Regulation of Discoidin Domain Receptor 2 by Cyclic Mechanical Stretch in Cultured Rat Vascular Smooth Muscle Cells

Fibroblast Diversity and Epigenetic Regulation in Cardiac Fibrosis

Cardiac fibrosis, a process characterized by excessive extracellular matrix (ECM) deposition, is a common pathological consequence of many cardiovascular diseases (CVDs) normally resulting in organ failure and death. Cardiac fibroblasts (CFs) play an essential role in deleterious cardiac remodeling and dysfunction. In response to injury, quiescent CFs become activated and adopt a collagen-secreting phenotype highly contributing to cardiac fibrosis. In recent years, studies have been focused on the exploration of molecular and cellular mechanisms implicated in the activation process of CFs, which allow the development of novel therapeutic approaches for the treatment of cardiac fibrosis. Transcriptomic analyses using single-cell RNA sequencing (RNA-seq) have helped to elucidate the high cellular diversity and complex intercellular communication networks that CFs establish in the mammalian heart. Furthermore, a significant body of work supports the critical role of epigenetic regulation on the expression of genes involved in the pathogenesis of cardiac fibrosis. The study of epigenetic mechanisms, including DNA methylation, histone modification, and chromatin remodeling, has provided more insights into CF activation and fibrotic processes. Targeting epigenetic regulators, especially DNA methyltransferases (DNMT), histone acetylases (HAT), or histone deacetylases (HDAC), has emerged as a promising approach for the development of novel anti-fibrotic therapies. This review focuses on recent transcriptomic advances regarding CF diversity and molecular and epigenetic mechanisms that modulate the activation process of CFs and their possible clinical applications for the treatment of cardiac fibrosis.

Defining cardiac cell populations and relative cellular composition of the early fetal human heart

While the adult human heart is primarily composed of cardiomyocytes, fibroblasts, endothelial and smooth muscle cells, the cellular composition during early development remains largely unknown. Reliable identification of fetal cardiac cell types using protein markers is critical to understand cardiac development and delineate the cellular composition of the developing human heart. This is the first study to use immunohistochemistry (IHC), flow cytometry and RT-PCR analyses to investigate the expression and specificity of commonly used cardiac cell markers in the early human fetal heart (8-12 post-conception weeks). The expression of previously reported protein markers for the detection of cardiomyocytes (Myosin Heavy Chain (MHC) and cardiac troponin I (cTnI), fibroblasts (DDR2, THY1, Vimentin), endothelial cells (CD31) and smooth muscle cells (α-SMA) were assessed. Two distinct populations of cTnI positive cells were identified through flow cytometry, with MHC positive cardiomyocytes showing high cTnI expression (cTnIHigh) while MHC negative non-myocytes showed lower cTnI expression (cTnILow). cTnI expression in non-myocytes was further confirmed by IHC and RT-PCR analyses, suggesting troponins are not cardiomyocyte-specific and may play distinct roles in non-muscle cells during early development. Vimentin (VIM) was expressed in cultured ventricular fibroblast populations and flow cytometry revealed VIMHigh and VIMLow cell populations in the fetal heart. MHC positive cardiomyocytes were VIMLow whilst CD31 positive endothelial cells were VIMHigh. Using markers investigated within this study, we characterised fetal human cardiac populations and estimate that 75-80% of fetal cardiac cells are cardiomyocytes and are MHC+/cTnIHigh/VIMLow, whilst non-myocytes comprise 20-25% of total cells and are MHC-/cTnILow/VIMHigh, with CD31+ endothelial cells comprising ~9% of this population. These findings show distinct differences from those reported for adult heart.

Discoidin Domain-Containing Receptor 2 Is Present in Human Atherosclerotic Plaques and Involved in the Expression and Activity of MMP-2

Discoidin domain-containing receptor 2 (DDR2) has been suggested to be involved in atherosclerotic progression, but its pathological role remains unknown. Using immunochemical staining, we located and compared the expression of DDR2 in the atherosclerotic plaques of humans and various animal models. Then, siRNA was applied to knock down the expression of DDR2 in vascular smooth muscle cells (VSMCs), and the migration, proliferation, and collagen Ι-induced expression of matrix metalloproteinases (MMPs) were evaluated. We found that an abundance of DDR2 was present in the atherosclerotic plaques of humans and various animal models and was distributed around fatty and necrotic cores. After incubation of oxidized low-density lipoprotein (ox-LDL), DDR2 was upregulated in VSMCs in response to such a proatherosclerotic condition. Next, we found that decreased DDR2 expression in VSMCs inhibited the migration, proliferation, and collagen Ι-induced expression of matrix metalloproteinases (MMPs). Moreover, we found that DDR2 is strongly associated with the protein expression and activity of MMP-2, suggesting that DDR2 might play a role in the etiology of unstable plaques. Considering that DDR2 is present in the atherosclerotic plaques of humans and is associated with collagen Ι-induced secretion of MMP-2, the clinical role of DDR2 in cardiovascular disease should be elucidated in further experiments.

EphrinA1-Fc Attenuates Ventricular Remodeling and Dysfunction in Chronically Nonreperfused WT but not EphA2-R-M mice

Background: EphrinA1-Fc abolishes acute I/R injury and attenuates nonreperfused cardiac injury 4 days after permanent occlusion in mice. The goal of this study was to assess the capacity of a single intramyocardial administration of ephrinA1-Fc at the time of coronary artery ligation, to determine the degree to which early salvage effects translate to reduced adverse remodeling after 4 weeks of nonreperfused myocardial infarction (MI) in wild-type B6 and EphA2-R-M (EphA2 receptor null) mice. Methods: At 4 weeks post-MI, echocardiography, histologic and immunohistochemical analyses of B6 mouse hearts were performed. Primary mouse cardiac fibroblasts (FBs) isolated from B6 mice cultured in the presence of low and high dose ephrinA1-Fc, both with and without pro-fibrotic TGF-β stimulation and Western blots, were probed for relative expression of remodeling proteins MMP-2, MMP-9 and TIMP-1, in addition to DDR2 and (p)SMAD2/3/totalSMAD2/3. Results: EphrinA1-Fc preserved a significant degree of contractile function, decreased adverse left ventricular remodeling, attenuated excessive compensatory hypertrophy, and decreased interstitial fibrosis in wild-type (WT) B6 mouse hearts. In contrast, most of these parameters were poorer in ephrinA1-Fc-treated EphA2-R-M mice. Of note, fibrosis was proportionately decreased, implying that other EphA receptor(s) are more important in regulating the pro-fibrotic response. Primary FBs showed disparate alteration of MMP-2, MMP-9 and TIMP-1, as well as DDR2 and p-SMAD2/3/totalSMAD2/3, which indicates that matrix remodeling and cardiac fibrosis in the injured heart are influenced by ephrinA1-Fc. Conclusion: This study demonstrates the capacity of a single administration of ephrinA1-Fc at the onset of injury to attenuate long-term nonreperfused post-MI ventricular remodeling that results in progressive heart failure, and the important role of EphA2 in mitigating the deleterious effects.

