Leader cells mechanically respond to aligned collagen architecture to direct collective migration

Leader cells direct collective migration through sensing cues in their microenvironment to determine migration direction. The mechanism by which leader cells sense the mechanical cue of organized matrix architecture culminating in a mechanical response is not well defined. In this study, we investigated the effect of organized collagen matrix fibers on leader cell mechanics and demonstrate that leader cells protrude along aligned fibers resulting in an elongated phenotype of the entire cluster. Further, leader cells show increased mechanical interactions with their nearby matrix compared to follower cells, as evidenced by increased traction forces, increased and larger focal adhesions, and increased expression of integrin-α2. Together our results demonstrate changes in mechanical matrix cues drives changes in leader cell mechanoresponse that is required for directional collective migration. Our findings provide new insights into two fundamental components of carcinogenesis, namely invasion and metastasis.

Differential regulation of fibronectin expression and fibrillogenesis by autocrine TGF-β1 signaling in malignant and benign mammary epithelial cells

Remodeling of the extracellular matrix (ECM) is a key hallmark of cancer progression. A critical component of ECM remodeling is the assembly of the glycoprotein fibronectin (FN) into insoluble fibrils, which provide a scaffold for invading vascular endothelial cells and escaping cancer cells, as well as a framework for collagen deposition and oncogenic cytokine tethering. FN fibril assembly is induced by Transforming Growth Factor-β1 (TGF-β1), which was originally identified for its role in malignant transformation. Addition of exogenous TGF-β1 drives FN fibril assembly while also upregulating endogenous TGF-β1 expression and autocrine signaling. In the current study, we sought to determine if autocrine TGF-β1 signaling plays a role in FN fibril formation in either MCF10A mammary epithelial cells, which behave similarly to healthy epithelia, or malignant MDA- MB-231 breast cancer cells. Our results show two interesting findings: first, malignant MDA-MB- 231 cells assemble less FN into fibrils, despite expressing and secreting more soluble FN; second, autocrine TGF-β1 signaling is required for FN fibril formation in MCF10A epithelial cells, even in the presence of exogenous, active TGF-β1. This suggests that autocrine TGF-β1 is signaling through distinct pathways from active exogenous TGF-β1. We hypothesized that this signaling was mediated by interactions between the TGF-β1 latency associated peptide (LAP) and αv integrins; indeed, incubating MCF10As with soluble LAP, even in the absence of the active TGF-β1 ligand, partially recovered FN fibril assembly. Taken together, these data suggests that autocrine TGF-β1 plays a critical role in FN fibril assembly, and this interaction is mediated by LAP-integrin signaling.

Spatial Gradients of E-Cadherin and Fibronectin in TGF-β1-Treated Epithelial Colonies Are Independent of Fibronectin Fibril Assembly

Epithelial to Mesenchymal Transition (EMT) is a dynamic, morphogenetic process characterized by a phenotypic shift in epithelial cells towards a motile and often invasive mesenchymal phenotype. We have previously demonstrated that EMT is associated with an increase in assembly of the extracellular matrix protein fibronectin (FN) into insoluble, viscoelastic fibrils. We have also demonstrated that Transforming Growth Factor-β1 (TGF-β1) localizes to FN fibrils, and disruption of FN assembly or disruption of TGF-β1 localization to FN fibrils attenuates EMT. Previous studies have shown that TGF-β1 induces spatial gradients of EMT in mammary epithelial cells cultured on FN islands, with cells at free edges of the island preferentially undergoing EMT. In the current work, we sought to investigate: (a) whether FN fibril assembly is also spatially patterned in response to TGF-β1, and (b) what effects FN fibril inhibition has on spatial gradients of E-Cadherin and FN fibrillogenesis. We demonstrate that mammary epithelial cells cultured on square micropatterns have fewer E-Cadherin-containing adherens junctions and assemble more FN fibrils at the periphery of the micropattern in response to increasing TGF-β1 concentration, indicating that TGF-β1 induces a spatial gradient of both E-Cadherin and FN fibrils. Inhibition of FN fibril assembly globally diminished E-Cadherin-containing adherens junctions and FN fibrillogenesis, but did not eliminate the spatial gradient of either. This suggests that global inhibition of FN reduces the degree of both FN fibrillogenesis and E-Cadherin-containing adherens junctions, but does not eliminate the spatial gradient of either, suggesting that spatial gradients of EMT and FN fibrillogenesis are influenced by additional factors.

Modeling Costs and Life-Years Gained by Population-Wide Next-Generation Sequencing or Single-Gene Testing in Nonsquamous Non-Small-Cell Lung Cancer in the United States

PURPOSE

Many patients with actionable driver oncogenes (ADOs) are never identified and thus never receive targeted treatment. This study evaluated the economic impact and the potential life-years gained (LYG) that can be attributed to the extent of next-generation sequencing (NGS) testing in the United States compared with single-gene testing (SGT) in patients with metastatic nonsquamous non-small-cell lung cancer in the United States.

METHODS

A model was developed to evaluate incremental rates of SGT or NSG testing on the basis of LYG and cost per LYG. ADOs included for NGS included EGFR, ALK, ROS1, BRAF, RET, MET, and NTRK. SGT included EGFR and ALK. Assumptions were made for expected incidence of ADOs. Survival distributions were fit to published trial averages of median and 5-year overall survival. Treatment costs were estimated from drug cost averages. Reimbursement costs were based on data from the Center for Medicare and Medicaid Services.

