Funding the Future for PCDH19

Investigating Cortex Microstructure in PCDH19 with Advanced Diffusion Magnetic Resonance Methods

Dr. Antonio Napolitano, Ph.D., Chiara Parrillo, and Camilla Rossi Espagnet – 2022

“PCDH19 clustering epilepsy (PCDH19-CE) is a rare form of drug-resistant epilepsy caused by mutations or partial deletions of the PCDH19 gene. Using advanced diffusion Magnetic Resonance Imaging (dMRI) methods, we are able to show how PCDH19 gene expression microscopically affects brain cortex at neuron level. Our method will allow assessing these morphological changes in a fully non-invasive way thus providing a first support of this altered neuron growth. Furthermore, electroencephalography (EEG) recording will help us to link these microscopic changes seen with dMRI to brain activity and cognitive abilities. This study aims then to help gain a clearer clinical view of this rare condition, supporting the future development of targeted therapies and treatments.”

Investigating the role of steroid hormone receptors and neurosteroids to improve outcomes for PCDH19 Clustering Epilepsy

Jozef Gecz, Ph.D., Raman Kumar, Ph.D., and Paul Thomas, Ph.D. – 2021

“Our research shows that one of the major forces behind the clinical complications of PCDH19 clustering epilepsy (CE) is hormonal imbalance in the affected individuals, boys and girls. This imbalance likely arises early in the development and through a fault or a loss of PCDH19 protein function. PCDH19 impacts not only estrogen receptor, but likely also androgen and progesterone receptors and vice versa. While we aim to work out which of the hormone receptors play the crucial role, we shall also be taking advantage of our PCDH19 CE in a dish model to test various hormone derivatives to suppress the ‘seizures’. These experiments will provide proof of principle evidence for hormones and/or their neuroactive derivatives to be considered for treatment of PCDH19 associated clinical presentation(s).”

PCDH19–N-cadherin Mismatch in PCDH19-Related Disorder

Hisashi Umemori, M.D., Ph.D. – 2021

“A mouse model of PCDH19-related disorder shows female-specific defects in hippocampal synapse development, which causes cognitive impairment, and abnormal cortical neuron sorting, which may contribute to epilepsy. We found that the hippocampal synaptic defects are caused by a mismatch between two cell adhesion molecules, PCDH19 and N-cadherin. PCDH19 interacts with N-cadherin and activates downstream signaling. In normal mice, PCDH19 is expressed by all neurons so that it binds across the synapse and induces downstream N-cadherin signaling. In male mutant mice with no PCDH19, unmasked N-cadherin can bind with each other across the synapse to induce the same downstream signaling. However, in female mutant mice, some cells express PCDH19 and some do not, due to random X-inactivation. Therefore, there is a mismatch between synapses that express PCDH19 on one side and only N-cadherin on the other, and hence, no downstream signaling happens. Indeed, restoring N-cadherin signaling in female mutant mice rescued the synaptic phenotype. In this project, we will test whether the PCDH19–N-cadherin mismatch also underlies abnormal cortical neuron sorting and contributes to “A mouse model of PCDH19-related disorder shows female-specific defects in hippocampal synapse development, which causes cognitive impairment, and abnormal cortical neuron sorting, which may contribute to epilepsy. We found that the hippocampal synaptic defects are caused by a mismatch between two cell adhesion molecules, PCDH19 and N-cadherin. PCDH19 interacts with N-cadherin and activates downstream signaling. In normal mice, PCDH19 is expressed by all neurons so that it binds across the synapse and induces downstream N-cadherin signaling. In male mutant mice with no PCDH19, unmasked N-cadherin can bind with each other across the synapse to induce the same downstream signaling. However, in female mutant mice, some cells express PCDH19 and some do not, due to random X-inactivation. Therefore, there is a mismatch between synapses that express PCDH19 on one side and only N-cadherin on the other, and hence, no downstream signaling happens. Indeed, restoring N-cadherin signaling in female mutant mice rescued the synaptic phenotype. In this project, we will test whether the PCDH19–N-cadherin mismatch also underlies abnormal cortical neuron sorting and contributes to epilepsy. We will then design appropriate strategies to treat PCDH19-related disorder based on the PCDH19–N-cadherin interaction we identified.”

