Augmenter of liver regeneration: its place in the universe of hepatic growth factors

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 protects the kidney against ischemia-reperfusion injury by inhibiting necroptosis

Necroptosis plays an important role in the pathogenesis of acute kidney injury (AKI), and necroptosis-related interventions may therefore be an important measure for the treatment of AKI. Our previous study has shown that augmenter of liver regeneration (ALR) inhibits renal tubular epithelial cell apoptosis and regulates autophagy; however, the influence of ALR on necroptosis remains unclear. In this study, we investigated the effect of ALR on necroptosis caused by ischemia-reperfusion and the underlying mechanism. In vivo experiments indicated that kidney-specific knockout of ALR aggravated the renal dysfunction and pathological damage induced by ischemia-reperfusion. Simultaneously, the expression of renal necroptosis-associated protein receptor-interacting protein 1 (RIP1), receptor-interacting protein 3 (RIP3), and mixed-lineage kinase domain-like protein (MLKL) significantly increased. In vitro experiments indicated that overexpression of ALR decreased the expression of hypoxia-reoxygenation-induced kidney injury molecules, the inflammation-associated factor tumor necrosis factor-alpha (TNF-α), and monocyte chemotactic protein. Additionally, the expression of RIP1, RIP3, and MLKL, which are elevated after hypoxia and reoxygenation, was also inhibited by ALR overexpression. Both in vivo and in vitro results indicated that ALR has a protective effect against acute kidney injury caused by ischemia-reperfusion, and the RIP1/RIP3/MLKL pathway should be further verified as a probable necroptosis regulating mechanism.

Netrin-1 promotes liver regeneration possibly by facilitating vagal nerve repair after partial hepatectomy in mice

Hepatic regeneration after hepatectomy is a great concern in clinical practice. Recently, the neuronal guidance protein netrin-1 has been reported to enhance regeneration after nerve injury. The goal of this study was to preliminarily investigate whether netrin-1 stimulates vagus nerve regeneration to promote liver regeneration after partial hepatectomy in mice. The expression of netrin-1 in murine remnant livers after partial hepatectomy (PHx) was evaluated in initial studies. C57BL/6 mice that received exogenous netrin-1 after PHx were used to examine liver regeneration. PHx was performed in wild-type mice after adeno-associated virus injection (Ntn1 gene silencing) to detect the impact of endogenous netrin-1. After PHx and hepatic branch vagotomy (HV), the mice were injected with or without netrin-1 to evaluate the effects on hepatic regeneration and vagal nerve recovery. Significant reductions in netrin-1 at the transcript and protein levels in murine liver tissue after hepatectomy were observed. Subsequent studies of netrin-1 administration revealed the promotion of hepatocyte proliferation and specific growth factors contributing to liver repair and a decrease in hepatic-specific injury enzymes. Furthermore, the opposite results were observed in the netrin-1 knockdown group. HV delayed liver regeneration after PHx. However, this retardation was reversed by exogenous netrin-1 supplementation. In addition, the results of nerve growth and vagal nerve repair in the remnant liver suggested that netrin-1 promoted vagal nerve regeneration after hepatectomy. Netrin-1 accelerates liver regeneration after partial hepatectomy in mice, and the potential mechanism is related to the promotion of vagus nerve repair and regeneration.

Elimination of the toxic effect of copper sulfate is accompanied by the normalization of liver function in fibrosis

The search for biologically active compounds that regulate liver function in fibrosis is an urgent medical and biological problem. A working hypothesis was tested, according to which low molecular weight biologically active compounds from Pleurotus ostreatus and Sacharamirses cerevisiae are capable of exerting immunomodulatory and antitoxic effects after intoxication of the body with ions of heavy metals, in particular copper sulfate. Elimination of the toxic effect caused by copper sulfate can also ensure the normalization of liver function in various pathologies, in particular with liver fibrosis. When determining toxicity, a study was carried out on Wistar rats, and when studying the effect of low molecular weight biologically active compounds on liver function, clinical trials were carried out on volunteers. The activity of alanine aminotransferase, aspartate aminotransferase, actonitase and glutathione peroxidase, as well as the content of bilirubin and lipid hydroperoxides were determined. It was shown that preliminary administration of biologically active compounds to rats at a dose of 0.05 mL/100 g of body weight provided the formation in some animals (up to 80%) of resistance to the toxic effect of copper sulfate (dose 2.5 mg/100 g of body weight). Such stability is associated with a shift in the balance of “prooxidants-antioxidants” towards antioxidants. The data obtained in the clinic on volunteers with liver fibrosis and hepatitis also testify in favour of the membranotropic action of biologically active compounds. Biologically active compounds provided a decrease or complete restoration of the activity of transferases (ALT and AST) in the blood serum of these patients, with the exception of one patient out of 20 examined. Our experiment has shown the relationship between the elimination of toxicity to the action of copper sulfate and the normalization of liver function in patients. The results obtained indicate that it will be promising to use a complex of low molecular weight components from P. ostreatus and S. cerevisiae as an antidote and hepatoprotective agent.

Hepatic Deficiency of Augmenter of Liver Regeneration Predisposes to Nonalcoholic Steatohepatitis and Fibrosis

BACKGROUND AND AIMS

The augmenter of liver regeneration (ALR) protein is critical for lipid homeostasis and mitochondrial function. We investigated high-fat/high-carbohydrate (HF/HC) diet-induced nonalcoholic fatty liver disease (NAFLD) in wild-type (WT), hepatocyte-specific ALR-knockout (ALR-H-KO), and ALR-heterozygous (ALR-H-HET) mice. ALR was measured in serum of human nonalcoholic steatohepatitis (NASH) and NASH-induced cirrhosis (serum and liver).

APPROACH AND RESULTS

HF/HC feeding decreased ALR expression in all groups of mice. The otherwise normal ALR-H-HET mice gained more weight and steatosis than WT mice when challenged metabolically with the HF/HC diet; ALR-H-KO mice gained the least weight and had the least steatosis. These findings were consistent with correspondingly increased triglycerides and cholesterol and altered expression of carnitine palmitoyltransferase 1a, sterol regulatory element-binding protein, acetyl coenzyme A carboxylase, and fatty acid synthase. All HF/HC-fed mice developed insulin resistance, the magnitude being lower in ALR-H-KO mice. HF/HC-fed ALR-H-HET mice were more resistant to glucose challenge than WT or ALR-H-KO mice. The frequency of tumor necrosis factor alpha-producing, interleukin 6 (IL6)-producing, and IL17-producing cells was greater in ALR-H-KO than ALR-H-HET and lowest in WT mice. HF/HC feeding did not increase their number in ALR-H-KO mice, and the increase in ALR-H-HET was greater than that in WT mice except for IL17 cells. Cluster of differentiation 25-positive (CD25⁺ ) forkhead box P3-positive CD4⁺ regulatory T-cell frequency was lower in ALR-H-HET than WT mice and further reduced in ALR-H-KO mice; HF/HC reduced regulatory T-cell frequency only in WT mice. HF/HC-fed ALR-H-HET, but not WT, mice developed fibrosis; and ALR-H-KO mice progressed to cirrhosis. White adipose tissue of HF/HC-fed ALR-deficient mice developed strong inflammation, indicating bidirectional interactions with the liver. Hepatic and serum ALR levels were significantly reduced in patients with NASH-cirrhosis. Serum ALR was also significantly lower in patients with NASH.

