Heparan sulfate is necessary for the early formation of nascent fibronectin and collagen I fibrils at matrix assembly sites.

TitleHeparan sulfate is necessary for the early formation of nascent fibronectin and collagen I fibrils at matrix assembly sites.
Publication TypeJournal Article
Year of Publication2022
AuthorsHill, KE, Lovett, BM, Schwarzbauer, JE
JournalJ Biol Chem
Date Published2022 Jan
KeywordsAnimals, CHO Cells, Collagen Type I, Cricetinae, Cricetulus, Extracellular Matrix, Fibronectins, Heparin, Heparitin Sulfate

<p>Fibronectin (FN), an essential component of the extracellular matrix (ECM), is assembled via a cell-mediated process in which integrin receptors bind secreted FN and mediate its polymerization into fibrils that extend between cells, ultimately forming an insoluble matrix. Our previous work using mutant Chinese hamster ovary (CHO) cells identified the glycosaminoglycan heparan sulfate (HS) and its binding to FN as essential for the formation of insoluble FN fibrils. In this study, we investigated the contributions of HS at an early stage of the assembly process using knockdown of exostosin-1 (EXT1), one of the glycosyltransferases required for HS chain synthesis. NIH 3T3 fibroblasts with decreased EXT1 expression exhibited a significant reduction in both FN and type I collagen in the insoluble matrix. We show that FN fibril formation is initiated at matrix assembly sites, and while these sites were formed by cells with EXT1 knockdown, their growth was stunted compared with wild-type cells. The most severe defect observed was in the polymerization of nascent FN fibrils, which was reduced 2.5-fold upon EXT1 knockdown. This defect was rescued by the addition of exogenous soluble heparin chains long enough to simultaneously bind multiple FN molecules. The activity of soluble heparin in this process indicates that nascent fibril formation depends on HS more so than on the protein component of a specific HS proteoglycan. Together, our results suggest that heparin or HS is necessary for concentrating and localizing FN molecules at sites of early fibril assembly.</p>

Alternate JournalJ Biol Chem
PubMed ID34890641
PubMed Central IDPMC8801470
Grant ListR01 AR073236 / AR / NIAMS NIH HHS / United States
T32 GM007388 / GM / NIGMS NIH HHS / United States