- Email: [email protected]
Prevalence study in Shanghai
P120
Symposia S3-02: Animal and Cellular Models
supports a catalyzed formation of pGlu-modified amyloid peptides in neurodegeneration. Conclusions: Our efforts have led to new, Alzheimer mouse models and initiated the discovery of potent and selective compounds as new drugs.
in neuronal activity. The clustering of hyperactive neurons in plaque-rich cortical regions may represent the cellular basis for the increased incidence of epileptic seizures in AD patients. S3-02-04
S3-02-02
SIRTUIN SIGNALING IN ALZHEIMER’S DISEASE
ABNORMAL MITOCHONDRIAL DYNAMICS IN ALZHEIMER’S DISEASE
Li Gan, Gladstone Institute of Neurological Disease, San Francisco, CA, USA. Contact e-mail: [email protected]
Xiongwei Zhu, Case Western Reserve University, Cleveland, OH, USA. Contact e-mail: [email protected]
Background: Aging is the predominant and unifying risk factor for neurodegenerative diseases, including Alzheimer’s disease (AD), the most common dementia in the elderly. SIRT1, a member of sirtuin family of histone deacetylases, supports and promotes longevity in diverse organisms and can extend lifespan when upregulated. In AD brains, SIRT1 levels are significantly lower than in nondemented controls and correlate negatively with the Braak stages of the disease. Methods: To determine how SIRT1 protects against neurodegeneration in AD, we used primary cortical cultures and transgenic mice that overexpress familial AD-mutant human amyloid precursor protein (hAPP) in neurons and have high levels of amyloid beta (Abeta) in the brain. Additional genetic manipulations are achieved with Lentiviral vectors or by cross breeding with knockout mice. Results: One of the main nonhistone substrates of SIRT1 is NF-kappa B, a key activator of inflammatory responses that have been implicated in neurodegeneration. In cultured microglia, SIRT1 activation protected against Abeta toxicity by inhibiting NF-kappa B signaling. Consistent with the observation that SIRT1 levels are reduced in AD patients, treatment with oligomeric Abeta markedly reduced SIRT1 protein and mRNA levels in microglial cultures. However, activation of the fractalkine receptor (CX3CR1), a microglia-specific chemokine receptor induced by binding to its exclusive ligand (CX3CL1) prevented the Abeta-induced SIRT1 downregulation seen in cultured microglia. In contrast, deletion of CX3CR1 in hAPP mice significantly increased the expression of inflammatory mediators and exacerbated amyloid beta-related neuronal deficits. These observations suggest that deficient CX3CR1 signaling could depress SIRT1 levels in microglia, leading to chronic NF-kappa B activation and microglial toxicity. Conclusions: Activation of sirtuin signaling pathways has diverse anti-aging effects and may provide new therapeutic avenues for preventing or delaying age-related ailments, including AD.
Background: Mitochondrial dysfunction is a prominent and early feature of Alzheimer disease (AD), although the underlying mechanisms remain elusive. Emerging evidence suggest that mitochondrial function is dependent on the dynamic balance of fission and fusion events which are regulated by a machinery involving large dynamin-related GTPases that exert opposing effects; i.e., dynamin-like protein 1 (DLP1) for fission, and Mitofusin 1 (Mfn1) for fusion. While an impaired balance of mitochondria fission and fusion is being increasingly implicated in various neurodegenerative diseases, few studies have examined this aspect in AD. To address this issue, we investigated mitochondria morphology and distribution in biopsy brains from normal subjects and those from AD patients and further explored the potential involvement of Abeta in causing abnormal mitochondrial dynamics and mitochondrial dysfunction. Methods: By confocal and electron microscopy, various mitochondrial parameters including morphology, distribution and function were assessed in human brain tissues and neuronal cultures. Results: We found disease-related changes in mitochondrial morphology and distribution as well as changes in the expression level and distribution of mitochondrial fission and fusion proteins. Overexpression or knockdown of fission/ fusion proteins in M17 cells or primary neuronal cultures, in situations where in vitro functional protein changes mimicked those seen in vivo in AD, led to mitochondrial abnormalities similar to that observed in AD neurons. We further demonstrated that overexpression of wild type or mutant APP, through the overproduction of Abeta, differentially modulate the expression of mitochondrial fission/fusion proteins and caused abnormal mitochondrial dynamics as well as mitochondrial dysfunction. Conclusions: Based on these data, we conclude that an impaired balanced of mitochondrial fission and fusion contributes to mitochondrial dysfunction and likely plays an important role in neuronal dysfunction in the pathogenesis of AD.