Closer to Nature Through Dynamic Culture Systems

Mechanics in the human body are required for normal cell function at a molecular level. It is now clear that mechanical stimulations play significant roles in cell growth, differentiation, and migration in normal and diseased cells. Recent studies have led to the discovery that normal and cancer cells have different mechanosensing properties. Here, we discuss the application and the physiological and pathological meaning of mechanical stimulations. To reveal the optimal conditions for mimicking an in vivo microenvironment, we must, therefore, discern the mechanotransduction occurring in cells.

Fibroblasts in the Infarcted, Remodeling, and Failing Heart

Expansion and activation of fibroblasts following cardiac injury is important for repair but may also contribute to fibrosis, remodeling, and dysfunction. The authors discuss the dynamic alterations of fibroblasts in failing and remodeling myocardium. Emerging concepts suggest that fibroblasts are not unidimensional cells that act exclusively by secreting extracellular matrix proteins, thus promoting fibrosis and diastolic dysfunction. In addition to their involvement in extracellular matrix expansion, activated fibroblasts may also exert protective actions, preserving the cardiac extracellular matrix, transducing survival signals to cardiomyocytes, and regulating inflammation and angiogenesis. The functional diversity of cardiac fibroblasts may reflect their phenotypic heterogeneity.

CTGF regulates cyclic stretch-induced vascular smooth muscle cell proliferation via microRNA-19b-3p

Cyclic stretch regulates proliferation of vascular smooth muscle cells (VSMCs) during hypertension-induced vascular remodeling, but the underlying mechanisms remain to be studied. Connective tissue growth factor (CTGF) has been reported associated with several cellular function such as proliferation，migration and adhesion. Herein, the role of CTGF in VSMCs was investigated in response to mechanical cyclic stretch. Here we show that CTGF is up-regulated both in vivo and in vitro during hypertension. Overexpression of CTGF markedly promoted VSMC proliferation, whereas CTGF knockdown attenuated cyclic stretch-induced proliferation. Furthermore, 3'UTR reporter assays revealed that microRNA-19b-3p (miR-19b-3p) directly regulates CTGF expression. Under pathological condition (e.g. 15% cyclic stretch), miR-19b-3p expression was significantly down-regulated; conversely miR-19b-3p overexpression blocked VSMC proliferation. Taken together, these findings indicate that pathological cyclic stretch induces vascular remodeling by promoting VSMC proliferation via miR-19b-3p/CTGF pathway, and point to CTGF as a potential therapeutic target for hypertension.

α5β1-Integrin promotes tension-dependent mammary epithelial cell invasion by engaging the fibronectin synergy site

Fibronectin-ligated α5β1 integrin promotes malignancy by inducing tissue tension.

Tumors are fibrotic and characterized by abundant, remodeled, and cross-linked collagen that stiffens the extracellular matrix stroma. The stiffened collagenous stroma fosters malignant transformation of the tissue by increasing tumor cell tension to promote focal adhesion formation and potentiate growth factor receptor signaling through kinase. Importantly, collagen cross-linking requires fibronectin (FN). Fibrotic tumors contain abundant FN, and tumor cells frequently up-regulate the FN receptor α5β1 integrin. Using transgenic and xenograft models and tunable two- and three-dimensional substrates, we show that FN-bound α5β1 integrin promotes tension-dependent malignant transformation through engagement of the synergy site that enhances integrin adhesion force. We determined that ligation of the synergy site of FN permits tumor cells to engage a zyxin-stabilized, vinculin-linked scaffold that facilitates nucleation of phosphatidylinositol (3,4,5)-triphosphate at the plasma membrane to enhance phosphoinositide 3-kinase (PI3K)-dependent tumor cell invasion. The data explain why rigid collagen fibrils potentiate PI3K activation to promote malignancy and offer a perspective regarding the consistent up-regulation of α5β1 integrin and FN in many tumors and their correlation with cancer aggression.

The Pressure of Aging

Significant hemodynamic changes ensue with aging, leading to an ever-growing epidemic of hypertension. Alterations in central arterial properties play a major role in these hemodynamic changes. These alterations are characterized by an initial decline in aortic distensibility and an increase of diastolic blood pressure, followed by a sharp increase in pulse wave velocity (PWV), and an increase in pulse pressure (PP) beyond the sixth decade. However, the trajectories of PWV and PP diverge with advancing age. There is an increased prevalence of salt-sensitive hypertension with advancing age that is, in part, mediated by marinobufagenin, an endogenous sodium pump ligand.

Defining the Cardiac Fibroblast

Cardiac fibrosis remains an important health concern, but the study of fibroblast biology has been hindered by a lack of effective means for identifying and tracking fibroblasts. Recent advances in fibroblast-specific lineage tags and reporters have permitted a better understanding of these cells. After injury, multiple cell types have been implicated as the source for extracellular matrix-producing cells, but emerging studies suggest that resident cardiac fibroblasts contribute substantially to the remodeling process. In this review, we discuss recent findings regarding cardiac fibroblast origin and identity. Our understanding of cardiac fibroblast biology and fibrosis is still developing and will expand profoundly in the next few years, with many of the recent findings regarding fibroblast gene expression and behavior laying down the groundwork for interpreting the purpose and utility of these cells before and after injury. (Circ J 2016; 80: 2269-2276).

