Dr. Blewitt has shown that inhibiting SMCHD1 allows several important protein-coding genes in the PWS to be expressed, but the effect is incomplete. Here she will determine the chromosomal landscape in the PWS region on the maternal chromosome and evaluate how that landscape changes when SMCHD1 is missing, paving the way for more efficient maternal gene activation to treat PWS.
Dr. Theresa Strong, Director of Research Programs, shares details on this project in this short video clip.
People without PWS normally express a cluster of genes inherited from their father; the copy from their mother is switched off. PWS occurs essentially because the copy from the father is absent, but as in people without disease, the maternal copy is switched off. Therefore, a potential therapy for PWS is to awaken the maternal copy of these genes by inhibiting factors that normally silence these genes on the maternal copy. SMCHD1 is one such factor, that we discovered more than 10 years ago, and have since shown in mouse models that it switches off several of the genes in PWS cluster. Our latest data shows that the same holds true in human cells, where removing SMCHD1 results in several genes in the PWS cluster being switched back on. Thus, inhibiting SMCHD1 is a potential new treatment for PWS. Importantly, targeting SMCHD1 would treat the cause of PWS, and thus have the best chance of most effectively treating the wide array of symptoms experienced by patients. This will offer significant advantage to current treatments that can only mitigate individual symptoms and are associated with numerous side effects precluding their use by all PWS patients.
Our preliminary data provide compelling evidence that targeting SMCHD1 is a valid consideration for PWS treatment. We are developing world-first chemicals that inhibit SMCHD1 function, which can be turned into new therapeutics. Therefore, it is timely to study how we might best employ such chemicals in the future to treat PWS. To best do this, we will investigate how SMCHD1 works to switch off the PWS genes. This is an area where we are experts and uniquely possess the required tools. We know that proteins involved in switching genes off usually work together in a hierarchy. Understanding this hierarchy is beneficial firstly to uncover the underlying biological mechanisms involved in switching PWS genes off. Equally importantly, knowledge of the hierarchy can reveal additional avenues for therapeutic intervention.
Our data show that when SMCHD1 is removed, the PWS genes are not switched on in every cell. Furthermore, only around half the genes in the PWS cluster are switched on upon removal of SMCHD1. These data suggest that SMCHD1 collaborates with other factors to switch off the PWS maternal allele. Here we will test which other factors SMCHD1 collaborates with, to reveal how we might best activate the PWS genes in patients. Such experiments have never been performed before for SMCHD1 and they will allow a more complete understanding of where this protein sits amongst the other regulators of the cluster. Importantly our data will allow us to specifically consider whether combination therapy, with drugs inhibiting SMCHD1 and the other factors SMCHD1 works with, may be beneficial for PWS patients in the future.
If our application is successful, based on the data generated in this project, we would trial combination therapies in PWS patient-derived cells to achieve optimal gene activation with minimal side effects. Therefore, this work is laying the foundation for therapeutic development targeting the underlying genetic cause of PWS, which is desperately needed by patients and families.
SMCHD1 is a factor that switches off the PWS locus genes in mouse. We are interested in how SMCHD1 switches off PWS genes in humans, because removing SMCHD1 to allow PWS gene activation provides a potential path for treatment of PWS. In this project we created a resource of PWS patient-derived induced pluripotent stem cell lines that have normal SMCHD1 and that have no SMCHD1, which can be used to study how SMCHD1 works into the future. Using these cells, we identified that loss of SMCHD1 does not alter germline or secondary imprint control region DNA methylation. However, we did observe destabilized methylation of a SNRPN alternative start site. In addition, we observed depleted H3K9 methylation across the cluster. Together these data suggest that the epigenetic state of the locus is disrupted in the absence of SMCHD1, which may be conducive to gene activation. Further work will be required to decipher exactly why DNA methylation at one site and H3K9 methylation more broadly is depleted in the absence of SMCHD1, which will help suggest how this knowledge might be utilized in PWS treatment.