Talin and Kindlin as Integrin-Activating Proteins: Focus on the Heart

Talin-1 variants associated with spontaneous coronary artery dissection (SCAD) highlight how even subtle changes in multi-functional scaffold proteins can manifest in disease

Variants of talin-1 (TLN1) have recently been linked with spontaneous coronary artery dissection (SCAD) a condition where a tear can form in the wall of a heart artery necessitating immediate medical care. One talin-1 variant, A2013T, has an extensive familial pedigree of SCAD, which led to the screening for, and identification of, further talin-1 variants in SCAD patients. Here we evaluated these variants with commonly used pathogenicity prediction tools and found it challenging to reliably classify SCAD-associated variants, even A2013T where the evidence of a causal role is strong. Using biochemical and cell biological methods, we show that SCAD-associated variants in talin-1, which would typically be classified as non-pathogenic, still cause a measurable impact on protein structure and cell behaviour, including cell movement and wound healing capacity. Together, this indicates that even subtle variants in central mechanosensitive adapter proteins, can give rise to significant health impacts at the individual level, suggesting the need for a possible re-evaluation of the scoring criteria for pathogenicity prediction for talin variants.

Mechanosensitive Cation Channel Piezo1 Is Involved in Renal Fibrosis Induction

Renal fibrosis, the result of different pathological processes, impairs kidney function and architecture, and usually leads to renal failure development. Piezo1 is a mechanosensitive cation channel highly expressed in kidneys. Activation of Piezo1 by mechanical stimuli increases cations influx into the cell with slight preference of calcium ions. Two different models of Piezo1 activation are considered: force through lipid and force through filament. Expression of Piezo1 on mRNA and protein levels was confirmed within the kidney. Their capacity is increased in the fibrotic kidney. The pharmacological tools for Piezo1 research comprise selective activators of the channels (Yoda1 and Jedi1/2) as well as non-selective inhibitors (spider peptide toxin) GsMTx4. Piezo1 is hypothesized to be the upstream element responsible for the activation of integrin. This pathway (calcium/calpain2/integrin beta1) is suggested to participate in profibrotic response induced by mechanical stimuli. Administration of the Piezo1 unspecific inhibitor or activators to unilateral ureter obstruction (UUO) mice or animals with folic acid-induced fibrosis modulates extracellular matrix deposition and influences kidney function. All in all, according to the recent data Piezo1 plays an important role in kidney fibrosis development. This channel has been selected as the target for pharmacotherapy of renal fibrosis.

SKAP2-A Molecule at the Crossroads for Integrin Signalling and Immune Cell Migration and Function

Src-kinase associated protein 2 (SKAP2) is an intracellular scaffolding protein that is broadly expressed in immune cells and is involved in various downstream signalling pathways, including, but not limited to, integrin signalling. SKAP2 has a wide range of binding partners and fine-tunes the rearrangement of the cytoskeleton, thereby regulating cell migration and immune cell function. Mutations in SKAP2 have been associated with several inflammatory disorders such as Type 1 Diabetes and Crohn's disease. Rodent studies showed that SKAP2 deficient immune cells have diminished pathogen clearance due to impaired ROS production and/or phagocytosis. However, there is currently no in-depth understanding of the functioning of SKAP2. Nevertheless, this review summarises the existing knowledge with a focus of its role in signalling cascades involved in cell migration, tissue infiltration and immune cell function.

Extracellular matrix stiffness aggravates urethral stricture through Igfbp3/Smad pathway

