Impaired neurogenesis, learning and memory and low seizure threshold associated with loss of neural precursor cell survivin

Cell death in glioblastoma and the central nervous system

Glioblastoma is the commonest and deadliest primary brain tumor. Glioblastoma is characterized by significant intra- and inter-tumoral heterogeneity, resistance to treatment and dismal prognoses despite decades of research in understanding its biological underpinnings. Encompassed within this heterogeneity and therapy resistance are severely dysregulated programmed cell death pathways. Glioblastomas recapitulate many neurodevelopmental and neural injury responses; in addition, glioblastoma cells are composed of multiple different transformed versions of CNS cell types. To obtain a greater understanding of the features underlying cell death regulation in glioblastoma, it is important to understand the control of cell death within the healthy CNS during homeostatic and neurodegenerative conditions. Herein, we review apoptotic control within neural stem cells, astrocytes, oligodendrocytes and neurons and compare them to glioblastoma apoptotic control. Specific focus is paid to the Inhibitor of Apoptosis proteins, which play key roles in neuroinflammation, CNS cell survival and gliomagenesis. This review will help in understanding glioblastoma as a transformed version of a heterogeneous organ composed of multiple varied cell types performing different functions and possessing different means of apoptotic control. Further, this review will help in developing more glioblastoma-specific treatment approaches and will better inform treatments looking at more direct brain delivery of therapeutic agents.

Dietary omega-3 fatty acid deficiency from pre-pregnancy to lactation affects expression of genes involved in hippocampal neurogenesis of the offspring

Maternal n-3 PUFA (omega-3) deficiency can affect brain development in utero and postnatally. Despite the evidence, the impacts of n-3 PUFA deficiency on the expression of neurogenesis genes in the postnatal hippocampus remained elusive. Since postnatal brain development requires PUFAs via breast milk, we examined the fatty acid composition of breast milk and hippocampal expression of neurogenesis genes in n-3 PUFA deficient 21d mice. In addition, the expression of fatty acid desaturases, elongases, free fatty acids signaling receptors, insulin and leptin, and glucose transporters were measured. Among the genes involved in neurogenesis, the expression of brain-specific tenascin-R (TNR) was downregulated to a greater extent (∼31 fold), followed by adenosine A2A receptor (A2AAR), dopamine receptor D2 (DRD2), glial cell line-derived neurotrophic factor (GDNF) expression in the n-3 PUFA deficient hippocampus. Increasing dietary LA to ALA (50:1) elevated the ARA to DHA ratio by ∼8 fold in the n-3 PUFA deficient breast milk, with an overall increase of total n-6/n-3 PUFAs by ∼15:1 (p<0.05) compared to n-3 PUFA sufficient (LA to ALA: 2:1) diet. The n-3 PUFA deficient mice exhibited upregulation of FADS1, FADS2, ELOVL2, ELOVL5, ELOVL6, GPR40, GPR120, LEPR, IGF1 and downregulation of GLUT1, GLUT3, and GLUT4 mRNA expression in hippocampus (p<0.05). Maternal n-3 PUFA deficiency affects the hippocampal expression of key neurogenesis genes in the offspring with concomitant expression of desaturase and elongase genes, suggesting the importance of dietary n-3 PUFA for neurodevelopment.

Non-histone substrates of histone deacetylases as potential therapeutic targets in epilepsy

Introduction: Epilepsy is a network-level neurological disorder characterized by unprovoked recurrent seizures and associated comorbidities. Aberrant activity and localization of histone deacetylases (HDACs) have been reported in epilepsy and HDAC inhibitors (HDACi) have been used for therapeutic purposes. Several non-histone targets of HDACs have been recognized whose reversible acetylation can modulate protein functions and can contribute to disease pathology. Areas covered: This review provides an overview of HDACs in epilepsy and reflects its action on non-histone substrates involved in the pathogenesis of epilepsy and explores the effectiveness of HDACi as anti-epileptic drugs (AEDs). It also covers the efforts undertaken to target the interaction of HDACs with their substrates. We have further discussed non-deacetylase activity possessed by specific HDACs that might be essential in unraveling the molecular mechanism underlying the disease. For this purpose, relevant literature from 1996 to 2020 was derived from PubMed. Expert opinion: The interaction of HDACs and their non-histone substrates can serve as a promising therapeutic target for epilepsy. Pan-HDACi offers limited benefits to the epileptic patients. Thus, identification of novel targets of HDACs contributing to the disease and designing inhibitors targeting these complexes would be more effective and holds a greater potential as an anti-epileptogenic therapy.

