Hepatocyte growth factor stimulates synthesis of lipids and secretion of lipoproteins in rat hepatocytes

Ube4A maintains metabolic homeostasis and facilitates insulin signaling in vivo

OBJECTIVE

Defining the regulators of cell metabolism and signaling is essential to design new therapeutic strategies in obesity and NAFLD/NASH. E3 ubiquitin ligases control diverse cellular functions by ubiquitination-mediated regulation of protein targets, and thus their functional aberration is associated with many diseases. The E3 ligase Ube4A has been implicated in human obesity, inflammation, and cancer. However, its in vivo function is unknown, and no animal models are available to study this novel protein.

METHODS

A whole-body Ube4A knockout (UKO) mouse model was generated, and various metabolic parameters were compared in chow- and high fat diet (HFD)-fed WT and UKO mice, and in their liver, adipose tissue, and serum. Lipidomics and RNA-Seq studies were performed in the liver samples of HFD-fed WT and UKO mice. Proteomic studies were conducted to identify Ube4A's targets in metabolism. Furthermore, a mechanism by which Ube4A regulates metabolism was identified.

RESULTS

Although the body weight and composition of young, chow-fed WT and UKO mice are similar, the knockouts exhibit mild hyperinsulinemia and insulin resistance. HFD feeding substantially augments obesity, hyperinsulinemia, and insulin resistance in both sexes of UKO mice. HFD-fed white and brown adipose tissue depots of UKO mice have increased insulin resistance and inflammation and reduced energy metabolism. Moreover, Ube4A deletion exacerbates hepatic steatosis, inflammation, and liver injury in HFD-fed mice with increased lipid uptake and lipogenesis in hepatocytes. Acute insulin treatment resulted in impaired activation of the insulin effector protein kinase Akt in liver and adipose tissue of chow-fed UKO mice. We identified the Akt activator protein APPL1 as a Ube4A interactor. The K63-linked ubiquitination (K63-Ub) of Akt and APPL1, known to facilitate insulin-induced Akt activation, is impaired in UKO mice. Furthermore, Ube4A K63-ubiquitinates Akt in vitro.

CONCLUSION

Ube4A is a novel regulator of obesity, insulin resistance, adipose tissue dysfunction and NAFLD, and preventing its downregulation may ameliorate these diseases.

Exploring the Gamut of Receptor Tyrosine Kinases for Their Promise in the Management of Non-Alcoholic Fatty Liver Disease

Recently, non-alcoholic fatty liver disease (NAFLD) has emerged as a predominant health concern affecting approximately a quarter of the world’s population. NAFLD is a spectrum of liver ailments arising from nascent lipid accumulation and leading to inflammation, fibrosis or even carcinogenesis. Despite its prevalence and severity, no targeted pharmacological intervention is approved to date. Thus, it is imperative to identify suitable drug targets critical to the development and progression of NAFLD. In this quest, a ray of hope is nestled within a group of proteins, receptor tyrosine kinases (RTKs), as targets to contain or even reverse NAFLD. RTKs control numerous vital biological processes and their selective expression and activity in specific diseases have rendered them useful as drug targets. In this review, we discuss the recent advancements in characterizing the role of RTKs in NAFLD progression and qualify their suitability as pharmacological targets. Available data suggests inhibition of Epidermal Growth Factor Receptor, AXL, Fibroblast Growth Factor Receptor 4 and Vascular Endothelial Growth Factor Receptor, and activation of cellular mesenchymal-epithelial transition factor and Fibroblast Growth Factor Receptor 1 could pave the way for novel NAFLD therapeutics. Thus, it is important to characterize these RTKs for target validation and proof-of-concept through clinical trials.

The administration of hepatocyte growth factor prevents total parenteral nutrition-induced hepatocellular injury in a rat model

PURPOSE

Total parenteral nutrition (TPN) sometimes induces parenteral nutrition-associated liver disease (PNALD). Hepatocyte growth factor (HGF) acts as a potent hepatocyte mitogen anti-inflammatory and antioxidant actions. We aimed to evaluate the effect of HGF on PNALD in a rat model of TPN.

METHODS

A catheter was placed in the right jugular vein for 7-day continuous TPN. All rats were divided into three groups: TPN alone (TPN group), TPN plus intravenous HGF at 0.3 mg/kg/day [TPN + HGF (low) group], and TPN plus HGF at 1.0 mg/kg/day [TPN + HGF (high) group]. On day 7, livers were harvested and the histology, inflammatory cytokines and apoptosis were evaluated.

RESULTS

Histologically, lipid droplets were apparent in the TPN group, but decreased in the TPN + HGF (low) and TPN + HGF (high) groups. The histological nonalcoholic fatty liver disease activity scores in the TPN + HGF (low) and TPN + HGF (high) groups were significantly lower than that in the TPN group (p < 0.01). There were no significant differences in the inflammatory cytokine levels of the three groups. The caspase-9 expression levels in the TPN + HGF (low) and TPN + HGF (high) groups were significantly decreased in comparison to that in the control group (p < 0.05).

CONCLUSION

The intravenous administration of HGF attenuated hepatic steatosis induced by 7-day TPN dose dependently.

