Matrix-Bound Hyaluronan Molecular Weight as a Regulator of Dendritic Cell Immune Potency

Hyaluronic acid (HA) is a glycosaminoglycan in the extracellular matrix with immunoregulatory properties depending on its molecular weight (MW). However, the impact of matrix-bound HA on dendritic cells (DCs) remains unclear due to varying distribution of HA MW under different physiological conditions. To investigate DCs in defined biosystems, 3D collagen matrices modified with HA of specific MW with similar microstructure and HA levels are used. It is found that HA MW influences cytokine binding to matrix, suggesting modulation of cytokine availability by the different HA MWs. These studies on DC immune potency reveal that low MW HA (8-15 kDa) enhances immature DC differentiation and antigen uptake, while medium (MMW-HA; 500-750 kDa) and high MW HA (HMW-HA; 1250-1500 kDa) increase cytokine secretion in mature DCs. The effect on DC phenotype and cytokine secretion by different MWs of HA is independent of CD44. However, blocking the CD44 receptor reveals its potential role in regulating acute inflammation through increased secretion of CCL2, CXCL8, and IL-6. Additionally, MMW- and HMW-HA matrices reduce migratory capacity of DCs, dependent on CD44. Overall, these findings provide insights into MW-dependent effects of matrix-bound HA on DCs, opening avenues for the design of DC-modulating materials to enhance DC-based therapy.

Photo-Controlled Reversible Uptake and Release of a Modified Sulfamethoxazole Antibiotic Drug from a Pillar[5]arene Cross-Linked Gelatin Hydrogel

Pillararene cross-linked gelatin hydrogels were designed and synthesized to control the uptake and release of antibiotics using light. A suite of characterization techniques ranging from spectroscopy (FT-IR, 1H and 13C NMR, and MAS NMR), X-ray crystallographic analysis, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) was employed to investigate the physicochemical properties of hydrogels. The azobenzene-modified sulfamethoxazole (Azo-SMX) antibiotic was noncovalently incorporated into the hydrogel via supramolecular host-guest interactions to afford the A-hydrogel. While in its ground state, the Azo-SMX guest has a trans configuration structure and forms a thermodynamically stable inclusion complex with the pillar[5]arene motif in the hydrogel matrix. When the A-hydrogel was exposed to 365 nm UV light, Azo-SMX underwent a photoisomerization reaction. This changed the structure of Azo-SMX from trans to cis, and the material was released into the environment. The Azo-SMX released from the hydrogel was effective against both Gram-positive and Gram-negative bacteria. Importantly, the A-hydrogel exhibited a striking difference in antibacterial activity when applied to bacterial colonies in the presence and absence of UV light, highlighting the switchable antibacterial activity of A-hydrogel aided by light. In addition, all hydrogels containing pillar[5]arenes have demonstrated biocompatibility and effectiveness as scaffolds for biological and medical purposes.

Effects of an aged tissue niche on the immune potency of dendritic cells using simulated microgravity

Microgravity accelerates the aging of various physiological systems, and it is well acknowledged that aged individuals and astronauts both have increased susceptibility to infections and poor response to vaccination. Immunologically, dendritic cells (DCs) are the key players in linking innate and adaptive immune responses. Their distinct and optimized differentiation and maturation phases play a critical role in presenting antigens and mounting effective lymphocyte responses for long-term immunity. Despite their importance, no studies to date have effectively investigated the effects of microgravity on DCs in their native microenvironment, which is primarily located within tissues. Here, we address a significantly outstanding research gap by examining the effects of simulated microgravity via a random positioning machine on both immature and mature DCs cultured in biomimetic collagen hydrogels, a surrogate for tissue matrices. Furthermore, we explored the effects of loose and dense tissues via differences in collagen concentration. Under these various environmental conditions, the DC phenotype was characterized using surface markers, cytokines, function, and transcriptomic profiles. Our data indicate that aged or loose tissue and exposure to RPM-induced simulated microgravity both independently alter the immunogenicity of immature and mature DCs. Interestingly, cells cultured in denser matrices experience fewer effects of simulated microgravity at the transcriptome level. Our findings are a step forward to better facilitate healthier future space travel and enhance our understanding of the aging immune system on Earth.

