Monophosphoryl lipid A induces protection against LPS in medullary thick ascending limb through a TLR4-TRIF-PI3K signaling pathway

Am J Physiol Renal Physiol. 2017 Jul 1;313(1):F103-F115. doi: 10.1152/ajprenal.00064.2017. Epub 2017 Mar 29.

Abstract

Monophosphoryl lipid A (MPLA) is a detoxified derivative of LPS that induces tolerance to LPS and augments host resistance to bacterial infections. Previously, we demonstrated that LPS inhibits [Formula: see text] absorption in the medullary thick ascending limb (MTAL) through a basolateral Toll-like receptor 4 (TLR4)-myeloid differentiation factor 88 (MyD88)-ERK pathway. Here we examined whether pretreatment with MPLA would attenuate LPS inhibition. MTALs from rats were perfused in vitro with MPLA (1 µg/ml) in bath and lumen or bath alone for 2 h, and then LPS was added to (and MPLA removed from) the bath solution. Pretreatment with MPLA eliminated LPS-induced inhibition of [Formula: see text] absorption. In MTALs pretreated with MPLA plus a phosphatidylinositol 3-kinase (PI3K) or Akt inhibitor, LPS decreased [Formula: see text] absorption. MPLA increased Akt phosphorylation in dissected MTALs. The Akt activation was eliminated by a PI3K inhibitor and in MTALs from TLR4-/- or Toll/IL-1 receptor domain-containing adaptor-inducing IFN-β (TRIF)-/- mice. The effect of MPLA to prevent LPS inhibition of [Formula: see text] absorption also was TRIF dependent. Pretreatment with MPLA prevented LPS-induced ERK activation; this effect was dependent on PI3K. MPLA alone had no effect on [Formula: see text] absorption, and MPLA pretreatment did not prevent ERK-mediated inhibition of [Formula: see text] absorption by aldosterone, consistent with MPLA's low toxicity profile. These results demonstrate that pretreatment with MPLA prevents the effect of LPS to inhibit [Formula: see text] absorption in the MTAL. This protective effect is mediated directly through MPLA stimulation of a TLR4-TRIF-PI3K-Akt pathway that prevents LPS-induced ERK activation. These studies identify detoxified TLR4-based immunomodulators as novel potential therapeutic agents to prevent or treat renal tubule dysfunction in response to bacterial infections.

Keywords: LPS; Toll-like receptor 4; kidney; monophosphoryl lipid A; sepsis.

MeSH terms

  • Adaptor Proteins, Vesicular Transport / deficiency
  • Adaptor Proteins, Vesicular Transport / genetics
  • Adaptor Proteins, Vesicular Transport / metabolism*
  • Animals
  • Bicarbonates / metabolism
  • Cytoprotection
  • Extracellular Signal-Regulated MAP Kinases / metabolism
  • In Vitro Techniques
  • Lipid A / analogs & derivatives*
  • Lipid A / pharmacology
  • Lipopolysaccharides / toxicity*
  • Loop of Henle / drug effects*
  • Loop of Henle / enzymology
  • Male
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Perfusion
  • Phosphatidylinositol 3-Kinase / metabolism*
  • Phosphoinositide-3 Kinase Inhibitors
  • Phosphorylation
  • Protein Kinase Inhibitors / pharmacology
  • Proto-Oncogene Proteins c-akt / metabolism
  • Rats, Sprague-Dawley
  • Renal Reabsorption / drug effects
  • Signal Transduction / drug effects*
  • Toll-Like Receptor 4 / drug effects*
  • Toll-Like Receptor 4 / genetics
  • Toll-Like Receptor 4 / metabolism

Substances

  • Adaptor Proteins, Vesicular Transport
  • Bicarbonates
  • Lipid A
  • Lipopolysaccharides
  • Phosphoinositide-3 Kinase Inhibitors
  • Protein Kinase Inhibitors
  • TICAM-1 protein, mouse
  • Tlr4 protein, mouse
  • Toll-Like Receptor 4
  • Phosphatidylinositol 3-Kinase
  • Proto-Oncogene Proteins c-akt
  • Extracellular Signal-Regulated MAP Kinases
  • monophosphoryl lipid A