IntroductionParkinson’s disease (PD) is a progressive neurodegenerative disorder characterized by the loss of dopaminergic neurons as well as the presence of proteinaceous inclusions named Lewy bodies. α-synuclein (α-syn) is a major constituent of Lewy bodies, and the first disease-causing protein characterized in PD. Several α-syn-based animal models of PD have been developed to investigate the pathophysiology of PD, but none of them recapitulate the full picture of the disease. Ageing is the most compelling and major risk factor for developing PD but its impact on α-syn toxicity remains however unexplored. In this study, we developed and exploited a recombinant adeno-associated viral (AAV) vector of serotype 9 overexpressing mutated α-syn to elucidate the influence of ageing on the dynamics of PD-related neurodegeneration associated with α-syn pathology in different mammalian species.ResultsIdentical AAV pseudotype 2/9 vectors carrying the DNA for human mutant p.A53T α-syn were injected into the substantia nigra to induce neurodegeneration and synucleinopathy in mice, rats and monkeys. Rats were used first to validate the ability of this serotype to replicate α-syn pathology and second to investigate the relationship between the kinetics of α-syn-induced nigrostriatal degeneration and the progressive onset of motor dysfunctions, strikingly reminiscent of the impairments observed in PD patients. In mice, AAV2/9-hα-syn injection into the substantia nigra was associated with accumulation of α-syn and phosphorylated hα-syn, regardless of mouse strain. However, phenotypic mutants with either accelerated senescence or resistance to senescence did not display differential susceptibility to hα-syn overexpression. Of note, p-α-syn levels correlated with nigrostriatal degeneration in mice. In monkeys, hα-syn-induced degeneration of the nigrostriatal pathway was not affected by the age of the animals. Unlike mice, monkeys did not exhibit correlations between levels of phosphorylated α-syn and neurodegeneration.ConclusionsIn conclusion, AAV2/9-mediated hα-syn induces robust nigrostriatal neurodegeneration in mice, rats and monkeys, allowing translational comparisons among species. Ageing, however, neither exacerbated nigrostriatal neurodegeneration nor α-syn pathology per se. Our unprecedented multi-species investigation thus favours the multiple-hit hypothesis for PD wherein ageing would merely be an aggravating, additive, factor superimposed upon an independent disease process.Electronic supplementary materialThe online version of this article (doi:10.1186/s40478-015-0222-2) contains supplementary material, which is available to authorized users.

The conformational strain diversity characterizing α-synuclein (α-syn) amyloid fibrils is thought to determine the different clinical presentations of neurodegenerative diseases underpinned by a synucleinopathy. Experimentally, various α-syn fibril polymorphs have been obtained from distinct fibrillization conditions by altering the medium constituents and were selected by amyloid monitoring using the probe thioflavin T (ThT). We report that, concurrent with classical ThT-positive products, fibrillization in saline also gives rise to polymorphs invisible to ThT (τ−). The generation of τ− fibril polymorphs is stochastic and can skew the apparent fibrillization kinetics revealed by ThT. Their emergence has thus been ignored so far or mistaken for fibrillization inhibitions/failures. They present a yet undescribed atomic organization and show an exacerbated propensity toward self-replication in cortical neurons, and in living mice, their injection into the substantia nigra pars compacta triggers a synucleinopathy that spreads toward the dorsal striatum, the nucleus accumbens, and the insular cortex.

A variety of viruses establish latency by integrating their genome into the host genome. The integration event generally occurs in a nonspecific manner, precluding the prediction of functional consequences from resulting disruptions of affected host genes. The nonpathogenic adeno-associated virus (AAV) is unique in its ability to stably integrate in a site-specific manner into the human MBS85 gene. To gain a better understanding of the integration mechanism and the consequences of MBS85 disruption, we analyzed the molecular structure of AAV integrants in various latently infected human cell lines. Our study led to the observation that AAV integration causes an extensive but partial duplication of the target gene. Intriguingly, the molecular organization of the integrant leaves the possibility that a functional copy of the disrupted target gene could potentially be preserved despite the resulting rearrangements. A latently infected, Mbs85-targeted mouse ES cell line was generated to study the functional consequences of the observed duplication-based integration mechanism. AAV-modified ES cell lines continued to self-renew, maintained their multilineage differentiation potential and contributed successfully to mouse development when injected into blastocysts. Thus, our study reveals a viral strategy for targeted genome addition with the apparent absence of functional consequences.

Fibrillization of α-synuclein is instrumental for the development of Parkinson's disease (PD), thus modulating this process can have profound impact on disease initiation/progression. Here, the impact of the p.G2019S mutation of leucine-rich repeat kinase 2 (LRRK2), which is most frequently associated with familial and sporadic PD, on α-synuclein pathology was investigated. G2019S knock-in mice and wild-type controls were injected with a recombinant adeno-associated viral vector serotype 2/9 (AAV2/9) overexpressing human mutant p.A53T α-synuclein (AAV2/9-hα-syn). Control animals were injected with AAV2/9 carrying green fluorescent protein. Motor behavior, transgene expression, α-syn and pSer129 α-syn load, number of nigral dopamine neurons and density of striatal dopaminergic terminals were evaluated. To investigate the effect of aging, experiments were performed in 3- and 12-month-old mice, evaluated 20 and 12 weeks after virus injection, respectively. hα-syn overexpression induced progressive motor deficits, loss of nigral dopaminergic neurons and striatal terminals, and appearance of proteinase K-resistant aggregates of pSer129 α-syn in both young and old mice. Although no genotype difference was observed in 3-month-old mice, degeneration of nigral dopaminergic neurons was higher in 12-month-old G2019S knock-in mice compared with age-matched wild-type controls (-55% vs -39%, respectively). Consistently, a two-fold higher load of pSer129 α-syn aggregates was found in 12-month-old G2019S knock-in mice. We conclude that G2019S LRRK2 facilitates α-synucleinopathy and degeneration of nigral dopaminergic neurons, and that aging is a major determinant of this effect.

