Biophysical Control of the Glioblastoma Immunosuppressive Microenvironment: Opportunities for Immunotherapy

GBM is the most aggressive and common form of primary brain cancer with a dismal prognosis. Current GBM treatments have not improved patient survival, due to the propensity for tumor cell adaptation and immune evasion, leading to a persistent progression of the disease. In recent years, the tumor microenvironment (TME) has been identified as a critical regulator of these pro-tumorigenic changes, providing a complex array of biomolecular and biophysical signals that facilitate evasion strategies by modulating tumor cells, stromal cells, and immune populations. Efforts to unravel these complex TME interactions are necessary to improve GBM therapy. Immunotherapy is a promising treatment strategy that utilizes a patient's own immune system for tumor eradication and has exhibited exciting results in many cancer types; however, the highly immunosuppressive interactions between the immune cell populations and the GBM TME continue to present challenges. In order to elucidate these interactions, novel bioengineering models are being employed to decipher the mechanisms of immunologically "cold" GBMs. Additionally, these data are being leveraged to develop cell engineering strategies to bolster immunotherapy efficacy. This review presents an in-depth analysis of the biophysical interactions of the GBM TME and immune cell populations as well as the systems used to elucidate the underlying immunosuppressive mechanisms for improving current therapies.

Cell morphology as a biological fingerprint of chondrocyte phenotype in control and inflammatory conditions

Introduction

Little is known how inflammatory processes quantitatively affect chondrocyte morphology and how single cell morphometric data could be used as a biological fingerprint of phenotype.

Methods

We investigated whether trainable high-throughput quantitative single cell morphology profiling combined with population-based gene expression analysis can be used to identify biological fingerprints that are discriminatory of control vs. inflammatory phenotypes. The shape of a large number of chondrocytes isolated from bovine healthy and human osteoarthritic (OA) cartilages was quantified under control and inflammatory (IL-1β) conditions using a trainable image analysis technique measuring a panel of cell shape descriptors (area, length, width, circularity, aspect ratio, roundness, solidity). The expression profiles of phenotypically relevant markers were quantified by ddPCR. Statistical analysis, multivariate data exploration, and projection-based modelling were used for identifying specific morphological fingerprints indicative of phenotype.

Results

Cell morphology was sensitive to both cell density and IL-1β. In both cell types, all shape descriptors correlated with expression of extracellular matrix (ECM)- and inflammatory-regulating genes. A hierarchical clustered image map revealed that individual samples sometimes responded differently in control or IL-1β conditions than the overall population. Despite these variances, discriminative projection-based modeling revealed distinct morphological fingerprints that discriminated between control and inflammatory chondrocyte phenotypes: the most essential morphological characteristics attributable to non-treated control cells was a higher cell aspect ratio in healthy bovine chondrocytes and roundness in OA human chondrocytes. In contrast, a higher circularity and width in healthy bovine chondrocytes and length and area in OA human chondrocytes indicated an inflammatory (IL-1β) phenotype. When comparing the two species/health conditions, bovine healthy and human OA chondrocytes exhibited comparable IL-1β-induced morphologies in roundness, a widely recognized marker of chondrocyte phenotype, and aspect ratio.

Discussion

Overall, cell morphology can be used as a biological fingerprint for describing chondrocyte phenotype. Quantitative single cell morphometry in conjunction with advanced methods for multivariate data analysis allows identifying morphological fingerprints that can discriminate between control and inflammatory chondrocyte phenotypes. This approach could be used to assess how culture conditions, inflammatory mediators, and therapeutic modulators regulate cell phenotype and function.

