Biology subjects

Snedeker, J. G.

Publications and source records attributed to Snedeker, J. G..

10 recordsLinked to original sources

bioRxiv2025

Matrix maturation and cytoskeletal tension define strain thresholds for stretch-induced calcium signaling in human tendon cells

The extracellular matrix (ECM) and mechanical loading shape cellular behavior, yet their interaction remains obscure. We developed a dynamic proto-tissue model using human tendon cells and live-cell calcium imaging to study how ECM and cell mechanics regulate mechanotransduction. Stretch-induced calcium signaling served as a functional readout. We discovered that ascorbic acid-dependent ECM deposition is essential for proto-tissue maturation and stretch-induced calcium signaling at physiological strains. Proto-tissue maturation enhanced stretch sensitivity, reducing the strain needed to trigger a calcium response from [~]40% in isolated cells to [~]5% in matured proto-tissues. A strong correlation between tissue rupture and calcium signaling suggests a mechanistic link to ECM damage. Disrupting ECM integrity, cell alignment, or cytoskeletal tension reduced mechanosensitivity, showcasing the influence of ECM and cytoskeletal mechanics on stretch-induced calcium signaling. Fundamentally, our work replicates calcium signaling observed in rodent tendon explants in vitro and bridges the gap between cell-scale and tissue-scale mechanotransduction. TeaserMatrix matters: tendon cells tune their response to stretch as their mechanical environment develops.

bioengineering↗

bioRxiv2025

Filamented Light (FLight) Biofabrication of Mini-Tendon Models Show Tunable Matrix Confinement and Nuclear Morphology

One hallmark of healthy tendon tissue is the high confinement of tenocytes between tightly packed, highly aligned collagen fibers. During tendinopathy, this organization becomes dysregulated, leading to cells with round-shaped morphology and collagen fibers which exhibit crimping and misalignment. The elongated nuclei in healthy tendons are linked to matrix homeostasis through distinct mechanotransduction pathways, and it is believed that the loss of nuclear confinement could upregulate genes associated with abnormal matrix remodeling. Replicating the cell and nuclear morphology of healthy and diseased states of tendon, however, remains a significant challenge for engineered in vitro tendon models. Here we report on a high throughput biofabrication of mini-tendons that mimick the tendon core compartment based on the Filamented Light (FLight) approach. Each mini-tendon, with a length of 4 mm, was composed of parallel hydrogel microfilaments (2-5 {micro}m diameter) and microchannels (2-10 {micro}m diameter) that confined the cells. We generated four distinct matrices with varying stiffness (7-40 kPa) and microchannel dimensions. After 14 days of culture, 29% of tenocytes in the softest matrix with the largest microchannel diameter were aligned, exhibiting an average nuclear aspect ratio (nAR) of 2.1. In contrast, 84% of tenocytes in the stiffest matrix with the smallest microchannel diameter were highly aligned, with a mean nAR of 3.4. When tenocytes were cultured on the FLight hydrogels (2D) as opposed to within the hydrogels (3D), the mean nAR was less than 1.9, indicating that nuclear morphology is significantly more confined in 3D environments. By tuning the stiffness and microarchitecture of the FLight matrix, we demonstrated that mechanical confinement can be modulated to exert control over the extent of nuclear confinement. This high-throughput, tunable platform offers a promising approach for studying the mechanobiology of healthy and diseased tendons and for eventual testing of drug compounds against tendinopathy.

bioengineering↗

bioRxiv2025

HIF1α gates tendon response to overload and drives tendinopathy independently of vascular recruitment

Tendons are mostly avascular dense connective tissues that link muscles to bones, withstanding some of the highest mechanical stresses in the body. Mechanical overload and tissue hypervascularity are implicated in tendinopathy, a common musculoskeletal disorder, but mechanistic understanding of their roles is largely lacking. Here, we identify HIF1 not only as a marker but as a driver of tendinopathy. Initial histological and multi-omics evaluation of human tendinopathic samples revealed extensive extracellular matrix remodeling, including pathological collagen crosslinking coinciding with active hypoxic signaling. Hypothesizing a causal contribution of hypoxia signaling, we generated mice with tenocyte-targeted deletions of the Von Hippel-Lindau (VHL) gene, which controls hypoxia signaling by regulating HIF degradation. We demonstrated that VHL inactivation suffices to induce pathological hallmarks of tendinopathy, such as collagen matrix disorganization, crosslinking, altered mechanics and neuro-vascular ingrowth. This phenotype was HIF1-dependent, since co-deleting HIF1 rescued tendon morphology and mechanics. Moreover, deleting vascular endothelial growth factor A (VEGFA) alongside VHL effectively decoupled the effects of vascular ingrowth from persistently aberrant extracellular matrix remodeling and mechanical dysfunction, emphasizing a direct role of HIF1 in driving tendon disease that is independent of angiogenesis. Mechanistically, we linked tendon mechanical overload to the onset of HIF1 signaling in primary cultured human tendon cells. Furthermore, genetically removing HIF1 from tenocytes prevented aberrant tendon remodeling in response to chronic overload. These findings position HIF1 signaling as a central driver of tendinopathy that acts through a maladaptive tissue response to chronic overload, providing mechanistic insights that could be leveraged for improved therapeutic approaches. One Sentence SummaryHIF1 activation promotes tendinopathy and its inhibition prevents overload-induced maladaptation, suggesting therapeutic potential.

