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

Abstract

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.

Keywords: AMPA receptor; Calcium dynamics; Electrophysiology; Spiny projection neurons; XDP; iPSC.