In the May 20th online early edition of PNAS, J. Chang et al. from the University of California, Los Angeles School of Dentistry published their study results on the effects of proinflammatory cytokines on inhibiting osteogenic differentiation of mesenchymal stem cells (MSCs). The invesitgators found that both proinflammatory cytokines "TNF and IL-17 stimulated the IkB kinase (IKK)-NF-kB impaired osteogenic differentiation of MSCs." Conversely, inhibiting activation of the IKK-NF-kB signaling pathway enhanced osteogenesis and subsequent MSC-mediated bone formation. Additionally, activation of IKK-NF-kB signaling pathway resulted in ubiquination and degradation of b-catenin via Smurf1 and Smurf2 induction. A small molecule inhibitior of IKK, IKKVI, enhanced osteogenic differentiation of MSCs in vitro and in vivo delivery promoted craniofacial bone regeneration. The authors concluded from their study results that " targeting IKKNF may have dual benefits in enhancing bone regeneration and repair and inhibiting inflammation."
In the May 15, 2013 online early edition of Cell, M. Tachibana et al. from the Oregon Health & Science University published their experimental results in which they were able to generate human embryonic stem cells (ESCs) by somatic cell nuclear transfer (SCNT). The investigators identified some of the technical hurdles such as early embryonic arrest of nuclear transfer (NT) embryos (at the 8-cell stage), premature exit from meiosis, and suboptimal activation of the nuclear transferred from humans. Cytoplasmic factors in the mature metaphase II (MII)-arrested oocytes reprogram the transplanted somatic cell nuclei to the embryonic/pluripotent state. A key optimization step in generating NT-ESCs was nuclear donor cell fusion with enucleated MII oocytes using the envelop of inactivated hemagglutinating virus of Japan (HVJ-E). Removal of the MII spindle prior to E-based cell fusion and pulse electroporation activation post fusion were important component in the optimization protocol. Additionally, caffeine, a protein phosphatase inhibitor, which protect the cytoplast from premature activation from premature activation during spindle remove and cell fusion was another factor for optimizing the SCNT protocol. The researchers also reported that NT-ESC lines were derived from as few as two oocytes and displayed normal diploid karyotypes. The authors also noted that "gene expression and differentiation profiles in human NT-ESCs were similar to embryo-derived ESCs, suggesting efficient reprogramming of somatic cells to a pluripotent state."
In the May 20th early edition of PNAS, M. V. Plikus et al. from the University of Southern California School of Medicine published their study results on the role of the circadian clock in regenerating hair follicles. The investigators identified two key sites (epithelial matrix and mesenchymal dermal papilla) where peripheral circadian clock activity influence daily mitotic rhythm of anagen hair follicles. In the epithelial matrix, the circadian clock influence of mitotic rhythmicity was attributed to hair growing faster in the morning than in the evening. Sensitivity to genotoxic stress was found to be time-of-day dependent such as susceptibility to DNA damage during mitosis. In mice, the researchers found that g-radiation induce dramatic hair loss in the morning, during peak mitosis, compared to minimal loss following radiation exposure in the evening. Additionally, the experimental data revealed that the diurnal radio-protective effect of the circadian clock was lost in circadian mutants where hair follicles undergo asynchronous mitosis. It was further demonstrated that circadian clock activity "coordinates cell cycle progression with genotoxic stress responses by synchronizing Cdc2/Cyclin B-mediated G2/M checkpoint."
In the May 9th online early publication of Cell Stem Cell, E. Apostolou et al. Massachusetts General Hospital reported their study results on genome-wide, pluripotency network involving the Nanog promoter. The experimental results revealed that the Nanog promoter formed a pluripotent chromatin interactome. The pluripotency-specific network is rearranged during differentiation and restored in induced pluripotent stem cells (iPSCs). In embryonic stem cells (ESCs), Nanog promoter interaction were maintained by binding of Mediator and cohesion in the chromatin. When these proteins were depleted the interactome acquired a differentiation-specific pattern prior to transcriptional and phenotypic changes. The investigators also noted that Nanog promoter interactions during reprogramming preceded increased gene expression of pluripotent-associated genes. The authors concluded from their observations that their experimental results describe "a complex, pluripotency-specific chromatin 'interactome' for Nanog and suggest a functional role for long-range genomic interactions in the maintenance and induction of pluripotency."
In the May 13th online early edition of PNAS, P. Wu et al. from University of Southern California published their study results on tooth renewal in alligators. The authors noted that alligators have well-organized teeth similar to mammals and can undergo life-long renewal. The investigators used multiple mitotic labeling to map stem cells to the enlarged bulge of the dental lamina which contains quiescent odontogenic progenitors. Activation of the progenitors and initiation of the tooth cycle correlates upregulation of the b-catenin signaling pathway and disappearance in the bulge of soluble frizzled-related protein 1. The researchers also found "that the dermal niche adjacent to the dermal lamina dynamically expresses neural cell adhesion molecule, tenascin-C, and other molecules. The authors further noted that "in development, asymmetric b-catenin localization leads to the formation of a heterochronous and complex tooth family unit configuration."
