Role of TLR4 signaling in the nephrotoxicity of heme and heme proteins

• Published in: American journal of physiology. Renal physiology Vol. 314; no. 5; pp. F906 - F914
• Main Authors: Nath, Karl A., Belcher, John D., Nath, Meryl C., Grande, Joseph P., Croatt, Anthony J., Ackerman, Allan W., Katusic, Zvonimir S., Vercellotti, Gregory M.
• Format: Journal Article
• Language: English
• Published: United States American Physiological Society 01.05.2018
• Subjects: Acute Kidney Injury - chemically induced; Acute Kidney Injury - metabolism; Acute Kidney Injury - pathology; Acute Kidney Injury - prevention & control; Animal models; Animals; Blood flow; Cell activation; Cell Line; Cells; Chemokine CCL2 - metabolism; Disease Models, Animal; Epithelial cells; Epithelial Cells - drug effects; Epithelial Cells - metabolism; Epithelial Cells - pathology; Genes; Glycerol; Heme oxygenase (decyclizing); Heme proteins; Hemin; Inflammation; Intravenous administration; Kidney - blood supply; Kidney - drug effects; Kidney - metabolism; Kidney - pathology; Kidney diseases; Kidneys; Male; Mice, Inbred C57BL; Mice, Knockout; Monocyte chemoattractant protein; Monocyte chemoattractant protein 1; Monocytes; NF-kappa B - metabolism; NF-κB protein; NRF2 protein; Oxygenase; Proteins; Rats; Renal Circulation - drug effects; Rodents; Signal Transduction - drug effects; Sulfonamides - pharmacology; TLR4 protein; Toll-Like Receptor 4 - antagonists & inhibitors; Toll-Like Receptor 4 - deficiency; Toll-Like Receptor 4 - genetics; Toll-Like Receptor 4 - metabolism; Toll-like receptors; Transcription activation; Vasoconstriction; Vasoconstriction - drug effects; MCP-1; heme oxygenase-1; heme; TLR4 receptor; sickle cell disease
• ISSN: 1931-857X; 1522-1466; 1522-1466
• DOI: 10.1152/ajprenal.00432.2017

Destabilized heme proteins release heme, and free heme is toxic. Heme is now recognized as an agonist for the Toll-like receptor-4 (TLR4) receptor. This study examined whether the TLR4 receptor mediates the nephrotoxicity of heme, specifically, the effects of heme on renal blood flow and inflammatory responses. We blocked TLR4 signaling by the specific antagonist TAK-242. Intravenous administration of heme to mice promptly reduced renal blood flow, an effect attenuated by TAK-242. In vitro, TAK-242 reduced heme-elicited activation of NF-κB and its downstream gene monocyte chemoattractant protein-1(MCP-1); in contrast, TAK-242 failed to reduce heme-induced activation of the anti-inflammatory transcription factor Nrf2 and its downstream gene heme oxygenase-1 (HO-1). TAK-242 did not reduce heme-induced renal MCP-1 upregulation in vivo. TAK-242 did not reduce dysfunction and histological injury in the glycerol model of heme protein-induced acute kidney injury (AKI), findings corroborated by studies in TLR4 +/+ and TLR4 −/− mice. We conclude that 1) acute heme-mediated renal vasoconstriction occurs through TLR4 signaling; 2) proinflammatory effects of heme in renal epithelial cells involve TLR4 signaling, whereas the anti-inflammatory effects of heme do not; 3) TLR4 signaling does not mediate the proinflammatory effects of heme in the kidney; and 4) major mechanisms underlying glycerol-induced, heme protein-mediated AKI do not involve TLR4 signaling. These findings in the glycerol model are in stark contrast with findings in virtually all other AKI models studied to date and emphasize the importance of TLR4-independent pathways of heme protein-mediated injury in this model. Finally, these studies urge caution when using observations derived in vitro to predict what occurs in vivo.