- Email: [email protected]
Phosphorylation of truncated tau is driven by its aberrant conformation
Poster Presentations P1 the Papez circuit, which is involved in memory storage and cortical control of emotion. P1-134
DEGENERATION OF CALRETININ INTERNEURONS IS ASSOCIATED TO THE EARLY ONSET OF EXTRACELLULAR AMYLOID PATHOLOGY IN ALZHEIMER MICE HIPPOCAMPUS
Antonia Guitierrez1, Ines Moreno-Gonzalez1, Raquel Sanchez-Varo1, Elisabeth Sanchez-Mejias1, Laura Trujillo-Estrada1, Sebastian Jimenez2, Manuel Torres2, Manuel Romero-Aceba1, Zafar Khan1, Diego Ruano2, Marisa Vizuete2, Javier Vitorica2, David Baglietto-Vargas1, 1Universidad de Malaga, Malaga, Spain; 2Universidad de Sevilla, Sevilla, Spain. Contact e-mail: [email protected] Background: Select neuronal populations are preferentially affected in the early stages of Alzheimer’s disease (AD). The distinct subpopulations of hippocampal inhibitory GABAergic system have been shown to display differential vulnerability to neurodegeneration in AD. We have previously reported a substantial loss of SOM/NPY interneurons, whereas those expressing parvalbumin were unaltered, in the hippocampus of 6 month-old PS1(M146L)/APP(751sl) transgenic mice. This AD model could mimic the initial stages of the pathology in humans and could be of great interest to analyze the age-dependent vulnerability of different neuronal subsets to this disease. Methods: In the present study, we investigated the pathological changes of hippocampal calretinin (CR) interneurons in this PS1/APP model from 2 to 12 months of age. We have quantitatively determined, by immunohistochemistry and stereological approaches, the total number of CR cells in CA1 and CA2/3 subfields compared to wild type (WT) and single transgenic PS1 littermates. In addition, the CR mRNA content was assessed by quantitative RT-PCR. Results: Our findings show: 1) a significant reduction (3545%) in the total number of CR-interneurons in CA1 and CA2/3 subfields of PS1/APP mice as early as 4 months of age which was accompanied by a reduced CR mRNA content; 2) there was not a progressive decline in CR-positive interneurons with aging and increased extracellular beta-amyloid pathology; 3) the reduction of CR-interneurons in this model was due to an early neurodegenerative process rather than loss of CR-expression; 4) the degeneration of CR-positive interneurons was associated to the early appearance of beta-amyloid deposits and the formation of axonal dystrophies; 5) this early degenerative process was selective for CR-interneurons whereas another hippocampal CR cells (CR-positive Cajal Retzius cells) were not affected. Conclusions: Hippocampal CR-interneurons are preferential early targets in this transgenic model with AD-like pathology. The loss of these GABAergic neurons may be influenced by the early onset of amyloid deposits in this brain area and the induction of axonal pathology. Finally, our findings highlight the diversity within this neurochemically identified GABAergic population and further supports the notion that amyloid pathology affects specific neuronal networks. P1-135
COMPARISON OF NEURONAL MORPHOLOGY IN PYRAMIDAL NEURONS OF THE CA1, DENTATE GYRUS, AND PREFRONTAL CORTEX OF APP KNOCKOUT AND APLP2 KNOCKOUT MICE
Jessica J. Walsh1, Sheue-Houy Tyan2, Brea Midthune2, Ann Yu-Jung Shih2, Simone Eggert2, Patrick R. Hof1, Edward Koo2, Dara L. Dickstein1, 1 Mount Sinai School of Medicine, New York, NY, USA; 2University of California San Diego, La Jolla, CA, USA. Contact e-mail: jjw2004@columbia. edu Background: The amyloid precursor protein (APP) plays a pivotal role in the pathogenesis of Alzheimer’s disease (AD). The processing of APP involves proteolytic cleavage by b- and g-secretases to produce amyloid b protein (Ab), the major protein component of the senile plaques in AD. The possible functions of APP include mediation of neurite outgrowth, cell adhesion, and regulation of synaptic plasticity and transmission. Many of these functions extend to the two homologues of APP, APLP1 and APLP2. Our recent studies suggest that mice lacking the APP gene show significant morphological alterations in dendrites of neurons located in brain regions asso-
S213
