Instruct: Given a scientific claim, retrieve passages that support or refute the claim.
Query: APOE4 expression in iPSC-derived neurons results in decreased tau phosphorylation.
Efforts to develop drugs for Alzheimer's disease (AD) have shown promise in animal studies, only to fail in human trials, suggesting a pressing need to study AD in human model systems. Using human neurons derived from induced pluripotent stem cells that expressed apolipoprotein E4 (ApoE4), a variant of the APOE gene product and the major genetic risk factor for AD, we demonstrated that ApoE4-expressing neurons had higher levels of tau phosphorylation, unrelated to their increased production of amyloid-β (Aβ) peptides, and that they displayed GABAergic neuron degeneration. ApoE4 increased Aβ production in human, but not in mouse, neurons. Converting ApoE4 to ApoE3 by gene editing rescued these phenotypes, indicating the specific effects of ApoE4. Neurons that lacked APOE behaved similarly to those expressing ApoE3, and the introduction of ApoE4 expression recapitulated the pathological phenotypes, suggesting a gain of toxic effects from ApoE4. Treatment of ApoE4-expressing neurons with a small-molecule structure corrector ameliorated the detrimental effects, thus showing that correcting the pathogenic conformation of ApoE4 is a viable therapeutic approach for ApoE4-related AD.
Within the developing mammalian CNS, growth factors direct multipotent precursors to generate neurons versus glia, a process that if perturbed might lead to neural dysfunction. In this regard, genetic mutations resulting in constitutive activation of the protein tyrosine phosphatase SHP-2 cause Noonan Syndrome (NS), which is associated with learning disabilities and mental retardation. Here, we demonstrate that genetic knockdown of SHP-2 in cultured cortical precursors or in the embryonic cortex inhibited basal neurogenesis and caused enhanced and precocious astrocyte formation. Conversely, expression of an NS SHP-2 mutant promoted neurogenesis and inhibited astrogenesis. Neural cell-fate decisions were similarly perturbed in a mouse knockin model that phenocopies human NS. Thus, SHP-2 instructs precursors to make neurons and not astrocytes during the neurogenic period, and perturbations in the relative ratios of these two cell types upon constitutive SHP-2 activation may contribute to the cognitive impairments in NS patients.
Reprogramming somatic cells to induced pluripotent stem cells (iPSCs) resets their identity back to an embryonic age and, thus, presents a significant hurdle for modeling late-onset disorders. In this study, we describe a strategy for inducing aging-related features in human iPSC-derived lineages and apply it to the modeling of Parkinson's disease (PD). Our approach involves expression of progerin, a truncated form of lamin A associated with premature aging. We found that expression of progerin in iPSC-derived fibroblasts and neurons induces multiple aging-related markers and characteristics, including dopamine-specific phenotypes such as neuromelanin accumulation. Induced aging in PD iPSC-derived dopamine neurons revealed disease phenotypes that require both aging and genetic susceptibility, such as pronounced dendrite degeneration, progressive loss of tyrosine hydroxylase (TH) expression, and enlarged mitochondria or Lewy-body-precursor inclusions. Thus, our study suggests that progerin-induced aging can be used to reveal late-onset age-related disease features in hiPSC-based disease models.
Neurodegenerative diseases, such as frontotemporal dementia (FTD), are often associated with behavioral deficits, but the underlying anatomical and molecular causes remain poorly understood. Here we show that forebrain-specific expression of FTD-associated mutant CHMP2B in mice causes several age-dependent neurodegenerative phenotypes, including social behavioral impairments. The social deficits were accompanied by a change in AMPA receptor (AMPAR) composition, leading to an imbalance between Ca(2+)-permeable and Ca(2+)-impermeable AMPARs. Expression of most AMPAR subunits was regulated by the brain-enriched microRNA miR-124, whose abundance was markedly decreased in the superficial layers of the cerebral cortex of mice expressing the mutant CHMP2B. We found similar changes in miR-124 and AMPAR levels in the frontal cortex and induced pluripotent stem cell-derived neurons from subjects with behavioral variant FTD. Moreover, ectopic miR-124 expression in the medial prefrontal cortex of mutant mice decreased AMPAR levels and partially rescued behavioral deficits. Knockdown of the AMPAR subunit Gria2 also alleviated social impairments. Our results identify a previously undescribed mechanism involving miR-124 and AMPARs in regulating social behavior in FTD and suggest a potential therapeutic avenue.
