Single-cell transcriptomics reveals gene signatures and alterations associated with aging in distinct neural stem/progenitor cell subpopulations.

Aging associated cognitive decline has been linked to dampened neural stem/progenitor cells (NSC/NPCs) activities manifested by decreased proliferation, reduced propensity to produce neurons, and increased differentiation into astrocytes. While gene transcription changes objectively reveal molecular alterations of cells undergoing various biological processes, the search for molecular mechanisms underlying aging of NSC/NPCs has been confronted by the enormous heterogeneity in cellular compositions of the brain and the complex cellular microenvironment where NSC/NPCs reside. Moreover, brain NSC/NPCs themselves are not a homogenous population, making it even more difficult to uncover NSC/NPC sub-type specific aging mechanisms. Here, using both population-based and single cell transcriptome analyses of young and aged mouse forebrain ependymal and subependymal regions and comprehensive "big-data" processing, we report that NSC/NPCs reside in a rather inflammatory environment in aged brain, which likely contributes to the differentiation bias towards astrocytes versus neurons. Moreover, single cell transcriptome analyses revealed that different aged NSC/NPC subpopulations, while all have reduced cell proliferation, use different gene transcription programs to regulate age-dependent decline in cell cycle. Interestingly, changes in cell proliferation capacity are not influenced by inflammatory cytokines, but likely result from cell intrinsic mechanisms. The Erk/Mapk pathway appears to be critically involved in regulating age-dependent changes in the capacity for NSC/NPCs to undergo clonal expansion. Together this study is the first example of using population and single cell based transcriptome analyses to unveil the molecular interplay between different NSC/NPCs and their microenvironment in the context of the aging brain.

Single-cell transcriptome analyses reveal signals to activate dormant neural stem cells.

The scarcity of tissue-specific stem cells and the complexity of their surrounding environment have made molecular characterization of these cells particularly challenging. Through single-cell transcriptome and weighted gene co-expression network analysis (WGCNA), we uncovered molecular properties of CD133(+)/GFAP(-) ependymal (E) cells in the adult mouse forebrain neurogenic zone. Surprisingly, prominent hub genes of the gene network unique to ependymal CD133(+)/GFAP(-) quiescent cells were enriched for immune-responsive genes, as well as genes encoding receptors for angiogenic factors. Administration of vascular endothelial growth factor (VEGF) activated CD133(+) ependymal neural stem cells (NSCs), lining not only the lateral but also the fourth ventricles and, together with basic fibroblast growth factor (bFGF), elicited subsequent neural lineage differentiation and migration. This study revealed the existence of dormant ependymal NSCs throughout the ventricular surface of the CNS, as well as signals abundant after injury for their activation.

The effect of calcium phosphate composite scaffolds on the osteogenic differentiation of rabbit dental pulp stem cells.

The objective of this study is to compare the effects of the two calcium phosphate composite scaffolds on the attachment, proliferation, and osteogenic differentiation of rabbit dental pulp stem cells (DPSCs). One nano-hydroxyapatite/collagen/poly (l-lactide) (nHAC/PLA), imitating the composition and the micro-structure characteristics of the natural bone, was made by Beijing Allgens Medical Science & Technology Co., Ltd. (China). The other beta-tricalcium phosphate (ß-TCP), being fully interoperability globular pore structure, was provided by Shanghai Bio-lu Biomaterials Co, Ltd. (China). We compared the absorption water rate and the protein adsorption rate of two scaffolds and the characterization of DPSCs cultured on the culture plate and both scaffolds under osteogenic differentiation media (ODM) treatment. The constructs were then implanted subcutaneously into the back of severely combined immunodeficient (SCID) mice for 8 and 12 weeks to compare their bone formation capacity. The results showed that the ODM-treated DPSCs expressed osteocalcin (OCN), bone sialoprotein (BSP), type I collagen (COLI) and osteopontin (OPN) by immunofluorescence staining. Positive alkaline phosphatase (ALP) staining, calcium deposition and calcium nodules were also observed on the ODM-treated DPSCs. The absorption water rate and protein adsorption rate of nHAC/PLA was significantly higher than ß-TCP. The initial attachment of DPSCs seeded onto nHAC/PLA was significantly higher than that onto ß-TCP; and the proliferation rate of the cells was also significantly higher than that of ß-TCP on 1, 3, and 7 days of cell culture. The ALP activity, calcium/phosphorus content and mineral formation of DPSCs + ß-TCP were significantly higher than DPSCs + nHAC/LA. When implanted into the back of SCID mice, nHAC/PLA alone had no new bone formation, newly formed mature bone and osteoid were only observed in ß-TCP alone, DPSCs + nHAC/PLA and DPSCs + ß-TCP, and this three groups displayed increased bone formation over the 12-week period. The percentage of total bone formation area had no difference between DPSCs + ß-TCP and DPSCs + nHAC/PLA at each time point, but the percentage of mature bone formation area of DPSCs + ß-TCP was significantly higher than that of DPSCs + nHAC/PLA. Our results demonstrated that the DPSCs on nHAC/PLA had a better proliferation, and that the DPSCs on ß-TCP had a more mineralization in vitro, much more newly formed mature bones in vivo were presented in DPSCs + ß-TCP group. These findings have provided a further knowledge that scaffold architecture has different influence on the attachment, proliferation and differentiation of cells. This study may provide insight into the clinical periodontal bone tissue repair with DPSCs + ß-TCP construct.

