| Current theory believes that there are two separated cell system in adult bone marrow. One is hematopoietic system, and another is non-hematopoietic system, or stromal cell system. Bone marrow stromal cells (BMSC) serve as heamatopoiesis microenvironment. However, recently studies demonstrated that BMSC could be potential not only to differentiate into mesoderm original bone, cartilage, muscle and adipocytes ect, but also into exoderm original neural cells and keratinocytes, and endoderm original gastrointestinal epithelial cells. Moreover, BMSCs also can give rise to heamatopoietic cells.Upon our primary study, we proposed a hypothesis that adult bone marrow harbors pluripotent non-adherent BMSCs that can migrate into any organ of the body through circulation in vivo. Furthermore, under the appropriate microenvironment, they can adhere, proliferate and differentiate into specialized cells of the target tissue, and then function normally in metabolism and in tissue repair.To test this hypothesis, three experiments have been conducted.I. To prove whether non-adherent bone marrow stromal cells (NA-BM-SCs) exist in adult bone marrow, different cell culture methods were employed to determine whether non-adherent BMCs can give rise to stromal cells; whether NA-BM-SCs can renew themselves; and whether NA-BM-SCs can differentiate into multi-lineage cells in vitro. The results showed that NA-BM-SCs not only gave rise to fibroblastic colony forming unite (CFU-f), but also could renew themselves and differentiate into osteoblasts, chondrocytes, adipocytes and glial cells.II. To determine whether NA-BMC-derived SCs (NA-BM-SCs) can differentiate into terminal cells of the multi-tissues and can function in normal metabolism and in repairing damaged tissues in vivo, NA-BMC-SCs from male wild-type mice were transplanted into lethal-dose irradiated female vitamin D receptor gene knockout (VDR-/-) mice. Organs from these lethal-dose irradiated mice were analyzed. The results showedthat all lethal-dose irradiated mice not transplanted with NA-BM-SCs died within 2 weeks with exhausted of haematopoietic system, severe putrescence of intestines and local necrosis of multi-tissues. However, 75% ^ 65% and 60% lethal-dose irradiated mice transplanted with NA-BM-SCs survived at 30, 60 and 90 days following the transplantation, respectively. In addition, the numbers of WBC, RBC and PUT in peripheral blood were recovered to normal levels at 30 days in survival transplant recipients. VDR gene was detected by PCR in various tissues of survival transplant VDRV recipients, such as heart, liver, spleen, lung, kidney, peripheral blood, bone marrow cells, skin and small intestine. By immunohistochemistry, VDR positive immunopositive reactions were observed in BMC, spleen cells and gastrointestinal epithelia of survival transplant VDRV" recipients. The results demonstrated that the transplantation of NA-BM-SCs could rescue lethal-dose irradiated VDRV' mice by reconstitution heamatopoeitic system and by repairing damaged tissues caused by the irradiation. The NA-BM-SCs could differentiate into terminal cells of the multi-tissues and function normally in metabolism and in repairing damaged tissues in vivo.III. To determine whether the transplantation of NA-BM-SCs can rescue the phenotypes of la-hydroxylase gene knock-out (laCOHjase''") mice, an animal model of I type genetic rachitic, NA-BM-SCs from male wild-type mice were transplanted into lethal-dose irradiated female la(OH)ase"A mice. The skeletal phenotype and peripheral blood were examined. The results showed that the survival rate of recipients was 70% in 2 months after the transplantation. RT-PCR analysis revealed a normal level of la(OH)ase mRNA in intestine and bone and a lower level in kidney. Serum 1,25(OH)2D3 levels were undetectable in la(OH)ase-/- mice and rose to 25% of WT mice in survival transplant recipients. Serum calcium and bone mineralization of survival transplant recipients improved but did not reach to the normal level, despite of the complete recovery of damaged osteoblasts caused by the irradiation. Surprisely, the transplantation of NA-BM-SCs could not only rescue most lethal-dose irradiated la(OH)ase"/" mice, but also normalize the decreased number of WBC in peripheral blood and CD4, CD8 positive cells in spleen in survival transplant recipients. These results suggest that only a few renal epithelial cells, which are major cells to product la(OH)ase, are donor original, whereas most bone marrow cells are donor original. This mightexplain why the rachitis was only rescued partially, whereas the abnormalities of blood were rescued completely.In conclusion, the experiments confirmed our hypothesis that adult bone marrow harbors pluripotent non-adherent BMSCs. These cells in vivo can migrate into most organ of the body through circulation. Furthermore, under the appropriate microenvironment, they can adhere, proliferate and differentiate into specialized cells of the target tissue, and then function normally in metabolism and in damaged tissue repair. |
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