Murine liver repair via transient activation of regenerative pathways in hepatocytes using lipid nanoparticle-complexed nucleoside-modified mRNA

Induction of intrinsic liver regeneration is an unmet need that can be achieved by temporally activating key hepatocyte regenerative pathways. Here, we establish an efficient, safe, non-integrative method to transiently express hepatocyte-growth-factor (HGF) and epidermal-growth-factor (EGF) in hepatocytes via nucleoside-modified, lipid-nanoparticle-encapsulated mRNA (mRNA-LNP) delivery in mice. We confirm specific hepatotropism of mRNA-LNP via intravenous injection of firefly luciferase encoding mRNA-LNP, with protein expression lasting about 3 days. In the liver, virtually all hepatocytes are transfected along with a subpopulation of endothelial and Kupffer cells. In homeostasis, HGF mRNA-LNP efficiently induce hepatocyte proliferation. In a chronic liver injury mouse model recapitulating non-alcoholic fatty liver disease, injections of both HGF and EGF mRNA-LNP sharply reverse steatosis and accelerate restoration of liver function. Likewise, HGF and EGF mRNA-LNP accelerate liver regeneration after acetaminophen-induced acute liver injury with rapid return to baseline ALT levels. This study introduces mRNA-LNP as a potentially translatable safe therapeutic intervention to harness liver regeneration via controlled expression of endogenous mitogens in vivo.

Lipidomic signatures of post-hepatectomy liver failure using porcine hepatectomy models

Background

Clinical diagnosis of post-hepatectomy liver failure (PHLF) can only be made on or after the 5th postoperative day. Biomarker for early diagnosis is considered as a critical unmet need.

Methods

Twenty domestic female crossbreed (Yorkshire-landrace and duroc) pigs underwent sham operation (n=6), 70% (n=7) and 90% (n=7) partial hepatectomy (PH). A comprehensive lipidomic analysis was conducted using sera collected at pre-operation (PO), 14, 30, and 48 h after PH using nanoflow ultrahigh performance liquid chromatography-electrospray ionization-tandem mass spectrometry.

Results

Of the 184 quantified lipids, 14 lipids showed significant differences between the two resection groups starting at 30 h after surgery. Four phosphatidylcholine (PC) plasmalogen species (P-16:0/16:0, P-18:0/18:2, P-18:0/20:4, and P-18:0/22:6) and PC 32:2 significantly increased in the 90% PH group while these returned to PO level after 30 h in the 70% PH group, presumably implying the failure markers. In contrast, eight triacylglycerol (TG) species (40:0, 42:1, 42:0, 44:1, 44:2, 46:1, 46:2, and 48:3) and sphingomyelin d18:1/20:0 showed an opposite trend, wherein they significantly decreased in the 90% PH group while these in the 70% PH group were abruptly increased until 30 h but returned to near PO levels at 48 h, implying the recovery markers. Same trends could also be observed in the level of whole lipid classes of PC plasmalogens and TGs, in addition to selected individual lipid species.

Conclusions

Characteristic lipidomic signatures of PHLF could be identified using large animal models. These candidates have a potential to serve as a tool for early diagnosis and may open new paths to the study to overcome PHLF.

Regulation of Energy Metabolism by Receptor Tyrosine Kinase Ligands

Metabolic diseases, such as diabetes, obesity, and fatty liver disease, have now reached epidemic proportions. Receptor tyrosine kinases (RTKs) are a family of cell surface receptors responding to growth factors, hormones, and cytokines to mediate a diverse set of fundamental cellular and metabolic signaling pathways. These ligands signal by endocrine, paracrine, or autocrine means in peripheral organs and in the central nervous system to control cellular and tissue-specific metabolic processes. Interestingly, the expression of many RTKs and their ligands are controlled by changes in metabolic demand, for example, during starvation, feeding, or obesity. In addition, studies of RTKs and their ligands in regulating energy homeostasis have revealed unexpected diversity in the mechanisms of action and their specific metabolic functions. Our current understanding of the molecular, biochemical and genetic control of energy homeostasis by the endocrine RTK ligands insulin, FGF21 and FGF19 are now relatively well understood. In addition to these classical endocrine signals, non-endocrine ligands can govern local energy regulation, and the intriguing crosstalk between the RTK family and the TGFβ receptor family demonstrates a signaling network that diversifies metabolic process between tissues. Thus, there is a need to increase our molecular and mechanistic understanding of signal diversification of RTK actions in metabolic disease. Here we review the known and emerging molecular mechanisms of RTK signaling that regulate systemic glucose and lipid metabolism, as well as highlighting unexpected roles of non-classical RTK ligands that crosstalk with other receptor pathways.

Effect of ethanol on lipid metabolism

Hepatic lipid metabolism is a series of complex processes that control influx and efflux of not only hepatic lipid pools, but also organismal pools. Lipid homeostasis is usually tightly controlled by expression, substrate supply, oxidation and secretion that keep hepatic lipid pools relatively constant. However, perturbations of any of these processes can lead to lipid accumulation in the liver. Although it is thought that these responses are hepatic arms of the 'thrifty genome', they are maladaptive in the context of chronic fatty liver diseases. Ethanol is likely unique among toxins, in that it perturbs almost all aspects of hepatic lipid metabolism. This complex response is due in part to the large metabolic demand placed on the organ by alcohol metabolism, but also appears to involve more nuanced changes in expression and substrate supply. The net effect is that steatosis is a rapid response to alcohol abuse. Although transient steatosis is largely an inert pathology, the chronicity of alcohol-related liver disease seems to require steatosis. Better and more specific understanding of the mechanisms by which alcohol causes steatosis may therefore translate into targeted therapies to treat alcohol-related liver disease and/or prevent its progression.