Urethral stricture refers to the narrowing of the urethral lumen. While previous studies have hinted at inflammation as the initial driver of this condition, the reasons and mechanisms behind its progression remain largely unknown. By Atomic force microscope (AFM), researchers measured the matrix stiffness of urethra to be 5.23 ± 0.37 kPa for normal tissue and 41.59 ± 2.48 kPa for stricture urethral scar. Similar results were observed in rat urethral stricture models, where the matrix stiffness of normal urethra was 4.29 ± 0.82 kPa, while 32.94 ± 7.12 kPa for urethral stricture scar. Notably, the matrix stiffness increased in rat models over time. To further investigate, polyacrylamide hydrogels were employed to mimic different levels of stiffness for normal and stricture condition. Interestingly, higher matrix stiffness led to an increased fibroblast-to-myofibroblast transition (FMT) in rat urethral fibroblasts, indicated by enhanced expression of α-SMA and Collagen I, as well as changing in the morphology of fibroblast. RNA-seq analysis suggested that Igfbp3/Smads might regulate the progressive FMT in urethral stricture. In the experiment where the expression of Igfbp3 was inhibited, increasing matrix stiffness lose the potential to stimulate FMT progression and the expression of p-Smad2/3 decreased. On the contrary, overexpression of Igfbp3 promoted the process of FMT in urethral fibroblasts. In conclusion, Igfbp3/Smad pathway appeared to be involved in the progression of urethral fibrosis. This finding suggested that Igfbp3/Smad might be an promising target for future research and treatment in this filed.

A defective mechanosensing pathway affects fibroblast-to-myofibroblast transition in the old male mouse heart

The cardiac fibroblast interacts with an extracellular matrix (ECM), enabling myofibroblast maturation via a process called mechanosensing. Although in the aging male heart, ECM is stiffer than in the young mouse, myofibroblast development is impaired, as demonstrated in 2-D and 3-D experiments. In old male cardiac fibroblasts, we found a decrease in actin polymerization, α-smooth muscle actin (α-SMA), and Kindlin-2 expressions, the latter an effector of the mechanosensing. When Kindlin-2 levels were manipulated via siRNA interference, young fibroblasts developed an old-like fibroblast phenotype, whereas Kindlin-2 overexpression in old fibroblasts reversed the defective phenotype. Finally, inhibition of overactivated extracellular regulated kinases 1 and 2 (ERK1/2) in the old male fibroblasts rescued actin polymerization and α-SMA expression. Pathological ERK1/2 overactivation was also attenuated by Kindlin-2 overexpression. In contrast, old female cardiac fibroblasts retained an operant mechanosensing pathway. In conclusion, we identified defective components of the Kindlin/ERK/actin/α-SMA mechanosensing axis in aged male fibroblasts.

Analysis of Integrin-Dependent Melanoblast Migration During Development

The neural crest is a transient embryonic structure that gives rise to a number of important cell types and tissues, including most of the peripheral and enteric nervous systems, pigment-producing skin cells known as melanocytes, and many craniofacial structures. Melanoblasts, the precursors of melanocytes, are derived from the so-called trunk neural crest cells. These cells delaminate and migrate along a dorsolateral pathway to colonize their final destination in the skin, and consequently, defects in melanoblast migration result in pigmentation defects. Studying melanocyte migration is a topic of great interest due to the involvement of melanocytes in highly metastatic skin cancer. A role for integrin-mediated adhesion is well established in neural crest migration, and our recent work has provided direct evidence for a key role for integrin-based adhesion in melanocyte migration. Imaging of melanoblast migration in the context of intact skin has proven to be a particularly powerful tool to study integrin-based adhesion during melanoblast migration. Here, we describe the use of skin explants combined with genetically encoded markers for melanocytes and high-resolution live imaging as a powerful and informative approach to analyze melanoblast migration in an ex vivo context.

Extracellular matrix stiffness-The central cue for skin fibrosis

Skin fibrosis is a physiopathological process featuring the excessive deposition of extracellular matrix (ECM), which is the main architecture that provides structural support and constitutes the microenvironment for various cellular behaviors. Recently, increasing interest has been drawn to the relationship between the mechanical properties of the ECM and the initiation and modulation of skin fibrosis, with the engagement of a complex network of signaling pathways, the activation of mechanosensitive proteins, and changes in immunoregulation and metabolism. Simultaneous with the progression of skin fibrosis, the stiffness of ECM increases, which in turn perturbs mechanical and humoral homeostasis to drive cell fate toward an outcome that maintains and enhances the fibrosis process, thus forming a pro-fibrotic "positive feedback loop". In this review, we highlighted the central role of the ECM and its dynamic changes at both the molecular and cellular levels in skin fibrosis. We paid special attention to signaling pathways regulated by mechanical cues in ECM remodeling. We also systematically summarized antifibrotic interventions targeting the ECM, hopefully enlightening new strategies for fibrotic diseases.

