Increased Calcium Influx through L-Type Calcium Channels in Hippocampal Neurons with Exogenous Expression of Presenilin-1 ΔE9 Mutant.

Mutations in the PSEN1 gene encoding presenilin-1 (PS1) protein are the most common cause of familial Alzheimer's disease. One of these, deletion of exon 9, results in the production of shortened PS1 protein (PS1ΔE9). Neuronal hyperexcitability and hyperactivation of L-type calcium channels were observed in cellular and animal models of familial Alzheimer's disease. However, the effect of PS1ΔE9 on L-type calcium channels has not been studied before. We demonstrate enhanced calcium entry through L-type calcium channels in hippocampal mouse neurons with exogenous expression of PS1ΔE9. Additionally, we show that the same effect of the exogenous PS1ΔE9 can be observed in cells with predominant expression of L-type calcium channels subunit Cav1.2. Further research is required to unravel molecular mechanisms underlying hyperactivation L-type calcium channels caused by PS1ΔE9 expression.

Selective expression of the neurexin substrate for presenilin in the adult forebrain causes deficits in associative memory and presynaptic plasticity.

Presenilins (PS) form the active subunit of the gamma-secretase complex, which mediates the proteolytic clearance of a broad variety of type-I plasma membrane proteins. Loss-of-function mutations in PSEN1/2 genes are the leading cause of familial Alzheimer's disease (fAD). However, the PS/gamma-secretase substrates relevant for the neuronal deficits associated with a loss of PS function are not completely known. The members of the neurexin (Nrxn) family of presynaptic plasma membrane proteins are candidates to mediate aspects of the synaptic and memory deficits associated with a loss of PS function. Previous work has shown that fAD-linked PS mutants or inactivation of PS by genetic and pharmacological approaches failed to clear Nrxn C-terminal fragments (NrxnCTF), leading to its abnormal accumulation at presynaptic terminals. Here, we generated transgenic mice that selectively recreate the presynaptic accumulation of NrxnCTF in adult forebrain neurons, leaving unaltered the function of PS/gamma-secretase complex towards other substrates. Behavioral characterization identified selective impairments in NrxnCTF mice, including decreased fear-conditioning memory. Electrophysiological recordings in medial prefrontal cortex-basolateral amygdala (mPFC-BLA) of behaving mice showed normal synaptic transmission and uncovered specific defects in synaptic facilitation. These data functionally link the accumulation of NrxnCTF with defects in associative memory and short-term synaptic plasticity, pointing at impaired clearance of NrxnCTF as a new mediator in AD.

Continuous Monitoring of Tau-Induced Neurotoxicity in Patient-Derived iPSC-Neurons.

Tau aggregation within neurons is a critical feature of Alzheimer's disease (AD) and related tauopathies. It is believed that soluble pathologic tau species seed the formation of tau aggregates in a prion-like manner and propagate through connected neurons during the progression of disease. Both soluble and aggregated forms of tau are thought to have neurotoxic properties. In addition, different strains of misfolded tau may cause differential neurotoxicity. In this work, we present an accelerated human neuronal model of tau-induced neurotoxicity that incorporates both soluble tau species and tau aggregation. Using patient-derived induced pluripotent stem cell (iPSC) neurons expressing a tau aggregation biosensor, we develop a cell culture system that allows continuous assessment of both induced tau aggregation and neuronal viability at single-cell resolution for periods of >1 week. We show that exogenous tau "seed" uptake, as measured by tau repeat domain (TauRD) reporter aggregation, increases the risk for subsequent neuronal death in vitro These results are the first to directly visualize neuronal TauRD aggregation and subsequent cell death in single human iPSC neurons. Specific morphologic strains or patterns of TauRD aggregation are then identified and associated with differing neurotoxicity. Furthermore, we demonstrate that familial AD iPSC neurons expressing the PSEN1 L435F mutation exhibit accelerated TauRD aggregation kinetics and a tau strain propagation bias when compared with control iPSC neurons.SIGNIFICANCE STATEMENT Neuronal intracellular aggregation of the microtubule binding protein tau occurs in Alzheimer's disease and related neurodegenerative tauopathies. Tau aggregates are believed to spread from neuron to neuron via prion-like misfolded tau seeds. Our work develops a human neuronal live-imaging system to visualize seeded tau aggregation and tau-induced neurotoxicity within single neurons. Using an aggregation-sensing tau reporter, we find that neuronal uptake and propagation of tau seeds reduces subsequent survival. In addition, human induced pluripotent stem cell (iPSC) neurons carrying an Alzheimer's disease-causing mutation in presenilin-1 undergo tau seeding more rapidly than control iPSC neurons. However, they do not show subsequent differences in neuronal survival. Finally, specific morphologies of tau aggregates are associated with increased neurotoxicity.

