Adhesion-dependent Caveolin-1 Tyrosine-14 phosphorylation is regulated by FAK in response to changing matrix stiffness

Integrin-mediated adhesion regulates cellular responses to changes in the mechanical and biochemical properties of the extracellular matrix. Cell-matrix adhesion regulates caveolar endocytosis, dependent on caveolin 1 (Cav1) Tyr14 phosphorylation (pY14Cav1), to control anchorage-dependent signaling. We find that cell-matrix adhesion regulates pY14Cav1 levels in mouse fibroblasts. Biochemical fractionation reveals endogenous pY14Cav1 to be present in caveolae and focal adhesions (FA). Adhesion does not affect caveolar pY14Cav1, supporting its regulation at FA, in which PF-228-mediated inhibition of focal adhesion kinase (FAK) disrupts. Cell adhesion on 2D polyacrylamide matrices of increasing stiffness stimulates Cav1 phosphorylation, which is comparable to the phosphorylation of FAK. Inhibition of FAK across varying stiffnesses shows it regulates pY14Cav1 more prominently at higher stiffness. Taken together, these studies reveal the presence of FAK-pY14Cav1 crosstalk at FA, which is regulated by cell-matrix adhesion.

TRPV4 Plays a Role in Matrix Stiffness-Induced Macrophage Polarization

Phenotypic polarization of macrophages is deemed essential in innate immunity and various pathophysiological conditions. We have now determined key aspects of the molecular mechanism by which mechanical cues regulate macrophage polarization. We show that Transient Receptor Potential Vanilloid 4 (TRPV4), a mechanosensitive ion channel, mediates substrate stiffness-induced macrophage polarization. Using atomic force microscopy, we showed that genetic ablation of TRPV4 function abrogated fibrosis-induced matrix stiffness generation in skin tissues. We have determined that stiffer skin tissue promotes the M1 macrophage subtype in a TRPV4-dependent manner; soft tissue does not. These findings were further validated by our in vitro results which showed that stiff matrix (50 kPa) alone increased expression of macrophage M1 markers in a TRPV4-dependent manner, and this response was further augmented by the addition of soluble factors; neither of which occurred with soft matrix (1 kPa). A direct requirement for TRPV4 in M1 macrophage polarization spectrum in response to increased stiffness was evident from results of gain-of-function assays, where reintroduction of TRPV4 significantly upregulated the expression of M1 markers in TRPV4 KO macrophages. Together, these data provide new insights regarding the role of TRPV4 in matrix stiffness-induced macrophage polarization spectrum that may be explored in tissue engineering and regenerative medicine and targeted therapeutics.

Matrix stiffness regulates myocardial differentiation of human umbilical cord mesenchymal stem cells

Myocardial infarction is a cardiovascular disease with high mortality. Human umbilical cord mesenchymal stem cells (hUC-MSCs) with strong self-renewal capacity and multipotency, provide the possibility of replacing injured cardiomyocytes. hUC-MSCs were cultured on polyacrylamide hydrogels with stiffnesses corresponding to Young's modulus of 13-16kPa and 62-68kPa which mimic the stiffnesses of healthy heart tissue and fibrotic myocardium. The expression of early myocardial markers Nkx2.5, GATA4, Mesp1 and the mature myocardial markers cTnT, cTnI, α-actin were detected by RT-PCR and Western Blot, which showed that soft matrix (13-16 kPa) tended to induce the differentiation of hUC-MSCs into myocardium, compared with stiff matrix (62-68 kPa). Piezos are mechanically sensitive non-selective cation channels. The expression of Piezo1 increased with the stiffness gradient of 1-10kPa, 13-16kPa, 35-38kPa and 62-68kPa on the 1^st day, but Piezo2 expression was irregular. The expression of integrin β1 and calcium ions were also higher on stiff substrate than on soft substrate. hUC-MSCs tend to differentiate into myocardium on the matrix stiffness of 13-16 kPa. The relationship among matrix stiffness, Piezo1 and myocardial differentiation needs further validation.

