Inflammation and immunomodulation related to materials and extracellular vesicles

Abstract

Cell-to-cell communication is a fundamental process at the implant–tissue interface. This communication is shaped by implant properties or by extracellular vesicles (EVs) that transfer regulatory cargo between cells. However, the influence of macrophage-derived EVs at the implant-tissue interface is not understood. This thesis investigated (1) the cellular and molecular changes by gas bubbles generated during magnesium implant degradation in a rat soft tissue model, (2) how macrophage-derived EVs modulate inflammation and immunity (i) in mesenchymal stem cells (MSCs) in vitro, and (ii) at the titanium implant–tissue interface in vivo. In the magnesium implant soft tissue model, bubbles altered cell morphology and mechanosensation, activated interferon regulatory factor-7 (IRF7)-mediated inflammation and cytoskeletal pathways as mapped by spatial transcriptomics, and induced distance-dependent transcriptional and protein changes relative to the implant interface. In vitro, the EV microRNA cargo from M1 versus M2 macrophages were involved in the activation of pathways such as toll-like receptor (TLR) signaling, inducible nitric oxide synthase (iNOS) signaling and macrophage classical activation signaling. MSCs exposed to macrophage EVs increased their expression of inflammatory mediators, such as interleukins (-6 and -1 beta). MSCs also efficiently internalized M1 EVs and exhibited a strong expression of IRF7 at the gene and protein levels, independently of lipopolysaccharide treatment. In the EV rat soft tissue model, the density and viability of cells at the titanium implant interface remained unchanged upon EV administration. However, M1 EVs promoted the infiltration of polymorphonuclear cells after 1 d, while both M1 and M2 EVs increased multinuclear giant cell formation after 21 d. Cells at the implant interface internalized M1 EVs more readily, with a higher expression of Irf7. By contrast, M2 EVs increased the expression of the fibrotic marker collagen 1a1 (Col1a1) and promoted a thicker peri-implant fibrous capsule formation compared with Ti and M1 EVs. Together, bubbles from magnesium implants orchestrate a complex local response, which modulates the peri-implant tissue healing. MSCs and the titanium implant-tissue interface exhibit macrophage phenotype-dependent immunomodulation: M1 EVs encourage a pro-inflammatory, yet transient state, whereas M2 EVs promote a less inflammatory but pro-fibrotic tissue response. The specific cargo of macrophage-derived EVs underpins these modulatory effects with opportunities for EV-based therapeutics at implant sites.