FAK signalling mediates NF-κB activation by mechanical stress in cardiac myocytes

Focal Adhesion's Role in Cardiomyocytes Function: From Cardiomyogenesis to Mechanotransduction

Mechanotransduction refers to the ability of cells to sense mechanical stimuli and convert them into biochemical signals. In this context, the key players are focal adhesions (FAs): multiprotein complexes that link intracellular actin bundles and the extracellular matrix (ECM). FAs are involved in cellular adhesion, growth, differentiation, gene expression, migration, communication, force transmission, and contractility. Focal adhesion signaling molecules, including Focal Adhesion Kinase (FAK), integrins, vinculin, and paxillin, also play pivotal roles in cardiomyogenesis, impacting cell proliferation and heart tube looping. In fact, cardiomyocytes sense ECM stiffness through integrins, modulating signaling pathways like PI3K/AKT and Wnt/β-catenin. Moreover, FAK/Src complex activation mediates cardiac hypertrophic growth and survival signaling in response to mechanical loads. This review provides an overview of the molecular and mechanical mechanisms underlying the crosstalk between FAs and cardiac differentiation, as well as the role of FA-mediated mechanotransduction in guiding cardiac muscle responses to mechanical stimuli.

Direction of epithelial folding defines impact of mechanical forces on epithelial state

Cell shape dynamics during development is tightly regulated and coordinated with cell fate determination. Triggered by an interplay between biochemical and mechanical signals, epithelia form complex tissues by undergoing coordinated cell shape changes, but how such spatiotemporal coordination is controlled remains an open question. To dissect biochemical signaling from purely mechanical cues, we developed a microfluidic system that experimentally triggers epithelial folding to recapitulate stereotypic deformations observed in vivo. Using this system, we observe that the apical or basal direction of folding results in strikingly different mechanical states at the fold boundary, where the balance between tissue tension and torque (arising from the imposed curvature) controls the spread of folding-induced calcium waves at a short timescale and induces spatial patterns of gene expression at longer timescales. Our work uncovers that folding-associated gradients of cell shape and their resulting mechanical stresses direct spatially distinct biochemical responses within the monolayer.

Integrins in cardiac hypertrophy: lessons learned from culture systems

Heart growth and pathological changes are accompanied by extracellular matrix‐dependent alterations in integrins and integrin‐associated proteins, suggesting their role in heart development and disease. Most of our knowledge on the involvement of integrins in heart pathology is provided by the in vivo experiments, including cardiac hypertrophy models. However, in vivo studies are limited by the complex organization of heart tissue and fail to discern cell types and particular integrins implicated in hypertrophic signalling. This problem is being addressed by isolated cardiomyocyte primary cultures, which have been successfully used in different in vitro disease models. This review aimed to analyse the general approaches to studying integrins and integrin‐associated signalling pathways in cardiac hypertrophy focusing on the in vitro systems. The lessons learned from culture experiments on the models of hypertrophy induced by stretch, stimulating factors, and/or extracellular matrix components are summarized, demonstrating the major involvement of integrin‐mediated signalling in cardiac hypertrophic response and its apparent crosstalk with signal pathways induced by stretch or hypertrophy stimulating factors. The benefits and perspectives of using cardiomyocyte primary culture as a hypertrophy model are discussed.

Influence of hyperocclusion on the remodeling of gingival tissues

OBJECTIVE

The purpose of this study was to observe the effect of hyperocclusion on the remodeling of gingival tissues and detect the related signaling pathways.

DESIGN

Hyperocclusion models were established by tooth extraction in mice. The mice were sacrificed at 3, 7, 14, 28, or 56 days after the surgery, and the left mandibular first molars with gingival tissues were isolated and examinations were focused on the gingival tissues. Apoptotic cells were examined using terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) technology. Proliferating cells, p65, inflammatory cytokines, and β-catenin were detected using immunohistochemical methods.

