Physical confinement alters cytoskeletal contributions towards human mesenchymal stem cell migration

Enhanced motility and interaction of nasopharyngeal carcinoma with epithelial cells in confined microwells

The three-dimensional (3D) structure of the extracellular matrix and cell-cell contacts are two important cues to altering cell migration behavior and the tumor formation process. In this work, we designed and fabricated microwell arrays with a grating-patterned bottom in polydimethylsiloxane platforms to systematically study the effects of confinement, changes in topography, and cell-cell contacts on the migration behavior of nasopharyngeal carcinoma (NPC43) and immortalized nasopharyngeal epithelial (NP460) cells by time-lapse imaging. When two types of cells were co-cultured in microwells, the migration speed and spreading area of NPC43 cells were significantly increased, which might be attributed to the heterotypic cell-cell contacts with NP460 cells. On a flat surface, NPC43 cells could not form clusters due to the frequent interruptions by the active movements of NP460 cells. However, in 3D microwell arrays, clusters of NPC43 cells formed on the bottom surface while the majority of NP460 cells migrated onto the sidewalls. These cell clusters could be further processed to form spheroids for drug screening. These results also revealed that the 3D microenvironments and cell-cell contacts could have significant implications for NPC cell migration and initiation of tumor formation, which will provide insight for NPC progression and dissemination.

Hydrogels for Salivary Gland Tissue Engineering

Mimicking the complex architecture of salivary glands (SGs) outside their native niche is challenging due their multicellular and highly branched organization. However, significant progress has been made to recapitulate the gland structure and function using several in vitro and ex vivo models. Hydrogels are polymers with the potential to retain a large volume of water inside their three-dimensional structure, thus simulating extracellular matrix properties that are essential for the cell and tissue integrity. Hydrogel-based culture of SG cells has seen a tremendous success in terms of developing platforms for cell expansion, building an artificial gland, and for use in transplantation to rescue loss of SG function. Both natural and synthetic hydrogels have been used widely in SG tissue engineering applications owing to their properties that support the proliferation, reorganization, and polarization of SG epithelial cells. While recent improvements in hydrogel properties are essential to establish more sophisticated models, the emphasis should still be made towards supporting factors such as mechanotransduction and associated signaling cues. In this concise review, we discuss considerations of an ideal hydrogel-based biomaterial for SG engineering and their associated signaling pathways. We also discuss the current advances made in natural and synthetic hydrogels for SG tissue engineering applications.

Recent Advances in Macroporous Hydrogels for Cell Behavior and Tissue Engineering

Hydrogels have been extensively used as scaffolds in tissue engineering for cell adhesion, proliferation, migration, and differentiation because of their high-water content and biocompatibility similarity to the extracellular matrix. However, submicron or nanosized pore networks within hydrogels severely limit cell survival and tissue regeneration. In recent years, the application of macroporous hydrogels in tissue engineering has received considerable attention. The macroporous structure not only facilitates nutrient transportation and metabolite discharge but also provides more space for cell behavior and tissue formation. Several strategies for creating and functionalizing macroporous hydrogels have been reported. This review began with an overview of the advantages and challenges of macroporous hydrogels in the regulation of cellular behavior. In addition, advanced methods for the preparation of macroporous hydrogels to modulate cellular behavior were discussed. Finally, future research in related fields was discussed.

Role of TRPC6 in periodontal tissue reconstruction mediated by appropriate stress

INTRODUCTION

The basis of orthodontic tooth movement (OTM) is the reconstruction of periodontal tissue under stress. Increasing the speed of OTM has always been the focus of attention.

OBJECTIVES

Periodontal ligament stem cells (PDLSCs) are direct effector cells of mechanical force, but the mechanism by which PDLSCs sense mechanical stimuli is unclear.

METHODS

Human PDLSCs (hPDLSCs) were analyzed in the presence or absence of force loading with the Flexcell loading system in vitro. Then, periodontal tissues were analyzed after mechanical stimulation in vivo. In addition, cells in a confined microenvironment were analyzed to observe changes in the cytoskeleton and migration. Finally, TRPC6^-/- mice were used to further verify the effect of TRPC6. After force application, the OTM distance, bone marrow density (BMD), TRPC6 and COL1 expression, and TRAP staining were evaluated in periodontal tissues.

