Jia-Yi Li

Lewy bodies in grafted neurons in subjects with Parkinson's disease suggest host-to-graft disease propagation.

Two subjects with Parkinsons disease who had long-term survival of transplanted fetal mesencephalic dopaminergic neurons (11–16 years) developed α-synuclein–positive Lewy bodies in grafted neurons. Our observation has key implications for understanding Parkinsons pathogenesis by providing the first evidence, to our knowledge, that the disease can propagate from host to graft cells. However, available data suggest that the majority of grafted cells are functionally unimpaired after a decade, and recipients can still experience long-term symptomatic relief.

α-Synuclein propagates from mouse brain to grafted dopaminergic neurons and seeds aggregation in cultured human cells

Post-mortem analyses of brains from patients with Parkinson disease who received fetal mesencephalic transplants show that α-synuclein-containing (α-syn-containing) Lewy bodies gradually appear in grafted neurons. Here, we explored whether intercellular transfer of α-syn from host to graft, followed by seeding of α-syn aggregation in recipient neurons, can contribute to this phenomenon. We assessed α-syn cell-to-cell transfer using microscopy, flow cytometry, and high-content screening in several coculture model systems. Coculturing cells engineered to express either GFP- or DsRed-tagged α-syn resulted in a gradual increase in double-labeled cells. Importantly, α-syn-GFP derived from 1 neuroblastoma cell line localized to red fluorescent aggregates in other cells expressing DsRed-α-syn, suggesting a seeding effect of transmitted α-syn. Extracellular α-syn was taken up by cells through endocytosis and interacted with intracellular α-syn. Next, following intracortical injection of recombinant α-syn in rats, we found neuronal uptake was attenuated by coinjection of an endocytosis inhibitor. Finally, we demonstrated in vivo transfer of α-syn between host cells and grafted dopaminergic neurons in mice overexpressing human α-syn. In summary, intercellularly transferred α-syn interacts with cytoplasmic α-syn and can propagate α-syn pathology. These results suggest that α-syn propagation is a key element in the progression of Parkinson disease pathology.

Transplantation of Human Embryonic Stem Cell‐Derived Cells to a Rat Model of Parkinson's Disease: Effect of In Vitro Differentiation on Graft Survival and Teratoma Formation

Human embryonic stem cells (hESCs) have been proposed as a source of dopamine (DA) neurons for transplantation in Parkinsons disease (PD). We have investigated the effect of in vitro predifferentiation on in vivo survival and differentiation of hESCs implanted into the 6‐OHDA (6‐hydroxydopamine)‐lesion rat model of PD. The hESCs were cocultured with PA6 cells for 16, 20, or 23 days, leading to the in vitro differentiation into DA neurons. Grafted hESC‐derived cells survived well and expressed neuronal markers. However, very few exhibited a DA neuron phenotype. Reversal of lesion‐induced motor deficits was not observed. Rats grafted with hESCs predifferentiated in vitro for 16 days developed severe teratomas, whereas most rats grafted with hESCs predifferentiated for 20 and 23 days remained healthy until the end of the experiment. This indicates that prolonged in vitro differentiation of hESCs is essential for preventing formation of teratomas.

Research in motion: the enigma of Parkinson's disease pathology spread

Neuropathological changes in Parkinsons disease progress slowly and spread according to a characteristic pattern. Recent papers have shed light on this progression of pathology by examining the fate of neurons grafted into the brains of patients with Parkinsons disease. Two of these studies demonstrate that grafted healthy neurons can gradually develop the same pathology as host neurons in the diseased brains. According to these studies, implanted neurons developed α-synuclein- and ubiquitin-positive Lewy bodies more than a decade after transplantation. We discuss the possible underlying mechanisms and their implications for how pathology spreads in Parkinsons disease.

Are synucleinopathies prion-like disorders?

A shared neuropathological feature of idiopathic Parkinsons disease, dementia with Lewy bodies, and multiple system atrophy is the development of intracellular aggregates of α-synuclein that gradually engage increasing parts of the nervous system. The pathogenetic mechanisms underlying these neurodegenerative disorders, however, are unknown. Several studies have highlighted similarities between classic prion diseases and these neurological proteinopathies. Specifically, identification of Lewy bodies in fetal mesencephalic neurons transplanted in patients with Parkinsons disease raised the hypothesis that α-synuclein, the main component of Lewy bodies, could be transmitted from the host brain to a graft of healthy neurons. These results and others have led to the hypothesis that a prion-like mechanism might underlie progression of synucleinopathy within the nervous system. We review experimental findings showing that misfolded α-synuclein can transfer between cells and, once transferred into a new cell, can act as a seed that recruits endogenous α-synuclein, leading to formation of larger aggregates. This model suggests that strategies aimed at prevention of cell-to-cell transfer of α-synuclein could retard progression of symptoms in Parkinsons disease and other synucleinopathies.

Characterization of Lewy body pathology in 12- and 16-year-old intrastriatal mesencephalic grafts surviving in a patient with Parkinson's disease.

We previously reported the occurrence of Lewy bodies in grafted human fetal mesencephalic neurons in two patients with Parkinsons disease. Here, we have used immunohistochemistry and electron microscopy to characterize the development of Lewy bodies in one of these cases. This patient was operated in putamen on both sides at 12 or 16 years before death, respectively. We demonstrate that 2% of the 12‐year‐old and 5% of the 16‐year‐old grafted, presumed dopaminergic neurons contained Lewy bodies immunoreactive for α‐synuclein. Based on morphological analysis, two forms of α‐synuclein‐positive aggregates were distinguished in the grafts, the first a classical and compact Lewy body, the other a loose meshwork aggregate. Lewy bodies in the grafts stained positively for ubiquitin and thioflavin‐S, and contained characteristic α‐synuclein immunoreactive electron dense fibrillar structures on electron microscopy. Our data indicate that Lewy bodies develop gradually in transplanted dopaminergic neurons in a fashion similar to that in dopaminergic neurons in the host substantia nigra.

