Differential protein expression in diverse brain areas of Parkinson's and Alzheimer's disease patients

Many hypotheses have been postulated to define the etiology of sporadic Parkinson's and Alzheimer's disorders (PD and AD) but there is no consensus on what causes these devastating age-related diseases. Braak staging of both pathologies helped researchers to better understand the progression and to identify their prodromal and symptomatic phases. Indeed, it is well accepted that Lewy body pathology and neurofibrillary tangles appearance correlates with disease progression and severity of symptoms in PD and AD, respectively. Additionally, several studies in PD and AD models try to disclose which cellular mechanisms are defaulted and trigger the neurodegenerative process that culminates with neuronal death causing PD and AD classical symptomatology. Herein, we determined expression levels of proteins involved in microtubule assembly, autophagic-lysosomal pathway and unfolded protein response in the cortex, hippocampus and SNpc of PD and AD patients, vascular dementia patients and aged-match controls. The differential expression allowed us to determine which pathways are determinant to synaptic dysfunction and to establish a time line for disease progression. Our results allow us to challenge the hypothesis that both PD and AD pathologies are caused by α-synuclein or Aβ pathology propagation throughout the brain in a prion-like manner.

Acetylation as a major determinant to microtubule-dependent autophagy: Relevance to Alzheimer's and Parkinson disease pathology

Protein post-translational modifications (PTMs) that potentiate protein aggregation have been implicated in several neurological disorders, including Alzheimer's (AD) and Parkinson's disease (PD). In fact, Tau and alpha-synuclein (ASYN) undergo several PTMs potentiating their aggregation and neurotoxicity. Recent data posits a role for acetylation in Tau and ASYN aggregation. Herein we aimed to clarify the role of Sirtuin-2 (SIRT2) and HDAC6 tubulin deacetylases as well as p300 acetyltransferase in AD and PD neurodegeneration. We used transmitochondrial cybrids that recapitulate pathogenic alterations observed in sporadic PD and AD patient brains and ASYN and Tau cellular models. We confirmed that Tau protein and ASYN are microtubules (MTs)-associated proteins (MAPs). Moreover, our results suggest that α-tubulin acetylation induced by SIRT2 inhibition is functionally associated with the improvement of MT dynamic determined by decreased Tau phosphorylation and by increased Tau/tubulin and ASYN/tubulin binding. Our data provide a strong evidence for a functional role of tubulin and MAPs acetylation on autophagic vesicular traffic and cargo clearance. Additionally, we showed that an accumulation of ASYN oligomers imbalance mitochondrial dynamics, which further compromise autophagy. We also demonstrated that an increase in Tau acetylation is associated with Tau phosphorylation. We found that p300, HDAC6 and SIRT2 influences Tau phosphorylation and autophagic flux in AD. In addition, we demonstrated that p300 and HDAC6 modulate Tau and Tubulin acetylation. Overall, our data disclose the role of Tau and ASYN modifications through acetylation in AD and PD pathology, respectively. Moreover, this study indicates that MTs can be a promising therapeutic target in the field of neurodegenerative disorders in which intracellular transport is altered.

The rescue of microtubule-dependent traffic recovers mitochondrial function in Parkinson's disease

In Parkinson's disease mitochondrial dysfunction can lead to a deficient ATP supply to microtubule protein motors leading to mitochondrial axonal transport disruption. Compromised axonal transport will then lead to a disorganized distribution of mitochondria and other organelles in the cell, as well as, the accumulation of aggregated proteins like alpha-synuclein. Moreover, axonal transport disruption can trigger synaptic accumulation of autophagosomes packed with damaged mitochondria and protein aggregates promoting synaptic failure. We previously observed that neuronal-like cells with an inherent mitochondrial impairment derived from PD patients contain a disorganized microtubule network, as well as, alpha-synuclein oligomer accumulation. In this work we provide new evidence that an agent that promotes microtubule network assembly, NAP (davunetide), improves microtubule-dependent traffic, restores the autophagic flux and potentiates autophagosome-lysosome fusion leading to autophagic vacuole clearance in Parkinson's disease cells. Moreover, NAP is capable of efficiently reducing alpha-synuclein oligomer content and its sequestration by the mitochondria. Most interestingly, NAP decreases mitochondrial ubiquitination levels, as well as, increases mitochondrial membrane potential indicating a rescue in mitochondrial function. Overall, we demonstrate that by improving microtubule-mediated traffic, we can avoid mitochondrial-induced damage and thus recover cell homeostasis. These results prove that NAP may be a promising therapeutic lead candidate for neurodegenerative diseases that involve axonal transport failure and mitochondrial impairment as hallmarks, like Parkinson's disease and related disorders.

