The Src Family Tyrosine Kinase fyn Protects Mice from Inflammation‐induced Lung Injury

Abstract

Endothelial cell apoptosis is an early event in the development of inflammatory lung diseases such as acute respiratory distress syndrome (ARDS) and bronchopulmonary dysplasia (BPD). In studies utilizing cultured human pulmonary endothelial cells we have shown that the Src family tyrosine kinase (STK) yes activated caspase‐3, while the STK fyn inhibited caspase‐3 activation. Therefore, in this study we tested the hypothesis that mice deficient in fyn will have more severe lipopolysaccharide (LPS)‐induced pulmonary apoptosis and lung injury than will similarly treated wild‐type mice. Wild‐type and fyn−/− mice (all on the same 129S1/SvImJ background) were given LPS 10 mg/kg intraperitoneally or saline for 24 hours and lungs were harvested for determination of proteins related to apoptosis. LPS treatment resulted in greater levels of cleaved caspase‐8, cleaved caspase‐9, cleaved caspase‐3, and p21 in the lungs from fyn−/− mice than in the lungs from wild‐type mice. In a second set of studies, lung sections from wild‐type and fyn−/− mice were stained for platelet endothelial cell adhesion molecule‐1 (PECAM‐1), we found that the fyn−/− mice had less PECAM‐1 expression, thicker alveolar septa, and more leukocyte infiltration than did wild‐type mice. In another set of studies wild‐type and fyn−/− mice were given LPS 2 mg/kg intratracheally or an equal volume of saline, and 24 hours later lung mechanics were measured using a Flexivent system (SCIREQ, Montreal, Canada). The fyn−/− mice had significantly (p<0.01) lower lung compliance (0.030 ± 0.003 ml/cmH2O) than did wild‐type mice (0.040 ± 0.001 ml/cmH2O). The fyn−/− mice also had significantly (p<0.05) higher tissue elastance (32.6 ± 3.1 cmH2O/mL) than did wild‐type mice (23.8 ± 0.8 cmH2O/mL). The fyn−/− mice had greater (p = 0.046) lung resistance (0.67±0.06 cmH2O/ml/s) than did wild‐type mice (0.55±0.02 cmH2O/ml/s). These results demonstrate that mice lacking fyn develop more apoptosis and more severe lung injury following LPS exposure than do wild‐type mice. These findings demonstrate that fyn is an important negative regulator of LPS‐induced apoptosis and the resultant lung injury in a mouse model of inflammatory lung diseases such as ARDS.