Complement component C1q modulates the phagocytosis of Abeta by microglia

Recent studies showing that microglia internalize the amyloid beta-peptide (Abeta) suggest that these cells have the potential for clearing Abeta deposits in Alzheimer's disease, and mechanisms that regulate the removal of Abeta may therefore be of clinical interest. Previous studies from this laboratory showing that C1q enhances phagocytosis of cellular targets by rat microglia prompted the current investigations characterizing the effects of C1q on microglial phagocytosis of Abeta. Microglia were shown to phagocytose Abeta1-42, in agreement with observations of other investigators. Uptake of Abeta1-42 was observed for concentrations of 5-50 microM, and phagocytosis of peptides containing (14)C or fluorescein (FM) labels was not affected by the interaction of microglia with C1q-coated surfaces. However, inclusion of C1q (125 nM-1.4 microM) in solutions of 50 microM Abeta1-42 inhibited the uptake of (14)C-Abeta1-42 and FM-Abeta1-42, suggesting that C1q blocks the interaction of Abeta with microglia. Uptake of Abeta was partially blocked by the scavenger receptor ligands polyinosinic acid and maleylated BSA. Inhibition of Abeta uptake by C1q may contribute to the accumulation of fibrillar, C1q-containing plaques that occurs in parallel with disease progression. These data suggest that mechanisms which interfere with the binding of C1q to Abeta may be of therapeutic value both through inhibition of the inflammatory events resulting from complement activation and via altered access of Abeta sites necessary for ingestion by microglia.     

Microglia, amyloid, and cognition in Alzheimer's disease: An [11C](R)PK11195-PET and [11C]PIB-PET study

[11C](R)PK11195-PET is a marker of activated microglia while [11C]PIB-PET detects raised amyloid load. Here we studied in vivo the distributions of amyloid load and microglial activation in Alzheimer's disease (AD) and their relationship with cognitive status. Thirteen AD subjects had [11C](R)PK11195-PET and [11C]PIB-PET scans. Ten healthy controls had [11C](R)PK11195-PET and 14 controls had [11C]PIB-PET scans. Region-of-interest analysis of [11C](R)PK11195-PET detected significant 20–35% increases in microglial activation in frontal, temporal, parietal, occipital and cingulate cortices (p < 0.05) of the AD subjects. [11C]PIB-PET revealed significant two-fold increases in amyloid load in these same cortical areas (p < 0.0001) and SPM (statistical parametric mapping) analysis confirmed the localisation of these increases to association areas. MMSE scores in AD subjects correlated with levels of cortical microglial activation but not with amyloid load. The inverse correlation between MMSE and microglial activation is compatible with a role of microglia in neuronal damage.     

Induction of cytokines in glial cells surrounding cortical β-amyloid plaques in transgenic Tg2576 mice with Alzheimer pathology

β-Amyloid plaque deposition observed in brains from Alzheimer patients, might function as immune stimulus for glial/macrophages activation, which is supported by observations of activated microglia expressing interleukin (IL)-1β and elevated IL-6 immunoreactivity in close proximity to amyloid plaques. To elucidate the mechanisms involved in β-amyloid-mediated inflammation, transgenic mice (Tg2576) expressing high levels of the Swedish double mutation of human amyloid precursor protein and progressively developing typical β-amyloid plaques in cortical brain regions including gliosis and astrocytosis, were examined for the expression pattern of a number of cytokines.Using ribonuclease protection assay, interleukin (IL)-1α,-β, IL-1 receptor antagonist, IL-6, IL-10, IL-12, IL-18, interferon-γ, and macrophage migration inhibitory factor (MIF) mRNA were not induced in a number of cortical areas of Tg2576 mice regardless of the postnatal ages studied ranging between 2 and 13 months. Using immunocytochemistry for IL-1α,β, IL-6, tumor necrosis factor (TNF)-α, and macrophage chemotactic protein (MCP)-1, only IL-1β was found to be induced in reactive astrocytes surrounding β-amyloid deposits detected in 14-month-old Tg2576 mice. Using non-radioactive in situ hybridization glial fibrillary acidic protein (GFAP) mRNA was detected to be expressed by reactive astrocytes in close proximity to β-amyloid plaques. The local immune response detected around cortical β-amyloid deposits in transgenic Tg2576 mouse brain is seemingly different to that observed in brains from Alzheimer patients but may represent an initial event of chronic neuroinflammation at later stages of the disease.     