cell biology↗

bioRxiv2023

IL-6 SIGNALING EXACERBATES HALLMARKS OF CHRONIC TENDON DISEASE BY STIMULATING PROGENITOR PROLIFERATION & MIGRATION TO DAMAGE.

Tendinopathies are debilitating diseases currently increasing in prevalence and associated costs. There is a need to deepen our understanding of the underlying cell signaling pathways to unlock effective treatments. In this work, we screen cell signaling pathways in human tendinopathies and find positively enriched IL-6/JAK/STAT signaling alongside signatures of cell populations typically activated by IL-6 in other tissues. In human tendinopathic tendons, we also confirm the strong presence and co-localization of IL-6, IL6R, and CD90, an established marker of reparative fibroblasts. To dissect the underlying causalities, we combine IL-6 knock-out mice with an explant-based assembloid model of tendon damage to successfully connect IL-6 signaling to reparative fibroblast activation and recruitment. Vice versa, we show that these reparative fibroblasts promote the development of tendinopathy hallmarks in the damaged explant upon IL-6 activation. We conclude that IL-6 activates tendon fibroblast populations which then initiate and deteriorate tendinopathy hallmarks.

bioengineering↗

bioRxiv2021

Sustained mechanical tension governs fibrogenic activation of tendon stromal cells in systemic sclerosis

Fibrosis is a pathological outcome of aberrant repair responses in systemic sclerosis and affects many tissues, including tendons. Progressive matrix stiffening is a key feature of this pathological remodeling. How dysregulated tissue mechanics contribute to the persistence of the fibrotic phenotype has been obscured by limited availability of experimental tissue models that are both controllable and capture essential aspects of the tendon biophysical niche. Here, we developed a modular, cantilever-based platform that allows culture of 3D tendon-like constructs under easily variable static tension, emulating this central tendon-specific structure function relationship. The system reveals that elevated matrix tension instigates fibroblast-to-myofibroblast activation eliciting scar-like phenotypes in vitro. By using this mechano-culture system and preclinical and clinical models of systemic sclerosis, we further show that 3D matrix stiffness is inversely correlated with the transcription of major pro-fibrotic collagens, but positively correlate with the expression of markers of stromal-immune interactions. Co-culture of tendon stromal fibroblasts and bone marrow-derived macrophages override stiffness-mediated downregulation of matrix transcription, suggesting that normal tension mediated checkpoints are superseded by the local tissue immune state. Our study highlights the power of 3D reductionist approaches in dissecting the contribution of the elevated matrix tension to the positive feedforward loops between activated fibroblasts and progressive ECM stiffening in systemic sclerosis.

cell biology↗

bioRxiv2021

The stiffness-sensitive transcriptome of human tendon stromal cells

Matrix stiffness and its effects on tensional homeostasis act as major regulators of cellular states in health and disease. Stiffness-sensing studies are typically performed using cells that have acquired "mechanical memory" through prolonged propagation in rigid mechanical environments, e.g. tissue culture plastic (TCP). This may potentially mask the full extent of the stiffness-driven mechanosensing programs. To address this, we developed a biomaterial system composed of two-dimensional mechano-variant silicone substrates that is permissive to large-scale cell culture expansion processes. We broadly mapped the stiffness-mediated mechano-responses by performing RNA sequencing on human tendon-derived stromal cells. We find that matrix rigidities approximating tendon microscale stiffness range (E. ~35 kPa) distinctly favor programs related to chromatin remodeling and Hippo signaling; whereas more compliant stiffnesses (E. 2 kPa) were enriched in responses related to pluripotency, synapse assembly and angiogenesis. We also find that tendon stromal cells undergo dramatic phenotypic drift on conventional TCP, with near-complete suppression of tendon-related genes and emergence of expression signatures skewed towards fibro-inflammatory and metabolic activation. Strikingly, mechano-variant substrates abrogate fibroblasts activation, with tenogenic stiffnesses inducing a transcriptional program that strongly correlate with established tendon tissue-specific signatures. Computational inference predicted that AKT1 and ERK1/2 are major signaling hubs mediating stiffness-sensing in tendon cells. Together, our findings highlight how the underlying biophysical cues may dictate the transcriptional identity of resident cells, and how matrix mechano-reciprocity regulates diverse sets of previously underappreciated mechanosensitive processes in tendon stromal fibroblasts.

