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Reduction of Tau phosphorylation via novel OGA inhibitors
Poster Presentations P3 P3-168
S571
NOVEL MECHANISMS OF STRESS-EVOKED MOOD AND COGNITIVE IMPAIRMENT - THE PATH FROM DEPRESSION TO ALZHEIMER’S DISEASE
Ioannis Sotiropoulos1, Vitor Pinto1, Akihiko Takashima2, Osborne Almeida3, Nuno Sousa2, 1ICVS institute, Health and Life Sciences School, University of Minho, Braga, Portugal; 2RIKEN BSI, Wako, Japan; 3 Max Planck Institute of Psychiatry, Munich, Germany. Background: Current lifestyle places individuals under increasingly greater loads of psychological and physical stress. Although the mechanisms triggered by stress are primarily adaptive to facilitate homeostasis, chronic stress can become maladaptive. Specifically, stress and its primary manifestation, glucocorticoid (GC) secretion is strongly associated with neuronal atrophy/dysfunction, impaired cognition, and mood and affective disorders, such as depression. A causal role of chronic stress in the etiopathology of Alzheimer’s disease (AD) has been also suggested. Although cumulative evidence suggests a continuum between depression and AD, stress is suggested to play a detrimental role in both diseases. Considerably less attention has been given to the suggested role of stress as a connecting risk factor. Methods: Using both transgenic and non-transgenic animals, we investigate the sequential interrelationships between these various pathogenic elements, in particular with respect to the mechanisms through which stress might precipitate brain pathology. Results: Our studies show that stress and GC trigger APP misprocessing towards the production of neurotoxic amyloid-ß (Aß) as well as abnormal tau hyperphosphorylation and aggregation, resulting in associated impairments of cognitive and emotional status. Furthermore, we show that the presence of tau predisposes to GC and/or stress exposure, tau protein is essential for excitotoxicity providing molecular, electrophysiological and bevarioval evidence. Conclusions: These studies suggest an essential role of tau in a critical mechanism through which stress and GC exert their neurodegenerative effects upon the substrates of cognition and emotion.
P3-169
REDUCTION OF TAU PHOSPHORYLATION VIA NOVEL OGA INHIBITORS
Graeme Horne, Sihong Chen, Renate van Well, Fraser Wilkes, Francis Wilson, Jon Tinsley, Summit plc, Abingdon, United Kingdom. Background: O-GlcNAcylation, a common post-translational modification of nucleocytoplasmic proteins, is markedly decreased in Alzheimer’s disease (AD) cerebrum. The decrease in O-GlcNAc correlates negatively with phosphorylation at most phosphorylation sites leading to hyperphosphorylation of certain proteins. One such example is the microtubule-associated protein tau, known to play a crucial role in the neurofibrillary degeneration of AD, where hyperphosphorylation leads to the generation of toxic aggregates. The reciprocal relationship between phosphorylation and O-GlcNAcylation of tau and the observed reduction in O-GlcNAcylated tau in AD brain suggests that the generation of inhibitors of O-GlcNAc hydrolysing enzyme OGA offers a novel therapeutic approach to protect neurons in AD brain. It has been shown that inhibition of OGA can effectively enhance O-GlcNAcylation at pathologically relevant sites in rat cortex and hippocampus, reducing tau phosphorylation and resulting aggregates. Methods: The primary aim is to develop potent, selective bioavailable inhibitors of OGA as a potential method for altering disease progression for AD and related tauopathies. This has been achieved through application of Summit’s proprietary second generation iminosugar (Seglin^a, Ô) technology and utilization of its unique in-house expertise in iminosugar chemistry and biology. Results: We have identified inhibitors of recombinant human OGA and generated lead compounds through a rationally designed lead optimisation program. These compounds are very selective, low-nanomolar inhibitors of OGA (Table 1). Treatment of neuronal cells in vitro with the compounds demonstrates increased cellular GlcNAcylation resulting in a significant lowering of the
levels of phosphorylated tau, with little evidence of toxicity. Optimisation of compounds for delivery to relevant tau disease models is on-going. Conclusions: Development of potent and selective inhibitors of OGA has the potential to provide a new disease modifying treatment paradigm for AD and associated tauopathies.
