Hippocampal Progenitor Research Articles

CB2 Cannabinoid Receptors Promote Neural Progenitor Cell Proliferation via mTORC1 Signaling

The endocannabinoid system is known to regulate neural progenitor (NP) cell proliferation and neurogenesis. In particular, CB(2) cannabinoid receptors have been shown to promote NP proliferation. As CB(2) receptors are not expressed in differentiated neurons, CB(2)-selective agonists are promising candidates to manipulate NP proliferation and indirectly neurogenesis by overcoming the undesired psychoactive effects of neuronal CB(1) cannabinoid receptor activation. Here, by using NP cells, brain organotypic cultures, and in vivo animal models, we investigated the signal transduction mechanism involved in CB(2) receptor-induced NP cell proliferation and neurogenesis. Exposure of hippocampal HiB5 NP cells to the CB(2) receptor-selective agonist HU-308 led to the activation of the phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin complex 1 (mTORC1) pathway, which, by inhibiting its downstream target p27Kip1, induced NP proliferation. Experiments conducted with the CB(2) receptor-selective antagonist SR144528, inhibitors of the PI3K/Akt/mTORC1 axis, and CB(2) receptor transient-transfection vector further supported that CB(2) receptors control NP cell proliferation via activation of mTORC1 signaling. Likewise, CB(2) receptor engagement induced cell proliferation in an mTORC1-dependent manner both in embryonic cortical slices and in adult hippocampal NPs. Thus, HU-308 increased ribosomal protein S6 phosphorylation and 5-bromo-2'-deoxyuridine incorporation in wild-type but not CB(2) receptor-deficient NPs of the mouse subgranular zone. Moreover, adult hippocampal NP proliferation induced by HU-308 and excitotoxicity was blocked by the mTORC1 inhibitor rapamycin. Altogether, these findings provide a mechanism of action and a rationale for the use of nonpsychotomimetic CB(2) receptor-selective ligands as a novel strategy for the control of NP cell proliferation and neurogenesis.

Levels of neural progenitors in the hippocampus predict memory impairment and relapse to drug seeking as a function of excessive methamphetamine self-administration.

Methamphetamine affects the hippocampus, a brain region crucial for learning and memory, as well as relapse to drug seeking. Rats self-administered methamphetamine for 1 h twice weekly (intermittent-short-I-ShA), 1 h daily (limited-short-ShA), or 6 h daily (extended-long-LgA) for 22 sessions. After 22 sessions, rats from each access group were withdrawn from self-administration and underwent spatial memory (Y-maze) and working memory (T-maze) tests followed by extinction and reinstatement to methamphetamine seeking or received one intraperitoneal injection of 5-bromo-2'-deoxyuridine (BrdU) to label progenitors in the hippocampal subgranular zone (SGZ) during the synthesis phase. Two-hour-old and 28-day-old surviving BrdU-immunoreactive cells were quantified. I-ShA rats performed better on the Y-maze and had a greater number of 2-h-old SGZ BrdU cells than nondrug controls. LgA rats, but not ShA rats, performed worse on the Y- and T-maze and had a fewer number of 2-h-old SGZ BrdU cells than nondrug and I-ShA rats, suggesting that new hippocampal progenitors, decreased by methamphetamine, were correlated with impairment in the acquisition of new spatial cues. Analyses of addiction-related behaviors after withdrawal and extinction training revealed methamphetamine-primed reinstatement of methamphetamine-seeking behavior in all three groups (I-ShA, ShA, and LgA), and this effect was enhanced in LgA rats compared with I-ShA and ShA rats. Protracted withdrawal from self-administration enhanced the survival of SGZ BrdU cells, and methamphetamine seeking during protracted withdrawal enhanced Fos expression in the dentate gyrus and medial prefrontal cortex in LgA rats to a greater extent than in ShA and I-ShA rats. These results indicate that changes in the levels of the proliferation and survival of hippocampal neural progenitors and neuronal activation of hippocampal granule cells predict the effects of methamphetamine self-administration (limited vs extended access) on cognitive performance and relapse to drug seeking and may contribute to the impairments that perpetuate the addiction cycle.

