Vascular smooth muscle differentiation of murine stroma: A sequential model

Precious studies by our group showed that stromal cells from human long-ter m marrow cultures were mesenchymal cells following a vascular smooth muscle pathway. The present study using 58 immortalized stromal lines from differ ent hematopoietic sites was conducted to verify whether this hypothesis als o held true for murine stroma, principal components analysis performed usin g cytoskeletal and extracellular matrix proteins allowed the segregation of five factors explaining more than 70% of the variance. Factor I, including osteopontin and vimentin, and factor II, laminins and fibronectins, were r epresentative of the mesenchyme. The remaining three factors mere represent ative of vascular smooth muscle: factor III, including alpha SM actin, SM a lpha actinin, SM22 alpha, EDa(+) fibronectin, and thrombospondin-1; factor IV, metavinculin and h-caldesmon; and factor V, smooth muscle myosin SM1 an d desmin. All lines expressed factors I and II; 53 lines expressed factor I II, 35 lines expressed factor IV; and II lines expressed factor V. A second principal components analysis including membrane antigens indicated the co segregration of vascular cell adhesion molecule-1 with osteopontin and that of Ly6A/E with vimentin, whereas CD34 and Thy-1 appeared to be independent factors. The heterogeneity of vascular smooth muscle markers expression su ggests that harmonious maintenance of hematopoiesis depends on the cooperat ion between different stromal cell clones. (C) 1999 International Society f or Experimental Hematology. Published by Elsevier Science Inc.