December 2017.
The Angelman Syndrome Alliance was established to facilitate parent organisations to join forces and funds to increase the financial support of dedicated research projects and thereby intensify research on Angelman Syndrome.
Angelman Syndrome Ireland as an Alliance member have supported a number of research projects over recent years. We have previously provided details of the individual projects and the outline below provides updates on these projects and progress to date. Also included is a glossary of terms.
Summary kindly compiled by Annette Kent, ASI. For further information contact admin@angelman.ie
Dr. Ben Philpot , Assistant Professor in Cell and Molecular Physiology.
Quantifying EEG abnormalities and identify biomarkers in AS
Prior to any clinical trial for Angelman syndrome (AS), researchers must first define biomarkers that be tracked in order to determine whether the intervention/treatment is successful. Dr. Ben Philpot’s laboratory, together with two clinical collaborators, Dr. Catherine Chu (Harvard Medical School/Massachusetts General Hospital) and Dr. Lynne Bird (University of California San Diego/Rady Children’s Hospital), tested whether EEG could be quantified and used as a biomarker for AS. In order for a biomarker to be valuable, it must be quantifiable and reliable. Thus, Dr. Philpot and colleagues focused on rigorously quantifying one particular EEG irregularity in children with AS – increased delta rhythms – that has been described but never quantified by clinicians. The researchers found that delta rhythms were broadly and reliably increased in children with AS, relative to non-affected children of the same age. Their work was recently published in the Journal of Neurodevelopmental Disorders in April 2017. They are currently working towards identifying new EEG signatures that may also have value as biomarkers.
Dr. Silvia Russo – Dr. Tizana Borsella
Characterisation of synapses of neurons in AS
The project aims to test the effect of JNK inhibition against AS using the specific cell-permeable JNK inhibitor peptide (D-JNKI1) to prevent JNK action in two AS experimental models: 1) the mouse model Ube3a and 2) the human in vitro IPSC derived neurons.
The in-vivo experiments which Prof. T. Borsello (IRCCS Istituto Mario Negri) plan to perform will run slightly late due to delays in receiving ministerial authorization which is progressing well. In the meantime, the research group are expanding the colony of mice and have succeeded in obtaining the correct genotype to then plan the treatment with the inhibitor peptide (D-JNKI) and analyse its effect in Ube3a mice.
The experiments on the in-vitro model will be carried on by dr Silvia Russo (IRCCS Istituto Auxologico Italiano). This model will consist of patient specific iPSC-derived neurons. IPSCs have been generated from three children with UBE3A mutation, one with a mosaic Imprinting defect and one with deletion. Two patients with UPD have also accepted to participate. Stem cells have been characterized in order to check their genome remains identical to that originally present in the patient’s blood. Differentiation into cortical neuron has been achieved for one patient and one control (the patient’s sister). Two controls and a patient have been characterized for the morphology of young neurons, and only in one control for electrophysiology in order to identify in our model the “differences” (e.g biomarkers) between controls and patients’ neurons.
Dr. Ben Distal, PhD, AMC Amsterdam
Target identification for E6AP
AS is caused by deletion or mutations of the UBE3A gene. The UBE3A gene encodes an enzyme called E6AP that marks proteins for destruction. Marked or tagged proteins are degraded by a large protease complex, the proteasome. The inability of mutated E6AP to mark target proteins for degradation, is believed to cause AS. Therefore, identification of the critical E6AP target(s) and understanding their contribution to the disorder is important for developing therapies for AS. To identify these critical targets, we have employed a protein-protein interaction screen and found several proteins that interact with E6AP (called UBE3a Interacting Protein = UIP). In addition, we have developed assays to assess if E6AP can mark these UIPs for destruction by the proteasome. A paper describing one of these assays has been submitted for publication.
Of the three proteins studied only one, UIP3, is ubiquitinated by E6AP while the two proteins (UIP2 and Rpn10 = UIP4) are not bona fide targets and seem to have different roles. Remarkably, E6AP-dependent ubiquitination of UIP3 in vivo does not result in proteasomal degradation of UIP3
indicating that its ubiquitination serves a different function. We discovered that UIP4 (also known as Rpn10) is a component of the proteasome, and that the E6AP- Rpn10 interaction is required for the association of E6AP with the proteasome. The fourth protein we have studied is PML and we have shown PML is ubiquitinated by E6AP. Papers on Rpn10 and PML, in which our data is combined with the in vivo results obtained by the Elgersma/van Woerden lab, are currently in preparation.
Dr. Geeske van Woerden, PHD – Prof. Dr. Ype Elgersma, Professor of Molecular Neuroscience.
Scientific director ENCORE Expertise Centre for Neurodevelopmental Disorders
In vivo characterization of proteins that interact with UBE3A.
The overall aim of this project funded by the ASA was to use our recently developed semi-high-throughput screen to test the importance of putative E6AP interacting proteins (UIPs, previously identified in our lab and/or in the Distel lab), in neuronal function, to get insight into what extent these putative E6AP targets play a role in the pathology underlying AS.
For most of the UIPs tested we found that their expression levels are not regulated by UBE3A. In addition, overexpression of these proteins does not affect neuronal development in a culture dish, nor does it affect neuronal functioning. Further research is needed to understand the physiological relevance of the interaction between these UIPs and UBE3A.
We also tested two known UIPs, Rpn10 and PML. When testing Rpn10 (known UBE3A interacting protein) we found that increased levels of Rpn10 did not affect neuronal morphology or function. However, for PML, a protein shown previously in literature to be regulated by UBE3A in non-neuronal tissue, we found that this protein plays an important role in the development of the brain and is potentially regulated by UBE3A in neurons.
Scientific manuscripts on Rpn10 and PML, in which our data is combined with the results obtained by the Distel lab, will soon be submitted.
Glossary
Assays – a procedure for measuring the biochemical or immunological activity of a sample.
Biomarker – A biomarker or biological marker, generally refers to a measurable indicator of some biological state or condition.
Genotype – the genetic constitution of an individual organism
In-vitro experiments are experiments carried in the lab or test tubes.
In-vivo experiments are experiments done within the living body of an animal or human.
IPSC – Induced Pluripotent Stem Cells (are derived from skin or blood cells that have been reprogrammed back into an embryonic-like pluripotent state that enables the development of an unlimited source of any type of human cell needed for therapeutic purposes.
Pluripotent stem cell – are master cells. They can potentially produce any cell or tissue the body needs to repair itself. This “master” property is called pluripotency.
Proteasomes and the ubiquitination process – is the main way that proteins are broken down in human cells. A breakdown in this process results in the accumulation of proteins and can be the basis of many diseases.
UPD – paternal unipaterental disomy, Uniparental disomy (UPD) occurs when a person receives two copies of a chromosome, or of part of a chromosome, from one parent and no copy from the other parent.
PML is promyelocytic leukemia protein. This protein is involved in many cellular processes including cell cycle progression, DNA damage repair and others.
Neuronal migration is the method by which neurons travel from they are created to their final position in the brain as the brain develops.
Synapses is a structure that allows a nerve cell to pass an electrical or chemical signal to another nerve.