Leptin restores adult hippocampal neurogenesis in a chronic unpredictable stress model of depression and reverses glucocorticoid-induced inhibition of GSK-3β/β-catenin signaling

Stress and glucocorticoid stress hormones inhibit neurogenesis, whereas antidepressants increase neurogenesis and block stress-induced decrease of neurogenesis. Our previous studies have shown leptin, an adipocyte-derived hormone with antidepressant-like properties 1, promotes baseline neurogenesis in the adult hippocampus 2. The present study aimed to determine whether leptin is able to restore stress-induced suppression of neurogenesis in a rat chronic unpredictable stress (CUS) model of depression. Chronic treatment with leptin reversed the CUS-induced reduction of hippocampal neurogenesis and depression-like behaviors. Leptin treatment elicited delayed long-lasting antidepressant-like effects in the behavioral despair test, and this effect was blocked by ablation of neurogenesis with X-irradiation. The functional isoform of the leptin receptor, LepRb, and the glucocorticoid receptor (GR) were colocalized in hippocampal neural stem/progenitor cells in vivo and in vitro. Leptin treatment reversed the GR agonist dexamethasone (DEX)-induced reduction of proliferation of cultured neural stem/progenitor cells from adult hippocampus. Further mechanistic analysis revealed that leptin and DEX converged on GSK3β and β-catenin. DEX decreased Ser9 phosphorylation and increased Tyr216 phosphorylation of GSK3β, while leptin increased Ser9 phosphorylation and attenuated the effects of DEX at both Ser9 and Tyr216 phosphorylation sites of GSK3β. Moreover, leptin increased total level and nuclear translocation of β-catenin, a primary substrate of GSK3 β and a key regulator in controlling neural progenitor proliferation, and reversed the inhibitory effects of DEX on β-catenin. Together, our results suggest that adult neurogenesis is involved in the delayed long-lasting antidepressant-like behavioral effects of leptin, and leptin treatment counteracts chronic stress and glucocorticoid-induced suppression of hippocampal neurogenesis via activating the GSK3β/β-catenin signaling pathway.

Adult neural progenitor cells reactivate superbursting in mature neural networks

Behavioral recovery in animal models of human CNS syndromes suggests that transplanted stem cell derivatives can augment damaged neural networks but the mechanisms behind potentiated recovery remain elusive. Here we use microelectrode array (MEA) technology to document neural activity and network integration as rat primary neurons and rat hippocampal neural progenitor cells (NPCs) differentiate and mature. The natural transition from neuroblast to functional excitatory neuron consists of intermediate phases of differentiation characterized by coupled activity. High-frequency network-wide bursting or “superbursting” is a hallmark of early plasticity that is ultimately refined into mature stable neural network activity. Microelectrode array (MEA)-plated neurons transition through this stage of coupled superbursting before establishing mature neuronal phenotypes in vitro. When plated alone, adult rat hippocampal NPC-derived neurons fail to establish the synchronized bursting activity that neurons in primary and embryonic stem cell-derived cultures readily form. However, adult rat hippocampal NPCs evoke re-emergent superbursting in electrophysiologically mature rat primary neural cultures. Developmental superbursting is thought to accompany transient states of heightened plasticity both in culture preparations and across brain regions. Future work exploring whether NPCs can re-stimulate developmental states in injury models would be an interesting test of their regenerative potential.

Phospholipase D1 mediates bFGF-induced Bcl-2 expression leading to neurite outgrowth in H19-7 cells