Targeting cell-matrix interface mechanobiology by integrating AFM with fluorescence microscopy

Mechanosensing at the interface of a cell and its surrounding microenvironment is an essential driving force of physiological processes. Understanding molecular activities at the cell-matrix interface has the potential to provide novel targets for improving tissue regeneration and early disease intervention. In the past few decades, the advancement of atomic force microscopy (AFM) has offered a unique platform for probing mechanobiology at this crucial microdomain. In this review, we describe key advances under this topic through the use of an integrated system of AFM (as a biomechanical testing tool) with complementary immunofluorescence (IF) imaging (as an in situ navigation system). We first describe the body of work investigating the micromechanics of the pericellular matrix (PCM), the immediate cell micro-niche, in healthy, diseased, and genetically modified tissues, with a focus on articular cartilage. We then summarize the key findings in understanding cellular biomechanics and mechanotransduction, in which, molecular mechanisms governing transmembrane ion channel-mediated mechanosensing, cytoskeleton remodeling, and nucleus remodeling have been studied in various cell and tissue types. Lastly, we provide an overview of major technical advances that have enabled more in-depth studies of mechanobiology, including the integration of AFM with a side-view microscope, multiple optomicroscopy, a fluorescence recovery after photobleaching (FRAP) module, and a tensile stretching device. The innovations described here have contributed greatly to advancing the fundamental knowledge of extracellular matrix biomechanics and cell mechanobiology for improved understanding, detection, and intervention of various diseases.

Reactive Oxygen Species Are Essential for Vasoconstriction upon Cold Exposure

Purpose

We explored the role of ROS in cold-induced vasoconstriction and corresponding mechanism.

Methods

Three experiments were performed. First, we measured blood flow in human hands before and after cold exposure. Second, 24 mice were randomly divided into 3 groups: 8 mice received saline injection, 8 received subcutaneous Tempol injection, and 8 received intrathecal Tempol injection. After 30 min, we determined blood flow in the skin before and after cold exposure. Finally, we used Tempol, CCG-1423, and Go 6983 to pretreat HAVSMCs and HUVECs for 24 h. Then, cells in the corresponding groups were exposed to cold (6 h, 4°C). After cold exposure, the cytoskeleton was stained. Intracellular Ca²⁺ and ROS levels were measured by flow cytometry and fluorescence microscopy. We measured protein expression via Western blotting.

Results

In the first experiment, after cold exposure, maximum skin blood flow decreased to 118.4 ± 50.97 flux units. Then, Tempol or normal saline pretreatment did not change skin blood flow. Unlike intrathecal Tempol injection, subcutaneous Tempol injection increased skin blood flow after cold exposure. Finally, cold exposure for 6 h shrank the cells, making them narrower, and increased intracellular Ca²⁺ and ROS levels in HUVECs and HAVSMCs. Tempol reduced cell shrinkage and decreased intracellular Ca²⁺ levels. In addition, Tempol decreased intracellular ROS levels. Cold exposure increased RhoA, Rock1, p-MLC-2, ET-1, iNOS, and p-PKC expression and decreased eNOS expression. Tempol or CCG-1423 pretreatment decreased RhoA, Rock1, and p-MLC-2 levels in HAVSMCs. Furthermore, Tempol or Go 6983 pretreatment decreased ET-1, iNOS, and p-PKC expression and increased eNOS expression in HUVECs.

Conclusion

ROS mediate the vasoconstrictor response within the cold-induced vascular response, and ROS in blood vessel tissues rather than nerve fibers are involved in vasoconstriction via the ROS/RhoA/ROCK1 and ROS/PKC/ET-1 pathways in VSMCs and endothelial cells.

Vascular smooth muscle stiffness and its role in aging

Vascular smooth muscle cells (VSMC) are now considered important contributors to the pathophysiological and biophysical mechanisms underlying arterial stiffening in aging. Here, we review mechanisms whereby VSMC stiffening alters vascular function and contributes to the changes in vascular stiffening observed in aging and cardiovascular disease. Vascular stiffening in arterial aging was historically associated with changes in the extracellular matrix; however, new evidence suggests that endothelial and vascular smooth muscle cell stiffness also contribute to overall blood vessel stiffness. Furthermore, VSMC play an integral role in regulating matrix deposition and vessel wall contractility via interaction between the actomyosin contractile unit and adhesion structures that anchor the cell within the extracellular matrix. Aged-induce phenotypic modulation of VSMC from a contractile to a synthetic phenotype is associated with decreased cellular contractility and increased cell stiffness. Aged VSMC also display reduced mechanosensitivity and adaptation to mechanical signals from their microenvironment due to impaired intracellular signaling. Finally, evidence for decreased contractility in arteries from aged animals demonstrate that changes at the cellular level result in decreased functional properties at the tissue level.

