Suppression of Parkin enhances nigrostriatal and motor neuron lesion in mice over-expressing human-mutated tau protein

Unique transcriptional signatures correlate with behavioral and psychological symptom domains in Alzheimer's disease

Despite the significant burden, cost, and worse prognosis of Alzheimer's disease (AD) with behavioral and psychological symptoms of dementia (BPSD), little is known about the molecular causes of these symptoms. Using antemortem assessments of BPSD in AD, we demonstrate that individual BPSD can be grouped into 4 domain factors in our cohort: affective, apathy, agitation, and psychosis. Then, we performed a transcriptome-wide analysis for each domain utilizing bulk RNA-seq of post-mortem anterior cingulate cortex (ACC) tissues. Though all 4 domains are associated with a predominantly downregulated pattern of hundreds of differentially expressed genes (DEGs), most DEGs are unique to each domain, with only 22 DEGs being common to all BPSD domains, including TIMP1. Weighted gene co-expression network analysis (WGCNA) yielded multiple transcriptional modules that were shared between BPSD domains or unique to each domain, and NetDecoder was used to analyze context-dependent information flow through the biological network. For the agitation domain, we found that all DEGs and a highly associated transcriptional module were functionally enriched for ECM-related genes including TIMP1, TAGLN, and FLNA. Another unique transcriptional module also associated with the agitation domain was enriched with genes involved in post-synaptic signaling, including DRD1, PDE1B, CAMK4, and GABRA4. By comparing context-dependent changes in DEGs between cases and control networks, ESR1 and PARK2 were implicated as two high-impact genes associated with agitation that mediated significant information flow through the biological network. Overall, our work establishes unique targets for future study of the biological mechanisms of BPSD and resultant drug development.

Parkin as a Molecular Bridge Linking Alzheimer’s and Parkinson’s Diseases?

Alzheimer’s (AD) and Parkinson’s (PD) diseases are two distinct age-related pathologies that are characterized by various common dysfunctions. They are referred to as proteinopathies characterized by ubiquitinated protein accumulation and aggregation. This accumulation is mainly due to altered lysosomal and proteasomal clearing processes and is generally accompanied by ER stress disturbance, autophagic and mitophagic defects, mitochondrial structure and function alterations and enhanced neuronal cell death. Genetic approaches aimed at identifying molecular triggers responsible for familial forms of AD or PD have helped to understand the etiology of their sporadic counterparts. It appears that several proteins thought to contribute to one of these pathologies are also likely to contribute to the other. One such protein is parkin (PK). Here, we will briefly describe anatomical lesions and genetic advances linked to AD and PD as well as the main cellular processes commonly affected in these pathologies. Further, we will focus on current studies suggesting that PK could well participate in AD and thereby act as a molecular bridge between these two pathologies. In particular, we will focus on the transcription factor function of PK and its newly described transcriptional targets that are directly related to AD- and PD-linked cellular defects.

Parkin regulates drug-taking behavior in rat model of methamphetamine use disorder

There is no FDA-approved medication for methamphetamine (METH) use disorder. New therapeutic approaches are needed, especially for people who use METH heavily and are at high risk for overdose. This study used genetically engineered rats to evaluate PARKIN as a potential target for METH use disorder. PARKIN knockout, PARKIN-overexpressing, and wild-type young adult male Long Evans rats were trained to self-administer high doses of METH using an extended-access METH self-administration paradigm. Reinforcing/rewarding properties of METH were assessed by quantifying drug-taking behavior and time spent in a METH-paired environment. PARKIN knockout rats self-administered more METH and spent more time in the METH-paired environment than wild-type rats. Wild-type rats overexpressing PARKIN self-administered less METH and spent less time in the METH-paired environment. PARKIN knockout rats overexpressing PARKIN self-administered less METH during the first half of drug self-administration days than PARKIN-deficient rats. The results indicate that rats with PARKIN excess or PARKIN deficit are useful models for studying neural substrates underlying "resilience" or vulnerability to METH use disorder and identify PARKIN as a novel potential drug target to treat heavy use of METH.