The purpose of the present study was to investigate the role of PLD (phospholipase D) in bFGF (basic fibroblast growth factor)-induced Bcl-2 expression and to examine whether overexpressed Bcl-2 influences neurite outgrowth in immortalized hippocampal progenitor cells (H19-7 cells). We found that Bcl-2 expression was maximally induced by bFGF within 24h, and that this effect was reduced by inhibiting PLD1 expression with PLD1 small interfering RNA or by overexpressing DN (dominant-negative)-PLD1, whereas PLD1 overexpression markedly induced Bcl-2 expression. bFGF treatment activated Ras, Src, PI3K (phosphoinositide 3-kinase), PLCγ (phospholipase Cγ) and PKCα (protein kinase Cα). Among these molecules, Src and PKCα were not required for Bcl-2 expression. PLD activity was decreased by Ras, PI3K or PLCγ inhibitor, suggesting that PLD1 activation occurred through Ras, PI3K or PLCγ. We found that Ras was the most upstream molecule among these proteins, followed by the PI3K/PLCγ pathway, indicating that bFGF-induced PLD activation took place through the Ras/PI3K/PLCγ pathway. Furthermore, PLD1 was required for activation of JNK (c-Jun N-terminal kinase), which led to activation of STAT3 (signal transducer and activator of transcription 3) and finally Bcl-2 expression. When Bcl-2 was overexpressed, neurite outgrowth was stimulated along with induction of neurotrophic factors such as brain-derived neurotrophic factor and neurotrophin 4/5. In conclusion, PLD1 acts as a downstream effector of bFGF/Ras/PI3K/PLCγ signalling and regulates Bcl-2 expression through JNK/STAT3, which leads to neurite outgrowth in H19-7 cells.

Secreted amyloid precursor proteins promote proliferation and glial differentiation of adult hippocampal neural progenitor cells

Amyloid precursor protein (APP) is an integral membrane glycoprotein present at high levels in nerve cells. Two soluble secreted forms, sAPPα and sAPPβ, are processed from APP by two mutually exclusive proteolytic pathways. sAPPα shows a range of neuroprotective and growth factor properties, including reduction of neuronal injury and improvement in memory performance, in contrast to the generally less potent sAPPβ. In addition, sAPPα has been shown to increase the proliferation of both embryonic neural stem cells and neural progenitor cells (NPCs) derived from the subventricular zone (SVZ) of the adult brain. However, an effect of sAPPα (or sAPPβ) on adult hippocampal progenitor cell proliferation and differentiation has not previously been observed. In this study, we examined the effect of both the α- and β-cleaved ectodomains of sAPP on adult NPCs isolated from the subgranular zone (SGZ) of the rat hippocampus in the presence or absence of depolarizing conditions. Assays were performed to examine the effect of sAPPα and sAPPβ on SGZ-derived adult NPC proliferation in parallel with SVZ-derived cells and on differentiation with SGZ-derived cells. We observed both sAPPα and sAPPβ increased the proliferation of SGZ-derived NPCs in vitro. Further, treatment of SGZ-derived NPCs with either sAPPα or sAPPβ increased the number of cells expressing the astrocytic marker GFAP and promoted cell survival. The effect on differential fate was observed in both the presence and absence of depolarizing conditions. Thus, both sAPPα and sAPPβ exert a complex range of effects on SGZ-derived adult NPCs, including increasing NPC proliferation, maintaining cell viability, yet promoting glial over neuronal differentiation. These findings provide the first direct support for the secreted forms of APP regulating SGZ-derived NPCs, and raise the possibility some or all of the effects may have therapeutic benefit in models of neurological disease.

Excitatory amino acid transporter 2 and excitatory amino acid transporter 1 negatively regulate calcium‐dependent proliferation of hippocampal neural progenitor cells and are persistently upregulated after injury

Using a transgenic mouse (Mus musculus) in which nestin-expressing progenitors are labeled with enhanced green fluorescent protein, we previously characterized the expression of excitatory amino acid transporter 2 (GltI) and excitatory amino acid transporter 1 (Glast) on early neural progenitors in vivo. To address their functional role in this cell population, we manipulated their expression in P7 neurospheres isolated from the dentate gyrus. We observed that knockdown of GltI or Glast was associated with decreased bromodeoxyuridine incorporation and neurosphere formation. Moreover, we determined that both glutamate transporters regulated progenitor proliferation in a calcium-dependent and metabotropic glutamate receptor-dependent manner. To address the relevance of this in vivo, we utilized models of acquired brain injury, which are known to induce hippocampal neurogenesis. We observed that GltI and Glast were specifically upregulated in progenitors following brain injury, and that this increased expression was maintained for many weeks. Additionally, we found that recurrently injured animals with increased expression of glutamate transporters within the progenitor population were resistant to subsequent injury-induced proliferation. These findings demonstrate that GltI and Glast negatively regulate calcium-dependent proliferation in vitro and that their upregulation after injury is associated with decreased proliferation after brain trauma.

