Biology subjects

Loiselle, A. E.

Publications and source records attributed to Loiselle, A. E..

At least 19 recordsLinked to original sources

bioRxiv2024

Loss of Cochlin drives impairments in tendon structure and function

Aging tendons undergo disruptions in homeostasis, increased susceptibility to injury, and reduced capacity for healing. Exploring the mechanisms behind this disruption in homeostasis is essential for developing therapeutics aimed at maintaining tendon health through the lifespan. We have previously identified that the extracellular matrix protein, Cochlin, which is highly expressed in healthy flexor tendon, is consistently lost during both natural aging and upon depletion of Scleraxis-lineage cells in young animals, which recapitulates many aging-associated homeostatic disruptions. Therefore, we hypothesized that loss of Cochlin would disrupt tendon homeostasis, including alterations in collagen fibril organization, and impaired tendon mechanics. By 3-months of age, Cochlin-/- flexor tendons exhibited altered collagen structure, with these changes persisting through at least 9-months. In addition, Cochlin-/- tendons demonstrated significant declines in structural and material properties at 6-months, and structural properties at 9-months. While Cochlin-/- did not drastically change the overall tendon proteome, consistent decreases in proteins associated with RNA metabolism, extracellular matrix production and the cytoskeleton were observed in Cochlin-/-. Interestingly, homeostatic disruption via Cochlin-/- did not impair the tendon healing process. Taken together, these data define a critical role for Cochlin in maintaining tendon homeostasis and suggest retention or restoration of Cochlin as a potential therapeutic approach to retain tendon structure and function through the lifespan.

molecular biology↗

bioRxiv2024

Pharmacological Antagonism of Ccr2+ Cell Recruitment to Facilitate Regenerative Tendon Healing

Successful tendon healing requires sufficient deposition and remodeling of new extracellular matrix at the site of injury, with this process mediating in part through fibroblast activation via communication with macrophages. Moreover, resolution of healing requires clearance or reversion of activated cells, with chronic interactions with persistent macrophages impairing resolution and facilitating the conversion the conversion to fibrotic healing. As such, modulation of the macrophage environment represents an important translational target to improve the tendon healing process. Circulating monocytes are recruited to sites of tissue injury, including the tendon, via upregulation of cytokines including Ccl2, which facilitates recruitment of Ccr2+ macrophages to the healing tendon. Our prior work has demonstrated that Ccr2-/-can modulate fibroblast activation and myofibroblast differentiation. However, this approach lacked temporal control and resulted in healing impairments. Thus, in the current study we have leveraged a Ccr2 antagonist to blunt macrophage recruitment to the healing tendon in a time-dependent manner. We first tested the effects of Ccr2 antagonism during the acute inflammatory phase and found that this had no effect on the healing process. In contrast, Ccr2 antagonism during the late inflammatory/ early proliferative period resulted in significant improvements in mechanical properties of the healing tendon. Collectively, these data demonstrate the temporally distinct impacts of modulating Ccr2+ cell recruitment and Ccr2 antagonism during tendon healing and highlight the translational potential of transient Ccr2 antagonism to improve the tendon healing process.

cell biology↗

bioRxiv2023

Development of a Nanoparticle-Based Tendon-Targeting Drug Delivery System to Pharmacologically Modulate Tendon Healing

Tendon regeneration following acute injury is marred by a fibrotic healing response that prevents complete functional recovery. Despite the high frequency of tendon injuries and the poor outcomes, including functional deficits and elevated risk of re-injury, there are currently no pharmacological therapies in clinical use to enhance the healing process. Several promising pharmacotherapies have been identified; however, systemic treatments lack tendon specificity, resulting in poor tendon biodistribution and perhaps explaining the largely limited beneficial effects of these treatments on the tendon healing process. To address this major unmet need, we leveraged our existing spatial transcriptomics dataset of the tendon healing process to identify an area of the healing tendon that is enriched for expression of Acp5. Acp5 encodes tartrate-resistant acid phosphatase (TRAP), and we demonstrate robust TRAP activity in the healing tendon. This unexpected finding allowed us to refine and apply our existing TRAP binding peptide (TBP) functionalized nanoparticle (NP) drug delivery system (DDS) to facilitate improved delivery of systemic treatments to the healing tendon. To demonstrate the translational potential of this drug delivery system, we delivered the S100a4 inhibitor, Niclosamide to the healing tendon. We have previously shown that genetic knockdown of S100a4 enhances tendon healing. While systemic delivery of Niclosamide did not affect the healing process, relative to controls, TBP-NP delivery of Niclosamide enhanced both functional and mechanical outcome measures. Collectively, these data identify a novel tendon-targeting drug delivery system and demonstrate the translational potential of this approach to enhance the tendon healing process.