The contributions of mesoderm-derived cells in liver development

The liver is an indispensable organ for metabolism and drug detoxification. The liver consists of endoderm-derived hepatobiliary lineages and various mesoderm-derived cells, and interacts with the surrounding tissues and organs through the ventral mesentery. Liver development, from hepatic specification to liver maturation, requires close interactions with mesoderm-derived cells, such as mesothelial cells, hepatic stellate cells, mesenchymal cells, liver sinusoidal endothelial cells and hematopoietic cells. These cells affect liver development through precise signaling events and even direct physical contact. Through the use of new techniques, emerging studies have recently led to a deeper understanding of liver development and its related mechanisms, especially the roles of mesodermal cells in liver development. Based on these developments, the current protocols for in vitro hepatocyte-like cell induction and liver-like tissue construction have been optimized and are of great importance for the treatment of liver diseases. Here, we review the roles of mesoderm-derived cells in the processes of liver development, hepatocyte-like cell induction and liver-like tissue construction.

Elental® amino acid component has protective effects on primary cultured hepatocytes and a rat model of acute liver injury

Amino acids can exert protective effects on the liver either when administered as a medication or following an operation. In this study, we examined the protective effects of amino acids on the liver using in vitro and in vivo models by studying their influence on the induction of inducible nitric oxide synthase (iNOS) and nitric oxide production as a liver injury marker in cultured hepatocytes and liver-protective effects in d-galactosamine and lipopolysaccharide (GalN/LPS)-treated rats, respectively. Primary cultured rat hepatocytes were treated with interleukin (IL)-1β in the presence or absence of Elental® amino acid component (EleAA; 17 amino acids). Rats were pretreated with either EleAA or a diet containing selected amino acids followed by GalN/LPS injection. Survival rate and mRNA expression were analyzed. EleAA inhibited iNOS induction through reduction of mRNA synthesis and stability in cultured hepatocytes, indicating prevention of liver injury, but did not show a liver-protective effect in GalN/LPS rats. Among EleAA, Lys, Trp, His, and Arg (4AA) markedly decreased nitric oxide production and inhibited nuclear factor-κB (NF-κB) activation. In GalN/LPS rats, 4AA (3% of each amino acid in diet) increased survival rate by 50% and decreased mRNA expression of iNOS, tumor necrosis factor-α, and cytokine-induced neutrophil chemoattractant-1 in the liver. 4AA reduced NF-κB activation induced by GalN/LPS. 4AA inhibited the expression of inflammatory mediators, in part through inhibition of NF-κB activation in cultured hepatocytes and GalN/LPS-treated rats. The results suggest that EleAA has therapeutic potential for organ injuries including liver.

Attenuation of Postoperative Acute Liver Failure by Mesenchymal Stem Cell Treatment Due to Metabolic Implications

OBJECTIVE

To prevent posthepatectomy acute liver failure after extended resection by treatment with mesenchymal stem cells (MSCs).

BACKGROUND

Liver tumors often require extended liver resection, overburdening metabolic and regenerative capacities of the remnant organ. Resulting dysfunction and failure may be improved by the proregenerative characteristics of MSCs.

METHODS

Extended liver resection was performed in (DPPIV)-deficient F344-Fischer rats. Wild-type animals served as donors of peritoneal adipose-derived MSCs. These were predifferentiated in vitro into hepatocytic cells and delivered to the liver by splenic application. Liver-related blood parameters (international normalized ratio, bilirubin, aspartate aminotransferase, alanine aminotransferase) and liver histology (hematoxylin-eosin, Sudan III) were determined to monitor liver function. Metabolic changes were assessed by metabolomic analyses in the remnant liver and the serum. Liver damage and regeneration were quantified by determination of the apoptotic and proliferation rates.

RESULTS

MSCs supported survival after partial hepatectomy. They decreased liver-related blood parameters indicative for the improvement of liver function. The extensive lipid accumulation in hepatocytes illustrating the metabolic overload after resection was attenuated. Treatment with MSCs normalized imbalance of amino acids, acylcarnitines, sphingolipids, and glycerophospholipids in the liver and blood. Furthermore, MSCs decreased the apoptotic rate and increased the proliferation rate. The experimental time period (48 hours) was too short to allow for integration of MSCs into the host liver. Thus, the mode of action was probably indirect.

CONCLUSIONS

MSCs ameliorated hepatic dysfunction and improved liver regeneration after extended resection by paracrine mechanisms. They may represent a new therapeutic option to treat posthepatectomy acute liver failure.

Expression of toll-like receptors 1-5 but not TLR 6-10 is elevated in livers of patients with non-alcoholic fatty liver disease

BACKGROUND & AIMS

Animal models of non-alcoholic fatty liver disease (NAFLD) suggest that an increased translocation of bacterial endotoxins, leading to an activation of toll-like receptor-dependent signalling cascades (TLRs) and increased formation of reactive oxygen species, may add to development of insulin resistance and induction of plasminogen activator inhibitor-1 (PAI-1) in the liver. If similar mechanisms are also involved in the development of NAFLD in humans remains to be determined.

METHODS

Toll-like receptor (1-10), myeloid differentiation primary response gene (MyD88), interferon regulatory transcription factor 3 (IRF-3) and insulin receptor substrate 1 (IRS-1) mRNA expression was determined in liver samples of 11 patients with NAFLD and 11 controls. Hepatic PA1-1 and 4-hydroxynonenal protein adducts (4-HNE) levels were determined by immunohistochemistry.

