Inhibition of cardiac myofibroblast formation and collagen synthesis by activation and overexpression of adenylyl cyclase

Hyperglycemia enhances function and differentiation of adult rat cardiac fibroblasts

Diabetes is an independent risk factor for cardiovascular disease that can eventually cause cardiomyopathy and heart failure. Cardiac fibroblasts (CF) are the critical mediators of physiological and pathological cardiac remodeling; however, the effects of hyperglycemia on cardiac fibroblast function and differentiation is not well known. Here, we performed a comprehensive investigation on the effects of hyperglycemia on cardiac fibroblasts and show that hyperglycemia enhances cardiac fibroblast function and differentiation. We found that high glucose treatment increased collagen I, III, and VI gene expression in rat adult cardiac fibroblasts. Interestingly, hyperglycemia increased CF migration and proliferation that is augmented by collagen I and III. Surprisingly, we found that short term hyperglycemia transiently inhibited ERK1/2 activation but increased AKT phosphorylation. Finally, high glucose treatment increased spontaneous differentiation of cardiac fibroblasts to myofibroblasts with increasing passage compared with low glucose. Taken together, these findings suggest that hyperglycemia induces cardiac fibrosis by modulating collagen expression, migration, proliferation, and differentiation of cardiac fibroblasts.

Increase in cellular cyclic AMP concentrations reverses the profibrogenic phenotype of cardiac myofibroblasts: a novel therapeutic approach for cardiac fibrosis

Tissue fibrosis is characterized by excessive production, deposition, and contraction of the extracellular matrix (ECM). The second messenger cAMP has antifibrotic effects in fibroblasts from several tissues, including cardiac fibroblasts (CFs). Increased cellular cAMP levels can prevent the transformation of CFs into profibrogenic myofibroblasts, a critical step that precedes increased ECM deposition and tissue fibrosis. Here we tested two hypotheses: 1) myofibroblasts have a decreased ability to accumulate cAMP in response to G protein-coupled receptor (GPCR) agonists, and 2) increasing cAMP will not only prevent, but also reverse, the myofibroblast phenotype. We found that myofibroblasts produce less cAMP in response to GPCR agonists or forskolin and have decreased expression of several adenylyl cyclase (AC) isoforms and increased expression of multiple cyclic nucleotide phosphodiesterases (PDEs). Furthermore, we found that forskolin-promoted increases in cAMP or N(6)-phenyladenosine-cAMP, a protein kinase A-selective analog, reverse the myofibroblast phenotype, as assessed by the expression of collagen Iα1, α-smooth muscle actin, plasminogen activator inhibitor-1, and cellular contractile abilities, all hallmarks of a fibrogenic state. These results indicate that: 1) altered expression of AC and PDE isoforms yield a decrease in cAMP concentrations of cardiac myofibroblasts (relative to CFs) that likely contributes to their profibrotic state, and 2) approaches to increase cAMP concentrations not only prevent fibroblast-to-myofibroblast transformation but also can reverse the profibrotic myofibroblastic phenotype. We conclude that therapeutic strategies designed to enhance cellular cAMP concentrations in CFs may provide a means to reverse excessive scar formation following injury and to treat cardiac fibrosis.

The adventitia: Essential role in pulmonary vascular remodeling

A rapidly emerging concept is that the vascular adventitia acts as a biological processing center for the retrieval, integration, storage, and release of key regulators of vessel wall function. It is the most complex compartment of the vessel wall and comprises a variety of cells including fibroblasts, immunomodulatory cells, resident progenitor cells, vasa vasorum endothelial cells, and adrenergic nerves. In response to vascular stress or injury, resident adventitial cells are often the first to be activated and reprogrammed to then influence tone and structure of the vessel wall. Experimental data indicate that the adventitial fibroblast, the most abundant cellular constituent of adventitia, is a critical regulator of vascular wall function. In response to vascular stresses such as overdistension, hypoxia, or infection, the adventitial fibroblast is activated and undergoes phenotypic changes that include proliferation, differentiation, and production of extracellular matrix proteins and adhesion molecules, release of reactive oxygen species, chemokines, cytokines, growth factors, and metalloproteinases that, collectively, affect medial smooth muscle cell tone and growth directly and that stimulate recruitment and retention of circulating inflammatory and progenitor cells to the vessel wall. Resident dendritic cells also participate in "sensing" vascular stress and actively communicate with fibroblasts and progenitor cells to simulate repair processes that involve expansion of the vasa vasorum, which acts as a conduit for further delivery of inflammatory/progenitor cells. This review presents the current evidence demonstrating that the adventitia acts as a key regulator of pulmonary vascular wall function and structure from the "outside in."

Sang-qi Granula Reduces Blood Pressure and Myocardial Fibrosis by Suppressing Inflammatory Responses Associated with the Peroxisome Proliferator-Activated Receptors and Nuclear Factor κ B Protein in Spontaneously Hypertensive Rats

Aim. Sang-qi Granula (SQ) is a compound prepared from Chinese herbs and is currently used for treatment of hypertension in China. Given its protective effects on cardial function in decreasing blood pressure, we investigated the mechanism of protective effects of SQ on myocardium. Methods. 16 male normal Wistar-Kyoto rats and 16 spontaneous hypertension rats (SHR) were employed without medical treatment. 16 SHR were employed with SQ treatment. Rats in each group were sacrificed at two time points (8-week treatment and 16-week treatment). Blood pressure (BP), and heart weight/body weight (HW/BW) were measured. The expression of myeloperoxidase (MCP-1), ICAM-1, TNF- α , and CD68-positive cells was assessed. The interstitial collagen volume fraction (CVF), perivascular collagen volume area (PVCA), and the expression of TGF- β , Smad-3, PPAR α , γ , and NF- κ B (P65 and P50) were observed. Results. SQ significantly inhibited the elevation of the blood pressure and HW/BW of SHR. Next, SQ prevented myocardial fibrosis. Finally, a proinflammatory mediator associated with NF- κ B (TNF- α , ICAM-1, MCP-1, CD68), TGF- β , and Smad-3 related to collagen deposition, which is upregulated in SHR group, was significantly suppressed by SQ. Expression of NF- κ B was decreased in SHQ+SQ group compared to PPAR α , and γ expression was increased by SQ. Conclusion. Treatment with SQ ameliorates cardial fibrosis induced by hypertension by attenuating the upregulation of ICAM-1, TNF- α , MCP-1, TGF- β , Smad-3, P65, and P50 expression and improving PPAR α and PPAR γ expression level. The results suggest that SQ may be an option for preventing cardial fibrosis through PPAR signalling pathway.

