Microfibril‐associated Protein 4 Binds to Surfactant Protein A (SP‐A) and Colocalizes with SP‐A in the Extracellular Matrix of the Lung

Abstract

Pulmonary surfactant protein A (SP‐A) is an oligomeric collectin that recognizes lipid and carbohydrate moieties present on broad range of micro‐organisms, and mediates microbial lysis and clearance. SP‐A also modulates multiple immune‐related functions including cytokine production and chemotaxis for phagocytes. Here we describe the molecular interaction between the extracellular matrix protein microfibril‐associated protein 4 (MFAP4) and SP‐A. MFAP4 is a collagen‐binding molecule containing a C‐terminal fibrinogen‐like domain and a N‐terminal located integrin‐binding motif. We produced recombinant MFAP4 with a molecular mass of 36 and 66 kDa in the reduced and unreduced states respectively. Gel filtration chromatography and chemical crosslinking showed that MFAP4 forms oligomers of four dimers. We demonstrated calcium‐dependent binding between MFAP4 and human SP‐A1 and SP‐A2. No binding was seen to recombinant SP‐A composed of the neck region and carbohydrate recognition domain of SP‐A indicating that the interaction between MFAP4 and SP‐A is mediated via the collagen domain of SP‐A. Monoclonal antibodies directed against MFAP4 and SP‐A were used for immunohistochemical analysis, which demonstrates that the two molecules colocalize both on the elastic fibres in the interalveolar septum and in elastic lamina of pulmonary arteries of chronically inflamed lung tissue. We conclude, that MFAP4 interacts with SP‐A via the collagen region in vitro, and that MFAP4 and SP‐A colocates in different lung compartments indicating that the interaction may be operative in vivo.

Physiology and immunology of mucosal barriers in catfish (Ictalurus spp.)

“…86 While the function of MFAP4 in mammals is poorly understood, it is known to bind to pulmonary surfactant protein A (SP-A), an oligomeric collectin that recognizes lipid and carbohydrate moieties present on broad range of micro-organisms, and mediates microbial lysis and clearance. 87 Additionally, in zebrafish, it is recognized as a specific marker for macrophages. 88 Future studies in catfish should utilize zebrafish MFAP4 reagents to better understand the role of these genes in mucosal immune responses.…”

CD163-L1 Is an Endocytic Macrophage Protein Strongly Regulated by Mediators in the Inflammatory Response

“…The membrane was washed extensively in TBST and incubated for 1 h in TBST with either alkaline phosphatase-coupled rabbit anti-mouse IgG (SigmaAldrich) diluted 1:2000, HRP-coupled goat anti-rabbit IgG (Sigma-Aldrich) diluted 1:10,000, or HRP-coupled rabbit anti-mouse IgG (Sigma-Aldrich) diluted 1:10,000. The membranes were washed extensively and developed as described by Schlosser et al (20) or using the ECL Plus kit, as described by the manufacturer (GE Healthcare).…”

“…At confluence, cells were washed three times in PBS and cultured without FBS in DMEM, 2 mM L-glutamine, 20 U/ml penicillin, and 20 mg/ml streptomycin (Invitrogen). Supernatants were harvested after 96 h, and recombinant CD163-L1 SRCR 1-7 and ectodomain were purified using a HisTrap HP column (GE Healthcare) as described by Schlosser et al (20).…”

Characterization of spontaneous air space enlargement in mice lacking microfibrillar-associated protein 4

“…MFAP4 was later detected in a variety of both elastic and nonelastic tissues in various species (4, 44 -46). In humans, this protein is highly expressed at sites that are rich in elastic fibers, including pulmonary arteries and the interalveolar walls of the lungs (19,38,49). Furthermore, it is present as a soluble protein in bronchoalveolar lavage (BAL) (38) and in systemic circulation (19,28,36).…”

“…The MFAP4 protein is a disulfide-linked dimer that forms higher homooligomeric structures via noncovalent interactions (26,38). FReDs are found in various human proteins involved in distinct functions, including innate immunity, tissue growth, and remodeling (43).…”