Interleukin-1β: A New Regulator of the Kynurenine Pathway Affecting Human Hippocampal Neurogenesis

Increased inflammation and reduced neurogenesis have been associated with the pathophysiology of major depression. Here, we show for the first time how IL-1β, a pro-inflammatory cytokine shown to be increased in depressed patients, decreases neurogenesis in human hippocampal progenitor cells. IL-1β was detrimental to neurogenesis, as shown by a decrease in the number of doublecortin-positive neuroblasts (-28%), and mature, microtubule-associated protein-2-positive neurons (-36%). Analysis of the enzymes that regulate the kynurenine pathway showed that IL-1β induced an upregulation of transcripts for indolamine-2,3-dioxygenase (IDO), kynurenine 3-monooxygenase (KMO), and kynureninase (42-, 12- and 30-fold increase, respectively, under differentiating conditions), the enzymes involved in the neurotoxic arm of the kynurenine pathway. Moreover, treatment with IL-1β resulted in an increase in kynurenine, the catabolic product of IDO-induced tryptophan metabolism. Interestingly, co-treatment with the KMO inhibitor Ro 61-8048 reversed the detrimental effects of IL-1β on neurogenesis. These observations indicate that IL-1β has a critical role in regulating neurogenesis whereas affecting the availability of tryptophan and the production of enzymes conducive to toxic metabolites. Our results suggest that inhibition of the kynurenine pathway may provide a new therapy to revert inflammatory-induced reduction in neurogenesis.

The opiate analgesic buprenorphine decreases proliferation of adult hippocampal neuroblasts and increases survival of their progeny

Although opiate drugs of abuse have been shown to decrease adult hippocampal neurogenesis, the impact of opiate analgesics has not been tested. North American regulatory boards governing the ethical treatment of experimental animals require the administration of analgesics, such as buprenorphine, following minor surgical interventions. Here, we show that two commonly used post-operative buprenorphine dosing regimes significantly inhibit the proliferation of doublecortin-positive neuroblasts but not other hippocampal stem and progenitor cell populations in adult mice. Buprenorphine, administered in schedules of three 0.05 mg/kg subcutaneous injections over a single day or seven 0.05 mg/kg injections over a 3-day period decreased the number of actively proliferating 5-iodo-2'-deoxyuridine-labeled doublecortin-positive cells for up to 6 days after opiate withdrawal. The minimal (three injection), but not standard (seven injection), analgesic paradigm also reduced basal indices of hippocampal progenitor cell apoptosis and enhanced survival of newly born cells for up to 28 days. Taken together, these data provide the first evidence that the routine administration of opiate analgesics has transient but long-lasting effects on neurogenesis and further emphasize that analgesic dosage and schedule should be reported and considered when interpreting the magnitude of neural stem and progenitor cell activation in response to in vivo intervention.

Rho GTPases Mediate the Mechanosensitive Lineage Commitment of Neural Stem Cells

Adult neural stem cells (NSCs) play important roles in learning and memory and are negatively impacted by neurological disease. It is known that biochemical and genetic factors regulate self-renewal and differentiation, and it has recently been suggested that mechanical and solid-state cues, such as extracellular matrix (ECM) stiffness, can also regulate the functions of NSCs and other stem cell types. However, relatively little is known of the molecular mechanisms through which stem cells transduce mechanical inputs into fate decisions, the extent to which mechanical inputs instruct fate decisions versus select for or against lineage-committed blast populations, or the in vivo relevance of mechanotransductive signaling molecules in native stem cell niches. Here we demonstrate that ECM-derived mechanical signals act through Rho GTPases to activate the cellular contractility machinery in a key early window during differentiation to regulate NSC lineage commitment. Furthermore, culturing NSCs on increasingly stiff ECMs enhances RhoA and Cdc42 activation, increases NSC stiffness, and suppresses neurogenesis. Likewise, inhibiting RhoA and Cdc42 or downstream regulators of cellular contractility rescues NSCs from stiff matrix- and Rho GTPase-induced neurosuppression. Importantly, Rho GTPase expression and ECM stiffness do not alter proliferation or apoptosis rates indicating that an instructive rather than selective mechanism modulates lineage distributions. Finally, in the adult brain, RhoA activation in hippocampal progenitors suppresses neurogenesis, analogous to its effect in vitro. These results establish Rho GTPase-based mechanotransduction and cellular stiffness as biophysical regulators of NSC fate in vitro and RhoA as an important regulatory protein in the hippocampal stem cell niche.

