Factor X: The Molecular Connection Between Hematopoietic Cells and Osteoblasts

Sylvia Lee¹,  Matthew Christopher and Daniel Link², Biology Department, Washington University, St. Louis, MO¹, Washington University School of Medicine²

The formation and development of hematopoietic cells and bone cells are closely related. Originating in the bone marrow, both cell types are able to send signals, which allow them to regulate each other.

Dr. Link’s lab researches the interactions between bone cells and hematopoietic cells. By treating mice with granulocyte-colony stimulating factor (G-CSF), a glycoprotein that stimulates neutrophil production, it has been discovered that the glycoprotein downregulates osteoblast number and function. Interestingly, hematopoietic cells have a receptor specifically for G-CSF, while osteoblasts do not. Therefore, in order for the osteoblast number/function to decrease when mice are treated, some factor (as of yet unknown) must be signaling the osteoblasts.

The hypothesis of this experiment was that transforming growth factor- β1 (TGF- β1), a candidate gene for “Factor X,” is indeed the molecule that regulates osteoblasts after being released by hematopoietic cells. TGF-β1 is a prime candidate for “Factor X” because it is a secreted cytokine that is known to regulate osteoblast development. Furthermore, it is produced by monocytes, which are regulated by G-CSF. To examine the hypothesis, two experiments were performed. The first experiment compared total bone marrow TGF- β1 mRNA expression in treated and untreated mice. The second experiment measured TGF- β1 mRNA expression in treated versus untreated cultured macrophages. In both cases, quantitative real time RT-PCR (q-RT-PCR) was performed. It was determined that the levels of TGF-β1 do not change in total bone marrow mRNA of mice that have been treated with G-CSF.  At this time, there is not sufficient data to make any conclusions about relative TGF- β1 mRNA expression from the cultured macrophages.

In the future, TGF- β1 will be further studied by continuing to experiment with the macrophage cultures as well as by looking at TGF-β1 protein (ELISA).