Mechanisms of PCDH19 Clustering Epilepsy

Julie Ziobro, MD, Ph.D. – 2021

“Protocadherin 19 (PCDH19)-clustering epilepsy (PCE) is a developmental and epileptic encephalopathy characterized by intractable seizure clusters, often provoked by fevers, and neuropsychiatric co-morbidities. The X-linked PCDH19 gene encodes a transmembrane cell adhesion molecule critical for cellular interactions during brain development. PCE affects females and rare mosaic males, while male carriers are asymptomatic. This unique inheritance pattern is thought to result from cellular interference associated with random X-inactivation, such that neurons expressing wild-type and those expressing mutant PCDH19 fail to interact properly during development. Our exciting data using female PCDH19 knockout mice crossed with male X-GFP mice to model PCE support this idea. Female offspring display a segregation pattern of separately clustered PCDH19+/GFP+ and PCDH19-/GFP- cells, most strikingly in the cortex and hippocampal CA1 region. How this unique histologic pattern relates to PCE phenotypes remains an unanswered question. We hypothesize that PCE mice develop altered inhibitory synaptogenesis in the CA1 region of the hippocampus (Aim 1) and that the degree of cell segregation correlates with neuronal hyperexcitability and a lowered seizure threshold (Aim 2). This hypothesis will be tested using our novel mouse PCE model with advanced histologic and electrophysiology techniques. Our findings should provide key insights into mechanisms of PCE and potential therapeutic strategies”

Exploring proof of concept for genetic therapy in PCHD19 preclinical models

Paul Thomas, Ph.D. and Stefka M. Tasheva, Ph.D. – 2019

“Changes in a brain gene called PCDH19 are a relatively common cause of epilepsy with and without intellectual disability. There is no current cure for the disorder and approximately half of the patients do not respond to anti-epileptic drugs. The aim of this project is to investigate the possibilities for using gene therapy to treat the disease. To this end, we have developed a unique Pcdh19 mouse model that mimics the genetic changes that cause epilepsy. Using this pre-clinical model we will identify when pathological changes first occur in the brain of the affected females. Importantly, we will also determine whether the pathological lesion is reversible and, if so, the latest developmental time point by which genetic intervention must occur. These experiments will provide unique insight into PCDH19 pathology and demonstrate for the first time whether it might be possible to cure PCDH19-GCE using genetic intervention.”

Modeling PCDH19-Related Epilepsy in human iPSC derived neurons and cerebral organoids

​Jack Parent, M.D. and Wei Niu, Ph.D. – 2018
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“PCDH19-Related Epilepsy (PRE) is caused by mutations in the PCDH19 gene located on the X-chromosome. How PCDH19 mutations result in epilepsy is poorly understood, as is the function of PCDH19 during human brain development. We use human pluripotent stem cells obtained by reprogramming patient skin cells or by CRISPR gene editing to generate brain cells that model PRE in cell culture. The studies described in this grant will take advantage of state-of-the-art stem cell approaches, including growing 3D “mini-brains” (cerebral organoids) in a dish, to determine the function of PCDH19 and how its mutations lead to seizure-like activity. Progress in our studies will help to identify PRE-related abnormalities in brain development and seizure mechanisms that should lead to novel therapies.”

PCDH19: Proteolytic processing and gene regulatory function

​Isabel Martinez Garay, Ph.D. – 2017
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“Girls with changes in PCDH19 develop epilepsy and, in many cases, cognitive impairment. We still do not know much about the roles of PCDH19 in the brain, possibly because this protein might have more than one function. As an adhesion protein, PCDH19 expressed at the cell surface helps cells to recognize and establish contacts with other cells. But PCDH19 can also influence gene expression. Because these functions take place in two different locations within the cell (membrane and nucleus), it is important to understand how PCDH19 fulfills these two roles and how they are regulated. In this project, we will use mouse embryonic stem cells to investigate if different cellular “scissors” cut PCDH19 at the cell membrane. This could release a fragment that is then shipped to the nucleus to regulate gene expression. We will also determine the genes that are turned on or off by PCDH19 in neuronal progenitors and neurons. These experiments will increase our knowledge about the basic biology of PCDH19, an essential step to understand why lack of PCDH19 in a subset of cells has such detrimental effects.”