Nuclear envelope proteins modulate proliferation of vascular smooth muscle cells during cyclic stretch application

Cyclic stretch is an important inducer of vascular smooth muscle cell (VSMC) proliferation, which is crucial in vascular remodeling during hypertension. However, the molecular mechanism remains unclear. We studied the effects of emerin and lamin A/C, two important nuclear envelope proteins, on VSMC proliferation in hypertension and the underlying mechano-mechanisms. In common carotid artery of hypertensive rats in vivo and in cultured cells subjected to high (15%) cyclic stretch in vitro, VSMC proliferation was increased significantly, and the expression of emerin and lamin A/C was repressed compared with normotensive or normal (5%) cyclic stretch controls. Using targeted siRNA to mimic the repressed expression of emerin or lamin A/C induced by 15% stretch, we found that VSMC proliferation was enhanced under static and 5%-stretch conditions. Overexpression of emerin or lamin A/C reversed VSMC proliferation induced by 15% stretch. Hence, emerin and lamin A/C play critical roles in suppressing VSMC hyperproliferation induced by hyperstretch. ChIP-on-chip and MOTIF analyses showed that the DNAs binding with emerin contain three transcription factor motifs: CCNGGA, CCMGCC, and ABTTCCG; DNAs binding with lamin A/C contain the motifs CVGGAA, GCCGCYGC, and DAAGAAA. Protein/DNA array proved that altered emerin or lamin A/C expression modulated the activation of various transcription factors. Furthermore, accelerating local expression of emerin or lamin A/C reversed cell proliferation in the carotid artery of hypertensive rats in vivo. Our findings establish the pathogenetic role of emerin and lamin A/C repression in stretch-induced VSMC proliferation and suggest mechanobiological mechanism underlying this process that involves the sequence-specific binding of emerin and lamin A/C to specific transcription factor motifs.

Megakaryocytic Maturation in Response to Shear Flow Is Mediated by the Activator Protein 1 (AP-1) Transcription Factor via Mitogen-activated Protein Kinase (MAPK) Mechanotransduction

Megakaryocytes (MKs) are exposed to shear flow as they migrate from the bone marrow hematopoietic compartment into circulation to release pro/preplatelets into circulating blood. Shear forces promote DNA synthesis, polyploidization, and maturation in MKs, and platelet biogenesis. To investigate mechanisms underlying these MK responses to shear, we carried out transcriptional analysis on immature and mature stem cell-derived MKs exposed to physiological shear. In immature (day (d)9) MKs, shear exposure up-regulated genes related to growth and MK maturation, whereas in mature (d12) MKs, it up-regulated genes involved in apoptosis and intracellular transport. Following shear-flow exposure, six activator protein 1 (AP-1) transcripts (ATF4,JUNB,JUN,FOSB,FOS, andJUND) were up-regulated at d9 and two AP-1 proteins (JunD and c-Fos) were up-regulated both at d9 and d12. We show that mitogen-activated protein kinase (MAPK) signaling is linked to both the shear stress response and AP-1 up-regulation. c-Jun N-terminal kinase (JNK) phosphorylation increased significantly following shear stimulation, whereas JNK inhibition reduced shear-induced JunD expression. Although p38 phosphorylation did not increase following shear flow, its inhibition reduced shear-induced JunD and c-Fos expression. JNK inhibition reduced fibrinogen binding and P-selectin expression of d12 platelet-like particles (PLPs), whereas p38 inhibition reduced fibrinogen binding of d12 PLPs. AP-1 expression correlated with increased MK DNA synthesis and polyploidization, which might explain the observed impact of shear on MKs. To summarize, we show that MK exposure to shear forces results in JNK activation, AP-1 up-regulation, and downstream transcriptional changes that promote maturation of immature MKs and platelet biogenesis in mature MKs.

Molecular basis and functional significance of Angiotensin II-induced increase in Discoidin Domain Receptor 2 gene expression in cardiac fibroblasts

Delineation of mechanisms underlying the regulation of fibrosis-related genes in the heart is an important clinical goal as cardiac fibrosis is a major cause of myocardial dysfunction. This study probed the regulation of Discoidin Domain Receptor 2 (DDR2) gene expression and the regulatory links between Angiotensin II, DDR2 and collagen in Angiotensin II-stimulated cardiac fibroblasts. Real-time PCR and western blot analyses showed that Angiotensin II enhances DDR2 mRNA and protein expression in rat cardiac fibroblasts via NADPH oxidase-dependent reactive oxygen species induction. NF-κB activation, demonstrated by gel shift assay, abolition of DDR2 expression upon NF-κB inhibition, and luciferase and chromatin immunoprecipitation assays confirmed transcriptional control of DDR2 by NF-κB in Angiotensin II-treated cells. Inhibitors of Phospholipase C and Protein kinase C prevented Angiotensin II-dependent p38 MAPK phosphorylation that in turn blocked NF-κB activation. Angiotensin II also enhanced collagen gene expression. Importantly, the stimulatory effects of Angiotensin II on DDR2 and collagen were inter-dependent as siRNA-mediated silencing of one abolished the other. Angiotensin II promoted ERK1/2 phosphorylation whose inhibition attenuated Angiotensin II-stimulation of collagen but not DDR2. Furthermore, DDR2 knockdown prevented Angiotensin II-induced ERK1/2 phosphorylation, indicating that DDR2-dependent ERK1/2 activation enhances collagen expression in cells exposed to Angiotensin II. DDR2 knockdown was also associated with compromised wound healing response to Angiotensin II. To conclude, Angiotensin II promotes NF-κB activation that up-regulates DDR2 transcription. A reciprocal regulatory relationship between DDR2 and collagen, involving cross-talk between the GPCR and RTK pathways, is central to Angiotensin II-induced increase in collagen expression in cardiac fibroblasts.

Discoidin domain receptor 2 (DDR2) promotes breast cancer cell metastasis and the mechanism implicates epithelial-mesenchymal transition programme under hypoxia

A wide range of genes involved in breast cancer metastasis have been reported to be related to the microenvironment. We studied the role of discoidin domain receptor 2 (DDR2), a collagen-binding receptor, in breast cancer progression under hypoxic conditions. We showed that DDR2 protein expression closely correlated with the expression of hypoxic marker HIF-1α in clinical breast cancer specimens. The in vitro data demonstrated that hypoxia treatment increased the levels of both expression and phosphorylation of DDR2 in human breast cancer cell lines. In vivo, orthotopic breast tumour xenografts with DDR2 knockdown displayed reduced dissemination and significant prevention in pulmonary and lymphatic metastasis; conversely, these processes were significantly facilitated by the enforced expression of the activated form of DDR2. Further mechanism studies indicated that DDR2 plays an indispensable role in a series of hypoxia-induced behaviours of breast cancer cells, including migration, invasion, and epithelial-mesenchymal transition (EMT). The transcription factor Snail was found to mediate DDR2-induced down-regulation of the cell-cell adhesion molecule E-cadherin. It was also documented that there is a correlation between DDR2 and E-cadherin expression with the presence of lymph node metastases in 160 cases of invasive human breast carcinoma. In addition, we provided evidence that DDR2 silencing in breast cancer cells prevents the hypoxia-induced activation of ERK MAPK, suggesting its potential involvement in mediating the effect of DDR2 on hypoxia-induced signalling. Based on the results of this study, we conclude that DDR2 participates in hypoxia-induced breast cancer metastasis through the regulation of cell migration, invasion, and EMT, and thus may serve as an accessible therapeutic target for the treatment of breast cancer.

