Extracellular Matrix Lumican Promotes Bacterial Phagocytosis, and Lum−/− Mice Show Increased Pseudomonas aeruginosa Lung Infection Severity

• Published in: The Journal of biological chemistry 2012-10, Vol.287 (43), p.35860-35872
• Main Authors: Shao, HanJuan, Lee, Seakwoo, Gae-Scott, Sherri, Nakata, Chiaki, Chen, Shoujun, Hamad, Abdel R., Chakravarti, Shukti
• Format: Article
• Language: English
• Subjects: Amino Acid Substitution; Animals; CD14; CD18 Antigens - genetics; CD18 Antigens - immunology; CD18 Antigens - metabolism; Chondroitin Sulfate Proteoglycans - genetics; Chondroitin Sulfate Proteoglycans - immunology; Chondroitin Sulfate Proteoglycans - metabolism; Extracellular Matrix; Glycobiology and Extracellular Matrices; Innate Immunity; Keratan Sulfate - genetics; Keratan Sulfate - immunology; Keratan Sulfate - metabolism; Lipopolysaccharide Receptors - genetics; Lipopolysaccharide Receptors - immunology; Lipopolysaccharide Receptors - metabolism; Lumican; Macrophages, Peritoneal - immunology; Macrophages, Peritoneal - metabolism; Macrophages, Peritoneal - microbiology; Mice; Mice, Knockout; Mutation, Missense; Phagocytosis; Phagocytosis - immunology; Pneumonia, Bacterial - genetics; Pneumonia, Bacterial - immunology; Pneumonia, Bacterial - metabolism; Proteoglycan; Pseudomonas; Pseudomonas aeruginosa - immunology; Pseudomonas Infections - genetics; Pseudomonas Infections - immunology; Pseudomonas Infections - metabolism; TLR4
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M112.380550

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 (KA = 2.15 × 106m−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. Background: Lumican, an extracellular matrix protein, promotes host response to LPS endotoxins. Results:Lum−/− mice show increased lung infection. Phagocytosis of nonopsonized bacteria is reduced in Lum−/− macrophages and restored by recombinant wild type lumican but not mutated rLumY20A. Conclusion: Lumican interaction with CD14 at an N-terminal tyrosine is important for bacterial phagocytosis. Significance: A broader function is implicated for lumican and other LRR ECM proteins in host pathogen interactions.