Innate immunity conferred by Toll-like receptors 2 and 4 and myeloid differentiation factor 88 expression is pivotal to monosodium urate monohydrate crystal-induced inflammation.
OBJECTIVE
In gout, incompletely defined molecular factors alter recognition of dormant articular and bursal monosodium urate monohydrate (MSU) crystal deposits, thereby inducing self-limiting bouts of characteristically severe neutrophilic inflammation. To define primary determinants of cellular recognition, uptake, and inflammatory responses to MSU crystals, we conducted a study to test the role of Toll-like receptor 2 (TLR-2), TLR-4, and the cytosolic TLR adapter protein myeloid differentiation factor 88 (MyD88), which are centrally involved in innate immune recognition of microbial pathogens.


METHODS
We isolated bone marrow-derived macrophages (BMDMs) in TLR-2-/-, TLR-4-/-, MyD88-/-, and congenic wild-type mice, and assessed phagocytosis and cytokine expression in response to endotoxin-free MSU crystals under serum-free conditions. MSU crystals also were injected into mouse synovium-like subcutaneous air pouches.


RESULTS
TLR-2-/-, TLR-4-/-, and MyD88-/- BMDMs demonstrated impaired uptake of MSU crystals in vitro. MSU crystal-induced production of interleukin-1beta (IL-1beta), tumor necrosis factor alpha, keratinocyte-derived cytokine/growth-related oncogene alpha, and transforming growth factor beta1 also were significantly suppressed in TLR-2-/- and TLR-4-/- BMDMs and were blunted in MyD88-/- BMDMs in vitro. Neutrophil influx and local induction of IL-1beta in subcutaneous air pouches were suppressed 6 hours after injection of MSU crystals in TLR-2-/- and TLR-4-/- mice and were attenuated in MyD88-/- mice.


CONCLUSIONS
The murine host requires TLR-2, TLR-4, and MyD88 for macrophage activation and development of full-blown neutrophilic, air pouch inflammation in response to MSU crystals. Our findings implicate innate immune cellular recognition of naked MSU crystals by specific TLRs as a major factor in determining the inflammatory potential of MSU crystal deposits and the course of gouty arthritis.
Liu-Bryan
Ru
R
VA Medical Center, University of California, San Diego 92161, USA. rliu@vapop.ucsd.edu
Scott
Peter
P
Sydlaske
Anya
A
Rose
David M
DM
Terkeltaub
Robert
R
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D000943:Antigens, Differentiation / Q000235:genetics / Q000378:metabolism*; D015210:Arthritis, Gouty / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D001854:Bone Marrow Cells / Q000187:drug effects / Q000378:metabolism; D016207:Cytokines / Q000378:metabolism; D004195:Disease Models, Animal; D007113:Immunity, Innate / Q000276:immunology*; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D053594:Myeloid Differentiation Factor 88; D010587:Phagocytosis / Q000187:drug effects; D011971:Receptors, Immunologic / Q000235:genetics / Q000378:metabolism*; D013047:Specific Pathogen-Free Organisms; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D014527:Uric Acid / Q000276:immunology / Q000633:toxicity
D048868:Adaptor Proteins, Signal Transducing; D000943:Antigens, Differentiation; D016207:Cytokines; C507780:Myd88 protein, mouse; D053594:Myeloid Differentiation Factor 88; D011971:Receptors, Immunologic; C493486:Tlr2 protein, mouse; C493487:Tlr4 protein, mouse; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D014527:Uric Acid