Dissecting the Role of PCDH19 in Clustering Epilepsy by Exploiting Patient-Specific Models of Neurogenesis

Abstract

PCDH19-related epilepsy is a rare genetic disease caused by defective function of PCDH19, a calcium-dependent cell–cell adhesion protein of the cadherin superfamily. This disorder is characterized by a heterogeneous phenotypic spectrum, with partial and generalized febrile convulsions that are gradually increasing in frequency. Developmental regression may occur during disease progression. Patients may present with intellectual disability (ID), behavioral problems, motor and language delay, and a low motor tone. In most cases, seizures are resistant to treatment, but their frequency decreases with age, and some patients may even become seizure-free. ID generally persists after seizure remission, making neurological abnormalities the main clinical issue in affected individuals. An effective treatment is lacking. In vitro studies using patient-derived induced pluripotent stem cells (iPSCs) reported accelerated neural differentiation as a major endophenotype associated with PCDH19 mutations. By using this in vitro model system, we show that accelerated in vitro neurogenesis is associated with a defect in the cell division plane at the neural progenitors stage. We also provide evidence that altered PCDH19 function affects proper mitotic spindle orientation. Our findings identify an altered equilibrium between symmetric versus asymmetric cell division as a previously unrecognized mechanism contributing to the pathogenesis of this rare epileptic encephalopathy.

Modeling PCDH19-CE: From 2D Stem Cell Model to 3D Brain Organoids

“…Moreover, comparing the differentiation process of mixed iPSCs with control ones, it emerged that, as in the pathological condition, neural rosettes appeared earlier and showed a disorganized structure with a reduced lumen [ 59 ], in line with the findings by Homan and co-workers [ 22 ]. To investigate the mechanism underlying this early differentiation, the same authors showed that PCDH19 loss of function results in significant centrosome hyper-amplification in mitotic iPSCs and an increase in asymmetrical cell division by progenitor cells close to the center of the rosettes [ 59 ]. This altered cell behavior is most probably responsible for the increase in cell differentiation and defective neural progenitor cell proliferation [ 62 ].…”

“…In particular, Homan and co-workers suggested that the coexistence of cells expressing mutated and wild-type PCDH19 proteins was associated with a loss of apical-basal polarity and an increased rate of neuronal differentiation. In a recent work [ 59 ], Borghi and co-workers confirmed accelerated cortical differentiation in vitro using iPSC derived from a mosaic male patient (PCDH19-iPSCs). As in [ 22 ], PCDH19-iPSCs were mixed with wild-type iPSCs to recreate the mosaic condition.…”

“…The first brain organoid model for PCDH19-CE was developed using iPSCs derived from a mosaic male patient [ 59 ]. The data showed that the patient-derived organoids were smaller than the controls [ 59 ], which is consistent with the mild microcephaly observed in some patients [ 14 ] and the increased neural differentiation observed in 2D cultures [ 59 ] and mouse models [ 20 , 22 ]. These findings suggest premature neurogenesis, similar to what has been observed for brain organoids modelling Miller-Dieker syndrome [ 78 ].…”

The Broad Clinical Spectrum of Epilepsies Associated With Protocadherin 19 Gene Mutation

“…Moreover, it is possible that PCDH19 mutations can alter the correct positioning of the mitotic spindle causing a higher number of asymmetric divisions leading to accelerating neural differentiation. An altered equilibrium between symmetric vs. asymmetric cell division may contribute to the pathogenesis of the disease ( 11 ). The synaptogenesis role of PCDH19 was confirmed by Mincheva-Tasheva et al who showed disruption of excitatory synaptic contacts between PCDH19-knock-out and wild-type neurons in “mosaic” neuronal cultures ( 12 ).…”

Protocadherin 19 Clustering Epilepsy and Neurosteroids: Opportunities for Intervention

“…These experiments were performed in MCF-7 cancer cells, which may not be the best model for investigating the consequences of PCDH19 variation that causes heterogenous neurological phenotypes [ 2 ]. Other immunofluorescence studies in proliferating iPSCs and polarized cells of the neural rosette lumen show that PCDH19 localises to the mitotic spindle pole of the dividing cells and affects its formation, suggesting that PCDH19 may play a role in regulating asymmetric versus symmetric cell division during neurogenesis [ 56 , 57 ]. Taken together, these data indicate differences in the localisation and possible function of PCDH19 in different cell types and at different cell cycle stages.…”