Micro/nano-net guides M2-pattern macrophage cytoskeleton distribution via Src-ROCK signalling for enhanced angiogenesis

Implant surface topography has been proven to determine the fate of adhered macrophage polarization, which is closely related to the cytoskeletal arrangement during adhesion. Our purpose was to establish a topography that is favourable to M2 macrophage switching by regulating macrophage cytoskeleton distribution. Two micro/nano-net structures with different pore sizes were generated by alkali bathing at medium (SAM) or high (SAH) temperature based on the micro-level surface. Their surface characteristics, in vitro macrophage polarization and impact on endothelial cells were analysed. The in vivo macrophage response and osseointegration were also tested. The results showed that the micro/nano-net has high hydrophilicity and moderate roughness. In the SAH and SAM groups, macrophages exhibited an elongated cytoskeleton with tiny protrusions and had a high M2/M1 polarization ratio with enhanced angiogenic ability, and in vivo studies also showed faster angiogenesis and bone formation in these groups. SAH showed even better results than SAM. For cytoskeleton related pathway explanation, ROCK expression was upregulated and Src expression was downregulated at the early or late adhesion stage in both the SAH and SAM groups. These results indicated that the micro/nano-net structure guides elongated macrophage adhesion states via Src-ROCK signalling and switches macrophages towards the M2 phenotype, which provides a cytoskeleton-oriented topography design for an ideal immune response.

The impact of culture dimensionality on behavioral epigenetic memory contributing to pluripotent state of iPS cells

Three-dimensional (3D) culture platforms have been explored to establish physiologically relevant cell culture environment and permit expansion scalability; however, little is known about the mechanisms underlying the regulation of pluripotency of human induced pluripotent stem cells (hiPSCs). This study elucidated epigenetic modifications contributing to pluripotency of hiPSCs in response to 3D culture. Unlike two-dimensional (2D) monolayer cultures, 3D cultured cells aggregated with each other to form ball-like aggregates. 2D cultured cells expressed elevated levels of Rac1 and RhoA; however, Rac1 level was significantly lower while RhoA level was persisted in 3D aggregates. Compared with 2D monolayers, the 3D aggregates also exhibited significantly lower myosin phosphorylation. Histone methylation analysis revealed remarkable H3K4me3 upregulation and H3K27me3 maintenance throughout the duration of 3D culture; in addition, we observed the existence of naïve pluripotency signatures in cells grown in 3D culture. These results demonstrated that hiPSCs adapted to 3D culture through alteration of the Rho-Rho kinase-phospho-myosin pathway, influencing the epigenetic modifications and transcriptional expression of pluripotency-associated factors. These results may help design culture environments for stable and high-quality hiPSCs.

Lysyl oxidases: Emerging biomarkers and therapeutic targets for various diseases

Therapeutic targeting of extracellular proteins has attracted huge attention in treating human diseases. The lysyl oxidases (LOXs) are a family of secreted copper-dependent enzymes which initiate the covalent crosslinking of collagen and elastin fibers in the extracellular microenvironment, thereby facilitating extracellular matrix (ECM) remodeling and ECM homeostasis. Apart from ECM-dependent roles, LOXs are also involved in other biological processes such as epithelial-to-mesenchymal transition (EMT) and transcriptional regulation, especially following hypoxic stress. Dysregulation of LOXs is found to underlie the onset and progression of multiple pathologies, such as carcinogenesis and cancer metastasis, fibrotic diseases, neurodegeneration and cardiovascular diseases. In this review, we make a comprehensive summarization of clinical and experimental evidences that support roles of for LOXs in disease pathology and points out LOXs as promising therapeutic targets for improving prognosis. Additionally, we also propose that LOXs reshape cell-ECM interaction or cell-cell interaction due to ECM-dependent and ECM-independent roles for LOXs. Therapeutic intervention of LOXs may have advantages in the maintenance of communication between ECM and cell or intercellular signaling, finally recovering organ function.

