Neural stem cell transplantation at critical period improves learning and memory through restoring synaptic impairment in Alzheimer's disease mouse model.

Alzheimer's disease (AD) is characterized by neuronal loss in several regions of the brain. Recent studies have suggested that stem cell transplantation could serve as a potential therapeutic strategy to halt or ameliorate the inexorable disease progression. However, the optimal stage of the disease for stem cell transplantation to have a therapeutic effect has yet to be determined. Here, we demonstrated that transplantation of neural stem cells into 12-month-old Tg2576 brains markedly improved both cognitive impairments and neuropathological features by reducing ß-amyloid processing and upregulating clearance of ß-amyloid, secretion of anti-inflammatory cytokines, endogenous neurogenesis, as well as synapse formation. In contrast, the stem cell transplantation did not recover cognitive dysfunction and ß-amyloid neuropathology in Tg2576 mice aged 15 months when the memory loss is manifest. Overall, this study underscores that stem cell therapy at optimal time frame is crucial to obtain maximal therapeutic effects that can restore functional deficits or stop the progression of AD.

MiR-29b controls fetal mouse neurogenesis by regulating ICAT-mediated Wnt/ß-catenin signaling.

ß-Catenin has been widely implicated in the regulation of mammalian development and cellular homeostasis. However, the mechanisms by which Wnt/ß-catenin signaling components regulate physiological events during brain development remain undetermined. Inactivation of glycogen synthase kinase (GSK)-3ß leads to ß-catenin accumulation in the nucleus, where it couples with T-cell factor (TCF), an association that is disrupted by ICAT (inhibitor of ß-catenin and T cell factor). In this study, we sought to determine whether regulation of ICAT by members of the microRNA-29 family plays a role during neurogenesis and whether deregulation of ICAT results in defective neurogenesis due to impaired ß-catenin-mediated signaling. We found that miR-29b, but not miR-29a or 29c, is significantly upregulated in three-dimensionally cultured neural stem cells (NSCs), whereas ICAT is reduced as aged. Treatment with a miR-29b reduced the reporter activity of a luciferase-ICAT 3'-UTR construct whereas a control (scrambled) miRNA oligonucleotide did not, indicating that miR-29b directly targets the 3'-UTR of ICAT. We also found that treatment with miR-29b diminished NSC self-renewal and proliferation, and controlled their fate, directing their differentiation along certain cell lineages. Furthermore, our in vivo results showed that inhibition of miR-29b by in utero electroporation induced a profound defect in corticogenesis during mouse development. Taken together, our results demonstrate that miR-29b plays a pivotal role in fetal mouse neurogenesis by regulating ICAT-mediated Wnt/ß-catenin signaling.

Neuregulin-1 protects against neurotoxicities induced by Swedish amyloid precursor protein via the ErbB4 receptor.

Neuregulin-1 (NRG1) plays an important role in the development and plasticity of the brain and exhibits potent neuroprotective properties. However, little information on its role in Alzheimer's disease (AD) is known. The neuroprotective effect and mechanisms of NRG1 in SH-SY5Y cells overexpressing the Swedish mutant form of amyloid precursor protein (Swe-APP) and primary cortical neuronal cells treated with amyloid beta peptide(1-42) (Aß(1-42)) were investigated in this study. NRG1 attenuated Swe-APP- or Aß(1-42)-induced lactate dehydrogenase (LDH) release in a concentration-dependent manner. The mitigating effects of NRG1 on neuronal cell death were blocked by ErbB4 inhibition, a key NRG1 receptor, which suggests a role of ErbB4 in the neuroprotective function of NRG1. Moreover, NRG1 reduced the number of Swe-APP- and Aß(1-42)-induced TUNEL-positive SH-SY5Y cells and primary cortical neurons, respectively. NRG1 reduced the accumulation of reactive oxygen species and attenuated Swe-APP-induced mitochondrial membrane potential loss. NRG1 also induced the upregulation of the expression of the anti-apoptotic protein, Bcl-2, and decreased caspase-3 activation. Collectively, our results demonstrate that NRG1 exerts neuroprotective effects via the ErbB4 receptor, which suggests the neuroprotective potential of NRG1 in AD.

