Kupffer Cells Support Hepatic Erythropoiesis Induced by Nitrogencontaining Bisphosphonate in Splenectomized Mice

Abstract

Purpose: Our previous study indicated that nitrogen-containing bisphosphonate (NBP) induced the extramedullary erythropoiesis in the spleen by the depletion of bone marrow resident macrophages, which support erythropoiesis. In this study, we focused on the liver as the site of extramedullary hematopoiesis in NBP-treated splenectomized mice. Methods: Splenectomized mice were treated with NBP (4-amino-1-hydroxybutylidene-1, 1-bisphosphonate, 40μmol/kg). At several indicated times, livers and bone marrows were analyzed by histological, immunohistochemical, ultrastructural and molecular biological methods. Blood samples were examined by hematocrit value and ELISA for erythropoietin.FigureResults: F4/80 positive macrophages were depleted and TER119 positive erythroid cells were significantly decreased in bone marrow of NBP-treated mice while NBP-treated mice did not display anemia or significant change in EPO production. In the liver of NBP-treated mice, erythropoiesis, megakaryopoiesis and CD34 positive hematopoietic precursor cells were constantly observed. Erythroblastic islands were detected in the sinusoidal lumen. By RT-PCR analysis, several mRNA related to hematopoiesis were also up-regulated in the liver of NBP treated mice. Moreover, Kupffer cells expressed VCAM-1 following NBP treatment, which molecular is an important factor for formation of erythroblastic island and erythroblast differentiation. Cl2MBP-liposome treatment depleted the erythroblastic islands in the liver. Colony forming assays indicated the decrease of the number of hematopoietic cells in the liver. Conclusion: In this study, we have established extramedullary erythropoiesis in the liver of a splenectomized mice following NBP treatment for depleting bone marrow resident macrophages. Our data indicate that Kupffer cells support hepatic erythropoiesis, acting as stromal cells in the liver by the change their phenotype. Furthermore, Kupffer cell might regulate the differentiation and proliferation of other hematopoietic cells by acting as a niche for hematopoietic precursor cells in an emergency. This study was supported by Grant-in-Aid for Scientific Research (21592342, 20592148) from the Ministry of Education, Culture, Sports, Science and Technology of Japan, and High-Tech Research Center Project for Private Universities from Ministry of Education, Culture, Sports, Science and Technology, Japan.