Recent studies clearly showed that neurogenesis continued to occur in the certain brain regions including hippocampus. The stem or progenitor cells are divided equally (proliferation) or unequally, survive apoptosis and differentiate to mature neuron and glia. Such newborn cells integrate into existing neuronal networks, make synaptic contacts and finally change the plasticity. The proliferation is decreased by stress, but chronic treatment of antidepressants increases it. We have shown the involvement of cAMP-CREB cascade in mature granule cells of dentate gyrus (DG) around stem/progenitor cells in the drug action. And to see the direct effect of some psychotropic drugs, we established the culture system of adult rat DG-derived neural precursor cell (ADP). Several antidepressants did not affect the proliferation. Moreover 5-HT did not promote the proliferation of ADPs. On the other hand, noradrenaline and lithium directly increase the proliferation. Further investigation is needed to develop new antidepressant drugs.

In this review, we discuss recent issues about cancer stem cells, especially in solid tumors. Cancer stem cells show the ability to self-renew; and they possess multi-potential differentiation and tumorigenic potential. Cancer stem cells are reported to show resistance to anticancer drugs and radiotherapy, and therefore, they are involved in progression, recurrence, and metastasis in cancer. The existence of cancer stem cells in leukemia has long been known, since early times. In recent years cancer stem cells have been identified in solid tumors of breast, prostate, lung, brain, colon, and pancreas, owing to the development of identification techniques using cell surface markers. Although many features remain to be addressed, it is expected that cancer stem cells could be a main target for cancer therapy in the near future.

Stem cells supply differentiated cells that compose the body organs. Stem cell research is increasing and their use in regenerative medicine is drawing a lot of attention. In ophthalmology, regenerative medicine of the corneal epithelium is already practiced by clinicians, and there is constant improvement in the culture methods. Research leading to the isolation of corneal epithelial stem cells, a kind of adult stem cell whose existence has been suggested, is done using various methods such as flow cytometry and selective culture methods. In this review, regenerative medicine of the corneal epithelium, stem cell isolation and culture methods are explained; and our new discoveries of stem cells' features such as their high adhesive ability is explained.

Induced pluripotent stem (iPS) cells, which are generated from somatic cells by transducing four genes, are expected to have broad application to regenerative medicine. Although establishment of an efficient gene transfer system for iPS cells is considered to be essential for differentiating them into functional cells, the detailed transduction characteristics of iPS cells have not been examined. By using an adenovirus (Ad) vector containing the cytomegalovirus enhancer/beta-actin (CA) promoters, we have developed an efficient transduction system for mouse mesenchymal stem cells and embryonic stem (ES) cells. Also, we applied our transduction system to mouse iPS cells and investigated whether efficient differentiation could be achieved by Ad vector-mediated transduction of a functional gene. As in the case of ES cells, the Ad vector could efficiently transduce transgenes into mouse iPS cells. We found that the CA promoter had potent transduction ability in iPS cells. Moreover, exogenous expression of a PPARγ gene or a Runx2 gene into mouse iPS cells by an optimized Ad vector enhanced adipocyte or osteoblast differentiation, respectively. These results suggest that Ad vector-mediated transient transduction is sufficient to promote cellular differentiation and that our transduction methods would be useful for therapeutic applications based on iPS cells.

Suicide gene therapy with retroviral vector-producing cells was feasible as an adjuvant to the surgical resection of recurrent glioblastoma, although any benefit appeared to be marginal. Further evaluation of the therapeutic strategy with the vector-producing cells must incorporate improved delivery of vectors and transgenes to the target cells. We have previously demonstrated the ability of vector-producing tumor cells engineered by the adenovirus-retrovirus hybrid vector to destroy satellite tumor cells, although therapeutic efficacy for aggressive tumor has to be further evaluated by the systemic delivery of the vector-producing cells. Mesenchymal stem cells (MSCs) should be an effective delivery vehicle to seek out tumor cells in vivo and transport cancer-killing gene or immune products with minimal rejection reaction by the host. We developed vector-producing tumor-tracking cells to improve suicide cancer gene therapy. Nucleofection was attempted to deliver retrovirus vector components into rodent MSCs. Athymic nude mice with subcutaneous 9L glioma were received vector-producing MSCs through the left ventricular cavity. Optical bioluminescence imaging in vivo revealed accumulation of the MSCs into the subcutaneous 9L tumors but not Rat-1 transplants. Consequently, the vector-producing MSCs significantly enhanced pro-drug killing of glioma cells compared to MSCs without ability to generate progeny virus. Our study demonstrated the effective MSCs-mediated tumor transduction with progeny vector production to improve suicide gene therapy. Although therapeutic benefit in the various orthotopic or metastatic tumor models has to be further validated, this transduction strategy would eradicate evasive tumors in situ.

