title: The role of Toll-like receptor proteins (TLR) 2 and 4 in mediating inflammation in proximal tubules.
abstract: Inflammatory responses are central to the pathogenesis of diabetic nephropathy. Toll-like receptors (TLRs) are ligand-activated membrane-bound receptors which induce inflammatory responses predominantly through the activation of NF-κB. TLR2 and 4 are present in proximal tubular cells and are activated by endogenous ligands upregulated in diabetic nephropathy, including high-mobility group box-1 (HMGB1) and fibronectin. Human proximal tubules were exposed to 5 mM (control), 11.2 mM (approximating the clinical diagnostic threshold for diabetes mellitus), and 30 mM (high) glucose for 72 h or 7 days. Cells were harvested for protein, mRNA, and nuclear extract to assess for TLR2, 4, and inflammatory markers. Glucose (11.2 mM) maximally increased TLR2 and 4 expression, HMGB1 release, and NF-κB activation with increased expression of cytokines. However, only TLR2 expression and subsequent NF-κB binding were sustained at 7 days. Recombinant HMGB1 induced NF-κB activation, which was prevented by both TLR2 silencing [small interfering (si)RNA] and TLR4 inhibition. Peroxisome proliferator-activated receptor-γ (PPAR-γ) transcription was reduced by exposure to 11.2 mM glucose with an increase observed at 30 mM glucose at 24 h. This may reflect a compensatory increase in PPAR-γ induced by exposure to 30 mM glucose, limiting the inflammatory response. Therefore, short-term moderate increases in glucose in vitro increase HMGB1, which mediates NF-κB activation through both TLR2 and 4. Furthermore, in vivo, streptozotocin-induced diabetic mice exhibited an increase in tubular TLR2 and HMGB1 expression. These results collectively suggest that TLR2 is likely to be the predominant long-term mediator of NF-κB activation in transducing inflammation in diabetic nephropathy.
authors.affiliation: Renal Research Group, Kolling Institute of Medical Research, University of Sydney, Royal North Shore Hospital, St. Leonards, New South Wales, Australia.
authors.forename: Harshini
authors.initials: H
authors.lastname: Mudaliar
authors.forename: Carol
authors.initials: C
authors.lastname: Pollock
authors.forename: Muralikrishna Gangadharan
authors.initials: MG
authors.lastname: Komala
authors.forename: Steven
authors.initials: S
authors.lastname: Chadban
authors.forename: Huiling
authors.initials: H
authors.lastname: Wu
authors.forename: Usha
authors.initials: U
authors.lastname: Panchapakesan
mesh_terms: D000818:Animals; D002460:Cell Line; D003928:Diabetic Nephropathies / Q000378:metabolism*; D005353:Fibronectins / Q000378:metabolism; D020868:Gene Silencing; D005947:Glucose / Q000378:metabolism; D024243:HMGB1 Protein / Q000378:metabolism*; D006801:Humans; D006943:Hyperglycemia / Q000378:metabolism; D007249:Inflammation / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D016328:NF-kappa B / Q000378:metabolism; D047495:PPAR gamma / Q000378:metabolism; D051195:Toll-Like Receptor 2 / Q000378:metabolism*; D051197:Toll-Like Receptor 4 / Q000378:metabolism*; D015854:Up-Regulation
chemical_list: D005353:Fibronectins; D024243:HMGB1 Protein; C582808:HMGB1 protein, mouse; D016328:NF-kappa B; D047495:PPAR gamma; C493486:Tlr2 protein, mouse; C493487:Tlr4 protein, mouse; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D005947:Glucose
keywords: HMGB1; NF-κB; Toll-like receptor 2; Toll-like receptor 4; diabetic nephropathy