Effects of cyclic stretch on the molecular regulation of myocardin in rat aortic vascular smooth muscle cells

BACKGROUND

The expression of myocardin, a cardiac-restricted gene, increases during environmental stress. How mechanical stretch affects the regulation of myocardin in vascular smooth muscle cells (VSMCs) is not fully understood. We identify the mechanisms and pathways through which mechanical stretch induces myocardin expression in VSMCs.

RESULTS

Rat VSMCs grown on a flexible membrane base were stretched to 20% of maximum elongation, at 60 cycles per min. An in vivo model of aorta-caval shunt in adult rats was also used to investigate myocardin expression. Cyclic stretch significantly increased myocardin and angiotensin II (AngII) expression after 18 and 6 h of stretch. Addition of extracellular signal-regulated kinases (ERK) pathway inhibitor (PD98059), ERK small interfering RNA (siRNA), and AngII receptor blocker (ARB; losartan) before stretch inhibited the expression of myocardin protein. Gel shift assay showed that myocardin-DNA binding activity increased after stretch. PD98059, ERK siRNA and ARB abolished the binding activity induced by stretch. Stretch increased while myocardin-mutant plasmid, PD98059, and ARB abolished the promoter activity. Protein synthesis by measuring [3H]proline incorporation into the cells increased after cyclic stretch, which represented hypertrophic change of VSMCs. An in vivo model of aorta-caval shunt also demonstrated increased myocardin protein expression in the aorta. Confocal microscopy showed increased VSMC size 24 h after cyclic stretch and VSMC hypertrophy after creation of aorta-caval shunt for 3 days.

CONCLUSIONS

Cyclic stretch enhanced myocardin expression mediated by AngII through the ERK pathway in cultured rat VSMCs. These findings suggest that myocardin plays a role in stretch-induced VSMC hypertrophy.

Effects of verapamil on the immediate-early gene expression of bone marrow mesenchymal stem cells stimulated by mechanical strain in vitro

Background

To study the effects of verapamil on the immediate-early genes (IEGs) expression of bone marrow mesenchymal stem cells (MSCs) stimulated by cyclic mechanical strain, in order to deduce the role of calcium ion channel in the cell signaling responses of MSCs to mechanical strain.

Material/Methods

MSCs were isolated and cultured, and the passage of 3–6 MSCs were stimulated by mechanical strain and pretreated with or without verapamil. After that, flow cytometry was used to measure the fluorescence intensity of intracellular Ca²⁺ immediately. The expression of early-response genes/proteins (c-fos, c-jun and c-myc) were examined by RT-PCR, immunohistochemistry and Western blot.

Results

Intracellular Ca²⁺ concentration of MSCs significantly changed when stimulated by cyclic strain, and the expression of c-fos, c-jun and c-myc remarkably increased in both mRNA and protein levels, while verapamil pre-treatment partially inhibited these effects (P<0.01).

Conclusions

The changes of the intracellular calcium concentration of MSCs induced by mechanical strain, dependent on the regulation of calcium channel activation, might play a role in the early response of MSCs to cyclic strain.

Cardiac fibroblasts, fibrosis and extracellular matrix remodeling in heart disease

Fibroblasts comprise the largest cell population in the myocardium. In heart disease, the number of fibroblasts is increased either by replication of the resident myocardial fibroblasts, migration and transformation of circulating bone marrow cells, or by transformation of endothelial/epithelial cells into fibroblasts and myofibroblasts. The primary function of fibroblasts is to produce structural proteins that comprise the extracellular matrix (ECM). This can be a constructive process; however, hyperactivity of cardiac fibroblasts can result in excess production and deposition of ECM proteins in the myocardium, known as fibrosis, with adverse effects on cardiac structure and function. In addition to being the primary source of ECM proteins, fibroblasts produce a number of cytokines, peptides, and enzymes among which matrix metalloproteinases (MMPs) and their inhibitors, tissue inhibitor of metalloproteinases (TIMPs), directly impact the ECM turnover and homeostasis. Function of fibroblasts can also in turn be regulated by MMPs and TIMPs. In this review article, we will focus on the function of cardiac fibroblasts in the context of ECM formation, homeostasis and remodeling in the heart. We will discuss the origins and multiple roles of cardiac fibroblasts in myocardial remodeling in different types of heart disease in patients and in animal models. We will further provide an overview of what we have learned from experimental animal models and genetically modified mice with altered expression of ECM regulatory proteins, MMPs and TIMPs.

Angiotensin II mediates urotensin II expression by hypoxia in cultured cardiac fibroblast

BACKGROUND

Urotensin II plays a role in myocardial remodelling. Cardiac fibroblasts play a critical role in the development of cardiac fibrosis. The effect of hypoxia on urotensin II expression in cardiac fibroblasts is poorly understood. We sought to investigate the regulation of urotensin II by hypoxia in cardiac fibroblasts and the effect of angiotensin II in the interaction with urotensin II.

METHODS AND RESULTS

Rat cardiac fibroblasts were cultured in hypoxic chamber. Hypoxia significantly increased urotensin II expression and reactive oxygen species (ROS) production in cultured cardiac fibroblasts. Hypoxia-induced increase in urotensin II protein and ROS was significantly attenuated after the addition of SP600125, JNK siRNA or N-acetylcysteine before hypoxia treatment. The phosphorylated JNK protein was induced by hypoxia and was abolished by pretreatment with SP600125, losartan (an angiotensin II receptor antagonist) or N-acetylcysteine. The increased urotensin II expression by exogenous addition of angiotensin II was similar to that by hypoxia. Addition of losartan and angiotensin II antibody before hypoxia almost completely inhibited the increase in urotensin II induced by hypoxia. Hypoxia significantly increased the secretion of angiotensin II from cardiac fibroblasts and increased the collagen I protein expression. Hypoxia significantly increased the urotensin II promoter activity by 4·3-fold as compared to normoxic control. Urotensin II siRNA almost completely attenuated the collagen I protein expression induced by hypoxia.

