Augmenter of liver regeneration: Mitochondrial function and steatohepatitis

Augmenter of liver regeneration (ALR), a ubiquitous fundamental life protein, is expressed more abundantly in the liver than other organs. Expression of ALR is highest in hepatocytes, which also constitutively secrete it. ALR gene transcription is regulated by NRF2, FOXA2, SP1, HNF4α, EGR-1 and AP1/AP4. ALR's FAD-linked sulfhydryl oxidase activity is essential for protein folding in the mitochondrial intermembrane space. ALR's functions also include cytochrome c reductase and protein Fe/S maturation activities. ALR depletion from hepatocytes leads to increased oxidative stress, impaired ATP synthesis and apoptosis/necrosis. Loss of ALR's functions due to homozygous mutation causes severe mitochondrial defects and congenital progressive multiorgan failure, suggesting that individuals with one functional ALR allele might be susceptible to disorders involving compromised mitochondrial function. Genetic ablation of ALR from hepatocytes induces structural and functional mitochondrial abnormalities, dysregulation of lipid homeostasis and development of steatohepatitis. High-fat diet-fed ALR-deficient mice develop non-alcoholic steatohepatitis (NASH) and fibrosis, while hepatic and serum levels of ALR are lower than normal in human NASH and NASH-cirrhosis. Thus, ALR deficiency may be a critical predisposing factor in the pathogenesis and progression of NASH.

Augmenter of liver regeneration: Essential for growth and beyond

Liver regeneration is a well-orchestrated process that is triggered by tissue loss due to trauma or surgical resection and by hepatocellular death induced by toxins or viral infections. Due to the central role of the liver for body homeostasis, intensive research was conducted to identify factors that might contribute to hepatic growth and regeneration. Using a model of partial hepatectomy several factors including cytokines and growth factors that regulate this process were discovered. Among them, a protein was identified to specifically support liver regeneration and therefore was named ALR (Augmenter of Liver Regeneration). ALR protein is encoded by GFER (growth factor erv1-like) gene and can be regulated by various stimuli. ALR is expressed in different tissues in three isoforms which are associated with multiple functions: The long forms of ALR were found in the inner-mitochondrial space (IMS) and the cytosol. Mitochondrial ALR (23 kDa) was shown to cooperate with Mia40 to insure adequate protein folding during import into IMS. On the other hand short form ALR, located mainly in the cytosol, was attributed with anti-apoptotic and anti-oxidative properties as well as its inflammation and metabolism modulating effects. Although a considerable amount of work has been devoted to summarizing the knowledge on ALR, an investigation of ALR expression in different organs (location, subcellular localization) as well as delineation between the isoforms and function of ALR is still missing. This review provides a comprehensive evaluation of ALR structure and expression of different ALR isoforms. Furthermore, we highlight the functional role of endogenously expressed and exogenously applied ALR, as well as an analysis of the clinical importance of ALR, with emphasis on liver disease and in vivo models, as well as the consequences of mutations in the GFER gene.

Augmenter of Liver Regeneration Protects against Ethanol-Induced Acute Liver Injury by Promoting Autophagy

Alcoholic liver disease is associated with high morbidity and mortality, and treatment options are limited to date. Augmenter of liver regeneration (ALR) may protect against hepatic injury from chemical poisons, including ethanol. Autophagy appears to positively influence survival in cases of liver dysfunction, although the mechanisms are poorly understood. Herein, we investigated effects of ALR-induced autophagy in vitro and in vivo in an ethanol-induced model of acute liver injury. Decreased serum levels of alanine aminotransferase and aspartate aminotransferase and reduced histologic lesions revealed that mice overexpressing ALR experienced less liver damage than wild-type. ALR-knockdown mice experienced more severe liver damage than wild-type. ALR-transfected HepG2 cells showed increased survival rates, improved maintenance of mitochondrial membrane potential, and increased ATP levels after ethanol treatment. The observed protection was associated with up-regulation of autophagy-markers, including light chain 3II, beclin-1, and autophagy-related gene 5, and down-regulation of p62 by ALR. Autophagy was inhibited in ALR-knockdown mice and HepG2 cells, and autophagy inhibitor bafilomycin A1 attenuated the protective effects of ALR. Results showed phosphorylated mammalian target of rapamycin (mTOR) was down-regulated when ALR was overexpressed and up-regulated when ALR was knocked down. These data show that ALR is protective against ethanol-induced acute liver injury by promoting autophagy, probably via repressing the mTOR pathway. These results have potential implications for the clinical treatment of alcoholic liver disease patients.

