Simvastatin augments activation of liver regeneration through attenuating transforming growth factor-β1 induced-apoptosis in obstructive jaundice rats

Signaling pathways of liver regeneration: Biological mechanisms and implications

The liver possesses a unique regenerative ability to restore its original mass, in this regard, partial hepatectomy (PHx) and partial liver transplantation (PLTx) can be executed smoothly and safely, which has important implications for the treatment of liver disease. Liver regeneration (LR) can be the very complicated procedure that involves multiple cytokines and transcription factors that interact with each other to activate different signaling pathways. Activation of these pathways can drive the LR process, which can be divided into three stages, namely, the initiation, progression, and termination stages. Therefore, it is important to investigate the pathways involved in LR to elucidate the mechanism of LR. This study reviews the latest research on the key signaling pathways in the different stages of LR.

The roles of the glucagon-like peptide-2 and the serum TGF-β1 levels in the intestinal barrier and immune functions in rats with obstructive jaundice

OBJECTIVE

To determine the mechanisms by which glucagon-like peptide-2 (GLP-2) impacts the intestinal barrier function, the immune function, and the serum transforming growth factor-β1 (TGF-β1) levels in rats with obstructive jaundice.

METHODS

Overall, 72 SPF-grade healthy Wistar rats were randomly divided into 4 groups containing 18 rats each: the observation group (ligation of common bile duct, intraperitoneal GLP-2 injection), the control group (ligation of common bile duct, normal saline), the sham-operated group (common bile duct exposed without ligation, normal saline), and the blank group. The serum immune function and the TGF-β1 levels were measured on days 3, 7, and 14 after the intervention.

RESULTS

The body mass was determined to be significantly less in the control group than in the other three groups on day 14 after the intervention (P < 0.05). The TGF-β1, endotoxin, alanine aminotransferase (ALT), and bilirubin were expressed at significantly higher levels in the control group compared with the blank and sham-operated groups and were the highest at each time point, but the levels in the observation group were significantly decreased after the intervention (P < 0.05).

CONCLUSIONS

We found that GLP-2 can decrease the serum TGF-β1 levels, regulate the immune function, reduce the endotoxin and bilirubin, and protect the intestinal barrier function in rats with obstructive jaundice.

Liver regeneration and inflammation: from fundamental science to clinical applications

Liver regeneration is a complex process involving the crosstalk of multiple cell types, including hepatocytes, hepatic stellate cells, endothelial cells and inflammatory cells. The healthy liver is mitotically quiescent, but following toxic damage or resection the cells can rapidly enter the cell cycle to restore liver mass and function. During this process of regeneration, epithelial and non-parenchymal cells respond in a tightly coordinated fashion. Recent studies have described the interaction between inflammatory cells and a number of other cell types in the liver. In particular, macrophages can support biliary regeneration, contribute to fibrosis remodelling by repressing hepatic stellate cell activation and improve liver regeneration by scavenging dead or dying cells in situ. In this Review, we describe the mechanisms of tissue repair following damage, highlighting the close relationship between inflammation and liver regeneration, and discuss how recent findings can help design novel therapeutic approaches.

Dexmedetomidine activates the PI3K/Akt pathway to inhibit hepatocyte apoptosis in rats with obstructive jaundice

Obstructive jaundice (OJ) is a common disease in clinical surgery. The present study aimed to determine the effects of dexmedetomidine (Dex) on hepatocyte apoptosis in rats with OJ and also to explore the underlying mechanism. A total of 30 adult male Sprague Dawley rats were randomly divided into 3 groups: Sham group, bile duct ligation (BDL) group, and BDL+Dex group. The serum liver function index, expression levels of serum inflammatory factor interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α), and the liver pathological changes were compared amongst groups. The serum liver function index and expression levels of inflammatory factors in the BDL group and BDL+Dex group were higher compared with the sham group. The serum liver function index and expression levels of inflammatory factors were lower in the BDL+Dex group compared with the BDL group. The severity of hepatic injury was diminished in the BDL+Dex group compared with the BDL group. Compared with the sham group, the hepatocyte apoptosis rate increased significantly in the BDL group and BDL+Dex group. The present findings suggested that Dex improved the liver function of rats with OJ, reduced the production of inflammatory factors and inhibited the apoptosis of hepatocytes. Dex demonstrated a protective effect on liver damage potentially via activation of the phosphoinositide 3-kinase/protein kinase B signaling pathway.

Elevated circulating TGFβ1 during acute liver failure activates TGFβR2 on cortical neurons and exacerbates neuroinflammation and hepatic encephalopathy in mice

BACKGROUND

Acute liver failure resulting from drug-induced liver injury can lead to the development of neurological complications called hepatic encephalopathy (HE). Hepatic transforming growth factor beta 1 (TGFβ1) is upregulated due to liver failure in mice and inhibiting circulating TGFβ reduced HE progression. However, the specific contributions of TGFβ1 on brain cell populations and neuroinflammation during HE are not known. Therefore, the aim of this study was to characterize hepatic and brain TGFβ1 signaling during acute liver failure and its contribution to HE progression using a combination of pharmacological and genetic approaches.

METHODS

C57Bl/6 or neuron-specific transforming growth factor beta receptor 2 (TGFβR2) null mice (TGFβR2^ΔNeu) were treated with azoxymethane (AOM) to induce acute liver failure and HE. The activity of circulating TGFβ1 was inhibited in C57Bl/6 mice via injection of a neutralizing antibody against TGFβ1 (anti-TGFβ1) prior to AOM injection. In all mouse treatment groups, liver damage, neuroinflammation, and neurological deficits were assessed. Inflammatory signaling between neurons and microglia were investigated in in vitro studies through the use of pharmacological inhibitors of TGFβ1 signaling in HT-22 and EOC-20 cells.

RESULTS

TGFβ1 was expressed and upregulated in the liver following AOM injection. Pharmacological inhibition of TGFβ1 after AOM injection attenuated neurological decline, microglia activation, and neuroinflammation with no significant changes in liver damage. TGFβR2^ΔNeu mice administered AOM showed no effect on liver pathology but significantly reduced neurological decline compared to control mice. Microglia activation and neuroinflammation were attenuated in mice with pharmacological inhibition of TGFβ1 or in TGFβR2^ΔNeu mice. TGFβ1 increased chemokine ligand 2 (CCL2) and decreased C-X3-C motif ligand 1 (CX3CL1) expression in HT-22 cells and reduced interleukin-1 beta (IL-1ß) expression, tumor necrosis factor alpha (TNFα) expression, and phagocytosis activity in EOC-20 cells.

CONCLUSION

Increased circulating TGFβ1 following acute liver failure results in activation of neuronal TGFβR2 signaling, driving neuroinflammation and neurological decline during AOM-induced HE.