Lipidomic Alterations in the Mitochondria of Aged Parkin Null Mice Relevant to Autophagy

Mitochondrial quality control is important in neurological diseases, but in genetic Parkinson’s disease caused by mutations in PINK and parkin mitochondrial degradation through autophagy is crucial. Reductions in autophagy and mitophagy are implicated in aging, age related diseases and Parkinson. The parkin null mice (PK-KO) show only a subtle phenotype, apparent with age or with stressors. We have studied the changes in the lipidomic composition of the mitochondrial membranes isolated from the brains of young and old PK-KO mice and compared them to wild type in order to determine possible implications for Parkinson’s disease pathology. We observed an increase in the levels of phosphatidylethanolamine in the young PK-KO mice that is lost in the old and correlate to changes in the phosphatidylserine decarboxylase. PK-KO old mice mitochondria showed lower phosphatidylglicerol and phosphatidylinositol levels and higher levels of some forms of hydroxylated ceramides. Regarding cardiolipins there were changes in the degree of saturation mainly with age. The lipidomic composition discriminates between the study groups using partial least square discriminant analysis. We discuss the relevance of the lipid changes for the autophagic activity, the mitophagy, the mitochondrial activity and the Parkinson’s disease pathology in absence of parkin.

Characterization of Dopaminergic System in the Striatum of Young Adult Park2-/- Knockout Rats

Mutations in parkin gene (Park2) are linked to early-onset autosomal recessive Parkinson's disease (PD) and young-onset sporadic PD. Park2 knockout (PKO) rodents; however, do not display neurodegeneration of the nigrostriatal pathway, suggesting age-dependent compensatory changes. Our goal was to examine dopaminergic (DAergic) system in the striatum of 2 month-old PKO rats in order to characterize compensatory mechanisms that may have occurred within the system. The striata form wild type (WT) and PKO Long Evans male rats were assessed for the levels of DAergic markers, for monoamine oxidase (MAO) A and B activities and levels, and for the levels of their respective preferred substrates, serotonin (5-HT) and ß-phenylethylamine (ß-PEA). The PKO rats displayed lower activities of MAOs and higher levels of ß-PEA in the striatum than their WT counterparts. Decreased levels of ß-PEA receptor, trace amine-associated receptor 1 (TAAR-1), and postsynaptic DA D2 (D2L) receptor accompanied these alterations. Drug-naive PKO rats displayed normal locomotor activity; however, they displayed decreased locomotor response to a low dose of psychostimulant methamphetamine, suggesting altered DAergic neurotransmission in the striatum when challenged with an indirect agonist. Altogether, our findings suggest that 2 month-old PKO male rats have altered DAergic and trace aminergic signaling.

Parkin overexpression ameliorates hippocampal long-term potentiation and β-amyloid load in an Alzheimer's disease mouse model

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by a severe decline of memory performance. A widely studied AD mouse model is the APPswe/PSEN1ΔE9 (APP/PS1) strain, as mice exhibit amyloid plaques as well as impaired memory capacities. To test whether restoring synaptic plasticity and decreasing β-amyloid load by Parkin could represent a potential therapeutic target for AD, we crossed APP/PS1 transgenic mice with transgenic mice overexpressing the ubiquitin ligase Parkin and analyzed offspring properties. Overexpression of Parkin in APP/PS1 transgenic mice restored activity-dependent synaptic plasticity and rescued behavioral abnormalities. Moreover, overexpression of Parkin was associated with down-regulation of APP protein expression, decreased β-amyloid load and reduced inflammation. Our data suggest that Parkin could be a promising target for AD therapy.

AGC1-malate aspartate shuttle activity is critical for dopamine handling in the nigrostriatal pathway

The mitochondrial transporter of aspartate-glutamate Aralar/AGC1 is a regulatory component of the malate-aspartate shuttle. Aralar deficiency in mouse and human causes a shutdown of brain shuttle activity and global cerebral hypomyelination. A lack of neurofilament-labeled processes is detected in the cerebral cortex, but whether different types of neurons are differentially affected by Aralar deficiency is still unknown. We have now found that Aralar-knockout (Aralar-KO) post-natal mice show hyperactivity, anxiety-like behavior, and hyperreactivity with a decrease of dopamine (DA) in terminal-rich regions. The striatum is the brain region most affected in terms of size, amino acid and monoamine content. We find a decline in vesicular monoamine transporter-2 (VMAT2) levels associated with increased DA metabolism through MAO activity (DOPAC/DA ratio) in Aralar-KO striatum. However, no decrease in DA or in the number of nigral tyrosine hydroxylase-positive cells was detected in Aralar-KO brainstem. Adult Aralar-hemizygous mice presented also increased DOPAC/DA ratio in striatum and enhanced sensitivity to amphetamine. Our results suggest that Aralar deficiency causes a fall in GSH/GSSG ratio and VMAT2 in striatum that might be related to a failure to produce mitochondrial NADH and to an increase of reactive oxygen species (ROS) in the cytosol. The results indicate that the nigrostriatal dopaminergic system is a target of Aralar deficiency.

