(Last updated Aug. 2020)
PIGA Cell Line and Mouse Model Creation
In 2017, Dr. Taroh Kinoshita and Dr. Yoshiko Murakami of Osaka University, leading experts in the GPI-anchor pathway and related disorders including PIGA-CDG, began work to create PIGA deficient cell lines for in-vitro (in cell) testing. In 2018, that work expanded to include development of a “knock-out” mouse model for in-vivo testing. In 2019, the first attempts to develop a “knock-in” mouse model were started.
The purpose of the creation of PIGA cell lines and mouse models is to allow for testing of different supplements, molecules and therapies to determine if they help restore cell functionality.
Current Status: The knock-in PIGA mouse model is in the process of being created.
Gene Therapy
In 2018, we began to explore the viability of a gene replacement therapy approach for PIGA-CDG. Based on extensive consultations with various companies specializing in gene therapy for rare disorders, we concluded that PIGA-CDG is a suitable candidate for an AAV-based (adenoassociated virus) gene therapy approach. We are currently working with Dr. Kathrin Meyer of Nationwide Children’s Hospital, in collaboration with Dr. Kinoshita and Dr. Murakami, on building an AAV9 gene therapy program for PIGA-CDG. Dr. Meyer has experience developing an AAV9 gene therapy product that has been approved by the FDA for Spinal Muscular Atrophy (SMA), and is currently developing other gene therapy products in Central Nervous System (CNS) disorders in various stages of clinical testing.
Current Status: The first PIGA AAV9 vector was tested in PIGA deficient cell lines at Osaka University and was found to be successful in restoring levels of GPI-anchored proteins. The PIGA AAV9 vector will be tested in knock-in PIGA mice once available.
Small Molecule Therapy
PIGA is part of a seven-enzyme complex involved in the very first step of GPI-anchor biosynthesis; the “end product” of this enzyme complex is a molecule called GlcNAc-PI (more on this here). The hypothesis is that the supplementation of GlcNAc-PI into a PIGA-deficient patient, akin to “substrate replacement therapy,” could be effective in bypassing the function of the mutant PIGA gene and improving functionality of the GPI-anchor pathway. In 2017, Dr. Peter Seeberger of the Max Planck Institute of Colloids and Interfaces in Germany, a carbohydrate chemist experienced in GPI-anchor molecule synthesis, initiated the process of synthesizing the GlcNAc-PI molecule. In 2018, Dr. Seeberger’s lab completed the synthesis of both an unmodified GlcNAc-PI molecule and a modified peracetylated version (for improved bioavailability or permeability).
Current Status: Testing of the GlcNAc-PI molecule in cell lines produced promising results in terms of improving the expression of GPI-anchored proteins. Initial in vivo testing in knock-out PIGA mice was inconclusive. More work needs to be done to create different variations of the molecule’s “packaging” so that it can better permeate the cell; the successful creation of the knock-in PIGA mouse model will also facilitate further GlcNAc-PI testing.
Fly Model Creation
In 2018, Dr. Clement Chow of the Department of Human Genetics at the University of Utah School of Medicine initiated a project to create a drosophila (fly) model of PIGA deficiency to better understand how the loss of PIGA function contributes to disease. (Read about it on the Chow Lab’s blog here.) Dr. Chow has previously published an analysis of a fly model on NGLY1 deficiency, a rare metabolic disorder of deglycosylation.
Current Status: Knock-out PIGA fly models were successfully created and distinct symptoms were observed depending on the affected cell type in the model. Patient-specific PIGA fly models were then generated; characterization of symptoms is currently underway. Future work will involve a modifier screen to evaluate to what extent phenotypic variation of PIGA-deficient flies can be explained by genotypic variation.
Drug Discovery Screening
Dr. Chow will be conducting a medium-throughput drug screening for PIGA-CDG. This screening will potentially identify whether an existing drug may be beneficial for the treatment of PIGA-CDG, by testing of thousands of existing medications on PIGA-deficient flies and evaluating any improvement in symptoms.
Current Status: To be initiated in 2021; completion TBD.