Biology subjects

Wells, R. G.

Publications and source records attributed to Wells, R. G..

At least 19 recordsLinked to original sources

bioRxiv2026

Nuclear confinement from matrix stiffness drives epigenomic reprogramming of gingival fibroblasts

Periodontal disease is characterized by progressive degradation of the gingival extracellular matrix and loss of the physical confinement it imposes on resident stromal cells. In human periodontal tissue, ECM collagen integrity is inversely correlated with facultative nuclear histone acetylation in stromal cells. We hypothesized that matrix stiffness directly coordinates an epigenomic shift in stromal cells. We use a three-dimensional mechanically tunable hydrogel system to independently tune the storage moduli across the mechanical range of healthy and periodontitis-affected gingival tissue. Matrix stiffness drives a genome-wide response in donor-derived human gingival fibroblasts. Matrix-induced confinement leads to an isotropic nuclear geometry and a folded nuclear envelope architecture compared with more permissive, soft matrices. H3K27Ac is suppressed through a stiffness and actomyosin contractility-dependent mechanism. DNMT inhibition in stiff matrices restores the high-acetylation chromatin state with persistent nuclear envelope folding. At the genomic level, stiff matrix confinement drives global CpG methylation gain concentrated at pericentromeric satellite repeats and repeat-dense regions, while collagen synthesis gene promoters and CTCF binding sites are selectively hypomethylated. Non-canonical NF-{kappa}B inflammatory signaling is attenuated through promoter methylation of MAP3K14, and pharmacological NIK inhibition reduces TLR2-stimulated IL-6 secretion in soft-matrix fibroblasts to levels comparable to the stiff condition. These findings identify the gingival ECM as an active epigenomic regulator of stromal inflammatory competence and provide a mechanistic rationale for targeting matrix mechanics to restore stromal homeostasis in periodontitis. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=85 SRC="FIGDIR/small/728299v1_ufig1.gif" ALT="Figure 1"> View larger version (44K): org.highwire.dtl.DTLVardef@131db0borg.highwire.dtl.DTLVardef@23ba0borg.highwire.dtl.DTLVardef@18b67d9org.highwire.dtl.DTLVardef@14ede81_HPS_FORMAT_FIGEXP M_FIG C_FIG The mechanobiological state of human gingival fibroblasts differs between healthy, stiff extracellular matrices and degraded, soft matrices characteristic of periodontal disease. In a healthy environment, stiff matrices impose physical confinement that enforces an isotropic nuclear geometry, driving dense heterochromatin formation, high global CpG methylation, and reduced histone acetylation. Conversely, the loss of mechanical confinement in soft matrices enables cell spreading and an open euchromatin state, fundamentally rewiring the cellular epigenome to promote non-canonical NF-{kappa}B signaling and chronic inflammation.

bioengineering↗

bioRxiv2026

Reduction in Hepatic Phosphatidylcholine Biosynthesis Promotes MASH Through Copper Deficiency

Metabolic dysfunction-associated steatohepatitis (MASH) is a progressive liver disease for which the mechanisms linking lipid dysregulation to fibrosis remain poorly defined. Hepatic phosphatidylcholine (PC) content is reduced in MASH, but how this alteration drives disease progression is unclear. Here, we identify a role for copper (Cu) homeostasis as a downstream effector of impaired PC biosynthesis. Using single-nucleus RNA sequencing in complementary genetic and dietary mouse models, we found that reduced hepatic PC is associated with marked depletion of hepatic Cu and a concomitant increase in circulating Cu, indicating disrupted Cu distribution. Mechanistically, PC depletion impaired plasma membrane localization of the high-affinity Cu transporter CTR1 (SLC31A1) in hepatocytes, limiting Cu uptake. In human hepatic stellate cells, Cu promoted fibrogenic activation, whereas suppression of Cu import or pharmacologic inhibition of MAPK signaling attenuated fibronectin deposition. In vivo, liver-directed Cu supplementation restored hepatic Cu levels and reduced steatosis but failed to improve fibrosis. In contrast, pharmacologic Cu chelation with bathocuproinedisulfonic acid (BCS) reduced fibrosis without affecting inflammation. Together, these findings identify Cu redistribution as a consequence of impaired PC biosynthesis and implicate Cu-dependent signaling in stellate cell activation, fibrogenesis and MASH pathogenesis. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=141 SRC="FIGDIR/small/723926v1_ufig1.gif" ALT="Figure 1"> View larger version (39K): org.highwire.dtl.DTLVardef@1c2bd52org.highwire.dtl.DTLVardef@1b8295org.highwire.dtl.DTLVardef@1a129dorg.highwire.dtl.DTLVardef@1bc2b87_HPS_FORMAT_FIGEXP M_FIG C_FIG