Collagen Fibril Orientation Instructs Fibroblast Differentiation Via Cell Contractility

Collagen alignment is one of the key microarchitectural signatures of many pathological conditions, including scarring and fibrosis. Investigating how collagen alignment modulates cellular functions will pave the way for understanding tissue scarring and regeneration and new therapeutic strategies. However, current approaches for the fabrication of three-dimensional (3D) aligned collagen matrices are low-throughput and require special devices. To overcome these limitations, a simple approach to reconstitute homogeneous 3D collagen matrices with adjustable degree of fibril alignment using 3D printed inclined surfaces is developed. By characterizing the mechanical properties of reconstituted matrices, it is found that the elastic modulus of collagen matrices is enhanced with an increase in the alignment degree. The reconstituted matrices are used to study fibroblast behavior to reveal the progression of scar formation where a gradual enhancement of collagen alignment can be observed. It is found that matrices with aligned fibrils trigger fibroblast differentiation into myofibroblasts via cell contractility, while collagen stiffening through a crosslinker does not. The results suggest the impact of collagen fibril organization on the regulation of fibroblast differentiation. Overall, this approach to reconstitute 3D collagen matrices with fibril alignment opens opportunities for biomimetic pathological-relevant tissue in vitro, which can be applied for other biomedical research.

Phenotype Switching of Breast Cancer Cells upon Matrix Interface Crossing

Tumor cell growth, invasion, and metastasis are dependent on the tumor microenvironment. Many studies emphasize a correlation between the material characteristics of the tumor extracellular matrix (ECM) and the invasive properties of tumor cells and even a trigger of tumor aggressiveness. Herein, we report that the previously observed trigger of migration characteristics of MDA-MB-231 breast cancer cells during transmigration across interfaces of two differently porous matrices is strongly correlated with a persistent change in cell invasiveness and aggressiveness. Using an in vitro 3D model of fibrillar collagen-I matrices, we found an increase in migration directionality, strongly elongated morphology, higher proliferation, and an increase in aggressive markers in the genetic profile after cells crossed the interface from dense to open porous matrix microstructure. Moreover, our results indicate strong nuclear deformation and increased DNA damage during transmigration of the matrix interface as a possible trigger of the more aggressive phenotype. These findings suggest that distinct tissue interfaces or altered ECM conditions with differences in microstructure may instruct or even reprogram tumor cells toward more aggressive phenotypes in vivo. The biomedical relevance of our results is corroborated by additional findings that the transmigrated cells exhibit an increased resistance against a common breast cancer therapeutic.

Degradation products of crosslinked silk fibroin scaffolds modulate the immune response but not cell toxicity

Silk fibroin (SF) scaffolds have widely been used as functional materials for tissue engineering and implantation. For long-term applications, many cross-linking strategies have been developed to enhance the stability and enzymatic degradation of scaffolds. Although the biocompatibility of SF scaffolds has been investigated, less is known about the extent to which the degradation products of these scaffolds affect the host response in the long term after implantation. In this work, we first studied the effect of two different crosslinkers, namely, 1-ethyl-3-(3-dimethylaminopropyl-carbodiimide hydrochloride) (EDC) and glutaraldehyde (GA), on the topology, mechanical stability and enzymatic degradation of SF scaffolds. We found that the SF scaffolds treated with GA (GA-SF) appeared to show an increase in the sheet thickness and a higher elastic modulus when compared to that treated with EDC (EDC-SF) at a similar level of crosslinking degree. The uncrosslinked and both crosslinked SF scaffolds were completely digested by proteinase K but were not susceptible to degradation by collagenase type IV and trypsin. We next investigated the effect of the degradation of SF on the cytotoxicity, genotoxicity, and immunogenicity. The results demonstrated that the degradation products of the uncrosslinked and crosslinked SFs did not trigger cell proliferation, cell death, or genotoxicity in primary human cells, while they appeared to modulate the phenotypes of macrophages. The degradation products of GA-SF promoted pro-inflammatory phenotypes, while those from EDC-SF enhanced polarization towards anti-inflammatory macrophages. Our results demonstrated that the degradation products of SF scaffolds can mediate the immune modulation of macrophages, which can be implemented as a therapeutic strategy to control the long-term immune response during implantation.