CONCLUSIONS

Hepatic ALR deficiency may be a critical predisposing factor for aggressive NAFLD progression.

Lack of Augmenter of Liver Regeneration Disrupts Cholesterol Homeostasis of Liver in Mice by Inhibiting the AMPK Pathway

It is well known that excessive cholesterol accumulation within hepatocytes deteriorates nonalcoholic fatty liver disease (NAFLD). Augmenter of liver regeneration (ALR) has been reported to alleviate NAFLD through anti-apoptosis; however, whether ALR could protect liver from cholesterol-induced NAFLD remains unclear. Mice with heterozygous deletion of Gfer (the gene for ALR, Gfer ^+/-) were generated, and liver steatosis was induced by either choline-deficient ethionine-supplemented, methionine choline-deficient diet for 4 weeks, or high-fat diet for 16 weeks. The results showed that Gfer ^+/- mice developed a more severe fatty liver phenotype than Gfer ^+/+ mice. The livers of Gfer ^+/- mice exhibited a higher concentration of cholesterol and low-density lipoprotein compared with the normal mice. Transcriptome-based analysis predicts low-density lipoprotein receptor (LDLR) primarily involved in the metabolic pathway. The experiments further indicate that cholesterol accumulation within hepatocytes is closely associated with enhancing the expression of LDLR and activation of sterol regulatory element binding protein 2 (SREBP2). Because adenosine monophosphate-activated protein kinase (AMPK) is a critical regulator of SREBP2 activation, we measured whether the activity of AMPK was regulated by ALR. We found that knockdown of ALR expression inhibited the phosphorylation of LKB1, an upstream activator of AMPK, followed by AMPK inactivation and SREBP2 maturation/nuclear translocation, leading to extensive cholesterol accumulation. Meanwhile, cellular oxidative stress increased as a result of ALR knockdown, indicating that ALR might also have a role in suppressing reactive oxygen species production. Conclusion: Our results confirm that ALR regulates cholesterol metabolism and alleviates hepatic steatosis probably through the LKB1-AMPK-SREBP2-LDLR pathway in vivo and in vitro, providing a putative mechanism for combating fatty liver disease.

Hemodynamic changes in ALPPS influence liver regeneration and function: results from a prospective study

BACKGROUND

Excessive increase of portal flow and pressure following extended hepatectomy have been associated to insufficient growth or function of the future liver remnant (FLR), with the risk of post-hepatectomy liver failure (PHLF). We prospectively assess the influence of liver hemodynamics on FLR regeneration and function in Associating Liver Partition and Portal vein ligation for Staged hepatectomy (ALPPS).

METHODS

Twenty-three patients underwent ALPPS; liver hemodynamics were assessed throughout the procedures. Volume and function of the FLR were evaluated by angio-CT and 99mTc-Mebrofenin-scintigraphy.

RESULTS

The portal vein flow at the end of stage-1 correlated with the increase of the FLR volume (p = 0.002). Patients with portal vein pressure (PVP) < 20 mmHg and hepatic to portal vein gradients (HVPG) < 15 mmHg at the end of ALPPS-1 showed higher FLR regeneration (76.7% vs. 30.6%, p = 0.04) and function (26.7% vs. -0.13%, p = 0.02). FLR regeneration was inversely correlated with baseline FLR/Total Liver Volume (p = 0.002) and FLR/Body Weight (p = 0.02). No correlation was found between volumes and function (p = 0.13).

CONCLUSION

Liver hemodynamic stress at the end of ALPPS-1 influences the increase of the FLR volume and function, which is higher with PVP < 20 and HVPG < 15 mmHg. Liver volume overestimates liver function and could be imprecise to set stage-2 timing.

Augmenter of liver regeneration protein deficiency promotes hepatic steatosis by inducing oxidative stress and microRNA-540 expression

Levels of augmenter of liver regeneration (ALR), a multifunctional protein, are reduced in steatohepatitis. ALR depletion from ALR flox/flox/Alb-Cre [ALR-L-knockout (KO)] mouse causes robust steatosis and apoptosis of hepatocytes, and pericellular fibrosis between 1 and 2 wk postbirth. Steatosis regresses by 4 wk upon reappearance of ALR-expressing hepatocytes. We investigated mechanisms of ALR depletion-induced steatosis. ALR-L-KO mice (1-, 2-, and 4 wk old) and Adeno-Cre-transfected ALR flox/flox hepatocytes were used for in vivo and in vitro studies. ALR depletion from hepatocytes in vivo downregulated peroxisome proliferator-activated receptor (PPAR)-α, carnitine palmitoyl transferase I (CPT1)a, peroxisomal membrane protein 70 (PMP70) (modest down-regulation), and acyl-CoA oxidase 1 (ACOX1). The markedly up-regulated (20X) novel microRNA-540 (miR-540) was identified to target PPARα, PMP70, ACOX1, and CPT1a. ALR depletion from primary hepatocytes increased oxidative stress, miR-540 expression, and steatosis and down-regulated PPARα, ACOX1, PMP70, and CPT1a expression. Anti-miR-540 mitigated ALR depletion-induced steatosis and prevented loss of PPARα, ACOX1, PMP70, and CPT1a expression. Antioxidant N-acetylcysteine and recombinant ALR (rALR) both inhibited ALR depletion-induced miR-540 expression and lipid accumulation in hepatocytes. Finally, treatment of ALR-L-KO mice with rALR between 1 and 2 wk prevented miR-540 expression, and arrested steatosis and fibrosis. We conclude that ALR deficiency-mediated oxidative stress induces generation of miR-540, which promotes steatosis by dysregulating peroxisomal and mitochondrial lipid homeostasis.-Kumar, S., Rani, R., Karns, R., Gandhi, C. R. Augmenter of liver regeneration protein deficiency promotes hepatic steatosis by inducing oxidative stress and microRNA-540 expression.