ciated with AD pathology, specifically CA1 and dentate gyrus (DG) in the hippocampus, and prefrontal cortex (PFC). Methods: We compared the possible changes in neuronal morphology, in aged APP-/- mice to aged APLP2-/- mice. Mice were perfused and intracellular injections of Lucifer Yellow were made in neurons in the CA1, DG, and PFC regions. Neurons were traced using Neurolucida software (MBF Bioscience) and Sholl analysis was performed to quantify dendritic length and complexity. Results: CA1 neurons show shorter apical length and decreased number of intersections in aged APP-/- mice compared to APLP2-/- (p < 0.05), along with significant differences in Sholl analysis of basal dendritic length and number of intersections (p < 0.05). DG granule cells showed no appreciable difference in mean dendritic length and number of intersections. PFC pyramidal neurons showed significant differences in shorter apical length and number of intersections, along with apparent differences in Sholl analysis of basal dendritic length and number of intersections. These results are consistent with the in vitro findings. Conclusions: These findings suggest that APP plays a key role in the formation and complexity of dendrites. Knocking out APLP2 does not produce any noteworthy changes in dendritic length or complexity, suggesting that it is not necessary for neurite outgrowth. However, APP-/mice do show marked decreases in dendritic morphology. Furthermore, the deficits seen in the APP-/- mice suggest that APLP2 and APLP1 cannot compensate for the loss. Further studies will focus on the alternations in spine density and spine types in these animals. P1-136
PHOSPHORYLATION OF TRUNCATED TAU IS DRIVEN BY ITS ABERRANT CONFORMATION
Branislav Kovacech1,2, Juraj Kucerak1, Zuzana Flachbartova1, Jozef Hanes1,2, Michal Novak1,2, 1Institute of Neuroimmunology, Bratislava, Slovakia; 2Axon Neuroscience GmbH, Vienna, Austria. Contact e-mail: Branislav.Kovacech@ savba.sk Background: Neurofibrillary tangles and neuropil threads, the main forms of tau lesions in AD, exhibit a characteristic temporal and spatial distribution pattern that strongly indicates a direct causal connection to the disease progression. In spite of intense research, however, the primary impetus that initiates formation of these insoluble lesions remains elusive. It is generally assumed that hyperphosphorylation of tau is an essential component of the pathological tau cascade and that it is brought about by an imbalance between kinases and phosphatases. In our work we tested the possibility that altered conformation of the substrate (truncated tau) influences its phosphorylation status. Methods: We used a rat model of tauopathy expressing a human truncated tau as a transgene. By western blotting we compared the phosphorylation levels of endogenous rat tau, truncated transgenic tau and the levels of the relevant tau kinases. Results: The transgene, truncated tau in a rat model of tauopathies, exhibited high phosphorylation levels throughout the life of the animals, while the normal endogenous rat tau proteins were unaffected. Furthermore, transgenic animals did not exhibit elevated levels of most relevant tau kinases or their activated phospho-forms when compared with wild type animals. In vitro analysis of the phosphorylation rate of the recombinant human tau proteins in an in vitro kinase reaction revealed that truncated human tau becomes phosphorylated faster and to a higher degree than the full length tau protein at several phosphorylation sites relevant for AD pathology. Conclusions: We present evidence that conformational abnormalities of the truncated tau protein are sufficient to induce its abnormal phosphorylation and initiate the cascade of events leading to the formation of the insoluble misfolded forms. P1-137
AGGREGATED VERSUS SOLUBLE AND INTRACELLULAR SPECIES OF THE AMYLOIDBETA PEPTIDE: LESSONS FROM THE APPXPS1-KI MOUSE MODEL
Benoit Delatour1, Myriam Ly1, Charles Duyckaerts2, 1CNRS, Paris, France; 2INSERM, Paris, France. Contact e-mail: [email protected] Background: According to the cascade hypothesis it is proposed to posit amyloid-beta peptide (A-beta) deposition as a culprit in the physiopathogeny of Alzheimer’s disease (AD). It remains however unclear which conformations and topographies of A-beta conspire in the predisposition-progression
