Genetic association studies have yielded a wealth of information on specific variants that lead to the development of disease, but our mechanistic understanding for most of them is lacking. Unbiased, comparative study of protein-protein interactions (PPI) for protein coding variants is a very promising approach to fill this gap. To yield data that can inform us on tissue-specific pathologies (e.g. cardiovascular, neurological disease) we need to study PPIs in the cell types affected by the disease. In a similar fashion, studying proteins expressed endogenously would allow us to overcome issues related to gene expression or dose-dependent protein function, which is a feature of many of these pathologies.

Here I present my work trying to unravel the mechanism mutations in the BAG3 chaperone gene lead to disease. To address this, I used a combination of induced pluripotent stem (iPS) cell technology (to generate cardiac myocytes), genome engineering (to induce specific disease-modifying mutations and protein fusions) and affinity purification coupled to mass spectrometry (to compare PPIs between variants). The results show that disease-related variants of BAG3 display a different profile of protein partners, some of them cardiac-specific, pointing towards interactions that potentially underlie the disease mechanism and tissue specificity. We also observed a cell culture phenotype for BAG3 deficiency and for some of the protein-coding variants, which sets the ground for the exploration of the role of BAG3 interactions in disease.

Overall, this piece of work proves the value of studying cardiac disease-related genetic variability using a disease-relevant iPS-derived model and genome engineering to explore multiple variants. In particular, we provide new clues on the role of BAG3 in the heart, and how that role is compromised by disease-related mutations. We hope that the knowledge gained on BAG3 genetics and mechanism will be useful for the development of therapeutic strategies in the future.