Augmenter of liver regeneration: A key protein in liver regeneration and pathophysiology

Augmenter of liver regeneration knockout aggravates tubular ferroptosis and macrophage activation by regulating carnitine palmitoyltransferase-1A-induced lipid metabolism in diabetic nephropathy

AIM

Ferroptosis is a novel type of programmed cell death that performs a critical function in diabetic nephropathy (DN). Augmenter of liver regeneration (ALR) exists in the inner membrane of mitochondria, and inhibits inflammation, apoptosis, and oxidative stress in acute kidney injury; however, its role in DN remains unexplored. Here, we aimed to identify the role of ALR in ferroptosis induction and macrophage activation in DN.

METHODS

The expression of ALR was examined in DN patients, db/db DN mice, and HK-2 cells treated with high glucose (HG). The effects of ALR on ferroptosis and macrophage activation were investigated with ALR conditional knockout, lentivirus transfection, transmission electron microscopy, qRT-PCR and western blotting assay. Mass spectrometry and rescue experiments were conducted to determine the mechanism of ALR.

RESULTS

ALR expression was reduced in the kidney tissues of DN patients and mice, serum of DN patients, and HG-HK-2 cells. Moreover, the inhibition of ALR promoted ferroptosis, macrophage activation, and DN progression. Mechanistically, ALR can directly bind to carnitine palmitoyltransferase-1A (CPT1A), the key rate-limiting enzyme of fatty acid oxidation (FAO), and inhibit the expression of CPT1A to regulate lipid metabolism involving FAO and lipid droplet-mitochondrial coupling in DN.

CONCLUSION

Taken together, our findings revealed a crucial protective role of ALR in ferroptosis induction and macrophage activation in DN and identified it as an alternative diagnostic marker and therapeutic target for DN.

Oxidative protein folding in the intermembrane space of human mitochondria

The mitochondrial intermembrane space hosts a machinery for oxidative protein folding, the mitochondrial disulfide relay. This machinery imports a large number of soluble proteins into the compartment, where they are retained through oxidative folding. Additionally, the disulfide relay enhances the stability of many proteins by forming disulfide bonds. In this review, we describe the mitochondrial disulfide relay in human cells, its components, and their coordinated collaboration in mechanistic detail. We also discuss the human pathologies associated with defects in this machinery and its protein substrates, providing a comprehensive overview of its biological importance and implications for health.

Role of augmenter of liver regeneration on testicular ischemia and ischemia/reperfusion injury: An experimental study

Background

Testicular torsion causes ischemic injury, and torsion causes reperfusion injury.

Aim

Evaluating the role of augmenter of liver regeneration (ALR) in testicular ischemia and ischemia/reperfusion injury.

Materials and Method(s)

Seventy-eight (78) healthy Wistar albino male rats were randomly divided into four groups; control (C) (n = 6), sham (S) (n = 24), torsion (T) (n = 24), and torsion/detorsion (T/D) (n = 24). S, T, and T/D groups were divided into four subgroups (n = 6) as 1st, 2nd, 3rd, and 4th hours. Blood, tissue ALR, and histology analyses were performed between groups and subgroups.

Results

The increase in plasma ALR values at the 3rd and 4th hours compared to the 1st hour in the T group were significant (P < 0.01, P < 0.001, respectively). In the T/D group, a significant increase was observed in plasma ALR values at the 3rd and 4th hours compared to the 1st hour (P < 0.05, P < 0.001, respectively). Plasma ALR values at the 1st, 2nd, 3rd, and 4th hours were higher in the T and T/D groups than in the C group (P < 0.001, P < 0.05, respectively). Plasma ALR values were higher in the T group at the 1st, 2nd, 3rd, and 4th hours than in the S group (P < 0.05). A significant increase was observed in tissue ALR at the 3rd and 4th hours than at the 1st hour in the T group (P < 0.05, P < 0.001, respectively). A significant increase was observed in tissue ALR at the 3rd and 4th hours than in the 1st hour in the T/D group (P < 0.05, P < 0.001, respectively).

Discussion

ALR in plasma and testicular tissue has a potential role in the early diagnosis of testicular torsion and in predicting the prognosis of T and T/D.

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.

