Interleukin 6 is important for survival after partial hepatectomy in mice

The response to partial hepatectomy (PH) is impaired in interleukin 6 (IL-6)-deficient mice. IL-6 is well known for its role in the induction of the acute phase (AP) response, and the impairment of this response after surgery and hepatectomy could explain the defective hepatocyte regeneration. In addition, it was proposed that IL-6 has an important role in stimulating the reentry of quiescent cells into the cell cycle within the first 2 to 4 hours after PH. To further analyze the role for IL-6, we performed two third hepatectomies in wild-type mice, in IL-6 knockout (KO) mice, and in IL-6 KO mice that were treated 30 minutes before surgery with intravenous (IV) (short acting) or subcutaneous (SC) (long acting) injections of recombinant IL-6. The high postoperative mortality of IL-6-deficient mice could be completely prevented by SC, but not by IV IL-6 treatment, showing the requirement of a sustained action of IL-6. However, there is a subset of IL-6 KO mice that survives a PH in good health even without IL-6 treatment. When we analyzed these mice, we found an intact liver regeneration and no indication of a block in cell cycle reentry. We conclude that the major role of IL-6 is the induction of an adaptive response to PH that ensures body homeostasis and survival.     

Contribution of Toll-like receptor/myeloid differentiation factor 88 signaling to murine liver regeneration

Toll-like receptors (TLRs) act as innate immune signal sensors and play central roles in host defense. Myeloid differentiation factor (MyD) 88 is a common adaptor molecule required for signaling mediated by TLRs. When the receptors are activated, cells bearing TLRs produce various proinflammatory cytokines in a MyD88-dependent manner. Liver regeneration following partial hepatectomy (PH) requires innate immune responses, particularly interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-alpha) production by Kupffer cells, although the recognition and activation processes are still unknown. We investigated whether TLR/MyD88 signaling is critical for induction of innate immune responses after PH. In Myd88(-/-) mice after PH, induction of expression of immediate early genes involved in hepatocyte replication and phosphorylation of STAT3 in the liver, and production of TNF-alpha/IL-6 by and activation of NF-kappaB in the Kupffer cells were grossly subnormal and were associated with impaired liver regeneration. However, TLR2, 4 and 9, which recognize gram-negative and -positive bacterial products, are not essential for NF-kappaB activation and IL-6 production after PH, which excludes a possible contribution of TLR2/TLR4 or TLR9 to MyD88-mediated pathways. In conclusion, the TLR/MyD88 pathway is essential for incidental liver restoration, particularly its early phase.     

Demonstration of cooperative contribution of MET- and EGFR-mediated STAT3 phosphorylation to liver regeneration by exogenous suppressor of cytokine signalings

BACKGROUND/AIMS: As conditional knockout mice for stat3 are impaired in liver regeneration after partial hepatectomy while those for gp130 have defects in early STAT3 phosphorylation but have normal DNA synthesis, late STAT3 phosphorylation induced independently of gp130 seems to be essential for liver regeneration. Since HGF and EGF can activate STAT3 via gp130-independent MET and EGFR, respectively, we assumed that these factors account for STAT3-dependent liver regeneration. Here, we investigated this hypothesis by introducing suppressor of cytokine signaling (SOCS)-1 and SOCS3, potent negative regulators of STAT3 signaling, selectively in hepatocytes. METHODS: We generated recombinant adenoviruses expressing socs1 and socs3. RESULTS: Hepatocytes infected with socs1-virus lacked STAT3 phosphorylation in response to IL-6 and HGF, while cells infected with socs3-virus lacked the response to all of IL-6, HGF and EGF, indicating that those SOCS proteins differently regulate EGFR signaling. Mice infected with socs3-virus exhibited severe and persistent impairment while those with socs1-virus showed only delayed regeneration, indicating requirement of both MET and EGFR signalings. CONCLUSIONS: These results clearly demonstrated that MET- and EGFR-mediated STAT3 signalings cooperatively contribute to liver regeneration and could provide new insights into tissue homeostasis.     

Delayed liver regeneration in peroxisome proliferator-activated receptor-alpha-null mice

