MyD88 functions as a negative regulator of TLR3/TRIF-induced corneal inflammation by inhibiting activation of c-Jun N-terminal kinase.
The adaptor molecule MyD88 is necessary for responses to all Toll-like receptors except TLR3 and a subset of TLR4 signaling events, which are mediated by the adaptor molecule TRIF. To determine the role of TRIF in host inflammatory responses, corneal epithelium of C57BL/6, TLR3(-/-), TRIF(-/-), and MyD88(-/-) mice was abraded and stimulated with the synthetic TLR3 ligand poly(I:C). We found that poly(I:C) induced a pronounced cellular infiltration into the corneal stroma, which was TLR3- and TRIF-dependent. Unexpectedly, the inflammatory response was exacerbated in MyD88(-/-) mice, with enhanced neutrophil and F4/80(+) cell infiltration into the corneal stroma and elevated corneal haze, which is an indicator of loss of corneal transparency. To determine whether MyD88-dependent inhibition of TLR3/TRIF responses is a general phenomenon, we examined cytokine production by MyD88(-/-) bone marrow-derived macrophages; however, no significant difference was observed between MyD88(+/+) or MyD88(-/-) macrophages. In contrast, human corneal epithelial cells (HCECs) transfected with MyD88 small interfering RNA had significantly increased (2.5-fold) CCL5/RANTES production compared with control HCECs, demonstrating a negative regulatory role for MyD88 in TLR3/TRIF responses in these cells. Finally, knockdown of MyD88 in HCECs resulted in increased phosphorylation of c-Jun N-terminal kinase (JNK), but not p38, IRF-3, or NF-kappaB. Consistent with this finding, the JNK inhibitor SP600125, but not p38 inhibitor SB203580, ablated this response. Taken together, these findings demonstrate a novel JNK-dependent inhibitory role for MyD88 in the TLR3/TRIF activation pathway.
Department of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, Ohio 44106, USA.
Angela C
AC
Johnson
Xiaoxia
X
Li
Eric
E
Pearlman
D033942:Adaptor Proteins, Vesicular Transport / Q000502:physiology*; D000818:Animals; D002461:Cell Line, Transformed; D004789:Enzyme Activation; D050838:Interferon Regulatory Factor-3 / Q000502:physiology; D048031:JNK Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D007634:Keratitis / Q000201:enzymology / Q000209:etiology* / Q000503:physiopathology; D051379:Mice; D008810:Mice, Inbred C57BL; D053594:Myeloid Differentiation Factor 88 / Q000502:physiology*; D016328:NF-kappa B / Q000502:physiology; D034622:RNA Interference; D051196:Toll-Like Receptor 3 / Q000502:physiology*
D033942:Adaptor Proteins, Vesicular Transport; D050838:Interferon Regulatory Factor-3; D048031:JNK Mitogen-Activated Protein Kinases; D053594:Myeloid Differentiation Factor 88; D016328:NF-kappa B; D051196:Toll-Like Receptor 3; C494233:Irf3 protein, mouse; C507780:Myd88 protein, mouse; C476286:Ticam1 protein, mouse; C519703:TLR3 protein, mouse