CONCLUSIONS

Hypoxia-induced urotensin II expression in cardiac fibroblast is mediated by angiotensin II and through ROS and JNK pathway. Urotensin II is a mediator of angiotensin II-induced cardiac fibrosis under hypoxia.

Mechanism of the inhibitory effect of atorvastatin on leptin expression induced by angiotensin II in cultured human coronary artery smooth muscle cells

Leptin contributes to the pathogenesis of atherosclerosis. Ang II (angiotensin II), a proatherogenic cytokine, increases leptin synthesis in cultured adipocytes. Statin suppresses leptin expression in adipocytes and human coronary artery endothelial cells. However, the effect of Ang II and statin on leptin expression in VSMCs (vascular smooth muscle cells), the major cell types in atheroma, is poorly understood. Thus the aim of the present study was to investigate the molecular mechanism of atorvastatin for reducing leptin expression after Ang II stimulation in VSMCs. VSMCs from human coronary artery were cultured. Ang II stimulation increased leptin protein and mRNA and phospho-JNK (c-Jun N-terminal kinase) expression. Exogenous addition of Dp44mT (2,2′-dipyridyl-N,N-dimethylsemicarbazone) and mevalonate increased leptin protein expression similarly to Ang II. Atorvastatin, SP600125, JNK siRNA (small interfering RNA) and NAC (N-acetylcysteine) completely attenuated the leptin and phospho-JNK protein expression induced by Ang II. Ang II significantly increased ROS (reactive oxygen species) formation in human VSMCs. Addition of atorvastatin and NAC significantly attenuated the formation of ROS induced by Ang II. Addition of atorvastatin and SP600125 inhibited the phosphorylation of Rac1 induced by Ang II. The gel shift and promoter activity assay showed that Ang II increased AP-1 (activator protein-1)-binding activity and leptin promoter activity, while SP600125, NAC and atorvastatin inhibited the AP-1-binding activity and leptin promoter activity induced by Ang II. Ang II significantly increased the migration and proliferation of cultured VSMCs, while addition of atorvastatin, SP600125, NAC and leptin siRNA before Ang II stimulation significantly inhibited the migration and proliferation of VSMCs induced by Ang II. Ang II significantly increased secretion of leptin from human VSMCs, and addition of SP600125, atorvastatin and NAC before Ang II stimulation almost completely inhibited the leptin secretion induced by Ang II. In conclusion, Ang II induces leptin expression in human VSMCs, and atorvastatin could inhibit the leptin expression induced by Ang II. The inhibitory effect of atorvastatin on Ang II-induced leptin expression was mediated by Rac, ROS and JNK pathways.

Deletion of discoidin domain receptor 2 does not affect smooth muscle cell adhesion, migration, or proliferation in response to type I collagen

Collagen receptors expressed on vascular smooth muscle cells include the discoidin domain receptors (DDR1 and DDR2). DDR1 is known to play important roles in mediating smooth muscle cell responses to vascular injury, including neointimal hyperplasia, but much less is known about the function of DDR2. In this study, we harvested smooth muscle cells from DDR2 wild-type and knockout mice and studied the cells using in vitro models of migration and growth. There were no significant differences in the ability of Ddr2(+/+) or Ddr2(-/-) smooth muscle cells to attach to, migrate, or proliferate on type I collagen. Furthermore, neither matrix metalloproteinase (MMP) 2 nor MMP-9 activity nor type I collagen expression was different between the cell types. We conclude that in vitro, endogenous DDR2 is not required for smooth muscle cell hyperplastic responses to collagen.

Resistin contributes to neointimal formation via oxidative stress after vascular injury

Resistin may play a major potential role in vascular remodelling and may contribute to atherogenesis. However, the role of VSMC (vascular smooth muscle cell)-derived resistin in neointimal formation is not well understood. We hypothesize that endogenous resistin derived from VSMCs may contribute to neointimal formation after vascular injury. VSMCs from thoracic aorta of adult Wistar rats were cultured. The carotid artery from adult Wistar rats was injured by balloon catheter. Resistin significantly increased migration and proliferation of VSMCs. Resistin siRNA (small interfering RNA) and resistin antibody significantly inhibited migration and proliferation of VSMCs induced by conditioned medium from stretched VSMCs. Resistin protein and mRNA expression significantly increased at 14 days after carotid injury. Resistin siRNA and NAC (N-acetylcysteine) significantly reduced resistin protein and mRNA expression induced by balloon injury. Carotid artery injury increased ROS (reactive oxygen species) production. Treatment with NAC and resistin siRNA decreased ROS production. The neointimal area was significantly increased after carotid injury and was significantly reduced by resistin siRNA and NAC. In conclusion, resistin increases migration and proliferation of VSMCs, and expression of resistin in carotid artery significantly increases after injury. Resistin siRNA attenuates neointimal formation after carotid injury partly through an antioxidative mechanism. Resistin may play a pivotal role in the pathogenesis of neointimal thickening after mechanical injury.

Cyclic stretch enhances the expression of toll-like receptor 4 gene in cultured cardiomyocytes via p38 MAP kinase and NF-kappaB pathway

Background

Toll-like receptor 4 (TLR4) plays an important role in innate immunity. The role of TLR4 in stretched cardiomyocytes is not known. We sought to investigate whether mechanical stretch could regulate TLR4 expression, as well as the possible molecular mechanisms and signal pathways mediating the expression of TLR4 by cyclic mechanical stretch in cardiomyocytes.

Methods

Neonatal Wistar rat cardiomyocytes grown on a flexible membrane base were stretched by vacuum to 20% of maximum elongation at 60 cycles/min. Western blot, real-time polymerase chain reaction, and promoter activity assay were performed. In vitro monocyte adhesion to stretched myocyte was detected.