Mechanotransduction and Stiffness-Sensing: Mechanisms and Opportunities to Control Multiple Molecular Aspects of Cell Phenotype as a Design Cornerstone of Cell-Instructive Biomaterials for Articular Cartilage Repair

Since material stiffness controls many cell functions, we reviewed the currently available knowledge on stiffness sensing and elucidated what is known in the context of clinical and experimental articular cartilage (AC) repair. Remarkably, no stiffness information on the various biomaterials for clinical AC repair was accessible. Using mRNA expression profiles and morphology as surrogate markers of stiffness-related effects, we deduced that the various clinically available biomaterials control chondrocyte (CH) phenotype well, but not to equal extents, and only in non-degenerative settings. Ample evidence demonstrates that multiple molecular aspects of CH and mesenchymal stromal cell (MSC) phenotype are susceptible to material stiffness, because proliferation, migration, lineage determination, shape, cytoskeletal properties, expression profiles, cell surface receptor composition, integrin subunit expression, and nuclear shape and composition of CHs and/or MSCs are stiffness-regulated. Moreover, material stiffness modulates MSC immuno-modulatory and angiogenic properties, transforming growth factor beta 1 (TGF-β1)-induced lineage determination, and CH re-differentiation/de-differentiation, collagen type II fragment production, and TGF-β1- and interleukin 1 beta (IL-1β)-induced changes in cell stiffness and traction force. We then integrated the available molecular signaling data into a stiffness-regulated CH phenotype model. Overall, we recommend using material stiffness for controlling cell phenotype, as this would be a promising design cornerstone for novel future-oriented, cell-instructive biomaterials for clinical high-quality AC repair tissue.

Rho-kinase inhibitor coupled to peptide-modified albumin carrier reduces portal pressure and increases renal perfusion in cirrhotic rats

Rho-kinase (ROCK) activation in hepatic stellate cells (HSC) is a key mechanism promoting liver fibrosis and portal hypertension (PTH). Specific delivery of ROCK-inhibitor Y-27632 (Y27) to HSC targeting mannose-6-phosphate-receptors reduces portal pressure and fibrogenesis. In decompensated cirrhosis, presence of ascites is associated with reduced renal perfusion. Since in cirrhosis, platelet-derived growth factor receptor beta (PDGFRβ) is upregulated in the liver as well as the kidney, this study coupled Y27 to human serum albumin (HSA) substituted with PDGFRβ-recognizing peptides (pPB), and investigated its effect on PTH in cirrhotic rats. In vitro collagen contraction assays tested biological activity on LX2 cells. Hemodynamics were analyzed in BDL and CCl₄ cirrhotic rats 3 h, 6 h and 24 h after i.v. administration of Y27pPBHSA (0.5/1 mg/kg b.w). Phosphorylation of moesin and myosin light chain (MLC) assessed ROCK activity in liver, femoral muscle, mesenteric artery, kidney and heart. Three Y27 molecules were coupled to pPBHSA as confirmed by HPLC/MS, which was sufficient to relax LX2 cells. In vivo, Y27pPBHSA-treated rats exhibited lower portal pressure, hepatic vascular resistance without effect on systemic vascular resistance, but a tendency towards lower cardiac output compared to non-treated cirrhotic rats. Y27pPBHSA reduced intrahepatic resistance by reduction of phosphorylation of moesin and MLC in Y27pPBHSA-treated cirrhotic rats. Y27pPBHSA was found in the liver of rats up to 6 hours after its injection, in the HSC demonstrated by double-immunostainings. Interestingly, Y27pPBHSA increased renal arterial flow over time combined with an antifibrotic effect as shown by decreased renal acta2 and col1a1 mRNA expression. Therefore, targeting the ROCK inhibitor Y27 to PDGFRβ decreases portal pressure with potential beneficial effects in the kidney. This unique approach should be tested in human cirrhosis.

