Loss of Ataxin-1 Potentiates Alzheimer's Pathogenesis by Elevating Cerebral BACE1 Transcription.

Expansion of CAG trinucleotide repeats in ATXN1 causes spinocerebellar ataxia type 1 (SCA1), a neurodegenerative disease that impairs coordination and cognition. While ATXN1 is associated with increased Alzheimer's disease (AD) risk, CAG repeat number in AD patients is not changed. Here, we investigated the consequences of ataxin-1 loss of function and discovered that knockout of Atxn1 reduced CIC-ETV4/5-mediated inhibition of Bace1 transcription, leading to increased BACE1 levels and enhanced amyloidogenic cleavage of APP, selectively in AD-vulnerable brain regions. Elevated BACE1 expression exacerbated Aß deposition and gliosis in AD mouse models and impaired hippocampal neurogenesis and olfactory axonal targeting. In SCA1 mice, polyglutamine-expanded mutant ataxin-1 led to the increase of BACE1 post-transcriptionally, both in cerebrum and cerebellum, and caused axonal-targeting deficit and neurodegeneration in the hippocampal CA2 region. These findings suggest that loss of ataxin-1 elevates BACE1 expression and Aß pathology, rendering it a potential contributor to AD risk and pathogenesis.

Inhibition of death-associated protein kinase 1 attenuates the phosphorylation and amyloidogenic processing of amyloid precursor protein.

Extracellular deposition of amyloid-beta (Aß) peptide, a metabolite of sequential cleavage of amyloid precursor protein (APP), is a critical step in the pathogenesis of Alzheimer's disease (AD). While death-associated protein kinase 1 (DAPK1) is highly expressed in AD brains and its genetic variants are linked to AD risk, little is known about the impact of DAPK1 on APP metabolism and Aß generation. In this study, we demonstrated a novel effect of DAPK1 in the regulation of APP processing using cell culture and mouse models. DAPK1, but not its kinase deficient mutant (K42A), significantly increased human Aß secretion in neuronal cell culture models. Moreover, knockdown of DAPK1 expression or inhibition of DAPK1 catalytic activity significantly decreased Aß secretion. Furthermore, DAPK1, but not K42A, triggered Thr668 phosphorylation of APP, which may initiate and facilitate amyloidogenic APP processing leading to the generation of Aß. In Tg2576 APPswe-overexpressing mice, knockout of DAPK1 shifted APP processing toward non-amyloidogenic pathway and decreased Aß generation. Finally, in AD brains, elevated DAPK1 levels showed co-relation with the increase of APP phosphorylation. Combined together, these results suggest that DAPK1 promotes the phosphorylation and amyloidogenic processing of APP, and that may serve a potential therapeutic target for AD.

FE65 and FE65L1 amyloid precursor protein-binding protein compound null mice display adult-onset cataract and muscle weakness.

FE65 and FE65L1 are cytoplasmic adaptor proteins that bind a variety of proteins, including the amyloid precursor protein, and that mediate the assembly of multimolecular complexes. We previously reported that FE65/FE65L1 double knockout (DKO) mice display disorganized laminin in meningeal fibroblasts and a cobblestone lissencephaly-like phenotype in the developing cortex. Here, we examined whether loss of FE65 and FE65L1 causes ocular and muscular deficits, 2 phenotypes that frequently accompany cobblestone lissencephaly. Eyes of FE65/FE65L1 DKO mice develop normally, but lens degeneration becomes apparent in young adult mice. Abnormal lens epithelial cell migration, widespread small vacuole formation, and increased laminin expression underneath lens capsules suggest impaired interaction between epithelial cells and capsular extracellular matrix in DKO lenses. Cortical cataracts develop in FE65L1 knockout (KO) mice aged 16 months or more but are absent in wild-type or FE65 KO mice. FE65 family KO mice show attenuated grip strength, and the nuclei of DKO muscle cells frequently locate in the middle of muscle fibers. These findings reveal that FE65 and FE65L1 are essential for the maintenance of lens transparency, and their loss produce phenotypes in brain, eye, and muscle that are comparable to the clinical features of congenital muscular dystrophies in humans.

