Augmenter of liver regeneration promotes hepatic regeneration depending on the integrity of Kupffer cell in rat small-for-size liver transplantation

Immunological mechanisms and emerging therapeutic targets in alcohol-associated liver disease

Alcohol-associated liver disease (ALD) is a major global health challenge, with inflammation playing a central role in its progression. As inflammation emerges as a critical therapeutic target, ongoing research aims to unravel its underlying mechanisms. This review explores the immunological pathways of ALD, highlighting the roles of immune cells and their inflammatory mediators in disease onset and progression. We also examine the complex interactions between inflammatory cells and non-parenchymal liver cells, as well as their crosstalk with extra-hepatic organs, including the gut, adipose tissue, and nervous system. Furthermore, we summarize current clinical research on anti-inflammatory therapies and discuss promising therapeutic targets. Given the heterogeneity of ALD-associated inflammation, we emphasize the need for precision medicine to optimize treatment strategies and improve patient outcomes.

Kupffer cells, the limelight in the liver regeneration

Kupffer cells are pivotal in initiating hepatocyte proliferation and establishing connections between different cell types during liver regeneration following partial hepatectomy. As resident macrophages within the liver, Kupffer cells collaborate with hepatocytes and non-parenchymal cells to release various inflammatory mediators that promote hepatocyte proliferation through induction signals like STAT3 phosphorylation. Additionally, the regeneration and replenishment of Kupffer cells themselves are integral components of liver regeneration. The supplementation of the Kupffer cell pool primarily occurs through two pathways: one involves local proliferation of Kupffer cells in their original location, while the other entails infiltration of circulating monocytes into the liver, followed by acquiring Kupffer cell phenotypes under the combined influence of multiple inducing factors. Extensive research has focused on intercellular crosstalk among various types of liver cells during liver regeneration, highlighting the crucial role played by Kupffer cells. This article aims to introduce Kupffer cells and their involvement in liver regeneration, as well as discuss the steady-state balance of Kupffer cell pools during this process.

RegⅢγ promotes the proliferation, and inhibits inflammation response of macrophages by Akt, STAT3 and NF-κB pathways

As an inflammatory regulator, intestinal regenerating islet-derived 3 gamma (RegⅢγ) contributes to alleviating liver injury in liver diseases and colitis. However, it is unclear whether hepatic RegⅢγ exerts a vital impact on liver regeneration (LR). In this study, the expression profile and localization of RegⅢγ in LR were demonstrated by microarray analysis, qRT-PCR and immunofluorescence staining. Then, RAW264.7 cells with RegⅢγ deficiency and overexpression were obtained by the CRISPR/Cas9 system and lentivirus infection, respectively. MTT, flow cytometry, EdU, transwell, neutral red phagocytosis, and NO assays were performed to detect the functions of RegⅢγ in RAW264.7 cell proliferation and inflammation. Finally, the regulatory mechanism of RegⅢγ was explored by co-immunoprecipitation and Western blot assays. According to our findings, RegⅢγ showed significant expression changes in Kupffer cells during LR, and RegⅢγ overexpression stimulated the viability, proliferation, phagocytosis and migration of RAW264.7 cells, whereas RegⅢγ deficiency reversed these effects. Similarly, RegⅢγ overexpression facilitated the expression of HO-1 and IL-10, while RegⅢγ deficiency promoted NO production and p-Akt, p-STAT3, p-p65 and TNF-α expression. In conclusion, RegⅢγ may facilitate LR by promoting the proliferation of macrophages and inhibiting their inflammatory response through Akt, STAT3 and NF-κB pathways in the priming stage of LR.

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.

Targeting inflammation for the treatment of alcoholic liver disease

Alcoholic liver disease (ALD) is a leading cause of chronic liver disease with a wide spectrum of manifestations including simple steatosis to steatohepatitis, cirrhosis, and hepatocellular carcinoma. Liver injury in ALD is caused by chronic inflammation, which has been actively investigated as a therapeutic target for the treatment of ALD for over the last four decades. In this review, we summarize a wide variety of inflammatory mediators that have been shown to contribute to the pathogenesis of ALD, and discuss the therapeutic potential of these mediators for the treatment of ALD.

Immune cells in liver regeneration

After partial hepatectomy, hepatocytes proliferate to restore mass and function of the liver. Macrophages, natural killer (NK) cells, natural killer T (NKT) cells, dendritic cells (DC), eosinophils, gamma delta T (γδT) cells, and conventional T cells, as well as other subsets of the immune cells residing in the liver control liver regeneration, either through direct interactions with hepatocytes or indirectly by releasing inflammatory cytokines. Here, we review recent progress regarding the immune cells in the liver and their functions during liver regeneration.