physiology↗

bioRxiv2025

Matrix Stiffness Governs Fibroblast-Driven Immune Homeostasis in Gingival Tissues

Periodontal disease is associated with inflamed gingival tissues and degradation of the gingival extracellular matrix (ECM), yet the role of mechanical cues is poorly understood. Gingival ECM in periodontal disease showed a loss of fibrillar collagen compared to healthy samples. We hypothesized that ECM softening in periodontal disease contributes to inflammation due to dysregulated gingival fibroblasts (GFs). A mechanically tunable hydrogel model of the gingival ECM was developed to investigate the mechano-immune crosstalk. Stiff collagen-alginate hydrogels matched the rheological properties of gingival biopsies. Human donor GFs encapsulated in these stiff hydrogels showed significantly suppressed toll-like receptor inflammatory responses compared to soft. Stiffness-dependent inflammatory responses of GFs were directed by the non-canonical NF{kappa}B pathway and epigenetic nuclear organization. The direct impact of mechanical cues on immune responses was investigated with human donor cells ex vivo by co-culture of human GFs with myeloid cells and in human gingival explants. Myeloid progenitors co-cultured with GFs in stiff hydrogels differentiated into immunomodulatory dendritic cells. Ex vivo crosslinking of human gingival tissue increased stiffness and reduced inflammatory cytokines. Gingival mechano-immune regulation provides a new avenue for biomaterials-based treatments in periodontitis.

bioengineering↗

bioRxiv2025

Liver Viscosity Decreases Before the Onset of Fibrosis in Metabolic Dysfunction-Associated 1 Steatohepatitis (MASH)

Background and AimMetabolic dysfunction-associated steatohepatitis (MASH) is an increasingly prevalent condition worldwide, associated with biomechanical liver changes and detectable by magnetic resonance elastography (MRE). This study explored the pathophysiological features and their biomechanical manifestations at different stages of MASH in a mouse dietary model. MethodsUsing MRE on a clinical 3 Tesla MRI scanner, we measured liver stiffness, viscosity, fat fraction and water diffusion in 45 male mice. These values were correlated with histopathology and proteomics analyses to further characterize the liver microstructural and metabolic changes during MASH progression. ResultsWe found in a high-fat, low amino-acid model that early MASH was marked by fat accumulation and increasing inflammatory activity, while later stages showed a reduction in fat despite persistent inflammation. These changes in microstructure were associated with biomechanical adaptations, including a progressive decrease in hepatic viscosity and the water diffusion. Notably, viscosity was inversely correlated with lobular inflammation, cell adhesion, antioxidant activity, and metabolic adaptations such as enhanced ketone body synthesis. These findings, which precede the onset of fibrosis and tissue stiffening, show that tissue viscosity is highly sensitive to early microstructural and metabolic alterations in MASH. ConclusionSteatosis and inflammation significantly alter liver biophysical properties, particularly viscosity, in a mouse dietary model of MASH, even in the absence of fibrosis. These findings suggest that viscosity is a potential early and clinically translatable biomarker for the development and progression of MASH.

biophysics↗

bioRxiv2024

Intrahepatic crystals from elevated dietary cholesterol are sufficient to stiffen the liver

