Differential levels of dermatan sulfate generate distinct Collagen I gel architectures

Collagen I is the most abundant extracellular matrix (ECM) protein in vertebrate tissues. As an endogenously synthesized fibrillar biopolymer or as a synthetic hydrogel, it provides mechanical durability to tissue microenvironments and regulates cell function. Predominant regulators of its fibrillogenesis are dermatan sulfate proteoglycans (DSPGs), proteins conjugated with iduronic acid containing DS glycosaminoglycans (GAGs). Although DS is known to regulate tissue function through its modulation of Collagen I architecture, a precise quantifiable understanding of the latter remains elusive. We investigate this problem by visualizing the pattern of structural elements within fixed Collagen I gels polymerized in the presence of varying concentrations of DS (50-, 200- and 400- g/mL) using second harmonic generation microscopy (SHG). Measuring four independent imaging parameters: fibril density, mean SHG signal (which estimates the ordering of the fibrils), surface occupancy (which estimates the space occupied by fibrils), and the fibril width allows us to construct an informative model of the effects of DS on Collagen I element architecture. Supported by confocal microscopy, our observations indicate that the effect on collagen fibril pattern of DS is contextual upon its concentrations. Lower levels of DS result in more numerous disorganized fibrils; higher levels restore organization, but at lower fibril densities. Such Collagen I gel pattern-tuning of DS is likely of relevance for understanding its functions in disease progression and biomaterial applications.