Crosstalk between Cell Adhesion Complexes in Regulation of Mechanotransduction

Dynamic substrate topographies drive actin- and vimentin-mediated nuclear mechanoprotection events in human fibroblasts

BACKGROUND

Dynamic physical changes in the extracellular environment of living tissues present a mechanical challenge for resident cells that can lead to damage to the nucleus, genome, and DNA. Recent studies have started to uncover nuclear mechanoprotection mechanisms that prevent excessive mechanical deformations of the nucleus. Here, we hypothesized that dynamic topographical changes in the cellular environment can be mechanically transmitted to the nucleus and trigger nuclear mechanoprotection events. We tested this using a photoresponsive hydrogel whose surface topography can be reversibly changed on demand upon light illumination, allowing us to subject cells to recurring microscale topographical changes.

RESULTS

With each recurring topographical change, fibroblasts were found to increasingly compact and relocate their nuclei away from the dynamic regions of the hydrogel. These cell-scale reorganization events were accompanied by an increase of global histone acetylation and decreased methylation in cells on the dynamic topographies, resulting in a minimization of DNA strand breakage. We further found that these nuclear mechanoprotection events were mediated by both vimentin intermediate filaments and the actin cytoskeleton.

CONCLUSIONS

Together, these data reveal that fibroblasts actively protect their nuclei in the presence of dynamic topographical changes through cytoskeleton-mediated mechanisms. Broadly, these results stress the importance of gaining a deeper fundamental understanding of the cellular mechanoresponse under dynamically changing conditions.

Sustained Strain Applied at High Rates Drives Dynamic Tensioning in Epithelial Cells

Epithelial cells experience long lasting loads of different magnitudes and rates. How they adapt to these loads strongly impacts tissue health. Yet, much remains unknown about the evolution of cellular stress in response to sustained strain. Here, by subjecting cell pairs to sustained strain, we report a bimodal stress response, where in addition to the typically observed stress relaxation, a subset of cells exhibits a dynamic tensioning process with significant elevation in stress within 100s, resembling active pulling-back in muscle fibers. Strikingly, the fraction of cells exhibiting tensioning increases with increasing strain rate. The tensioning response is accompanied by actin remodeling, and perturbation to actin abrogates it, supporting cell contractility's role in the response. Collectively, our data show that epithelial cells adjust their tensional states over short timescales in a strain-rate dependent manner to adapt to sustained strains, demonstrating that the active pulling-back behavior could be a common protective mechanism against environmental stress.

The role and regulation of integrins in cell migration and invasion

Integrin receptors are the main molecular link between cells and the extracellular matrix (ECM) as well as mediating cell-cell interactions. Integrin-ECM binding triggers the formation of heterogeneous multi-protein assemblies termed integrin adhesion complexes (IACs) that enable integrins to transform extracellular cues into intracellular signals that affect many cellular processes, especially cell motility. Cell migration is essential for diverse physiological and pathological processes and is dysregulated in cancer to favour cell invasion and metastasis. Here, we discuss recent findings on the role of integrins in cell migration with a focus on cancer cell dissemination. We review how integrins regulate the spatial distribution and dynamics of different IACs, covering classical focal adhesions, emerging adhesion types and adhesion regulation. We discuss the diverse roles integrins have during cancer progression from cell migration across varied ECM landscapes to breaching barriers such as the basement membrane, and eventual colonization of distant organs.

Alterations in the microenvironment of junctional epidermolysis bullosa keratinocytes: A gene expression study

Integrin α6β4 subunits and type XVII collagen are critical transmembrane proteins involved in cell-matrix adhesion in skin, while laminin 332 serves as their ligand in the basement membrane zone (BMZ). Those proteins contribute to the composition of hemidesmosomes (HDs) and pathogenic variants in their corresponding genes cause junctional epidermolysis bullosa (JEB). Although the genotype-phenotype relationships in JEB have been extensively studied, the pathogenetic changes of extracellular matrix (ECM) and cell-matrix adhesion resulting from gene mutations remain unclear. We conducted a global unbiased transcriptome analysis using bulk RNA sequencing (RNA-seq) on selected JEB donor-derived cell lines lacking integrin β4 subunit (ITGB4-), type XVII collagen (COL17-) and laminin β3 chain (LAMB3-), respectively. Additional JEB cell lines and JEB donor skin samples were used for validation of relevant findings. Collectively, the results revealed similar dysregulation patterns of ECM and focal adhesion (FAs) associated genes in ITGB4- and COL17- cell lines, while LAMB3- cells displayed a relatively opposite tendency. Importantly, key nodes in the dysregulated network were associated with ECM proteins involved in wound healing processes. Additionally, a group of inflammatory-associated genes was disclosed to be up-regulated in JEB keratinocytes and could not be normalized by the adhesion rescue. The functional assay further revealed the hierarchy of stable adhesion among mutant cell lines COL17->ITGB4->LAMB3-, which correlates with the severity of their clinical manifestations. Our results indicated a wound healing associated ECM and inflammatory microenvironment established by JEB keratinocytes.

High matrix stiffness accelerates migration of hepatocellular carcinoma cells through the integrin β1-Plectin-F-actin axis

BACKGROUND

Abundant research indicates that increased extracellular matrix (ECM) stiffness significantly enhances the malignant characteristics of hepatocellular carcinoma (HCC) cells. Plectin, an essential cytoskeletal linker protein, has recently emerged as a promoter of cancer progression, particularly in the context of cancer cell invasion and metastasis. However, the responsiveness of plectin to changes in ECM stiffness and its impact on HCC progression remain unclear. In this study, we aimed to investigate whether plectin responds to variations in ECM stiffness and to explore its involved molecular mechanisms in regulating HCC cell migration.

RESULTS

Our results showed that, when compared with control group (7 kPa), high ECM stiffness (53 kPa) boosts HCC cell migration by upregulating plectin and integrin β1 expression and increasing F-actin polymerization. Knockdown of integrin β1 negated the high stiffness-upregulated plectin expression. Furthermore, reducing either plectin or integrin β1 levels, or using latrunculin A, effectively prevented the high ECM stiffness-induced F-actin polymerization and HCC cell migration.

CONCLUSIONS

These findings demonstrate that integrin β1-plectin-F-actin axis is necessary for high matrix stiffness-driven migration of HCC cells, and provide evidence for the critical role of plectin in mechanotransduction in HCC cells.

Focal adhesions, reticular adhesions, flat clathrin lattices: what divides them, what unites them?

The majority of cells within multicellular organisms requires anchorage to their surroundings in the form of cell-cell or cell-matrix adhesions. In regards to cell-matrix adhesions, the transmembrane receptors of the integrin family have long been recognized as the central scaffold around which these adhesion complexes are built. Via their extracellular domains integrins bind extracellular matrix ligands while their intracellular tails interact with a plethora of proteins that link integrin-based adhesions to the cytoskeleton and turn them also into important signaling platforms. Depending on the specific intracellular interactome of the integrins, different types of integrin adhesion complexes have been classified. The best-studied ones are the focal adhesions, in which integrins become firmly linked to contractile actomyosin fibers, allowing force transduction. But integrins also form an integral part of adhesion structures that lack the strong actomyosin link and are enriched in endocytic proteins. These have been named reticular adhesions, flat clathrin lattices, or clathrin plaques. Initially, the different types of integrin adhesion complexes have been viewed as discrete entities with their own separate life cycles. However, in the past years it has become more and more apparent how closely intertwined they are. In fact, it was shown that they can trigger each other's biogenesis or can even directly convert into each other. Here, we describe similarities as well as differences between integrin adhesion complexes, focusing on the versatile αvβ5 integrins, and discuss the recently discovered close links and interconversion modes between the different αvβ5 integrin adhesion types.