The T Cell Journey: A Tour de Force

T cells act as the puppeteers in the adaptive immune response, and their dysfunction leads to the initiation and progression of pathological conditions. During their lifetime, T cells experience myriad forces that modulate their effector functions. These forces are imposed by interacting cells, surrounding tissues, and shear forces from fluid movement. In this review, a journey with T cells is made, from their development to their unique characteristics, including the early studies that uncovered their mechanosensitivity. Then the studies pertaining to the responses of T cell activation to changes in antigen-presenting cells' physical properties, to their immediate surrounding extracellular matrix microenvironment, and flow conditions are highlighted. In addition, it is explored how pathological conditions like the tumor microenvironment can hinder T cells and allow cancer cells to escape elimination.

May the Force Be with You (Or Not): The Immune System under Microgravity

All terrestrial organisms have evolved and adapted to thrive under Earth's gravitational force. Due to the increase of crewed space flights in recent years, it is vital to understand how the lack of gravitational forces affects organisms. It is known that astronauts who have been exposed to microgravity suffer from an array of pathological conditions including an impaired immune system, which is one of the most negatively affected by microgravity. However, at the cellular level a gap in knowledge exists, limiting our ability to understand immune impairment in space. This review highlights the most significant work done over the past 10 years detailing the effects of microgravity on cellular aspects of the immune system.

Engineered Microvessel for Cell Culture in Simulated Microgravity

As the number of manned space flights increase, studies on the effects of microgravity on the human body are becoming more important. Due to the high expense and complexity of sending samples into space, simulated microgravity platforms have become a popular way to study these effects on earth. In addition, simulated microgravity has recently drawn the attention of regenerative medicine by increasing cell differentiation capability. These platforms come with many advantages as well as limitations. A main limitation for usage of these platforms is the lack of high-throughput capability due to the use of large cell culture vessels. Therefore, there is a requirement for microvessels for microgravity platforms that limit waste and increase throughput. In this work, a microvessel for commercial cell culture plates was designed. Four 3D printable (polycarbonate (PC), polylactic acid (PLA) and resin) and castable (polydimethylsiloxane (PDMS)) materials were assessed for biocompatibility with adherent and suspension cell types. PDMS was found to be the most suitable material for microvessel fabrication, long-term cell viability and proliferation. It also allows for efficient gas exchange, has no effect on cell culture media pH and does not induce hypoxic conditions. Overall, the designed microvessel can be used on simulated microgravity platforms as a method for long-term high-throughput biomedical studies.

Dendritic cell immune potency on 2D and in 3D collagen matrices

Dendritic cells (DCs) are antigen-presenting cells capable of either activating the immune response or inducing and maintaining immune tolerance. Understanding how biophysical properties affect DC behaviors will provide insight into the biology of a DC and its applications. In this work, we studied how cell culture dimensionality (two-dimensional (2D) and three-dimensional (3D)), and matrix density of 3D collagen matrices modulate differentiation and functions of DCs. Besides, we aimed to point out the different conceptual perspectives in modern immunological research, namely tissue-centric and cell-centric perspectives. The tissue-centric perspective intends to reveal how specific microenvironments dictate DC differentiation and in turn modulate DC functionalities, while the cell-centric perspective aims to demonstrate how pre-differentiated DCs behave in specific microenvironments. DC plasticity was characterized in terms of cell surface markers and cytokine secretion profiles. Subsequently, antigen internalization and T cell activation were quantified to demonstrate the cellular functions of immature DCs (iDCs) and mature DCs (mDCs), respectively. In the tissue-centric perspective, we found that expressed surface markers and secreted cytokines of both iDCs and mDCs are generally higher in 2D culture, while they are regulated by matrix density in 3D culture. In contrast, in the cell-centric perspective, we found enhanced expression of cell surface markers as well as distinct cytokine secretion profiles in both iDCs and mDCs. By analyzing cellular functions of cells in the tissue-centric perspective, we found matrix density dependence in antigen uptake by iDCs, as well as on mDC-mediated T cell proliferation in 3D cell culture. On the other hand, in the cell-centric perspective, both iDCs and mDCs appeared to lose their functional potentials to internalization antigen and T cell stimulation. Additionally, mDCs from tissue- and cell-centric perspectives modulated T cell differentiation by their distinct cytokine secretion profiles towards Th1 and Th17, respectively. In sum, our work emphasizes the importance of dimensionality, as well as collagen fibrillar density in the regulation of the immune response of DCs. Besides this, we demonstrated that the conceptual perspective of the experimental design could be an essential key point in research in immune cell-material interactions and biomaterial-based disease models of immunity.