Matrix stiffness-mediated effects on macrophages polarization and their LOXL2 expression

Previously, we reported that the secreted lysyl oxidase like 2 (LOXL2) from hepatocellular carcinoma (HCC) cells under higher stiffness stimulation contributed to the formation of lung premetastatic niche. To further clarify whether matrix stiffness also alters LOXL2 expression in other cells within tumor microenvironment, we developed a gel-based culture system combined with a model of macrophage polarization to evaluate the effects of matrix stiffness on the polarization of M2 macrophages and their LOXL2 expression. THP-1 cells cultured on 6KPa, 10KPa, and 16KPa stiffness substrates were first incubated with 100nM phorbol 12-myristate 13-acetate (PMA) for 24 hours and subsequently treated with 20nM interleukin-4 (IL-4) and 20nM interleukin-13 (IL-13) for 48 hours. The polarization states of M2 macrophages under different stiffness stimulation were comparatively analyzed, and their LOXL2 expressions as well as the underlying molecular mechanism were further explored. Our results demonstrated that increased matrix stiffness remarkably strengthened M2 macrophage polarization and promoted their LOXL2 expression. Activation of integrin β5-FAK-MEK1/2-ERK1/2 pathway participated in matrix stiffness-mediated HIF-1α upregulation, and HIF-1α upregulation resulted in a significant improvement in LOXL2 expression. Additionally, M2 macrophage polarization state and LOXL2 expression in HCC tissues with COL1^High /LOX^High were consistent with the results in vitro, further confirming the regulation roles of matrix stiffness in macrophage polarization and LOXL2 expression. The findings about LOXL2 upregulation in the polarized macrophages under higher stiffness stimulation will be helpful to better understand the underlying mechanism of matrix stiffness-induced premetastatic niche formation in HCC.

Matrix Stiffness-Upregulated MicroRNA-17-5p Attenuates the Intervention Effects of Metformin on HCC Invasion and Metastasis by Targeting the PTEN/PI3K/Akt Pathway

Background

Metformin, a traditional first-line anti-hyperglycemic agent for diabetes, recently exhibits better antitumor effect in hepatocellular carcinoma (HCC). However, its resistance and tolerance mechanism in HCC remains largely unknown. Here, we investigated whether increased matrix stiffness attenuated the intervention effects of metformin on HCC invasion and metastasis, and explored its underlying molecular mechanism.

Methods

FN-coated gel substrates with 6, 10, and 16 kPa, which simulated the stiffness of normal, fibrotic, and cirrhotic liver tissues respectively, were established to evaluate matrix stiffness-mediated effects on HCC cells. Alterations in morphology, proliferation, motility, and invasive/metastatic-associated genes (PTEN, MMP2, MMP9) of HCC cells grown on different-stiffness substrates were comparatively analyzed before and after metformin intervention. Subsequently, the underlying molecular mechanism by which higher matrix stiffness attenuates antitumor effects of metformin in HCC was further elucidated.

Results

Metformin significantly inhibited proliferation, migration, and invasion of HCC cells. Compared with the controls on lower-stiffness substrate, HCC cells grown on higher-stiffness substrate exhibited an obvious resistance to intervention effects of metformin on proliferation, migration, invasion and metastasis. High stiffness stimulation significantly activated the miR-17-5p/PTEN/PI3K/Akt signaling pathway in HCC cells via integrin β1 and in turn resulted in MMP2 and MMP9 upregulation. Meanwhile, integrin β1 knockdown or PI3K inhibitor partially reversed the activation of the above signaling molecules. For HCC cells grown on the same-stiffness substrate, metformin remarkably upregulated PTEN expression and suppressed the activation of the PI3K/Akt/MMP pathway, but no effect on integrin β1 expression. Importantly, the increase in fold of PTEN expression and decrease in folds of Akt phosphorylation level and MMP2 and MMP9 expressions in the treated HCC cells with metformin on 16-kPa stiffness substrate were evidently weakened compared with those in the controls on the 6-kPa stiffness substrate.

Conclusions:

Increased matrix stiffness significantly attenuates the inhibitory effect of metformin on HCC invasion and metastasis, and a common pathway of PTEN/PI3K/Akt/MMPs activated by mechanical stiffness signal and inactivated by metformin contributes to matrix stiffness-caused metformin resistance. To the best of our knowledge, this is the first report to clarify the mechanism of metformin intervention resistance from the perspective of tumor biophysical microenvironment.

