FcγRIIb mediates amyloid-β neurotoxicity and memory impairment in Alzheimer’s disease

Amyloid-β (Aβ) induces neuronal loss and cognitive deficits and is believed to be a prominent cause of Alzheimer’s disease (AD); however, the cellular pathology of the disease is not fully understood. Here, we report that IgG Fcγ receptor II-b (FcγRIIb) mediates Aβ neurotoxicity and neurodegeneration. We found that FcγRIIb is significantly upregulated in the hippocampus of AD brains and neuronal cells exposed to synthetic Aβ. Neuronal FcγRIIb activated ER stress and caspase-12, and Fcgr2b KO primary neurons were resistant to synthetic Aβ-induced cell death in vitro. Fcgr2b deficiency ameliorated Aβ-induced inhibition of long-term potentiation and inhibited the reduction of synaptic density by naturally secreted Aβ. Moreover, genetic depletion of Fcgr2b rescued memory impairments in an AD mouse model. To determine the mechanism of action of FcγRIIb in Aβ neurotoxicity, we demonstrated that soluble Aβ oligomers interact with FcγRIIb in vitro and in AD brains, and that inhibition of their interaction blocks synthetic Aβ neurotoxicity. We conclude that FcγRIIb has an aberrant, but essential, role in Aβ-mediated neuronal dysfunction.

The pathological features of Alzheimer’s disease (AD), including memory loss and neuronal degeneration, are believed to be associated with the accumulation of amyloid-β (Aβ) in the brain (1, 2), but the mechanism underlying this pathogenesis remains uncertain. Of particular note, the membrane proteins responsible for Aβ neurotoxicity and memory impairment have not yet been identified, though there are several Aβ-binding proteins thought to be involved in AD pathology, including receptors for advanced glycation end-products (RAGE), Aβ-binding alcohol dehydrogenase (ABAD), and cellular prion protein (PrP^c) (3–5). RAGE was originally reported to interact with Aβ in neurotoxicity and was found to act in the blood-brain barrier as a transporter of Aβ into the brain (3, 6). ABAD is an intracellular binding partner of Aβ, acting on mitochondria (4). PrP^c was recently reported to act as a receptor for the Aβ oligomer, but this is still controversial and needs to be further clarified (5, 7–10). Despite a growing number of reports, the identification of a plausible membrane receptor responsible for Aβ neurotoxicity and memory impairment has yet to be made. Therefore, identification of such a neuronal receptor will be important and greatly beneficial for understanding and controlling AD pathology.

We previously isolated a cytosolic mediator of Aβ neurotoxicity, E2-25K/Hip-2, based on a global analysis of the genes expressed in the primary cortical neurons exposed to Aβ_1-42 (11, 12). Using the same approach, we found that Aβ_1-42 strongly upregulated the expression of FcγRIIb in the cortical neurons. FcγRIIb was initially identified as a type of IgG receptor, which binds to IgG immune complexes containing relevant antigens and is mainly expressed in B cells, macrophages, and neutrophils (13). In B cells, FcγRIIb acts to inhibit B cell receptor–mediated (BCR-mediated) immune responses and plays a key role in preventing autoimmunity (14). Thus, Fcgr2b KO mice display an elevated humoral immune response and are highly susceptible to autoimmune disease in the B6 strain (15, 16). Also, a mutation replacing Ile232 with Thr (I232T) in the transmembrane domain impairs the ability of FcγRIIb to function as an inhibitory receptor and leads to autoimmunity (14). Further, it was proposed that BCR-independent aggregation of FcγRIIb induces apoptosis in B cells (14). Recently, it was reported that FcγRIIb is also expressed in Purkinje cells and regulates cerebellar functions in the brain (17). Although there are a growing number of reports showing the expression and function of IgG-binding Fcγ receptors (FcγRs) in the CNS (18, 19), the neuronal function of FcγRIIb in the brain is largely unknown.

Here, we report that FcγRIIb plays a critical role in the Aβ neurotoxicity and memory impairment that appear to be relevant to AD pathogenesis. FcγRIIb deficiency prevented Aβ-induced inhibition of long-term potentiation (LTP) and synaptic dysfunction and rescued the memory impairments in an AD mouse model, demonstrating that FcγRIIb is essential for Aβ_1-42-induced neurotoxicity.

Induction of FcγRIIb expression in neurons incubated with Aβ and in AD brains. We first analyzed the expression of FcγRIIb in the brains of AD patients using anti-human FcγRIIb antibody (EP888Y), which did not show any cross-reactivity with FcγRIIa and FcγRIIIb on Western blot analysis (Supplemental Figure 1A; supplemental material available online with this article; doi: 10.1172/JCI66827DS1). FcγRIIb was detected in the brains, and we found its expression level to be significantly increased in the hippocampal regions of the AD patients, while the level of NeuN was slightly reduced compared with normal control or mild cognitive impairment (MCI) patients (Figure 1, A and B, and Supplemental Table 1). Increased neuronal expression of FcγRIIb was also observed in the NeuN-positive hippocampal neurons of AD patients (Figure 1C and Supplemental Figure 2A). Interestingly, intraneuronal Aβ visualized by Nu-1 antibody, which detected Aβ-derived diffusible ligands (ADDLs), including monomeric and oligomeric forms (20), colocalized with the immunoreactivity of FcγRIIb in the hippocampal neurons of AD patients (Figure 1D). Western blot analysis identified FcγRIIb expression in the mouse brains and the lack of its expression in Fcgr2b KO mouse brains (Supplemental Figure 1B). Furthermore, FcγRIIb was expressed in most parts of the brain, especially in the cortex, hippocampus, and cerebellum (Supplemental Figure 2, B and C). Compared with age-matched WT mice, the level of FcγRIIb was increased in the cortex of the 6- and 17-month-old AD-model mice (J20 line), which express familial AD mutant amyloid precursor protein (hAPP) and show learning and memory deficits (21), while the FcγRIIb level was not significantly changed in the 2-month-old J20 mice (Supplemental Figure 2D).