Metformin inhibits angiotensin II-induced differentiation of cardiac fibroblasts into myofibroblasts

Differentiation of cardiac fibroblasts into myofibroblasts is a critical event in the progression of cardiac fibrosis that leads to pathological cardiac remodeling. Metformin, an antidiabetic agent, exhibits a number of cardioprotective properties. However, much less is known regarding the effect of metformin on cardiac fibroblast differentiation. Thus, in the present study, we examined the effect of metformin on angiotensin (Ang) II-induced differentiation of cardiac fibroblasts into myofibroblasts and its underlying mechanism. Adult rat cardiac fibroblasts were stimulated with Ang II (100 nM) in the presence or absence of metformin (10–200 µM). Ang II stimulation induced the differentiation of cardiac fibroblasts into myofibroblasts, as indicated by increased expression of α-smooth muscle actin (α-SMA) and collagen types I and III, and this effect of Ang II was inhibited by pretreatment of cardiac fibroblasts with metformin. Metformin also decreased Ang II-induced reactive oxygen species (ROS) generation in cardiac fibroblasts via inhibiting the activation of the PKC-NADPH oxidase pathway. Further experiments using PKC inhibitor calphostin C and NADPH oxidase inhibitor apocynin confirmed that inhibition of the PKC-NADPH oxidase pathway markedly attenuated Ang II-induced ROS generation and myofibroblast differentiation. These data indicate that metformin inhibits Ang II-induced myofibroblast differentiation by suppressing ROS generation via the inhibition of the PKC-NADPH oxidase pathway in adult rat cardiac fibroblasts. Our results provide new mechanistic insights regarding the cardioprotective effects of metformin and provide an efficient therapeutic strategy to attenuate cardiac fibrosis.

cAMP level modulates scleral collagen remodeling, a critical step in the development of myopia

The development of myopia is associated with decreased ocular scleral collagen synthesis in humans and animal models. Collagen synthesis is, in part, under the influence of cyclic adenosine monophosphate (cAMP). We investigated the associations between cAMP, myopia development in guinea pigs, and collagen synthesis by human scleral fibroblasts (HSFs). Form-deprived myopia (FDM) was induced by unilateral masking of guinea pig eyes. Scleral cAMP levels increased selectively in the FDM eyes and returned to normal levels after unmasking and recovery. Unilateral subconjunctival treatment with the adenylyl cyclase (AC) activator forskolin resulted in a myopic shift accompanied by reduced collagen mRNA levels, but it did not affect retinal electroretinograms. The AC inhibitor SQ22536 attenuated the progression of FDM. Moreover, forskolin inhibited collagen mRNA levels and collagen secretion by HSFs. The inhibition was reversed by SQ22536. These results demonstrate a critical role of cAMP in control of myopia development. Selective regulation of cAMP to control scleral collagen synthesis may be a novel therapeutic strategy for preventing and treating myopia.

Perfused culture of gingival fibroblasts in a degradable/polar/hydrophobic/ionic polyurethane (D-PHI) scaffold leads to enhanced proliferation and metabolic activity

Periodontal diseases cause the breakdown of the tooth-supporting gingival tissue. In treatments aimed at gingival tissue regeneration, tissue engineering is preferred over the common treatments such as scaling. Perfused (dynamic) culture has been shown to increase cell growth in tissue-engineered scaffolds. Since gingival tissues are highly vascularized, it was desired to investigate the influence of perfusion on the function of human gingival fibroblasts (HGF) when cultured in a degradable/polar/hydrophobic/ionic polyurethane scaffold during the early culture phase (4weeks) of engineering gingival tissues. It was observed that the growth of HGF was continuous over 28days in dynamic culture (3-fold increase, p<0.05), while it was reduced after 14days in static culture (i.e. no flow condition). Cell metabolic activity, as measured by a WST-1 assay, and total protein production show that HGF were in different metabolic states in the dynamic vs. static cultures. Observations from scanning electron microscopy and type I collagen (Col I) production measured by Western blotting suggest that medium perfusion significantly promoted collagen production in HGF after the first 4weeks of culture (p<0.05). The different proliferative and metabolic states for HGF in the perfused scaffolds suggest a different cell phenotype which may favour tissue regeneration.

Hydrolysis of extracellular ATP by ectonucleoside triphosphate diphosphohydrolase (ENTPD) establishes the set point for fibrotic activity of cardiac fibroblasts

The establishment of set points for cellular activities is essential in regulating homeostasis. Here, we demonstrate key determinants of the fibrogenic set point of cardiac fibroblasts (CFs) by focusing on the pro-fibrotic activity of ATP, which is released by CFs. We tested the hypothesis that the hydrolysis of extracellular ATP by ectonucleoside triphosphate diphosphohydrolases (ENTPDs) regulates pro-fibrotic nucleotide signaling. We detected two ENTPD isoforms, ENTPD-1 and -2, in adult rat ventricular CFs. Partial knockdown of ENTPD-1 and -2 with siRNA increased basal extracellular ATP concentration and enhanced the pro-fibrotic effect of ATP stimulation. Sodium polyoxotungstate-1, an ENTPD inhibitor, not only enhanced the pro-fibrotic effects of exogenously added ATP but also increased basal expression of α-smooth muscle actin, plasminogen activator inhibitor-1 and transforming growth factor (TGF)-β, collagen synthesis, and gel contraction. Furthermore, we found that adenosine, a product of ATP hydrolysis by ENTPD, acts via A2B receptors to counterbalance the pro-fibrotic response to ATP. Removal of extracellular adenosine or inhibition of A2B receptors enhanced pro-fibrotic ATP signaling. Together, these results demonstrate the contribution of basally released ATP in establishing the set point for fibrotic activity in adult rat CFs and identify a key role for the modulation of this activity by hydrolysis of released ATP by ENTPDs. These findings also imply that cellular homeostasis and fibrotic response involve the integration of signaling that is pro-fibrotic by ATP and anti-fibrotic by adenosine and that is regulated by ENTPDs.

