Expression of alpha-smooth muscle actin in murine bone marrow stromal cells.
Human fibrotic bone marrow (BM) stroma has been shown to contain alpha-smooth muscle actin (alpha-SMA)-positive cells. These closely resemble myofibroblasts that were described in other fibrotic tissues. We studied the expression of alpha-SMA in a series of murine BM-derived stromal cell lines to investigate the cellular origin and functional significance of myofibroblast-like cells in hematopoietic tissues. Although these cell lines differed in their biologic properties, most of them expressed alpha-SMA under certain conditions. Cells expressing alpha-SMA constituted a minor population in post-confluent, growth-arrested cultures. However, the incidence of cells expressing alpha-SMA increased significantly when cultures were transferred to nonconfluent conditions. A similar increase in alpha-SMA-positive cells occurred after a strip of cells was scraped away from the confluent cell layer; the cells of the affected area acquired alpha-SMA-positive contractile phenotype. The relationship between alpha-SMA expression and hematopoietic activity was studied using a cloned cell line of BM origin (14F1.1). The ability of these endothelial-adipocyte cells to support hematopoiesis in vitro was maximal under confluent conditions, whereas their expression of alpha-SMA under such conditions was residual. Moreover, in long-term BM cultures supported by confluent 14F1.1 cells, stromal areas associated with proliferating hematopoietic precursors, known as "cobblestone areas," were devoid of alpha-SMA-positive cells. These observations suggest that the expression of alpha-SMA is reversible and inversely related to hematopoietic activity.
Peled
A
A
Department of Cell Biology, Weizmann Institute of Science, Rehovot, Israel.
Zipori
D
D
Abramsky
O
O
Ovadia
H
H
Shezen
E
E
D000199:Actins / Q000032:analysis* / Q000096:biosynthesis; D000818:Animals; D000911:Antibodies, Monoclonal; D015153:Blotting, Western; D001853:Bone Marrow / Q000502:physiology*; D001854:Bone Marrow Cells; D002460:Cell Line; D002999:Clone Cells; D005455:Fluorescent Antibody Technique; D007124:Immunoenzyme Techniques; D051379:Mice; D009130:Muscle, Smooth / Q000502:physiology; D011863:Radioimmunoassay; D014746:Vimentin / Q000032:analysis
D000199:Actins; D000911:Antibodies, Monoclonal; D014746:Vimentin