Figure 1

Increased expression of FcγRIIb in the neurons of AD brains. (A) Increased expression of FcγRIIb in AD patients. Hippocampal homogenates from normal, MCI (Braak III), and AD patients with Braak stage V/VI were analyzed by Western blotting. PHF1 antibody detecting phospho-tau was used as a marker for AD. (B) Levels of FcγRIIb (left) and NeuN (right) were quantified by densitometric measurement. Values are the mean ± SEM. *P < 0.05; **P < 0.005; ***P < 0.001; 2-tailed t test. (C) Immunohistochemical detection of FcγRIIb in the NeuN-positive hippocampal neurons of AD patients. Tissue samples from normal and AD patients (n = 3) were immunostained using anti-FcγRIIb and anti-NeuN antibodies and examined under a confocal microscope. Scale bars: 20 μm. (D) Immunohistochemical detection of FcγRIIb and Aβ in the hippocampus of AD patients. Tissue samples were immunostained using anti-FcγRIIb and anti-Aβ antibodies and then examined under a confocal microscope. Scale bars: 10 μm. (E) Immunoblot analysis showing FcγRIIb induction by Aβ_1-42 in neuronal cells. Primary cortical neurons and SH-SY5Y cells were incubated with 5 μM Aβ_1-42 for 36 hours, and cell extracts were analyzed with Western blotting using anti-FcγRIIb antibody (left, 2.4G2; right, EP888Y). The signals on the blots were quantified by densitometric analysis (bottom). (F) Increase in Fcgr2b mRNA by Aβ_1-42 in primary cortical neurons. Neurons cultured from WT and Fcgr2b KO mice were incubated with 5 μM Aβ_1-42 for 36 hours, after which total RNA was isolated for RT-PCR analysis with synthetic primers (top). Levels of mRNA in WT neurons were quantified by densitometric measurement (bottom). Values are the mean ± SD (n = 3). *P < 0.05; 2-tailed t test.

Western blot analysis showed that FcγRIIb expression was markedly increased by Aβ_1-42 in the primary cultured neurons and SH-SY5Y neuroblastoma cells (Figure 1E). Interestingly, among FcγRs, it was Fcgr2b that was induced by Aβ_1-42 in the primary cortical neurons, as examined by RT-PCR analysis (Figure 1F). Thus, we investigated the molecular mechanism by which FcγRIIb expression is regulated by Aβ_1-42. We first found that Aβ_1-42 activated c-Jun N-terminal protein kinase (JNK) and its downstream transcription factor, c-Jun, in WT cortical neurons, but not in Fcgr2b KO neurons (Supplemental Figure 3A). In addition, the JNK inhibitor (SP600125), but not the ERK1/2 inhibitor (U0126), suppressed Aβ-triggered FcγRIIb expression in both mRNA and protein levels in SH-SY5Y cells (Supplemental Figure 3B) and inhibited an Aβ-triggered increase in the reporter activity that was driven by the FCGR2B promoter (Supplemental Figure 3C). Moreover, the JNK inhibitor suppressed Aβ_1-42-induced neurotoxicity in both primary cortical neurons and HT22 mouse hippocampal cells (Supplemental Figure 3, D and E). Together with the previous report showing that the AP-1 complex regulates FCGR2B gene expression through direct interaction of c-Jun with the FCGR2B promoter (22), our results suggest that Aβ_1-42 regulates FCGR2B gene expression at the transcriptional level via JNK-c-Jun.

Neurotoxic role of FcγRIIb in Aβ signaling. Given that the oligomeric form is reportedly one of the primary neurotoxic Aβ species (23–25) and that neuronal Aβ is apparently seen in AD (26, 27), we examined the role of FcγRIIb in Aβ neurotoxicity. We prepared the toxic oligomers and confirmed their species using SDS PAGE and atomic force microscopy. Oligomeric species of Aβ were formed (Figure 2A, left) as described in ADDLs (20) and contained nonfibrillar and globular particles (Figure 2A, right). Notably, unlike WT neurons, cultured hippocampal neurons from Fcgr2b KO mice were quite resistant to the neurotoxicity of synthetic Aβ_1-42 containing soluble oligomers (Figure 2B and Supplemental Figure 4A). Resistance to Aβ neurotoxicity was also observed in cultured Fcgr2b KO cortical neurons and Fcgr2b knockdown (KD) B103 rat neuroblastoma cells (data not shown). Conversely, ectopic expression of FcγRIIb induced significant HT22 cell death, while an I232T FcγRIIb mutant failed to do so and, rather, suppressed Aβ neurotoxicity (Figure 2C). These results suggest that FcγRIIb is required for Aβ neurotoxicity in cultured cells and that the neurotoxic signaling triggered by Aβ might be shared with the immune inhibitory activity of FcγRIIb.

Figure 2

FcγRIIb is required for Aβ neurotoxicity. (A) Characterization of Aβ_1-42 oligomers. The prepared Aβ_1-42 oligomers were identified by SDS-PAGE (left) and atomic force microscopy (right). Scale bars: 0.5 μm. (B) Fcgr2b KO neurons are resistant to Aβ toxicity. Primary hippocampal neurons (5 DIV) were incubated with Aβ_1-42 oligomers for 2 days, after which the relative neuronal viability was determined by MTT assay. Data are the mean ± SD (n = 6). ***P < 0.001, 1-way ANOVA. (C) FcγRIIb I232T mutant potently inhibits Aβ toxicity. HT22 cells transfected and incubated with or without Aβ_1-42. Bars depict the incidence of cell death. Values are the mean ± SD (n = 3). *P < 0.05; ***P < 0.001, unpaired t test (top). Expression of constructs was identified by Western blotting (bottom). (D) FcγRIIb sensitizes Aβ-induced cell death. HT22 cells transfected with the indicated constructs were incubated for 48 hours with or without CHO-CM, 7PA2-CM, or 1 μM of synthetic Aβ_1-42. Values are the mean ± SD (n = 3). *P < 0.05; **P < 0.005, unpaired t test. NS, not significant. (E and F) Inhibition of Aβ_1-42-induced FcγRIIb expression and neuronal death by the addition of purified hFcγRIIb-ED protein. SH-SY5Y cells (E) and primary cortical neurons (F) were incubated for 48 hours with Aβ_1-42 with or without 50 μg/ml of hFcγRIIb-ED protein. Cell extracts were subjected to Western blot analysis (E); cell viability was determined using Calcein-AM (F). Values are the mean ± SD (n = 4).

Many studies have used synthetic Aβ_1-42 to induce neuronal death in vitro (9, 28, 29). However, the concentration of synthetic Aβ is high compared with Aβ oligomers found in the human brain, although AD brains have locally and highly concentrated Aβ near the plaques. Thus, to assess whether low-dose soluble Aβ contributes to FcγRIIb-mediated neurotoxicity, we used cell-derived, naturally secreted Aβ oligomers (24). Immunoprecipitation analysis confirmed the presence of soluble Aβ monomers and oligomers in the conditioned medium (CM) of Chinese hamster ovary (CHO) cells that stably expressed human APP bearing the V717F familial AD mutation (7PA2 cells) (Supplemental Figure 4B). The concentration of soluble Aβ_1-42 in 7PA2-CM was estimated by ELISA to be 200 pg/ml (Supplemental Figure 4C). There was no significant incidence of neurotoxicity when HT22 cells were incubated with 7PA2-CM only (Figure 2D). On the other hand, 7PA2-CM sensitized the HT22 cells, which were transfected with and thus overexpressed FcγRIIb, resulting in cell death. Similarly, synthetic Aβ was also sufficiently potent to enhance FcγRIIb-mediated cell death (Figure 2D). In addition, when HT22 cells expressing FcγRIIb were cocultivated with 7PA2 cells, the incidence of HT22 cell death was enhanced (Supplemental Figure 4D).

