RB and RB2/P130 genes cooperate with extrinsic signals to promote differentiation of rat neural stem cells

The histone demethylase PHF8 regulates astrocyte differentiation and function

Epigenetic factors have been shown to play a crucial role in X-linked intellectual disability (XLID). Here, we investigate the contribution of the XLID-associated histone demethylase PHF8 to astrocyte differentiation and function. Using genome-wide analyses and biochemical assays in mouse astrocytic cultures, we reveal a regulatory crosstalk between PHF8 and the Notch signaling pathway that balances the expression of the master astrocytic gene Nfia. Moreover, PHF8 regulates key synaptic genes in astrocytes by maintaining low levels of H4K20me3. Accordingly, astrocytic-PHF8 depletion has a striking effect on neuronal synapse formation and maturation in vitro. These data reveal that PHF8 is crucial in astrocyte development to maintain chromatin homeostasis and limit heterochromatin formation at synaptogenic genes. Our studies provide insights into the involvement of epigenetics in intellectual disability.

Circular RNA TTC3 regulates cerebral ischemia-reperfusion injury and neural stem cells by miR-372-3p/TLR4 axis in cerebral infarction

Background

Stroke serves as a prevalent cerebrovascular disorder with severe cerebral ischemia/reperfusion (CIR) injury, in which neural stem cells (NSCs) play critical roles in the recovery of cerebral function. Circular RNAs (circRNAs) have been widely found to participate in stroke and NSC modulation. However, the role of circRNA TTC3 (circTTC3) in the regulation of CIR injury and NSCs remains elusive. Here, we aimed to explore the impact of circTTC3 on CIR injury and NSCs.

Methods

The middle cerebral artery occlusion/repression (MCAO/R) model was established in C57BL/6J mice. The primary astrocytes were isolated from the cerebellum from C57BL/6J mice. The primary NSCs were obtained from rat embryos. The effect of circTTC3 on CIR injury and NSCs was analyzed by TTC staining, qPCR, Western blot, LDH colorimetric kits, MTT assays, Annexin V-FITC Apoptosis Detection Kit, luciferase reporter gene assays, and others in the system.

Results

Significantly, the expression of circTTC3 was elevated in the MCAO/R mice and oxygen and glucose deprivation (OGD)-treated astrocytes. The depletion of circTTC3 attenuated cerebral infarction, neurological score, and brain water content. The OGD treatment induced apoptosis and the levels of lactate dehydrogenase (LDH) in the astrocytes, in which circTTC3 depletion reduced this phenotype in the system. Moreover, the depletion of circTTC3 promoted the proliferation and upregulated the nestin and β-tubulin III expression in NSCs. Mechanically, circTTC3 was able to sponge miR-372-3p, and miR-372-3p can target Toll-like receptor 4 (TLR4) in NSCs. The miR-372-3p inhibitor or TLR4 overexpression could reverse circTTC3 depletion-mediated astrocyte OGD injury and NSC regulation.

Conclusion

Thus, we conclude that circTTC3 regulates CIR injury and NSCs by the miR-372-3p/TLR4 axis in cerebral infarction. Our finding presents new insight into the mechanism by which circTTC3 modulates CIR injury and NSC dysfunction. CircTTC3, miR-372-3p, and TLR4 may serve as potential targets for the treatment of CIR injury during stroke.

Lineage specific transcription factors and epigenetic regulators mediate TGFβ-dependent enhancer activation

During neurogenesis, dynamic developmental cues, transcription factors and histone modifying enzymes regulate the gene expression programs by modulating the activity of neural-specific enhancers. How transient developmental signals coordinate transcription factor recruitment to enhancers and to which extent chromatin modifiers contribute to enhancer activity is starting to be uncovered. Here, we take advantage of neural stem cells as a model to unravel the mechanisms underlying neural enhancer activation in response to the TGFβ signaling. Genome-wide experiments demonstrate that the proneural factor ASCL1 assists SMAD3 in the binding to a subset of enhancers. Once located at the enhancers, SMAD3 recruits the histone demethylase JMJD3 and the remodeling factor CHD8, creating the appropriate chromatin landscape to allow enhancer transcription and posterior gene activation. Finally, to analyze the phenotypical traits owed to cis-regulatory regions, we use CRISPR–Cas9 technology to demonstrate that the TGFβ-responsive Neurog2 enhancer is essential for proper neuronal polarization.

Divide or Commit - Revisiting the Role of Cell Cycle Regulators in Adult Hippocampal Neurogenesis

The adult dentate gyrus continuously generates new neurons that endow the brain with increased plasticity, helping to cope with changing environmental and cognitive demands. The process leading to the birth of new neurons spans several precursor stages and is the result of a coordinated series of fate decisions, which are tightly controlled by extrinsic signals. Many of these signals act through modulation of cell cycle (CC) components, not only to drive proliferation, but also for linage commitment and differentiation. In this review, we provide a comprehensive overview on key CC components and regulators, with emphasis on G₁ phase, and analyze their specific functions in precursor cells of the adult hippocampus. We explore their role for balancing quiescence versus self-renewal, which is essential to maintain a lifelong pool of neural stem cells while producing new neurons “on demand.” Finally, we discuss available evidence and controversies on the impact of CC/G₁ length on proliferation versus differentiation decisions.

