Seminars in Cell & Developmental Biology, 2017
The neuronal gene Arc is essential for long-lasting information storage in the mammalian brain an... more The neuronal gene Arc is essential for long-lasting information storage in the mammalian brain and has been implicated in various neurological disorders. However, little is known about Arc's evolutionary origins. Recent studies suggest that mammalian Arc originated from a vertebrate lineage of Ty3/gypsy retrotransposons, which are also ancestral to retroviruses. In particular, Arc contains homology to the Gag polyprotein that forms the viral capsid and is essential for viral infectivity. This surprising connection raises the intriguing possibility that Arc may share molecular characteristics of retroviruses.
Arc (activity-regulated cytoskeleton-associated protein) is a neuron-specific immediate early gen... more Arc (activity-regulated cytoskeleton-associated protein) is a neuron-specific immediate early gene that is required for enduring forms of synaptic plasticity and memory in the mammalian brain. Arc expression is highly dynamic, and tightly regulated by neuronal activity and experience. Local translation of Arc protein at synapses is critical for synaptic plasticity, which is mediated by Arc-dependent trafficking of AMPA (α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid)-type glutamate receptors. To date, few structural or biophysical properties of Arc protein have been investigated. Recent studies, including that of Myrum et al. published in the 468:1 issue of the Biochemical Journal, now shed light on some intriguing biophysical properties of Arc. These findings show that Arc contains large N- and C-terminal domains around a flexible linker region and that purified Arc protein is capable of self-oligomerization. Intriguingly, these domains show homology with the viral capsid pro...
Autism spectrum disorder (ASD) and Fragile X syndrome (FXS) are relatively common childhood neuro... more Autism spectrum disorder (ASD) and Fragile X syndrome (FXS) are relatively common childhood neurodevelopmental disorders with increasing incidence in recent years. They are currently accepted as disorders of the synapse with alterations in different forms of synaptic communication and neuronal network connectivity. The major excitatory neurotransmitter system in brain, the glutamatergic system, is implicated in learning and memory, synaptic plasticity, neuronal development. While much attention is attributed to the role of metabotropic glutamate receptors in ASD and FXS, studies indicate that the ionotropic glutamate receptors (iGluRs) and their regulatory proteins are also altered in several brain regions. Role of iGluRs in the neurobiology of ASD and FXS is supported by a weight of evidence that ranges from human genetics to in vitro cultured neurons. In this review we will discuss clinical, molecular, cellular and functional changes in NMDA, AMPA and kainate receptors and the synaptic proteins that regulate them in the context of ASD and FXS. We will also discuss the significance for the development of translational biomarkers and treatments for the core symptoms of ASD and FXS.
. Notably, the memory and cognitive decline observed in AD patients correlates better with the sy... more . Notably, the memory and cognitive decline observed in AD patients correlates better with the synaptic pathology than either plaques or tangles, and thus, synaptic dysfunction is likely the most significant factor contributing to the initial stages of memory Gene-targeted and transgenic mice have proven to be invaluable for modeling various aspects of AD neuro-University of California, Irvine Irvine, California 92697 pathology, although no mouse model fully recapitulates its entire neuropathological spectrum (Wong et al., 3 Department of Neuroscience and Pharmacology Mayo Clinic Jacksonville 2002). Numerous models have successfully replicated amyloid plaque deposition, generally by deriving mice Jacksonville, Florida 32224 4 Laboratory of Neurosciences with relatively high levels of APP overexpression, and inclusion of a mutant PS1 allele can accelerate the depo-Gerontology Research Center National Institute on Aging sition rate as well as exacerbate the pathological severity. The discovery of tau gene mutations in frontotempo-Baltimore, Maryland 21224 ral dementia with parkinsonism linked to chromosome 17 kindreds facilitated the development of tauopathies in transgenic mice (Gotz et al., 2001a; Higuchi et al., Summary 2002; Lewis et al., 2000) . One surprising aspect of the overwhelming majority of extant AD models has been The neuropathological correlates of Alzheimer's disease (AD) include amyloid- (A) plaques and neuro-that the successful development of one hallmark pathological lesion has in and of itself been insufficient to fibrillary tangles. To study the interaction between A and tau and their effect on synaptic function, we de-trigger the development of the other signature lesion. Consequently, the concomitant manifestation of both rived a triple-transgenic model (3ϫTg-AD) harboring PS1 M146V , APP Swe , and tau P301L transgenes. Rather than plaques and tangles has required the introduction of multiple transgenes into the same mouse, which has crossing independent lines, we microinjected two transgenes into single-cell embryos from homozygous generally been achieved by crossing several independent transgenic lines, or alternatively, by microinjecting PS1 M146V knockin mice, generating mice with the same genetic background. 