RESULTS

Each incremental 10% increase in NGS testing produces an average of 2,627.4 additional LYG, with an average cost savings per LYG of $75 US dollars (USD). Replacing SGT at the current rate of 80% with NGS testing would result in an average additional 21,09.6 LYG and reduce cost per LYG by an average of $599 USD. If 100% of eligible patients were tested with NGS and each identified patient had matched treatment, the total average cost per LYG would be $16,641.57 USD.

CONCLUSION

On the basis of current evidence, population-level simulations demonstrate that clinically relevant gains in survival with non-negligible reduction in costs are obtainable from widespread adoption of NGS testing and appropriate treatment matching for patients with advanced nonsquamous non-small-cell lung cancer.

Interplay of Immunosuppression and Immunotherapy Among Patients With Cancer and COVID-19

Importance

Cytokine storm due to COVID-19 can cause high morbidity and mortality and may be more common in patients with cancer treated with immunotherapy (IO) due to immune system activation.

Objective

To determine the association of baseline immunosuppression and/or IO-based therapies with COVID-19 severity and cytokine storm in patients with cancer.

Design, Setting, and Participants

This registry-based retrospective cohort study included 12 046 patients reported to the COVID-19 and Cancer Consortium (CCC19) registry from March 2020 to May 2022. The CCC19 registry is a centralized international multi-institutional registry of patients with COVID-19 with a current or past diagnosis of cancer. Records analyzed included patients with active or previous cancer who had a laboratory-confirmed infection with SARS-CoV-2 by polymerase chain reaction and/or serologic findings.

Exposures

Immunosuppression due to therapy; systemic anticancer therapy (IO or non-IO).

Main Outcomes and Measures

The primary outcome was a 5-level ordinal scale of COVID-19 severity: no complications; hospitalized without requiring oxygen; hospitalized and required oxygen; intensive care unit admission and/or mechanical ventilation; death. The secondary outcome was the occurrence of cytokine storm.

Results

The median age of the entire cohort was 65 years (interquartile range [IQR], 54-74) years and 6359 patients were female (52.8%) and 6598 (54.8%) were non-Hispanic White. A total of 599 (5.0%) patients received IO, whereas 4327 (35.9%) received non-IO systemic anticancer therapies, and 7120 (59.1%) did not receive any antineoplastic regimen within 3 months prior to COVID-19 diagnosis. Although no difference in COVID-19 severity and cytokine storm was found in the IO group compared with the untreated group in the total cohort (adjusted odds ratio [aOR], 0.80; 95% CI, 0.56-1.13, and aOR, 0.89; 95% CI, 0.41-1.93, respectively), patients with baseline immunosuppression treated with IO (vs untreated) had worse COVID-19 severity and cytokine storm (aOR, 3.33; 95% CI, 1.38-8.01, and aOR, 4.41; 95% CI, 1.71-11.38, respectively). Patients with immunosuppression receiving non-IO therapies (vs untreated) also had worse COVID-19 severity (aOR, 1.79; 95% CI, 1.36-2.35) and cytokine storm (aOR, 2.32; 95% CI, 1.42-3.79).

Conclusions and Relevance

This cohort study found that in patients with cancer and COVID-19, administration of systemic anticancer therapies, especially IO, in the context of baseline immunosuppression was associated with severe clinical outcomes and the development of cytokine storm.

Trial Registration

ClinicalTrials.gov Identifier: NCT04354701.

Cell-Matrix Interactions in Renal Fibrosis

Renal fibrosis is a hallmark of end-stage chronic kidney disease. It is characterized by increased accumulation of extracellular matrix (ECM), which disrupts cellular organization and function within the kidney. Here, we review the bi-directional interactions between cells and the ECM that drive renal fibrosis. We will discuss the cells involved in renal fibrosis, changes that occur in the ECM, the interactions between renal cells and the surrounding fibrotic microenvironment, and signal transduction pathways that are misregulated as fibrosis proceeds. Understanding the underlying mechanisms of cell-ECM crosstalk will identify novel targets to better identify and treat renal fibrosis and associated renal disease.

A data-assimilation approach to predict population dynamics during epithelial-mesenchymal transition

Epithelial-mesenchymal transition (EMT) is a biological process that plays a central role in embryonic development, tissue regeneration, and cancer metastasis. Transforming growth factor-β (TGFβ) is a potent inducer of this cellular transition, comprising transitions from an epithelial state to partial or hybrid EMT state(s), to a mesenchymal state. Recent experimental studies have shown that, within a population of epithelial cells, heterogeneous phenotypical profiles arise in response to different time- and TGFβ dose-dependent stimuli. This offers a challenge for computational models, as most model parameters are generally obtained to represent typical cell responses, not necessarily specific responses nor to capture population variability. In this study, we applied a data-assimilation approach that combines limited noisy observations with predictions from a computational model, paired with parameter estimation. Synthetic experiments mimic the biological heterogeneity in cell states that is observed in epithelial cell populations by generating a large population of model parameter sets. Analysis of the parameters for virtual epithelial cells with biologically significant characteristics (e.g., EMT prone or resistant) illustrates that these sub-populations have identifiable critical model parameters. We perform a series of in silico experiments in which a forecasting system reconstructs the EMT dynamics of each virtual cell within a heterogeneous population exposed to time-dependent exogenous TGFβ dose and either an EMT-suppressing or EMT-promoting perturbation. We find that estimating population-specific critical parameters significantly improved the prediction accuracy of cell responses. Thus, with appropriate protocol design, we demonstrate that a data-assimilation approach successfully reconstructs and predicts the dynamics of a heterogeneous virtual epithelial cell population in the presence of physiological model error and parameter uncertainty.

