Biology subjects

Stowers, R. S.

Publications and source records attributed to Stowers, R. S..

8 recordsLinked to original sources

bioRxiv2026

Glycoconjugates tune the viscoelastic signature of mammary tumor progression

Breast cancer progression involves extensive remodeling of the tumor extracellular matrix (ECM), resulting in changes in mechanical properties. Tumors are viscoelastic, exhibiting both an initial elastic response to loading and a time-dependent viscous response. While it is well established that tumor elasticity or stiffness is elevated, changes in tissue viscoelasticity during breast cancer progression remain poorly characterized. Here, using a mouse model that recapitulates stages of human breast cancer progression (mouse mammary tumor virus-polyoma middle T antigen, MMTV-PyMT), we show that tumors from both early and late disease time points were significantly more viscoelastic than normal mammary glands. Spatial microindentation revealed that while local stiffness and viscoelasticity are strongly coupled in soft regions of normal tissue, this relationship weakens in late carcinoma. Compared to normal glands, carcinoma tissues also exhibited marked upregulation of glycosaminoglycans (GAGs) and glycoproteins. Selective enzymatic degradation of sulfated GAGs, mucins, or O/N-linked glycans reduced viscoelasticity without altering stiffness, establishing glycoconjugates as major contributors to tumor viscoelasticity. In vitro, increasing matrix viscoelasticity drove non-transformed mammary epithelial cells (MCF10A) toward a malignant phenotype through focal adhesion kinase mechanosignaling. Our work establishes increased viscoelasticity as a defining mechanical feature of breast cancer progression, driven in part by the accumulation of glycoconjugates. These findings provide a fuller picture of tumor mechanical evolution and a benchmark for recapitulating matrix viscoelasticity in engineered models of breast cancer.

cancer biology↗

bioRxiv2026

Matrix stiffness and stress relaxation regulate matrix-bound nanovesicle release from alginate hydrogels

Matrix-bound nanovesicles (MBVs) are a recently discovered subclass of small extracellular vesicles (EVs) that reside within the extracellular matrix of non-mineralized tissues throughout the body. Functionally, MBVs exhibit unique immunomodulatory properties that have been leveraged therapeutically to treat various tissue pathologies, including periprosthetic osteolysis, rheumatoid arthritis, and skeletal muscle injury. However, like other EVs, the therapeutic efficacy of MBV applications is limited by delivery methods, namely bolus injections, that offer poor control of EV persistence and bioavailability at the site of administration. We hypothesized that a superior MBV delivery platform could be developed by entrapping MBVs in a tunable, engineered alginate matrix to control retention and release of MBVs on therapeutically relevant timescales. To this end, we encapsulated dermal fibroblast MBVs in bioinert alginate hydrogels of varying stiffness and stress relaxation rates to determine the impact of matrix mechanical properties on MBV release and retention over a 14-day period. We found that stiffer matrices increased MBV release compared to their softer counterparts. Additionally, fast-relaxing matrices exhibited release of MBVs in the first four days of release experiments, in contrast with slow-relaxing matrices, which promoted long-term sequestration of nearly all encapsulated MBVs regardless of differences in matrix stiffness. Our results offer promise that alginate hydrogels can be utilized for more precise control of MBV delivery in the body and may overcome limitations associated with current EV administration methods.

bioengineering↗

bioRxiv2026

Matrix viscoelasticity regulates dermal fibroblast activation in a three-dimensional fibrillar microenvironment