Results

Cyclic stretch significantly increased TLR4 protein and mRNA expression after 2 h to 24 h of stretch. Addition of SB203580, TNF-α antibody, and p38α MAP kinase siRNA 30 min before stretch inhibited the induction of TLR4 protein. Cyclic stretch increased, while SB203580 abolished the phosphorylated p38 protein. Gel shifting assay showed significant increase of DNA-protein binding activity of NF-κB after stretch and SB203580 abolished the DNA-protein binding activity induced by cyclic stretch. DNA-binding complexes induced by cyclic stretch could be supershifted by p65 monoclonal antibody. Cyclic stretch increased TLR4 promoter activity while SB203580 and NF-κB siRNA decreased TLR4 promoter activity. Cyclic stretch increased adhesion of monocyte to cardiomyocytes while SB203580, TNF-α antibody, and TLR4 siRNA attenuated the adherence of monocyte. TNF-α and Ang II significantly increased TLR4 protein expression. Addition of losartan, TNF-α antibody, or p38α siRNA 30 min before Ang II and TNF-α stimulation significantly blocked the increase of TLR4 protein by AngII and TNF-α.

Conclusions

Cyclic mechanical stretch enhances TLR4 expression in cultured rat neonatal cardiomyocytes. The stretch-induced TLR4 is mediated through activation of p38 MAP kinase and NF-κB pathways. TLR4 up-regulation by cyclic stretch increases monocyte adherence.

Regulation of resistin by cyclic mechanical stretch in cultured rat vascular smooth muscle cells

Resistin has a potential role in atherosclerosis; however, the molecular mechanism underlying the increase in resistin expression in atherosclerosis remains unclear. As mechanical stretch plays an important role in atherosclerosis, in the present study we sought to investigate the cellular and molecular mechanisms underlying the regulation of resistin by cyclic mechanical stretch in VSMCs (vascular smooth muscle cells). VSMCs from thoracic aorta of adult Wistar rats were cultured and subjected to cyclic stretch. Cyclic mechanical stretch significantly increased resistin protein and mRNA expression as compared with control cells without stretch. The specific p38 MAPK (mitogen-activated protein kinase) inhibitor SB203580, the antioxidant N-acetylcysteine and p38 MAPK siRNA (small interfering RNA) attenuated the induction of resistin protein by cyclic stretch. Cyclic stretch significantly increased the phosphorylation of p38 MAPK, whereas pre-treatment with SB203580 and N-acetylcysteine significantly inhibited this effect. Cyclic stretch significantly increased ROS (reactive oxygen species) production, and pre-treatment with N-acetylcysteine significantly inhibited stretch-induced ROS production. Cyclic stretch also increased STAT3 (signal transducer and activator of transcription 3)-binding activity and resistin promoter activity, and resistin promoter activity was abolished when STAT3 in the promoter area was mutated. Pre-treatment with SB203580 and N-acetylcysteine significantly attenuated resistin promoter activity induced by cyclic stretch. Cyclic stretch increased the secretion of AngII (angiotensin II) and resistin from cultured VSMCs. Exogenous AngII increased resistin expression, and AngII receptor inhibition attenuated this effect. In conclusion, cyclic mechanical stretch increases resistin expression in cultured rat VSMCs. Stretch-induced resistin expression is mediated through ROS, and the p38 MAPK and STAT3 pathways. Therefore resistin induced by cyclic stretch may contribute to the pathogenesis of atherosclerosis under haemodynamic overload.

Hyperbaric oxygen activates discoidin domain receptor 2 via tumour necrosis factor-alpha and the p38 MAPK pathway to increase vascular smooth muscle cell migration through matrix metalloproteinase 2

DDR2 (discoidin domain receptor 2) regulates collagen turnover mediated by SMCs (smooth muscle cells) in atherosclerosis. HBO (hyperbaric oxygen) has been used in medical practice; however, the molecular mechanism of the beneficial effects of HBO is poorly understood. Furthermore, the effect of HBO on DDR2 has not been reported previously. In the present study, we investigated the cellular and molecular mechanisms of DDR2 regulation by HBO in VSMCs (vascular SMCs). Cells were exposed to 2.5 ATA (atmosphere absolute) of oxygen in a hyperbaric chamber. DDR2 protein (3.63-fold) and mRNA (2.34-fold) expression were significantly increased after exposure to 2.5 ATA HBO for 1 h. Addition of SB203580 and p38 MAPK (mitogen-activated protein kinase) siRNA (small interfering RNA) 30 min before HBO inhibited the induction of DDR2 protein. HBO also significantly increased DNA-protein binding activity of Myc/Max. Addition of SB203580 and an anti-TNF-alpha (tumour necrosis factor-alpha) monoclonal antibody 30 min before HBO abolished the DNA-protein binding activity induced by HBO. HBO significantly increased the secretion of TNF-alpha from cultured VSMCs. Exogenous addition of TNF-alpha significantly increased DDR2 protein expression, whereas anti-TNF-alpha and anti-(TNF-alpha receptor) antibodies blocked the induction of DDR2 protein expression. HBO significantly increased VSMC migration and proliferation, whereas DDR2 siRNA inhibited the migration induced by HBO. HBO increased activated MMP2 (matrix metalloproteinase 2) protein expression, and DDR2 siRNA abolished the induction of activated MMP2 expression induced by HBO. In conclusion, HBO activates DDR2 expression in cultured rat VSMCs. HBO-induced DDR2 is mediated by TNF-alpha and at least in part through the p38 MAPK and Myc pathways.

Cellular and molecular effects of mechanical stretch on vascular cells and cardiac myocytes

Cells in the cardiovascular system are permanently subjected to mechanical forces due to the pulsatile nature of blood flow and shear stress, created by the beating heart. These haemodynamic forces play an important role in the regulation of vascular development, remodelling, wound healing and atherosclerotic lesion formation. Mechanical stretch can modulate several different cellular functions in VSMCs (vascular smooth muscle cells). These functions include, but are not limited to, cell alignment and differentiation, migration, survival or apoptosis, vascular remodelling, and autocrine and paracrine functions. Laminar shear stress exerts anti-apoptotic, anti-atherosclerotic and antithrombotic effects on ECs (endothelial cells). Mechanical stretch of cardiac myocytes can modulate growth, apoptosis, electric remodelling, alterations in gene expression, and autocrine and paracrine effects. The aim of the present review is primarily to summarize the cellular and molecular effects of mechanical stretch on vascular cells and cardiac myocytes, emphasizing the molecular mechanisms underlying the regulation. Knowledge of the impact of mechanical stretch on the cardiovascular system is vital to the understanding of the pathogenesis of cardiovascular diseases, and is also crucial to provide new insights into the prevention and therapy of cardiovascular diseases.

