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Hepatocyte-specific deletion of hepatocyte nuclear factor-4? in adult mice results in increased hepatocyte proliferation.

ABSTRACT: Hepatocyte nuclear factor-4? (HNF4?) is known as the master regulator of hepatocyte differentiation. Recent studies indicate that HNF4? may inhibit hepatocyte proliferation via mechanisms that have yet to be identified. Using a HNF4? knockdown mouse model based on delivery of inducible Cre recombinase via an adeno-associated virus 8 viral vector, we investigated the role of HNF4? in the regulation of hepatocyte proliferation. Hepatocyte-specific deletion of HNF4? resulted in increased hepatocyte proliferation. Global gene expression analysis showed that a majority of the downregulated genes were previously known HNF4? target genes involved in hepatic differentiation. Interestingly, ?500 upregulated genes were associated with cell proliferation and cancer. Furthermore, we identified potential negative target genes of HNF4?, many of which are involved in the stimulation of proliferation. Using chromatin immunoprecipitation analysis, we confirmed binding of HNF4? at three of these genes. Furthermore, overexpression of HNF4? in mouse hepatocellular carcinoma cells resulted in a decrease in promitogenic gene expression and cell cycle arrest. Taken together, these data indicate that, apart from its role in hepatocyte differentiation, HNF4? actively inhibits hepatocyte proliferation by repression of specific promitogenic genes.

SUBMITTER: Walesky C

PROVIDER: S-EPMC3543634 | biostudies-literature | 2013 Jan

REPOSITORIES: biostudies-literature

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Hepatocyte-specific deletion of hepatocyte nuclear factor-4α in adult mice results in increased hepatocyte proliferation.

Walesky Chad C Gunewardena Sumedha S Terwilliger Ernest F EF Edwards Genea G Borude Prachi P Apte Udayan U

American journal of physiology. Gastrointestinal and liver physiology 20121025 1

Hepatocyte nuclear factor-4α (HNF4α) is known as the master regulator of hepatocyte differentiation. Recent studies indicate that HNF4α may inhibit hepatocyte proliferation via mechanisms that have yet to be identified. Using a HNF4α knockdown mouse model based on delivery of inducible Cre recombinase via an adeno-associated virus 8 viral vector, we investigated the role of HNF4α in the regulation of hepatocyte proliferation. Hepatocyte-specific deletion of HNF4α resulted in increased hepatocyte ...[more]

PMID: 23104559

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Project description:Aims/hypothesisMitochondria are highly dynamic organelles continuously undergoing fission and fusion, referred to as mitochondrial dynamics, to adapt to nutritional demands. Evidence suggests that impaired mitochondrial dynamics leads to metabolic abnormalities such as non-alcoholic steatohepatitis (NASH) phenotypes. However, how mitochondrial dynamics are involved in the development of NASH is poorly understood. This study aimed to elucidate the role of mitochondrial fission factor (MFF) in the development of NASH.MethodsWe created mice with hepatocyte-specific deletion of MFF (MffLiKO). MffLiKO mice fed normal chow diet (NCD) or high-fat diet (HFD) were evaluated for metabolic variables and their livers were examined by histological analysis. To elucidate the mechanism of development of NASH, we examined the expression of genes related to endoplasmic reticulum (ER) stress and lipid metabolism, and the secretion of triacylglycerol (TG) using the liver and primary hepatocytes isolated from MffLiKO and control mice.ResultsMffLiKO mice showed aberrant mitochondrial morphologies with no obvious NASH phenotypes during NCD, while they developed full-blown NASH phenotypes in response to HFD. Expression of genes related to ER stress was markedly upregulated in the liver from MffLiKO mice. In addition, expression of genes related to hepatic TG secretion was downregulated, with reduced hepatic TG secretion in MffLiKO mice in vivo and in primary cultures of MFF-deficient hepatocytes in vitro. Furthermore, thapsigargin-induced ER stress suppressed TG secretion in primary hepatocytes isolated from control mice.Conclusions/interpretationWe demonstrated that ablation of MFF in liver provoked ER stress and reduced hepatic TG secretion in vivo and in vitro. Moreover, MffLiKO mice were more susceptible to HFD-induced NASH phenotype than control mice, partly because of ER stress-induced apoptosis of hepatocytes and suppression of TG secretion from hepatocytes. This study provides evidence for the role of mitochondrial fission in the development of NASH.