In the May 9th online early edition of PNAS, F. Wang et al. from New York University Langone Medical Center reported their study results in the ability to detect telomere length in individual cells. Accurately measuring telomere length is particular important as a tool for studying cell senescence and aging, malignancy, and stem cell renewal. Large population of cells are usually required which are technically challenging and masks telomere length heterogeneity in single cells. From individual cells, the investigators used quantitative PCR (qPCR) to determine the ration between telomeres (T) and reference genes (R) in a preamplified amplicon specific for teleomeres and reference genes. This single-cell telomere length measurement (SCT-pqPCR) assay was able to detect telomere length in quiescent cells and the T/R ratio correlated with a "given cell population measured by regular qPCR." Additionally , T/R values of "human fibroblasts at later passages and from old donors were lower and more heterogeneous than those of early passages and from young donors. The authors also noted "that cancer cell lines show heterogeneous telomere lengths; human oocytes and polar bodies have nearly identical telomere lengths; and, that the telomere lengths progressively increase from the zygote, two-cell to four-cell embryo.
M. Sundberg et al. from Harvard Medical School reported in the May 10th online early publication of Stem Cells their study results on comparing the difference in safety and efficacy between dopaminergic neurons (DA) neurons derived from both human embryonic and induced pluripotent stem cells (iPSCs) and non-human iPSCs. With fluorescence-activated cell storting (FACS), the investigators enriched for a population of dopaminergic neurons having a NCAM+/CD29low phenotype. The sorted NCAM+/CD29low DA neurons differentiated from iPSCs were positive for FOXA2/TH and EN1/TH as well as having increased expression levels of FOXA2, LMX1A, TH, GIRK2,PITX3, EN1, NURR1 mRNA compared to unsorted neural cell populations. The experimental results revealed that non-primate iPSC-derived NCAM+/CD29low DA neurons restored motor in Parkinsonian rat model (6-OHDA lesioned rats) 16 weeks after implantation. Additionally, transplanted sorted cells were found to integrate into striatium of the rodent brain. One year survival of autologous transplantation of primate iPSC-derived (FOXA2/TH positive) neurons was observed in the striatum of 1/2 primate without immunosuppression.
In the May 7th online early edition of PNAS, G. M. de Peepo et al. from the New York Stem Cell Foundation reported their experimental results on the utility of using human-induced pluripotent stem cells (hiPSCs) for bone tissue engineering. The investigators used three hiPSC cell lines for differentiating the reprogrammed cells into mesenchymal lineages. The cell line exhibiting the most potent osteogeneic potential were subsequently cultured in osteoconductive scaffolds in a perfusion bioreactor for 12 weeks. The experimental data revealed that bone substitutes generated in the perfusion bioreactors expressed bone lineage genes concomitant with a global repression of cell proliferation genes. The authors concluded from their study observations that their "results pave the way for growing patient-specific bone substitutes for reconstructive treatments of the skeletal system and for constructing qualified experimental models of development and disease."
Category: Stem Cells and Cancer
In the May 6th online early publication of PNAS, P. Mao et al. from Ohio State University reported their experimental results on identifying two subpopulations of glioma stem cells (GSCs) based upon their distinct dysregulated signaling pathways and mRNA profiles. The investigators identified both a proneural (PN) and mesenchymak (Mes) GSCs. Mes GSCs were found to be the more aggressive phenotype both in vitro and in intracranial xenografts in mice. Mes GSCs were more radiation resistant compared to PN GSCs as well as the glycolytic pathway involving the aldehyde dehydrogenase family of genes, particularly, ALDH1A3 are highly enriched in Mes GSCs. Inhibition in the expression of ALDH1A3 attenuated the growth of Mes, but not in PN GSCs. Interestingly, PN GSCs exposure to radiation upregulated Mes-associated markers concomitant with downregulation of PN-associated markers. The researchers found that inhibiting ALDH1A3 in PN reduced the radiation-associated gain of Mes markers. The authors concluded from their study observations that their "data suggest that two subtypes of GSCs, harboring distinct metabolic signaling pathways, represent intertumoral glioma heterogeneity and highlight previously unidentified roles of ALDH1A3-associated signaling that promotes aberrant proliferation of Mes HGGs and GSCs."
In the April 29th online early publication of PNAS, L. Lei and A.C. Spradling from the Howard Hughes Medical Institute at the Carnegies Institution for Science (Baltimore, MD) published their study findings on whether germ-line stem cells are needed to generate in adult, mammalian females new oocytes in order to sustain the ovarian follicle pool. The investigators found that primordial follicles generated during fetal life were "sufficient to sustain adult oogenesis without self-renewal." With lineage tracing analysis, the experimental results revealed that the primordial follicles were highly stable with a half-life of 10 months in adult female mice. Single label oocytes were used to followed the kinetics of fetal follicle formation from which the authors concluded that "adult female mice neither require nor contain active germ-line stem cells or produce new oocytes in vivo."