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Purine biosynthesis and metabolism,conserved in all living organisms,is essential for cellular energy homeostasis and nucleic acid synthesis. The de novo synthesis of purine precursors is under tight negative feedback regulation mediated by adenosine and guanine nucleotides. We describe a distinct early-onset neurodegenerative condition resulting from mutations in the adenosine monophosphate deaminase 2 gene (AMPD2). Patients have characteristic brain imaging features of pontocerebellar hypoplasia (PCH) due to loss of brainstem and cerebellar parenchyma. We found that AMPD2 plays an evolutionary conserved role in the maintenance of cellular guanine nucleotide pools by regulating the feedback inhibition of adenosine derivatives on de novo purine synthesis. AMPD2 deficiency results in defective GTP-dependent initiation of protein translation,which can be rescued by administration of purine precursors. These data suggest AMPD2-related PCH as a potentially treatable early-onset neurodegenerative disease. ?? 2013 Elsevier Inc. View Publication

Human embryonic stem cells (hESCs) are emerging as an attractive alternative source for cell replacement therapy since the cells can be expanded in culture indefinitely and differentiated into any cell types in the body. In order to optimize cell-to-cell interaction,cell proliferation and differentiation into specific lineages as well as tissue organization,it is important to provide a microenvironment for the hESCs which mimics the stem cell niche. One approach is to provide a three-dimensional (3D) environment such as encapsulation. We present an approach to culture and differentiate hESCs into midbrain dopamine (mdDA) neurons in a 3D microenvironment using alginate microcapsules for the first time. A detailed gene and protein expression analysis during neuronal differentiation showed an increased gene and protein expression of various specific DA neuronal markers,particularly tyrosine hydroxylase (TH) by textgreater100 folds after 2weeks and at least 50% higher expression after 4weeks respectively,compared to cells differentiated under conventional two-dimensional (2D) platform. The encapsulated TH+ cells co-expressed mdDA neuronal markers,forkhead box protein A-2 (FOXA2) and pituitary homeobox-3 (PITX3) after 4weeks and secreted approximately 60pg/ml/106 cells higher DA level when induced. We propose that the 3D platform facilitated an early onset of DA neuronal generation compared to that with conventional 2D system which also secretes more DA under potassium-induction. It is a very useful model to study the proliferation and directed differentiation of hESCs to various lineages,particularly to mdDA neurons. This 3D system also allows the separation of feeder cells from hESCs during the process of differentiation and also has potential for immune-isolation during transplantation studies. ?? 2013 Elsevier B.V. View Publication

Development of therapeutics for genetically complex neurodegenerative diseases such as sporadic amyotrophic lateral sclerosis (ALS) has largely been hampered by lack of relevant disease models. Reprogramming of sporadic ALS patients' fibroblasts into induced pluripotent stem cells (iPSC) and differentiation into affected neurons that show a disease phenotype could provide a cellular model for disease mechanism studies and drug discovery. Here we report the reprogramming to pluripotency of fibroblasts from a large cohort of healthy controls and ALS patients and their differentiation into motor neurons. We demonstrate that motor neurons derived from three sALS patients show de novo TDP-43 aggregation and that the aggregates recapitulate pathology in postmortem tissue from one of the same patients from which the iPSC were derived. We configured a high-content chemical screen using the TDP-43 aggregate endpoint both in lower motor neurons and upper motor neuron like cells and identified FDA-approved small molecule modulators including Digoxin demonstrating the feasibility of patient-derived iPSC-based disease modeling for drug screening. View Publication

