Altered Pulmonary Response to Hyperoxia in Clara Cell Secretory Protein Deficient Mice

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Abstract
Clara cell secretory protein (CCSP) is an abundant component of the extracellular lining fluid of airways. Even though the in vivo function of CCSP is unknown, in vitro studies support a potential role of CCSP in the control of inflammatory responses. CCSP-deficient mice (CCSP -/-) were generated to investigate the in vivo function of this protein (13). In this study, we used hyperoxia exposure as a model to investigate phenotypic consequences of CCSP deficiency following acute lung injury. The pathologic response of the mouse lung to hyperoxia, and recovery of the lung, include inflammatory cell infiltrate and edema. Continuous exposure to > 95% O2 was associated with significantly reduced survival time among CCSP -/- mice as compared with strain-, age-, and sex-matched wild-type control mice. Differences in survival were associated with early onset of lung edema in CCSP -/- mice as compared with wild-type controls. To further investigate these differences in response, mice were exposed to > 95% O2 for either 48 h or 68 h with one group receiving 68 h of hyperoxia followed by room-air recovery. Lung RNA was characterized for changes in the abundance of cytokine messenger RNA (mRNA) using a ribonuclease (RNase) protection assay. After 68 h of hyperoxia, interleukin-6 (IL-6), IL-1beta, and IL-3 mRNAs were 14-, 3-, and 2.5-fold higher, respectively, in CCSP -/- mice than in similarly exposed wild-type control mice. Increased expression of IL-1beta mRNA in hyperoxia-exposed CCSP -/- mice was localized principally within the lung parenchyma, suggesting that the effects of CCSP deficiency were not confined to the airway epithelium. We conclude that CCSP deficiency results in increased sensitivity to hyperoxia-induced lung injury as measured by increased mortality, early onset of lung edema, and induction of proinflammatory cytokine mRNAs.

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