Ambient particulate matter affects occludin distribution and increases alveolar transepithelial electrical conductance.
OBJECTIVE
Inhaled particulate matter (PM) causes lung inflammation and epithelial dysfunction. However, the direct effect of PM on alveolar epithelial barrier integrity is not well understood. Our aim is to determine whether PM exposure affects the alveolar epithelial cells (AEC) transepithelial electrical conductance (Gt) and tight junction (TJ) proteins.


METHODS
Human AEC (A549) and primary rat AEC were exposed to PM of <10 µm in size (PM(10) ) and diesel exhaust particles (DEP), using titanium dioxide (TiO(2) ) as a control for particle size effects. Gt and permeability to fluorescein isothiocyanate-dextran (FITC-Dextran) were measured to assess barrier integrity. TJ integrity was evaluated by analysing penetration of Lanthanum nitrate (La(3+) ) under transmission electron microscopy. Surface proteins were labelled with biotin and analysed by western blot. Immunofluorescence was performed to assess colocalization of TJ proteins including occludin and zonula occludens-1 (ZO-1). PM induced dissociation of occludin-ZO-1 was evaluated by co-immunoprecipitation.


RESULTS
PM(10) and DEP increased Gt and disrupted TJ after 3 h of treatment. PM(10) and DEP induced occludin internalization from the plasma membrane into endosomal compartments and dissociation of occludin from ZO-1. Overexpression of antioxidant enzymes manganese superoxide dismutase (MnSOD) and catalase, prevented PM-induced Gt increase, occludin reduction from the plasma membrane and its dissociation from ZO-1.


CONCLUSIONS
PM induces alveolar epithelial dysfunction in part via occludin reduction at the plasma membrane and ZO-1 dissociation in AEC. Furthermore, these effects are prevented by overexpression of two different antioxidant enzymes.
Internal Medicine Department, University of Iowa, Iowa City, Iowa 52242, USA.
Juan C
JC
Caraballo
Cecilia
C
Yshii
Whitney
W
Westphal
Thomas
T
Moninger
Alejandro P
AP
Comellas
D000818:Animals; D002374:Catalase / Q000378:metabolism; D002460:Cell Line; D002463:Cell Membrane Permeability / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D003911:Dextrans; D004553:Electric Conductivity; D016650:Fluorescein-5-isothiocyanate / Q000031:analogs & derivatives; D006801:Humans; D007811:Lanthanum; D008297:Male; D008565:Membrane Proteins / Q000187:drug effects / Q000502:physiology*; D062793:Occludin; D052638:Particulate Matter / Q000494:pharmacology*; D010750:Phosphoproteins / Q000187:drug effects / Q000502:physiology; D011650:Pulmonary Alveoli / Q000187:drug effects / Q000201:enzymology / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013482:Superoxide Dismutase / Q000378:metabolism; D019108:Tight Junctions / Q000187:drug effects / Q000502:physiology; D014025:Titanium / Q000378:metabolism / Q000502:physiology; D001335:Vehicle Emissions / Q000032:analysis; D062826:Zonula Occludens-1 Protein
D003911:Dextrans; D008565:Membrane Proteins; C568985:OCLN protein, human; D062793:Occludin; C568987:Ocln protein, rat; D052638:Particulate Matter; D010750:Phosphoproteins; C569042:TJP1 protein, human; C569044:Tjp1 protein, rat; D001335:Vehicle Emissions; D062826:Zonula Occludens-1 Protein; C015219:fluorescein isothiocyanate dextran; C009495:titanium dioxide; C016534:lanthanide nitrate; D007811:Lanthanum; D014025:Titanium; D002374:Catalase; D013482:Superoxide Dismutase; D016650:Fluorescein-5-isothiocyanate