Amyloid beta a4 precursor protein-binding family B member 1 (FE65) interactomics revealed synaptic vesicle glycoprotein 2A (SV2A) and sarcoplasmic/endoplasmic reticulum calcium ATPase 2 (SERCA2) as new binding proteins in the human brain.

FE65 is a cytosolic adapter protein and an important binding partner of amyloid precursor protein. Dependent on Thr668 phosphorylation in amyloid precursor protein, which influences amyloidogenic amyloid precursor protein processing, FE65 undergoes nuclear translocation, thereby transmitting a signal from the cell membrane to the nucleus. As this translocation may be relevant in Alzheimer disease, and as FE65 consists of three protein-protein interaction domains able to bind and affect a variety of other proteins and downstream signaling pathways, the identification of the FE65 interactome is of central interest in Alzheimer disease research. In this study, we identified 121 proteins as new potential FE65 interacting proteins in a pulldown/mass spectrometry approach using human post-mortem brain samples as protein pools for recombinantly expressed FE65. Co-immunoprecipitation assays further validated the interaction of FE65 with the candidates SV2A and SERCA2. In parallel, we investigated the whole cell proteome of primary hippocampal neurons from FE65/FE65L1 double knockout mice. Notably, the validated FE65 binding proteins were also found to be differentially abundant in neurons derived from the FE65 knockout mice relative to wild-type control neurons. SERCA2 is an important player in cellular calcium homeostasis, which was found to be up-regulated in double knockout neurons. Indeed, knock-down of FE65 in HEK293T cells also evoked an elevated sensitivity to thapsigargin, a stressor specifically targeting the activity of SERCA2. Thus, our results suggest that FE65 is involved in the regulation of intracellular calcium homeostasis. Whereas transfection of FE65 alone caused a typical dot-like phenotype in the nucleus, co-transfection of SV2A significantly reduced the percentage of FE65 dot-positive cells, pointing to a possible role for SV2A in the modulation of FE65 intracellular targeting. Given that SV2A has a signaling function at the presynapse, its effect on FE65 intracellular localization suggests that the SV2A/FE65 interaction might play a role in synaptic signal transduction.

Analysis of brain region-specific mRNA synthesis and stability by utilizing adult mouse brain slice culture.

Utilization of live animals for mechanistic study is challenging yet pivotal to elucidate pathogenesis of neurological diseases. Here, we present a protocol that employs cultured brain slices derived from adult mice to examine mRNA metabolism. We describe the preparation of acute brain slices and the treatments of RNA synthesis inhibitor and nucleotide analog to examine the effects of ataxin-1 loss-of-function on Bace1 mRNA stability and transcription in cortex. This protocol also includes electrophysiological recording of spontaneous neuronal activity in hippocampus. For complete details on the use and execution of this protocol, please refer to Suh et al. (2019).

FE65 proteins regulate NMDA receptor activation-induced amyloid precursor protein processing.

Amyloid precursor protein (APP) family members and their proteolytic products are implicated in normal nervous system function and Alzheimer's disease pathogenesis. APP processing and Aß secretion are regulated by neuronal activity. Various data suggest that NMDA receptor (NMDAR) activity plays a role in both non-amyloidogenic and amyloidogenic APP processing depending on whether synaptic or extrasynaptic NMDARs are activated, respectively. The APP-interacting FE65 proteins modulate APP trafficking and processing in cell lines, but little is known about their contribution to APP trafficking and processing in neurons, either in vivo or in vitro. In this study, we examined the contribution of the FE65 protein family to APP trafficking and processing in WT and FE65/FE65L1 double knockout neurons under basal conditions and following NMDAR activation. We report that FE65 proteins facilitate neuronal Aß secretion without affecting APP fast axonal transport to pre-synaptic terminals. In addition, FE65 proteins facilitate an NMDAR-dependent non-amyloidogenic APP processing pathway. Generation of high-molecular weight (HMW) species bearing an APP C-terminal epitope was also observed following NMDAR activation. These HMW species require proteasomal and calpain activities for their accumulation. Recovery of APP polypeptide fragments from electroeluted HMW species having molecular weights consistent with calpain I cleavage of APP suggests that HMW species are complexes formed from APP metabolic products. Our results indicate that the FE65 proteins contribute to physiological APP processing and accumulation of APP metabolic products resulting from NMDAR activation.