Pathogenesis of Alzheimer’s disease (AD), which is characterised by accumulation of extracellular deposits of β-amyloid peptide (Aβ) in the brain, has recently been linked to vascular disorders such as ischemia and stroke. Aβ is constantly produced in the brain from amyloid precursor protein (APP) through its cleavage by β- and γ-secretases and certain Aβ species are toxic for neurones. The brain has an endogenous mechanism of Aβ removal via proteolytic degradation and the zinc metalloproteinase neprilysin (NEP) is a critical regulator of Aβ concentration. Down-regulation of NEP could predispose to AD. By comparing the effects of hypoxia and oxidative stress on expression and activity of the Aβ-degrading enzyme NEP in human neuroblastoma NB7 cells and rat primary cortical neurones we have demonstrated that hypoxia reduced NEP expression at the protein and mRNA levels as well as its activity. On contrary in astrocytes hypoxia increased NEP mRNA expression.
Down syndrome (DS), or Trisomy 21 (T21) syndrome, one of the most common chromosomal abnormalities, is caused by an extra duplication of chromosome 21. In studies of neuron development, experimental models based on human cells are considered to be the most desired and accurate for basic research. The generation of diseased induced pluripotetn stem (iPS) cell is a critical step in understanding the developmental stages of complex neuronal diseases. Here, we generated human DS iPS cell lines from second trimester amniotic fluid (AF) cells with T21 by co-expressing Yamanaka factors through lentiviral delivery and subsequently differentiated them into neuronal progenitor cells (NPCs) for further analyses. T21 AF-iPS cells were characterized for the expression of pluripotent markers and for their ability to differentiate into all three germ layers by forming embryoid bodies in vitro and teratomas in vivo. The T21 AF-iPS cells maintained their unique pattern of chromosomal karyotypes: three pairs of chromosome 21. The level of amyloid precursor protein was significantly increased in NPCs derived from T21 AF-iPS cells compared with NPCs from normal AF-iPS cells. The expression levels of miR-155 and miR-802 in T21 AF-iPS-NPCs were highly elevated in the presence of low expression of MeCP2. We observed that T21 iPS-NPCs generated fewer neurons compared with controls. T21 iPS-NPCs exhibit developmental defects during neurogenesis. Our findings suggest that T21 AF-iPS cells serve as a good source to further elucidate the impairment neurogenesis of DS and the onset of Alzheimer's disease.
The loss of a glutamic acid residue in the AAA-ATPase (ATPases associated with diverse cellular activities) torsinA is responsible for most cases of early onset autosomal dominant primary dystonia. In this study, we found that snapin, which binds SNAP-25 (synaptosome-associated protein of 25,000 Da) and enhances the association of the SNARE complex with synaptotagmin, is an interacting partner for both wild type and mutant torsinA. Snapin co-localized with endogenous torsinA on dense core granules in PC12 cells and was recruited to perinuclear inclusions containing mutant DeltaE-torsinA in neuroblastoma SH-SY5Y cells. In view of these observations, synaptic vesicle recycling was analyzed using the lipophilic dye FM1-43 and an antibody directed against an intravesicular epitope of synaptotagmin I. We found that overexpression of wild type torsinA negatively affects synaptic vesicle endocytosis. Conversely, overexpression of DeltaE-torsinA in neuroblastoma cells increases FM1-43 uptake. Knockdown of snapin and/or torsinA using small interfering RNAs had a similar inhibitory effect on the exo-endocytic process. In addition, down-regulation of torsinA causes the persistence of synaptotagmin I on the plasma membrane, which closely resembles the effect observed by the overexpression of the DeltaE-torsinA mutant. Altogether, these findings suggest that torsinA plays a role together with snapin in regulated exocytosis and that DeltaE-torsinA exerts its pathological effects through a loss of function mechanism. This may affect neuronal uptake of neurotransmitters, such as dopamine, playing a role in the development of dystonic movements.
