Functional integration of grafted hiPSC derived dopamine neurons in a mouse model of Parkinson's disease
Résumé
Parkinson's disease (PD) is a complex neurological disorder associated with progressive degeneration of dopamine (DA) neurons in the substantia nigra pars compacta (SNpc) inducing major imbalances in basal ganglia loop and subsequent motor dysfunctions. Multiple therapeutic strategies have been well-established and among the most promising ones, cell therapy is emerging as a major research axis to replace lost neurons by new functional DA neurons. In this perspective, we aim to address functional nigral integration of DA neurons derived from human induced-pluripotent stem cells (DAhiPSCs) in 6-OHDA RAG2-KO mouse model of PD. After nigral dopaminergic lesion by intracerebral 6-OHDA injection, mice were grafted with DA-hiPSCs in the SNpc. From the 8 to 12 months post-transplantation, we investigated electrophysiological functionality of grafted-DA neurons using unit extracellular recordings in vivo in anesthetized mouse to compare their electrophysiological parameters to those of nigral DA neurons from control mice. We demonstrated similar main electrophysiological criteria in grafted-DA and nigral DA neurons including slow rate firing (1-12Hz), large biphasic spike waveform (>2ms duration) and 3 distinct firing patterns (irregular, regular or pacemaker-like, and bursting). Our data are consistent with those previously described in literature in SNpc and ventral tegmental area in vivo . Therefore, grafted hiPSCs-derived DA precursors became mature and exhibited functional characteristics of nigral DA neurons in addition to display all DA markers as we previously shown (Brot et al., 2022). Indeed, grafted-DA neurons shared same mechanical characteristics with native nigral DA neurons, specifically an intrinsic membrane potential oscillation leading to the regular pattern. Finally, we indirectly shown grafted-DA neurons received functional modulatory afferences since they displayed two other firing patterns (bursting and irregular) than the regular one. Actually, glutamatergic and cholinergic inputs from pedunculopontine tegmental and subthalamic nuclei drive burst firing whereas strong GABAergic inputs from striatonigral pathway modulate irregular pattern. These data highlight the functional integration of grafted DA-hiPSCs and challenge the next step determining DA functional release since we shown DAergic fibers from the transplant to target structures including striatum.