Combined effects of interleukin-1α and transforming growth factor-β1 on modulation of human cardiac fibroblast function

During cardiac remodeling, cardiac fibroblasts (CF) are influenced by increased levels of interleukin-1α (IL-1α) and transforming growth factor-β1 (TGFβ1). The present study investigated the interaction between these two important cytokines on function of human CF and their differentiation to myofibroblasts (CMF). CF were isolated from human atrial appendage and exposed to IL-1α and/or TGFβ1 (both 0.1 ng/ml). mRNA expression levels of selected genes were determined after 6-24h by real-time RT-PCR, while protein levels were analyzed at 24-48 h by ELISA or western blot. Activation of canonical signaling pathways (NFκB, Smad3, p38 MAPK) was determined by western blotting. Differentiation to CMF was examined by collagen gel contraction assays. Exposure of CF to IL-1α alone enhanced levels of IL-6, IL-8, matrix metalloproteinase-3 (MMP3) and collagen III (COL3A1), but reduced the CMF markers α-smooth muscle actin (αSMA) and connective tissue growth factor (CTGF/CCN2). By contrast, TGFβ1 alone had minor effects on IL-6, IL-8 and MMP3 levels, but significantly increased levels of the CMF markers αSMA, CTGF, COL1A1 and COL3A1. Co-stimulation with both IL-1α and TGFβ1 increased MMP3 expression synergistically. Furthermore, while TGFβ1 had no effect on IL-1α-induced IL-6 or IL-8 levels, co-stimulation inhibited the TGFβ1-induced increase in αSMA and blocked the gel contraction caused by TGFβ1. Combining IL-1α and TGFβ1 had no apparent effect on their canonical signaling pathways. In conclusion, IL-1α and TGFβ1 act synergistically to stimulate MMP3 expression in CF. Moreover, IL-1α has a dominant inhibitory effect on the phenotypic switch of CF to CMF induced by TGFβ1.

Regulation of myofibroblast differentiation and bleomycin-induced pulmonary fibrosis by adrenomedullin

Myofibroblast differentiation induced by transforming growth factor-β (TGF-β) is characterized by the expression of smooth muscle α-actin (SMA) and extracellular matrix proteins. We and others have previously shown that these changes are regulated by protein kinase A (PKA). Adrenomedullin (ADM) is a vasodilator peptide that activates cAMP/PKA signaling through the calcitonin-receptor-like receptor (CRLR) and receptor-activity-modifying proteins (RAMP). In this study, we found that recombinant ADM had little effect on cAMP/PKA in quiescent human pulmonary fibroblasts, whereas it induced a profound activation of cAMP/PKA signaling in differentiated (by TGF-β) myofibroblasts. In contrast, the prostacyclin agonist iloprost was equally effective at activating PKA in both quiescent fibroblasts and differentiated myofibroblasts. TGF-β stimulated a profound expression of CRLR with a time course that mirrored the increased PKA responses to ADM. The TGF-β receptor kinase inhibitor SB431542 abolished expression of CRLR and attenuated the PKA responses of cells to ADM but not to iloprost. CRLR expression was also dramatically increased in lungs from bleomycin-treated mice. Functionally, ADM did not affect initial differentiation of quiescent fibroblasts in response to TGF-β but significantly attenuated the expression of SMA, collagen-1, and fibronectin in pre-differentiated myofibroblasts, which was accompanied by decreased contractility of myofibroblasts. Finally, sensitization of ADM signaling by transgenic overexpression of RAMP2 in myofibroblasts resulted in enhanced survival and reduced pulmonary fibrosis in the bleomycin model of the disease. In conclusion, differentiated pulmonary myofibroblasts gain responsiveness to ADM via increased CRLR expression, suggesting the possibility of using ADM for targeting pathological myofibroblasts without affecting normal fibroblasts.

Type II diabetes promotes a myofibroblast phenotype in cardiac fibroblasts

AIMS

Cardiovascular disease is the leading cause of death for individuals diagnosed with type II diabetes mellitus (DM). Changes in cardiac function, left ventricular wall thickness and fibrosis have all been described in patients and animal models of diabetes; however, the factors mediating increased matrix deposition remain unclear. The goal of this study was to evaluate whether cardiac fibroblast function is altered in a rat model of type II DM.

MAIN METHODS

Cardiac fibroblasts were isolated from 14 week old Zucker diabetic and lean control (LC) adult male rat hearts. Fibroblasts were examined for their ability to remodel 3-dimensional collagen matrices, their adhesion, migration and proliferation on collagen and changes in gene expression associated with collagen remodeling.

KEY FINDINGS

Cardiac fibroblasts from diabetic animals demonstrated significantly greater ability to contract 3-dimensional collagen matrices compared to cardiac fibroblasts from LC animals. The enhanced contractile behavior was associated with an increase in diabetic fibroblast proliferation and elevated expression of α-smooth muscle actin and type I collagen, suggesting the transformation of diabetic fibroblasts into a myofibroblast phenotype.

SIGNIFICANCE

Cardiac fibrosis is a common complication in diabetic cardiomyopathy which may contribute to the observed cardiac dysfunction associated with this disease. Identifying and understanding the changes in fibroblast behavior which contribute to the increased deposition of collagen and other matrix proteins may provide novel therapeutic targets for reducing the devastating effects of diabetes on the heart.