Augmenter of liver regeneration potentiates doxorubicin anticancer efficacy by reducing the expression of ABCB1 and ABCG2 in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is highly chemoresistant and therefore challenges both physicians and patients. Augmenter of liver regeneration (ALR), previously also known as 'hepatic stimulator substance', is reported to inhibit the epithelial-mesenchymal transition (EMT) in HCC, one of the frequent events that occur in cancer metastasis, suggesting that ALR is involved in HCC. In this study, we report for the first time that the transfection of ALR enhances the antitumor effect of chemotherapy with doxorubicin, a typical anticancer drug, on HCC in vitro and in vivo. The efflux of doxorubicin from ALR-transfected HCC cells is efficiently suppressed. This implies the intracellular retention of doxorubicin in tumor cells, which is at least partly attributable to the effective inhibition of ABCB1 and ABCG2 transporter expression in ALR-expressing cells. The downregulation of ALR expression by short hairpin RNA diminishes the antitumor effect of ALR. We further demonstrate that ALR inhibits the AKT/Snail signaling pathway, resulting in the downregulation of ABCB1 and ABCG2 expression. In conclusion, our results suggest that ALR is a potential chemotherapeutic agent against HCC.

Alleviation of Ischemia-Reperfusion Injury in Liver Steatosis by Augmenter of Liver Regeneration Is Attributed to Antioxidation and Preservation of Mitochondria

BACKGROUND

Fatty liver is one of the major impediments to liver surgery and liver transplantation because steatotic hepatocytes are more susceptible to ischemia-reperfusion injury (IRI). In this study, the effects of augmenter of liver regeneration (ALR) on hepatic IRI in steatotic mice were investigated.

METHODS

In vivo, liver steatosis of mice was induced by feeding a methionine-choline-deficient diet for 2 weeks. Three days before hepatic partial warm IRI, mice were transfected with the ALR-containing adenovirus. In an in vitro study, the protective effect of ALR on steatotic HepG2 cells was analyzed after hypoxia/reoxygenation (HR) treatment.

RESULTS

The transfection of the ALR gene into steatotic mice attenuated liver injury, inhibiting hepatic oxidative stress, increasing antioxidation capacities, promoting liver regeneration, and consequently suppressing cell apoptosis/death. Furthermore, resistance to HR injury was notably increased in ALR-transfected cells compared with the vector-transfected cells. The HR-induced rise in the mitochondrial reactive oxygen species was reduced, and cellular antioxidant activities were enhanced. The ALR transfection prevented cells from apoptosis, which can be attributed to the preservation of the mitochondrial membrane potential, enhancement of oxygen consumption rate and production of adenosine triphosphate.

CONCLUSIONS

ALR protects steatotic hepatocytes from IRI by attenuating oxidative stress and mitochondrial dysfunction, as well as improving antioxidant effect. ALR may be used as a potential therapeutic agent when performing surgery and transplantation of steatotic liver.

Erzhi Pill® Repairs Experimental Liver Injury via TSC/mTOR Signaling Pathway Inhibiting Excessive Apoptosis

