RESUMO
The current dogma is that obesity-associated hepatic inflammation is due to increased Kupffer cell (KC) activation. However, recruited hepatic macrophages (RHMs) were recently shown to represent a sizable liver macrophage population in the context of obesity. Therefore, we assessed whether KCs and RHMs, or both, represent the major liver inflammatory cell type in obesity. We used a combination of in vivo macrophage tracking methodologies and adoptive transfer techniques in which KCs and RHMs are differentially labeled with fluorescent markers. With these approaches, the inflammatory phenotype of these distinct macrophage populations was determined under lean and obese conditions. In vivo macrophage tracking revealed an approximately sixfold higher number of RHMs in obese mice than in lean mice, whereas the number of KCs was comparable. In addition, RHMs comprised smaller size and immature, monocyte-derived cells compared with KCs. Furthermore, RHMs from obese mice were more inflamed and expressed higher levels of tumor necrosis factor-α and interleukin-6 than RHMs from lean mice. A comparison of the MCP-1/C-C chemokine receptor type 2 (CCR2) chemokine system between the two cell types showed that the ligand (MCP-1) is more highly expressed in KCs than in RHMs, whereas CCR2 expression is approximately fivefold greater in RHMs. We conclude that KCs can participate in obesity-induced inflammation by causing the recruitment of RHMs, which are distinct from KCs and are not precursors to KCs. These RHMs then enhance the severity of obesity-induced inflammation and hepatic insulin resistance.
Assuntos
Gluconeogênese/fisiologia , Fígado/metabolismo , Macrófagos/metabolismo , Obesidade/metabolismo , Animais , Dieta Hiperlipídica/efeitos adversos , Fígado Gorduroso/metabolismo , Fígado Gorduroso/patologia , Interleucina-6/metabolismo , Células de Kupffer/metabolismo , Células de Kupffer/patologia , Fígado/patologia , Macrófagos/patologia , Masculino , Camundongos , Camundongos Obesos , Obesidade/etiologia , Obesidade/patologia , Receptores CCR2/metabolismo , Fator de Necrose Tumoral alfa/metabolismoRESUMO
Obesity-induced inflammation is a key component of systemic insulin resistance, which is a hallmark of type 2 diabetes. A major driver of this inflammation/insulin resistance syndrome is the accumulation of proinflammatory macrophages in adipose tissue and liver. We found that the orphan GPCR Gpr21 was highly expressed in the hypothalamus and macrophages of mice and that whole-body KO of this receptor led to a robust improvement in glucose tolerance and systemic insulin sensitivity and a modest lean phenotype. The improvement in insulin sensitivity in the high-fat diet-fed (HFD-fed) Gpr21 KO mouse was traced to a marked reduction in tissue inflammation caused by decreased chemotaxis of Gpr21 KO macrophages into adipose tissue and liver. Furthermore, mice lacking macrophage expression of Gpr21 were protected from HFD-induced inflammation and displayed improved insulin sensitivity. Results of in vitro chemotaxis studies in human monocytes suggested that the defect in chemotaxis observed ex vivo and in vivo in mice is also translatable to humans. Cumulatively, our data indicate that GPR21 has a critical function in coordinating macrophage proinflammatory activity in the context of obesity-induced insulin resistance.