Reprogramming of somatic cells into pluripotency stem cell state has opened new opportunities in cell replacement therapy and disease modeling in a number of neurological disorders. It still remains unknown, however, to what degree the grafted human-induced pluripotent stem cells (hiPSCs) differentiate into a functional neuronal phenotype and if they integrate into the host circuitry. Here, we present a detailed characterization of the functional properties and synaptic integration of hiPSC-derived neurons grafted in an in vitro model of hyperexcitable epileptic tissue, namely organotypic hippocampal slice cultures (OHSCs), and in adult rats in vivo. The hiPSCs were first differentiated into long-term self-renewing neuroepithelial stem (lt-NES) cells, which are known to form primarily GABAergic neurons. When differentiated in OHSCs for 6 weeks, lt-NES cell-derived neurons displayed neuronal properties such as tetrodotoxin-sensitive sodium currents and action potentials (APs), as well as both spontaneous and evoked postsynaptic currents, indicating functional afferent synaptic inputs. The grafted cells had a distinct electrophysiological profile compared to host cells in the OHSCs with higher input resistance, lower resting membrane potential, and APs with lower amplitude and longer duration. To investigate the origin of synaptic afferents to the grafted lt-NES cell-derived neurons, the host neurons were transduced with Channelrhodopsin-2 (ChR2) and optogenetically activated by blue light. Simultaneous recordings of synaptic currents in grafted lt-NES cell-derived neurons using whole-cell patch-clamp technique at 6 weeks after grafting revealed limited synaptic connections from host neurons. Longer differentiation times, up to 24 weeks after grafting in vivo, revealed more mature intrinsic properties and extensive synaptic afferents from host neurons to the lt-NES cell-derived neurons, suggesting that these cells require extended time for differentiation/maturation and synaptogenesis. However, even at this later time point, the grafted cells maintained a higher input resistance. These data indicate that grafted lt-NES cell-derived neurons receive ample afferent input from the host brain. Since the lt-NES cells used in this study show a strong propensity for GABAergic differentiation, the host-to-graft synaptic afferents may facilitate inhibitory neurotransmitter release, and normalize hyperexcitable neuronal networks in brain diseases, for example, such as epilepsy.
Mutations or duplications in MECP2 cause Rett and Rett-like syndromes, neurodevelopmental disorders characterized by mental retardation, motor dysfunction, and autistic behaviors. MeCP2 is expressed in many mammalian tissues and functions as a global repressor of transcription; however, the molecular mechanisms by which MeCP2 dysfunction leads to the neural-specific phenotypes of RTT remain poorly understood. Here, we show that neuronal activity and subsequent calcium influx trigger the de novo phosphorylation of MeCP2 at serine 421 (S421) by a CaMKII-dependent mechanism. MeCP2 S421 phosphorylation is induced selectively in the brain in response to physiological stimuli. Significantly, we find that S421 phosphorylation controls the ability of MeCP2 to regulate dendritic patterning, spine morphogenesis, and the activity-dependent induction of Bdnf transcription. These findings suggest that, by triggering MeCP2 phosphorylation, neuronal activity regulates a program of gene expression that mediates nervous system maturation and that disruption of this process in individuals with mutations in MeCP2 may underlie the neural-specific pathology of RTT.
Alzheimer’s disease is the most common form of dementia, characterized by two pathological hallmarks: amyloid-β plaques and neurofibrillary tangles. The amyloid hypothesis of Alzheimer’s disease posits that the excessive accumulation of amyloid-β peptide leads to neurofibrillary tangles composed of aggregated hyperphosphorylated tau. However, to date, no single disease model has serially linked these two pathological events using human neuronal cells. Mouse models with familial Alzheimer’s disease (FAD) mutations exhibit amyloid-β-induced synaptic and memory deficits but they do not fully recapitulate other key pathological events of Alzheimer’s disease, including distinct neurofibrillary tangle pathology. Human neurons derived from Alzheimer’s disease patients have shown elevated levels of toxic amyloid-β species and phosphorylated tau but did not demonstrate amyloid-β plaques or neurofibrillary tangles. Here we report that FAD mutations in β-amyloid precursor protein and presenilin 1 are able to induce robust extracellular deposition of amyloid-β, including amyloid-β plaques, in a human neural stem-cell-derived three-dimensional (3D) culture system. More importantly, the 3D-differentiated neuronal cells expressing FAD mutations exhibited high levels of detergent-resistant, silver-positive aggregates of phosphorylated tau in the soma and neurites, as well as filamentous tau, as detected by immunoelectron microscopy. Inhibition of amyloid-β generation with β- or γ-secretase inhibitors not only decreased amyloid-β pathology, but also attenuated tauopathy. We also found that glycogen synthase kinase 3 (GSK3) regulated amyloid-β-mediated tau phosphorylation. We have successfully recapitulated amyloid-β and tau pathology in a single 3D human neural cell culture system. Our unique strategy for recapitulating Alzheimer’s disease pathology in a 3D neural cell culture model should also serve to facilitate the development of more precise human neural cell models of other neurodegenerative disorders.