We then determined the molecular mechanism of FcγRIIb-mediated neuronal death by Aβ_1-42. We first found that Aβ- and FcγRIIb-mediated cell death was significantly suppressed by salubrinal, a selective eIF2α dephosphorylation inhibitor, thus protecting against ER stress–mediated neurotoxicity (30) (Supplemental Figure 5, A and B) and suggesting that FcγRIIb mediates Aβ_1-42 neurotoxicity through ER stress. Consistently, Aβ_1-42-induced upregulation of the typical ER stress markers, GRP78 and CHOP, observed in WT cortical neurons was markedly suppressed in Fcgr2b KO cortical neurons (Supplemental Figure 5C). Conversely, overexpressed FcγRIIb, but not the I232T FcγRIIb mutant, induced similar ER stress responses in HT22 cells (Supplemental Figure 5D). Of particular note, Aβ_1-42-induced activation of caspase-12, a key player in ER stress- and Aβ-mediated apoptosis (12, 31), was abrogated in Fcgr2b KO cortical neurons (Supplemental Figure 5C). Furthermore, ectopic expression of the caspase-12 active site mutant (C298S) significantly suppressed FcγRIIb-mediated HT22 cell death, while caspase-12 significantly enhanced it (Supplemental Figure 5E). These observations suggest that homoaggregation of FcγRIIb by Aβ_1-42 transduces the toxic signal into neurons to induce ER stress, which in turn activates caspase-12, leading to neuronal death.

We then assessed the possible role of FcγRIIb as a membrane receptor of Aβ_1-42 in Aβ_1-42 neurotoxicity. As observed in cultured primary neurons, incubation of SH-SY5Y cells with Aβ_1-42 increased the expression of FcγRIIb (Figure 2E). On the other hand, the addition of the purified ectodomain (hFcγRIIb-ED) hFcγRIIb protein to culture medium abolished the induction of FcγRIIb expression and JNK activation triggered by Aβ_1-42. In parallel, the addition of the FcγRIIb-ED protein also inhibited cell death of primary rat cortical neurons, which were exposed to Aβ_1-42 (Figure 2F). Thus, the blockade of Aβ neurotoxicity by hFcγRIIb-ED protein on the extracellular side led us to examine whether FcγRIIb is able to bind to Aβ_1-42.

Interaction between FcγRIIb and Aβ_1-42. To determine the mode of action of FcγRIIb, we addressed the direct interaction between FcγRIIb and Aβ both in vitro and in vivo. We first performed a set of in vitro binding assays using the purified hFcγRIIb-ED protein. We used soluble fractions of cell-derived Aβ and synthetic Aβ to exclude the nonspecific precipitation of aggregated Aβ. In an in vitro pulldown assay, we found that monomeric and oligomeric forms of both cell-derived Aβ and synthetic Aβ1-42 were coimmunoprecipitated with FcγRIIb-ED protein (Figure 3A and Supplemental Figure 6, A and B), though boiling of the samples for Western blotting converted the oligomeric forms of Aβ1-42 into monomers. Interestingly, FcγRIIb-ED protein bound more effectively to the oligomeric forms of Aβ1-42, a pathogenic form of Aβ, than to Aβ1-40 (Supplemental Figure 6C). It is not yet clear whether the differing oligomeric states of these Aβ peptides cause this difference in binding. We further investigated the direct interaction of Aβ with FcγRIIb and the kinetics of this interaction using surface plasmon resonance (SPR) analysis (Figure 3B). Interestingly, Aβ_1-42 potently interacted with hFcγRIIb-ED (K_d = 5.67 × 10^–8 M), while human IgG1 (hIgG1) bound to hFcγRIIb-ED with relatively low affinity (K_d = 9.43 × 10^–6 M) (Figure 3B and Supplemental Figure 6D).

Figure 3

Interaction of FcγRIIb with Aβ_1-42. (A) In vitro binding of FcγRIIb-ED protein to cell-derived Aβ. Purified GST or hFcγRIIb-ED protein was incubated with CHO- or 7PA2-CM for 6 hours and then immunoprecipitated with anti-GST or anti-FcγRIIb antibody. The precipitates were analyzed by Western blotting. L.C., light chain. (B) Direct interaction of FcγRIIb-ED with Aβ_1-42 in SPR analysis. BSA or oligomeric Aβ_1-42 was immobilized and the interactions with hFcγRIIb-ED were analyzed using Biacore 3000. (C) Interaction of FcγRIIb with oligomeric Aβ_1-42 in AD patients. Hippocampal extracts from AD patients and controls (C) were subjected to immunoprecipitation assays using IgG or Nu-1 antibody, and the precipitates were analyzed with Western blotting. Asterisk indicates nonspecific signal, which differs in size from the Aβ monomer. (D) Computational simulation showing the structure of the FcγRIIb-Aβ_1-42 complex. The N terminus of Aβ_1-42 and IgG-binding region of hFcγRIIb were handled using the Affinity program. (E) Inhibition of Aβ_1-42-induced reporter activation of the FcγRIIb-ED/CD40-Luc chimera by Aβ_1-9 or FcγRIIb_107-114. Synthetic peptides spanning the predicted interaction regions of FcγRIIb and Aβ_1-42 and their mutants are represented (top). The reporter assay was performed with or without synthetic peptides with a molar ratio of 1:3 (bottom). (F) Binding of Aβ_1-42 to the Ig2 domain of FcγRIIb. Domain structures of FcγRIIb and its deletion constructs are presented (top). HEK293T cells were transfected with the constructs and treated with 1 μM Aβ_1-42 for 1 hour. Cell lysates were subjected to immunoprecipitation analysis using Aβ antibody or preimmune (Pre), and the precipitates were analyzed with Western blotting. Expression of each FcγRIIb protein was checked in whole cell lysates. IP, immunoprecipitation.

Using immunoprecipitation assays, we also detected in vivo interaction between FcγRIIb and monomeric and oligomeric forms of Aβ in the hippocampal extracts of AD patients (Figure 3C). In contrast, this interaction was not observed in the control tissues. We used the tissues showing similar expression of FcγRIIb to exclude the effect of different amounts of FcγRIIb protein. The reverse immunoprecipitation assay using FcγRIIb antibody was unsuccessful, probably because the amount of the precipitated Aβ was too low to be detected. The interaction between Aβ_1-42 and HA-tagged FcγRIIb was also assessed in cultured cells. We found that synthetic Aβ oligomers and FcγRIIb were coimmunoprecipitated in FcγRIIb-expressing cell lines (Supplemental Figure 6, E and F). We further examined the interaction with reporter assays using a FcγRIIb(ED)-CD40 chimera. The chimera consisted of the extracellular domain of FcγRIIb for Aβ binding and the transmembrane and cytosolic domains of CD40 for nuclear factor-κB (NF-κB) activation (Supplemental Figure 7A). In the reporter assay, we observed that Aβ_1-42 treatment increased the luciferase activity, which is under the control of NF-κB DNA elements, by about 4 fold in NIH3T3 cells expressing FcγRIIb(ED)-CD40, but not in cells expressing CD40 (Supplemental Figure 7B). Apparently, Aβ_1-42 binds to FcγRIIb-ED to activate NF-κB, further supporting the notion that FcγRIIb binds to extracellular Aβ.

