Primate retinal cones express phosphorylated tau associated with neuronal degeneration yet survive in old age

Photoreceptor cells have high energy demands and suffer significantly with age. In aged rodents both rods and cones are lost, but in primates there is no evidence for aged cone loss, although their function declines. Here we ask if aged primate cones suffer from reduced function because of declining metabolic ability. Tau is a microtubule associated protein critical for mitochondrial function in neurons. Its phosphorylation is a feature of neuronal degeneration undermining respiration and mitochondrial dynamics. We show that total tau is widely distributed in the primate outer retina with little age-related change, being present in both rods and cones and their processes. However, all cones specifically accumulate phosphorylated tau, which was not seen in rods. The presence of this protein will likely undermine cone cell function. However, tau phosphorylation inhibits apoptosis. These data may explain why aged primate cones have reduced function but appear to be resistant to cell death. Consequently, therapies designed to remove phosphorylated tau may carry the risk of inducing cone photoreceptor cell death and further undermine ageing visual function

Tauopathies with parkinsonism: clinical spectrum, neuropathologic basis, biological markers, and treatment options

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73913/1/j.1468-1331.2008.02513.x.pd

Protection by the NDI1 Gene against Neurodegeneration in a Rotenone Rat Model of Parkinson's Disease

It is widely recognized that mitochondrial dysfunction, most notably defects in the NADH-quinone oxidoreductase (complex I), is closely related to the etiology of sporadic Parkinson's disease (PD). In fact, rotenone, a complex I inhibitor, has been used for establishing PD models both in vitro and in vivo. A rat model with chronic rotenone exposure seems to reproduce pathophysiological conditions of PD more closely than acute mouse models as manifested by neuronal cell death in the substantia nigra and Lewy body-like cytosolic aggregations. Using the rotenone rat model, we investigated the protective effects of alternative NADH dehydrogenase (Ndi1) which we previously demonstrated to act as a replacement for complex I both in vitro and in vivo. A single, unilateral injection of recombinant adeno-associated virus carrying the NDI1 gene into the vicinity of the substantia nigra resulted in expression of the Ndi1 protein in the entire substantia nigra of that side. It was clear that the introduction of the Ndi1 protein in the substantia nigra rendered resistance to the deleterious effects caused by rotenone exposure as assessed by the levels of tyrosine hydroxylase and dopamine. The presence of the Ndi1 protein also prevented cell death and oxidative damage to DNA in dopaminergic neurons observed in rotenone-treated rats. Unilateral protection also led to uni-directional rotation of the rotenone-exposed rats in the behavioral test. The present study shows, for the first time, the powerful neuroprotective effect offered by the Ndi1 enzyme in a rotenone rat model of PD

Successful Amelioration of Mitochondrial Optic Neuropathy Using the Yeast NDI1 Gene in a Rat Animal Model

Background: Leber’s hereditary optic neuropathy (LHON) is a maternally inherited disorder with point mutations in mitochondrial DNA which result in loss of vision in young adults. The majority of mutations reported to date are within the genes encoding the subunits of the mitochondrial NADH-quinone oxidoreductase, complex I. Establishment of animal models of LHON should help elucidate mechanism of the disease and could be utilized for possible development of therapeutic strategies. Methodology/Principal Findings: We established a rat model which involves injection of rotenone-loaded microspheres into the optic layer of the rat superior colliculus. The animals exhibited the most common features of LHON. Visual loss was observed within 2 weeks of rotenone administration with no apparent effect on retinal ganglion cells. Death of retinal ganglion cells occurred at a later stage. Using our rat model, we investigated the effect of the yeast alternative NADH dehydrogenase, Ndi1. We were able to achieve efficient expression of the Ndi1 protein in the mitochondria of all regions of retinal ganglion cells and axons by delivering the NDI1 gene into the optical layer of the superior colliculus. Remarkably, even after the vision of the rats was severely impaired, treatment of the animals with the NDI1 gene led to a complete restoration of the vision to the normal level. Control groups that received either empty vector or the GFP gene had no effects

Automatic Morphological Subtyping Reveals New Roles of Caspases in Mitochondrial Dynamics

