diet but not a HFD. Male Paigen diet-fed mice lacking Fancd2 had significant biliary hyperplasia, increased serum bile acid concentration, and increased hepatic pathology. In contrast, female mice were similarly impacted by Paigen diet feeding regardless of Fancd2 status. Upon Paigen diet challenge, male Fancd2-/- mice had altered expression of genes encoding hepatic bile acid transporters and cholesterol and fatty acid metabolism proteins, including Scp2/x, Abcg5/8, Abca1, Ldlr, Srebf1, and Scd-1 Untargeted lipidomic profiling in liver tissue revealed 132 lipid species, including sphingolipids, glycerophospholipids, and glycerolipids, that differed significantly in abundance depending on Fancd2 status in male mice. We conclude that the FA pathway has sex-specific impacts on hepatic lipid and bile acid metabolism, findings that expand the known functions of the FA pathway and may provide mechanistic insight into the metabolic disease predisposition in individuals with FA

Hepatocyte p53 ablation induces metabolic dysregulation that is corrected by food restriction and vertical sleeve gastrectomy in mice.

P53 has been implicated in the pathogenesis of obesity and diabetes; however, the mechanisms and tissue sites of action are incompletely defined. Therefore, we investigated the role of hepatocyte p53 in metabolic homeostasis using a hepatocyte-specific p53 knockout mouse model. To gain further mechanistic insight, we studied mice under two complementary conditions of restricted weight gain: vertical sleeve gastrectomy (VSG) or food restriction. VSG or sham surgery was performed in high-fat diet-fed male hepatocyte-specific p53 wild-type and knockout littermates. Sham-operated mice were fed ad libitum or food restricted to match their body weight to VSG-operated mice. Hepatocyte-specific p53 ablation in sham-operated ad libitum-fed mice impaired glucose homeostasis, increased body weight, and decreased energy expenditure without changing food intake. The metabolic deficits induced by hepatocyte-specific p53 ablation were corrected, in part by food restriction, and completely by VSG. Unlike food restriction, VSG corrected the effect of hepatocyte p53 ablation to lower energy expenditure, resulting in a greater improvement in glucose homeostasis compared with food restricted mice. These data reveal an important new role for hepatocyte p53 in the regulation of energy expenditure and body weight and suggest that VSG can improve alterations in energetics associated with p53 dysregulation

<i>Ccr2^−/−</i> and <i>Cd44^−/−</i> mice display altered inflammatory cell recruitment during LD feeding.

<p>(A–I) Composition of Liver Leukocytes in mice fed SD or LD (*P<0.05 compared to SD controls; **P<0.05 compared to all other groups). Cells are identified as in figure legend 2.</p

LD fed hepatitis susceptible B6 mice display uniform increases in hepatic leukocyte populations.

<p>(A–H) Composition of liver leukocytes in B6, BALB/c, and AKR mice fed SD or LD (*P<0.05 compared to SD controls). Leukocyte populations are defined as follows: NK cells, CD49b⁺ CD3⁻; NK-T cells, CD3⁺ CD49b⁺; B-cells, CD19⁺ B220⁺; dendritic cells, CD11c⁺, macrophages, CD11b⁺ Ly6C⁻, neutrophils, CD11b⁺ Ly6C⁺.</p

Hepatic leukocytes from B6 mice bind to hyaluronic acid in a CD44 dependent manner.

<p>(A) HA binding of CD45⁺ cells from a representative SD fed B6, <i>Ccr2^−/−</i> and <i>Cd44^−/−</i>mouse. (B) HA binding of CD45⁺ cells from a representative four week LD fed B6, <i>Ccr2^−/−</i> and <i>Cd44^−/−</i>mouse. (C) Cumulative HA binding results over time (n = 3–6 per group). (D) In CD45⁺ leukocytes from LD fed B6 mice, HA binding occurs on a subpopulation of CD44⁺ cells.</p

Monocytes in the liver of LD fed mice display an inflammatory phenotype.

<p>Co-expression of CCR2 and Gr-1 (A), as well as CCR2 and iNOS (B) in livers of CCR2 reporter mice. Flow cytometric analysis of hepatic CCR2⁺, CD11b⁺, Ly6C⁻ cells (solid line) confirms increase expression of Gr-1 (C) and iNOS (D) on CCR2⁺, CD11b⁺ cells compared to gray shaded regions which represent CCR2⁺, CD11b⁻⁻ populations stained for the same markers.</p