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Mechanisms of hybrid oligomer formation in the pathogenesis of combined Alzheimer's and Parkinson's diseases.

Tsigelny IF, Crews L, Desplats P, Shaked GM, Sharikov Y, Mizuno H, Spencer B, Rockenstein E, Trejo M, Platoshyn O, Yuan JX, Masliah E - PLoS ONE (2008)

Bottom Line: While progressive accumulation of amyloid beta protein (Abeta) oligomers has been identified as one of the central toxic events in AD, accumulation of alpha-synuclein (alpha-syn) resulting in the formation of oligomers and protofibrils has been linked to PD and Lewy body Disease (LBD).These results support the contention that Abeta directly interacts with alpha-syn and stabilized the formation of hybrid nanopores that alter neuronal activity and might contribute to the mechanisms of neurodegeneration in AD and PD.The broader implications of such hybrid interactions might be important to the pathogenesis of other disorders of protein misfolding.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California, United States of America.

ABSTRACT

Background: Misfolding and pathological aggregation of neuronal proteins has been proposed to play a critical role in the pathogenesis of neurodegenerative disorders. Alzheimer's disease (AD) and Parkinson's disease (PD) are frequent neurodegenerative diseases of the aging population. While progressive accumulation of amyloid beta protein (Abeta) oligomers has been identified as one of the central toxic events in AD, accumulation of alpha-synuclein (alpha-syn) resulting in the formation of oligomers and protofibrils has been linked to PD and Lewy body Disease (LBD). We have recently shown that Abeta promotes alpha-syn aggregation and toxic conversion in vivo, suggesting that abnormal interactions between misfolded proteins might contribute to disease pathogenesis. However the molecular characteristics and consequences of these interactions are not completely clear.

Methodology/principal findings: In order to understand the molecular mechanisms involved in potential Abeta/alpha-syn interactions, immunoblot, molecular modeling, and in vitro studies with alpha-syn and Abeta were performed. We showed in vivo in the brains of patients with AD/PD and in transgenic mice, Abeta and alpha-synuclein co-immunoprecipitate and form complexes. Molecular modeling and simulations showed that Abeta binds alpha-syn monomers, homodimers, and trimers, forming hybrid ring-like pentamers. Interactions occurred between the N-terminus of Abeta and the N-terminus and C-terminus of alpha-syn. Interacting alpha-syn and Abeta dimers that dock on the membrane incorporated additional alpha-syn molecules, leading to the formation of more stable pentamers and hexamers that adopt a ring-like structure. Consistent with the simulations, under in vitro cell-free conditions, Abeta interacted with alpha-syn, forming hybrid pore-like oligomers. Moreover, cells expressing alpha-syn and treated with Abeta displayed increased current amplitudes and calcium influx consistent with the formation of cation channels.

Conclusion/significance: These results support the contention that Abeta directly interacts with alpha-syn and stabilized the formation of hybrid nanopores that alter neuronal activity and might contribute to the mechanisms of neurodegeneration in AD and PD. The broader implications of such hybrid interactions might be important to the pathogenesis of other disorders of protein misfolding.