OUP accepted manuscript

Introduction

The epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor osimertinib was recently approved for resected EGFR-mutant stages IB-IIIA non-small cell lung cancer due to improved disease-free survival (DFS) in this population compared with placebo. This study aimed to evaluate the cost-effectiveness (CE) of this strategy.

Materials and Methods

We constructed a Markov model using post-resection health state transitions with digitized DFS data from the ADAURA trial to compare cost and quality-adjusted life years (QALYs) of 3 years of adjuvant osimertinib versus placebo over a 10-year time horizon. An overall survival (OS) benefit of 5% was assumed. Costs and utility values were derived from Medicare reimbursement data and literature. A CE threshold of 3 times the gross domestic product per capita was used. Sensitivity analyses were performed.

Results

The incremental cost-effectiveness ratio for adjuvant osimertinib was $317 119 per QALY-gained versus placebo. Initial costs of osimertinib are higher in years 1-3. Costs due to progressive disease (PD) are higher in the placebo group through the first 6.5 years. Average pre-PD, post-PD, and total costs were $2388, $379 047, and $502 937, respectively, in the placebo group, and $505 775, $255 638, and $800 697, respectively, in the osimertinib group. Sensitivity analysis of OS gains reaches CE with an hazard ratio (HR) of 0.70-0.75 benefit of osimertinib over placebo. A 50% discount to osimertinib drug cost yielded an ICER of $115 419.

Conclusions

Three-years of adjuvant osimertinib is CE if one is willing to pay $317 119 more per QALY-gained. Considerable OS benefit over placebo or other economic interventions will be needed to reach CE.

Immunofluorescence Image Feature Analysis and Phenotype Scoring Pipeline for Distinguishing Epithelial-Mesenchymal Transition

Epithelial–mesenchymal transition (EMT) is an essential biological process, also implicated in pathological settings such as cancer metastasis, in which epithelial cells transdifferentiate into mesenchymal cells. We devised an image analysis pipeline to distinguish between tissues comprised of epithelial and mesenchymal cells, based on extracted features from immunofluorescence images of differing biochemical markers. Mammary epithelial cells were cultured with 0 (control), 2, 4, or 10 ng/mL TGF-β1, a well-established EMT-inducer. Cells were fixed, stained, and imaged for E-cadherin, actin, fibronectin, and nuclei via immunofluorescence microscopy. Feature selection was performed on different combinations of individual cell markers using a Bag-of-Features extraction. Control and high-dose images comprised the training data set, and the intermediate dose images comprised the testing data set. A feature distance analysis was performed to quantify differences between the treatment groups. The pipeline was successful in distinguishing between control (epithelial) and the high-dose (mesenchymal) groups, as well as demonstrating progress along the EMT process in the intermediate dose groups. Validation using quantitative PCR (qPCR) demonstrated that biomarker expression measurements were well-correlated with the feature distance analysis. Overall, we identified image pipeline characteristics for feature extraction and quantification of immunofluorescence images to distinguish progression of EMT.

Effects of substrate stiffness and actin velocity on in silico fibronectin fibril morphometry and mechanics

Assembly of the extracellular matrix protein fibronectin (FN) into insoluble, viscoelastic fibrils is a critical step during embryonic development and wound healing; misregulation of FN fibril assembly has been implicated in many diseases, including fibrotic diseases and cancer. We have previously developed a computational model of FN fibril assembly that recapitulates the morphometry and mechanics of cell-derived FN fibrils. Here we use this model to probe two important questions: how is FN fibril formation affected by the contractile phenotype of the cell, and how is FN fibril formation affected by the stiffness of the surrounding tissue? We show that FN fibril formation depends strongly on the contractile phenotype of the cell, but only weakly on in vitro substrate stiffness, which is an analog for in vivo tissue stiffness. These results are consistent with previous experimental data and provide a better insight into conditions that promote FN fibril assembly. We have also investigated two distinct phenotypes of FN fibrils that we have previously identified; we show that the ratio of the two phenotypes depends on both substrate stiffness and contractile phenotype, with intermediate contractility and high substrate stiffness creating an optimal condition for stably stretched fibrils. Finally, we have investigated how re-stretch of a fibril affects cellular response. We probed how the contractile phenotype of the re-stretching cell affects the mechanics of the fibril; results indicate that the number of myosin motors only weakly affects the cellular response, but increasing actin velocity results in a decrease in the apparent stiffness of the fibril and a decrease in the stably-applied force to the fibril. Taken together, these results give novel insights into the combinatorial effects of substrate stiffness and cell contractility on FN fibril assembly.