Apoptosis in subicular neurons: A comparison between suicide and Addison's disease.

BACKGROUND: Stress and depression shows possible links to neuronal death in hippocampus. Subiculum plays a prominent role in limbic stress integration and direct effect of corticosteroids on subicular neurons needs to be defined to assess its subsequent impact on hippocampal plasticity. AIM: This study was intended to assess apoptosis in subicular neurons of a young depressed suicide victim, where presumably stress induced excess of corticosteroids and a case of young Addison's disease with low level of corticosteroids. MATERIALS AND METHOD: Both bilateral adrenal glands (Addison's) and subiculum (both cases) were initially stained with hematoxylin and eosin; subicular neurons of both cases were examined for the degree of apoptosis using 'ApopTag Kit'. Apoptotic cell counts were expressed as average number of labeled cells/mm 2 and the results were analysed statistically using a non-parametric Mann-Whitney U test. RESULT: Apoptotic neurons were detected in the subicular region of both suicide and Addison victims, and it is statistically significant in both right and left between the cases (P < 0.05). In suicide victim, the neuronal apoptosis is considerably significant between the two hemispheres (P < 0.05), in contrast to Addison disease where the number of neuronal cell death between right and left was statistically insignificant (P > 0.05). CONCLUSION: The present study confirms the vulnerability of the subicular neurons to apoptosis, possibly due to corticosteroids in both ends of spectrum.

Intracellular domains of amyloid precursor-like protein 2 interact with CP2 transcription factor in the nucleus and induce glycogen synthase kinase-3beta expression.

Amyloid precursor protein (APP) is a member of a gene family that includes two APP-like proteins, APLP1 and 2. Recently, it has been reported that APLP1 and 2 undergo presenilin-dependent gamma-secretase cleavage, as does APP, resulting in the release of an approximately 6 kDa intracellular C-terminal domain (ICD), which can translocate into the nucleus. In this study, we demonstrate that the APLP2-ICDs interact with CP2/LSF/LBP1 (CP2) transcription factor in the nucleus and induce the expression of glycogen synthase kinase 3beta (GSK-3beta), which has broad-ranged substrates such as tau- and beta-catenin. The significance of this finding is substantiated by the in vivo evidence of the increase in the immunoreactivities for the nuclear C-terminal fragments of APLP2, and for GSK-3beta in the AD patients' brain. Taken together, these results suggest that APLP2-ICDs contribute to the AD pathogenesis, by inducing GSK-3beta expression through the interaction with CP2 transcription factor in the nucleus.

Mitochondrial dysfunction induces aberrant insulin signalling and glucose utilisation in murine C2C12 myotube cells.

AIMS/HYPOTHESIS: Mitochondrial dysfunction is considered a critical component in the development of diabetes. The aim of this study was to elucidate the molecular mechanisms involved in the development of insulin resistance and diabetes through investigation of mitochondrial retrograde signalling. MATERIALS AND METHODS: Mitochondrial function of C2C12 myotube cells was impaired by genetic (ethidium bromide) and metabolic (oligomycin) stress, and changes in target molecules related to insulin signalling were analysed. RESULTS: Concomitant with reductions in mitochondrial membrane potential (DeltaPsim) and ATP synthesis, production of IRS1 and solute carrier family 2 (facilitated glucose transporter), member 4 (SLC2A4, formerly known as GLUT4) were reduced. Moreover, serine phosphorylation of IRS1 increased, resulting in decreased tyrosine phosphorylation. This indicates that mitochondrial dysfunction decreases insulin-stimulated SLC2A4 translocation and glucose uptake. Mitochondrial stress activated c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (p38 MAPK) signalling in a Ca(2+)-dependent manner, and removal of free Ca(2+) by BAPTA-AM, as well as inhibition of JNK and p38 MAPK, abrogated mitochondrial stress-induced reductions in IRS1 and SLC2A4 production. Mitochondrial dysfunction after oligomycin treatment significantly increased levels of activating transcription factor 3 (ATF3), which represses Irs1 promoter activity. Removal of the 5' flanking region of Irs1 demonstrated that the promoter region within 191 bases from the transcription site may be involved in the transcriptional repression of Irs1 by mitochondrial stress. CONCLUSIONS/INTERPRETATION: We show distinct mitochondrial retrograde signalling, where Irs1 is downregulated through ATF3 in a Ca(2+)-, JNK- and p38 MAPK-dependent manner, and IRS1 is inactivated. Therefore, mitochondrial dysfunction causes aberrant insulin signalling and abnormal utilisation of glucose, as observed in many insulin resistance states.