Isolated Amyloid-β(1-42) Protofibrils, But Not Isolated Fibrils, Are Robust Stimulators of Microglia

Senile plaques composed of amyloid-β protein (Aβ) are an unshakable feature of the Alzheimer's disease (AD) brain. Although there is significant debate on the role of the plaques in AD progression, there is little disagreement on their role in stimulating a robust inflammatory response within the context of the disease. Significant inflammatory markers such as activated microglia and cytokines are observed almost exclusively surrounding the plaques. However, recent evidence suggests that the plaque exterior may contain a measurable level of soluble Aβ aggregates. The observations that microglia activation in vivo is selectively stimulated by distinct Aβ deposits led us to examine what specific form of Aβ is the most effective proinflammatory mediator in vitro. We report here that soluble prefibrillar species of Aβ(1-42) were better than fibrils at inducing microglial tumor necrosis factor α (TNFα) production in either BV-2 and primary murine microglia. Reconstitution of Aβ(1-42) in NaOH followed by dilution into F-12 media and isolation with size exclusion chromatography (SEC) revealed classic curvilinear β-sheet protofibrils 100 nm in length. The protofibrils, but not monomers, markedly activated BV-2 microglia. Comparisons were also made between freshly isolated protofibrils and Aβ(1-42) fibrils prepared from SEC-purified monomer. Surprisingly, while isolated fibrils had a much higher level of thioflavin T fluorescence per mole, they were not effective at stimulating either primary or BV-2 murine microglia compared to protofibrils. Furthermore, SEC-isolated Aβ(1-40) protofibrils exhibited significantly less activity than concentration-matched Aβ(1-42). This report is the first to demonstrate microglial activation by SEC-purified protofibrils, and the overall findings indicate that small, soluble Aβ(1-42) protofibrils induce much greater microglial activation than mature insoluble fibrils.     

Autoradiographical imaging of PPARγ agonist effects on PBR/TSPO binding in TASTPM mice

Chronic inflammation is known to occur in the brains of Alzheimer's Disease (AD) patients, including the presence of activated microglia close to amyloid plaques. We utilised real time autoradiography and immunohistochemistry to investigate microglial activation and the potential anti-inflammatory effects of PPARγ agonists in the Thy-1 APP695swe/Thy-1 PS-1.M146V (TASTPM) overexpressing transgenic mouse model of AD. An age dependent increase in specific [³H](R)-PK11195 binding to peripheral benzodiazepine receptors (PBR)/translocator protein (18 kDa) (TSPO) was observed in the cortex of TASTPM mice compared to wild type mice, indicative of microglial activation. This was consistent with immunohistochemical data showing age-dependent increases in CD68 immunoreactivity co-localised with amyloid β (Aβ) deposits. In 10 month old TASTPM mice, pioglitazone (20 mg/kg) and ciglitazone (50 mg/kg) significantly reduced [³H](R)-PK11195 and [³H]DPA-713 binding in cortex and hippocampus, indicative of reduced microglial activation. In AD brain, significant [³H](R)-PK11195 and [³H]DPA-713 binding was observed across all stages of the disease. These results support the use of PBR/TSPO autoradiography in TASTPM mice as a functional readout of microglial activation to assess anti-inflammatory drugs prior to evaluation in AD patients.     

The Presence of Isoaspartic Acid in β-Amyloid Plaques Indicates Plaque Age

Extracellular deposits of fibrillar β-amyloid are a characteristic neuropathology of Alzheimer's disease (AD). We have developed a novel antibody to a hypothesized “older isomer” of the amyloid protein. This antibody, raised against a synthetic β-amyloid peptide containing isoaspartic acid at position 7 (isoaspartic-7-Aβ), reacts with isoaspartic-7-Aβ, a nonenzymatic modification found in long-lived proteins. Plaques stained with this antibody are thioflavine positive and are found throughout the frontal and entorhinal cortices of AD cases. In frontal cortex, isoaspartic-7-Aβ plaques are clustered but have a widespread distribution in all cortical layers. Isoaspartic-7-Aβ is found primarily in the core of individual plaques surrounded by nonisomerized amyloid. Activated microglia are associated with plaques containing isomerized and nonisomerized amyloid. In contrast to AD, isoaspartic-7-Aβ plaques in Down's syndrome (DS) cases are found primarily in the superficial layers of frontal cortex. Using image analysis isoaspartic-7-Aβ deposition was correlated with dementia severity in AD and with age in DS. The results indicate that this antibody against altered aspartyl amyloid could be a useful indicator of the age of amyloid plaques.     

