Annual Report of Activities CNC 2008 - Center for Neuroscience and ...

Molecular Mechanisms of Disease | Head: Cláudia PereiraObjectivesAlzheimer’s disease (AD), Parkinson’s disease (PD)and prion‐related encephalopathies (PRE) areprogressive neurodegenerative disorders characterizedby the extracellular deposition of amyloid‐betapeptide (Aβ), alpha‐synuclein and the scrapie isoformof prion protein (PrPSc), respectively. Although theaberrant peptide accumulation is recognized as animportant common feature in these neurodegenerativediseases, the mechanisms of pathogenesis remain animportant subject of competing hypothesis anddebate. The aim of the Molecular Mechanisms ofDisease group during 2008 was to investigate theprimary molecular and cellular events induced bythese disease‐related peptides and their causalrelationships in order to identify potential targets fortherapeutic intervention.The involvement of mitochondria dysfunction, whichhas emerged as a potential ‘lowest commondenominator’ linking several neurodegenerativedisorders, was investigated in studies conducted inmitochondrial DNA‐depleted rho0 cells and incultured neurons isolated from rat brain cortexexposed to Aβ or PrP peptides or to MPP+ (whichcauses parkinsonism by killing dopamine‐producingneurons in the substantia nigra). Using these AD, PDand PRE cell models, we further explored themitochondria/endoplasmic reticulum (ER) cross‐talkas a primary molecular mechanism leading toneuronal loss. To get a better insight into the role ofmitochondrial dysfunction in AD and PD we haveused cybrid cells obtained from the fusion of rho0cells with platelets isolated from AD or PD patients(or age‐matched controls) that recapitulate the focalmitochondrial respiratory chain defects, and alsohuman brain tissue (cortex and hippocampus) andfibroblasts from AD patients and control subjects.Using the triple transgenic mouse model of AD(3xTg‐AD), we analysed pathogenic mechanisms, inparticular, oxidative stress and cell cycle reactivation,during the progression of AD‐like neuropathology.Another focus of research of our group during 2008was the role of neuroinflammation in AD and PRE.Using co‐cultures of microglia/cortical neuronschallenged with Aβ or PrP or Aβ‐treated culturedastrocytes, we investigated the involvement of gliaactivation in neuronal injury.Main AchievementsOne of the group’s achievements was that theinterplay between ER and mitochondria represents aprimary mechanism leading to neuronal losstriggered by Aβ, PrP or MPP+. Data obtained incortical neurons, corroborated by studies in rho0 cells,demonstrate that Aβ and PrP activate the ER stressmediatedapoptotic pathway by a mitochondrialdependentprocess. ER stress was also shown to beinvolved in GSK3β‐mediated tau phosphorylationinduced by Aβ. Additionally, the Aβ‐inducedabnormal mitochondrial dynamics via differentialmodulation of fission/fusion proteins was revealed.In Aβ‐ or PrP‐treated neurons, Cdk5 is activatedleading to tau phosphorylation and also apoptosisdue to abortive cell cycle reactivation. In 3xTg‐ADmice, neuronal cell cycle reactivation is not a directconsequence of Aβ and tau pathologies. In thistransgenic model, oxidative stress was shown to be anearly event during the neuropathological process.Data obtained with human AD brain tissue cosubstantiatethe existence of prominent mitochondrialrelatedoxidative stress and showed that mitochondriaare key targets of increased autophagic degradation.Our data supports the role of neuroglia dysregulationin AD and PRE. In co‐cultures of microglia/corticalneurons challenged with Aβ or PrP, IL‐6 released byactivated microglia contributes to neuronal injury. Aβalso regulates the activity/levels of glutamatetransporters in cultured astrocytes decreasingglutamate clearance.We also contributed to elucidate the mechanismsunderlying cell degeneration in PD. Using rho0 cellsand PD cybrids, we demonstrated that mitochondriaimpairment leads to oxidative stress, inducing proteasomalderegulation. Moreover, we showed the impact ofmitochondrial dysfunction in microtubule depolymerizationand its relevance to alpha‐synuclein aggregation.26