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  • br Transparency document br Introduction Neurodegenerative d

    2019-07-05


    Transparency document
    Introduction Neurodegenerative diseases are a heterogeneous group of chronic, progressive disorders characterized by the gradual loss of neurons in the central nervous system, which leads to deficits in specific glpbio Ezatiostat functions (memory, movement, cognition) [1]. The mechanism that drives chronic progression of AD and PD age-related neurodegenerative disorders remains elusive and effective treatments are still lacking. Remarkably, both diseases share a common neuropathological feature such as the deposition of specific misfolded proteins [2]. In PD there is the presence of intracytoplasmic inclusions (Lewy bodies, LBs) which comprise a dense core of different proteins, being the main one ASYN [3] whereas in AD there is the presence of amyloid plaques, composed of amyloid-β (Aβ), a cleavage peptide derived from amyloid precursor protein (APP), and neurofibrillary tangles (NFTs), primarily composed of hyperphosphorylated Tau [4]. Notwithstanding, Tau deposition is found in other neurodegenerative brain diseases. The fact that Tau mutations can cause familial dementia proved that aberrant Tau itself can trigger neurodegenerative processes. The mechanisms by which Tau mutations cause neurodegeneration are still controversial but alterations in PTMs are believed to underlie the demise of affected brain cells. The first link established between ASYN and PD come from the disclosure that mutations in the ASYN gene lead to the disease. In fact, duplications or triplications of the ASYN locus in separate families cause autosomal-dominant PD involving altered kinetics of the aggregation of the protein [5]. The accumulation of toxic oligomeric species of ASYN may be one of the key processes for PD pathology. To study our hypothesis we used cytoplasmatic hybrids with patients platelet mtDNA that recapitulate pathogenic features observed in sporadic PD and AD brains [23,24]. Furthermore a model of tauopathy, SH-5Y5Y Tau P301L cells, which are characterized by abnormal accumulation of phosphorylated Tau [25] and ASYN overexpressing cells that mimic multiplication of the ASYN locus leading to enhanced ASYN aggregation [26] were used to model familial AD and PD respectively. To modulate Tau, ASYN and tubulin acetylation we ascertained the contribution of p300, HDAC6 and SIRT2 to phenotypic changes, using the specific inhibitors C646, Tubastatin A and AK1, respectively. Using sporadic and familial cellular models we also tackled fundamental differences in tubulin, ASYN and tau acetylation levels, and its contribution to the neurodegenerative process.
    Materials and methods
    Results
    Discussion Given that axonal transport is disrupted in PD and knowing that Tau protein is a MAP with the function of stabilizing the MT, this research aimed to clarify the role of Tau protein in PD. Interestingly ASYN cells and sPD cells show enhanced phospho-Tau levels at ser396 and thr181 indicating that ASYN accumulation leads to Tau hyperphosphorylation and MT disassembly as confirmed by reduced tubulin acetylation. Surprisingly, with this work we showed that there is a direct link between Tau dysfunction and PD. In fact, mutations in the Tau gene are associated to parkinsonism linked to chromosome 17 (FTDP-17) [46]. Corroborating these data we also found reduced co-localization of Tau with MTs. Tau hyperphosphorylation leads to a reduced ability of Tau to interact with MTs inducing the assembly of Tau into toxic filaments. Similarly we found that in ASYN cells and in cells harboring sPD patient mitochondria ASYN also binds poorly to tubulin. The aforementioned results raise the possibility that in PD, MT network disruption can lead or can result in decreased association of ASYN and Tau to tubulin. Our results clearly support that ASYN accumulation underlies MT disruption by affecting MAP function of ASYN leading to Tau phosphorylation, which contributes to impaired Tau-MT interactions. Interestingly another PTM of ASYN have been identified namely N-terminal acetylation, which seems to contribute to ASYN oligomerization and cytotoxicity [47]. However, herein in conjunction with decreased ASYN interaction with MTs we found that ASYN is less acetylated in PD cells. Taking into account that PD cells with mitochondrial DNA from sporadic PD patients show cytoskeleton alterations, which manifest as MT depolymerization and increased formation of ASYN oligomers [48], we can hypothesize that ASYN acetylation protects ASYN from oligomerization. Remarkably a recent report showed that N-terminal acetylation protected ASYN from oligomerization by preserving its native conformation against pathological aggregation [49]. In this study we demonstrated the role of SIRT2 in MT instability via α-tubulin deacetylation and Tau hyperphosphorylation. We provide evidence that α-tubulin acetylation via SIRT2 inhibition is functionally associated with the improvement of intracellular trafficking, providing a better autophagic turnover in PD cybrids and ASYN overexpressing cells. These data are consistent with previous reports demonstrating that ASYN-mediated neurotoxicity in several models of PD is partially due to deacetylation of α-tubulin by SIRT2 [12]. Additionally, dysfunctional mitochondria degradation by autophagy is dependent on a differential regulation of fusion-fission events that seems to be altered in sPD and ASYN overexpressing cells [37,38].