Activation of human microglia by fibrillar prion protein-related peptides is enhanced by amyloid-associated factors SAP and C1q

Complement activation products C1q and C3d, serum amyloid P component (SAP) and activated glial cells accumulate in amyloid deposits of conformationally changed prion protein (PrP(Sc)) in Creutzfeldt-Jakob disease, Gerstmann-Str?ussler-Scheinker disease and scrapie-infected mouse brain. Biological properties, including the potential to activate microglia, relate to prion (PrP) peptide fibrillogenic abilities. We investigated if SAP and C1q influence the fibrillogenic properties of human and mouse PrP peptide and concomitantly their stimulatory effects on human microglia in vitro. PrP-peptide induced microglial IL-6 and TNF-alpha release significantly increased in the presence of SAP and C1q. Also, SAP and C1q enhanced PrP-peptide fibril formation as revealed by electron microscopy and thioflavin S-based quantitative assays. This suggests that SAP and C1q contribute to fibrillar state-dependent cellular effects of PrP. Combined, ultrastructural and thioflavin assays, together with microglial cytokine release measurements, provide a test system to screen potential, fibrillarity impeding therapeutics for prion disease.     

Microglia and cytokines in neurological disease,with special reference to AIDS and Alzheimer's disease

Microglia are associated with central nervous system (CNS) pathology of both Alzheimer's disease (AD) and the acquired immunodeficiency syndrome (AIDS). In AD, microglia, especially those associated with amyloid deposits, have a phenotype that is consistent with a state of activation, including immunoreactivity with antibodies to class II major histocompatibility antigens and to inflammatory cytokines (interleukin-1-β and tumor necrosis factor-α). Evidence from other studies in rodents indicate that microglia can be activated by neuronal degeneration. These results suggest that microglial activation in AD may be secondary to neurodegeneration and that, once activated, microglia may participate in a local inflammatory cascade that promotes tissue damage and contributes to amyloid formation. In AIDS, microglia are the primary target of retroviral infection. Both ramified and ameboid microglia, in addition to multinucleated giant cells, are infected by the human immunodeficiency virus (HIV-1). The mechanism of microglial infection is not known since microglia lack CD4, the HIV-1 receptor. Microglia display high affinity receptors for immunoglobulins, which makes antibody-mediated viral uptake a possible mechanism of infection. In AIDS, the extent of active viral infection and cytokine production may be critically dependent upon other factors, such as the presence of coinfecting agents. In the latter circumstance, very severe CNS pathology may emerge, including necrotizing lesions. In other circumstances, HIV infection microglia probably leads to CNS pathology by indirect mechanisms, including release of viral proteins (gp120) and toxic cytokines. Such a mechanism is the best hypothesis for the pathogenesis of vacuolar myelopathy in adults and the diffuse gliosis that characterizes pediatric AIDS, in which very little viral antigen can be detected.     

Microglial CX3CR1 production increases in Alzheimer's disease and is regulated by noradrenaline

The loss of noradrenergic neurons and subsequent reduction of brain noradrenaline (NA) levels are associated with the progression of Alzheimer's disease (AD). This seems to be due mainly to the ability of NA to reduce the activation of microglial cells. We previously observed that NA induces the production of the chemokine Fractalkine/CX3CL1 in neurons. The activation of microglial CX3CR1, sole receptor for CX3CL1, reduces the activation of microglia, which is known to largely contribute to the neuronal damage characteristic of AD. Therefore, alterations of CX3CR1 production in microglia could translate into the enhancement or inhibition of CX3CL1 anti‐inflammatory effects. In order to determine if microglial CX3CR1 production is altered in AD and if NA can control it, CX3CR1 expression and synthesis were analyzed in 5xFAD mice and human AD brain samples. In addition, the effects of NA and its reuptake inhibitor reboxetine were analyzed in microglial cultures and mice respectively. Our results indicate that in AD CX3CR1 production is increased in the brain cortex and that reboxetine administration further increases it and enhances microglial reactivity toward amyloid beta plaques. However, direct administration of NA to primary rat microglia or human HMC3 cells inhibits CX3CR1 production, suggesting that microglia responses to NA may be altered in the absence of CX3CL1‐producing neurons or other nonmicroglial external factors.     

