The role of cell adhesion and cytoskeleton dynamics in the pathogenesis of Ehlers-Danlos syndrome

Ehlers-Danlos syndromes (EDS) are connective tissue disorders characterised by joint hypermobility, skin hyperextensibility, and tissue fragility. They are primarily considered collagen disorders, as most subtypes result from mutations in collagen-related genes. However, the exact nature of the collagen defect(s) and the underlying pathogenic mechanism remain poorly understood. As a result, diagnostic and therapeutic options for EDS are limited, leaving many patients with a diminished quality of life. This thesis proposes a novel pathomechanism for EDS, suggesting that ECM composition changes disrupt cell adhesion and mechanotransduction, ultimately compromising connective tissue integrity. The pathomechanism was investigated using an interdisciplinary approach, combining genetic, extracellular matrix (ECM), and mechanophenotypic analyses. A native ECM culture system was developed to enable the study of ECM composition and fibroblast mechanophenotype in a physiologically relevant environment. Solid-state NMR spectroscopy revealed altered amino acid composition in the ECM of both cEDS and hEDS. Additionally, successful 13C-labelling of native ECM was achieved, facilitating future structural investigations at atomic resolution. Mechanophenotypic analysis demonstrated distinct alterations in fibroblast adhesion and contractility. hEDS fibroblasts exhibited reduced α2β1 integrin expression and a striking overexpression of αvβ3 integrin, which formed highly striated structures along actin filaments. These changes coincided with complete fibronectin matrix disintegration and an increased proportion of αSMA-positive cells, indicating a hypercontractile phenotype. In contrast, cEDS fibroblasts also showed increased αvβ3 and decreased α2β1 expression but exhibited fewer αSMA-positive cells, suggesting a distinct mechanotransduction pathway. These findings provide novel evidence linking ECM alterations with fibroblast mechanophenotypic changes, reinforcing the proposed pathomechanism. This interdisciplinary approach underscores the importance of investigating EDS beyond genetics and lays the groundwork for future research into this under-recognised disorder. This study represents a significant advancement in understanding EDS, with the potential to improve diagnostic and therapeutic strategies for EDS patients.