RESULTS

Hepatic TLR 1-5 mRNAs expression was significantly higher in livers of NAFLD patients than in controls, whereas expression of TLR 6-10 mRNAs did not differ between groups. Expression of MyD88 but not IRF-3 was also significantly higher in livers of NAFLD patients than in controls. These alterations were associated with significantly higher levels of 4-HNE and PAI-1 protein levels in livers of NAFLD patients than in controls, whereas IRS-1 mRNA expression was ~80% lower in livers of NAFLD patients than in controls.

CONCLUSIONS

Taken together, these findings add further weight to the hypothesis that alterations at the level of intestine and intestinal barrier function may be critical in the development of NAFLD in humans.

Liver zonation: Novel aspects of its regulation and its impact on homeostasis

Liver zonation, the spatial separation of the immense spectrum of different metabolic pathways along the liver sinusoids, is fundamental for proper functioning of this organ. Recent progress in elucidating localization and interactions of different metabolic pathways by using “omics” techniques and novel approaches to couple them with refined spatial resolution and in characterizing novel master regulators of zonation by using transgenic mice has created the basis for a deeper understanding of core mechanisms of zonation and their impact on liver physiology, pathology and metabolic diseases. This review summarizes the fascinating technical achievements for investigating liver zonation and the elucidation of an emerging network of master regulators of zonation that keep the plethora of interrelated and sometimes opposing functions of the liver in balance with nutritional supply and specific requirements of the entire body. In addition, a brief overview is given on newly described zonated functions and novel details on how diverse the segmentation of metabolic zonation may be. From these facts and developments a few fundamental principles are inferred which seem to rule zonation of liver parenchyma. In addition, we identify important questions that still need to be answered as well as interesting fields of research such as the connection of zonation with circadian rhythm and gender dimorphism which need to be pushed further, in order to improve our understanding of metabolic zonation. Finally, an outlook is given on how disturbance of liver zonation and its regulation may impact on liver pathology and the development of metabolic diseases.

Alcoholic liver disease and the potential role of plasminogen activator inhibitor-1 and fibrin metabolism

Plasminogen activator inhibitor-1 (PAI-1) is a major player in fibrinolysis due to its classical role of inhibiting plasminogen activators. Although increased fibrinolysis is common in alcoholic cirrhosis, decreased fibrinolysis (driven mostly by elevated levels of PAI-1) is common during the development of alcoholic liver disease (ALD). However, whether or not PAI-1 plays a causal role in the development of early ALD was unclear. Recent studies in experimental models have suggested that PAI-1 may contribute to the development of early (steatosis), intermediate (steatohepatitis) and late (fibrosis) stages of ALD. For example, fatty liver owing to both acute and chronic ethanol was blunted by the genetic inhibition of PAI-1. This effect of targeting PAI-1 appears to be mediated, at least in part, by an increase in very low-density lipoprotein (VLDL) synthesis in the genetic absence of this acute phase protein. Results from a two-hit model employing ethanol and lipopolysaccharide administration suggest that PAI-1 plays a critical role in hepatic inflammation, most likely due to its ability to cause fibrin accumulation, which subsequently sensitizes the liver to ensuing damaging insults. Lastly, the role of PAI-1 in hepatic fibrosis is less clear and appears that PAI-1 may serve a dual role in this pathological change, both protective (enhancing regeneration) and damaging (blocking matrix degradation). In summary, results from these studies suggest that PAI-1 may play multiple roles in the various stages of ALD, both protective and damaging. The latter effect is mediated by its influence on steatosis (i.e. decreasing VLDL synthesis), inflammation (i.e. impairing fibrinolysis) and fibrosis (i.e. blunting matrix degradation), whereas the former is mediated by maintaining hepatocyte division after an injury.

Fructose-induced steatosis in mice: role of plasminogen activator inhibitor-1, microsomal triglyceride transfer protein and NKT cells

Plasminogen activator inhibitor-1 (PAI-1) is an acute-phase protein known to be involved in alcoholic liver disease and hepatic fibrosis. In the present study, the hypothesis that PAI-1 is causally involved in the onset of fructose-induced hepatic steatosis was tested in a mouse model. Wild-type C57BL/6J and PAI-1⁻/⁻ mice were fed with 30% fructose solution or water for 8 weeks. Markers of hepatic steatosis, expression of PAI-1, apolipoprotein B (ApoB), cluster of differentiation 1d (CD1d), markers of natural killer T (NKT) cells, protein levels of phospho-c-Met and tumor necrosis factor-α (TNF-α) were determined. Activity of the microsomal triglyceride transfer protein (MTTP) was measured in liver tissue. In comparison with water controls, chronic intake of 30% fructose solution caused a significant increase in hepatic triglycerides, PAI-1 expression and plasma alanine aminotransferase levels in wild-type mice. This effect of fructose feeding was markedly attenuated in PAI-1⁻/⁻ mice. Despite no differences in portal endotoxin levels and hepatic TNF-α protein levels between fructose-fed groups, the protective effect of the loss of PAI-1 against the onset of fructose-induced steatosis was associated with a significant increase in phospho-c-Met, phospho Akt, expression of ApoB and activity of MTTP in livers of PAI-1⁻/⁻ mice in comparison with fructose-fed wild types. Moreover, in PAI-1⁻/⁻ mice, expressions of CD1d and markers of CD1d-reactive NKT cells were markedly higher than in wild-type mice; however, expression of markers of activation of CD1d-reactive NKT cells (eg, interleukin-15 and interferon-γ) were only found to be increased in livers of fructose-fed PAI-1⁻/⁻ mice. Taken together, these data suggest that PAI-1 has a causal role in mediating the early phase of fructose-induced liver damage in mice through signaling cascades downstream of Kupffer cells and TNF-α.