Multi-drug resistance protein 4 (MRP4)-mediated regulation of fibroblast cell migration reflects a dichotomous role of intracellular cyclic nucleotides

It has long been known that cyclic nucleotides and cyclic nucleotide-dependent signaling molecules control cell migration. However, the concept that it is not just the absence or presence of cyclic nucleotides, but a highly coordinated balance between these molecules that regulates cell migration, is new and revolutionary. In this study, we used multidrug resistance protein 4 (MRP4)-expressing cell lines and MRP4 knock-out mice as model systems and wound healing assays as the experimental system to explore this unique and emerging concept. MRP4, a member of a large family of ATP binding cassette transporter proteins, localizes to the plasma membrane and functions as a nucleotide efflux transporter and thus plays a role in the regulation of intracellular cyclic nucleotide levels. Here, we demonstrate that mouse embryonic fibroblasts (MEFs) isolated from Mrp4(-/-) mice have higher intracellular cyclic nucleotide levels and migrate faster compared with MEFs from Mrp4(+/+) mice. Using FRET-based cAMP and cGMP sensors, we show that inhibition of MRP4 with MK571 increases both cAMP and cGMP levels, which results in increased migration. In contrast to these moderate increases in cAMP and cGMP levels seen in the absence of MRP4, a robust increase in cAMP levels was observed following treatment with forskolin and isobutylmethylxanthine, which decreases fibroblast migration. In response to externally added cell-permeant cyclic nucleotides (cpt-cAMP and cpt-cGMP), MEF migration appears to be biphasic. Altogether, our studies provide the first experimental evidence supporting the novel concept that balance between cyclic nucleotides is critical for cell migration.

TRPV4 channels mediate cardiac fibroblast differentiation by integrating mechanical and soluble signals

The phenotypic switch underlying the differentiation of cardiac fibroblasts into hypersecretory myofibroblasts is critical for cardiac remodeling following myocardial infarction. Myofibroblasts facilitate wound repair in the myocardium by secreting and organizing extracellular matrix (ECM) during the wound healing process. However, the molecular mechanisms involved in myofibroblast differentiation are not well known. TGF-β has been shown to promote differentiation and this, combined with the robust mechanical environment in the heart, lead us to hypothesize that the mechanotransduction and TGF-β signaling pathways play active roles in the differentiation of cardiac fibroblasts to myofibroblasts. Here, we show that the mechanosensitve ion channel TRPV4 is required for TGF-β1-induced differentiation of cardiac fibroblasts into myofibroblasts. We found that the TRPV4-specific antagonist AB159908 and siRNA knockdown of TRPV4 significantly inhibited TGFβ1-induced differentiation as measured by incorporation of α-SMA into stress fibers. Further, we found that TGF-β1-induced myofibroblast differentiation was dependent on ECM stiffness, a response that was attenuated by TRPV4 blockade. Finally, TGF-β1 treated fibroblasts exhibited enhanced TRPV4 expression and TRPV4-mediated calcium influx compared to untreated controls. Taken together these results suggest for the first time that the mechanosensitive ion channel, TRPV4, regulates cardiac fibroblast differentiation to myofibroblasts by integrating signals from TGF-β1 and mechanical factors.

Molecular analysis of the TGF-beta controlled gene expression program in chicken embryo dermal myofibroblasts

The myofibroblast is a mesenchymal cell characterized by synthesis of the extracellular matrix, plus contractile and secretory activities. Myofibroblasts participate in physiological tissue repair, but can also cause devastating fibrosis. They are present in the tumor stroma of carcinomas and contribute to tumor growth and spreading. As myofibroblasts derive from various cell types and appear in a variety of tissues, there is marked variability in their phenotype. As regulatory mechanisms of wound healing are likely conserved among vertebrates, detailed knowledge of these mechanisms in more distant species will help to distinguish general from specific phenomena. To provide this as yet missing comparison, we analyzed the impact of the chemical inhibition of TGF-beta signaling on gene expression in chicken embryo dermal myofibroblasts. We revealed genes previously reported in mammalian systems (e.g. SPON2, ASPN, COMP, LUM, HAS2, IL6, CXCL12, VEGFA) as well as novel TGF-beta dependent genes, among them PGF, VEGFC, PTN, FAM180A, FIBIN, ZIC1, ADCY2, RET, HHIP and DNER. Inhibition of TGF-beta signaling also induced multiple genes, including NPR3, AGTR2, MTUS1, SOD3 and NOV. We also analyzed the effects of long term inhibition, and found that it is not able to induce myofibroblast dedifferentiation.

cAMP and Epac in the regulation of tissue fibrosis

Fibrosis, the result of excess deposition of extracellular matrix (ECM), in particular collagen, leads to scarring and loss of function in tissues that include the heart, lung, kidney and liver. The second messenger cAMP can inhibit the formation and extent of ECM during this late phase of inflammation, but the mechanisms for these actions of cAMP and of agents that elevate tissue cAMP levels are not well understood. In this article, we review the fibrotic process and focus on two recently recognized aspects of actions of cAMP and its effector Epac (Exchange protein activated by cAMP): (a) blunting of epithelial-mesenchymal transformation (EMT) and (b) down-regulation of Epac expression by profibrotic agents (e.g. TGF-β, angiotensin II), which may promote tissue fibrosis by decreasing Epac-mediated antifibrotic actions. Pharmacological approaches that raise cAMP or blunt the decrease in Epac expression by profibrotic agents may thus be strategies to block or perhaps reverse tissue fibrosis. LINKED ARTICLES This article is part of a themed section on Novel cAMP Signalling Paradigms. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.166.issue-2.

A-kinase anchoring proteins: molecular regulators of the cardiac stress response

In response to stress or injury the heart undergoes a pathological remodeling process, associated with hypertrophy, cardiomyocyte death and fibrosis, that ultimately causes cardiac dysfunction and heart failure. It has become increasingly clear that signaling events associated with these pathological cardiac remodeling events are regulated by scaffolding and anchoring proteins, which allow coordination of pathological signals in space and time. A-kinase anchoring proteins (AKAPs) constitute a family of functionally related proteins that organize multiprotein signaling complexes that tether the cAMP-dependent protein kinase (PKA) as well as other signaling enzymes to ensure integration and processing of multiple signaling pathways. This review will discuss the role of AKAPs in the cardiac response to stress. Particular emphasis will be given to the adaptative process associated with cardiac hypoxia as well as the remodeling events linked to cardiac hypertrophy and heart failure. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Cardiac Pathways of Differentiation, Metabolism and Contraction.

