Figure 7: Inhibition of IL-1R1/MyD88 signalling promotes MSC-driven bone regeneration.

(a) Design of the MyD88 inhibitor peptide (α₂PI_1-8-MyD88-I). A fibrin-binding sequence derived from α₂-PI_1-8 (NQEQVSPL, in grey) is followed by a plasmin/matrix metalloproteinase-sensitive sequence (VPMSMRGG, in blue), a membrane translocation sequence (RQIKIWFQNRRMKWKK, in orange) and the MyD88 inhibitor peptide (RDVLPGTCVNS, in red). The peptide is covalently crosslinked into fibrin fibres (in grey) during the natural polymerization process of the matrix via the transglutaminase activity of factor XIIIa. Then, following matrix remodeling, the peptide is released by proteases (represented as scissors), translocates into cells, and ultimately inhibits IL-1R1/MyD88 signalling. (b,c) Critical size calvarial defects (5 mm diameter) in mice were treated with or without MSCs delivered by a fibrin matrix. Fibrin matrices were functionalized with IL-1Ra (1 μg) or α₂PI_1-8-MyD88-I (4 μg). Eight weeks after treatment, bone regeneration was measured by microCT as coverage of the defect and bone volume. Data are means±s.e.m. (n=6 per condition). ANOVA with Bonferroni post hoc test for pair-wise comparisons; **P<0.01, ***P<0.001. Representative calvarial reconstructions are shown in c. Original defect area is shaded with a red dotted outline. ANOVA, analysis of variance.