AD, a devastating neurodegenerative disorder, is the most common cause of dementia in the elderly. Patients with AD are characterized by three hallmarks of neuropathology including neuritic plaque deposition, neurofibrillary tangle formation, and neuronal loss. Growing evidences indicate that dysregulation of regulator of calcineurin 1 (RCAN1) plays an important role in the pathogenesis of AD. Aberrant RCAN1 expression facilitates neuronal apoptosis and Tau hyperphosphorylation, leading to neuronal loss and neurofibrillary tangle formation. This review aims to describe the recent advances of the regulation of RCAN1 expression and its physiological functions. Moreover, the AD risk factors-induced RCAN1 dysregulation and its role in promoting neuronal loss, synaptic impairments and neurofibrillary tangle formation are summarized. Furthermore, we provide an outlook into the effects of RCAN1 dysregulation on APP processing, Aβ generation and neuritic plaque formation, and the possible underlying mechanisms, as well as the potential of targeting RCAN1 as a new therapeutic approach.
Induced pluripotent stem (iPS) cells derived from disease patients are an invaluable resource for biomedical research and may provide a source for replacement therapies. In this study, we have generated iPS cells from Asian patients with chronic degenerative diseases of the nervous system, including spinal muscular atrophy (SMA), Parkinson disease (PD) and amyotrophic lateral sclerosis (ALS) by transduction with four factors (KLF4, SOX2, OCT4 and c-MYC). All of the iPS cells showed pluripotency similar to that of human embryonic stem cells (hESCs) and were able to differentiate into various somatic cell types in vitro and in vivo. Furthermore, the iPS cells also can be committed to differentiate into neural cells, the cell type that is affected in chronic degenerative diseases. Therefore, the patient-specific iPS cells we generated offer a cellular model in which to investigate disease mechanisms, discover and test novel drugs and develop new therapies for chronic neurodegenerative diseases.
Genetic mutations in TAR DNA-binding protein 43 (TARDBP, also known as TDP-43) cause amyotrophic lateral sclerosis (ALS), and an increase in the presence of TDP-43 (encoded by TARDBP) in the cytoplasm is a prominent histopathological feature of degenerating neurons in various neurodegenerative diseases. However, the molecular mechanisms by which TDP-43 contributes to ALS pathophysiology remain elusive. Here we have found that TDP-43 accumulates in the mitochondria of neurons in subjects with ALS or frontotemporal dementia (FTD). Disease-associated mutations increase TDP-43 mitochondrial localization. In mitochondria, wild-type (WT) and mutant TDP-43 preferentially bind mitochondria-transcribed messenger RNAs (mRNAs) encoding respiratory complex I subunits ND3 and ND6, impair their expression and specifically cause complex I disassembly. The suppression of TDP-43 mitochondrial localization abolishes WT and mutant TDP-43-induced mitochondrial dysfunction and neuronal loss, and improves phenotypes of transgenic mutant TDP-43 mice. Thus, our studies link TDP-43 toxicity directly to mitochondrial bioenergetics and propose the targeting of TDP-43 mitochondrial localization as a promising therapeutic approach for neurodegeneration.
Understanding molecular mechanisms mediating epileptogenesis is critical for developing more effective therapies for epilepsy. We recently found that the mammalian target of rapamycin (mTOR) signaling pathway is involved in epileptogenesis, and mTOR inhibitors prevent epilepsy in a mouse model of tuberous sclerosis complex. Here, we investigated the potential role of mTOR in a rat model of temporal lobe epilepsy initiated by status epilepticus. Acute kainate-induced seizures resulted in biphasic activation of the mTOR pathway, as evident by an increase in phospho-S6 (P-S6) expression. An initial rise in P-S6 expression started approximately 1 h after seizure onset, peaked at 3-6 h, and returned to baseline by 24 h in both hippocampus and neocortex, reflecting widespread stimulation of mTOR signaling by acute seizure activity. After resolution of status epilepticus, a second increase in P-S6 was observed in hippocampus only, which started at 3 d, peaked 5-10 d, and persisted for several weeks after kainate injection, correlating with the development of chronic epileptogenesis within hippocampus. The mTOR inhibitor rapamycin, administered before kainate, blocked both the acute and chronic phases of seizure-induced mTOR activation and decreased kainate-induced neuronal cell death, neurogenesis, mossy fiber sprouting, and the development of spontaneous epilepsy. Late rapamycin treatment, after termination of status epilepticus, blocked the chronic phase of mTOR activation and reduced mossy fiber sprouting and epilepsy but not neurogenesis or neuronal death. These findings indicate that mTOR signaling mediates mechanisms of epileptogenesis in the kainate rat model and that mTOR inhibitors have potential antiepileptogenic effects in this model.