Project description:Alterations in the energy homeostasis contribute to sepsis-mediated multiple organ failure. The liver plays a central role in metabolism and participates to the innate immune and inflammatory responses of sepsis. Several clinical and experimental studies have suggested that females are less susceptible to the adverse outcome of sepsis. However, underlying mechanisms of organ damage in sepsis remain largely undefined. AMP-activated protein kinase (AMPK) is an important regulator of mitochondrial quality control. The AMPK catalytic ?1 isoform is abundantly expressed in the liver. Here, we determined the role of hepatocyte AMPK?1 in sepsis by using hepatocyte-specific AMPK?1 knockout mice (H-AMPK?1 KO) generated with Cre-recombinase expression under the control of the albumin promoter. Using a clinically relevant model of polymicrobial sepsis by cecal ligation and puncture (CLP), we observed that male H-AMPK?1 KO mice had higher plasma levels of tumor necrosis factor-? and interleukin-6 and exhibited a more severe liver and lung injury than male H-AMPK?1 WT mice, as evaluated by histology and neutrophil infiltration at 18 h after CLP. Plasma levels of interleukin-10 and the keratinocyte-derived chemokine were similarly elevated in both KO and WT male mice. At transmission electron microscopy analysis, male H-AMPK?1 KO mice exhibited higher liver mitochondrial damage, which was associated with a significant decrease in liver ATP levels when compared to WT mice at 18 h after sepsis. Mortality rate was significantly higher in the male H-AMPK?1 KO group (91%) when compared to WT mice (60%) at 7 days after CLP. Female H-AMPK?1 WT mice exhibited a similar degree of histological liver and lung injury, but significantly milder liver mitochondrial damage and higher autophagy when compared to male WT mice after CLP. Interestingly, H-AMPK?1 KO female mice had lower organ neutrophil infiltration, lower liver mitochondrial damage and lower levels of cytokines than WT female mice. There was no significant difference in survival rate between WT and KO mice in the female group. In conclusion, our study demonstrates that AMPK?1 is a crucial hepatoprotective enzyme during sepsis. Furthermore, our results suggest that AMPK-dependent liver metabolic functions may influence the susceptibility to multiple organ injury in a sex-dependent manner.

Project description:Transforming growth factor (TGF)-?-activated kinase 1 (TAK1) is activated in different cytokine signaling pathways. Deletion of Tak1 from hepatocytes results in spontaneous development of hepatocellular carcinoma (HCC), liver inflammation, and fibrosis. TGF-? activates TAK1 and Smad signaling, which regulate cell death, proliferation, and carcinogenesis. However, it is not clear whether TGF-? signaling in hepatocytes, via TGF-? receptor-2 (Tgfbr2), promotes HCC and liver fibrosis.We generated mice with hepatocyte-specific deletion of Tak1 (Tak1?Hep), as well as Tak1/Tgfbr2DHep and Tak1/Smad4?Hep mice. Tak1flox/flox, Tgfbr2?Hep, and Smad4?Hep mice were used as controls, respectively. We assessed development of liver injury, inflammation, fibrosis, and HCC. Primary hepatocytes isolated from these mice were used to assess TGF-?-mediated signaling.Levels of TGF-?, TGF-?R2, and phospho-Smad2/3 were increased in HCCs from Tak1?Hep mice, which developed liver fibrosis and inflammation by 1 month and HCC by 9 months. However, Tak1/Tgfbr2?Hep mice did not have this phenotype, and their hepatocytes did not undergo spontaneous cell death or compensatory proliferation. Hepatocytes from Tak1?Hep mice incubated with TGF-? did not activate p38, c-Jun N-terminal kinase, or nuclear factor-?B; conversely, TGF-?-mediated cell death and phosphorylation of Smad2/3 were increased, compared with control hepatocytes. Blocking the Smad pathway inhibited TGF-?-mediated death of Tak1-/- hepatocytes. Accordingly, disruption of Smad4 reduced the spontaneous liver injury, inflammation, fibrosis, and HCC that develops in Tak1?Hep mice. Levels of the anti-apoptotic protein Bcl-xL, ?-catenin, connective tissue growth factor, and vascular endothelial growth factor were increased in HCC from Tak1?Hep mice, but not in HCCs from Tak1/Tgfbr2?Hep mice. Injection of N-nitrosodiethylamine induced HCC formation in wild-type mice, but less in Tgfbr2?Hep mice.TGF-? promotes development of HCC in Tak1?Hep mice by inducing hepatocyte apoptosis and compensatory proliferation during early phases of tumorigenesis, and inducing expression of anti-apoptotic, pro-oncogenic, and angiogenic factors during tumor progression.

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Hepatocyte-specific deletion of hepatocyte nuclear factor-4? in adult mice results in increased hepatocyte proliferation.

Publications

Hepatocyte-specific deletion of hepatocyte nuclear factor-4α in adult mice results in increased hepatocyte proliferation.

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