Parkinson's disease mouse models in translational research

Animal models with high predictive power are a prerequisite for translational research. The closer the similarity of a model to Parkinson’s disease (PD), the higher is the predictive value for clinical trials. An ideal PD model should present behavioral signs and pathology that resemble the human disease. The increasing understanding of PD stratification and etiology, however, complicates the choice of adequate animal models for preclinical studies. An ultimate mouse model, relevant to address all PD-related questions, is yet to be developed. However, many of the existing models are useful in answering specific questions. An appropriate model should be chosen after considering both the context of the research and the model properties. This review addresses the validity, strengths, and limitations of current PD mouse models for translational research.

Trehalose ameliorates dopaminergic and tau pathology in parkin deleted/tau overexpressing mice through autophagy activation

Tauopathies are neurodegenerative diseases, sporadic or familial, mainly characterized by dementia and parkinsonism associated to atrophy of the frontotemporal cortex and the basal ganglia, with deposition of abnormal tau in brain. Hereditary tauopathies are related with mutations of the tau gene. Up to the present, these diseases have not been helped by any disease-modifying treatment, and patients die a few years after the onset of symptoms. We have developed and characterized a mouse model of tauopathy with parkinsonism, overexpressing human mutated tau protein with deletion of parkin (PK(-/-)/Tau(VLW)). At 3 months of age, these mice present abnormal dopamine-related behavior, severe dropout of dopamine neurons in the ventral midbrain, reduced dopamine levels in the striatum and abundant phosphorylated tau-positive neuritic plaques, neurofibrillary tangles, astrogliosis, and, at 12 months old, plaques of murine beta-amyloid in the hippocampus. Trehalose is a natural disaccharide that increases the removal of abnormal proteins through enhancement of autophagy. In this work, we tested if 1% trehalose in the drinking water reverts the PK(-/-)/Tau(VLW) phenotype. The treatment with trehalose of 3-month-old PK(-/-)/Tau(VLW) mice for 2.5 months reverted the dropout of dopamine neurons, which takes place in the ventral midbrain of vehicle treated PK(-/-)/Tau(VLW) and the reduced dopamine-related proteins levels in the midbrain and striatum. The number of phosphorylated tau-positive neuritic plaques and the levels of phosphorylated tau decreased, as well as astrogliosis in brain regions. The autophagy markers in the brain, the autophagic vacuoles isolated from the liver, and the electron microscopy data indicate that these effects of trehalose are mediated by autophagy. The treatment with trehalose for 4 months of 3-month-old PK(-/-)/Tau(VLW) mice maintained the amelioration of the tau pathology and astrogliosis but failed to revert DA-related pathology in the striatum. Furthermore, the 3-week treatment with trehalose of 14-month-old PK(-/-)/Tau(VLW) mice, at the limit of their life expectancy, improved the motor behavior and anxiety of these animals, and reduced their levels of phosphorylated tau and the number of murine beta-amyloid plaques. Trehalose is neuroprotective in this model of tauopathy. Since trehalose is free of toxic effects at high concentrations, this study opens the way for clinical studies of the effects of trehalose in human tauopathies.