Hypoxia induces discoidin domain receptor-2 expression via the p38 pathway in vascular smooth muscle cells to increase their migration

Discoidin domain receptor-2 (DDR2) is a receptor tyrosine kinase that binds to the extracellular matrix. We investigated the role of hypoxia in DDR2 expression in vascular smooth muscle cells (VSMCs) and the underlying mechanism. Subjecting VSMCs to hypoxia (2.5% O(2)) induced DDR2 expression; treatments with a specific inhibitor (SB203580) of p38 mitogen-activated protein kinase (MAPK) or p38-specific small interference RNA (siRNA) abolished this hypoxia-induced DDR2 expression. Gel shifting assays showed that hypoxia increased the Myc-Max-DNA binding activity in the promoter region of DDR2; inhibition of p38 MAPK activation by SB203580 and p38-specific siRNA blocked hypoxia-induced DDR2 promoter activity. Hypoxia also induced matrix metalloproteinase-2 (MMP-2) activity in VSMCs and increased their migration. These VSMC responses to hypoxia were inhibited by DDR2- and p38-specific siRNAs. Our results suggested that hypoxia induces DDR2 expression in VSMCs at the transcriptional level, which is mediated by the p38 MAPK pathway and contributes to VSMC migration.

Upregulation of discoidin domain receptor 2 in nasopharyngeal carcinoma

BACKGROUND

Nasopharyngeal carcinoma (NPC) is associated with Epstein-Barr virus (EBV) and has high metastatic potential. Discoidin domain receptors (DDR1, DDR2) are receptor-type tyrosine kinases activated by collagen. Their ability to induce expression of matrix metalloproteinase is related with tumor invasion. Therefore, we aim to investigate DDRs gene expression and its regulation in NPC.

METHODS AND RESULTS

By use of real-time quantitative polymerase chain reaction (Q-PCR), DDR2 gene expression but not DDR1 was significantly higher in primary and metastatic NPC. DDR2 was predominantly distributed in NPC tumor cells rather than in infiltrating lymphocytes. EBV Z-transactivator (Zta) transfection may distinctly elevate DDR2 level. Furthermore, data from reporter assay indicate that Zta could transactivate DDR2 promoter activity, suggesting the possible upregulation mechanism.

CONCLUSION

DDR2 was differentially upregulated in NPC and modulated by EBV Zta protein. DDR2 may play a role in NPC invasion and serve as a diagnostic and therapeutic target.

RNA interference for discoidin domain receptor 2 attenuates neointimal formation in balloon injured rat carotid artery

OBJECTIVE

Discoidin domain receptor 2 (DDR2) plays potential roles in the regulation of collagen turnover mediated by smooth muscle cells (SMCs) in atherosclerosis. Little is known about the function of DDR2 in vascular system. We investigated whether inhibition of DDR2 by small interfering RNA (siRNA) can reduce neointimal formation after arterial injury.

METHODS AND RESULTS

SMCs from thoracic aorta of adult Wistar rats were cultured. The carotid artery from adult Wistar rats was injured by balloon catheter. DDR2 significantly increased migration and proliferation of SMCs. DDR2 siRNA inhibited 86% of DDR2 protein expression in cultured SMCs. DDR2 protein and mRNA expression significantly increased at 14 days after carotid injury. DDR2 siRNA significantly reduced DDR2 protein and mRNA expression induced by balloon injury. The immunohistochemical stain demonstrated that DDR2 siRNA decreased MMP2 protein labeling induced by balloon injury, a pattern similar to that of DDR2 protein labeling. Neointimal area was significantly increased after carotid injury and was significantly reduced by DDR2 siRNA.

CONCLUSIONS

DDR2 increases migration and proliferation of SMCs, and expression of DDR2 in carotid artery significantly increases after injury. DDR2 siRNA attenuates neointimal formation after carotid injury. DDR2 may play a pivotal role in the pathogenesis of neointimal thickening after mechanical injury.

Changes in surface topologies of chondrocytes subjected to mechanical forces: an AFM analysis

The cartilage is composed of chondrocytes embedded in a matrix of collagen fibrils interspersed within a network of proteoglycans and is constantly exposed to biomechanical forces during normal joint movement. Characterization of the surface morphology, cytoskeletal structure, adherance and elastic properties of these mechanosensitive cells are crucial in understanding the effects of mechanical forces around a cell and how a cell responds to changes in its physical environment. In this work, we employed the atomic force microscope (AFM) to image cultured chondrocytes before and after subjecting them to mechanical forces in the presence or absence of interleukin-1beta to mimic inflammatory conditions. Nanoscale imaging and quantitative measurements from AFM data revealed that there are distinct changes in cell-surface topology and cytoskeleton arrangement in the cells following treatment with mechanical forces, IL-1beta or both. Our findings for the first time demonstrate that cultured chondrocytes are amenable to high-resolution AFM imaging and dynamic tensile forces may help overcome the effect of inflammatory factors on chondrocyte response.

The molecular regulation of GADD153 in apoptosis of cultured vascular smooth muscle cells by cyclic mechanical stretch

AIMS

The expression of GADD153 (growth arrest and DNA damage-inducible gene 153), an apoptosis-regulated gene, increases during endoplasmic reticulum (ER) stress. How mechanical stretch affects the regulation of GADD153 in vascular smooth muscle cells (VSMCs) during apoptosis is not fully understood. We aimed to test the hypothesis that mechanical stretch induces GADD153 expression in VSMCs undergoing apoptosis.

METHODS AND RESULTS

Rat VSMCs grown on a flexible membrane base were stretched by vacuum to 20% of maximum elongation, at 60 cycles/min. An in vivo model of aorta-caval shunt in adult rats was used to investigate GADD153 expression. Cyclic stretch significantly increased GADD153 protein and mRNA expression after 18 h of stretch. Addition of c-jun N-terminal kinase (JNK) inhibitor SP600125, JNK siRNA, tumour necrosis factor-alpha (TNF-alpha) and TNF-alpha receptor antibody 30 min before stretch inhibited the induction of GADD153 protein. Gel shift assay showed that DNA-binding activity of activating factor 1 (AP-1) increased after stretch. SP600125, JNK siRNA and TNF-alpha antibody abolished the binding activity induced by stretch. Stretch increased while GADD153-Mut plasmid, SP600125, and c-jun antibody abolished the promoter activity. Both conditioned media from stretched VSMCs and exogenous administration of TNF-alpha recombinant protein to the non-stretched VSMCs increased GADD153 protein expression similar to that seen after stretch. An in vivo model of aorta-caval shunt in adult rats also demonstrated the increased GADD153 protein expression in the aorta.

