Kuppfer Cells Trigger Nonalcoholic Steatohepatitis Development in Diet-induced Mouse Model through Tumor Necrosis Factor-α Production

Nonalcoholic steatohepatitis (NASH), characterized by lipid deposits within hepatocytes (steatosis), is associated with hepatic injury and inflammation and leads to the development of fibrosis, cirrhosis, and hepatocarcinoma. However, the pathogenic mechanism of NASH is not well understood. To determine the role of distinct innate myeloid subsets in the development of NASH, we examined the contribution of liver resident macrophages (i.e. Kupffer cells) and blood-derived monocytes in triggering liver inflammation and hepatic damage. Employing a murine model of NASH, we discovered a previously unappreciated role for TNFα and Kupffer cells in the initiation and progression of NASH. Sequential depletion of Kupffer cells reduced the incidence of liver injury, steatosis, and proinflammatory monocyte infiltration. Furthermore, our data show a differential contribution of Kupffer cells and blood monocytes during the development of NASH; Kupffer cells increased their production of TNFα, followed by infiltration of CD11b^intLy6C^hi monocytes, 2 and 10 days, respectively, after starting the methionine/choline-deficient (MCD) diet. Importantly, targeted knockdown of TNFα expression in myeloid cells decreased the incidence of NASH development by decreasing steatosis, liver damage, monocyte infiltration, and the production of inflammatory chemokines. Our findings suggest that the increase of TNFα-producing Kupffer cells in the liver is crucial for the early phase of NASH development by promoting blood monocyte infiltration through the production of IP-10 and MCP-1.     

Pioglitazone prevents hepatic steatosis, fibrosis, and enzyme-altered lesions in rat liver cirrhosis induced by a choline-deficient L-amino acid-defined diet

Non-alcoholic steatohepatitis (NASH) may progress to liver cirrhosis, and NASH patients with liver cirrhosis have a risk of development of hepatocellular carcinoma. Peroxisome proliferator-activated receptor (PPAR) gamma ligand has recently been reported to have improved the condition of patients with NASH. The aim of this study was to investigate whether pioglitazone, a PPARgamma ligand, has any influence on the animal model of NASH as well as isolated hepatic stellate cells. In vivo, the effects of pioglitazone were examined using the choline-deficient L-amino acid-defined (CDAA)-diet liver fibrosis model. After two weeks, pioglitazone improved hepatic steatosis, prevented liver fibrosis, and reduced preneoplastic lesions in the liver after 10 weeks. Pioglitazone reduced the expression of TIMP-1 and TIMP-2 mRNA without changing MMP-13 mRNA expression compared to the liver fed a CDAA diet alone. In vitro, pioglitazone prevented the activation of hepatic stellate cells resulting in reducing the expression of type I procollagen, MMP-2, TIMP-1, and TIMP-2 mRNA with increased MMP-13 mRNA expression. These results indicate that pioglitazone may be one of the candidates for the benefit drugs for the liver disease of patients with NASH.     

Pharmacological Inhibition of the Chemokine CXCL16 Diminishes Liver Macrophage Infiltration and Steatohepatitis in Chronic Hepatic Injury

Non-alcoholic fatty liver disease (NAFLD) is a major cause of morbidity and mortality in developed countries, resulting in steatohepatitis (NASH), fibrosis and eventually cirrhosis. Modulating inflammatory mediators such as chemokines may represent a novel therapeutic strategy for NAFLD. We recently demonstrated that the chemokine receptor CXCR6 promotes hepatic NKT cell accumulation, thereby controlling inflammation in experimental NAFLD. In this study, we first investigated human biopsies (n = 20), confirming that accumulation of inflammatory cells such as macrophages is a hallmark of progressive NAFLD. Moreover, CXCR6 gene expression correlated with the inflammatory activity (ALT levels) in human NAFLD. We then tested the hypothesis that pharmacological inhibition of CXCL16 might hold therapeutic potential in NAFLD, using mouse models of acute carbon tetrachloride (CCl₄)- and chronic methionine-choline-deficient (MCD) diet-induced hepatic injury. Neutralizing CXCL16 by i.p. injection of anti-CXCL16 antibody inhibited the early intrahepatic NKT cell accumulation upon acute toxic injury in vivo. Weekly therapeutic anti-CXCL16 administrations during the last 3 weeks of 6 weeks MCD diet significantly decreased the infiltration of inflammatory macrophages into the liver and intrahepatic levels of inflammatory cytokines like TNF or MCP-1. Importantly, anti-CXCL16 treatment significantly reduced fatty liver degeneration upon MCD diet, as assessed by hepatic triglyceride levels, histological steatosis scoring and quantification of lipid droplets. Moreover, injured hepatocytes up-regulated CXCL16 expression, indicating that scavenging functions of CXCL16 might be additionally involved in the pathogenesis of NAFLD. Targeting CXCL16 might therefore represent a promising novel therapeutic approach for liver inflammation and steatohepatitis.     