The present study aimed to investigate the mechanism of hepatoprotective effect of Erzhi Pill (EZP) on the liver injury via observing TSC/mTOR signaling pathway activation. The experimental liver injury was induced by 2-acetylaminofluorene (2-AAF) treatment combined with partial hepatectomy (PH). EZP treated 2-AAF/PH-induced liver injury by the therapeutic and prophylactic administration. After the administration of EZP, the activities of aspartic transaminase (AST), alanine aminotransferase (ALT), alkaline phosphatase (AKP), and gamma-glutamyl transpeptidase (γ-GT) were decreased, followed by the decreased levels of hepatocyte apoptosis and caspase-3 expression. However, the secretion of albumin, liver weight, and index of liver weight were elevated. Microscopic examination showed that EZP restored pathological liver injury. Meanwhile, Rheb and mammalian target of rapamycin (mTOR) activation were suppressed, and tuberous sclerosis complex (TSC) expression was elevated in liver tissues induced by 2-AAF/PHx and accompanied with lower-expression of Bax, Notch1, p70S6K, and 4E-EIF and upregulated levels of Bcl-2 and Cyclin D. Hepatoprotective effect of EZP was possibly realized via inhibiting TSC/mTOR signaling pathway to suppress excessive apoptosis of hepatocyte.

Hepatic stimulator substance inhibits calcium overflow through the mitochondria-associated membrane compartment during nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease is considered a disorder of the endoplasmic reticulum (ER) and mitochondria. Recent studies have shown that the ER and mitochondrial membranes overlap by 15-20%, a region referred to as the 'mitochondria-associated ER membrane' (MAM). Some proteins, including sarco/ER calcium ATPase (SERCA), are located in the MAM and have an important role in Ca²⁺ signaling and homeostasis between the ER and the mitochondria. Our previous study showed that hepatic stimulator substance (HSS) inhibits the ER stress induced by reactive oxygen species, thus reducing mitochondrial damage. However, the mechanism underlying the protective effect of HSS on the ER and ER-mitochondrial interaction remains unclear. In this study, we confirmed that the exogenous expression of HSS protected the liver from steatosis in mice with nonalcoholic steatohepatitis. More importantly, the protection provided by HSS allowed SERCA in the MAM compartment to function well, preventing the extensive influx of cytosolic free Ca²⁺ to the mitochondria, thus preserving the mitochondrial functions from calcium overload and relieving palmitic-acid-induced hepatocyte steatosis. Our results suggest that the protective effect of HSS on SERCA expression is associated with the maintenance of calcium homeostasis within the MAM, thus ameliorating the disordered Ca²⁺ communication between the ER and mitochondria.

Effect of inhibiting mitochondrial fission on energy metabolism in rat hippocampal neurons during ischemia/reperfusion injury

OBJECTIVE

Previous studies have shown that mitochondrial division inhibitor 1 (mdivi-1) protects rat brain from ischemia/reperfusion (I/R) injury, but the precise mechanisms are unclear. This study aims to elucidate the effect of mdivi-1 on energy metabolism and neuronal apoptosis induced by I/R in vitro.

METHODS

Cultured hippocampal neurons from Wistar rats were randomly divided into four treatment groups: control (C), vehicle (V), I/R (I), and I/R plus mdivi-1 (M). Ischemia/reperfusion was induced by oxygen-glucose deprivation for 6 h followed by normoxic/normoglycemic reperfusion for 20 h. Neurons in the M group were pretreated with mdivi-1 for 40 min before I/R. Expression levels of the mdiv-1 target dynamin-related protein 1 and apoptosis regulators Bcl-2 and Bax were examined by Western blotting. Mitochondrial membrane potential ( ) was measured by flow cytometry. Intracellular ATP content and the activities of mitochondrial complexes I-IV, Na⁺-K⁺-ATPase, and Ca²⁺-Mg²⁺-ATPase were measured by standard assays.

RESULTS

Compared to group I neurons, group M neurons exhibited markedly reduced Drp-1 and Bax expression, higher Bcl-2 expression, , and intracellular ATP, and elevated mitochondrial complex I-IV, Na⁺-K⁺-ATPase, and Ca²⁺-Mg²⁺-ATPase activities.

CONCLUSION

Inhibition of mitochondrial fission significantly improved mitochondrial function and suppressed apoptotic signaling induced by I/R.