We were eager to understand the mode of interaction between FcγRIIb and Aβ_1-42, but Aβ_1-42 was readily aggregated and resisted crystallization. Oligomeric structures of Aβ_1-42 and Aβ_1-40 were computationally predicted to show that the hydrophilic N termini of Aβ_1-42 and Aβ_1-40 are exposed, whereas C termini bind together to form oligomers (32). In particular, the N terminus of Aβ_1-42 is more extended and flexible than that of Aβ_1-40 (32), which may provide a hint as to why Aβ_1-42 is more toxic to neurons than Aβ_1-40 (33). Moreover, the neurotoxicity of oligomeric Aβ isolated from AD patients is protected by Aβ N-terminal antibodies, but not by Aβ C-terminal antibodies (25). Our observations that FcγRIIb interacted with Aβ_1-42 better than Aβ_1-40 led us to examine whether the extended N-terminus of Aβ_1-42 and the IgG-binding region of FcγRIIb contributed to Aβ neurotoxicity. Using in silico modeling of the structure of each domain (34, 35), the mode of interaction was predicted (Figure 3D) and the interaction specificity was addressed. The N-terminal region of Aβ_1-42 was predicted to bind to the Ig-like domain 2 of FcγRIIb, and ⁴phenylalanine of Aβ_1-42 and ¹¹¹tryptophan of FcγRIIb were important in this interaction.

Then, to address the interaction specificity, we prepared synthetic peptides derived from Aβ_1-42 and FcγRIIb and performed binding competition assays between Aβ_1-42 and these peptides using an FcγRIIb(ED)-CD40 reporter. Synthetic peptides derived from the N-terminal region (Aβ_1-9 #1; ¹DAEFRHDSG⁹) of Aβ_1-42 or from the IgG-binding region (FcγRIIb_107-114 #9; ¹⁰⁷RCHSWRNK¹¹⁴) of FcγRIIb (36), but not other FcγRIIb_95-101 (#8, ⁹⁵QLVFLEG¹⁰¹) peptides, effectively inhibited the interaction of Aβ_1-42 with FcγRIIb in a reporter assay (Figure 3E). In addition, the peptides also suppressed Aβ_1-42 neurotoxicity in cultured hippocampal and cortical neurons (Supplemental Figure 8). However, the inhibitory actions of these Aβ_1-9 (#1) and FcγRIIb_107-114 (#9) peptides were lost upon introduction of mutations into the amino acids that were predicted to be involved in these interactions (⁴phenylalanine and ⁷aspartate in Aβ_1-9 and ¹¹¹tryptophan in FcγRIIb_107-114) (Figure 3, D and E). We therefore propose that the N terminus of Aβ_1-42 is required for the binding of Aβ_1-42 to FcγRIIb and for Aβ_1-42 neurotoxicity. Further, in immunoprecipitation analysis using hFcγRIIb deletion mutants lacking either 1 of 2 Ig-like domains present in the extracellular region, we found that the hFcγRIIb ΔIg2 mutant lacking the second Ig-like domain failed to interact with Aβ_1-42 (Figure 3F). The second Ig-like domain is also known to bind to IgG (13). Collectively, these observations indicate that the second Ig-like domain of hFcγRIIb is critical for interaction with Aβ_1-42.

Requirement of FcγRIIb in synaptic dysfunction and memory impairment in AD mice. Many reports have proposed that the oligomeric forms of Aβ_1-42 suppress LTP, a measure of synaptic plasticity (24, 37). To explore whether FcγRIIb accounts for Aβ_1-42-mediated impairment of synaptic plasticity, we performed extracellular recordings of field excitatory postsynaptic potentials (fEPSPs) in the hippocampal slices of WT or Fcgr2b KO mice. Treatment with synthetic Aβ_1-42 (400 nM) inhibited hippocampal LTP after high-frequency stimulation in WT mice (Figure 4, A and B). On the contrary, there was no inhibition of LTP by Aβ_1-42 in the Fcgr2b KO hippocampal slices and synaptic response was normal (Figure 4, A and B). We also identified the role of FcγRIIb in LTP inhibition using an AD model mouse. We crossed the AD-mutant hAPP transgenic mice (J20 line) with Fcgr2b KO mice to generate double-transgenic mice (hAPP/KO) and recorded their fEPSPs. Consistently, FcγRIIb deficiency rescued LTP deficits in hAPP mice (Supplemental Figure 9A). Collectively, these observations indicate that FcγRIIb is required for Aβ_1-42-induced inhibition of LTP in hippocampal tissue.

Figure 4

Requirement of FcγRIIb in Aβ_1-42-mediated inhibition of hippocampal LTP and synaptic dysfunction. (A) Lack of Aβ_1-42-induced inhibition of hippocampal LTP in Fcgr2b-deficient mice. WT and Fcgr2b KO hippocampal slices were microinjected with PBS (n = 7 slices from 6 WT mice, n = 7 slices from 5 KO mice) or 400 nM Aβ_1-42 (n = 7 slices from 4 WT mice, n = 7 slices from 4 KO mice) for 30 to 50 minutes before HFS. Insets show fEPSP traces of average baseline (black) and after HFS (red). Scale bars: 5 msec and 0.2 mV. (B) Summary bar graphs represent the magnitude of LTP between 50 and 60 minutes. Data are the mean ± SEM. ***P < 0.001, 1-way ANOVA. (C) Abrogation of Aβ-induced synaptic loss in Fcgr2b-deficient neurons. Cultured hippocampal neurons were transfected with pEGFP-N1 and further incubated with CHO- or 7PA2-CM for 5 days. Images represent dendrites of neurons from WT and Fcgr2b KO embryos. Scale bars: 10 μm (left). Quantification of dendrite spine density from 10 randomly chosen neurons measuring 100 μm in length. Bars depict the mean ± SD. ***P < 0.001, 1-way ANOVA (right). (D) Requirement of FcγRIIb-Aβ interaction in Aβ-induced spine density reduction. Primary hippocampal neurons were transfected with pEGFP-N1 and incubated with CHO- or 7PA2-CM for 5 days with or without purified hFcγRIIb-ED protein. Scale bars: 5 μm (left). Average spine density for neurons is indicated as in C. Bars depict the mean ± SD. ***P < 0.001, 1-way ANOVA (right).