Electronegative LDL is linked to high-fat,high-cholesterol diet–induced nonalcoholic steatohepatitis in hamsters

The pathogenesis of nonalcoholic steatohepatitis (NASH), like that of atherosclerosis, involves lipid accumulation, inflammation and fibrosis. Recent studies suggest that oxidized LDL (oxLDL) may be a risk factor for NASH, but oxLDL levels were not directly measured in these studies. The aim of this study was to examine whether there was an association between electronegative LDL [LDL(−)], a mildly oxLDL found in the blood, and the development of NASH using two animal models. Golden Syrian hamsters and C57BL/6 mice were fed a high-fat, high-cholesterol (HFC) diet for 6 or 12 weeks, then liver lipid and histopathology, plasma lipoprotein profile and LDL(−) levels were examined. The HFC-diet-fed hamsters and mice had similar levels of hepatic lipid but different histopathological changes, with microvesicular steatosis, hepatocellular hypertrophy, inflammation and bridging fibrosis in the hamsters, but only in mild steatohepatitis with low inflammatory cell infiltration in the mice. It also resulted in a significant increase in plasma levels of LDL cholesterol and LDL(−) in hamsters, but only a slight increase in mice. Moreover, enlarged Kupffer cells, LDL(−) and accumulation of unesterified cholesterol were detected in the portal area of HFC-diet-fed hamsters, but not HFC-diet-fed mice. An in vitro study showed that LDL(−) from HFC-diet-fed hamsters induced TNF-α secretion in rat Kupffer cell through a LOX-1-dependent pathway. Our results strongly suggest that LDL(−) is one of the underlying causes of hepatic inflammation and plays a critical role in the development of NASH.     

β-Cryptoxanthin Alleviates Diet-Induced Nonalcoholic Steatohepatitis by Suppressing Inflammatory Gene Expression in Mice

Recent nutritional epidemiological surveys showed that serum β-cryptoxanthin inversely associates with the risks for insulin resistance and liver dysfunction. Consumption of β-cryptoxanthin possibly prevents nonalcoholic steatohepatitis (NASH), which is suggested to be caused by insulin resistance and oxidative stress from nonalcoholic fatty liver disease. To evaluate the effect of β-cryptoxanthin on diet-induced NASH, we fed a high-cholesterol and high-fat diet (CL diet) with or without 0.003% β-cryptoxanthin to C56BL/6J mice for 12 weeks. After feeding, β-cryptoxanthin attenuated fat accumulation, increases in Kupffer and activated stellate cells, and fibrosis in CL diet-induced NASH in the mice. Comprehensive gene expression analysis showed that although β-cryptoxanthin histochemically reduced steatosis, it was more effective in inhibiting inflammatory gene expression change in NASH. β-Cryptoxanthin reduced the alteration of expression of genes associated with cell death, inflammatory responses, infiltration and activation of macrophages and other leukocytes, quantity of T cells, and free radical scavenging. However, it showed little effect on the expression of genes related to cholesterol and other lipid metabolism. The expression of markers of M1 and M2 macrophages, T helper cells, and cytotoxic T cells was significantly induced in NASH and reduced by β-cryptoxanthin. β-Cryptoxanthin suppressed the expression of lipopolysaccharide (LPS)-inducible and/or TNFα-inducible genes in NASH. Increased levels of the oxidative stress marker thiobarbituric acid reactive substances (TBARS) were reduced by β-cryptoxanthin in NASH. Thus, β-cryptoxanthin suppresses inflammation and the resulting fibrosis probably by primarily suppressing the increase and activation of macrophages and other immune cells. Reducing oxidative stress is likely to be a major mechanism of inflammation and injury suppression in the livers of mice with NASH.     