Complement component C3 and complement receptor type 3 contribute to the phagocytosis and clearance of fibrillar Aβ by microglia

Complement components and their receptors are found within and around amyloid β (Aβ) cerebral plaques in Alzheimer's disease (AD). Microglia defend against pathogens through phagocytosis via complement component C3 and/or engagement of C3 cleavage product iC3b with complement receptor type 3 (CR3, Mac-1). Here, we provide direct evidence that C3 and Mac-1 mediate, in part, phagocytosis and clearance of fibrillar amyloid-β (fAβ) by murine microglia in vitro and in vivo. Microglia took up not only synthetic fAβ₄₂ but also amyloid cores from patients with AD, transporting them to lysosomes in vitro. Fibrillar Aβ₄₂ uptake was significantly attenuated by the deficiency or knockdown of C3 or Mac-1 and scavenger receptor class A ligands. In addition, C3 or Mac-1 knockdown combined with a scavenger receptor ligand, fucoidan, further attenuated fibrillar Aβ₄₂ uptake by N9 microglia. Fluorescent fibrillar Aβ₄₂ microinjected cortically was significantly higher in C3 and Mac-1 knockout mice compared with wild-type mice 5 days after surgery, indicating reduced clearance in vivo. Together, these results demonstrate that C3 and Mac-1 are involved in phagocytosis and clearance of fAβ by microglia, providing support for a potential beneficial role for microglia and the complement system in AD pathogenesis. © 2012 Wiley Periodicals, Inc.     

Microglia contributes to plaque growth by cell death due to uptake of amyloid β in the brain of Alzheimer's disease mouse model

Pathological hallmarks of Alzheimer's disease (AD) include extracellularly accumulated amyloid β (Aβ) plaques and intracellular neurofibrillary tangles in the brain. Activated microglia, brain‐resident macrophages, are also found surrounding Aβ plaques. The study of the brain of AD mouse models revealed that Aβ plaque formation is completed by the consolidation of newly generated plaque clusters in vicinity of existed plaques. However, the dynamics of Aβ plaque formation, growth and the mechanisms by which microglia contribute to Aβ plaque formation are unknown. In the present study, we confirmed how microglia are involved in Aβ plaque formation and their growth in the brain of 5XFAD mice, the Aβ‐overexpressing AD transgenic mouse model, and performed serial intravital two‐photon microscopy (TPM) imaging of the brains of 5XFAD mice crossed with macrophage/microglia‐specific GFP‐expressing CX3CR1^GFP/GFP mice. We found that activated microglia surrounding Aβ plaques take up Aβ, which are clusters developed inside activated microglia in vivo and this was followed by microglial cell death. These dying microglia release the accumulated Aβ into the extracellular space, which contributes to Aβ plaque growth. This process was confirmed by live TPM in vivo imaging and flow cytometry. These results suggest that activated microglia can contribute to formation and growth of Aβ plaques by causing microglial cell death in the brain. GLIA 2016;64:2274–2290     

Ultrastructure of the microglia that phagocytose amyloid and the microglia that produce β-amyloid fibrils

Summary The function of microglia associated with -amyloid deposits still remains a controversial issue. On the basis of recent ultrastructural data, microglia were postulated to be cells that form amyloid fibrils, not phagocytes that remove amyloid deposits. In this electron microscopic study, we examined the ability of microglia to ingest and digest exogenous amyloid fibrils in vitro. We demonstrate that amyloid fibrils are ingested by cultured microglial cells and collected and stored in phagosomes. The ingested, nondegraded amyloid remains within phagosomes for up to 20 days, suggesting a very limited effectiveness of microglia in degrading -amyloid fibrils. On the other hand, we showed that in microglial cells of classical plaques in brain cortex of patients with Alzheimer's disease, amyloid fibrils appear first in altered endoplasmic reticulum and deep infoldings of cell membranes. These differences in intracellular distribution of amyloid fibrils in microglial cells support our observations that microglial cells associated with amyloid plaques are engaged in production of amyloid, but not in phagocytosis.Supported by funds from the the New York State Office of Mental Retardation and Developmental Disabilities and a grant from the National Institutes of Health, National Institute on Aging, Grant No. PO1-AGO-4220, AGO-5892     

Amyloid-β peptide activates cultured astrocytes: morphological alterations, cytokine induction and nitric oxide release