S3-02-03
SELECTIVE INCREASE IN NEURONAL ACTIVITY IN THE VICINITY OF AMYLOID PLAQUES IN A MOUSE MODEL OF ALZHEIMER’S DISEASE
S3-02-05
LIPID-DEPENDENT PRODUCTION OF NEUROTOXIC ABETA PROTOFIBRILS FROM FIBRILS
Olga Garaschuk, University of Tu¨bingen, Tu¨bingen, Germany. Contact e-mail: [email protected]
Frederic Rousseau, VIB and University of Brussels (VUB), Brussels, Belgium. Contact e-mail: [email protected]
Background: The neurodegeneration observed in Alzheimer’s disease (AD) is commonly associated with synaptic dismantling and a progressive decrease in neuronal activity. Anatomical studies support this notion by showing that already early stages of AD are associated with a decrease in the density of cortical synapses and dendritic spines. Furthermore, results obtained in various animal models of the disease show amyloid ß (Aß)-mediated inhibition of synaptic currents, disruption of synaptic plasticity as well as endocytosis of glutamate receptors. Methods: To test this hypothesis we combined for the first time amyloid plaque visualization and in vivo twophoton Ca2þ imaging in a mouse model of AD. Results: Our data demonstrate that the functional impairment is more complex than previously anticipated. In line with the ‘synaptic failure’ hypothesis we observed a 4-fold increase in the number of ‘silent’ cortical neurons, showing no Ca2þ transients during the recording period. Unexpectedly, however, more than 20% of layer 2/3 cortical cells displayed a marked increase in the frequency of Ca2þ transients reflecting an increased firing of action potentials. These ‘hyperactive’ neurons were found exclusively in the close vicinity of amyloid plaques (< 60 mm from the plaque border) and only in Aß depositing mice. Their appearance correlated with a distinct impairment of cognitive behavior. We obtained evidence that this hyperactivity is due to a relative decrease in synaptic inhibition in the peri-plaque regions. Conclusions: Our results indicate that amyloid deposition causes a marked redistribution of synaptic drive between silent and hyperactive neurons, rather than an overall decrease
Background: While soluble oligomeric and protofibrillar assemblies of Ab-amyloid peptide cause synaptotoxicity and potentially contribute to Alzheimer’s Disease (AD), the role of mature Ab-fibrils in the amyloid plaques remains controversial. A widely held view in the field suggests that the fibrillisation reaction proceeds forward from the monomeric Ab peptide through toxic protofibrillar intermediates which further mature into the amyloid fibrils that are found in plaques, and which are thought to be stable and biologically inert. Methods: Using a combination of biophysical methods, cell biological studies and behavioural studies on mice we here investigate the effect of biological lipids on the stability and cytotoxicity of mature Abeta amyloid fibrils. Results: We show that natural lipids can rapidly induce fiber destabilization and resolubilization. Interestingly, the equilibrium is not reversed towards monomeric Ab but rather towards the soluble amyloid protofibrils, which we thus call backward protofibrils to distinguish from the species obtained during the ‘‘forward’’ aggregation process of monomeric Ab42. Backward protofibrils are biochemically and biophysically very similar to forward protofibrils; They consist of a wide range of molecular masses, are toxic to primary neurons and cause memory impairment and tau phosphorylation in mouse. In addition, they diffuse rapidly through the brain and accumulate in areas relevant to AD. Conclusions: Our findings suggest that amyloid plaques are potentially major sources of toxic Abeta-aggregates that can be activated by changes in physiological conditions such as the presence of free lipids.