RESULTS

RNA sequencing (RNA-seq) and western blot analyses revealed that TRPC6 was important during mechanical force application to hPDLSCs. Appropriate mechanical force application also induced TRPC6 activation in the OTM model and the confined microenvironment. Under a slightly confined microenvironment, treatment with the TRPC6 inhibitor SKF96365 and TRPC6 knockout decreased the migration speed of hPDLSCs and mouse bone marrow mesenchymal stem cells (mBMSCs). In addition, TRPC6^-/- mice showed lower OTM distances and reduced osteogenic and osteoclastic differentiation.

CONCLUSION

In summary, TRPC6 activation in PDLSCs mediated by appropriate mechanical force application contributes to periodontal tissue reconstruction. PDLSCs modulate periodontal tissue remodeling under appropriate mechanical stimulation through TRPC6; however, under excessive stress, alveolar bone and tooth roots are readily absorbed. Under this condition, environmental factors play a leading role, and the regulatory effect of TRPC6 is not obvious.

Morphological Phenotyping of Organotropic Brain- and Bone-Seeking Triple Negative Metastatic Breast Tumor Cells

Triple negative breast cancer (TNBC) follows a non-random pattern of metastasis to the bone and brain tissue. Prior work has found that brain-seeking breast tumor cells display altered proteomic profiles, leading to alterations in pathways related to cell signaling, cell cycle, metabolism, and extracellular matrix remodeling. Given the unique microenvironmental characteristics of brain and bone tissue, we hypothesized that brain- or bone-seeking TNBC cells may have altered morphologic or migratory phenotypes from each other, or from the parental TNBC cells, as a function of the biochemical or mechanical microenvironment. In this study, we utilized TNBC cells (MDA-MB-231) that were conditioned to metastasize solely to brain (MDA-BR) or bone (MDA-BO) tissue. We quantified characteristics such as cell morphology, migration, and stiffness in response to cues that partially mimic their final metastatic niche. We have shown that MDA-BO cells have a distinct protrusive morphology not found in MDA-P or MDA-BR. Further, MDA-BO cells migrate over a larger area when on a collagen I (abundant in bone tissue) substrate when compared to fibronectin (abundant in brain tissue). However, migration in highly confined environments was similar across the cell types. Modest differences were found in the stiffness of MDA-BR and MDA-BO cells plated on collagen I vs. fibronectin-coated surfaces. Lastly, MDA-BO cells were found to have larger focal adhesion area and density in comparison with the other two cell types. These results initiate a quantitative profile of mechanobiological phenotypes in TNBC, with future impacts aiming to help predict metastatic propensities to organ-specific sites in a clinical setting.

Push or pull: how cytoskeletal crosstalk facilitates nuclear movement through 3D environments

As cells move from two-dimensional (2D) surfaces into complex 3D environments, the nucleus becomes a barrier to movement due to its size and rigidity. Therefore, moving the nucleus is a key step in 3D cell migration. In this review, we discuss how coordination between cytoskeletal and nucleoskeletal networks is required to pull the nucleus forward through complex 3D spaces. We summarize recent migration models which utilize unique molecular crosstalk to drive nuclear migration through different 3D environments. In addition, we speculate about the role of proteins that indirectly crosslink cytoskeletal networks and the role of 3D focal adhesions and how these protein complexes may drive 3D nuclear migration.

Current hydrogel advances in physicochemical and biological response-driven biomedical application diversity