Chronic lipid accumulation is a hallmark of metabolic dysfunction-associated steatotic liver disease (MASLD), and dyslipidemia is associated with disease progression and poorer patient outcomes. Tissue stiffening is an established fibrogenic cue, but how changes in lipid accumulation affect tissue mechanics is not fully understood. Here we show that cholesterol-containing lipid crystals stiffen steatotic liver tissue. We show that rats fed elevated dietary cholesterol develop both liquid and solid cholesterol-containing lipid crystals in the liver. While steatotic livers without crystals are softer than control livers, livers with lipid crystals show increased baseline stiffness and compression stiffening as well as increased progression to fibrosis. Lipid extracts from livers containing crystals stiffen fibrous tissue mimics, while depletion of cholesterol using methyl--cyclodextrin reduces both crystal abundance and tissue stiffness. Our results demonstrate in a rat model that a high cholesterol diet leads to formation of liquid and solid crystals and that cholesterol-containing crystals stiffen tissues. This work implicates lipid crystals arising from dyslipidemia as a key driver of MASLD progression. The presence of cholesterol crystals could lead to new diagnostic tools for progressive MASLD and could be a therapeutic target.

physiology↗

bioRxiv2024

Metabolically intact nuclei are fluidized by the activity of the chromatin remodeling motor BRG1

The structure and dynamics of the cell nucleus regulate nearly every facet of the cell. Changes in nuclear shape limit cell motility and gene expression. Although the nucleus is generally seen as the stiffest organelle in the cell, cells can nevertheless deform the nucleus to large strains by small mechanical stresses. Here, we show that the mechanical response of the cell nucleus exhibits active fluidization that is driven by the BRG 1 motor of the SWI/SNF/BAF chromatin-remodeling complex. Atomic force microscopy measurements show that the nucleus alters stiffness in response to the cell substrate stiffness, which is retained after the nucleus is isolated and that the work of nuclear compression is mostly dissipated rather than elastically stored. Inhibiting BRG 1 stiffens the nucleus and eliminates dissipation and nuclear remodeling both in isolated nuclei and in intact cells. These findings demonstrate a novel link between nuclear motor activity and global nuclear mechanics.

cell biology↗

bioRxiv2023

Microcystin-RR is a biliary toxin selective for neonatal cholangiocytes

BACKGROUND AND AIMSBiliary atresia is a fibrosing cholangiopathy affecting neonates that is thought to be caused by a prenatal environmental insult to the bile duct. Biliatresone, a plant toxin with an -methylene ketone group, was previously implicated in toxin-induced biliary atresia in Australian livestock, but is found in a limited location and is highly unlikely to be a significant human toxin. We hypothesized that other molecules with -methylene ketone groups, some with the potential for significant human exposure, might also be biliary toxins. APPROACH AND RESULTSWe focused on the family of microcystins, cyclic peptide toxins from blue-green algae that have an -methylene ketone group and are found worldwide, particularly during harmful algal blooms. We found that microcystin-RR, but not 6 other microcystins, caused damage to cell spheroids made using cholangiocytes isolated from 2-3-day-old mice, but not from adult mice. We also found that microcystin- RR caused occlusion of extrahepatic bile duct explants from 2-day-old mice, but not 18-day-old mice. Microcystin-RR caused elevated reactive oxygen species in neonatal cholangiocytes, and treatment with N-acetyl cysteine partially prevented microcystin-RR- induced lumen closure, suggesting a role for redox homeostasis in its mechanism of action. CONCLUSIONSThis study highlights the potential for environmental toxins to cause neonatal biliary disease and identifies microcystin-RR acting via increased redox stress as a possible neonatal bile duct toxin.

pharmacology and toxicology↗

bioRxiv2023

Human Vascularized Bile Duct-on-a Chip: A multi-cellular micro-physiological system for studying Primary Sclerosing Cholangitis

Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease in which the bile ducts of the liver become inflamed and scarred. Scarred bile ducts eventually narrow and obstruct and can cause additional liver pathology including liver failure, repeated infections, and tumors. The pathogenesis of PSC remains largely unknown, partly due to difficulty in obtaining cholangiocytes and partly due to a paucity of in vitro models that capture the various factors contributing to disease progression. Here we report the development of a human vascularized bile duct-on-a-chip that models blood vessels and bile ducts structurally and functionally in three dimensions and includes cholangiocytes derived from control and PSC patient tissue and bile. The flow of blood and bile was modeled by perfusion of cell-lined channels, and cholangiocytes and endothelial cells displayed differential responses to perfusion. Normal and PSC cholangiocytes polarized normally, formed mature tight junctions and displayed similar permeability, comparable to ex vivo measurements. The model with PSC cholangiocytes, however, became more inflammatory than the normal under the stimulation of IL-17A, which induced PBMC and differentiated Th17 cells in the vascular channel to transmigrate more through the endothelial layer of the vascular compartment. In sum, this human vascularized bile duct-on-a-chip recapitulated the vascular-biliary interface structurally and functionally and represents a novel multicellular platform to study inflammatory and fibrotic cholangiopathies such as PSC.