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: A key protein in liver regeneration and pathophysiology

Liver is constantly exposed to pathogens, viruses, chemicals, and toxins, and several of them cause injury, leading to the loss of liver mass and sometimes resulting in cirrhosis and cancer. Under physiological conditions, liver can regenerate if the loss of cells is less than the proliferation of hepatocytes. If the loss is more than the proliferation, the radical treatment available is liver transplantation. Due to this reason, the search for an alternative therapeutic agent has been the focus of liver research. Liver regeneration is regulated by several growth factors; one of the key factors is augmenter of liver regeneration (ALR). Involvement of ALR has been reported in crucial processes such as oxidative phosphorylation, maintenance of mitochondria and mitochondrial biogenesis, and regulation of autophagy and cell proliferation. Augmenter of liver regeneration has been observed to be involved in liver regeneration by not only overcoming cell cycle inhibition but by maintaining the stem cell pool as well. These observations have created curiosity regarding the possible role of ALR in maintenance of liver health. Thus, this review brings a concise presentation of the work done in areas exploring the role of ALR in normal liver physiology and in liver health maintenance by fighting liver diseases, such as liver failure, non-alcoholic fatty liver disease/non-alcoholic steatohepatitis, viral infections, cirrhosis, and hepatocellular carcinoma.

Lack of hepatic stimulator substance expression promotes hepatocellular carcinoma metastasis partly through ERK-activated epithelial-mesenchymal transition

Hepatocellular carcinoma (HCC) is one of the most lethal malignancies due to its high frequency of metastasis via the epithelial-mesenchymal transition (EMT) pathway. Hepatic stimulator substance (HSS) can protect hepatocytes from injury and promote liver growth. Recent studies indicated that HSS expression is increased in HCC tissues; however, whether HSS expression is potentially associated with HCC metastasis, particularly through the EMT pathway, remains largely unknown. In this study, the relationship between HSS expression and HCC metastasis was investigated in clinical samples of HCC. Meanwhile, the regulation of HCC metastasis and EMT progression by HSS were also analyzed in both in vitro and in vivo models. The results showed that the expression of 23 kDa HSS was significantly decreased among HCC tissues with angioinvasion. A decrease in HSS predicted poor prognosis with a lower survival rate. Furthermore, the growth of xenograft tumors after inoculating MHCC97H-HSS-shRNA (HCC) cells into nude mice was notably accelerated compared to those inoculated with HSS-expressing cells. Further analysis revealed that knockdown of HSS expression in both MHCC97H and HepG2 cells could enhance the migration of these HCC cells. Concurrently, interference of HSS expression by shRNA promoted conversion of morphologically epithelial-like HCC cells into mesenchymal-like cells, together with downregulations of epithelial markers (such as E-cadherin and zonula occludens-1) and upregulation of mesenchymal-like makers (such as α-SMA, β-catenin, and fibronectin). Furthermore, it was demonstrated that, as well as promoting EMT, HSS-shRNA induced the phosphorylation of extracellular signal-regulated kinase (ERK) and elevated the expression of the EMT-related transcription factor Snail. Specific inhibition of HSS-shRNA-induced ERK phosphorylation by PD98059 attenuated HCC cell migration in a dose-dependent manner. In conclusion, we demonstrated that downregulation of HSS expression contributes to HCC metastasis partially through the ERK-activated EMT pathway.

Progress in research of augmenter of liver regeneration

Augmenter of liver regeneration (ALR), also known as hepatic stimulatory substance or hepatopoietin, is expressed ubiquitously in all organs, and exclusively in hepatocytes in the liver. Over the past decade, research indicates that ALR is able to promote growth of hepatocytes in the regenerating or injured liver, and plays an important role in hepatocyte transplantation, the pathogenesis of fulminant hepatitis, liver regeneration, and the development of hepatocellular carcinoma.

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.

Effects of mesenchymal stem cells and VEGF on liver regeneration following major resection

PURPOSE

The study aims to determine the effects of mesenchymal stem cell (MSC) therapy and a combination therapy of MSCs transfected with vascular endothelial growth factor (VEGF) for liver regeneration after major resection.

METHODS

Thirty-eight rats were divided into four groups: group 1: control (sham operation); group 2: control (70 % hepatic resection); group 3: 70 % hepatic resection + systemically transplanted MSCs; and group 4: 70 % hepatic resection + systemically transplanted MSCs transfected with the VEGF gene. MSCs were injected via the portal vein route in study groups 3 and 4. Expression levels of VEGF, fibroblast growth factor (FGF), platelet-derived growth factor (PDGF), epidermal growth factor (EGF), transforming growth factor (TGF), hepatocyte growth factor (HGF), and augmenter of liver regeneration (ALR) were analyzed in the remnant liver tissue. We investigated the levels of angiogenic factors, VEGF-receptor, angiopoietin-1 (Angpt1) and Angpt2. Biochemical parameters of liver function in blood samples were measured and a histologic assessment of the livers was performed. The postoperative liver weight and volume of each rat were measured 14 days after surgery.

RESULTS

The expression levels of all measured growth factors were significantly increased in groups 3 and 4 compared to the control groups. The levels of Angpt1 and Angpt2 correlated with levels of VEGF and thus were also significantly higher in the study groups. There were significant differences between the estimated liver weights and volumes of group 4 and the resected controls in group 2. With the exception of portal inflammation, levels of all histological parameters were observed to be higher in MSC-treated groups when compared with the resected controls in group 2.

CONCLUSIONS

Transplanted stem cells and MSCs transfected with VEGF significantly accelerated many parameters of the healing process following major hepatic resection. After the injection of MSCs and VEGF-transfected MSCs into the portal vein following liver resection, they were engrafted in the liver. They increased bile duct and liver hepatocyte proliferation, and secreted many growth factors including HGF, TGFβ, VEGF, PDGF, EGF, and FGF via paracrine effects. These effects support liver function, regeneration, and liver volume/weight.

Augmenter of liver regeneration (ALR) restrains concanavalin A-induced hepatitis in mice

Augmenter of liver regeneration (ALR), produced and released by hepatocytes, has cytoprotective and immunoregulatory effects on liver injury, and has been used in many experimental applications. However, little attention has been paid to the effects of ALR on concanavalin A (Con A)-induced hepatitis. The purpose of this paper is to explore the protective effect of ALR on Con A-induced hepatitis and elucidate potential mechanisms. We found that the ALR pretreatment evidently reduced the amount of ALT and AST in serum. In addition, pro-inflammatory cytokines, chemokines and iNOS were suppressed. ALR pretreatment also decreased CD4(+), CD8(+) T cell infiltration in liver. Besides, we observed that ALR pretreatment was capable of suppressing the activation of several signaling pathways in Con A-induced hepatitis. These findings suggest that ALR can obviously weaken Con A-induced hepatitis and ALR has some certain immune regulation function.

The Level of ALR is Regulated by the Quantity of Mitochondrial DNA

Augmenter of liver regeneration (ALR) contributes to mitochondrial biogenesis, maintenance and to the physiological operation of mitochondria. The depletion of ALR has been widely studied and had serious consequences on the mitochondrial functions. However the inverse direction, the effect of the depletion of mitochondrial electron transfer chain and mtDNA on ALR expression has not been investigated yet. Thus mtDNA depleted, ρ(0) cell line was prepared to investigate the role of mitochondrial electron transfer chain and mtDNA on ALR expression. The depletion of mtDNA has not caused any difference at mRNA level, but at protein level the expression of ALR has been markedly increased. The regulatory role of ATP and ROS levels could be ruled out because the treatment of the parental cell line with different respiratory inhibitors and uncoupling agent could not provoke any changes in the protein level of ALR. The effect of mtDNA depletion on the protein level of ALR has been proved not to be liver specific, since the phenomenon could be observed in the case of two other, non-hepatic cell lines. It seems the level of mtDNA and/or its products may have regulatory role on the protein level of ALR. The up-regulation of ALR can be a part of the adaptive response in ρ(0) cells that preserves the structural integrity and the transmembrane potential despite the absence of protein components encoded by the mtDNA.