Overexpression of short heterodimer partner recovers impaired glucose-stimulated insulin secretion of pancreatic beta-cells overexpressing UCP2.

The short heterodimer partner (SHP) (NR0B2) is an orphan nuclear receptor whose function in pancreatic beta-cells is unclear. Mitochondrial uncoupling protein (UCP2) in beta-cells is upregulated in obesity-related diabetes, causing impaired glucose-stimulated insulin secretion (GSIS). We investigated whether SHP plays a role in UCP2-induced GSIS impairment. We overexpressed SHP in normal islet cells and in islet cells overexpressing UCP2 by an adenovirus-mediated infection technique. We found that SHP overexpression enhanced GSIS in normal islets, and restored GSIS in UCP2-overexpressing islets. SHP overexpression increased the glucose sensitivity of ATP-sensitive K+ (KATP) channels and enhanced the ATP/ADP ratio. A peroxisome proliferator-activated receptor gamma (PPARgamma) antagonist, GW9662, did not block the SHP effect on GSIS. SHP overexpression also corrected the impaired sensitivity of UCP2-overexpressing beta-cells to methylpyruvate, another energy fuel that bypasses glycolysis and directly enters the Krebs cycle. KATP channel inhibition mediated by dihydroxyacetone, which gives reducing equivalents directly to complex II of the electron transport system, was similar in Ad-Null-, Ad-UCP2- and Ad-UCP2+Ad-SHP-infected cells. The mitochondrial metabolic inhibitor sodium azide totally blocked the effect of SHP overexpression on GSIS. These results suggest that SHP positively regulates GSIS in beta-cells and restores glucose sensitivity in UCP2-overexpressing beta-cells by enhancing mitochondrial glucose metabolism, independent of PPARgamma activation.

Estrogen attenuates cell death induced by carboxy-terminal fragment of amyloid precursor protein in PC12 through a receptor-dependent pathway.

In the present study, we investigated effects of estrogen on cell death induced by carboxy-terminal fragment of amyloid precursor protein (CT), a candidate causative substance in the pathogenesis of Alzheimer's disease. 17 beta-Estradiol attenuated CT-induced cell death in PC12 cells, whereas 17 alpha-estradiol, nonestrogenic stereoisomer, did not exert any significant protective effect on CT-induced cell death. These results suggest that protective effects of estrogen may be mediated by estrogen receptor (ER) in PC12 cells. To confirm the results, we determined the effects of tamoxifen, an estrogen receptor antagonist. Tamoxifen blocked the protective effects of 17 beta-estradiol, although it did not affect those of 17 alpha-estradiol. Overall, it might be thought that the protective effect of estradiol on CT-induced cell death is achieved by hormonal properties mediated through the estrogen receptor rather than the structural properties as a reducing agent.

C-terminal fragment of amyloid precursor protein induces astrocytosis.

