NF-κB activation persists into the remodeling phase of tendon healing and promotes myofibroblast survival

Abstract

Although inflammation is necessary during the early phases of tissue repair, persistent inflammation contributes to fibrosis. Acute tendon injuries often heal through a fibrotic mechanism, which impedes regeneration and functional recovery. Because inflammation mediated by nuclear factor κB (NF-κB) signaling is implicated in this process, we examined the spatial, temporal, and cell type–specific activation profile of canonical NF-κB signaling during tendon healing. NF-κB signaling was maintained through all phases of tendon healing in mice, including the remodeling phase, and tenocytes and myofibroblasts from the Scleraxis (Scx) lineage were the predominant populations that retained NF-κB activation into the late stages of repair. We confirmed persistent NF-κB activation in myofibroblasts in human tendon scar tissue. Deleting the canonical NF-κB kinase, IKKβ, in Scx-lineage cells in mice increased apoptosis and the deposition of the matrix protein periostin during the late stages of tendon repair, suggesting that persistent NF-κB signaling may facilitate myofibroblast survival and fibrotic progression. Consistent with this, myofibroblasts in human tendon scar samples displayed enhanced prosurvival signaling compared to control tissue. Together, these data suggest that NF-κB may contribute to fibrotic tendon healing through both inflammation-dependent and inflammation-independent functions, such as NF-κB–mediated cell survival.

Reparative and Maladaptive Inflammation in Tendon Healing

“…Knockdown of NFκB signaling desensitized tenocytes to IL1β insult ( Abraham et al, 2019 ). More directly, deletion of NFκB in mice resulted in increased apoptosis of myofibroblasts indicating NFκB signaling promotes myofibroblast survival ( Best et al, 2020 ). In humans, tenocytes isolated from tendon biopsies 2 to 4 years post-treatment demonstrated increased expression of IL6, IL8, and activated fibroblast marker podoplanin (PDPN) when stimulated with IL1β, in comparison to IL1β-treated healthy controls ( Dakin et al, 2017 ).…”

Defining the activation profile and fate trajectory of adult Scleraxis-lineage cells during tendon healing by combining lineage tracing and spatial transcriptomics

“…Based on these data, and our previous work demonstrating that the broad Scx Lin cell pool (Scx-Cre) contributes to a persistent myofibroblast population 23 , we wanted to better define this population. Given that there are likely on-going ‘additions’ to this overall Scx Lin pool during healing 5 with cells turning on Scx expression at different times post-injury, we aimed to gain a more comprehensive understanding of the relationship between active Scx expression, adult Scx Ai9 cells and myofibroblast fate.…”

Short-Duration RAGE Antagonism Transiently Disrupts Tendon Homeostasis and does not Alter Diabetic Tendon Healing

“…Tendon injury and repair surgery: At 16-weeks of age, mice underwent surgical injury and repair of the flexor digitorum longus (FDL) tendon as previously described [23][24][25] . Briefly, mice received sustained-release buprenorphine (15 to 20 μ g) prior to surgery.…”

“…Functional and biomechanical outcome assessment: Tendon functional outcomes were assessed as previously described 23,[25][26][27][28] . Briefly, hindlimbs were dissected at the knee joint and the proximal end of the FDL tendon was isolated at the myotendinous junction.…”