Morphological dynamics of mitochondria is associated with key cellular processes related to aging and neuronal degenerative diseases, but the lack of standard quantification of mitochondrial morphology impedes systematic investigation. This paper presents an automated system for the quantification and classification of mitochondrial morphology. We discovered six morphological subtypes of mitochondria for objective quantification of mitochondrial morphology. These six subtypes are small globules, swollen globules, straight tubules, twisted tubules, branched tubules and loops. The subtyping was derived by applying consensus clustering to a huge collection of more than 200 thousand mitochondrial images extracted from 1422 micrographs of Chinese hamster ovary (CHO) cells treated with different drugs, and was validated by evidence of functional similarity reported in the literature. Quantitative statistics of subtype compositions in cells is useful for correlating drug response and mitochondrial dynamics. Combining the quantitative results with our biochemical studies about the effects of squamocin on CHO cells reveals new roles of Caspases in the regulatory mechanisms of mitochondrial dynamics. This system is not only of value to the mitochondrial field, but also applicable to the investigation of other subcellular organelle morphology

Disruption of Mitochondrial DNA Replication in Drosophila Increases Mitochondrial Fast Axonal Transport In Vivo

Mutations in mitochondrial DNA polymerase (pol γ) cause several progressive human diseases including Parkinson's disease, Alper's syndrome, and progressive external ophthalmoplegia. At the cellular level, disruption of pol γ leads to depletion of mtDNA, disrupts the mitochondrial respiratory chain, and increases susceptibility to oxidative stress. Although recent studies have intensified focus on the role of mtDNA in neuronal diseases, the changes that take place in mitochondrial biogenesis and mitochondrial axonal transport when mtDNA replication is disrupted are unknown. Using high-speed confocal microscopy, electron microscopy and biochemical approaches, we report that mutations in pol γ deplete mtDNA levels and lead to an increase in mitochondrial density in Drosophila proximal nerves and muscles, without a noticeable increase in mitochondrial fragmentation. Furthermore, there is a rise in flux of bidirectional mitochondrial axonal transport, albeit with slower kinesin-based anterograde transport. In contrast, flux of synaptic vesicle precursors was modestly decreased in pol γ−α mutants. Our data indicate that disruption of mtDNA replication does not hinder mitochondrial biogenesis, increases mitochondrial axonal transport, and raises the question of whether high levels of circulating mtDNA-deficient mitochondria are beneficial or deleterious in mtDNA diseases

Rapid Changes in Phospho-MAP/Tau Epitopes during Neuronal Stress: Cofilin-Actin Rods Primarily Recruit Microtubule Binding Domain Epitopes

Abnormal mitochondrial function is a widely reported contributor to neurodegenerative disease including Alzheimer's disease (AD), however, a mechanistic link between mitochondrial dysfunction and the initiation of neuropathology remains elusive. In AD, one of the earliest hallmark pathologies is neuropil threads comprising accumulated hyperphosphorylated microtubule-associated protein (MAP) tau in neurites. Rod-like aggregates of actin and its associated protein cofilin (AC rods) also occur in AD. Using a series of antibodies - AT270, AT8, AT100, S214, AT180, 12E8, S396, S404 and S422 - raised against different phosphoepitopes on tau, we characterize the pattern of expression and re-distribution in neurites of these phosphoepitope labels during mitochondrial inhibition. Employing chick primary neuron cultures, we demonstrate that epitopes recognized by the monoclonal antibody 12E8, are the only species rapidly recruited into AC rods. These results were recapitulated with the actin depolymerizing drug Latrunculin B, which induces AC rods and a concomitant increase in the 12E8 signal measured on Western blot. This suggests that AC rods may be one way in which MAP redistribution and phosphorylation is influenced in neurons during mitochondrial stress and potentially in the early pathogenesis of AD

Annonacin, a Natural Complex I Inhibitor of the Mitochondrial Respiratory Chain, causes Tau Pathology in Cultured Neurons.

