Product(s) used in this publication: Reference Peptides for Targeted Proteomics - SpikeTides™ & SpikeMix™
Joint diseases are often characterized by inflammatory processes that result in pathological changes in joint tissues, including cartilagedegradation and release of components into the synovial fluid. The complementsystem plays a central role in promoting the inflammation. Because several cartilage proteins are known to interact with complement, causing either activation or inhibition of the system, we aimed to investigate these interactions comprehensively. Bovine cartilage explants were cultured with IL-1α to induce cartilagedegradation, followed by incubation with human serum. Label-free selected reaction monitoring massspectrometry was used to specifically quantify complement proteins interacting with the cartilage explant. In parallel, the time-dependent degradation of cartilage was detected using massspectrometry analysis (liquid chromatography-tandem massspectrometry). Complement proteins resulting from activation of the classical, alternative, and terminal pathways were detected on IL-1α-stimulated cartilage at time points when clear alterations in extracellular matrix composition had occurred. Increased levels of the complement activation product C4d, as detected by ELISA in serum after incubation with IL-1α-stimulated cartilage, confirmed the selected reaction monitoring results indicating complement activation. Further, typical activated (cleaved) C3 fragments were detected by Western blotting in extracts of IL-1α-stimulated cartilage. No complement activation was triggered by cartilage cultured in the absence of IL-1α. Components released from IL-1α-stimulated cartilage during culture had an inhibitory effect on complement activation. These were released after a longer incubation period with IL-1α and may represent a feedback reaction to cartilage-triggered complement activation observed after a shorter incubation period.
Copyright © 2016 by The American Association of Immunologists, Inc.