Rosiglitazone Promotes Bone Marrow Adipogenesis to Impair Myelopoiesis under Stress.

OBJECTIVE: The therapeutic use of thiazolidinediones (TZDs) causes unwanted hematological side effects, although the underlying mechanisms of these effects are poorly understood. This study tests the hypothesis that rosiglitazone impairs the maintenance and differentiation of hematopoietic stem/progenitor cells, which ultimately leads to hematological abnormalities. METHODS: Mice were fed a rosiglitazone-supplemented diet or a normal diet for 6 weeks. To induce hematopoietic stress, all mice were injected once with 250 mg/kg 5-fluorouracil (5-Fu) intraperitoneally. Next, hematopoietic recovery, hematopoietic stem/progenitor cells (HSPCs) subsets, and myeloid differentiation after 5-Fu treatment were evaluated. The adipogenesis induced by rosiglitazone was assessed by histopathology and oil red O staining. The effect of adipocytes on HSPCs was studied with an in vitro co-culture system. RESULTS: Rosiglitazone significantly enhanced bone marrow adipogenesis and delayed hematopoietic recovery after 5-Fu treatment. Moreover, rosiglitazone inhibited proliferation of a granulocyte/monocyte progenitor (GMP) cell population and granulocyte/macrophage colony-stimulating factor (GM-CSF) colonies, although the proliferation and mobilization of Lin-c-kit+Sca-1+ cells (LSK) was maintained following hematopoietic stress. These effects could be partially reversed by the selective PPARγ antagonist BADGE. Finally, we demonstrated in a co-culture system that differentiated adipocytes actively suppressed the myeloid differentiation of HSPCs. CONCLUSION: Taken together, our results demonstrate that rosiglitazone inhibits myeloid differentiation of HSPCs after stress partially by inducing bone marrow adipogenesis. Targeting the bone marrow microenvironment might be one mechanism by which rosiglitazone impairs stress-induced hematopoiesis.

[Establishment of an mouse model of iron-overload and its impact on bone marrow hematopoiesis].

OBJECTIVE: To establish a mouse model of iron overload by intraperitoneal injection of iron dextran and investigate the impact of iron overload on bone marrow hematopoiesis. METHODS: A total of 40 C57BL/6 mice were divided into control group, low-dose iron group (12.5 mg/ml), middle-dose iron group (25 mg/ml), and high-dose iron group (50 mg/ml). The control group received normal saline (0.2 ml), and the rest were injected with intraperitoneal iron dextran every three days for six weeks. Iron overload was confirmed by observing the bone marrow, hepatic, and splenic iron deposits and the bone marrow labile iron pool. In addition, peripheral blood and bone marrow mononuclear cells were counted and the hematopoietic function was assessed. RESULTS: Iron deposits in bone marrow, liver, and spleen were markedly increased in the mouse models. Bone marrow iron was deposited mostly within the matrix with no significant difference in expression of labile iron pool.Compared with control group, the ability of hematopoietic colony-forming in three interventional groups were decreased significantly (P<0.05). Bone marrow mononuclear cells counts showed no significant difference. The amounts of peripheral blood cells (white blood cells, red blood cells, platelets, and hemoglobin) in different iron groups showed no significant difference among these groups;although the platelets were decreased slightly in low-dose iron group [(780.7±39.60)×10(9)/L], middle dose iron group [(676.2±21.43)×10(9)/L], and high-dose iron group [(587.3±19.67)×10(9)/L] when compared with the control group [(926.0±28.23)×10(9)/L], there was no significant difference(P>0.05). CONCLUSIONS: The iron-overloaded mouse model was successfully established by intraperitoneal administration of iron dextran. Iron overload can damage the hepatic, splenic, and bone marrow hematopoietic function, although no significant difference was observed in peripheral blood count.

Free iron catalyzes oxidative damage to hematopoietic cells/mesenchymal stem cells in vitro and suppresses hematopoiesis in iron overload patients.

OBJECTIVES: Transfusional iron overload is of major concern in hematological disease. Iron-overload-related dyserythropoiesis and reactive oxygen species (ROS)-related damage to hematopoietic stem cell (HSC) function are major setbacks in treatment for such disorders. We therefore aim to investigate the effect of iron overload on hematopoiesis in the patients and explore the role of ROS in iron-induced oxidative damage in hematopoietic cells and microenvironment in vitro. PATIENTS AND METHODS: The hematopoietic colony-forming capacity and ROS level of bone marrow cells were tested before and after iron chelation therapy. In vitro, we first established an iron overload model of bone marrow mononuclear cells (BMMNC) and umbilical cord-derived mesenchymal stem cells (UC-MSC). ROS level, cell cycle, and apoptosis were measured by FACS. Function of cells was individually studied by Colony-forming cell (CFC) assay and co-culture system. Finally, ROS-related signaling pathway was also detected by Western blot. RESULTS: After administering deferoxamine (DFO), reduced blood transfusion, increased neutrophil, increased platelet, and improved pancytopenia were observed in 76.9%, 46.2%, 26.9%, and 15.4% of the patients, respectively. Furthermore, the colony-forming capacity of BMMNC from iron overload patient was deficient, and ROS level was higher, which were partially recovered following iron chelation therapy. In vitro, exposure of BMMNC to ferric ammonium citrate (FAC) for 24 h decreased the ratio of CD34(+) cell from 0.91 ± 0.12% to 0.39 ± 0.07%. Excessive iron could also induce apoptosis, arrest cell cycle, and decrease function of BMMNC and UC-MSC, which was accompanied by increased ROS level and stimulated p38MAPK, p53 signaling pathway. More importantly, N-acetyl-L-cysteine (NAC) or DFO could partially attenuate cell injury and inhibit the signaling pathway induced by excessive iron. CONCLUSIONS: Our study shows that iron overload injures the hematopoiesis by damaging hematopoietic cell and hematopoietic microenvironment, which is mediated by ROS-related signaling proteins.