Multi-tissue modelling of a lysosomal storage disorder using patient-derived iPSCs – a pathway to Precision Medicine

Lysosomal storage disorders (LSDs) are a heterogeneous group of rare heritable diseases caused by defects in lysosomal function which result in a gradual accumulation of substrates and to cell and tissue dysfunction. Despite a related aetiology, LSDs show disease-specific organ involvement and considerable patient-to-patient disease variability. This research will focus on understanding Fabry disease (FD) as an exemplar LSD. FD is a multi-organ disorder which by early adulthood frequently displays heart and kidney involvement. It is caused by mutations in GLA encoding the enzyme a-galactosidase A (a-gal A) which breaks down the glycosphingolipid Gb3, but the molecular cascade downstream of this defect remains opaque. As with many LSDs, clinicians have the challenge of managing different disease subtypes and presentations, gene variants of unknown significance (VUS), and unpredictable disease life courses. For FD, the major treatment options, enzyme replacement therapy (ERT) and chaperone therapy (for amenable mutations) can slow disease progression when initiated at an early stage, but each has limitations. Evidence of inadequate efficacy for ERT in heart and kidney is of major concern — lipid accumulation in these organs is a cause of tissue fibrosis and related cardiac arrhythmia, functional decline and organ failure. Delivering more personalised, accessible and efficacious therapies is an urgent priority for increasing the healthspan and quality of life of patients. This research aims to improve our understanding of the pathogenic mechanisms and patient variability of FD using induced pluripotent stem cell (iPSC)-based models, supporting progress towards ‘precision medicine’ for this disease and by extension for other complex inherited conditions. In advance of this application, our privileged access to the largest cohort of FD patients in Northern England enabled us to generate four FD patient-derived iPSC lines, providing the opportunity to address these aims expeditiously supported by a leading physician in the field. A major challenge of in vitro disease modelling is to accurately recreate disease phenotypes which take years to develop in patients. To tackle this, our first goal will be to identify and experimentally limit compensatory mechanisms to enhance the rate of Gb3 accumulation in FD cells. These efforts will focus on lysosome regulating proteins LIMP-2 and Cx43, both of which can become elevated downstream of a-gal A dysfunction. By generating 3D in vitro tissue models of heart, kidney and lung using organoid technologies, we will be able to study multiple organs and cell types impacted by FD. Since the immune system is a major contributor to LSDs and may drive the development of fibrosis and organ failure in FD, we will incorporate iPSC-derived macrophages into the organoids. Comprehensive structural characterisations together with proteomics and single cell RNA sequencing (scRNA-seq) will enable us to discover mechanisms of disease, pathogenesis-associated gene regulatory networks and potential causes of patient variability in organ involvement and age of onset. We will also discover novel cell type- and stage-specific disease biomarkers of potential clinical value. The approach is scalable and highly transferable to other inherited diseases. Moreover, these models will serve as platforms for drug and gene therapy testing, including gene correction technology. Together this research has the potential to deliver better patient stratification and to widely unlock therapeutic opportunities.