Hydroxyapatite Particle Density Regulates Osteoblastic Differentiation Through β-Catenin Translocation

Substrate surface characteristics such as roughness, wettability and particle density are well-known contributors of a substrate's overall osteogenic potential. These characteristics are known to regulate cell mechanics as well as induce changes in cell stiffness, cell adhesions, and cytoskeletal structure. Pro-osteogenic particles, such as hydroxyapatite, are often incorporated into a substrate to enhance the substrates osteogenic potential. However, it is unknown which substrate characteristic is the key regulator of osteogenesis. This is partly due to the lack of understanding of how these substrate surface characteristics are transduced by cells. In this study substrates composed of polycaprolactone (PCL) and carbonated hydroxyapatite particles (HAp) were synthesized. HAp concentration was varied, and a range of surface characteristics created. The effect of each substrate characteristic on osteoblastic differentiation was then examined. We found that, of the characteristics examined, only HAp density, and indeed a specific density (85 particles/cm²), significantly increased osteoblastic differentiation. Further, an increase in focal adhesion maturation and turnover was observed in cells cultured on this substrate. Moreover, β-catenin translocation from the membrane bound cell fraction to the nucleus was more rapid in cells on the 85 particle/cm² substrate compared to cells on tissue culture polystyrene. Together, these data suggest that particle density is one pivotal factor in determining a substrates overall osteogenic potential. Additionally, the observed increase in osteoblastic differentiation is a at least partly the result of β-catenin translocation and transcriptional activity suggesting a β-catenin mediated mechanism by which substrate surface characteristics are transduced.

Rheological characterization of poly-dimethyl siloxane formulations with tunable viscoelastic properties

Studies from the past two decades have demonstrated convincingly that cells are able to sense the mechanical properties of their surroundings. Cells make major decisions in response to this mechanosensation, including decisions regarding cell migration, proliferation, survival, and differentiation. The vast majority of these studies have focused on the cellular mechanoresponse to changing substrate stiffness (or elastic modulus) and have been conducted on purely elastic substrates. In contrast, most soft tissues in the human body exhibit viscoelastic behavior; that is, they generate responsive force proportional to both the magnitude and rate of strain. While several recent studies have demonstrated that viscous effects of an underlying substrate affect cellular mechanoresponse, there is not a straightforward experimental method to probe this, particularly for investigators with little background in biomaterial fabrication. In the current work, we demonstrate that polymers comprised of differing polydimethylsiloxane (PDMS) formulations can be generated that allow for control over both the strain-dependent storage modulus and the strain rate-dependent loss modulus. These substrates requires no background in biomaterial fabrication to fabricate, are shelf-stable, and exhibit repeatable mechanical properties. Here we demonstrate that these substrates are biocompatible and exhibit similar protein adsorption characteristics regardless of mechanical properties. Finally, we develop a set of empirical equations that predicts the storage and loss modulus for a given blend of PDMS formulations, allowing users to tailor substrate mechanical properties to their specific needs.

We have generated novel formulations of polydimethyl siloxane with varying viscoelastic properties that can be used to study cellular response. We present equations that can be used to predict the storage and loss moduli of these polymers.

A hybrid model of intercellular tension and cell-matrix mechanical interactions in a multicellular geometry

Epithelial cells form continuous sheets of cells that exist in tensional homeostasis. Homeostasis is maintained through cell-to-cell junctions that distribute tension and balance forces between cells and their underlying matrix. Disruption of tensional homeostasis can lead to epithelial-mesenchymal transition (EMT), a transdifferentiation process in which epithelial cells adopt a mesenchymal phenotype, losing cell-cell adhesion and enhancing cellular motility. This process is critical during embryogenesis and wound healing, but is also dysregulated in many disease states. To further understand the role of intercellular tension in spatial patterning of epithelial cell monolayers, we developed a multicellular computational model of cell-cell and cell-substrate forces. This work builds on a hybrid cellular Potts model (CPM)-finite element model to evaluate cell-matrix mechanical feedback of an adherent multicellular cluster. Cellular movement is governed by thermodynamic constraints from cell volume, cell-cell and cell-matrix contacts, and durotaxis, which arises from cell-generated traction forces on a finite element substrate. Junction forces at cell-cell contacts balance these traction forces, thereby producing a mechanically stable epithelial monolayer. Simulations were compared to in vitro experiments using fluorescence-based junction force sensors in clusters of cells undergoing EMT. Results indicate that the multicellular CPM model can reproduce many aspects of EMT, including epithelial monolayer formation dynamics, changes in cell geometry, and spatial patterning of cell-cell forces in an epithelial tissue.

Utilization of COVID-19 Treatments and Clinical Outcomes among Patients with Cancer: A COVID-19 and Cancer Consortium (CCC19) Cohort Study

Among 2,186 U.S. adults with invasive cancer and laboratory-confirmed SARS-CoV-2 infection, we examined the association of COVID-19 treatments with 30-day all-cause mortality and factors associated with treatment. Logistic regression with multiple adjustments (e.g., comorbidities, cancer status, baseline COVID-19 severity) was performed. Hydroxychloroquine with any other drug was associated with increased mortality versus treatment with any COVID-19 treatment other than hydroxychloroquine or untreated controls; this association was not present with hydroxychloroquine alone. Remdesivir had numerically reduced mortality versus untreated controls that did not reach statistical significance. Baseline COVID-19 severity was strongly associated with receipt of any treatment. Black patients were approximately half as likely to receive remdesivir as white patients. Although observational studies can be limited by potential unmeasured confounding, our findings add to the emerging understanding of patterns of care for patients with cancer and COVID-19 and support evaluation of emerging treatments through inclusive prospective controlled trials. SIGNIFICANCE: Evaluating the potential role of COVID-19 treatments in patients with cancer in a large observational study, there was no statistically significant 30-day all-cause mortality benefit with hydroxychloroquine or high-dose corticosteroids alone or in combination; remdesivir showed potential benefit. Treatment receipt reflects clinical decision-making and suggests disparities in medication access.This article is highlighted in the In This Issue feature, p. 1426.