Down-Regulated Receptor Interacting Protein 140 Is Involved in Lipopolysaccharide-Preconditioning-Induced Inactivation of Kupffer Cells and Attenuation of Hepatic Ischemia Reperfusion Injury

Background

Lipopolysaccharide (LPS) preconditioning is known to attenuate hepatic ischemia/reperfusion injury (I/RI); however, the precise mechanism remains unclear. This study investigated the role of receptor-interacting protein 140 (RIP140) on the protective effect of LPS preconditioning in hepatic I/RI involving Kupffer cells (KCs).

Methods

Sprague—Dawley rats underwent 70% hepatic ischemia for 90 minutes. LPS (100 μg/kg) was injected intraperitoneally 24 hours before ischemia. Hepatic injury was observed using serum and liver samples. The LPS/NF-κB (nuclear factor-κB) pathway and hepatic RIP140 expression in isolated KCs were investigated.

Results

LPS preconditioning significantly inhibited hepatic RIP140 expression, NF-κB activation, and serum proinflammatory cytokine expression after I/RI, with an observation of remarkably reduced serum enzyme levels and histopathologic scores. Our experiments showed that protection effects could be effectively induced in KCs by LPS preconditioning, but couldn’t when RIP140 was overexpressed in KCs. Conversely, even without LPS preconditioning, protective effects were found in KCs if RIP140 expression was suppressed with siRNA.

Conclusions

Down-regulated RIP140 is involved in LPS-induced inactivation of KCs and hepatic I/RI attenuation.

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 Role of IL-1 Family Members and Kupffer Cells in Liver Regeneration

Interleukin-1 (IL-1) family and Kupffer cells are linked with liver regeneration, but their precise roles remain unclear. IL-1 family members are pleiotropic factors with a range of biological roles in liver diseases, inducing hepatitis, cirrhosis, and hepatocellular carcinoma, as well as liver regeneration. Kupffer cells are the main source of IL-1 and IL-1 receptor antagonist (IL-1Ra), the key members of IL-1 family. This systemic review highlights a close association of IL-1 family members and Kupffer cells with liver regeneration, although their specific roles are inconclusive. Moreover, IL-1 members are proposed to induce effects on liver regeneration through Kupffer cells.

Stereological assessment of sexual dimorphism in the rat liver reveals differences in hepatocytes and Kupffer cells but not hepatic stellate cells

There is long-standing evidence that male and female rat livers differ in enzyme activity. More recently, differences in gene expression profiling have also been found to exist; however, it is still unclear whether there is morphological expression of male/female differences in the normal liver. Such differences could help to explain features seen at the pathological level, such as the greater regenerative potential generally attributed to the female liver. In this paper, hepatocytes (HEP), Kupffer cells (KC) and hepatic stellate cells (HSC) of male and female rats were examined to investigate hypothesised differences in number, volume and spatial co-localisation of these cell types. Immunohistochemistry and design-based stereology were used to estimate total numbers, numbers per gram and mean cell volumes. The position of HSC within lobules (periportal vs. centrilobular) and their spatial proximity to KC was also assessed. In addition, flow cytometry was used to investigate the liver ploidy. In the case of HEP and KC, differences in the measured cell parameters were observed between male and female specimens; however, no such differences were detected for HSC. Female samples contained a higher number of HEP per gram, with more binucleate cells. The HEP nuclei were smaller in females, which was coincident with more abundant diploid particles in these animals. The female liver also had a greater number of KC per gram, with a lower percentage of KC in the vicinity of HSC compared with males. In this study, we document hitherto unknown morphological sexual dimorphism in the rat liver, namely in HEP and KC. These differences may account for the higher regenerative potential of the female liver and lend weight to the argument for considering the rat liver as a sexually dimorphic organ.

Improving Research Practice in Rat Orthotopic and Partial Orthotopic Liver Transplantation: A Review, Recommendation, and Publication Guide

Background: Due to a worldwide shortage of donor organs for liver transplantation, alternative approaches, such as split and living donor liver transplantations, were introduced to increase the donor pool and reduce mortality on liver transplant waiting lists. Numerous details concerning the mechanisms and pathophysiology of liver regeneration, small-for-size syndrome, rejection, and tolerance in partial liver transplantation facilitated the development of various animal models. The high number of preclinical animal studies contributed enormously to our understanding of many clinical aspects of living donor and partial liver transplantations. Summary: Microsurgical rat models of partial orthotopic liver transplantation are well established and widely used. Nevertheless, several issues regarding this procedure are controversial, not clarified, or not yet properly standardized (graft rearterialization, size reduction techniques, etc.). The major aim of this literature review is to give the reader a current overview of rat orthotopic liver transplantation models with a special focus on partial liver transplantation. The aspects of model evolution, microsurgical training, and different technical problems are analyzed and discussed in detail. Our further aim in this paper is to elaborate a detailed publication guide in order to improve the quality of reporting in the field of rat liver transplantation according to the ARRIVE guidelines and the 3R principle. Key Messages: Partial orthotopic liver transplantation in rats is an indispensable, reliable, and cost-efficient model for transplantation research. A certain consensus on different technical issues and a significant improvement in scientific reporting are essential to improve transparency and comparability in this field as well as to foster refinement.