RESULTS

A series of apoptosis and proliferation responses were triggered in stressed gingival tissues. It was observed that the levels of p65, proinflammatory factors including interleukin-1β and tumor necrosis factor-α in extraction group were higher compared with those from mice with intact dentition, and peaked on days 14, 14 and 7 respectively. The expression of β-catenin was increased under hyperocclusion situations, peaked on day 14, and declined to the initial levels over time.

CONCLUSIONS

The results of this study suggest that hyperocclusion causes remodeling of the gingival tissues by activating a series of adaptive responses. Both nuclear factor kappa B and Wnt/β-catenin signaling pathways may be responsible for those adaptive responses though the exact mechanism is not clear.

Sensing and Responding of Cardiomyocytes to Changes of Tissue Stiffness in the Diseased Heart

Cardiomyocytes are permanently exposed to mechanical stimulation due to cardiac contractility. Passive myocardial stiffness is a crucial factor, which defines the physiological ventricular compliance and volume of diastolic filling with blood. Heart diseases often present with increased myocardial stiffness, for instance when fibrotic changes modify the composition of the cardiac extracellular matrix (ECM). Consequently, the ventricle loses its compliance, and the diastolic blood volume is reduced. Recent advances in the field of cardiac mechanobiology revealed that disease-related environmental stiffness changes cause severe alterations in cardiomyocyte cellular behavior and function. Here, we review the molecular mechanotransduction pathways that enable cardiomyocytes to sense stiffness changes and translate those into an altered gene expression. We will also summarize current knowledge about when myocardial stiffness increases in the diseased heart. Sophisticated in vitro studies revealed functional changes, when cardiomyocytes faced a stiffer matrix. Finally, we will highlight recent studies that described modulations of cardiac stiffness and thus myocardial performance in vivo. Mechanobiology research is just at the cusp of systematic investigations related to mechanical changes in the diseased heart but what is known already makes way for new therapeutic approaches in regenerative biology.

Role of FAK signaling in chagasic cardiac hypertrophy

Cardiac hypertrophy and dysfunction are a significant complication of chronic Chagas disease, with heart failure, stroke, and sudden death related to disease progression. Thus, understanding the signaling pathways involved in the chagasic cardiac hypertrophy may provide potential targets for pharmacological therapy. Herein, we investigated the implication of focal adhesion kinase (FAK) signaling pathway in triggering hypertrophic phenotype during acute and chronic T. cruzi infection. C57BL/6 mice infected with T. cruzi (Brazil strain) were evaluated for electrocardiographic (ECG) changes, plasma levels of endothelin-1 (ET-1) and activation of signaling pathways involved in cardiac hypertrophy, including FAK and ERK1/2, as well as expression of hypertrophy marker and components of the extracellular matrix in the different stages of T. cruzi infection (60-210 dpi). Heart dysfunction, evidenced by prolonged PR interval and decrease in heart rates in ECG tracing, was associated with high plasma ET-1 level, extracellular matrix remodeling and FAK signaling activation. Upregulation of both FAK tyrosine 397 (FAK-Y397) and serine 910 (FAK-S910) residues phosphorylation as well as ERK1/2 activation, lead to an enhancement of atrial natriuretic peptide gene expression in chronic infection. Our findings highlight FAK-ERK1/2 signaling as a regulator of cardiac hypertrophy in Trypanosoma cruzi infection. Both mechanical stress, induced by cardiac extracellular matrix (ECM) augment and cardiac overload, and ET-1 stimuli orchestrated FAK signaling activation with subsequent activation of the fetal cardiac gene program in the chronic phase of infection, highlighting FAK as an attractive target for Chagas disease therapy.

