Chondronoids for Studying Collagen-II Homeostasis and Diseases

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PROJECT SUMMARY/ABSTRACT Type II collagenopathies are a class of disease caused by mutations in collagen-II, the most abundant protein in cartilage. These diseases present with various symptoms affecting joint structure, cartilage properties, and skeletal development. Currently, they have no cure. Patients rely on palliative treatments as their symptoms arise. Two examples are the chondrodysplasias caused by mutations in COL2A1 leading to either the G1170S or R719C substitutions in collagen-II. Patients present with one or more of the following symptoms: precocious osteoarthritis, avascular necrosis of the femoral head, and Legg-Calvé-Perthes disease. Previous cell and mouse models hindered research on these diseases owing to poor recapitulation of the human phenotype, and poor adaptability for the necessary molecular biology and biochemical assays required to understand molecular origins of the disorders. In the absence of amenable models to probe the effect of collagen-II misfolding on cells and tissues, progress on identifying therapeutic targets and novel treatment options remains slow. These challenges can be overcome by using a panel of induced pluripotent stem cell (iPSC) lines capable of being differentiated into cartilage-producing chondrocytes to elucidate the underlying collagen production and misfolding defects. Harnessing a panel of previously generated gene-edited, genetically matched iPSCs harboring the G1170S and R719C collagen-II mutations and wild-type control, the underpinnings of the disease can be examined in vitro with unprecedented resolution. This highly pertinent system will help illuminate the biochemical manifestations of disease-causing collagen- II mutations at tissue, cellular, and protein levels. Thanks to outstanding facilities and experts at MIT, training will include a wide variety of broadly useful techniques such as proteomics, RNA-sequencing, stem cell culture, and organoid generation to examine characteristics such as matrix composition and structure, collagen stability, and activation of stress pathways. At the molecular-level, state-of-the-art mass spectrometry and biochemical assays will enable investigation of the interactions required for wild-type and misfolding-prone collagen-II to assemble, fold, and be secreted. This approach based in a highly relevant model will elucidate how the wild-type protein folds, while also probing the specific molecular causes of pathology by harnessing a hypothesis-driven, direct investigation of how mutant collagen-II misfolds and diverges from the normal proteostasis pathways. Overall, this research is expected to make a considerable contribution to our understanding of collagen-II homeostasis in health and disease, and to lay a strong foundation for identifying novel therapeutic targets to solve the collagen misfolding problem in this and potentially the many other related collagenopathies.