bioengineering↗

bioRxiv2021

A G protein-coupled receptor is required in cartilaginous and dense connective tissues to maintain spine alignment

Adolescent idiopathic scoliosis (AIS) is the most common spine disorder affecting children worldwide, yet little is known about the pathogenesis of this disorder. Here, we demonstrate that genetic regulation of structural components of the axial skeleton, the intervertebral discs and dense connective tissues (e.g., ligaments and tendons), are essential for maintenance of spinal alignment. We show that the G-coupled protein receptor Adgrg6, previously implicated in human AIS association studies, is required in these tissues to maintain typical spine morphology. We show that Adgrg6 regulates biomechanical properties of tendon and stimulates CREB signaling governing gene expression in cartilaginous tissues of the spine. Treatment with an cAMP agonist was able to mirror aspects of receptor function in culture defining core pathways for regulation of these axial connective tissues. As ADGRG6 is a key gene involved in human AIS, these findings open up novel therapeutic opportunities for human scoliosis. HighlightsO_LIKnockout mice lacking Adgrg6 function in the tendons and ligaments of the spine develop perinatal-onset thoracic scoliosis. C_LIO_LILoss of Adgrg6 function in cartilaginous tissues of the discs contribute to the incidence and severity of scoliosis. C_LIO_LIThe loss of Adgrg6 function in spine tissues provide a model of construct validity for human adolescent idiopathic scoliosis C_LIO_LIFine tuning of the biomechanical properties of dense connective tissues is essential for maintaining spine alignment. C_LI

developmental biology↗

bioRxiv2020

Time-controlled Multichannel Dynamic Traction Imaging of Biaxially Stretched Adherent Cells

Here, a dynamic traction force microscopy method is described which enables sub-second temporal resolution imaging of transient subcellular events secondary to extrinsic stretch of adherent single cells. The system employs a novel tracking approach with minimal computational overhead to compensate substrate-based stretch-induced motion/drift of stretched single cells in real time, allowing capture of biophysical phenomena on multiple channels by fluorescent multichannel imaging on a single camera, thus avoiding the need for beam splitting with associated loss of light. The potential impact of the technique is demonstrated by characterizing transient subcellular forces and corresponding nuclear deformations in equibiaxial stretching experiments, uncovering a high frequency strain-rate dependent response in the transfer of substrate strains to the nucleus.

cell biology↗

bioRxiv2019

The Protein Mat(ters) - Revealing Biologically Relevant Mechanical Contribution of Collagen and Fibronectin Coated Micropatterns

Understanding cell-material interactions requires accurate characterization of substrate mechanics, which are generally measured by indentation-type atomic force microscopy. Although model extracellular matrix coatings are used to facilitate cell-substrate adhesion, their tensile mechanical properties are generally unknown. In this study a novel tensile mechanical characterization of collagen and fibronectin micropatterned polyacrylamide hydrogels is performed. Our findings reveal that the protein coating itself has measurable and biologically relevant consequences, with ligand-specific tensile resistance of the patterned regions relative to the non-patterned surfaces. To our knowledge our study is the first to uncover a direction-dependent mechanical behavior of the protein coatings and to demonstrate that it affects cellular response relative to substrate mechanics.

cell biology↗

bioRxiv2019

Tendon response to matrix unloading is determined by the patho-physiological niche

Aberrant matrix turnover with elevated matrix proteolysis is a hallmark of tendon pathology. While tendon disease mechanisms remain obscure, mechanical cues are central regulators. Unloading of tendon explants in standard culture conditions provokes rapid cell-mediated tissue breakdown. Here we show that biological response to tissue unloading depends on the mimicked physiological context. Our experiments reveal that explanted tendon tissues remain functionally stable in a simulated avascular niche of low temperature and oxygen, regardless of the presence of serum. This hyperthermic and hyperoxic niche-dependent catabolic switch was shown by whole transcriptome analysis (RNA-seq) to be a strong pathological driver of an immune-modulatory phenotype, with a stress response to reactive oxygen species (ROS) and associated activation of catabolic extracellular matrix proteolysis that involved lysosomal activation and transcription of a range of proteolytic enzymes. Secretomic and degradomic analysis through terminal amine isotopic labeling of substrates (TAILS) confirmed that proteolytic activity in unloaded tissues was strongly niche dependent. Through targeted pharmacological inhibition we isolated ROS mediated oxidative stress as a major checkpoint for matrix proteolysis. We conclude from these data that the tendon stromal compartment responds to traumatic mechanical unloading in a manner that is highly dependent on the extrinsic niche, with oxidative stress response gating the proteolytic breakdown of the functional collagen backbone.

molecular biology↗