Hyperresponsivity to low-dose endotoxin during progression to nonalcoholic steatohepatitis is regulated by leptin-mediated signaling

Although bacterial endotoxin, such as lipopolysaccharide (LPS), plays a key role in the pathogenesis of nonalcoholic steatohepatitis (NASH), detailed mechanisms of this pathogenesis remain unclear. Here, we demonstrate that upregulation of CD14 by leptin-mediated signaling is critical to hyperreactivity against endotoxin during NASH progression. Upregulation of CD14 in Kupffer cells and hyperreactivity against low-dose LPS were observed in high-fat diet (HFD)-induced steatosis mice, but not chow-fed-control mice. Hyperresponsivity against low-dose LPS led to accelerated NASH progression, including liver inflammation and fibrosis. Administering leptin in chow-fed mice caused increased hepatic expression of CD14 via STAT3 signaling, resulting in hyperreactivity against low-dose LPS without steatosis. In contrast, a marked decrease in hepatic CD14 expression was observed in leptin-deficient ob/ob mice, despite severe steatosis. Our results indicate that obesity-induced leptin plays a crucial role in NASH progression via enhanced responsivity to endotoxin, and we propose a mechanism of bacteria-mediated progression of NASH.     

Eicosapentaenoic Acid Ameliorates Non-Alcoholic Steatohepatitis in a Novel Mouse Model Using Melanocortin 4 Receptor-Deficient Mice

Many attempts have been made to find novel therapeutic strategies for non-alcoholic steatohepatitis (NASH), while their clinical efficacy is unclear. We have recently reported a novel rodent model of NASH using melanocortin 4 receptor-deficient (MC4R-KO) mice, which exhibit the sequence of events that comprise hepatic steatosis, liver fibrosis, and hepatocellular carcinoma with obesity-related phenotypes. In the liver of MC4R-KO mice, there is a unique histological feature termed hepatic crown-like structures (hCLS), where macrophages interact with dead hepatocytes and fibrogenic cells, thereby accelerating inflammation and fibrosis. In this study, we employed MC4R-KO mice to examine the effect of highly purified eicosapentaenoic acid (EPA), a clinically available n-3 polyunsaturated fatty acid, on the development of NASH. EPA treatment markedly prevented the development of hepatocyte injury, hCLS formation and liver fibrosis along with lipid accumulation. EPA treatment was also effective even after MC4R-KO mice developed NASH. Intriguingly, improvement of liver fibrosis was accompanied by the reduction of hCLS formation and plasma kallikrein-mediated transforming growth factor-β activation. Moreover, EPA treatment increased the otherwise reduced serum concentrations of adiponectin, an adipocytokine with anti-inflammatory and anti-fibrotic properties. Collectively, EPA treatment effectively prevents the development and progression of NASH in MC4R-KO mice along with amelioration of hepatic steatosis. This study unravels a novel anti-fibrotic mechanism of EPA, thereby suggesting a clinical implication for the treatment of NASH.     

Hepatic Crown-Like Structure: A Unique Histological Feature in Non-Alcoholic Steatohepatitis in Mice and Humans

Although macrophages are thought to be crucial for the pathogenesis of chronic inflammatory diseases, how they are involved in disease progression from simple steatosis to non-alcoholic steatohepatitis (NASH) is poorly understood. Here we report the unique histological structure termed “hepatic crown-like structures (hCLS)” in the mouse model of human NASH; melanocortin-4 receptor deficient mice fed a Western diet. In hCLS, CD11c-positive macrophages aggregate to surround hepatocytes with large lipid droplets, which is similar to those described in obese adipose tissue. Histological analysis revealed that hCLS is closely associated with activated fibroblasts and collagen deposition. When treatment with clodronate liposomes effectively depletes macrophages scattered in the liver, with those in hCLS intact, hepatic expression of inflammatory and fibrogenic genes is unaffected, suggesting that hCLS is an important source of inflammation and fibrosis during the progression of NASH. Notably, the number of hCLS is positively correlated with the extent of liver fibrosis. We also observed increased number of hCLS in the liver of non-alcoholic fatty liver disease/NASH patients. Collectively, our data provide evidence that hCLS is involved in the development of hepatic inflammation and fibrosis, thereby suggesting its pathophysiologic role in disease progression from simple steatosis to NASH.     