The role of cardiac fibroblasts in the transition from inflammation to fibrosis following myocardial infarction

Cardiac fibroblasts (CF) play a pivotal role in the repair and remodeling of the heart that occur following myocardial infarction (MI). The transition through the inflammatory, granulation and maturation phases of infarct healing is driven by cellular responses to local levels of cytokines, chemokines and growth factors that fluctuate in a temporal and spatial manner. In the acute inflammatory phase early after MI, CF contribute to the inflammatory milieu through increased secretion of proinflammatory cytokines and chemokines, and they promote extracellular matrix (ECM) degradation by increasing matrix metalloproteinase (MMP) expression and activity. In the granulation phase, CF migrate into the infarct zone, proliferate and produce MMPs and pro-angiogenic molecules to facilitate revascularization. Fibroblasts also undergo a phenotypic change to become myofibroblasts. In the maturation phase, inflammation is reduced by anti-inflammatory cytokines, and increased levels of profibrotic stimuli induce myofibroblasts to synthesize new ECM to form a scar. The scar is contracted through the mechanical force generated by myofibroblasts, preventing cardiac dilation. In this review we discuss the transition from myocardial inflammation to fibrosis with particular focus on how CF respond to alterations in proinflammatory and profibrotic signals. By furthering our understanding of these events, it is hoped that new therapeutic interventions will be developed that selectively reduce adverse myocardial remodeling post-MI, while sparing essential repair mechanisms.

Defining the cellular repertoire of GPCRs identifies a profibrotic role for the most highly expressed receptor, protease-activated receptor 1, in cardiac fibroblasts

G-protein-coupled receptors (GPCRs) have many roles in cell regulation and are commonly used as drug targets, but the repertoire of GPCRs expressed by individual cell types has not been defined. Here we use an unbiased approach, GPCR RT-PCR array, to define the expression of nonchemosensory GPCRs by cardiac fibroblasts (CFs) isolated from Rattus norvegicus. CFs were selected because of their importance for cardiac structure and function and their contribution to cardiac fibrosis, which occurs with advanced age, after acute injury (e.g., myocardial infarction), and in disease states (e.g., diabetes mellitus, hypertension). We discovered that adult rat CFs express 190 GPCRs and that activation of protease-activated receptor 1 (PAR1), the most highly expressed receptor, raises the expression of profibrotic markers in rat CFs, resulting in a 60% increase in collagen synthesis and conversion to a profibrogenic myofibroblast phenotype. We use siRNA knockdown of PAR1 (90% decrease in mRNA) to show that the profibrotic effects of thrombin are PAR1-dependent. These findings, which define the expression of GPCRs in CFs, provide a proof of principle of an approach to discover previously unappreciated, functionally relevant GPCRs and reveal a potential role for thrombin and PAR1 in wound repair and pathophysiology of the adult heart.

GPCR expression in tissues and cells: are the optimal receptors being used as drug targets?

G-protein-coupled receptors [GPCRs, also known as 7-transmembrane (7-TM) receptors] comprise the largest family of membrane receptors in humans and other species and, in addition, represent the greatest number of current drug targets. In this article, we review methods to define GPCR expression and data indicating that individual cells express >100 different GPCRs. Results from studies that have quantified expression of these receptors lead us to conclude that the optimal GPCRs may not be currently used as therapeutic targets. We propose that studies of GPCR expression in individual cells will likely reveal new insights regarding cellular physiology and therapeutic approaches. Findings that define and characterize the most highly expressed GPCRs thus have important potential in terms of identifying new drug targets and novel therapies directed at a wide range of clinical disorders.

Effect of ascorbic acid on reactive oxygen species production in chemotherapy and hyperthermia in prostate cancer cells

Cellular reactive oxygen species (ROS) production is increased by both temperature and anticancer drugs. Antioxidants are known to suppress ROS production while cancer patients may take them as dietary supplement during chemotherapy and hyperthermic therapy. We examined changes in ROS production in prostate cancer cells in the presence of various anticancer drugs and antioxidants at different temperatures. ROS production was increased with temperature in cancer cells, but not in normal cells; this increase was potently inhibited by ascorbic acid. ROS production was also increased in the presence of some anticancer drugs, such as vinblastine, but not by others. Dietary antioxidant supplements, such as β-carotene, showed variable effects. Ascorbic acid potently inhibited ROS production, even in the presence of anticancer drugs, while β-carotene showed no inhibition. Accordingly, our results suggest that cancer patients should carefully choose antioxidants during their cancer chemotherapy and/or hyperthermic therapy.

ATP released from cardiac fibroblasts via connexin hemichannels activates profibrotic P2Y2 receptors

Cardiac fibroblasts (CFs) play an essential role in remodeling of the cardiac extracellular matrix. Extracellular nucleotide signaling may provoke a profibrotic response in CFs. We tested the hypothesis that physical perturbations release ATP from CFs and that ATP participates in profibrotic signaling. ATP release was abolished by the channel inhibitor carbenoxolone and inhibited by knockdown of either connexin (Cx)43 or Cx45 (47 and 35%, respectively), implying that hypotonic stimulation induces ATP release via Cx43 and Cx45 hemichannels, although pannexin 1 may also play a role. ATP released by hypotonic stimulation rapidly (<10 min) increased phosphorylated ERK by 5-8 fold, an effect largely eliminated by P2Y(2) receptor knockdown or ATP hydrolysis with apyrase. ATP stimulation of P2Y(2) receptors increased α-smooth muscle actin (α-SMA) production, and in an ERK-dependent manner, ATP increased collagen accumulation by 60% and mRNA expression of profibrotic markers: plasminogen activator inhibitor-1 and monocyte chemotactic protein-1 by 4.5- and 4.0-fold, respectively. Apyrase treatment substantially reduced the basal profibrotic phenotype, decreasing collagen and α-SMA content and increasing matrix metalloproteinase expression. Thus, ATP release activates P2Y(2) receptors to mediate profibrotic responses in CFs, implying that nucleotide release under both basal and activated states is likely an important mechanism for fibroblast homeostasis.