ROCK/PKA Inhibition Rescues Hippocampal Hyperexcitability and GABAergic Neuron Alterations in a Oligophrenin-1 Knock-Out Mouse Model of X-Linked Intellectual Disability

Oligophrenin-1 (Ophn1) encodes a Rho GTPase activating protein whose mutations cause X-linked intellectual disability (XLID) in humans. Loss of function of Ophn1 leads to impairments in the maturation and function of excitatory and inhibitory synapses, causing deficits in synaptic structure, function and plasticity. Epilepsy is a frequent comorbidity in patients with Ophn1-dependent XLID, but the cellular bases of hyperexcitability are poorly understood. Here we report that male mice knock-out (KO) for Ophn1 display hippocampal epileptiform alterations, which are associated with changes in parvalbumin-, somatostatin- and neuropeptide Y-positive interneurons. Because loss of function of Ophn1 is related to enhanced activity of Rho-associated protein kinase (ROCK) and protein kinase A (PKA), we attempted to rescue Ophn1-dependent pathological phenotypes by treatment with the ROCK/PKA inhibitor fasudil. While acute administration of fasudil had no impact on seizure activity, seven weeks of treatment in adulthood were able to correct electrographic, neuroanatomical and synaptic alterations of Ophn1 deficient mice. These data demonstrate that hyperexcitability and the associated changes in GABAergic markers can be rescued at the adult stage in Ophn1-dependent XLID through ROCK/PKA inhibition.SIGNIFICANCE STATEMENT In this study we demonstrate enhanced seizure propensity and impairments in hippocampal GABAergic circuitry in Ophn1 mouse model of X-linked intellectual disability (XLID). Importantly, the enhanced susceptibility to seizures, accompanied by an alteration of GABAergic markers were rescued by Rho-associated protein kinase (ROCK)/protein kinase A (PKA) inhibitor fasudil, a drug already tested on humans. Because seizures can significantly impact the quality of life of XLID patients, the present data suggest a potential therapeutic pathway to correct alterations in GABAergic networks and dampen pathological hyperexcitability in adults with XLID.

Maternal dietary of n-3 polyunsaturated fatty acids affects the neurogenesis and neurochemical in female rat at weaning

Long-chain polyunsaturated fatty acids (LC-PUFAs) are rapidly accumulated in brain during pre- and neonatal life, which is important for the development and function of central nervous system. Deficiency of biologically important n-3 PUFA docosahexaenoic acid (C22:6n-3, DHA) is associated with impaired visual, attention and cognition, and would precipitate psychiatric symptoms. However, clinical studies of the potential mechanism on the effect of dietary DHA deficiency on neural development remain unclear. In addition, the effects of n-6 PUFAs and n-3 PUFAs ingestion on the dynamic process of the cell proliferation in neurogenesis of offspring were investigated using immunefluorescence. And GC-MS was used to determine the fatty acid content in the liver of offspring. To further investigate the neurochemical influence on maternal PUFAs levels, we assessed the functioning of various neurotransmitter systems including glutamatergic, dopaminergic, norepinephrinergic and serotoninergic systems in the brain of female rats at weaning by HPLC-MS/MS. Lastly, we analyzed the turnover rates and between-metabolite ratios (the ratios between metabolites of monoamine neurotransmitters) to seek potential links between the neurotransmitters and dietary fatty acids compositions. There were significant differences between the deficiency group and the control or supplementary group in liver fatty acids compositions, showing that n-3 PUFAs were largely replaced by n-6 PUFAs. The generation of n-3 PUFAs deficiency rats exhibited abnormal neurogenesis and neurochemical. Altered dopamine or norepinephrine transmission and between-metabolite ratios in brain areas may be a key neuronal mechanism that contributes to the potential detrimental effects of n-3 PUFAs deficiency for mental health.

