Differential expression of CCAAT enhancer binding protein family in rat alveolar epithelial cell proliferation and in acute lung injury

Although alveolar reorganization after acute lung injury depends on regeneration of alveolar epithelial cells, there is little knowledge of regulation of pulmonary healing process. Transcription factors may play key roles in this regulation. To investigate whether the CCAAT enhancer binding protein (C/EBP) family, alpha, beta, and delta, were involved in alveolar reorganization after injury, we examined expression of C/EBP proteins and mRNAs in lung injuries induced by lipopolysaccharide (LPS) or bleomycin (Bleo) and in cell proliferation by keratinocyte growth factor (KGF). By immunohistochemistry, we demonstrated that C/EBP alpha and C/EBP beta were expressed in alveolar type II cells and alveolar macrophages, but C/EBP delta was expressed restrictedly in some of alveolar type II cells in a spatial pattern in the control lungs. Further, these three C/EBP family members were differentially expressed in alveolar cell proliferation and in acute lung injury, in which, interestingly, C/EBP alpha and C/EBP delta were reciprocally expressed in alveolar type II cell proliferation and in pulmonary fibrosis. However, expressions of their mRNAs by in situ hybridization were dramatically increased in the affected lesions of the lungs by LPS and Bleo, and Northern blot analysis showed an increased abundance of the mRNA for C/EBP beta in LPS-treated lungs and for C/EBP delta in Bleo-treated lungs, compared with those in the control lungs. Thus, differential expression of the C/EBP family may be required to maintain and reorganize the basic integrity of alveolar structure during pathological states, which suggests an important role for the C/EBP family in maintaining normal alveolar architecture and function and in repairing the damaged epithelium after injury.