Human pluripotent stem cells (hPSCs) have been differentiated to astroglia,but the utilization of hPSC-derived astroglia as cell therapy for neurological diseases has not been well studied. Astroglia are heterogeneous,and not all astroglia are equivalent in promoting neural repair. A prerequisite for cell therapy is to derive defined cell populations with superior therapeutic effects. Here we use an Olig2-GFP human embryonic stem cell (hESC) reporter to demonstrate that hESC-derived Olig2(+) progenitors generate a subtype of previously uncharacterized astroglia (Olig2PC-Astros). These Olig2PC-Astros differ substantially from astroglia differentiated from Olig2-negative hESC-derived neural progenitor cells (NPC-Astros),particularly in their neuroprotective properties. When grafted into brains subjected to global ischaemia,Olig2PC-Astros exhibit superior neuroprotective effects and improved behavioural outcome compared to NPC-Astros. Thus,this new paradigm of human astroglial differentiation is useful for studying the heterogeneity of human astroglia,and the unique Olig2PC-Astros may constitute a new cell therapy for treating cerebral ischaemia and other neurological diseases. View Publication

Little is known about chromosomal loopings involving proximal promoter and distal enhancer elements regulating GABAergic gene expression,including changes in schizophrenia and other psychiatric conditions linked to altered inhibition. Here,we map in human chromosome 2q31 the 3D configuration of 200 kb of linear sequence encompassing the GAD1 GABA synthesis enzyme gene locus,and we describe a loop formation involving the GAD1 transcription start site and intergenic noncoding DNA elements facilitating reporter gene expression. The GAD1-TSS(-50kbLoop) was enriched with nucleosomes epigenetically decorated with the transcriptional mark,histone H3 trimethylated at lysine 4,and was weak or absent in skin fibroblasts and pluripotent stem cells compared with neuronal cultures differentiated from them. In the prefrontal cortex of subjects with schizophrenia,GAD1-TSS(-50kbLoop) was decreased compared with controls,in conjunction with downregulated GAD1 expression. We generated transgenic mice expressing Gad2 promoter-driven green fluorescent protein-conjugated histone H2B and confirmed that Gad1-TSS(-55kbLoop),the murine homolog to GAD1-TSS(-50kbLoop),is a chromosomal conformation specific for GABAergic neurons. In primary neuronal culture,Gad1-TSS(-55kbLoop) and Gad1 expression became upregulated when neuronal activity was increased. We conclude that 3D genome architectures,including chromosomal loopings for promoter-enhancer interactions involved in the regulation of GABAergic gene expression,are conserved between the rodent and primate brain,and subject to developmental and activity-dependent regulation,and disordered in some cases with schizophrenia. More broadly,the findings presented here draw a connection between noncoding DNA,spatial genome architecture,and neuronal plasticity in development and disease. View Publication

The recently identified GGGGCC repeat expansion in the noncoding region of C9ORF72 is the most common pathogenic mutation in patients with frontotemporal dementia (FTD) or amyotrophic lateral sclerosis (ALS). We generated a human neuronal model and investigated the pathological phenotypes of human neurons containing GGGGCC repeat expansions. Skin biopsies were obtained from two subjects who had textgreater1,000 GGGGCC repeats in C9ORF72 and their respective fibroblasts were used to generate multiple induced pluripotent stem cell (iPSC) lines. After extensive characterization,two iPSC lines from each subject were selected,differentiated into postmitotic neurons,and compared with control neurons to identify disease-relevant phenotypes. Expanded GGGGCC repeats exhibit instability during reprogramming and neuronal differentiation of iPSCs. RNA foci containing GGGGCC repeats were present in some iPSCs,iPSC-derived human neurons and primary fibroblasts. The percentage of cells with foci and the number of foci per cell appeared to be determined not simply by repeat length but also by other factors. These RNA foci do not seem to sequester several major RNA-binding proteins. Moreover,repeat-associated non-ATG (RAN) translation products were detected in human neurons with GGGGCC repeat expansions and these neurons showed significantly elevated p62 levels and increased sensitivity to cellular stress induced by autophagy inhibitors. Our findings demonstrate that key neuropathological features of FTD/ALS with GGGGCC repeat expansions can be recapitulated in iPSC-derived human neurons and also suggest that compromised autophagy function may represent a novel underlying pathogenic mechanism. View Publication