Integrin αVβ5/Akt/Sp1 pathway participates in matrix stiffness-mediated effects on VEGFR2 upregulation in vascular endothelial cells

Our previous study has validated that higher matrix stiffness obviously improves vascular endothelial growth factor (VEGF) expression in HCC cells, highlighting a linkage between matrix stiffness and HCC angiogenesis. However, the effects of matrix stiffness on vascular endothelial cells in HCC and its underlying mechanism remain largely uncharacterized. Here we further analyzed the expression of vascular endothelial growth factor receptor 2 (VEGFR2) in human umbilical vein endothelial cells (HUVECs) grown on different stiffness substrates and explored its regulatory mechanism for better understanding matrix stiffness-regulated angiogenesis in HCC. Our results revealed that increased matrix stiffness significantly upregulated the expression of VEGFR2 in HUVECs, and the expression level of VEGFR2 was positively correlated with the expression levels of COL1 and lysyl oxidase in human HCC tissues and rat HCC tissue, moreover VEGFR2 and CD34 were co-localized at blood vessel of HCC tissues, indicating an obvious regulation role of matrix stiffness in VEGFR2 expression. Simultaneously, increased matrix stiffness also elevated the phosphorylation level of Akt and the expressions of integrin αV/β5 and nuclear Sp1 in HUVECs. Inhibition of integrin αVβ5 remarkably reversed the expression of VEGFR2 and phosphorylation level of Akt in HUVECs grown on higher stiffness substrate. Except that, PI3K inhibitor also suppressed the phosphorylation level of Akt and the expressions of VEGFR2 and nuclear Sp1 evidently. Taken together, higher matrix stiffness increased VEGFR2 expression in HUVECs, and integrin αVβ5/Akt/Sp1 pathway participated in stiffness-mediated effects on VEGFR2 upregulation. This study combining with our previous report discloses a new paradigm in which higher matrix stiffness as an initiator drives HCC angiogenesis via upregulating both VEGFR2 expression in vascular endothelial cells and VEGF expression in HCC cells.

Extracellular Matrix Stiffness and Composition Regulate the Myofibroblast Differentiation of Vaginal Fibroblasts

Fibroblast to myofibroblast differentiation is a key feature of wound-healing in soft tissues, including the vagina. Vaginal fibroblasts maintain the integrity of the vaginal wall tissues, essential to keep pelvic organs in place and avoid pelvic organ prolapse (POP). The micro-environment of vaginal tissues in POP patients is stiffer and has different extracellular matrix (ECM) composition than healthy vaginal tissues. In this study, we employed a series of matrices with known stiffnesses, as well as vaginal ECMs, in combination with vaginal fibroblasts from POP and healthy tissues to investigate how matrix stiffness and composition regulate myofibroblast differentiation in vaginal fibroblasts. Stiffness was positively correlated to production of α-smooth muscle actin (α-SMA). Vaginal ECMs induced myofibroblast differentiation as both α-SMA and collagen gene expressions were increased. This differentiation was more pronounced in cells seeded on POP-ECMs that were stiffer than those derived from healthy tissues and had higher collagen and elastin protein content. We showed that stiffness and ECM content regulate vaginal myofibroblast differentiation. We provide preliminary evidence that vaginal fibroblasts might recognize POP-ECMs as scar tissues that need to be remodeled. This is fundamentally important for tissue repair, and provides a rational basis for POP disease modelling and therapeutic innovations in vaginal reconstruction.

Matrix Rigidity Controls Epithelial-Mesenchymal Plasticity and Tumor Metastasis via a Mechanoresponsive EPHA2/LYN Complex

Mechanical cues from the extracellular matrix (ECM) regulate various cellular processes via distinct mechanotransduction pathways. In breast cancer, increased ECM stiffness promotes epithelial-to-mesenchymal transition (EMT), cell invasion, and metastasis. Here, we identify a mechanosensitive EPHA2/LYN protein complex regulating EMT and metastasis in response to increasing ECM stiffness during tumor progression. High ECM stiffness leads to ligand-independent phosphorylation of ephrin receptor EPHA2, which recruits and activates the LYN kinase. LYN phosphorylates the EMT transcription factor TWIST1 to release TWIST1 from its cytoplasmic anchor G3BP2 to enter the nucleus, thus triggering EMT and invasion. Genetic and pharmacological inhibition of this pathway prevents breast tumor invasion and metastasis in vivo. In human breast cancer samples, activation of this pathway correlates with collagen fiber alignment, a marker of increasing ECM stiffness. Our findings reveal an EPHA2/LYN/TWIST1 mechanotransduction pathway that responds to mechanical signals from the tumor microenvironment to drive EMT, invasion, and metastasis.

