Tendon Cell Deletion of IKKβ/NF-κB Drives Functionally Deficient Tendon Healing and Altered Cell Survival Signaling In Vivo

Acute tendon injuries are characterized by excessive matrix deposition that impedes regeneration and disrupts functional improvements. Inflammation is postulated to drive pathologic scar tissue formation, with nuclear factor kappa B (NF-{kappa}B) signaling emerging as a candidate pathway in this process. However, characterization of the spatial and temporal activation of canonical NF-{kappa}B signaling during tendon healing in vivo, including identification of the cell populations activating NF-{kappa}B, is currently unexplored. Therefore, we aimed to determine which cell populations activate canonical NF-{kappa}B signaling following flexor tendon repair with the goal of delineating cell-specific functions of NF-{kappa}B signaling during scar mediated tendon healing. Immunofluorescence revealed that both tendon cells and myofibroblasts exhibit prolonged activation of canonical NF-{kappa}B signaling into the remodeling phase of healing. Using cre-mediated knockout of the canonical NF-{kappa}B kinase (IKK{beta}), we discovered that suppression of canonical NF-{kappa}B signaling in Scleraxis-lineage cells increased myofibroblast content and scar tissue formation. Interestingly, Scleraxis-lineage specific knockout of IKK{beta} increased the incidence of apoptosis, suggesting that canonical NF-{kappa}B signaling may be mediating cell survival during tendon healing. These findings suggest indispensable roles for canonical NF-{kappa}B signaling during flexor tendon healing. One Sentence SummaryScleraxis-lineage specific knockdown of persistent canonical IKK{beta}/NF-{kappa}B drives scar formation and apoptotic signaling during flexor tendon healing.