bioengineering↗

bioRxiv2023

Identification of Periostin as a critical niche for myofibroblast dynamics and fibrosis during tendon healing

Tendon injuries are a major clinical problem, with poor patient outcomes caused by abundant scar tissue deposition during healing. Myofibroblasts play a critical role in the initial restoration of structural integrity after injury. However, persistent myofibroblast activity drives the transition to fibrotic scar tissue formation. As such, disrupting myofibroblast persistence is a key therapeutic target. While myofibroblasts are typically defined by the presence of SMA+ stress fibers, SMA is expressed in other cell types including the vasculature. As such, modulation of myofibroblast dynamics via disruption of SMA expression is not a translationally tenable approach. Recent work has demonstrated that Periostin-lineage (PostnLin) cells are a precursor for cardiac fibrosis-associated myofibroblasts. In contrast to this, here we show that PostnLin cells contribute to a transient SMA+ myofibroblast population that is required for functional tendon healing, and that Periostin forms a supportive matrix niche that facilitates myofibroblast differentiation and persistence. Collectively, these data identify the Periostin matrix niche as a critical regulator of myofibroblast fate and persistence that could be targeted for therapeutic manipulation to facilitate regenerative tendon healing.

cell biology↗

bioRxiv2023

Epitenon-derived cells comprise a distinct progenitor population that contributes to both tendon fibrosis and regeneration following acute injury

Flexor tendon injuries are common and heal poorly owing to both the deposition of function-limiting peritendinous scar tissue and insufficient healing of the tendon itself. Therapeutic options are limited due to a lack of understanding of the cell populations that contribute to these processes. Here, we identified the epitenon as a major source of cells that contribute to both peritendinous fibrosis and regenerative tendon healing following acute tendon injury. Using a combination of genetic lineage tracing and single cell RNA-sequencing (scRNA-seq), we profiled the behavior and contributions of each cell fate to the healing process in a spatio-temporal manner. Integrated scRNA-seq analysis of mouse healing with human peritendinous scar tissue revealed remarkable transcriptional similarity between mouse epitenon-derived cells and fibroblasts present in human peritendinous scar tissue, which was further validated by immunofluorescent staining for conserved markers. Finally, ablation of pro-fibrotic epitenon-derived cells post-tendon injury significantly improved functional recovery. Combined, these results clearly identify the epitenon as the cellular origin of an important progenitor cell population that could be leveraged to improve tendon healing.

cell biology↗

bioRxiv2023

Increased Ca2+ signaling through CaV1.2 induces tendon hypertrophy with increased collagen fibrillogenesis and biomechanical properties

Tendons are tension-bearing tissues transmitting force from muscle to bone for body movement. This mechanical loading is essential for tendon development, homeostasis, and healing after injury. While Ca2+ signaling has been studied extensively for its roles in mechanotransduction, regulating muscle, bone and cartilage development and homeostasis, knowledge about Ca2+ signaling and the source of Ca2+ signals in tendon fibroblast biology are largely unknown. Here, we investigated the function of Ca2+ signaling through CaV1.2 voltage-gated Ca2+ channel in tendon formation. Using a reporter mouse, we found that CaV1.2 is highly expressed in tendon during development and downregulated in adult homeostasis. To assess its function, we generated ScxCre;CaV1.2TS mice that express a gain-of-function mutant CaV1.2 channel (CaV1.2TS) in tendon. We found that tendons in the mutant mice were approximately 2/3 larger and had more tendon fibroblasts, but the cell density of the mutant mice decreased by around 22%. TEM analyses demonstrated increased collagen fibrillogenesis in the hypertrophic tendon. Biomechanical testing revealed that the hypertrophic Achilles tendons display higher peak load and stiffness, with no changes in peak stress and elastic modulus. Proteomics analysis reveals no significant difference in the abundance of major extracellular matrix (ECM) type I and III collagens, but mutant mice had about 2-fold increase in other ECM proteins such as tenascin C, tenomodulin, periostin, type XIV and type VIII collagens, around 11-fold increase in the growth factor of TGF-{beta} family myostatin, and significant elevation of matrix remodeling proteins including Mmp14, Mmp2 and cathepsin K. Taken together, these data highlight roles for increased Ca2+ signaling through CaV1.2 on regulating expression of myostatin growth factor and ECM proteins for tendon collagen fibrillogenesis during tendon formation.