Charged multivesicular body protein 2B (CHMP2B) - a component of the endosomal complex required for transport-III (ESCRT-III) - is responsible for the vital membrane deformation functions in autophagy and endolysosomal trafficking. A dominant mutation in CHMP2B (CHMP2BIntron5) is associated with a subset of heritable frontotemporal dementia - frontotemporal dementia linked to chromosome 3 (FTD-3). ESCRT-III recruits Vps4, an AAA-ATPase that abscises the membrane during various cellular processes including autophagy and intraluminal vesicle formation. CHMP2BIntron5 results in a C-terminus truncation removing an important Vps4 binding site as well as eliminating the normal autoinhibitory resting state of CHMP2B. CHMP2B is expressed in most cell types but seems to be especially vital for proper neuronal function. CHMP2BIntron5-mediated phenotypes include misregulation of transmembrane receptors, accumulation of multilamellar structures, abnormal lysosomal morphology, down regulation of a brain-specific micro RNA (miRNA-124), abnormal dendritic spine morphology, decrease in dendritic arborization, and cell death. Currently, transgenic-fly,-mouse, and -human cell lines are being used to better understand the diverse phenotypes and develop therapeutic approaches for the CHMP2BIntron5-induced FTD-3. This article is part of a Special Issue entitled SI:Autophagy.
The amyloid cascade hypothesis posits that deposition of the amyloid β (Aβ) peptide in the brain is a key event in the initiation of Alzheimer's disease (AD). Nonetheless, it now seems increasingly unlikely that amyloid toxicity is the cause of sporadic AD, which leads to cognitive decline. Here, using accelerated-senescence nontransgenic OXYS rats, we confirmed that aggregation of Aβ is a later event in AD-like pathology. We showed that an age-dependent increase in the levels of Aβ₁₋₄₂ and extracellular Aβ deposits in the brain of OXYS rats occur later than do synaptic losses, neuronal cell death, mitochondrial structural abnormalities, and hyperphosphorylation of the tau protein. We identified the variants of the genes that are strongly associated with the risk of either late-onset or early-onset AD, including App, Apoe4, Bace1, Psen1, Psen2, and Picalm. We found that in OXYS rats nonsynonymous SNPs were located only in the genes Casp3 and Sorl1. Thus, we present proof that OXYS rats may be a model of sporadic AD. It is possible that multiple age-associated pathological processes may precede the toxic amyloid accumulation, which in turn triggers the final stage of the sporadic form of AD and becomes a hallmark event of the disease.
The long-term goal of nuclear transfer or alternative reprogramming approaches is to create patient-specific donor cells for transplantation therapy, avoiding immunorejection, a major complication in current transplantation medicine. It was recently shown that the four transcription factors Oct4, Sox2, Klf4, and c-Myc induce pluripotency in mouse fibroblasts. However, the therapeutic potential of induced pluripotent stem (iPS) cells for neural cell replacement strategies remained unexplored. Here, we show that iPS cells can be efficiently differentiated into neural precursor cells, giving rise to neuronal and glial cell types in culture. Upon transplantation into the fetal mouse brain, the cells migrate into various brain regions and differentiate into glia and neurons, including glutamatergic, GABAergic, and catecholaminergic subtypes. Electrophysiological recordings and morphological analysis demonstrated that the grafted neurons had mature neuronal activity and were functionally integrated in the host brain. Furthermore, iPS cells were induced to differentiate into dopamine neurons of midbrain character and were able to improve behavior in a rat model of Parkinson's disease upon transplantation into the adult brain. We minimized the risk of tumor formation from the grafted cells by separating contaminating pluripotent cells and committed neural cells using fluorescence-activated cell sorting. Our results demonstrate the therapeutic potential of directly reprogrammed fibroblasts for neuronal cell replacement in the animal model.