3ϫTg-AD mice progressively de-pathological protein into the brains of single-transgenic mice (Gotz et al., 2001b; Lewis et al., 2001). velop plaques and tangles. Synaptic dysfunction, including LTP deficits, manifests in an age-related man-Here, we describe the development of a novel tripletransgenic model (3ϫTg-AD). Instead of crossing three ner, but before plaque and tangle pathology. Deficits in long-term synaptic plasticity correlate with the ac-independent lines, we derived our transgenic model by directly introducing two additional transgenes into the cumulation of intraneuronal A. These studies suggest a novel pathogenic role for intraneuronal A with re-germline of a genetically modified mouse. We report that (to our knowledge) this is the first transgenic model gards to synaptic plasticity. The recapitulation of salient features of AD in these mice clarifies the relation-to develop both plaque and tangle pathology in ADrelevant brain regions. The 3ϫTg-AD mice develop ex-ships between A, synaptic dysfunction, and tangles and provides a valuable model for evaluating potential tracellular A deposits prior to tangle formation, consistent with the amyloid cascade hypothesis. These mice AD therapeutics as the impact on both lesions can be assessed. exhibit deficits in synaptic plasticity, including long-term potentiation (LTP) that occurs prior to extracellular A Introduction deposition and tangles but is associated with intracellular A immunoreactivity. Double-transgenic mice (2ϫTg) Alzheimer's disease (AD), a progressive neurodegeneralacking the human APP transgene (but containing tive disorder that is the most common cause of dementia PS1 M146V and tau P301L ) do not develop any extracellular in the elderly, is characterized by two hallmark lesions: plaques nor do they show any significant intraneuronal diffuse and neuritic plaques, which are predominantly A immunoreactivity. Notably, the 2ϫTg mice do not composed of the A peptide, and neurofibrillary tangles, exhibit any LTP deficits, despite expressing the tau composed of filamentous aggregates of hyperphostransgene to comparable levels as the 3ϫTg-AD mice. phorylated tau protein (Selkoe, 2001). Loss of neuronal Therefore, such findings suggest a novel pathophysiosynaptic density and synapse number represent another logic role for intraneuronal A and indicate that synaptic invariant feature of the disease that appears to precede dysfunction is a proximal defect in the pathobiology of overt neuronal degeneration (DeKosky and Scheff, 1990; AD, preceding extracellular plaque formation and tangles. These 3ϫTg-AD mice will be useful for studying the impact of A and tau on synaptic plasticity and for ELISAs and Immunoblot A ELISAs were performed essentially as described previously Su-References zuki et al., 1994). For immunoblot, brains from transgenic and control mice were dounce homogenized in a solution of 2% SDS in H 2 0 Bliss, T.V., and Collingridge, G.L. (1993). A synaptic model of memcontaining 0.7 mg/ml Pepstatin A supplemented with complete Mini ory: long-term potentiation in the hippocampus. Nature 361, 31-39. protease inhibitor tablet (Roche 1836153). The homogenized mixes Caroni, P. (1997). Overexpression of growth-associated proteins in were briefly sonicated to shear the DNA and centrifuged at 4ЊC for the neurons of adult transgenic mice. J. Neurosci. Methods 71, 3-9. 1 hr at 100,000 ϫ g. The supernatant was used for immunoblot analysis. Proteins were resolved by SDS/PAGE (10% Bis-Tris from Chapman, P.F., White, G.L., Jones, M.W., Cooper-Blacketer, D., Invitrogen) under reducing conditions and transferred to nitrocellu-Marshall, V.J., Irizarry, M., Younkin, L., Good, M.A., Bliss, T.V., Hylose membrane. The membrane was incubated in a 5% solution of man, B.T., et al. (1999). Impaired synaptic plasticity and learning in nonfat milk for 1 hr at 20ЊC. After overnight incubation at 4ЊC with aged amyloid precursor protein transgenic mice. Nat. Neurosci. 2, the primary antibody, the blots were washed in Tween-TBS for 20 271-276. min and incubated at 20ЊC with the secondary antibody. The blots Chui, D.H., Tanahashi, H., Ozawa, K., Ikeda, S., Checler, F., Ueda, O., were washed in T-TBS for 20 min and incubated for 5 min with Suzuki, H., Araki, W., Inoue, H., Shirotani, K., et al. (1999). Transgenic Super Signal (Pierce). mice with Alzheimer presenilin 1 mutations show accelerated neurodegeneration without amyloid plaque formation. Nat. Med. 5, 560-564. Immunohistochemistry Formalin-fixed, paraffin-embedded brains were sectioned at 5 m, DeKosky, S.T., and Scheff, S.W. (1990). Synapse loss in frontal cortex biopsies in Alzheimer's disease: correlation with cognitive sever-mounted onto silane-coated slides and processed as described. The following antibodies were used: anti-A 6E10 and 4G8 (Signet ity. Ann. Neurol. 