New role of plasminogen activator inhibitor-1 in alcohol-induced liver injury

Plasminogen activator inhibitor-1 (PAI-1) is the main inhibitor of plasminogen activators, thereby playing a major role in fibrinolysis. Whereas hyperfibrinolysis is common in alcoholic cirrhosis, hypofibrinolysis (driven mostly by elevated levels of PAI-1) is common during the development of alcoholic liver disease (ALD). However, whether or not PAI-1 plays a causal role in the development of ALD has been unclear. The role of PAI-1 was therefore investigated in models of early (steatosis), intermediate (inflammation/necrosis) and late (fibrosis) stages of alcoholic liver disease. For example, hepatic steatosis caused by both acute and chronic ethanol was blunted by inhibiting PAI-1 activation. This effect of inhibiting PAI-1 appears to be mediated, at least in part, by an increase in very low-density lipoprotein (VLDL) synthesis in the absence of PAI-1. The results from that study also indicated that PAI-1 plays a critical role in both acute and chronic hepatic inflammation. Lastly, knocking out PAI-1 potently protected against experimental hepatic fibrosis; the mechanism of this protective effect appears to be mediated predominantly by extracellular matrix (ECM) resolution by matrix metalloproteases, which are indirectly inhibited by PAI-1. In summary, targeting PAI-1 protects against all three stages of ALD in model systems. The mechanisms by which PAI-1 contributes to these disease stages appear to not only involve the 'classical' function of PAI-1 (i.e. in mediating fibrinolysis), but also other functions of this protein. These data support a role of PAI-1 in the initiation and progression of ALD, and suggest that PAI-1 may be a useful target for clinical therapy to halt or blunt disease progression.

HGF ameliorates a high-fat diet-induced fatty liver

Hepatocyte growth factor (HGF) has various effects especially on epithelial cells. However, the precise role of HGF on lipogenesis is still not fully understood. A high-fat diet was administered to HGF transgenic mice and wild-type control mice in vivo. Furthermore, recombinant human HGF (rhHGF) was administered to HepG2 cell line in vitro. We performed an analysis regarding the factors relating to lipid metabolism. An overexpression of HGF dramatically ameliorates a high-fat diet-induced fatty liver. HGF transgenic mice showed an apparently reduced lipid accumulation in the liver. The activation of microsomal triglyceride transfer protein (MTP) and apolipoprotein B (ApoB) accompanying higher triglyceride levels in the serum were found in HGF transgenic mice on a normal diet. Interestingly, this upregulation of the MTP activation became more apparent in the high-fat diet. In addition, the administration of rhHGF stimulated MTP and ApoB expression while reducing reduced the intracellular lipid content in HepG2 cell line. However, this induction of MTP and ApoB by HGF was clearly inhibited by PD98059 (MAPK inhibitor). In conclusion, the data presented in this study indicated that HGF ameliorates a high-fat diet-induced fatty liver via the activation of MTP and ApoB.

Adenovirus-mediated hepatic syndecan-1 overexpression induces hepatocyte proliferation and hyperlipidaemia in mice

BACKGROUND

Heparan sulfate proteoglycans (HSPGs) have been involved in the regulation of cell growth, apoptosis and lipid metabolism in vitro; however, their functional role in vivo remains unknown.

AIM

Here, we describe hepatic tissue and lipid metabolism changes after liver overexpression of syndecan-1 (SDC-1), the main hepatic HSPG, in mice induced by adenoviral gene transfer.

RESULTS

SDC-1 overexpression was associated with marked hepatocyte proliferation, cell-isolated apoptosis and increased plasma alanine aminotransferase (ALT) levels. Additionally, SDC-1 liver overexpression significantly raised plasma cholesterol and triglyceride concentrations due to an increase in all lipoprotein particles, including the appearance of large and apolipoprotein (apo) E-enriched high-density lipoprotein (HDL) particles. Hepatic very low-density lipoprotein (VLDL) production was not affected by SDC-1 overexpression, suggesting a delayed plasma clearance of apo B lipoproteins as the underlying hyperlipidaemic mechanism. These pleotropic effects were qualitatively equivalent, even though less intense, in mice overexpressing a cytoplasmic C-terminal domain-deleted SDC-1.

CONCLUSIONS

This is the first report in vivo of the biological effects induced by a specific HSPG in the liver, with potential implications in both regenerative biology and molecular lipidology.

Proteomic analysis of serum marker proteins in recipient mice with liver cirrhosis after bone marrow cell transplantation

We previously found that transplantation with bone marrow cells (BMCs) improves liver function and liver fibrosis in cirrhotic mice. In the presence of liver damage induced by carbon tetrachloride (CCl4), transplanted BMC migrated into the peri-portal region and trans-differentiated into hepatocytes that produce albumin. Thus under these conditions, BMC transplantation induces liver regeneration. Detecting serum marker proteins is important to monitor the recovery of liver function of cirrhotic mice after BMC transplantation. We therefore initially resolved proteins extracted from serum samples at 48 h after BMC transplantation by 2-DE and compared spot intensity between control and BMC groups of mice. Six protein spots increased in the BMC group compared with the control group. MS revealed that these spots comprised apolipoprotein A1 (apoA1), apolipoprotein C3 (apoC3), vitamin D-binding protein, alpha-1-antitrypsin and proteasome subunit alpha type 1. We subsequently confirmed the levels of apoA1 in serum and liver samples by immunoblotting. ApoA1 increased at early stage (48 h and 1 wk) after BMC transplantation in this mouse model of liver cirrhosis. The early elevation of apoA1 might be useful to predict liver regeneration in cirrhotic mice after BMC transplantation.

