Pericyte MyD88 and IRAK4 control inflammatory and fibrotic responses to tissue injury
Irina A. Leaf, … , William A. Altemeier, Jeremy S. Duffield
Irina A. Leaf, … , William A. Altemeier, Jeremy S. Duffield
Published November 21, 2016
Citation Information: J Clin Invest. 2017;127(1):321-334. https://doi.org/10.1172/JCI87532.
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Research Article Inflammation Nephrology

Pericyte MyD88 and IRAK4 control inflammatory and fibrotic responses to tissue injury

Abstract

Fibrotic disease is associated with matrix deposition that results in the loss of organ function. Pericytes, the precursors of myofibroblasts, are a source of pathological matrix collagens and may be promising targets for treating fibrogenesis. Here, we have shown that pericytes activate a TLR2/4- and MyD88-dependent proinflammatory program in response to tissue injury. Similarly to classic immune cells, pericytes activate the NLRP3 inflammasome, leading to IL-1β and IL-18 secretion. Released IL-1β signals through pericyte MyD88 to amplify this response. Unexpectedly, we found that MyD88 and its downstream effector kinase IRAK4 intrinsically control pericyte migration and conversion to myofibroblasts. Specific ablation of MyD88 in pericytes or pharmacological inhibition of MyD88 signaling by an IRAK4 inhibitor in vivo protected against kidney injury by profoundly attenuating tissue injury, activation, and differentiation of myofibroblasts. Our data show that in pericytes, MyD88 and IRAK4 are key regulators of 2 major injury responses: inflammatory and fibrogenic. Moreover, these findings suggest that disruption of this MyD88-dependent pathway in pericytes might be a potential therapeutic approach to inhibit fibrogenesis and promote regeneration.

Authors

Irina A. Leaf, Shunsaku Nakagawa, Bryce G. Johnson, Jin Joo Cha, Kristen Mittelsteadt, Kevin M. Guckian, Ivan G. Gomez, William A. Altemeier, Jeremy S. Duffield

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Figure 3

TLR2/4 and MyD88 control fibrogenic responses of mouse and human pericytes.

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TLR2/4 and MyD88 control fibrogenic responses of mouse and human pericyt...
(A) Representative images showing migratory response of WT, Myd88–/–, and Tlr2/4DKO pericytes to 24-hour TGF-β treatment. Blue lines mark the boundaries of the scratch at 0 hours; red area designates scratch boundaries at 24 hours. (B) Quantification of TGF-β migration assays. (C and D) Transcription of Acta2 and Col1a1 induced by TGF-β. (E–G) Responses of WT, Myd88–/–, and Tlr2/4DKO pericytes at 24 hours to kidney DAMP treatment. (E) Quantification of migration. (F and G) Transcription of Acta2 and Col1a1. (H) Effect of Tlr2 or Tlr4 silencing with siRNA on upregulation of Col1a1 stimulated by DAMPs. (I) Stress fiber formation shown by phalloidin staining in human kidney pericytes treated with TGF-β, histones, or kidney DAMPs. (J and K) Representative images (J) and quantification (K) of migratory response of human pericytes to TGF-β, histones, or DAMPs in the presence of a MyD88 inhibitor or vehicle. (L) Quantification of migration induced by TGF-β or DAMPs in the presence or absence of TGF-β1,2,3 neutralizing antibody (NAb) or TGFRβI/II inhibitor LY2109761, 24 hours after treatment. (M) Transcription of myofibroblast marker Acta2 in response to TGF-β or DAMPs in the presence or absence of the TGFRβI/II inhibitor LY2109761, in mouse pericytes after 24-hour treatment. (Scale bar: 25 μm; n = 3–6 per group; *P < 0.05, 2-tailed Student’s t test or 2-way ANOVA, Bonferroni’s multiple comparisons test.)