27, 457-464. Laboratories, Dedham, MA), anti-A 1560 (Chemicon), A11 (Kayed Dickson, D.W., Crystal, H.A., Bevona, C., Honer, W., Vincent, I., and et al., 2003), anti-APP 22C11 (Chemicon), anti-Tau HT7, AT8, AT180 Davies, P. (1995). Correlations of synaptic and pathological markers (Innogenetics), Tau C17 (Santa Cruz), Tau 5 (Calbiochem), anti-GFAP with cognition of the elderly. Neurobiol. Aging 16, 285-304. (Dako), and anti-actin (Sigma). Primary antibodies were applied at Fitzjohn, S.M., Morton, R.A., Kuenzi, F., Rosahl, T.W., Shearman, dilutions of 1:3000 for GFAP; 1:1000 for 6E10; 1:500 for 1560, AT8, M., Lewis, H., Smith, D., Reynolds, D.S., Davies, C.H., Collingridge, AT180, and Tau5; and 1:200 for HT7. G.L., et al. (2001). Age-related impairment of synaptic transmission but normal long-term potentiation in transgenic mice that overexpress the human APP695SWE mutant form of amyloid precursor Electrophysiology protein. J. Neurosci. 21, 4691-4698. Mice were anaesthetized with halothane, decapitated, and the brains were rapidly removed in ice-cold artificial cerebrospinal fluid Flood, D.G., and Coleman, P.D. (1990). Hippocampal plasticity in (aCSF; 125 mM NaCl, 2.5 mM KCl, 1.25 mM KH 2 PO 4 , 25 mM NaHCO 3 , normal aging and decreased plasticity in Alzheimer's disease. Prog. 1.2 mM MgSO 4 , 2 mM CaCl 2 , and 10 mM dextrose, bubbled with Brain Res. 83, 435-443. 95% O 2 , 5% CO 2 [pH 7.4]). Transverse hippocampal slices (400 m) Gotz, J., Chen, F., Barmettler, R., and Nitsch, R.M. (2001a). Tau were prepared in aCSF using a vibroslice and left to equilibrate for filament formation in transgenic mice expressing P301L tau. J. Biol. at least 1 hr prior to recording in a holding chamber containing aCSF Chem. 276, 529-534. at room temperature. Gotz, J., Chen, F., van Dorpe, J., and Nitsch, R.M. (2001b). Formation Slices were placed in an interface chamber, continuously perfused of neurofibrillary tangles in P301l tau transgenic mice induced by with aCSF at 34ЊC, and covered with a continuous flow of warmed Abeta 42 fibrils. Science 293, 1491-1495. humidified gas (95% O 2 , 5% CO 2 ). Field excitatory postsynaptic potentials (fEPSPs) were recorded in the stratum radiatum of the et al. CA1 using glass microelectrodes (1-5⍀, ف 5 m diameter) filled with aCSF. Synaptic responses were evoked by stimulation of the (2000). Intraneuronal Abeta42 accumulation in human brain. Am. J. Pathol. 156, 15-20. Schaffer collateral/commissural pathway with a concentric bipolar stimulating electrode with 0.1 ms pulse width. Input/output curves Grundke-Iqbal, I., Iqbal, K., George, L., Tung, Y.C., Kim, K.S., and were generated using stimulus intensities from 0 to 300 A in incre-Wisniewski, H.M. (1989). Amyloid protein and neurofibrillary tangles ments of 20 A. PPF was assessed using an interstimulus interval coexist in the...
A myriad of mechanisms are suggested to account for the full richness of visual cortical plastici... more A myriad of mechanisms are suggested to account for the full richness of visual cortical plasticity. We report that visual cortex lacking Arc is impervious to the effects of deprivation or experience. Using intrinsic signal imaging and chronic visually evoked potential recordings, we find that Arc −/− mice do not exhibit depression of deprived eye responses or a shift in ocular dominance after brief monocular deprivation. Extended deprivation also fails to elicit a shift in ocular dominance or open eye potentiation. Moreover, Arc −/− mice lack stimulus-selective response potentiation. Although Arc −/− mice exhibit normal visual acuity, baseline ocular dominance is abnormal and resembles that observed after dark-rearing. These data suggest that Arc is required for the experience-dependent processes that normally establish and modify synaptic connections in visual cortex.
It has been suggested that gene expression and protein synthesis are required for both long-term ... more It has been suggested that gene expression and protein synthesis are required for both long-term memory consolidation and late phases of long-term potentiation and long-term depression (LTD). The necessary genes and the specific transcription factor binding sites in their promoters remain unknown. We found that inhibition of the transcription factor SRF or its cofactor MAL blocked the late phase of LTD in mouse cultured cerebellar Purkinje cells, as did deletion of the immediate early gene Arc. Using neuronal bacterial artificial chromosome (BAC) transfection, we found that, in Arc −/− cells transfected with a wild-type
Many proteins have been implicated in synaptic and experience-dependent plasticity. However, few ... more Many proteins have been implicated in synaptic and experience-dependent plasticity. However, few demonstrate the exquisite regulation of expression and breadth of functional importance as the immediate early gene product Arc. Here we review and attempt to synthesize the disparate views of Arc in neuronal function. The main conclusion garnered from this body of work is that Arc is a critical effector molecule downstream of many molecular signaling pathways and that dysregulation of Arc expression can have dire consequences for normal brain function.
