Quantitative Analysis of Growth Factor Production in the Mechanism of Fibrosis in Agnogenic Myeloid Metaplasia.

There are previous reports that growth factors including TGF-β1, PDGF and FGF produced by megakaryocytes are responsible for the etiology of fibrosis in agnogenic myeloid metaplasia (AMM). Due to the technical difficulty in isolating enough megakaryocytes from the inaspirable bone marrow from patients with AMM, a quantitative analysis of these growth factors produced by the megakaryocytes and correlated to the degree of myelofibrosis has not been able to be performed. The present study employed the cell culture technique to grow megakaryocytes from blood CD 34⁺ cells and then perform the quantitative analysis of these growth factors, compared with other sources such as monocyte-macrophage lineages and correlated to the degree of bone marrow fibrosis. We found TGF-β1, PDGF and FGF produced by the megakaryocytes were significantly elevated in AMM compared with normal controls (p<0.05) and TGF-β1 was more abundantly produced than PDGF or FGF. While these growth factors are several fold elevated in AMM compared with other MPD including essential thrombocythemia (ET), polycythemia vera (PV), it was not statistically significant. A quantitative analysis of these growth factors produced by the CD 14⁺ cells in the blood and bone marrow showed that these growth factors were not significantly elevated in AMM compared with other MPD or controls and were significantly elevated only in some patients (defined as elevation of more than 2 SD of the controls). The correlation of these growth factors produced by the megakaryocytes or monocyte-macrophage lineages with degree of myelofibrosis in 12 patients with AMM were r=0.73 and 0.23 respectively (Non parametric (Spearman) correlation with two-tailed analysis was used to calculate the correlation). We concluded:

1. In AMM, these fibrosing growth factors are mainly produced by the megakaryocytes and in some patients, monocyte-macrophage lineages may contribute to the production of these growth factor production.

2. TGF-β1 is more abundantly produced from the megakaryocytes than PDGF or FGF confirming TGF-β1 is the most important fibrosing growth factor in the pathogenesis of myelofibrosis in AMM.

3. A statistically significant correlation of the growth factor and degree of myelofibrosis in AMM suggests that these fibroing growth factors produced by the megakaryocytes are main etiology of bone marrow fibrosis in AMM.