Cell-specific expression of the α1(I) collagen promoter-CAT transgene in skin and lung: A response to TGF-β subcutaneous injection and bleomycin endotracheal instillation

Abstract

Transgenic mice containing a rat collagen α1(I) promoter (3.6 kilobases) fused to the reporter gene chloramphenicol acetyl transferase (CAT) express the reporter gene parallel to endogenous gene in most connective tissues other than vascular tissue [Pavlin et al. (1992): J Cell Biol 116:227–236; Bedalov et al. (1994): J Biol Chem 269:4903–4909]. We have challenged transgenic mice with subcutaneous injections of transforming growth factor-β (TGF-β) or intratracheal instillation of bleomycin. In situ hybridization studies of skin revealed increased CAT expression in the papillary dermis of TGF-β treated animals. In contrast, α1(I) collagen mRNA was expressed throughout the dermis including granulation tissue and reticular dermis. Therefore, the transgenic promoter responds to TGF-β in a subset of dermal fibroblasts. Endotracheal instillation of bleomycin induces lung fibrosis which is thought to be mediated in part by TGF-β. CAT gene expression in lungs was increased 6–8-fold at 2 weeks post bleomycin treatment. In situ hybridization studies revealed focal areas of cells expressing both CAT and collagen genes in the interstitium. However, most regions, especially around airways, contained a subset of cells expressing the endogenous gene with little or no CAT expression as judged by in situ hybridization. These cells could be myofibroblasts that require additional cis-acting elements to activate α1(I) collagen gene expression similar to smooth muscle cells. © 1996 Wiley-Liss, Inc.