Then, we determined whether FcγRIIb contributed to Aβ-induced synaptic loss in cultured hippocampal neurons. After incubation with 7PA2-CM containing soluble Aβ, the neuronal synaptic spine densities were quantified. Compared with the untreated controls, spine density was reduced in the WT hippocampal neurons, but not in the Fcgr2b KO hippocampal neurons (Figure 4C). Similarly, spine density was reduced by incubation with synthetic Aβ_1-42 in the WT neurons, but not in the Fcgr2b KO neurons (Supplemental Figure 9B). Furthermore, the addition of hFcγRIIb-ED protein to 7PA2-CM prevented a decrease in the dendritic spine density of cultured neurons (Figure 4D), indicating that the interaction of Aβ with FcγRIIb is required for Aβ-induced synaptic loss. We also found that synaptophysin immunoreactivity was significantly reduced in the CA1 regions of hAPP mice, but not in those of hAPP/Fcgr2b KO mice (Supplemental Figure 9C). Together, these observations suggest that FcγRIIb plays an essential role in Aβ_1-42-mediated synaptic loss and dysfunction.

Because the synaptic dysfunction evoked by Aβ provides a molecular and cellular basis for memory deficits and neuropathological features of dementia in AD (38, 39), we investigated the role of FcγRIIb in learning and memory deficits using an AD mouse model. Fcgr2b KO mice did not show any detectable memory impairment compared with WT mice up to 12 months (data not shown). Comparisons of each group’s behavior showed that the defects in spatial working memory of 4- to 6-month-old hAPP mice were significantly improved by FcγRIIb deficiency in a Y-maze test (Figure 5A). In the novel object recognition test, hAPP/Fcgr2b KO mice spent more time exploring the novel object than the other object that they had explored 1 day before, but hAPP mice had no preference for the new object (Figure 5B). Thus, the recognition memory deficit of hAPP mice was also blocked by the removal of FcγRIIb. We further examined passive avoidance memory. During training, step-through latency was similar in each group (data not shown). After training, only the hAPP mice failed to learn and showed impaired task performance, whereas the other 3 groups performed well (Figure 5C). On the other hand, Fcgr2b deficiency did not affect the hyperactivity in hAPP mice that might also be related to memory impairment (40), as reflected in the Y-maze test (Supplemental Figure 10). Because Aβ_1-42 and Αβ_1-40 levels were similar in the hAPP and hAPP/KO mice (Supplemental Figure 11) and 4- to 6-month-old hAPP mice had not yet shown amyloid plaques (41), we ruled out the possibility that FcγRIIb altered Aβ levels or plaque formation. Together, these results suggest that FcγRIIb is required for learning and memory impairment in the hAPP transgenic mice.

Figure 5

FcγRIIb deficiency ameliorates learning and memory deficits in hAPP mice. (A) Suppression of spatial memory defects in hAPP/Fcgr2b-deficient mice. Spatial memory of 4- to 6-month-old WT, Fcgr2b-deficient (KO), hAPP, and hAPP/Fcgr2b-deficient (hAPP/KO) mice was represented as spontaneous alteration on the Y maze (n = 7–18 mice per group; WT, 10 males and 8 females; KO, 4 males and 8 females; hAPP, 4 males and 3 females; hAPP/KO, 10 males and 8 females). Data are the mean ± SEM; *P < 0.05, unpaired t test. (B) Recovered recognition memory impairment in hAPP/Fcgr2b KO mice. Object recognition memory was reflected by the percentage of time each group of mice spent exploring a familiar versus a novel object (n = 9–18 mice per genotype). Values are the mean ± SEM; ***P < 0.001 versus familiar object, paired t test. (C) Prevention of passive avoidance memory defects of hAPP mice by Fcgr2b deficiency (n = 9–13 mice per group). Bars depict the mean ± SEM; *P < 0.05 as indicated by the bracket, unpaired t test.

We then addressed the effects of the inhibitory peptides, Aβ_1-9 #1 and FcγRIIb_107-114 #9, on memory impairment using i.c.v. injection assays. First, we confirmed the acute memory impairment model triggered by i.c.v.-injected Aβ_1-42. When injected with sublethal doses of Aβ_1-42 (410 pmol per mouse), the WT mice exhibited significantly impaired spontaneous alteration behavior (Figure 6A), step-through escape latency (Figure 6B), and recognition memory (Figure 6C), as compared with the mice injected with Aβ_40-1. However, Fcgr2b KO mice were tolerant to the memory impairment triggered by i.c.v.-injected Aβ_1-42 (Figure 6, A–C). Interestingly, when we coinjected Aβ_1-42 with either Aβ_1-9 (#1) or FcγRIIb_107-114 (#9) peptides, Aβ_1-42-induced impairments of spontaneous alteration behavior and step-through escape latency were significantly blocked (Figure 6, D and E). However, Aβ_1-9 (#7) mutant peptide did not affect those impairments (Figure 6, D and E). Thus, it appears that the interaction of Aβ_1-42 with FcγRIIb is important in Aβ_1-42-induced neurotoxic activities in vivo such as memory impairment.

Figure 6

Interaction of FcγRIIb with Aβ_1-42 is linked to i.c.v. Aβ_1-42-induced memory impairment. (A–C) Suppression of i.c.v. Aβ_1-42-induced cognitive defects in Fcgr2b-deficient mice. Mice were i.c.v. injected with nontoxic Aβ_40-1 or Aβ_1-42 (410 pm). One day later, Y-maze (A; **P < 0.005, 1-way ANOVA), passive avoidance (B; n = 10 for each group; *P < 0.05, 1-way ANOVA), and novel object recognition (C; n = 10 for each group) tests were performed as described in the methods. Bars represent the mean ± SEM. (D and E) Suppression of i.c.v. Aβ_1-42-induced memory impairment by the peptides inhibiting the interaction between Aβ_1-42 and FcγRIIb. WT mice (2-month-old) were i.c.v. injected with Aβ_40-1 or Aβ_1-42 (410 pm) alone or together with Aβ_1-9 (#1), Aβ_1-9 mutant (#7), or FcγRIIb_107-114 (#9) peptide (molar ratio of 1:3). One day later, the mice were analyzed using Y-maze (D) and passive avoidance (E) tests (n = 8–10). Bars represent the mean ± SEM. **P < 0.005; ***P < 0.001; 1-way ANOVA.