molecular biology↗

bioRxiv2022

The Micromechanical Environment of the Impinged Achilles Tendon Insertion

Mechanical deformation applied to tendon at the tissue-scale is transferred to the microscale -- including the extracellular matrix (ECM), the pericellular matrix (PCM), the cell and the nucleus -- through a process known as strain transfer. Microscale strains, in turn, trigger biological activity that plays an important role in the maintenance of tendon phenotype and homeostasis. Although tendon predominantly experiences longitudinal tensile forces, transverse forces due to bony impingement have been implicated in both physiological (e.g., maintenance of the tendon insertion) and pathophysiological (e.g. insertional Achilles tendinopathy) processes. However, to our knowledge, prior studies have not characterized the micromechanical strain environment in the context of tendon impingement. Therefore, the objective of this study was to characterize the micromechanical strain environment in the impinged Achilles tendon insertion using a novel mouse hindlimb explant model in combination with finite element (FE) modeling. We hypothesized that impingement would generate large magnitudes of transverse compressive strain at the local matrix, PCM, and cell scales. Mouse hindlimb explants were imaged on a multiphoton microscope, and image stacks of the same population of tendon cells were obtained at the Achilles tendon insertion before and after dorsiflexion-induced impingement. Using an innovative multiphoton elastography approach, three-dimensional Green-Lagrange and principal strains were measured at the matrix scale, while longitudinal strain and aspect ratio were measured at the PCM and cell scales. Our results demonstrate that impingement generated substantial transverse compression at the matrix-scale, which led to longitudinal stretching of cells, an increase in cell aspect ratio, and -- surprisingly -- longitudinal compression of the tendon PCM. These experimental results were corroborated by an FE model developed to simulate the micromechanical environment in impinged regions of the Achilles tendon. Moreover, in both experiments and simulations, impingement-generated microscale stresses and strains were highly dependent on initial cell-cell gap spacing. Understanding the factors that influence the microscale strain environment generated by impingement could contribute to a more mechanistic understanding of impingement-induced tendinopathies and inform the development of approaches that disrupt the progression of pathology.

bioengineering↗

bioRxiv2022

CCR2 identifies tendon resident macrophage and T cell populations while CCR2 deficiency impedes late tendon healing

During tendon healing, macrophages are thought to be a key mediator of scar tissue formation, which prevents successful functional restoration of the tendon. However, macrophages are critical for successful tendon healing as they aid in wound debridement, extracellular matrix deposition, and promote fibroblast proliferation. Recent work has sought to better define the multi-faceted functions of macrophages using depletion studies, while other studies have identified a tendon resident macrophage population. To begin to delineate the functions of tendon-resident versus circulation-derived macrophages, we examined the tendon healing phenotype in Chemokine Receptor 2 (CCR2) reporter (CCR2GFP/+), and knockout mice. CCR2 is a chemokine receptor primarily found on the surface of circulating bone marrow derived monocytes, with CCR2 being an important mediator of macrophage recruitment to wound environments. Surprisingly, CCR2GFP/+ cells were present in the tendon during adult homeostasis, and single cell RNA sequencing identified these cells as tendon-resident macrophages and T cells. During both homeostasis and healing, CCR2 knockout resulted in a substantial decrease in CCR2GFP+ cells and pan-macrophages. Additionally, loss of CCR2 resulted in reduced numbers of myofibroblasts and impeded functional recovery during late healing. This study highlights the heterogeneity of tendon-resident and recruited immune cells and their contributions following injury, and establishes an important role for CCR2 in modulating both the adult tendon cell environment and tendon healing process.