Oral Treponema denticola Infection Induces Aß1-40 and Aß1-42 Accumulation in the Hippocampus of C57BL/6 Mice.

Accumulation of amyloid-ß (Aß) in the brain is a central component of pathology in Alzheimer's disease. A growing volume of evidence demonstrates close associations between periodontal pathogens including Porphyromonas gingivalis (P. gingivalis) and Treponema denticola (T. denticola) and AD. However, the effect and mechanisms of T. denticola on accumulation of Aß remain to be unclear. In this study, we demonstrated that T. denticola was able to enter the brain and act directly on nerve cells resulting in intra- and extracellular Aß1-40 and Aß1-42 accumulation in the hippocampus of C57BL/6 mice by selectively activating both ß-secretase and γ-secretase. Furthermore, both KMI1303, an inhibitor of ß-secretase, as well as DAPT, an inhibitor of γ- secretase, were found to be able to inhibit the effect of T. denticola on Aß accumulation in N2a neuronal cells. Overall, it is concluded that T. denticola increases the expression of Aß1-42 and Aß1-40 by its regulation on beta-site amyloid precursor protein cleaving enzyme-1 and presenilin 1.

Neural stem cell transplantation improves learning and memory by protecting cholinergic neurons and restoring synaptic impairment in an amyloid precursor protein/presenilin 1 transgenic mouse model of Alzheimer's disease.

Alzheimer's disease (AD) is the most prevalent age­related neurodegenerative disorder. It is featured by the progressive accumulation of ß­amyloid (Aß) plaques and neurofibrillary tangles. This can eventually lead to a decrease of cholinergic neurons in the basal forebrain. Stem cell transplantation is an effective treatment for neurodegenerative diseases. Previous studies have revealed that different types of stem or progenitor cells can mitigate cognition impairment in different Alzheimer's disease mouse models. However, understanding the underlying mechanisms of neural stem cell (NSC) therapies for AD requires further investigation. In the present study, the effects and the underlying mechanisms of the treatment of AD by NSCs are reported. The latter were labelled with the enhanced green fluorescent protein (EGFP) prior to implantation into the bilateral hippocampus of an amyloid precursor protein (APP)/presenilin 1 (PS1) transgenic (Tg) mouse model of AD. It was observed that the number of basal forebrain cholinergic neurons was restored and the expression of choline acetyltransferase (ChAT) protein was increased. Moreover, the levels of synaptophysin (SYP), postsynaptic density protein 95 (PSD­95) and microtubule­associated protein (MAP­2) were significantly increased in the hippocampus of NSC­treated AD mice. Notably, spatial learning and memory were both improved after transplantation of NSCs. In conclusion, the present study revealed that NSC transplantation improved learning and memory functions in an AD mouse model. This treatment allowed repairing of basal forebrain cholinergic neurons and increased the expression of the cognition­related proteins SYP, PSD­95 and MAP­2 in the hippocampus.

Antagonist of neuronal store-operated calcium entry exerts beneficial effects in neurons expressing PSEN1ΔE9 mutant linked to familial Alzheimer disease.

Alzheimer's disease (AD) is the neurodegenerative disorder with no cure. Recent studies suggest that dysregulated postsynaptic store-operated calcium entry (nSOCE) may underlie mushroom spine loss that is related to AD pathology. In the present study we observed that PSEN1ΔE9 familial AD (FAD) mutation causes mushroom spine loss in hippocampal neuronal cultures. We also demonstrated that amplitude of TRPC6-mediated nSOCE is increased in PSEN1ΔE9-expressing neurons and we suggested that inhibition of nSOCE may help to rescue synaptic defects in this model. We further established that nSOCE antagonist EVP4593 decreases PSEN1ΔE9-mediated nSOCE upregulation and rescues mushroom spines in PSEN1ΔE9-expressing neurons. Obtained results further highlight the connection between dysregulation of endoplasmic reticulum calcium signaling and synaptic loss in AD and suggest that calcium signaling modulators may have a therapeutic value for treatment of memory loss in AD.

