Pluripotent stem cells (PSCs) have been considered as the most important cells in regenerative medicine as they are able to differentiate into all types of cells in the human body. PSCs have been established from several sources of embryo tissue or by reprogramming of terminally differentiated adult tissue by transduction of so-called Yamanaka factors (Oct4, Sox2, Klf4, and cMyc). Interestingly, accumulating evidence has demonstrated the residence of PSCs in adult tissue and with the ability to differentiate into multiple types of tissue-committed stem cells (TCSCs). We also recently demonstrated that a population of pluripotent Oct4(+) SSEA-1(+)Sca-1(+)Lin-CD45(-) very small embryonic-like stem cells (VSELs) resides in the adult murine bone marrow (BM) and in other murine tissue. These very small (~3-6 microm) cells express pluripotent markers such as Oct4, Nanog, and SSEA-1. VSELs could be specified into several tissue-residing TCSCs in response to tissue/organ injury, and thus suggesting that these cells have a physiological role in the rejuvenation of a pool of TCSCs under steady-state conditions. In this review article, we discuss the molecular nature of the rare population of VSELs which have a crucial role in regulating the pluripotency, proliferation, differentiation, and aging of these cells.
Adult* ; Aging ; Antigens, CD15 ; Bone Marrow ; DNA Methylation ; Embryonic Structures ; Genomic Imprinting ; Human Body ; Humans ; Pluripotent Stem Cells ; Regenerative Medicine ; Rejuvenation ; Stem Cells*

PURPOSE: To evaluate the therapeutic effect of human embryonic stem cell (hESC)-derived multipotent mesenchymal stem cells (M-MSCs) on ketamine-induced cystitis (KC) in rats. METHODS: To induce KC, 10-week-old female rats were injected with 25-mg/kg ketamine hydrochloride twice weekly for 12 weeks. In the sham group, phosphate buffered saline (PBS) was injected instead of ketamine. One week after the final injection of ketamine, the indicated doses (0.25, 0.5, and 1×106 cells) of M-MSCs (KC+M-MSC group) or PBS vehicle (KC group) were directly injected into the bladder wall. One week after M-MSC injection, the therapeutic outcomes were evaluated via cystometry, histological analyses, and measurement of gene expression. Next, we compared the efficacy of M-MSCs at a low dose (1×105 cells) to that of an identical dose of adult bone marrow (BM)-derived MSCs. RESULTS: Rats in the KC group exhibited increased voiding frequency and reduced bladder capacity compared to rats of the sham group. However, these parameters recovered after transplantation of M-MSCs at all doses tested. KC bladders exhibited markedly increased mast cell infiltration, apoptosis, and tissue fibrosis. Administration of M-MSCs significantly reversed these characteristic histological alterations. Gene expression analyses indicated that several genes associated with tissue fibrosis were markedly upregulated in KC bladders. However the expression of these genes was significantly suppressed by the administration of M-MSCs. Importantly, M-MSCs ameliorated bladder deterioration in KC rats after injection of a low dose (1×105) of cells, at which point BM-derived MSCs did not substantially improve bladder function. CONCLUSIONS: This study demonstrates for the first time the therapeutic efficacy of hESC-derived M-MSCs on KC in rats. M-MSCs restored bladder function more effectively than did BM-derived MSCs, protecting against abnormal changes including mast cell infiltration, apoptosis and fibrotic damage.
Adult ; Animals ; Apoptosis ; Bone Marrow ; Cystitis ; Female ; Fibrosis ; Gene Expression ; Human Embryonic Stem Cells ; Humans ; Ketamine ; Mast Cells ; Mesenchymal Stromal Cells ; Multipotent Stem Cells ; Pelvic Pain ; Rats ; Urinary Bladder