Profibrotic and proinflammatory pulmonary response to bleomycin in a Swiss nude mice model

Abstract

Mesenchymal stem cell therapy is a promising strategy to treat idiopathic pulmonary fibrosis (IPF) and xenotransplantation of human cells into immunodeficient mice might lead to a suitable experimental approach. Bleomycin (BLM)-induced pulmonary fibrosis (PF) is the most used animal model for the study of IPF. We aimed to characterize the BLM effects on the lungs of the outbred Swiss nude Crl:NU(Ico)-Foxn1^nu mice. Nude (nu/nu) and heterozygous (nu/+) male mice were intratracheally instilled with a single 2 U/kg BLM dose and sacrificed at key time-points. At days 4, 10 and 14 some nu/+ mice showed increased bronchoalveolar lavage fluid (BALF) total cell count and inflammatory markers. Col1a1 and Fn1 expression was induced (P<0.05) at day 10. Body weight was unchanged. Effects were attenuated in nu/nu mice. Ashcroft score of lungs indicated mild PF in both genotypes. To generate a more robust degree of PF, female nu/nu mice were challenged with a single or three bi-weekly 6 U/kg instillations. The single dose triggered a moderate degree of PF according to the Ashcroft score. Air space quantification of haematoxylin-eosin stained lungs and expression of Col1a1 and Fn1 indicated no increase in PF degree with a three-dose protocol. However, only repetitive BLM administration increased total BALF cell count (P<0.01). Further cytometry analysis revealed that myeloid-origin cells accounted for the increase (P<0.05). In conclusion, Swiss nude mice are rather resistant to BLM-induced PF and display heterogeneous response. Molecular markers analysis is required to further characterize the PF in these mice and protocol refinement would be necessary before implementing the cell therapy approach.