Deciphering the biophysical basis by which Glycosaminoglycans CONtrol growth factor signaling during development: a biomimetic approach (GlyCON)

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During recent years, increasing evidence has been accumulated that the activity and bioavailability of growth factors (GFs) in the tissue is determined by the extracellular matrix, in particular by the heparan sulfate (HS) chains of proteoglycans, which interact with distinct basic domains of the GFs. Nevertheless, it is largely unknown how the HS structure (the sequence of N- and O- sulfation) and the binding sites of the GFs (the sequence of basic amino acids) affect the interaction at the molecular level. Moreover, chondroitin sulfate (CS), a glycosaminoglycan (GAG) with structural similarities to that of HS also binds to many GFs, although with reduced affinity. Preliminary evidence gained by the consortium indicates that CS levels are increased in chondrocytes of mouse mutants with a defective HS structure pointing to a compensatory function of CS at least in chondrocytes. How the composition of GAGs in a tissue affects GF activity has however not been systematically investigated. With GlyCON, we have established a multidisciplinary project bridging material science and developmental biology. Three international teams interact in a tight collaboration to gain basic insight into the mechanism by which HS and CS control the activity, presentation and distribution GFs. Based on the scientific expertise of the partners, we will use the process of embryonic endochondral ossification as a model to investigate the molecular mechanisms that determine the interaction of HS and CS with bone morphogenetic proteins (BMP) and Indian hedgehog (Ihh). In our multi-disciplinary approach, we will decipher basic principles of how the GAG structure controls the bioactivity of these GFs and how alterations in the GAG composition affect developmental processes, tissue homeostasis and HS related diseases, like multiple osteochondromas (MO) in vivo.Specifically, we will create a library of HS oligosaccharides exhibiting distinct sulfation patterns and immobilize these on biomimetic platforms. These platforms will be developed for biophysical studies of the binding affinity and stoichiometry of the HS-BMP and HS-Ihh interactions and for subsequent biological investigation of how the HS structure determines the bioactivity of the GF towards co-cultured cells. The impact of changes in the HS structure on tissue homeostasis will be investigated by the in vivo analyses of mouse mutants carrying specific defects in HS synthesizing enzymes. In the second part, we will anlayze the biophysical interaction of GF with CS and determine how the relative composition of both GAGs (HS and CS) affects the bioactivity of GFs in vitro using cells cultured on biomimetic platforms and in vivo in primary cells of mouse mutants.Our final aim is to generate detailed knowledge on the molecular basis of the GAG–GF interaction, thereby paving the way for future studies of other GF, tissues and rare GAGs associated diseases and ultimately for new therapeutic approaches.