Dp71 depleted HBE cells displayed increased DNA damage and apoptosis induced by H2O2

Human bronchial epithelium (HBE)-Dp71 anti-sense(AS)cells with stably transfected Dp71 siRNA plasmids were prepared for further exploration of Dp71 biological traits in cells other than PC12. HBE-Dp71AS cells displayed increased DNA damage induced by H2O2. Apoptosis of HBE-Dp71AS cells induced by H2O2 was increased via enhancing caspase 3, caspase 8 and caspase 9. HBE-Dp71AS cells also displayed decreased proliferation and clonogenic formation. RAD51 was proved to be a new binding partner of Dp71 by co-immunoprecipitation (Ip) and immunofluorescence. Reduced RAD51 mRNA and protein levels were observed in HBE-Dp71AS cells. Decreased lamin B1, focal adhesion kinase (FAK), phosphorylated focal adhesion kinase (p-FAK) and phosphorylated protein kinase B (p-AKT) were detected in the HBE-Dp71AS cells, which functioned together with RAD51 as the molecular explanations for the character alterations of HBE-Dp71AS cells.

Pediatric acute respiratory distress syndrome - current views

Acute respiratory distress syndrome (ARDS) mainly involves acute respiratory failure. In addition to this affected patients feel progressive arterial hypoxemia, dyspnea, and a marked increase in the work of breathing. The only clinical solution for the above pathological state is ventilation. Mechanical ventilation is necessary to support life in ARDs but it itself worsen lung injury and the term is known clinically as ‘ventilation induced lung injury’ (VILI). At the cellular level, respiratory epithelial cells are subjected to cyclic stretch, i.e. repeated cycles of positive and negative strain, during normal tidal ventilation. In aerated areas of diseased lungs, or even normal lungs subjected to injurious positive pressure mechanical ventilation, the cells are at risk of being over distended, and worsening injury by disrupting the alveolar epithelial barrier. Further, hypercapnic acidosis (HCA) in itself confers protection from stretch injury, potentially via a mechanisms involving inhibition of nuclear factor κB (NF-κB), a transcription factor central to inflammation, injury and repair. Mesenchymal stem cells are the latest in the field and are being investigated as a possible therapy for ARDS.

Electrical and mechanical stimulation of cardiac cells and tissue constructs

The field of cardiac tissue engineering has made significant strides over the last few decades, highlighted by the development of human cell derived constructs that have shown increasing functional maturity over time, particularly using bioreactor systems to stimulate the constructs. However, the functionality of these tissues is still unable to match that of native cardiac tissue and many of the stem-cell derived cardiomyocytes display an immature, fetal like phenotype. In this review, we seek to elucidate the biological underpinnings of both mechanical and electrical signaling, as identified via studies related to cardiac development and those related to an evaluation of cardiac disease progression. Next, we review the different types of bioreactors developed to individually deliver electrical and mechanical stimulation to cardiomyocytes in vitro in both two and three-dimensional tissue platforms. Reactors and culture conditions that promote functional cardiomyogenesis in vitro are also highlighted. We then cover the more recent work in the development of bioreactors that combine electrical and mechanical stimulation in order to mimic the complex signaling environment present in vivo. We conclude by offering our impressions on the important next steps for physiologically relevant mechanical and electrical stimulation of cardiac cells and engineered tissue in vitro.

TGFβ induces epithelial-mesenchymal transition of thyroid cancer cells by both the BRAF/MEK/ERK and Src/FAK pathways

