Objective: Our objective was to generate an in vitro model of XDP based on striatal neurons differentiated from induced pluripotent stem cells (iPSC), followed by characterization through electrophysiology and calcium imaging.

Background: X-linked dystonia-parkinsonism (XDP) is a neurodegenerative disorder, affecting mainly male patients with roots to Panay Island (Philippines). Patients show a clinical picture combining focal dystonia and parkinsonism. Genetic changes in the TAF1 gene have been associated with XDP. However, the causative mutation remains unclear. The disease is associated with a degeneration of striatal spiny projection neurons of the direct pathway (dSPN), followed by neurons of the indirect pathway (iSPN). Due to the lack of animal models, there is no knowledge about pathogenic mechanisms available.

Methods: We generated iPSC from fibroblasts of XDP patients and ethnically matched controls. Reprogramming was achieved through a sendai virus based reprogramming system. We analyzed a total number of six iPSC lines (3 patients, 3 controls). Dual SMAD-inhibition for neural induction and application of small molecules led to directed differentiation towards spiny projection neurons. After 80 to 100 days in culture about 40% of all neurons co-expressed DARPP32, associated with striatal SPN. We characterized SPN by perforated patch clamp recordings and calcium imaging after loading cells with FURA-2. We put a special emphasis on glutamatergic and GABAergic response.

Results: We observed no differences in basic electrophysiological properties of XDP and control neurons. Neurons received a pronounced GABAergic input. Glutamatergic input mediated by AMPA receptors was much lower, input by NMDA receptors virtually absent. Application of the AMPA-antagonist NBQX lead to a more pronounced reduction of miniature postsynaptic currents (mPSC) in XDP neurons. Conversely, application of AMPA led to a lower calcium response amplitude in XDP neurons. Calcium levels were lower in neurons derived from XDP patients, but cells with spontaneous calcium release were more frequent.

Conclusions: In conclusion, our data demonstrates a reduced input mediated by AMPA-receptors and altered calcium dynamics in SPN derived from XDP-patients, while basic properties did not differ to controls. However, the notably low input through NMDA receptors will require refinement of the culture system in future studies.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/altered-glutamate-response-and-calcium-dynamics-in-ipsc-derived-striatal-neurons-from-xdp-patients/