Altered glutamate response and calcium dynamics in iPSC-derived striatal neurons from XDP patients.

X-linked dystonia-parkinsonism (XDP) is a neurodegenerative disorder endemic to Panay Island (Philippines). Patients present with generalizing dystonia and parkinsonism. Genetic changes surrounding the TAF1 (TATA-box binding protein associated factor 1) gene have been associated with XDP inducing a degeneration of striatal spiny projection neurons. There is little knowledge about the pathophysiology of this disorder. Our objective was to generate and analyze an in-vitro model of XDP based on striatal neurons differentiated from induced pluripotent stem cells (iPSC). We generated iPSC from patient and healthy control fibroblasts (3 affected, 3 controls), followed by directed differentiation of the cultures towards striatal neurons. Cells underwent characterization of immunophenotype as well as neuronal function, glutamate receptor properties and calcium dynamics by whole-cell patch-clamp recordings and calcium imaging. Furthermore, we evaluated expression levels of AMPA receptor subunits and voltage-gated calcium channels by quantitative real-time PCR. We observed no differences in basic electrophysiological properties. Application of the AMPA antagonist NBQX led to a more pronounced reduction of postsynaptic currents in XDP neurons. There was a higher expression of AMPA receptor subunits in patient-derived neurons. Basal calcium levels were lower in neurons derived from XDP patients and cells with spontaneous calcium transients were more frequent. Our data suggest altered glutamate response and calcium dynamics in striatal XDP neurons.

Biochemical mechanisms of pallidal deep brain stimulation in X-linked dystonia parkinsonism.

OBJECTIVE: Invasive techniques such as in-vivo microdialysis provide the opportunity to directly assess neurotransmitter levels in subcortical brain areas. METHODS: Five male Filipino patients (mean age 42.4, range 34-52 years) with severe X-linked dystonia-parkinsonism underwent bilateral implantation of deep brain leads into the internal part of the globus pallidus (GPi). Intraoperative microdialysis and measurement of gamma aminobutyric acid and glutamate was performed in the GPi in three patients and globus pallidus externus (GPe) in two patients at baseline for 25/30 min and during 25/30 min of high-frequency GPi stimulation. RESULTS: While the gamma-aminobutyric acid concentration increased in the GPi during high frequency stimulation (231 ± 102% in comparison to baseline values), a decrease was observed in the GPe (22 ± 10%). Extracellular glutamate levels largely remained unchanged. CONCLUSIONS: Pallidal microdialysis is a promising intraoperative monitoring tool to better understand pathophysiological implications in movement disorders and therapeutic mechanisms of high frequency stimulation. The increased inhibitory tone of GPi neurons and the subsequent thalamic inhibition could be one of the key mechanisms of GPi deep brain stimulation in dystonia. Such a mechanism may explain how competing (dystonic) movements can be suppressed in GPi/thalamic circuits in favour of desired motor programs.

Histological findings on fetal striatal grafts in a Huntington's disease patient early after transplantation.

Cell transplantation is a promising therapeutic approach that has the potential to replace damaged host striatal neurons and, thereby, slow down or even reverse clinical signs and symptoms during the otherwise fatal course of Huntington's disease (HD). Open-labeled clinical trials with fetal neural transplantation for HD have demonstrated long-term clinical benefits for HD patients. Here we report a postmortem analysis of an individual with HD 6 months after cell transplantation and demonstrate that cells derived from grafted fetal striatal tissue had developed into graft-derived neurons expressing dopamine-receptor related phosphoprotein (32 kDa) (DARPP-32), neuronal nuclear antigen (NeuN), calretinin and somatostatin. However, a fully mature phenotype, considered by the expression of developmental markers, is not reached by engrafted neurons and not all types of interneurons are being replaced at 6 months, which is the earliest time point human fetal tissue being implanted in a human brain became available for histological analysis. Host-derived tyrosine hydroxylase (TH) fibers had already heavily innervated the transplants and formed synaptic contacts with graft-derived DARPP-32 positive striatal neurons. In parallel, the transplants contained a considerable number of immature neuroepithelial cells (doublecortin+, Sox2+, Prox-1+, ss3-tubulin+) that exhibited a pronounced migration into the surrounding host striatal tissue and considerable mitotic activity. Graft-derived astrocytes could also be found. Interestingly, the immunological host response in the grafted area showed localized increase of immunocompetent host cells within perivascular spaces without deleterious effects on engrafted cells under continuous triple immunosuppressive medication. Thus this study provides for a better understanding of the developmental processes of grafted human fetal striatal neurons in HD and, in addition, has implications for stem cell-based transplantation approaches in the CNS.