In this review, we have summarized our recent studies on the functionality of ionotropic (iGluR) and metabotropic (mGluR) glutamate receptors expressed by undifferentiated neural progenitor cells (NPC) isolated from embryonic rat and mouse brains. NPC are primitive cells with the self-renewal capacity as well as the multipotentiality to generate different neural lineages including neurons, astrocytes, and oligodendrocytes. Isolated cells were cultured in the presence of growth factors for the formation of round spheres by clustered cells so-called 'neurospheres' under floating conditions. Reverse transcription polymerase chain reaction analyses revealed expression of mRNA for particular iGluR and mGluR subtypes in NPC. Moreover, sustained exposure to an agonist for the N-methyl-D-aspartate receptor (NMDAR) not only inhibited the formation of neurospheres but also promoted differentiation of NPC into cells immunoreactive to a neuronal marker protein on immunocytochemistry and western blot analyses. On the other hand, sustained exposure to an agonist for the group III mGluR subtype led to suppression of proliferation activity in these neurospheres along with facilitation of the subsequent differentiation into astrocytes. Accordingly, glutamate could play a pivotal role in the mechanisms underlying proliferation for self-replication, together with determination of the subsequent differentiation fate toward particular progeny lineages through activation of NMDAR and group III mGluR subtypes in NPC.

It is well known that bone marrow macrophages differentiate into osteoclasts in response to M-CSF and RANKL in culture. However, the characteristics and dynamics of osteoclast precursors in vivo are not clear. Cell cycle arrest in osteoclast precursors is a prerequisite step for their differentiation into osteoclasts. We named such precursors "QOPs (cell cycle-arrested quiescent osteoclast precursors) " . Injection of 2MD [a potent analogue of 1α, 25 (OH) (2)D(3)] , RANKL, or M-CSF to mice induced osteoclast differentiation from QOPs. Moreover, osteoclasts appearing in BMP (bone morphogenetic protein) -induced ectopic bone were also differentiated from QOPs without cell proliferation. These results indicate that (1)osteoclasts are formed from QOPs in response to bone resorbing stimuli in vivo, (2) QOPs circulate in the bloodstream and settle in the right place for osteoclastogenesis. Here I review recent advances in our understanding of osteoclast precursors in vivo.

The bony skeleton enables the locomotive activity, the storage of calcium, and the harboring of the hematopoietic stem cells from which blood and immune cells are derived. The immune and skeletal systems share various molecules including cytokines, signaling molecules, transcription factors and membrane receptors. Investigation into rheumatoid arthritis (RA) as well as cloning of RANKL and various bone phenotypes found in immune-compromised gene deficient mice has highlighted the importance of the dynamic interplay between the both systems. These findings have recently led to both the emergence and subsequent rapid evolution of the field of osteoimmunology. The scope of osteoimmunology has been extended to encompass a wide range of molecular and cellular interactions, the elucidation of which will provide a scientific basis for future therapeutic approaches to diseases related to the immune and skeletal systems.

Neurons and glias are produced from neural stem cells. These phenomena are called "Neurogenesis." Neurogenesis largely occurs in developmental stages. However, it is now known that active neurogenesis continues throughout life in discrete regions such as the hippocampus of the adult brain of all mammals, including humans. Neurogenesis can be affected by various genetic or environmental factors. Neurogenesis is related to learning and memory and may also have a function in the vulnerability to the onset of mental illness (Neurogenesis theory). We have studied this theory by using rodents and tried to improve psychotic behavior by enhancing postnatal neurogenesis. Our results showed that administration of polyunsaturated fatty acids or breeding the animals in exciting environments improved psychotic behavior, suggesting their usefulness in preventing or curing mental illness which follows declining neurogenesis.

It was recently revealed that ES-cell like pluripotent stem cells, designated as iPS cells, can be generated from somatic cells. iPS cells could be used as not only a source of regeneration medicine, but also a source of cell vaccine. Pluripotent stem cells are characterized by pluripotency and infinite propagation capacity. Non-virus-mediated methods for gene transfer have been established. Genetic modification of pluripotent stem cells and subsequent in vitro differentiation to dendritic cells would be an attractive strategy. Here we describe the previous studies about cancer immunotherapy by utilizing dendritic cells derived from pluripotent stem cells.

