Hydrocortisone regulates types I and III collagen gene expression and collagen synthesis in human marrow stromal...

Hematopoiesis is the resultant of the orderly molecular and cellular interactions between progenitor cells and stroma. In vitro studies (Dexter-type cultures) have shown that initiation of hematopoiesis only occurs after establishment of a hydrocortisone-dependent layer of stromal cells. Although the molecular basis for the requirement of hydrocortisone are not well understood, data have shown that synthesis/assembly of extracellular matrix molecules (proteoglycans and fibronectin) is regulated by hydrocortisone. Since interstitial collagens are abundantly expressed in the marrow stroma, we investigated whether hydrocortisone may also modulate the expression of collagen types I and III. For these studies, human bone marrow fibroblast cultures were grown in standard culture medium either in the absence or presence of 10(-7) M hydrocortisone. Under both conditions, bone marrow fibroblasts synthesized collagen types I and III, and expressed the respective genes. However, hydrocortisone produced a decrease in the synthesis of interstitial collagens and also in the relative abundance of pro-alpha 1(I) and pro-alpha 1(III) mRNAs. The results of this study are consistent with the assumption that glucocorticoids regulate the expression of several extracellular matrix molecules in the marrow stroma and thus permit in vitro hematopoiesis to occur.