Clinical impact of COVID-19 on patients with cancer (CCC19): a cohort study

BACKGROUND

Data on patients with COVID-19 who have cancer are lacking. Here we characterise the outcomes of a cohort of patients with cancer and COVID-19 and identify potential prognostic factors for mortality and severe illness.

METHODS

In this cohort study, we collected de-identified data on patients with active or previous malignancy, aged 18 years and older, with confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection from the USA, Canada, and Spain from the COVID-19 and Cancer Consortium (CCC19) database for whom baseline data were added between March 17 and April 16, 2020. We collected data on baseline clinical conditions, medications, cancer diagnosis and treatment, and COVID-19 disease course. The primary endpoint was all-cause mortality within 30 days of diagnosis of COVID-19. We assessed the association between the outcome and potential prognostic variables using logistic regression analyses, partially adjusted for age, sex, smoking status, and obesity. This study is registered with ClinicalTrials.gov, NCT04354701, and is ongoing.

FINDINGS

Of 1035 records entered into the CCC19 database during the study period, 928 patients met inclusion criteria for our analysis. Median age was 66 years (IQR 57-76), 279 (30%) were aged 75 years or older, and 468 (50%) patients were male. The most prevalent malignancies were breast (191 [21%]) and prostate (152 [16%]). 366 (39%) patients were on active anticancer treatment, and 396 (43%) had active (measurable) cancer. At analysis (May 7, 2020), 121 (13%) patients had died. In logistic regression analysis, independent factors associated with increased 30-day mortality, after partial adjustment, were: increased age (per 10 years; partially adjusted odds ratio 1·84, 95% CI 1·53-2·21), male sex (1·63, 1·07-2·48), smoking status (former smoker vs never smoked: 1·60, 1·03-2·47), number of comorbidities (two vs none: 4·50, 1·33-15·28), Eastern Cooperative Oncology Group performance status of 2 or higher (status of 2 vs 0 or 1: 3·89, 2·11-7·18), active cancer (progressing vs remission: 5·20, 2·77-9·77), and receipt of azithromycin plus hydroxychloroquine (vs treatment with neither: 2·93, 1·79-4·79; confounding by indication cannot be excluded). Compared with residence in the US-Northeast, residence in Canada (0·24, 0·07-0·84) or the US-Midwest (0·50, 0·28-0·90) were associated with decreased 30-day all-cause mortality. Race and ethnicity, obesity status, cancer type, type of anticancer therapy, and recent surgery were not associated with mortality.

INTERPRETATION

Among patients with cancer and COVID-19, 30-day all-cause mortality was high and associated with general risk factors and risk factors unique to patients with cancer. Longer follow-up is needed to better understand the effect of COVID-19 on outcomes in patients with cancer, including the ability to continue specific cancer treatments.

FUNDING

American Cancer Society, National Institutes of Health, and Hope Foundation for Cancer Research.

Cell Fate Forecasting: A Data-Assimilation Approach to Predict Epithelial-Mesenchymal Transition

Epithelial-mesenchymal transition (EMT) is a fundamental biological process that plays a central role in embryonic development, tissue regeneration, and cancer metastasis. Transforming growth factor-β (TGFβ) is a potent inducer of this cellular transition, which is composed of transitions from an epithelial state to intermediate or partial EMT state(s) to a mesenchymal state. Using computational models to predict cell state transitions in a specific experiment is inherently difficult for reasons including model parameter uncertainty and error associated with experimental observations. In this study, we demonstrate that a data-assimilation approach using an ensemble Kalman filter, which combines limited noisy observations with predictions from a computational model of TGFβ-induced EMT, can reconstruct the cell state and predict the timing of state transitions. We used our approach in proof-of-concept “synthetic” in silico experiments, in which experimental observations were produced from a known computational model with the addition of noise. We mimic parameter uncertainty in in vitro experiments by incorporating model error that shifts the TGFβ doses associated with the state transitions and reproduces experimentally observed variability in cell state by either shifting a single parameter or generating “populations” of model parameters. We performed synthetic experiments for a wide range of TGFβ doses, investigating different cell steady-state conditions, and conducted parameter studies varying properties of the data-assimilation approach including the time interval between observations and incorporating multiplicative inflation, a technique to compensate for underestimation of the model uncertainty and mitigate the influence of model error. We find that cell state can be successfully reconstructed and the future cell state predicted in synthetic experiments, even in the setting of model error, when experimental observations are performed at a sufficiently short time interval and incorporate multiplicative inflation. Our study demonstrates the feasibility and utility of a data-assimilation approach to forecasting the fate of cells undergoing EMT.

Mechanochemical Signaling of the Extracellular Matrix in Epithelial-Mesenchymal Transition

Epithelial-Mesenchymal Transition (EMT) is a critical process in embryonic development in which epithelial cells undergo a transdifferentiation into mesenchymal cells. This process is essential for tissue patterning and organization, and it has also been implicated in a wide array of pathologies. While the intracellular signaling pathways that regulate EMT are well-understood, there is increasing evidence that the mechanical properties and composition of the extracellular matrix (ECM) also play a key role in regulating EMT. In turn, EMT drives changes in the mechanics and composition of the ECM, creating a feedback loop that is tightly regulated in healthy tissues, but is often dysregulated in disease. Here we present a review that summarizes our understanding of how ECM mechanics and composition regulate EMT, and how in turn EMT alters ECM mechanics and composition.