Heterozygous knockout of cytosolic phospholipase A2α attenuates Alzheimer's disease pathology in APP/PS1 transgenic mice.

Cytosolic phospholipase A2α (cPLA2α) is a key enzyme in regulation of inflammation process and neuromembrane homeostasis, both of which are critical in pathogenesis of Alzheimer's diseases. By hybride APP/PS1 Tg-AD mice with cPLA2α knockout mice, three lines of APP/PS1 Tg-AD mice were produced with genotypes of cPLA2α+/+, cPLA2α+/- and cPLA2α-/-. Compared to cPLA2α+/+ Tg-AD mice, the amyloid plaque formation was significantly downregulated in the brain of cPLA2α+/- Tg-AD mice, but not in cPLA2α-/- Tg-AD mice. The reactive gliosis were also significantly downregulated in both cPLA2α+/- and cPLA2α-/- Tg-AD mouse lines. The paradoxical effects of cPLA2α on the amyloid plaques reveal a complex role of cPLA2α in pathogenesis of AD and could be a potential target for prevention and treatment of AD.

YY-1224, a terpene trilactone-strengthened Ginkgo biloba, attenuates neurodegenerative changes induced by ß-amyloid (1-42) or double transgenic overexpression of APP and PS1 via inhibition of cyclooxygenase-2.

BACKGROUND: Ginkgo biloba has been reported to possess free radical-scavenging antioxidant activity and anti-inflammatory properties. In our pilot study, YY-1224, a terpene trilactone-strengthened extract of G. biloba, showed anti-inflammatory, neurotrophic, and antioxidant effects. RESULTS: We investigated the pharmacological potential of YY-1224 in ß-amyloid (Aß) (1-42)-induced memory impairment using cyclooxygenase-2 (COX-2) knockout (-/-) and APPswe/PS1dE9 transgenic (APP/PS1 Tg) mice. Repeated treatment with YY-1224 significantly attenuated Aß (1-42)-induced memory impairment in COX-2 (+/+) mice, but not in COX-2 (-/-) mice. YY-1224 significantly attenuated Aß (1-42)-induced upregulation of platelet-activating factor (PAF) receptor gene expression, reactive oxygen species, and pro-inflammatory factors. In addition, YY-1224 significantly inhibited Aß (1-42)-induced downregulation of PAF-acetylhydrolase-1 (PAF-AH-1) and peroxisome proliferator-activated receptor γ (PPARγ) gene expression. These changes were more pronounced in COX-2 (+/+) mice than in COX-2 (-/-) mice. YY-1224 significantly attenuated learning impairment, Aß deposition, and pro-inflammatory microglial activation in APP/PS1 Tg mice, whereas it significantly enhanced PAF-AH and PPARγ expression. A preferential COX-2 inhibitor, meloxicam, did not affect the pharmacological activity by YY-1224, suggesting that the COX-2 gene is a critical mediator of the neuroprotective effects of YY-1224. The protective activity of YY-1224 appeared to be more efficacious than a standard G. biloba extract (Gb) against Aß insult. CONCLUSIONS: Our results suggest that the protective effects of YY-1224 against Aß toxicity may be associated with its PAF antagonistic- and PPARγ agonistic-potential as well as inhibition of the Aß-mediated pro-inflammatory switch of microglia phenotypes through suppression of COX-2 expression.

The expression of presenilin 1 enhances carcinogenesis and metastasis in gastric cancer.

