Stem cells posses both capabilities of self-renewal and differentiation into various tissue-specific cells. Traditionally, stem cells have been divided into two groups; embryonic stem (ES) and somatic stem cells. Although human ES cells have the potential to generate new tissues in regenerative medicine, the establishment of human ES cell lines requires ethically problematic destruction of a human embryo and it remains to be resolved more extensively, along with the problem of the teratoma formation after transplantation. Now all regenerative medicine has been performed using somatic stem cells. For pre-clinical study of regenerative medicine using somatic stem cells it is anxious to establish a novel model mouse in which human somatic stem cells are able to proliferate and differentiate into appropriate mature cells. Recently, we developed a new strain of immunodeficient mouse (NOG mouse), which carried various immunological abnormalities. Successful engraftment was achieved even if a small number of human somatic stem cell were transplanted into NOG mice without administration of human cytokines. When human hematopoietic stem cells (HSC) expanded ex vivo were transplanted into the mice, multi-lineage reconstitution including a large number of human myeloid, B, T, NK, NKT, DC, erythroid cells and megakaryocytes were confirmed in various hematopoietic organs.
Stem cell plasticity, safety and ethical issues underlying the regenerative medicine are also discussed in this review.

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In our previous studies, we examined the molecular mechanisms of adhesive interactions between lymphocytes and human gingival fibroblasts (HGF) that occur at inflammatory gingival connective tissues. We found that activation of lymphocytes led to their increased adhesiveness to HGF, and that adhesion pathways involving at least VLA integrins, LFA-1/ICAM-1, and CD44/hyaluronate play crucial roles in the binding of activated lymphocytes to HGF. Furthermore, possible activation of HGF by adhesive interactions with lymphocytes was examined by monitoring the inflammatory cytokine expression. IL-1 and IL-6 mRNA expression in the HGF was increased when HGF directly interacted with lymphocytes. These results strongly suggest that adhesive interaction between these heterotypic cell types transduces activation signals into HGF that induce an increase in inflammatory cytokine mRNA expression. Recently, we examined by monitoring the expression of CD13 (aminopeptidase N) whether the direct interactions between lymphocytes and HGF can also stimulate the lymphocytes. Peripheral blood T cells (PBT) which had been cultured in the presence or absence of PMA were added to the HGF monolayers. After incubation, the PBT were harvested and CD13 expression on the cell surfaces was analyzed by flow cytometry. Furthermore, the presence of CD13 positive T cells in inflamed gingival tissues was also examined in vivo. Interestingly, CD13 expression was induced on PMA-activated PBT only when they were cultured on HGF. When HGF and PMA-activated PBT were cultured in the same well but separated by a membrane, no expression of CD13 on the PBT was observed. In addition, CD13 positive T cells, which were not detected in PBT of the same patients, were isolated from gingival tissues. These results indicate that direct interactions with HGF were essential for the induction of CD13 expression on T cells, which were observed in periodontitis lesions.

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Membrane-associated prostaglandin (PG) E₂ synthase (mPGES) is an inducible terminal enzyme in the biosynthetic pathway for PGE₂, which participates in many biological processes. In this study, we investigated the molecular mechanism controlling the inducible expression of mPGES. The mouse mPGES gene consisted of three exons, and its 5'-proximal promoter contained consensus motifs for the binding of several transcription factors. Deletion and site-specific mutation analyses of the 5'-flanking region demonstrated that stimulus-inducible expression of mouse and human mPGES required tandem GC boxes adjacent to the initiation site. The stimulus-induced GC box-binding activity was present in nuclear extracts of cells, in which the proximal GC box was essential for binding. An 80-kDa stimulus-inducible nuclear protein that bound to this GC box was identified as the transcription factor Egr-1 (for early growth response-1). These results suggest that Egr-1 is a key transcription factor in regulating the inducible expression of mPGES.

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Neovascularization observed in the synovial tissue of rheumatoid arthritis is essential for the nutrition of proliferating synovial tissue; therefore, attempts have recently been made to use angiogenesis-inhibiting drugs for the treatment of arthritis. Endostatin is a C-terminal noncollagen-region fragment of type XVIII collagen, and has a potent angiogenesis-inhibiting effect. Recently, we have systemically administered endostatin to arthritic mice to investigate its arthritis-inhibiting effect. We induced the development of arthritis in 6-week-old female Balb/c mice by administrating four kinds of monoclonal anti-type II collagen antibodies followed by LPS 3 days later. Three endostatin groups of mice received 0.2 mg/kg/day, 2 mg/kg/day, or 10 mg/kg/day for 13 days before the development of arthritis, and a control group received PBS. Arthritis was evaluated by arthritis scores and hind paw thickness. In addition, the left and right foot joints were collected on the 22nd day of administration of monoclonal anti-type II collagen antibody, and histopathological preparations were made. Arthritis scores and hind paw thickness were lower in the 10 mg/kg/day group than in the control group. Histopathological examination showed that pannus formation and bone destruction were suppressed in the endostatin group compared with the control group. No severe side effects occurred in the endostatin-administered mice. These results suggest that endostatin is a promising new antiarthritic drug with few side effects and a novel mechanism of action.

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Imatinib mesylate, a competitive inhibitor for of ABL tyrosine kinase, is highly active against Philadelphia-positive (Ph⁺) chronic myelocytic leukemia. However, recent studies demonstrated the existence of primary and/or acquired imatinib-resistant Ph⁺ clones those would affect the treatment outcome. For the development of the strategies those strengthen the effect of imatinib, we selected Ras related proteins as an alternative molecular target, because these proteins enhance the oncogenetic property of BCR/ABL as downstream signaling effector. Based on the previous findings showing the inhibitory effect for Ras related proteins of the third-generation bisphosphonate, zoledronate (ZOL), we examined its anti-leukemic potencies and the combination effect with imatinib against Ph⁺ leukemia both in vivo and in vitro. ZOL showed a time- and concentration-dependent anti-proliferative effect in all examined leukemic cell lines by inducing apoptosis. During the apoptotic execution, ZOL inactivated Ras related proteins via prevention of the posttranslational prenylation. The combination of imatinib and ZOL showed the synergistic anti-proliferative effects against Ph⁺ leukemic cell lines in vitro, and, intriguingly, this combination could prolong the survival of mice xenografted with Ph⁺ BV173 cell line in comparison with mice treated with imatinib or ZOL alone. These suggest that ZOL is a potent anti-leukemic agent that synergistically augments the effect of imatinib.

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Hair follicle is composed primarily of epithelial and dermal components that develop from embryonic ectoderm and mesoderm respectively. Hair growth cycle is coordinated and complex processes that are dependent on the interactions of epithelial and dermal components. Beard and frontal scalp dermal papilla cells (DPCs) were recently shown to possess the characteristics of androgen target cells. These DPCs expressed androgen receptor and type II 5α-reductase mRNA. To know the mode of androgen action in human hair follicles, we developed an in vitro coculture system using DPCs and follicular keratinocytes. Androgen significantly stimulated the proliferation of keratinocytes cocultured with beard DPCs, suggesting that these DPCs produce androgen-dependent diffusible growth factors. Insulin-like growth factor-I (IGF-I) was identified as one of the androgen dependent paracrine growth factors from beard DPCs. On the contrary, we could identify inhibitory roles of androgen on the growth of keratinocytes cocultured with DPCs from human balding frontal scalp, when DPCs were transfected with the AR expression vector. The inhibitory effect was mediated by TGF-β1 from the DPCs. Minoxidil and Finasteride were recently introduced for the treatment of androgenetic alopecia, and TGF-β1 is a next target for the innovative treatment.

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