Metformin prevents alcohol-induced liver injury in the mouse: Critical role of plasminogen activator inhibitor-1

BACKGROUND & AIMS

The biguanide drug metformin has recently been found to improve steatosis and liver damage in animal models and in humans with nonalcoholic steatohepatitis.

METHODS

The aim of the present study was to determine whether metformin also prevents steatosis and liver damage in mouse models of acute and chronic alcohol exposure.

RESULTS

Acute ethanol exposure caused a >20-fold increase in hepatic lipids, peaking 12 hours after administration. Metformin treatment significantly blunted the ethanol effect by >60%. Although metformin is a known inducer of AMP kinase (AMPK) activity, the hepatoprotective property of metformin did not correlate with activation of AMPK or of AMPK-dependent pathways. Instead, the protective effects of metformin correlated with complete prevention of the upregulation of plasminogen activator inhibitor (PAI)-1 caused by ethanol. Indeed, a similar protective effect against acute alcohol-induced lipid accumulation was observed in PAI-1-/- mice. Hepatic fat accumulation caused by chronic enteral ethanol feeding was also prevented by metformin or by knocking out PAI-1. Under these conditions, necroinflammatory changes caused by ethanol were also significantly attenuated.

CONCLUSIONS

Taken together, these findings suggest a novel mechanism of action for metformin and identify a new role of PAI-1 in hepatic injury caused by ethanol.

Transforming growth factor-beta down-regulates apolipoprotein M in HepG2 cells

Apolipoprotein M (apoM) is a novel apolipoprotein presented mostly in high-density lipoprotein (HDL) in human plasma, and is exclusively expressed in liver and in kidney. The pathophysiological function of apoM has not yet been elucidated. Apolipoprotein B (apoB), the characteristic apolipoprotein of low-density lipoprotein (LDL), is like apoM, a very hydrophobic protein, and thereafter they both must co-circulate with lipoprotein particles in plasma. The cytokine, transforming growth factor-beta (TGF-beta), has been shown to decreased apoB secretion in HepG2 cells, and we hypothesized that TGF-beta may have the same effects on apoM expression in HepG2 cells. In the present study, we used real-time RT-PCR to analyze apoM and apoB mRNA levels during administration of TGF-beta, as well as TGF-alpha, epidermal growth factor (EGF) and hepatic growth factor (HGF). TGF-beta significantly inhibited both apoM and apoB mRNA expression in HepG2 cells. The inhibitory effects of TGF-beta were dose-dependent, i.e. 1 ng/ml of TGF-beta decreased apoM mRNA levels by 30%, and 10 or 100 ng/ml of TGF-beta decreased apoM mRNA levels more than 65%. The effect of TGF-beta on apoB mRNA expression was slightly weaker than that of apoM, with a maximum effect at 10 or 100 ng/ml TGF-beta where apoB mRNA levels decreased about 55%. The inhibitory effects of TGF-beta on apoM and apoB mRNA levels also increased with increasing incubation time, where the maximum effect was obtained at 24 h. Moreover TGF-alpha, EGF and HGF all decreased both apoM and apoB mRNA levels, but to a less extent than TGF-beta. Further, all four cytokines had more pronounced effects on apoM mRNA expression than apoB mRNA expression. The present study suggested that apoM, like apoB, may be involved in the hepatic lipoprotein assembly in vivo.

Pioglitazone prevents alcohol-induced fatty liver in rats through up-regulation of c-Met

BACKGROUND & AIMS

Treatment of steatosis is important in preventing development of fibrosis in alcoholic liver diseases. This study aimed to examine if pioglitazone, an antidiabetic reagent serving as a ligand of peroxisome proliferator-activated receptor gamma (PPAR gamma), could prevent alcoholic fatty liver.

METHODS

Rats fed with an ethanol-containing liquid diet were given the reagent at 10 mg/kg per day intragastrically for 6 weeks. Hepatic genes involved in actions of the reagent were mined by transcriptome analyses, and their changes were confirmed by real-time polymerase chain reaction and Western blotting analyses. The direct effects of pioglitazone on primary-cultured hepatocytes were also assessed in vitro.

RESULTS

Pioglitazone significantly attenuated steatosis and lipid peroxidation elicited by chronic ethanol exposure without altering insulin resistance. Mechanisms for improving effects of the reagent appeared to involve restoration of the ethanol-induced down-regulation of c-Met and up-regulation of stearoyl-CoA desaturase (SCD). Such effects of pioglitazone on the c-Met signaling pathway resulted from its tyrosine phosphorylation and resultant up-regulation of the apolipoprotein B (apoB)-mediated lipid mobilization from hepatocytes through very low-density lipoprotein (VLDL) as well as down-regulation of sterol regulatory element binding protein (SREBP) -1c and SCD levels and a decrease in triglyceride synthesis in the liver.

CONCLUSIONS

Pioglitazone activates c-Met and VLDL-dependent lipid retrieval and suppresses triglyceride synthesis and thereby serves as a potentially useful stratagem to attenuate ethanol-induced hepatic steatosis.

Hepatocyte growth factor inhibits insulin-stimulated glycogen synthesis in primary cultured hepatocytes

BACKGROUND/AIMS

Hepatocyte growth factor (HGF) plays an important role as a mitogen in liver regeneration. However, little is known about the metabolic effects of HGF in the liver. Studies were performed to examine whether HGF influences carbohydrate metabolism, which is drastically changed in the early course of the regeneration.