Maternal diet of polyunsaturated fatty acid altered the cell proliferation in the dentate gyrus of hippocampus and influenced glutamatergic and serotoninergic systems of neonatal female rats

Background

Long-chain polyunsaturated fatty acids (PUFAs) are major components of the phospholipids that forming the cell membrane. Insufficient availability of PUFAs during prenatal period decreases accretion of docosahexaenoic acid (DHA) in the developing brain. DHA deficiency is associated with impaired attention and cognition, and would precipitate psychiatric symptoms. However, clinical studies on the potential benefits of dietary DHA supplementation to neural development have yielded conflicting results.

Methods

To further investigate the neurochemical influence of maternal PUFAs levels, we assessed the functioning of various neurotransmitter systems including glutamatergic, dopaminergic, norepinephrinergic and serotoninergic systems in the brain of neonatal female rats by HPLC-MS/MS. Meanwhile, the cell proliferation of neonatal rats was investigated using immunefluorescence.

Results

Different maternal n-3 PUFAs dietary influenced the FA composition, cell proliferation in the dentate gyrus of hippocampus and the contents of γ-aminobutyric acid (GABA), glutamine (GLN), dopamine (DA) and its metabolites [3,4- dihydroxyphenyl acetic acid (DOPAC) and homovanillic acid (HVA)], norepinephrine (NE), vanilmandelic acid (VMA) and 5-HT turnover in the brain of neonatal rats. However, the mRNA expression of key synthase of neurotransmitters remains stable.

Conclusions

Our study showed that maternal deficiency of n-3 PUFAs might play an important role in central nervous system of neonatal female rats mainly through impairing the normal neurogenesis and influencing glutamatergic system and 5-HT turnover.

Electronic supplementary material

The online version of this article (doi:10.1186/s12944-016-0236-1) contains supplementary material, which is available to authorized users.

Downregulation of survivin regulates adult hippocampal neurogenesis and apoptosis, and inhibits spatial learning and memory following traumatic brain injury

Survivin, a unique member of the inhibitor of the apoptosis protein (IAP) family, has been suggested to play a crucial role in promoting the cell cycle and mediates mitosis during embryonic development. However, the role of survivin following traumatic brain injury (TBI) in adult neurogenesis and apoptosis in the mouse dentate gyrus (DG) remains only partially understood. We adopted adenovirus-mediated RNA interference (RNAi) as a means of suppressing the expression of survivin and observed its effects on adult regeneration and neurological function in mice after brain injury. The mice were subjected to TBI, and the ipsilateral hippocampus was then examined using reverse transcription polymerase chain reaction (RT-PCR) and Western blotting analyses. Brain slices were stained for 5'-bromo-2'-deoxyuridine (BrdU) and doublecortin (DCX). Our data showed that survivin knockdown inhibits the proliferation and differentiation of neural precursor cells (NPCs) in the DG of the hippocampus soon after TBI. Furthermore, downregulation of survivin results in a significant increase in programmed cell death in the DG, as assessed using terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) and 4',6-diamidino-2-phenylindole (DAPI) double staining. The Morris water maze (MWM) test was adopted to evaluate neurological function, which confirmed that knockdown of survivin worsened the memory capacity that was already compromised following TBI. Survivin in adult mice brains after TBI can be successfully down-regulated by RNAi, which inhibited adult hippocampal neurogenesis, promoted apoptotic cell death, and resulted in a negative role in the recovery of dysfunction following injury.

Survivin Is a transcriptional target of STAT3 critical to estradiol neuroprotection in global ischemia

Transient global ischemia causes selective, delayed death of hippocampal CA1 pyramidal neurons in humans and animals. It is well established that estrogens ameliorate neuronal death in animal models of focal and global ischemia. However, the role of signal transducer and activator of transcription-3 (STAT3) and its target genes in estradiol neuroprotection in global ischemia remains unclear. Here we show that a single intracerebral injection of 17β-estradiol to ovariectomized female rats immediately after ischemia rescues CA1 neurons destined to die. Ischemia promotes activation of STAT3 signaling, association of STAT3 with the promoters of target genes, and STAT3-dependent mRNA and protein expression of prosurvival proteins in the selectively vulnerable CA1. In animals subjected to ischemia, acute postischemic estradiol further enhances activation and nuclear translocation of STAT3 and STAT3-dependent transcription of target genes. Importantly, we show that STAT3 is critical to estradiol neuroprotection, as evidenced by the ability of STAT3 inhibitor peptide and STAT3 shRNA delivered directly into the CA1 of living animals to abolish neuroprotection. In addition, we identify survivin, a member of the inhibitor-of-apoptosis family of proteins and known gene target of STAT3, as essential to estradiol neuroprotection, as evidenced by the ability of shRNA to survivin to reverse neuroprotection. These findings indicate that ischemia and estradiol act synergistically to promote activation of STAT3 and STAT3-dependent transcription of survivin in insulted CA1 neurons and identify STAT3 and survivin as potentially important therapeutic targets in an in vivo model of global ischemia.