The role of the dystrophin glycoprotein complex in muscle cell mechanotransduction

Dystrophin is the central protein of the dystrophin-glycoprotein complex (DGC) in skeletal and heart muscle cells. Dystrophin connects the actin cytoskeleton to the extracellular matrix (ECM). Severing the link between the ECM and the intracellular cytoskeleton has a devastating impact on the homeostasis of skeletal muscle cells, leading to a range of muscular dystrophies. In addition, the loss of a functional DGC leads to progressive dilated cardiomyopathy and premature death. Dystrophin functions as a molecular spring and the DGC plays a critical role in maintaining the integrity of the sarcolemma. Additionally, evidence is accumulating, linking the DGC to mechanosignalling, albeit this role is still less understood. This review article aims at providing an up-to-date perspective on the DGC and its role in mechanotransduction. We first discuss the intricate relationship between muscle cell mechanics and function, before examining the recent research for a role of the dystrophin glycoprotein complex in mechanotransduction and maintaining the biomechanical integrity of muscle cells. Finally, we review the current literature to map out how DGC signalling intersects with mechanical signalling pathways to highlight potential future points of intervention, especially with a focus on cardiomyopathies.

A review of the function of the Dystrophic Glycoprotein Complex (DGC) in mechanosignaling provides an overview of the various components of DGC and potential mechanopathogenic mechanisms, particularly as they relate to muscular dystrophy.

Transcriptomic Profile of Genes Regulating the Structural Organization of Porcine Atrial Cardiomyocytes during Primary In Vitro Culture

Numerous cardiovascular diseases (CVD) eventually lead to severe myocardial dysfunction, which is the most common cause of death worldwide. A better understanding of underlying molecular mechanisms of cardiovascular pathologies seems to be crucial to develop effective therapeutic options. Therefore, a worthwhile endeavor is a detailed molecular characterization of cells extracted from the myocardium. A transcriptomic profile of atrial cardiomyocytes during long-term primary cell culture revealed the expression patterns depending on the duration of the culture and the heart segment of origin (right atrial appendage and right atrium). Differentially expressed genes (DEGs) were classified as involved in ontological groups such as: “cellular component assembly”, “cellular component organization”, “cellular component biogenesis”, and “cytoskeleton organization”. Transcriptomic profiling allowed us to indicate the increased expression of COL5A2, COL8A1, and COL12A1, encoding different collagen subunits, pivotal in cardiac extracellular matrix (ECM) structure. Conversely, genes important for cellular architecture, such as ABLIM1, TMOD1, XIRP1, and PHACTR1, were downregulated during in vitro culture. The culture conditions may create a favorable environment for reconstruction of the ECM structures, whereas they may be suboptimal for expression of some pivotal transcripts responsible for the formation of intracellular structures.

Integrinβ3 mediates the protective effects of soluble receptor for advanced glycation end-products during myocardial ischemia/reperfusion through AKT/STAT3 signaling pathway

Soluble receptor for advanced glycation end-product (sRAGE) was reported to protect myocardial ischemia/reperfusion (I/R) injuries via directly interacting with cardiomyocytes besides competing with RAGE for AGEs. However, the specific molecule for the interaction between sRAGE and cardiomyocytes are not clearly defined. Integrins which were reported to interact with RAGE on leukocytes were also expressed on myocardial cells, therefore it was supposed that sRAGE might interact with integrins on cardiomyocytes to protect hearts from ischemia/reperfusion injuries. The results showed that sRAGE increased the expression of integrinβ3 but not integrinβ1, β2, β4 or β5 in cardiomyocytes during I/R injuries. Meanwhile, the suppressive effects of sRAGE on cardiac function, cardiac infraction size and apoptosis in mice were cancelled by inhibition of integrinβ3 with cilengitide (CLG, 75 mg/kg). The results from cultured cardiomyocytes also proved that sRAGE attenuated myocardial apoptosis and autophagy through interacting with integrinβ3 to activate Akt and STAT3 pathway during oxygen and glucose deprivation/reperfusion (OGD/R) treatment. Furthermore, the phosphorylation of STAT3 was significantly downregulated by the inhibition of Akt (LY294002, 10 μM) in OGD/R and sRAGE treated cardiomyocytes, which suggested that STAT3 pathway was induced by Akt in I/R and sRAGE treated cardiomyocytes. The present study contributes to the understanding of myocardial I/R pathogenesis and provided a novel integrinβ3-dependent therapy strategy for sRAGE ameliorating I/R injuries.

