Publications

The identity and functional potential of dopamine neurons derived in vitro from embryonic stem cells are critical for the development of a stem cell-based replacement therapy for Parkinson's disease. Using a parthenogenetic primate embryonic stem cell line, we have generated dopamine neurons that display persistent expression of midbrain regional and cell-specific transcription factors, which establish their proper identity and allow for their survival. We show here that transplantation of parthenogenetic dopamine neurons restores motor function in hemi-parkinsonian, 6-hydroxy-dopamine-lesioned rats. Exposure to Wnt5a and fibroblast growth factors (FGF) 20 and 2 at the final stage of in vitro differentiation enhanced the survival of dopamine neurons and, correspondingly, the extent of motor recovery of transplanted animals. Importantly for future development of clinical applications, dopamine neurons were post-mitotic at the time of transplantation and there was no tumour formation. These data provide proof for the concept that parthenogenetic stem cells are a suitable source of functional neurons for therapeutic applications.

BACKGROUND: The etiology of Parkinson's disease (PD) remains elusive despite identification of several genetic mutations. It is more likely that multiple factors converge to give rise to PD than any single cause. Here we report that inflammation can trigger degeneration of dopamine (DA) neurons in an animal model of Parkinson's disease.

METHODS: We examined the effects of inflammation on the progressive 6-OHDA rat model of Parkinson's disease using immunohistochemistry, multiplex ELISA, and cell counting stereology.

RESULTS: We show that a non-toxic dose of lipopolysaccharide (LPS) induced secretion of cytokines and predisposed DA neurons to be more vulnerable to a subsequent low dose of 6-hydroxydopamine. Alterations in cytokines, prominently an increase in interleukin-1beta (IL-1beta), were identified as being potential mediators of this effect that was associated with activation of microglia. Administration of an interleukin-1 receptor antagonist resulted in significant reductions in tumor necrosis factor-alpha and interferon-gamma and attenuated the augmented loss of DA neurons caused by the LPS-induced sensitization to dopaminergic degeneration.

CONCLUSION: These data provide insight into the etiology of PD and support a role for inflammation as a risk factor for the development of neurodegenerative disease.

Infusion of transforming growth factor alpha (TGFalpha) into the adult dopamine (DA)-depleted striatum generates a local population of nestin(+)/proliferating cell nuclear antigen (PCNA)(+) newborn cells. The precise origin and fate of these new striatal cells are unknown, making it difficult to direct them for neural repair in Parkinson's disease. Experiments in rats using 5-bromo-2'-deoxyuridine (BrdU) to label neural progenitor cells showed that during TGFalpha infusion in the DA-depleted striatum, newborn striatal cells formed a homogeneous population of precursors, with the majority coexpressing nestin, Mash1, Olig2, and epidermal growth factor receptor, consistent with the phenotype of multipotent C cells. Upon TGFalpha pump withdrawal, the subventricular zone (SVZ) was repopulated by neuroblasts. Strikingly, during this period, numerous clusters of doublecortin(+)/polysialylated neuronal cell adhesion molecule(+) neuroblasts were also produced in the ipsilateral medial striatum. In parallel, striatal BrdU(+)/glial fibrillary acidic protein(+) astrocytes were generated, but no BrdU(+)/O4(+)/CNPase(+) oligodendrocytes were generated. Infusion of the neuralizing bone morphogenetic protein antagonist noggin after TGFalpha pump withdrawal increased the neuroblast-to-astrocyte ratio among new striatal cells by blocking glial differentiation but did not alter striatal neurogenesis. At no time or treatment condition were differentiated neurons generated, including DA neurons. Using 6-hydroxydopamine-lesioned nestin-CreER(T2)/R26R-YFP mice that allow genetic fate-mapping of SVZ nestin(+) cells, we show that TGFalpha-generated striatal cells originate from SVZ nestin(+) precursors that confirmed data from the rats on the phenotype and fate of striatal nestin(+)/PCNA(+) cells upon TGFalpha withdrawal. This work demonstrates that a large population of multipotent striatal C-like cells can be generated in the DA-depleted striatum that do not spontaneously differentiate into DA neurons.

OFF-L-dopa dyskinesias have been a surprising side-effect of intrastriatal foetal ventral mesencephalic transplantation in patients with Parkinson's disease. It has been proposed that excessive and unregulated dopaminergic stimulation of host post-synaptic striatal neurons by the grafts could be responsible for these dyskinesias. To address this issue we transplanted foetal dopaminergic neurons from mice lacking the dopamine transporter (DATKO) or from wild-type mice, into a rat model of Parkinson's disease and L-dopa-induced dyskinesias. Both wild-type and DATKO grafts reinnervated the host striatum to a similar extent, but DATKO grafts produced a greater and more diffuse increase in extra-cellular striatal dopamine levels. Interestingly, grafts containing wild-type dopaminergic neurons improved parkinsonian signs to a similar extent as DATKO grafts, but provided a more complete reduction of L-dopa induced dyskinesias. Neither DATKO nor wild-type grafts induced OFF-L-dopa dyskinesias. Behavioural and receptor autoradiography analyses demonstrated that DATKO grafts induced a greater normalization of striatal dopaminergic receptor supersensitivity than wild-type grafts. Both graft types induced a similar downregulation and normalization of PEnk and fosb/Deltafosb in striatal neurons. In summary, DATKO grafts causing high and diffuse extra-cellular dompamine levels do not per se alter graft-induced recovery or produce OFF-L-dopa dyskinesias. Wild-type dopaminergic neurons appear to be the most effective neuronal type to restore function and reduce L-dopa-induced dyskinesias.

BACKGROUND: Understanding the mechanisms of amyloid-beta protein (Abeta) production and clearance in the brain has been essential to elucidating the etiology of Alzheimer disease (AD). Chronically decreasing brain Abeta levels is an emerging therapeutic approach for AD, but no such disease-modifying agents have achieved clinical validation. Certain proteases are responsible for the catabolism of brain Abeta in vivo, and some experimental evidence suggests they could be used as therapeutic tools to reduce Abeta levels in AD. The objective of this study was to determine if enhancing the clearance of Abeta in the brain by ex vivo gene delivery of an Abeta-degrading protease can reduce amyloid plaque burden.

METHODS AND FINDINGS: We generated a secreted form of the Abeta-degrading protease neprilysin, which significantly lowers the levels of naturally secreted Abeta in cell culture. We then used an ex vivo gene delivery approach utilizing primary fibroblasts to introduce this soluble protease into the brains of beta-amyloid precursor protein (APP) transgenic mice with advanced plaque deposition. Brain examination after cell implantation revealed robust clearance of plaques at the site of engraftment (72% reduction, p = 0.0269), as well as significant reductions in plaque burden in both the medial and lateral hippocampus distal to the implantation site (34% reduction, p = 0.0020; and 55% reduction, p = 0.0081, respectively).

CONCLUSIONS: Ex vivo gene delivery of an Abeta-degrading protease reduces amyloid plaque burden in transgenic mice expressing human APP. These results support the use of Abeta-degrading proteases as a means to therapeutically lower Abeta levels and encourage further exploration of ex vivo gene delivery for the treatment of Alzheimer disease.