Mechanisms of myelofibrosis
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Primary Myelofibrosis (PMF) is characterized by an increase in megakaryocyte (MK) number, augmented bone marrow collagen cross-linking, osteosclerosis and splenomegaly. This thesis focuses on elucidating mechanisms behind myelofibrosis and osteosclerosis by using the Gata-1low mouse model of PMF, which displays the above hallmarks of PMF. Lysyl oxidase (LOX), a facilitator of collagen cross-linking, was reported to promote myelofibrosis in the Gata-1low mice. In past studies, Epidermal growth factor like 7 (Egfl7) was shown to bind and inhibit LOX. We generated transgenic mice with Egfl7 upregulated in MKs on a Gata-1low mouse background (PF4-Egfl7/Gata-1low founders # 2 and # 19) to test the hypothesis that Egfl7 inhibits LOX and decreases myelofibrosis. We found an increase in MK Egfl7 mRNA expression in transgenic mice over Gata-llow controls, but Egfl7 protein was not detected by western blotting in in vitro differentiated mature MK lysate and supernatant. At 30 weeks of age, the percentage of bone marrow MKs (WT n=4; Gata-1low n=5; #19 n=6; #2 n=2), platelet count (WT n=3; Gata-1low n=10; #19 n=11; #2 n=4), spleen weight/body weight (WT n=3; Gata-1low n=11; #19 n=11; #2 n=4) and bone marrow fibrosis (WT n=5; Gata-1low n=8; #19 n=4; #2 n=3) were not statistically different in the experimental groups, with platelet number tending to be greater in transgenic compared to Gata-1low mice. More studies are needed to measure Egfl7 protein in blood serum and primary MKs, to increase sample size, and to examine our hypothesis in mice with greater transgenic expression of Egfl7. Osteosclerosis is an increase in trabecular bone formation in the medullary cavity of the femur. Our studies showed an increase in the progression of trabecular bone infiltration into the medullary cavity of the Gata-1low female versus Gata-1low male mice at ages 10-30 weeks old that was not due to differences in Gata-1 mRNA expression levels, osteoclast number per bone surface area (these cells promote bone resorption), or MK number (source of growth factors) in the bone marrow. This finding opens possibilities for studies that focus on the role of sex hormones and osteoblast differentiation in the progression of osteosclerosis in the Gata-1low mice.