Tumor Biomechanics-Inspired Future Medicine

Malignant tumors pose a significant global health challenge, severely threatening human health. Statistics from the World Health Organization indicate that, in 2022, there were nearly 20 million new cancer cases and 9.7 million cancer-related deaths. Therefore, it is urgently necessary to study the pathogenesis of cancer and explore effective diagnostic and treatment strategies. In recent years, research has highlighted the importance of mechanical cues in tumors, which have become a new hallmark of cancer and a key factor in regulating tumor behavior. This suggests that studying the mechanical properties of tumors may open potential new avenues for understanding the pathogenesis, diagnosis, and therapeutic intervention of cancer. This review summarizes the mechanical characteristics of tumors and the development of tumor diagnostics and treatments targeting specific mechanical factors. Finally, we propose new ideas and insights for the application of mechanomedicine in cancer diagnosis and treatment in the future.

Dynamic duo: Cell-extracellular matrix interactions in hair follicle development and regeneration

Ectodermal organs, such as hair follicles, originate from simple epithelial and mesenchymal sheets through a complex developmental process driven by interactions between these cell types. This process involves dermal condensation, placode formation, bud morphogenesis, and organogenesis, and all of these processes require intricate interactions among various tissues. Recent research has emphasized the crucial role of reciprocal and dynamic interactions between cells and the extracellular matrix (ECM), referred to as the "dynamic duo", in the development of ectodermal organs. These interactions provide spatially and temporally changing biophysical and biochemical cues within tissues. Using the hair follicle as an example, this review highlights two types of cell-ECM adhesion units-focal adhesion-type and hemidesmosome-type adhesion units-that facilitate communication between epithelial and mesenchymal cells. This review further explores how these adhesion units, along with other cell-ECM interactions, evolve during hair follicle development and regeneration, underscoring their importance in guiding both developmental and regenerative processes.

The unfolded protein response sensor PERK mediates mechanical stress-induced maturation of focal adhesion complexes in glioblastoma cells

Stiffening of the brain extracellular matrix (ECM) in glioblastoma promotes tumor progression. Previously, we discovered that protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK) plays a role in glioblastoma stem cell (GSC) adaptation to matrix stiffness through PERK/FLNA-dependent F-actin remodeling. Here, we examined the involvement of PERK in detecting stiffness changes via focal adhesion complex (FAC) formation. Compared to control GSCs, PERK-deficient GSCs show decreased vinculin and tensin expression, while talin and integrin-β1 remain constant. Furthermore, vimentin was also reduced while tubulin increased, and a stiffness-dependent increase of the differentiation marker GFAP expression was absent in PERK-deficient GSCs. In conclusion, our study reveals a novel role for PERK in FAC formation during matrix stiffening, which is likely linked to its regulation of F-actin remodeling.

DDAH1 deficiency exacerbates cerebral vascular endothelial dysfunction by aggravating BBB disruption and oxidative stress in thoracic blast-induced brain injury

As terrorist incidents and underground explosion events have become more frequent around the world, brain injury caused by thoracic blast exposure has been more highlighted due to its injured organ, subsequent social and economic burden. It has been reported dimethylarginine dimethylaminohydrolase 1 (DDAH1) plays important roles in regulating vascular endothelial injury repair and angiogenesis, but its role in thoracic blast-induced brain injury remains to be explained. This study seeks to investigate the mechanism of DDAH1 on thoracic blast-induced brain injury. 40 C57BL/6 wild type mice and 40 DDAH1 knockout mice were randomly and equally divided into control group and blast group, respectively. The integrity of blood-brain barrier (BBB) was detected by Evans blue test. The serum inflammatory factors, nitric oxide (NO) contents, and asymmetric dimethylarginine (ADMA) levels were determined through ELISA. HE staining and reactive oxygen species (ROS) detection were performed for histopathological changes. Western blot was used to detect the proteins related to oxidative stress, tight junction, focal adhesion, vascular endothelial injury, and the DDAH1/ADMA/eNOS signaling pathway. DDAH1 deficiency aggravated thoracic blast-induced BBB leakage, inflammatory response, and the increased levels of inflammatory-related factors. Additionally, DDAH1 deficiency also increased ROS generation, MDA and IRE-α expression. Regarding cerebral vascular endothelial dysfunction, DDAH1 deficiency increased the expression of MCAM, FN1, LIMK1, VEGF, MMP9, Vimentin and N-cadherin, while lowering the expression of FMR1, Occludin, claudin-3, claudin-5, Lyn, LIMA1, Glrb, Sez6, Dystrophin, and phosphorylation of VASP. Also, DDAH1 deficiency exacerbated explosion-induced increase of ADMA and decrease of eNOS activity and NO contents. Thus, we conclude that DDAH1 could prevent cerebral vascular endothelial dysfunction and related injury by inhibiting ADMA signaling and increasing eNOS activity in thoracic blast induced brain injury.

Reduced Cell Migration in Human Chondrocyte Sheets Increases Tissue Stiffness and Cartilage Protein Production

BACKGROUND

Chondrogenic differentiation medium (CDM) is usually used to maintain chondrogenic activity during chondrocyte sheet production. However, tissue qualities remain to be determined as to what factors improve cell functions. Moreover, the relationship between CDM and cell migration proteins has not been reported.

METHOD

In this study, the effect of CDM on the behavior of chondrocyte sheets was investigated. Structural analysis, mechanical testing and proteomics were performed to observe tissue qualities. The relationship between CDM and cell migration proteins were investigated using time-lapse observations and bioinformatic analysis.

RESULTS

During 48 h, CDM affected the chondrocyte behaviors by reducing cell migration. Compared to the basal medium, CDM impacted the contraction of monolayered chondrocyte sheets. At day 7, the contracted sheets increased tissue thickness and improved tissue stiffness. Cartilage specific proteins were also upregulated. Remarkedly, the chondrocyte sheets in CDM displayed downregulated proteins related to cell migration. Bioinformatic analysis revealed that TGFβ1 was shown to be associated with cartilage functions and cell migration. Pathway analysis of chondrocyte sheets in CDM also revealed the presence of a TGFβ pathway without activating actin production, which might be involved in synthesizing cartilage-specific proteins. Cell migration pathway showed MAPK signaling in both cultures of the chondrocyte sheets.

CONCLUSION

Reduced cell migration in the chondrocyte sheet affected the tissue quality. Using CDM, TGFβ1 might trigger cartilage protein production through the TGFβ pathway and be involved in cell migration via the MAPK signaling pathway. Understanding cell behaviors and their protein expression would be beneficial for developing high-quality tissue-engineered cartilage.

The role of cell-cell and cell-matrix junctional complexes in sebaceous gland homeostasis and differentiation

Sebaceous glands (SG) are essential for maintaining skin integrity, as their lipid-rich secretion (sebum) lubricates and protects the epidermis and hairs. In addition, these glands have an emerging role in immunomodulation and may affect whole-body energy metabolism, besides being an appealing model for research in topics as lipogenesis, stem cell biology and tumorigenesis. In spite of the increasing interest in studying SGs pathophysiology, sebocyte cell-cell and cell-matrix adhesion processes have been only superficially examined, and never in a systematic way. This is regrettable considering the key role of cellular adhesion in general, the specific expression pattern of indivdual junctional complexes, and the reports of structural changes in SGs after altered expression of adhesion-relevant proteins. Here, we review the available information on structural and functional aspects of cell-cell and cell-matrix junctions in sebocytes, and how these processes change under pathological conditions. This information will contribute for better understanding sebocyte differentiation and sebum secretion, and may provide hints for novel therapeutic strategies for skin diseases.