Assemblies of β-amyloid (Aβ) peptides are pathological mediators of Alzheimer's Disease (AD) and ... more Assemblies of β-amyloid (Aβ) peptides are pathological mediators of Alzheimer's Disease (AD) and are produced by the sequential cleavages of amyloid precursor protein (APP) by β-secretase (BACE1) and γ-secretase. The generation of Aβ is coupled to neuronal activity, however the molecular basis is unknown. Here, we report that the immediate early gene Arc is required for activity-dependent generation of Aβ. Arc is a postsynaptic protein that recruits endophilin2/3 and dynamin to early/recycling endosomes that traffic AMPA receptors to reduce synaptic strength in both Hebbian and non-Hebbian forms of plasticity. The Arc-endosome also traffics APP and BACE1, and Arc physically associates with presenilin1 (PS1) to regulate γ-secretase trafficking and confer activity-dependence. Genetic deletion of Arc reduces Aβ load in a transgenic mouse model of AD. In concert with the finding that patients with AD can express anomalously high levels of Arc, we hypothesize that Arc participates in the pathogenesis of AD.
Experience shapes and molds the brain throughout life. These changes in neuronal circuits are pro... more Experience shapes and molds the brain throughout life. These changes in neuronal circuits are produced by a myriad of molecular and cellular processes. Simplistically, circuits are modified through changes in neurotransmitter release or through neurotransmitter detection at synapses. The predominant neurotransmitter receptor in excitatory transmission, the AMPA-type glutamate receptor (AMPAR), is exquisitely sensitive to changes in experience and synaptic activity. These ion channels are usually impermeable to calcium, a property conferred by the GluA2 subunit. However, GluA2-lacking AMPARs are permeable to calcium and have recently been shown to play a unique role in synaptic function. In this review, I will describe new findings on the role of calcium permeable AMPARs (CP-AMPARs) in experience-dependent and synaptic plasticity. These studies suggest that CP-AMPARs play a prominent role in maintaining circuits in a labile state where further plasticity can occur, thus promoting metaplasticity. Moreover, the abnormal expression of CP-AMPARs has been implicated in drug addiction and memory disorders and thus may be a novel therapeutic target.
Homeostatic plasticity may compensate for Hebbian forms of synaptic plasticity, such as long-term... more Homeostatic plasticity may compensate for Hebbian forms of synaptic plasticity, such as long-term potentiation (LTP) and depression (LTD), by scaling neuronal output without changing the relative strength of individual synapses. This delicate balance between neuronal output and distributed synaptic weight may be necessary for maintaining efficient encoding of information across neuronal networks. Here, we demonstrate that Arc/Arg3.1, an immediate-early gene (IEG) that is rapidly induced by neuronal activity associated with information encoding in the brain, mediates homeostatic synaptic scaling of AMPA type glutamate receptors (AMPARs) via its ability to activate a novel and selective AMPAR endocytic pathway. High levels of Arc/Arg3.1 block the homeostatic increases in AMPAR function induced by chronic neuronal inactivity. Conversely, loss of Arc/Arg3.1 results in increased AMPAR function and abolishes homeostatic scaling of AMPARs. These observations, together with evidence that Arc/Arg3.1 is required for memory consolidation, reveal the importance of Arc/Arg3.1's dynamic expression as it exerts continuous and precise control over synaptic strength and cellular excitability.
Annual Review of Cell and Developmental Biology, 2007
The cellular processes that govern neuronal function are highly complex, with many basic cell bio... more The cellular processes that govern neuronal function are highly complex, with many basic cell biological pathways uniquely adapted to perform the elaborate information processing achieved by the brain. This is particularly evident in the trafficking and regulation of membrane proteins to and from synapses, which can be a long distance away from the cell body and number in the thousands. The regulation of neurotransmitter receptors, such as the AMPA-type glutamate receptors (AMPARs), the major excitatory neurotransmitter receptors in the brain, is a crucial mechanism for the modulation of synaptic transmission. The levels of AMPARs at synapses are very dynamic, and it is these plastic changes in synaptic function that are thought to underlie information storage in the brain. Thus, understanding the cellular machinery that controls AMPAR trafficking will be critical for understanding the cellular basis of behavior as well as many neurological diseases. Here we describe the life cycle of AMPARs, from their biogenesis, through their journey to the synapse, and ultimately through their demise, and discuss how the modulation of this process is essential for brain function. 613 Annu. Rev. Cell Dev. Biol. 2007.23:613-643. Downloaded from arjournals.annualreviews.org by University of California -San Diego on 04/10/08. For personal use only.
The neuropathological correlates of Alzheimer's disease (AD) include amyloid-β (Aβ) plaques and n... more The neuropathological correlates of Alzheimer's disease (AD) include amyloid-β (Aβ) plaques and neurofibrillary tangles. To study the interaction between Aβ and tau and their effect on synaptic function, we derived a triple-transgenic model (3×Tg-AD) harboring PS1M146V, APPSwe, and tauP301L transgenes. Rather than crossing independent lines, we microinjected two transgenes into single-cell embryos from homozygous PS1M146V knockin mice, generating mice with the same genetic background. 3×Tg-AD mice progressively develop plaques and tangles. Synaptic dysfunction, including LTP deficits, manifests in an age-related manner, but before plaque and tangle pathology. Deficits in long-term synaptic plasticity correlate with the accumulation of intraneuronal Aβ. These studies suggest a novel pathogenic role for intraneuronal Aβ with regards to synaptic plasticity. The recapitulation of salient features of AD in these mice clarifies the relationships between Aβ, synaptic dysfunction, and tangles and provides a valuable model for evaluating potential AD therapeutics as the impact on both lesions can be assessed.
