Estradiol Promotes Hematopoietic Recovery of HSCT in Mice by Improving Bone Marrow Microenvironment

Although hematopoietic stem cell transplantation (HSCT) has made great progress in recent years, the transplant success rate needs to be further improved. Due to the poorly hematopoietic recovery, part of the patients who received donated bone marrow can not go out of danger safely. A small mount of cord blood for adult's hematopoietic reconstitution is often not enough. Therefore, to further enhance the donor HSC engraftment and improve hematopoietic recovery is crucial. Studies have been reported that the hematopoietic microenvironment including mesenchymal stem cells(MSCs), endothelial cells, osteoblasts, and so on has been injured during conditioning regimens by irradiation or drugs. Recent reports showed that estradiol not only induced MSCs into osteoblasts, but also inhibited differentiation of them into adipocytes, promoted their proliferation, protected them from hydrogen peroxide-induced apoptosis, and enhanced the recruitment of endothelial progenitor cells. Accordingly, we observed the effects of estradiol on hematopoietic recovery after HSCT in mice.

180 female BALB/c mice(7–9 weeks old) were separated randomly into control group(I), TBI group(II, myeloablative total body irradiation of 8.5 Gy ⁶⁰Co γ ray), TBI plus HSCT group(III, irradiation of 8.5 Gy ⁶⁰Co γ ray, transplanted with 5.0×10⁵ Lin#x2610;⁻, Sca-1⁺, c-kit^#x2610;+ cells separated from bone marrow by MACS kit per mouse), and TBI plus HSCT and estradiol group(IV, irradiation of 8.5 Gy ⁶⁰Co γ ray, administrated estradiol using slow-release pellets(100ng/d for 1 month), transplanted with 5.0×10⁵ Lin#x2610;⁻, Sca-1⁺, c-kit^#x2610;+ cells each mouse), 40 mice for each group, the rest were used to separate HSCs. Mice were subjected to irradiation of 8.5 Gy at rate of 0.65Gy/min with a distance of 2.43 meters from the source. The general condition of all mice was continuously observed: like mental state, vitality, coat color, body weight, diet, etc. Peripheral blood white blood cells(WBC) were counted, and pathological changes of bone marrow were evaluated by hematoxylin and eosin stain under microscope at Day 3, 6, 12, 18, 24, and 30 after administration, analyzing 8 mice of each group at every time point. The basement membranes were observed by the transmission electron microscope (TEM). PAS-8000 pathological image analysis system was used to measure the percentage of intramedullary fat cells area in sections.

General conditions of control group mice were good during observation, and there were few adipocytes in bone marrow. Peripheral blood WBC count of control group mice was stable, which was (10.8±1.7)×10⁹ cells/L on the 3rd day, significantly different from that of other groups mice. General conditions of experimental groups mice were worse, especially group II, of which the mice died of hematopoietic disorders during Day 8 –14. WBC count of three experimental groups dropped rapidly, while the amount of adipocytes in bone marrow increased significantly on the 6th day, reaching a peak on the 24th day. Percents of fat vacuoles area in bone marrow of group III mice were (19.2±3.0)%, (64.6±5.1)%, (85.6±6.1)%, (91.7±7.3)%, and (84.2±6.5)% at Day 6, 12, 18, 24, and 30, respectively, and corresponding WBC count were (5.3±1.1)×10⁵, (8.6±1.2)×10⁶, (6.7±1.1)×10⁷, and (7.8±1.1)×10⁹, (9.7±1.8)×10⁹ cells/L, respectively. But group IV had less adipocytes than other two experimental groups at corresponding time points. Percents of fat vacuoles area in group IV mice were (10.7±2.9)%, (33.4±4.9)%, (55.6±6.1)%, (81.5±6.8)%,and (69.2±6.7)%, respectively, and corresponding WBC count were (6.8±1.4)×10⁵, (1.6±0.4)×10⁷, (2.6±0.7)×10⁸, and (8.9±1.1)×10^9, (10.1±2.1)×10⁹ cells/L, respectively. Moreover, there was less intramedullary hemorrhage in bone marrow of the group IV mice than in group II and III at Day 3. Basement membranes were more completed showed by TEM.

Estradiol promoted hematopoietic recovery of HSCT in mice, which might through improving bone marrow microenvironment.

Liu:National Natural Science Fundation of China: Research Funding. Liu:National Natural Science Foundation of China: Research Funding.