Prodromal metabolic phenotype in MCI cybrids: implications for Alzheimer's disease

Mild cognitive impairment (MCI) is considered a nosological entity or a translational state between normal aging and sporadic Alzheimer's disease (AD). From brain tissue to peripheral blood samples, it is evident that the early markers of metabolic dysfunction observed in AD have also been found in MCI subjects. These observations obtained from MCI and AD subjects leave open the possibility that mitochondrial dysfunction-induced oxidative damage happening a priori of symptom onset, may trigger other pathological hallmarks, namely Aβ oligomerization. In this study, we used a citoplasmic hybrid (cybrid) model created by the repopulation of human teratocarcinoma (NT2) cells depleted of endogenous mitochondrial DNA (mtDNA) with platelets from age-matched controls, MCI and AD subjects. We found mitochondrial deficits in MCI and AD cybrids as compared with controls, such as a decrease in cytochrome c oxidase (COX) activity, a decrease in mitochondrial membrane potential and in mitochondrial cytochrome c content. Consequently, we analyzed parameters of oxidative damage and found that AD and MCI cybrids exhibit an increase in lipid peroxides, higher production of superoxide radicals, and higher content in protein carbonyls. Since our data clearly show alterations in mitochondrial-mediated oxidative damage in MCI cybrids we propose that mitochondrial dysfunction is an early event in idiopathic AD. Moreover, we found that mitochondrial Aβ oligomeric content increases in AD, which may exacerbate initial mitochondrial damage. Altogether, our data strongly supports a key role for mitochondria/ mtDNA in aged-driven AD pathology.

Mitochondrial metabolic control of microtubule dynamics impairs the autophagic pathway in Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is a progressive neurodegenerative disorder where the loss of dopaminergic neurons in the substantia nigra and the presence of Lewy bodies in surviving neurons are primary histopathological hallmarks. Recent evidence points to mitochondrial dysfunction as a common upstream event in PD etiopathology.

OBJECTIVE

In this overview, we will discuss some of our findings that provide support for the mitochondrial cascade hypothesis, whereas mitochondrial deficits trigger PD pathology through alterations in microtubule integrity and macroautophagy.

METHODS

Using, as a PD model, cells that have PD patients' mitochondrial DNA, cells without mitochondrial DNA and MPP(+)-treated cells, we showed that mitochondrial metabolism alteration may underlie changes in the microtubular net and in the autophagic-lysosomal pathway.

CONCLUSIONS

Finally, we will endow a potential new therapeutic target for PD pathology.

Mitochondria: the common upstream driver of amyloid-β and tau pathology in Alzheimer's disease

Mitochondrial dysfunction has been widely implicated in the etiology of Alzheimer's disease (AD). Evidence shows a mitochondrial-mediated impairment of autophagy that potentiates amyloid-β (Aβ) deposition. Accordingly, recent data obtained from AD models, in which mitochondrial alterations are a prominent feature, demonstrated abnormalities in microtubule network, involving tubulin and tau post-translational modifications. In this review we will discuss mitochondrial-regulated processes where mitochondrial malfunction is likely to start a sequence of events leading to sirtuin-2 activation, microtubule network breakdown, and impairment of the autophagic pathway. Because sirtuin-2 activity depends on cellular NAD+ availability, mitochondrial regulation of NAD+ levels may contribute to an increase in sirtuin-mediated tubulin deacetylation. A vicious cycle become installed which potentiates tau hyperphosphorylation, together with Aβ overproduction and deposition. Overall, targeting microtubule network constitutes a promising strategy for pharmacological therapy in AD.

Mitochondrial Dysfunction: The Road to Alpha-Synuclein Oligomerization in PD

While the etiology of Parkinson's disease remains largely elusive, there is accumulating evidence suggesting that mitochondrial dysfunction occurs prior to the onset of symptoms in Parkinson's disease. Mitochondria are remarkably primed to play a vital role in neuronal cell survival since they are key regulators of energy metabolism (as ATP producers), of intracellular calcium homeostasis, of NAD(+)/NADH ratio, and of endogenous reactive oxygen species production and programmed cell death. In this paper, we focus on mitochondrial dysfunction-mediated alpha-synuclein aggregation. We highlight some of the findings that provide proof of evidence for a mitochondrial metabolism control in Parkinson's disease, namely, mitochondrial regulation of microtubule-dependent cellular traffic and autophagic lysosomal pathway. The knowledge that microtubule alterations may lead to autophagic deficiency and may compromise the cellular degradation mechanisms that culminate in the progressive accumulation of aberrant protein aggregates shields new insights to the way we address Parkinson's disease. In line with this knowledge, an innovative window for new therapeutic strategies aimed to restore microtubule network may be unlocked.

Mitochondrial control of autophagic lysosomal pathway in Alzheimer's disease

When first described by Alois Alzheimer in 1907, AD was seen as a disorder that causes dementia and characterized by two defining neuropathological lesions, later associated with all forms of AD. While the etiology of AD remains largely unclear, there is accumulating evidence suggesting that mitochondrial dysfunction occurs prior to the onset of symptoms in AD. Mitochondria are exceptionally poised to play a crucial role in neuronal cell survival or death because they are regulators of both energy metabolism and apoptotic pathways. This review is mainly focused in the discussion of evidence suggesting a clear association between mitochondrial dysfunction, autophagy impairment and amyloid-beta accumulation in Alzheimer's disease pathophysiology. The knowledge that autophagic insufficiency may compromise the cellular degradation mechanisms that may culminate in the progressive accumulation of dysfunctional mitochondria, aberrant protein aggregates buildup and lysossomal burden shield new insights to the way we address Alzheimer's disease. In line with this knowledge an innovative window for new therapeutic strategies aimed to activate or ameliorate macroautophagy may be opened.