Multi-Compartment Lymph-Node-on-a-Chip Enables Measurement of Immune Cell Motility in Response to Drugs

Organs On-a-Chip represent novel platforms for modelling human physiology and disease. The lymph node (LN) is a relevant immune organ in which B and T lymphocytes are spatially organized in a complex architecture, and it is the place where the immune response initiates. The present study addresses the utility of a recently designed LN-on-a-chip to dissect and understand the effect of drugs delivered to cells in a fluidic multicellular 3D setting that mimics the human LN. To do so, we analyzed the motility and viability of human B and T cells exposed to hydroxychloroquine (HCQ). We show that the innovative LN platform, which operates at a microscale level, allows real-time monitoring of co-cultured B and T cells by imaging, and supports cellular random movement. HCQ delivered to cells through a constant and continuous flow induces a reduction in T cell velocity while promotes persistent rotational motion. We also find that HCQ increases the production of reactive oxygen species in T cells. Taken together, these results highlight the potential of the LN-on-a-chip to be applied in drug screening and development, and in cellular dynamics studies.

Modeling Adipogenesis: Current and Future Perspective

Adipose tissue is contemplated as a dynamic organ that plays key roles in the human body. Adipogenesis is the process by which adipocytes develop from adipose-derived stem cells to form the adipose tissue. Adipose-derived stem cells’ differentiation serves well beyond the simple goal of producing new adipocytes. Indeed, with the current immense biotechnological advances, the most critical role of adipose-derived stem cells remains their tremendous potential in the field of regenerative medicine. This review focuses on examining the physiological importance of adipogenesis, the current approaches that are employed to model this tightly controlled phenomenon, and the crucial role of adipogenesis in elucidating the pathophysiology and potential treatment modalities of human diseases. The future of adipogenesis is centered around its crucial role in regenerative and personalized medicine.

Matrix Remodeling and Hyaluronan Production by Myofibroblasts and Cancer-Associated Fibroblasts in 3D Collagen Matrices

The tumor microenvironment is a key modulator in cancer progression and has become a novel target in cancer therapy. An increase in hyaluronan (HA) accumulation and metabolism can be found in advancing tumor progression and are often associated with aggressive malignancy, drug resistance and poor prognosis. Wound-healing related myofibroblasts or activated cancer-associated fibroblasts (CAF) are assumed to be the major sources of HA. Both cell types are capable to synthesize new matrix components as well as reorganize the extracellular matrix. However, to which extent myofibroblasts and CAF perform these actions are still unclear. In this work, we investigated the matrix remodeling and HA production potential in normal human dermal fibroblasts (NHFB) and CAF in the absence and presence of transforming growth factor beta -1 (TGF-β1), with TGF-β1 being a major factor of regulating fibroblast differentiation. Three-dimensional (3D) collagen matrix was utilized to mimic the extracellular matrix of the tumor microenvironment. We found that CAF appeared to response insensitively towards TGF-β1 in terms of cell proliferation and matrix remodeling when compared to NHFB. In regards of HA production, we found that both cell types were capable to produce matrix bound HA, rather than a soluble counterpart, in response to TGF-β1. However, activated CAF demonstrated higher HA production when compared to myofibroblasts. The average molecular weight of produced HA was found in the range of 480 kDa for both cells. By analyzing gene expression of HA metabolizing enzymes, namely hyaluronan synthase (HAS1-3) and hyaluronidase (HYAL1-3) isoforms, we found expression of specific isoforms in dependence of TGF-β1 present in both cells. In addition, HAS2 and HYAL1 are highly expressed in CAF, which might contribute to a higher production and degradation of HA in CAF matrix. Overall, our results suggested a distinct behavior of NHFB and CAF in 3D collagen matrices in the presence of TGF-β1 in terms of matrix remodeling and HA production pointing to a specific impact on tumor modulation.

