Patrik Brundin

Neuronal Properties, In Vivo Effects, and Pathology of a Huntington's Disease Patient‐Derived Induced Pluripotent Stem Cells

Induced pluripotent stem cells (iPSCs) generated from somatic cells of patients can be used to model different human diseases. They may also serve as sources of transplantable cells that can be used in novel cell therapies. Here, we analyzed neuronal properties of an iPSC line derived from a patient with a juvenile form of Huntingtons disease (HD) carrying 72 CAG repeats (HD‐iPSC). Although its initial neural inducing activity was lower than that of human embryonic stem cells, we found that HD‐iPSC can give rise to GABAergic striatal neurons, the neuronal cell type that is most susceptible to degeneration in HD. We then transplanted HD‐iPSC‐derived neural precursors into a rat model of HD with a unilateral excitotoxic striatal lesion and observed a significant behavioral recovery in the grafted rats. Interestingly, during our in vitro culture and when the grafts were examined at 12 weeks after transplantation, no aggregate formation was detected. However, when the culture was treated with a proteasome inhibitor (MG132) or when the cells engrafted into neonatal brains were analyzed at 33 weeks, there were clear signs of HD pathology. Taken together, these results indicate that, although HD‐iPSC carrying 72 CAG repeats can form GABAergic neurons and give rise to functional effects in vivo, without showing an overt HD phenotype, it is highly susceptible to proteasome inhibition and develops HD pathology at later stages of transplantation. These unique features of HD‐iPSC will serve as useful tools to study HD pathology and develop novel therapeutics. Stem Cells2012;30:2054–2062

Widespread transneuronal propagation of α-synucleinopathy triggered in olfactory bulb mimics prodromal Parkinson’s disease

Rey et al. generate a mouse model for the spatial propagation of α-synuclein pathology that mimics prodromal Parkinsons disease.

Extensive graft-derived dopaminergic innervation is maintained 24 years after transplantation in the degenerating parkinsonian brain

Significance Parkinson’s disease is the most common movement disorder. Here we describe the histopathological analysis of a unique patient with Parkinson’s disease who underwent unilateral cell transplantation in the putamen with human embryonic mesencephalic tissue at 24 y before death. The patient enjoyed major clinical benefits for at least a decade after transplantation. After a quarter of a century, complete graft-derived dopaminergic reinnervation was still evident in the transplanted putamen. α-Synuclein–positive inclusions, some with the appearance of typical Lewy bodies, were present in 11–12% of the grafted dopaminergic neurons, reflecting spread of pathology from the host brain to the transplant. The clinical improvements were gradually lost from 14 y posttransplantation, indicating that even extensive graft-derived dopaminergic reinnervation loses its efficacy in a severely degenerating brain. Clinical trials using cells derived from embryonic ventral mesencephalon have shown that transplanted dopaminergic neurons can survive and function in the long term, as demonstrated by in vivo brain imaging using 18F-fluorodopa and 11C-raclopride positron emission tomography. Here we report the postmortem analysis of a patient with Parkinson’s disease who 24 y earlier underwent unilateral transplantation of embryonic dopaminergic neurons in the putamen and subsequently exhibited major motor improvement and recovery of striatal dopaminergic function. Histopathological analysis showed that a dense, near-normal graft-derived dopaminergic reinnervation of the putamen can be maintained for a quarter of a century despite severe host brain pathology and with no evidence of immune response. In addition, ubiquitin- and α-synuclein–positive inclusions were seen, some with the appearance of typical Lewy bodies, in 11–12% of the grafted dopaminergic neurons, reflecting the spread of pathology from the host brain to the transplants. Because the clinical benefits induced by transplantation in this patient were gradually lost after 14 y posttransplantation, our findings provide the first reported evidence, to our knowledge, that even a viable dopaminergic graft giving rise to extensive striatal reinnervation may lose its efficacy if widespread degenerative changes develop in the host brain.

Review: The future of cell therapies and brain repair: Parkinson's disease leads the way

During the past 40 years brain tissue grafting techniques have been used both to study fundamental neurobiological questions and to treat neurological diseases. Motor symptoms of Parkinsons disease are largely due to degeneration of midbrain dopamine neurones. Because the nigrostriatal pathology is relatively focused anatomically, Parkinsons disease is considered the ideal candidate for brain repair by neural grafting and dopamine neurone transplantation for it has led the way in the neural transplantation research field. In this mini‐review, we briefly highlight four important areas of development. First, we describe marked functional benefits up to 18 years after transplantation surgery in patients with Parkinsons disease. This is proof‐of‐principle that, using optimal techniques and patient selection, grafted dopamine neurones can work in humans and the duration of the benefit exceeds placebo effects associated with surgery. Second, we describe that eventually protein aggregates containing α‐synuclein, identical to Lewy bodies, develop inside foetal dopamine neurones transplanted to patients with Parkinsons disease. This gives clues about pathogenetic mechanisms operating in Parkinsons disease, and also raises the question whether neural graft function will eventually decline as the result of the disease process. Third, we describe new emerging sources of transplantable dopamine neurones derived from pluripotent stem cells or reprogrammed adult somatic cells. Fourth, we highlight an important European Union‐funded multicentre clinical trial involving transplantation of foetal dopamine neurones in Parkinsons disease. We describe the design of this ongoing trial and how it can impact on the overall future of cell therapy in Parkinsons disease.