Identifying the pathological mechanism of PCDH19 Epilepsy

Paul Thomas, Ph.D. – 2016
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“Changes in the PCDH19 gene cause epilepsy and, in some cases, intellectual disability. An unusual and poorly understood feature of PCDH19-associated epilepsy is that it only affects girls. To investigate the underlying cause of PCDH19 associated epilepsy, we have developed Pcdh19 mouse models that mimic the genetic changes that cause epilepsy in girls and allow us to identify neurons in which the PCDH19 gene is active. We have recently found that PCDH19 is active in a subset of neurons that are responsible for “dampening down” electrical activity in the brain. We have also shown that changes in the Pcdh19 gene in female mice affect neuron connections. The aim of this project is to further investigate these preliminary results through detailed analysis of brain development and function in our mouse models. We will also begin to translate our research findings into a clinical context by looking for subtle changes in brain structure in affected girls. These experiments will lead to greater understanding of how changes in PCDH19 cause epilepsy in girls and facilitate the development of new treatments.”

Using IPS cells to understand PCDH19-related encephalopathy

Dr. Sergiu Pasca – 2016

“PCDH19 is a severe disease characterized by onset of epileptic seizures in infancy, intellectual disability and autism. The condition is caused by mutations in the PCDH19 gene present on X chromosome. PCDH19 codes for the protein protocadherin-19. Protocadherins are cell adhesion molecules involved in establishing connections between neurons. Our preliminary findings suggest that protocadherin-19 regulates the trafficking of GABA(A)Rs to synapses. GABA(A)Rs mediate fast inhibitory transmission in the brain. If GABA(A)R presence at synapses is affected, the correct balance between inhibition and stimulation of neurons is upset, possibly giving rise to epilepsy and disorders of neurodevelopment. However, details of PCDH19’s function in the brain are largely unknown. We propose to investigate the role of PCDH19 in mammalian neurons and neuronal circuits, by working both with cultured neurons and with animal models in which PCDH19 has been mutated in a subset of brain cells. Our study will help us better understand how the mutation gives rise to dysfunction at the synapse, in the neuron, and in neuronal circuits, in order to guide the future development of treatments for the disease.”

In Vivo Investigation of the Cellular Interference Model Using Unique PCDH19 Mouse Model and Brain Tissue from a PCDH19 Affected Female

​Jozef Gecz Ph.D. and Paul Thomas Ph.D. – 2015

“Changes in the PCDH19 gene cause epilepsy and, in some cases, intellectual disability. An unusual and poorly understood feature of PCDH19-associated epilepsy is that it only affects girls. To investigate the underlying cause of PCDH19-associated epilepsy, we have developed Pcdh19 mouse models that mimic the genetic changes that cause epilepsy in girls and allow us to identify neurons in which the PCDH19 gene is active. We have recently found that PCDH19 is active in a subset of neurons that are responsible for “dampening down” electrical activity in the brain. We have also shown that changes in the Pcdh19 gene in female mice affect neuron connections. The aim of this project is to further investigate these preliminary results through detailed analysis of brain development and function in our mouse models. We will also begin to translate our research findings into a clinical context through analysis of a brain sample from an affected female. These experiments will lead to greater understanding of how changes in PCDH19 cause epilepsy in girls and facilitate the development of new treatments.”

Unraveling the Molecular Mechanisms of PCDH19 in Cultured Neurons and in PCDH19 KO Mouse Model

Maria Passafaro Ph.D. – 2015

“PCDH19 is a severe disease characterized by onset of epileptic seizures in infancy, intellectual disability and autism. The condition is caused by mutations in the PCDH19 gene present on the X chromosome. PCDH19 codes for the protein protocadherin-19. Protocadherins are cell adhesion molecules involved in establishing connections between neurons. Our preliminary findings suggest that protocadherin-19 regulates the trafficking of GABA(A)Rs to synapses. GABA(A)Rs mediate fast inhibitory transmission in the brain. If GABA(A)R presence at synapses is affected, the correct balance between inhibition and stimulation of neurons is upset, possibly giving rise to epilepsy and disorders of neurodevelopment. However, details of PCDH19’s function in the brain are largely unknown. We propose to investigate the role of PCDH19 in mammalian neurons and neuronal circuits, by working both with cultured neurons and with animal models in which PCDH19 has been mutated in a subset of brain cells. Our study will help us better understand how the mutation gives rise to dysfunction at the synapse, in the neuron, and in neuronal circuits, in order to guide the future development of treatments for the disease.”