The Importance of Mechanical Forces for in vitro Endothelial Cell Biology

Blood and lymphatic vessels are lined by endothelial cells which constantly interact with their luminal and abluminal extracellular environments. These interactions confer physical forces on the endothelium, such as shear stress, stretch and stiffness, to mediate biological responses. These physical forces are often altered during disease, driving abnormal endothelial cell behavior and pathology. Therefore, it is critical that we understand the mechanisms by which endothelial cells respond to physical forces. Traditionally, endothelial cells in culture are grown in the absence of flow on stiff substrates such as plastic or glass. These cells are not subjected to the physical forces that endothelial cells endure in vivo, thus the results of these experiments often do not mimic those observed in the body. The field of vascular biology now realize that an intricate analysis of endothelial signaling mechanisms requires complex in vitro systems to mimic in vivo conditions. Here, we will review what is known about the mechanical forces that guide endothelial cell behavior and then discuss the advancements in endothelial cell culture models designed to better mimic the in vivo vascular microenvironment. A wider application of these technologies will provide more biologically relevant information from cultured cells which will be reproducible to conditions found in the body.

TRPV4 is a regulator in P. gingivalis lipopolysaccharide-induced exacerbation of macrophage foam cell formation

Porphyromonas gingivalis (P.g), a major causative agent of periodontitis, has been linked to atherosclerosis, a chronic inflammatory vascular disease. Recent studies have suggested a link between periodontitis and arterial stiffness, a risk factor for atherosclerosis. However, the mechanisms by which P.g infection contributes to atherogenesis remain elusive. The formation of lipid-laden macrophage "foam cells" is critically important to development and progression of atherosclerosis. We have obtained evidence that TRPV4 (transient receptor potential channel of the vanilloid subfamily 4), a mechanosensitive channel, is a regulator of macrophage foam cell formation both in response to P.g-derived lipopolysaccharide (PgLPS) or to an increase in matrix stiffness. Importantly, we found that TRPV4 activity (Ca²⁺ influx) was increased in response to PgLPS. Genetic deletion or chemical antagonism of TRPV4 channels blocked PgLPS-triggered exacerbation of oxidized LDL (oxLDL)-mediated foam cell formation. Mechanistically, we found that (1) TRPV4 regulated oxLDL uptake but not its cell surface binding in macrophages; (2) reduced foam cell formation in TRPV4 null cells was independent of expression of CD36, a predominant receptor for oxLDL, and (3) co-localization of TRPV4 and CD36 on the macrophage plasma membrane was sensitive to the increased level of matrix stiffness occurring in the presence of PgLPS. Altogether, our results suggest that TRPV4 channels play an essential role in P.g-induced exacerbation of macrophage foam cell generation through a mechanism that modulates uptake of oxLDL.

CXCR4 mediates matrix stiffness-induced downregulation of UBTD1 driving hepatocellular carcinoma progression via YAP signaling pathway

Rational: Increasing evidence indicates that the physical environment is a critical mediator of tumor behavior. Hepatocellular carcinoma (HCC) develops in an altered biomechanical environment, and increased matrix stiffness is a strong predictor of HCC development. C-X-C chemokine receptor type 4 (CXCR4) is known to trigger HCC progression. However, CXCR4 as a mediator of mechanical cues in HCC is not well characterized.

Methods: qRT-PCR, Western blot and IHC were used to detect the CXCR4 expression in different matrix stiffness gels. MTT was used to measure the cell proliferation of HCC cells. Immunoblotting was used for detection of epithelial-to-mesenchymal transition (EMT) and stemness on the matrix stiffness. Immunofluorescence (IF) was used to detect the nuclear location in HCC cells. IP was used to show the interaction between YAP, UbcH5c and β-TrCP.

Results: We identified CXCR4 as a critical intracellular signal transducer that relays matrix stiffness signals to control mechano-sensitive cellular activities through ubiquitin domain-containing protein 1 (UBTD1)-mediated YAP signaling pathway. We found that CXCR4 expression was remarkably up-regulated in HCC cells with increasing matrix stiffness and mediated proliferation, epithelial to mesenchymal transition, and stemness. Mechanistically, matrix stiffness acts through CXCR4 to decrease the levels of UBTD1, which is involved in the proteasome-dependent degradation of YAP, a major cell mechano-transducer. UBTD1 interacted with components of the YAP degradation complex and promoted the interaction between YAP and its E3 ubiquitin ligase β-TrCP. UBTD1 knockdown decreased YAP ubiquitylation and resulted in the activation of YAP-targeted genes and YAP downstream signaling. Downregulation of UBTD1 in HCC tissues correlated with malignant prognostic features and overall survival. Finally, luteolin, a natural product, suppressed matrix stiffness-induced biological effects and CXCR4-mediated YAP signaling pathway in HCC cells.