Seminars in Cell & Developmental Biology, 2017
The neuronal gene Arc is essential for long-lasting information storage in the mammalian brain an... more The neuronal gene Arc is essential for long-lasting information storage in the mammalian brain and has been implicated in various neurological disorders. However, little is known about Arc's evolutionary origins. Recent studies suggest that mammalian Arc originated from a vertebrate lineage of Ty3/gypsy retrotransposons, which are also ancestral to retroviruses. In particular, Arc contains homology to the Gag polyprotein that forms the viral capsid and is essential for viral infectivity. This surprising connection raises the intriguing possibility that Arc may share molecular characteristics of retroviruses.
Arc (activity-regulated cytoskeleton-associated protein) is a neuron-specific immediate early gen... more Arc (activity-regulated cytoskeleton-associated protein) is a neuron-specific immediate early gene that is required for enduring forms of synaptic plasticity and memory in the mammalian brain. Arc expression is highly dynamic, and tightly regulated by neuronal activity and experience. Local translation of Arc protein at synapses is critical for synaptic plasticity, which is mediated by Arc-dependent trafficking of AMPA (α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid)-type glutamate receptors. To date, few structural or biophysical properties of Arc protein have been investigated. Recent studies, including that of Myrum et al. published in the 468:1 issue of the Biochemical Journal, now shed light on some intriguing biophysical properties of Arc. These findings show that Arc contains large N- and C-terminal domains around a flexible linker region and that purified Arc protein is capable of self-oligomerization. Intriguingly, these domains show homology with the viral capsid pro...
Autism spectrum disorder (ASD) and Fragile X syndrome (FXS) are relatively common childhood neuro... more Autism spectrum disorder (ASD) and Fragile X syndrome (FXS) are relatively common childhood neurodevelopmental disorders with increasing incidence in recent years. They are currently accepted as disorders of the synapse with alterations in different forms of synaptic communication and neuronal network connectivity. The major excitatory neurotransmitter system in brain, the glutamatergic system, is implicated in learning and memory, synaptic plasticity, neuronal development. While much attention is attributed to the role of metabotropic glutamate receptors in ASD and FXS, studies indicate that the ionotropic glutamate receptors (iGluRs) and their regulatory proteins are also altered in several brain regions. Role of iGluRs in the neurobiology of ASD and FXS is supported by a weight of evidence that ranges from human genetics to in vitro cultured neurons. In this review we will discuss clinical, molecular, cellular and functional changes in NMDA, AMPA and kainate receptors and the synaptic proteins that regulate them in the context of ASD and FXS. We will also discuss the significance for the development of translational biomarkers and treatments for the core symptoms of ASD and FXS.
. Notably, the memory and cognitive decline observed in AD patients correlates better with the sy... more . Notably, the memory and cognitive decline observed in AD patients correlates better with the synaptic pathology than either plaques or tangles, and thus, synaptic dysfunction is likely the most significant factor contributing to the initial stages of memory Gene-targeted and transgenic mice have proven to be invaluable for modeling various aspects of AD neuro-University of California, Irvine Irvine, California 92697 pathology, although no mouse model fully recapitulates its entire neuropathological spectrum (Wong et al., 3 Department of Neuroscience and Pharmacology Mayo Clinic Jacksonville 2002). Numerous models have successfully replicated amyloid plaque deposition, generally by deriving mice Jacksonville, Florida 32224 4 Laboratory of Neurosciences with relatively high levels of APP overexpression, and inclusion of a mutant PS1 allele can accelerate the depo-Gerontology Research Center National Institute on Aging sition rate as well as exacerbate the pathological severity. The discovery of tau gene mutations in frontotempo-Baltimore, Maryland 21224 ral dementia with parkinsonism linked to chromosome 17 kindreds facilitated the development of tauopathies in transgenic mice (Gotz et al., 2001a; Higuchi et al., Summary 2002; Lewis et al., 2000) . One surprising aspect of the overwhelming majority of extant AD models has been The neuropathological correlates of Alzheimer's disease (AD) include amyloid- (A) plaques and neuro-that the successful development of one hallmark pathological lesion has in and of itself been insufficient to fibrillary tangles. To study the interaction between A and tau and their effect on synaptic function, we de-trigger the development of the other signature lesion. Consequently, the concomitant manifestation of both rived a triple-transgenic model (3ϫTg-AD) harboring PS1 M146V , APP Swe , and tau P301L transgenes. Rather than plaques and tangles has required the introduction of multiple transgenes into the same mouse, which has crossing independent lines, we microinjected two transgenes into single-cell embryos from homozygous generally been achieved by crossing several independent transgenic lines, or alternatively, by microinjecting PS1 M146V knockin mice, generating mice with the same genetic background. 