Timing Specific Requirement of microRNA Function is Essential for Embryonic and Postnatal Hippocampal Development

The adult hippocampus consists of the dentate gyrus (DG) and the CA1, CA2 and CA3 regions and is essential for learning and memory functions. During embryonic development, hippocampal neurons are derived from hippocampal neuroepithelial cells and dentate granular progenitors. The molecular mechanisms that control hippocampal progenitor proliferation and differentiation are not well understood. Here we show that noncoding microRNAs (miRNAs) are essential for early hippocampal development in mice. Conditionally ablating the RNAase III enzyme Dicer at different embryonic time points utilizing three Cre mouse lines causes abnormal hippocampal morphology and affects the number of hippocampal progenitors due to altered proliferation and increased apoptosis. Lack of miRNAs at earlier stages causes early differentiation of hippocampal neurons, in particular in the CA1 and DG regions. Lack of miRNAs at a later stage specifically affects neuronal production in the CA3 region. Our results reveal a timing requirement of miRNAs for the formation of specific hippocampal regions, with the CA1 and DG developmentally hindered by an early loss of miRNAs and the CA3 region to a late loss of miRNAs. Collectively, our studies indicate the importance of the Dicer-mediated miRNA pathway in hippocampal development and functions.

Bacterial Meningitis Impairs Hippocampal Neurogenesis

Bacterial meningitis causes persisting neurofunctional sequelae. Theoccurrence of apoptotic cell death in the hippocampal subgranular zone of the dentate gyrus characterizes the disease in patients and relates to deficits in learning and memory in corresponding experimental models. Here, we investigated why neurogenesis fails to regenerate the damage in the hippocampus associated with the persistence of neurofunctional deficits. In an infant rat model of bacterial meningitis, the capacity of hippocampal-derived cells to multiply and form neurospheres was significantly impaired comparedto that in uninfected littermates. In an in vitro model of differentiating hippocampal cells, challenges characteristic of bacterial meningitis (i.e. bacterial components, tumor necrosis factor [20 ng/mL], or growth factor deprivation) caused significantly more apoptosis in stem/progenitor cells and immature neurons than in mature neurons. These results demonstrate that bacterial meningitis injures hippocampal stem and progenitor cells, a finding that may explain the persistence of neurofunctional deficits after bacterial meningitis.

P2X7 Receptor–Pannexin 1 Hemichannel Association: Effect of Extracellular Calcium on Membrane Permeabilization

Activation of P2X(7) receptor (P2X(7)R) and pannexin have been implicated in membrane permeabilization associated with ischemic cell death and many other inflammatory processes. P2X(7)R has a unique property of forming large pore upon repeated or prolonged application of agonist like ATP or 2', 3'-(4-benzoyl) benzoyl ATP. It has been proposed that pannexin 1 (panx1) hemichannel associates with P2X(7)R to form large pore, though the actual mechanism is not yet understood. Calcium concentration in extracellular milieu drops in many patho-physiological conditions, e.g. ischemia, when P2X(7)R/pannexin is also known to be activated. Therefore, we hypothesize that extracellular calcium ([Ca(2+)](o)) plays an important role in the coupling of P2X(7)R-panx1 and subsequent membrane permeabilization. In this study we show that membrane permeability of the P2X(7)R and panx1 expressing N2A cell increases in ([Ca(2+)](o))-free solution. In [Ca(2+)](o)-free solution, fluorescent dye calcein trapped cells exhibited time-dependent dye leakage resulting in about 50% decrease of fluorescence intensity in 30 min. Control cells in 2 mM [Ca(2+)](o) did not show such leakage. Like N2A cells, mixed culture of neuron and glia, derived from hippocampal progenitor cells showed similar dye leakage. Dye leakage was blocked either by pannexin-specific blocker, carbenoxolone or P2X(7)R antagonists, Brilliant Blue G, and oxidized ATP. Furthermore P2X(7)R and panx1 were co-immunoprecipitated. The amount of P2X(7)R protein pulled-down with panx1, increased by twofold when cells were incubated 30 min in [Ca(2+)](o)-free buffer. Taken together, the results of this study demonstrate the activation and association of P2X(7)R-panx1, triggered by the removal of [Ca(2+)](o).