Malignant glioma is one of the most lethal diseases in adulthood. The median survival of patients with the Grade IV glioma, glioblastoma multiforme (GBM), is shorter than 15 months and the current first-line therapies for this devastating disease have only a palliative effect. The cancer stem cell hypothesis has recently attracted a great deal of attention, owing to the promise of a novel cellular target for the treatment of tumors including GBM. Recent studies have demonstrated that existence of cancer stem cells in brain tumors (BTSC) accounts, at least in part, for the intractability of malignant glioma. From the therapeutic standpoint, characterization of the mechanism for tumor initiation and maintenance of the "stem-like state" of BTSC is crucial. However, multiple heterogeneous subtypes of cancer stem cells have recently been identified from malignant glioma, making the idea of cancer stem cell complicated. In addition, in some cancer types (e.g. melanoma), a considerable proportion of tumor cells may possess the stem cell property, indicating cancer stem cells may not be a rare cell population in tumors, at least in some organs. Based on the extensive genetic and epigenetic characterization of tumor growth mechanisms, various molecularly-targeted therapies have already been applied for patients, demonstrating a varying degree of success in cancer treatment. A significant improvement in patient prognosis was achieved in several cancer types including leukemia and breast cancer. It is no doubt that continuous effort is required to bring hope for patients with malignant glioma. In this study, we summarize the recent findings and approaches in the cancer stem cell field, mainly focusing on malignant glioma stem cells, and also describe potential future directions in this area.

Because of the growth characteristics of malignant gliomas that are highly invasive and deeply infiltrate the surrounding brain area; the surgical resection of these gliomas with preservation of neural functions is almost always noncurative. The residual tumor cells are usually resistant to standard adjuvant radiochemotherapy, and therefore, the tumors inevitably recur after a certain period and finally cause the death of the patients. Neural and mesenchymal stem cells have been extensively studied for the development of new strategies for treating malignant gliomas because of these cells possess the intrinsic property of homing toward tumor cells. By using neural and mesenchymal stem cells as vehicles for drug carriers, it is possible to deliver anticancer drugs to the tumor cells that infiltrate functioning normal brain tissue and are difficult to remove. Several cytokines and suicide genes have been tested, and promising results have been reported in animal brain tumor models. However, further studies involving safety issues such as secondary cancer formation are required before human trials of stem cell therapies. In the present paper, the author has reviewed the recent concepts involved in the treatment of malignant gliomas with stem cells, especially mesenchymal stem cells that are much easier to obtain from the patients themselves.

We examined the effects of serum-free medium on the gene expression changes in human mesenchymal stem cells (hMSCs) during the in vitro culture using a DNA microarray analysis. In this study, we cultured hMSCs with two kinds of medium; 1) MSCGM (contain 10% fetal bovine serum) or 2) STK2 (serum-free medium developed for mesechymal stem cells multiplication), and compared hMSCs proliferation, cell morphology, and gene expression changes until 50 days culture. Expression analysis was performed with Affymetrix GeneChip Human Genome U133 Plus 2.0 Array. hMSC proliferation was significantly higher in STK2 medium than in MSCGM medium. The cell morphology of hMSC cultured with STK2 was not significantly changed in 50 days culture. The gene expression changes in hMSCs during the in vitro culture were significantly higher in STK2 than in MSCGM. After 50 days culture, 1991 genes were significantly changed the expression levels compared with 3 days in STK2 but not MSCGM. The expressions of genes related to cell cycle, cancer, proliferation, and cell growth were significantly changed by STK2 for 50 days culture. It was also changed by STK2 that the expressions of genes related to the signaling pathways contain various growth factors, such as IGF-1, FGF, TGF-β, EGF, proliferation, and cell cycle. These results suggest that STK2 may be useful to obtain an enough number of hMSC cells for tissue engineered medical devices in short-term, however, it should be recognized that STK2 would alter the expressions of genes related to a variety of signaling pathways in hMSC if the culture period would be extended to obtain a large number of cells.

Parkinson's disease (PD) is an age-related neurodegenerative disorder in whose brain massive loss of dopaminergic neurons and formation of Lewy bodies occur in the substantia nigra (SN). L-Dihydroxyphenylamine (L-DOPA) substitution is still considered the gold standard of antiparkinsonian drug therapy. However, there has been little information available on neuroprotective and regenerative therapies. Recently, we have found that pramipexole and talipexole (D(2)/D(3)-dopaminergic agonists) inhibit dopaminergic neurotoxin-induced production of reactive oxygen species and apoptotic cell death. In addition, treatment with these drugs induces enhancement of anti-apoptotic Bcl-2 expression and inhibition of α-synuclein aggregation. Interestingly, recent study suggests that pramipexole treatment delays the progression of early PD symptom. On the other hand, we investigated the transplantation strategy for PD by assessing whether double-transplants of mouse embryonic stem (ES) cell-derived neurons in the striatum (ST) and SN, or subthalamic nucleus (STN), induce functional recovery in rat hemi-parkinsonian model. The study indicates that both the involvement of ST as a place of transplantation and the number of ES cell-derived neurons are essential factors for efficacy on PD animal model. Interestingly, an invertebrate planarian can regenerate complete organs, including a well-organized central nervous system (brain), within about 7 days. The regeneration process of the planarian dopaminergic neural network (tiara) may be divided into five steps: 1) anterior blastema formation, 2) brain rudiment formation, 3) brain pattern formation, 4) the formation of dopaminergic tiara, and 5) functional recovery of dopaminergic motor regulation, with several kinds of genes and molecular cascades acting at each step.