Potential late-onset Alzheimer's disease-associated mutations in the ADAM10 gene attenuate {alpha}-secretase activity.

ADAM10, a member of a disintegrin and metalloprotease family, is an alpha-secretase capable of anti-amyloidogenic proteolysis of the amyloid precursor protein. Here, we present evidence for genetic association of ADAM10 with Alzheimer's disease (AD) as well as two rare potentially disease-associated non-synonymous mutations, Q170H and R181G, in the ADAM10 prodomain. These mutations were found in 11 of 16 affected individuals (average onset age 69.5 years) from seven late-onset AD families. Each mutation was also found in one unaffected subject implying incomplete penetrance. Functionally, both mutations significantly attenuated alpha-secretase activity of ADAM10 (>70% decrease), and elevated Abeta levels (1.5-3.5-fold) in cell-based studies. In summary, we provide the first evidence of ADAM10 as a candidate AD susceptibility gene, and report two potentially pathogenic mutations with incomplete penetrance for late-onset familial AD.

Hypoxic ischemia and proteasome dysfunction alter tau isoform ratio by inhibiting exon 10 splicing.

Alternative splicing of tau exon 10 influences microtubule assembly and stability during development and in pathological processes of the central nervous system. However, the cellular events that underlie this pre-mRNA splicing remain to be delineated. In this study, we examined the possibility that ischemic injury, known to change the cellular distribution and expression of several RNA splicing factors, alters the splicing of tau exon 10. Transient occlusion of the middle cerebral artery reduced tau exon 10 inclusion in the ischemic cortical area within 12 h, resulting in the induction of three-repeat (3R) tau in cortical neurons. Ubiquitinated protein aggregates and reduced proteasome activity were also observed. Administration of proteasome inhibitors such as MG132, proteasome inhibitor I and lactacystin reduced tau exon 10 splicing in cortical cell cultures. Decreased levels of Tra2beta, an RNA splicing factor responsible for tau exon 10 inclusion, were detected both in cortical cell cultures exposed to MG132 and in cerebral cortex after ischemic injury. Taken together, these findings suggest that transient focal cerebral ischemia reduces tau exon 10 splicing through a mechanism involving proteasome-ubiquitin dysfunction and down-regulation of Tra2beta.

Tissue inhibitor of metalloproteinases-3 (TIMP-3) expression is increased during serum deprivation-induced neuronal apoptosis in vitro and in the G93A mouse model of amyotrophic lateral sclerosis: a potential modulator of Fas-mediated apoptosis.

Cortical neurons deprived of serum undergo apoptosis that is sensitive to inhibitors of macromolecule synthesis. Proteomic analysis revealed differential expression of 49 proteins in cortical neurons 8 h after serum deprivation. Tissue inhibitor of metalloproteinases-3 (TIMP-3), a pro-apoptotic protein in various cancer cells, was increased during serum deprivation-induced apoptosis (SDIA), but not during necrosis induced by excitotoxicity or oxidative stress. Levels of TIMP-3 were markedly increased in degenerating motor neurons in a transgenic model of familial amyotrophic lateral sclerosis. The TIMP-3 expression was accompanied by increase in Fas-FADD interaction, activated caspase-8, and caspase-3 during SDIA and in vulnerable spinal cord of the ALS mouse. SDIA and activation of the Fas pathway were prevented by addition of an active MMP-3. Timp-3 deletion by RNA interference attenuated SDIA in N2a cells. These findings provide evidence that TIMP-3 is an upstream mediator of neuronal apoptosis and likely contributes to neuronal loss in neurodegenerative diseases such as amyotrophic lateral sclerosis.

2-Acetylaminofluorene inhibits interleukin-1beta production in LPS-stimulated macrophages by blocking NF-kappaB/Rel activation.