Extracellular Matrix Components and Mechanosensing Pathways in Health and Disease

Glycosaminoglycans (GAGs) and proteoglycans (PGs) are essential components of the extracellular matrix (ECM) with pivotal roles in cellular mechanosensing pathways. GAGs, such as heparan sulfate (HS) and chondroitin sulfate (CS), interact with various cell surface receptors, including integrins and receptor tyrosine kinases, to modulate cellular responses to mechanical stimuli. PGs, comprising a core protein with covalently attached GAG chains, serve as dynamic regulators of tissue mechanics and cell behavior, thereby playing a crucial role in maintaining tissue homeostasis. Dysregulation of GAG/PG-mediated mechanosensing pathways is implicated in numerous pathological conditions, including cancer and inflammation. Understanding the intricate mechanisms by which GAGs and PGs modulate cellular responses to mechanical forces holds promise for developing novel therapeutic strategies targeting mechanotransduction pathways in disease. This comprehensive overview underscores the importance of GAGs and PGs as key mediators of mechanosensing in maintaining tissue homeostasis and their potential as therapeutic targets for mitigating mechano-driven pathologies, focusing on cancer and inflammation.

The extracellular matrix component perlecan/HSPG2 regulates radioresistance in prostate cancer cells

Radiotherapy of prostate cancer (PC) can lead to the acquisition of radioresistance through molecular mechanisms that involve, in part, cell adhesion-mediated signaling. To define these mechanisms, we employed a DU145 PC model to conduct a comparative mass spectrometry-based proteomic analysis of the purified integrin nexus, i.e., the cell-matrix junction where integrins bridge assembled extracellular matrix (matrisome components) to adhesion signaling complexes (adhesome components). When parental and radioresistant cells were compared, the expression of integrins was not changed, but cell radioresistance was associated with extensive matrix remodeling and changes in the complement of adhesion signaling proteins. Out of 72 proteins differentially expressed in the parental and radioresistant cells, four proteins were selected for functional validation based on their correlation with biochemical recurrence-free survival. Perlecan/heparan sulfate proteoglycan 2 (HSPG2) and lysyl-like oxidase-like 2 (LOXL2) were upregulated, while sushi repeat-containing protein X-linked (SRPX) and laminin subunit beta 3 (LAMB3) were downregulated in radioresistant DU145 cells. Knockdown of perlecan/HSPG2 sensitized radioresistant DU145 RR cells to irradiation while the sensitivity of DU145 parental cells did not change, indicating a potential role for perlecan/HSPG2 and its associated proteins in suppressing tumor radioresistance. Validation in androgen-sensitive parental and radioresistant LNCaP cells further supported perlecan/HSPG2 as a regulator of cell radiosensitivity. These findings extend our understanding of the interplay between extracellular matrix remodeling and PC radioresistance and signpost perlecan/HSPG2 as a potential therapeutic target and biomarker for PC.

Biophysical aspects of migrasome organelle formation and their diverse cellular functions

The transient cellular organelles known as migrasomes, which form during cell migration along retraction fibers, have emerged as a crutial factor in various fundamental cellular processes and pathologies. These membrane vesicles originate from local membrane swellings, encapsulate specific cytoplasmic content, and are eventually released to the extracellular environment or taken up by recipient cells. Migrasome biogenesis entails a sequential membrane remodeling process involving a complex interplay between various molecular factors such as tetraspanin proteins, and mechanical properties like membrane tension and bending rigidity. In this review, we summarize recent studies exploring the mechanism of migrasome formation. We emphasize how physical forces, together with molecular factors, shape migrasome biogenesis, and detail the involvement of migrasomes in various cellular processes and pathologies. A comprehensive understanding of the exact mechanism underlying migrasome formation and the identification of key molecules involved hold promise for advancing their therapeutic and diagnostic applications.

Microfluidics single-cell encapsulation reveals that poly-l-lysine-mediated stem cell adhesion to alginate microgels is crucial for cell-cell crosstalk and its self-renewal

Microfluidic cell encapsulation has provided a platform for studying the behavior of individual cells and has become a turning point in single-cell analysis during the last decade. The engineered microenvironment, along with protecting the immune response, has led to increasingly presenting the results of practical and pre-clinical studies with the goals of disease treatment, tissue engineering, intelligent control of stem cell differentiation, and regenerative medicine. However, the significance of cell-substrate interaction versus cell-cell communications in the microgel is still unclear. In this study, monodisperse alginate microgels were generated using a flow-focusing microfluidic device to determine how the cell microenvironment can control human bone marrow-derived mesenchymal stem cells (hBMSCs) viability, proliferation, and biomechanical features in single-cell droplets versus multi-cell droplets. Collected results show insufficient cell proliferation (234 % and 329 %) in both single- and multi-cell alginate microgels. Alginate hydrogels supplemented with poly-l-lysine (PLL) showed a better proliferation rate (514 % and 780 %) in a comparison of free alginate hydrogels. Cell stiffness data illustrate that hBMSCs cultured in alginate hydrogels have higher membrane flexibility and migration potency (Young's modulus equal to 1.06 kPa), whereas PLL introduces more binding sites for cell attachment and causes lower flexibility and migration potency (Young's modulus equal to 1.83 kPa). Considering that cell adhesion is the most important parameter in tissue engineering, in which cells do not run away from a 3D substrate, PLL enhances cell stiffness and guarantees cell attachments. In conclusion, cell attachment to PLL-mediated alginate hydrogels is crucial for cell viability and proliferation. It suggests that cell-cell signaling is good enough for stem cell viability, but cell-PLL attachment alongside cell-cell signaling is crucial for stem cell proliferation and self-renewal.

Tetraspanin proteins in membrane remodeling processes

Membrane remodeling is a fundamental cellular process that is crucial for physiological functions such as signaling, membrane fusion and cell migration. Tetraspanins (TSPANs) are transmembrane proteins of central importance to membrane remodeling events. During these events, TSPANs are known to interact with themselves and other proteins and lipids; however, their mechanism of action in controlling membrane dynamics is not fully understood. Since these proteins span the membrane, membrane properties such as rigidity, curvature and tension can influence their behavior. In this Review, we summarize recent studies that explore the roles of TSPANs in membrane remodeling processes and highlight the unique structural features of TSPANs that mediate their interactions and localization. Further, we emphasize the influence of membrane curvature on TSPAN distribution and membrane domain formation and describe how these behaviors affect cellular functions. This Review provides a comprehensive perspective on the multifaceted function of TSPANs in membrane remodeling processes and can help readers to understand the intricate molecular mechanisms that govern cellular membrane dynamics.

Mechanotransduction in the Vocal Fold Microenvironment: A Narrative Review

PURPOSE

The vocal fold tissues undergo nearly continuous and repeated cycles of injury and repair throughout the course of an individual's lifetime. It is well established that certain individuals are at greater risk of lesion development based on personality and behavioral classification. However, these characteristics alone do not wholly predict or explain lesion development or severity. In this review, we discuss current knowledge of mechanotransduction proteins and their potential relevance to tissue homeostasis in the vocal folds.

METHOD

A review of literature surrounding mechanotransduction and tissue homeostasis as it relates to the vocal folds was conducted. Review of the literature included searches of PubMed, Google Scholar, and other various online peer-reviewed sources. Search terms pertained to mechanosensation, mechanotransduction, mechanically activated channels, mechanical cellular regulation, and other associated concepts and terms. Additional literature was identified through the reference lists of identified papers. Findings of this literature review were then applied to known physiology and pathophysiology of the vocal folds in order to speculate on the contribution of mechanically mediated mechanisms within the vocal fold.

