PURPOSE: Lung transplantation offers a treatment option for a variety of end-stage pulmonary diseases. Bronchiolitis obliterans syndrome (BOS) occurs in the majority of lung allograft recipients, causing substantial morbidity and mortality. We have instituted both toxicant-induced and transplantation-induced animal models of BO to evaluate diagnostic profiles and test immune hypotheses. Both demonstrate collagen degradation and remodeling and our toxicant-induced model hints at TIMP-1 involvement (Svetlecic, Lung, 05). The matrix metalloproteinase, MMP-9, is activated in both toxicant and transplantation BOS. We hypothesized that BOS involves remodeling through both MMP-9 and increased neutrophil elastase activity through its increase in TGF-Beta.
METHODS: To test our hypothesis, MMP-9 –latent, active, and lipocalin complexed was evaluated by zymography in lung tissue and compared to levels of TGF-Beta in both toxicant and transplant BOS models. Tissue cell profiles were made on lung sections. Toxicant-induced BOS was initiated in outbred SD rats by Alzet pump tracheal instillation of papaverine for 30 days. Tracheas of DA inbred rats were implanted in (MHC mismatched) BBDR recipients to produce transplant BOS. Lungs, harvested at 4 and 6 weeks respectively were sampled for histology and flash frozen until homogenized and tissue supernatant measured by gelatin zymography for MMP-9 fractions or TGF-Beta by ELISA.
RESULTS: MMP-9 (activated as percent of total) was significantly elevated (p=0.04)in both toxicant and transplant, but was more elevated in the transplant group. TGF-Beta was only slightly elevated which was unexpected, as surface MMP-9 is reported to proteolytically cleave and activate latent TGF-Beta. The neutrophil-bound enzyme, lipocalin-related MMP-9, was greatly elevated in the toxicant-induced BOS, suggesting that more PMN-related activity occurred with toxicant disease, not transplant BOS. Histopathology corroborated the zymography and ELISA findings.
CONCLUSION: Our BOS models indicate transplant remodeling emphasizes active MMP-9 over the TGF-Beta pathway, and the toxicant-induced BOS may additionally be mediated by neutrophil-associated MMP-9.
CLINICAL IMPLICATIONS: Our data have implications for future strategies as we seek mechanisms to attenuate BOS development and progression. Therapy for BOS could enhance the longevity of transplant recipients.
DISCLOSURE: Jennifer Svetlecic, None.