Tenomodulin is essential for prevention of adipocyte accumulation and fibrovascular scar formation during early tendon healing

Abstract

Tenomodulin (Tnmd) is the best-known mature marker for tendon and ligament lineage cells. It is important for tendon maturation, running performance and has key implications for the resident tendon stem/progenitor cells (TSPCs). However, its exact functions during the tendon repair process still remain elusive. Here, we established an Achilles tendon injury model in a Tnmd knockout (Tnmd−/−) mouse line. Detailed analyses showed not only a very different scar organization with a clearly reduced cell proliferation and expression of certain tendon-related genes, but also increased cell apoptosis, adipocyte and blood vessel accumulation in the early phase of tendon healing compared with their wild-type (WT) littermates. In addition, Tnmd−/− tendon scar tissue contained augmented matrix deposition of biglycan, cartilage oligomeric matrix protein (Comp) and fibronectin, altered macrophage profile and reduced numbers of CD146-positive cells. In vitro analysis revealed that Tnmd−/− TSPCs exhibited significantly reduced migration and proliferation potential compared with that of WT TSPCs. Furthermore, Tnmd−/− TSPCs had accelerated adipogenic differentiation accompanied with significantly increased peroxisome proliferator-activated receptor gamma (Pparγ) and lipoprotein lipase (Lpl) mRNA levels. Thus, our results demonstrate that Tnmd is required for prevention of adipocyte accumulation and fibrovascular scar formation during early tendon healing.

Loss of tenomodulin expression is a risk factor for age‐related intervertebral disc degeneration

“…Photomicrographs were taken on the Observer Z1 microscope equipped with the Axiocam MRm camera (Carl Zeiss). Quantitative histomorphometry was carried out via an automated quantitative image analysis according to algorithms from literature (Hsieh et al, ; Lin et al, ). In brief, using ImageJ (National Institutes of Health), the following algorithm was applied: (a) area of interest was manually designated using the “drawing/selection” tool; (b) “set measurements” for area, integrated density and mean gray value was selected from the analyze menu; and (c) lastly, the corrected total cryosections fluorescence (CTCF) representing the Acan, Col I, Col X, Fmod, Fn, Lum, MMP3, MMP‐9, p65, and Tnmd expression were exported and calculated in Excel (Microsoft) as follows CTCF = media of integrated density − (media of area of selected area × mean fluorescence).…”

“…Photomicrographs were taken on the Observer Z1 microscope equipped with the Axiocam MRm camera (Carl Zeiss). Quantitative histomorphometry was carried out via an automated quantitative image analysis according to algorithms from literature (Hsieh et al, 2016;Lin et al, 2017). In brief, using ImageJ (National Institutes of Health), the following algorithm was applied: (a) area of interest was manually designated using the "drawing/selection" tool; (b) "set measurements" for area, integrated density and mean gray value was selected from the analyze menu;…”

EGR1 Transcription Factor is a Multifaceted Regulator of Matrix Production in Tendons and Other Connective Tissues

“…The cellular basis of tendon fibrosis is not well understood and involves the contribution of intrinsic (tendon sheeths) and extrinsic (circulating cells) cell populations, recently rewiewed by [168]. The molecular basis underlying tendon fibrosis involves the main fibrotic signalling pathway, TGFβ [102], the transmenbrane protein TNMD [169], and the SCX transcription factor [170], which are also the main actors involved in tendon development [9,171,172]. Interestingly, SCX directly regulates the transcription of the Acta2 gene (a fibrotic marker) in cardiac fibrosis [173].…”

Absence of estrogen receptor beta leads to abnormal adipogenesis during early tendon healing by an up‐regulation of PPARγ signalling

“…After fixing in 4% buffered formalin at 4°C for 24 hours followed by 30% sucrose at 4℃ for 24 hours, tendons were dehydrated and embedded in optimal cutting temperature compound (OCT) and processed for longitudinal sections (7 μm). Haematoxylin and eosin (HE) staining was used to examine the histology of Achilles tendon at defected zone and then graded by two blinded investigators to analyse the histological score modified by us based on histological scoring system of Stoll et al given in Table S1 according to Lin et al 23…”