DEGENERATION OF CALRETININ INTERNEURONS IS ASSOCIATED TO THE EARLY ONSET OF EXTRACELLULAR AMYLOID PATHOLOGY IN ALZHEIMER MICE HIPPOCAMPUS
Antonia Guitierrez1, Ines Moreno-Gonzalez1, Raquel Sanchez-Varo1, Elisabeth Sanchez-Mejias1, Laura Trujillo-Estrada1, Sebastian Jimenez2, Manuel Torres2, Manuel Romero-Aceba1, Zafar Khan1, Diego Ruano2, Marisa Vizuete2, Javier Vitorica2, David Baglietto-Vargas1, 1Universidad de Malaga, Malaga, Spain; 2Universidad de Sevilla, Sevilla, Spain. Contact e-mail: [email protected] Background: Select neuronal populations are preferentially affected in the early stages of Alzheimer’s disease (AD). The distinct subpopulations of hippocampal inhibitory GABAergic system have been shown to display differential vulnerability to neurodegeneration in AD. We have previously reported a substantial loss of SOM/NPY interneurons, whereas those expressing parvalbumin were unaltered, in the hippocampus of 6 month-old PS1(M146L)/APP(751sl) transgenic mice. This AD model could mimic the initial stages of the pathology in humans and could be of great interest to analyze the age-dependent vulnerability of different neuronal subsets to this disease. Methods: In the present study, we investigated the pathological changes of hippocampal calretinin (CR) interneurons in this PS1/APP model from 2 to 12 months of age. We have quantitatively determined, by immunohistochemistry and stereological approaches, the total number of CR cells in CA1 and CA2/3 subfields compared to wild type (WT) and single transgenic PS1 littermates. In addition, the CR mRNA content was assessed by quantitative RT-PCR. Results: Our findings show: 1) a significant reduction (3545%) in the total number of CR-interneurons in CA1 and CA2/3 subfields of PS1/APP mice as early as 4 months of age which was accompanied by a reduced CR mRNA content; 2) there was not a progressive decline in CR-positive interneurons with aging and increased extracellular beta-amyloid pathology; 3) the reduction of CR-interneurons in this model was due to an early neurodegenerative process rather than loss of CR-expression; 4) the degeneration of CR-positive interneurons was associated to the early appearance of beta-amyloid deposits and the formation of axonal dystrophies; 5) this early degenerative process was selective for CR-interneurons whereas another hippocampal CR cells (CR-positive Cajal Retzius cells) were not affected. Conclusions: Hippocampal CR-interneurons are preferential early targets in this transgenic model with AD-like pathology. The loss of these GABAergic neurons may be influenced by the early onset of amyloid deposits in this brain area and the induction of axonal pathology. Finally, our findings highlight the diversity within this neurochemically identified GABAergic population and further supports the notion that amyloid pathology affects specific neuronal networks. P1-135
COMPARISON OF NEURONAL MORPHOLOGY IN PYRAMIDAL NEURONS OF THE CA1, DENTATE GYRUS, AND PREFRONTAL CORTEX OF APP KNOCKOUT AND APLP2 KNOCKOUT MICE
Jessica J. Walsh1, Sheue-Houy Tyan2, Brea Midthune2, Ann Yu-Jung Shih2, Simone Eggert2, Patrick R. Hof1, Edward Koo2, Dara L. Dickstein1, 1 Mount Sinai School of Medicine, New York, NY, USA; 2University of California San Diego, La Jolla, CA, USA. Contact e-mail: jjw2004@columbia. edu Background: The amyloid precursor protein (APP) plays a pivotal role in the pathogenesis of Alzheimer’s disease (AD). The processing of APP involves proteolytic cleavage by b- and g-secretases to produce amyloid b protein (Ab), the major protein component of the senile plaques in AD. The possible functions of APP include mediation of neurite outgrowth, cell adhesion, and regulation of synaptic plasticity and transmission. Many of these functions extend to the two homologues of APP, APLP1 and APLP2. Our recent studies suggest that mice lacking the APP gene show significant morphological alterations in dendrites of neurons located in brain regions asso-
S213