The epithelial-mesenchymal transition (EMT) is a crucial process in tumour progression, by which epithelial cells acquire a mesenchymal phenotype, increasing its motility and the ability to invade distant sites. Here, we describe the molecular mechanisms by which ^V600E BRAF, TGFβ and the Src/FAK complex cooperatively regulate EMT induction and cell motility of anaplastic thyroid cancer cells. Analysis of EMT marker levels reveals a positive correlation between TGFβ and Snail expression, with a concomitant downregulation of E-cadherin, accompanied by an increase of cell migration and invasion. Furthermore, we show that ^V600E BRAF depletion by siRNA or inhibition of its activity by treatment with its inhibitor PLX4720 reverses the TGFβ-mediated effects on Snail, E-cadherin, migration and invasion. Moreover, ^V600E BRAF induces TGFβ secretion through a MEK/ERK-dependent mechanism. In addition, TGFβ activates the Src/FAK complex, which in turn regulates the expression of Snail and E-cadherin as well as cell migration. The inhibition of Src with the inhibitor SU6656 or abrogation of FAK expression with a specific siRNA reverses the TGFβ-induced effects. Interestingly, we demonstrate that activation of the Src/FAK complex by TGFβ is independent of ^V600E BRAF signalling, since inhibition of this oncogene does not affect its phosphorylation. Our data strongly suggest that TGFβ induces EMT and aggressiveness of thyroid cancer cells by parallel mechanisms involving both the ^V600E BRAF/MEK/ERK and Src/FAK pathways independently. Thus, we describe novel functions for Src/FAK in mediating the EMT program and aggressiveness regulated by TGFβ, establishing the inhibition of these proteins as a possible effective approach in preventing tumour progression of ^V600E BRAF-expressing thyroid tumours. © 2015 Wiley Periodicals, Inc.

Loss of p53 enhances NF-κB-dependent lamellipodia formation

Tumor suppressor p53 prevents tumorigenesis and tumor growth by suppressing the activation of several transcription factors, including nuclear factor-κB (NF-κB) and STAT3. On the other hand, p53 stimulates actin cytoskeleton remodeling and integrin-related signaling cascades. Here, we examined the p53-mediated link between regulation of the actin cytoskeleton and activation of NF-κB and STAT3 in MCF-7 cells and mouse embryonic fibroblasts (MEFs). In the absence of p53, STAT3 was constitutively activated. This activation was attenuated by depleting the expression of p65, a component of NF-κB. Integrin β3 expression and lamellipodia formation were also downregulated by NF-κB depletion. Inhibition of integrin αvβ3, Rac1 or Arp2/3, which diminished lamellipodia formation, suppressed STAT3 activation induced by p53 depletion. These results suggest that loss of p53 leads to STAT3 activation via NF-κB-dependent lamellipodia formation. Our study proposes a novel role for p53 in modulating the actin cytoskeleton through suppression of NF-κB, which restricts STAT3 activation.

Abnormal cell properties and down-regulated FAK-Src complex signaling in B lymphoblasts of autistic subjects

Recent studies suggest that one of the major pathways to the pathogenesis of autism is reduced cell migration. Focal adhesion kinase (FAK) has an important role in neural migration, dendritic morphological characteristics, axonal branching, and synapse formation. The FAK-Src complex, activated by upstream reelin and integrin β1, can initiate a cascade of phosphorylation events to trigger multiple intracellular pathways, including mitogen-activated protein kinase-extracellular signal-regulated kinase and phosphatidylinositol 3-kinase-Akt signaling. In this study, by using B lymphoblasts as a model, we tested whether integrin β1 and FAK-Src signaling are abnormally regulated in autism and whether abnormal FAK-Src signaling leads to defects in B-lymphoblast adhesion, migration, proliferation, and IgG production. To our knowledge, for the first time, we show that protein expression levels of both integrin β1 and FAK are significantly decreased in autistic lymphoblasts and that Src protein expression and the phosphorylation of an active site (Y416) are also significantly decreased. We also found that lymphoblasts from autistic subjects exhibit significantly decreased migration, increased adhesion properties, and an impaired capacity for IgG production. The overexpression of FAK in autistic lymphoblasts countered the adhesion and migration defects. In addition, we demonstrate that FAK mediates its effect through the activation of Src, phosphatidylinositol 3-kinase-Akt, and mitogen-activated protein kinase signaling cascades and that paxillin is also likely involved in the regulation of adhesion and migration in autistic lymphoblasts.