Polysaccharide from Echinacea purpurea plant ameliorates oxidative stress-induced liver injury by promoting Parkin-dependent autophagy

BACKGROUND

Acetaminophen (APAP) overdose represents one of the most common drug-induced liver injuries (DILI) worldwide. Oxidative damage to the hepatocytes and their resultant autophagy are the key components in the APAP-induced DILI. Echinacea purpurea polysaccharide (EPPS), the component extracted from the root of Echinacea purpurea (L.) Moench, shows various biological functions including immunoregulation and antioxidant activity.

PURPOSE

This study aimed to elucidate the protective effect of EPPS against APAP-induced DILI and the underlying mechanisms.

RESULTS

EPPS attenuates APAP overdose induced DILI in mice and ameliorates inflammation and oxidative stress in mice with APAP overdose-induced DILI. Furthermore, EPPS protected the hepatocytes against APAP-induced liver injury by suppressing apoptosis. EPPS ameliorates APAP-induced DILI via an autophagy-dependent mechanism in vivo and increases autophagy with a reduction in oxidative stress and inflammation in vitro. Parkin knockdown prevents the autophagic-dependent manner of EPPS effects in APAP-treated hepatocytes.

CONCLUSIONS

EPPS exhibited a strong hepatoprotective effect against APAP-induced DILI and was correlated with reduction of autophagy-dependent oxidant response, inflammation, and apoptosis. Moreover, the findings indicated that EPPS exerts its hepatoprotective effect against APAP mainly via Parkin-dependent autophagy, and the use of EPPS can serve as a promising novel therapeutic strategy for APAP-induced DILI.

Maternal high-fat diet consumption programs male offspring to mitigate complications in liver regeneration

In the last decades, obesity and nonalcoholic fatty liver disease (NAFLD) have become increasingly prevalent in wide world. Fatty liver can be detrimental to liver regeneration (LR) and offspring of obese dams (HFD-O) are susceptible to NAFLD development. Here we evaluated LR capacity in HFD-O after partial hepatectomy (PHx). HFD-O re-exposed or not to HFD in later life were evaluated for metabolic parameters, inflammation, proliferation, tissue repair markers and survival rate after PHx. Increasing adiposity and fatty liver were observed in HFD-O. Despite lower IL-6 levels, Ki67 labeling, cells in S phase and Ciclin D1/PCNA protein content, a lower impact on survival rate was found after PHx, even when re-exposed to HFD. However, no difference was observed between offspring of control dams (SC-O) and HFD-O after surgery. Although LR impairment is dependent of steatosis development, offspring of obese dams are programmed to be protected from the damage promoted by HFD.

Molecular pathways of liver regeneration: A comprehensive review

The liver is a unique parenchymal organ with a regenerative capacity allowing it to restore up to 70% of its volume. Although knowledge of this phenomenon dates back to Greek mythology (the story of Prometheus), many aspects of liver regeneration are still not understood. A variety of different factors, including inflammatory cytokines, growth factors, and bile acids, promote liver regeneration and control the final size of the organ during typical regeneration, which is performed by mature hepatocytes, and during alternative regeneration, which is performed by recently identified resident stem cells called “hepatic progenitor cells”. Hepatic progenitor cells drive liver regeneration when hepatocytes are unable to restore the liver mass, such as in cases of chronic injury or excessive acute injury. In liver maintenance, the body mass ratio is essential for homeostasis because the liver has numerous functions; therefore, a greater understanding of this process will lead to better control of liver injuries, improved transplantation of small grafts and the discovery of new methods for the treatment of liver diseases. The current review sheds light on the key molecular pathways and cells involved in typical and progenitor-dependent liver mass regeneration after various acute or chronic injuries. Subsequent studies and a better understanding of liver regeneration will lead to the development of new therapeutic methods for liver diseases.