Cardiac lineage protein-1 (CLP-1) regulates cardiac remodeling via transcriptional modulation of diverse hypertrophic and fibrotic responses and angiotensin II-transforming growth factor β (TGF-β1) signaling axis

It is well known that the renin-angiotensin system contributes to left ventricular hypertrophy and fibrosis, a major determinant of myocardial stiffness. TGF-β1 and renin-angiotensin system signaling alters the fibroblast phenotype by promoting its differentiation into morphologically distinct pathological myofibroblasts, which potentiates collagen synthesis and fibrosis and causes enhanced extracellular matrix deposition. However, the atrial natriuretic peptide, which is induced during left ventricular hypertrophy, plays an anti-fibrogenic and anti-hypertrophic role by blocking, among others, the TGF-β-induced nuclear localization of Smads. It is not clear how the hypertrophic and fibrotic responses are transcriptionally regulated. CLP-1, the mouse homolog of human hexamethylene bis-acetamide inducible-1 (HEXIM-1), regulates the pTEFb activity via direct association with pTEFb causing inhibition of the Cdk9-mediated serine 2 phosphorylation in the carboxyl-terminal domain of RNA polymerase II. It was recently reported that the serine kinase activity of Cdk9 not only targets RNA polymerase II but also the conserved serine residues of the polylinker region in Smad3, suggesting that CLP-1-mediated changes in pTEFb activity may trigger Cdk9-dependent Smad3 signaling that can modulate collagen expression and fibrosis. In this study, we evaluated the role of CLP-1 in vivo in induction of left ventricular hypertrophy in angiotensinogen-overexpressing transgenic mice harboring CLP-1 heterozygosity. We observed that introduction of CLP-1 haplodeficiency in the transgenic α-myosin heavy chain-angiotensinogen mice causes prominent changes in hypertrophic and fibrotic responses accompanied by augmentation of Smad3/Stat3 signaling. Together, our findings underscore the critical role of CLP-1 in remodeling of the genetic response during hypertrophy and fibrosis.

Glycogen synthase kinase-3α limits ischemic injury, cardiac rupture, post-myocardial infarction remodeling and death

BACKGROUND

The molecular pathways that regulate the extent of ischemic injury and post-myocardial infarction (MI) remodeling are not well understood. We recently demonstrated that glycogen synthase kinase-3α (GSK-3α) is critical to the heart's response to pressure overload. However, the role, if any, of GSK-3α in regulating ischemic injury and its consequences is not known.

METHODS AND RESULTS

MI was induced in wild-type (WT) versus GSK-3α((-/-)) (KO) littermates by left anterior descending coronary artery ligation. Pre-MI, WT, and KO hearts had comparable chamber dimensions and ventricular function, but as early as 1 week post-MI, KO mice had significantly more left ventricular dilatation and dysfunction than WT mice. KO mice also had increased mortality during the first 10 days post-MI (43% versus 22%; P=0.04), and postmortem examination confirmed cardiac rupture as the cause of most of the deaths. In the mice that survived the first 10 days, left ventricular dilatation and dysfunction remained worse in the KO mice throughout the study (8 weeks). Hypertrophy, fibrosis, and heart failure were all increased in the KO mice. Given the early deaths due to rupture and the significant reduction in left ventricular function evident as early as 1 week post-MI, we examined infarct size following a 48-hour coronary artery ligation and found it to be increased in the KO mice. This was accompanied by increased apoptosis in the border zone of the MI. This increased susceptibility to ischemic injury-induced apoptosis was also seen in cardiomyocytes isolated from the KO mice that were exposed to hypoxia. Finally, Bax translocation to the mitochondria and cytochrome C release into the cytosol were increased in the KO mice.

CONCLUSION

GSK-3α confers resistance to ischemic injury, at least in part, via limiting apoptosis. Loss of GSK-3α promotes ischemic injury, increases risk of cardiac rupture, accentuates post-MI remodeling and left ventricular dysfunction, and increases the progression to heart failure. These findings are in striking contrast to multiple previous reports in which deletion or inhibition of GSK-3β is protective.

Cyclic nucleotide phosphodiesterase 1A: a key regulator of cardiac fibroblast activation and extracellular matrix remodeling in the heart

Cardiac fibroblasts become activated and differentiate to smooth muscle-like myofibroblasts in response to hypertension and myocardial infarction (MI), resulting in extracellular matrix (ECM) remodeling, scar formation and impaired cardiac function. cAMP and cGMP-dependent signaling have been implicated in cardiac fibroblast activation and ECM synthesis. Dysregulation of cyclic nucleotide phosphodiesterase (PDE) activity/expression is also associated with various diseases and several PDE inhibitors are currently available or in development for treating these pathological conditions. The objective of this study is to define and characterize the specific PDE isoform that is altered during cardiac fibroblast activation and functionally important for regulating myofibroblast activation and ECM synthesis. We have found that Ca(2+)/calmodulin-stimulated PDE1A isoform is specifically induced in activated cardiac myofibroblasts stimulated by Ang II and TGF-β in vitro as well as in vivo within fibrotic regions of mouse, rat, and human diseased hearts. Inhibition of PDE1A function via PDE1-selective inhibitor or PDE1A shRNA significantly reduced Ang II or TGF-β-induced myofibroblast activation, ECM synthesis, and pro-fibrotic gene expression in rat cardiac fibroblasts. Moreover, the PDE1 inhibitor attenuated isoproterenol-induced interstitial fibrosis in mice. Mechanistic studies revealed that PDE1A modulates unique pools of cAMP and cGMP, predominantly in perinuclear and nuclear regions of cardiac fibroblasts. Further, both cAMP-Epac-Rap1 and cGMP-PKG signaling was involved in PDE1A-mediated regulation of collagen synthesis. These results suggest that induction of PDE1A plays a critical role in cardiac fibroblast activation and cardiac fibrosis, and targeting PDE1A may lead to regression of the adverse cardiac remodeling associated with various cardiac diseases.