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Related in: MedlinePlus

Immunoblot and co-immunoprecipitation analysis of aggregated α-syn in brains of LBD cases and tg mice.(A, B) Representative western blot (A) and semi-quantitative analysis (B) of levels of α-syn dimers and oligomers in membrane fractions from the frontal cortex of age-matched non-demented control, AD and LBD brains. In cases with LBD there was a significant increase in the levels of α-syn dimers and oligomers when compared to controls. (C) Immunoprecipitation of homogenates from control, LBD and AD cases with monoclonal antibodies against Aβ (upper panel) or α-syn (lower panel). Immunoblots were probed with monoclonal antibodies against α-syn (upper panel) or Aβ (lower panel). Aβ and α-syn pure proteins were included on the immunoblots as positive controls (first and second lanes). (D, E) Representative western blot (D) and semi-quantitative analysis (E) of levels of α-syn dimers and oligomers in the membrane fractions from nontg, APP tg, α-syn tg, and APP/α-syn double tg brains. In APP/α-syn tg mice there was a significant increase in the levels of α-syn dimers and oligomers when compared to nontg or single tg animals. (F) Immunoprecipitation of brain homogenates from nontg, APP tg, α-syn tg, and APP/α-syn double tg animals with monoclonal antibodies against Aβ (upper panel) or α-syn (lower panel). Immunoblots were probed with monoclonal antibodies against α-syn (upper panel) or Aβ (lower panel). Bar graphs represent the mean of n = 4 cases per group. *P<0.05 compared to control human brains or nontg mouse brains (by one-way ANOVA with post-hoc Tukey-Kramer test).
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pone-0003135-g001: Immunoblot and co-immunoprecipitation analysis of aggregated α-syn in brains of LBD cases and tg mice.(A, B) Representative western blot (A) and semi-quantitative analysis (B) of levels of α-syn dimers and oligomers in membrane fractions from the frontal cortex of age-matched non-demented control, AD and LBD brains. In cases with LBD there was a significant increase in the levels of α-syn dimers and oligomers when compared to controls. (C) Immunoprecipitation of homogenates from control, LBD and AD cases with monoclonal antibodies against Aβ (upper panel) or α-syn (lower panel). Immunoblots were probed with monoclonal antibodies against α-syn (upper panel) or Aβ (lower panel). Aβ and α-syn pure proteins were included on the immunoblots as positive controls (first and second lanes). (D, E) Representative western blot (D) and semi-quantitative analysis (E) of levels of α-syn dimers and oligomers in the membrane fractions from nontg, APP tg, α-syn tg, and APP/α-syn double tg brains. In APP/α-syn tg mice there was a significant increase in the levels of α-syn dimers and oligomers when compared to nontg or single tg animals. (F) Immunoprecipitation of brain homogenates from nontg, APP tg, α-syn tg, and APP/α-syn double tg animals with monoclonal antibodies against Aβ (upper panel) or α-syn (lower panel). Immunoblots were probed with monoclonal antibodies against α-syn (upper panel) or Aβ (lower panel). Bar graphs represent the mean of n = 4 cases per group. *P<0.05 compared to control human brains or nontg mouse brains (by one-way ANOVA with post-hoc Tukey-Kramer test).

Mentions: Previous studies have shown that Aβ plays a key role in promoting α-syn aggregation [31], [32], however it is unclear to what extent both of these molecules interact in vivo. For this purpose, immunoblot analysis was performed with brain samples from cases with LBD and APP/α-syn tg mice. Compared to non-demented controls and AD cases, in the membrane fractions of the LBD brain homogenates there was extensive accumulation of α-syn oligomers including dimers, trimers, pentamers and higher-order aggregates (Figure 1A,B). Similarly, in the APP/α-syn double tg animals, which produce high levels of Aβ, there was a significant increase in the levels of α-syn oligomers compared to single tg and non-tg controls (Figure 1D,E).


Mechanisms of hybrid oligomer formation in the pathogenesis of combined Alzheimer's and Parkinson's diseases.

Tsigelny IF, Crews L, Desplats P, Shaked GM, Sharikov Y, Mizuno H, Spencer B, Rockenstein E, Trejo M, Platoshyn O, Yuan JX, Masliah E - PLoS ONE (2008)

Immunoblot and co-immunoprecipitation analysis of aggregated α-syn in brains of LBD cases and tg mice.(A, B) Representative western blot (A) and semi-quantitative analysis (B) of levels of α-syn dimers and oligomers in membrane fractions from the frontal cortex of age-matched non-demented control, AD and LBD brains. In cases with LBD there was a significant increase in the levels of α-syn dimers and oligomers when compared to controls. (C) Immunoprecipitation of homogenates from control, LBD and AD cases with monoclonal antibodies against Aβ (upper panel) or α-syn (lower panel). Immunoblots were probed with monoclonal antibodies against α-syn (upper panel) or Aβ (lower panel). Aβ and α-syn pure proteins were included on the immunoblots as positive controls (first and second lanes). (D, E) Representative western blot (D) and semi-quantitative analysis (E) of levels of α-syn dimers and oligomers in the membrane fractions from nontg, APP tg, α-syn tg, and APP/α-syn double tg brains. In APP/α-syn tg mice there was a significant increase in the levels of α-syn dimers and oligomers when compared to nontg or single tg animals. (F) Immunoprecipitation of brain homogenates from nontg, APP tg, α-syn tg, and APP/α-syn double tg animals with monoclonal antibodies against Aβ (upper panel) or α-syn (lower panel). Immunoblots were probed with monoclonal antibodies against α-syn (upper panel) or Aβ (lower panel). Bar graphs represent the mean of n = 4 cases per group. *P<0.05 compared to control human brains or nontg mouse brains (by one-way ANOVA with post-hoc Tukey-Kramer test).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2519786&req=5