Conclusion: Our findings reveal CXCR4 as a molecular switch in mechano-transduction, thereby defining a mechano-signaling pathway from matrix stiffness to the nucleus.

Matrix Stiffness and Colorectal Cancer

In recent years, a growing consensus is emerging that the mechanical microenvironment of tumors is far more critical in the onset of tumor, tumor progression, invasion, and metastasis. Matrix stiffness, one of the sources of mechanical stimulation, affects tumor cells as well as non-tumor cells in multiple different molecular signaling pathways in solid tumors such as colorectal tumors, which lead to tumor invasion and metastasis, immune evasion and drug resistance. This review will illustrate the relationship between matrix stiffness and colorectal cancer from the following aspects. First, briefly introduce the mechanical microenvironment and colorectal cancer, then explain the origin of colorectal cancer extracellular matrix stiffness, and then synthesize the study of matrix stiffness of colorectal cancer in recent years to elaborate the effects of extracellular matrix stiffness in colorectal cancer’s biological behavior and signaling pathways, and finally we will discuss the transformation treatment for the matrix stiffness of colorectal cancer. An in-depth understanding of matrix stiffness and colorectal cancer can help researchers conduct further experiments to find new targets for the treatment of colorectal cancer.

H-Ras Transformation of Mammary Epithelial Cells Induces ERK-Mediated Spreading on Low Stiffness Matrix

Oncogenic transformation of mammary epithelial cells (MECs) is a critical step in epithelial-to-mesenchymal transition (EMT), but evidence also shows that MECs undergo EMT with increasing matrix stiffness; the interplay of genetic and environmental effects on EMT is not clear. To understand their combinatorial effects on EMT, premalignant MCF10A and isogenic Ras-transformed MCF10AT are cultured on polyacrylamide gels ranging from normal mammary stiffness, ≈150 Pa, to tumor stiffness, ≈5700 Pa. Though cells spread on stiff hydrogels independent of transformation, only 10AT cells exhibit heterogeneous spreading behavior on soft hydrogels. Within this mixed population, spread cells exhibit an elongated, mesenchymal-like morphology, disrupted localization of the basement membrane, and nuclear localization of the EMT transcription factor TWIST1. MCF10AT spreading is not driven by typical mechanosensitive pathways including YAP and TGF-β or by myosin contraction. Rather, ERK activation induces spreading of MCF10AT cells on soft hydrogels and requires dynamic microtubules. These findings indicate the importance of oncogenic signals, and their hierarchy with substrate mechanics, in regulating MEC EMT.

miRNA-mediated macrophage behaviors responding to matrix stiffness and ox-LDL

Atherosclerosis is one of the leading causes of morbidity and mortality, mainly due to the immune response triggered by the recruitment of monocytes/macrophages in the artery wall. Accumulating evidence have shown that matrix stiffness and oxidized low-density lipoproteins (ox-LDL) play important roles in atherosclerosis through modulating cellular behaviors. However, whether there is a synergistic effect for ox-LDL and matrix stiffness on macrophages behavior has not been explored yet. In this study, we developed a model system to investigate the synergistic role of ox-LDL and matrix stiffness on macrophage behaviors, such as migration, inflammatory and apoptosis. We found that there was a matrix stiffness-dependent behavior of monocyte-derived macrophages stimulated with ox-LDL. What's more, macrophages were more sensitive to ox-LDL on the stiff matrices compared to cells cultured on the soft matrices. Through next-generation sequencing, we identified miRNAs in response to matrix stiffness and ox-LDL and predicted pathways that showed the capability of miRNAs in directing macrophages fates. Our study provides a novel understanding of the important synergistic role of ox-LDL and matrix stiffness in modulating macrophages behaviors, especially through miRNAs signaling pathways, which could be potential key regulators in atherosclerosis and immune-targeted therapies.