Interstitial fluid flow and cyclic strain differentially regulate cardiac fibroblast activation via AT1R and TGF-β1

Cardiac fibroblasts are exposed to both cyclic strain and interstitial fluid flow in the myocardium. The balance of these stimuli is affected by fibrotic scarring, during which the fibroblasts transition to a myofibroblast phenotype. The present study investigates the mechanisms by which cardiac fibroblasts seeded in three-dimensional (3D) collagen gels differentiate between strain and fluid flow. Neonatal cardiac fibroblast-seeded 3D collagen gels were exposed to interstitial flow and/or cyclic strain and message levels of collagens type I and III, transforming growth factor β1 (TGF-β1), and α-smooth muscle actin (α-SMA) were assessed. Flow was found to significantly increase and strain to decrease expression of myofibroblast markers. Corresponding immunofluorescence indicated that flow and strain differentially regulated α-SMA protein expression. The effect of flow was inhibited by exposure to losartan, an angiotensin II type 1 receptor (AT1R) blocker, and by introduction of shRNA constructs limiting AT1R expression. Blocking of TGF-β also inhibited the myofibroblast transition, suggesting that flow-mediated cell signaling involved both AT1R and TGF-β1. Reduced smad2 phosphorylation in response to cyclic strain suggested that TGF-β is part of the mechanism by which cardiac fibroblasts differentiate between strain-induced and flow-induced mechanical stress. Our experiments show that fluid flow and mechanical deformation have distinct effects on cardiac fibroblast phenotype. Our data suggest a mechanism in which fluid flow directly acts on AT1R and causes increased TGF-β1 expression, whereas cyclic strain reduces activation of smad proteins. These results have relevance to the pathogenesis and treatment of heart failure.

Cytotoxic T lymphocyte antigen-2 alpha induces apoptosis of murine T-lymphoma cells and cardiac fibroblasts and is regulated by cAMP/PKA

The mechanism of cAMP-promoted apoptosis is not well defined. In wild-type (WT) murine S49 lymphoma cells, cAMP promotes apoptosis in a protein kinase A (PKA)-dependent manner. We find that treatment of WT S49 cells with 8-CPT-cAMP prominently increases the expression (as determined by DNA microarray analysis, real-time PCR and immunblotting) of cytotoxic T lymphocyte antigen-2α (CTLA-2α), a cathepsin L-like cysteine protease inhibitor. By contrast, CTLA-2α expression is only slightly increased by 8-CPT-cAMP treatment of D-S49 cells, which lack cAMP/PKA-promoted apoptosis. Raising endogenous cAMP (by use of forskolin or inhibition of phosphodiesterase [PDE] 4) or a PKA-selective, but not an Epac-selective, cAMP analogue, increases CTLA-2α mRNA expression; PKA, and not Epac, thus mediates the increase in CTLA-2α expression. An adenoviral CLTA-2α (Ad-CTLA-2α) construct induces apoptosis and enhances cAMP-promoted apoptosis in WT S49 cells but such cells do not have an increase in cathepsin L activity nor does a cathepsin L inhibitor alter cAMP-promoted apoptosis. 8-CPT-cAMP also increases CTLA-2α expression and induces apoptosis in murine cardiac fibroblasts; knockdown of CTLA-2α expression by siRNA blocks 8-CPT-cAMP-promoted apoptosis. Thus, cAMP increases CTLA-2α expression in murine lymphoma and cardiac fibroblasts and this increase in CTLA-2α contributes to cAMP/PKA-promoted apoptosis by mechanisms that are independent of the ability of CTLA-2α to inhibit cathepsin L.

Notch signaling may negatively regulate neonatal rat cardiac fibroblast-myofibroblast transformation

Cardiac fibroblast-myofibroblast transformation (CMT) is a critical event in the initiation of myocardial fibrosis. Notch signaling has been shown to regulate myofibroblast transformation from other kinds of cells. However, whether Notch signaling is also involved in CMT remains unclear. In the present study, expressions of Notch receptors in cardiac fibroblasts (CFs) were examined, effects of Notch signaling inhibitor N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester (DAPT) and transforming growth factor-beta1 (TGF-beta1) on CMT were determined by increasing alpha-smooth muscle actin (alpha-SMA) expression and collagen synthesis, and Notch signaling was examined by analyzing expressions of Notch receptors. The results showed that: (1) Notch receptor 1, 2, 3 and 4 were all expressed in CFs; (2) DAPT promoted CMT in a time-dependent manner; (3) During the period of CMT induced by TGF-beta1, expressions of Notch receptor 1, 3 and 4 in CFs were down-regulated, whereas there was no change for Notch receptor 2. Moreover, the downtrends of Notch 1, 3 and 4 were corresponding to the trend growth of alpha-SMA expression and collagen synthesis. These results suggested that inhibiting of Notch signaling might promote CMT. The down-regulations of Notch receptor 1, 3 and 4 induced by TGF-beta1 may facilitate CMT. In conclusion, inhibition of Notch signaling might be a novel mechanism of CMT in myocardial fibrosis.

Cardiac fibroblasts in cell culture systems: myofibroblasts all along?

The cytoarchitecture of the working myocardium is characterized by densely packed cardiomyocytes that are embedded in a three-dimensional network of numerous fibroblasts. Although the importance of cardiac fibroblasts in maintaining an orderly structured extracellular matrix is well recognized, less is known about their potential paracrine and electrotonic interactions with cardiomyocytes. This is partly the result of the complex intermingling of both cell types in vivo that tends to preclude a direct investigation of heterocellular crosstalk. It is for that reason that most of our present knowledge regarding stromal-parenchymal cell interactions is based on culture systems that permit direct access to either cell type. An often disregarded feature of such studies is that cardiac fibroblasts in standard two-dimensional cell culture have a pronounced tendency to undergo a phenotype switch to myofibroblasts. This cell type typically appears in injured hearts where it contributes importantly to fibrotic remodeling. The present review focuses on recent insights into electrical and paracrine crosstalk between myofibroblasts and cardiomyocytes while acknowledging that a comprehensive understanding of stromal-parenchymal cell interactions will depend on future methodological developments that permit retaining the fibroblast phenotype in cell culture systems and that will, most importantly, allow direct investigations of heterocellular crosstalk in intact tissue.