While it has been believed that the CNS is immune privileged, molecular understanding of the immune system’s role in the progression of or protection against neurodegeneration in the CNS is rapidly growing (42–44). Although IgG is absent or extremely low-level in the CNS, FcγRs also accumulate in the plaques and microglial cells of AD brains (18). Further, one immune inhibitory receptor, CD33, was isolated as an AD risk factor in genome-wide association studies (GWAS) (45). We believe the present report is the first to show FcγRIIb’s role in Aβ neurotoxicity as a binding partner of Aβ_1-42 in the CNS. Compared with IgG1, our data show that FcγRIIb bound to Aβ_1-42 with higher affinity (K_d = 5.67 × 10^–8 M). While the second Ig-like domain of FcγRIIb is required for its binding to both IgG and Aβ_1-42, it is likely that there is a subtle difference in their interaction modes. When we injected Aβ_1-42 together with IgG1, Aβ-induced impairment of spontaneous alteration behavior and recognition memory was not rescued (data not shown). As seen in other membrane proteins such as RAGE, PrP^c, and EphB2 (5, 6, 41), FcγRIIb is not the only binding partner for Aβ oligomers. Along with the essential role of FcγRIIb in Aβ-induced neurotoxicity, synaptic dysfunction, and memory impairment, there is a possibility that FcγRIIb functionally interacts with other Aβ-binding proteins. In addition, the observation that FcγRIIb-ED seems to bind better to the oligomeric forms of Aβ_1-42 than those of Aβ_1-40 also implies that the receptors have preferential binding affinity for different species and oligomeric forms of Aβ. Thus, as seen in FcγRIIb, it will be interesting to define the critical residues in Aβ_1-42 that are involved in the interaction with these proteins and to compare their binding abilities with those of Aβ_1-40.

Given an earlier report that homoaggregation of FcγRIIb transduces death signals in B cells (14), another persuasive model may be that oligomeric forms of Aβ_1-42 induce similar aggregation of FcγRIIb to generate a neurotoxic signal, including ER stress response and caspase-12 activation. Unlike FcγRIIb, the I232T FcγRIIb mutant, which shows low activity and a decreased affinity of FcγRIIb for lipid rafts (46), failed to induce cell death. On the other hand, Aβ_1-42 appeared to bind equally to both FcγRIIb and the I232T mutant in an immunoprecipitation assay (data not shown). These observations imply that the I232T FcγRIIb mutant may act as a decoy receptor to deplete extracellular Aβ or as a dominant negative mutant to suppress FcγRIIb induction. FcγRs have high structural homology in their extracellular domains and need to be analyzed in detail for their expression pattern in the CNS and their ability to bind to Aβ. Among the FcγRs, however, FcγRIIb is the only inhibitory receptor that contains an immunoreceptor tyrosine-based inhibitory motif (ITIM) in its cytoplasmic portion, while the other FcγRs (FcγRI, FcγRIIa, FcγRIII, and FcγRIV) have an immunoreceptor tyrosine-based activating motif (ITAM) (19). We also observed that replacement of the tyrosine residue in the ITIM with phenylalanine (Y273F) caused a loss of FcγRIIb’s proapoptotic activity (data not shown), indicating that FcγRIIb possesses a unique neurotoxic feature among the FcγRs.

The hAPP transgenic mouse (J20 line) shows relatively high expression of the hAPP gene and generates various APP fragments as well as a high level of Aβ. Though the multiple assembly forms of Aβ were presented throughout the lives of the J20 mice (47), various oligomeric Aβs, including Aβ*56 and Aβ trimers, were already detected in the J20 mice before their behavioral defects were observed (48). In J20 mice, more importantly, learning and memory deficits were correlated with certain species of soluble oligomers, such as Aβ*56, but not with plaque load or hAPP and β-CTF levels (49), indicating that Aβ-mediated neurotoxicity is a primary cause of pathology. In addition, Fcgr2b KO mice of the B6 strain are highly susceptible to death due to autoimmunity (15). Although the 129sv/B6 mouse strain may be tolerable to autoimmunity caused by FcγRIIb deficiency (15), AD model mice expressing APP in 129 derivative strains did not show behavioral abnormality in many assessments, including the water maze test (50, 51). Thus, we believe that the J20 mouse showing early learning and memory deficits is a plausible model for demonstrating the role of FcγRIIb in Aβ neurotoxicity in vivo. In our investigation, we used 4- to 6-month-old J20 mice that did not yet show clear-cut pathological endpoints like the formation of plaque burden (52), supporting our proposition that FcγRIIb mediates soluble Aβ–related pathology, such as memory deficits, in these mice. In AD model mice, however, the possibility that FcγRIIb in nonneuronal cells may also contribute to memory impairment through other activity such as neuroinflammation requires further elucidation. Given the previous reports that anti-Aβ antibodies prevented AD-like phenotypes through Fc receptor–mediated phagocytosis in AD model mice (53, 54), immune inhibitory FcγRIIb deficiency may also contribute to rescuing such pathology by eliminating the negative regulation of antibody effector functions.

An acute memory loss model triggered by i.c.v.-injected Aβ_1-42 may not be representative for the mental retardation found in AD. Nonetheless, we believe that it is the best model for clarifying the effect of the inhibitory peptides on memory defects. Also, an i.c.v. injection assay of Aβ ADDLs is a useful way to study the role of a subportion or partition of Aβ forms. In this assay, the mice showed no significant differences in their movement, and their acute memory deficits were fully recovered after 3 weeks (data not shown). These observations imply that a single i.c.v. injection of synthetic Aβ_1-42 does not interfere with learning and memory nor cause emotional turbulence or physical malaise, and that the synaptic activity impaired by i.c.v-injected Aβ_1-42 is not irreversible.

In conclusion, FcγRIIb is responsible for soluble Aβ–associated toxicity, including neuronal death, synaptic dysfunction, and behavioral defects in mice in which the interaction of FcγRIIb with Aβ is critical. Thus, we believe that selective inhibition in the interaction of FcγRIIb with Aβ_1-42 can be considered a new therapeutic against the neuropathology caused by Aβ_1-42.

View Supplemental data

The authors thank U. Hammerling for FcγRIIb monoclonal antibody (K9.361 hybridoma); J. Cambier for rabbit polyclonal antibody; D.J. Selkoe (Harvard Medical School, Cambridge, Massachusetts) for CHO and 7PA2 cells; and J.H. Yu (Seoul National University, Seoul, Republic of Korea) for use of the Biacore. T.I. Kam and Y. Gwon were in part supported by the BK21 program and the Global PhD program, respectively. AD tissues were provided by the Harvard Brain Tissue Resource Center of McLean Hospital. This work was supported by grants from the Brain Research Center (2012K001122) of the 21st Century Frontier Research Program and Global Research Laboratory program (K21004000002-12A0500-00210) and the KIST R&D institutional program (2E22650, to K.S. Kim) funded by the Ministry of Education, Science and Technology (MEST); and by an AD grant (A092058-1113-0000400) from the Korean Ministry of Human Health and Welfare and the AD Foundation in USA.

Address correspondence to: Yong-Keun Jung, School of Biological Sciences, Seoul National University, 599 Gwanak-ro, Gwanak-gu, Seoul 151-747, Republic of Korea. Phone: 82.2.880.4401; Fax: 82.2.873.7524; E-mail: ykjung@snu.ac.kr.

Conflict of interest: The authors have declared that no conflict of interest exists.

Reference information: J Clin Invest. 2013;123(7):2791–2802. doi:10.1172/JCI66827.