Stroke is a leading cause of human death and disability in the adult population in the United States and around the world. While stroke treatment is limited,stem cell transplantation has emerged as a promising regenerative therapy to replace or repair damaged tissues and enhance functional recovery after stroke. Recently,the creation of induced pluripotent stem (iPS) cells through reprogramming of somatic cells has revolutionized cell therapy by providing an unlimited source of autologous cells for transplantation. In addition,the creation of vector-free and transgene-free human iPS (hiPS) cells provides a new generation of stem cells with a reduced risk of tumor formation that was associated with the random integration of viral vectors seen with previous techniques. However,the potential use of these cells in the treatment of ischemic stroke has not been explored. In the present investigation,we examined the neuronal differentiation of vector-free and transgene-free hiPS cells and the transplantation of hiPS cell-derived neural progenitor cells (hiPS-NPCs) in an ischemic stroke model in mice. Vector-free hiPS cells were maintained in feeder-free and serum-free conditions and differentiated into functional neurons in vitro using a newly developed differentiation protocol. Twenty eight days after transplantation in stroke mice,hiPS-NPCs showed mature neuronal markers in vivo. No tumor formation was seen up to 12 months after transplantation. Transplantation of hiPS-NPCs restored neurovascular coupling,increased trophic support and promoted behavioral recovery after stroke. These data suggest that using vector-free and transgene-free hiPS cells in stem cell therapy are safe and efficacious in enhancing recovery after focal ischemic stroke in mice. View Publication

Neural stem cells (NSCs) possess immunosuppressive characteristics,but effects of NSCs on human dendritic cells (DCs),the most important antigen presenting cells,are less well studied. We used an in vitro approach to evaluate the effects of human NSCs on differentiation of human blood CD14+ monocytes into DCs. NSCs derived from H1 human embryonic stem cells (hESC-NSCs) and human ReNcell NSC line,as well as human bone marrow derived mesenchymal stem cells (MSCs),were tested. We observed that in response to treatment with interleukin-4 and granulocyte macrophage colony-stimulating factor CD14+ monocytes co-cultured with NSCs were able to down-regulate CD14 and up-regulate the differentiation marker CD1a,whereas MSC co-culture strongly inhibited CD1a expression and supported prolonged expression of CD14. A similar difference between NSCs and MSCs was noted when lipopolysaccharides were included to induce maturation of monocyte-derived DCs. However,when effects on the function of derived DCs were investigated,NSCs suppressed the elevation of the DC maturation marker CD83,although not the up-regulation of costimulatory molecules CD80,CD86 and CD40,and impaired the functional capacity of the derived DCs to stimulate alloreactive T cells. We did not observe any obvious difference between hESC-NSCs and ReNcell NSCs in inhibiting DC maturation and function. Our data suggest that although human NSCs are less effective than human MSCs in suppressing monocyte differentiation into DCs,these stem cells can still affect the function of DCs,ultimately regulating specific immune responses. View Publication

Induced pluripotent stem cells (iPSCs) hold promise for the treatment of motoneuron diseases because of their distinct features including pluripotency,self-derivation and potential ability to differentiate into motoneurons. However,it is still unknown whether human iPSC-derived motoneurons can functionally innervate target muscles in vivo,which is the definitive sign of successful cell therapy for motoneuron diseases. In the present study,we demonstrated that human iPSCs derived from mesenchymal cells of the umbilical cord possessed a high yield in neural differentiation. Using a chemically-defined in vitro system,human iPSCs efficiently differentiated into motoneurons which displayed typical morphology,expressed specific molecules,and generated repetitive trains of action potentials. When transplanted into the injured musculocutaneous nerve of rats,they survived robustly,extended axons along the nerve,and formed functional connections with the target muscle (biceps brachii),thereby protecting the muscle from atrophy. Our study provides evidence for the first time that human iPSC-derived motoneurons are truly functional not only in vitro but also in vivo,and they have potential for stem cell-based therapies for motoneuron diseases. textcopyright 2013 Elsevier B.V. View Publication

