Altered TGFB1 regulated pathways promote accelerated tendon healing in the superhealer MRL/MpJ mouse

Abstract

To better understand the molecular mechanisms of tendon healing, we investigated the Murphy Roths Large (MRL) mouse, which is considered a model of mammalian tissue regeneration. We show that compared to C57Bl/6J (C57) mice, injured MRL tendons have reduced fibrotic adhesions and cellular proliferation, with accelerated improvements in biomechanical properties. Transcriptional analysis of biological drivers showed positive enrichment of TGFB1 in both C57 and MRL healing tendons. However, only MRL tendons exhibited downstream transcriptional effects of cell cycle regulatory genes, with negative enrichment of the cell senescence-related regulators, compared to the positively-enriched inflammatory and ECM organization pathways in the C57 tendons. Serum cytokine analysis revealed decreased levels of circulating senescence-associated circulatory proteins (SASP) in response to injury in the MRL mice compared to the C57 mice. These data collectively demonstrate altered TGFB1 regulated inflammatory, fibrosis, and cell cycle pathways in flexor tendon repair.

Reparative and Maladaptive Inflammation in Tendon Healing

“…In tendon, latent TGFβ is present in the tendon matrix and is critical for tendon maintenance and regeneration in neonatal mice ( Maeda et al, 2011 ; Kaji et al, 2020 ; Tan et al, 2020 ). However, while it is clear that TGFβ signaling in Scx + tenocytes is critical for tendon healing as well as scar and adhesion formation ( Katzel et al, 2011 ; Goodier et al, 2016 ; Kallenbach et al, 2021 ), it is unclear whether TGFβ released following ECM disruption during injury plays an additional role in immune modulation.…”

Characterization of TGFβ-induced tendon-like structure in scaffold-free three-dimensional tendon cell culture

“…Previous studies suggested that growth factors could be essential for maintaining the engineered tendon constructs (29,31,32). Transforming growth factor beta (Tgf) is one of the well-known growth factors and is critical for tendon development and tenogenic differentiation in vivo and in vitro (16,31,(36)(37)(38)(39)(40)(41)(42)(43). These previous studies prompted us to use Tgf in the 3D tendon culture.…”

Regenerative MRL/MpJ Tendon Cells Exhibit Sex Differences in Morphology, Proliferation, Mechanosensitivity, and Cell-Matrix Remodeling

“…[20][21][22][23][24][25] In particular, our group and others have established that MRL/MpJ mice elicit a scarless healing capacity following acute injury of the patellar, flexor digitorum longus, and supraspinatus tendons compared to those of non-healer C57BL/6 (B6) mice. [20][21][22][23]25,26 We have previously determined using ex vivo organ culture that the local tissue environment rather than systemic contributions (i.e., the immune response) serves as the primary driver of MRL/MpJ (which was not certified by peer review) is the author/funder. All rights reserved.…”

“…[20][21][22][23][24][25] In particular, our group and others have established that MRL/MpJ mice elicit a scarless healing capacity following acute injury of the patellar, flexor digitorum longus, and supraspinatus tendons compared to those of non-healer C57BL/6 (B6) mice. [20][21][22][23]25,26 We have previously determined using ex vivo organ culture that the local tissue environment rather than systemic contributions (i.e., the immune response) serves as the primary driver of MRL/MpJ tendon healing 23 . We have also demonstrated that the administration of decellularized MRL/MpJ tendon injured/provisional ECM and cell-derived soluble factors in vitro shifts B6 cells toward a regenerative cellular phenotype 23,27 , which illustrates the promising utility of isolating constituents of the MRL/MpJ tendon biological environment to guide the development of mechanisticallyinformed therapeutics.…”