Mechanism of neutrophil activation by an unopsonized inflammatory particulate. Monosodium urate crystals induce pertussis toxin-insensitive hydrolysis of phosphatidylinositol 4,5-bisphosphate.
Monosodium urate crystals are believed to trigger acute inflammation via the direct stimulation of leukocytes. Unopsonized urate crystals activate neutrophil (PMN) membrane G proteins in a pertussis toxin (PT)-sensitive manner, but induce PT-insensitive cytosolic [Ca2+]i elevation. Thus, we have further defined the mechanism of PMN responsiveness to urate crystals in this study. Though urate crystals can increase membrane permeability by lytic effects, we observed elevation of PMN cytosolic [Ca2+]i in the absence of extracellular [Ca2+]i. In addition, the early, crystal-induced cytosolic [Ca2+]i transient was buffered in cells loaded with a [Ca2+]i-chelator. This suggested mobilization of internal [Ca2+]i stores, which was supported by demonstrating rapid phosphatidylinositol bisphosphate (PIP2) hydrolysis, and the formation of inositol (1,4,5) trisphosphate (as well as phosphatidic acid) in a PT-insensitive manner. Importantly, PMN activation by urate crystals was discriminatory, as evidenced by the absence of phosphatidylinositol trisphosphate formation, a PT-sensitive event triggered by chemotactic factors. Urate crystal-induced PIP2 hydrolysis was not a nonspecific consequence of the early cytosolic [Ca2+]i transient itself, and it did not require phagocytosis. However, crystal-induced O2- release was markedly inhibited by buffering of the early cytosolic [Ca2+]i transient under conditions where crystal phagocytosis and PMA-induced O2- release were unaffected. We conclude that urate crystals activate PT-insensitive PIP2 hydrolysis, resulting in IP3 generation, and early urate crystal-induced mobilization of cytosolic [Ca2+]i. This pathway appears to modulate crystal-induced O2- release.
Onello
E
E
San Diego VA Medical Center, CA 92161.
Traynor-Kaplan
A
A
Sklar
L
L
Terkeltaub
R
R
D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D003460:Crystallization; D006801:Humans; D006868:Hydrolysis; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D009504:Neutrophils / Q000187:drug effects* / Q000502:physiology; D037342:Pertussis Toxin; D010587:Phagocytosis; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism*; D013481:Superoxides / Q000378:metabolism; D014527:Uric Acid / Q000494:pharmacology*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology*
D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D010566:Virulence Factors, Bordetella; D013481:Superoxides; D014527:Uric Acid; D015544:Inositol 1,4,5-Trisphosphate; D037342:Pertussis Toxin; D002118:Calcium