PurposeFibrosis is the pathological remodeling of the extracellular matrix (ECM) that is largely orchestrated by activated fibroblasts. The mechanical properties of the ECM change drastically during fibrosis, and fibroblasts become increasingly activated by mechanical environments that mimic the properties of fibrotic tissues. While the effects of increased elastic modulus (stiffness) on fibroblast activation have been well-studied, the impact of changes in viscoelasticity are less clear. Here, we sought to determine how fibroblast activation is altered by changes in viscoelasticity in a three-dimensional, fibrillar microenvironment. MethodsWe employed 3D alginate collagen I hydrogels with independently tunable stiffness and stress relaxation rates. Dermal fibroblasts were encapsulated in hydrogels with four distinct mechanical profiles (soft: 3 kPa or stiff: 10 kPa, fast stress relaxing: {tau}1/2 {approx} 160 s or slow stress relaxing: {tau}1/2 {approx} 1600 s). We assessed fibroblast activation by changes in cell morphology, expression of key activation markers, and evidence of ECM remodeling. ResultsFibrillar alginate collagen networks enhanced fibroblast spreading, -smooth muscle actin stress fiber formation, and fibroblast activation protein- expression in matrices that were slow relaxing or stiff. The presence of the fibrillar network further enhanced fibroblast activation, independent of the changes driven by matrix viscoelasticity. ECM remodeling was also promoted by slow relaxing matrices, with increased fibronectin deposition and more remodeling of the local collagen fiber network. ConclusionsOur results demonstrate that fibroblast activation is highly responsive to matrix stress relaxation rate, and that models incorporating fibrillar, viscoelastic networks can provide new insights into the role of ECM mechanics driving fibroblast activation.

bioengineering↗

bioRxiv2025

Two classes of amine/glutamate multi-transmitter neurons innervate Drosophila internal male reproductive organs

The essential outcome of a successful mating is the transfer of genetic material from males to females in sexually reproducing animals from insects to mammals. In males, this culminates in ejaculation, a precisely timed sequence of organ contractions driven by the concerted activity of interneurons, sensory neurons, and motor neurons. Although central command circuits that trigger copulation have been mapped, the motor architecture and the chemical logic that couple specific neuronal subclasses to organ specific contractility, seminal fluid secretion, and sperm emission remain largely uncharted. This gap in knowledge limits our ability to explain how neural circuits adapt to varying contexts and how their failure contributes to infertility. Here we present an in-depth anatomical and functional analysis of the motor neurons that innervate the internal male reproductive tract of Drosophila melanogaster. We identify two classes of multi-transmitter motor neurons based on neurotransmitter usage, namely octopamine and glutamate neurons (OGNs) and serotonin and glutamate neurons (SGNs), each with a biased pattern of innervation: SGNs predominate in the accessory glands, OGNs in the ejaculatory duct, with equal contributions of each to the seminal vesicles. Both classes co-express vesicular transporters for glutamate (vGlut) and amines (vMAT), confirming their dual chemical identity. Their target organs differentially express receptors for glutamate, octopamine, and serotonin, suggesting combinatorial neuromodulation of contractility. Functional manipulations show that SGNs are essential for male fertility but OGNs are dispensable. Glutamatergic transmission from both classes is also dispensable for fertility. These findings provide the first high-resolution map linking multi-transmitter motor neurons to specific reproductive organs, reveal an unexpected division of labor between serotonergic and octopaminergic signaling pathways, and establish a framework for dissecting conserved neural principles that govern ejaculation and male fertility.

neuroscience↗

bioRxiv2025

Matrix stiffness and stress relaxation regulate osteogenesis through histone demethylases KDM4B and KDM6B

Stem cells sense biophysical cues within their extracellular microenvironment and respond via mechanotransduction signaling pathways that induce changes in gene expression and associated cell fate outcomes. Histone modifying enzymes are known to drive stem cell differentiation through changes in chromatin accessibility, but little is understood as to how extracellular matrix (ECM) mechanics regulate epigenomic remodeling. Here, we utilize alginate hydrogels with tunable mechanical properties to investigate the role of both matrix stiffness and viscoelasticity on histone demethylase expression and activity during osteogenic differentiation of human bone marrow-derived mesenchymal stem cells (hBMSCs). Our results reveal that the expression of two histone demethylases, KDM4B and KDM6B, are upregulated during osteogenesis in response to stiff, viscoelastic matrix conditions. Inhibition of mechanotransduction signaling pathways reduces expression of KDM4B and KDM6B and hinders osteogenic differentiation overall. Interestingly, phosphorylation of SMAD 1/5/8 was shown to increase in cells cultured in stiff, stress relaxing matrices, and pharmacological inhibition of SMAD 1/5/8 activation reduced expression of KDM4B and KDM6B and decreased osteogenic differentiation. Taken together, our results reveal novel impacts of stem cell mechanotransduction signaling events that promote osteogenesis through epigenetic remodeling.

cell biology↗

bioRxiv2025

Sp1 mechanotransduction regulates breast cancer cell invasion in response to multiple tumor-mimicking extracellular matrix cues

