Objective: Investigate whether the Parkinson’s disease (PD) VPS35 D620N mutation leads to synaptic dysfunction in human cortical iPSC-derived neurons.

Background: Early presynaptic dysfunction and cortico-striatal inputs have been implicated in the pathophysiology of PD. IPSC derived neurons from patients suffering from monogenetic PD are increasingly being used to gain insight into pathomechanisms of PD. A missense mutation D620N in VPS35 has been identified as a rare cause of familial PD. VPS35 is part of the retromer complex which is involved in endosomal trafficking. VPS35 has been shown to be important for trafficking of plasma membrane receptors like the AMPA-type and synaptic vesicle endocytosis.

Method: IPSC-derived neurons from two controls and two PD patients with the VPS35 D620N mutation were differentiated into cortical neurons and cultured in an autaptic cell culture system. Analyses were performed over a period of 6 weeks. Whole-cell patch clamp in voltage and current mode were used to examine membrane properties and synaptic properties. In addition, cells were stained with MAP2 as a dendritic, Synapsin 1/2 as a presynaptic and Shank2 as a postsynaptic marker for fluorescence imaging. Dendrite length and cell complexity were assessed using Imaris and Sholl analysis. Synapse numbers were counted by co-localisation of pre- and postsynaptic markers.

Results: Cells derived from controls and PD patients developed into functional neurons with physiologic membrane passive and active properties and action potential firing patterns. However, patient-derived cortical neurons were less likely to develop synaptic responses than control cells (p<0.0001, 3-way ANOVA). They had a reduced number of synapses (p<0.0001, 3-way ANOVA) and smaller EPSC amplitudes (p= 0.0006, 3-way-ANOVA). Furthermore, their total dendrite length was shorter (p 0.0014, 3-way-ANOVA) and their cell complexity was reduced (p 0.0006, 3-way ANOVA).

Conclusion: Human cortical neurons iPSC-derived neurons from PD patients carrying the VPS35 D620N mutation showed signs of impaired neurogenesis and synaptogenesis and altered synaptic strength compared to control cells at a single cell level. Other PD genes like LRRK2 have been associated with synaptic dysfunction. Therefore, our data supports the importance of synaptic dysfunction for the pathophysiology of PD.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/ipsc-derived-cortical-neurons-from-parkinsons-patients-with-vps35-mutation-show-defects-in-synapto-and-neurogenesis/