Innate tissue properties drive improved tendon healing in MRL/MpJ and harness cues that enhance behavior of canonical healing cells

Abstract

Development of tendon therapeutics has been hindered by the lack of informative adult mammalian models of regeneration. Murphy Roth's Large (MRL/MpJ) mice exhibit improved healing following acute tendon injuries, but the driver of this regenerative healing response remains unknown. The tissue‐specific attributes of this healing response, despite a shared systemic environment within the mouse, support the hypothesis of a tissue‐driven mechanism for scarless healing. Our objective was to investigate the potential of MRL/MpJ tendon extracellular matrix (ECM)‐derived coatings to regulate scar‐mediated healing. We found that deviations in the composition of key structural proteins within MRL/MpJ vs C57Bl/6 tendons occur synergistically to mediate the improvements in structure and mechanics following a 1‐mm midsubstance injury. Improvement in mechanical properties of healing MRL/MpJ vs C57Bl/6 tendons that were isolated from systemic contributions via organ culture, highlighted the innate tendon environment as the driver of scarless healing. Finally, we established that decellularized coatings derived from early‐deposited MRL/MpJ tendon provisional extracellular matrix (provisional‐ECM), can modulate canonical healing B6 tendon cell behavior by inducing morphological changes and increasing proliferation in vitro. This study supports that the unique compositional cues in MRL/MpJ provisional‐ECM have the therapeutic capability to motivate canonically healing cells toward improved behavior; enhancing our ability to develop effective therapeutics.

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

“…It is also possible that intrinsic genetic differences in the tendon fibroblasts and infiltrating inflammatory cells could explain the dichotomous responses downstream of TGFB1. A third possibility is that the innate tissue properties in the MRL mouse tendon (Paredes et al, 2020) bleomycin induced pulmonary fibrosis is prevented (Shetty et al, 2017) and its absence reduces chronic renal injury (Higgins et al, 2018). Furthermore, the antifibrotic agent used to treat IPF, Pirfenidone, has been shown to induce cell cycle arrest (Ruwanpura et al, 2020, Sun et al, 2018, Usugi et al, 2019.…”

“…Development of fibrotic flexor tendon adhesions, particularly in zone II of the hand (Elliot et al, 2016, Tang et al, 2013), limits their natural gliding function, strength, and intricate joint flexion (Tang, 2013, Tang et al, 2013, Zhou et al, 2017). Recent biological advances in scarless repair of tendon injuries (George et al, 2020, Paredes et al, 2020, Paredes et al, 2018, Freeberg et al, 2019) have begun to elucidate the complex cellular and transcriptional interplay in restoring native tissue properties to injured tendons. For example, previous studies demonstrate that MRL tendon injuries heal to near normal biomechanical properties (Lalley et al, 2015, Arble et al, 2016), have reduced infiltrating immune cells (Lalley et al, 2015), attenuated inflammatory expression (George et al, 2020, Paredes et al, 2018), lower catabolic enzyme activity (Sebastian et al, 2018), heightened MMP activity (George et al, 2020), and improved ECM alignment (Paredes et al, 2020).…”

“…Recent biological advances in scarless repair of tendon injuries (George et al, 2020, Paredes et al, 2020, Paredes et al, 2018, Freeberg et al, 2019) have begun to elucidate the complex cellular and transcriptional interplay in restoring native tissue properties to injured tendons. For example, previous studies demonstrate that MRL tendon injuries heal to near normal biomechanical properties (Lalley et al, 2015, Arble et al, 2016), have reduced infiltrating immune cells (Lalley et al, 2015), attenuated inflammatory expression (George et al, 2020, Paredes et al, 2018), lower catabolic enzyme activity (Sebastian et al, 2018), heightened MMP activity (George et al, 2020), and improved ECM alignment (Paredes et al, 2020). These reports are consistent with our current findings in flexor tendons, but the biological drivers of this regenerative tendon healing phenotype have hitherto not been fully understood.…”

“…Even though uninjured tendon is hypovascular, a recent patellar tendon defect study removed the central third of the patellar tendon from MRL and C57BL/6J (C57) mice and demonstrated that MRL patellar tendons recapitulate near native biomechanical properties (Lalley et al, 2015). More recent studies injured the patellar tendon with a 0.75mm tendon mid-substance biopsy punch and again demonstrated that MRL patellar tendons heal to near native biomechanical properties with an attenuated inflammatory response, heightened MMP activity, and improved ECM alignment (George et al, 2020, Paredes et al, 2020, Paredes et al, 2018). While the MRL enhanced regenerative potential within musculoskeletal tissues may depend on tissue-specificity and injury severity, recent transcriptomic (Podolak-Popinigis et al, 2015, Sebastian et al, 2018), proteomic (Caldwell et al, 2008), and metabolomic (Tseng et al, 2019, Podolak-Popinigis et al, 2015) techniques point to novel mechanistic insights.…”

“…Multifarious studies have identified the Murphy Roth’s Large (MRL/MpJ) mouse as a promising mouse model of mammalian tissue regeneration due to its ability to restore native-like tissue structures and properties within the ear (Clark et al, 1998), skin (Beare et al, 2006), skeletal muscle (Heydemann et al, 2012, Mull et al, 2014, Sinha et al, 2019, Tseng et al, 2019), articular cartilage (Fitzgerald, 2017, Fitzgerald et al, 2008, Leonard et al, 2015, Mak et al, 2016, Rai and Sandell, 2014, Ward et al, 2008), and tendon (George et al, 2020, Lalley et al, 2015, Paredes et al, 2020, Paredes et al, 2018, Sereysky et al, 2013). Originally hypothesized that the immunomodulated systemic environment in MRL mice drove these regenerative phenotypes (Fitzgerald, 2017, Fitzgerald et al, 2008), studies show the necessity of blood flow or vasculature to recapitulate native tissue structures such as skin (Davis et al, 2005), while more avascular tissue injuries such as cartilage demonstrate minimal improvements (Fitzgerald, 2017, Fitzgerald et al, 2008).…”