CONCLUSION

Cyclic stretch enhanced GADD153 expression in cultured rat VSMCs. The stretch-induced GADD153 is mediated by TNF-alpha, at least in part, through the JNK and AP-1 pathway. These findings suggest that GADD153 plays a role in stretch-induced VSMC apoptosis.

Structural similarities and functional diversity of eukaryotic discoidin-like domains

The discoidin domain is a approximately 150 amino acid motif common in both eukaryotic and prokaryotic proteins. It is found in a variety of extracellular, intracellular and transmembrane multidomain proteins characterized by a considerable functional diversity, mostly involved in developmental processes. The biological role of the domain depends on its interactions with different molecules, including growth factors, phospholipids and lipids, galactose or its derivatives, and collagen. The conservation of the motif, as well as the serious physiological consequences of discoidin domain disorders underscore the importance of the fold, while the ability to accommodate such an extraordinarily broad range of ligand molecules makes it a fascinating research target. In present review we characterize the distinctive features of discoidin domains and briefly outline the biological role of this module in various eukaryotic proteins.

Divergent and convergent effects on gene expression and function in acute versus chronic endothelial activation

Activation of the vascular endothelium with cytokines such as TNF is widely used to study the role of the vasculature in proinflammatory disease. To gain insight into mechanisms of prolonged vascular endothelial activation we compared changes in gene expression induced by continuous activation in stable tmTNF-expressing cells with changes due to acute TNF challenge in vitro. Affymetrix Genechip analysis was performed on RNA from control, acute and continuous TNF-activated endothelial cells. Only 36% of the significant changes in gene expression were convergent between the acute and continuously activated endothelial cells compared with the control. From the divergently regulated genes, for example the cytokine ENA-78 was specifically induced in chronically activated cells, while E-selectin, a cell adhesion molecule, was upregulated only in acutely activated endothelial cells. Antioxidant SOD gene induction was noted in acute activation, while a regulatory NADPH oxidase subunit was selectively upregulated in continuously activated endothelium in accordance with significant reactive oxygen species induction occurred only in these cells. Accordingly, p38 and ERK1/2, two MAP kinases downstream of reactive oxygen species, were activated in stable transmembrane-spanning precursor (tm) TNF-expressing cells and were refractory to activation with soluble TNF or VEGF. In consequence, the increased p38 MAP kinase activity contributed to increased endothelial cell migration in tmTNF-expressing cells. These data suggest that continuous activation of endothelial cells leads to specific expression and functional changes, consistent with alterations observed in dysfunctional endothelium exposed to or involved in chronic inflammation.

Hydrogen peroxide stimulates macrophages and monocytes to actively release HMGB1

High mobility group box 1 (HMGB1) can be actively secreted by macrophages/monocytes in response to exogenous and endogenous inflammatory stimuli (such as bacterial endotoxin, TNF-alpha, IL-1, and IFN-gamma) or passively released by necrotic cells and mediates innate and adaptive inflammatory responses to infection and injury. Here, we demonstrated that a reactive oxygen species, hydrogen peroxide (H(2)O(2)), induces active and passive HMGB1 release from macrophage and monocyte cultures in a time- and dose-dependent manner. At nontoxic doses (e.g., 0.0125-0.125 mM), H(2)O(2) induced HMGB1 cytoplasmic translocation and active release within 3-24 h. At higher concentrations (e.g., 0.25 mM), however, H(2)O(2) exhibited cytotoxicity to macrophage and monocyte cell cultures and consequently, triggered active and passive HMGB1 release. In addition, H(2)O(2) stimulated potential interaction of HMGB1 with a nuclear export factor, chromosome region maintenance (CRM1), in macrophage/monocyte cultures. Inhibitors specific for the JNK (SP600125) and MEK (PD98059), but not p38 MAPK (SB203580), abrogated H(2)O(2)-induced, active HMGB1 release. Together, these data establish an important role for oxidative stress in inducing active HMGB1 release, potentially through a MAPK- and CRM1-dependent mechanism.

Discoidin domain receptor 2 is involved in the activation of bone marrow-derived dendritic cells caused by type I collagen

Discoidin domain receptors (DDRs), DDR1 and DDR2, are non-integrin receptor tyrosine kinases for collagen in many cell types. In this study, we investigated the contributions of DDRs to the activation of mouse bone marrow-derived dendritic cells (DCs) by type I collagen (ColI). Our data showed that transcript and protein of DDR2 were expressed constitutively in immature DCs and upregulated in TNF-alpha-stimulated mature DCs. ColI treatment induced DDR2 phosphorylation and subsequently induced the upregulation of IL-12 production, CD86 expression, and antigen uptake activity by immature DCs. Depletion of DDR2 by specific siRNA attenuated significantly an increase in expression of IL-12 and CD86 in ColI-treated DCs. Additionally, DDR2-ColI interaction upregulated the ability of mature DCs to activate allogeneic T cells. These findings suggest that DDR2 is a critical collagen receptor for DC activation and that DDR2-collagen interaction plays an important role in the functional capacity of DCs regulating immune responses.

Sensing extracellular matrix: an update on discoidin domain receptor function

Discoidin Domain Receptors (DDRs) have recently emerged as non-integrin-type receptors for collagen. The two mammalian gene products Discoidin Domain Receptor 1 and -2 constitute a subfamily of tyrosine kinase receptors that are selectively expressed in a number of different cell types and organs. Upon collagen activation, DDRs regulate cell adhesion, proliferation and extracellular matrix remodeling. Here we review the various signaling pathways and cellular responses evoked by activated DDRs. Additionally, we give an overview of the more recent advances in understanding the role of DDRs in various human diseases, in particular during tumor progression, atherosclerosis, inflammation and tissue fibrosis. Furthermore, we discuss potential roles of genes homologous to mammalian DDRs identified in flies, worms and sponges. We show that the structural organization of these DDR-related genes is highly conserved throughout evolution suggesting that invertebrate DDRs may also function as receptors for collagen. By highlighting current questions about these unusual collagen receptors, we hope to attract new research on DDRs from a variety of different fields.