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.

Recombinant human augmenter of liver regeneration protects hepatocyte mitochondrial DNA in rats with obstructive jaundice

BACKGROUND

Hepatocyte mitochondrial DNA (mtDNA) damage is an important cause of mitochondrial and hepatic function impairment in obstructive jaundice (OJ). This study investigated the protective effect of recombinant human augmenter of liver regeneration (rhALR) on hepatocyte mtDNA in rats with OJ.

MATERIALS AND METHODS

Wistar rats were randomly divided into three groups as follows: sham-operation, biliary obstruction and recanalization with rhALR treatment (BDO-RBF-rhALR), and BDO-RBF-Vehicle (n = 48 per group). After biliary obstruction, rats were intraperitoneally injected with 40 μg/kg rhALR in BDO-RBF-rhALR group and same volume of normal saline in other two groups once every 12 h, until sacrifice. Mitochondrial transcription factor A (mtTFA) and nuclear respiratory factor-1 (NRF-1) expression in hepatocytes were detected by real-time reverse transcription-polymerase chain reaction and Western blot. Hepatocyte mtDNA damage was evaluated by real-time-polymerase chain reaction. Mitochondrial and hepatic functions were also assessed.

RESULTS

After biliary obstruction, hepatic function was clearly impaired, as shown by the increases in serum alanine aminotransferase, aspartate aminotransferase, and total bilirubin levels, and the decrease in albumin level. Mitochondrial respiratory control ratio, phosphorus oxygen ratio, and ATP levels (all indicators of mitochondrial function) were decreased. The relative amount of total mtDNA, mtTFA, and NRF-1 expression in rat liver tissues were decreased, whereas the relative amount of deleted mtDNA was increased. However, the damage was significantly improved in the BDO-RBF-rhALR group. After recanalization, these changes were gradually restored, but the recovery was faster in the BDO-RBF-rhALR group than in BDO-RBF-Vehicle group.

CONCLUSIONS

rhALR may protect and improve mitochondrial and hepatic functions in rats with OJ by promoting the expression of mtTFA and NRF-1 and by protecting and repairing damaged mtDNA.

ALR, the multifunctional protein

ALR is a mystic protein. It has a so called “long” 22 kDa and a “short” 15 kDa forms. It has been described after partial hepatectomy and it has just been considered as a key protein of liver regeneration. At the beginning of the 21st century it has been revealed that the “long” form is localized in the mitochondrial intermembrane space and it is an element of the mitochondrial protein import and disulphide relay system. Several proteins of the substrates of the mitochondrial disulphide relay system are necessary for the proper function of the mitochondria, thus any mutation of the ALR gene leads to mitochondrial diseases. The “short” form of ALR functions as a secreted extracellular growth factor and it promotes the protection, regeneration and proliferation of hepatocytes. The results gained on the recently generated conditional ALR mutant mice suggest that ALR can play an important role in the pathogenesis of alcoholic and non-alcoholic steatosis. Since the serum level of ALR is modified in several liver diseases it can be a promising marker molecule in laboratory diagnostics. Orv. Hetil., 2015, 156(13), 503–509.

Liver-specific deletion of augmenter of liver regeneration accelerates development of steatohepatitis and hepatocellular carcinoma in mice

BACKGROUND & AIMS

Augmenter of liver regeneration (ALR, encoded by GFER) is a widely distributed pleiotropic protein originally identified as a hepatic growth factor. However, little is known about its roles in hepatic physiology and pathology. We created mice with liver-specific deletion of ALR to study its function.

METHODS

We developed mice with liver-specific deletion of ALR (ALR-L-KO) using the albumin-Cre/LoxP system. Liver tissues were collected from ALR-L-KO mice and ALR(floxed/floxed) mice (controls) and analyzed by histology, reverse-transcription polymerase chain reaction, immunohistochemistry, electron microscopy, and techniques to measure fibrosis and lipids. Liver tissues from patients with and without advanced liver disease were determined by immunoblot analysis.

RESULTS

Two weeks after birth, livers of ALR-L-KO mice contained low levels of ALR and adenosine triphosphate (ATP); they had reduced mitochondrial respiratory function and increased oxidative stress, compared with livers from control mice, and had excessive steatosis, and hepatocyte apoptosis. Levels of carbamyl-palmitoyl transferase 1a and ATP synthase subunit ATP5G1 were reduced in livers of ALR-L-KO mice, indicating defects in mitochondrial fatty acid transport and ATP synthesis. Electron microscopy showed mitochondrial swelling with abnormalities in shapes and numbers of cristae. From weeks 2-4 after birth, levels of steatosis and apoptosis decreased in ALR-L-KO mice, and numbers of ALR-expressing cells increased, along with ATP levels. However, at weeks 4-8 after birth, livers became inflamed, with hepatocellular necrosis, ductular proliferation, and fibrosis; hepatocellular carcinoma developed by 1 year after birth in nearly 60% of the mice. Hepatic levels of ALR were also low in ob/ob mice and alcohol-fed mice with liver steatosis, compared with controls. Levels of ALR were lower in liver tissues from patients with advanced alcoholic liver disease and nonalcoholic steatohepatitis than in control liver tissues.

CONCLUSIONS

We developed mice with liver-specific deletion of ALR, and showed that it is required for mitochondrial function and lipid homeostasis in the liver. ALR-L-KO mice provide a useful model for investigating the pathogenesis of steatohepatitis and its complications.

Augmenter of liver regeneration ameliorates renal fibrosis in rats with obstructive nephropathy

Renal fibrosis is a hallmark in CKD (chronic kidney disease) and is strongly correlated to the deterioration of renal function that is characterized by tubulointerstitial fibrosis, tubular atrophy, glomerulosclerosis and disruption of the normal architecture of the kidney. ALR (augmenter of liver regeneration) is a growth factor with biological functions similar to those of HGF (hepatocyte growth factor). In this study, our results indicate that endogenous ALR is involved in the pathological progression of renal fibrosis in UUO (unilateral ureteral obstruction) rat model. Moreover, we find that administration of rhALR (recombinant human ALR) significantly alleviates renal interstitial fibrosis and reduces renal-fibrosis-related proteins in UUO rats. Further investigation reveals that rhALR suppresses the up-regulated expression of TGF-β1 (transforming growth factor β1) induced by UUO operation in the obstructed kidney, and inhibits Smad2 and Smad3 phosphorylation activated by the UUO-induced injury in the animal model. Therefore we suggest that ALR is involved in the progression of renal fibrosis and administration of rhALR protects the kidney against renal fibrosis by inhibition of TGF-β/Smad activity.