Symposia S3-02: Animal and Cellular Models
supports a catalyzed formation of pGlu-modified amyloid peptides in neurodegeneration. Conclusions: Our efforts have led to new, Alzheimer mouse models and initiated the discovery of potent and selective compounds as new drugs.
in neuronal activity. The clustering of hyperactive neurons in plaque-rich cortical regions may represent the cellular basis for the increased incidence of epileptic seizures in AD patients. S3-02-04
S3-02-02
SIRTUIN SIGNALING IN ALZHEIMER’S DISEASE
ABNORMAL MITOCHONDRIAL DYNAMICS IN ALZHEIMER’S DISEASE
Li Gan, Gladstone Institute of Neurological Disease, San Francisco, CA, USA. Contact e-mail: [email protected]
Xiongwei Zhu, Case Western Reserve University, Cleveland, OH, USA. Contact e-mail: [email protected]
Background: Aging is the predominant and unifying risk factor for neurodegenerative diseases, including Alzheimer’s disease (AD), the most common dementia in the elderly. SIRT1, a member of sirtuin family of histone deacetylases, supports and promotes longevity in diverse organisms and can extend lifespan when upregulated. In AD brains, SIRT1 levels are significantly lower than in nondemented controls and correlate negatively with the Braak stages of the disease. Methods: To determine how SIRT1 protects against neurodegeneration in AD, we used primary cortical cultures and transgenic mice that overexpress familial AD-mutant human amyloid precursor protein (hAPP) in neurons and have high levels of amyloid beta (Abeta) in the brain. Additional genetic manipulations are achieved with Lentiviral vectors or by cross breeding with knockout mice. Results: One of the main nonhistone substrates of SIRT1 is NF-kappa B, a key activator of inflammatory responses that have been implicated in neurodegeneration. In cultured microglia, SIRT1 activation protected against Abeta toxicity by inhibiting NF-kappa B signaling. Consistent with the observation that SIRT1 levels are reduced in AD patients, treatment with oligomeric Abeta markedly reduced SIRT1 protein and mRNA levels in microglial cultures. However, activation of the fractalkine receptor (CX3CR1), a microglia-specific chemokine receptor induced by binding to its exclusive ligand (CX3CL1) prevented the Abeta-induced SIRT1 downregulation seen in cultured microglia. In contrast, deletion of CX3CR1 in hAPP mice significantly increased the expression of inflammatory mediators and exacerbated amyloid beta-related neuronal deficits. These observations suggest that deficient CX3CR1 signaling could depress SIRT1 levels in microglia, leading to chronic NF-kappa B activation and microglial toxicity. Conclusions: Activation of sirtuin signaling pathways has diverse anti-aging effects and may provide new therapeutic avenues for preventing or delaying age-related ailments, including AD.
Background: Mitochondrial dysfunction is a prominent and early feature of Alzheimer disease (AD), although the underlying mechanisms remain elusive. Emerging evidence suggest that mitochondrial function is dependent on the dynamic balance of fission and fusion events which are regulated by a machinery involving large dynamin-related GTPases that exert opposing effects; i.e., dynamin-like protein 1 (DLP1) for fission, and Mitofusin 1 (Mfn1) for fusion. While an impaired balance of mitochondria fission and fusion is being increasingly implicated in various neurodegenerative diseases, few studies have examined this aspect in AD. To address this issue, we investigated mitochondria morphology and distribution in biopsy brains from normal subjects and those from AD patients and further explored the potential involvement of Abeta in causing abnormal mitochondrial dynamics and mitochondrial dysfunction. Methods: By confocal and electron microscopy, various mitochondrial parameters including morphology, distribution and function were assessed in human brain tissues and neuronal cultures. Results: We found disease-related changes in mitochondrial morphology and distribution as well as changes in the expression level and distribution of mitochondrial fission and fusion proteins. Overexpression or knockdown of fission/ fusion proteins in M17 cells or primary neuronal cultures, in situations where in vitro functional protein changes mimicked those seen in vivo in AD, led to mitochondrial abnormalities similar to that observed in AD neurons. We further demonstrated that overexpression of wild type or mutant APP, through the overproduction of Abeta, differentially modulate the expression of mitochondrial fission/fusion proteins and caused abnormal mitochondrial dynamics as well as mitochondrial dysfunction. Conclusions: Based on these data, we conclude that an impaired balanced of mitochondrial fission and fusion contributes to mitochondrial dysfunction and likely plays an important role in neuronal dysfunction in the pathogenesis of AD.