DISCUSSION AND CONCLUSION

Because the vocal folds are such mechanically active structures, withstanding nearly constant external forces, there is strong support for the idea that mechanically sensitive molecular pathways within the vocal fold tissue play a major role in tissue homeostasis in the presence of these considerable forces. As such, mechanotransduction within the vocal fold should be considered and targeted in future biological studies of vocal fold physiology.

Desmosomes at a glance

Desmosomes are relatives of ancient cadherin-based junctions, which emerged late in evolution to ensure the structural integrity of vertebrate tissues by coupling the intermediate filament cytoskeleton to cell-cell junctions. Their ability to dynamically counter the contractile forces generated by actin-associated adherens junctions is particularly important in tissues under high mechanical stress, such as the skin and heart. Much more than the simple cellular 'spot welds' depicted in textbooks, desmosomes are in fact dynamic structures that can sense and respond to changes in their mechanical environment and external stressors like ultraviolet light and pathogens. These environmental signals are transmitted intracellularly via desmosome-dependent mechanochemical pathways that drive the physiological processes of morphogenesis and differentiation. This Cell Science at a Glance article and the accompanying poster review desmosome structure and assembly, highlight recent insights into how desmosomes integrate chemical and mechanical signaling in the epidermis, and discuss desmosomes as targets in human disease.

Roles for epithelial integrin α3β1 in regulation of the microenvironment during normal and pathological tissue remodeling

Integrin receptors for the extracellular matrix activate intracellular signaling pathways that are critical for tissue development, homeostasis, and regeneration/repair, and their loss or dysregulation contributes to many developmental defects and tissue pathologies. This review will focus on tissue remodeling roles for integrin α3β1, a receptor for laminins found in the basement membranes (BMs) that underlie epithelial cell layers. As a paradigm, we will discuss literature that supports a role for α3β1 in promoting ability of epidermal keratinocytes to modify their tissue microenvironment during skin development, wound healing, or tumorigenesis. Preclinical and clinical studies have shown that this role depends largely on ability of α3β1 to govern the keratinocyte's repertoire of secreted proteins, or the "secretome," including 1) matrix proteins and proteases involved in matrix remodeling and 2) paracrine-acting growth factors/cytokines that stimulate other cells with important tissue remodeling functions (e.g., endothelial cells, fibroblasts, inflammatory cells). Moreover, α3β1 signaling controls gene expression that helps epithelial cells carry out these functions, including genes that encode secreted matrix proteins, proteases, growth factors, or cytokines. We will review what is known about α3β1-dependent gene regulation through both transcription and posttranscriptional mRNA stability. Regarding the latter, we will discuss examples of α3β1-dependent alternative splicing (AS) or alternative polyadenylation (APA) that prevents inclusion of cis-acting mRNA sequences that would otherwise target the transcript for degradation via nonsense-mediated decay or destabilizing AU-rich elements (AREs) in the 3'-untranslated region (3'-UTR). Finally, we will discuss prospects and anticipated challenges of exploiting α3β1 as a clinical target for the treatment of cancer or wound healing.

Reverse Mechanotransduction: Driving Chromatin Compaction to Decompaction Increases Cell Adhesion Strength and Contractility

Mechanical extracellular signals elicit chromatin remodeling via the mechanotransduction pathway, thus determining cellular function. However, the reverse pathway is an open question: does chromatin remodeling shape cells, regulating their adhesion strength? With fluidic force microscopy, we can directly measure the adhesion strength of epithelial cells by driving chromatin compaction to decompaction with chromatin remodelers. We observe that chromatin compaction, induced by performing histone acetyltransferase inhibition or ATP depletion, leads to a reduction in nuclear volume, disrupting actin cytoskeleton and focal adhesion assembly, and ultimately decreases in cell adhesion strength and traction force. Conversely, when chromatin decompaction is drived by removing the remodelers, cells recover their original shape, adhesion strength, and traction force. During chromatin decompaction, cells use depolymerized proteins to restore focal adhesion assemblies rather than neo-synthesized cytoskeletal proteins. We conclude that chromatin remodeling shapes cells, regulating adhesion strength through a reverse mechanotransduction pathway from the nucleus to the cell surface involving RhoA activation.

Acoustic Wave-Induced Stroboscopic Optical Mechanotyping of Adherent Cells

In this study, a novel, high content technique using a cylindrical acoustic transducer, stroboscopic fast imaging, and homodyne detection to recover the mechanical properties (dynamic shear modulus) of living adherent cells at low ultrasonic frequencies is presented. By analyzing the micro-oscillations of cells, whole populations are simultaneously mechanotyped with sub-cellular resolution. The technique can be combined with standard fluorescence imaging allowing to further cross-correlate biological and mechanical information. The potential of the technique is demonstrated by mechanotyping co-cultures of different cell types with significantly different mechanical properties.

Diversity of Intercellular Communication Modes: A Cancer Biology Perspective

From the moment a cell is on the path to malignant transformation, its interaction with other cells from the microenvironment becomes altered. The flow of molecular information is at the heart of the cellular and systemic fate in tumors, and various processes participate in conveying key molecular information from or to certain cancer cells. For instance, the loss of tight junction molecules is part of the signal sent to cancer cells so that they are no longer bound to the primary tumors and are thus free to travel and metastasize. Upon the targeting of a single cell by a therapeutic drug, gap junctions are able to communicate death information to by-standing cells. The discovery of the importance of novel modes of cell-cell communication such as different types of extracellular vesicles or tunneling nanotubes is changing the way scientists look at these processes. However, are they all actively involved in different contexts at the same time or are they recruited to fulfill specific tasks? What does the multiplicity of modes mean for the overall progression of the disease? Here, we extend an open invitation to think about the overall significance of these questions, rather than engage in an elusive attempt at a systematic repertory of the mechanisms at play.

Segregation of co-cultured multicellular systems: review and modeling consideration

Cell segregation caused by collective cell migration (CCM) is crucial for morphogenesis, functional development of tissue parts, and is an important aspect in other diseases such as cancer and its metastasis process. Efficiency of the cell segregation depends on the interplay between: (1) biochemical processes such as cell signaling and gene expression and (2) physical interactions between cells. Despite extensive research devoted to study the segregation of various co-cultured systems, we still do not understand the role of physical interactions in cell segregation. Cumulative effects of these physical interactions appear in the form of physical parameters such as: (1) tissue surface tension, (2) viscoelasticity caused by CCM, and (3) solid stress accumulated in multicellular systems. These parameters primarily depend on the interplay between the state of cell-cell adhesion contacts and cell contractility. The role of these physical parameters on the segregation efficiency is discussed on model systems such as co-cultured breast cell spheroids consisting of two subpopulations that are in contact. This review study aims to: (1) summarize biological aspects related to cell segregation, mechanical properties of cell collectives, effects along the biointerface between cell subpopulations and (2) describe from a biophysical/mathematical perspective the same biological aspects summarized before. So that overall it can illustrate the complexity of the biological systems that translate into very complex biophysical/mathematical equations. Moreover, by presenting in parallel these two seemingly different parts (biology vs. equations), this review aims to emphasize the need for experiments to estimate the variety of parameters entering the resulting complex biophysical/mathematical models.