Transient GFER knockdown in vivo impairs liver regeneration after partial hepatectomy

BACKGROUND AND AIMS

Augmenter of Liver Regeneration is a protein encoded by the Growth Factor Erv1-Like gene. Its biological properties are crucial for cell survival since knock-out mice for Growth Factor Erv1-Like gene do not survive. In this study, we injected hepatotropic adenoviral particles harboring oligonucleotide sequences against Growth Factor Erv1-Like gene into 70% partially hepatectomized rats and studied the effect of gene silencing on the progression liver regeneration.

METHODS

Partially hepatectomized rats were divided into three groups of animals and, before surgery, received either phosphate buffer saline, or adenoviral particles alone or adenoviral particles harboring the oligonucleotide silencing sequence. In each group, rats were sacrificed at 12, 24 and 48 h after surgery. Liver tissues were collected to analyze the expression of Augmenter of Liver Regeneration, Bax, Bcl-2 and activated Caspase-9 and -3, as well as hepatocyte proliferation and apoptosis, polyamines levels and histological and ultrastructural features.

RESULTS

Growth Factor Erv1-Like gene silencing reduced the compensatory hepatocellular proliferation triggered by surgery through (i) the reduction of polyamines synthesis, hepatocyte proliferation and anti-apoptotic gene expression and (ii) the increase of pro-apoptotic gene expression and caspase activation.

CONCLUSIONS

For the first time, using a technique of gene silencing in vivo, our results demonstrate that Growth Factor Erv1-Like gene knock-down, i.e., the lack of Augmenter of Liver Regeneration, modifies the expression of genes involved in cell apoptosis and inhibits early phase of DNA synthesis. As a consequence, a promotion of cell death and a reduction of cell proliferation occurs.

Dynamic and coordinated regulation of KEAP1-NRF2-ARE and p53/p21 signaling pathways is associated with acetaminophen injury responsive liver regeneration

Acetaminophen (APAP) overdose is the leading cause of drug-induced liver injury. Compensatory liver regeneration is crucial for the final outcome of toxicant-induced injury. However, the molecular mechanisms underlying compensatory liver regeneration in mice after APAP-induced liver injury are not completely understood. This study aimed to investigate the role of dynamic and coordinated regulation of Kelch-like ECH-associated protein 1 (KEAP1)-nuclear factor erythroid 2-related factor 2 (NRF2)- antioxidant response element (ARE) and p53/p21 pathways in APAP injury-responsive liver regeneration. We found that mice exhibited massive hepatic toxicity during the first 12 hours after 400 mg/kg APAP treatment, but responsive liver recovery occurred beyond 24 hours as demonstrated by histopathological and biochemical assessments. The expression and nuclear accumulation of NRF2 was increased after APAP treatment. The expression of

NAD(P)H

quinone oxidoreductase 1, glutamate-cysteine ligase modifier subunit, and heme oxygenase-1 was inhibited during the first 24 hours and then induced to limit oxidative damage. The content of p53 and its downstream target p21 were significantly increased upon APAP exposure and subsequently decreased to normal levels at 48 hours. Furthermore, levels of cyclin D1, cyclin D-dependent kinase 4, proliferating cell nuclear antigen, and augmenter of liver regeneration at 48 hours were enhanced, suggesting initiation of hepatocyte proliferation and tissue repair. These results demonstrated that dynamic and coordinated regulation of KEAP1-NRF2-ARE and p53/p21 signaling pathways was associated with compensatory liver regeneration after APAP-induced acute liver injury.

Exogenous augmenter of liver regeneration (ALR) attenuates inflammatory response in renal hypoxia re-oxygenation injury

Recent studies have highlighted the role of the innate immune system in initiating the inflammatory cascade which leads to detrimental changes in renal ischemia reperfusion (I/R) injury. The augmenter of liver regeneration (ALR) is an anti-apoptosis factor which is highly expressed in renal tubulars of renal cortex and medulla after inducing renal I/R injury in rats. It has been shown that exogenous ALR can enhance renal tubular regeneration. However, whether ALR's protective effect against renal I/R injury results from its immune regulatory function remains unknown. Using rat renal tubular epithelial cell (NRK-52E), we investigate the effect of recombinant rat ALR (rrALR) on immune inflammatory response in hypoxia re-oxygenation (H/R) injury in vitro, and further discuss the possible mechanisms. Cultured NRK-52E cells subjected to hypoxia for 6 h followed by re-oxygenation for 12, 24 and 72 h are administered with different doses of rrALR. Expression of Toll-like receptor 4 (TLR4) and transcription nuclear factor-κB (NF-κB) is assessed by reverse-transcriptase polymerase chain reaction (RT-PCR) and western blot. Expression of interleukin (IL)-6 and IL-1β are determined by enzyme-linked immunosorbent assay (ELISA). In rrALR intervened H/R cells, TLR4 and NF-κB are down regulated at both mRNA and protein levels compare with those in control cells. Also, rrALR appears to downregulate IL-6 and IL-1β expression in concentration-dependent manners. In conclusion, rrALR protects NRK-52E cells from H/R injury possibly by relieving the inflammatory response through regulation of TLR4-NF-κB signaling pathway.

Relationship between insulin/insulin-like growth factor and liver regeneration

Hepatocellular carcinoma is one of the most common cancers, and the main treatments include intervention, radiofrequency ablation, surgical resection and liver transplantation. Metastasis and recurrence contribute greatly to the high mortality rate of hepatocellular carcinoma. Currently, many efforts have been taken to find the ways to promote liver regeneration after liver resection. This article will discuss the relationship between liver regeneration and insulin/insulin-like growth factor.

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.

Inhibitory effect of Coptis chinensis on inflammation in LPS-induced endotoxemia

ETHNOPHARMACOLOGICAL RELEVANCE

Rhizoma coptidis (RC) has been used as a remedy for inflammation-related diseases in traditional medicine. Although it is known to have anti-inflammatory activities, its mechanism of action on lipopolysaccharide (LPS)-induced inflammation has not yet been identified in detail.

AIM OF THE STUDY

This study was designed to assess the beneficial effects of pretreatment with RC in ameliorating LPS-induced liver inflammation.

MATERIALS AND METHODS

Mice were orally administered RC (500, 1000 mg/kg) for three days in a row. 1h after the last RC administration, the mice were intraperitoneally injected with LPS (35 mg/kg). After treatment, histological alterations and inflammatory factor levels in the liver and proinflammatory cytokines in the serum associated with inflammation were examined.