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.

Augmenter of liver regeneration attenuates inflammation of renal ischemia/reperfusion injury through the NF-kappa B pathway in rats

PURPOSE

The effects of augmenter of liver regeneration (ALR) on the acute kidney injury (AKI) rats were investigated by measuring the inflammatory response associated with transcription factor nuclear factory (NF-κB) pathway.

METHODS

The model of AKI rats was established by occluded the renal pedicles for 60 min and then released. After that, animals were treated with ALR (100 or 200 μg/kg). All rats were killed at different time points (24, 48, 72 h). Renal function and kidney histological changes were measured. The apoptosis of tubular cells was evaluated by TdT-mediated dUTP nick end labeling assay. Cytokines and chemokines were assessed by immunohistochemistry, enzyme-linked immunosorbent assay and real-time polymerase chain reaction (RT-PCR). The NF-κB p65 protein was analyzed by immunohistochemistry and RT-PCR, respectively.

RESULTS

Ischemia reperfusion induced tubular cells necrosis and apoptosis, and ALR can significantly reduce this damages. The productions of MCP-1, IL-1β and IL-6 were lower in the group of ALR treatment, especially in the high-dose group. The inflammatory infiltrates were lower in the rats with administration of ALR. ALR mediated the level of cytokines and chemokines through inhibited the activation of NF-κB.

CONCLUSION

ALR can improve renal function and inhibit the expression of inflammatory factors. This protects against renal ischemia reperfusion injury, which may be associated with preventing NF-κB activation in rats.

Blockade of the apelin-APJ system promotes mouse liver regeneration by activating Kupffer cells after partial hepatectomy

BACKGROUND

Liver regeneration after massive hepatectomy or living donor liver transplantation is critical. The apelin-APJ system is involved in the regulation of cardiovascular function, inflammation, fluid homeostasis, the adipo-insular axis, and angiogenesis, but its function in liver regeneration remains unclear.

METHODS

We investigated the impact of pharmacologic blockade of the apelin-APJ system, using the specific APJ antagonist F13A on liver regeneration after hepatectomy in mice.

RESULTS

F13A-treated mice had significantly higher serum concentrations of tumor necrosis factor (TNF)-α and interleukin (IL)-6 than control mice, due to F13A-promoted activation of Kupffer cells. Compared with untreated mice, F13A enhanced the signal transducer and activator of transcription 3 and mitogen-activated protein kinase pathways, stimulated cell-cycle progression, and promoted hepatocyte proliferation and liver regeneration without inducing apoptosis or inflammation in regenerating livers. In vitro, Kupffer cells expressed APJ and were activated directly by F13A treatment, releasing TNF-α and IL-6. Moreover, F13A-treated mice had a higher survival rate than untreated mice in the extended hepatectomy model.

CONCLUSIONS

F13A treatment promotes early phase liver regeneration after hepatectomy by promoting the activation of Kupffer cells and increasing serum levels of TNF-α and IL-6. F13A treatment may become a therapeutic option to facilitate efficient liver regeneration after liver surgery.

Chronological changes in the liver after temporary partial portal venous occlusion

AIM: To investigate time-dependent changes caused by temporal portal vein obstruction and subsequent reperfusion in the lobe with or without an occluded portal vein.

METHODS: The portal vein (PV) of the anterior lobe of the liver of a male Wistar rat (8 wk-old) was obstructed (70%) for 12, 24, 36 and 48 h, respectively, and models were sacrificed at 48 h after reperfusion (each group: n = 10). The histological changes and the status of liver regeneration were compared between a liver biopsy performed on each lobe after temporary obstruction of the portal vein in the same rat liver, and the liver extracted at the time of sacrifice (48 h after reperfusion).

RESULTS: With regard to the obstructed lobe, the liver weight/body weight ratio significantly decreased according to obstruction time. On the other hand, in the non-obstructed lobe, there were no significant differences within each group. The duration of PV occlusion did not seem to be strong enough to introduce liver weight increase. Stimulation of liver regeneration was brought about in the non-occluded lobe by 12-h occlusion, and was sustained even at 48 h after reperfusion. The obstructed lobe atrophied with the passage of time in the obstructed state. However, the proliferating-cell nuclear antigen labeling index also increased at 48 h after reperfusion, and a repair mechanism was observed.

CONCLUSION: Temporary blood flow obstruction of the portal vein may become a significant trigger for liver regeneration, even with an obstruction of 12 h.