Albumin mediates the transcytosis of myeloperoxidase by means of caveolae in endothelial cells

AUTOR(ES)

Tiruppathi, Chinnaswamy

FONTE

National Academy of Sciences

RESUMO

Myeloperoxidase (MPO), the phagocyte hemoprotein involved in neutrophil host defense and consuming nitric oxide (•NO), induces the nitration of extracellular matrix proteins and tissue remodeling subsequent to its transcytosis across the endothelial barrier. We addressed the role of an interaction of MPO with albumin as a requirement for MPO transport across the endothelium. Matrix-assisted laser desorption/ionization MS analysis of 80- and 60-kDa proteins purified from human lung tissue [with a human serum albumin (HSA)-affinity column] identified these albumin-binding proteins as MPO and MPO-heavy chain. A peptide corresponding to the MPO-heavy chain residues 425–454 demonstrated high-affinity binding to HSA. Replacement of the positively charged residues, R and K with G, prevented the binding of HSA to the peptide. We observed that albumin increased the binding of 125I-MPO to lung microvascular endothelial cells by 2-fold and the rate of transendothelial flux of 125I-MPO in cultured monolayers and intact vessels. Disruption of caveolae with cyclodextrin prevented the albumin-induced increase in transendothelial flux of 125I-MPO. We also observed by confocal imaging that albumin induced the rapid internalization of MPO and its colocalization with albumin-labeled vesicles. MPO colocalized with the caveolae markers cholera toxin subunit B and caveolin 1 in the endocytosed vesicles. Thus, transcytosis of MPO by caveolae induced by its charge-dependent interaction with albumin is an important means of delivering MPO to the subendothelial space. Albumin-mediated transport of MPO may thereby regulate NO bioavailability and formation of NO-derived oxidants in the vessel wall.

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