Brain-Cell Discovery Suggests New Antidepressant Target

Back to table of contents Previous article Next article Clinical & Research NewsFull AccessBrain-Cell Discovery Suggests New Antidepressant TargetJoan Arehart-TreichelJoan Arehart-TreichelSearch for more papers by this authorPublished Online:2 Sep 2011https://doi.org/10.1176/pn.46.17.psychnews_46_17_22AbstractDuring the past few years, it has become apparent that antidepressants activate the birth of new neurons in the hippocampus. But how do they do it? Via glucocorticoid receptors present on hippocampal neural progenitor cells, British scientists have found.The findings also have clinical implications, the scientists believe. Glucocorticoid receptors on hippocampal neural progenitor cells might offer a novel target for the development of new, more effective antidepressants. Scientists cultured hippocampal neural progenitor cells, then exposed them to the antidepressant sertraline. The treatment stimulated the cells to differentiate into neurons (pictured here).Credit: Carmine Pariante, MD, PhD, et al., Molecular Psychiatry, July 2011The lead investigator was Christoph Anacker, a doctoral student at the Institute of Psychiatry, King's College, London. The senior investigator was Carmine Pariante, M.D., Ph.D., a reader in biological psychiatry at the Institute. The results appeared in the July Molecular Psychiatry.Glucocorticoids are a class of steroid hormones, such as cortisol, that regulate the metabolism of glucose. They exert their effects through the glucocorticoid receptors. Anacker and his group had previously found that antidepressants influence the function of glucocorticoid receptors. So this time they looked to see whether glucocorticoid receptors might be involved in antidepressants' ability to stimulate nerve generation in the hippocampus. They cultured hippocampal neural progenitor cells, then exposed them to the SSRI sertraline. They found that the treatment not only stimulated the cells to differentiate into nerve cells, but that it evoked certain changes in glucocorticoid receptors present on the cells, for example, in the receptors' phosphorylation by cyclic AMP-protein kinase activities. They also found that when they added a glucocorticoid receptor antagonist to their culture, the SSRI-prompted nerve differentiation effect was abolished. These findings, they concluded, suggest that glucocorticoid receptors are pivotal to antidepressant-induced hippocampal formation of new neurons. Yet if glucocorticoid receptors are crucial for antidepressant-induced hippocampal nerve differentiation, then why is this the case? "Glucocorticoid receptors, it is true, are receptors for glucocorticoid hormones, yet while these hormones are involved in glucose metabolism, the receptor is not itself affected by glucose," Pariante told Psychiatric News. "So glucose is unlikely to be the mechanism. On the other hand, the glucocorticoid receptors are also transcription factors—that is, they regulate the synthesis of other genes. What likely happens is that antidepressants activate the glucocorticoid receptors, and the receptors in turn increase the synthesis of genes that increase neurogenesis." In an interview, still another possible scenario was suggested by Maura Boldrini, M.D., Ph.D., an assistant professor of psychiatry at Columbia University and an expert on the subject. "Stress is known to reduce hippocampal neurogenesis throughout species.... Antidepressants have shown a significant role in reversing the negative effect of stress on neurogenesis.... Therefore the study by Anacker et al. confirms in human progenitor cells that one of the mechanisms of action of antidepressants on neurogenesis might be via the reversal of the glucocorticoid receptor changes induced by stress. Such a finding should be confirmed in postmortem human brains comparing subjects with mood disorders treated with antidepressants and untreated cases." Whether either of these explanations is correct, the findings definitely have clinical implications, Pariante said. The glucocorticoid receptors on the hippocampal progenitor cells offer "a novel potential target for the development of new and more effective antidepressants." The study was funded by the Institute of Psychiatry, the South London and Maudsley National Health Service Foundation Trust, the United Kingdom Medical Research Council, and the Commission of European Communities. "Antidepressants Increase Human Hippocampal Neurogenesis by Activating the Glucocorticoid Receptor" is posted at <www.nature.com/mp/journal/v16/n7/pdf/mp201126a.pdf>. ISSUES NewArchived

