The role of Sf-Stk in stress erythropoiesis

Open Access
- Author:
- Shi, Lei
- Graduate Program:
- Integrative Biosciences
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- January 12, 2011
- Committee Members:
- Robert Paulson, Dissertation Advisor/Co-Advisor
Robert Paulson, Committee Chair/Co-Chair
Pamela Hankey, Committee Member
Wendy Hanna Rose, Committee Member
Zhi Chun Lai, Committee Member
Naomi S Altman, Committee Member - Keywords:
- stress erythropoiesis
Sf-Stk
Friend Virus - Abstract:
- Erythropoiesis refers to the differentiation from LT-HSC through CMP, BFU-E and CFU-E to mature erythrocytes. Homeostatic erythropoiesis occurs in bone marrow in a slow and steady rate to replace old red blood cells. Stress erythropoiesis, on the other hand, occurs in adult liver and spleen to produce large quantity of red blood cell in a short period of time in response to acute anemia. It relies on high Epo concentration and utilizes unique erythroid progenitors other than homeostatic erythropoiesis. Except for Epo, BMP4, SCF and Shh are also required in stress erythropoiesis. The results in our lab in the past decades suggest that erythroid progenitors in bone marrow migrate to spleen where they respond to several factors including GDF15, Shh and SCF and differentiate into BMP4 responsive cells. BMP4R give rise to stress BFU-E when BMP4 is present. Stress BFU-Es respond to high concentration of Epo and give rise to large quantity of erythrocytes in a short period of time. Friend virus is another good model to study stress erythropoiesis. Friend virus induces erythroleukemia in Friend virus sensitive mice through a two stage progression. During the first step, Friend virus induces polyclonal expansion of infected erythroid progenitors in the absence of Epo. In the second stage, a proviral insertion activates Pu.1 gene which keeps infected erythroid progenitors in undifferentiating stage and leads to erythroleukemia. Only one viral protein – gp55, is required to induce this Epo independent polyclonal expansion. Recent research suggested that gp55 interact with a truncate form of stem-cell tyrosine kinase (Sf-Stk) on the cell surface to promote the proliferation of infected erythroid progenitors. Since the similarity between Friend virus induced polyclonal expansion of erythroid progenitors and stress erythropoiesis, it has been proposed that Friend virus utilize the stress erythropoiesis pathway to infect target cells. Further experiments from our lab demonstrate that hypoxia and BMP4 can increase Friend virus target cells in spleen which are also stress erythroid progenitors. f/f mutant mice which have a delay recovery from acute anemia are defective in Friend virus targets. Since the important role Sf-Stk in Friend virus induced polyclonal expansion, we hypothesize that Sf-Stk may play an intrinsic role in stress erythropoiesis. In the second chapter, we demonstrated that stress erythropoiesis is induced in adult liver during tissue hypoxia in the absence of spleen. Splenectomized f/f mice exhibit similar defects in stress erythropoiesis as f/f mice. BMP4 is expressed in liver corresponding to the expansion of stress BFU-E. Furthermore the splenectomized f/f mice are defective in liver erythropoiesis as well which correspond to the defect in BMP4 expression which indicates a role of BMP4 pathway in liver stress erythropoiesis as well. We concluded that BMP4 signal pathway plays a role in extramedullary erythropoiesis, which primarily occurs in spleen and fetal liver or adult liver when spleen is absent. In the third chapter, we tested the expansion and differentiation of erythroid progenitors in the Sf-Stk deficient mice. The data reveal that Sf-Stk-/- mice have fewer stress BFU-Es as well as CFU-Es in spleen. The mutant stress BFU-Es have less potential to expand into erythrocytes. We also observed greater mortality rate in Sf-Stk-/- mice during the recovery from bone marrow transplantation which indicate that the expansion of erythroid progenitors in bone marrow is also affected by Sf-Stk deficiency. Further studies on bone marrow cells reveal that the Sf-Stk deficient bone marrow cells have an early expansion of stress BFU-Es during in vitro culturing than control mice which corresponds with the observation that mutant spleen cells have early terminal differentiation during in vitro culturing. A study of the RBC life span indicates that there is an early expansion of RBCs in Sf-Stk-/- mice during the recovery from bone marrow transplantation. Those early emerged RBCs are defective and removed early during the recovery. This disruption of new RBC in Sf-Stk-/- mice during the recovery corresponds with the death of Sf-Stk-/- mice after bone marrow transplantation. Combining all those observations we propose that Sf-Stk may participate in promoting the proliferating and/or suppressing the differentiating of erythroid progenitors. When Sf-Stk expression is abrogated, stress erythroid progenitors fail to amplify and differentiate early which exhaust the pool of erythroid progenitors. The early expansion of erythroid progenitors generate defective new RBCs which were removed early leading to higher mortality rate during the recovery from bone marrow transplantation induced acute anemia.