hyaluronic acid networks in wound healing

Abstract

Regeneration is the process by which an organism fully restores the form and function of damaged tissues. Mammals, however, have a limited capacity for regeneration, and the mechanisms underlying incomplete or abnormal healing are poorly understood. Diseases that hinder regeneration in humans often involve an abnormal accumulation of extracellular matrix (ECM)–a network of molecules occupying the space outside of cells. Beyond structural support, the ECM plays a crucial role in directing cell behavior through biomechanical and biochemical signals. However, the very process of wound healing can compromise the integrity of the ECM, potentially impairing tissue repair. Gaining a deeper understanding of the ECM’s role in both successful regeneration and dysregulated wound repair could provide valuable insights for developing therapeutic strategies that enhance wound healing. Here, two models of regeneration were investigated: digit amputation and femoral bone fracture. Using single-cell transcriptomics, major fibroblast subtypes were identified during wound healing that synthesize key ECM components, namely hyaluronic acid (HA) and associated proteins. In digits, these ECM networks were upregulated in regeneration, and their knockdown markedly impaired healing and enhanced deposition of collagen. Atomic force microscopy revealed that HA networks are important determinants of the mechanical properties of tissues, and culturing fibroblasts on stiffness-tunable hydrogels showed the impact of mechanical stress on responses to cytokine signaling. Importantly, I demonstrated that stabilization of HA networks can promote wound healing. Then, to study fracture healing, I first coupled genetic cell-labeling with single-cell transcriptomics to characterize bone marrow stromal cells, a subset of which were putative perivascular progenitor cells. I revealed that different perivascular cell sub-types in the bone marrow perform distinct roles in maintaining the niche, including mediating the extracellular milieu. HA biosynthesis pathways were upregulated among cells highly expressing ECM genes. After a fracture injury, these perivascular cells were activated, and HA accumulated at the injury site through mechanisms that were distinct from digit regeneration. Lastly, I showed that aged mice lose their ability to mount a robust HA response, which may explain the reduced fracture healing capacity in the elderly. Altogether, these studies have informed ongoing experiments aimed at augmenting wound healing by stabilizing HA networks.