Differential expression of collagenase by human fibroblasts and bone marrow stromal cells

The bone marrow stroma, represented in long-term marrow culture by cells of the adherent layer, is composed of a heterogenous mixture of macrophages and mesenchymal cells, including fibroblasts, endothelial cells and adipocytes, in association with a proteoglycan matrix. This matrix, which is synthesized by the stroma, is capable of binding hematopoietic growth factors, and likely plays a major role in hematopoietic regulation. Clonally-derived non-transformed bone marrow stromal cells, propagated in the presence of basic fibroblast growth factor, were studied for expression of collagenase, an enzyme whose substrate, collagen, is a major component of the extracellular matrix. Expression of steady-state collagenase mRNA was undetectable in both unstimulated dermal fibroblasts and non-transformed marrow stromal cells. However, stimulation with interleukin 1 alpha (10 U/ml) for 24 h resulted in marked accumulation of collagenase mRNA in dermal fibroblast cells, yet failed to elicit a similar response in bone marrow stromal cells. Both marrow stromal cells and dermal fibroblasts constitutively expressed transcripts of collagen I, and rhIL-1 alpha upregulated transcripts of interleukin 6 in both these cells as well. Although similar in morphology, these data indicate that bone marrow stromal cells differ from fibroblasts in their response to IL-1. In the marrow microenvironment, where IL-1 may be secreted by a variety of cell types, such suppression of collagenase expression may serve to prevent unwanted mobilization of collagen from the glycoprotein matrix by marrow stromal cells.