Amelioration of nonalcoholic fatty liver disease by hepatic stimulator substance via preservation of carnitine palmitoyl transferase-1 activity

Nonalcoholic steatohepatitis (NASH) is the progressive form of nonalcoholic fatty liver disease and so far is supposed to be related with mitochondrial impairment. Hepatic stimulator substance (HSS) has been defined as a liver-protective factor promoting hepatocyte DNA synthesis and hepatic proliferation after liver intoxication. We previously reported that HSS ameliorated hepatocyte death, probably because of its preservation of mitochondria. This study aims to explore whether HSS could protect carnitine palmitoyl transferase-1 (CPT-1), an essential enzyme responsible for β-oxidation of free fatty acids in mitochondria, from lipotoxicity, thus alleviating hepatic lipid deposition. To test this, the HSS gene was delivered into C57BL/6J mice and efficiently expressed in the liver. NASH mice were prepared with high-fat diet or methionine-choline-deficient diet. The results showed that hepatic inflammation and liver functions were alleviated in the HSS-transfected mice; meanwhile, the activity of CPT-1 was obviously protected. Moreover, oleic acid (OA) treatment resulted in remarkable lipid accumulation in HepG2 cells; this deposition was improved by HSS transfection. Simultaneously, the CPT-1 activity, which was impaired by OA treatment, was profoundly rescued in the HSS-expressing cells. CPT-1 activity was more severely impaired if the OA treatment was combined with S15176, a CPT-1 inhibitor. However, this impairment was effectively reduced by the HSS transfection, and the effect was enhanced by C75, a CPT-1 activator. Interestingly, if the cells were transfected with HSS-siRNA, the preservation of CPT-1 provided by HSS was again diminished. In conclusion, HSS reduces lipotoxicity to mitochondria most likely via preservation of CPT-1.

Deceleration of liver regeneration by knockdown of augmenter of liver regeneration gene is associated with impairment of mitochondrial DNA synthesis in mice

Hepatic stimulator substance, also known as augmenter of liver regeneration (ALR), is a novel hepatic mitogen that stimulates liver regeneration after partial hepatectomy (PH). Recent work has indicated that a lack of ALR expression inhibited liver regeneration in rats, and the mechanism seems to be related to increased cell apoptosis. The mitochondria play an important role during liver regeneration. Adequate ATP supply, which is largely dependent on effective mitochondrial biogenesis, is essential for progress of liver regeneration. However, ALR gene expression during liver regeneration, particularly its function with mitochondrial DNA synthesis, remains poorly understood. In this study, ALR expression in hepatocytes of mice was suppressed with ALR short-hairpin RNA interference or ALR deletion (knockout, KO). The ALR-defective mice underwent PH, and the liver was allowed to regenerate for 1 wk. Analysis of liver growth and its correlation with mitochondrial biogenesis showed that both ALR mRNA and protein levels increased robustly in control mice with a maximum at days 3 and 4 post-PH. However, ALR knockdown inhibited hepatic DNA synthesis and decelerated liver regeneration after PH. Furthermore, both in the ALR-knockdown and ALR-KO mice, expression of mitochondrial transcription factor A and peroxisome proliferator-activated receptor-γ coactivator-1α were reduced, resulting in impaired mitochondrial biogenesis. In conclusion, ALR is apparently required to ensure appropriate liver regeneration following PH in mice, and deletion of the ALR gene may delay liver regeneration in part due to impaired mitochondrial biogenesis.

Uncoupling protein 2 regulates palmitic acid-induced hepatoma cell autophagy

Mitochondrial uncoupling protein 2 (UCP2) is suggested to have a role in the development of nonalcoholic steatohepatitis (NASH). However, the mechanism remains unclear. Autophagy is an important mediator of many pathological responses. This study aims to investigate the relationship between UCP2 and hepatoma cells autophagy in palmitic acid- (PA-) induced lipotoxicity. H4IIE cells were treated with palmitic acid (PA), and cell autophagy and apoptosis were examined. UCP2 expression, in association with LC3-II and caspase-3, which are indicators of cell autophagy and apoptosis, respectively,was measured. Results demonstrated that UCP2 was associated with autophagy during PA-induced hepatic carcinoma cells injury. Tests on reactive oxygen species (ROS) showed that UCP2 overexpression strongly decreases PA-induced ROS production and apoptosis. Conversely, UCP2 inhibition by genipin or UCP2 mRNA silencing enhances PA-induced ROS production and apoptosis. Autophagy partially participates in this progress. Moreover, UCP2 was associated with ATP synthesis during PA-induced autophagy. In conclusion, increasing UCP2 expression in hepatoma cells may contribute to cell autophagy and antiapoptotic as result of fatty acid injury. Our results may bring new insights for potential NASH therapies.

