Bioenergetic dysfunction occurs in Alzheimer's disease (AD) and mild cognitive impairment (MCI), a clinical syndrome that frequently precedes symptomatic AD. In this study, we modeled AD and MCI bioenergetic dysfunction by transferring mitochondria from MCI, AD and control subject platelets to mtDNA-depleted SH-SY5Y cells. Bioenergetic fluxes and bioenergetics-related infrastructures were characterized in the resulting cytoplasmic hybrid (cybrid) cell lines. Relative to control cybrids, AD and MCI cybrids showed changes in oxygen consumption, respiratory coupling and glucose utilization. AD and MCI cybrids had higher ADP/ATP and lower NAD+/NADH ratios. AD and MCI cybrids exhibited differences in proteins that monitor, respond to or regulate cell bioenergetic fluxes including HIF1α, PGC1α, SIRT1, AMPK, p38 MAPK and mTOR. Several endpoints suggested mitochondrial mass increased in the AD cybrid group and probably to a lesser extent in the MCI cybrid group, and that the mitochondrial fission-fusion balance shifted towards increased fission in the AD and MCI cybrids. As many of the changes we observed in AD and MCI cybrid models are also seen in AD subject brains, we conclude reduced bioenergetic function is present during very early AD, is not brain-limited and induces protean retrograde responses that likely have both adaptive and mal-adaptive consequences.

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Multiple lines of evidence state a major role for mitochondrial dysfunction in sporadic Alzheimer's disease (AD) etiopathogenesis. However, the molecular mechanism(s) triggered by mitochondrial deficits that lead to neurodegeneration remain elusive. Herein, we propose a new mechanism by which mitochondrial loss of potential leads to a dysfunction in autophagy/mitophagy due to the overactivation of SIRT2, a tubulin deacetylase that regulates microtubule network acetylation, and provide insights into the association between metabolism, phosphorylation, and Aβ aggregation. We observed an increase in SIRT2 levels and a decrease in the acetylation of lys40 of tubulin in AD cells containing patient mtDNA as well as in AD brains. SIRT2 loss of function either with AK1 (a specific SIRT2 inhibitor) or by SIRT2 knockout recovers microtubule stabilization and improves autophagy, favoring cell survival through the elimination of toxic Aβ oligomers. Our data provide strong evidence for a functional role of tubulin acetylation on autophagic vesicle traffic and mitochondria degradation. We propose that SIRT2 inhibition may improve microtubule assembly thus representing a valid approach as disease-modifying therapy for AD.

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.

Abnormal presence of autophagic vacuoles is evident in brains of patients with Parkinson's disease (PD), in contrast to the rare detection of autophagosomes in a normal brain. However, the actual cause and pathological significance of these observations remain unknown. Here, we demonstrate a role for mitochondrial metabolism in the regulation of the autophagy-lysosomal pathway in ex vivo and in vitro models of PD. We show that transferring mitochondria from PD patients into cells previously depleted of mitochondrial DNA is sufficient to reproduce the alterations in the autophagic system observed in PD patient brains. Although the initial steps of this pathway are not compromised, there is an increased accumulation of autophagosomes associated with a defective autophagic activity. We prove that this functional decline was originated from a deficient mobilization of autophagosomes from their site of formation toward lysosomes due to disruption in microtubule-dependent trafficking. This contributed directly to a decreased proteolytic flux of α-synuclein and other autophagic substrates. Our results lend strong support for a direct impact of mitochondria in autophagy as defective autophagic clearance ability secondary to impaired microtubule trafficking is driven by dysfunctional mitochondria. We uncover mitochondria and mitochondria-dependent intracellular traffic as main players in the regulation of autophagy in PD.

Accumulating data suggests that mitochondrial deficits may underline both sporadic and familial Parkinson's disease (PD) neurodegenerative process. Impairment of mitochondrial dynamics results in reactive oxygen species (ROS) production, decreases mitochondrial membrane potential, and could potentiate the accumulation of dysfunctional mitochondria. Excessive mitochondrial fragmentation is associated with the pathology of sporadic PD. Therefore, we modulated mitochondria fusion and fission in different sporadic PD cellular models. We found alterations in two proteins known to regulate mitochondrial fusion and fission events (OPA1 and Drp1, respectively). OPA1 long isoform cleavage seems to be, at least in part, responsible for mitochondrial fragmented pattern observed in sporadic PD cellular models. Moreover, mitochondrial fragmentation can also occur due to an increase in Drp1 that is translocated into the mitochondria by phosphorylation. To disclose the relevance of these alterations to the fragmentation of the mitochondrial network, we overexpressed OPA1 and knock down Drp1. OPA1 overexpression did not rescue MPP(+)-induced increase in ROS. Nevertheless, Drp1 knockdown due to an increase in mitochondrial elongation and interconnectivity rescued mitochondrial membrane potential and decreased ROS production in sporadic PD cells. Overall, our findings suggest that Drp1-dependent mitochondrial fragmentation plays a crucial role in mediating mitochondrial DNA induced mitochondria abnormalities and cellular dysfunction in sporadic PD.

The multifactorial nature of Alzheimer's disease (AD), and the absence of a disease modifying drug, makes the development of new multifunctional drugs an attractive therapeutic strategy. Taking into account the hallmarks of AD patient brains, such as low levels of acetylcholine, misfolding of proteins and associated beta-amyloid (Aβ) aggregation, oxidative stress and metal dyshomeostasis, we have developed a series of compounds that merge three different approaches: metal attenuation, anti-Aβ aggregation and anti-acetylcholinesterase activity. Therefore, 3-hydroxy-4-pyridinone (3,4-HP) and benzothiazole molecular moieties were selected as starting frameworks due to their well known affinity for iron and Aβ peptides, respectively. The linkers between these two main functional groups were selected on the basis of virtual screening, so that the final molecule could further inhibit the acetylcholinesterase, responsible for the cholinergic losses. We describe herein the design and synthesis of the new hybrid compounds, followed by the assessment of solution properties, namely iron chelation and anti-oxidant capacity. The compounds were bioassayed for their capacity to inhibit AChE, as well as self- and Zn mediated-Aβ(1-42) aggregation. Finally, we assessed their effects on the viability of neuronal cells stressed with Aβ(42).

Alterations in microtubule-dependent transport, mitochondrial dysfunction, and autophagic pathology are involved in neurodegeneration observed in sporadic Parkinson's disease. However, the mechanistic link connecting these events remains elusive. We observed that NAD metabolism is altered in sporadic Parkinson's disease patient-derived cells, which contributes to Sirtuin-2 activation and subsequent decrease in acetylated-α-tubulin levels. Pharmacological inhibition of sirtuin-2 deacetylase activity selectively enhanced α-tubulin acetylation and facilitated the trafficking and clearance of misfolded proteins. Sirtuin-2 knock-out mice neurons had no alteration in microtubule assembly after exposure to MPP, allowing the maintenance of a normal autophagic flux. These data were validated using MPTP-treated sirtuin-2 knock-out mice, where no alterations in motor behavior were observed. Biochemical analysis of sporadic Parkinson's disease patient brains supports the in vitro and in vivo data. Our data provide strong evidence that sirtuin-2 controls the functional ability of the autophagic system through acetylation and highlight the association between mitochondrial metabolism and neurodegeneration in sporadic Parkinson's disease.