Mechanosensitive Piezo1 channels mediate renal fibrosis

Kidney fibrosis is the final common pathway of progressive kidney diseases, the underlying mechanisms of which is not fully understood. The purpose of the current study is to investigate a role of Piezo1, a mechanosensitive nonselective cation channel, in kidney fibrosis. In human fibrotic kidneys, Piezo1 protein expression was markedly upregulated. The abundance of Piezo1 protein in kidneys of mice with UUO or with folic-acid treatment was significantly increased. Inhibition of Piezo1 with GsMTx4 markedly ameliorated UUO or folic acid-induced kidney fibrosis. Mechanical stretch, compression or stiffness induced Piezo1 activation and pro-fibrotic responses in human HK2 cells and primary cultured mouse proximal tubular cells (mPTCs), which were greatly prevented by inhibition or silence of Piezo1. TGFβ-1 induced increased Piezo1 expression and pro-fibrotic phenotypic alterations in HK2 cells and mPTCs, which was again markedly prevented by inhibition of Piezo1. Activation of Piezo1 by Yoda1, a Piezo1 agonist, caused calcium influx and profibrotic responses in HK2 cells and induced calpain2 activation, followed by talin1 cleavage and upregulation of integrinβ1. Also, Yoda1 promoted the link between ECM and integrinβ1. In conclusion, Piezo1 is involved in the progression of kidney fibrosis and pro-fibrotic alterations in renal proximal tubular cells, likely through activating calcium-calpain2-integrinβ1 pathway.

Matrix Metalloproteinases Shape the Tumor Microenvironment in Cancer Progression

Cancer progression with uncontrolled tumor growth, local invasion, and metastasis depends largely on the proteolytic activity of numerous matrix metalloproteinases (MMPs), which affect tissue integrity, immune cell recruitment, and tissue turnover by degrading extracellular matrix (ECM) components and by releasing matrikines, cell surface-bound cytokines, growth factors, or their receptors. Among the MMPs, MMP-14 is the driving force behind extracellular matrix and tissue destruction during cancer invasion and metastasis. MMP-14 also influences both intercellular as well as cell-matrix communication by regulating the activity of many plasma membrane-anchored and extracellular proteins. Cancer cells and other cells of the tumor stroma, embedded in a common extracellular matrix, interact with their matrix by means of various adhesive structures, of which particularly invadopodia are capable to remodel the matrix through spatially and temporally finely tuned proteolysis. As a deeper understanding of the underlying functional mechanisms is beneficial for the development of new prognostic and predictive markers and for targeted therapies, this review examined the current knowledge of the interplay of the various MMPs in the cancer context on the protein, subcellular, and cellular level with a focus on MMP14.

Key Roles of RGD-Recognizing Integrins During Cardiac Development, on Cardiac Cells, and After Myocardial Infarction

Cardiac cells interact with the extracellular matrix (ECM) proteins through integrin mechanoreceptors that control many cellular events such as cell survival, apoptosis, differentiation, migration, and proliferation. Integrins play a crucial role in cardiac development as well as in cardiac fibrosis and hypertrophy. Integrins recognize oligopeptides present on ECM proteins and are involved in three main types of interaction, namely with collagen, laminin, and the oligopeptide RGD (Arg-Gly-Asp) present on vitronectin and fibronectin proteins. To date, the specific role of integrins recognizing the RGD has not been addressed. In this review, we examine their role during cardiac development, their role on cardiac cells, and their upregulation during pathological processes such as heart fibrosis and hypertrophy. We also examine their role in regenerative and angiogenic processes after myocardial infarction (MI) in the peri-infarct area. Specific targeting of these integrins may be a way of controlling some of these pathological events and thereby improving medical outcomes.

