Abstract
Gout is a chronic arthritis caused by the deposition of poorly soluble monosodium urate monohydrate (MSU) crystals in peripheral joints. Resident macrophages initiate inflammation in response to MSU mediated by NF-κB nuclear translocation and NLRP3 inflammasome activation. We investigated the role of CD44, a transmembrane receptor, in mediating MSU phagocytosis by macrophages. We used an antibody that sheds the extracellular domain (ECD) of CD44 to study the role of the receptor and its associated protein phosphatase 2A (PP2A) in macrophage activation. We also studied the significance of CD44 in mediating MSU inflammation in-vivo. Cd44−/− BMDMs showed reduced MSU phagocytosis, LDH release, IL-1β expression and production compared to Cd44+/+ BMDMs. Elevated CD44 staining was detected intracellularly and CD44 colocalized with α-tubulin as a result of MSU exposure and ECD-shedding reduced MSU phagocytosis in murine and human macrophages. Anti-CD44 antibody treatment reduced NF-κB p65 subunit nuclear levels, IL-1β expression, pro-IL-1β and IL-8 production in MSU stimulated THP-1 macrophages (p < 0.01). The effect of the antibody was mediated by an enhancement in PP2A activity. CD44 ECD-shedding reduced the conversion of procaspase-1 to active caspase-1, caspase-1 activity and resultant generation of mature IL-1β in macrophages. Neutrophil and monocyte influx and upregulated production of IL-1β was evident in wildtype mice. MSU failed to trigger neutrophil and monocyte recruitment in Cd44−/− mice and lower IL-1β levels were detected in peritoneal lavages from Cd44−/− mice (p < 0.01). Anti-CD44 antibody treatment reduced neutrophil and monocyte recruitment and resulted in reduced lavage IL-1β levels in the same model. CD44 plays a biologically significant role in mediating phagocytosis of MSU and downstream inflammation and is a novel target in gout treatment.
Highlights
Www.nature.com/scientificreports phagocytosis by joint macrophages is not entirely understood
To investigate whether the reduced MSU crystal uptake by Cd44−/− bone marrow derived macrophages (BMDMs) was due to a cytotoxic effect by the crystals, we studied lactate dehydrogenase (LDH) release by Cd44−/− and Cd44+/+ BMDMs
We investigated the role of the cluster determinant-44 (CD44) receptor in mediating urate crystal phagocytosis by macrophages of different origins and examined the associated signaling pathway triggered by shedding the receptor’s extracellular domain
Summary
Www.nature.com/scientificreports phagocytosis by joint macrophages is not entirely understood. We have shown that recombinant human proteoglycan-4 (rhPRG4) reduced urate crystal phagocytosis by macrophages, inhibited nuclear factor kappa b (NF-κB) pathway, NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasome activation, and suppressed IL-1β expression and secretion[24]. Engagement of CD44 by the antibody resulted in protein phosphatase-2 A (PP2A) activation, and inhibition of PP2A activity reversed the anti-inflammatory effect of the antibody[34] The aim of this investigation was to evaluate the singular role of CD44 in facilitating urate crystal phagocytosis by macrophages and study its function in regulating downstream NF-κB nuclear translocation and NLRP3 inflammasome activation and IL-1β production in vitro and in vivo using a peritoneal model of acute gout. We hypothesized that CD44 mediates the phagocytosis of urate crystals by macrophages and CD44 receptor neutralization and/or deficiency reduces crystal phagocytosis, NF-κB translocation and NLRP3 inflammasome activation and suppresses urate crystal-linked inflammation
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
