Toll-like receptor (TLR4) shedding and depletion: acute proximal tubular cell responses to hypoxic and toxic injury

Abstract

Zager RA, Johnson ACM, Lund S, Randolph-Habecker J. Toll-like receptor (TLR4) shedding and depletion: acute proximal tubular cell responses to hypoxic and toxic injury. Am J Physiol Renal Physiol 292: F304 -F312, 2007. First published August 1, 2006; doi:10.1152/ajprenal.00237.2006.-Acute renal failure (ARF) induces tubular hyperresponsiveness to TLR4 ligands, culminating in exaggerated renal cytokine/chemokine production. However, the fate of TLR4 protein during acute tubular injury remains unknown. The study sought new insights into this issue. Male CD-1 mice were subjected to 1) unilateral ischemia-reperfusion (I/R), 2) cisplatin (CP) nephrotoxicity, or 3) glycerol-induced myohemoglobinuric ARF. Renal cortical TLR4 protein (Western blotting, immunohistochemistry) and TLR4 mRNA levels (RT-PCR) were determined thereafter (90 min-4 days). Urinary TLR4 excretion post-I/R or CP injection was also assessed. To gain proximal tubule-specific results, TLR4 protein and mRNA were quantified in posthypoxic or oxidant (Fe)-challenged isolated mouse tubules. Finally, TLR4 mRNA was determined in antimycin A-injured cultured proximal tubular (HK-2) cells. Acute in vivo renal injury reduced proximal tubule TLR4 content. These changes corresponded with the appearance of TLR4 fragment(s) in urine and a persistent increase in renal cortical TLR4 mRNA. Isolated proximal tubules responded to injury with rapid TLR4 reductions, dramatic extracellular TLR4 release, and increases in TLR4 mRNA. Glycine blocked these processes, implying membrane pore formation was involved. HK-2 cell injury increased TLR4 mRNA, but not protein levels, suggesting intact transcriptional, but not translational, pathways. Diverse forms of acute tubular injury rapidly reduce proximal tubular TLR4 content. Plasma membrane TLR4 release through glycine-suppressible pores, possibly coupled with a translation block, appears to be involved. Rapid postinjury urinary TLR4 excretion suggests its potential utility as a "biomarker" of impending ARF. acute renal failure; iron; oxidant stress; cisplatin; biomarkers IT IS WELL ACCEPTED that renal inflammation significantly contributes to the pathogenesis of nephrotoxic and postischemic acute renal failure (ARF) (e.g., 3,7,12,14,15,22). The innate immune response/Toll-like receptor (TLR) pathway may be intimately involved in this process. TLRs are a family of ϳ11 plasma membrane glycoproteins that bind a variety of pathogen (e.g., endotoxins 3 TLR4; lipoteichoic acids 3 TLR2)-and nonpathogen (e.g., damaged RNA/DNA; heat shock proteins)-associated molecules (1,2,10,11,13,17,18,21). Once ligation occurs, downstream adaptor proteins (MyD88; Trif; Traf, NF-B) are recruited, culminating in increased cytokine and chemokine production (4,8,9). This process is hyperactive in the acutely damaged kidney (25-27). For example, when mice with diverse forms of ARF [ischemia-reperfusion (I/R), cisplatin (CP), myoglobinuria, urinary tract obstruction] are challenged with specific TLR ligands (endotoxin; lipoteichoic acid), greatly exagge...

Alterations in Membrane Transport Function and Cell Viability Induced by ATP Depletion in Primary Cultured Rabbit Renal Proximal Tubular Cells

“…Cytoprotective effect of amino acids such as glycine and alanine against ischemia/reperfusion injury in vivo has been reported in various tissues and organs including kidney, liver, and heart (Weinberg, 1991;Yin et al, 2002;Zhong et al, 2003;Habib et al, 2006). Amino acids also prevent hypoxic/ATP depletion-induced injury in vitro in renal epithelial cells (Pan et al, 2005;Zager et al, 2007). Consistent with these reports, the present study showed that impairment of Na ＋ -dependent phosphate uptake and cell death was prevented by addition of glycine and alanine (Fig.…”

TLR4 Signaling Mediates Inflammation and Tissue Injury in Nephrotoxicity

“…The specificity of the immunostaining was confirmed in Tlr4-deficient mice. Zager et al 54 observed primarily proximal tubule TLR4 staining with some accentuation in the brush borders. After acute renal injury, they noted a loss of staining in the epithelium and appearance of TLR4 immunoreactivity in the tubular lumens.…”

Attenuation of cisplatin nephrotoxicity by inhibition of soluble epoxide hydrolase

“…The role of inflammation in cisplatin nephrotoxicity is becoming more apparent (Ramesh and Reeves 2002;Jo et al 2005;Ramesh et al 2007;Zager et al 2007). Both the Jun Nterminal kinase (Francescato et al 2007) and peroxisome proliferator-activated receptor (Li et al 2005;Lee et al 2006) pathways have been shown to mediate the production of inflammatory cytokines; interestingly, inhibition of these pathways is protective against cisplatin-induced nephrotoxicity (Lee et al 2006;Francescato et al 2007).…”