Matrix stiffness and its influence on pancreatic diseases

The matrix stiffness of the extracellular matrix(ECM), which is the slow elastic force on cells, has gradually become investigated. And a higher stiffness could induce changes in cell biological behaviors and activation of internal signaling pathways. Imbalanced stiffness of ECM is associated with a number of diseases, including pancreatic disease. In this review, we discuss the components of the ECM and the increased stiffness caused by unbalanced ECM changes. Next, we describe how matrix stiffness transmits mechanical signals and what signaling pathways are altered within the cell in detail. Finally, we discuss the effect of ECM on the behavior of pancreatic diseases from the perspective of matrix stiffness.

High Plasma Levels of Soluble Talin-1 in Patients with Coronary Artery Disease

Aims

Talin-1 is a cytoskeletal protein that binds integrin, thereby leading to integrin activation and affecting focal adhesions. Recently, talin-1 expression was reported to be downregulated in human atherosclerotic plaques. However, blood levels of soluble talin-1 (sTalin-1) in patients with atherosclerotic disease, such as coronary artery disease (CAD), have not been elucidated.

Methods

We measured plasma sTalin-1 levels in 349 patients undergoing elective coronary angiography. The severity of CAD was represented as the number of stenotic coronary vessels and segments.

Results

Of the 349 study patients, CAD was found in 194 patients, of whom 88 had 1-vessel disease (1-VD), 60 had 2-vessel disease (2-VD), and 46 had 3-vessel disease (3-VD). Plasma sTalin-1 levels were higher in 194 patients with CAD than in 155 without CAD (CAD(-) group) (median 0.30 vs. 0.23 ng/mL, P < 0.005). A stepwise increase in sTalin-1 levels was found depending on the number of >50% stenotic coronary vessels: 0.23 in CAD(-), 0.29 in 1-VD, 0.30 in 2-VD, and 0.32 ng/mL in 3-VD group, respectively, (P < 0.05). High sTalin-1 level (>0.28 ng/mL) was found in 36% of CAD(-), 51% of 1-VD, 53% of 2-VD, and 59% of 3-VD group (P < 0.025). sTalin-1 levels also correlated with the number of >50% stenotic segments (r = 0.14, P < 0.02). The multivariate analysis revealed that sTalin-1 levels were independently associated with CAD. The odds ratio for CAD was 1.83 (95%CI = 1.14 - 2.93) for high sTalin-1 level (>0.28 ng/mL) (P < 0.02).

Conclusions

Plasma sTalin-1 levels in patients with CAD were found to be high and to be associated with the presence and severity of CAD, suggesting a role of sTalin-1 in the progression of coronary atherosclerosis.

Implications of the complex biology and micro-environment of cardiac sarcomeres in the use of high affinity troponin antibodies as serum biomarkers for cardiac disorders

Cardiac troponin I (cTnI), the inhibitory-unit, and cardiac troponin T (cTnT), the tropomyosin-binding unit together with the Ca-binding unit (cTnC) of the hetero-trimeric troponin complex signal activation of the sarcomeres of the adult cardiac myocyte. The unique structure and heart myocyte restricted expression of cTnI and cTnT led to their worldwide use as biomarkers for acute myocardial infarction (AMI) beginning more than 30 years ago. Over these years, high sensitivity antibodies (hs-cTnI and hs-cTnT) have been developed. Together with careful determination of history, physical examination, and EKG, determination of serum levels using hs-cTnI and hs-cTnT permits risk stratification of patients presenting in the Emergency Department (ED) with chest pain. With the ability to determine serum levels of these troponins with high sensitivity came the question of whether such measurements may be of diagnostic and prognostic value in conditions beyond AMI. Moreover, the finding of elevated serum troponins in physiological states such as exercise and pathological states where cardiac myocytes may be affected requires understanding of how troponins may be released into the blood and whether such release may be benign. We consider these questions by relating membrane stability to the complex biology of troponin with emphasis on its sensitivity to the chemo-mechanical and micro-environment of the cardiac myocyte. We also consider the role determinations of serum troponins play in the precise phenotyping in personalized and precision medicine approaches to promote cardiac health.

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Serum levels of cardiac TnI and cardiac TnT permit stratification of patients with chest pain.

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Release of troponins into blood involves not only frank necrosis but also programmed necroptosis.

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Genome wide analysis of serum troponin levels in the general population may be prognostic about cardiovascular health.

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Significant levels of serum troponins with exhaustive exercise may not be benign.

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Troponin in serum can lead to important data related to personalized and precision medicine.