Adenoviral gene transfer of hepatic stimulator substance confers resistance against hepatic ischemia-reperfusion injury by improving mitochondrial function

Hepatic stimulator substance (HSS) has been suggested to protect liver cells from various toxins. However, the precise role of HSS in hepatic ischemia-reperfusion (I/R) injury remains unknown. This study aims to elucidate whether overexpression of HSS could attenuate hepatic ischemia-reperfusion injury and its possible mechanisms. Both in vivo hepatic I/R injury in mice and in vitro hypoxia-reoxygenation (H/R) in a cell model were used to evaluate the effect of HSS protection after adenoviral gene transfer. Moreover, a possible mitochondrial mechanism of HSS protection was investigated. Efficient transfer of the HSS gene into liver inhibited hepatic I/R injury in mice, as evidenced by improvement in liver function tests, the preservation of hepatic morphology, and a reduction in hepatocyte apoptosis. HSS overexpression also inhibited H/R-induced cell death, as detected by cell viability and cell apoptosis assays. The underlying mechanism of this hepatic protection might involve the attenuation of mitochondrial dysfunction and mitochondrial-dependent cell apoptosis, as shown by the good preservation of mitochondrial ultrastructure, mitochondrial membrane potential, and the inhibition of cytochrome c leakage and caspase activity. Moreover, the suppression of H/R-induced mitochondrial ROS production and the maintenance of mitochondrial respiratory chain complex activities may participate in this mechanism. This new function of HSS expands the possibility of its application for the prevention of I/R injury, such as hepatic resection and liver transplantation in clinical practice.

Enhanced endoplasmic reticulum SERCA activity by overexpression of hepatic stimulator substance gene prevents hepatic cells from ER stress-induced apoptosis

Although the potential pathogenesis of nonalcoholic fatty liver disease (NAFLD) is unclear, increasing evidence indicates that endoplasmic reticulum (ER) stress may link free fatty acids to NAFLD. Since we previously reported that hepatic stimulator substance (HSS) could protect the liver from steatosis, this study is aimed to investigate whether HSS protection could be related with its inhibition on ER stress. The HSS gene was stably transfected into BEL-7402 hepatoma cells and effectively expressed in ER. The palmitic acid (PA)-induced heptocyte lipotoxicity was reproduced in the HSS-transfected cells, and HSS alleviation of the ER stress and apoptosis were subsequently examined. The results showed that PA treatment led to a heavy accumulation of fatty acids within the cells and a remarkable increase in reactive oxygen species (ROS). However, in the HSS-expressing cells, production of ROS was inhibited and ER stress-related marker glucose-regulated protein 78 (GRP-78), sterol regulatory element-binding protein (SREBP), anti-phospho-PRK-1ike ER kinase (p-PERK), anti-phospho-eukaryotic initiation factor 2α (p-eIF2α), and anti-C/EBP homologous protein (CHOP) were downregulated compared with the wild-type or mutant HSS-transfected cells. Furthermore, PA treatment severely impaired the activity of sarco-endoplasmic reticulum Ca(2+)-ATPase (SERCA), leading to imbalanced calcium homeostasis during ER stress, which could be rescued in the HSS-trasfected cells. The protection provided by HSS to the SERCA is identical to that observed with N-acetyl-l-cysteine (NAC) and sodium dimercaptopropane sulfonate (Na-DMPS), which are two typical free radical scavengers. As a consequence, the rate of ER stress-mediated apoptosis in the HSS-expressing cells was significantly reduced. In conclusion, the protective effect of HSS against ER stress may be associated with the removal of ROS to restore the activity of the SERCA.

