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 nuclear factor-kappa B (NF-ĸB). 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 5mM (control), 11.2mM (approximating the clinical diagnostic threshold for diabetes mellitus) and 30mM (high) glucose for 72 hours or 7 days. Cells were harvested for protein, mRNA and nuclear extract to assess for TLR2, 4 and inflammatory markers. 11.2mM glucose maximally increased TLR2 and 4 expression, HMGB1 release and NF-ĸB activation with increased expression of cytokines. However, only TLR2 expression and subsequent NF-ĸB binding were sustained at 7 days. Recombinant HMGB1 induced NF-ĸB activation which was prevented by both TLR2 silencing (siRNA) and TLR4 inhibition. Peroxisome proliferator-activated receptor gamma (PPARγ) transcription was reduced by exposure to 11.2mM glucose with an increase observed at 30mM glucose at 24 hours. This may reflect a compensatory increase in PPARγ induced by exposure to 30mM glucose, limiting the inflammatory response. Therefore, short term moderate increases in glucose in vitro increase HMGB1, which mediates NF-ĸB 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-ĸB activation in transducing inflammation in diabetic nephropathy.
- : Diabetic Nephropathy
- Toll-like receptor 2
- Toll-like receptor 4
- Copyright © 2012, American Journal of Physiology - Renal Physiology