Myosin-independent stiffness sensing by fibroblasts is regulated by the viscoelasticity of flowing actin

The stiffness of the extracellular matrix induces differential tension within integrin-based adhesions, triggering differential mechanoresponses. However, it has been unclear if the stiffness-dependent differential tension is induced solely by myosin activity. Here, we report that in the absence of myosin contractility, 3T3 fibroblasts still transmit stiffness-dependent differential levels of traction. This myosin-independent differential traction is regulated by polymerizing actin assisted by actin nucleators Arp2/3 and formin where formin has a stronger contribution than Arp2/3 to both traction and actin flow. Intriguingly, despite only slight changes in F-actin flow speed observed in cells with the combined inhibition of Arp2/3 and myosin compared to cells with sole myosin inhibition, they show a 4-times reduction in traction than cells with myosin-only inhibition. Our analyses indicate that traditional models based on rigid F-actin are inadequate for capturing such dramatic force reduction with similar actin flow. Instead, incorporating the F-actin network's viscoelastic properties is crucial. Our new model including the F-actin viscoelasticity reveals that Arp2/3 and formin enhance stiffness sensitivity by mechanically reinforcing the F-actin network, thereby facilitating more effective transmission of flow-induced forces. This model is validated by cell stiffness measurement with atomic force microscopy and experimental observation of model-predicted stiffness-dependent actin flow fluctuation.

Mechano-regulation by clathrin pit-formation and passive cholesterol-dependent tubules during de-adhesion

Adherent cells ensure membrane homeostasis during de-adhesion by various mechanisms, including endocytosis. Although mechano-chemical feedbacks involved in this process have been studied, the step-by-step build-up and resolution of the mechanical changes by endocytosis are poorly understood. To investigate this, we studied the de-adhesion of HeLa cells using a combination of interference reflection microscopy, optical trapping and fluorescence experiments. We found that de-adhesion enhanced membrane height fluctuations of the basal membrane in the presence of an intact cortex. A reduction in the tether force was also noted at the apical side. However, membrane fluctuations reveal phases of an initial drop in effective tension followed by saturation. The area fractions of early (Rab5-labelled) and recycling (Rab4-labelled) endosomes, as well as transferrin-labelled pits close to the basal plasma membrane, also transiently increased. On blocking dynamin-dependent scission of endocytic pits, the regulation of fluctuations was not blocked, but knocking down AP2-dependent pit formation stopped the tension recovery. Interestingly, the regulation could not be suppressed by ATP or cholesterol depletion individually but was arrested by depleting both. The data strongly supports Clathrin and AP2-dependent pit-formation to be central to the reduction in fluctuations confirmed by super-resolution microscopy. Furthermore, we propose that cholesterol-dependent pits spontaneously regulate tension under ATP-depleted conditions.

Extracellular Matrix Cues Regulate Mechanosensing and Mechanotransduction of Cancer Cells

Extracellular biophysical properties have particular implications for a wide spectrum of cellular behaviors and functions, including growth, motility, differentiation, apoptosis, gene expression, cell-matrix and cell-cell adhesion, and signal transduction including mechanotransduction. Cells not only react to unambiguously mechanical cues from the extracellular matrix (ECM), but can occasionally manipulate the mechanical features of the matrix in parallel with biological characteristics, thus interfering with downstream matrix-based cues in both physiological and pathological processes. Bidirectional interactions between cells and (bio)materials in vitro can alter cell phenotype and mechanotransduction, as well as ECM structure, intentionally or unintentionally. Interactions between cell and matrix mechanics in vivo are of particular importance in a variety of diseases, including primarily cancer. Stiffness values between normal and cancerous tissue can range between 500 Pa (soft) and 48 kPa (stiff), respectively. Even the shear flow can increase from 0.1-1 dyn/cm2 (normal tissue) to 1-10 dyn/cm2 (cancerous tissue). There are currently many new areas of activity in tumor research on various biological length scales, which are highlighted in this review. Moreover, the complexity of interactions between ECM and cancer cells is reduced to common features of different tumors and the characteristics are highlighted to identify the main pathways of interaction. This all contributes to the standardization of mechanotransduction models and approaches, which, ultimately, increases the understanding of the complex interaction. Finally, both the in vitro and in vivo effects of this mechanics-biology pairing have key insights and implications for clinical practice in tumor treatment and, consequently, clinical translation.

New Insights into YAP/TAZ-TEAD-Mediated Gene Regulation and Biological Processes in Cancer

The Hippo pathway is conserved across species. Key mammalian Hippo pathway kinases, including MST1/2 and LATS1/2, inhibit cellular growth by inactivating the TEAD coactivators, YAP, and TAZ. Extensive research has illuminated the roles of Hippo signaling in cancer, development, and regeneration. Notably, dysregulation of Hippo pathway components not only contributes to tumor growth and metastasis, but also renders tumors resistant to therapies. This review delves into recent research on YAP/TAZ-TEAD-mediated gene regulation and biological processes in cancer. We focus on several key areas: newly identified molecular patterns of YAP/TAZ activation, emerging mechanisms that contribute to metastasis and cancer therapy resistance, unexpected roles in tumor suppression, and advances in therapeutic strategies targeting this pathway. Moreover, we provide an updated view of YAP/TAZ's biological functions, discuss ongoing controversies, and offer perspectives on specific debated topics in this rapidly evolving field.

Mechanotransduction: Forcing a change in metabolism

Epithelial and endothelial cells experience numerous mechanical cues throughout their lifetimes. Cells resist these forces by fortifying their cytoskeletal networks and adhesions. This reinforcement is energetically costly. Here we describe how these energetic demands are met. We focus on the response of epithelial and endothelial cells to mechanical cues, describe the energetic needs of epithelia and endothelia, and identify the mechanisms these cells employ to increase glycolysis, oxidative phosphorylation, and fatty acid metabolism. We discuss the similarities and differences in the responses of the two cell types.

Integrin α7β1 represses intestinal absorptive cell differentiation

Intestinal epithelial cell differentiation is a highly controlled and orderly process occurring in the crypt so that cells migrating out to cover the villi are already fully functional. Absorptive cell precursors, which originate from the stem cell population located in the lower third of the crypt, are subject to several cycles of amplification in the transit amplifying (TA) zone, before reaching the terminal differentiation compartment located in the upper third. There is a large body of evidence that absorptive cell differentiation is halted in the TA zone through various epigenetic, transcriptional and intracellular signalling events or mechanisms allowing the transient expansion of this cell population but how these mechanisms are themself regulated remains obscure. One clue can be found in the epithelial cell-matrix microenvironment located all along the crypt-villus axis. Indeed, a previous study from our group revealed that α5-subunit containing laminins such as lamimin-511 and 512 inhibit early stages of differentiation in Caco-2/15 cells. Among potential receptors for laminin 511/512 is the integrin α7β1, which has previously been reported to be expressed in the human intestinal crypts and in early stages of Caco-2/15 cell differentiation. In this study, the effects of knocking down ITGA7 in Caco-2/15 cells were studied using shRNA and CRISPR/Cas9 strategies. Abolition of the α7 integrin subunit resulted in a significant increase in the level of differentiation and polarization markers as well as the morphological features of intestinal cells. Activities of focal adhesion kinase and Src kinase were both reduced in α7-knockdown cells while the three major intestinal pro-differentiation factors CDX2, HNFα1 and HNF4α were overexpressed. Two epigenetic events associated with intestinal differentiation, the reduction of tri-methylated lysine 27 on histone H3 and the increase of acetylation of histone H4 were also observed in α7-knockdown cells. On the other hand, the ablation of α7 had no effect on cell proliferation. In conclusion, these data indicate that integrin α7β1 acts as a major repressor of absorptive cell terminal differentiation in the Caco-2/15 cell model and suggest that the laminin-α7β1 integrin interaction occurring in the transit amplifying zone of the adult intestine is involved in the transient halting of absorptive cell terminal differentiation.

