Final Report Summary - MITOABETA (Investigation of Beta-Amyloid Peptide Effects On Mitochondria Protein Homeostasis: From Pathogenesis to Therapy of Alzheimer Disease)
Introduction.
Alzheimer disease (AD) is a progressive neurodegenerative disease. It is the most common cause of dementia in the elderly. Currently an effective medical treatment and a definitive diagnosis of AD are not available yet. The two major neuropathological hallmarks of AD are extracellular beta amyloid plaques and intracellular neurofibrillary tangles (NFTs). The production of beta amyloid peptides is the result of cleavage of the precursor called amyloid precursor protein (APP). The vast majority of AD cases are sporadic, meaning that they are not genetically inherited. During the past years, several hypotheses have been proposed to explain the etiology and the pathogenesis of AD. Although some genes may act as risk factors, the only risk factor well accepted by scientific community is aging. Mitochondrion, a subcellular organelle that contain many enzymes important for cell metabolism, have been recognized as one of the main contributor of aging because due to the accumulation of mitochondrial DNA mutations and reactive oxygen species (ROS) production leading to an oxidative stress condition. Mitochondria contain an endogenous quality control system consisting of chaperones and protease systems fundamental for the maintenance of protein homeostasis. The involvement of mitochondrial quality control system in neurodegenerative diseases is still unknown. But, mitochondrial dysfunctions are consensually accepted as a general pathological feature in brain and peripheral compartment in AD patients.
The main aim of this proposal is to investigate the biochemistry of how beta amyloid peptides and the precursor APP affect mitochondrial functions and quality control system. There are already experimental evidences about a direct effect of intracellular beta amyloid peptides and the precursor APP on mitochondria leading to mitochondrial dysfunction. This project could not only unravel the biochemical mechanisms underlying mitochondrial dysfunction in neurodegenerative disease such as AD, but it could potentially provide new potential candidates for a therapeutic intervention and early diagnosis.
Results.
1) Association of beta amyloid peptides and Amyloid Precursor Protein (APP) in mitochondria:
Using an "in organello model", beta amyloid peptides and APP translocation, localization, and processing inside the mitochondria were studied in detail. The obtained data in this part of the project suggest that beta amyloid peptides and the precursor APP are able to bind the mitochondria outer membrane (MOM), but they are not processed by mitochondria neither imported inside the mitochondria by canonical ways. The most common forms of beta amyloid peptides, beta amyloid 40 and beta amyloid 42, were analyzed and have shown different behaviors in binding the MOM. This might have indirectly effects on mitochondrial functions.
2) Effect of beta amyloid peptides and the precursor APP on mitochondrial translocation of a control pre-protein:
Here it was investigated if beta amyloid peptides and the precursor APP may affect the mitochondrial import of precursor protein, a fundamental function for the maintenance of mitochondrial homeostasis. Using an "in organello" model,it was shown that beta amyloid peptides, but not the precursor APP, were able to inhibit the mitochondrial import of control proteins. The effect was not restricted to a specific mitochondrial import pathway, but it was more a general effect on a mitochondrial function. The mechanism of how beta amyloid peptides and APP affect the mitochondrial import were studied in detail. Analyzing all the data got in this part of the project, it was found that most probably beta amyloid peptides were able to aggregate with the control protein causing interference with the mitochondrial import of the control protein.
3) Recovery effect by extra-mitochondrial molecules on beta amyloid peptides effect on mitochondrial function:
In this part of the project, using an "in organello" model, it was investigated how the presence of other cellular components affects the beta amyloid peptides effect on mitochondrial import. Interestingly, the other sub-cellular fractions did not interfere with the mitochondrial import of the control protein, but they were able to revert the beta amyloid peptides-inhibition effect on mitochondrial import.
Conclusion.
In summary, using a biochemical approach, it was possible to study and show that beta amyloid peptides are able to interact with the mitochondria. For the first time it was demonstrated an important consequence of this association that is the inhibition of the mitochondrial precursor protein import, a fundamental function for the correct homeostasis of the mitochondria. This effect is reverted by the presence of other sub-cellular components. The data are quite interesting, innovative, consistent, and reproducible. They are important in the field of Alzheimer disease because they have been able to reveal a new aspect of the beta amyloid peptides biochemistry. This could help in the discovery of new candidates for the pharmacological treatment and early diagnosis not only of Alzheimer disease, but also of all the diseases in which misfolding and aggregation of proteins are involved.
The future plans are to extent and confirm these results in more complex models of Alzheimer disease, other neurodegenerative diseases and in human specimens.