A common feature of many neurodegenerative disorders is an abundance of activated glial cells (astrocytes and microglia). In Alzheimer's disease (AD), activated astrocytes are in close apposition to and surrounding the amyloid plaques. The mechanisms by which the astrocytes become activated in AD and the consequences of reactive astrocytosis to disease progression are not known. We examined the possibility that the amyloid-β (Aβ) peptide, a major constituent of the amyloid plaque, could act as a stimulus leading to activation. We found that treatment of rat cortical astrocyte cultures with aggregated Aβ 1–42 peptide induces activation, as assessed by reactive morphological changes and upregulation of selective glial mRNA and proteins, such as the inflammatory cytokine interleukin-1β. Aβ also stimulates inducible nitric oxide synthase (iNOS) mRNA levels and nitric oxide (NO) release. Aβ 1–42, a major form of amyloid associated with neurotoxicity, activated astrocytes in a time- and dose-dependent manner, whereas a scrambled Aβ 1–42 sequence or Aβ 17–42 had little or no effect. We also determined that the Aβ activity can be found in a supernatant fraction containing soluble Aβ oligomers. Our data suggest that Aβ plays a role in the reactive astrocytosis of AD and that the inflammatory response induced upon glial activation is a critical component of the neurodegenerative process.     

Synergy of TRIF-dependent TLR3 and MyD88-dependent TLR7 in up-regulating expression of mouse FPR2, a promiscuous G-protein-coupled receptor, in microglial cells

Human G-protein-coupled formyl peptide receptor-like 1 and its mouse homologue formyl peptide receptor 2 mediate the chemotactic activity of a variety of pathogen and host-derived peptides, including amyloid β₄₂, a key causative factor in Alzheimer's disease (AD).Here, we found that polyinosine–polycytidylic acid (Poly(I:C)), which is a specific TLR3 ligand, and Imiquimod (R837), which is a specific TLR7 ligand, when used alone, each increased MAPK-dependent functional mFPR2 expression in microglial cells, and the combination of Poly(I:C) and R837 exhibited additive effect by enhancing the level of IκB-α phosphorylation. Our results indicated that RNA virus infection may actively participate in the pathogenic processes of brain inflammation and neurodegenerative diseases by TLR3- and TLR7-mediated TRIF-dependent and MyD88-dependent signaling pathways.     

DW14006 as a direct AMPKα1 activator improves pathology of AD model mice by regulating microglial phagocytosis and neuroinflammation

Alzheimer’s disease (AD) is a progressively neurodegenerative disease with typical hallmarks of amyloid β (Aβ) plaque accumulation, neurofibrillary tangle (NFT) formation and neuronal death extension. In AD brain, activated microglia phagocytose Aβ and neuronal debris, but also aggravate inflammation stress by releasing inflammatory factors and cytotoxins. Improving microglia on Aβ catabolism and neuroinflammatory intervention is thus believed to be a promising therapeutic strategy for AD. AMP-activated protein kinase (AMPK) is highly expressed in microglia with AMPKα1 being tightly implicated in neuroinflammatory events. Since indirect AMPKα1 activators may cause side effects with undesired intracellular AMP/ATP ratio, we focused on direct AMPKα1 activator study by exploring its potential function in ameliorating AD-like pathology of AD model mice. Here, we reported that direct AMPKα1 activator DW14006 (2-(3-(7-chloro-6-(2′-hydroxy-[1,1′-biphenyl]-4-yl)-2-oxo-1,2-dihydroquinolin-3-yl)phenyl)acetic acid) effectively improved learning and memory impairments of APP/PS1 mice, and the underlying mechanisms have been intensively investigated. DW14006 reduced amyloid plaque deposition by promoting microglial o-Aβ₄₂ phagocytosis and ameliorated innate immune response by polarizing microglia to an anti-inflammatory phenotype. It selectively enhanced microglial phagocytosis of o-Aβ₄₂ by upgrading scavenger receptor CD36 through AMPKα1/PPARγ/CD36 signaling and suppressed inflammation by AMPKα1/IκB/NFκB signaling. Together, our work has detailed the crosstalk between AMPKα1 and microglia in AD model mice, and highlighted the potential of DW14006 in the treatment of AD.     