Role of autophagy in alcohol and drug-induced liver injury

Alcohol-related liver disease (ALD) and drug-induced liver injury (DILI) are common causes of severe liver disease, and successful treatments are lacking. Autophagy plays a protective role in both ALD and DILI by selectively removing damaged mitochondria (mitophagy), lipid droplets (lipophagy), protein aggregates and adducts in hepatocytes. Autophagy also protects against ALD by degrading interferon regulatory factor 1 (IRF1) and damaged mitochondria in hepatic macrophages. Specifically, we will discuss selective autophagy for removal of damaged mitochondria and lipid droplets in hepatocytes and autophagy-mediated degradation of IRF1 in hepatic macrophages as protective mechanisms against alcohol-induced liver injury and steatosis. In addition, selective autophagy for removal of damaged mitochondria and protein adducts for protection against DILI is discussed in this review. Development of new therapeutics for ALD and DILI is greatly needed, and selective autophagy pathways may provide promising targets. Drug and alcohol effects on autophagy regulation as well as protective mechanisms of autophagy against DILI and ALD are highlighted in this review.

Augmenter of liver regeneration enhances cell proliferation through the microRNA-26a/Akt/cyclin D1 pathway in hepatic cells

AIM

Hepatocytes can proliferate and regenerate when injured by toxins, viral infections, and so on. Augmenter of liver regeneration (ALR) is a key regulator of liver regeneration, but the mechanism is unknown. The role of ALR in other cell types is not known. In the present study, we investigated the relationship between microRNA (miRNA)-26a and ALR in the Huh7 cell line and adipose tissue-derived mesenchymal cells from chronic liver disease patients and healthy individuals.

METHODS

Huh7 cells were transfected independently with ALR and miRNA-26a expression vectors, and their effects on cell proliferation, the expression of miRNA-26a, and activation of the phosphatase and tensin homolog and Akt signaling pathways were determined. The experiments were repeated on mesenchymal stem cells derived from healthy individuals and chronic liver disease patients to see whether the observations can be replicated in primary cells.

RESULTS

Overexpression of ALR or miRNA-26a resulted in an increase of the phosphorylation of Akt and cyclin D1 expression, whereas it resulted in decreased levels of p-GSK-3β and phosphatase and tensin homolog in Huh7 cells. The inhibition of ALR expression by ALR siRNA or anti-miR-26a decreased the Akt/cyclin D1 signaling pathway, leading to decreased proliferation. Mesenchymal stem cells isolated from the chronic liver disease patients had a higher ALR expression, while the mesenchymal stem cells isolated from healthy volunteers responded to the growth factor treatments for increased ALR expression. It was found that there was a significant increase in miRNA-26a expression and proliferation.

CONCLUSIONS

These data clearly showed that ALR induced the expression of miRNA-26a, which downregulated phosphatase and tensin homolog, resulting in an increased p-Akt/cyclin D1 pathway and enhanced proliferation in hepatic cells.

Discrepancy between volume and functional recovery in early phase liver regeneration following extended hepatectomy with extrahepatic bile duct resection

AIM

To elucidate the clinical factors having an impact on liver regeneration rate following preoperative portal vein embolization (PVE) and subsequent extended hepatectomy. The correlation between liver volume and functional recovery after extended hepatectomy was also investigated.

METHODS

Records of patients who underwent extended hepatectomy with extrahepatic bile duct resection following PVE for perihilar cholangiocarcinoma were reviewed retrospectively with attention to liver regeneration. All patients underwent computed tomography before PVE, after PVE (immediately before surgery), and on postoperative day (POD) 7. The kinetic growth rate (KGR) was calculated as the percent increase in liver volume relative to the future liver remnant volume per day after PVE (KGR_PVE ) and after POD 7 (KGR_POD7 ) using the computed tomography images before PVE, after PVE, and on POD 7.

RESULTS

In the 289 study patients, the median of KGR_PVE was 1.35%/day whereas that of KGR_POD7 was 5.56%/day. The extent of liver resection had the greatest impact on both KGR_PVE and KGR_POD7 and the impacts of other factors were less. There was a significant negative correlation between KGR_PVE and KGR_POD7 (P = 0.002). No correlations were observed between KGR_PVE or KGR_POD7 and serum total bilirubin and prothrombin time - international normalized ratio on POD 7, nor in the incidence of liver failure after surgery.

CONCLUSIONS

Early phase liver regeneration after extended hepatectomy was largely influenced by the extent of liver resection and showed no correlation with the indices of liver failure. There was a discrepancy between volume and functional recovery in early phase liver regeneration.