Cell death pathways in Parkinson's disease: proximal triggers, distal effectors, and final steps

Parkinson's disease (PD) is a common neurodegenerative disorder. Neuronal cell death in PD is still poorly understood, despite a wealth of potential pathogenic mechanisms and pathways. Defects in several cellular systems have been implicated as early triggers that start cells down the road toward neuronal death. These include abnormal protein accumulation, particularly of alpha-synuclein; altered protein degradation via multiple pathways; mitochondrial dysfunction; oxidative stress; neuroinflammation; and dysregulated kinase signaling. As dysfunction in these systems mounts, pathways that are more explicitly involved in cell death become recruited. These include JNK signaling, p53 activation, cell cycle re-activation, and signaling through bcl-2 family proteins. Eventually, neurons become overwhelmed and degenerate; however, even the mechanism of final cell death in PD is still unsettled. In this review, we will discuss cell death triggers and effectors that are relevant to PD, highlighting important unresolved issues and implications for the development of neuroprotective therapies.

Hyperphosphorylated tau aggregates in the cortex and hippocampus of transgenic mice with mutant human FTDP-17 Tau and lacking the PARK2 gene

Mutations in the PARK2 gene encoding parkin cause autosomal recessive juvenile parkinsonism, but have also been found in patients diagnosed with certain tauopathies. Conversely, mutations in the MAPT gene encoding tau are present in some types of parkinsonism. In order to investigate the possible relationship between these two proteins, we generated a double mutant mouse that is deficient in PARK2 and that over-expresses the hTauVLW transgene, a mutant form of the tau protein present in FTDP-17. Independent deletion of PARK2 or over-expression of the hTauVLW transgene produces mild phenotypic alterations, while a substantial increase in parkin expression is observed in hTauVLW transgenic mice. However, double mutant mice present memory and exploratory deficits, and accumulation of PHF-1 and AT8 hyperphosphorylated tau epitopes in neurons. These phenomena are coupled with reactive astrocytosis, DNA fragmentation, and variable cerebral atrophy. Here, we show that cortical and hippocampal neurons of double mutant mice develop argyrophilic Gallyas-Braak aggregates of phosphorylated tau from 3 months of age. Their number decreases in old animals. Moreover, numerous phosphorylated tau aggregates were identified with the conformation-dependent Alz-50 antibody and the S-Thioflavin staining. Ventral motor nuclei of the spinal cord also present Alz-50, AT8, and PHF1 hyperphosphorylated tau aggregates when parkin is deleted in mice over-expressing the hTauVLW transgene, begining at early ages. Thus, the combination of PARK2 gene deletion with hTauVLW over-expression in mice produces abnormal hyperphosphorylated tau aggregates, similar to those observed in the brain of patients diagnosed with certain tauopathies. In the light of these changes, these mice may help to understand the molecular processes responsible for these diseases, and they may aid the development of new therapeutic strategies to treat neurodegenerative diseases related to tau and parkin proteins.

NP7 protects from cell death induced by oxidative stress in neuronal and glial midbrain cultures from parkin null mice

Parkin mutations produce Parkinson's disease (PD) in humans and nigrostriatal dopamine lesions related to increased free radicals in mice. We examined the effects of NP7, a synthetic, marine derived, free radical scavenger which enters the brain, on H(2)O(2) toxicity in cultured neurons and glia from wild-type (WT) and parkin null mice (PK-KO). NP7, 5-10 microM, prevented the H(2)O(2) induced apoptosis and necrosis of midbrain neuronal and glial cultures from WT and PK-KO mice. NP7 suppressed microglial activation and the H(2)O(2) induced drop-out of dopamine neurons(.) Furthermore, NP7 prevented the increased phosphorylation of ERK and AKT induced by H(2)O(2). NP7 may be a promising neuroprotector against oxidative stress in PD.

Glial Cells as Players in Parkinsonism: The “Good,” the “Bad,” and the “Mysterious” Glia

