title: Extracellular matrix lumican promotes bacterial phagocytosis, and Lum-/- mice show increased Pseudomonas aeruginosa lung infection severity.
abstract: Phagocytosis is central to bacterial clearance, but the exact mechanism is incompletely understood. Here, we show a novel and critical role for lumican, the connective tissue extracellular matrix small leucine-rich repeat proteoglycan, in CD14-mediated bacterial phagocytosis. In Psuedomonas aeruginosa lung infections, lumican-deficient (Lum(-/-)) mice failed to clear the bacterium from lungs, tissues, and showed a dramatic increase in mortality. In vitro, phagocytosis of nonopsonized gram-negative Escherichia coli and P. aeruginosa was inhibited in Lum(-/-) peritoneal macrophages (MΦs). Lumican co-localized with CD14, CD18, and bacteria on Lum(+/+) MΦ surfaces. Using two different P. aeruginosa strains that require host CD14 (808) or CD18/CR3 (P1) for phagocytosis, we showed that lumican has a larger role in CD14-mediated phagocytosis. Recombinant lumican (rLum) restored phagocytosis in Lum(-/-) MΦs. Surface plasmon resonance showed specific binding of rLum to CD14 (K(A) = 2.15 × 10(6) M(-1)), whereas rLumY20A, and not rLumY21A, where a tyrosine in each was replaced with an alanine, showed 60-fold decreased binding. The rLumY20A variant also failed to restore phagocytosis in Lum(-/-) MΦs, indicating Tyr-20 to be functionally important. Thus, in addition to a structural role in connective tissues, lumican has a major protective role in gram-negative bacterial infections, a novel function for small leucine-rich repeat proteoglycans.
authors.affiliation: Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
authors.forename: HanJuan
authors.initials: H
authors.lastname: Shao
authors.forename: Seakwoo
authors.initials: S
authors.lastname: Lee
authors.forename: Sherri
authors.initials: S
authors.lastname: Gae-Scott
authors.forename: Chiaki
authors.initials: C
authors.lastname: Nakata
authors.forename: Shoujun
authors.initials: S
authors.lastname: Chen
authors.forename: Abdel R
authors.initials: AR
authors.lastname: Hamad
authors.forename: Shukti
authors.initials: S
authors.lastname: Chakravarti
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D018821:CD18 Antigens / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D011508:Chondroitin Sulfate Proteoglycans / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D007632:Keratan Sulfate / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D018950:Lipopolysaccharide Receptors / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D000071234:Lumican; D017737:Macrophages, Peritoneal / Q000276:immunology* / Q000378:metabolism / Q000382:microbiology; D051379:Mice; D018345:Mice, Knockout; D020125:Mutation, Missense; D010587:Phagocytosis / Q000276:immunology*; D018410:Pneumonia, Bacterial / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D011552:Pseudomonas Infections / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D011550:Pseudomonas aeruginosa / Q000276:immunology*
chemical_list: D018821:CD18 Antigens; D011508:Chondroitin Sulfate Proteoglycans; D018950:Lipopolysaccharide Receptors; C000604307:Lum protein, mouse; D000071234:Lumican; D007632:Keratan Sulfate