Fibronectin Conformation and Assembly: Analysis of Fibronectin Deletion Mutants and Fibronectin Glomerulopathy (GFND) Mutants

To study fibronectin (FN) conformation and assembly, we generated several deletion mutants: FNΔ^I1-5, FNΔ^III1-3, FNΔ^III4-8, and FNΔ^III11-14. A monomeric form, FNmono, which lacked the C-terminal dimerization region, was also created. FNtnA-D was generated by swapping FNIII domains 1-8 in FNΔ^III11-14 with seven FNIII domains from tenascin-C. The conformations of these mutants were analyzed by glycerol gradient sedimentation under low-salt (20 mM NaCl) and high-salt (200 mM NaCl) conditions. Surprisingly, most of the mutants showed a compact conformation under low-salt conditions, except for FNtnA-D. When we tested these mutants in cell culture, FNΔ^I1-5, FNΔ^III1-3, and FNtnA-D were unable to form a matrix. Interestingly, FNΔ^III1-3 and FNtnA-D were capable of co-assembly with full-length FN, while FNΔ^I1-5 was not. This indicates that the segment ^I1-5 is crucial for matrix assembly and segment ^III1-3 is also important. Mutations in FN are associated with glomerulopathy, but when we studied mutant proteins, the single-nucleotide mutations had only minor effects on conformation and matrix assembly. The mutations may destabilize their FNIII domains or generate dimers of dimers by disulfide cross-linking.

Mechanotransduction Dynamics at the Cell-Matrix Interface

The ability of cells to sense and respond to mechanical cues from the surrounding environment has been implicated as a key regulator of cell differentiation, migration, and proliferation. The extracellular matrix (ECM) is an oft-overlooked component of the interface between cells and their surroundings. Cells assemble soluble ECM proteins into insoluble fibrils with unique mechanical properties that can alter the mechanical cues a cell receives. In this study, we construct a model that predicts the dynamics of cellular traction force generation and subsequent assembly of fibrils of the ECM protein fibronectin (FN). FN fibrils are the primary component in primordial ECM and, as such, FN assembly is a critical component in the cellular mechanical response. The model consists of a network of Hookean springs, each representing an extensible domain within an assembling FN fibril. As actomyosin forces stretch the spring network, simulations predict the resulting traction force and FN fibril formation. The model accurately predicts FN fibril morphometry and demonstrates a mechanism by which FN fibril assembly regulates traction force dynamics in response to mechanical stimuli and varying surrounding substrate stiffness.

Fibronectin fibrils regulate TGF-β1-induced Epithelial-Mesenchymal Transition

Epithelial-Mesenchymal Transition (EMT) is a dynamic process through which epithelial cells transdifferentiate from an epithelial phenotype into a mesenchymal phenotype. Previous studies have demonstrated that both mechanical signaling and soluble growth factor signaling facilitate this process. One possible point of integration for mechanical and growth factor signaling is the extracellular matrix. Here we investigate the role of the extracellular matrix (ECM) protein fibronectin (FN) in this process. We demonstrate that inhibition of FN fibrillogenesis blocks activation of the Transforming Growth Factor-Beta (TGF-β) signaling pathway via Smad2 signaling, decreases cell migration and ultimately leads to inhibition of EMT. Results show that soluble FN, FN fibrils, or increased contractile forces are insufficient to independently induce EMT. We further demonstrate that inhibition of latent TGF-β1 binding to FN fibrils via either a monoclonal blocking antibody against the growth factor binding domain of FN or through use of a FN deletion mutant that lacks the growth factor binding domains of FN blocks EMT progression, indicating a novel role for FN in EMT in which the assembly of FN fibrils serves to localize TGF-β1 signaling to drive EMT.

Nesprin-2G, a Component of the Nuclear LINC Complex, Is Subject to Myosin-Dependent Tension

The nucleus of a cell has long been considered to be subject to mechanical force. Despite the observation that mechanical forces affect nuclear geometry and movement, how forces are applied onto the nucleus is not well understood. The nuclear LINC (linker of nucleoskeleton and cytoskeleton) complex has been hypothesized to be the critical structure that mediates the transfer of mechanical forces from the cytoskeleton onto the nucleus. Previously used techniques for studying nuclear forces have been unable to resolve forces across individual proteins, making it difficult to clearly establish if the LINC complex experiences mechanical load. To directly measure forces across the LINC complex, we generated a fluorescence resonance energy transfer-based tension biosensor for nesprin-2G, a key structural protein in the LINC complex, which physically links this complex to the actin cytoskeleton. Using this sensor we show that nesprin-2G is subject to mechanical tension in adherent fibroblasts, with highest levels of force on the apical and equatorial planes of the nucleus. We also show that the forces across nesprin-2G are dependent on actomyosin contractility and cell elongation. Additionally, nesprin-2G tension is reduced in fibroblasts from Hutchinson-Gilford progeria syndrome patients. This report provides the first, to our knowledge, direct evidence that nesprin-2G, and by extension the LINC complex, is subject to mechanical force. We also present evidence that nesprin-2G localization to the nuclear membrane is altered under high-force conditions. Because forces across the LINC complex are altered by a variety of different conditions, mechanical forces across the LINC complex, as well as the nucleus in general, may represent an important mechanism for mediating mechanotransduction.