S3-02-03
SELECTIVE INCREASE IN NEURONAL ACTIVITY IN THE VICINITY OF AMYLOID PLAQUES IN A MOUSE MODEL OF ALZHEIMER’S DISEASE
S3-02-05
LIPID-DEPENDENT PRODUCTION OF NEUROTOXIC ABETA PROTOFIBRILS FROM FIBRILS
Olga Garaschuk, University of Tu¨bingen, Tu¨bingen, Germany. Contact e-mail: [email protected]
Frederic Rousseau, VIB and University of Brussels (VUB), Brussels, Belgium. Contact e-mail: [email protected]
Background: The neurodegeneration observed in Alzheimer’s disease (AD) is commonly associated with synaptic dismantling and a progressive decrease in neuronal activity. Anatomical studies support this notion by showing that already early stages of AD are associated with a decrease in the density of cortical synapses and dendritic spines. Furthermore, results obtained in various animal models of the disease show amyloid ß (Aß)-mediated inhibition of synaptic currents, disruption of synaptic plasticity as well as endocytosis of glutamate receptors. Methods: To test this hypothesis we combined for the first time amyloid plaque visualization and in vivo twophoton Ca2þ imaging in a mouse model of AD. Results: Our data demonstrate that the functional impairment is more complex than previously anticipated. In line with the ‘synaptic failure’ hypothesis we observed a 4-fold increase in the number of ‘silent’ cortical neurons, showing no Ca2þ transients during the recording period. Unexpectedly, however, more than 20% of layer 2/3 cortical cells displayed a marked increase in the frequency of Ca2þ transients reflecting an increased firing of action potentials. These ‘hyperactive’ neurons were found exclusively in the close vicinity of amyloid plaques (< 60 mm from the plaque border) and only in Aß depositing mice. Their appearance correlated with a distinct impairment of cognitive behavior. We obtained evidence that this hyperactivity is due to a relative decrease in synaptic inhibition in the peri-plaque regions. Conclusions: Our results indicate that amyloid deposition causes a marked redistribution of synaptic drive between silent and hyperactive neurons, rather than an overall decrease
Background: While soluble oligomeric and protofibrillar assemblies of Ab-amyloid peptide cause synaptotoxicity and potentially contribute to Alzheimer’s Disease (AD), the role of mature Ab-fibrils in the amyloid plaques remains controversial. A widely held view in the field suggests that the fibrillisation reaction proceeds forward from the monomeric Ab peptide through toxic protofibrillar intermediates which further mature into the amyloid fibrils that are found in plaques, and which are thought to be stable and biologically inert. Methods: Using a combination of biophysical methods, cell biological studies and behavioural studies on mice we here investigate the effect of biological lipids on the stability and cytotoxicity of mature Abeta amyloid fibrils. Results: We show that natural lipids can rapidly induce fiber destabilization and resolubilization. Interestingly, the equilibrium is not reversed towards monomeric Ab but rather towards the soluble amyloid protofibrils, which we thus call backward protofibrils to distinguish from the species obtained during the ‘‘forward’’ aggregation process of monomeric Ab42. Backward protofibrils are biochemically and biophysically very similar to forward protofibrils; They consist of a wide range of molecular masses, are toxic to primary neurons and cause memory impairment and tau phosphorylation in mouse. In addition, they diffuse rapidly through the brain and accumulate in areas relevant to AD. Conclusions: Our findings suggest that amyloid plaques are potentially major sources of toxic Abeta-aggregates that can be activated by changes in physiological conditions such as the presence of free lipids.