Artificial Biosystem for Modulation of Interactions between Antigen-Presenting Cells and T Cells

T cell activation is triggered by signal molecules on the surface of antigen-presenting cells (APC) and subsequent exertion of cellular forces. Deciphering the biomechanical and biochemical signals in this complex process is of interest and will contribute to an improvement in immunotherapy strategies. To address underlying questions, coculture and biomimetic models are established. Mature dendritic cells (mDC) are first treated with cytochalasin B (CytoB), a cytoskeletal disruption agent known to lower apparent cellular stiffness and reduction in T cell proliferation is observed. It is attempted to mimic mDC and T cell interactions using polyacrylamide (PA) gels with defined stiffness corresponding to mDC (0.2-25 kPa). Different ratios of anti-CD3 (aCD3) and anti-CD28 (aCD28) antibodies are immobilized onto PA gels. The results show T cell proliferation is triggered by both aCD3 and aCD28 in a stiffness-dependent manner. Cells cultured on aCD3 immobilized on gels has significantly enhanced proliferation and IL-2 secretion, compared to aCD28. Furthermore, ZAP70 phosphorylation is enhanced in stiffer substrate a in a aCD3-dependent manner. The biosystem provides an approach to study the reduction of T cell proliferation observed on CytoB-treated mDC. Overall, the biosystem allows distinguishing the impact of biophysical and biochemical signals of APC and T cell interactions in vitro.

Collagen microarchitecture mechanically controls myofibroblast differentiation

Altered microarchitecture of collagen type I is a hallmark of wound healing and cancer that is commonly attributed to myofibroblasts. However, it remains unknown which effect collagen microarchitecture has on myofibroblast differentiation. Here, we combined experimental and computational approaches to investigate the hypothesis that the microarchitecture of fibrillar collagen networks mechanically regulates myofibroblast differentiation of adipose stromal cells (ASCs) independent of bulk stiffness. Collagen gels with controlled fiber thickness and pore size were microfabricated by adjusting the gelation temperature while keeping their concentration constant. Rheological characterization and simulation data indicated that networks with thicker fibers and larger pores exhibited increased strain-stiffening relative to networks with thinner fibers and smaller pores. Accordingly, ASCs cultured in scaffolds with thicker fibers were more contractile, expressed myofibroblast markers, and deposited more extended fibronectin fibers. Consistent with elevated myofibroblast differentiation, ASCs in scaffolds with thicker fibers exhibited a more proangiogenic phenotype that promoted endothelial sprouting in a contractility-dependent manner. Our findings suggest that changes of collagen microarchitecture regulate myofibroblast differentiation and fibrosis independent of collagen quantity and bulk stiffness by locally modulating cellular mechanosignaling. These findings have implications for regenerative medicine and anticancer treatments.

Multi-Compartment 3D-Cultured Organ-on-a-Chip: Towards a Biomimetic Lymph Node for Drug Development

The interaction of immune cells with drugs and/or with other cell types should be mechanistically investigated in order to reduce attrition of new drug development. However, they are currently only limited technologies that address this need. In our work, we developed initial but significant building blocks that enable such immune-drug studies. We developed a novel microfluidic platform replicating the Lymph Node (LN) microenvironment called LN-on-a-chip, starting from design all the way to microfabrication, characterization and validation in terms of architectural features, fluidics, cytocompatibility, and usability. To prove the biomimetics of this microenvironment, we inserted different immune cell types in a microfluidic device, which showed an in-vivo-like spatial distribution. We demonstrated that the developed LN-on-a-chip incorporates key features of the native human LN, namely, (i) similarity in extracellular matrix composition, morphology, porosity, stiffness, and permeability, (ii) compartmentalization of immune cells within distinct structural domains, (iii) replication of the lymphatic fluid flow pattern, (iv) viability of encapsulated cells in collagen over the typical timeframe of immunotoxicity experiments, and (v) interaction among different cell types across chamber boundaries. Further studies with this platform may assess the immune cell function as a step forward to disclose the effects of pharmaceutics to downstream immunology in more physiologically relevant microenvironments.

