Normal development of fetal hepatic haematopoiesis during the second trimester of gestation is upregulated by fibronectin expression in the stromal cells of the portal triads.

OBJECTIVE in midtrimester fetuses the principal site of hematopoiesis is the liver. In hematopoietic organs, stromal cells such as fibroblasts, epithelial cells, and macrophage-like cells develop networks to maintain hematopoiesis, i.e. hematopoietic stem cell self-renewal, proliferation, and growth, by interaction with hematopoietic progenitor cells. ECM glycoproteins produced by the stromal cells are known to play a critical role in the regulation of cell growth and differentiation. Numerous soluble and membrane-bound factors directly regulating haematopoiesis have been documented, but little is known about fetal hepatic stromal cell activity and stromal extracellular matrix protein-fibronectin, on fetal hepatic haematopoiesis. The binding of late stage erythroid cells to fibronectin has been well characterized and is believed to be critical for the terminal stages of erythroid differentiation. The intention of this article is to determine the role of fibronectin in fetal hepatic hematopoietic proliferation and differentiation in different stages of development. MATERIAL AND METHOD we examined and compared the immunohistochemical expression of fibronectin in the hepatic stromal portal fields in the 1st, 2nd, and 3rd trimester of gestation respectively, in relation to the appearance of CD34 progenitor hematopoietic, stromal progenitor and vascular endothelial positive cells. RESULTS our results demonstrated a quantitative difference in the second trimester of gestation concerning the expression of fibronectin in the connective tissue stroma of the hepatic portal fields over the equivalent expression of the protein in the first (p < 0.0001, t-test) and third trimester (p < 0.0001, t-test). Similar changes in the above period were found concerning the expression of CD34 during the second trimester of gestation, over the first (p < 0.0001, t-test) and third trimesters (p < 0.0001, t-test), suggesting a direct involvement of fibronectin in the sustaining of hematopoietic activity. CONCLUSIONS our data provide evidence that an ECM glycoprotein component, fibronectin, plays a relevant role in hematopoiesis through interaction between stromal cells and hematopoietic progenitor cells.