Hydrogel is a type of versatile platform with various biomedical applications after rational structure and functional design that leverages on material engineering to modulate its physicochemical properties (e.g., stiffness, pore size, viscoelasticity, microarchitecture, degradability, ligand presentation, stimulus-responsive properties, etc.) and influence cell signaling cascades and fate. In the past few decades, a plethora of pioneering studies have been implemented to explore the cell-hydrogel matrix interactions and figure out the underlying mechanisms, paving the way to the lab-to-clinic translation of hydrogel-based therapies. In this review, we first introduced the physicochemical properties of hydrogels and their fabrication approaches concisely. Subsequently, the comprehensive description and deep discussion were elucidated, wherein the influences of different hydrogels properties on cell behaviors and cellular signaling events were highlighted. These behaviors or events included integrin clustering, focal adhesion (FA) complex accumulation and activation, cytoskeleton rearrangement, protein cyto-nuclei shuttling and activation (e.g., Yes-associated protein (YAP), catenin, etc.), cellular compartment reorganization, gene expression, and further cell biology modulation (e.g., spreading, migration, proliferation, lineage commitment, etc.). Based on them, current in vitro and in vivo hydrogel applications that mainly covered diseases models, various cell delivery protocols for tissue regeneration and disease therapy, smart drug carrier, bioimaging, biosensor, and conductive wearable/implantable biodevices, etc. were further summarized and discussed. More significantly, the clinical translation potential and trials of hydrogels were presented, accompanied with which the remaining challenges and future perspectives in this field were emphasized. Collectively, the comprehensive and deep insights in this review will shed light on the design principles of new biomedical hydrogels to understand and modulate cellular processes, which are available for providing significant indications for future hydrogel design and serving for a broad range of biomedical applications.

Progress in the mechanical modulation of cell functions in tissue engineering

In mammals, mechanics at multiple stages-nucleus to cell to ECM-underlie multiple physiological and pathological functions from its development to reproduction to death. Under this inspiration, substantial research has established the role of multiple aspects of mechanics in regulating fundamental cellular processes, including spreading, migration, growth, proliferation, and differentiation. However, our understanding of how these mechanical mechanisms are orchestrated or tuned at different stages to maintain or restore the healthy environment at the tissue or organ level remains largely a mystery. Over the past few decades, research in the mechanical manipulation of the surrounding environment-known as substrate or matrix or scaffold on which, or within which, cells are seeded-has been exceptionally enriched in the field of tissue engineering and regenerative medicine. To do so, traditional tissue engineering aims at recapitulating key mechanical milestones of native ECM into a substrate for guiding the cell fate and functions towards specific tissue regeneration. Despite tremendous progress, a big puzzle that remains is how the cells compute a host of mechanical cues, such as stiffness (elasticity), viscoelasticity, plasticity, non-linear elasticity, anisotropy, mechanical forces, and mechanical memory, into many biological functions in a cooperative, controlled, and safe manner. High throughput understanding of key cellular decisions as well as associated mechanosensitive downstream signaling pathway(s) for executing these decisions in response to mechanical cues, solo or combined, is essential to address this issue. While many reports have been made towards the progress and understanding of mechanical cues-particularly, substrate bulk stiffness and viscoelasticity-in regulating the cellular responses, a complete picture of mechanical cues is lacking. This review highlights a comprehensive view on the mechanical cues that are linked to modulate many cellular functions and consequent tissue functionality. For a very basic understanding, a brief discussion of the key mechanical players of ECM and the principle of mechanotransduction process is outlined. In addition, this review gathers together the most important data on the stiffness of various cells and ECM components as well as various tissues/organs and proposes an associated link from the mechanical perspective that is not yet reported. Finally, beyond addressing the challenges involved in tuning the interplaying mechanical cues in an independent manner, emerging advances in designing biomaterials for tissue engineering are also explored.

Mechanosensing of Mechanical Confinement by Mesenchymal-Like Cells

Mesenchymal stem cells (MSCs) and tumor cells have the unique capability to migrate out of their native environment and either home or metastasize, respectively, through extremely heterogeneous environments to a distant location. Once there, they can either aid in tissue regrowth or impart an immunomodulatory effect in the case of MSCs, or form secondary tumors in the case of tumor cells. During these journeys, cells experience physically confining forces that impinge on the cell body and the nucleus, ultimately causing a multitude of cellular changes. Most drastically, confining individual MSCs within hydrogels or confining monolayers of MSCs within agarose wells can sway MSC lineage commitment, while applying a confining compressive stress to metastatic tumor cells can increase their invasiveness. In this review, we seek to understand the signaling cascades that occur as cells sense confining forces and how that translates to behavioral changes, including elongated and multinucleated cell morphologies, novel migrational mechanisms, and altered gene expression, leading to a unique MSC secretome that could hold great promise for anti-inflammatory treatments. Through comparison of these altered behaviors, we aim to discern how MSCs alter their lineage selection, while tumor cells may become more aggressive and invasive. Synthesizing this information can be useful for employing MSCs for therapeutic approaches through systemic injections or tissue engineered grafts, and developing improved strategies for metastatic cancer therapies.