Neural stem cells from a mouse model of Rett syndrome are prone to senescence, show reduced capacity to cope with genotoxic stress, and are impaired in the differentiation process

Several aspects of stem cell life are governed by epigenetic variations, such as DNA methylation, histone modifications, and chromatin remodeling. Epigenetic events are also connected with the impairment of stem cell functions. For example, during senescence, there are significant changes in chromatin organization that alter transcription. The MECP2 protein can bind methylated cytosines and contribute to regulating gene expression at one of the highest hierarchical levels. Researchers are particularly interested in this protein, as up to 90% of Rett syndrome patients have an MECP2 gene mutation. Nevertheless, the role of MECP2 in this disease remains poorly understood. We used a mouse model of Rett syndrome to evaluate whether residual MECP2 activity in neural stem cells (NSCs) induced the senescence phenomena that could affect stem cell function. Our study clearly demonstrated that the reduced expression of MECP2 is connected with an increase in senescence, an impairment in proliferation capacity, and an accumulation of unrepaired DNA foci. Mecp2^+/− NSCs did not cope with genotoxic stress in the same way as the control cells did. Indeed, after treatment with different DNA-damaging agents, the NSCs from mice with mutated Mecp2 accumulated more DNA damage foci (γ-H2AX+) and were more prone to cell death than the controls. Senescence in Mecp2^+/− NSCs decreased the number of stem cells and progenitors and gave rise to a high percentage of cells that expressed neither stem/progenitor nor differentiation markers. These cells could be senescent and dysfunctional.

In Rett syndrome, neural stem cells lose some of their “stem cell like” properties, impairing brain functions. Patients with this rare neurological condition, almost exclusively girls, show impaired movement and speech beginning at 6–18 months of age. Mutations in the MECP2 gene are known to be involved, but the specifics are poorly understood. Umberto Galderisi at Temple University in Philadelphia and co-workers in Italy used a mouse model to trace how MECP2 mutations affect neural stem cells. They found that the mutated cells lost key stem cell abilities, including the capacity to renew themselves by dividing, and the ability to differentiate, or turn into other cell types. The cells were also highly susceptible to DNA damage and unable to repair it. These results improve our understanding of Rett syndrome and may help develop new treatments.

Cooperativity between MAPK and PI3K signaling activation is required for glioblastoma pathogenesis

BACKGROUND

Glioblastoma (GBM) genomes feature recurrent genetic alterations that dysregulate core intracellular signaling pathways, including the G1/S cell cycle checkpoint and the MAPK and PI3K effector arms of receptor tyrosine kinase (RTK) signaling. Elucidation of the phenotypic consequences of activated RTK effectors is required for the design of effective therapeutic and diagnostic strategies.

METHODS

Genetically defined, G1/S checkpoint-defective cortical murine astrocytes with constitutively active Kras and/or Pten deletion mutations were used to systematically investigate the individual and combined roles of these 2 RTK signaling effectors in phenotypic hallmarks of glioblastoma pathogenesis, including growth, migration, and invasion in vitro. A novel syngeneic orthotopic allograft model system was used to examine in vivo tumorigenesis.

RESULTS

Constitutively active Kras and/or Pten deletion mutations activated both MAPK and PI3K signaling. Their combination led to maximal growth, migration, and invasion of G1/S-defective astrocytes in vitro and produced progenitor-like transcriptomal profiles that mimic human proneural GBM. Activation of both RTK effector arms was required for in vivo tumorigenesis and produced highly invasive, proneural-like GBM.

CONCLUSIONS

These results suggest that cortical astrocytes can be transformed into GBM and that combined dysregulation of MAPK and PI3K signaling revert G1/S-defective astrocytes to a primitive gene expression state. This genetically-defined, immunocompetent model of proneural GBM will be useful for preclinical development of MAPK/PI3K-targeted, subtype-specific therapies.

Efficient cultivation of neural stem cells with controlled delivery of FGF-2

Neural stem cells (NSCs) raised the hope for cell-based therapies in human neurodevelopmental and neurodegenerative diseases. Current research strategies aim to isolate, enrich, and propagate homogeneous populations of neural stem cells. Unfortunately, several concerns with NSC cultures currently may limit their therapeutic promise. Exhaustion of growth factors and/or their uncontrolled release with burst and fall in their concentration may greatly affect the in vitro behavior of NSCs. In this context, we investigate whether a device containing heparan sulfate (HS), which is a co-factor in growth factor-mediated cell proliferation and differentiation, could potentiate and prolong the delivery of fibroblast growth factor-2 (FGF-2) and thus improve in vitro NSC cultivation. We demonstrated that NSCs cultivated in media with a controlled release of FGF-2 from a polyelectrolyte polymer showed a higher proliferation rate, and reduced apoptosis and senescence. In these experimental conditions NSCs preserve their stemness properties for a longer period of time compared with controls. Also of interest is that cell fate properties are conserved as well. The controlled release of FGF-2 reduced the level of oxidative stress and this is associated with a lower level of damaged DNA. This result may explain the reduced level of senescence and apoptosis in NSCs cultivated in the presence of hydrogel-releasing FGF-2.