Mitochondrial uncoupler carbonyl cyanide M-chlorophenylhydrazone induces the multimer assembly and activity of repair enzyme protein L-isoaspartyl methyltransferase

The protein L-isoaspartyl methyltransferase (PIMT) repairs damaged aspartyl residues in proteins. It is commonly described as a cytosolic protein highly expressed in brain tissues. Here, we report that PIMT is an active monomeric as well as a multimeric protein in mitochondria isolated from neuroblastoma cells. Upon treatments with mitochondrial uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP), PIMT monomers level decreased by half while that of PIMT multimers was higher. Gel electrophoresis under reducing conditions of CCCP-induced PIMT multimers led to PIMT monomers accumulation, indicating that multimers resulted from disulfide-linked PIMT monomers. The antioxidant ascorbic acid significantly lowered CCCP-induced formation of PIMT multimers, suggesting that reactive oxygen species contributed to PIMT multimerization. In addition, the elevation of PIMT multimers catalytic activity upon treatments with CCCP was severely inhibited by the reducing agent dithiothreitol. This indicated that PIMT monomers have lower enzymatic activity following CCCP treatments and that activation of PIMT multimers is essentially dependent on the formation of disulfide-linked monomers of PIMT. Furthermore, the perturbation of mitochondrial function by CCCP promoted the accumulation of damaged aspartyl residues in proteins with high molecular weights. Thus, this study demonstrates the formation of active PIMT multimers associated with mitochondria that could play a key role in repairing damaged proteins accumulating during mitochondrial dysfunction.

Hepatic stimulator substance alleviates toxin-induced and immune-mediated liver injury and fibrosis in rats

BACKGROUND

Liver fibrosis is a common scarring response to chronic liver injury. It is a precursor to cirrhosis and liver carcinoma. Hepatic stimulator substance (HSS), a known liver-specific but species-nonspecific growth factor, has been shown to protect hepatocytes from various toxins.

METHODS

We have investigated the effects of HSS therapy on carbon tetrachloride (CCl(4))-induced and porcine-serum-mediated hepatic injury and fibrosis. We hypothesize that HSS might attenuate liver injury and fibrosis by suppressing oxidative stress, down-regulating profibrogenic factors, and blocking HSCs activation.

RESULTS

This report demonstrated that HSS therapy diminished α-smooth muscle actin expression, decreased intrahepatic reactive oxygen species (ROS) level, and down-regulated transforming growth factor (TGF)-β1, platelet-derived growth factor (PDGF)-BB, and tissue inhibitor of metalloproteinase (TIMP)-1 expression. In addition, HSS treatment significantly protected the liver from injury by improving liver function tests and histological architecture of the liver.

CONCLUSIONS

These results provided novel insights into the mechanisms of HSS in the protection of the liver. Our results suggested that HSS might be a therapeutic antifibrotic agent for the treatment of liver fibrosis.

Augmenter of liver regeneration (ALR) gene therapy attenuates CCl₄-induced liver injury and fibrosis in rats

Liver fibrosis represents a process of healing and scarring in response to chronic liver injury. Augmenter of liver regeneration (ALR) has been shown to protect hepatocytes from various toxins. The aim of this study was to investigate the effects of ALR gene therapy on liver injury and fibrosis induced by CCl(4) in rats and further explore the underlying mechanisms. Human ALR expression plasmid was delivered via the tail vein. ALR gene therapy might protect the liver from CCl(4)-induced injury and fibrogenesis by attenuating the mitochondrial dysfunction, suppressing oxidative stress, and inhibiting activation of HSCs. This report demonstrated that ALR gene therapy protected against the ATP loss, increased the activity of ATPase, decreased intrahepatic reactive oxygen species level, and down-regulated transforming growth factor-β1, platelet-derived growth factor-BB, and α-smooth muscle actin expression. Following gene transfer liver function tests were significantly improved. In brief, ALR gene therapy might be an effective therapeutic reagent for liver fibrosis with potential clinical applications.