Whole brain radiation-induced vascular cognitive impairment: mechanisms and implications

Mild cognitive impairment is a well-documented consequence of whole brain radiation therapy (WBRT) that affects 40-50% of long-term brain tumor survivors. The exact mechanisms for the decline in cognitive function after WBRT remain elusive and no treatment or preventative measures are available for use in the clinic. Here, we review recent findings indicating how changes in the neurovascular unit may contribute to the impairments in learning and memory. In addition to affecting neuronal development, WBRT induces profound capillary rarefaction within the hippocampus - a region of the brain important for learning and memory. Therapeutic strategies such as hypoxia, which restore the capillary density, result in the rescue of cognitive function. In addition to decreasing vascular density, WBRT impairs vasculogenesis and/or angiogenesis, which may also contribute to radiation-induced cognitive decline. Further studies aimed at uncovering the specific mechanisms underlying these WBRT-induced changes in the cerebrovasculature are essential for developing therapies to mitigate the deleterious effects of WBRT on cognitive function.

Survivin, a key component of the Wnt/β-catenin signaling pathway, contributes to traumatic brain injury-induced adult neurogenesis in the mouse dentate gyrus

The enhancement of endogenous neurogenesis has been suggested in the treatment of traumatic brain injury (TBI); however, the factors that trigger the process of adult neurogenesis following TBI remain elusive. In the adult mammalian central nervous system, there are 2 neurogenic regions: the subgranular zone (SGZ) of the hippocampus and the subventricular zone (SVZ) of the lateral ventricles, both of which maintain relatively quiescent states in a stable microenvironment. However, once stimulated by intrinsic and extrinsic events, relevant signals are activated in these 2 regions. In this study, in order to explore the mechanisms behind endogenous neurogenesis following TBI, we investigated potential factors regulating this process. We observed that the expression of survivin, an anti-apoptotic protein, increased in a time-dependent manner in the hippocampus in a mouse model of TBI. In addition, the number of survivin (+) cells, as well as that of BrdU (+) cells increased in the SGZ of the dentate gyrus (DG) in the hippocampus following TBI, as shown by immunofluorescence double staining; the co-localization of survivin and BrdU was shown in the merged images. The expression of survivin was also significantly increased in the doublecortin (DCX) (+) immature neurons in the DG of the hippocampus soon after the induction of TBI. Taken together, these data confirm the connection between the expression of survivin and adult neurogenesis following TBI; our data also suggest the therapeutic potential of upregulating survivin expression as a novel strategy for the effective treatment of TBI.

Sox2 protects neural stem cells from apoptosis via up-regulating survivin expression

The transcription factor Sox2 [SRY (sex-determining region Y)-box 2] is essential for the regulation of self-renewal and homoeostasis of NSCs (neural stem cells) during brain development. However, the downstream targets of Sox2 and its underlying molecular mechanism are largely unknown. In the present study, we found that Sox2 directly up-regulates the expression of survivin, which inhibits the mitochondria-dependent apoptotic pathway in NSCs. Although overexpression of Sox2 elevates survivin expression, knockdown of Sox2 results in a decrease in survivin expression, thereby initiating the mitochondria-dependent apoptosis related to caspase 9 activation. Furthermore, cell apoptosis owing to knockdown of Sox2 can be rescued by ectopically expressing survivin in NSCs as well as in the mouse brain, as demonstrated by an in utero-injection approach. In short, we have found a novel Sox2/survivin pathway that regulates NSC survival and homoeostasis, thus revealing a new mechanism of brain development, neurological degeneration and such aging-related disorders.