Apoptotic caspases regulate induction of iPSCs from human fibroblasts

The molecular mechanisms involved in the derivation of induced pluripotent stem cells (iPSCs) from differentiated cells are poorly understood. Here we report that caspases 3 and 8, two proteases associated with apoptotic cell death, play critical roles in induction of iPSCs from human fibroblasts. Activation of caspases 3 and 8 occurs soon after transduction of iPSC-inducing transcription factors. Oct-4, a key iPSC transcription factor, is responsible for the activation. Inhibition of caspase 3 or 8 in human fibroblast cells partially or completely (respectively) prevents the induction of iPSCs. Furthermore, retinoblastoma susceptibility (Rb) protein appears to be one of the factors that act downstream of the caspases. We propose that caspases are key facilitators of nuclear reprogramming in iPSC induction.

The rb pathway and cancer therapeutics

The retinoblastoma gene, Rb, was originally identified as the tumor suppressor gene mutated in a rare childhood cancer called retinoblastoma (reviewed in [1]). Subsequent studies showed that Rb functions in a pathway that is often functionally inactivated in a large majority of human cancers. Interestingly, recent studies showed that in certain types of cancers, Rb function is actually required for cancer development. The intimate link between the Rb pathway and cancer development suggests that the status of Rb activity can potentially be used to develop targeted therapy. However, a prerequisite will be to understand the role of Rb and its interaction with other signaling pathways in cancer development. In this review, we will discuss the roles of Rb in proliferation, apoptosis and differentiation by reviewing the recent findings in both mammalian systems and different model organisms. In addition, we will discuss strategies that can be employed that specifically target cancer cells based on the status of the Rb pathway.

Cyclin-dependent kinase 2-associating protein 1 commits murine embryonic stem cell differentiation through retinoblastoma protein regulation

Mouse embryonic stem cells (mESCs) maintain pluripotency and indefinite self-renewal through yet to be defined molecular mechanisms. Leukemia inhibitory factor has been utilized to maintain the symmetrical self-renewal and pluripotency of mESCs in culture. It has been suggested that molecules with significant cellular effects on retinoblastoma protein (pRb) or its related pathways should have functional impact on mESC proliferation and differentiation. However, the involvement of pRb in pluripotent differentiation of mESCs has not been extensively elaborated. In this paper, we present novel experimental data indicating that Cdk2ap1 (cyclin-dependent kinase 2-associating protein 1), an inhibitor of G(1)/S transition through down-regulation of CDK2 and an essential gene for early embryonic development, confers competency for mESC differentiation. Targeted disruption of Cdk2ap1 in mESCs resulted in abrogation of leukemia inhibitory factor withdrawal-induced differentiation, along with altered pRb phosphorylation. The differentiation competency of the Cdk2ap1(-/-) mESCs was restored upon the ectopic expression of Cdk2ap1 or a nonphosphorylatable pRb mutant (mouse Ser(788) --> Ala), suggesting that the CDK2AP1-mediated differentiation of mESCs was elicited through the regulation of pRb. Further analysis on mESC maintenance or differentiation-related gene expression supports the phosphorylation at serine 788 in pRb plays a significant role for the CDK2AP1-mediated differentiation of mESCs. These data clearly demonstrate that CDK2AP1 is a competency factor in the proper differentiation of mESCs by modulating the phosphorylation level of pRb. This sheds light on the role of the establishment of the proper somatic cell type cell cycle regulation for mESCs to enter into the differentiation process.

Differentiation is coupled to changes in the cell cycle regulatory apparatus of human embryonic stem cells

Mouse embryonic stem cells (mESC) exhibit cell cycle properties entirely distinct from those of somatic cells. Here we investigated the cell cycle characteristics of human embryonic stem cells (hESC). HESC could be sorted into populations based on the expression level of the cell surface stem cell marker GCTM-2. Compared to mESC, a significantly higher proportion of hESC (GCTM-2(+) Oct-4(+) cells) resided in G(1) and retained G(1)-phase-specific hypophosphorylated retinoblastoma protein (pRb). We showed that suppression of traverse through G(1) is sufficient to promote hESC differentiation. Like mESC, hESC expressed cyclin E constitutively, were negative for D-type cyclins, and did not respond to CDK-4 inhibition. By contrast, cyclin A expression was periodic in hESC and coincided with S and G(2)/M phase progression. FGF-2 acted solely to sustain hESC pluripotency rather than to promote cell cycle progression or inhibit apoptosis. Differentiation increased G(1)-phase content, reinstated cyclin D activity, and restored the proliferative response to FGF-2. Treatment with CDK-2 inhibitor delayed hESC in G(1) and S phase, resulting in accumulation of cells with hypophosphorylated pRb, GCTM-2, and Oct-4 and, interestingly, a second pRb(+) GCTM-2(+) subpopulation lacking Oct-4. We discuss evidence for a G(1)-specific, pRb-dependent restriction checkpoint in hESC closely associated with the regulation of pluripotency.