Fibronectin fibrillogenesis facilitates mechano-dependent cell spreading, force generation, and nuclear size in human embryonic fibroblasts

Cells respond to mechanical cues from the substrate to which they are attached. These mechanical cues drive cell migration, proliferation, differentiation, and survival. Previous studies have highlighted three specific mechanisms through which substrate stiffness directly alters cell function: increasing stiffness drives (1) larger contractile forces; (2) increased cell spreading and size; and (3) altered nuclear deformation. While studies have shown that substrate mechanics are an important cue, the role of the extracellular matrix (ECM) has largely been ignored. The ECM is a crucial component of the mechanosensing system for two reasons: (1) many ECM fibrils are assembled by application of cell-generated forces, and (2) ECM proteins have unique mechanical properties that will undoubtedly alter the local stiffness sensed by a cell. We specifically focused on the role of the ECM protein fibronectin (FN), which plays a critical role in de novo tissue production. In this study, we first measured the effects of substrate stiffness on human embryonic fibroblasts by plating cells onto microfabricated pillar arrays (MPAs) of varying stiffness. Cells responded to increasing substrate stiffness by generating larger forces, spreading to larger sizes, and altering nuclear geometry. These cells also assembled FN fibrils across all stiffnesses, with optimal assembly occurring at approximately 6 kPa. We then inhibited FN assembly, which resulted in dramatic reductions in contractile force generation, cell spreading, and nuclear geometry across all stiffnesses. These findings suggest that FN fibrils play a critical role in facilitating cellular responses to substrate stiffness.

Endothelial matrix assembly during capillary morphogenesis: insights from chimeric TagRFP-fibronectin matrix

Biologically relevant, three-dimensional extracellular matrix is an essential component of in vitro vasculogenesis models. WI-38 fibroblasts assemble a 3D matrix that induces endothelial tubulogenesis, but this model is challenged by fibroblast senescence and the inability to distinguish endothelial cell-derived matrix from matrix made by WI-38 fibroblasts. Matrices produced by hTERT-immortalized WI-38 recapitulated those produced by wild type fibroblasts. ECM fibrils were heavily populated by tenascin-C, fibronectin, and type VI collagen. Nearly half of the total type I collagen, but only a small fraction of the type IV collagen, were incorporated into ECM. Stable hTERT-WI-38 transfectants expressing TagRFP-fibronectin incorporated TagRFP into ~90% of the fibronectin in 3D matrices. TagRFP-fibronectin colocalized with tenascin-C and with type I collagen in a pattern that was similar to that seen in matrices from wild type WI-38. Human Umbilical Vein Endothelial Cells (HUVEC) formed 3D adhesions and tubes on WI38-hTERT-TagRFP-FN-derived matrices, and the TagRFP-fibronectin component of this new 3D human fibroblast matrix model facilitated the demonstration of concentrated membrane type 1 metalloprotease and new HUVEC FN and collagen type IV fibrils during EC tubulogenesis. These findings indicate that WI-38-hTERT- and WI-38-hTERT-TagRFP-FN-derived matrices provide platforms for the definition of new matrix assembly and remodeling events during vasculogenesis.

Probing the folded state of fibronectin type III domains in stretched fibrils by measuring buried cysteine accessibility

Fibronectin (FN) is an extracellular matrix protein that is assembled into fibrils by cells during tissue morphogenesis and wound healing. FN matrix fibrils are highly elastic, but the mechanism of elasticity has been debated: it may be achieved by mechanical unfolding of FN-III domains or by a conformational change of the molecule without domain unfolding. Here, we investigate the folded state of FN-III domains in FN fibrils by measuring the accessibility of buried cysteines. Four of the 15 FN-III domains (III-2, -3, -9, and -11) appear to unfold in both stretched fibrils and in solution, suggesting that these domains spontaneously open and close even in the absence of tension. Two FN-III domains (III-6 and -12) appear to unfold only in fibrils and not in solution. These results suggest that domain unfolding can at best contribute partially to the 4-fold extensibility of fibronectin fibrils.

FAK potentiates Rac1 activation and localization to matrix adhesion sites: a role for betaPIX

FAK, a cytoplasmic protein tyrosine kinase, is activated and localized to focal adhesions upon cell attachment to extracellular matrix. FAK null cells spread poorly and exhibit altered focal adhesion turnover. Rac1 is a member of the Rho-family GTPases that promotes membrane ruffling, leading edge extension, and cell spreading. We investigated the activation and subcellular location of Rac1 in FAK null and FAK reexpressing fibroblasts. FAK reexpressers had a more robust pattern of Rac1 activation after cell adhesion to fibronectin than the FAK null cells. Translocation of Rac1 to focal adhesions was observed in FAK reexpressers, but seldom in FAK null cells. Experiments with constitutively active L61Rac1 and dominant negative N17Rac1 indicated that the activation state of Rac1 regulated its localization to focal adhesions. We demonstrated that FAK tyrosine-phosphorylated betaPIX and thereby increased its binding to Rac1. In addition, betaPIX facilitated the targeting of activated Rac1 to focal adhesions and the efficiency of cell spreading. These data indicate that FAK has a role in the activation and focal adhesion translocation of Rac1 through the tyrosine phosphorylation of betaPIX.