ciated with AD pathology, specifically CA1 and dentate gyrus (DG) in the hippocampus, and prefrontal cortex (PFC). Methods: We compared the possible changes in neuronal morphology, in aged APP-/- mice to aged APLP2-/- mice. Mice were perfused and intracellular injections of Lucifer Yellow were made in neurons in the CA1, DG, and PFC regions. Neurons were traced using Neurolucida software (MBF Bioscience) and Sholl analysis was performed to quantify dendritic length and complexity. Results: CA1 neurons show shorter apical length and decreased number of intersections in aged APP-/- mice compared to APLP2-/- (p < 0.05), along with significant differences in Sholl analysis of basal dendritic length and number of intersections (p < 0.05). DG granule cells showed no appreciable difference in mean dendritic length and number of intersections. PFC pyramidal neurons showed significant differences in shorter apical length and number of intersections, along with apparent differences in Sholl analysis of basal dendritic length and number of intersections. These results are consistent with the in vitro findings. Conclusions: These findings suggest that APP plays a key role in the formation and complexity of dendrites. Knocking out APLP2 does not produce any noteworthy changes in dendritic length or complexity, suggesting that it is not necessary for neurite outgrowth. However, APP-/mice do show marked decreases in dendritic morphology. Furthermore, the deficits seen in the APP-/- mice suggest that APLP2 and APLP1 cannot compensate for the loss. Further studies will focus on the alternations in spine density and spine types in these animals. P1-136
PHOSPHORYLATION OF TRUNCATED TAU IS DRIVEN BY ITS ABERRANT CONFORMATION
Branislav Kovacech1,2, Juraj Kucerak1, Zuzana Flachbartova1, Jozef Hanes1,2, Michal Novak1,2, 1Institute of Neuroimmunology, Bratislava, Slovakia; 2Axon Neuroscience GmbH, Vienna, Austria. Contact e-mail: Branislav.Kovacech@ savba.sk Background: Neurofibrillary tangles and neuropil threads, the main forms of tau lesions in AD, exhibit a characteristic temporal and spatial distribution pattern that strongly indicates a direct causal connection to the disease progression. In spite of intense research, however, the primary impetus that initiates formation of these insoluble lesions remains elusive. It is generally assumed that hyperphosphorylation of tau is an essential component of the pathological tau cascade and that it is brought about by an imbalance between kinases and phosphatases. In our work we tested the possibility that altered conformation of the substrate (truncated tau) influences its phosphorylation status. Methods: We used a rat model of tauopathy expressing a human truncated tau as a transgene. By western blotting we compared the phosphorylation levels of endogenous rat tau, truncated transgenic tau and the levels of the relevant tau kinases. Results: The transgene, truncated tau in a rat model of tauopathies, exhibited high phosphorylation levels throughout the life of the animals, while the normal endogenous rat tau proteins were unaffected. Furthermore, transgenic animals did not exhibit elevated levels of most relevant tau kinases or their activated phospho-forms when compared with wild type animals. In vitro analysis of the phosphorylation rate of the recombinant human tau proteins in an in vitro kinase reaction revealed that truncated human tau becomes phosphorylated faster and to a higher degree than the full length tau protein at several phosphorylation sites relevant for AD pathology. Conclusions: We present evidence that conformational abnormalities of the truncated tau protein are sufficient to induce its abnormal phosphorylation and initiate the cascade of events leading to the formation of the insoluble misfolded forms. P1-137
AGGREGATED VERSUS SOLUBLE AND INTRACELLULAR SPECIES OF THE AMYLOIDBETA PEPTIDE: LESSONS FROM THE APPXPS1-KI MOUSE MODEL
Benoit Delatour1, Myriam Ly1, Charles Duyckaerts2, 1CNRS, Paris, France; 2INSERM, Paris, France. Contact e-mail: [email protected] Background: According to the cascade hypothesis it is proposed to posit amyloid-beta peptide (A-beta) deposition as a culprit in the physiopathogeny of Alzheimer’s disease (AD). It remains however unclear which conformations and topographies of A-beta conspire in the predisposition-progression