Augmenter of liver regeneration inhibits TGF-β1-induced renal tubular epithelial-to-mesenchymal transition via suppressing TβR II expression in vitro

The protective roles of augmenter of liver regeneration in hepatocytes in the non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) occurs in 25% of the global population and manifests as lipid deposition, hepatocyte injury, activation of Kupffer and stellate cells, and steatohepatitis. Predominantly expressed in hepatocytes, the augmenter of liver regeneration (ALR) is a key factor in liver regulation that can alleviate fatty liver disease and protect the liver from abnormal liver lipid metabolism. ALR has three isoforms (15-, 21-, and 23-kDa), amongst which 23-kDa ALR is the most extensively studied. The 23-kDa ALR isoform is a sulfhydryl oxidase that resides primarily in the mitochondrial intermembrane space (IMS), whereby it protects the liver against various types of injury. In this review, we describe the role of ALR in regulating hepatocytes in the context of NAFLD. We also discuss questions about ALR that remain to be explored in the future. In conclusion, ALR appears to be a promising therapeutic target for treating NAFLD.

Augmenter of Liver Regeneration (ALR) Protects Kidney from Ischemia/Reperfusion (I/R) Injury via Regulation of TLR4/MAPK Signaling Pathway

Toll-like receptor 4 (TLR4) can mediate innate activation and inflammation, and it is typically expressed within the ischemic kidney. Augmenter of liver regeneration (ALR) acts as an immunoregulator with a high expression in the kidney induced by renal ischemia/reperfusion (I/R) injury. Exogenous ALR has indicated a role in protecting the kidney from I/R injury. The protective effect of ALR is due to the immune regulatory function which remains to be elucidated. In this study, rats induced by renal I/R were treated with recombinant human ALR (rhALR) and demonstrated that the animals were protected from kidney I/R injury, implying that the rhALR-treated rats had less tubular damage than those untreated rats. Meanwhile, tubular epithelial cell apoptosis, neutrophil (24 h) and macrophage (72 h) infiltration to tubulointerstitium, and levels of inflammatory cytokines were decreased considerably in the rhALR-treated rats as compared to control. Additionally, rhALR could downregulate mRNA expression of TLR4 endogenous ligands and restrain its activation in renal I/R injury rats. It has also been proved that anti-rhALR antibody blocked the inhibition of rhALR of the immune inflammatory response in hypoxia/reoxygenation (H/R) injury in vitro. In rhALR+anti-rhALR antibody-intervened H/R cells, the expression of inflammatory cytokines was upregulated compared with the rhALR-treated cells. Taken together, rhALR could regulate the TLR4 signaling pathway to relieve inflammatory response, thereby protecting renal I/R injury, indicating that ALR is likely to be introduced to develop novel immune therapies for renal I/R injury.

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.

Augmenter of Liver Regeneration Alleviates Renal Hypoxia-Reoxygenation Injury by Regulating Mitochondrial Dynamics in Renal Tubular Epithelial Cells

Mitochondria are highly dynamic organelles that constantly undergo fission and fusion processes that closely related to their function. Disruption of mitochondrial dynamics has been demonstrated in acute kidney injury (AKI), which could eventually result in cell injury and death. Previously, we reported that augmenter of liver regeneration (ALR) alleviates renal tubular epithelial cell injury. Here, we gained further insights into whether the renoprotective roles of ALR are associated with mitochondrial dynamics. Changes in mitochondrial dynamics were examined in experimental models of renal ischemia-reperfusion (IR). In a model of hypoxia-reoxygenation (HR) injury in vitro , dynamin-related protein 1 (Drp1) and mitochondrial fission process protein 1 (MTFP1), two key proteins of mitochondrial fission, were downregulated in the Lv-ALR + HR group. ALR overexpression additionally had an impact on phosphorylation of Drp1 Ser637 during AKI. The inner membrane fusion protein, Optic Atrophy 1 (OPA1), was significantly increased whereas levels of outer membrane fusion proteins Mitofusin-1 and -2 (Mfn1, Mfn2) were not affected in the Lv-ALR + HR group, compared with the control group. Furthermore, the mTOR/4E-BP1 signaling pathway was highly activated in the Lv-ALR + HR group. ALR overexpression led to suppression of HR-induced apoptosis. Our collective findings indicate that ALR gene transfection alleviates mitochondrial injury, possibly through inhibiting fission and promoting fusion of the mitochondrial inner membrane, both of which contribute to reduction of HK-2 cell apoptosis. Additionally, fission processes are potentially mediated by promoting tubular cell survival through activating the mTOR/4E-BP1 signaling pathway.

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.

Inflammation and renal fibrosis: Recent developments on key signaling molecules as potential therapeutic targets

Chronic kidney disease (CKD) is a major public health issue. At the histological level, renal fibrosis is the final common pathway of progressive kidney disease irrespective of the initial injury. Considerable evidence now indicates that renal inflammation plays a central role in the initiation and progression of CKD. Some of the inflammatory signaling molecules involved in CKD include: monocyte chemoattractant protein-1 (MCP-1), bradykinin B₁ receptor (B₁R), nuclear factor κB (NF-κB), tumor necrosis factor-α (TNFα), transforming growth factor β (TGF-β), and platelet-derived growth factor (PDGF). Multiple antifibrotic factors, such as interleukin-10 (IL-10), interferon-γ (IFN-γ), bone morphogenetic protein-7 (BMP-7), hepatocyte growth factor (HGF) are also downregulated in CKD. Therefore, restoration of the proper balance between pro- and antifibrotic signaling pathways could serve as a guiding principle for the design of new antifibrotic strategies that simultaneously target many pathways. The purpose of this review is to summarize the existing body of knowledge regarding activation of cytokine pathways and infiltration of inflammatory cells as a starting point for developing novel antifibrotic therapies to prevent progression of CKD.