METHODS

Primary cultured rat hepatocytes were treated with glucoregulatory hormones such as insulin, glucagon and adrenaline in the presence or absence of HGF. Cellular glycogen deposition and activities of its metabolic enzymes were compared.

RESULTS

HGF inhibited insulin-stimulated glycogen deposition, but had no effect on glycogen degradation stimulated by glucagon and adrenaline. HGF decreased glycogen synthase activity and increased glycogen phosphorylase activity in insulin-stimulated hepatocytes, resulting in the inhibition of glycogen synthesis. Experiments with immunoprecipitation revealed that HGF had no effect on the upstream of insulin signaling including an activation of its receptor and association of insulin receptor substrate with phosphatidylinositol 3-kinase, indicating that HGF presumably affects further downstream of these events.

CONCLUSIONS

These results demonstrate that HGF interacts with insulin on glucose metabolism in hepatocytes. HGF may be involved in glucose regulation, and contribute to cell growth and maturation in addition to its mitogenic action during liver regeneration.

Development of hepatocytes from ES cells after transfection with the HNF-3beta gene

We have attempted to generate embryonic stem (ES) cell-derived hepatocytes expressing liver-specific functional properties by use of ES cell technology. It was found that ES cells are allowed to differentiate into hepatocytes possessing high metabolic activities when hepatocyte nuclear factor (HNF)-3beta-transfected ES cells are cultured in alpha-MEM medium supplemented with 10% fetal bovine serum (FBS) and fibroblast growth factor (FGF)-2 in the three-dimensional cell culture system at 5% CO2. The differentiated cells induced albumin, triacylglycerol, urea, and glycogen synthesis as well as further expression of metabolic proteins and serum factors as markers of hepatocytic differentiation for at least 4 months. The cells differentiated from HNF-3beta-transfected ES cells also had hepatocyte-like ultrastructural characteristics, including several endoplasmic reticula, mitochondrion, and glycogen. Our findings indicate that generation of hepatocytes maintaining high metabolic functions developed from mouse ES cells will facilitate the study of the basic mechanism for hepatogenesis and will certainly provide new opportunities for tissue transplantation.

Hypolipidemic action of the soybean isoflavones genistein and genistin in glomerulonephritic rats

Effects of genistein and its glycoside genistin were studied in nephritic rats with endogenous hyperlipidemia. Male Wistar rats with glomerulonephritis caused by a single intravenous injection of nephrotoxic serum were orally given 5 mg of genistein or 8 mg of genistin/d/100 g body weight for 12 d. These isoflavones suppressed nephritis-induced severe hypercholesterolemia and hypertriglyceridemia, and their hypolipidemic action was almost identical. Fecal steroid excretion was unchanged by administration of the two isoflavones. Genistein inhibited the incorporation of [1-14C]acetate into cholesterol and FA in liver slices from nephritic rats when added to an incubation buffer, whereas genistin did not. These results suggest that genistin may be hydrolyzed to genistein and that genistein itself and/or its metabolite(s) may be intracorporal entities suppressing hepatic lipid syntheses. They also suggest that the suppression of hepatic lipid synthesis may be one mechanism of the hypolipidemic action of genistein.

Recombinant human hepatocyte growth factor protects the liver against hepatic ischemia and reperfusion injury in rats

BACKGROUND

Recent evidence indicates that hepatocyte growth factor (HGF) has a cytoprotective effect against hepatic injury caused by hepatotoxins and inflammatory cytokines. Studies were performed to determine whether HGF influences the survival rate of rats subjected to hepatic warm ischemia/reperfusion (WI/Rp) injury.

METHODS

Male Sprague-Dawley rats were subjected to total or segmental hepatic ischemia by occluding the hepatic artery, portal vein, and bile duct with a microvascular clip. Rats were treated with four intravenous injections of recombinant human HGF (rhHGF 1 mg/kg) or the vehicle 72, 48, 24, and 12 h before surgery.

RESULTS

None of the eight animals in the control group were alive 12 h after total hepatic WI/Rp. Seven of eight animals in the rhHGF-treated group were alive more than 2 days after the reperfusion. In the model of segmental hepatic ischemia, rhHGF inhibited the increase in cytokine-induced neutrophil chemoattractant in serum. The number of neutrophils infiltrating the liver was significantly lower in the rhHGF-treated group than in the control group. rhHGF prevented increases in the activity of serum alanine transaminase and in hepatic necrosis. Experiments with proliferating cell nuclear antigen staining demonstrated that hepatocyte proliferation markedly increased in rhHGF-treated rats as compared with controls.

CONCLUSIONS

These results indicate that HGF facilitates recovery of the liver from hepatic WI/Rp injury, at least in part through the prevention of neutrophil infiltration and the activation of hepatocyte proliferation.

HGF/SF activates glycolysis and oxidative phosphorylation in DA3 murine mammary cancer cells

Hepatocyte growth factor/scatter factor (HGF/SF) is a paracrine growth factor which increases cellular motility and has also been implicated in tumor development and progression and in angiogenesis. Little is known about the metabolic alteration induced in cells following Met-HGF/SF signal transduction. The hypothesis that HGF/SF alters the energy metabolism of cancer cells was investigated in perfused DA3 murine mammary cancer cells by nuclear magnetic resonance (NMR) spectroscopy, oxygen and glucose consumption assays and confocal laser scanning microscopy (CLSM). 31P NMR demonstrated that HGF/SF induced remarkable alterations in phospholipid metabolites, and enhanced the rate of glucose phosphorylation (P < .05). 13C NMR measurements, using [13C1]-glucose-enriched medium, showed that HGS/SF reduced the steady state levels of glucose and elevated those of lactate (P < .05). In addition, HGF/SF treatment increased oxygen consumption from 0.58+/-0.02 to 0.71+/-0.03 micromol/hour per milligram protein (P < .05). However, it decreased CO2 levels, and attenuated pH decrease. The mechanisms of these unexpected effects were delineated by CLSM, using NAD(P)H fluorescence measurements, which showed that HGF/SF increased the oxidation of the mitochondrial NAD system. We propose that concomitant with induction of ruffling, HGF/SF enhances both the glycolytic and oxidative phosphorylation pathways of energy production.