[Study of radiographic method of increasing vertical angle for identifying double root in maxillary premolar with cone-beam CT].

PURPOSE: To explore the feasibility of radiography method of increasing vertical angle for identifying double root in maxillary premolar with cone-beam computed tomography(CBCT). METHODS: Thirty-one patients with 109 maxillary premolars who needed CT scan for maxillary teeth were selected and scanned by CBCT. The interested region was chosen to reconstruct the image of maxillary premolar at axial, coronal and sagittal section. The actual diameter of root in maxillary premolar and the projection diameter at the center vertical angle of 45° and horizontal angle of 38.5° were measured with CBCT. The data was analyzed with SPSS12.0 software package for Student's t test. RESULTS: There were no significant differences between the actual diameter of double root tip which was (3.74±0.22)mm and projection diameter which was (3.69±0.16)mm of maxillary premolar at the central vertical angle of 45° and horizontal angle of 38.5° with CBCT (P>0.05); There were also no significant difference between the actual diameter of middle 1/3 section of buccal-lingual diameter (7.87±0.66)mm and projection diameter (7.95±0.52)mm of maxillary premolar at the center vertical angle of 45° and horizontal angle of 38.5° with CBCT (P>0.05). CONCLUSION: CBCT can provide an evidence for radiographic method of increasing vertical angle for identifying double root of maxillary premolar.

Generation of male germ cells from induced pluripotent stem cells (iPS cells): an in vitro and in vivo study.

Recent studies have reported that induced pluripotent stem (iPS) cells from mice and humans can differentiate into primordial germ cells. However, whether iPS cells are capable of producing male germ cells is not known. The objective of this study was to investigate the differentiation potential of mouse iPS cells into spermatogonial stem cells and late-stage male germ cells. We used an approach that combines in vitro differentiation and in vivo transplantation. Embryoid bodies (EBs) were obtained from iPS cells using leukaemia inhibitor factor (LIF)-free medium. Quantitative PCR revealed a decrease in Oct4 expression and an increase in Stra8 and Vasa mRNA in the EBs derived from iPS cells. iPS cell-derived EBs were induced by retinoic acid to differentiate into spermatogonial stem cells (SSCs), as evidenced by their expression of VASA, as well as CDH1 and GFRα1, which are markers of SSCs. Furthermore, these germ cells derived from iPS cells were transplanted into recipient testes of mice that had been pre-treated with busulfan. Notably, iPS cell-derived SSCs were able to differentiate into male germ cells ranging from spermatogonia to round spermatids, as shown by VASA and SCP3 expression. This study demonstrates that iPS cells have the potential to differentiate into late-stage male germ cells. The derivation of male germ cells from iPS cells has potential applications in the treatment of male infertility and provides a model for uncovering the molecular mechanisms underlying male germ cell development.

Reconstruction of alveolar bone defects using bone morphogenetic protein 2 mediated rabbit dental pulp stem cells seeded on nano-hydroxyapatite/collagen/poly(L-lactide).