RESULTS

We found that pretreatment with RC (500 and 1000 mg/kg) exerted a significant protective effect by attenuating liver histopathological changes in endotoxemic mice. The results also demonstrated that RC suppressed secretion of LPS-stimulated pro-inflammatory cytokines, such as interleukin-6 (IL-6). Furthermore, RC inhibited LPS-mediated nuclear factor (NF)-κB activation via the prevention of IκB-α phosphorylation, as well as the phosphorylation of ERK1/2, JNK, and p38 MAPKs. These results were associated with decreases in the expression of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (I-NOS).

CONCLUSIONS

The results presented here clearly demonstrate that RC could significantly protect mice against LPS-induced acute liver injury.

Nrf2 activates augmenter of liver regeneration (ALR) via antioxidant response element and links oxidative stress to liver regeneration

Liver regeneration can be impaired by permanent oxidative stress and activation of nuclear factor erythroid 2-related factor 2 (Nrf2), known to regulate the cellular antioxidant response, and has been shown to improve the process of liver regeneration. A variety of factors regulate hepatic tissue regeneration, among them augmenter of liver regeneration (ALR), attained great attention as being survival factors for the liver with proproliferative and antiapoptotic properties. Here we determined the Nrf2/antioxidant response element (ARE) regulated expression of ALR and show ALR as a target gene of Nrf2 in vitro and in vivo. The ALR promoter comprises an ARE binding site and, therefore, ALR expression can be induced by ARE-activator tertiary butylhydroquinone (tBHQ) in hepatoma cells and primary human hepatocytes (PHH). Promoter activity and expression of ALR were enhanced after cotransfection of Nrf2 compared with control and dominant negative mutant of Nrf2. Performing partial hepatectomy in livers from Nrf2+/+ mice compared with Nrf2-/- knock-out (KO) mice, we found increased expression of ALR in addition to known antioxidant ARE-regulated genes. Furthermore, we observed increased ALR expression in hepatitis B virus (HBV) compared with hepatitis C virus (HCV) positive hepatoma cells and PHH. Recently, it was demonstrated that HBV infection activates Nrf2 and, now, we add results showing increased ALR expression in liver samples from patients infected with HBV. ALR is regulated by Nrf2, acts as a liver regeneration and antioxidative protein and, therefore, links oxidative stress to hepatic regeneration to ensure survival of damaged cells.

Augmenter of liver regeneration improves therapeutic effect of hepatocyte homotransplantation in acute liver failure rats

Hepatocyte transplantation (HCT) is an available option on treatment for acute liver failure (ALF). However, short-term survival of engraftment and immunological rejections of recipient are major obstacles. Augmenter of liver regeneration (ALR) has cytoprotective and immunoregulatory effects in liver injury, and has been used in many experimental applications. In the present study, we investigated the potential effect and mechanism of recombinant human ALR (rhALR) on ALF rats treated with intraperitoneal HCT. ALF rats induced by d-galactosamine (GalN) were studied in vivo, and were intraperitoneal injected with or without hepatocytes and rhALR 24h after the induction. Animal survival, serum and ascites liver enzymes, tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) were assessed. Histological examination was performed, and liver regeneration, apoptosis and immunological responses were identified by immunohistochemistry assay. Our results showed that rhALR promoted hepatocytes regeneration, attenuated liver injury and suppressed immunological responses. The ascites liver enzyme, serum and ascites pro-inflammatory cytokines (TNF-α, IL-1β), liver histological injury, apoptotic hepatocytes and activated immunocytes were significantly reduced in ALF rats treated with rhALR and HCT compared with those without rhALR. The proliferative and mitotic hepatocytes were markedly increased, and overall survival improved with rhALR. The administration of rhALR improved survival and promoted liver recovery in HCT treatment for ALF, which was associated with the role of proliferative promoter and immunosuppressor. This study suggests that co-treated with rhALR and HCT can provide a promising strategy for the treatment of ALF.

Augmenter of liver regeneration (ALR) is a novel biomarker of hepatocellular stress/inflammation: in vitro, in vivo and in silico studies

The liver is a central organ involved in inflammatory processes, including the elaboration of acute-phase proteins. Augmenter of liver regeneration (ALR) protein, expressed and secreted by hepatocytes, promotes liver regeneration and maintains viability of hepatocytes. ALR also stimulates secretion of inflammatory cytokines (tumor necrosis factor [TNF]-α and interleukin [IL]-6) and nitric oxide from Kupffer cells. We hypothesized that ALR may be involved in modulating inflammation induced by various stimuli. We found that hepatic ALR levels are elevated at 24 h, before or about the same time as an increase in the mRNA expression of TNF-α and IL-6, after portacaval shunt surgery in rats. Serum ALR also increased, but significantly only on d 4 when pathological changes in the liver become apparent. In rats, serum ALR was elevated after intraperitoneal administration of lipopolysaccharide alone and in a model of gram-negative sepsis. Serum ALR increased before alanine aminotransferase (ALT) in endotoxemia and in the same general time frame as TNF-α and IL-6 in the bacterial sepsis model. Furthermore, mathematical prediction of tissue damage correlated strongly with alterations in serum ALR in a mouse model of hemorrhagic shock. In vitro, monomethyl sulfonate, TNF-α, actinomycin D and lipopolysaccharide all caused increased release of ALR from rat hepatocytes, which preceded the loss of cell viability and/or inhibition of DNA synthesis. ALR may thus serve as a potential diagnostic marker of hepatocellular stress and/or acute inflammatory conditions.

Augmenter of liver regeneration

'Augmenter of liver regeneration' (ALR) (also known as hepatic stimulatory substance or hepatopoietin) was originally found to promote growth of hepatocytes in the regenerating or injured liver. ALR is expressed ubiquitously in all organs, and exclusively in hepatocytes in the liver. ALR, a survival factor for hepatocytes, exhibits significant homology with ERV1 (essential for respiration and viability) protein that is essential for the survival of the yeast, Saccharomyces cerevisiae. ALR comprises 198 to 205 amino acids (approximately 22 kDa), but is post-translationally modified to three high molecular weight species (approximately 38 to 42 kDa) found in hepatocytes. ALR is present in mitochondria, cytosol, endoplasmic reticulum, and nucleus. Mitochondrial ALR may be involved in oxidative phosphorylation, but also functions as sulfhydryl oxidase and cytochrome c reductase, and causes Fe/S maturation of proteins. ALR, secreted by hepatocytes, stimulates synthesis of TNF-α, IL-6, and nitric oxide in Kupffer cells via a G-protein coupled receptor. While the 22 kDa rat recombinant ALR does not stimulate DNA synthesis in hepatocytes, the short form (15 kDa) of human recombinant ALR was reported to be equipotent as or even stronger than TGF-α or HGF as a mitogen for hepatocytes. Altered serum ALR levels in certain pathological conditions suggest that it may be a diagnostic marker for liver injury/disease. Although ALR appears to have multiple functions, the knowledge of its role in various organs, including the liver, is extremely inadequate, and it is not known whether different ALR species have distinct functions. Future research should provide better understanding of the expression and functions of this enigmatic molecule.