pone-0003135-g001: Immunoblot and co-immunoprecipitation analysis of aggregated α-syn in brains of LBD cases and tg mice.(A, B) Representative western blot (A) and semi-quantitative analysis (B) of levels of α-syn dimers and oligomers in membrane fractions from the frontal cortex of age-matched non-demented control, AD and LBD brains. In cases with LBD there was a significant increase in the levels of α-syn dimers and oligomers when compared to controls. (C) Immunoprecipitation of homogenates from control, LBD and AD cases with monoclonal antibodies against Aβ (upper panel) or α-syn (lower panel). Immunoblots were probed with monoclonal antibodies against α-syn (upper panel) or Aβ (lower panel). Aβ and α-syn pure proteins were included on the immunoblots as positive controls (first and second lanes). (D, E) Representative western blot (D) and semi-quantitative analysis (E) of levels of α-syn dimers and oligomers in the membrane fractions from nontg, APP tg, α-syn tg, and APP/α-syn double tg brains. In APP/α-syn tg mice there was a significant increase in the levels of α-syn dimers and oligomers when compared to nontg or single tg animals. (F) Immunoprecipitation of brain homogenates from nontg, APP tg, α-syn tg, and APP/α-syn double tg animals with monoclonal antibodies against Aβ (upper panel) or α-syn (lower panel). Immunoblots were probed with monoclonal antibodies against α-syn (upper panel) or Aβ (lower panel). Bar graphs represent the mean of n = 4 cases per group. *P<0.05 compared to control human brains or nontg mouse brains (by one-way ANOVA with post-hoc Tukey-Kramer test).
Mentions: Previous studies have shown that Aβ plays a key role in promoting α-syn aggregation [31], [32], however it is unclear to what extent both of these molecules interact in vivo. For this purpose, immunoblot analysis was performed with brain samples from cases with LBD and APP/α-syn tg mice. Compared to non-demented controls and AD cases, in the membrane fractions of the LBD brain homogenates there was extensive accumulation of α-syn oligomers including dimers, trimers, pentamers and higher-order aggregates (Figure 1A,B). Similarly, in the APP/α-syn double tg animals, which produce high levels of Aβ, there was a significant increase in the levels of α-syn oligomers compared to single tg and non-tg controls (Figure 1D,E).

Bottom Line: While progressive accumulation of amyloid beta protein (Abeta) oligomers has been identified as one of the central toxic events in AD, accumulation of alpha-synuclein (alpha-syn) resulting in the formation of oligomers and protofibrils has been linked to PD and Lewy body Disease (LBD).These results support the contention that Abeta directly interacts with alpha-syn and stabilized the formation of hybrid nanopores that alter neuronal activity and might contribute to the mechanisms of neurodegeneration in AD and PD.The broader implications of such hybrid interactions might be important to the pathogenesis of other disorders of protein misfolding.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California, United States of America.

ABSTRACT

Background: Misfolding and pathological aggregation of neuronal proteins has been proposed to play a critical role in the pathogenesis of neurodegenerative disorders. Alzheimer's disease (AD) and Parkinson's disease (PD) are frequent neurodegenerative diseases of the aging population. While progressive accumulation of amyloid beta protein (Abeta) oligomers has been identified as one of the central toxic events in AD, accumulation of alpha-synuclein (alpha-syn) resulting in the formation of oligomers and protofibrils has been linked to PD and Lewy body Disease (LBD). We have recently shown that Abeta promotes alpha-syn aggregation and toxic conversion in vivo, suggesting that abnormal interactions between misfolded proteins might contribute to disease pathogenesis. However the molecular characteristics and consequences of these interactions are not completely clear.

Methodology/principal findings: In order to understand the molecular mechanisms involved in potential Abeta/alpha-syn interactions, immunoblot, molecular modeling, and in vitro studies with alpha-syn and Abeta were performed. We showed in vivo in the brains of patients with AD/PD and in transgenic mice, Abeta and alpha-synuclein co-immunoprecipitate and form complexes. Molecular modeling and simulations showed that Abeta binds alpha-syn monomers, homodimers, and trimers, forming hybrid ring-like pentamers. Interactions occurred between the N-terminus of Abeta and the N-terminus and C-terminus of alpha-syn. Interacting alpha-syn and Abeta dimers that dock on the membrane incorporated additional alpha-syn molecules, leading to the formation of more stable pentamers and hexamers that adopt a ring-like structure. Consistent with the simulations, under in vitro cell-free conditions, Abeta interacted with alpha-syn, forming hybrid pore-like oligomers. Moreover, cells expressing alpha-syn and treated with Abeta displayed increased current amplitudes and calcium influx consistent with the formation of cation channels.

Conclusion/significance: These results support the contention that Abeta directly interacts with alpha-syn and stabilized the formation of hybrid nanopores that alter neuronal activity and might contribute to the mechanisms of neurodegeneration in AD and PD. The broader implications of such hybrid interactions might be important to the pathogenesis of other disorders of protein misfolding.

Show MeSH
Related in: MedlinePlus