The extent of synchronous initiation and termination of DNA synthesis in regenerating mouse liver is dependent on connexin32 expressing gap junctions

BACKGROUND/AIMS

It has previously been shown in rat liver that the gap junctional proteins connexin32 and connexin26 are downregulated when murine hepatocytes are in the S-phase of the cell cycle. Therefore, it has been hypothesized that loss of functional gap junctions could affect proliferation of hepatocytes. This study aimed to check this hypothesis.

METHODS

We searched for differences in liver regeneration after two-thirds partial hepatectomy between connexin32-deficient and wild-type mice.

RESULTS

The ratio of liver to body weight in regenerating liver was not affected by loss of the connexin32 gene. The peak of DNA synthesis occurred at the same time, i.e. 36 to 96 h after partial hepatectomy, in connexin32-deficient and wild-type liver. During this time, however, only about half as many nuclei of hepatocytes in connexin32-deficient liver incorporated bromodeoxyuridine, compared to wild-type liver. Furthermore, 1-2 weeks after full recovery of liver mass, we detected a higher level of bromodeoxyuridine incorporation into hepatocytes of connexin32-deficient than in wild-type liver.

CONCLUSIONS

Loss of connexin32 protein and/or diminished expression of connexin26 did not promote G0/1-S transition of hepatocytes in two-thirds hepatectomized mouse livers. Instead, the extent of synchronous initiation and termination of DNA synthesis in regenerating liver was altered in connexin32-deficient mice.

Morphologic alteration of hepatocytes and sinusoidal endothelial cells in rat fatty liver during cold preservation and the protective effect of hepatocyte growth factor

BACKGROUND

Fatty liver grafts are considered to be one of the main factors of primary nonfunctioning graft in transplantation. We investigated here, the hepatic damage during cold preservation in a rat fatty liver model by ultrastructural observation, and examined the effect of human recombinant hepatocyte growth factor (hrHGF) on amelioration of the cold-preserved graft condition.

METHODS

Wistar rats were fed a choline-deficient diet (CDD) for 7 days. Livers were stored in cold University of Wisconsin (UW) solution for 0, 4, and 24 hr. We evaluated the ultrastructural alteration of the hepatocytes, sinusoidal architecture, and endothelial cells (SECs) by scanning and transmission electron microscopy. Ex vivo, we measured alanine aminotransferase (ALT) in first effluent as an index of hepatocyte injury and the hyaluronic uptake rate (HUR) as that of SEC damage. We injected hrHGF into rats fed CDD for 7 days through the portal vein and also added it to the UW solution to determine whether or not the agent ameliorated the hepatic damage in cold-preserved fatty livers.

RESULTS

In rats fed CDD for 7 days, the lesion occupied by fat deposits appeared to enlarge with the duration of cold preservation leading to the disarrangement of sinusoidal architecture. Furthermore, sinusoidal endothelial damage, in which gaps, blebs, microvilli, and sinusoid denudation were detected, appeared to be more severe in these livers than in the corresponding control livers. ALT significantly increased in the 4-hr cold-preserved livers of rats fed CDD for 7 days. HUR decreased with 4-hr cold preservation and/or with CDD feeding. Administration of hrHGF prevented the expansion of fatty droplets and reduced SEC injury as detected by morphological observations. Increase of ALT in first effluent was inhibited to about one fourth the level observed in the 4-hr cold-preserved livers of rats fed CDD. Moreover, HUR significantly increased with the pretreatment of hrHGF.

CONCLUSION

The hepatic injury in both hepatocytes and SECs in cold-preserved fatty liver graft developed more rapidly and severely than in the corresponding controls and demonstrated a protective effect of hrHGF.

Hepatocyte growth factor leads to recovery from alcohol-induced fatty liver in rats

A fatty liver is characterized by the hyperaccumulation of lipids within hepatocytes and is often caused by excessive alcohol intake. Rats fed ethanol-containing diets for 37 days showed remarkable increase in hepatic lipids and lipid droplet accumulation in the hepatocytes, indicating the onset of alcoholic fatty liver. Administration of hepatocyte growth factor (HGF) for the last seven days of ethanol treatment markedly decreased hepatic lipids to a level lower than that seen before HGF treatment. In contrast, serum levels of lipids and lipoproteins increased with HGF administration. Primary cultured hepatocytes prepared from the fatty liver retained lipid droplets during a 48-hour culture. However, when cultured in the presence of HGF, intracellular lipid concentrations decreased and lipid secretion was enhanced. Consistent with these events, HGF stimulated the rate of protein synthesis of apolipoprotein B (apoB) and enhanced subsequent mobilization of lipids into the medium. These results indicate that HGF administration induced recovery from the fatty liver, at least in part, by enhancing apoB synthesis and the subsequent mobilization of lipids from hepatocytes with fatty change. The possibility that HGF can be therapeutic for subjects with an alcohol-related fatty liver warrants further attention.