cell biology↗

bioRxiv2022

A Murine Model of Abductor Insufficiency Accelerates the Development of Hip Osteoarthritis

Osteoarthritis (OA) of the hip is a common and debilitating painful joint disease. A growing body of evidence suggests that there may be an association between periarticular myotendinous pathology and the development of hip OA. Thus, we hypothesized that a murine model of hip OA could be achieved through selective injury of the abductor complex around the hip. C57BL6/J mice were randomized to sham surgery or abductor injury, in which the myotendinous insertion at the third trochanter and greater trochanter were surgically detached. Mice were allowed free, active movement until sacrifice at either 3 weeks or 20 weeks post-injury. Histologic analyses and immunohistochemical staining (IHC) of the femoral head articular cartilage were performed, along with CT analysis to assess subchondral bone remodeling. We observed that mice receiving abductor injury exhibited significant OA severity with loss of Type II Collagen staining compared to sham control mice at 20 weeks post-surgery, comparable MMPI13 expression was observed between injury and sham groups. No significant differences in subchondral bone were found on CT after 20 weeks following injury. Our study suggests a link between abductor dysfunction and the development of hip OA, which are common pathomorphologies encountered in routine orthopaedic clinical practice. Further, this novel animal model may provide a valuable tool for future investigations into the pathogenesis and treatment of hip OA.

pathology↗

bioRxiv2022

Inducible depletion of Scleraxis-lineage cells during tendon healing impairs multi-scale restoration of tendon structure

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 (DTR) 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 DTR were not significantly different than wildtype repairs. Collectively, these data offer fundamental knowledge on the dynamics and roles of ScxLin cells during tendon healing.

cell biology↗

bioRxiv2022

Depletion of Scleraxis-lineage cells accelerates tendon ECM aging and promotes retention of a specialized remodeling tenocyte population that drives enhanced tendon healing

Aged tendons have disrupted homeostasis, increased injury risk, and impaired healing capacity. Understanding mechanisms of homeostatic disruption is crucial for developing therapeutics to retain tendon health through the lifespan. Here, we developed a novel model of accelerated tendon extracellular matrix (ECM) aging via depletion of Scleraxis-lineage (ScxLin) cells in young mice (DTR). DTR recapitulates many aspects of tendon aging including comparable declines in cellularity, alterations in ECM structure, organization, and composition. Single cell RNA-sequencing demonstrated a conserved decline in tenocytes associated with ECM biosynthesis in aged and DTR tendons, identifying the requirement for ScxLin cells during homeostasis. However, the remaining cells in aged and DTR tendons demonstrate functional divergence. Aged tenocytes become pro-inflammatory and lose proteostasis. In contrast, DTR tenocytes demonstrate enhanced remodeling capacity. Collectively, this study defines DTR a novel model of accelerated tendon ECM aging and identifies novel biological intervention points to maintain tendon function through the lifespan.

cell biology↗

bioRxiv2021

Characterization of scar tissue biomechanics during adult murine flexor tendon healing

Tendon injuries are very common and result in significant impairments in mobility and quality of life. During healing, tendons produce a scar at the injury site, characterized by abundant and disorganized extracellular matrix and by permanent deficits in mechanical integrity compared to healthy tendon. Although a significant amount of work has been done to understand the healing process of tendons and to develop potential therapeutics for tendon regeneration, there is still a significant gap in terms of assessing the direct effects of therapeutics on the functional and material quality specifically of the scar tissue, and thus, on the overall tendon healing process. In this study, we focused on characterizing the mechanical properties of only the scar tissue in flexor digitorum longus (FDL) tendons during the proliferative and remodeling healing phases and comparing these properties with the mechanical properties of the composite healing tissue. Our method was sensitive enough to identify significant differences in structural and material properties between the scar and tendon-scar composite tissues. To account for possible inaccuracies due to the small aspect ratio of scar tissue, we also applied inverse finite element analysis (iFEA) to compute mechanical properties based on simulated tests with accurate specimen geometries and boundary conditions. We found that the scar tissue linear tangent moduli calculated from iFEA were not significantly different from those calculated experimentally at all healing timepoints, validating our experimental findings, and suggesting the assumptions in our experimental calculations were accurate. Taken together, this study first demonstrates that due to the presence of uninjured stubs, testing composite healing tendons without isolating the scar tissue overestimates the material properties of the scar itself. Second, our scar isolation method promises to enable more direct assessment of how different treatment regimens (e.g., cellular ablation, biomechanical and/or biochemical stimuli, tissue engineered scaffolds) affect scar tissue function and material quality in multiple different types of tendons.