Integrins are the necessary links to hypertrophic growth in cardiomyocytes

To compensate for hemodynamic overload of the heart, an event which stretches the myocardium, growth and survival signaling are activated in cardiac muscle cells (cardiomyocytes). Integrins serve as the signaling receptors of cardiomyocytes responsible for mechanotransduction toward intracellular signaling. The main integrin heterodimers on the cardiomyocyte surface are α(5)β(1) and α(v)β(3), and elimination of either β(1) or β(3) integrins impedes pressure-induced hypertrophic signaling and leads to increased mortality. The growth signaling pathways downstream of β(1) and β(3) integrins are well characterized. However, new integrin pathways responsible for inhibiting apoptosis induced by hemodynamic overload are emerging. β(1) and β(3) integrins activate differential survival signaling, yet both integrins initiate survival signaling downstream of ubiquitination and the kinase pathway including phosphoinositol-3-kinase (PI3K)/Akt. Further characterization of these integrin-signaling mechanisms may lead to drug targets to prevent decompensation to heart failure.

Mechanical stretch activates signaling events for protein translation initiation and elongation in C2C12 myoblasts

It has been proposed that mechanically induced tension is the critical factor in the induction of muscle hypertrophy. However, the molecular mechanisms involved in this process are still under investigation. In the present study, the effect of mechanical stretch on intracellular signaling for protein translation initiation and elongation was studied in C2C12 myoblasts. Cells were grown on a silicone elastomer chamber and subjected to 30-min of 5 or 15% constant static or cyclic (60 cycles/min) uniaxial stretch. Western blot analyses revealed that p70 S6 kinase (p70S6K) and eukaryotic elongation factor 2 (eEF2), which are the markers for translation initiation and peptide chain elongation, respectively, were activated by both static and cyclic stretch. The magnitude of activation was greater in response to the 15% cyclic stretch. Cyclic stretch also increased the phosphorylation of MAP kinases (p38 MAPK, ERK1/2 and JNK). However, the pharmacological inhibition of MAP kinases did not block the stretch-induced activation of p70S6K and eEF2. An inhibitor of the mammalian target of rapamycin (mTOR) blocked the stretch-induced phosphorylation of p70S6K but did not affect the eEF2 activation. A broad-range tyrosine kinase inhibitor, genistein, blocked the stretch-induced activation of p70S6K and eEF2, whereas Src tyrosine kinase and Janus kinase (JAK) inhibitors did not. These results suggest that the stretch-induced activation of protein translation initiation and elongation in mouse myoblast cell lines is mediated by tyrosine kinase(s), except for Src kinase or JAK.

The Load-Bearing Mechanosome Revisited

We introduced the mechanosome hypothesis in 2003 as a heuristic model for investigating mechanotransduction in bone (Pavalko et al., J Cell Biochem, 2003, 88(1):104-112). This model suggested specific approaches for investigating how mechanical information is conveyed from the membrane of the sensor bone cell to the target genes and how this transmitted information from the membrane is converted into changes in transcription. The key concepts underlying the mechanosome hypothesis are that load-induced deformation of bone deforms the sensor cell membrane; embedded in the membrane are the focal adhesion and cadherin-catenin complexes, which in turn are physically connected to the chromatin via a solid-state scaffold. The physical stimulation of the membrane launches multiprotein complexes (mechanosomes) from the adhesion platforms while concomitantly tugging target genes into position for contact with the incoming mechanosomes, the carriers of the mechanical information to the nucleus. The mechanosome is comprised of an adhesion-associated protein and a nucleocytoplasmic shuttling transcription factor. Upon arrival at the target gene, mechanosomes alter DNA conformation and thus influence the interactions between trans-acting proteins along the gene, changing gene activity. Here, we update significant progress related to the mechanosome concept since publication of our original hypothesis. The launching of adhesion- and cytoskeletal-associated proteins into the nucleus toward target genes appears to be a common mechanism for regulating cell response to changes in its mechanical microenvironment.