In the present study, we demonstrate the inhibitory effect of 2-acetylaminofluorene (AAF) on interleukin-1beta (IL-1beta) gene expression in lipopolysaccharide (LPS)-stimulated macrophages. Acetylaminofluorene inhibited IL-1 production in LPS-stimulated splenic macrophages and RAW 264.7 cells. Additionally, AAF also suppressed LPS-induced mRNA expression of IL-1beta in macrophages. To further characterize the molecular mechanism responsible for AAF-mediated suppression of IL-1beta, we investigated the effect of AAF on LPS-mediated activation of transcription factors, such as NF-kappaB, AP-1, CRE and NF-IL6, which are known to be important for LPS-induced gene expression of IL-1beta. Treatment of AAF caused a dose-related inhibition of LPS-induced NF-kappaB/Rel transcriptional activation, while the transcriptional activation of AP-1, CRE and NF-IL6 was not affected by AAF. Furthermore, LPS-induced NF-kappaB/Rel DNA binding was also suppressed by AAF treatment. These results suggest that AAF inhibits IL-1beta gene expression by blocking NF-kappaB/Rel activation.

A multi-center, late phase II clinical trial of Genexol (paclitaxel) and cisplatin for patients with advanced gastric cancer.

Because of unsatisfactory treatment results with 5-fluorouracil-based palliative combination chemotherapy for advanced gastric cancer, the evaluation of new effective and well-tolerated regimens is needed. We conducted a multi-center, late phase II trial to evaluate the efficacy and safety of Genexol (a paclitaxel formulation) combined chemotherapy with cisplatin in patients with previously untreated metastatic or unresectable measurable gastric adenocarcinoma. All patients were between 18 and 75 years of age, with an Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1, and had an adequate baseline major organ function. Genexol 175 mg/m(2) was administered as a 3-h infusion, followed by cisplatin 75 mg/m(2) as an intravenous infusion day 1, once every 3 weeks. Thirty-six patients were enrolled from 7 hospitals between November 2002 and April 2003. Of these, 33 patients were assessable for efficacy and 35 for toxicity. Based on an intent-to-treat analysis, 16 patients (46%) achieved a partial response, 7 (20%) stable disease, and 10 (29%) progressed, giving an overall response rate of 46% (95% CI, 29% to 63%). The median duration of response was 7.1 months (95% CI, 6.3 to 7.9 months), and the median time to progression and overall survival were 4.9 months (95% CI, 3.2 to 6.6 months) and 13.8 months (95% CI, 10.8 to 16.8 months), respectively. The major toxicity was neutropenia, with grade 3/4 intensity in 10 patients (29%). However, no febrile neutropenia occurred, and non-hematologic toxicity was usually mild. Grade 3/4 toxicities included nausea (9% of the patients), vomiting (9%), peripheral neuropathy (9%), alopecia (9%), and myalgia (6%). In conclusion, the combination of Genexol and cisplatin was found to be an active and relatively well-tolerated regimen for the treatment of advanced gastric carcinoma.

ADAM10 missense mutations potentiate ß-amyloid accumulation by impairing prodomain chaperone function.

The generation of Aß, the main component of senile plaques in Alzheimer's disease (AD), is precluded by α-secretase cleavage within the Aß domain of the amyloid precursor protein (APP). We identified two rare mutations (Q170H and R181G) in the prodomain of the metalloprotease, ADAM10, that cosegregate with late-onset AD (LOAD). Here, we addressed the pathogenicity of these mutations in transgenic mice expressing human ADAM10 in brain. In Tg2576 AD mice, both mutations attenuated α-secretase activity of ADAM10 and shifted APP processing toward ß-secretase-mediated cleavage, while enhancing Aß plaque load and reactive gliosis. We also demonstrated ADAM10 expression potentiates adult hippocampal neurogenesis, which is reduced by the LOAD mutations. Mechanistically, both LOAD mutations impaired the molecular chaperone activity of ADAM10 prodomain. Collectively, these findings suggest that diminished α-secretase activity, owing to LOAD ADAM10 prodomain mutations, leads to AD-related pathology, strongly supporting ADAM10 as a promising therapeutic target for this devastating disease.

Induction of the unfolded protein response and cell death pathway in Alzheimer's disease, but not in aged Tg2576 mice.

