Delayed Tagging of ED-A Fibronectin-Mimetic Peptide in an RGD-Decorated Synthetic Matrix Induces Fibroblast-to-Myofibroblast Transition

Abstract

Synthetic hydrogels with bioactive ligands have been utilized to develop 3D models to gain mechanistic insight into how discrete extracellular matrix (ECM) cues direct cell fate. While the RGD motif is ubiquitously present in healthy and diseased tissues, the EDGIHEL (EDG) sequence is present only in the extra domain A-containing fibronectin (ED-A FN), which is transiently deposited in the provisional matrix in the wound bed. Here, we explore the potential of covalently tethered EDG in conjunction with RGD to promote fibroblast-to-myofibroblast transition (FMT). Normal human lung fibroblasts (NHLFs) were maintained in bioorthogonally constructed, hyaluronan-based hydrogel (BOHAGel) with tethered RGD ligands. When EDG was introduced on day 0 during cell encapsulation, cellular expression of Toll-like receptor 4 (TLR4) was upregulated, and a pro-inflammatory matrix remodeling response was observed, but myofibroblast differentiation was not detected. To mimic the transition from a healthy to an injured state, we leveraged the temporal tunability of BOHAGel by supplementing cell culture media with trans-cyclooctene (TCO)-tagged EDG after cells were primed in the RGD environment for 8 days. As the TCO species diffused through the hydrogel, EDG was instantaneously coupled to the network through immobilized tetrazine functionalities. Delayed introduction of profibrotic EDG motifs increased mRNA levels of the myofibroblast marker (ACTA2), ECM proteins (COL1A1, COL3A1, FN1), and transforming growth factor beta1 (TGFbeta1) downstream targets (VEGFA, CTGF), as well as matrix remodeling enzymes (MMP2, TIMP1). These changes were accompanied by the formation of alpha-SMA stress fibers, confirming complete FMT. Delayed EDG conjugation also enhanced and reinforced alpha1 integrin expression. Importantly, removing the RGD signal from the gel failed to induce myofibroblast differentiation. Collectively, our results suggest that FMT depends on ligand identities and the timing of their emergence in engineered matrices.