Project description:Little is understood about the roles of tendon cells during flexor tendon healing. To better understand tendon cell functions, the Scx-Cre mouse was crossed to the DTR mouse model to facilitate scleraxis lineage cell depletion prior to acute flexor tendon injury and repair. WT (cre-) and experimental (cre+) mice underwent complete transection and repair of the flexor digitorum longus tendon. Repaired tendons were harvested at 14 and 28 days post-repair for bulk RNA-Seq analysis to examine possible mechanisms driving differential healing due to Scx lineage cell depletion.
Project description:Purpose: The goal of this study is to compare transcriptional profiles of flexor tendon healing in wild-type (WT, C57Bl/6J) to superhealer (MRL/MpJ) miceto gain insights in the biological drivers of the tendon injury response between the C57 and MRL mice. Methods: RNA was isolated from patially lacerated or uninjured flexor tendon 7 days post-injury. Results: Transcriptional analysis of biological drivers showed positive enrichment of TGFB1 in both C57 and MRL healing tendons. 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. Conclusions: There is altered TGFB1 regulated inflammatory, fibrosis, and cell cycle pathways in flexor tendon repair.
Project description:Adhesion formation after flexor tendon repair remains a clinical problem. Early postoperative motion after tendon repair has been demonstrated to reduce adhesion formation while increasing tendon strength. It is hypothesized that during mobilization, tendon cells experience mechanical shear forces that alter their biology in a fashion that reduces scar formation but also activates key genes involved in tendon healing. To test this hypothesis, primary intrinsic tenocyte cultures were established from flexor tendons of 20 Sprague-Dawley rats and sheared at 50 rpm (0.41 Pa) using a cone viscometer for 6 and 12 hours. Total RNA was harvested and compared with time-matched unsheared controls using cDNA microarrays and Northern blot analysis. Microarray analysis demonstrated that mechanical shear stress induced an overall "antifibrotic" expression pattern with decreased transcription of collagen type I and collagen type III. Shear stress down-regulated profibrotic molecules in the platelet-derived growth factor, insulin-like growth factor, and fibroblast growth factor signaling pathways. In addition, shear stress induced an overall decrease in transforming growth factor (TGF)-beta signaling pathway molecules with down-regulation of TGF-beta2, TGF-beta3, TGF-RI, and TGF-RII expression. Moreover, sheared tendon cells increased expression of matrix metalloproteinases and decreased expression of tissue inhibitors of metalloproteinase, an expression pattern consistent with an antifibrotic increase in extracellular matrix degradation. However, up-regulation of genes implicated in tendon healing, specifically, vascular endothelial growth factor-A and several bone morphogenetic proteins. Interestingly, the known mechanoresponsive gene, TGF-beta1, also implicated in tendon healing, was differentially up-regulated by shear stress. Northern blot validation of our results for TGF-beta1, TGF-beta2, TGF-beta3, and collagen type I demonstrated direct correlation with microarray data.
Project description:Adhesion formation after flexor tendon repair remains a clinical problem. Early postoperative motion after tendon repair has been demonstrated to reduce adhesion formation while increasing tendon strength. It is hypothesized that during mobilization, tendon cells experience mechanical shear forces that alter their biology in a fashion that reduces scar formation but also activates key genes involved in tendon healing. To test this hypothesis, primary intrinsic tenocyte cultures were established from flexor tendons of 20 Sprague-Dawley rats and sheared at 50 rpm (0.41 Pa) using a cone viscometer for 6 and 12 hours. Total RNA was harvested and compared with time-matched unsheared controls using cDNA microarrays and Northern blot analysis. Microarray analysis demonstrated that mechanical shear stress induced an overall "antifibrotic" expression pattern with decreased transcription of collagen type I and collagen type III. Shear stress down-regulated profibrotic molecules in the platelet-derived growth factor, insulin-like growth factor, and fibroblast growth factor signaling pathways. In addition, shear stress induced an overall decrease in transforming growth factor (TGF)-beta signaling pathway molecules with down-regulation of TGF-beta2, TGF-beta3, TGF-RI, and TGF-RII expression. Moreover, sheared tendon cells increased expression of matrix metalloproteinases and decreased expression of tissue inhibitors of metalloproteinase, an expression pattern consistent with an antifibrotic increase in extracellular matrix degradation. However, up-regulation of genes implicated in tendon healing, specifically, vascular endothelial growth factor-A and several bone morphogenetic proteins. Interestingly, the known mechanoresponsive gene, TGF-beta1, also implicated in tendon healing, was differentially up-regulated by shear stress. Northern blot validation of our results for TGF-beta1, TGF-beta2, TGF-beta3, and collagen type I demonstrated direct correlation with microarray data. Groups of assays that are related as part of a time series. Computed
Project description:Injuries to flexor tendons can be complicated by fibrotic adhesions, which severely impair the function of the hand. Adhesions have been associated with PAI-1, a master suppressor of protease activity including matrix metalloproteinases (MMP). In the present study, we used next generation RNA sequencing (RNA-seq) to assess genome-wide differences in mRNA expression due to PAI-1 deficiency after zone II flexor tendon injury. Ingenuity pathway analysis was used to characterize molecular pathways and biological drivers associated with differentially expressed genes. Analysis of hundreds of overlapping and differentially-expressed genes in PAI-1 knockout and C57Bl/6J mice during tendon healing revealed common and distinct biological processes associated with the regulation of matrix organization, cell cycle, and immune response. Most importantly, we identified the activation of PTEN signaling and the inhibition of FOXO1-associated biological processes as a unique transcriptional signature of the healing tendon in the PAI-1 KO mice. The differences in transcriptomics between the two mouse strains are transcriptionally related to complex cross-talk between PI3K/Akt/mTOR, PKC, and MAPK signaling cascades that drive differences in transcriptional regulation of cell proliferation, survival and senescence, and chronic inflammation as potential drivers of fibrotic healing and adhesions in the C57Bl/6J injured tendons. These transcriptional observations should guide future studies to develop an improved understanding of the biological limitations of tendon healing as the basis for rational design of targeted therapeutics for scar-free regenerative healing of tendon.