bioengineering↗

bioRxiv2023

Biliatresone treatment of pregnant mice causes changes in bile metabolism and liver inflammation in their offspring

Background & AimsBiliary atresia is a neonatal disease characterized by bile duct and liver damage, fibrosis, inflammation and abnormal bile metabolism. It appears to result from a prenatal exposure that spares the mother and affects the fetus. Our aim was to define the phenotype in neonatal mice after maternal exposure to low-dose biliatresone, a plant toxin implicated in biliary atresia in livestock. MethodsPregnant mice were treated orally with low-doses of biliatresone. Histological changes, bile acid profiles and immune profiles were analyzed in postnatal day 5 and 21 pups born to treated mothers. ResultsThe pups of mothers treated with this dose of biliatresone had no evidence of significant liver or ductular injury or fibrosis at postnatal day 5 or 21 and they grew normally. However, serum levels of glycocholic acid were elevated at postnatal day 5, suggesting altered bile metabolism, and bile metabolism became increasingly abnormal through postnatal day 21, with enhanced glycine conjugation of bile acids. There was also immune cell activation observed in the liver at postnatal day 21. ConclusionPrenatal exposure to low doses of an environmental toxin can cause liver inflammation and aberrant bile metabolism even in the absence of histological changes. Lay summaryPrenatal exposure to low doses of an environmental toxin can cause changes in bile metabolism in neonatal mice.

pharmacology and toxicology↗

bioRxiv2022

Injury and a program of fetal wound healing in the fetal and neonatal extrahepatic bile duct

IntroductionBiliary atresia (BA) is an obstructive cholangiopathy that initially affects the extrahepatic bile ducts (EHBDs) of neonates. The etiology is uncertain, but evidence points to a prenatal cause; however, the response of the fetal EHBD to injury remains unknown. The objective of this study was to define the fetal response to EHBD injury and to determine whether it follows a fetal wound healing paradigm. MethodsMouse, rat, sheep, and human EHBD samples were studied at different developmental time points. Models included a fetal sheep model of prenatal hypoxia, human BA EHBD remnants and liver samples taken at the time of the Kasai procedure, EHBDs isolated from neonatal rats and mice, and spheroids and other models generated from primary neonatal mouse cholangiocytes. ResultsA wide layer of high molecular weight HA encircling the lumen was characteristic of the normal perinatal but not adult EHBD. This layer, which was surrounded by collagen, expanded in injured ducts in parallel with extensive peribiliary gland (PBG) hyperplasia, increased mucus production and elevated serum bilirubin levels. BA EHBD remnants similarly showed increased HA centered around ductular structures compared with age-appropriate controls. High molecular weight HA typical of the fetal/neonatal ducts caused increased cholangiocyte spheroid growth, whereas low molecular weight HA induced abnormal epithelial morphology; low molecular weight HA caused matrix swelling in a bile duct-on-a-chip device. ConclusionThe fetal/neonatal EHBD, including in human EHBD remnants from Kasai surgeries, demonstrated an injury response with high levels of HA typical of the regenerative, scarless program termed fetal wound healing. Although generally beneficial, the expanded peri-luminal HA layer may swell and lead to elevated bilirubin levels and obstruction of the EHBD.

physiology↗

bioRxiv2022

Glisson's capsule structure and function is altered in cirrhotic patients irrespective of etiology

