Increased synthesis of extracellular spleen glycosaminoglycans in an experimental myeloproliferative syndrome.

The changes occurring in the hematopoietic extracellular matrix in an experimental myeloproliferative syndrome were explored by comparing the glycosaminoglycan (GAG) composition of normal mouse spleens and spleens infected with myeloproliferative sarcoma virus (MPSV). Large quantities of hyaluronate and of sulfated GAGs accumulated in the extracellular matrix of infected spleens, as shown by histoimmunoassay and alcian blue staining, respectively. The splenic GAGs were either labeled with 35S-sulfate injected in vivo or unlabeled. The spleens were fractionated to separate hematopoietic cells from the stromal component containing extracellular matrix material and fibroblasts, and the GAGs were extracted from each fraction. Specific degradative treatments and electrophoresis indicated that sulfated GAGs were mostly chondroitin sulfate and heparan sulfate. Three hours after in vivo injection of 35S-sulfate, the amount of 35S-GAGs was increased approximately fivefold per mg stromal proteins. The bulk of these 35S-GAGs (70%) was recovered in the stromal fraction. The higher amount of sulfated GAGs in leukemic spleen was due both to the presence of more producer cells (infected fibroblasts and hematopoietic cells) and to a stimulation of GAG synthesis per cell, as evidenced 35S-labeling in in vitro experiments. Chondroitin sulfate was the main sulfated GAG present in the culture medium of both hematopoietic and fibroblastic cells and in the pericellular material released by trypsin from fibroblastic cells. High amounts of chondroitin sulfate, which has a possible role in the detachment of hematopoietic cells from the stromal cells, may favour the release of hematopoietic cells from the spleen into the peripheral blood. Heparan sulfate was produced by fibroblastic cells and it was principally present in their pericellular material. Considering the capacity of heparan sulfate to retain cytokines, as demonstrated by others in vitro, large amounts of heparan sulfate may result in the retention of large amounts of the cytokines, which production is enhanced in the infected spleen. This phenomenon may contribute to promote the hematopoietic stem cell proliferation characteristic of the MPSV-induced myeloproliferative disease.