Immobilized RGD concentration and proteolytic degradation synergistically enhance vascular sprouting within hydrogel scaffolds of varying modulus

Insufficient vascularization limits the volume and complexity of engineered tissue. The formation of new blood vessels (neovascularization) is regulated by a complex interplay of cellular interactions with biochemical and biophysical signals provided by the extracellular matrix (ECM) necessitating the development of biomaterial approaches that enable systematic modulation in matrix properties. To address this need poly(ethylene) glycol-based hydrogel scaffolds were engineered with a range of decoupled and combined variations in integrin-binding peptide (RGD) ligand concentration, elastic modulus and proteolytic degradation rate using free-radical polymerization chemistry. The modularity of this system enabled a full factorial experimental design to simultaneously investigate the individual and interaction effects of these matrix cues on vascular sprout formation in 3 D culture. Enhancements in scaffold proteolytic degradation rate promoted significant increases in vascular sprout length and junction number while increases in modulus significantly and negatively impacted vascular sprouting. We also observed that individual variations in immobilized RGD concentration did not significantly impact 3 D vascular sprouting. Our findings revealed a previously unidentified and optimized combination whereby increases in both immobilized RGD concentration and proteolytic degradation rate resulted in significant and synergistic enhancements in 3 D vascular spouting. The above-mentioned findings would have been challenging to uncover using one-factor-at-time experimental analyses.

Extracellular Matrix in Secondary Palate Development

The secondary palate arises from outgrowths of epithelia-covered embryonic mesenchyme that grow from the maxillary prominence, remodel to meet over the tongue, and fuse at the midline. These events require the coordination of cell proliferation, migration, and gene expression, all of which take place in the context of the extracellular matrix (ECM). Palatal cells generate their ECM, and then stiffen, degrade, or otherwise modify its properties to achieve the required cell movement and organization during palatogenesis. The ECM, in turn, acts on the cells through their matrix receptors to change their gene expression and thus their phenotype. The number of ECM-related gene mutations that cause cleft palate in mice and humans is a testament to the crucial role the matrix plays in palate development and a reminder that understanding that role is vital to our progress in treating palate deformities. This article will review the known ECM constituents at each stage of palatogenesis, the mechanisms of tissue reorganization and cell migration through the palatal ECM, the reciprocal relationship between the ECM and gene expression, and human syndromes with cleft palate that arise from mutations of ECM proteins and their regulators. Anat Rec, 2019. © 2019 American Association for Anatomy.

The Effect of Matrix Stiffness of Biomimetic Gelatin Nanofibrous Scaffolds on Human Cardiac Pericyte Behavior

Congenital heart disease (CHD) is the most common and deadly congenital anomaly, accounting for up to 7.5% of all infant deaths. Survival in children born with CHD has improved dramatically over the past several decades (this positive trend being counterbalanced by the fact that more patients develop heart failure). Seminal data indicate an alteration of the extracellular matrix occurs with time in these hearts due to diffuse and abundant interstitial fibrosis. This results in an escalation in the stiffness of the local myocardial microenvironment. However, the influence of matrix stiffness in regulating the function of resident human stromal cells has not been reported. The objective of this study was to determine the impact of scaffold stiffness on the antigenic and functional profile of cardiac pericytes (CPs) isolated from patients with CHD. To this end, we have first manufactured gelatin nanofibrous scaffolds with varying degrees of stiffness using an in situ cross-linking electrospinning technique in a pure water solvent system. We assessed Young's modulus and performed a comprehensive physicochemical characterization of the scaffolds employing scanning electron microscopy and Fourier transform infrared spectroscopy. We next evaluated the changes induced by a different scaffold stiffness on CP morphology, antigenic profile, viability, proliferation, angiocrine activity, and induced differentiation. Results indicate that soft matrixes with a fiber diameter of ∼400 nm increase CP proliferation, secretion of angiopoietin 2, and F-actin stress fiber formation, without affecting the antigenic profile, viability, or differentiation. These data indicate for the first time that human CPs can be functionally influenced by slight changes in matrix stiffness. The study elucidates the importance of mechanical/morphological cues in modulating the behavior of stromal cells isolated from patients with CHD.

Matrix Mechanics as Regulatory Factors and Therapeutic Targets in Hepatic Fibrosis

The hallmark of liver fibrosis is excessive extracellular matrix (ECM) synthesis and deposition that improve liver matrix remodeling and stiffening. Increased matrix stiffness is not only a pathological consequence of liver fibrosis in traditional view, but also recognized as a key driver in pathological progression of hepatic fibrosis. Cells can perceive changes in the mechanical characteristics of hepatic matrix and respond by means of mechanical signal transduction pathways to regulate cell behavior. In this review, the authors first classify causes of liver matrix stiffening during fibrotic progression, such as higher degree of collagen cross-linking. The latest advances of the research on the matrix mechanics in regulating activation of HSCs or fibroblasts under two-dimensional (2D) and three-dimensional (3D) microenvironment is also classified and summarized. The mechanical signaling pathways involved in the process of hepatic matrix stiffening, such as YAP-TAZ signaling pathway, are further summarized. Finally, some potential therapeutic concepts and strategies based on matrix mechanics will be detailed. Collectively, these findings reinforce the importance of matrix mechanics in hepatic fibrosis, and underscore the value of clarifying its modulation in hopes of advancing the development of novel therapeutic targets and strategies for hepatic fibrosis.