Biomechanics of Endothelial Tubule Formation Differentially Modulated by Cerebral Cavernous Malformation Proteins

At early stages of organismal development, endothelial cells self-organize into complex networks subsequently giving rise to mature blood vessels. The compromised collective behavior of endothelial cells leads to the development of a number of vascular diseases, many of which can be life-threatening. Cerebral cavernous malformation is an example of vascular diseases caused by abnormal development of blood vessels in the brain. Despite numerous efforts to date, enlarged blood vessels (cavernomas) can be effectively treated only by risky and complex brain surgery. In this work, we use a comprehensive simulation model to dissect the mechanisms contributing to an emergent behavior of the multicellular system. By tightly integrating computational and experimental approaches we gain a systems-level understanding of the basic mechanisms of vascular tubule formation, its destabilization, and pharmacological rescue, which may facilitate the development of new strategies for manipulating collective endothelial cell behavior in the disease context.

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A biophysical model reveals the differential effects of CCM proteins on cell behavior

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CCM proteins are critical for the balance of cell-cell and cell-matrix interactions

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Altered cell biomechanics explains the limited phenotype rescue by ROCK inhibition

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Knockdown of CCM3 expression leads to unique defects in the actomyosin organization

Vascular Smooth Muscle Contractile Function Declines With Age in Skeletal Muscle Feed Arteries

Aging induces a progressive decline in vasoconstrictor responses in central and peripheral arteries. This study investigated the hypothesis that vascular smooth muscle (VSM) contractile function declines with age in soleus muscle feed arteries (SFA). Contractile function of cannulated SFA isolated from young (4 months) and old (24 months) Fischer 344 rats was assessed by measuring constrictor responses of denuded (endothelium removed) SFA to norepinephrine (NE), phenylephrine (PE), and angiotensin II (Ang II). In addition, we investigated the role of RhoA signaling in modulation of VSM contractile function. Structural and functional characteristics of VSM cells were evaluated by fluorescence imaging and atomic force microscopy (AFM). Results indicated that constrictor responses to PE and Ang II were significantly impaired in old SFA, whereas constrictor responses to NE were preserved. In the presence of a Rho-kinase inhibitor (Y27632), constrictor responses to NE, Ang II, and PE were significantly reduced in young and old SFA. In addition, the age-group difference in constrictor responses to Ang II was eliminated. ROCK1 and ROCK2 content was similar in young and old VSM cells, whereas pROCK1 and pROCK2 were significantly elevated in old VSM cells. Aging was associated with a reduction in smooth muscle α-actin stress fibers and recruitment of proteins to cell-matrix adhesions. Old VSM cells presented an increase in integrin adhesion to the matrix and smooth muscle γ-actin fibers that was associated with increased cell stiffness. In conclusion, our results indicate that VSM contractile function declined with age in SFA. The decrement in contractile function was mediated in part by RhoA/ROCK signaling. Upregulation of pROCK in old VSM cells was not able to rescue contractility in old SFA. Collectively, these results indicate that changes at the VSM cell level play a central role in the reduced contractile function of aged SFA.