The role of AMPKα2 in the HFD-induced nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is associated with hepatic steatosis, inflammation and liver fibrosis and has become one of the leading causes of hepatocellular carcinoma and liver failure. However, the underlying molecular mechanism of hepatic steatosis and the progression to nonalcoholic steatohepatitis (NASH) are not fully understood. Herein, we discovered that AMPKα2 catalytic subunit showed reduced expression in the liver following high fat diet (HFD) feeding to mice. Importantly, knockout of AMPKα2 in mice aggravated NAFLD, hepatic steatosis, inflammation and fibrosis. On the other hand, hepatocyte-targeted overexpression of AMPKα2 prevented or reversed NAFLD indications. In vivo mechanistic studies revealed that increased phosphorylation of IKKα/β and NF-κB in HFD-fed AMPKα2^−/− mice compared to WT mice, and treatment of these mouse cohorts with an inhibitor of NF-κB signaling for 4 weeks, effectively attenuated the progression of steatohepatitis and metabolic disorder features. In summary, AMPKα2 provides a protective role in the process of hepatic steatosis to NASH progression through suppression of liver NF-κB signaling.     

Liver Injury and Fibrosis Induced by Dietary Challenge in the Ossabaw Miniature Swine

BackgroundOssabaw miniature swine when fed a diet high in fructose, saturated fat and cholesterol (NASH diet) develop metabolic syndrome and nonalcoholic steatohepatitis (NASH) characterized by liver injury and fibrosis. This study was conducted to further characterize the development of NASH in this large animal model.MethodsOssabaw swine were fed standard chow (control group; n = 6) or NASH diet (n = 6) for 24 weeks. Blood and liver tissue were collected and liver histology were characterized at 0, 8, 16 and 24 weeks of dietary intervention. Hepatic apoptosis and lipid levels were assessed at week 24.ResultsThe NASH diet group developed metabolic syndrome and progressive histologic features of NASH including: (a) hepatocyte ballooning at 8 weeks which progressed to extensive ballooning (>90% hepatocytes), (b) hepatic fibrosis at week 16, which progressed to moderate fibrosis, and (c) Kupffer cell accumulation with vacuolization at 8 weeks which progressed through week 24. The NASH diet group showed increased hepatocyte apoptosis that correlated with hepatic total and free cholesterol and free fatty acids, but not esterified cholesterol or triglycerides.ConclusionsThis report further characterizes the progression of diet-induced NASH in the Ossabaw swine model. In Ossabaw swine fed the NASH diet: (a) hepatocyte injury and fibrosis can occur without macrovesicular steatosis or excess triglyceride accumulation; (b) hepatocyte ballooning generally precedes the development of fibrosis; (c) there is increased hepatocyte apoptosis, and it is correlated more significantly with hepatic free cholesterol than hepatic free fatty acids and had no correlation with hepatic triglycerides.     

Dietary cholesterol exacerbates hepatic steatosis and inflammation in obese LDL receptor-deficient mice

Non-alcoholic fatty liver disease (NAFLD), the hepatic manifestation of the metabolic syndrome, can progress to steatohepatitis (NASH) and advanced liver disease. Mechanisms that underlie this progression remain poorly understood, partly due to lack of good animal models that resemble human NASH. We previously showed that several metabolic syndrome features that develop in LDL receptor-deficient (LDLR-/-) mice fed a diabetogenic diet are worsened by dietary cholesterol. To test whether dietary cholesterol can alter the hepatic phenotype in the metabolic syndrome, we fed LDLR-/- mice a high-fat, high-carbohydrate diabetogenic diet (DD) without or with added cholesterol (DDC). Both groups of mice developed obesity and insulin resistance. Hyperinsulinemia, dyslipidemia, hepatic triglyceride, and alanine aminotransferase (ALT) elevations were greater with DDC. Livers of DD-fed mice showed histological changes resembling NAFLD, including steatosis and modest fibrotic changes; however, DDC-fed animals developed micro- and macrovesicular steatosis, inflammatory cell foci, and fibrosis resembling human NASH. Dietary cholesterol also exacerbated hepatic macrophage infiltration, apoptosis, and oxidative stress. Thus, LDLR-/- mice fed diabetogenic diets may be useful models for studying human NASH. Dietary cholesterol appears to confer a second "hit" that results in a distinct hepatic phenotype characterized by increased inflammation and oxidative stress.     