Decreased expression of the augmenter of liver regeneration results in increased apoptosis and oxidative damage in human-derived glioma cells

The mammalian growth factor erv1-like (GFER) gene encodes a sulfhydryl oxidase enzyme, named Augmenter of Liver Regeneration (ALR). Recently it has been demonstrated that ALR supports cell proliferation acting as an anti-apoptotic factor. This effect is determined by ALR ability to support the anti-apoptotic gene expression and to preserve cellular normoxic conditions. We recently demonstrated that the addition of recombinant ALR (rALR) in the culture medium of H₂O₂-treated neuroblastoma cells reduces the lethal effects induced by the hydrogen peroxide. Similar data have been reported in the regenerating liver tissue from partially hepatectomized rats treated with rALR. The purpose of the present study was to evaluate the effect of the GFER inhibition, via the degradation of the complementary mRNA by the specific siRNA, on the behaviour of the apoptosis (apoptotic gene and caspase expression and apoptotic cell number) and of the oxidative stress-induced parameters (reactive oxygen species (ROS), clusterin expression and mitochondrial integrity) in T98G glioma cells. The results revealed a reduction of (i) ALR, (ii) clusterin and (iii) bcl-2 and an increase of (iv) caspase-9, activated caspase-3, ROS, apoptotic cell number and mitochondrial degeneration. These data confirm the anti-apoptotic role of ALR and its anti-oxidative properties, and shed some light on the molecular pathways through which ALR modulates its biological effects.

Quiescin sulfhydryl oxidase (QSOX) is expressed in the human atheroma core: possible role in apoptosis

Quiescin sulfhydryl oxidases (QSOXs) catalyze the formation of disulfide bonds in peptides and proteins, and in vertebrates comprise two proteins: QSOX1 and QSOX2. QSOX1, the most extensively studied type, has been implicated in protein folding, production of extracellular matrix, redox regulation, protection from apoptosis, angiogenesis, and cell differentiation. Atherosclerosis is an immunopathological condition in which redox processes, apoptosis, cell differentiation, and matrix secretion/maturation have critical roles. Considering these data, we hypothesized that QSOX1 could be involved in this disease, possibly reducing apoptosis and angiogenesis inside the plaque. QSOX1 labeling in normal human carotid vessels showed predominant expression by endothelium, subendothelium, and adventitia. In atherosclerotic plaques, however, QSOX1 was highly expressed in macrophages at the lipid core. QSOX1 expression was also studied in terms of mRNA and protein in cell types present in plaques under apoptotic or activating stimuli, emulating conditions found in the atherosclerotic process. QSOX1 mRNA increased in endothelial cells and macrophages after the induction of apoptosis. At the protein level, the correlation between apoptosis and QSOX1 expression was not evident in all cell types, possibly because of a rapid secretion of QSOX1. Our results propose for the first time possible roles for QSOX1 in atherosclerosis, being upregulated in endothelial cells and macrophages by apoptosis and cell activation, and possibly controlling these processes, as well as angiogenesis. The quantitative differences in QSOX1 induction may depend on the cell type and also on local factors.

Molecular recognition and substrate mimicry drive the electron-transfer process between MIA40 and ALR

Oxidative protein folding in the mitochondrial intermembrane space requires the transfer of a disulfide bond from MIA40 to the substrate. During this process MIA40 is reduced and regenerated to a functional state through the interaction with the flavin-dependent sulfhydryl oxidase ALR. Here we present the mechanistic basis of ALR-MIA40 interaction at atomic resolution by biochemical and structural analyses of the mitochondrial ALR isoform and its covalent mixed disulfide intermediate with MIA40. This ALR isoform contains a folded FAD-binding domain at the C-terminus and an unstructured, flexible N-terminal domain, weakly and transiently interacting one with the other. A specific region of the N-terminal domain guides the interaction with the MIA40 substrate binding cleft (mimicking the interaction of the substrate itself), without being involved in the import of ALR. The hydrophobicity-driven binding of this region ensures precise protein-protein recognition needed for an efficient electron transfer process.

Alrp, a survival factor that controls the apoptotic process of regenerating liver after partial hepatectomy in rats

Augmenter of Liver Regeneration (Alrp) enhances, through unknown mechanism/s, hepatocyte proliferation only when administered to partially hepatectomized (PH) rats. Liver resection, besides stimulating hepatocyte proliferation, induces reactive oxygen species (ROS), triggering apoptosis. To clarify the role of Alrp in the process of liver regeneration, hepatocyte proliferation, apoptosis, ROS-induced parameters and morphological findings of regenerating liver were studied from PH rats Alrp-treated for 72 h after the surgery. The same parameters, evaluated on regenerating liver from albumin-treated PH rats, were used as control. The results demonstrated that Alrp administration induces the anti-apoptotic gene expression, inhibits hepatocyte apoptosis and reduces ROS-induced cell damage. These and similar data from in vitro studies and the presence of 'Alrp homologous proteins' in viruses as well as in mammals (i) allow to hypothesize that Alrp activity/ies may not be exclusive for regenerating liver and (ii) suggest the use of Alrp in the treatment of oxidative stress-related diseases.

Epidermal growth factor down-regulates the expression of human hepatic stimulator substance via CCAAT/enhancer-binding protein β in HepG2 cells

hHSS (human hepatic stimulator substance), acting as a hepatotrophic growth factor, promotes liver regeneration. However, the regulatory mechanisms for hHSS transcription are still poorly understood. In the present study, we investigated transcription of hHSS triggered by EGF (epidermal growth factor) and the role of C/EBPβ (CCAAT/enhancer-binding protein β) as a potential core factor responsible for hHSS transcription in HepG2 cells. The results show that EGF suppresses hHSS mRNA expression at early time points. Using a promoter deletion assay, we identified a proximal region (−358/−212) that is required for EGF suppression. Overexpression of C/EBPβ enhances EGF suppression of hHSS, and mutation of the C/EBPβ-binding site at −292/−279 or siRNA (short interfering RNA) interference abolishes EGF suppression. Furthermore, using an electrophoretic mobility-shift assay and chromatin immunoprecipitation analysis, we found that C/EBPβ specifically binds to the −292/−279 site that is responsible for EGF inhibition. Moreover, using a knockin (overexpression) and knockdown strategy (siRNA), we confirmed that C/EBPβ is a key factor responsible for inhibition of hHSS mRNA expression. Pre-treatment with an inhibitor of JNK (c-Jun N-terminal kinase) or down-regulation of JNK1 with specific siRNA reverses EGF-inhibited hHSS expression. Our results provide a crucial regulatory mechanism for EGF in hHSS transcription within the promoter proximal region.