Ascent of atomic force microscopy as a nanoanalytical tool for exosomes and other extracellular vesicles

Over the last 30 years, atomic force microscopy (AFM) has made several significant contributions to the field of biology and medicine. In this review, we draw our attention to the recent applications and promise of AFM as a high-resolution imaging and force sensing technology for probing subcellular vesicles: exosomes and other extracellular vesicles. Exosomes are naturally occurring nanoparticles found in several body fluids such as blood, saliva, cerebrospinal fluid, amniotic fluid and urine. Exosomes mediate cell-cell communication, transport proteins and genetic content between distant cells, and are now known to play important roles in progression of diseases such as cancers, neurodegenerative disorders and infectious diseases. Because exosomes are smaller than 100 nm (about 30-120 nm), the structural and molecular characterization of these vesicles at the individual level has been challenging. AFM has revealed a new degree of complexity in these nanosized vesicles and generated growing interest as a nanoscale tool for characterizing the abundance, morphology, biomechanics, and biomolecular make-up of exosomes. With the recent interest in exosomes for diagnostic and therapeutic applications, AFM-based characterization promises to contribute towards improved understanding of these particles at the single vesicle and sub-vesicular levels. When coupled with complementary methods like optical super resolution STED and Raman, AFM could further unlock the potential of exosomes as disease biomarkers and as therapeutic agents.

Nck deficiency is associated with delayed breast carcinoma progression and reduced metastasis

Nck promotes breast carcinoma progression and metastasis by directing the polarized interaction of carcinoma cells with collagen fibrils, decreasing actin turnover, and enhancing the localization and activity of MMP14 at the cell surface through modulation of the spatiotemporal activation of Cdc42 and RhoA.

Although it is known that noncatalytic region of tyrosine kinase (Nck) regulates cell adhesion and migration by bridging tyrosine phosphorylation with cytoskeletal remodeling, the role of Nck in tumorigenesis and metastasis has remained undetermined. Here we report that Nck is required for the growth and vascularization of primary tumors and lung metastases in a breast cancer xenograft model as well as extravasation following injection of carcinoma cells into the tail vein. We provide evidence that Nck directs the polarization of cell–matrix interactions for efficient migration in three-dimensional microenvironments. We show that Nck advances breast carcinoma cell invasion by regulating actin dynamics at invadopodia and enhancing focalized extracellular matrix proteolysis by directing the delivery and accumulation of MMP14 at the cell surface. We find that Nck-dependent cytoskeletal changes are mechanistically linked to enhanced RhoA but restricted spatiotemporal activation of Cdc42. Using a combination of protein silencing and forced expression of wild-type/constitutively active variants, we provide evidence that Nck is an upstream regulator of RhoA-dependent, MMP14-mediated breast carcinoma cell invasion. By identifying Nck as an important driver of breast carcinoma progression and metastasis, these results lay the groundwork for future studies assessing the therapeutic potential of targeting Nck in aggressive cancers.

Dasatinib inhibits actin fiber reorganization and promotes endothelial cell permeability through RhoA-ROCK pathway

Treatment with dasatinib, a tyrosine kinase inhibitor, is associated with edema, pleural effusion, and pulmonary edema. We investigated the effect of dasatinib on the barrier function of human microvascular endothelial cells‐1 (HMEC‐1) in vitro and in vivo. The permeability of HMEC‐1 to fluorescein isothiocyante (FITC)‐dextran increased in Transwell chambers within 5 min following the addition of therapeutic concentrations of dasatinib. The change in permeability was associated with increased activation of RhoA GTPase and its effector Rho‐associated coiled‐coil kinase 1(ROCK1). RhoA inhibitor C3 transferase almost completely inhibited dasatinib‐induced increase in permeability. Under similar conditions, imatinib had no effect on permeability or activation of RhoA. Since integrin‐induced cell spreading suppresses RhoA activation, we examined the effect of dasatinib on cell spreading on fibronectin substrate. Dasatinib impaired endothelial cell spreading in a concentration‐dependent manner and induced disorganization of actin fibers. Tyrosine kinases play an essential role in transmitting signals from integrins to RhoA and we examined tyrosine phosphorylation of several cytoskeletal proteins. Dasatinib markedly inhibited tyrosine phosphorylation of p130 Crk‐associated substrate (p130cas), paxillin and vinculin. These results suggest that the inhibition of tyrosine phosphorylation of the focal adhesion plaque components by dasatinib may alter the assembly of actin fibers resulting in the activation of RhoA/ROCK pathway. Consistent with these findings, dasatinib‐induced increase in the permeability was blocked by ROCK inhibitor y27632. In vivo administration of y27632, significantly inhibited the dasatinib‐induced extravasation of Evans blue in mice and dasatinib‐induced increase in microvascular permeability was attenuated in ROCK1‐deficient mice. These findings suggest that ROCK inhibitors could serve as therapeutic modalities to ameliorate the dasatinib‐induced pulmonary changes.