MAP4K4 regulates forces at cell-cell and cell-matrix adhesions to promote collective cell migration

Collective cell migration is not only important for development and tissue homeostasis but can also promote cancer metastasis. To migrate collectively, cells need to coordinate cellular extensions and retractions, adhesion sites dynamics, and forces generation and transmission. Nevertheless, the regulatory mechanisms coordinating these processes remain elusive. Using A431 carcinoma cells, we identify the kinase MAP4K4 as a central regulator of collective migration. We show that MAP4K4 inactivation blocks the migration of clusters, whereas its overexpression decreases cluster cohesion. MAP4K4 regulates protrusion and retraction dynamics, remodels the actomyosin cytoskeleton, and controls the stability of both cell-cell and cell-substrate adhesion. MAP4K4 promotes focal adhesion disassembly through the phosphorylation of the actin and plasma membrane crosslinker moesin but disassembles adherens junctions through a moesin-independent mechanism. By analyzing traction and intercellular forces, we found that MAP4K4 loss of function leads to a tensional disequilibrium throughout the cell cluster, increasing the traction forces and the tension loading at the cell-cell adhesions. Together, our results indicate that MAP4K4 activity is a key regulator of biomechanical forces at adhesion sites, promoting collective migration.

Reticular adhesions are assembled at flat clathrin lattices and opposed by active integrin α5β1

Reticular adhesions (RAs) consist of integrin αvβ5 and harbor flat clathrin lattices (FCLs), long-lasting structures with similar molecular composition as clathrin-mediated endocytosis (CME) carriers. Why FCLs and RAs colocalize is not known. Here, we show that RAs are assembled at FCLs in a process controlled by fibronectin (FN) and its receptor, integrin α5β1. We observed that cells on FN-rich matrices displayed fewer FCLs and RAs. CME machinery inhibition abolished RAs and live-cell imaging showed that RA establishment requires FCL coassembly. The inhibitory activity of FN was mediated by the activation of integrin α5β1 at Tensin1-positive fibrillar adhesions. Conventionally, endocytosis disassembles cellular adhesions by internalizing their components. Our results present a novel paradigm in the relationship between these two processes by showing that endocytic proteins can actively function in the assembly of cell adhesions. Furthermore, we show this novel adhesion assembly mechanism is coupled to cell migration via unique crosstalk between cell-matrix adhesions.

Cell Adhesion Molecules in Fibrotic Diseases

Mechanisms underlying the pathogenesis of tissue fibrosis remain incompletely understood. Emerging evidence suggests that cell adhesion molecules (CAMs) are critical in fibrotic progression in many organs, including lung, kidney, skin, and liver. CAMs promote cell-cell and cell-extracellular matrix (ECM) interactions to maintain tissue architecture and normal function in homeostasis. However, dysregulated expression and function of CAMs can lead to chronic inflammation and tissue fibrosis. The major families of CAMs include integrins, cadherins, selectins, and immunoglobulins. Here, we review the role of the CAMs in fibrosis development across various organs with a focus on integrins and cadherins, and discuss their respective roles in the development of pulmonary fibrosis.

Cellular Senescence: From Mechanisms to Current Biomarkers and Senotherapies

An increase in life expectancy in developed countries has led to a surge of chronic aging-related diseases. In the last few decades, several studies have provided evidence of the prominent role of cellular senescence in many of these pathologies. Key traits of senescent cells include cell cycle arrest, apoptosis resistance, and secretome shift to senescence-associated secretory phenotype resulting in increased secretion of various intermediate bioactive factors important for senescence pathophysiology. However, cellular senescence is a highly phenotypically heterogeneous process, hindering the discovery of totally specific and accurate biomarkers. Also, strategies to prevent the pathologic effect of senescent cell accumulation during aging by impairing senescence onset or promoting senescent cell clearance have shown great potential during in vivo studies, and some are already in early stages of clinical translation. The adaptability of these senotherapeutic approaches to human application has been questioned due to the lack of proper senescence targeting and senescence involvement in important physiologic functions. In this review, we explore the heterogeneous phenotype of senescent cells and its influence on the expression of biomarkers currently used for senescence detection. We also discuss the current evidence regarding the efficacy, reliability, development stage, and potential for human applicability of the main existing senotherapeutic strategies. SIGNIFICANCE STATEMENT: This paper is an extensive review of what is currently known about the complex process of cellular senescence and explores its most defining features. The main body of the discussion focuses on how the multifeature fluctuation of the senescence phenotype and the physiological role of cellular senescence have both caused a limitation in the search for truly reliable senescence biomarkers and the progression in the development of senotherapies.

The Extracellular Matrix: Its Composition, Function, Remodeling, and Role in Tumorigenesis

The extracellular matrix (ECM) is a ubiquitous member of the body and is key to the maintenance of tissue and organ integrity. Initially thought to be a bystander in many cellular processes, the extracellular matrix has been shown to have diverse components that regulate and activate many cellular processes and ultimately influence cell phenotype. Importantly, the ECM's composition, architecture, and stiffness/elasticity influence cellular phenotypes. Under normal conditions and during development, the synthesized ECM constantly undergoes degradation and remodeling processes via the action of matrix proteases that maintain tissue homeostasis. In many pathological conditions including fibrosis and cancer, ECM synthesis, remodeling, and degradation is dysregulated, causing its integrity to be altered. Both physical and chemical cues from the ECM are sensed via receptors including integrins and play key roles in driving cellular proliferation and differentiation and in the progression of various diseases such as cancers. Advances in 'omics' technologies have seen an increase in studies focusing on bidirectional cell-matrix interactions, and here, we highlight the emerging knowledge on the role played by the ECM during normal development and in pathological conditions. This review summarizes current ECM-targeted therapies that can modify ECM tumors to overcome drug resistance and better cancer treatment.

Vascular mechanotransduction

This review aims to survey the current state of mechanotransduction in vascular smooth muscle cells (VSMCs) and endothelial cells (ECs), including their sensing of mechanical stimuli and transduction of mechanical signals that result in the acute functional modulation and longer-term transcriptomic and epigenetic regulation of blood vessels. The mechanosensors discussed include ion channels, plasma membrane-associated structures and receptors, and junction proteins. The mechanosignaling pathways presented include the cytoskeleton, integrins, extracellular matrix, and intracellular signaling molecules. These are followed by discussions on mechanical regulation of transcriptome and epigenetics, relevance of mechanotransduction to health and disease, and interactions between VSMCs and ECs. Throughout this review, we offer suggestions for specific topics that require further understanding. In the closing section on conclusions and perspectives, we summarize what is known and point out the need to treat the vasculature as a system, including not only VSMCs and ECs but also the extracellular matrix and other types of cells such as resident macrophages and pericytes, so that we can fully understand the physiology and pathophysiology of the blood vessel as a whole, thus enhancing the comprehension, diagnosis, treatment, and prevention of vascular diseases.

Fucoidan and topography modification improved in situ endothelialization on acellular synthetic vascular grafts

Thrombogenesis remains the primary failure of synthetic vascular grafts. Endothelial coverage is crucial to provide an antithrombogenic surface. However, most synthetic materials do not support cell adhesion, and transanastomotic endothelial migration is limited. Here, a surface modification strategy using fucoidan and topography was developed to enable fast in situ endothelialization of polyvinyl alcohol, which is not endothelial cell-adhesive. Among three different immobilization approaches compared, conjugation of aminated-fucoidan promoted endothelial monolayer formation while minimizing thrombogenicity in both in vitro platelet rich plasma testing and ex vivo non-human primate shunt assay. Screening of six topographical patterns showed that 2 μm gratings increased endothelial cell migration without inducing inflammation responses of endothelial cells. Mechanistic studies demonstrated that fucoidan could attract fibronectin, enabling integrin binding and focal adhesion formation and activating focal adhesion kinase (FAK) signaling, and 2 μm gratings further enhanced FAK-mediated cell migration. In a clinically relevant rabbit carotid artery end-to-side anastomosis model, 60% in situ endothelialization was observed throughout the entire lumen of 1.7 mm inner diameter modified grafts, compared to 0% of unmodified graft, and the four-week graft patency also increased. This work presents a promising strategy to stimulate in situ endothelialization on synthetic materials for improving long-term performance.