One of the pathophysiological features of Alzheimer's disease is astrocytosis around senile plaques. Reactive astrocytes may produce proinflammatory mediators, nitric oxide, and subsequent reactive oxygen intermediates such as peroxynitrites. In the present study, we investigated the possible role of the C-terminal fragment of amyloid precursor protein (CT-APP), which is another constituent of amyloid senile plaque and an abnormal product of APP metabolism, as an inducer of astrocytosis. We report that 100 nM recombinant C-terminal 105 amino acid fragment (CT105) of APP induced astrocytosis morphologically and immunologically. CT105 exposure resulted in activation of mitogen-activated protein kinase (MAPK) pathways as well as transcription factor NF-kappaB. Pretreatment with PD098059 and/or SB203580 decreased nitric oxide (NO) production and nuclear factor-kappa B (NF-kappaB) activation. But inhibitors of NF-kappaB activation did not affect MAPKs activation whereas they abolished NO production and attenuated astrocytosis. Furthermore, conditioned media derived from CT105-treated astrocytes enhanced neurotoxicity and pretreatment with NO and peroxynitrite scavengers attenuated its toxicity. These suggest that CT-APP may participate in Alzheimer's pathogenesis through MAPKs- and NF-kappaB-dependent astrocytosis and iNOS induction.

Effects of the beta-amyloid and carboxyl-terminal fragment of Alzheimer's amyloid precursor protein on the production of the tumor necrosis factor-alpha and matrix metalloproteinase-9 by human monocytic THP-1.

To explore the direct role of beta-amyloid (Abeta) and carboxyl-terminal fragments of amyloid precursor protein in the inflammatory processes possibly linked to neurodegeneration associated with Alzheimer's disease, the effects of the 105-amino acid carboxyl-terminal fragment (CT(105)) of amyloid precursor protein on the production of tumor necrosis factor-alpha (TNF-alpha) and matrix metalloproteinase-9 (MMP-9) were examined in a human monocytic THP-1 cell line and compared with that of Abeta. CT(105) elicited a marked increase in TNF-alpha and MMP-9 production in the presence of interferon-gamma in a dose- and time-dependent manner. Similar patterns were obtained with Abeta despite its low magnitude of induction. Autocrine TNF-alpha is likely to be a main mediator of the induction of MMP-9 because the neutralizing antibody to TNF-alpha inhibits MMP-9 production. Genistein, a specific inhibitor of tyrosine kinase, dramatically diminished both TNF-alpha secretion and subsequent MMP-9 release in response to CT(105) or Abeta. Furthermore, PD98059 and SB202190, specific inhibitors of ERK or p38 MAPK respectively, efficiently suppressed CT(105)-induced effects whereas only PD98059 was effective at reducing Abeta-induced effects. Our results suggest that CT(105) in combination with interferon-gamma might serve as a more potent activator than Abeta in triggering inflammatory processes and that both tyrosine kinase and MAPK signaling pathways may represent potential therapeutic targets for the control of Alzheimer's disease progression.

Use-dependent effects of amyloidogenic fragments of (beta)-amyloid precursor protein on synaptic plasticity in rat hippocampus in vivo.

The Alzheimer's disease-related beta-amyloid precursor protein (beta-APP) is metabolized to a number of potentially amyloidogenic peptides that are believed to be pathogenic. Application of relatively low concentrations of the soluble forms of these peptides has previously been shown to block high-frequency stimulation-induced long-term potentiation (LTP) of glutamatergic transmission in the hippocampus. The present experiments examined how these peptides affect low-frequency stimulation-induced long-term depression (LTD) and the reversal of LTP (depotentiation). We discovered that beta-amyloid peptide (Abeta1-42) and the Abeta-containing C -terminus of beta-APP (CT) facilitate the induction of LTD in the CA1 area of the intact rat hippocampus. The LTD was frequency- and NMDA receptor-dependent. Thus, although low-frequency stimulation alone was ineffective, after intracerebroventricular injection of Abeta1-42, it induced an LTD that was blocked by d-(-)-2-amino-5-phosphonopentanoic acid. Furthermore, an NMDA receptor-dependent depotentiation was induced in a time-dependent manner, being evoked by injection of CT 10 min, but not 1 hr, after LTP induction. These use- and time-dependent effects of the amyloidogenic peptides on synaptic plasticity promote long-lasting reductions in synaptic strength and oppose activity-dependent strengthening of transmission in the hippocampus. This will result in a profound disruption of information processing dependent on hippocampal synaptic plasticity.

