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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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Electron microscopy analysis of hybrid oligomers and fibrils of Aβ and α-syn.In vitro cell-free preparations of vehicle, Aβ alone, α-syn alone, or Aβ and α-syn were incubated for 6 hrs or 48 hrs and prepared for electron microscopy analysis. (A–D) After 6 hrs of incubation, compared to vehicle alone (A), Aβ (B) and α-syn (C) alone formed globular structures of 5–10 nm in diameter, while incubation of Aβ and α-syn together (D) resulted in the formation of larger, well-defined ring-like structures with a central channel. (E) Analysis of numbers of ring-like structures formed after 6 hrs incubation. (F–I) After 48 hrs of incubation, compared to vehicle alone (F), Aβ (G) and α-syn (H) alone or in combination (I) formed fibrils of about 11 nm in diameter. (J–M) After 6 hrs incubation in the presence of lipid monolayers, compared to vehicle alone (J), Aβ (K) and α-syn (L) alone formed globular structures of 5–8 nm in diameter, while incubation of Aβ and α-syn together (M) resulted in enhanced formation of larger, well-defined, ring-like structures. Scale bar, 10 nm (A–D, J–M); 100 nm (F–I).
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pone-0003135-g006: Electron microscopy analysis of hybrid oligomers and fibrils of Aβ and α-syn.In vitro cell-free preparations of vehicle, Aβ alone, α-syn alone, or Aβ and α-syn were incubated for 6 hrs or 48 hrs and prepared for electron microscopy analysis. (A–D) After 6 hrs of incubation, compared to vehicle alone (A), Aβ (B) and α-syn (C) alone formed globular structures of 5–10 nm in diameter, while incubation of Aβ and α-syn together (D) resulted in the formation of larger, well-defined ring-like structures with a central channel. (E) Analysis of numbers of ring-like structures formed after 6 hrs incubation. (F–I) After 48 hrs of incubation, compared to vehicle alone (F), Aβ (G) and α-syn (H) alone or in combination (I) formed fibrils of about 11 nm in diameter. (J–M) After 6 hrs incubation in the presence of lipid monolayers, compared to vehicle alone (J), Aβ (K) and α-syn (L) alone formed globular structures of 5–8 nm in diameter, while incubation of Aβ and α-syn together (M) resulted in enhanced formation of larger, well-defined, ring-like structures. Scale bar, 10 nm (A–D, J–M); 100 nm (F–I).

Mentions: Previous studies have shown in vitro that Aβ [48] and α-syn aggregates can independently form oligomers with a ring-like morphology [25], [49]. However the ultrastructural characteristics of the hybrid Aβ and α-syn multimers are unclear. Consistent with the MD simulations and the immunoblot analysis, electron microscopy studies showed that compared to the vehicle control (Figure 6A), when incubated separately for 6 hrs, Aβ and α-syn generated ill-defined globular structures ranging in size between 5 to 10 nm (Figure 6B,C). In contrast, at 6 hrs the mixture between Aβ and α-syn resulted in well-defined ring-like structures measuring 9–15 nm with a central channel of approximately 3–5 nm (Figure 6D). The mixture of Aβ and α-syn showed increased numbers of ring-like structures after 6 hrs (Figure 6E). At longer periods of incubation, Aβ and α-syn alone, and the mixture formed fibrils of approximately 11 nm in diameter that increased in number in the samples containing a mixture of Aβ and α-syn (Figure 6F–I).


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)

Electron microscopy analysis of hybrid oligomers and fibrils of Aβ and α-syn.In vitro cell-free preparations of vehicle, Aβ alone, α-syn alone, or Aβ and α-syn were incubated for 6 hrs or 48 hrs and prepared for electron microscopy analysis. (A–D) After 6 hrs of incubation, compared to vehicle alone (A), Aβ (B) and α-syn (C) alone formed globular structures of 5–10 nm in diameter, while incubation of Aβ and α-syn together (D) resulted in the formation of larger, well-defined ring-like structures with a central channel. (E) Analysis of numbers of ring-like structures formed after 6 hrs incubation. (F–I) After 48 hrs of incubation, compared to vehicle alone (F), Aβ (G) and α-syn (H) alone or in combination (I) formed fibrils of about 11 nm in diameter. (J–M) After 6 hrs incubation in the presence of lipid monolayers, compared to vehicle alone (J), Aβ (K) and α-syn (L) alone formed globular structures of 5–8 nm in diameter, while incubation of Aβ and α-syn together (M) resulted in enhanced formation of larger, well-defined, ring-like structures. Scale bar, 10 nm (A–D, J–M); 100 nm (F–I).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2519786&req=5

pone-0003135-g006: Electron microscopy analysis of hybrid oligomers and fibrils of Aβ and α-syn.In vitro cell-free preparations of vehicle, Aβ alone, α-syn alone, or Aβ and α-syn were incubated for 6 hrs or 48 hrs and prepared for electron microscopy analysis. (A–D) After 6 hrs of incubation, compared to vehicle alone (A), Aβ (B) and α-syn (C) alone formed globular structures of 5–10 nm in diameter, while incubation of Aβ and α-syn together (D) resulted in the formation of larger, well-defined ring-like structures with a central channel. (E) Analysis of numbers of ring-like structures formed after 6 hrs incubation. (F–I) After 48 hrs of incubation, compared to vehicle alone (F), Aβ (G) and α-syn (H) alone or in combination (I) formed fibrils of about 11 nm in diameter. (J–M) After 6 hrs incubation in the presence of lipid monolayers, compared to vehicle alone (J), Aβ (K) and α-syn (L) alone formed globular structures of 5–8 nm in diameter, while incubation of Aβ and α-syn together (M) resulted in enhanced formation of larger, well-defined, ring-like structures. Scale bar, 10 nm (A–D, J–M); 100 nm (F–I).
Mentions: Previous studies have shown in vitro that Aβ [48] and α-syn aggregates can independently form oligomers with a ring-like morphology [25], [49]. However the ultrastructural characteristics of the hybrid Aβ and α-syn multimers are unclear. Consistent with the MD simulations and the immunoblot analysis, electron microscopy studies showed that compared to the vehicle control (Figure 6A), when incubated separately for 6 hrs, Aβ and α-syn generated ill-defined globular structures ranging in size between 5 to 10 nm (Figure 6B,C). In contrast, at 6 hrs the mixture between Aβ and α-syn resulted in well-defined ring-like structures measuring 9–15 nm with a central channel of approximately 3–5 nm (Figure 6D). The mixture of Aβ and α-syn showed increased numbers of ring-like structures after 6 hrs (Figure 6E). At longer periods of incubation, Aβ and α-syn alone, and the mixture formed fibrils of approximately 11 nm in diameter that increased in number in the samples containing a mixture of Aβ and α-syn (Figure 6F–I).

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