A review on regulation of cell cycle by extracellular matrix

The extracellular matrix (ECM) is a network of structural proteins, glycoproteins and proteoglycans that assists independent cells in aggregating and forming highly organized functional structures. ECM serves numerous purposes and is an essential component of tissue structure and functions. Initially, the role of ECM was considered to be confined to passive functions like providing mechanical strength and structural identity to tissues, serving as barriers and platforms for cells. The doors to understanding ECM's proper role in tissue functioning opened with the discovery of cellular receptors, integrins to which ECM components binds and influences cellular activities. Understanding and utilizing ECM's potential to control cellular function has become a topic of much interest in recent decades, providing different outlooks to study processes involved in developmental programs, wound healing and tumour progression. On another front, the regulatory mechanisms operating to prevent errors in the cell cycle have been topics of a titanic amount of studies. This is expected as many diseases, most infamously cancer, are associated with defects in their functioning. This review focuses on how ECM, through different methods, influences the progression of the somatic cell cycle and provides deeper insights into molecular mechanisms of functional communication between adhesion complex, signalling pathways and cell cycle machinery.

Active wetting of epithelial tissues: modeling considerations

Morphogenesis, tissue regeneration, and cancer invasion involve transitions in tissue morphology. These transitions, caused by collective cell migration (CCM), have been interpreted as active wetting/de-wetting transitions. This phenomenon is considered based on a model system as wetting of a cell aggregate on a rigid substrate, which includes cell aggregate movement and isotropic/anisotropic spreading of a cell monolayer around the aggregate depending on the substrate rigidity and aggregate size. This model system accounts for the transition between 3D epithelial aggregate and 2D cell monolayer as a product of: (1) tissue surface tension, (2) surface tension of substrate matrix, (3) cell-matrix interfacial tension, (4) interfacial tension gradient, (5) viscoelasticity caused by CCM, and (6) viscoelasticity of substrate matrix. These physical parameters depend on the cell contractility and state of cell-cell and cell-matrix adhesion contacts, as well as the stretching/compression of cellular systems caused by CCM. Despite extensive research devoted to study cell wetting, we still do not understand the interplay among these physical parameters which induces an oscillatory trend of cell rearrangement. This review focuses on these physical parameters in governing the cell rearrangement in the context of epithelial aggregate wetting/de-wetting, and on modeling approaches aimed at reproducing and understanding these biological systems. In this context, we not only review previously published biophysical models for cell rearrangement caused by CCM, but also propose new extensions of those models to point out the interrelation between cell-matrix interfacial tension and epithelial viscoelasticity and the role of the interfacial tension gradient in cell spreading.

Organization, dynamics and mechanoregulation of integrin-mediated cell-ECM adhesions

The ability of animal cells to sense, adhere to and remodel their local extracellular matrix (ECM) is central to control of cell shape, mechanical responsiveness, motility and signalling, and hence to development, tissue formation, wound healing and the immune response. Cell-ECM interactions occur at various specialized, multi-protein adhesion complexes that serve to physically link the ECM to the cytoskeleton and the intracellular signalling apparatus. This occurs predominantly via clustered transmembrane receptors of the integrin family. Here we review how the interplay of mechanical forces, biochemical signalling and molecular self-organization determines the composition, organization, mechanosensitivity and dynamics of these adhesions. Progress in the identification of core multi-protein modules within the adhesions and characterization of rearrangements of their components in response to force, together with advanced imaging approaches, has improved understanding of adhesion maturation and turnover and the relationships between adhesion structures and functions. Perturbations of adhesion contribute to a broad range of diseases and to age-related dysfunction, thus an improved understanding of their molecular nature may facilitate therapeutic intervention in these conditions.

Actomyosin-mediated cellular tension promotes Yap nuclear translocation and myocardial proliferation through α5 integrin signaling

The cardiomyocyte phenotypic switch from a proliferative to terminally differentiated state results in the loss of regenerative potential of the mammalian heart shortly after birth. Nonmuscle myosin IIB (NM IIB)-mediated actomyosin contractility regulates cardiomyocyte cytokinesis in the embryonic heart, and NM IIB levels decline after birth, suggesting a role for cellular tension in the regulation of cardiomyocyte cell cycle activity in the postnatal heart. To investigate the role of actomyosin contractility in cardiomyocyte cell cycle arrest, we conditionally activated ROCK2 kinase domain (ROCK2:ER) in the murine postnatal heart. Here, we show that α5/β1 integrin and fibronectin matrix increase in response to actomyosin-mediated tension. Moreover, activation of ROCK2:ER promotes nuclear translocation of Yap, a mechanosensitive transcriptional co-activator, and enhances cardiomyocyte proliferation. Finally, we show that reduction of myocardial α5 integrin rescues the myocardial proliferation phenotype in ROCK2:ER hearts. These data demonstrate that cardiomyocytes respond to increased intracellular tension by altering their intercellular contacts in favor of cell-matrix interactions, leading to Yap nuclear translocation, thus uncovering a function for nonmuscle myosin contractility in promoting cardiomyocyte proliferation in the postnatal heart.

Predicting YAP/TAZ nuclear translocation in response to ECM mechanosensing

Cells translate mechanical cues from the extracellular matrix (ECM) into signaling that can affect the nucleus. One pathway by which such nuclear mechanotransduction occurs is a signaling axis that begins with integrin-ECM bonds and continues through a cascade of chemical reactions and structural changes that lead to nuclear translocation of YAP/TAZ. This signaling axis is self-reinforcing, with stiff ECM promoting integrin binding and thus facilitating polymerization and tension in the cytoskeletal contractile apparatus, which can compress nuclei, open nuclear pore channels, and enhance nuclear accumulation of YAP/TAZ. We previously developed a computational model of this mechanosensing axis for the linear elastic ECM by assuming that there is a linear relationship between the nucleocytoplasmic ratio of YAP/TAZ and nuclear flattening. Here, we extended our previous model to more general ECM behaviors (e.g., viscosity, viscoelasticity, and viscoplasticity) and included detailed YAP/TAZ translocation dynamics based on nuclear deformation. This model was predictive of diverse mechanosensing responses in a broad range of cells. Results support the hypothesis that diverse mechanosensing phenomena across many cell types arise from a simple, unified set of mechanosensing pathways.