Peroxisome proliferator chemicals, acting via the peroxisome proliferator-activated receptor-alpha (Pparalpha), are potent hepatic mitogens and carcinogens in mice and rats. To test whether Pparalpha is required for hepatic growth in response to other stimuli, we studied liver regeneration and hepatic gene expression following partial hepatectomy (PH) of wild-type and Pparalpha-null mice. Pparalpha-null mice had a 12- to 24-hour delay in liver regeneration associated with a delayed onset and lower peak magnitude of hepatocellular DNA synthesis. Furthermore, these mice had a 24-hour lag in the hepatic expression of the G(1)/S checkpoint regulator genes Ccnd1 and cMyc and increased expression of the IL-1beta cytokine gene. Hepatic expression of Ccnd1, cMyc, IL-1r1, and IL-6r was induced in wild-type mice, but not Pparalpha-null mice, after acute exposure to the potent Pparalpha agonist Wy-14,643, indicating a role for Pparalpha in regulating the expression of these genes. Expression of the fatty acid omega-hydroxylase gene Cyp4a14, a commonly used indicator gene for Pparalpha activation, was strongly induced in wild-type mice after hepatectomy, suggesting that altered hepatocyte lipid processing may also contribute to the impaired regeneration in mice lacking the Pparalpha gene. In conclusion, liver regeneration in Pparalpha-null mice is transiently impaired and is associated with altered expression of genes involved in cell cycle control, cytokine signaling, and fat metabolism.     

STAT3 signaling within hepatocytes is required for anemia of inflammation in vivo

Background

Anemia of inflammation, commonly observed in patients with chronic diseases, is associated with decreased serum iron. Hepcidin, mainly produced by hepatocytes in a STAT3- and/or SMAD-dependent manner, is involved in iron homeostasis. What remains to be established is whether or not the hepatic IL-6/STAT3 signal has a role in anemia of inflammation in vivo.

Methods

Turpentine oil was subcutaneously injected into wild-type mice or hepatocyte-specific STAT3-deficient mice (L-STAT3KO) to induce inflammation.

Results

Turpentine injection increased serum IL-6 levels. It activated liver STAT3 in wild-type mice, but not in L-STAT3KO mice. In chronic inflammation, wild-type mice showed decreased serum iron levels and anemia with up-regulation of hepcidin levels in the liver. In contrast, L-STAT3KO mice showed no increase in hepatic hepcidin levels or anemia.

Conclusions

Liver STAT3 is critically involved in the development of anemia of inflammation via the expression of hepcidin. The liver regulates anemia of inflammation through STAT3 signaling.     

Hepatocyte proliferation and tissue remodeling is impaired after liver injury in oncostatin M receptor knockout mice

Oncostatin M (OSM) is a member of the IL-6 family of cytokines. Mice deficient in the OSM receptor (OSMR(-/-)) showed impaired liver regeneration with persistent parenchymal necrosis after carbon tetrachloride (CCl(4)) exposure. The recovery of liver mass from partial hepatectomy was also significantly delayed in OSMR(-/-) mice. In contrast to wildtype mice, CCl(4) administration only marginally induced expression of tissue inhibitor of metalloproteinase (TIMP)-1 and TIMP-2 genes in OSMR(-/-) mice, correlating with the increased gelatinase activity of matrix metalloproteinase (MMP)-9 and matrix degradation in injured livers. The activation of STAT3 and expression of immediate early genes and cyclins were decreased in OSMR(-/-) liver, indicating that OSM signaling is required for hepatocyte proliferation and tissue remodeling during liver regeneration. We also found that CCl(4) administration in IL-6(-/-) mice failed to induce OSM expression and that OSM administration in IL-6(-/-) mice after CCl(4) injection induced the expression of cyclin D1 and proliferating cell nuclear antigen, suggesting that OSM is a key mediator of IL-6 in liver regeneration. Consistent with these results, administration of OSM ameliorated liver injury in wildtype mice by preventing hepatocyte apoptosis as well as tissue destruction. In conclusion, OSM and its signaling pathway may provide a useful therapeutic target for liver regeneration.     

CEBPs及其调节的基因与大鼠肝再生相关性分析

目的:探讨基因转录水平CCAAT增强子结合蛋白(CEBPs)及其调节基因在肝再生(LR)中的作用.方法:将与肝再生相关的CEBPs家族转录因子输入NCBI(www.ncbi.nlm.nih.gov)和RGD(rgd.mcw.edu)等网站查找与其转录功能相关的文献,从中得出大鼠、小鼠和人的CEBPs家族下游基因.然后将人和小鼠基因与大鼠比对,筛选出与大鼠不重复的人和小鼠基因.再将他们与Rat Genome 230 2.0芯片的检测结果进行比对确认,把其中表达上调或下调2倍以上的基因视为有意义变化的大鼠同源基因.用Rat Genome 230 2.0芯片检测他们在大鼠再生肝中的表达情况,用真、假手术比较方法确定肝再生相关基因.结果:27个基因与肝再生相关,其中11个基因表达上调,6个基因表达下调,10个基因在有的时点表达上调,有的时点表达下调(简称上/下调表达).他们的上调范围为对照的2-128倍,下调范围为对照的2-16倍.肝再生启动[部分肝切除(PH)后0.5-4 h]、G_0/G_1过渡(PH后4-6 h)、细胞增殖(PH后6-66 h)、细胞分化和组织结构功能重建(PH后72-168 h)等4个阶段起始表达的基因数分别为18,3,8和1;基因的总表达次数分别为18,11,25和16.表明相关基因主要在肝再生启动阶段起始表达,在不同阶段发挥作用.他们共表达上调126次,下调76次.表明肝再生中表达上调基因多于表达下调基因.结论:CEBPs及其调节的基因与肝再生中细胞增殖、细胞分化、细胞凋亡、炎症反应、应激反应、脂类代谢和细胞外基质变化等密切相关.     

