Abstract
Previously we demonstrated that basolateral LPS inhibits HCO(3)(-) absorption in the renal medullary thick ascending limb (MTAL) through TLR4-dependent ERK activation. Here we report that the response of the MTAL to basolateral LPS requires TLR2 in addition to TLR4. The basolateral addition of LPS (ultrapure Escherichia coli K12) decreased HCO(3)(-) absorption in isolated, perfused MTALs from wild-type mice but had no effect in MTALs from TLR2(-/-) mice. In contrast, inhibition of HCO(3)(-) absorption by lumen LPS was preserved in TLR2(-/-) MTALs, indicating that TLR2 is involved specifically in mediating the basolateral LPS response. LPS also did not increase ERK phosphorylation in MTALs from TLR2(-/-) mice. TLR2 deficiency had no effect on expression of TLR4, MD-2, or MyD88. However, LPS-induced recruitment of MyD88 to the basolateral membrane was impaired in TLR2(-/-) MTALs. Inhibition of HCO(3)(-) absorption by LPS did not require CD14. Co-immunoprecipitation studies demonstrated an association between TLR4 and TLR2. Inhibition of HCO(3)(-) absorption by TLR2-specific ligands was preserved in MTALs from TLR4(-/-) mice. These results indicate that the effect of basolateral LPS to inhibit HCO(3)(-) absorption in the MTAL through MyD88-dependent ERK activation depends on a novel interaction between TLR4 and TLR2. TLR2 plays a dual role in the induction of intracellular signals that impair MTAL function, both through cooperation with TLR4 to mediate ERK signaling by LPS and through a TLR4-independent signaling pathway activated by Gram-positive bacterial ligands. Regulation of TLR2 expression and its interaction with TLR4 may provide new mechanisms for controlling and therapeutic targeting of TLR4-mediated LPS responses.
Highlights
Bacterial molecules act through Toll-like receptors to impair renal tubule function
To test whether the response of the medullary thick ascending limb (MTAL) to LPS is influenced by TLR2, we examined the effects of LPS on HCO3Ϫ absorption in isolated, perfused MTALs from wild-type and TLR2Ϫ/Ϫ mice
The effect of bath addition of E. coli O111:B4 LPS to inhibit HCO3Ϫ absorption [14] is eliminated in TLR2Ϫ/Ϫ MTALs, indicating that the absence of basolateral LPS response is not specific for ultrapure E. coli K12 LPS. These results indicate that inhibition of HCO3Ϫ absorption by basolateral LPS in the MTAL requires TLR2 in addition to TLR4 and that TLR2 is involved in mediating the basolateral LPS response
Summary
Bacterial molecules act through Toll-like receptors to impair renal tubule function. Results: Activation of ERK and inhibition of bicarbonate absorption by LPS requires both TLR4 and TLR2 in thick ascending limb. The inhibition by Grampositive bacterial components is additive to inhibition by basolateral LPS, due to the TLR2 and TLR4 agonists activating different cell signaling pathways [15] These findings have important implications for the pathogenesis of kidney dysfunction during polymicrobial sepsis because they show that Gramnegative and Gram-positive bacterial molecules can act independently and additively to impair renal tubule function by activating different intracellular signals through different TLRs [15]. The TLR4-mediated inhibition of HCO3Ϫ absorption by lumen LPS does not depend on TLR2, indicating that TLR2 is required for the basolateral LPS response These findings reveal a novel requirement for TLR2 in LPS-induced TLR4 signaling and suggest that interaction between TLR4 and TLR2 may play a role in mediating renal tubule dysfunction during sepsis
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