Presenilin 1 (PS-1, encoded by PSEN1) is a part of the gamma- (γ-) secretase complex. Mutations in PSEN1 cause the majority of cases of familial Alzheimer's disease (FAD). Although in recent years PS-1 has been implicated as a tumor enhancer in various cancers, nothing is known regarding its role in gastric cancer (GC). In the present study, we investigate the role and clinical significance of PS-1 in GC. We observed that PS-1 was significantly upregulated and amplified in GC tissues and cell lines, and its aberrant expression was positively correlated with lymph node metastasis and with poor overall survival. Furthermore, PS-1 promoted tumor invasion and metastasis of GC both in vitro and vivo without affecting the proliferation of GC cells (MGC-803 and MKN-45). The results of treatment with the γ-secretase inhibitor DAPT were consistent with the outcomes of PS-1 silencing. PS-1/γ-secretase cleaves E-cadherin and releases its bound protein partner, ß-catenin, from the actin cytoskeleton, thereby allowing it to translocate into the nucleus and to activate the TCF/LEF-1 transcriptional activator, which may promote GC invasion and metastasis.In conclusion, PS-1 promotes invasion and metastasis in GC and may represent a novel prognostic biomarker and potential therapeutic target for GC treatment.

miR-193a-3p regulation of chemoradiation resistance in oesophageal cancer cells via the PSEN1 gene.

Chemoradiation therapy is an important component of the curative treatment for oesophageal carcinomas. These therapeutic effects are prevented in patients according to radioresistance and multi-drug resistance, and the cause of such resistance remains unclear. In this study, we identified the role of miR-193a-3p in modulating the radioresistance and chemoresistance of oesophageal cancer cells. We found that KYSE150 and KYSE410 cells could be characterized as relatively radiation-sensitive and radiation-resistant cells, respectively. Similarly, KYSE150 and KYSE410 cells were found to be chemosensitive and chemoresistant, respectively. Over-expression of miR-193a-3p increased the radioresistance and chemoresistance of oesophageal squamous cell carcinoma (ESCC) cells. In contrast, the down-regulation of miR-193a-3p decreased the radioresistance and chemoresistance of ESCC cells. In addition, miR-193a-3p inducing DNA damage has also been demonstrated through measuring the level of gamma-H2AX associated with miR-193a-3p. Moreover, a small interfering RNA(siRNA)-induced repression of the PSEN1 gene had an effect similar to that of miR-193a-3p up-regulation. The above processes also inhibited oesophageal cancer cells apoptosis. These findings suggest that miR-193a-3p contributes to the radiation and chemotherapy resistance of oesophageal carcinoma by down-regulating PSEN1. Thus, miR-193a-3p and PSEN1 might be potential biomarkers for chemoradiation resistant cancers.

Cellular FLICE-like Inhibitory Protein (c-FLIP) and PS1-associated Protein (PSAP) Mediate Presenilin 1-induced γ-Secretase-dependent and -independent Apoptosis, Respectively.

Presenilin 1 (PS1) has been implicated in apoptosis; however, its mechanism remains elusive. We report that PS1-induced apoptosis was associated with cellular FLICE-like inhibitory protein (c-FLIP) turnover and that γ-secretase inhibitor blocked c-FLIP turnover and also partially blocked PS1-induced apoptosis. A complete inhibition of PS1-induced apoptosis was achieved by knockdown of PS1-associated protein (PSAP), a mitochondrial proapoptotic protein that forms a complex with Bax upon induction of apoptosis, in the presence of γ-secretase inhibitor. PS1-induced apoptosis was partially inhibited by knockdown of caspase-8, Fas-associated protein with death domain (FADD), or Bid. However, knockdown of Bax or overexpression of Bcl-2 resulted in complete inhibition of PS1-induced apoptosis. These data suggest that PS1 induces apoptosis through two pathways: the γ-secretase-dependent pathway mediated by turnover of c-FLIP and the γ-secretase-independent pathway mediated by PSAP-Bax complex formation. These two pathways converge on Bax to activate mitochondria-dependent apoptosis. These findings provide new insight into the mechanisms by which PS1 is involved in apoptosis and the mechanism by which PS1 exerts its pathogenic effects. In addition, our results suggest that PS2 induces apoptosis through a pathway that is different from that of PS1.

The miR-193a-3p regulated PSEN1 gene suppresses the multi-chemoresistance of bladder cancer.