3ϫTg-AD mice progressively de-pathological protein into the brains of single-transgenic mice (Gotz et al., 2001b; Lewis et al., 2001). velop plaques and tangles. Synaptic dysfunction, including LTP deficits, manifests in an age-related man-Here, we describe the development of a novel tripletransgenic model (3ϫTg-AD). Instead of crossing three ner, but before plaque and tangle pathology. Deficits in long-term synaptic plasticity correlate with the ac-independent lines, we derived our transgenic model by directly introducing two additional transgenes into the cumulation of intraneuronal A. These studies suggest a novel pathogenic role for intraneuronal A with re-germline of a genetically modified mouse. We report that (to our knowledge) this is the first transgenic model gards to synaptic plasticity. The recapitulation of salient features of AD in these mice clarifies the relation-to develop both plaque and tangle pathology in ADrelevant brain regions. The 3ϫTg-AD mice develop ex-ships between A, synaptic dysfunction, and tangles and provides a valuable model for evaluating potential tracellular A deposits prior to tangle formation, consistent with the amyloid cascade hypothesis. These mice AD therapeutics as the impact on both lesions can be assessed. exhibit deficits in synaptic plasticity, including long-term potentiation (LTP) that occurs prior to extracellular A Introduction deposition and tangles but is associated with intracellular A immunoreactivity. Double-transgenic mice (2ϫTg) Alzheimer's disease (AD), a progressive neurodegeneralacking the human APP transgene (but containing tive disorder that is the most common cause of dementia PS1 M146V and tau P301L ) do not develop any extracellular in the elderly, is characterized by two hallmark lesions: plaques nor do they show any significant intraneuronal diffuse and neuritic plaques, which are predominantly A immunoreactivity. Notably, the 2ϫTg mice do not composed of the A peptide, and neurofibrillary tangles, exhibit any LTP deficits, despite expressing the tau composed of filamentous aggregates of hyperphostransgene to comparable levels as the 3ϫTg-AD mice. phorylated tau protein (Selkoe, 2001). Loss of neuronal Therefore, such findings suggest a novel pathophysiosynaptic density and synapse number represent another logic role for intraneuronal A and indicate that synaptic invariant feature of the disease that appears to precede dysfunction is a proximal defect in the pathobiology of overt neuronal degeneration (DeKosky and Scheff, 1990; AD, preceding extracellular plaque formation and tangles. These 3ϫTg-AD mice will be useful for studying the impact of A and tau on synaptic plasticity and for ELISAs and Immunoblot A ELISAs were performed essentially as described previously Su-References zuki et al., 1994). For immunoblot, brains from transgenic and control mice were dounce homogenized in a solution of 2% SDS in H 2 0 Bliss, T.V., and Collingridge, G.L. (1993). A synaptic model of memcontaining 0.7 mg/ml Pepstatin A supplemented with complete Mini ory: long-term potentiation in the hippocampus. Nature 361, 31-39. protease inhibitor tablet (Roche 1836153). The homogenized mixes Caroni, P. (1997). Overexpression of growth-associated proteins in were briefly sonicated to shear the DNA and centrifuged at 4ЊC for the neurons of adult transgenic mice. J. Neurosci. Methods 71, 3-9. 1 hr at 100,000 ϫ g. The supernatant was used for immunoblot analysis. Proteins were resolved by SDS/PAGE (10% Bis-Tris from Chapman, P.F., White, G.L., Jones, M.W., Cooper-Blacketer, D., Invitrogen) under reducing conditions and transferred to nitrocellu-Marshall, V.J., Irizarry, M., Younkin, L., Good, M.A., Bliss, T.V., Hylose membrane. The membrane was incubated in a 5% solution of man, B.T., et al. (1999). Impaired synaptic plasticity and learning in nonfat milk for 1 hr at 20ЊC. After overnight incubation at 4ЊC with aged amyloid precursor protein transgenic mice. Nat. Neurosci. 2, the primary antibody, the blots were washed in Tween-TBS for 20 271-276. min and incubated at 20ЊC with the secondary antibody. The blots Chui, D.H., Tanahashi, H., Ozawa, K., Ikeda, S., Checler, F., Ueda, O., were washed in T-TBS for 20 min and incubated for 5 min with Suzuki, H., Araki, W., Inoue, H., Shirotani, K., et al. (1999). Transgenic Super Signal (Pierce). mice with Alzheimer presenilin 1 mutations show accelerated neurodegeneration without amyloid plaque formation. Nat. Med. 5, 560-564. Immunohistochemistry Formalin-fixed, paraffin-embedded brains were sectioned at 5 m, DeKosky, S.T., and Scheff, S.W. (1990). Synapse loss in frontal cortex biopsies in Alzheimer's disease: correlation with cognitive sever-mounted onto silane-coated slides and processed as described. The following antibodies were used: anti-A 6E10 and 4G8 (Signet ity. Ann. Neurol. 