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Abstract: SA-PO301

Induction of the Intracellular Immunomodulator Toll-Interacting Protein (Tollip) Mediates Monophosphoryl Lipid A (MPLA)-Induced Protection Against Lipopolysaccharide in Medullary Thick Ascending Limb (MTAL)

Session Information

Category: Fluid and Electrolytes

  • 901 Fluid and Electrolytes: Basic

Authors

  • Watts, Bruns A., University of Texas Medical Branch, Galveston, Texas, United States
  • Tamayo, Esther, University of Texas Medical Branch, Galveston, Texas, United States
  • Sherwood, Edward R., Vanderbilt University Medical Center, Nashville, Tennessee, United States
  • Good, David W., University of Texas Medical Branch, Galveston, Texas, United States
Background

LPS inhibits HCO3- absorption in the MTAL through activation of a basolateral TLR4-MyD88-IRAK-1-ERK pathway that is upregulated by sepsis. Recently we reported that pretreatment with the nontoxic immunomodulator MPLA prevents inhibition of HCO3- absorption by LPS through activation of a TLR4-TRIF-PI3K pathway that prevents LPS-induced activation of IRAK-1. Here, we examined the molecular mechanism by which MPLA pretreatment suppresses IRAK-1 activation. We investigated the role of Tollip, an inducible intracellular protein that negatively regulates LPS signaling by inhibiting activation of IRAK-1 downstream of TLR4. The expression and functional significance of Tollip in renal tubules are undefined.

Methods

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Results

We found that treatment with MPLA in vitro increased Tollip protein level in mouse and rat MTALs and that the increase in Tollip expression occurs within a time frame (2 h) sufficient to account for the effect of MPLA pretreatment to inhibit LPS-induced IRAK-1 activation. The MPLA-induced increase in Tollip expression was prevented by PI3K inhibitors. In coimmunoprecipitation experiments in inner stripe of outer medulla, treatment with MPLA increased the amount of IRAK-1 stably bound to Tollip, an interaction shown to inhibit IRAK-1 activation after LPS stimulation. Treatment of mice with MPLA increased Tollip protein level in the MTAL and this increase was prevented by administration of a PI3K inhibitor. Thus, the ability of MPLA to upregulate Tollip expression in the MTAL in vitro translates to the MTAL in vivo.

Conclusion

We conclude that pretreatment with MPLA increases expression of Tollip in the MTAL through a PI3K-dependent pathway. Tollip, in turn, inhibits LPS-induced TLR4 signaling by suppressing activation of IRAK-1, thereby preventing downstream activation of ERK that inhibits HCO3- absorption. These results provide new evidence that MPLA induces immune reprogramming of MTAL cells that protects against LPS stimulation and that Tollip can function as an endogenous negative regulator of inflammatory TLR4-IRAK-1 signaling in renal tubule epithelial cells. Strategies targeted to manipulate Tollip expression may aid in protecting renal tubule function against infectious and inflammatory challenge.

Funding

  • NIDDK Support