The role of glia in Parkinson's disease (PD) is very interesting because it may open new therapeutic strategies in this disease. Traditionally it has been considered that astrocytes and microglia play different roles in PD: Astroglia are considered the “good” glia and have traditionally been supposed to be neuroprotective due to their capacity to quench free radicals and secrete neurotrophic factors, whereas microglia, considered the “bad” glia, are thought to play a critical role in neuroinflammation. The proportion of astrocytes surrounding dopamine (DA) neurons in the substantia nigra, the target nucleus for neurodegeneration in PD, is the lowest for any brain area, suggesting that DA neurons are more vulnerable in terms of glial support than any neuron in other brain areas. Astrocytes are critical in the modulation of the neurotoxic effects of many toxins that induce experimental parkinsonism and they produce substances in vitro that could modify the effects of L-DOPA from neurotoxic to neurotrophic. There is a great interest in the role of inflammation in PD, and in the brains of these patients there is evidence for microglial production of cytokines and other substances that could be harmful to neurons, suggesting that microglia of the substantia nigra could be actively involved, primarily or secondarily, in the neurodegeneration process. There is, however, evidence in favor of the role of neurotoxic diffusible signals from microglia to DA neurons. More recently a third glial player, oligodendroglia, has been implicated in the pathogenesis of PD. Oligodendroglia play a key role in myelination of the nervous system. Recent neuropathological studies suggested that the nigrostriatal dopamine neurons, which were considered classically as the primary target for neurodegeneration in PD, degenerate at later stages than other neurons with poor myelination. Therefore, the role of oligodendroglia, which also secrete neurotrophic factors, has entered the center of interest of neuroscientists.

Motor alterations are reduced in mice lacking the PARK2 gene in the presence of a human FTDP-17 mutant form of four-repeat tau

Independent deletion of the PARK2 gene and hTauVLW over-expression in mice produce mild alterations in the brain. However, the presence of both mutations in a parkin-deficient and hTauVLW double mutant mouse causes a tau neuropathology, reactive astrocytosis, and neuronal loss in the cortex and hippocampus, as well as lesions in nigrostriatal and motor neurons. Moreover, these mutants display some memory and exploratory defects that reflect a functional link between parkin and tau proteins. We have tested the motor activity and coordination of these double mutant mice to determine the effects of parkin deletion in mice over-expressing the hTauVLW transgene. While the loss of parkin alone produces increased exploration and alterations in gait and motor coordination, in hTauVLW transgenic mice the absence of parkin causes less prominent motor impairments. These effects suggest the existence of some compensatory mechanisms that are activated when the hTauVLW transgene is over-expressed in the absence of parkin. This mouse model will hopefully help to study the causes of the motor deficits associated with certain neuropathologies related to the tau and parkin proteins, and to find appropriate treatments.

Parkin deletion causes cerebral and systemic amyloidosis in human mutated tau over-expressing mice

Deposition of proteins leading to amyloid takes place in some neurodegenerative diseases such as Alzheimer's disease and Huntington's disease. Mutations of tau and parkin proteins produce neurofibrillary abnormalities without deposition of amyloid. Here we report that mature, parkin null, over-expressing human mutated tau (PK(-/-)/Tau(VLW)) mice have altered behaviour and dopamine neurotransmission, tau pathology in brain and amyloid deposition in brain and peripheral organs. PK(-/-)/Tau(VLW) mice have abnormal behaviour and severe drop out of dopamine neurons in the ventral midbrain, up to 70%, at 12 months and abundant phosphorylated tau positive neuritic plaques, neuro-fibrillary tangles, astrogliosis, microgliosis and plaques of murine beta-amyloid in the hippocampus. PK(-/-)/Tau(VLW) mice have organomegaly of the liver, spleen and kidneys. The electron microscopy of the liver confirmed the presence of a fibrillary protein deposits with amyloid characteristics. There is also accumulation of mouse tau in hepatocytes. These mice have lower levels of CHIP-HSP70, involved in the proteosomal degradation of tau, increased oxidative stress, measured as depletion of glutathione which, added to lack of parkin, could trigger tau accumulation and amyloidogenesis. This model is the first that demonstrates beta-amyloid deposits caused by over-expression of tau and without modification of the amyloid precursor protein, presenilins or secretases. PK(-/-)/Tau(VLW) mice provide a link between the two proteins more important for the pathogenesis of Alzheimer disease.