The endoplasmic reticulum (ER) stress results from disrupted protein folding triggered by protein mutation or oxidation, reduced proteasome activity, and altered Ca2+ homeostasis. ER stress is accompanied by activation of the unfolded protein response (UPR) and cell death pathway. We examined if the UPR and cell death pathway would be activated in Alzheimer's disease (AD). RT-PCR experiments revealed increased splicing of X-box binding protein-1 (XBP-1), an UPR transcription factor, in AD compared with age-matched control. Among target genes of XBP-1, expression of protein disulfide isomerase (PDI), but not glucose-regulated protein 78 (GRP78), was increased in AD, suggesting disturbed activation of the UPR in AD. C/EBP homologous protein (CHOP), caspase-3, caspase-4, and caspase-12, downstream mediators of cell death pathway, were activated in AD. Neither the UPR nor cell death pathway was induced in aged Tg2576 mice, a transgenic mouse model of Alzheimer's disease that reveals both plaque pathology and some cognitive deficits. The present study suggests that disturbed induction of the UPR and activation of the pro-apoptotic proteins contribute to neuropathological process in AD irrespective of amyloid beta and senile plaque.

Induction and attenuation of neuronal apoptosis by proteasome inhibitors in murine cortical cell cultures.

Evidence has accumulated showing that pharmacological inhibition of proteasome activity can both induce and prevent neuronal apoptosis. We tested the hypothesis that these paradoxical effects of proteasome inhibitors depend on the degree of reduced proteasome activity and investigated underlying mechanisms. Murine cortical cell cultures exposed to 0.1 microM MG132 underwent widespread neuronal apoptosis and showed partial inhibition of proteasome activity down to 30-50%. Interestingly, administration of 1-10 microM MG132 almost completely blocked proteasome activity but resulted in reduced neuronal apoptosis. Similar results were produced in cortical cultures exposed to other proteasome inhibitors, proteasome inhibitor I and lactacystin. Administration of 0.1 microM MG132 led to activation of a mitochondria-dependent apoptotic signaling cascade involving cytochrome c, caspase-9, caspase-3 and degradation of tau protein; such activation was markedly reduced with 10 microM MG132. High doses of MG132 prevented the degradation of inhibitor of apoptosis proteins (IAPs) cIAP and X chromosome-linked IAP, suggesting that complete blockade of proteasome activity interferes with progression of apoptosis. In support of this, addition of high doses of proteasome inhibitors attenuated apoptosis of cortical neurons deprived of serum. Taken together, the present results indicate that inhibition of proteasome activity can induce or prevent neuronal cell apoptosis through regulation of mitochondria-mediated apoptotic pathways and IAPs.

Antagonism of aryl hydrocarbon receptor-dependent induction of CYP1A1 and inhibition of IgM expression by di-ortho-substituted polychlorinated biphenyls.

Halogenated aromatic hydrocarbons (HAHs) are ubiquitous environment contaminants that produce many of their toxic effects by binding to the aryl hydrocarbon receptor (AhR). However, several investigations have demonstrated that certain polychlorinated biphenyl (PCB) congeners, principally di-ortho-chlorinated PCB congeners, or mixtures containing multiple di-ortho-chlorinated PCBs, inhibit AhR-mediated responses induced by other toxic HAHs. Most relevant to the present study are past reports demonstrating antagonism by these uniquely acting PCB congeners on AhR agonist-mediated inhibition of humoral immune responses. The mechanism responsible for antagonism of AhR agonists by certain PCBs is presently unknown. The present study evaluated the antagonist activity of several di-ortho-substituted PCB congeners [PCB47 (2,2',4,4'), PCB52 (2,2',5,5'), PCB128 (2,2',3,3',4,4'), and PCB153 (2,2',4,4',5,5')] when present in combination with AhR agonists [TCDD (2,3,7,8,-tetrachlorodibenzo-p-dioxin), PCB126 (3,3',4,4',5), and PCB77 (3,3',4,4')] on CYP1A1 induction and inhibition of lipopolysaccharide (LPS)-induced immunoglobulin production in the CH12.LX B cell line. In contrast to non-ortho-substituted PCB (PCB77), which showed additive effects on CYP1A1 induction in combination with TCDD, all of the di-ortho-substituted PCBs examined produced antagonism. Di-ortho-substituted PCB (PCB52) also antagonized TCDD- or PCB126- mediated inhibition of IgM secretion and immunoglobulin heavy chain mRNA expression in the LPS-activated B cells. In addition, PCB52 inhibited TCDD-induced AhR DNA binding to a dioxin-responsive element. Collectively, these results suggest that the mechanism responsible for antagonism by di-ortho-substituted PCB congeners of AhR agonist-mediated CYP1A1 induction and inhibition of antibody responses in B cells occurs through interference with agonist activation of the cytosolic AhR complex.