Chemoresistance prevents the curative cancer therapy, our understanding of which remains inadequate. Among the differentially expressed genes between the chemosensitive (5637) and chemoresistant (H-bc) bladder cancer cell lines, the expression level of the PSEN1 gene (presenilin 1), a key component of the γ-secretase, is negatively correlated with chemoresistance. A small interfering RNA mediated repression of the PSEN1 gene suppresses cell apoptosis and de-sensitizes 5637 cells, while overexpression of the presenilin 1 sensitizes H-bc cells to the drug-triggered cell death. As a direct target of microRNA-193a-3p that promotes the multi-chemoresistance of the bladder cancer cell, PSEN1 acts as an important executor for the microRNA-193a-3p's positive impact on the multi-chemoresistance of bladder cancer, probably via its activating effect on DNA damage response pathway. In addition to the mechanistic insights, the key players in this microRNA-193a-3p/PSEN1 axis are likely the diagnostic and/or therapeutic targets for an effective chemotherapy of bladder cancer.

Notch2 activation is protective against anticancer effects of zerumbone in human breast cancer cells.

We showed previously that zerumbone (ZER), a sesquiterpene isolated from subtropical ginger, inhibited in vitro (MCF-7 and MDA-MB-231cells) and in vivo (MDA-MB-231 cells) growth of human breast cancer cells in association with apoptosis induction. Here, we investigated the role of Notch receptors in anticancer effects of ZER (cell migration inhibition and apoptosis induction) using breast cancer cells. Western blotting was performed to determine protein expression changes. Effect of ZER on transcriptional activity of Notch was assessed by luciferase reporter assays. Transfection with small hairpin RNA or small interfering RNA was performed for knockdown of Notch2 or Presenilin-1 protein. Cell migration and apoptosis were quantitated by Boyden chamber assay and flow cytometry, respectively. Exposure of MDA-MB-231, MCF-7, and SUM159 cells to ZER resulted in increased cleavage of Notch2 in each cell line. On the other hand, levels of cleaved Notch1 and Notch4 proteins were decreased following ZER treatment. Increased cleavage of Notch2 in ZER-treated cells was accompanied by induction of Presenilin-1 protein and transcriptional activation of Notch. Inhibition of cell migration as well as apoptosis induction resulting from ZER exposure was significantly augmented by knockdown of Notch2 protein. ZER-mediated cleavage of Notch2 protein in MDA-MB-231 cells was markedly attenuated upon RNA interference of Presenilin-1. Knockdown of Presenilin-1 protein also resulted in escalation of ZER-induced apoptosis. The present study indicates that Notch2 activation by ZER inhibits its proapoptotic and anti-migratory response at least in breast cancer cells.

An ancestral non-proteolytic role for presenilin proteins in multicellular development of the social amoeba Dictyostelium discoideum.

Mutations in either of two presenilin genes can cause familial Alzheimer's disease. Presenilins have both proteolysis-dependent functions, as components of the γ-secretase complex, and proteolysis-independent functions in signalling. In this study, we investigate a conserved function of human presenilins in the development of the simple model organism Dictyostelium discoideum. We show that the block in Dictyostelium development caused by the ablation of both Dictyostelium presenilins is rescued by the expression of human presenilin 1, restoring the terminal differentiation of multiple cell types. This developmental role is independent of proteolytic activity, because the mutation of both catalytic aspartates does not affect presenilin ability to rescue development, and the ablation of nicastrin, a γ-secretase component that is crucial for proteolytic activity, does not block development. The role of presenilins during Dictyostelium development is therefore independent of their proteolytic activity. However, presenilin loss in Dictyostelium results in elevated cyclic AMP (cAMP) levels and enhanced stimulation-induced calcium release, suggesting that presenilins regulate these intracellular signalling pathways. Our data suggest that presenilin proteins perform an ancient non-proteolytic role in regulating intracellular signalling and development, and that Dictyostelium is a useful model for analysing human presenilin function.

The effects of dietary restriction and aging on amyloid precursor protein and presenilin-1 mRNA and protein expression in rat brain.