Predicting Confined 1D Cell Migration from Parameters Calibrated to a 2D Motor-Clutch Model

Biological tissues contain micrometer-scale gaps and pores, including those found within extracellular matrix fiber networks, between tightly packed cells, and between blood vessels or nerve bundles and their associated basement membranes. These spaces restrict cell motion to a single-spatial dimension (1D), a feature that is not captured in traditional in vitro cell migration assays performed on flat, unconfined two-dimensional (2D) substrates. Mechanical confinement can variably influence cell migration behaviors, and it is presently unclear whether the mechanisms used for migration in 2D unconfined environments are relevant in 1D confined environments. Here, we assessed whether a cell migration simulator and associated parameters previously measured for cells on 2D unconfined compliant hydrogels could predict 1D confined cell migration in microfluidic channels. We manufactured microfluidic devices with narrow channels (60-μm2 rectangular cross-sectional area) and tracked human glioma cells that spontaneously migrated within channels. Cell velocities (vexp = 0.51 ± 0.02 μm min-1) were comparable to brain tumor expansion rates measured in the clinic. Using motor-clutch model parameters estimated from cells on unconfined 2D planar hydrogel substrates, simulations predicted similar migration velocities (vsim = 0.37 ± 0.04 μm min-1) and also predicted the effects of drugs targeting the motor-clutch system or cytoskeletal assembly. These results are consistent with glioma cells utilizing a motor-clutch system to migrate in confined environments.

Integration of Mesenchymal Stem Cells into a Novel Micropillar Confinement Assay

Mechanical cues such as stiffness have been shown to influence cell gene expression, protein expression, and cell behaviors critical for tissue engineering. The mechanical cue of confinement is also a pervasive parameter affecting cells in vivo and in tissue-engineered constructs. Despite its prevalence, the mechanical cue of confinement lacks assays that provide precise control over the degree of confinement induced on cells, yield a large sample size, enable long-term culture, and enable easy visualization of cells over time. In this study, we developed a process to systematically confine cells using micropillar arrays. Using photolithography and polydimethylsiloxane (PDMS) molding, we created PDMS arrays of micropillars that were 5, 10, 20, or 50 μm in spacing and between 13 and 17 μm in height. The tops of micropillars were coated with Pluronic F127 to inhibit cell adhesion, and we observed that mesenchymal stem cells (MSCs) robustly infiltrated into the micropillar arrays. MSC and nucleus morphology were altered by narrowing the micropillar spacing, and cytoskeletal elements within MSCs appeared to become more diffuse with increasing confinement. Specifically, MSCs exhibited a ring of actin around their periphery and punctate focal adhesions. MSC migration speed was reduced by narrowing micropillar spacing, and distinct migration behaviors of MSCs emerged in the presence of micropillars. MSCs continued to proliferate within micropillar arrays after 3 weeks in culture, displaying our assay's capability for long-term studies. Our assay also has the capacity to provide adequate cell numbers for quantitative assays to investigate the effect of confinement on gene and protein expression. Through deeper understanding of cell mechanotransduction in the context of confinement, we can modify tissue-engineered constructs to be optimal for a given purpose. Impact Statement In this study, we developed a novel process to systematically confine cells using micropillar arrays. Our assay provides insight into cell behavior in response to mechanical confinement. Through deeper understanding of how cells sense and respond to confinement, we can fine tune tissue-engineered constructs to be optimal for a given purpose. By combining confinement with other physical cues, we can harness mechanical properties to encourage or inhibit cell migration, direct cells down a particular lineage, induce cell secretion of specific cytokines or extracellular vesicles, and ultimately direct cells to behave in a way conducive to tissue engineering.