P3-170
TRKB ALTERNATIVE TRANSCRIPT EXPRESSION IN ALZHEIMER’S DISEASE
Jenny Wong, Brett Garner, University of Wollongong, Wollongong, Australia. Background: Brain-derived neurotrophic factor (BDNF) signaling is vital for neuronal differentiation, growth, survival, and plasticity. In Alzheimer’s disease (AD), alterations in hippocampal mRNA and protein expression of the BDNF receptor, tropomyosin-related kinase B (TrkB), have been reported. While most studies report decreases in full length TrkB (TrkB-TK+) and increases in tyrosine kinase-lacking truncated TrkB (TrkB-TK-) expression, gene expression changes of other TrkB receptor isoforms, including the neuron-specific TrkB-Shc and newly characterized exon 17-skipped TrkB-D17, have yet to be described. In this study, we examine TrkB-Shc and TrkB-D17 mRNA expression in the brains of patients with AD as well as in an AD mouse model with early AD pathology; the latter used to determine whether changes in TrkB isoform expression occur before the onset of significant pathology or cognitive decline. Methods: Using a cohort of n¼6/6 controls and AD cases; and a cohort of n¼10/10 C57/B6 wild-type and APP/PS1 transgenic mice, we measured TrkB-TK+, TrkB-TK-, TrkB-Shc, and TrkB-D17 mRNA expression in the hippocampus and cerebellum by quantitative real-time PCR. Results: Using pan-TrkB primers, we found elevated TrkB mRNA expression in the hippocampus of AD patients (p¼0.04). When we screened for individual TrkB transcripts, we observed no significant change in TrkB-TK+ mRNA, but found significant increases in truncated TrkB transcripts including TrkB-TK- (consistent with previous findings) (p¼0.03) and TrkB-Shc (p¼0.004), as well as the exon 17-skipped TrkB-D17 (p¼0.04). No significant change was observed for the same transcripts in the cerebellum. In two-month old APP/PS1 transgenic mice (which have yet to develop significant pathology or cognitive deficits), we found significant increases in TrkB-Shc mRNA levels (p¼0.03) but no change in TrkB-TK- or TrkBD17. Conclusions: Increased transcript levels of the neuron-specific TrkB-Shc in the hippocampus of AD patients and young APP/PS1 mice suggest TrkB-Shc may represent a gene expression marker of AD. Because TrkB-TK- and TrkB-D17 are known to be expressed in glia, increased expression of these transcripts in the hippocampus of AD patients but lack of change in young APP/PS1 mice implies that increases in TrkB-TKand TrkB-D17 may be associated with gliosis in senile plaques during the later stages of AD.
S571
NOVEL MECHANISMS OF STRESS-EVOKED MOOD AND COGNITIVE IMPAIRMENT - THE PATH FROM DEPRESSION TO ALZHEIMER’S DISEASE
Ioannis Sotiropoulos1, Vitor Pinto1, Akihiko Takashima2, Osborne Almeida3, Nuno Sousa2, 1ICVS institute, Health and Life Sciences School, University of Minho, Braga, Portugal; 2RIKEN BSI, Wako, Japan; 3 Max Planck Institute of Psychiatry, Munich, Germany. Background: Current lifestyle places individuals under increasingly greater loads of psychological and physical stress. Although the mechanisms triggered by stress are primarily adaptive to facilitate homeostasis, chronic stress can become maladaptive. Specifically, stress and its primary manifestation, glucocorticoid (GC) secretion is strongly associated with neuronal atrophy/dysfunction, impaired cognition, and mood and affective disorders, such as depression. A causal role of chronic stress in the etiopathology of Alzheimer’s disease (AD) has been also suggested. Although cumulative evidence suggests a continuum between depression and AD, stress is suggested to play a detrimental role in both diseases. Considerably less attention has been given to the suggested role of stress as a connecting risk factor. Methods: Using both transgenic and non-transgenic animals, we investigate the sequential interrelationships between these various pathogenic elements, in particular with respect to the mechanisms through which stress might precipitate brain pathology. Results: Our studies show that stress and GC trigger APP misprocessing towards the production of neurotoxic amyloid-ß (Aß) as well as abnormal tau hyperphosphorylation and aggregation, resulting in associated impairments of cognitive and emotional status. Furthermore, we show that the presence of tau predisposes to GC and/or stress exposure, tau protein is essential for excitotoxicity providing molecular, electrophysiological and bevarioval evidence. Conclusions: These studies suggest an essential role of tau in a critical mechanism through which stress and GC exert their neurodegenerative effects upon the substrates of cognition and emotion.