Background and AimsGlissons capsule is the interstitial connective tissue that surrounds the liver. As part of its normal physiology, it withstands significant daily changes in liver size. The pathophysiology of the capsule in disease is not well understood. The aim of this study was to characterize the changes in capsule matrix, cellular composition, and mechanical properties that occur in liver disease and to determine whether these correlate with disease severity or etiology. Methods10 control, 6 steatotic, 7 moderately fibrotic and 37 cirrhotic patient samples were collected from autopsies, intraoperative biopsies and liver explants. Matrix proteins and cell markers were assessed by staining and second harmonic generation imaging. Mechanical tensile testing was performed on a test frame. ResultsCapsule thickness was significantly increased in cirrhotic samples compared to normal controls irrespective of disease etiology (69.62 {+/-} 9.99 and 171.269 {+/-} 16.65 {micro}m respectively), whereas steatosis and moderate fibrosis had no effect on thickness (62.15 {+/-} 4.97 {micro}m). Changes in cirrhosis included an increase in cell number (fibroblasts, vascular cells, infiltrating immune cells and biliary epithelial cells). Key matrix components (collagens 1 and 3, hyaluronan, versican and elastin) were all deposited in the lower capsule although only the relative amounts per area of hyaluronan and versican were increased. Organizational features including crimping and alignment of collagen fibers were also altered in cirrhosis. Unexpectedly, capsules from cirrhotic livers had decreased resistance to loading in comparison to controls. ConclusionsThe liver capsule, like the parenchyma, is an active site of disease, demonstrating changes in matrix and cell composition as well as mechanical properties. Lay summaryWe assessed the changes in composition and response to stretching of the liver outer sheath, the capsule, in human liver disease. We find an increase in key structural components and numbers of cells as well as a change in matrix organization of the capsule in the later stages of disease. This allows the diseased capsule to stretch more under any given force, suggesting it is less stiff than healthy tissue. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=116 SRC="FIGDIR/small/505570v1_ufig1.gif" ALT="Figure 1"> View larger version (32K): org.highwire.dtl.DTLVardef@10a9b60org.highwire.dtl.DTLVardef@15eea52org.highwire.dtl.DTLVardef@69b874org.highwire.dtl.DTLVardef@cccd03_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIThe capsule is an active site of disease: thickness and cellularity increase markedly in cirrhosis C_LIO_LIExtracellular matrix composition and organization change in cirrhosis C_LIO_LIThe cirrhotic capsule stretches more and is less stiff C_LI

physiology↗

bioRxiv2022

Lipid droplets are intracellular mechanical stressors in fatty hepatocytes

Matrix stiffening and external mechanical stress have been linked to disease and cancer development in multiple tissues, including the liver, where cirrhosis (which increases stiffness markedly) is the major risk factor for hepatocellular carcinoma. Patients with non-alcoholic fatty liver disease and lipid-droplet-filled hepatocytes, however, can develop cancer in non-cirrhotic, relatively soft tissue. Here, we show that lipid droplets are intracellular mechanical stressors with similar effects to tissue stiffening, including nuclear deformation, chromatin condensation, and hepatocyte dedifferentiation. Mathematical modelling of lipid droplets as inclusions that have only mechanical interactions with other cellular components generated results consistent with our experiments. These data show that lipid droplets are intracellular sources of mechanical stress and suggest that nuclear membrane tension integrates cell responses to combined internal and external stresses. Significance StatementDeformation of the nucleus as a result of extracellular sources of stress, including increased substrate stiffness, constricted migration, and compression, has been well documented to lead to increased nuclear rupture, changes in gene expression, and accumulation of DNA damage. Lipid droplet accumulation in hepatocytes provides a unique scenario to investigate potential intracellular mechanical stresses and sources of nuclear deformation. Our results show that lipid droplets are significant mechanical elements in the cell, deforming the nucleus in a way that promotes hepatocyte dedifferentiation and resisting cytoskeletal contraction and alignment.

cell biology↗

bioRxiv2022

Local fat content determines global and local stiffness in fatty livers

Fat accumulation during liver steatosis precedes inflammation and fibrosis in fatty liver diseases, and is associated with disease progression. Despite a large body of evidence that liver mechanics play a major role in liver disease progression, the effect of fat accumulation by itself on liver mechanics remains unclear. Thus, we conducted ex vivo studies of liver mechanics in rodent models of simple steatosis to isolate and examine the mechanical effects of intrahepatic fat accumulation, and found that fat accumulation softens the liver. Using a novel adaptation of microindentation to permit association of local mechanics with microarchitectural features, we found evidence that the softening of fatty liver results from local softening of fatty regions rather than uniform softening of the liver. These results suggest that fat accumulation itself exerts a softening effect on liver tissue. This, along with the localized heterogeneity of softening within the liver, has implications in what mechanical mechanisms are involved in the progression of liver steatosis to more severe pathologies and disease. Finally, the ability to examine and associate local mechanics with microarchitectural features is potentially applicable to the study of the role of heterogeneous mechanical microenvironments in both other liver pathologies and other organ systems.