The objective of this study was to examine the effects of aging and long-term dietary restriction (DR) on the level of amyloid precursor protein (APP) and presenilin-1 (PS-1), proteins that are critically involved in Alzheimer's disease. Changes in mRNA and protein expression were assessed by real-time PCR and western blot analysis during aging and long-term DR in the cortex and hippocampus of 6-, 12-, 18-, and 24-month-old rats. Prominent regional changes in expression were observed in response to aging and DR. Although the hippocampus displayed significant alterations in APP mRNA and protein expression and no significant changes in PS-1 expression, an opposite pattern was observed in the cortex. DR counteracted the age-related changes in APP mRNA expression in both structures of old animals. The observed DR-induced increase in mRNA levels in the hippocampus was accompanied by an increase in the level of full-length protein APP. These results indicate that although both structures are very sensitive to aging, a specific spatial pattern of changes in APP and PS-1 occurs during aging. Furthermore, these findings provide evidence that DR can affect APP and PS-1 expression in a manner consistent with its proposed 'antiaging' effect.

Amyloid beta1₋42 (Aß42) up-regulates the expression of sortilin via the p75(NTR)/RhoA signaling pathway.

Sortilin, a Golgi sorting protein and a member of the VPS10P family, is the co-receptor for proneurotrophins, regulates protein trafficking, targets proteins to lysosomes, and regulates low density lipoprotein metabolism. The aim of this study was to investigate the expression and regulation of sortilin in Alzheimer's disease (AD). A significantly increased level of sortilin was found in human AD brain and in the brains of 6-month-old swedish-amyloid precursor protein/PS1dE9 transgenic mice. Aß42 enhanced the protein and mRNA expression levels of sortilin in a dose- and time-dependent manner in SH-SY5Y cells, but had no effect on sorLA. In addition, proBDNF also significantly increased the protein and mRNA expression of sortilin in these cells. The recombinant extracellular domain of p75(NTR) (P75ECD-FC), or the antibody against the extracellular domain of p75(NTR), blocked the up-regulation of sortilin induced by Amyloid-ß protein (Aß), suggesting that Aß42 increased the expression level of sortilin and mRNA in SH-SY5Y via the p75(NTR) receptor. Inhibition of ROCK, but not Jun N-terminal kinase, suppressed constitutive and Aß42-induced expression of sortilin. In conclusion, this study shows that sortilin expression is increased in the AD brain in human and mice and that Aß42 oligomer increases sortilin gene and protein expression through p75(NTR) and RhoA signaling pathways, suggesting a potential physiological interaction of Aß42 and sortilin in Alzheimer's disease.

Trans-dominant negative effects of pathogenic PSEN1 mutations on γ-secretase activity and Aß production.

Mutations in the PSEN1 gene encoding Presenilin-1 (PS1) are the predominant cause of familial Alzheimer's disease (FAD), but the underlying mechanisms remain unresolved. To reconcile the dominant action of pathogenic PSEN1 mutations with evidence that they confer a loss of mutant protein function, we tested the hypothesis that PSEN1 mutations interfere with γ-secretase activity in a dominant-negative manner. Here, we show that pathogenic PSEN1 mutations act in cis to impair mutant PS1 function and act in trans to inhibit wild-type PS1 function. Coexpression of mutant and wild-type PS1 at equal gene dosage in presenilin-deficient mouse embryo fibroblasts resulted in trans-dominant-negative inhibition of wild-type PS1 activity, suppressing γ-secretase-dependent cleavage of APP and Notch. Surprisingly, mutant PS1 could stimulate production of Aß42 by wild-type PS1 while decreasing its production of Aß40. Mutant and wild-type PS1 efficiently coimmunoprecipitated, suggesting that mutant PS1 interferes with wild-type PS1 activity via physical interaction. These results support the conclusion that mutant PS1 causes wild-type PS1 to adopt an altered conformation with impaired catalytic activity and substrate specificity. Our findings reveal a novel mechanism of action for pathogenic PSEN1 mutations and suggest that dominant-negative inhibition of presenilin activity plays an important role in FAD pathogenesis.

Presenilin 1 and 2 are expressed differentially in the cerebral cortex of mice during development.