Seizures in focal epilepsies are sustained by a highly synchronous neuronal discharge that arises at restricted brain sites and subsequently spreads to large portions of the brain. Despite intense experimental research in this field, the earlier cellular events that initiate and sustain a focal seizure are still not well defined. Their identification is central to understand the pathophysiology of focal epilepsies and to develop new pharmacological therapies for drug-resistant forms of epilepsy. The prominent involvement of astrocytes in ictogenesis was recently proposed. We test here whether a cooperation between astrocytes and neurons is a prerequisite to support ictal (seizure-like) and interictal epileptiform events. Simultaneous patch-clamp recording and Ca2+ imaging techniques were performed in a new in vitro model of focal seizures induced by local applications of N-methyl-D-aspartic acid (NMDA) in rat entorhinal cortex slices. We found that a Ca2+ elevation in astrocytes correlates with both the initial development and the maintenance of a focal, seizure-like discharge. A delayed astrocyte activation during ictal discharges was also observed in other models (including the whole in vitro isolated guinea pig brain) in which the site of generation of seizure activity cannot be precisely monitored. In contrast, interictal discharges were not associated with Ca2+ changes in astrocytes. Selective inhibition or stimulation of astrocyte Ca2+ signalling blocked or enhanced, respectively, ictal discharges, but did not affect interictal discharge generation. Our data reveal that neurons engage astrocytes in a recurrent excitatory loop (possibly involving gliotransmission) that promotes seizure ignition and sustains the ictal discharge. This neuron-astrocyte interaction may represent a novel target to develop effective therapeutic strategies to control seizures.
Recent experimental evidence suggests that transcellular propagation of fibrillar protein aggregates drives the progression of neurodegenerative diseases in a prion-like manner. This phenomenon is now well described in cell and animal models and involves the release of protein aggregates into the extracellular space. Free aggregates then enter neighboring cells to seed further fibrillization. The mechanism by which aggregated extracellular proteins such as tau and α-synuclein bind and enter cells to trigger intracellular fibril formation is unknown. Prior work indicates that prion protein aggregates bind heparan sulfate proteoglycans (HSPGs) on the cell surface to transmit pathologic processes. Here, we find that tau fibril uptake also occurs via HSPG binding. This is blocked in cultured cells and primary neurons by heparin, chlorate, heparinase, and genetic knockdown of a key HSPG synthetic enzyme, Ext1. Interference with tau binding to HSPGs prevents recombinant tau fibrils from inducing intracellular aggregation and blocks transcellular aggregate propagation. In vivo, a heparin mimetic, F6, blocks neuronal uptake of stereotactically injected tau fibrils. Finally, uptake and seeding by α-synuclein fibrils, but not huntingtin fibrils, occurs by the same mechanism as tau. This work suggests a unifying mechanism of cell uptake and propagation for tauopathy and synucleinopathy.
Adult neurogenesis persists in the subventricular zone and the dentate gyrus and can be induced upon central nervous system injury. However, the final contribution of newborn neurons to neuronal networks is limited. Here we show that in neural stem cells, stimulation of the "death receptor" CD95 does not trigger apoptosis but unexpectedly leads to increased stem cell survival and neuronal specification. These effects are mediated via activation of the Src/PI3K/AKT/mTOR signaling pathway, ultimately leading to a global increase in protein translation. Induction of neurogenesis by CD95 was further confirmed in the ischemic CA1 region, in the naive dentate gyrus, and after forced expression of CD95L in the adult subventricular zone. Lack of hippocampal CD95 resulted in a reduction in neurogenesis and working memory deficits. Following global ischemia, CD95-mediated brain repair rescued behavioral impairment. Thus, we identify the CD95/CD95L system as an instructive signal for ongoing and injury-induced neurogenesis.
The molecular mechanisms that regulate adult neural precursor cell (NPC) survival, and thus maintain adult neurogenesis, are not well defined. Here, we investigate the role of p63, a p53 family member, in adult NPC function in mice. Conditional ablation of p63 in adult NPCs or p63 haploinsufficiency led to reduced numbers of NPCs and newborn neurons in the neurogenic zones of the hippocampus and lateral ventricles and in the olfactory bulb. These reductions were attributable to enhanced apoptosis of NPCs and newborn neurons and were rescued by inhibition of caspase activity, p53, or the p53 apoptotic effector PUMA (p53-upregulated modulator of apoptosis). Moreover, these cellular deficits were functionally important because they led to perturbations in hippocampus-dependent memory formation. These results indicate that p63 regulates the numbers of adult NPCs and adult-born neurons as well as neural stem cell-dependent cognitive functions, and that it does so, at least in part, by inhibiting p53-dependent cell death.