Influence of hydrogel network microstructures on mesenchymal stem cell chondrogenesis in vitro and in vivo

Hydrogels, which provide three-dimensional (3D) niches for encapsulating bone marrow mesenchymal stem cells (BMSCs), are becoming a promising tissue engineering solution for chondrogenic differentiation of BMSCs. However, it remains a challenge to design a hydrogel material for effective chondrogenesis of BMSCs because of the complexity of cartilage ECM and cell-matrix interactions. Thus far, various studies have shown the physical-chemical cues of hydrogel materials to impact BMSCs chondrogenesis, but the design of the 3D network microstructure of the hydrogel to induce BMSCs chondrogenesis is still far from optimized. In this study, we successfully prepared two types of collagen hydrogels, namely, the fibrous network and porous network, with the same chemical composition and similar mechanical strength but with two distinct network microstructures. The two different network microstructures significantly influenced mass transfer, protein adsorption, degradability, and contraction of the collagen hydrogels. Moreover, the cells presented distinct proliferation and morphology in the two hydrogels, which consequently modulated chondrogenic differentiation of BMSCs derived from rat. Collagen hydrogels with a fibrous network promoted more chondrogenic differentiation of BMSCs without additional growth factors in vitro and subcutaneous implantation in vivo than those with a porous network. Moreover, fibrous network resulted in less ECM calcification than porous network. However, the fibrous network could not prevent hypertrophy of the chondrogenic cells induced by BMSCs. Overall, these results revealed that the 3D network microstructure of a hydrogel was a key design parameter for the chondrogenic differentiation of BMSCs. STATEMENT OF SIGNIFICANCE: Hydrogels had been used to induce the chondrogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) in cartilage tissue engineering, but the key design parameters remain unoptimized. This was mainly due to the different material properties including composition, strength, and microstructure, which would interplay with each other and result in difficulties to investigate the effects for one factor. In this study, we fabricated two collagen hydrogels with the same chemical composition and mechanical strength, but two distinct network microstructures. The effects of the two network microstructures on the chondrogenic differentiation of BMSCs were investigated by in vitro and in vivo assays. The results highlight the effects of network microstructures and provide important information about optimizing the design of future hydrogels in cartilage tissue engineering.

Nuclear Deformation in Response to Mechanical Confinement is Cell Type Dependent

Mechanosensing of the mechanical microenvironment by cells regulates cell phenotype and function. The nucleus is critical in mechanosensing, as it transmits external forces from the cellular microenvironment to the nuclear envelope housing chromatin. This study aims to elucidate how mechanical confinement affects nuclear deformation within several cell types, and to determine the role of cytoskeletal elements in controlling nuclear deformation. Human cancer cells (MDA-MB-231), human mesenchymal stem cells (MSCs), and mouse fibroblasts (L929) were seeded within polydimethylsiloxane (PDMS) microfluidic devices containing microchannels of varying cross-sectional areas, and nuclear morphology and volume were quantified via image processing of fluorescent cell nuclei. We found that the nuclear major axis length remained fairly constant with increasing confinement in MSCs and MDA-MB-231 cells, but increased with increasing confinement in L929 cells. Nuclear volume of L929 cells and MSCs decreased in the most confining channels. However, L929 nuclei were much more isotropic in unconfined channels than MSC nuclei. When microtubule polymerization or myosin II contractility was inhibited, nuclear deformation was altered only in MSCs in wide channels. This work informs our understanding of nuclear mechanics in physiologically relevant spaces, and suggests diverging roles of the cytoskeleton in regulating nuclear deformation in different cell types.

Myosin II Activity Is Selectively Needed for Migration in Highly Confined Microenvironments in Mature Dendritic Cells