The deficit in folate and vitamin B12 triggers liver macrovesicular steatosis and inflammation in rats with dextran sodium sulfate-induced colitis

The risks of nonalcoholic steatohepatitis (NASH) and deficiency in vitamin B12 and folate (methyl donor deficiency, MDD) are increased in inflammatory bowel disease (IBD). We investigated the influence of MDD on NASH in rats with DSS-induced colitis. Two-month-old male Wistar rats were subjected to MDD diet and/or ingestion of DSS and compared to control animals. We studied steatosis, inflammation, fibrosis, plasma levels of metabolic markers, cytokines and lipopolysaccharide, and inflammatory pathways in liver. MDD triggered a severe macrovesicular steatosis with inflammation in DSS animals that was not observed in animals subjected to DSS or MDD only. The macrovesicular steatosis was closely correlated to folate, vitamin B12, homocysteine plasma level and liver S-adenosyl methionine/S-adenosyl homocysteine (SAM/SAH) ratio. Liver inflammation was evidenced by activation of nuclear factor kappa B (NFκB) pathway and nuclear translocation of NFκB phospho-p65. MDD worsened the increase of interleukin 1-beta (IL-1β) and abolished the increase of IL10 produced by DSS colitis. It increased monocyte chemoattractant protein 1 (MCP-1). MDD triggers liver macrovesicular steatosis and inflammation through imbalanced expression of IL-1β vs. IL10 and increase of MCP-1 in DSS colitis. Our results suggest evaluating whether IBD patients with MDD and increase of MCP-1 are at higher risk of NASH.     

利用NASH大鼠原代肝细胞与原代Kupffer细胞共培养建立NASH原代细胞模型*

目的: 通过分离并提纯非酒精性脂肪性肝炎(NASH)大鼠原代肝细胞以及原代Kupffer细胞建立体外NASH原代细胞模型,为研究NASH提供可靠的细胞实验技术支持。方法: 选择SD大鼠40只,随机分为2组(n=20):对照组和NASH组,对照组大鼠利用普通饲料喂养,NASH组大鼠利用高脂饲料(88%基础饲料+10%猪油+ 2%胆固醇)喂养,6～8周后,利用NASH评分表,病理观察下肝组织切片脂肪变+小叶内炎症+气球样变评分≥4 分,表明大鼠NASH模型的成功建立,利用胶原酶原位灌注法分离并提纯NASH模型大鼠原代肝细胞以及原代Kupffer细胞,利用CK-18及CD68免疫荧光以及墨汁吞墨实验进行细胞鉴定,利用油红O染色、试剂盒测定谷丙转氨酶(ALT)、谷草转氨酶(AST)含量观察NASH大鼠原代肝细胞脂质累积和肝功情况,Western blot检测原代Kupffer细胞炎症因子表达情况,最后采用原代肝细胞:原代Kupffer细胞=6∶1比例共培养,显微镜下观察细胞状态。结果: 实验成功分离并提纯NASH原代肝细胞以及原代Kupffer细胞,通过油红O染色,NASH组大鼠原代肝细胞存在明显的脂肪沉积,且NASH组大鼠原代肝细胞中AST、ALT明显高于对照组,存在明显肝损伤(P＜0.05),Western blot测定原代Kupffer细胞TNF-α、IL-1β以及MCP-1,NASH组大鼠明显高于对照组(P＜0.05)。结论: 通过胶原酶原位灌注法可以成功分离NASH大鼠原代肝细胞以及原代Kupffer细胞,同时成功建立比例共培养大鼠体外原代细胞NASH模型。     