Presenilin (PS) 1 and PS2 are multi-pass transmembrane proteins involved in vital brain functions. Studies using transgenic or conditional knockout models show that PS1 is implicated in crucial brain developmental processes. Conversely, PS2 knockout mice do not exhibit any abnormality in the brain morphology, suggesting that PS2 may not be involved in brain development. However, there is no holistic information available for endogenous expression of PS during brain development. Therefore, we have examined the distribution and expression profile of PS1 and PS2 mRNA and protein in the cerebral cortex of prenatal, neonatal and postnatal mice. The results revealed that the distribution and expression profile of PS1 and PS2 mRNA varied significantly in the cerebral cortex during development. In prenatal stages, both PS1 and PS2 mRNA showed high expression at embryonic day (E) 12.5 and downregulation at E18.5. Postnatally, PS1 mRNA showed upregulation from postnatal day 0 (P0) to P45 and thereafter reduction at 20 weeks, but PS2 mRNA showed no significant alteration. However, they did not exhibit any significant regional variation except at E18.5, when PS2 showed reduction in temporal and medial temporal lobes as compared to frontal and parietal lobes. Furthermore, PS1 showed significant change in protein expression similar to its mRNA profile. However, PS2 protein expression did not correspond to its mRNA; it was highest at E12.5, downregulated up to P20 and then upregulated at P45 and 20 weeks. Taken together, our study demonstrates for the first time that the distribution and expression profile of PS2 is different from PS1 in the mouse cerebral cortex during development.

Intraperitoneal injection of JNK-specific inhibitor SP600125 inhibits the expression of presenilin-1 and Notch signaling in mouse brain without induction of apoptosis.

Presenilin-1 (PS1) is a multifunctional protein involved in many cellular functions including the processing of type 1 membrane proteins such as ß-amyloid precursor protein (APP) and Notch 1 receptor. PS1 acts as the catalytic subunit of the γ-secretase complex, and participates in Notch 1 processing to release Notch intracellular domain (NICD) in the cytoplasm. NICD subsequently migrates to the nucleus and causes Notch signaling by increasing the expression of the Hes1 gene. We have previously shown that inhibition of basal activity of c-jun-NH2-terminal kinase (JNK) with JNK-specific inhibitor SP600125 represses the expression of PS1 and γ-secretase activity by increasing p53 level in SK-N-SH cell line in vitro (Lee and Das, 2008, 2010). However, it is largely unknown whether PS1 can be effectively suppressed in vivo in adult mouse brains. In this report we showed that intraperitoneal (i.p) injection of JNK-specific inhibitor SP600125 decreased p-JNK level, and reduced PS1 expression by increasing p53 level in adult mouse brains. We also showed that suppression of PS1 expression by SP600125 reduced γ-secretase activity which decreased Notch 1 processing to reduce NICD in mouse brains. Furthermore, inhibition of Notch 1 processing by SP600125 decreased Notch 1 signaling by reducing the expression of the NICD target Hes1 gene in mouse brains without induction of apoptosis. These results provide insights for further study on PS1-mediated reduction of Notch 1 and APP processing for the treatment of Alzheimer's disease.

Impaired TrkB receptor signaling contributes to memory impairment in APP/PS1 mice.

Brain-derived neurotrophic factor (BDNF) plays an important role in neuronal plasticity, learning, and memory. Levels of BDNF and its main receptor TrkB (TrkB.TK) have been reported to be decreased while the levels of the truncated TrkB (TrkB.T1) are increased in Alzheimer's disease. We show here that incubation with amyloid-ß increased TrkB.T1 receptor levels and decreased TrkB.TK levels in primary neurons. In vivo, APPswe/PS1dE9 transgenic mice (APdE9) showed an age-dependent relative increase in cortical but not hippocampal TrkB.T1 receptor levels compared with TrkB.TK. To investigate the role of TrkB isoforms in Alzheimer's disease, we crossed AP mice with mice overexpressing the truncated TrkB.T1 receptor (T1) or the full-length TrkB.TK isoform. Overexpression of TrkB.T1 in APdE9 mice exacerbated their spatial memory impairment while the overexpression of TrkB.TK alleviated it. These data suggest that amyloid-ß changes the ratio between TrkB isoforms in favor of the dominant-negative TrkB.T1 isoform both in vitro and in vivo and supports the role of BDNF signaling through TrkB in the pathophysiology and cognitive deficits of Alzheimer's disease.