Upon infection, mature dendritic cells (mDCs) migrate from peripheral tissue to lymph nodes (LNs) to activate T lymphocytes and initiate the adaptive immune response. This fast and tightly regulated process is tuned by different microenvironmental factors, such as the physical properties of the tissue. Mechanistically, mDCs migration mostly relies on acto-myosin flow and contractility that depend on non-muscular Myosin IIA (MyoII) activity. However, the specific contribution of this molecular motor for mDCs navigation in complex microenvironments has yet to be fully established. Here, we identified a specific role of MyoII activity in the regulation of mDCs migration in highly confined microenvironments. Using microfluidic systems, we observed that during mDCs chemotaxis in 3D collagen gels under defined CCL21 gradients, MyoII activity was required to sustain their fast speed but not to orientate them toward the chemokine. Indeed, despite the fact that mDCs speed declined, these cells still migrated through the 3D gels, indicating that this molecular motor has a discrete function during their motility in this irregular microenvironment. Consistently, using microchannels of different sizes, we found that MyoII activity was essential to maintain fast cell speed specifically under strong confinement. Analysis of cell motility through micrometric holes further demonstrated that cell contractility facilitated mDCs passage only over very small gaps. Altogether, this work highlights that high contractility acts as an adaptation mechanism exhibited by mDCs to optimize their motility in restricted landscapes. Hence, MyoII activity ultimately facilitates their navigation in highly confined areas of structurally irregular tissues, contributing to the fine-tuning of their homing to LNs to initiate adaptive immune responses.

[An integral view of cancer (I). The study, classification and reprogramming of the tumoral microclimate]

The group of diseases that we call cancer share a biological structure formed by a complex ecosystem, with altered intercellular communication, information fields, development and tissue function. Beyond the genetic alterations of the tumor cell, the demonstration of an altered ecosystem, with interconnections at systemic levels, opens up a new perspective on cancer biology and behavior. Different tumor facets, such as morphology, classification, clinical aggressiveness, prognosis and response to treatment now appear under a comprehensive vision that offers a new horizon of study, research and clinical management. The Somatic Mutation Theory in cancer, in force for more than one hundred years, is now completed by the study of the tumor microenvironment, the extracellular matrix, the stromal cells, the immune response, the innervation, the nutrition, the mitochondria, the metabolism, the interstitial fluid, the mechanical and electromagnetic properties of the tissue and many other areas of emerging knowledge; thus opening the door to a reprogramming exercise of the tumor phenotype through the modification of the keys offered by this new paradigm. Its recognition makes it possible to go from considering the oncological process as a cellular problem to a supracellular alteration based on the disorganization of tissues, immersed in the relationships of the complex system of the living being.

Physical confinement alters sarcoma cell cycle progression and division

Tumor cells experience physical confinement on one or multiple axes, both in the primary tumor and at multiple stages during metastasis. Recent work has shown that confinement in a 3D spheroid alters nucleus geometry and delays cell division, and that vertical confinement impairs mitotic spindle rounding, resulting in abnormal division events. Meanwhile, the effects of bi-axial confinement on cell cycle progression has received little attention. Given the critical role of nuclear shape and mechanics in cell division, we hypothesized that bi-axial physical confinement of the cell body and nucleus would alter cell cycle progression. We used sarcoma cells stably expressing the fluorescence ubiquitination cell cycle indicator (FUCCI), along with fibronectin-coated microchannel devices, and explored the impact of bi-axial physical confinement on cell cycle progression. Our results demonstrate that bi-axial physical confinement reduces the frequency of cell division, which we found to be attributed to an arrest in the S/G2/M phase of the cell cycle, and increases the frequency of abnormal division events. Cell and nuclear morphology were both altered in confinement, with the most confining channels preventing cells from undergoing the normal increase in size from G1 to S/G2/M during cell cycle progression. Finally, our results suggest that confinement induces a mechanical memory to the cells, given our observation of lasting effects on cell division and morphology, even after cells exited confinement. Together, our results provide new insights into the possible impact of mechanical forces on primary and secondary tumor formation and growth.

Force-Mediating Magnetic Nanoparticles to Engineer Neuronal Cell Function

Cellular processes like membrane deformation, cell migration, and transport of organelles are sensitive to mechanical forces. Technically, these cellular processes can be manipulated through operating forces at a spatial precision in the range of nanometers up to a few micrometers through chaperoning force-mediating nanoparticles in electrical, magnetic, or optical field gradients. But which force-mediating tool is more suitable to manipulate cell migration, and which, to manipulate cell signaling? We review here the differences in forces sensation to control and engineer cellular processes inside and outside the cell, with a special focus on neuronal cells. In addition, we discuss technical details and limitations of different force-mediating approaches and highlight recent advancements of nanomagnetics in cell organization, communication, signaling, and intracellular trafficking. Finally, we give suggestions about how force-mediating nanoparticles can be used to our advantage in next-generation neurotherapeutic devices.