27, 457-464. Laboratories, Dedham, MA), anti-A 1560 (Chemicon), A11 (Kayed Dickson, D.W., Crystal, H.A., Bevona, C., Honer, W., Vincent, I., and et al., 2003), anti-APP 22C11 (Chemicon), anti-Tau HT7, AT8, AT180 Davies, P. (1995). Correlations of synaptic and pathological markers (Innogenetics), Tau C17 (Santa Cruz), Tau 5 (Calbiochem), anti-GFAP with cognition of the elderly. Neurobiol. Aging 16, 285-304. (Dako), and anti-actin (Sigma). Primary antibodies were applied at Fitzjohn, S.M., Morton, R.A., Kuenzi, F., Rosahl, T.W., Shearman, dilutions of 1:3000 for GFAP; 1:1000 for 6E10; 1:500 for 1560, AT8, M., Lewis, H., Smith, D., Reynolds, D.S., Davies, C.H., Collingridge, AT180, and Tau5; and 1:200 for HT7. G.L., et al. (2001). Age-related impairment of synaptic transmission but normal long-term potentiation in transgenic mice that overexpress the human APP695SWE mutant form of amyloid precursor Electrophysiology protein. J. Neurosci. 21, 4691-4698. Mice were anaesthetized with halothane, decapitated, and the brains were rapidly removed in ice-cold artificial cerebrospinal fluid Flood, D.G., and Coleman, P.D. (1990). Hippocampal plasticity in (aCSF; 125 mM NaCl, 2.5 mM KCl, 1.25 mM KH 2 PO 4 , 25 mM NaHCO 3 , normal aging and decreased plasticity in Alzheimer's disease. Prog. 1.2 mM MgSO 4 , 2 mM CaCl 2 , and 10 mM dextrose, bubbled with Brain Res. 83, 435-443. 95% O 2 , 5% CO 2 [pH 7.4]). Transverse hippocampal slices (400 m) Gotz, J., Chen, F., Barmettler, R., and Nitsch, R.M. (2001a). Tau were prepared in aCSF using a vibroslice and left to equilibrate for filament formation in transgenic mice expressing P301L tau. J. Biol. at least 1 hr prior to recording in a holding chamber containing aCSF Chem. 276, 529-534. at room temperature. Gotz, J., Chen, F., van Dorpe, J., and Nitsch, R.M. (2001b). Formation Slices were placed in an interface chamber, continuously perfused of neurofibrillary tangles in P301l tau transgenic mice induced by with aCSF at 34ЊC, and covered with a continuous flow of warmed Abeta 42 fibrils. Science 293, 1491-1495. humidified gas (95% O 2 , 5% CO 2 ). Field excitatory postsynaptic potentials (fEPSPs) were recorded in the stratum radiatum of the et al. CA1 using glass microelectrodes (1-5⍀, ف 5 m diameter) filled with aCSF. Synaptic responses were evoked by stimulation of the (2000). Intraneuronal Abeta42 accumulation in human brain. Am. J. Pathol. 156, 15-20. Schaffer collateral/commissural pathway with a concentric bipolar stimulating electrode with 0.1 ms pulse width. Input/output curves Grundke-Iqbal, I., Iqbal, K., George, L., Tung, Y.C., Kim, K.S., and were generated using stimulus intensities from 0 to 300 A in incre-Wisniewski, H.M. (1989). Amyloid protein and neurofibrillary tangles ments of 20 A. PPF was assessed using an interstimulus interval coexist in the...
A myriad of mechanisms are suggested to account for the full richness of visual cortical plastici... more A myriad of mechanisms are suggested to account for the full richness of visual cortical plasticity. We report that visual cortex lacking Arc is impervious to the effects of deprivation or experience. Using intrinsic signal imaging and chronic visually evoked potential recordings, we find that Arc −/− mice do not exhibit depression of deprived eye responses or a shift in ocular dominance after brief monocular deprivation. Extended deprivation also fails to elicit a shift in ocular dominance or open eye potentiation. Moreover, Arc −/− mice lack stimulus-selective response potentiation. Although Arc −/− mice exhibit normal visual acuity, baseline ocular dominance is abnormal and resembles that observed after dark-rearing. These data suggest that Arc is required for the experience-dependent processes that normally establish and modify synaptic connections in visual cortex.
It has been suggested that gene expression and protein synthesis are required for both long-term ... more It has been suggested that gene expression and protein synthesis are required for both long-term memory consolidation and late phases of long-term potentiation and long-term depression (LTD). The necessary genes and the specific transcription factor binding sites in their promoters remain unknown. We found that inhibition of the transcription factor SRF or its cofactor MAL blocked the late phase of LTD in mouse cultured cerebellar Purkinje cells, as did deletion of the immediate early gene Arc. Using neuronal bacterial artificial chromosome (BAC) transfection, we found that, in Arc −/− cells transfected with a wild-type
Many proteins have been implicated in synaptic and experience-dependent plasticity. However, few ... more Many proteins have been implicated in synaptic and experience-dependent plasticity. However, few demonstrate the exquisite regulation of expression and breadth of functional importance as the immediate early gene product Arc. Here we review and attempt to synthesize the disparate views of Arc in neuronal function. The main conclusion garnered from this body of work is that Arc is a critical effector molecule downstream of many molecular signaling pathways and that dysregulation of Arc expression can have dire consequences for normal brain function.