Chronic myeloid leukemia(CML)is a clonal disease of the hematopoietic stem cells that is characterized by excessive proliferation, but retains of the capacity for differentiation duringthe chronic phase of the disease. This phase is followed after 4-6 years by rapid progression, an accelerated phase, and consequently a fatal acute leukemia a blast crisis. The hallmark abnormality of CML is the Philadelphia chromosome that generates a BCR-ABL fusion gene, resulting in the expression of a leukemia-specific oncoprotein, Bcr-Abl. Bcr-Abl is a potent tyrosine kinase and plays a central role in CML pathogenesis. Recently, the treatment of CML has been revolutionized by the introduction of imatinib mesylate(IM). With daily IM treatment, more than 80% of chronic-phase CML patients achieve a complete cytogenetic response. Nevertheless, a small percentage of CML patients are primarily refractory or acquire secondary resistance against IM. Nilotinib is a highly selective Abl kinase inhibitor that possesses greater potency and selectivity for Abl kinase than IM. In addition to being more potent than IM against wild-type BCR-ABL, nilotinib is significantly active against many IM-resistant BCR-ABL mutants. In preclinical studies, nilotinib has produced hematologic and cytogenetic responses in CML patients, with either IM resistance or IM intolerance. As second-line treatment, both nilotinib and dasatinib may be used in case of suboptimal response or failure, which is defined in the efficacy criteria of the European Leukemia Net Consensus. The choice of second-generation tyrosine kinase inhibitors may be made after the mutation analyses of the kinase domain. It is recommended that nilotinib or dasatinib whichever was shown to be active against the specific mutation, should be chosen for treatment. For patients with no mutations or patients with IM intolerance, it is recommended that either second-generation tyrosine kinase inhibitor be chosen, based on the patient's disease history.

Bone, as well as the lung and liver, is among the sites of predilection for cancer metastasis. The bone stores large amounts of growth factors such as insulin-like growth factors and transforming growth factor-b, and provides fertile soil for metastatic cancer cells by continuously releasing these bone-stored growth factors, which are a consequence of osteoclastic bone resorption. Metastatic cancer cells in turn produce osteoclast-stimulating cytokines such as parathyroid hormone-related protein( PTH-rP), prostaglandin E2.(PGE2), and various interleukins(ILs). These cancer-produced osteoclast-stimulating cytokines bind to their cognitive receptors and promote the expression of ligands for the receptor activators of nuclear factor kB (RANKL)in osteoblasts. RANKL then binds to its receptor RANK, expressed in pre-osteoclasts, stimulates mature osteoclast formation, and subsequently, osteoclastic bone resorption. This vicious cycle between metastatic cancer cells and osteoclasts is critical to the development and progression of bone metastases. In addition, it is likely that metastatic cancer cells are influenced by bone environments(or niche)and acquire additional capacities such as an epithelial-mesenchymal transition(EMT), allowing them to be resistant to chemotherapy or apoptosis, to survive in a dormant state, or to aggressively spread to distant organs including lung and liver. Thus, the bone can serve as transit port. Disrupting this cycle by inhibiting osteoclastic bone resorption, antagonizing bone-derived growth factors, and neutralizing RANKL or PTH-rP, should be a promising therapeutic intervention for bone metastases. Bisphosphonates(BP)are specific inhibitors of osteoclasts, and have been shown to significantly reduce skeletal-related events(SRE)associated with bone metastasis. Denosumab is a neutralizing monoclonal antibody to RANKL and has recently been found to inhibit SRE more effectively than BP. Further understanding of the crosstalk communication between metastatic cancer cells and bone at the molecular level should lead us to design novel, more effective and specific treatments for cancer patients with bone metastases.

Attempts to treat congenital protein deficiencies using bone marrow-derived cells have been reported. These efforts have been based on the concepts of stem cell plasticity. We aimed to clarify whether bone marrow transplantation (BMT) treatment can rescue epidermolysis bullosa (EB) caused by defects in keratinocyte structural proteins. BMT treatment of adult collagen XVII (Col17) knockout mice induced donor-derived keratinocytes and Col17 expression associated with the recovery of hemidesmosomal structure and better skin manifestations, as well improving the survival rate. Furthermore, human cord blood CD34+ cells also differentiated into keratinocytes and expressed human skin component proteins in transplanted immunocompromised mice. The current conventional BMT techniques have significant potential as a systemic therapeutic approach for the treatment of human EB.

Articular cartilage has the poor capacity for cartilage regeneration, which lead to develop osteoarthritis when cartilage injury occurs. Autologous chondrocyte implantation using three dimensional culture within atelocollagen gel has obtained good clinical results for articular cartilage injury. However, there are two concerns associated with this technique : the number of harvested chondrocyte is limited and arthrotomy is required for implantation of tissue-engineered cartilage. To improve the cell-based articular cartilage treatment, the use of other cell source such as mesenchymal stem cells, and development of less invasive and more efficient cell delivery system should be needed. Translational research will has more and more important implication for clinical application of articular cartilage repair.

Cell transplantation has shown to be a promising strategy to repair cartilage defects. Mesenchymal stem cells derived from synovium have been shown to be a superior cell source for cartilage regeneration to those from other mesenchymal tissues due to their higher rates of colony formation, proliferation potential with autologous serum, and in vitro/vivo chondrogenic potentials. We have found that approximately 60% of synovial mesenchymal stem cells placed on cartilage defects adhered to the defect within 10 min, and the addition of magnesium enhanced this percentage further, which resulted in better cartilage regeneration. Based upon several basic research studies performed in our lab, we have begun the transplantation of synovial stem cells arthroscopically in a clinical study for the treatment of cartilage defects. To date, no adverse events have been reported in the study. Regeneration of cartilage, reduction in defect size and an improvement of symptoms have been obtained in most patients over the last 3 years.