Oxidized low-density lipoprotein-dependent endothelial arginase II activation contributes to impaired nitric oxide signaling

Oxidized low-density lipoprotein (OxLDL) impairs NO signaling and endothelial function, and contributes to the pathogenesis of atherosclerosis. Arginase reciprocally regulates NO levels in endothelial cells by competing with NO synthase for the substrate l-arginine. In human aortic endothelial cells, OxLDL stimulation increased arginase enzyme activity in a time- and dose-dependent manner. Arginase activity reached its maximum as early as 5 minutes, was maintained for a period of more than 48 hours, and was associated with a reciprocal decrease in NO metabolite (NOx [nitrite and nitrate]) production. Furthermore, OxLDL induced arginase II mRNA expression after 4 hours. Small interfering RNA targeted to arginase II decreased both the quantity and the activity of arginase from baseline, prevented OxLDL-dependent increases in arginase activity, and induced an increase in NOx production. Immunofluorescence analysis revealed an association of arginase II with the microtubule cytoskeleton. Microtubule disruption with nocodazole caused a dramatic redistribution of arginase II to a diffuse cytosolic pattern, increased arginase activity, and decreased NOx production, which was restored in the presence of the specific arginase inhibitor (S)-(2-boronoethyl)-l-cysteine (BEC). On the other hand, epothilone B prevented microtubule disruption and inhibited OxLDL-dependent increases in arginase activity and attenuated OxLDL-dependent decreases in NOx. Preincubation of rat aortic rings with OxLDL resulted in an increase in arginase activity and a decrease in NOx production. This was reversed by arginase inhibition with the BEC. Thus, OxLDLs increase arginase activity by a sequence of regulatory events that involve early activation through decreased association with microtubules and a later increase in transcription. Furthermore, increased arginase activity contributes to OxLDL-dependent impairment of NOx production. Arginase, therefore, represents a novel target for therapy in atherosclerosis.

An inhibitory role for FAK in regulating proliferation: a link between limited adhesion and RhoA-ROCK signaling

Focal adhesion kinase (FAK) transduces cell adhesion to the extracellular matrix into proliferative signals. We show that FAK overexpression induced proliferation in endothelial cells, which are normally growth arrested by limited adhesion. Interestingly, displacement of FAK from adhesions by using a FAK−/− cell line or by expressing the C-terminal fragment FRNK also caused an escape of adhesion-regulated growth arrest, suggesting dual positive and negative roles for FAK in growth regulation. Expressing kinase-dead FAK-Y397F in FAK−/− cells prevented uncontrolled growth, demonstrating the antiproliferative function of inactive FAK. Unlike FAK overexpression–induced growth, loss of growth control in FAK−/− or FRNK-expressing cells increased RhoA activity, cytoskeletal tension, and focal adhesion formation. ROCK inhibition rescued adhesion-dependent growth control in these cells, and expression of constitutively active RhoA or ROCK dysregulated growth. These findings demonstrate the ability of FAK to suppress and promote growth, and underscore the importance of multiple mechanisms, even from one molecule, to control cell proliferation.

Shear force at the cell-matrix interface: enhanced analysis for microfabricated post array detectors

The interplay of mechanical forces between the extracellular environment and the cytoskeleton drives development, repair, and senescence in many tissues. Quantitative definition of these forces is a vital step in understanding cellular mechanosensing. Microfabricated post array detectors (mPADs) provide direct measurements of cell-generated forces during cell adhesion to extracellular matrix. A new approach to mPAD post labeling, volumetric imaging, and an analysis of post bending mechanics determined that cells apply shear forces and not point moments at the matrix interface. In addition, these forces could be accurately resolved from post deflections by using images of post tops and bases. Image analysis tools were then developed to increase the precision and throughput of post centroid location. These studies resulted in an improved method of force measurement with broad applicability and concise execution using a fully automated force analysis system. The new method measures cell-generated forces with less than 5% error and less than 90 seconds of computational time. Using this approach, we demonstrated direct and distinct relationships between cellular traction force and spread cell surface area for fibroblasts, endothelial cells, epithelial cells and smooth muscle cells.

Nitric oxide regulates the heart by spatial confinement of nitric oxide synthase isoforms

Subcellular localization of nitric oxide (NO) synthases with effector molecules is an important regulatory mechanism for NO signalling. In the heart, NO inhibits L-type Ca2+ channels but stimulates sarcoplasmic reticulum (SR) Ca2+ release, leading to variable effects on myocardial contractility. Here we show that spatial confinement of specific NO synthase isoforms regulates this process. Endothelial NO synthase (NOS3) localizes to caveolae, where compartmentalization with beta-adrenergic receptors and L-type Ca2+ channels allows NO to inhibit beta-adrenergic-induced inotropy. Neuronal NO synthase (NOS1), however, is targeted to cardiac SR. NO stimulation of SR Ca2+ release via the ryanodine receptor (RyR) in vitro, suggests that NOS1 has an opposite, facilitative effect on contractility. We demonstrate that NOS1-deficient mice have suppressed inotropic response, whereas NOS3-deficient mice have enhanced contractility, owing to corresponding changes in SR Ca2+ release. Both NOS1-/- and NOS3-/- mice develop age-related hypertrophy, although only NOS3-/- mice are hypertensive. NOS1/3-/- double knockout mice have suppressed beta-adrenergic responses and an additive phenotype of marked ventricular remodelling. Thus, NOS1 and NOS3 mediate independent, and in some cases opposite, effects on cardiac structure and function.