bioengineering↗

bioRxiv2021

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

The tendon healing process is regulated by the coordinated interaction of multiple cell types and molecular processes. However, these processes are not well-defined leading to a paucity of therapeutic approaches to enhance tendon healing. Scleraxis-lineage (ScxLin) cells are the major cellular component of adult tendon and make time-dependent contributions to the healing process. Prior work from our lab and others suggests heterogeneity within the broader ScxLin population over the course of tendon healing; therefore delineating the temporal and spatial contributions of these cells is critical to understanding and improving the healing process. In the present study we utilize lineage tracing of the adult aScxLin population to determine whether these cells undergo cellular activation and subsequent myofibroblast differentiation, which is associated with both proper healing and fibrotic progression in many tissues. We show that adult aScxLin cells undergo transient activation in the organized cellular bridge at the tendon repair site, contribute to the formation of an organized neotendon, and contribute to a persistent myofibroblast population in the native tendon stubs. The mechanisms dictating this highly specialized spatial response are unknown. We therefore utilized spatial transcriptomics to better define the spatio-molecular program of tendon healing. Integrated transcriptomic analyses across the healing time-course identifies five distinct molecular regions, including key interactions between the inflammatory bridging tissue and highly reactive tendon tissue at the repair site, with adult ScxLin cells being a central player in the transition from native tendon to reactive, remodeling tendon. Collectively, these data provide important insights into both the role of adult ScxLin cells during healing as well as the molecular mechanisms that underpin and coordinate the temporal and spatial healing phenotype, which can be leveraged to enhance the healing process.

bioinformatics↗

bioRxiv2021

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

Obesity and type II Diabetes Mellitus (T2DM) have substantial pathological effects on tendon homeostasis, including loss of collagen organization and increased risk of tendon rupture. Moreover, following rupture or acute injury, the healing process is impaired by T2DM. We have previously demonstrating that restoring normal metabolic function in a murine model of obesity/ T2DM is insufficient to blunt or reverse the progression of diabetic tendinopathy, indicating the need for identification of novel therapeutic approaches to both maintain tendon homeostasis, and to improve the healing process. RAGE, the Receptor for Advanced Glycation Endproducts has been implicated as a key driver of several diabetic pathologies. We have demonstrated that pharmacological antagonism of RAGE is sufficient to partially improve tendon healing in non-diabetic animals. Therefore, in the current study we tested the efficacy of blunted RAGE signaling, via treatment with a RAGE Antagonist Peptide (RAP), to improve tendon healing in the context of T2DM. While our study did not find a beneficial effect of short-term RAP treatment on the healing process of T2DM mice, we did identify several important challenges brought about by this model of diet-induced obesity and T2DM. Both high fat (HFD) and low fat diet (LFD) feeding shifted the temporal molecular profile of healing compared to standard laboratory chow fed mice. Moreover, RAP treatment resulted in a transient disruption in homeostasis in the contralateral control tendons of both HFD and LFD mice, and this was due to a potential interaction with the systemic response to tendon injury as this response was not observed in HFD and LFD fed mice that did not undergo tendon repair surgery. Collectively, these data highlight the complications associated with models of diet induced obesity, and the lean control diets that should be considered in future studies.

pathology↗

bioRxiv2021

Impact of isolation method on cellular activation and presence of specific tendon cell subpopulations during in vitro culture