Augmenter of liver regeneration promotes mitochondrial biogenesis in renal ischemia-reperfusion injury

Mitochondria are the center of energy metabolism in the cell and the preferential target of various toxicants and ischemic injury. Renal ischemia-reperfusion (I/R) injury triggers proximal tubule injury and the mitochondria are believed to be the primary subcellular target of I/R injury. The promotion of mitochondrial biogenesis (MB) is critical for the prevention I/R injury. The results of our previous study showed that augmenter of liver regeneration (ALR) has anti-apoptotic and anti-oxidant functions. However, the modulatory mechanism of ALR remains unclear and warrants further investigation. To gain further insight into the role of ALR in MB, human kidney (HK)-2 cells were treated with lentiviruses carrying ALR short interfering RNA (siRNA) and a model of hypoxia reoxygenation (H/R) injury in vitro was created. We observed that knockdown of ALR promoted apoptosis of renal tubular cells and aggravated mitochondrial injury, as evidenced by the decrease in the mitochondrial respiratory proteins adenosine triphosphate (ATP) synthase subunit β, cytochrome c oxidase subunit 1, and nicotinamide adenine dinucleotide dehydrogenase (ubiquinone) beta subcomplex 8. Meanwhile, the production of reactive oxygen species was increased and ATP levels were decreased significantly in HK-2 cells, as compared with the siRNA/control group (p < 0.05). In addition, the mitochondrial DNA copy number and membrane potential were markedly decreased. Furthermore, critical transcriptional regulators of MB (i.e., peroxisome proliferator-activated receptor-gamma coactivator 1 alpha, mitochondrial transcription factor A, sirtuin-1, and nuclear respiratory factor-1) were depleted in the siRNA/ALR group. Taken together, these findings unveil essential roles of ALR in the inhibition of renal tubular cell apoptosis and attenuation of mitochondrial dysfunction by promoting MB in AKI.

Analysis of the mechanism underlying liver diseases using human induced pluripotent stem cells

Results of recent studies have shown that disease models using human induced pluripotent stem (iPS) cells have recapitulated the pathophysiology of genetic liver diseases, viral hepatitis and hepatic fibrosis. The utilization of human iPS cells as a model of liver diseases has several substantial advantages compared with primary hepatocytes and cancer cell lines, such as the potential for unlimited expansion and similarity of biological characteristics to normal liver cells. In this review, we have focused on modeling liver diseases using human iPS cells and discussed the experimental evidence that supports the utility of such disease models, including that in our recent studies. Genetically modified or patient-derived human iPS cells can mimic congenital liver disease phenotypes. Human iPS-derived hepatic cells can be infected with the hepatitis viruses. The co-culture of human iPS-derived hepatocytes and mesenchyme partially mimics the process of liver fibrosis. Human iPS cell-derived hepatic cells and the co-culture system of such cells will contribute to the progress of studies on the pathophysiology of genetic and non-genetic liver diseases and development of novel therapeutic strategies for treating liver diseases.

TGF-β induces liver fibrosis via miRNA-181a-mediated down regulation of augmenter of liver regeneration in hepatic stellate cells

OBJECTIVE

To study the role of miRNA-181a and augmenter of liver regeneration in TGF-β-induced fibrosis in hepatic stellate cells.

METHODS

LX2 cells were treated with 20 ng/ml TGF-β for 24 h. miRNA-181a, ALR plasmid and empty vectors were transfected using siPORT NeoFx reagent. Cells were harvested after 48 h or 72 h of transfection for protein or RNA analysis. Western blotting was performed for ALR, TGF-β receptor II (TGFβ-RII), collagen 1A1 (COLL1A1), alpha-smooth muscle cell actin (α-SMA), rac1, E-cadherin and β-actin. Quantitative RT-PCR was performed for ALR, GAPDH, miRNA-181a or 5S rRNA.

RESULTS

TGF-β induced the expression of miRNA-181a, which in turn down-regulated ALR thereby induced the fibrosis markers, such as COLL1A1, α-SMA and rac1 in hepatic stellate cells. Over-expression of miRNA-181a down-regulated expression of ALR and up-regulated expression of fibrosis markers. On the other hand, ALR over-expression resulted in a decrease in miRNA-181a expression and fibrosis markers. Over-expression of ALR also inhibited the expression of TGFβ-RII and increased expression E-cadherin.