X11α haploinsufficiency enhances Aβ amyloid deposition in Alzheimer's disease transgenic mice

The neuronal adaptor protein X11α/mint-1/APBA-1 binds to the cytoplasmic domain of the amyloid precursor protein (APP) to modulate its trafficking and metabolism. We investigated the consequences of reducing X11α in a mouse model of Alzheimer's disease (AD). We crossed hAPPswe/PS-1ΔE9 transgenic (AD tg) mice with X11α heterozygous knockout mice in which X11α expression is reduced by approximately 50%. The APP C-terminal fragments C99 and C83, as well as soluble Aβ40 and Aβ42, were increased significantly in brain of X11α haploinsufficient mice. Aβ/amyloid plaque burden also increased significantly in the hippocampus and cortex of one year old AD tg/X11α (+/−) mice compared to AD tg mice. In contrast, the levels of sAPPα and sAPPβ were not altered significantly in AD tg/X11α (+/−) mice. The increased neuropathological indices of AD in mice expressing reduced X11α suggest a normal suppressor role for X11α on CNS Aβ/amyloid deposition.     

C1q, the recognition subcomponent of the classical pathway of complement, drives microglial activation

Microglia, central nervous system (CNS) resident phagocytic cells, persistently police the integrity of CNS tissue and respond to any kind of damage or pathophysiological changes. These cells sense and rapidly respond to danger and inflammatory signals by changing their cell morphology; by release of cytokines, chemokines, or nitric oxide; and by changing their MHC expression profile. We have shown previously that microglial biosynthesis of the complement subcomponent C1q may serve as a reliable marker of microglial activation ranging from undetectable levels of C1q biosynthesis in resting microglia to abundant C1q expression in activated, nonramified microglia. In this study, we demonstrate that cultured microglial cells respond to extrinsic C1q with a marked intracellular Ca(2+) increase. A shift toward proinflammatory microglial activation is indicated by the release of interleukin-6, tumor necrosis factor-alpha, and nitric oxide and the oxidative burst in rat primary microglial cells, an activation and differentiation process similar to the proinflammatory response of microglia to exposure to lipopolysaccharide. Our findings indicate 1) that extrinsic plasma C1q is involved in the initiation of microglial activation in the course of CNS diseases with blood-brain barrier impairment and 2) that C1q synthesized and released by activated microglia is likely to contribute in an autocrine/paracrine way to maintain and balance microglial activation in the diseased CNS tissue.     

Accumulation of a repulsive axonal guidance molecule RGMa in amyloid plaques: a possible hallmark of regenerative failure in Alzheimer's disease brains

J. Satoh, H. Tabunoki, T. Ishida, Y. Saito and K. Arima (2013) Neuropathology and Applied Neurobiology 39, 109–120 Accumulation of a repulsive axonal guidance molecule RGMa in amyloid plaques: a possible hallmark of regenerative failure in Alzheimer's disease brains Aims: RGMa is a repulsive guidance molecule that induces the collapse of axonal growth cones by interacting with the receptor neogenin in the central nervous system during development. It remains unknown whether RGMa plays a role in the neurodegenerative process of Alzheimer's disease (AD). We hypothesize that RGMa, if it is concentrated on amyloid plaques, might contribute to a regenerative failure of degenerating axons in AD brains. Methods: By immunohistochemistry, we studied RGMa and neogenin (NEO1) expression in the frontal cortex and the hippocampus of 6 AD and 12 control cases. The levels of RGMa expression were determined by qRT‐PCR and Western blot in cultured human astrocytes following exposure to cytokines and amyloid beta (Aβ) peptides. Results: In AD brains, an intense RGMa immunoreactivity was identified on amyloid plaques and in the glial scar. In the control brains, the glial scar and vascular foot processes of astrocytes expressed RGMa immunoreactivity, while oligodendrocytes and microglia were negative for RGMa. In AD brains, a small subset of amyloid plaques expressed a weak NEO1 immunoreactivity, while some reactive astrocytes in both AD and control brains showed an intense NEO1 immunoreactivity. In human astrocytes, transforming growth factor beta‐1 (TGFβ₁), Aβ_1–40 or Aβ_1–42 markedly elevated the levels of RGMa, and TGFβ₁ also increased its own levels. Coimmunoprecipitation analysis validated the molecular interaction between RGMa and the C‐terminal fragment β of amyloid beta precursor protein (APP). Furthermore, recombinant RGMa protein interacted with amyloid plaques in situ. Conclusions: RGMa, produced by TGFβ‐activated astrocytes and accumulated in amyloid plaques and the glial scar, could contribute to the regenerative failure of degenerating axons in AD brains.