Assemblies of β-amyloid (Aβ) peptides are pathological mediators of Alzheimer's Disease (AD) and ... more Assemblies of β-amyloid (Aβ) peptides are pathological mediators of Alzheimer's Disease (AD) and are produced by the sequential cleavages of amyloid precursor protein (APP) by β-secretase (BACE1) and γ-secretase. The generation of Aβ is coupled to neuronal activity, however the molecular basis is unknown. Here, we report that the immediate early gene Arc is required for activity-dependent generation of Aβ. Arc is a postsynaptic protein that recruits endophilin2/3 and dynamin to early/recycling endosomes that traffic AMPA receptors to reduce synaptic strength in both Hebbian and non-Hebbian forms of plasticity. The Arc-endosome also traffics APP and BACE1, and Arc physically associates with presenilin1 (PS1) to regulate γ-secretase trafficking and confer activity-dependence. Genetic deletion of Arc reduces Aβ load in a transgenic mouse model of AD. In concert with the finding that patients with AD can express anomalously high levels of Arc, we hypothesize that Arc participates in the pathogenesis of AD.
Experience shapes and molds the brain throughout life. These changes in neuronal circuits are pro... more Experience shapes and molds the brain throughout life. These changes in neuronal circuits are produced by a myriad of molecular and cellular processes. Simplistically, circuits are modified through changes in neurotransmitter release or through neurotransmitter detection at synapses. The predominant neurotransmitter receptor in excitatory transmission, the AMPA-type glutamate receptor (AMPAR), is exquisitely sensitive to changes in experience and synaptic activity. These ion channels are usually impermeable to calcium, a property conferred by the GluA2 subunit. However, GluA2-lacking AMPARs are permeable to calcium and have recently been shown to play a unique role in synaptic function. In this review, I will describe new findings on the role of calcium permeable AMPARs (CP-AMPARs) in experience-dependent and synaptic plasticity. These studies suggest that CP-AMPARs play a prominent role in maintaining circuits in a labile state where further plasticity can occur, thus promoting metaplasticity. Moreover, the abnormal expression of CP-AMPARs has been implicated in drug addiction and memory disorders and thus may be a novel therapeutic target.
Homeostatic plasticity may compensate for Hebbian forms of synaptic plasticity, such as long-term... more Homeostatic plasticity may compensate for Hebbian forms of synaptic plasticity, such as long-term potentiation (LTP) and depression (LTD), by scaling neuronal output without changing the relative strength of individual synapses. This delicate balance between neuronal output and distributed synaptic weight may be necessary for maintaining efficient encoding of information across neuronal networks. Here, we demonstrate that Arc/Arg3.1, an immediate-early gene (IEG) that is rapidly induced by neuronal activity associated with information encoding in the brain, mediates homeostatic synaptic scaling of AMPA type glutamate receptors (AMPARs) via its ability to activate a novel and selective AMPAR endocytic pathway. High levels of Arc/Arg3.1 block the homeostatic increases in AMPAR function induced by chronic neuronal inactivity. Conversely, loss of Arc/Arg3.1 results in increased AMPAR function and abolishes homeostatic scaling of AMPARs. These observations, together with evidence that Arc/Arg3.1 is required for memory consolidation, reveal the importance of Arc/Arg3.1's dynamic expression as it exerts continuous and precise control over synaptic strength and cellular excitability.
Annual Review of Cell and Developmental Biology, 2007
The cellular processes that govern neuronal function are highly complex, with many basic cell bio... more The cellular processes that govern neuronal function are highly complex, with many basic cell biological pathways uniquely adapted to perform the elaborate information processing achieved by the brain. This is particularly evident in the trafficking and regulation of membrane proteins to and from synapses, which can be a long distance away from the cell body and number in the thousands. The regulation of neurotransmitter receptors, such as the AMPA-type glutamate receptors (AMPARs), the major excitatory neurotransmitter receptors in the brain, is a crucial mechanism for the modulation of synaptic transmission. The levels of AMPARs at synapses are very dynamic, and it is these plastic changes in synaptic function that are thought to underlie information storage in the brain. Thus, understanding the cellular machinery that controls AMPAR trafficking will be critical for understanding the cellular basis of behavior as well as many neurological diseases. Here we describe the life cycle of AMPARs, from their biogenesis, through their journey to the synapse, and ultimately through their demise, and discuss how the modulation of this process is essential for brain function. 613 Annu. Rev. Cell Dev. Biol. 2007.23:613-643. Downloaded from arjournals.annualreviews.org by University of California -San Diego on 04/10/08. For personal use only.
The neuropathological correlates of Alzheimer's disease (AD) include amyloid-β (Aβ) plaques and n... more The neuropathological correlates of Alzheimer's disease (AD) include amyloid-β (Aβ) plaques and neurofibrillary tangles. To study the interaction between Aβ and tau and their effect on synaptic function, we derived a triple-transgenic model (3×Tg-AD) harboring PS1M146V, APPSwe, and tauP301L transgenes. Rather than crossing independent lines, we microinjected two transgenes into single-cell embryos from homozygous PS1M146V knockin mice, generating mice with the same genetic background. 3×Tg-AD mice progressively develop plaques and tangles. Synaptic dysfunction, including LTP deficits, manifests in an age-related manner, but before plaque and tangle pathology. Deficits in long-term synaptic plasticity correlate with the accumulation of intraneuronal Aβ. These studies suggest a novel pathogenic role for intraneuronal Aβ with regards to synaptic plasticity. The recapitulation of salient features of AD in these mice clarifies the relationships between Aβ, synaptic dysfunction, and tangles and provides a valuable model for evaluating potential AD therapeutics as the impact on both lesions can be assessed.
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