Collagen Fibril Density Modulates Macrophage Activation and Cellular Functions during Tissue Repair

Monocytes circulate in the bloodstream, extravasate into the tissue and differentiate into specific macrophage phenotypes to fulfill the immunological needs of tissues. During the tissue repair process, tissue density transits from loose to dense tissue. However, little is known on how changes in tissue density affects macrophage activation and their cellular functions. In this work, monocytic cell line THP-1 cells were embedded in three-dimensional (3D) collagen matrices with different fibril density and were then differentiated into uncommitted macrophages (MPMA) using phorbol-12-myristate-13-acetate (PMA). MPMA macrophages were subsequently activated into pro-inflammatory macrophages (MLPS/IFNγ) and anti-inflammatory macrophages (MIL-4/IL-13) using lipopolysaccharide and interferon-gamma (IFNγ), and interleukin 4 (IL-4) and IL-13, respectively. Although analysis of cell surface markers, on both gene and protein levels, was inconclusive, cytokine secretion profiles, however, demonstrated differences in macrophage phenotype. In the presence of differentiation activators, MLPS/IFNγ secreted high amounts of IL-1β and tumor necrosis factor alpha (TNFα), while M0PMA secreted similar cytokines to MIL-4/IL-13, but low IL-8. After removing the activators and further culture for 3 days in fresh cell culture media, the secretion of IL-6 was found in high concentrations by MIL-4/IL-13, followed by MLPS/IFNγ and MPMA. Interestingly, the secretion of cytokines is enhanced with an increase of fibril density. Through the investigation of macrophage-associated functions during tissue repair, we demonstrated that M1LPS/IFNγ has the potential to enhance monocyte infiltration into tissue, while MIL-4/IL-13 supported fibroblast differentiation into myofibroblasts via transforming growth factor beta 1 (TGF-β1) in dependence of fibril density, suggesting a M2a-like phenotype. Overall, our results suggest that collagen fibril density can modulate macrophage response to favor tissue functions. Understanding of immune response in such complex 3D microenvironments will contribute to the novel therapeutic strategies for improving tissue repair, as well as guidance of the design of immune-modulated materials.

Biomimetic tissue models reveal the role of hyaluronan in melanoma proliferation and invasion

Biomimetic matrix models demonstrate the role of the size-dependent effect of hyaluronan in melanoma progression and reveal an alternative explanation forin vivofindings of hyaluronan dependent melanoma growth.

Deconstructing Immune Microenvironments of Lymphoid Tissues for Reverse Engineering

The immune microenvironment presents a diverse panel of cues that impacts immune cell migration, organization, differentiation, and the immune response. Uniquely, both the liquid and solid phases of every specific immune niche within the body play an important role in defining cellular functions in immunity at that particular location. The in vivo immune microenvironment consists of biomechanical and biochemical signals including their gradients, surface topography, dimensionality, modes of ligand presentation, and cell-cell interactions, and the ability to recreate these immune biointerfaces in vitro can provide valuable insights into the immune system. This manuscript reviews the critical roles played by different immune cells and surveys the current progress of model systems for reverse engineering of immune microenvironments with a focus on lymphoid tissues.

Fibril bending stiffness of 3D collagen matrices instructs spreading and clustering of invasive and non-invasive breast cancer cells