Reg2 inactivation increases sensitivity to Fas hepatotoxicity and delays liver regeneration post-hepatectomy in mice

Reg2/RegIIIbeta is the murine homologue of the human secreted HIP/PAP C-type lectin. HIP/PAP transgenic mice were protected against acetaminophen-induced acute liver failure and were stimulated to regenerate post-hepatectomy. To assess the role of Reg2, we used Reg2-/- mice in a model of fulminant hepatitis induced by Fas and in the post-hepatectomy regeneration. Within 4 hours of J0-2 treatment (0.5 microg/g), only 50% of the Reg2-/- mice were alive but with an increased sensitivity to Fas-induced oxidative stress and a decreased level of Bcl-xL. In contrast, HIP/PAP transgenic mice were resistant to Fas, with HIP/PAP serving as a sulfhydryl buffer to slow down decreases in glutathione and Bcl-xL. In Reg2-/- mice, liver regeneration was markedly impaired, with 29% mortality and delay of the S-phase and the activation of ERK1/2 and AKT. Activation of STAT3 began on time at 3 hours but persisted strongly up to 72 hours despite significant accumulation of SOCS3. Thus, Reg2 deficiency induced exaggerated IL-6/STAT-3 activation and mito-inhibition. Because the Reg2 gene was activated between 6 and 24 hours after hepatectomy in wild-type mice, Reg2 could mediate the TNF-alpha/IL-6 priming signaling by exerting a negative feed-back on STAT3/IL-6 activation to allow the hepatocytes to progress through the cell cycle. In conclusion, Reg2 deficiency enhanced liver sensitivity to Fas-induced oxidative stress and delayed liver regeneration with persistent TNF-alpha/IL6/STAT3 signaling. In contrast, overexpression of human HIP/PAP promoted liver resistance to Fas and accelerated liver regeneration with early activation/deactivation of STAT3. Reg2/HIP/PAP is therefore a critical mitogenic and antiapoptotic factor for the liver.     

Expression patterns and action analysis of genes associated with blood coagulation responses during rat liver regeneration

INTRODUCTION The liver is the main site where coagulation factors are synthesized[1]. Tissue damage is often companied with angiorrhexis, bleeding and blood coagulation. Blood coagulation is a complex hemostatic process in which zymogens convert into coag…     

Expression pattern and action analysis of genes associated with the responses to chemical stimuli during rat liver regeneration

INTRODUCTION The liver has tremendous capacity to regenerate itself[1,2]. Liver cells proliferate rapidly to compensate the lost liver tissues after liver injury or chemical stimulus, which is called liver regeneration (LR)[1,3]. Generally, based on the c…     

CXCL10 regulates liver innate immune response against ischemia and reperfusion injury

We have shown that activation of toll-like receptor 4 (TLR4) and its interferon regulatory factor 3 (IRF3)-dependent downstream signaling pathway are required for the development of liver ischemia/reperfusion injury (IRI). This study focused on the role of TLR4-IRF3 activation pathway products, in particular, chemokine (C-X-C motif) ligand 10 (CXCL10). The induction of CXCL10 by liver IR was rapid (1 hour postreperfusion), restricted (ischemic lobes), and specific (no CXCL9 and CXCL11 induction). Functionally, CXCL10 was critical for IR-induced liver inflammation and hepatocellular injury. CXCL10 knockout (KO) mice were protected from IRI, as evidenced by reduced serum alanine aminotransferase (sALT) levels and preserved liver histological detail. The induction of pro-inflammatory genes, such as tumor necrosis factor alpha (TNF-alpha), interleukin 1beta (IL-1beta), IL-6, and IL-12beta was diminished, whereas the induction of the IL-10 gene remained intact in CXCL10 KO mice, indicating an altered liver response against IR. This was accompanied by selective down-regulation of extracellular signal-regulated kinase (ERK), but intact Jun N-terminal kinase (JNK), activation in the KO IR livers. This altered liver inflammation response was (1) specific to IR, because lipopolysaccharide (LPS) induced a comparable pro-inflammatory response in CXCL10 KO and wild-type (WT) mice; and (2) responsible for liver cytoprotection from IR, because neutralization of IL-10 restored local inflammation and hepatocellular damage. Conclusion: CXCL10 regulates liver inflammation response against IRI, and its deficiency protected livers from IRI by local IL-10-mediated cytoprotection. Targeting CXCL10 may provide a novel therapeutic means to ameliorate liver IRI in clinics.