Critical issues of clinical human embryonic stem cell therapy for brain repair.

Embryonic stem cells (ESCs) provide hope as a potential regenerative therapy for neurological conditions such as Parkinsons disease and spinal cord injury. Currently, ESC-based nervous system repair faces several problems. One major hurdle is related to problems in generating large and defined populations of the desired types of neurons from human ESCs (hESCs). Moreover, survival of grafted hESC-derived cells has varied and functional recovery in recipient animals has often been disappointing. Importantly, in clinical trials, adverse effects after surgery, including tumors or vigorous immune reactions, must be avoided. Here we highlight attempts to overcome these hurdles with hESCs intended for central nervous system repair. We focus on hESC-derived dopamine-producing neurons that can be grafted in Parkinsons disease and identify critical experiments that need to be conducted before clinical trials can occur.

Reduced hippocampal neurogenesis in R6/2 transgenic Huntington's disease mice

We investigated whether cell proliferation and neurogenesis are altered in R6/2 transgenic Huntingtons disease mice. Using bromodeoxyuridine (BrdU), we found a progressive decrease in the number of proliferating cells in the dentate gyrus of R6/2 mice. This reduction was detected in pre-symptomatic mice, and by 11.5 weeks, R6/2 mice had 66% fewer newly born cells in the hippocampus. The results were confirmed by immunohistochemistry for the cell cycle markers Ki-67 and proliferating cell nuclear antigen (PCNA). We did not observe changes in cell proliferation in the R6/2 subventricular zone, indicating that the decrease in cell proliferation is specific for the hippocampus. This decrease corresponded to a reduction in actual hippocampal neurogenesis as assessed by double immunostaining for BrdU and the neuronal marker neuronal nuclei (NeuN) and by immunohistochemistry for the neuroblast marker doublecortin. Reduced hippocampal neurogenesis may be a novel neuropathological feature in R6/2 mice that could be assessed when evaluating potential therapies.

Synaptic dysfunction in Huntington's disease: a new perspective.

Abstract.Huntington’s disease (HD) is caused by a polyglutamine expansion in the protein huntingtin and is characterized by intraneuronal inclusions and widespread neuronal death at the late stage of the disease. In research, most of the emphasis has been on understanding the cell death and its mechanisms. Until recently, it was believed that the vast majority, if not all, of the symptoms in HD are a direct consequence of neurodegeneration. However, increasing evidence shows that subtle alterations in synaptic function could underlie the early symptoms. It is of particular interest to understand the nature of this neuronal dysfunction. Normal huntingtin interacts with various cytoskeletal and synaptic vesicle proteins that are essential for exocytosis and endocytosis. Altered interactions of mutant huntingtin with its associated partners could contribute to abnormal synaptic transmission in HD. This review describes recent advances in understanding synaptic dysfunction in HD.

Differential localization of α-, β- and γ-synucleins in the rat CNS

Abstract α-Synuclein is a presynaptic protein that normally participates in the homeostasis of synaptic vesicles. Missense mutations in its gene cause the protein to participate actively in the development of heritable forms of Parkinson’s disease. Moreover, its metabolism is perturbed in all cases of Parkinson’s disease where α-synuclein accumulates in a filamentous form in the Lewy body nerve cell lesion. Lewy bodies also develop in other common neurodegenerative disorders, like dementia with Lewy bodies and Lewy body variant of Alzheimer’s disease. In the present study, we have studied the detailed distribution of α-, β- and γ-synuclein in the rat CNS. α-Synuclein was not observed in perikarya, but was distributed with high intensity in nerve terminals in the caudate and putamen and ventral pallidum, where β-synuclein was much weaker and less densely distributed in the caudate and putamen. γ-Synuclein was not found in the caudate and putamen. α-Synuclein was robustly distributed in the substantia nigra pars reticulata, but was very weak or virtually absent from the perikarya of the neurons in the pars compacta. In contrast, β-synuclein was very weak or absent from the substantia nigra. γ-Synuclein was absent from the terminals of substantia nigra pars reticulata, but sparsely distributed γ-synuclein-containing neurons were detected in the substantia nigra pars compacta. In the brainstem, α-synuclein as well as γ-synuclein were present in the locus coeruleus with high intensity, while β-synuclein was very weak. In addition, α-synuclein was intense in the vagus nucleus, but weak in the oculomotor, facial, hypoglossal, accessory and ambiguous nuclei, where β-synuclein was very intensely present. Furthermore, γ-synuclein was localized in the terminals and in cell bodies of the Edinger–Westphal nucleus, the red nucleus, locus coeruleus, and most cranial nerve-related nuclei. In the spinal cord, α- and γ-synucleins were intensely present in laminae I and II and in the preganglionic sympathetic nuclei, whereas β-synuclein was very weak. These results indicate that α-synuclein is abundant in central catecholaminergic regions. β-Synuclein is more localized in the somatic cholinergic components, while it is particularly weak or absent from catecholaminergic neurons. γ-Synuclein appears to be present in both cholinergic and catecholaminergic regions, but very weak in the forebrain.