Objective: In our previous study, human neural stem cells (HNSCs) proliferated in vitro for more than a year and transplanted into 24-month-old rat brains migrated and differentiated into neural cells and significantly improved the cognitive functions of these animals. Although HNSCs are a valuable source of transplantable material as an alternative to fetal neural tissue, the ideal replacement therapy would be autologous transplantation. In this study, we investigated the possibility of neuroreplacement therapy using adult stem cells pre-existing in an individual patient.
Designs: Although stem cells are often defined as self-renewing and multipotent, their ability to become a certain type of cell is particularly limited in adulthood in a tissue-specific manner. We propose: (1) Alteration of the fate decisions of adult peripheral stem cells and (2) Augmentation of endogenous NSC populations by drug treatment.
Materials and Method:
1) A subset of stromal cells in bone marrow, which has been referred to as mesenchymal stem cells (MeSCs), is capable of producing various connective tissues. Since the fate of stem cells is greatly influenced by contextual cues and stem cells can respond and differentiate into specific cell types according to environmental cues, we co-cultured HMSCs with differentiated HNSCs that may produce factors similar to those of brain tissue following treatment with 3 µM bromodeoxyuridine (BrdU) for 5 days. We also transplanted the BrdU-treated MeSCs into adult rodent brains, then 4-6 weeks after transplantation these brains were dissected out and sliced. Differentiation and migration patterns of the MeSCs were analyzed by inmmunocytochemistry using antibodies recognizing betaIII-tubulin (neuronal marker), glial fibrillary acidic protein (GFAP, astrocyte marker) and BrdU.
(2) MS-818, a pyrimidine derivative (3 mg/kg/day i.p.), was injected into rodents for five days. Then to analyze the stem cell population in the brain, 100 mg/kg/day of BrdU was injected (i.p.) for three days. The distribution of proliferating cells and the differentiation pattern of the BrdU-positive cells were assessed by a combination of BrdU and betaIII-tubulin immunohistochemistry, respectively.
Results:
(1) HMeSCs expressed various neuronal and astrocyte markers with a morphology similar to the neural cells derived from HNSCs after co-culturing for one week or four weeks after transplantation. These results indicate that MeSCs overcome their mesenchymal commitment by mean of the BrdU treatment and their exposure to appropriate environmental cues.
(2) MS-818 treatment increased the number of BrdU-positive cells more than seven-fold in the cortex of 27-month old rats compared with control animals. Four weeks after MS-818 treatment, BrdU-positive cells expressed betaIII-tubulin immunoreactivity. These results indicate that MS-818 increases endogenous NSC population, and more importantly, that endogenous stem cells, which have proliferated using MS-818 treatment, may beome differentiated into neurons
Conclusion: Since HMeSCs are relatively easy to isolate from bone marrow and MS-818 utilizes endogenouse stem cells, these technologies may provide an autologous cell therapies alternative to HNSCs transplantation for neuro-replacement.
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