1. Mattson MP. Pathways towards and away from Alzheimer’s disease. Nature. 2004;430(7000):631–639.
   View this article via: PubMed CrossRef Google Scholar
2. Golde TE, Janus C. Homing in on intracellular Aβ? Neuron. 2005;45(5):639–642.
   View this article via: PubMed CrossRef Google Scholar
3. Deane R, et al. RAGE mediates amyloid-beta peptide transport across the blood-brain barrier and accumulation in brain. Nat Med. 2003;9(7):907–913.
   View this article via: PubMed CrossRef Google Scholar
4. Lustbader JW, et al. ABAD directly links Abeta to mitochondrial toxicity in Alzheimer’s disease. Science. 2004;304(5669):448–452.
   View this article via: PubMed CrossRef Google Scholar
5. Laurén J, Gimbel DA, Nygaard HB, Gilbert JW, Strittmatter SM. Cellular prion protein mediates impairment of synaptic plasticity by amyloid-β oligomers. Nature. 2009;457(7233):1128–1132.
   View this article via: PubMed CrossRef Google Scholar
6. Yan SD, et al. RAGE and amyloid-beta peptide neurotoxicity in Alzheimer’s disease. Nature. 1996;382(6593):685–691.
   View this article via: PubMed CrossRef Google Scholar
7. Gimbel DA, et al. Memory impairment in transgenic Alzheimer mice requires cellular prion protein. J Neurosci. 2010;30(18):6367–6374.
   View this article via: PubMed CrossRef Google Scholar
8. Kessels HW, Nguyen LN, Nabavi S, Malinow R. The prion protein as a receptor for amyloid-beta. Nature. 2010;466(7308):discussion E4–E5.
   View this article via: PubMed Google Scholar
9. Balducci C, et al. Synthetic amyloid-β oligomers impair long-term memory independently of cellular prion protein. Proc Natl Acad Sci U S A. 2010;107(5):2295–2300.
   View this article via: PubMed CrossRef Google Scholar
10. Cissé M, Sanchez PE, Kim DH, Ho K, Yu GQ, Mucke L. Ablation of cellular prion protein does not ameliorate abnormal neural network activity or cognitive dysfunction in the J20 line of human amyloid precursor protein transgenic mice. J Neurosci. 2011;31(29):10427–10431.
    View this article via: PubMed CrossRef Google Scholar
11. Song S, et al. Essential role of E2-25K/Hip-2 in mediating amyloid-beta neurotoxicity. Mol Cell. 2003;12(3):553–563.
    View this article via: PubMed CrossRef Google Scholar
12. Song S, et al. E2-25K/Hip-2 regulates caspase-12 in ER stress-mediated Abeta neurotoxicity. J Cell Biol. 2008;182(4):675–684.
    View this article via: PubMed CrossRef Google Scholar
13. Katz HR. Inhibitory receptors and allergy. Curr Opin Immunol. 2002;14(6):698–704.
    View this article via: PubMed CrossRef Google Scholar
14. Pritchard NR, Smith KG. B cell inhibitory receptors and autoimmunity. Immunology. 2003;108(3):263–273.
    View this article via: PubMed CrossRef Google Scholar
15. Bolland S, Ravetch JV. Spontaneous autoimmune disease in Fc(gamma) RIIB-deficient mice results from strain-specific epistasis. Immunity. 2000;13(2):277–285.
    View this article via: PubMed CrossRef Google Scholar
16. Takai T, Ono M, Hikida M, Ohmori H, Ravetch JV. Augmented humoral and anaphylactic responses in Fc gamma RII-deficient mice. Nature. 1996;379(6563):346–349.
    View this article via: PubMed CrossRef Google Scholar
17. Nakamura K, et al. CD3 and immunoglobulin G Fc receptor regulate cerebellar functions. Mol Cell Biol. 2007;27(14):5128–5134.
    View this article via: PubMed CrossRef Google Scholar
18. Peress NS, Fleit HB, Perillo E, Kuljis R, Pezzullo C. Identification of Fc gamma RI, II and III on normal human brain ramified microglia and on microglia in senile plaques in Alzheimer’s disease. J Neuroimmunol. 1993;48(1):71–79.
    View this article via: PubMed CrossRef Google Scholar
19. Okun E, Mattson MP, Arumugam TV. Involvement of Fc receptors in disorders of the central nervous system. Neuromolecular Med. 2010;12(2):164–178.
    View this article via: PubMed CrossRef Google Scholar
20. Lambert MP, et al. Vaccination with soluble Abeta oligomers generates toxicity-neutralizing antibodies. J Neurochem. 2001;79(3):595–605.
    View this article via: PubMed CrossRef Google Scholar
21. Roberson ED, et al. Reducing endogenous tau ameliorates amyloid-β-induced deficits in an Alzheimer’s disease mouse model. Science. 2007;316(5825):750–754.
    View this article via: PubMed CrossRef Google Scholar
22. Olferiev M, Masuda E, Tanaka S, Blank MC, Pricop L. The role of activating protein 1 in the transcriptional regulation of the human FCGR2B promoter mediated by the -343 G→C polymorphism associated with systemic lupus erythematosus. J Biol Chem. 2007; 282 (3):1738–1746.
    View this article via: PubMed Google Scholar
23. Cleary JP, et al. Natural oligomers of the amyloid-beta protein specifically disrupt cognitive function. Nat Neurosci. 2005;8(1):79–84.
    View this article via: PubMed CrossRef Google Scholar
24. Walsh DM, et al. Naturally secreted oligomers of amyloid beta protein potently inhibit hippocampal long-term potentiation in vivo. Nature. 2002;416(6880):535–539.
    View this article via: PubMed CrossRef Google Scholar
25. Shankar GM, et al. Amyloid-beta protein dimers isolated directly from Alzheimer’s brains impair synaptic plasticity and memory. Nat Med. 2008;14(8):837–842.
    View this article via: PubMed CrossRef Google Scholar
26. Oddo S, et al. Triple-transgenic model of Alzheimer’s disease with plaques and tangles: intracellular Abeta and synaptic dysfunction. Neuron. 2003;39(3):409–421.
    View this article via: PubMed CrossRef Google Scholar
27. Billings LM, Oddo S, Green KN, McGaugh JL, Laferla FM. Intraneuronal Abeta causes the onset of early Alzheimer’s disease-related cognitive deficits in transgenic mice. Neuron. 2005;45(5):675–688.
    View this article via: PubMed CrossRef Google Scholar
28. Kumar-Singh S, et al. In vitro studies of Flemish, Dutch, and wild-type β-amyloid provide evidence for two-staged neurotoxicity. Neurobiol Dis. 2002;11(2):330–340.
    View this article via: PubMed CrossRef Google Scholar
29. Sotthibundhu A, Sykes AM, Fox B, Underwood CK, Thangnipon W, Coulson EJ. β-Amyloid_1-42 induces neuronal death through the p75 neurotrophin receptor. J Neurosci. 2008;28(15):3941–3946.