Biomechanical Microenvironment Regulates Fusogenicity of Breast Cancer Cells

Fusion of cancer cells is thought to contribute to tumor development and drug resistance. The low frequency of cell fusion events and the instability of fused cells have hindered our ability to understand the molecular mechanisms that govern cell fusion. We have demonstrated that several breast cancer cell lines can fuse into multinucleated giant cells in vitro, and the initiation and longevity of fused cells can be regulated solely by biophysical factors. Dynamically tuning the adhesive area of the patterned substrates, reducing cytoskeletal tensions pharmacologically, altering matrix stiffness, and modulating pattern curvature all supported the spontaneous fusion and stability of these multinucleated giant cells. These observations highlight that the biomechanical microenvironment of cancer cells, including the matrix rigidity and interfacial curvature, can directly modulate their fusogenicity, an unexplored mechanism through which biophysical cues regulate tumor progression.

The Role of Cancer Stem Cells and Mechanical Forces in Ovarian Cancer Metastasis

Ovarian cancer is an extremely lethal gynecologic disease; with the high-grade serous subtype predominantly associated with poor survival rates. Lack of early diagnostic biomarkers and prevalence of post-treatment recurrence, present substantial challenges in treating ovarian cancers. These cancers are also characterized by a high degree of heterogeneity and protracted metastasis, further complicating treatment. Within the ovarian tumor microenvironment, cancer stem-like cells and mechanical stimuli are two underappreciated key elements that play a crucial role in facilitating these outcomes. In this review article, we highlight their roles in modulating ovarian cancer metastasis. Specifically, we outline the clinical relevance of cancer stem-like cells, and challenges associated with their identification and characterization and summarize the ways in which they modulate ovarian cancer metastasis. Further, we review the mechanical cues in the ovarian tumor microenvironment, including, tension, shear, compression and matrix stiffness, that influence (cancer stem-like cells and) metastasis in ovarian cancers. Lastly, we outline the challenges associated with probing these important modulators of ovarian cancer metastasis and provide suggestions for incorporating these cues in basic biology and translational research focused on metastasis. We conclude that future studies on ovarian cancer metastasis will benefit from the careful consideration of mechanical stimuli and cancer stem cells, ultimately allowing for the development of more effective therapies.

Fibrinogen-Based Hydrogel Modulus and Ligand Density Effects on Cell Morphogenesis in Two-Dimensional and Three-Dimensional Cell Cultures

There is a need to further explore the convergence of mechanobiology and dimensionality with systematic investigations of cellular response to matrix mechanics in 2D and 3D cultures. Here, a semisynthetic hydrogel capable of supporting both 2D and 3D cell culture is applied to investigate cell response to matrix modulus and ligand density. The culture materials are fabricated from adducts of polyethylene glycol (PEG) or PluronicF127 and fibrinogen fragments, formed into hydrogels by free-radical polymerization, and characterized by shear rheology. Control over the modulus of the materials is accomplished by changing the concentration of synthetic PEG-diacrylate crosslinker (0.5% w/v), and by altering the molecular length of the PEG (10 and 20 kDa). Control over ligand density is accomplished by changing fibrinogen concentrations from 3 to 12 mg mL^-1 . In 2D culture, cell motility parameters, including cell speed and persistence time are significantly increased with increasing modulus. In both 2D and 3D culture, cells express vinculin and there is evidence of focal adhesion formation in the high stiffness materials. The modulus- and ligand-dependent morphogenesis response from the cells in 2D culture is contradictory to the same measured response in 3D culture. In 2D culture, anchorage-dependent cells become more elongated and significantly increase their size with increasing ligand density and matrix modulus. In 3D culture, the same anchorage-dependent cells become less spindled and significantly reduce their size in response to increasing ligand density and matrix modulus. These differences arise from dimensionality constraints, most notably the encapsulation of cells in a non-porous hydrogel matrix. These insights underscore the importance of mechanical properties in regulating cell morphogenesis in a 3D culture milieu. The versatility of the hydrogel culture environment further highlights the significance of a modular approach when developing materials that aim to optimize the cell culture environment.