Unter dem Begriff Tauopathien fasst man eine Gruppe chronisch progredienter neurodegenerativer Erkrankungen zusammen, die durch abnorme Akkumulation von hyperphosphoryliertem Tau Protein im Perykarion neuraler Zellen gekennzeichnet sind. Tau gehört zur Familie der axonalen Mikrotubuli-assoziierten Proteine. Die physiologische Funktion von Tau ist die Stabilisierung von Mikrotubuli und die Regulation axonaler Transportvorgänge. Eine neurodegenerative Tauopathie, die auf der karibischen Insel Guadeloupe endemisch ist, wurde epidemiologisch mit dem Konsum von Annonaceae-Pflanzen assoziiert. Diese enthalten Annonacin, den prototypischen Vertreter der Substanzklasse der Acetogenine, einer Gruppe von lipophilen Inhibitoren von Komplex I der Atmungskette. Vorausgehende experimentelle Arbeiten unserer Arbeitsgruppe konnten folgendes zeigen: Chronische systemische Behandlung von Ratten mit Annonacin führt zu Nervenzellverlust im Gehirn in einem Verteilungsmuster, wie es bei den Patienten auf Guadeloupe in postmortem Untersuchungen gefunden wurden. Annonacin führt durch Energie-Verarmung in Konzentrations-abhängiger Weise zu Zelltod in mesenzephalen Kulturen. Zur weiterführenden Überprüfung der Hypothese, dass Annonacin kausal an der Ätiologie der Erkrankung auf Guaedloupe beteiligt ist, untersuchten wir, ob Annonacin die Phosphorylierung und die intrazelluläre Verteilung des Tau Proteins beeinflusst. Wir fanden, dass eine 48-stündige Behandlung von primären Nervenzellen aus dem Striatum embryonaler Ratten in vitro mit Annonacin zu einer Konzentrations-abhängigen Umverteilung von Tau aus dem Axon in das Perykarion führt. Das umverteilte Tau war an mehreren Epitopen phosphoryliert, wie durch Phospho-spezifische Antikörper nachgewiesen wurde. Der primäre molekulare Wirkmechanismus von Annonacin, die Inhibition von Komplex I, hat zwei primäre intrazelluläre Konsequenzen, nämlich erstens eine Zunahme von Sauerstoffradikalen und zweitens eine Abnahme der ATP-Konzentration. Obwohl Radikal-Fänger die Annonacin-induzierten Sauerstoffradikale neutralisieren konnten, verhinderten sie nicht die Redistribution von Tau. Dies wurde aber wohl verhindert durch eine Stimulation der ATP-Produktion via anaerobe Glycolyse. Diese Beobachtungen legen nahe, dass die Annonacin-induzierte Umverteilung von phosphoryliertem Tau nicht aus oxydativem Stress, sondern aus Energie-Verarmung resultiert. Diese Interpretation wurde unterstützt durch die Beobachtung, dass andere zu Energie-Verarmung führende Neurotoxine (MPP+, 3-NP) ebenfalls zu intrazellulärer Umverteilung von phosphoryliertem Tau führten. Eine Elektronen-mikroskopische Analyse zeigte, dass Annonacin auch zu einer Akkumulation von Mitochondrien im Perykarion von kultivierten Nervenzellen führt. Ca. 30% des phosphorylierten Tau im Zytoplasma erschien Elektronen-mikroskopisch an die äußere Membran von Mitochondrien gebunden. Video-Mikroskopie von lebenden Nervenzellen zeigte, dass Annonacin rasch zu einem umfassenden retrograden Transport von Mitochondrien aus den Neuriten in das Perykarion führte. Wir schlussfolgerten, dass die Annonacin-induzierte Umverteilung von Tau und Mitochondrien funktionell verknüpft sind, da Taxol, eine Substanz, die Microtubuli stabilisiert und Tau von Mikrotubuli verdrängt, sowohl den retrograden Transport von Mitochondrien als auch die Akkumulation von phosphoryliertem Tau im Perykarion vollständige blockierte. Schließlich fanden wir, dass Annonacin infolge der Tau-Umverteilung zu einer Tau-Verarmung in den Axonen und konsekutiv zu einer ultrastrukturell darstellbaren Destabilisierung von Mikrotubuli führte. Daher scheint Annonacin zu einer Akkumulation von phosphoryliertem Tau im neuronalen Perykarion durch retrograden axonalen Transport und zu konsekutiver axonaler Schädigung zu führen. In ihrer Gesamtheit legen diese Untersuchungen nahe, dass Annonacin in der Lage ist, Veränderungen im Phosphorylierung-Zustand und in der intrazellularen Verteilung des Mikrotubuli-assoziierten Proteins Tau in einer Weise zu verändern, wie sie charakteristisch für humane Erkrankungen vom Typ der Tauopathien ist. Daher untermauern diese Ergebnisse weiter die Hypothese, dass regelmäßiger Konsum von Annonaceae Pflanzen in der Tat an der Ätiologie der Tauopathie auf Guadeloupe beteiligt sein könnte