Biology subjects

Nichols, A. E.

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

10 recordsLinked to original sources

bioRxiv2026

Physiological load via voluntary wheel running maintains Achilles tendon homeostasis by region-specific cellular responses

Physiological load is vital for maintaining tendon homeostasis, preserving the organized extracellular matrix that enables tendons to withstand extreme forces. Although tenocytes are regarded as the primary regulators of extracellular matrix production, precisely how cells facilitate the maintenance of homeostasis in response to physiological load is poorly understood. Here, we used Voluntary Wheel Running (VWR) as a model of physiological load to delineate the specific cellular contributions to mouse Achilles tendon homeostasis. Eight weeks of VWR led to a smaller cross-sectional area, increased mechanical and material properties at the midsubstance, which corresponded to a decreased proportion of small (0-60 nm) collagen fibrils and an increased proportion of larger (100-60 nm) collagen fibrils compared to sedentary controls. Using Visium HD spatial transcriptomics, we identified region-specific cell clusters (insertion vs. midsubstance). In response to physiological load, cells in the insertion and midsubstance upregulate distinct genes that reinforce the fibrocartilage interface and collagen-rich tendon matrix, respectively. Notably, Clu, Myoc, and Ccdc80 were upregulated with VWR in the midsubstance, with previously uncharacterized roles in tendon homeostasis. Together, our findings suggest that in response to physiological load, tendon cells maintain homeostasis by region-specific responses. Given that insertional and midsubstance tendinopathy is function-limiting and painful, defining the region-specific cellular responses will be key to advancing therapeutic prospects for tendon health. New and NoteworthyThis study is the first spatially rigorous characterization of the tendon response to physiological load using a Voluntary Wheel Running (VWR) model. VWR led to smaller, stronger, but not stiffer tendons at the midsubstance compared to sedentary controls. This corresponded with significant decreased proportion of small collagen fibrils and a shift toward an increased proportion of large collagen fibrils. Using Visium HD spatial transcriptomics, we identified region-specific transcriptional responses to physiological load that maintain homeostasis. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=67 SRC="FIGDIR/small/722285v1_ufig1.gif" ALT="Figure 1"> View larger version (19K): org.highwire.dtl.DTLVardef@13aa717org.highwire.dtl.DTLVardef@1afe3f1org.highwire.dtl.DTLVardef@9e1137org.highwire.dtl.DTLVardef@17c47bc_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

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↗

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

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

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↗