Gut feelings about smoking and coffee in Parkinson's disease

Strong epidemiologic evidence suggests that smokers and coffee drinkers have a lower risk of Parkinsons disease (PD). The explanation for this finding is still unknown, and the discussion has focused on two main hypotheses. The first suggests that PD patients have premorbid personality traits associated with dislike for coffee‐drinking and smoking. The second posits that caffeine and nicotine are neuroprotective. We propose an alternative third hypothesis, in which both cigarette and coffee consumption change the composition of the microbiota in the gut in a way that mitigates intestinal inflammation. This, in turn, would lead to less misfolding of the protein alpha‐synuclein in enteric nerves, reducing the risk of PD by minimizing propagation of the protein aggregates to the central nervous system, where they otherwise can induce neurodegeneration.

Alpha-synuclein propagation: New insights from animal models.

Aggregation of alpha‐synuclein is implicated in several neurodegenerative diseases collectively termed synucleinopathies. Emerging evidence strongly implicates cell‐to‐cell transmission of misfolded alpha‐synuclein as a common pathogenetic mechanism in synucleinopathies. The impact of alpha‐synuclein pathology on neuronal dysfunction and behavioral impairments is being explored in animal models. This review provides an update on how research in animal models supports the concept that misfolded alpha‐synuclein spreads from cell to cell and describes how findings in animal models might relate to the disease process in humans. Finally, we discuss the current underlying molecular and cellular mechanisms and future therapeutic strategies targeting alpha‐synuclein propagation.

What’s to like about the prion-like hypothesis for the spreading of aggregated α-synuclein in Parkinson disease?

α-Synuclein is a key protein in Parkinson disease. Not only is it the major protein component of Lewy bodies, but it is implicated in several cellular processes that are disrupted in Parkinson disease. Misfolded α-synuclein has also been shown to spread from cell-to-cell and, in a prion-like fashion, trigger aggregation of α-synuclein in the recipient cell. In this mini-review we explore the evidence that misfolded α-synuclein underlies the spread of pathology in Parkinson disease and discuss why it should be considered a prion-like protein.

A cell culture model for monitoring α-synuclein cell-to-cell transfer

The transfer of α-synuclein (α-syn) between cells has been proposed to be the primary mechanism of disease spreading in Parkinsons disease. Several cellular models exist that monitor the uptake of recombinant α-syn from the culture medium. Here we established a more physiologically relevant model system in which α-syn is produced and transferred between mammalian neurons. We generated cell lines expressing either α-syn tagged with fluorescent proteins or fluorescent tags alone then we co-cultured these cell lines to measure protein uptake. We used live-cell imaging to demonstrate intercellular α-syn transfer and used flow cytometry and high content analysis to quantify the transfer. We then successfully inhibited intercellular protein transfer genetically by down-regulating dynamin or pharmacologically using dynasore or heparin. In addition, we differentiated human induced pluripotent stem cells carrying a triplication of the α-syn gene into dopaminergic neurons. These cells secreted high levels of α-syn, which was taken up by neighboring neurons. Collectively, our co-culture systems provide simple but physiologically relevant tools for the identification of genetic modifiers or small molecules that inhibit α-syn cell-to-cell transfer.

Review: Spreading the word: precise animal models and validated methods are vital when evaluating prion-like behaviour of alpha-synuclein.

Synucleinopathies are characterized by abnormal proteinaceous aggregates, mainly composed of fibrillar α‐synuclein (α‐syn). It is now believed that α‐syn can form small aggregates in a restricted number of cells, that propagate to neighbouring cells and seed aggregation of endogenous α‐syn, in a ‘prion‐like manner’. This process could underlie the stereotypical progression of Lewy bodies described by Braak and colleagues across different stages of Parkinsons disease (PD). This prion‐like behaviour of α‐syn has been recently investigated in animal models of PD or multiple system atrophy (MSA). These models investigate the cell‐to‐cell transfer of α‐syn seeds, or the induction and spreading of α‐syn pathology in transgenic or wild‐type rodent brain. In this review, we first outline the involvement of α‐syn in Lewy body diseases and MSA, and discuss how ‘prion‐like’ mechanisms can contribute to disease. Thereon, we debate the relevance of animal models used to study prion‐like propagation. Finally, we review current main histological methods used to assess α‐syn pathology both in animal models and in human samples and their relevance to the disease. Specifically, we discuss using α‐syn phosphorylated at serine 129 as a marker of pathology, and the novel methods available that allow for more sensitive detection of early pathology, which has relevance for modelling synucleinopathies.

Prying into the Prion Hypothesis for Parkinson's Disease.

In Parkinsons disease, intracellular α-synuclein inclusions form in neurons. We suggest that prion-like behavior of α-synuclein is a key component in Parkinsons disease pathogenesis. Although multiple molecular changes are involved in the triggering of the disease process, we propose that neuron-to-neuron transfer is a crucial event that is essential for Lewy pathology to spread from one brain region to another. In this review, we describe key findings in human postmortem brains, cultured cells, and animal models of disease that support the idea that α-synuclein can act as a prion. We consider potential triggers of the α-synuclein misfolding and why the aggregates escape cellular degradation under disease conditions. We also discuss whether different strains of α-synuclein fibrils can underlie differences in cellular and regional distribution of aggregates in different synucleinopathies. Our conclusion is that α-synuclein probably acts as a prion in human diseases, and a deeper understanding of this step in the pathogenesis of Parkinsons disease can facilitate the development of disease-modifying therapies in the future. Dual Perspectives Companion Paper: Parkinsons Disease Is Not Simply a Prion Disorder, by D. James Surmeier, José A. Obeso, and Glenda M. Halliday