CD99 regulates the transport of MHC class I molecules from the Golgi complex to the cell surface.

The down-regulation of surface expression of MHC class I molecules has recently been reported in the CD99-deficient lymphoblastoid B cell line displaying the characteristics of Hodgkin's and Reed-Sternberg phenotype. Here, we demonstrate that the reduction of MHC class I molecules on the cell surface is primarily due to a defect in the transport from the Golgi complex to the plasma membrane. Loss of CD99 did not affect the steady-state expression levels of mRNA and protein of MHC class I molecules. In addition, the assembly of MHC class I molecules and the transport from the endoplasmic reticulum to the cis-Golgi occurred normally in the CD99-deficient cells, and no difference was detected between the CD99-deficient and the control cells in the pattern and degree of endocytosis. Instead, the CD99-deficient cells displayed the delayed transport of newly synthesized MHC class I molecules to the plasma membrane, thus causing accumulation of the molecules within the cells. The accumulated MHC class I molecules in the CD99-deficient cells were colocalized with alpha-mannosidase II and gamma-adaptin in the Golgi compartment. These results suggest that CD99 may be associated with the post-Golgi trafficking machinery by regulating the transport to the plasma membrane rather than the endocytosis of surface MHC class I molecules, providing a novel mechanism of MHC class I down-regulation for immune escape.

Roles of A beta and carboxyl terminal peptide fragments of amyloid precursor protein in Alzheimer disease.

Several lines of evidence indicate that A beta may play an important role in the pathogenesis of AD. However, there are several discrepancies between the production of A beta and the development of the disease. Thus, A beta may not be the sole active fragment of beta-amyloid precursor protein (betaAPP) in the neurotoxicity assiciated with AD. We focused on the amyloidegenic carboxyl terminal fragments of betaAPP containing the full length of A beta (CT105). We synthesized a recombinant carboxyl-terminal 105 amino acid fragment of betaAPP and examined the effects of CT105 and A beta on cultured neurons, Ca++ uptake into rat brain microsomes, Na+-Ca++ exchange activity, ion channel forming activity in lipid bilayers and passive avoidance performance of mice. Our results suggest that the cytotoxic and channel inducing effects of CT105 are much more potent than that of A beta and toxic mechanisms of CT105 are different from those of A beta. Taken together, these lines of evidence postulate that CT is an alternative toxic element important in the generation of the symptoms common to AD.

Regulation of cytokine production by exogenous nitric oxide in murine splenocyte and peritoneal macrophage.

Nitric oxide (NO), products of activated macrophages, have a great impact on the regulation of cytokine production. The role of NO in non-specific host cells is commonly accepted. On the contrary, its role as an immuno-regulatory molecule is still controversial. In this study, we have investigated the effect of NO on the production of cytokines from murine splenocytes and macrophages. S-nitroso-L-glutathione inhibited the release of both interferone-gamma and interleukin-2 produced by Th1 cells and tumor necrosis factor-alpha and interleukin-1beta produced by macrophages, but did not affect the release of interleukin-4 and interleukin-10 produced by Th2 cells. These results suggest that NO exerts a down-regulatory effect on the secretion of cytokines from Th1 cells and macrophages which are implicated in immune response. Thus, NO may have an important role as an immuno-modulatory as well as effector molecule in the immune system.

Toxic effect of the beta-amyloid precursor protein C-terminus fragment and Na+/Ca2+ gradients.

There is evidence to suggest that certain metabolic fragments of the beta-amyloid precursor protein (betaAPP) containing the whole of the beta-amyloid (Abeta) sequence are toxic to cells. We showed previously that the 105-amino acid C-terminal peptide (CT105) fragment, incorporating Abeta, is particularly toxic to Xenopus oocytes as well as to mammalian neurons. Here, we investigated the contributions of Na+ and Ca2+ gradients to intracellular CT105-induced toxicity in oocytes, monitored by measuring the membrane resting potential. The concentration gradients of Na+ and Ca2+ were manipulated to determine the involvement of the trans-membrane concentration gradients of these ions in the mode of action of CT105. The results suggested that Na+ influx and intracellular events are mainly responsible for the observed CT105-induced toxicity.