Alzheimer's disease (AD) is the most common cause of dementia in those over the age of 65. While a numerous of disease-causing genes and risk factors have been identified, the exact etiological mechanisms of AD are not yet completely understood, due to the inability to test theoretical hypotheses on non-postmortem and patient-specific research systems. The use of recently developed and optimized induced pluripotent stem cells (iPSCs) technology may provide a promising platform to create reliable models, not only for better understanding the etiopathological process of AD, but also for efficient anti-AD drugs screening. More importantly, human-sourced iPSCs may also provide a beneficial tool for cell-replacement therapy against AD. Although considerable progress has been achieved, a number of key challenges still require to be addressed in iPSCs research, including the identification of robust disease phenotypes in AD modeling and the clinical availabilities of iPSCs-based cell-replacement therapy in human. In this review, we highlight recent progresses of iPSCs research and discuss the translational challenges of AD patients-derived iPSCs in disease modeling and cell-replacement therapy.
Human induced pluripotent stem cells (iPSCs) present exciting opportunities for studying development and for in vitro disease modeling. However, reported variability in the behavior of iPSCs has called their utility into question. We established a test set of 16 iPSC lines from seven individuals of varying age, sex and health status, and extensively characterized the lines with respect to pluripotency and the ability to terminally differentiate. Under standardized procedures in two independent laboratories, 13 of the iPSC lines gave rise to functional motor neurons with a range of efficiencies similar to that of human embryonic stem cells (ESCs). Although three iPSC lines were resistant to neural differentiation, early neuralization rescued their performance. Therefore, all 16 iPSC lines passed a stringent test of differentiation capacity despite variations in karyotype and in the expression of early pluripotency markers and transgenes. This iPSC and ESC test set is a robust resource for those interested in the basic biology of stem cells and their applications.
Forkhead box transcription factor, class O (FOXO) is a mammalian homologue of DAF-16, which is known to regulate the lifespan of Caenorhabditis elegans and includes subfamilies of forkhead transcription factors such as AFX, FKHRL1, and FKHR. FKHR is phosphorylated on three sites (Thr-24, Ser-256, and Ser-319) in a phosphatidylinositol 3-kinase (PI3K)/Akt-dependent manner, thereby inhibiting death signals. We here documented dephosphorylation of FKHR following transient forebrain ischemia with its concomitant translocation into the nucleus in neurons in gerbil and mouse brains. The activation of FKHR preceded delayed neuronal death in the vulnerable hippocampal regions following ischemic brain injury. The FKHR activation was accompanied by an increase in DNA binding activity for FKHR-responsive element on the Fas ligand promoter. We also defined FKHR-induced downstream targets such as Fas ligand and Bim in brain ischemia. Therefore, we propose a new strategy to rescue neurons from delayed neuronal death by promoting the survival signaling. Sodium orthovanadate, a protein tyrosine phosphatase inhibitor, up-regulated Akt activity in the brain and in turn rescue neurons from delayed neuronal death by inhibiting FKHR-dependent or -independent death signals in neurons.
Afferent activity can induce fast, feed-forward changes in synaptic efficacy that are synapse specific. Using combined electrophysiology, caged molecule photolysis, and Ca(2+) imaging, we describe a plasticity in which the recruitment of astrocytes in response to afferent activity causes a fast and feed-forward, yet distributed increase in the amplitude of quantal synaptic currents at multiple glutamate synapses on magnocellular neurosecretory cells in the hypothalamic paraventricular nucleus. The plasticity is largely multiplicative, consistent with a proportional increase or "scaling" in the strength of all synapses on the neuron. This effect requires a metabotropic glutamate receptor-mediated rise in Ca(2+) in the astrocyte processes surrounding the neuron and the release of the gliotransmitter ATP, which acts on postsynaptic purinergic receptors. These data provide evidence for a form of distributed synaptic plasticity that is feed-forward, expressed quickly, and mediated by the synaptic activation of neighboring astrocytes.