The lipid phosphatidylinositol 3,5-bisphosphate (PtdIns(3,5)P 2),synthesised by PIKfyve,regulates a number of intracellular membrane trafficking pathways. Genetic alteration of the PIKfyve complex,leading to even a mild reduction in PtdIns(3,5)P 2,results in marked neurodegeneration via an uncharacterised mechanism. In the present study we have shown that selectively inhibiting PIKfyve activity,using YM-201636,significantly reduces the survival of primary mouse hippocampal neurons in culture. YM-201636 treatment promoted vacuolation of endolysosomal membranes followed by apoptosis-independent cell death. Many vacuoles contained intravacuolar membranes and inclusions reminiscent of autolysosomes. Accordingly,YM-201636 treatment increased the level of the autophagosomal marker protein LC3-II,an effect that was potentiated by inhibition of lysosomal proteases,suggesting that alterations in autophagy could be a contributing factor to neuronal cell death. View Publication

The mammalian central nervous system (CNS) undergoes significant expansion postnatally,producing astrocytes,oligodendrocytes and inhibitory neurons to modulate the activity of neural circuits. This is coincident in humans with the emergence of pediatric epilepsy,a condition commonly treated with valproate/valproic acid (VPA),a potent inhibitor of histone deacetylases (HDACs). The sequential activity of specific HDACs,however,may be essential for the differentiation of distinct subpopulations of neurons and glia. Here,we show that different subsets of CNS neural stem cells (NSCs) and progenitors switch expression of HDAC1 and HDAC2 as they commit to a neurogenic lineage in the subventricular zone (SVZ) and dentate gyrus (DG). The administration of VPA for only one week from P7-P14,combined with sequential injections of thymidine analogs reveals that VPA stimulates a significant and differential decrease in the production and differentiation of progeny of NSCs in the DG,rostral migratory stream (RMS),and olfactory bulb (OB). Cross-fostering VPA-treated mice revealed,however,that a postnatal failure to thrive induced by VPA treatment had a greater effect on DG neurogenesis than VPA action directly. By one month after VPA,OB interneuron genesis was significantly and differentially reduced in both periglomerular and granule neurons. Using neurosphere assays to test if VPA directly regulates NSC activity,we found that short term treatment with VPA in vivo reduced neurosphere numbers and size,a phenotype that was also obtained in neurospheres from control mice treated with VPA and an alternative HDAC inhibitor,Trichostatin A (TSA) at 0 and 3 days in vitro (DIV). Collectively,these data show that clinically used HDAC inhibitors like VPA and TSA can perturb postnatal neurogenesis; and their use should be carefully considered,especially in individuals whose brains are actively undergoing key postnatal time windows of development. View Publication

Neurogenesis decreases during aging and following cranial radiotherapy,causing a progressive cognitive decline that is currently untreatable. However,functional neural stem cells remained present in the subventricular zone of high dose-irradiated and aged mouse brains. We therefore investigated whether alterations in the neurogenic niches are perhaps responsible for the neurogenesis decline. This hypothesis was supported by the absence of proliferation of neural stem cells that were engrafted into the vascular niches of irradiated host brains. Moreover,we observed a marked increase in TGF-β1 production by endothelial cells in the stem cell niche in both middle-aged and irradiated mice. In co-cultures,irradiated brain endothelial cells induced the apoptosis of neural stem/progenitor cells via TGF-β/Smad3 signalling. Strikingly,the blockade of TGF-β signalling in vivo using a neutralizing antibody or the selective inhibitor SB-505124 significantly improved neurogenesis in aged and irradiated mice,prevented apoptosis and increased the proliferation of neural stem/progenitor cells. These findings suggest that anti-TGF-β-based therapy may be used for future interventions to prevent neurogenic collapse following radiotherapy or during aging. View Publication