Subcellular localization of presenilins during mouse preimplantation development.

The genes defective in familial Alzheimer's disease encode the proteins presenilin 1 and 2 (PS1 and 2). Expression of presenilins (PSs) and their proteolytic processing are regulated during neuronal development. Even though these proteins are detected and regulated mainly in Golgi and endoplasmic reticulum, their subcellular distribution during the development is not known. The present study aimed to investigate the localization of PSs and their role during early developmental stage using mouse embryo model. At preimplantation stage, PSs were detected not only in cytoplasm, but also in the nucleus from oocyte to 2.5 dpc (day postcoitum), then disappeared in the nucleus at blastocyst stage (3.5 dpc). Antisense against PS1 and PS2 decreased the transition to blastocyst stage, whereas each antisense alone had no effect. Treatment with lactacystin (26S proteosome inhibitor), which arrest cell cycle at M phase, redistributed PSs into centrosome-kinetochore microtubule. PS2 overexpression in HEK 293 cell arrested cell cycle at S phase. These data suggest that PSs play key roles in cell division and differentiation during early development.

Carboxyl-terminal fragment of Alzheimer's APP destabilizes calcium homeostasis and renders neuronal cells vulnerable to excitotoxicity.

Numerous lines of evidence indicate that some of the neurotoxicity associated with Alzheimer's disease (AD) is due to proteolytic fragments of the amyloid precursor protein (APP). Most research has focused on the amyloid beta peptide (Abeta). However, the possible role of other cleaved products of APP is less clear. We have previously shown that a recombinant carboxy-terminal 105 amino acid fragment (CT 105) of APP induced strong nonselective inward currents in Xenopus oocyte; it also revealed neurotoxicity in PC12 cells and primary cortical neurons, blocked later phase of long-term potentiation in rat hippocampus in vivo, and induced memory deficits and neuropathological changes in mice. We report here that the pretreatment with CT 105 for 24 h at a 10 microM concentration increases intracellular calcium concentration by about twofold in SK-N-SH and PC 12 cells, but not in U251 cells, originated from human glioblastoma. In addition, the calcium increase and toxicity induced by CT 105 were reduced by cholesterol and MK 801 in SK-N-SH and PC 12 cells, whereas the toxicity of Abeta(1-42) was attenuated by nifedipine and verapamil. CT 105 rendered SK-N-SH cells and rat primary cortical neurons more vulnerable to glutamate-induced excitotoxicity. Also, conformational studies using circular dichroism experiments showed that CT 105 has approximately 15% of beta-sheet content in phosphate buffer and aqueous 2,2, 2-trifluoroethanol solutions. However, the content of beta-sheet conformation in dodecyl phosphocholine micelle or in the negatively charged vesicles, is increased to 22%-23%. The results of this study showed that CT 105 disrupts calcium homeostasis and renders neuronal cells more vulnerable to glutamate-induced excitotoxicity, and that some portion of CT 105 has partial beta-sheet conformation in various environments, which may be related to the self-aggregation and toxicity. This may be significantly possibly involved in inducing the neurotoxicity characteristic of AD.

Glutamate and aspartate impair memory retention and damage hypothalamic neurons in adult mice.

We examined the effects of systemic administration of monosodium glutamate (MSG) or aspartate (ASP) on the memory retention and neuronal damage in the brains of adult mice. Compared with the control mice, a single intraperitoneal injection of either 4.0 mg/g MSG or 0.5 mg/g ASP after acquisition trial significantly shortened the response latency in the passive avoidance test, accompanying by the transient weight loss. Histopathological analysis of the brains of these mice revealed that neurons in the arcuate nucleus of hypothalamus were damaged markedly by MSG (4.0 mg/g) or ASP (0.5 mg/g). Other brain areas including cerebral cortex and hippocampus did not show any pathological changes. These findings suggest that systemic administration of MSG or ASP could impair memory retention and damage hypothalamic neurons in adult mice.