Loss of survivin in neural precursor cells results in impaired long-term potentiation in the dentate gyrus and CA1-region

In adult mammals, newborn neural precursor cells (NPCs) derived from either the subventricular zone (SVZ) or the subgranular zone (SGZ) migrate into the olfactory bulb and the dentate gyrus (DG), respectively, where some of them mature into excitatory and inhibitory neurons. There is increasing evidence that this neurogenesis process is important for some types of learning and synaptic plasticity and vice versa. Survivin, a member of the inhibitor-of-apoptosis protein (IAP) family, has been suggested to have a central role in the regulation of neurogenesis. The protein is abundantly expressed in nervous tissue during embryonic development while being restricted postnatally to proliferating and migrating NPCs in SVZ and SGZ. Here we examined adult Survivin(Camcre) mice with a conditional deletion of the survivin gene in embryonic neurogenic regions. Although the deletion of survivin had no effect on basic excitability in DG and CA1-region, there was a marked impairment of long-term potentiation (LTP) in these areas. Our data support a function of survivin in hippocampal synaptic plasticity and learning and underline the importance of adult brain neurogenesis for proper operation of the hippocampal tri-synaptic circuit and the physiological functions that depend on it.

Subventricular zone neural progenitors protect striatal neurons from glutamatergic excitotoxicity

The functional significance of adult neural stem and progenitor cells in hippocampal-dependent learning and memory has been well documented. Although adult neural stem and progenitor cells in the subventricular zone are known to migrate to, maintain and reorganize the olfactory bulb, it is less clear whether they are functionally required for other processes. Using a conditional transgenic mouse model, selective ablation of adult neural stem and progenitor cells in the subventricular zone induced a dramatic increase in morbidity and mortality of central nervous system disorders characterized by excitotoxicity-induced cell death accompanied by reactive inflammation, such as 4-aminopyridine-induced epilepsy and ischaemic stroke. To test the role of subventricular zone adult neural stem and progenitor cells in protecting central nervous system tissue from glutamatergic excitotoxicity, neurophysiological recordings of spontaneous excitatory postsynaptic currents from single medium spiny striatal neurons were measured on acute brain slices. Indeed, lipopolysaccharide-stimulated, but not unstimulated, subventricular zone adult neural stem and progenitor cells reverted the increased frequency and duration of spontaneous excitatory postsynaptic currents by secreting the endocannabinod arachidonoyl ethanolamide, a molecule that regulates glutamatergic tone through type 1 cannabinoid receptor (CB(1)) binding. In vivo restoration of cannabinoid levels, either by administration of the type 1 cannabinoid receptor agonist HU210 or the inhibitor of the principal catabolic enzyme fatty acid amide hydrolase, URB597, completely reverted the increased morbidity and mortality of adult neural stem and progenitor cell-ablated mice suffering from epilepsy and ischaemic stroke. Our results provide the first evidence that adult neural stem and progenitor cells located within the subventricular zone exert an 'innate' homeostatic regulatory role by protecting striatal neurons from glutamate-mediated excitotoxicity.

Whole brain radiation-induced impairments in learning and memory are time-sensitive and reversible by systemic hypoxia

Whole brain radiation therapy (WBRT) is commonly used for treatment of primary and metastatic brain tumors; however, cognitive impairment occurs in 40–50% of brain tumor survivors. The etiology of the cognitive impairment following WBRT remains elusive. We recently reported that radiation-induced cerebrovascular rarefaction within hippocampal subregions could be completely reversed by systemic hypoxia. However, the effects of this intervention on learning and memory have not been reported. In this study, we assessed the time-course for WBRT-induced impairments in contextual and spatial learning and the capacity of systemic hypoxia to reverse WBRT-induced deficits in spatial memory. A clinical fractionated series of 4.5Gy WBRT was administered to mice twice weekly for 4 weeks, and after various periods of recovery, behavioral analyses were performed. To study the effects of systemic hypoxia, mice were subjected to 11% (hypoxia) or 21% oxygen (normoxia) for 28 days, initiated 1 month after the completion of WBRT. Our results indicate that WBRT induces a transient deficit in contextual learning, disruption of working memory, and progressive impairment of spatial learning. Additionally, systemic hypoxia completely reversed WBRT-induced impairments in learning and these behavioral effects as well as increased vessel density persisted for at least 2 months following hypoxia treatment. Our results provide critical support for the hypothesis that cerebrovascular rarefaction is a key component of cognitive impairment post-WBRT and indicate that processes of learning and memory, once thought to be permanently impaired after WBRT, can be restored.