Platelet-rich plasma promotes peripheral nerve regeneration after sciatic nerve injury

The effect of platelet-rich plasma on nerve regeneration remains controversial. In this study, we established a rabbit model of sciatic nerve small-gap defects with preserved epineurium and then filled the gaps with platelet-rich plasma. Twenty-eight rabbits were divided into the following groups (7 rabbits/group): model, low-concentration PRP (2.5–3.5-fold concentration of whole blood platelets), medium-concentration PRP (4.5–6.5-fold concentration of whole blood platelets), and high-concentration PRP (7.5–8.5-fold concentration of whole blood platelets). Electrophysiological and histomorphometrical assessments and proteomics analysis were used to evaluate regeneration of the sciatic nerve. Our results showed that platelet-rich plasma containing 4.5–6.5- and 7.5–8.5-fold concentrations of whole blood platelets promoted repair of sciatic nerve injury. Proteomics analysis was performed to investigate the possible mechanism by which platelet-rich plasma promoted nerve regeneration. Proteomics analysis showed that after sciatic nerve injury, platelet-rich plasma increased the expression of integrin subunit β-8 (ITGB8), which participates in angiogenesis, and differentially expressed proteins were mainly enriched in focal adhesion pathways. Additionally, two key proteins, ribosomal protein S27a (RSP27a) and ubiquilin 1 (UBQLN1), which were selected after protein-protein interaction analysis, are involved in the regulation of ubiquitin levels in vivo. These data suggest that platelet-rich plasma promotes peripheral nerve regeneration after sciatic nerve injury by affecting angiogenesis and intracellular ubiquitin levels.

Plasma polymerized bio-interface directs fibronectin adsorption and functionalization to enhance "epithelial barrier structure" formation via FN-ITG β1-FAK-mTOR signaling cascade

BACKGROUND

Transepithelial medical devices are increasing utilized in clinical practices. However, the damage of continuous natural epithelial barrier has become a major risk factor for the failure of epithelium-penetrating implants. How to increase the "epithelial barrier structures" (focal adhesions, hemidesmosomes, etc.) becomes one key research aim in overcoming this difficulty. Directly targeting the in situ "epithelial barrier structures" related proteins (such as fibronectin) absorption and functionalization can be a promising way to enhance interface-epithelial integration.

METHODS

Herein, we fabricated three plasma polymerized bio-interfaces possessing controllable surface chemistry. Their capacity to adsorb and functionalize fibronectin (FN) from serum protein was compared by Liquid Chromatography-Tandem Mass Spectrometry. The underlying mechanisms were revealed by molecular dynamics simulation. The response of gingival epithelial cells regarding the formation of epithelial barrier structures was tested.

RESULTS

Plasma polymerized surfaces successfully directed distinguished protein adsorption profiles from serum protein pool, in which plasma polymerized allylamine (ppAA) surface favored adsorbing adhesion related proteins and could promote FN absorption and functionalization via electrostatic interactions and hydrogen bonds, thus subsequently activating the ITG β1-FAK-mTOR signaling and promoting gingival epithelial cells adhesion.

CONCLUSION

This study offers an effective perspective to overcome the current dilemma of the inferior interface-epithelial integration by in situ protein absorption and functionalization, which may advance the development of functional transepithelial biointerfaces. Tuning the surface chemistry by plasma polymerization can control the adsorption of fibronectin and functionalize it by exposing functional protein domains. The functionalized fibronectin can bind to human gingival epithelial cell membrane integrins to activate epithelial barrier structure related signaling pathway, which eventually enhances the formation of epithelial barrier structure.

Different Extracellular β-Amyloid (1-42) Aggregates Differentially Impair Neural Cell Adhesion and Neurite Outgrowth through Differential Induction of Scaffold Palladin

Extracellular amyloid β-protein (1-42) (Aβ42) aggregates have been recognized as toxic agents for neural cells in vivo and in vitro. The aim of this study was to investigate the cytotoxic effects of extracellular Aβ42 aggregates in soluble (or suspended, SAβ42) and deposited (or attached, DAβ42) forms on cell adhesion/re-adhesion, neurite outgrowth, and intracellular scaffold palladin using the neural cell lines SH-SY5Y and HT22, and to elucidate the potential relevance of these effects. The effect of extracellular Aβ42 on neural cell adhesion was directly associated with their neurotrophic or neurotoxic activity, with SAβ42 aggregates reducing cell adhesion and associated live cell de-adherence more than DAβ42 aggregates, while causing higher mortality. The reduction in cell adhesion due to extracellular Aβ42 aggregates was accompanied by the impairment of neurite outgrowth, both in length and number, and similarly, SAβ42 aggregates impaired the extension of neurites more severely than DAβ42 aggregates. Further, the disparate changes of intracellular palladin induced by SAβ42 and DAβ42 aggregates, respectively, might underlie their aforementioned effects on target cells. Further, the use of anti-oligomeric Aβ42 scFv antibodies revealed that extracellular Aβ42 aggregates, especially large DAβ42 aggregates, had some independent detrimental effects, including physical barrier effects on neural cell adhesion and neuritogenesis in addition to their neurotoxicity, which might be caused by the rigid C-terminal clusters formed between adjacent Aβ42 chains in Aβ42 aggregates. Our findings, concerning how scaffold palladin responds to extracellular Aβ42 aggregates, and is closely connected with declines in cell adhesion and neurite outgrowth, provide new insights into the cytotoxicity of extracellular Aβ42 aggregates in Alzheimer disease.

Junctional epithelium and hemidesmosomes: Tape and rivets for solving the "percutaneous device dilemma" in dental and other permanent implants

The percutaneous device dilemma describes etiological factors, centered around the disrupted epithelial tissue surrounding non-remodelable devices, that contribute to rampant percutaneous device infection. Natural percutaneous organs, in particular their extracellular matrix mediating the "device"/epithelium interface, serve as exquisite examples to inspire longer lasting long-term percutaneous device design. For example, the tooth's imperviousness to infection is mediated by the epithelium directly surrounding it, the junctional epithelium (JE). The hallmark feature of JE is formation of hemidesmosomes, cell/matrix adhesive structures that attach surrounding oral gingiva to the tooth's enamel through a basement membrane. Here, the authors survey the multifaceted functions of the JE, emphasizing the role of the matrix, with a particular focus on hemidesmosomes and their five main components. The authors highlight the known (and unknown) effects dental implant - as a model percutaneous device - placement has on JE regeneration and synthesize this information for application to other percutaneous devices. The authors conclude with a summary of bioengineering strategies aimed at solving the percutaneous device dilemma and invigorating greater collaboration between clinicians, bioengineers, and matrix biologists.

How Nanoparticles Open the Paracellular Route of Biological Barriers: Mechanisms, Applications, and Prospects

Biological barriers are essential physiological protective systems and obstacles to drug delivery. Nanoparticles (NPs) can access the paracellular route of biological barriers, either causing adverse health impacts on humans or producing therapeutic opportunities. This Review introduces the structural and functional influences of NPs on the key components that govern the paracellular route, mainly tight junctions, adherens junctions, and cytoskeletons. Furthermore, we evaluate their interaction mechanisms and address the influencing factors that determine the ability of NPs to open the paracellular route, which provides a better knowledge of how NPs can open the paracellular route in a safer and more controllable way. Finally, we summarize limitations in the research models and methodologies of the existing research in the field and provide future research direction. This Review demonstrates the in-depth causes for the reversible opening or destruction of the integrity of barriers generated by NPs; more importantly, it contributes insights into the design of NP-based medications to boost paracellular drug delivery efficiency.

Cell-3D matrix interactions: recent advances and opportunities

Tissues consist of cells and their surrounding extracellular matrix (ECM). Cell-ECM interactions play crucial roles in embryonic development, differentiation, tissue remodeling, and diseases including fibrosis and cancer. Recent research advances in characterizing cell-matrix interactions include detailed descriptions of hundreds of ECM and associated molecules, their complex intermolecular interactions in development and disease, identification of distinctive modes of cell migration in different 3D ECMs, and new insights into mechanisms of organ formation. Exploring the roles of the physical features of different ECM microenvironments and the bidirectional regulation of cell signaling and matrix organization emphasize the dynamic nature of these interactions, which can include feedback loops that exacerbate disease. Understanding mechanisms of cell-matrix interactions can potentially lead to targeted therapeutic interventions.