Increased hepatic apoptosis in high-fat diet-induced NASH in rats may be associated with downregulation of hepatic stimulator substance

The mechanisms of progression from fatty liver to steatohepatitis and cirrhosis are not well elucidated. Hepatocellular apoptosis could be one of the key factors in the pathogenesis of non-alcoholic steatohepatitis (NASH). Hepatic stimulator substance (HSS) protects liver cells from various toxins. We previously reported that HSS is critically important for the survival of hepatocytes due to its mitochondrial association. This study aims to investigate the relationship between HSS and hepatocellular apoptosis in vivo models of high-fat diet-induced NASH and in vitro models of palmitic acid-induced hepatocyte injury. Sprague-Dawley rats were fed a high-fat diet for 8, 12 and 16 weeks. Hepatic histological lesions, liver function and apoptosis were examined. HSS expression, in association with caspase-3 and cytochrome c leakage, which are both indicators of cell apoptosis, was measured. Results showed that a high-fat diet altered liver function and histology in a manner resembling NASH. Hepatic protein and mRNA HSS expression was decreased as NASH progressed. Meanwhile, cell apoptosis increased as result of caspase-3 activation and cytochrome c release, indicating that HSS might be involved in NASH pathogenesis. Furthermore, in palmitic acid-induced hepatic cell damage, over-expression of HSS decreased cells apoptosis. In contrast, repression of HSS expression by siRNA increased cell apoptosis. In conclusion, these data imply that cell apoptosis contributes to the pathogenesis of NASH, during which HSS expression is downregulated. Increasing HSS expression in hepatocytes may forestall cell apoptosis as result of fatty acid insult.

Administration of naked plasmid encoding hepatic stimulator substance by hydrodynamic tail vein injection protects mice from hepatic failure by suppressing the mitochondrial permeability transition

Acute liver failure is a devastating illness of various causes with considerable mortality. Hepatic stimulator substance (HSS) has been suggested for use as a protective agent against acute hepatic injury induced by chemical poisons because it has a variety of biological activities. However, the mechanism whereby HSS protects against hepatotoxins is poorly understood. In this study, we established a hepatic gene transfer system via hydrodynamic tail vein injection to deliver a naked plasmid containing the human HSS gene (hHSS) and analyzed HSS-mediated protection of the liver during fulminant hepatic failure (FHF) induced by D-galactosamine (D-gal) and lipopolysaccharide (LPS). The results showed that the reporter gene, enhanced green fluorescent protein, was efficiently expressed in the liver of BALB/c mice. Hydrodynamic-based transfection of hHSS yielded a 70% survival rate compared with 36.7% for the control group at 24 h after D-gal/LPS treatment. In addition, hHSS expression preserved liver morphology and function. It is noteworthy that hHSS hydrodynamic-based transfer ameliorated indices of the mitochondrial permeability transition (MPT) resulting from the toxic effects of d-gal/LPS on the liver such as mitochondrial swelling, mitochondrial transmembrane potential disruption, and cytochrome c translocation. Furthermore, mitochondrial morphology and ATP levels were maintained in hHSS-administered mice. HSS-mediated protection was similar to that observed with the MPT inhibitor N-methyl-4-isoleucine-cyclosporin (NIM811), indicating a possible role for HSS in the regulation of MPT. In conclusion, a single dose of hHSS plasmid protected mice from FHF, and this hepatoprotective effect seemed to correlate with the inhibition of MPT.

The conserved CXXC motif of hepatic stimulator substance is essential for its role in mitochondrial protection in H2O2-induced cell apoptosis

Hepatic stimulator substance (HSS) protects liver cells from various toxins by alleviating lesions caused in the mitochondria. This paper demonstrates the necessity of the conserved CXXC catalytic motif (C62-C65) for the mitochondria-targeted anti-apoptotic activity of HSS. Mutating the conserved CXXC motif eliminated the protective effects against H(2)O(2)-induced apoptosis and diminished the protection of the mitochondria. However, the mutation of the other disulfide bond C91-C108 mainly preserved the protection of mitochondria by HSS, implying that the conserved CXXC motif and sulfhydryl oxidase (SOX) activity are essential for mitochondrial protection.