Oxidized alpha2-macroglobulin (alpha2M) differentially regulates receptor binding by cytokines/growth factors: implications for tissue injury and repair mechanisms in inflammation.
Alpha2M binds specifically to TNF-alpha, IL-1beta, IL-2, IL-6, IL-8, basic fibroblast growth factor (bFGF), beta-nerve growth factor (beta-NGF), platelet-derived growth factor (PDGF), and TGF-beta. Since many of these cytokines are released along with neutrophil-derived oxidants during acute inflammation, we hypothesize that oxidation alters the ability of alpha2M to bind to these cytokines, resulting in differentially regulated cytokine functions. Using hypochlorite, a neutrophil-derived oxidant, we show that oxidized alpha2M exhibits increased binding to TNF-alpha, IL-2, and IL-6 and decreased binding to beta-NGF, PDGF-BB, TGF-beta1, and TGF-beta2. Hypochlorite oxidation of methylamine-treated alpha2M (alpha2M*), an analogue of the proteinase/alpha2M complex, also results in decreased binding to bFGF, beta-NGF, PDGF-BB, TGF-beta1, and TGF-beta2. Concomitantly, we observed decreased ability to inhibit TGF-beta binding and regulation of cells by oxidized alpha2M and alpha2M*. We then isolated alpha2M from human rheumatoid arthritis synovial fluid and showed that the protein is extensively oxidized and has significantly decreased ability to bind to TGF-beta compared with alpha2M derived from plasma and osteoarthritis synovial fluid. We, therefore, propose that oxidation serves as a switch mechanism that down-regulates the progression of acute inflammation by sequestering TNF-alpha, IL-2, and IL-6, while up-regulating the development of tissue repair processes by releasing bFGF, beta-NGF, PDGF, and TGF-beta from binding to alpha2M.
Wu
S M
SM
Department of Pathology, Duke University Medical Center, Durham, NC 27710, USA.
Patel
D D
DD
Pizzo
S V
SV
D000818:Animals; D001172:Arthritis, Rheumatoid / Q000276:immunology; D002460:Cell Line; D016207:Cytokines / Q000276:immunology / Q000378:metabolism*; D006133:Growth Substances / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D010084:Oxidation-Reduction; D018121:Receptors, Cytokine / Q000276:immunology / Q000378:metabolism*; D015398:Signal Transduction / Q000276:immunology*; D000511:alpha-Macroglobulins / Q000737:chemistry / Q000276:immunology / Q000378:metabolism*
D016207:Cytokines; D006133:Growth Substances; D018121:Receptors, Cytokine; D000511:alpha-Macroglobulins