Polychlorinated biphenyl-induced apoptosis of murine spleen cells is aryl hydrocarbon receptor independent but caspases dependent.

Polychlorinated biphenyls (PCBs) are ubiquitous environmental contaminants and many of their toxic effects, including their immunotoxicities, are mediated by the activation of aryl hydrocarbon receptor (AhR). We previously reported that Aroclor 1254, one of the most widely used PCB mixtures, increased DNA fragmentation in mouse spleen cells, suggesting that apoptosis was correlated with the immunotoxicity of PCB (Yoo et al., Toxicol. Lett. 91, 83-89, 1997). In the present study we investigated the mechanism by which PCB induces apoptosis and the involvement of AhR in the PCB-mediated apoptosis of mouse spleen cells. Aroclor 1254 induced DNA fragmentation without AhR activation, and the apoptosis was unaffected by alpha-naphtoflavone, a well-known antagonist of AhR. Moreover, the PCB congeners (PCB 47, 52, 128, and 153), which have little affinity for AhR, induced DNA fragmentation, whereas congeners (PCB 77, 126, and 169) that have high affinity for AhR did not induce fragmentation. The di-ortho form of PCB (PCB 153) and Aroclor 1254 induced DNA fragmentation in the spleen cells of both AhR knockout mice and Ah low-response mice, whereas the non-ortho form of PCB (PCB 126) did not induce DNA fragmentation. In the light of these findings, it is evident that AhR is not involved in PCB-mediated apoptosis. PCB 153 significantly increased caspase-3 activity in both spleen cells and human leukemia cells, and z-VAD-fmk, a general inhibitor of caspases, prevented PCB-induced DNA fragmentation. Based on our findings, the most likely mechanism that can account for this biological effect involves the induction of caspase-dependent apoptotic cell death.

Aryl hydrocarbon receptor-dependent inhibition of AP-1 activity by 2,3,7,8-tetrachlorodibenzo-p-dioxin in activated B cells.

B cells have been identified as sensitive cellular targets responsible for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-mediated suppression of humoral immunity. In previous studies, TCDD was shown to produce a significant inhibition of IgM secretion and mu gene expression in LPS-activated CH12.LX B cells (AhR expressing) but not in BCL-1 B cells (AhR deficient). The present studies extend these previous findings by investigating the effect of TCDD on AP-1 and nuclear factor (NF)-kappaB, both of which play an important role in B-cell activation, differentiation, and immunoglobulin (Ig) gene expression. Electrophoretic mobility shift assays and chloramphenicol acetyl transferase reporter gene experiments demonstrated that lipopolysaccharide (LPS)-induced DNA binding and transcriptional activity of AP-1 was markedly inhibited by TCDD at 24, 48, and 72 h after cellular activation of CH12.LX cells. Conversely, TCDD treatment produced no significant change on the activity of NF-kappaB. Two AhR antagonists, alpha-naphthoflavone and 2,2',5,5'-tetrachlorobiphenyl, attenuated TCDD-induced inhibition of AP-1 binding in CH12.LX cells. Concordant with this result, TCDD did not inhibit LPS-induced AP-1 activity in BCL-1 B cells. Moreover, supershift analysis revealed the major component of the AP-1 complex in LPS-activated CH12.LX cells was c-Jun. Additional studies revealed that the nuclear c-jun and c-jun steady-state mRNA expression was inhibited by TCDD treatment. Collectively, these results suggest that TCDD-induced inhibition of IgM expression by B cells may be mediated, at least in part, through a down-regulation of AP-1 activity in an AhR-dependent manner.