ABSTRACT
Mincle (macrophage-inducible C-type lectin, Clec4e) is a transmembrane pattern recognition receptor involving the innate immunity, but its role in kidney disease is still unexplored. In the obstructed kidney of the unilateral ureteral obstruction model of renal injury, Mincle was specifically detected in the infiltrating M1 macrophages (CD68+iNOS+ cells) on day one but was rapidly reduced following reduction of M1 macrophages during the progression of kidney injury. Interestingly, Mincle-expressing macrophages were progressively increased in the cisplatin-induced acute kidney injury model, where iNOS expression was detected in the CD68+ cells following Mincle induction. Adaptive transfer of Mincle+ M1 macrophages largely promoted cisplatin-induced renal inflammation, which was prevented by the knockdown of Mincle in the transferred cells. Mincle was tightly regulated by TLR4/NF-κB signaling as evidenced by the binding of NF-κB/p65 to the promoter region of Mincle in LPS-primed macrophages. Blocking TLR4 or NF-κB suppressed LPS-induced Mincle expression on macrophages. Importantly, Mincle was found to be essential for maintaining the inflammatory phenotypes of M1 macrophages through the Syk signaling pathway since knockdown of Mincle or inhibition of Syk suppressed LPS-induced IL-1ß, MCP-1, and iNOS expression. Thus, Mincle is induced specifically on M1 macrophages, where Mincle-Syk signaling promotes and maintains inflammatory phenotypes of M1 macrophages in acute renal inflammation. Hence, targeting Mincle may be a novel therapy for acute kidney injury associated with M1 macrophages.
Subject(s)
Acute Kidney Injury/metabolism , Kidney/metabolism , Lectins, C-Type/metabolism , Macrophage Activation , Macrophages/metabolism , Membrane Proteins/metabolism , Nephritis/metabolism , Receptors, Pattern Recognition/metabolism , Acute Kidney Injury/genetics , Acute Kidney Injury/immunology , Acute Kidney Injury/pathology , Adoptive Transfer , Animals , Antigens, CD/metabolism , Antigens, Differentiation, Myelomonocytic/metabolism , Binding Sites , Cisplatin , Disease Models, Animal , Gene Expression Regulation , Humans , Kidney/immunology , Kidney/pathology , Lectins, C-Type/genetics , Lectins, C-Type/immunology , Macrophages/immunology , Macrophages/pathology , Macrophages/transplantation , Membrane Proteins/genetics , Membrane Proteins/immunology , Mice , Mice, Inbred C57BL , Mice, Transgenic , Nephritis/genetics , Nephritis/immunology , Nephritis/pathology , Nitric Oxide Synthase Type II/metabolism , Phenotype , Promoter Regions, Genetic , RAW 264.7 Cells , RNA Interference , Receptors, Pattern Recognition/genetics , Receptors, Pattern Recognition/immunology , Signal Transduction , Syk Kinase/metabolism , Time Factors , Toll-Like Receptor 4/metabolism , Transcription Factor RelA/metabolism , Transfection , Ureteral Obstruction/complicationsABSTRACT
BACKGROUND: This study aimed to investigate the possible synergistic effects of lipid disorder with renin-angiotensin system (RAS) activation in non-alcoholic fatty liver disease (NAFLD). METHODS: Apolipoprotein E gene-knockout mice, angiotensin II (Ang II) type 1 receptor (AT1) gene-knockout mice and human hepatoblastoma cell line (HepG2) were used for experiments. Lipid accumulation was examined by Filipin staining and intracellular cholesterol quantitative assay. The gene and protein expression of molecules involved in RAS and low-density lipoprotein receptor (LDLr) pathway was examined by real-time PCR, immunofluorescent staining and Western blot. RESULTS: There was significantly increased expression of RAS components and extracellular matrix (ECM) in livers of high-fat-diet-fed apolipoprotein E gene-knockout mice compared with controls. Upregulation of RAS components was positively associated with increased plasma levels of lipid profile. The in vitro study further confirmed that cholesterol loading increased supernatant renin activity and Ang II level of HepG2 cells, accompanied by increased ECM production that was positively associated with increased expression of intracellular RAS components. Interestingly, Ang II treatment increased lipid accumulation in livers of C57BL/6 mice and HepG2 cells. Furthermore, Ang II treatment increased gene and protein expression of sterol regulatory element-binding protein (SREBP) cleavage activating protein (SCAP), SREBP-2 and LDLr, which were mediated by enhanced SCAP/SREBP-2 complex translocation from endoplasmic reticulum to Golgi. However, LDLr pathway was accordingly downregulated in livers of AT1 gene-knockout C57BL/6 mice or in HepG2 cells treated by telmisartan. CONCLUSION: These findings demonstrate that lipid disorder and intrahepatic RAS activation synergistically accelerate NAFLD progression.