RIP1 kinase activity promotes steatohepatitis through mediating cell death and inflammation in macrophages

Hepatocyte cell death and liver inflammation have been well recognized as central characteristics of nonalcoholic steatohepatitis (NASH), however, the underlying molecular basis remains elusive. The kinase receptor-interacting protein 1 (RIP1) is a multitasking molecule with distinct functions in regulating apoptosis, necroptosis, and inflammation. Dissecting the role of RIP1 distinct functions in different pathophysiology has absorbed huge research enthusiasm. Wild-type and RIP1 kinase-dead (Rip1^K45A/K45A) mice were fed with high-fat diet (HFD) to investigate the role of RIP1 kinase activity in the pathogenesis of NASH. Rip1^K45A/K45A mice exhibited significantly alleviated NASH phenotype of hepatic steatosis, liver damage, fibrosis as well as reduced hepatic cell death and inflammation compared to WT mice. Our results also indicated that both in vivo lipotoxicity and in vitro saturated fatty acids (palmitic acid) treatment were able to induce the kinase activation of RIP1 in liver macrophages. RIP1 kinase was required for mediating inflammasome activation, apoptotic and necrotic cell death induced by palmitic acid in both bone marrow-derived macrophage and mouse primary Kupffer cells. Results from chimeric mice established through lethal irradiation and bone marrow transplantation further confirmed that the RIP1 kinase in hematopoietic-derived macrophages contributed mostly to the disease progression in NASH. Consistent with murine models, we also found that RIP1 kinase was markedly activated in human NASH, and the kinase activation mainly occurred in liver macrophages as indicated by immunofluorescence double staining. In summary, our study indicated that RIP1 kinase was phosphorylated and activated mainly in liver macrophages in both experimental and clinical NASH. We provided direct genetic evidence that the kinase activity of RIP1 especially in hematopoietic-derived macrophages contributes to the pathogenesis of NASH, through mediating inflammasome activation and cell death induction. Macrophage RIP1 kinase represents a specific and potential therapeutic target for NASH.Subject terms: Cell death and immune response, Chronic inflammation     

The relationship between oxidative stress and nonalcoholic fatty liver disease: Its effects on the development of nonalcoholic steatohepatitis

Abstract

Nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) are the most common underlying causes of chronic liver injury. They are associated with a wide spectrum of hepatic disorders including basic steatosis, steatohepatitis, and cirrhosis. The molecular and cellular mechanisms underlying hepatic injury in NAFLD and NASH are still unknown. This review describes the roles of oxidative stress and inflammatory responses in the pathogenesis of NAFLD and its progression to NASH.     

Extracts of bilberry (Vaccinium myrtillus L.) fruits improve liver steatosis and injury in mice by preventing lipid accumulation and cell death

ABSTRACT

Bilberry has been reported to have anti-oxidant and anti-inflammatory properties. We studied the effect of bilberry (Vaccinium myrtillus L.) fruits extracts (BEs) on the pathogenesis caused by lipid accumulation in fatty liver and non-alcoholic steatohepatitis (NASH). 5 μg/ml of BEs was enough to suppress lipid accumulation in the fatty liver model of the mouse hepatic AML12 cells. BEs increased cell viability and anti-oxidant capacity, presumably by activating (phosphorylating) Akt/STAT3 and inducing MnSOD/catalase. BEs also significantly reduced Rubicon and induced p62/SQSTM1, possibly contributing to reduce cellular lipids (lipophagy). When the mice were fed supplemented with BEs (5% or 10%, w/w), hepatic steatosis, injury, and hypercholesterolemia/hyperglycemia were significantly improved. Furthermore, histological and cytokine studies indicated that BEs possibly suppress hepatic inflammation (hepatitis) and fibrosis. Therefore, BEs improved liver steatosis and injury, and potentially suppress fibrosis by suppressing inflammatory response, which therefore may prevent the progression of fatty liver to NASH.     