Form of dual-specificity tyrosine-(Y)-phosphorylation-regulated kinase 1A nonphosphorylated at tyrosine 145 and 147 is enriched in the nuclei of astroglial cells, adult hippocampal progenitors, and some cholinergic axon terminals

Compelling lines of evidence indicate that overexpression of dual-specificity tyrosine-(Y)-phosphorylation regulated kinase 1A (DYRK1A) in subjects with trisomy 21 (Down syndrome[DS]) contributes to the abnormal structure and function of the DS brain. In the present study, we used a novel, phospho-dependent antibody recognizing DYRK1A only with nonphosphorylated tyrosine 145 and 147 (DYRK1A Tyr-145/147P(-)), to investigate the expression pattern of this DYRK1A species in trisomic and disomic human and mouse brains. Immunoblotting and dephosphorylation experiments demonstrated higher levels of DYRK1A Tyr-145/147P(-) in postnatal trisomic brains in comparison with controls (by ∼40%) than those of the DYRK1A visualized by three other N- and C-terminally directed antibodies to DYRK1A. By immunofluorescence, the immunoreactivity to DYRK1A Tyr-145/147P(-) was the strongest in the nuclei of astroglial cells, which contrasted with the predominantly neuronal localization of DYRK1A visualized by the three other antibodies to DYRK1A we used. In addition, DYRK1A Tyr-145/147P(-) was enriched in the nuclei of neuronal progenitors and newly born neurons in the adult hippocampal proliferative zone and also occurred in some cholinergic axonal terminals. Our data show a distinctive expression pattern of DYRK1A forms nonphosphorylated at Tyr-145 and Tyr-147 in the brain tissue and suggest that DS subjects may exhibit not only upregulation of total DYRK1A, but also more subtle differences in phosphorylation levels of this kinase in comparison with control individuals.

Ghrelin has direct stimulatory effects in rat adult hippocampal progenitor cells. Ghrelin promotes proliferation and differentiation of rat adult hippocampal progenitor cells and regulates cell-cycle gene expression

Ghrelin has direct stimulatory effects in rat adult hippocampal progenitor cells. Ghrelin promotes proliferation and differentiation of rat adult hippocampal progenitor cells and regulates cell-cycle gene expression

Extended access methamphetamine decreases immature neurons in the hippocampus which results from loss and altered development of neural progenitors without altered dynamics of the S-phase of the cell cycle

Methamphetamine addicts demonstrate impaired hippocampal-dependent cognitive function that could result from methamphetamine-induced maladaptive plasticity in the hippocampus. Reduced adult hippocampal neurogenesis observed in a rodent model of compulsive methamphetamine self-administration partially contributes to the maladaptive plasticity in the hippocampus. The potential mechanisms underlying methamphetamine-induced inhibition of hippocampal neurogenesis were identified in the present study. Key aspects of the cell cycle dynamics of hippocampal progenitors, including proliferation and neuronal development, were studied in rats that intravenously self-administered methamphetamine in a limited access (1h/day: short access (ShA)-4days and ShA-13days) or extended access (6h/day: long access (LgA)-4days and LgA-13days) paradigm. Immunohistochemical analysis of Ki-67 cells with 5-chloro-2′-deoxyuridine (CldU) demonstrated that LgA methamphetamine inhibited hippocampal proliferation by decreasing the proliferating pool of progenitors that are in the synthesis (S)-phase of the cell cycle. Double S-phase labeling with CldU and 5-iodo-2′-deoxyuridine (IdU) revealed that reduced S-phase cells were not due to alterations in the length of the S-phase. Further systematic analysis of Ki-67 cells with GFAP, Sox2, and DCX revealed that LgA methamphetamine-induced inhibition of hippocampal neurogenesis was attributable to impairment in the development of neuronal progenitors from preneuronal progenitors to immature neurons. Methamphetamine concomitantly increased hippocampal apoptosis, changes that were evident during the earlier days of self-administration. These findings demonstrate that methamphetamine self-administration initiates allostatic changes in adult neuroplasticity maintained by the hippocampus, including increased apoptosis, and altered dynamics of hippocampal neural progenitors. These data suggest that altered hippocampal plasticity by methamphetamine could partially contribute to methamphetamine-induced impairments in hippocampal function.