Foxa2 (HNF-3beta) regulates expression of hepatotrophic factor ALR in liver cells

Liver regeneration is a multistep and well-orchestrated process which is initiated by injuries such as tissue loss, infectious or toxic insults. Augmenter of liver regeneration (ALR) is a hepatotrophic growth factor which has been shown to stimulate hepatic regeneration after partial hepatectomy and therefore seems to be regulated during the regenerative process in the liver. Our aim was to analyze how ALR is regulated in hepatic tissues and which transcription factors might regulate its tissue-specific expression. Promoter studies of ALR (-733/+527 bp) revealed potential regulatory elements for various transcription factors like Foxa2, IL-6 RE-BP and C/EBPbeta. Analysis of the promoter activity by performing luciferase assays revealed that co-transfection with Foxa2 significantly induced the activity of ALR promoter in HepG2 cells. EMSA and Supershift analysis using anti-Foxa2 antibody confirmed the specific binding of Foxa2 to ALR promoter and this binding was inducible when the cells were simultaneously stimulated with IL-6. The increased binding after activation with IL-6 and/or Foxa2 was confirmed by elevated ALR protein levels using Western blot technique. In addition, we could not detect any binding of C/EBPbeta and IL-6 RE-BP to the promoter of ALR. In conclusion, these results indicate that ALR is regulated by Foxa2, and this regulation may be amplified by IL-6.

Cholera toxin-sensitive GTP-binding protein-coupled activation of augmenter of liver regeneration (ALR) receptor and its function in rat kupffer cells

Mitogenic effect of augmenter of liver regeneration (ALR), a protein produced and released by hepatocytes, on hepatocytes in vivo but not in vitro suggests that the effect is mediated by nonparenchymal cells. Since mediators produced by Kupffer cells are implicated in hepatic regeneration, we investigated receptor for ALR and its functions in rat Kupffer cells. Kupffer cells were isolated from rat liver by enzymatic digestion and centrifugal elutriation. Radioligand ([(125)I] ALR) receptor binding, ALR-induced GTP/G-protein association, and nitric oxide (NO), tumor necrosis factor (TNF)-alpha, and interleukin-6 (IL-6) synthesis were determined. High-affinity receptor for ALR, belonging to the G-protein family, with K(d) of 1.25 +/- 0.18 nM and B(max) of 0.26 +/- 0.02 fmol/microg DNA was identified. ALR stimulated NO, TNF-alpha, and IL-6 synthesis via cholera toxin-sensitive G-protein, as well as p38-MAPK activity and nuclear translocation of NFkappaB. While inhibitor of NFkappaB (MG132) inhibited ALR-induced NO synthesis, MG132 and p38-MAPK inhibitor (SB203580) abrogated ALR-induced TNF-alpha and IL-6 synthesis. ALR also prevented the release of mediator(s) from Kupffer cells that cause inhibition of DNA synthesis in hepatocytes. Administration of ALR to 40% partially hepatectomized rats increased expression of TNF-alpha, IL-6, and inducible nitric oxide synthase (iNOS) and caused augmentation of hepatic regeneration. These results demonstrate specific G-protein coupled binding of ALR and its function in Kupffer cells and suggest that mediators produced by ALR-stimulated Kupffer cells may elicit physiologically important effects on hepatocytes.

Human augmenter of liver regeneration: Molecular cloning, biological activity and roles in liver regeneration

The complete amino acid sequence of human augmenter of liver regeneration (hALR) was reported by deduction from nucleotide sequence of its complementary DNA. The cDNA for hALR was isolated by screening a human fetal liver cDNA library and the sequencing of this insert revealed an open reading frame encoding a protein with 125aa and highly homologous (87%) with rat ALR encoding sequence. The recombinant hALR expressed from its cDNA in transient expression experiments in cos-7 cells could stimulate DNA synthesis of HTC hepatoma cell in the dose-dependent and heat-resistant way. Northern blot analysis with rat ALR cDNA as probe confirmed that ALR mRNA was expressed in the normal rat liver at low level and that dramatically increased in the regenerating liver after partial hepatectomied rat. This size of hALR mRNA is 1.4 kb long and expressed in human fetal liver, kidney and testis. These findings indicated that liver itself may be the resource of ALR and suggested that ALR seems to be an important paracrined regulator of liver regeneration.

Expression and localization of augmenter of liver regeneration in human muscle tissue

Mitochondrial DNA (mt-DNA) disorders and abnormal regulation of nuclear-derived proteins devoted to the cross-talk between the two cellular genomes have recently interested researchers in the field of neuromuscular diseases. We have identified, isolated and sequenced a new gene, augmenter of liver regeneration (ALR) that stimulates in vivo hepatocyte proliferation and up-regulates mt-DNA expression and ATP production. ALR protein (Alrp) is mainly located, in rat, in the mitochondrial inter-membrane space and its mRNA is particularly abundant in brain, muscle, testis and liver, tissues whose activity is mostly dependent on mitochondrial metabolism. Studies on rat Alrp sequence revealed the presence of homologous amino-acid sections into proteins derived from mouse, human, Drosophyla, plants and even DNA viruses. In this article, we evaluated ALR expression in normal human muscular tissues, both as protein and as mRNA. The data, obtained by molecular biology, immunohistochemistry and electron microscopy, demonstrated that: (i) Alrp and ALR mRNA are present in human muscular tissue; (ii) Alrp is particularly expressed in muscular fibres rich in mitochondria; (iii) Alrp is localized in the mitochondrial inter-membrane space or associated to mitochondrial cristae; and (iv) in subjects younger then 35 years of age, ALR mRNA expression is different between male and female subjects. In conclusion, the present data set Alrp, as a factor associated with mitochondria also in human tissue, call for future studies aimed at establishing Alrp as an important factor involved in the molecular events that trigger neuromuscular diseases.

Protective effect of augmenter of liver regeneration on hydrogen peroxide-induced apoptosis in SH-SY5Y human neuroblastoma cells

BACKGROUND

Hydrogen peroxide, as other reactive oxygen species (ROS) produced during redox processes, induces lipid membrane peroxidation and protein degeneration causing cell apoptosis. ROS are recently considered as messengers in cell signalling processes, which, through reversible protein disulphide bridges formation, activate regulatory factors of cell proliferation and apoptosis. Disulphide bridges formation is catalysed by sulphydryl oxidase enzymes.

AIM

The neuroprotective effect of ALR protein (Alrp), a sulphydryl oxidase enzyme, on H(2)O(2)-induced apoptosis in SH-SY5Y cells has been evaluated.

METHODS

Cell viability, flow cytometric evaluation of apoptotic cells, fluorescent changes of nuclear morphology, immunocytochemistry Alrp detection, Western blot evaluation of mitochondrial cyt c release and mitochondrial swelling were determined.

RESULTS

Alrp prevents the H(2)O(2)-induced cell viability loss, apoptotic cell death and mitochondrial swelling in SH-SY5Y cells in culture.

CONCLUSIONS

The data demonstrate that Alrp improves SH-SY5Y cells survival in H(2)O(2)-induced apoptosis. It is speculated that this effect could be related to the Alrp enzymatic activity.