Angiotensin II Upregulates Toll-Like Receptor 4 on Mesangial Cells

Abstract

Angiotensin II (AngII) mediates proinflammatory properties by activating NF-B transcription factor nuclear translocation and inducing the expression of chemokines. For examination of whether AngII modulates the expression of Toll-like receptor 4 (TLR4), a key element of the innate immune system that senses LPS, mouse mesangial cells (MMC) were treated with AngII. AngII upregulated TLR4 mRNA and protein in MMC, and this effect was mediated through AngII type 1 receptors. Reporter gene experiments indicate that an activating protein-1 (AP-1) as well as an E-26 specific sequence (Ets) binding site in the TLR4 promoter are responsible for the AngII-stimulated transcriptional activity of the TLR4 gene. Preincubation of MMC with AngII enhanced LPS-induced NF-B activation and chemokine expression. Immunohistochemical analyses revealed that double-transgenic rats that overexpressed human renin and angiotensinogen expressed higher levels of glomerular TLR4 compared with normal Sprague-Dawley rats. In vivo, infusion with AngII but not with norepinephrine into rats for 7 d also enhanced glomerular NF-B activation after systemic application of LPS, suggesting that the effects are independent of concomitantly induced hypertension. Together, these observations suggest that AngII leads to an activation of the innate immune system by a novel mechanism involving the upregulation of TLR4. Our data contribute to a better understanding of how exogenous infections may trigger renal autoimmune processes, particularly in pathophysiologic situations with high renal AngII concentrations. Because TLR4 binds endogenous ligands (e.g., extracellular matrix components) in addition to microbial products, AngII-mediated upregulation of TLR4 also could be relevant for the development of inflammation in many noninfectious renal diseases.

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YB-1 Is an Early and Central Mediator of Bacterial and Sterile Inflammation In Vivo

“…Other studies revealed that the blockade of one of these players results in reduced sepsis manifestations, as demonstrated for TLR4 (31), CCL5 (32), CXCL1, and CCL2 (33). The major involvement of TLR4 in immune cell recruitment and renal cell activation has been extensively described (31,34) and is perpetuated by NF k-L chain enhancer of activated B cells (NF-kB) (24). This activation results in the release of proinflammatory chemokines, such as CCL2, CCL5, and CXCL1, which mediate chemotaxis of immune cells during inflammatory processes (35).…”

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“…We recently demonstrated another mechanism for how AngII could contribute to renal inflammation. AngII upregulates on mesangial cells Toll-like 4 receptors that bind LPS (36). This AngII-mediated Toll-like 4 receptor upregulation resulted in enhanced NF-B activation (36).…”

“…AngII upregulates on mesangial cells Toll-like 4 receptors that bind LPS (36). This AngII-mediated Toll-like 4 receptor upregulation resulted in enhanced NF-B activation (36). The recruitment of inflammatory cells into the glomerulus as well as into the tubulointerstitium plays an pivotal role in progression of chronic renal disease.…”