YAP and ERK mediated mechanical strain-induced cell cycle progression through RhoA and cytoskeletal dynamics in rat growth plate chondrocytes

Yes-associated protein (YAP) and extracellular signal-regulated kinase (ERK) have been considered as key regulators in tissue homeostasis, organ development, and tumor formation. However, the roles of YAP and ERK in the mediating strain mechanosensing in the growth plate cartilage have not been determined. In this study, chondrocytes obtained from the growth plate cartilage of 2-week-old Sprague-Dawley rats were subjected to the mechanical strain with different magnitudes and durations at a frequency of 0.5 Hz. We found that YAP and ERK activation in response to mechanical strain was time and magnitude dependent. Pretreatment with a RhoA inhibitor (C3 toxin) or a microfilament cytoskeleton disrupting reagent (cytochalasin D) could suppress their activation. In addition, activated YAP and ERK were able to induce cell cycle progression by up-regulating the expression of cell cycle-related genes. These results shed new light on the function of YAP and ERK in mechanical strain-promoted growth plate development. Our results also provided evidence that RhoA and cytoskeletal dynamics are required for this mechanotransduction. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1121-1129, 2016.

Tissue stiffness dictates development, homeostasis, and disease progression

Tissue development is orchestrated by the coordinated activities of both chemical and physical regulators. While much attention has been given to the role that chemical regulators play in driving development, researchers have recently begun to elucidate the important role that the mechanical properties of the extracellular environment play. For instance, the stiffness of the extracellular environment has a role in orienting cell division, maintaining tissue boundaries, directing cell migration, and driving differentiation. In addition, extracellular matrix stiffness is important for maintaining normal tissue homeostasis, and when matrix mechanics become imbalanced, disease progression may ensue. In this article, we will review the important role that matrix stiffness plays in dictating cell behavior during development, tissue homeostasis, and disease progression.

Control of vascular smooth muscle function by Src-family kinases and reactive oxygen species in health and disease

Reactive oxygen species (ROS) are now recognised as second messenger molecules that regulate cellular function by reversibly oxidising specific amino acid residues of key target proteins. Amongst these are the Src-family kinases (SrcFKs), a multi-functional group of non-receptor tyrosine kinases highly expressed in vascular smooth muscle (VSM). In this review we examine the evidence supporting a role for ROS-induced SrcFK activity in normal VSM contractile function and in vascular remodelling in cardiovascular disease. VSM contractile responses to G-protein-coupled receptor stimulation, as well as hypoxia in pulmonary artery, are shown to be dependent on both ROS and SrcFK activity. Specific phosphorylation targets are identified amongst those that alter intracellular Ca(2+) concentration, including transient receptor potential channels, voltage-gated Ca(2+) channels and various types of K(+) channels, as well as amongst those that regulate actin cytoskeleton dynamics and myosin phosphatase activity, including focal adhesion kinase, protein tyrosine kinase-2, Janus kinase, other focal adhesion-associated proteins, and Rho guanine nucleotide exchange factors. We also examine a growing weight of evidence in favour of a key role for SrcFKs in multiple pro-proliferative and anti-apoptotic signalling pathways relating to oxidative stress and vascular remodelling, with a particular focus on pulmonary hypertension, including growth-factor receptor transactivation and downstream signalling, hypoxia-inducible factors, positive feedback between SrcFK and STAT3 signalling and positive feedback between SrcFK and NADPH oxidase dependent ROS production. We also discuss evidence for and against the potential therapeutic targeting of SrcFKs in the treatment of pulmonary hypertension.