Watts Bruns A, George Thampi, Sherwood Edward R, Good David W
Department of Internal Medicine, The University of Texas Medical Branch, Galveston, Texas.
Department of Anesthesiology, Vanderbilt University Medical Center, Nashville, Tennessee.
Am J Physiol Renal Physiol. 2017 Jul 1;313(1):F103-F115. doi: 10.1152/ajprenal.00064.2017. Epub 2017 Mar 29.
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.
单磷酰脂质A（MPLA）是脂多糖（LPS）的一种解毒衍生物，可诱导对LPS的耐受性并增强宿主对细菌感染的抵抗力。此前，我们证明LPS通过基底外侧Toll样受体4（TLR4）-髓样分化因子88（MyD88）-ERK途径抑制髓袢升支粗段（MTAL）中的[公式：见原文]吸收。在此，我们研究了用MPLA预处理是否会减弱LPS的抑制作用。将来自大鼠的MTALs在体外分别用浴槽和管腔中或仅浴槽中的MPLA（1μg/ml）灌注2小时，然后将LPS添加到浴槽溶液中（并从其中去除MPLA）。用MPLA预处理消除了LPS诱导的[公式：见原文]吸收抑制。在用MPLA加磷脂酰肌醇3激酶（PI3K）或Akt抑制剂预处理的MTALs中，LPS降低了[公式：见原文]吸收。MPLA增加了解剖后的MTALs中Akt的磷酸化。PI3K抑制剂以及来自TLR4或含Toll/IL-1受体结构域的接头诱导IFN-β（TRIF）小鼠的MTALs中消除了Akt激活。MPLA预防LPS抑制[公式：见原文]吸收的作用也依赖于TRIF。用MPLA预处理可防止LPS诱导的ERK激活；这种作用依赖于PI3K。单独使用MPLA对[公式：见原文]吸收没有影响，并且MPLA预处理不能防止醛固酮通过ERK介导的对[公式：见原文]吸收的抑制，这与MPLA的低毒性特征一致。这些结果表明，用MPLA预处理可防止LPS抑制MTAL中[公式：见原文]吸收的作用。这种保护作用是通过MPLA直接刺激TLR4-TRIF-PI3K-Akt途径介导的，该途径可防止LPS诱导的ERK激活。这些研究确定基于TLR4的解毒免疫调节剂是预防或治疗细菌感染引起的肾小管功能障碍的新型潜在治疗药物。