CONCLUSION

TGF-β induced miRNA-181a, which in turn induced fibrosis, at least in part, by inhibiting ALR. ALR inhibited TGF-β action by decreasing the expression of TGFβ-RII, thereby inhibiting miRNA-181a expression and fibrosis markers. ALR could serve as a potential molecule to inhibit liver fibrosis.

Understanding the Metabolic Profile of Macrophages During the Regenerative Process in Zebrafish

In contrast to mammals, lower vertebrates, including zebrafish (Danio rerio), have the ability to regenerate damaged or lost tissues, such as the caudal fin, which makes them an ideal model for tissue and organ regeneration studies. Since several diseases involve the process of transition between fibrosis and tissue regeneration, it is necessary to attain a better understanding of these processes. It is known that the cells of the immune system, especially macrophages, play essential roles in regeneration by participating in the removal of cellular debris, release of pro- and anti-inflammatory factors, remodeling of components of the extracellular matrix and alteration of oxidative patterns during proliferation and angiogenesis. Immune cells undergo phenotypical and functional alterations throughout the healing process due to growth factors and cytokines that are produced in the tissue microenvironment. However, some aspects of the molecular mechanisms through which macrophages orchestrate the formation and regeneration of the blastema remain unclear. In the present review, we outline how macrophages orchestrate the regenerative process in zebrafish and give special attention to the redox balance in the context of tail regeneration.

Augmenter of liver regeneration protects the kidney from ischaemia-reperfusion injury in ferroptosis

Acute kidney injury (AKI) is a common and severe clinical condition with high morbidity and mortality. Ischaemia‐reperfusion (I/R) injury remains the major cause of AKI in the clinic. Ferroptosis is a recently discovered form of programmed cell death (PCD) that is characterized by iron‐dependent accumulation of reactive oxygen species (ROS). Compelling evidence has shown that renal tubular cell death involves ferroptosis, although the underlying mechanisms remain unclear. Augmenter of liver regeneration (ALR) is a widely distributed multifunctional protein that is expressed in many tissues. Our previous study demonstrated that ALR possesses an anti‐oxidant function. However, the modulatory mechanism of ALR remains unclear and warrants further investigation. Here, to elucidate the role of ALR in ferroptosis, ALR expression was inhibited using short hairpin RNA lentivirals (shRNA) in vitro model of I/R‐induced AKI. The results suggest that the level of ferroptosis is increased, particularly in the shRNA/ALR group, accompanied by increased ROS and mitochondrial damage. Furthermore, inhibition of system xc‐ with erastin aggravates ferroptosis, particularly silencing of the expression of ALR. Unexpectedly, we demonstrate a novel signalling pathway of ferroptosis. In summary, we show for the first time that silencing ALR aggravates ferroptosis in an in vitro model of I/R. Notably, we show that I/R induced kidney ferroptosis is mediated by ALR, which is linked to the glutathione‐glutathione peroxidase (GSH‐GPx) system.

The impact of steatosis on liver regeneration

Alcoholic and non-alcoholic fatty liver diseases are the leading causes of cirrhosis in Western countries. These chronic liver diseases share common pathological features ranging from steatosis to steatohepatitis. Fatty liver is associated with primary liver graft dysfunction, a higher incidence of complications/mortality after surgery, in correlation with impaired liver regeneration. Liver regeneration is a multistep process including a priming phase under the control of cytokines followed by a growth factor receptor activation phase leading to hepatocyte proliferation. This process ends when the initial liver mass is restored. Deficiency in epidermal growth factor receptor (EGFR) liver expression, reduced expression of Wee1 and Myt1 kinases, oxidative stress and alteration in hepatocyte macroautophagy have been identified as mechanisms involved in the defective regeneration of fatty livers. Besides the mechanisms, we will also discuss in this review various treatments that have been investigated in the reversal of the regeneration defect, for example, omega-3 fatty acids, pioglitazone, fibroblast growth factor (FGF)19-based chimeric molecule or growth hormone (GH). Since dysbiosis impedes liver regeneration, targeting microbiota could also be an interesting therapeutic approach.