Faculty Bibliography

Adipose-derived adult stem cells (ASCs), like their bone-marrow derived counterparts, possess the ability to differentiate down osteogenic, chondrogenic, adipogenic, and myogenic pathways. For bone differentiation of mouse ASCs (mASCs), retinoic-acid mediated upregulation of BMPR-IB has been found to be necessary. Interestingly, our previous work has also shown Fibroblast Growth Factor-2 (FGF-2) to strongly inhibit this osteogenic differentiation, even in the presence of retinoic acid. In this report, we investigated the molecular mechanisms underlying FGF-2 mediated osteogenic inhibition, demonstrating that addition of exogenous FGF-2 to mASCs antagonizes upregulation of BMPR-IB gene expression in response to retinoic acid. In addition, constitutive expression of BMPR-IB, but not BMPR-IA or BMPR-II, was found to counteract the inhibitory effects of FGF-2. Finally, p53(-/-) mASCs and human ASCs, both of which express high levels of endogenous BMPR-IB, underwent normal osteogenic differentiation even in the presence of FGF-2. Collectively, our data therefore indicate that FGF-2 antagonizes the response of mASCs to retinoic acid and also suggest that threshold levels of BMPR-IB may play a crucial role both in counteracting the inhibitory role of FGF-2 and in promoting osteogenic differentiation of ASCs in the absence of retinoic acid. Moreover, the present study also indicates that differences exist between mouse and human ASCs in relationship to FGF-2 activity in the osteogenic context.

Adult tissue stem cells replicate infrequently, retaining DNA nucleotide label (BrdU) for much longer periods than mature, dividing cells in which the label is diluted during a chase period. Those 'label-retaining cells' (LRCs) have been identified as the tissue stem cells in skin, cornea, intestine, and prostate. However, in the urinary tract uroepithelial stem cells have not yet been identified. In this study, BrdU administration identified urothelial LRCs in the rat bladder with 9% of the epithelial basal cells retaining BrdU label 1 yr after its administration. Markers for stem cells in other tissues, Bcl, p63, cytokeratin 14, and beta1 integrin, were immunolocalized in the basal bladder epithelium in or near urothelial LRCs, but not uniquely limited to these cells. Flow cytometry demonstrated that urothelial LRCs were small, had low granularity, and were uniquely beta4 integrin bright. Urothelium from long-term labeled bladders was cultured and LRCs were found to be significantly more clonogenic and proliferative, characteristics of stem cells, than unlabeled urothelial cells. Thus, this work demonstrates that LRCs in the bladder localize to the basal layer, are small, low granularity, uniquely beta4 integrin rich, slowly cycling and demonstrate superior clonogenic and proliferative ability compared with unlabeled epithelial cells. We propose that LRCs represent putative urothelial stem cells

OBJECTIVES: To observe the effect of ultrashortwave (USW) therapy on nerve regeneration after acellular nerve allografts(ANA) repairing the sciatic nerve gap of rats and discuss its acting mechanisms. METHODS: Sixteen Wistar rats weighing 180-220 g were randomly divided into four groups with four rats in each group: normal control group; acellular group (ANA, treated by hypotonic-chemical detergent, was applied for bridging a 10 mm-long sciatic nerve defect); USW group (After 24 h of ANA repairing the sciatic nerve gap, low dose USW was administrated for 7 min, once a day, 20 times a course of treatment, three courses of treatment in all); and autografts group. 12 weeks after operation, a series of examinations was performed, including electrophysiological methods, the restoring rate of tibialis anterior muscle wet weight, histopathological observation (myelinated nerve number, myelin sheath thickness, and axon diameter), vascular endothelial growth factor (VEGF) mRNA expression of spinal cord, and muscle at injury site, and analyzed statistically. RESULTS: Compared to acellular nerve allografts alone, USW therapy can increase nerve conductive velocity, the restoring rate of tibialis anterior muscle wet weight, myelinated nerve number, axon diameter, VEGF mRNA expression of spinal cord, and muscle at injury site, the difference is significant. There were no differences between USW group and autografts group except myelin sheath thickness. CONCLUSIONS: USW therapy can promote nerve axon regeneration and Schwann cells proliferation after ANA repairing the sciatic nerve gap of rats, the upregulation of VEGF mRNA expression of spinal cord and muscle may play an important role.