Extracellular matrix stiffening of breast tissues has been clinically correlated with malignant transformation and poor prognosis. An increase of collagen fibril diameter and lysyl-oxidase mediated crosslinking has been observed in advanced tumor stages. Many current reports suggest that the local mechanical properties of single fibrillar components dominantly regulate cancer cell behavior. Here, we demonstrate by an independent control of fibril diameter and intrafibrillar crosslinking of three-dimensional (3D) collagen matrices that fibril bending stiffness instructs cell behavior of invasive and non-invasive breast cancer cells. Two types of collagen matrices with fibril diameter of either 650 nm or 800 nm at a similar pore size of 10 μm were reconstituted and further modified with the zero-length crosslinker 1-ethyl-3-(3-dimethyl aminopropyl)-carbodiimide (EDC) at concentrations of 0, 20, 100 and 500 mM. This approach yields two sets of collagen matrices with overlapping variation of matrix elasticity. With these matrices we could prove the common assumption that matrix elasticity of collagen networks is bending dominated with a linear dependence on fibril bending stiffness. We derive that the measured variation of matrix elasticity is directly correlated to the variation of fibril bending stiffness, being independently controlled either by fibril diameter or by intrafibrillar crosslinking. We use these defined matrices to demonstrate that the adjustment of fibril bending stiffness allows to instruct the behavior of two different breast cancer cell lines, invasive MDA-MB-231 (human breast carcinoma) and non-invasive MCF-7 cells (human breast adenocarcinoma). Invasiveness and spreading of invasive MDA-MB-231 cells as well as clustering of non-invasive MCF-7 cells is thereby investigated over a broad parameter range. Our results demonstrate and quantify the direct dependence of cancer cell phenotypes on the matrix mechanical properties on the scale of single fibrils.

Alterations in Cell Mechanics by Actin Cytoskeletal Changes Correlate with Strain-Specific Rubella Virus Phenotypes for Cell Migration and Induction of Apoptosis

The cellular cytoskeleton is central for key cellular functions, and as such is a marker for diseased and infected cell states. Here we analyzed infection with rubella virus (RV) strains with respect to phenotypes in cellular mechanical properties, cell movement, and viral cytopathogenicity. Real-time deformability cytometry (RT-DC), as a high-throughput platform for the assessment of cell mechanics, revealed a correlation of an increase in cortical filamentous-actin (F-actin) with a higher cellular stiffness. The additional reduction of stress fibers noted for only some RV strains as the most severe actin rearrangement lowered cell stiffness. Furthermore, a reduced collective and single cell migration speed in a wound healing assay was detected in addition to severe changes in cell morphology. The latter was followed by activation of caspase 3/7 as a sign for induction of apoptosis. Our study emphasizes RT-DC technology as a sensitive means to characterize viral cell populations and to implicate alterations of cell mechanical properties with cell functions. These interdependent events are not only promising options to elucidate viral spread and to understand viral pathologies within the infected host. They also contribute to any diseased cell state, as exemplified by RV as a representative agent for cytoskeletal alterations involved in a cytopathological outcome.

Fibroblast fate regulation by time dependent TGF-β1 and IL-10 stimulation in biomimetic 3D matrices

The presentation of TGF-β1 during the early stage of wound healing is a prerequisite for extracellular matrix (ECM) synthesis and remodeling by activated fibroblasts, called myofibroblasts. At later stages, clearance of myofibroblasts is needed to avoid overshooting ECM production. Apoptosis of myofibroblasts and the macrophage-released anti-inflammatory cytokine IL-10 are controversially discussed as regulating cues in this context. To reveal the regulating cues, defined biomaterial scaffolds are needed to conduct in-depth in vitro studies in a physiologically relevant context. In this work, we used an in vitro biomimetic wound healing model. It consists of a 3D fibrillar matrix from collagen I and fibronectin and different temporal stimuli by TGF-β1 and IL-10. Human dermal fibroblast behavior was investigated in terms of myofibroblast differentiation (αSMA expression), matrix remodeling, proliferation and migration in the permanent or sequential presence of TGF-β1 and IL-10 over 4 days. We could show that removal of TGF-β1 after initial stimulation resulted in an increase of apoptosis of myofibroblasts. In contrast, TGF-β1 stimulation followed by IL-10 treatment did not result in increased cell apoptosis but instead led to a significant increase of cell motility and reduction of myofibroblasts. The findings suggest that myofibroblasts are a transiently "activated" fibroblastic phenotype and can be de-differentiated to fibroblasts in the presence of IL-10. Overall, our 3D ECM model allows mimicking the early and late stages of wound healing and highlights the temporal sequence of TGF-β1 and IL-10 as an important cue for completion of tissue formation and maintenance of tissue homeostasis.