Tendon injuries are common and heal poorly, due in part to a lack of understanding of fundamental tendon cell biology. A major impediment to the study of tendon cells is the absence of robust, well-characterized in vitro models. Unlike other tissue systems, current tendon cell models do not account for how differences in isolation methodology may affect the activation state of tendon cells or the presence of various tendon cell sub-populations. The objective of this study was to characterize how common isolation methods affect the behavior, fate, and lineage composition of tendon cell cultures. Tendon cells isolated by explant exhibited reduced proliferative capacity, decreased expression of tendon marker genes, and increased expression of genes associated with fibroblast activation compared to digested cells. Consistently, explanted cells also displayed an increased propensity to differentiate to myofibroblasts compared to digested cells. Explanted cultures from multiple different tendons were substantially enriched for the presence of scleraxis-lineage (Scx-lin+) cells compared to digested cultures, while the overall percentage of S100a4-lineage (S100a4-lin+) cells was dependent on both isolation method and tendon of origin. Neither isolation method preserved the ratios of Scx-lin+ or S100a4-lin+ to non-lineage cells seen in tendons in vivo. Combined, these data indicate that further refinement of in vitro cultures models is required in order to more accurately understand the effects of various stimuli on tendon cell behavior. Statement of clinical significanceThe development of informed in vitro tendon cell models will facilitate enhanced screening of potential therapeutic candidates to improve tendon healing.

cell biology↗

bioRxiv2021

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

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.

cell biology↗

bioRxiv2020

Tendon Cell Deletion of IKKβ/NF-κB Drives Functionally Deficient Tendon Healing and Altered Cell Survival Signaling In Vivo

Acute tendon injuries are characterized by excessive matrix deposition that impedes regeneration and disrupts functional improvements. Inflammation is postulated to drive pathologic scar tissue formation, with nuclear factor kappa B (NF-{kappa}B) signaling emerging as a candidate pathway in this process. However, characterization of the spatial and temporal activation of canonical NF-{kappa}B signaling during tendon healing in vivo, including identification of the cell populations activating NF-{kappa}B, is currently unexplored. Therefore, we aimed to determine which cell populations activate canonical NF-{kappa}B signaling following flexor tendon repair with the goal of delineating cell-specific functions of NF-{kappa}B signaling during scar mediated tendon healing. Immunofluorescence revealed that both tendon cells and myofibroblasts exhibit prolonged activation of canonical NF-{kappa}B signaling into the remodeling phase of healing. Using cre-mediated knockout of the canonical NF-{kappa}B kinase (IKK{beta}), we discovered that suppression of canonical NF-{kappa}B signaling in Scleraxis-lineage cells increased myofibroblast content and scar tissue formation. Interestingly, Scleraxis-lineage specific knockout of IKK{beta} increased the incidence of apoptosis, suggesting that canonical NF-{kappa}B signaling may be mediating cell survival during tendon healing. These findings suggest indispensable roles for canonical NF-{kappa}B signaling during flexor tendon healing. One Sentence SummaryScleraxis-lineage specific knockdown of persistent canonical IKK{beta}/NF-{kappa}B drives scar formation and apoptotic signaling during flexor tendon healing.

molecular biology↗

bioRxiv2020

Development of a Murine Model of Pyogenic Flexor Tenosynovitis

BackgroundTo demonstrate the plausibility of a murine model of pyogenic flexor tenosynovitis. Methods2L of sterile PBS or bioluminescent Xen29 Staphylococcus aureus was administered to the tendon sheath of 36 male C57BL/6J mice. The infectious course was monitored by bioluminescence (BLI) signal via IVIS imaging and recording of weight change. The infected hind paws were harvested at four time points: 24 hours, 72 hours, 1 week and 2 weeks for histopathology using Alcian Blue hematoxylin staining. Two-way ANOVA with Sidaks multiple comparison test was used for statistical analysis. ResultsThe infected cohort displayed significantly elevated bioluminescent values, reductions in weight, and exhibited swelling of the infected digit throughout the course of infection. By day 7 most infected mice saw a substantial decrease in BLI signal intensity, however two infected mice exhibited persistent BLI intensity through day 14. Histopathology of the infected cohort showed tissue disorganization and the presence of a cellular infiltrate in and around the flexor tendon sheath. ConclusionsA murine model of pyogenic flexor tenosynovitis is possible. Further optimization of the model offers an experimental platform for investigation of the pathophysiology of pyogenic flexor tenosynovitis. Clinical RelevanceThis animal model can be utilized in order to elucidate the basic molecular/cellular mechanisms of pyogenic flexor tenosynovitis while simultaneously evaluating novel therapeutic strategies.

pathology↗