Breast cancer progression is marked by extracellular matrix (ECM) remodeling, including increased stiffness, faster stress relaxation, and elevated collagen levels. In vitro experiments have revealed a role for each of these factors to individually promote malignant behavior, but their combined effects remain unclear. To address this, we developed alginate-collagen hydrogels with independently tunable stiffness, stress relaxation, and collagen density. We show that these combined tumor-mimicking ECM cues reinforced invasive morphologies and promoted spheroid invasion in breast cancer and mammary epithelial cells. High stiffness and low collagen density in slow-relaxing matrices led to the greatest cell migration speed and displacement. RNA-seq revealed Sp1 target gene enrichment in response to both individual and combined ECM cues, with a greater enrichment observed under multiple cues. Notably, high expression of Sp1 target genes upregulated by fast stress relaxation correlated with poor patient survival. Mechanistically, we found that phosphorylated-Sp1 (T453) was increasingly located in the nucleus in stiff and/or fast relaxing matrices, which was regulated by PI3K and ERK1/2 signaling, as well as actomyosin contractility. This study emphasizes how multiple ECM cues in complex microenvironments reinforce malignant traits and supports an emerging role for Sp1 as a mechanoresponsive transcription factor.

bioengineering↗

bioRxiv2024

Stress relaxation rates of myocardium from failing and non-failing hearts

The heart is a dynamic pump whose function is influenced by its mechanical properties. The viscoelastic properties of the heart, i.e. its ability to exhibit both elastic and viscous characteristics upon deformation, influence cardiac function. Viscoelastic properties change during heart failure (HF), but, direct measurements of failing and non-failing myocardial tissue stress relaxation under constant displacement are lacking. Further, how consequences of tissue remodeling, such as fibrosis and fat accumulation, alter the stress relaxation remains unknown. To address this gap, we conducted stress relaxation tests on porcine myocardial tissue to establish baseline properties of cardiac tissue. We found porcine myocardial tissue to be fast relaxing, characterized by stress relaxation tests on both a rheometer and microindenter. We then measured human left ventricle (LV) epicardium and endocardium human tissue from non-failing, ischemic HF, and non-ischemic HF patients by microindentation. We found that the ischemic HF had slower stress relaxation than non-failing endocardium; and that slower stress relaxing tissues were correlated with increased collagen deposition and increased -smooth muscle actin (-SMA) stress fibers, a marker of fibrosis and cardiac fibroblast activation, respectively. In the epicardium, we found that ischemic HF had faster stress relaxation than non-ischemic HF and non-failing; and that faster stress relaxation correlated with Oil Red O staining, a marker for adipose tissue. These data show that changes in stress relaxation vary across the different layers of the heart during ischemic vs. non-ischemic HF. These findings reveal how the viscoelasticity of the heart changes, which will lead to better modeling of cardiac mechanics for in vitro and in silico HF models.

bioengineering↗

bioRxiv2021

Intact Drosophila Whole Brain Cellular Quantitation reveals Sexual Dimorphism

Establishing with precision the quantity and identity of the cell types of the brain is a prerequisite for a detailed compendium of gene and protein expression in the central nervous system. Currently however, strict quantitation of cell numbers has been achieved only for the nervous system of C.elegans. Here we describe the development of a synergistic pipeline of molecular genetic, imaging, and computational technologies designed to allow high-throughput, precise quantitation with cellular resolution of reporters of gene expression in intact whole tissues with complex cellular constitutions such as the brain. We have deployed the approach to determine with exactitude the number of functional neurons and glia in the entire intact larval Drosophila central nervous system (CNS), revealing fewer neurons and more glial cells than previously predicted. We also discover an unexpected divergence between the sexes at this juvenile developmental stage, with the female CNS having significantly more neurons than that of males. Topological analysis of our data establishes that this sexual dimorphism extends to deeper features of CNS organisation. We additionally extended our analysis to quantitate the expression of voltage-gated potassium channel family genes throughout the CNS and uncover substantial differences in abundance. Our methodology enables robust and accurate quantification of the number and positioning of cells within intact organs, facilitating sophisticated analysis of cellular identity, diversity, and gene expression characteristics.

neuroscience↗