Assuntos
Dieta Hiperlipídica/efeitos adversos , Resistência à Insulina , Obesidade/metabolismo , Receptores Acoplados a Proteínas G/genética , Animais , Transplante de Medula Óssea , Ingestão de Alimentos , Metabolismo Energético , Epididimo/metabolismo , Perfilação da Expressão Gênica , Glucose/metabolismo , Hipotálamo/metabolismo , Mediadores da Inflamação/metabolismo , Gordura Intra-Abdominal/metabolismo , Gordura Intra-Abdominal/patologia , Fígado/metabolismo , Macrófagos , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Obesidade/etiologia , Obesidade/patologia , Fenótipo , Reação em Cadeia da Polimerase em Tempo Real , Receptores Acoplados a Proteínas G/metabolismo , Deleção de Sequência , Transcrição Gênica , Aumento de PesoRESUMO
UNLABELLED: Mice lacking the Abc4 protein encoded by the multidrug resistance-2 gene (Mdr2(-/-)) develop chronic periductular inflammation and cholestatic liver disease resulting in the development of hepatocellular carcinoma (HCC). Inhibition of NF-κB by expression of an IκBα super-repressor (IκBαSR) transgene in hepatocytes was shown to prevent HCC development in Mdr2(-/-) mice, suggesting that NF-κB acts as a tumour promoter in this model of inflammation-associated carcinogenesis. On the other hand, inhibition of NF-κB by hepatocyte specific ablation of IKK2 resulted in increased liver tumour development induced by the chemical carcinogen DEN. To address the role of IKK2-mediated NF-κB activation in hepatocytes in the pathogenesis of liver disease and HCC in Mdr2(-/-) mice, we generated Mdr2-deficient animals lacking IKK2 specifically in hepatocytes using the Cre-loxP system. Mdr2(-/-) mice lacking IKK2 in hepatocytes developed spontaneously a severe liver disease characterized by cholestasis, major hyperbilirubinemia and severe to end-stage fibrosis, which caused muscle wasting, loss of body weight, lethargy and early spontaneous death. Cell culture experiments showed that primary hepatocytes lacking IKK2 were more sensitive to bile acid induced death, suggesting that hepatocyte-specific IKK2 deficiency sensitized hepatocytes to the toxicity of bile acids under conditions of cholestasis resulting in greatly exacerbated liver damage. Mdr2(-/-)IKK2(Hep-KO) mice remarkably recapitulate chronic liver failure in humans and might be of special importance for the study of the mechanisms contributing to the pathogenesis of end-stage chronic liver disease or its implications on other organs. CONCLUSION: IKK2-mediated signaling in hepatocytes protects the liver from damage under conditions of chronic inflammatory cholestasis and prevents the development of severe fibrosis and liver failure.
Assuntos
Subfamília B de Transportador de Cassetes de Ligação de ATP/deficiência , Doença Hepática Terminal/enzimologia , Doença Hepática Terminal/prevenção & controle , Hepatócitos/enzimologia , Quinase I-kappa B/metabolismo , Subfamília B de Transportador de Cassetes de Ligação de ATP/metabolismo , Animais , Ácidos e Sais Biliares/farmacologia , Morte Celular/efeitos dos fármacos , Proliferação de Células/efeitos dos fármacos , Células Cultivadas , Citoproteção/efeitos dos fármacos , Doença Hepática Terminal/patologia , Hepatócitos/efeitos dos fármacos , Hepatócitos/patologia , Icterícia/complicações , Icterícia/patologia , Fígado/efeitos dos fármacos , Fígado/enzimologia , Fígado/patologia , Cirrose Hepática/complicações , Cirrose Hepática/patologia , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Síndrome de Emaciação/complicações , Síndrome de Emaciação/patologia , Membro 4 da Subfamília B de Transportadores de Cassetes de Ligação de ATPRESUMO
Activation of c-Jun amino-terminal kinase (JNK) facilitates tumour necrosis factor (TNF)-induced cell death. The p38 mitogen-activated protein kinase pathway is induced by TNF stimulation, but it has not been implicated in TNF-induced cell death. Here, we show that hepatocyte-specific ablation of p38alpha in mice results in excessive activation of JNK in the liver after in vivo challenge with bacterial lipopolysaccharide (LPS). Despite increased JNK activity, p38alpha-deficient hepatocytes were not sensitive to LPS/TNF toxicity showing that JNK activation was not sufficient to mediate TNF-induced liver damage. By contrast, LPS injection caused liver failure in mice lacking both p38alpha and IkappaB kinase 2 (IKK2) in hepatocytes. Therefore, when combined with partial nuclear factor-kappaB inhibition, p38alpha deficiency sensitizes the liver to cytokine-induced damage. Collectively, these results reveal a new function of p38alpha in collaborating with IKK2 to protect the liver from LPS/TNF-induced failure by controlling JNK activation.