Gender differences and estrogen effects in parkin null mice

Estrogens are considered neurotrophic for dopamine neurons. Parkinson's disease is more frequent in males than in females, and more prevalent in females with short reproductive life. Estrogens are neuroprotective against neurotoxic agents for dopamine neurons in vivo and in vitro. Here, we have investigated the role of estrogens in wild-type (WT) and parkin null mice (PK-/-). WT mice present sexual dimorphisms in neuroprotective mechanisms (Bcl-2/Bax, chaperones, and GSH), but some of these inter-sex differences disappear in PK-/-. Tyrosine hydroxylase (TH) protein and TH+ cells decreased earlier and more severely in female than in male PK-/- mice. Neuronal cultures from midbrain of WT and PK-/- mice were treated with estradiol from 10 min to 48 h. Short-term treatments activated the mitogen-activated protein kinase pathway of WT and PK-/- neurons and the phosphatidylinositol 3'-kinase/AKT/glycogen synthase kinase-3 pathway of WT but not of PK-/- cultures. Long-term treatments with estradiol increased the number of TH+ neurons, the TH expression, and the extension of neurites, and decreased the level of apoptosis, the expression of glial fibrillary acidic protein, and the number of microglial cells in WT but not in PK-/- cultures. The levels of estrogen receptor-alpha were elevated in midbrain cultures and in the striatum of adult PK-/- male mice, suggesting that suppression of parkin changes the estrogen receptor-alpha turnover. From our data, it appears that parkin participates in the cellular estrogen response which could be of interest in the management of parkin-related Parkinson's disease patients.

Glial dysfunction in parkin null mice: effects of aging

Parkin mutations in humans produce parkinsonism whose pathogenesis is related to impaired protein degradation, increased free radicals, and abnormal neurotransmitter release. The role of glia in parkin deficiency is little known. We cultured midbrain glia from wild-type (WT) and parkin knock-out (PK-KO) mice. After 18-20 d in vitro, PK-KO glial cultures had less astrocytes, more microglia, reduced proliferation, and increased proapoptotic protein expression. PK-KO glia had greater levels of intracellular glutathione (GSH), increased mRNA expression of the GSH-synthesizing enzyme gamma-glutamylcysteine synthetase, and greater glutathione S-transferase and lower glutathione peroxidase activities than WT. The reverse happened in glia cultured in serum-free defined medium (EF12) or in old cultures. PK-KO glia was more susceptible than WT to transference to EF12 or neurotoxins (1-methyl-4-phenylpyridinium, blockers of GSH synthesis or catalase, inhibitors of extracellular signal-regulated kinase 1/2 and phosphatidylinositol 3 kinases), aging of the culture, or combination of these insults. PK-KO glia was less susceptible than WT to Fe2+ plus H2O2 and less responsive to protection by deferoxamine. Old WT glia increased the expression of heat shock protein 70, but PK-KO did not. Glia conditioned medium (GCM) from PK-KO was less neuroprotective and had lower levels of GSH than WT. GCM from WT increased the levels of dopamine markers in midbrain neuronal cultures transferred to EF12 more efficiently than GCM from PK-KO, and the difference was corrected by supplementation with GSH. PK-KO-GCM was a less powerful suppressor of apoptosis and microglia in neuronal cultures. Our data prove that abnormal glial function is critical in parkin mutations, and its role increases with aging.

Update of atypical parkinsonian disorders

PURPOSE OF REVIEW

This timely update discusses novel diagnostic approaches, recently identified genes, and innovative experimental symptomatic treatments for these devastating disorders.

RECENT FINDINGS

Differential patterns in the basal ganglia transcranial sonography, magnetic resonance diffusion-weighted imaging regional apparent diffusion coefficients in the brainstem, basal ganglia T2-weighted gradient echo sequences combined with fluid attenuated inversion recovery, or saccades error rates in single and mixed-task blocks could help differentiate the various parkinsonian disorders. In addition to the familial tauopathies (frontotemporal dementia associated with chromosome 17) presenting with an atypical parkinsonian phenotype, 'TDP-43opathies' and 'tataboxbinding or ataxinopathies', depending on the protein deposited in the brain, widen the scope of the familial atypical parkinsonian disorders. Recent identification of novel deep brain stimulation targets such as the pedunculopontine nucleus may help treat the balance and gait disorder in atypical parkinsonian disorders in the near future.

SUMMARY

These new findings are important for diagnosis, help better understanding of the nosology of these disorders, and will likely in the near future impact our clinical practice.

