Particulate Matter Induction of Pulmonary Gelatinase A, Gelatinase B, and Tissue Inhibitor of Metalloproteinase Expression

Gelatinase A and gelatinase B are matrix metalloproteinases (MMPs) that are capable of degrading type IV collagen as well as other major components of basement membranes. These MMPs are also involved in modulating inflammation and tissue remodeling. Previous studies have shown the induction of pulmonary matrilysin, another MMP, following exposure to either combustion or ambient particulate matter (PM). In the present study, we examined whether gelatinase A, gelatinase B, or tissue inhibitor of metalloproteinase (TIMP) was affected following exposure to PM. Sprague-Dawley rats were exposed to a combustion PM (residual oil fly ash, ROTA, 2.5 mg/rat) or saline by intratracheal instillation and examined at 6 to 72 h postexposure. Changes in gelatinase A, gelatinase B, and TIMP-1 and -2 m RNA levels were determined using reverse transcription (RT) polymerase chain reaction (PCR). ROTA exposure increased the mRNA levels of gelatinase A and TIMP-1. However, gelatinase B mRNA, not expressed in control animals, was significantly induced from 6 to 24 h following ROFA exposure. Western blot analysis confirmed the presence of gelatinase A and B protein in lung tissue following ROFA exposure. Immunocytochemical analysis revealed that alveolar epithelial cells and inflammatory cells were major cellular sources for the pulmonary gelatinase A and B expression. To compare the effects of ambient PM with that of combustion PM and to further examine effects of ambient PM size on MMP induction, animals were treated with the same dose of the size-fractionated ambient PM [PM1.7, PM1.7-3.7, PM37.20 (size indicated in micrometers) collected from Washington, DC], Gelatinase A, gelatinase B, and TIMP gene expression and cellular distributions were assessed using RT-PCR and immunocytochemistry, respectively. Interestingly, gelatinase B was significantly induced to the same extent by all three size-fractionated ambient PM. Celatinase A and TIMP-1 expression were not changed, while TIMP-2 expression was slightly decreased by PM1.7 and PM1.7-3.7. Immunocytochemically, gelatinase A, gelatinase B, and TIMP-2 expression were localized mainly to the terminal bronchiole region and associated with inflammatory cells in ambient PM exposed animals. Thus, we have provided further evidence that MMP and TIMP expression are altered following exposure to either combustion or ambient PM supporting the hypothesis that MMP may be involved in pathogenesis of PM-induced lung injury.