During development, many neural stem cells "age" as they sequentially generate distinct neuronal or glial cell types. In this issue, Maurange et al. (2008) now identify the temporal control factors in Drosophila neural stem cells (neuroblasts) that regulate the fate of stem cell progeny and signal the end of stem cell proliferation.

BACKGROUND: Homeodomain proteins play critical roles in shaping the development of the embryonic central nervous system in mammals. After birth, neurogenic activities are relegated to stem cell niches, which include the subgranular layer of the dentate gyrus of the hippocampus. Here, we have analyzed the function of HOP (Homeodomain only protein) in this stem cell niche and in human glioblastomas. RESULTS: We find that HOP is strongly expressed by radial astrocytes of the dentate gyrus in mice, which are stem cells that give rise to hippocampal granular neurons throughout adulthood. Deletion or down-regulation of HOP results in a decrease of apoptosis of these stem cells without changes in proliferation, and in an increase in the number of newly formed granule neurons. We also find that human glioblastomas largely lack HOP expression and that reintroduction of HOP function in glioma cells cultured as gliomaspheres leads to enhanced apoptosis in a subset of cases. In these cells, HOP function decreases clonogenicity. CONCLUSION: These data suggest that HOP participates in the regulation of the adult mouse hippocampal stem cell niche by negatively affecting cell survival. In addition, HOP may work as a tumor suppressor in a subset of glioblastomas. HOP function thus appears to be critical in the adult brain in a region of continued plasticity, and its deregulation may contribute to disease.

BACKGROUND: Basic helix-loop-helix E proteins are transcription factors that play crucial roles in T cell development by controlling thymocyte proliferation, differentiation and survival. E protein functions can be repressed by their naturally occurring inhibitors, Id proteins (Id1-4). Transgenic expression of Id1 blocks T cell development and causes massive apoptosis of developing thymocytes. However, the underlying mechanisms are not entirely understood due to relatively little knowledge of the target genes regulated by E proteins. RESULTS: We designed a unique strategy to search for genes directly controlled by E proteins and found RORgammat to be a top candidate. Using microarray analyses and reverse-transcriptase PCR assays, we showed that Id1 expression diminished RORgammat mRNA levels in T cell lines and primary thymocytes while induction of E protein activity restored RORgammat expression. E proteins were found to specifically bind to the promoter region of RORgammat, suggesting their role in activating transcription of the gene. Functional significance of E protein-controlled RORgammat expression was established based on the finding that RORgammat rescued apoptosis caused by Id1 overexpression. Furthermore, expression of RORgammat prevented Id1-induced p38 MAP kinase hyper-activation. CONCLUSION: These results suggest that E protein-dependent RORgammat gene expression aids the survival of developing thymocytes, which provides a possible explanation for the massive apoptosis found in Id1 transgenic mice.

The repair of wounds is one of the most complex biological processes that occur during human life. After an injury, multiple biological pathways immediately become activated and are synchronized to respond. In human adults, the wound repair process commonly leads to a non-functioning mass of fibrotic tissue known as a scar. By contrast, early in gestation, injured fetal tissues can be completely recreated, without fibrosis, in a process resembling regeneration. Some organisms, however, retain the ability to regenerate tissue throughout adult life. Knowledge gained from studying such organisms might help to unlock latent regenerative pathways in humans, which would change medical practice as much as the introduction of antibiotics did in the twentieth century

The burden of protein misfolding is believed to contribute to aging. However, the links between adaptations to conditions associated with protein misfolding and resistance to the time-dependent attrition of cellular function remain poorly understood. We report that worms lacking aip-1, a homologue of mammalian AIRAP (arsenic-inducible proteasomal 19S regulatory particle-associated protein), are not only impaired in their ability to resist exposure to arsenite but also exhibit shortened lifespan and hypersensitivity to misfolding-prone proteins under normal laboratory conditions. Mammals have a second, constitutively expressed AIRAP-like gene (AIRAPL) that also encodes a proteasome-interacting protein, which shares with AIRAP the property of enhancing peptide accessibility to the proteasome's active site. Genetic rescue experiments suggest that features common to the constitutively expressed worm AIP-1 and mammalian AIRAPL (but missing in the smaller, arsenite-inducible AIRAP) are important to lifespan extension. In worms, a single AIRAP-related protein links proteasomal adaptation to environmental stress with resistance to both proteotoxic insults and maintenance of animal life span under normal conditions