A Soft Matrix Enhances the Cancer Stem Cell Phenotype of HCC Cells

Cancer stem cells (CSCs) comprise a small portion of cancer cells, have greater self-renewal ability and metastatic potential than non-CSCs and are resistant to drugs and radiotherapy. CSCs and non-CSCs, which can reversibly change their stemness states, typically play roles in plasticity and cancer cell heterogeneity. Furthermore, the component that plays a key role in affecting CSC plasticity remains unknown. In this study, we utilized mechanically tunable polyacrylamide (PA) hydrogels to simulate different stiffnesses of the liver tissue matrix in various stages. Our results showed that hepatocellular carcinoma (HCC) cells were small and round in a soft matrix. The soft matrix increased the expression levels of liver cancer cells with stemness properties (LCSC) surface markers in HCC cells and the number of side population (SP) cells. Moreover, the soft matrix elicited early cell cycle arrest in the G1 phase and increased the cell sphere-forming ability. In addition, cells grown on the soft matrix showed enhanced chemoresistance and tumorigenicity potential. In summary, our study demonstrated that a soft matrix increases the stemness of HCC cells.

Mechanical cues modulate cellular uptake of nanoparticles in cancer via clathrin-mediated and caveolae-mediated endocytosis pathways

AIM

To investigate the influence of tissue mechanics on the cellular uptake efficiency of nanoparticles (NPs) in cancer.

MATERIALS & METHODS

Collagen-coated polyacrylamide gels were prepared as model substrates. Coumarin 6-loaded poly(lactic-co-glycolic) acid micelles (C6-NPs) were prepared to investigate the cellular uptake of NPs.

RESULTS

We demonstrated that substrate stiffness modulated the cellular uptake of NPs of cancer. Mechanistically, mechanical cues exerted influence on the clathrin-mediated endocytosis and caveolae-mediated endocytosis pathways, which mediated stiffness-regulated cellular uptake of NPs.

CONCLUSION

Our findings shed light on the regulatory role of the mechanical cues on the cellular uptake of NPs and will facilitate the selection of clinical patients who might benefit from a given nanotherapy.

UBTD1 is a mechano-regulator controlling cancer aggressiveness

Ubiquitin domain-containing protein 1 (UBTD1) is highly evolutionary conserved and has been described to interact with E2 enzymes of the ubiquitin-proteasome system. However, its biological role and the functional significance of this interaction remain largely unknown. Here, we demonstrate that depletion of UBTD1 drastically affects the mechanical properties of epithelial cancer cells via RhoA activation and strongly promotes their aggressiveness. On a stiff matrix, UBTD1 expression is regulated by cell-cell contacts, and the protein is associated with β-catenin at cell junctions. Yes-associated protein (YAP) is a major cell mechano-transducer, and we show that UBTD1 is associated with components of the YAP degradation complex. Interestingly, UBTD1 promotes the interaction of YAP with its E3 ubiquitin ligase β-TrCP Consequently, in cancer cells, UBTD1 depletion decreases YAP ubiquitylation and triggers robust ROCK2-dependent YAP activation and downstream signaling. Data from lung and prostate cancer patients further corroborate the in cellulo results, confirming that low levels of UBTD1 are associated with poor patient survival, suggesting that biological functions of UBTD1 could be beneficial in limiting cancer progression.

Matrix stiffness mediates stemness characteristics via activating the Yes-associated protein in colorectal cancer cells

Matrix stiffness is an essential physical microenvironment in solid cancer. However, its influence on cancer stemness still remains elusive. Colorectal cancer (CRC) cell line HCT-116 was cultured in the matrix with various stiffness. The siYAP was applied to detect the changes of stemness markers. The cancer stemness markers, Yes-associated protein (YAP), Lamin A/C and downstream protein molecules, and their activation were measured after the treatment with anti-β1-integrin and FAK inhibitors. In CRC tissue samples, collagen deposition and the expression of α-SMA and CD133 were detected. The study found that the expression level of stemness markers and Lamin A/C increased as the matrix stiffness raised and was regulated by YAP activation in CRC stem cells. Inhibition of β1-integrin and FAK activation in a high stiffness cell culture medium significantly decreased the activation of YAP, PI3K, and AKT. Collagen was highly deposited in the CRC invasive tumor front (ITF), and the expression of CD133 was higher in ITF compared with normal tissue and the tumor cells. Moreover, the expression level of α-SMA was positively correlated with CD133 expression level. Together, our results suggest that activation of YAP in CRC plays an important role in the promotion of cancer stem cell properties by extracellular matrix stiffness in CRC.