Mortality, oxidative stress and tau accumulation during ageing in parkin null mice

Young parkin null (pk-/-) mice have subtle abnormalities of behaviour, dopamine (DA) neurotransmission and free radical production, but no massive loss of DA neurons. We investigated whether these findings are maintained while ageing. Pk-/- mice have reduced life span and age-related reduced exploratory behaviour, abnormal walking and posture, and behaviours similar to those of early Parkinson's disease (PD), reduced number of nigrostriatal DA neurons and proapoptotic shifts in the survival/death proteins in midbrain and striatum. Contrary to young pk-/- animals 24-month-old pk-/- mice do not have compensatory elevation of GSH in striatum, glutathione reductase (GR) and glutathione peroxidase (GPx) activities are increased and catalase unchanged. Aged pk-/- mice accumulate high levels of tau and fail to up-regulate CHIP and HSP70. Our results suggest that aged pk-/- mice lack of the compensatory mechanisms that maintain a relatively normal DA function in early adulthood. This study could help to explain the effects of ageing in patients with genetic risks for Parkinson's disease.

A decade of tau transgenic animal models and beyond

The first tau transgenic mouse model was established more than a decade ago. Since then, much has been learned about the role of tau in Alzheimer's disease and related disorders. Animal models, both in vertebrates and invertebrates, were significantly improved and refined as a result of the identification of pathogenic mutations in Tau in human cases of frontotemporal dementia. They have been instrumental for dissecting the cross-talk between tau and the second hallmark lesion of Alzheimer's disease, the Abeta peptide-containing amyloid plaque. We discuss how the tau models have been used to unravel the pathophysiology of Alzheimer's disease, to search for disease modifiers and to develop novel treatment strategies. While tau has received less attention than Abeta, it is rapidly acquiring a more prominent position and the emerging view is one of a synergistic action of Abeta and tau in Alzheimer's disease. Moreover, the existence of a number of neurodegenerative diseases with tau pathology in the absence of extracellular deposits underscores the relevance of research on tau.

Las amiloidosis cerebrales y las demencias

Amyloid deposit in the brain causes neurologicaldiseases characterized by dementia. These depositsare constituted by fibrilar proteins with beta-planarshape whose origin is due to mutations, infectionsor exogenous alterations. Treatment of cerebralamyloid angiopathy depends on the cause and atpresent, the manipulation of the synthesis of theresponsible peptides, their chemical solubilizationor extraction outside of the nervous system, arebeing investigated.

Parkin: a multifaceted ubiquitin ligase

Mutations in the parkin gene are a common cause of autosomal recessive early-onset parkinsonism. Parkin functions as an E3 ubiquitin ligase where it can polyubiquitinate a number of its protein substrates, thus targeting them for degradation by the 26 S proteasomal complex. Recent studies have demonstrated that alternative modes of parkin-mediated ubiquitination may serve other non-degradative regulatory roles. In addition, parkin appears to function as a multipurpose neuroprotectant in a number of toxic paradigms. Coupled with these observations, parkin may integrate other gene products associated with parkinsonism, including α-synuclein, LRRK2 (leucine-rich repeat kinase 2), DJ-1 and PINK1 [PTEN (phosphatase and tensin homologue deleted on chromosome 10)-induced putative kinase 1], into a common biochemical pathway of potential relevance to disease pathogenesis. Parkin therefore represents a unique multifaceted ubiquitin ligase consistent with an important housekeeping role in maintaining the integrity or survival of dopaminergic neurons.

Current strategies for the treatment of Alzheimer’s disease and other tauopathies

The pathological hallmarks of Alzheimer's disease (AD) include abnormal intra- and extraneuronal tau and amyloid accumulation, respectively, accompanied by gliosis, oxidative stress and neuron loss. The discovery of mutations within the tau gene itself that cause clinical dementia (i.e., fronto-temporal dementia with Parkinsonism linked to chromosome 17 [FTDP17]) demonstrated that disruption of normal tau function independent of amyloidogenesis was sufficient to cause neuronal loss and clinical dementia. These studies demonstrate the need for therapeutics that either decrease the total pool of tau or selectively reduce aberrant forms of tau (i.e., hyperphosphorylated, misfolded etc.). To this point, therapeutic development for tauopathies, including AD, have primarily focused on either the phosphorylation of tau, as it is a downstream target for many kinases and signalling cascades, or inhibition of tau aggregation. Recent developments, however, suggest that pharmacological targeting of other mechanisms may hold therapeutic promise for the treatment of tauopathies.