physiology↗

bioRxiv2022

Versican binds collagen via its G3 domain and regulates the organization and mechanics of collagenous matrices

Type I collagen is the most abundant structural protein in the body and, with other fibrillar collagens, forms the fibrous network of the extracellular matrix (ECM). Another group of ECM polymers, the glycosaminoglycans (GAGs) and GAG-modified proteoglycans, play important roles in regulating collagen behaviors and contribute to the compositional, structural and mechanical complexity of the ECM. While the binding between collagen and small leucine-rich proteoglycans (SLRPs) has been studied in detail, the interactions between collagen and the large bottlebrush proteoglycan versican are not well understood. Here, we report that versican binds collagen directly and regulates collagen structure and mechanics. Versican colocalizes with collagen fibers in vivo and binds to collagen via its C-terminal G3 domain (a non-GAG-modified domain present in all known versican isoforms) in vitro; it promotes the deposition of a highly-aligned collagen-rich matrix by fibroblasts. Versican also shows an unexpected effect on the rheology of collagen gels in vitro, causing decreased stiffness and attenuated shear strain stiffening, and the cleavage of versican in liver results in reduced tissue compression stiffening. Thus, versican is an important collagen binding partner, playing a role in modulating collagen organization and mechanics.

cell biology↗

bioRxiv2022

Periductal bile acid exposure causes cholangiocyte injury and fibrosis

IntroductionBile duct integrity is essential for the maintenance of the structure and function of the biliary tree. We previously showed that cholangiocyte injury in a toxic model of biliary atresia leads to increased monolayer permeability. Increased epithelial permeability was also shown in other cholangiopathies. We hypothesized that after initial cholangiocyte injury, leakage of bile acids into the duct submucosa propagates cholangiocyte damage and fibrosis. We thus aimed to determine the impact of bile acid exposure on cholangiocytes and the potential therapeutic effect of a non-toxic bile acid. Materials and methodsExtrahepatic bile duct explants were isolated from adult and neonatal BALB/c mice. Explants were cultured with or without glycochenodeoxycholic acid and ursodeoxycholic acid. They were then fixed and stained. ResultsExplants treated with glycochenodeoxycholic acid demonstrated cholangiocyte injury with monolayer disruption and partial lumen obstruction compared to control ducts. Massons trichrome stains revealed increased collagen fibers. Myofibroblast marker -SMA stains were significantly elevated in the periductal region. The addition of ursodeoxycholic acid resulted in decreased cholangiocyte injury and reduced fibrosis. ConclusionsBile acid leakage into the submucosa after initial cholangiocyte injury may serve as a possible mechanism of disease propagation and progressive fibrosis in cholangiopathies.

physiology↗

bioRxiv2021

Efemp1 modulates elastic fiber formation and mechanics of the extrahepatic bile duct

EGF-Containing Fibulin Extracellular Matrix Protein 1 (EFEMP1, also called fibulin 3) is an extracellular matrix protein linked in a genome-wide association study to biliary atresia, a fibro-inflammatory disease of the neonatal extrahepatic bile duct. EFEMP1 is expressed in most tissues and Efemp1 null mice have decreased elastic fibers in visceral fascia; however, in contrast to other short fibulins (fibulins 4 and 5), EFEMP1 does not have a role in the development of large elastic fibers, and its overall function remains unclear. We demonstrated that EFEMP1 is expressed in the submucosa of both neonatal and adult mouse and human extrahepatic bile ducts and that, in adult Efemp1+/- mice, elastin organization into fibers is decreased. We used pressure myography, a technique developed to study the mechanics of the vasculature, to show that Efemp1+/- extrahepatic bile ducts are more compliant to luminal pressure, leading to increased circumferential stretch. We conclude that EFEMP1 has an important role in the formation of elastic fibers and mechanical properties of the extrahepatic bile duct. These data suggest that altered expression of EFEMP1 in the extrahepatic bile duct leads to an abnormal response to mechanical stress such as obstruction, potentially explaining the role of EFEMP1 in biliary atresia.

