Biology subjects

Muscat, S. N.

Publications and source records attributed to Muscat, S. N..

4 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↗

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↗

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↗