P3-169
REDUCTION OF TAU PHOSPHORYLATION VIA NOVEL OGA INHIBITORS
Graeme Horne, Sihong Chen, Renate van Well, Fraser Wilkes, Francis Wilson, Jon Tinsley, Summit plc, Abingdon, United Kingdom. Background: O-GlcNAcylation, a common post-translational modification of nucleocytoplasmic proteins, is markedly decreased in Alzheimer’s disease (AD) cerebrum. The decrease in O-GlcNAc correlates negatively with phosphorylation at most phosphorylation sites leading to hyperphosphorylation of certain proteins. One such example is the microtubule-associated protein tau, known to play a crucial role in the neurofibrillary degeneration of AD, where hyperphosphorylation leads to the generation of toxic aggregates. The reciprocal relationship between phosphorylation and O-GlcNAcylation of tau and the observed reduction in O-GlcNAcylated tau in AD brain suggests that the generation of inhibitors of O-GlcNAc hydrolysing enzyme OGA offers a novel therapeutic approach to protect neurons in AD brain. It has been shown that inhibition of OGA can effectively enhance O-GlcNAcylation at pathologically relevant sites in rat cortex and hippocampus, reducing tau phosphorylation and resulting aggregates. Methods: The primary aim is to develop potent, selective bioavailable inhibitors of OGA as a potential method for altering disease progression for AD and related tauopathies. This has been achieved through application of Summit’s proprietary second generation iminosugar (Seglin^a, Ô) technology and utilization of its unique in-house expertise in iminosugar chemistry and biology. Results: We have identified inhibitors of recombinant human OGA and generated lead compounds through a rationally designed lead optimisation program. These compounds are very selective, low-nanomolar inhibitors of OGA (Table 1). Treatment of neuronal cells in vitro with the compounds demonstrates increased cellular GlcNAcylation resulting in a significant lowering of the
levels of phosphorylated tau, with little evidence of toxicity. Optimisation of compounds for delivery to relevant tau disease models is on-going. Conclusions: Development of potent and selective inhibitors of OGA has the potential to provide a new disease modifying treatment paradigm for AD and associated tauopathies.
P3-170
TRKB ALTERNATIVE TRANSCRIPT EXPRESSION IN ALZHEIMER’S DISEASE
Jenny Wong, Brett Garner, University of Wollongong, Wollongong, Australia. Background: Brain-derived neurotrophic factor (BDNF) signaling is vital for neuronal differentiation, growth, survival, and plasticity. In Alzheimer’s disease (AD), alterations in hippocampal mRNA and protein expression of the BDNF receptor, tropomyosin-related kinase B (TrkB), have been reported. While most studies report decreases in full length TrkB (TrkB-TK+) and increases in tyrosine kinase-lacking truncated TrkB (TrkB-TK-) expression, gene expression changes of other TrkB receptor isoforms, including the neuron-specific TrkB-Shc and newly characterized exon 17-skipped TrkB-D17, have yet to be described. In this study, we examine TrkB-Shc and TrkB-D17 mRNA expression in the brains of patients with AD as well as in an AD mouse model with early AD pathology; the latter used to determine whether changes in TrkB isoform expression occur before the onset of significant pathology or cognitive decline. Methods: Using a cohort of n¼6/6 controls and AD cases; and a cohort of n¼10/10 C57/B6 wild-type and APP/PS1 transgenic mice, we measured TrkB-TK+, TrkB-TK-, TrkB-Shc, and TrkB-D17 mRNA expression in the hippocampus and cerebellum by quantitative real-time PCR. Results: Using pan-TrkB primers, we found elevated TrkB mRNA expression in the hippocampus of AD patients (p¼0.04). When we screened for individual TrkB transcripts, we observed no significant change in TrkB-TK+ mRNA, but found significant increases in truncated TrkB transcripts including TrkB-TK- (consistent with previous findings) (p¼0.03) and TrkB-Shc (p¼0.004), as well as the exon 17-skipped TrkB-D17 (p¼0.04). No significant change was observed for the same transcripts in the cerebellum. In two-month old APP/PS1 transgenic mice (which have yet to develop significant pathology or cognitive deficits), we found significant increases in TrkB-Shc mRNA levels (p¼0.03) but no change in TrkB-TK- or TrkBD17. Conclusions: Increased transcript levels of the neuron-specific TrkB-Shc in the hippocampus of AD patients and young APP/PS1 mice suggest TrkB-Shc may represent a gene expression marker of AD. Because TrkB-TK- and TrkB-D17 are known to be expressed in glia, increased expression of these transcripts in the hippocampus of AD patients but lack of change in young APP/PS1 mice implies that increases in TrkB-TKand TrkB-D17 may be associated with gliosis in senile plaques during the later stages of AD.