Project description:Adhesion formation after flexor tendon repair remains a clinical problem. Early postoperative motion after tendon repair has been demonstrated to reduce adhesion formation while increasing tendon strength. It is hypothesized that during mobilization, tendon cells experience mechanical shear forces that alter their biology in a fashion that reduces scar formation but also activates key genes involved in tendon healing. To test this hypothesis, primary intrinsic tenocyte cultures were established from flexor tendons of 20 Sprague-Dawley rats and sheared at 50 rpm (0.41 Pa) using a cone viscometer for 6 and 12 hours. Total RNA was harvested and compared with time-matched unsheared controls using cDNA microarrays and Northern blot analysis. Microarray analysis demonstrated that mechanical shear stress induced an overall "antifibrotic" expression pattern with decreased transcription of collagen type I and collagen type III. Shear stress down-regulated profibrotic molecules in the platelet-derived growth factor, insulin-like growth factor, and fibroblast growth factor signaling pathways. In addition, shear stress induced an overall decrease in transforming growth factor (TGF)-beta signaling pathway molecules with down-regulation of TGF-beta2, TGF-beta3, TGF-RI, and TGF-RII expression. Moreover, sheared tendon cells increased expression of matrix metalloproteinases and decreased expression of tissue inhibitors of metalloproteinase, an expression pattern consistent with an antifibrotic increase in extracellular matrix degradation. However, up-regulation of genes implicated in tendon healing, specifically, vascular endothelial growth factor-A and several bone morphogenetic proteins. Interestingly, the known mechanoresponsive gene, TGF-beta1, also implicated in tendon healing, was differentially up-regulated by shear stress. Northern blot validation of our results for TGF-beta1, TGF-beta2, TGF-beta3, and collagen type I demonstrated direct correlation with microarray data. Groups of assays that are related as part of a time series. Keywords: time_series_design
Project description:Tendons are composed of a heterogeneous cell environment, with Scleraxis-lineage (ScxLin) cells being the predominant population. Although ScxLin cells are required for maintenance of tendon homeostasis, their functions during tendon healing are unknown. To this end, we first characterized the spatiotemporal dynamics of ScxLin cells during tendon healing, and identified that the overall ScxLin pool continuously expands up to early remodeling healing phase. To better define the function of ScxLin cells during the late proliferative phase of healing, we inducibly depleted ScxLin cells from day 14-18 post-surgery using the Scx-Cre; Rosa-DTR mouse model, with local administration of diphtheria toxin inducing apoptosis of ScxLin cells in the healing tendon. At D28 post-surgery, ScxLin cell depleted tendons (DTRScxLin) had substantial impairments in structure and function, relative to WT, demonstrating the importance of ScxLin cells during tendon healing. Next, bulk RNAseq was utilized to identify the underlying mechanisms that were impaired with depletion and revealed that ScxLin depletion induced molecular and morphological stagnation of the healing process at D28. However, this stagnation was transient, such that by D56 tendon mechanics in DTRScxLin were not significantly different than wildtype repairs. Collectively, these data offer fundamental knowledge on the dynamics and roles of ScxLin cells during tendon healing.
Project description:Platelet-derived growth factor receptor (PDGFR) signaling plays an important role in the embryonic formation of many different tissues. There is a family of PDGF isoforms which signal through the PDGF receptors α (PDGFRα) and β (PDGFRβ). PDGF regulates many key cellular processes of mesenchymal cell function including proliferation, differentiation, migration and extracellular matrix (ECM) synthesis. While PDGF has been used to enhance flexor tendon healing in vivo, its role in postnatal tendon growth has remained largely unexplored. To determine the importance of PDGFR signaling in postnatal tendon growth, we performed pharmacological blockade of PDGFRα and PDGFRβ, and then induced tendon growth via mechanical overload using the hindlimb synergist ablation model. Our hypothesis was that inhibition of PDGFR signaling will restrict normal growth of tendon tissue in response to mechanical loading.
Project description:Partial tendon-to-bone interface (TBI) injuries heal in a mechanically inferior manner and redevelop healthy uninjured tissue morphology. The origin of the cells involved in tendon-to-bone healing remains unknown. We employed a rigorous approach to evaluate if mouse skeletal stem cells (mSSC) play a role in tendon-to-bone healing after partial-injury. Using fluorescence-activated cell sorting we identified that found that they are present within the TBI. Using a TBI-injury rainbow lineage tracing mouse model, we demonstrated that injury-responsive cells within the TBI and calcaneus proliferate polyclonally following partial-tendon injury at the TBI. These injury-responsive clonal cells express skeletal marker SP7. We quantified the differences in mSCC frequency after TBI-injury and found that mSSC respond to injury with a higher frequency and have associated changes in gene expression, with the specific down-regulation of the TGFβ signaling pathway. Exogenous delivery of TGFβ after injury was found to reduce the mSSC response after injury. These findings suggest that mSSC may facilitate tendon-to-bone healing by downregulating TGFβ signaling within the mSSC niche.