Amelioration of albuminuria and tubulointerstitial inflammation in STZ-induced diabetic TLR4-deficient mice

Abstract

BACKGROUND: We recently showed that tubular Toll-like receptor 4 (TLR4) expression was elevated in renal biopsies of histologically proven diabetic nephropathy (DN) and correlated with interstitial macrophage infiltration and HbA1c level. But the role of TLR4 in DN remains speculative. This study aims to study the role of TLR4 by using STZ-induced diabetic TLR4-deficient mice. METHODS: TLR4-/- mice and their wild type littermates (TLR4+/+) on C57BL6 background at 10-12 weeks old underwent uninephrectomy (Unx) or sham operation, and were then rendered diabetic by intraperitoneal injections of STZ. In vitro, the effect of an anti-TLR4 neutralizing antibody on high glucose (HG)-induced human proximal tubular epithelial cell (PTEC) inflammation was examined. RESULTS: At 12 weeks of diabetes, TLR4-/- mice demonstrated significantly ameliorated albuminuria and serum creatinine independent of blood glucose levels. This functional improvement was accompanied by substantially decreased F4/80+ macrophage infiltration into the tubulointerstitium and downregulation of cortical CCL-2, ICAM-1, and IL-1beta expression. At the signaling level, tubulointerstitial phosphorylated NF-κB/p65 activation was reduced in diabetic TLR4 -/- vs WT mice. The role of tubular TLR4 was confirmed in vitro. Pretreatment of PTEC with an anti-TLR4 neutralizing antibody significantly attenuated HG-induced NF-κB nuclear translocation and the downstream CCL-2 overexpression. CONCLUSIONS: Our data suggest a pathogenic role of TLR4 in tubulointerstitial inflammation of diabetic kidney injury, and TLR4 may be a promising therapeutic target for further investigation.