Cyclooxygenase-1 is involved in the inhibition of hippocampal neurogenesis after lipopolysaccharide-induced neuroinflammation

Growing evidence indicates that neuroinflammation can alter adult neurogenesis by mechanisms as yet unclear. We have previously demonstrated that the neuroinflammatory response and neuronal damage after lipopolysaccharide (LPS) injection is reduced in cyclooxygenase-1 deficient (COX-1-/-) mice. In this study, we investigated the role of COX-1 on hippocampal neurogenesis during LPS-induced neuroinflammation, using COX-1-/- and wild type (WT) mice. We found that LPS-induced neuroinflammation resulted in the decrease of proliferation, survival and differentiation of hippocampal progenitor cells in WT but not in COX-1-/- mice. Thus, we demonstrate for the first time that COX-1 is involved in the inhibition of BrdU progenitor cells in proliferation and hippocampal neurogenesis after LPS. These results suggest that COX-1 may represent a viable therapeutic target to reduce neuroinflammation and promote neurogenesis in neurodegenerative diseases with a strong inflammatory component.

Adolescent binge alcohol exposure alters hippocampal progenitor cell proliferation in rats: Effects on cell cycle kinetics

Binge alcohol exposure in adolescent rats potently inhibits adult hippocampal neurogenesis by altering neural progenitor cell (NPC) proliferation and survival; however, it is not clear whether alcohol results in an increase or decrease in net proliferation. Thus, the effects of alcohol on hippocampal NPC cell cycle phase distribution and kinetics were assessed in an adolescent rat model of an alcohol use disorder. Cell cycle distribution was measured using a combination of markers (Ki-67, bromodeoxyuridine incorporation, and phosphohistone H3) to determine the proportion of NPCs within G1, S, and G2/M phases of the cell cycle. Cell cycle kinetics were calculated using a cumulative bromodeoxyuridine injection protocol to determine the effect of alcohol on cell cycle length and S-phase duration. Binge alcohol exposure reduced the proportion of NPCs in S-phase, but had no effect on G1 or G2/M phases, indicating that alcohol specifically targets S-phase of the cell cycle. Cell cycle kinetics studies revealed that alcohol reduced NPC cell cycle duration by 36% and shortened S-phase by 62%, suggesting that binge alcohol exposure accelerates progression through the cell cycle. This effect would be expected to increase NPC proliferation, which was supported by a slight, but significant increase in the number of Sox-2+ NPCs residing in the hippocampal subgranular zone following binge alcohol exposure. These studies suggest the mechanism of alcohol inhibition of neurogenesis and also reveal the earliest evidence of the compensatory neurogenesis reaction that has been observed a week after binge alcohol exposure.

Expression and actions of transcription factors in adult hippocampal neurogenesis

Neurogenesis in the adult brain, a process once thought to be essentially absent, has now been demonstrated to occur throughout adult mammalian life within several brain regions. Adult neurogenesis normally occurs only within the subventricular zone (SVZ) bordering the lateral ventricles and the subgranular zone (SGZ) of the hippocampal dentate gyrus (DG). Neurogenic progenitors within these regions produce distinct neuron types, with progenitors in the SGZ giving rise to glutamatergic neurons that populate the DG granule cell layer and those within the SVZ producing neurons destined for the olfactory bulb. In this review, we highlight recent research on transcription factor expression and function during adult hippocampal neurogenesis. In this regard, recent evidence indicates that adult neurogenesis replicates important aspects of progenitor cell development in the embryonic brain. Specifically, work from our laboratory and others indicates that transcription factor cascades active in progenitor cells during neurogenesis in the embryonic cerebral cortex are also activated in adult hippocampal progenitor cells, where they play an important role in determining neuronal fate and regulating progenitor cell proliferation and maintenance. These findings suggest that conserved transcription factor cascades regulate genetic programs that delineate progenitor cell lineages and control progenitor cell proliferation and differentiation.