Despite some parts of this project are still in progress, a manuscript is in preparation and soon it will be submitted to some of high impact factor journal.
Alzheimer disease (AD) is a progressive neurodegenerative disease. It is the most common cause of dementia in the elderly. Currently an effective medical treatment and a definitive diagnosis of AD are not available yet. The two major neuropathological hallmarks of AD are extracellular beta amyloid plaques and intracellular neurofibrillary tangles (NFTs). The production of beta amyloid peptides is the result of cleavage of the precursor called amyloid precursor protein (APP). The vast majority of AD cases are sporadic, meaning that they are not genetically inherited. During the past years, several hypotheses have been proposed to explain the etiology and the pathogenesis of AD. Although some genes may act as risk factors, the only risk factor well accepted by scientific community is aging. Mitochondrion, a subcellular organelle that contain many enzymes important for cell metabolism, have been recognized as one of the main contributor of aging because due to the accumulation of mitochondrial DNA mutations and reactive oxygen species (ROS) production leading to an oxidative stress condition. Mitochondria contain an endogenous quality control system consisting of chaperones and protease systems fundamental for the maintenance of protein homeostasis. The involvement of mitochondrial quality control system in neurodegenerative diseases is still unknown. But, mitochondrial dysfunctions are consensually accepted as a general pathological feature in brain and peripheral compartment in AD patients.
The main aim of this proposal is to investigate the biochemistry of how beta amyloid peptides and the precursor APP affect mitochondrial functions and quality control system. There are already experimental evidences about a direct effect of intracellular beta amyloid peptides and the precursor APP on mitochondria leading to mitochondrial dysfunction. This project could not only unravel the biochemical mechanisms underlying mitochondrial dysfunction in neurodegenerative disease such as AD, but it could potentially provide new potential candidates for a therapeutic intervention and early diagnosis.
Results.
1) Association of beta amyloid peptides and Amyloid Precursor Protein (APP) in mitochondria:
Using an "in organello model", beta amyloid peptides and APP translocation, localization, and processing inside the mitochondria were studied in detail. The obtained data in this part of the project suggest that beta amyloid peptides and the precursor APP are able to bind the mitochondria outer membrane (MOM), but they are not processed by mitochondria neither imported inside the mitochondria by canonical ways. The most common forms of beta amyloid peptides, beta amyloid 40 and beta amyloid 42, were analyzed and have shown different behaviors in binding the MOM. This might have indirectly effects on mitochondrial functions.
2) Effect of beta amyloid peptides and the precursor APP on mitochondrial translocation of a control pre-protein:
Here it was investigated if beta amyloid peptides and the precursor APP may affect the mitochondrial import of precursor protein, a fundamental function for the maintenance of mitochondrial homeostasis. Using an "in organello" model,it was shown that beta amyloid peptides, but not the precursor APP, were able to inhibit the mitochondrial import of control proteins. The effect was not restricted to a specific mitochondrial import pathway, but it was more a general effect on a mitochondrial function. The mechanism of how beta amyloid peptides and APP affect the mitochondrial import were studied in detail. Analyzing all the data got in this part of the project, it was found that most probably beta amyloid peptides were able to aggregate with the control protein causing interference with the mitochondrial import of the control protein.
3) Recovery effect by extra-mitochondrial molecules on beta amyloid peptides effect on mitochondrial function:
In this part of the project, using an "in organello" model, it was investigated how the presence of other cellular components affects the beta amyloid peptides effect on mitochondrial import. Interestingly, the other sub-cellular fractions did not interfere with the mitochondrial import of the control protein, but they were able to revert the beta amyloid peptides-inhibition effect on mitochondrial import.
Conclusion.
In summary, using a biochemical approach, it was possible to study and show that beta amyloid peptides are able to interact with the mitochondria. For the first time it was demonstrated an important consequence of this association that is the inhibition of the mitochondrial precursor protein import, a fundamental function for the correct homeostasis of the mitochondria. This effect is reverted by the presence of other sub-cellular components. The data are quite interesting, innovative, consistent, and reproducible. They are important in the field of Alzheimer disease because they have been able to reveal a new aspect of the beta amyloid peptides biochemistry. This could help in the discovery of new candidates for the pharmacological treatment and early diagnosis not only of Alzheimer disease, but also of all the diseases in which misfolding and aggregation of proteins are involved.
The future plans are to extent and confirm these results in more complex models of Alzheimer disease, other neurodegenerative diseases and in human specimens.
Despite some parts of this project are still in progress, a manuscript is in preparation and soon it will be submitted to some of high impact factor journal.