    View this article via: PubMed CrossRef Google Scholar
30. Boyce M, et al. A selective inhibitor of eIF2alpha dephosphorylation protects cells from ER stress. Science. 2005;307(5711):935–939.
    View this article via: PubMed CrossRef Google Scholar
31. Nakagawa T, et al. Caspase-12 mediates endoplasmic-reticulum-specific apoptosis and cytotoxicity by amyloid-beta. Nature. 2000;403(6765):98–103.
    View this article via: PubMed CrossRef Google Scholar
32. Urbanc B, et al. In silico study of amyloid beta-protein folding and oligomerization. Proc Natl Acad Sci U S A. 2004;101(50):17345–17350.
    View this article via: PubMed CrossRef Google Scholar
33. Bush AI. The metallobiology of Alzheimer’s disease. Trends Neurosci. 2003;26(4):207–214.
    View this article via: PubMed CrossRef Google Scholar
34. Crescenzi O, et al. Solution structure of the Alzheimer amyloid beta-peptide (1–42) in an apolar microenvironment. Similarity with a virus fusion domain. Eur J Biochem. 2002;269(22):5642–5648.
    View this article via: PubMed CrossRef Google Scholar
35. Sondermann P, Huber R, Jacob U. Crystal structure of the soluble form of the human fcgamma-receptor IIb: a new member of the immunoglobulin superfamily at 1.7 Α resolution. EMBO J. 1999;18(5):1095–1103.
    View this article via: PubMed CrossRef Google Scholar
36. Goldsmith EB, Erickson BW, Thompson NL. Synthetic peptides from mouse Fc receptor (MoFc gamma RII) that alter the binding of IgG to MoFc gamma RII. Biochemistry. 1997;36(4):952–959.
    View this article via: PubMed CrossRef Google Scholar
37. Wang Q, Walsh DM, Rowan MJ, Selkoe DJ, Anwyl R. Block of long-term potentiation by naturally secreted and synthetic amyloid β-peptide in hippocampal slices is mediated via activation of the kinases c-Jun N-terminal kinase, cyclin-dependent kinase 5, and p38 mitogen-activated protein kinase as well as metabotropic glutamate receptor type 5. J Neurosci. 2004;24(13):3370–3378.
    View this article via: PubMed CrossRef Google Scholar
38. Selkoe DJ. Alzheimer’s disease is a synaptic failure. Science. 2002;298(5594):789–791.
    View this article via: PubMed CrossRef Google Scholar
39. Haass C, Selkoe DJ. Soluble protein oligomers in neurodegeneration: lessons from the Alzheimer’s amyloid beta-peptide. Nat Rev Mol Cell Biol. 2007;8(2):101–112.
    View this article via: PubMed CrossRef Google Scholar
40. Sanchez-Mejia RO, et al. Phospholipase A2 reduction amelioreate cognitive deficits in a mouse model of Alzheimer’s disease. Nat Neurosci. 2008;11(11):1311–1318.
    View this article via: PubMed CrossRef Google Scholar
41. Cissé M, et al. Reversing EphB2 depletion rescues cognitive functions in Alzheimer model. Nature. 2011;469(7328):47–52.
    View this article via: PubMed CrossRef Google Scholar
42. Britschgi M, Wyss-Coray T. Immune cells may fend off Alzheimer disease. Nat Med. 2007;13(4):408–409.
    View this article via: PubMed CrossRef Google Scholar
43. Siffrin V, Brandt AU, Herz J, Zipp F. New insights into adaptive immunity in chronic neuroinflammation. Adv Immunol. 2007;96:1–40.
    View this article via: PubMed Google Scholar
44. Vargas ME, Barres BA. Why is Wallerian degeneration in the CNS so slow? Annu Rev Neurosci. 2007;30:153–179.
    View this article via: PubMed CrossRef Google Scholar
45. Bertram L, et al. Genome-wide association analysis reveals putative Alzheimer’s disease susceptibility loci in addition to APOE. Am J Hum Genet. 2008;83(5):623–632.
    View this article via: PubMed CrossRef Google Scholar
46. Kono H, et al. FcγRIIB Ile232Thr transmembrane polymorphism associated with human systemic lupus erythematosus decreases affinity to lipid rafts and attenuates inhibitory effects on B cell receptor signaling. Hum Mol Genet. 2005;14(19):2881–2892.
    View this article via: PubMed CrossRef Google Scholar
47. Shankar GM, et al. Biochemical and immunohistochemical analysis of an Alzheimer’s disease mouse model reveals the presence of multiple cerebral Aβ assembly forms throughout life. Neurobiol Dis. 2009;36(2):293–302.
    View this article via: PubMed CrossRef Google Scholar
48. Meilandt WJ, et al. Neprilysin overexpression inhibits plaque formation but fails to reduce pathogenic Aβ oligomers and associated cognitive deficits in human amyloid precursor protein transgenic mice. J Neurosci. 2009;29(7):1977–1986.
    View this article via: PubMed CrossRef Google Scholar
49. Cheng IH, et al. Accelerating amyloid-β fibrillization reduces oligomer levels and functional deficits in Alzheimer disease mouse models. J Biol Chem. 2007;282(33):23818–23828.
    View this article via: PubMed CrossRef Google Scholar
50. Janus C, Chishti MA, Westaway D. Transgenic mouse models of Alzheimer’s disease. Biochim Biophys Acta. 2000;1502(1):63–75.
    View this article via: PubMed Google Scholar
51. Westerman MA, et al. The relationship between Abeta and memory in the Tg2576 mouse model of Alzheimer’s disease. J Neurosci. 2002;22(5):1858–1867.
    View this article via: PubMed Google Scholar
52. Cheng IH, Palop JJ, Esposito LA, Bien-Ly N, Yan F, Mucke L. Aggressive amyloidosis in mice expressing human amyloid peptides with the Arctic mutation. Nat Med. 2004;10(11):1190–1192.
    View this article via: PubMed CrossRef Google Scholar
53. Schenk D, et al. Immunization with amyloid-beta attenuates Alzheimer-disease-like pathology in the PDAPP mouse. Nature. 1999;400(6740):173–177.
    View this article via: PubMed CrossRef Google Scholar
54. Bard F, et al. Peripherally administered antibodies against amyloid beta-peptide enter the central nervous system and reduce pathology in a mouse model of Alzheimer disease. Nat Med. 2000;6(8):916–919.
    View this article via: PubMed Google Scholar
55. Park H, et al. Neuropathogenic role of adenylate kinase-1 in Aβ-mediated tau phosphorylation via AMPK and GSK3β. Hum Mol Genet. 2012;21(12):2725–2737.
    View this article via: PubMed CrossRef Google Scholar
56. Woo HN. et al. Inhibition of Bcl10-mediated activation of NF-kappa B by BinCARD, a Bcl10-interacting CARD protein. FEBS Lett. 2004;578(3):239–244.
    View this article via: PubMed CrossRef Google Scholar