Transplantation of Mouse Embryonic Stem Cell-Derived Dopaminergic Neurons in a Unilateral 6-Hydroxydopamine Lesion Rat Model of Parkinson’s Disease

Abstract

Embryonic stem (ES) cells are a promising option for cell replacement therapy in Parkinson's disease. Undifferentiated mouse ES cells differentiate into functional dopaminergic neurons after grafting in hemiparkinsonian rats but induce the formation of tumours. The aim of this thesis was to study the anatomical and functional integration of pre-differentiated mouse embryonic stem cells transplanted in adult rats with 6-hydroxydopamine-induced hemiparkinsonism. Mouse ES cells were differentiated on a PA6-feeder for 14 days, labelled with PKH26 and implanted intrastriatally in hemiparkinsonian adult rats with or without adjunctive cyclosporine A immunosuppression. PKH26 fluorescence was detected in all graft recipients up to five weeks post-grafting. Graft-derived dopaminergic neurons survived transplantation and alleviated amphetamine-induced rotation (in non-immunosuppressed animals). Cyclosporine-A immunosuppression enhanced the survival of the grafted dopaminergic neurons but was associated with several adverse side effects including impaired motor function, an increased risk of tumour formation and increased morbidity. Cytomorphological analyses revealed that a significant proportion of the surviving dopaminergic neurons lost neurites between one and five weeks post-grafting. There was no indication of a direct relationship between transplant vascularisation and the viability of graft-derived dopaminergic neurons. The number of striatal D1 receptor binding sites was not altered by denervation and/or the grafting of dopamine-producing cells. In contrast, denervation induced a loss of dopamine transporter binding in the ipsilateral striatum. This loss was not reversed by pre-differentiated mouse embryonic stem cell grafts at five weeks post grafting. In conclusion, these results demonstrate the potential of pre-differentiated embryonic stem cells for generating functional dopaminergic neurons for transplantation in Parkinson's disease. In order to optimise this therapeutic approach, novel strategies should be developed to direct efficient differentiation of embryonic stem cells and to promote the survival and integration of ES cell-derived dopaminergic neurons after transplantation in host brains.