Additive roles for MCP-1 and MCP-3 in CCR2-mediated recruitment of inflammatory monocytes during Listeria monocytogenes infection

Chemokine receptor-mediated recruitment of inflammatory cells is essential for innate immune defense against microbial infection. Recruitment of Ly6C(high) inflammatory monocytes from bone marrow to sites of microbial infection is dependent on CCR2, a chemokine receptor that responds to MCP-1 and MCP-3. Although CCR2(-/-) mice are markedly more susceptible to Listeria monocytogenes infection than are wild-type mice, MCP-1(-/-) mice have an intermediate phenotype, suggesting that other CCR2 ligands contribute to antimicrobial defense. Herein, we show that L. monocytogenes infection rapidly induces MCP-3 in tissue culture macrophages and in serum, spleen, liver, and kidney following in vivo infection. Only cytosol invasive L. monocytogenes induce MCP-3, suggesting that cytosolic innate immune detection mechanisms trigger chemokine production. MCP-3(-/-) mice clear bacteria less effectively from the spleen than do wild-type mice, a defect that correlates with diminished inflammatory monocyte recruitment. MCP-3(-/-) mice have significantly fewer Ly6C(high) monocytes in the spleen and bloodstream, and increased monocyte numbers in bone marrow. MCP-3(-/-) mice, like MCP-1(-/-) mice, have fewer TNF- and inducible NO synthase-producing dendritic cells (Tip-DCs) in the spleen following L. monocytogenes infection. Our data demonstrate that MCP-3 and MCP-1 provide parallel contributions to CCR2-mediated inflammatory monocyte recruitment and that both chemokines are required for optimal innate immune defense against L. monocytogenes infection.     

Estrogen deficiency worsens steatohepatitis in mice fed high-fat and high-cholesterol diet

Recent studies indicate an accelerated progression of nonalcoholic steatohepatitis (NASH) in postmenopausal women. Hypercholesterolemia, an important risk factor for NASH progression, is often observed after menopause. This study examined the effects of estrogen on NASH in ovariectomized (OVX) mice fed a high-fat and high-cholesterol (HFHC) diet. To investigate the effects of estrogen deficiency, OVX mice and sham-operated (SO) mice were fed normal chow or HFHC diet for 6 wk. Next, to investigate the effects of exogenous estrogen replenishment, OVX mice fed with HFHC diet were treated with implanted hormone release pellets (containing 17β-estradiol or placebo vehicle) for 6 wk. OVX mice on the HFHC diet showed enhanced liver injury with increased liver macrophage infiltration and elevated serum cholesterol levels compared with SO-HFHC mice. Hepatocyte monocyte chemoattractant protein-1 (MCP1) protein expression in OVX-HFHC mice was also enhanced compared with SO-HFHC mice. In addition, hepatic inflammatory gene expressions, including monocytes chemokine (C-C motif) receptor 2 (CCR2), were significantly elevated in OVX-HFHC mice. Estrogen treatment improved serum cholesterol levels, liver injury, macrophage infiltration, and inflammatory gene expressions in OVX-HFHC mice. Moreover, the elevated expression of liver CCR2 and MCP1 were decreased by estrogen treatment in OVX-HFHC mice, whereas low-density lipoprotein dose dependently enhanced CCR2 expression in THP1 monocytes. Our study demonstrated that estrogen deficiency accelerated NASH progression in OVX mice fed HFHC diet and that this effect was improved by estrogen therapy. Hypercholesterolemia in postmenopausal women would be a potential risk factor for NASH progression.     

Roles of heterogenous hepatic macrophages in the progression of liver diseases

Hepatic macrophages are key immune cells associated with the broad ranges of liver diseases including steatosis, inflammation and fibrosis. Hepatic macrophages interact with other immune cells and orchestrate hepatic immune circumstances. Recently, the heterogenous populations of hepatic macrophages have been discovered termed residential Kupffer cells and monocyte-derived macrophages, and identified their distinct population dynamics during the progression of various liver diseases. Liver injury lead to Kupffer cells activation with induction of inflammatory cytokines and chemokines, which triggers recruitment of inflammatory monocyte-derived macrophages. To understand liver pathology, the functions of different subtypes of liver macrophages should be regarded with different perspectives. In this review, we summarize recent advances in the roles of hepatic macrophages under liver damages and suggest hepatic macrophages as promising therapeutic targets for treating liver diseases.