Biomimetic tumor microenvironments based on collagen matrices

This review provides an overview of the current approaches to engineer defined 3D matrices for the investigation of tumor cell behaviorin vitro, with a focus on collagen-based fibrillar systems.

Mimicking Paracrine TGFβ1 Signals during Myofibroblast Differentiation in 3D Collagen Networks

TGFβ1 is a key regulator for induction of tissue remodeling after dermal wounding. We present a model of paracrine delivery of TGFβ1 for differentiation of dermal fibroblasts based on a fibrillar 3D collagen matrix and embedded TGFβ1 releasing microparticles. We found differentiation into myofibroblasts was achieved in a TGFβ1 dependent manner at much lower doses than systemic delivery. This effect is accounted to the slow and sustained TGFβ1 release mimicking paracrine cell signals.

Molecular weight specific impact of soluble and immobilized hyaluronan on CD44 expressing melanoma cells in 3D collagen matrices

Hyaluronan (HA) and its principal receptor CD44 are known to be involved in regulating tumor cell dissemination and metastasis. The direct correlation of CD44-HA interaction on proliferation and invasion of tumor cells in dependence on the molecular weight and the presentation form of HA is not fully understood because of lack of appropriate matrix models. To address this issue, we reconstituted 3D collagen (Coll I) matrices and functionalized them with HA of molecular weight of 30-50kDa (low molecular weight; LMW-HA) and 500-750kDa (high molecular weight; HMW-HA). A post-modification strategy was applied to covalently immobilize HA to reconstituted fibrillar Coll I matrices, resulting in a non-altered Coll I network microstructure and stable immobilization over days. Functionalized Coll I matrices were characterized regarding topological and mechanical characteristics as well as HA amount using confocal laser scanning microscopy, colloidal probe force spectroscopy and quantitative Alcian blue assay, respectively. To elucidate HA dependent tumor cell behavior, BRO melanoma cell lines with and without CD44 receptor expression were used for in vitro cell experiments. We demonstrated that only soluble LMW-HA promoted cell proliferation in a CD44 dependent manner, while HMW-HA and immobilized LMW-HA did not. Furthermore, an enhanced cell invasion was found only for immobilized LMW-HA. Both findings correlated with a very strong and specific adhesive interaction of LMW-HA and CD44+ cells quantified in single cell adhesion measurements using soft colloidal force spectroscopy. Overall, our results introduce an in vitro biomaterials model allowing to test presentation mode and molecular weight specificity of HA in a 3D fibrillar matrix thus mimicking important in vivo features of tumor microenvironments.

STATEMENT OF SIGNIFICANCE

Molecular weight and presentation form (bound vs. soluble) of hyaluronan (HA) are intensively discussed as key regulators in tumor progression and inflammation. We introduce 3D fibrillar collagen matrices with defined microstructure and stiffness allowing the presentation of specific molecular weight forms of HA in soluble and bound manner. Mimicking in that way important in vivo features of tumor microenvironments, we found that only low molecular weight HA (LMW-HA) in soluble form promoted proliferation of a melanoma cell line (BRO), while it enhanced cell invasion in bound form. The molecular weight specificity of LMW-HA was verified to be CD44 receptor dependent and was correlated to adhesive ligand-receptor interactions in quantitative colloidal force spectroscopy at single cell level.

Mimicking Tissue Boundaries by Sharp Multiparameter Matrix Interfaces

Engineering interfaces of distinct extracellular compartments mimicking native tissues are key for in-depth in vitro studies on developmental and disease processes in biology and medicine. Sharp interfaces of extracellular matrices are constructed based on fibrillar collagen I networks with a multiparameter control of topology, mechanics, and composition, and their distinct impact on triggering the directionality of cancer cell migration is demonstrated.

The interplay of fibronectin functionalization and TGF-β1 presence on fibroblast proliferation, differentiation and migration in 3D matrices

TGF-β1 dependent fibroblast behaviour in a wound healing context is mimicked by topologically and mechanically defined collagen matrices with fibronectin functionalization.