physiology↗

bioRxiv2021

Glycosaminoglycans Modulate Long-Range Mechanical Communication Between Cells in Collagen Networks

Cells can sense and respond to mechanical forces in fibrous extracellular matrices (ECM) over distances much greater than their size. This phenomenon, termed long-range force transmission, is enabled by the realignment (buckling) of collagen fibers along directions where the forces are tensile (compressive). However, whether other key structural components of the ECM, in particular glycosaminoglycans (GAGs), can affect the efficiency of cellular force transmission remains unclear. Here we developed a theoretical model of force transmission in collagen networks with interpenetrating GAGs, capturing the competition between tension-driven collagen-fiber alignment and the swelling pressure induced by GAGs. Using this model, we show that the swelling pressure provided by GAGs increases the stiffness of the collagen network by stretching the fibers in an isotropic manner. We found that the GAG-induced swelling pressure can help collagen fibers resist buckling as the cells exert contractile forces. This mechanism impedes the alignment of collagen fibers and decreases long-range cellular mechanical communication. We experimentally validated the theoretical predictions by comparing collagen fiber alignment between cellular spheroids cultured on collagen gels versus collagen-GAG co-gels. We found significantly less alignment of collagen in collagen-GAG co-gels, consistent with the prediction that GAGs can prevent collagen fiber alignment. The roles of GAGs in modulating force transmission uncovered in this work can be extended to understand pathological processes such as the formation of fibrotic scars and cancer metastasis, where cells communicate in the presence of abnormally high concentrations of GAGs. Statement of significanceGlycosaminoglycans (GAGs) are carbohydrates that are expressed ubiquitously in the human body and are among the key macromolecules that influence development, homeostasis, and pathology of native tissues. Abnormal accumulation of GAGs has been observed in metabolic disorders, solid tumors, and fibrotic tissues. Here we theoretically and experimentally show that tissue swelling caused by the highly polar nature of GAGs significantly affects the mechanical interactions between resident cells by altering the organization and alignment of the collagenous extracellular matrix. The roles of GAGs in modulating cellular force transmission revealed here can guide the design of biomaterial scaffolds in regenerative medicine and provides insights on the role of cell-cell communication in tumor progression and fibrosis.

biophysics↗

bioRxiv2021

Scaling concepts in 'omics: nuclear lamin-B scales with tumor growth and predicts poor prognosis, whereas fibrosis can be pro-survival

Spatiotemporal relationships between genes expressed in tissues likely reflect physicochemical principles that range from stoichiometric interactions to co-organized fractals with characteristic scaling. For key structural factors within the nucleus and extracellular matrix (ECM), gene-gene power laws are found to be characteristic across several tumor types in The Cancer Genome Atlas (TCGA) and across single-cell RNA-seq data. The nuclear filament LMNB1 scales with many tumor-elevated proliferation genes that predict poor survival in liver cancer, and cell line experiments show LMNB1 regulates cancer cell cycle. Also high in the liver, lung, and breast tumors studied here are the main fibrosis-associated collagens, COL1A1 and COL1A2, that scale stoichiometrically with each other and super-stoichiometrically with a pan-cancer fibrosis gene set. However, high fibrosis predicts prolonged survival of patients undergoing therapy and does not correlate with LMNB1. Single-cell RNA-seq data also reveal scaling consistent with the pan-cancer power laws obtained from bulk tissue, allowing new power law relations to be predicted. Lastly, although noisy data frustrate weak scaling, concepts such as stoichiometric scaling highlight a simple, internal consistency check to qualify expression data. ClassificationApplied Physical Sciences (major) and Cell Biology (minor) Significance StatementNon-linear scaling analyses pervade polymer physics and chemistry and conceivably provide new insight into polymeric assemblies of genes expressed in tissues as well as co-regulated gene sets. Fractal scaling and stoichiometric scaling are among the gene-gene power law results identified here for key structural polymers in nuclei or extracellular matrix in human cancer data. Among nuclear envelope factors that might scale with DNA mass, only one nuclear filament scales with tumor proliferation and predicts poor survival in some cancer types. Collagen-1 scales with fibrosis and also tends to increase in multiple tumor types, but patients in therapy surprisingly survive longest with the highest levels of fibrosis, consistent with a therapeutic response.

cancer biology↗