The objective of the present study was to evaluate the capacity of a tissue-engineered bone complex of recombinant human bone morphogenetic protein 2 (rhBMP-2)-mediated dental pulp stem cells (DPSCs) and nano-hydroxyapatite/collagen/poly(L-lactide) (nHAC/PLA) to reconstruct critical-size alveolar bone defects in New Zealand rabbit. Autologous DPSCs were isolated from rabbit dental pulp tissue and expanded ex vivo to enrich DPSCs numbers, and then their attachment and differentiation capability were evaluated when cultured on the culture plate or nHAC/PLA. The alveolar bone defects were treated with nHAC/PLA, nHAC/PLA+rhBMP-2, nHAC/PLA+DPSCs, nHAC/PLA+DPSCs+rhBMP-2, and autogenous bone (AB) obtained from iliac bone or were left untreated as a control. X-ray and a polychrome sequential fluorescent labeling were performed postoperatively and the animals were sacrificed 12 weeks after operation for histological observation and histomorphometric analysis. Our results showed that DPSCs expressed STRO-1 and vementin, and favored osteogenesis and adipogenesis in conditioned media. DPSCs attached and spread well, and retained their osteogenic phenotypes on nHAC/PLA. The rhBMP-2 could significantly increase protein content, alkaline phosphatase activity/protein, osteocalcin content, and mineral formation of DPSCs cultured on nHAC/PLA. The X-ray graph, the fluorescent, histological observation, and histomorphometric analysis showed that the nHAC/PLA+DPSCs+rhBMP-2 tissue-engineered bone complex had an earlier mineralization and more bone formation inside the scaffold than nHAC/PLA, nHAC/PLA+rhBMP-2, and nHAC/PLA+DPSCs, or even autologous bone. Implanted DPSCs' contribution to new bone was detected through transfected eGFP genes. Our findings indicated that stem cells existed in adult rabbit dental pulp tissue. The rhBMP-2 promoted osteogenic capability of DPSCs as a potential cell source for periodontal bone regeneration. The nHAC/PLA could serve as a good scaffold for autologous DPSC seeding, proliferation, and differentiation. The tissue-engineered bone complex with nHAC/PLA, rhBMP-2, and autologous DPSCs might be a better alternative to autologous bone for the clinical reconstruction of periodontal bone defects.

[Spontaneous differentiation potency of induced pluripotent stem cells into male germ cells in vitro].

OBJECTIVE: To explore the expression profile of male germ cell-associated genes during the spontaneous differentiation of induced pluripotent stem cells (iPS) and assess the potency of their spontaneous differentiation into male germ cells in vitro. METHODS: Embryoid body (EB) formation was used to promote the spontaneous differentiation of iPS into male germ cells, and the expressions of germ cell-associated genes were detected by real-time PCR and PCR. RESULTS: Real-time PCR and PCR revealed different expression levels of relevant genes at different times of iPS spontaneous differentiation into male germ cells. Each of the 9 genes analyzed exhibited one of the four temporal expression patterns: wavelike increase of Oct4, progressive decrease of Dppa3 and Stra8, wavelike decrease of Dazl, and decrease following initial increase of Tex14, Msy2, Scp1, Scp3 and Akap3. CONCLUSION: Induced pluripotent stem cells express male germ cell-associated genes and male haploid genes during their spontaneous differentiation through EB formation, and have the potency of differentiating into male gametes.

Evaluation of x-inactivation status and cytogenetic stability of human dermal fibroblasts after long-term culture.

Human primary fibroblasts are a popular type of somatic cells for the production of induced pluripotent stem (iPS) cells. Here we characterized biological properties of primary fibroblasts in terms of cell-growth rate, cytogenetic stability, and the number of inactive X chromosomes during long-term passaging. We produced eight lines of female human dermal fibroblasts (HDFs) and found normal karyotype and expected pattern of X chromosome inactivation (XCI) at low passages (Passage P1-5). However, four out of the eight HDF lines at high passage numbers (≥ P10) exhibited duplicated hallmarks of inactive X chromosome including two punctuate signals of histone H3 lysine 27 trimethylation (H3K27me3) and X inactive-specific transcript (XIST) RNA signals in approximately 8.5-18.5% of the cells. Our data suggest that the copy number of inactive X chromosomes in a subset of female HDF is increased by a two-fold. Consistently, DNA fluorescent in situ hybridization (FISH) identified 3-4 copies of X chromosomes in one nucleus in this subset of cells with two inactive Xs. We conclude that female HDF cultures exhibit a higher risk of genetic anomalies such as carrying an increased number of X chromosomes including both active and inactive X chromosomes at a high passage (≥ P10).