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Adeno-associated virus (AAV)-mediated gene delivery has emerged as an effective and safe tool for both preclinical and clinical studies of neurological disorders. The recent discovery that several serotypes are able to cross the blood–brain barrier when administered systemically has been a real breakthrough in the field of neurodegenerative diseases. Widespread transgene expression after systemic injection could spark interest as a therapeutic approach. Such strategy will avoid invasive brain surgery and allow non-focal gene therapy promising for CNS diseases affecting large portion of the brain. Here, we will review the recent results achieved through different systemic routes of injection generated in the last decade using systemic AAV-mediated delivery and propose a brief assessment of their values. In particular, we emphasize how the methods used for virus engineering could improve brain transduction after peripheral delivery.

The nonpathogenic human virus adeno-associated virus type 2 (AAV) has evolved the potentially unique strategy to establish latency by site-specifically integrating its genome into human chromosome 19 (19q13.3-qter) at a locus designated AAVS1. This nonhomologous, site-specific recombination of viral DNA with the human genome provides a basis for developing targeted gene therapy vectors. To assess whether the region surrounding AAVS1 might have contributed to the selection of the specific integration site, we have investigated this locus. Here, we show that AAVS1 is closely linked to the slow skeletal troponin T gene, TNNT1, which has been mapped previously to 19q13.4. In support of this idea, we demonstrate that site-specific AAV DNA integration can result in the formation of TNNT1-AAV junctions. The question now arises whether muscle represents a natural target tissue for latent AAV infection. This possibility is of additional interest in view of recent observations that muscle tissue is particularly well suited for AAV-mediated gene transfer. The question also occurs whether latent infection by AAV can lead to phenotypic changes of the multinucleated muscle fiber cells.T he human parvovirus adeno-associated virus type 2 (AAV) has adopted the strategy of alternate life styles to ensure a successful relationship with its host (1). This nonpathogenic virus productively replicates only in the presence of helper virus co-or superinfection (2). In the absence of such helper conditions, AAV has evolved a strategy potentially unique among eukaryotic viruses. On infection of the non-coinfected host cell, AAV establishes latency by integrating its genome sitespecifically into a region on the q arm of human chromosome 19 (19q13.3-qter) (3, 4), designated AAVS1.The 4.7-kb linear single-stranded genome contains two ORFs and is flanked by inverted terminal repeats (ITRs) (5). The right ORF encodes three capsid proteins, and the left ORF encodes the four nonstructural proteins (Rep proteins) that are involved in regulating all aspects of the viral life style (2).The 145-nt ITRs are the only viral sequences required in cis for DNA replication, packaging of the viral genome into the capsid, and site-specific DNA integration. Within the ITRs, a Rep binding site (RBS) allows for specific recruitment of the large Rep proteins (i.e., Rep68 and Rep78) to the origin of replication (6-8). A Rep-specific endonuclease site (terminal resolution site, TRS) is separated from the RBS by a 13-nt spacer (9-11). Together, RBS and TRS can act as a minimal origin for Rep-mediated DNA replication (12).To dissect the requirements for site specificity in targeted AAV DNA integration, an 8.2-kb fragment of AAVS1 has been isolated from embryonic lung fibroblast (WI38) DNA, and a 4-kb sequence was determined (13). It was shown by using an episomal model system that site specificity is determined by cellular sequences (14) and that a 33-nt sequence is necessary and sufficient for this targeted nonhomologous recombination event to occur (15). This 33-n...

The detection of DNA of the helper virus-dependent adeno-associated virus type 2 (AAV-2) in biopsies of material from spontaneous abortion and in tissue samples from the uterus raises the question of whether sequences of known helper viruses can be detected simultaneously within the same specimen despite the lack of histological evidence for the presence of lytic viruses. Therefore, we performed PCR analyses with primers detecting DNA sequences of viruses (adenovirus, herpes simplex virus and human cytomegalovirus) known for their helper activity in the replication of adeno-associated viruses. In addition, PCR was performed to detect DNA of human papillomaviruses (HPV), which were recently shown to be able to help AAV replication in vitro. In no cases were sequences of the known helper viruses found. However, HPV DNA was detected in $ 60 % of paraffin sections from uterus biopsies and cervical lesions containing AAV DNA and in $ 70 % of material from early miscarriage. This finding suggests that HPV may be a helper virus for AAV.Recently, DNA of the helper virus-dependent adenoassociated virus human type 2 (AAV-2) has been detected, for the first time, in genital biopsies including material from spontaneous abortion (Tobiasch et al., 1994). This observation