Proinflammatory protein CARD9 is essential for infiltration of monocytic fibroblast precursors and cardiac fibrosis caused by Angiotensin II infusion

Background

Angiotensin II (Ang II)–induced cardiac remodeling with the underlying mechanisms involving inflammation and fibrosis has been well documented. Cytosolic adaptor caspase recruitment domain 9 (CARD9) has been implicated in the innate immune response. We aimed to examine the role of CARD9 in inflammation and cardiac fibrosis induced by Ang II.

Methods

Two-month-old CARD9-deficient (CARD9^−/−) and wild-type (WT) male mice were infused with Ang II (1,500 ng/kg/min) or saline for 7 days. Heart sections were stained with hematoxylin and eosin and Masson trichrome and examined by immunohistochemistry; and activity and protein levels were measured in macrophages obtained from mice.

Results

WT mice with Ang II infusion showed a marked increase in CARD9⁺ macrophages in the heart, but CARD9^−/− mice showed significantly suppressed macrophage infiltration and expression of proinflammatory cytokines, including interleukin-1β (IL-1β) and connective tissue growth factor (CTGF). Importantly, Ang II–induced cardiac fibrosis (extracellular matrix and collagen I deposition) was diminished in CARD9^−/− hearts, as was the expression of transforming growth factor-β (TGF-β) and level of myofibroblasts positive for α-smooth muscle actin (α-SMA). Furthermore, Ang II activation of nuclear factor-κB (NF-κB), JNK and p38 mitogen-activated protein kinases (MAPKs) in WT macrophages was reduced in CARD9^−/− macrophages.

Conclusion

CARD9 plays an important role in regulating cardiac inflammation and fibrosis in response to elevated Ang II.

Reversal of TGF-β1 stimulation of α-smooth muscle actin and extracellular matrix components by cyclic AMP in Dupuytren's-derived fibroblasts

BACKGROUND

Myofibroblasts, a derived subset of fibroblasts especially important in scar formation and wound contraction, have been found at elevated levels in affected Dupuytren's tissues. Transformation of fibroblasts to myofibroblasts is characterized by expression of alpha- smooth muscle actin (α-SMA) and increased production of extracellular matrix (ECM) components, both events of relevance to connective tissue remodeling. We propose that increasing the activation of the cyclic AMP (cAMP)/protein kinase A signaling pathway will inhibit transforming growth factor-beta1 (TGF-β1)-induced ECM synthesis and myofibroblast formation and may provide a means to blunt fibrosis.

METHODS

Fibroblasts derived from areas of Dupuytren's contracture cord (DC), from adjacent and phenotypically normal palmar fascia (PF), and from palmar fascia from patients undergoing carpal tunnel release (CTR; CT) were treated with TGF-β1 (2 ng/ml) and/or forskolin (10 μM) (a known stimulator of cAMP). Total RNA and protein extracted was subjected to real time RT-PCR and Western blot analysis.

RESULTS

The basal mRNA expression levels of fibronectin- extra domain A (FN1-EDA), type I (COL1A2) and type III collagen (COL3A1), and connective tissue growth factor (CTGF) were all significantly increased in DC- and in PF-derived cells compared to CT-derived fibroblasts. The TGF-β1 stimulation of α-SMA, CTGF, COL1A2 and COL3A1 was greatly inhibited by concomitant treatment with forskolin, especially in DC-derived cells. In contrast, TGF-β1 stimulation of FN1-EDA showed similar levels of reduction with the addition of forskolin in all three cell types.

CONCLUSION

In sum, increasing cAMP levels show potential to inhibit the formation of myofibroblasts and accumulation of ECM components. Molecular agents that increase cAMP may therefore prove useful in mitigating DC progression or recurrence.

Lentivirus mediated IL-17R blockade improves diastolic cardiac function in spontaneously hypertensive rats

BACKGROUND

Hypertension causes cardiac fibrosis characterized by low-grade inflammation. We hypothesized that proinflammatory cytokine, interleukin-17 (IL-17) is important in hypertensive cardiac fibrosis. The pre-ligand assembly domain (PLAD) of IL-17 receptor A (IL-17RA) mediates receptor-chain associations essential for signaling. This study was designed to explore the role of IL-17 RA PLAD in hypertension-induced cardiac fibrosis.

METHODS

Eight-week-old male spontaneously hypertensive rats (SHRs) were divided into 2 groups, depending on receiving IL-17RA PLAD-Ig or green fluorescent protein (GFP) lentivirus. Age-matched Wistar Kyoto rats served as controls. Cardiac function was determined by echocardiography. Cardiac hypertrophy and fibrosis were histopathologically examined. Matrix metalloproteinase (MMP) and tissue inhibitors of metalloproteinase (TIMP) expression were quantified by immunoblotting. Collagen content was quantified.

RESULTS

Both cardiac systolic and diastolic function and myocardial fibrosis in SHRs was improved significantly by the IL-17RA PLAD. Expression of MMP-2 and MMP-9, TIMP-1 and -2, type I and type III collagen were statistically decreased by IL-17RA PLAD-Ig treatment. Collagen quantitation, as well as collagen concentration and collagen cross-linking, were reduced by IL-17/IL-17R signal blockade.

CONCLUSIONS

IL-17/IL-17RA signaling plays an important role in myocardial collagen metabolism in hypertension-induced diastolic dysfunction.

Stress-induced epinephrine levels compromise murine dermal fibroblast activity through β-adrenoceptors

Stress-induced catecholamine impairs the formation of granulation tissue acting directly in fibroblast activity; however, the mechanism by which high levels of catecholamines alter the granulation tissue formation is still unclear. Thus, the aim of this study was to investigate how high levels of epinephrine compromise the activity of murine dermal fibroblasts. Dermal fibroblasts isolated from the skin of neonatal Swiss mice were preincubated with α- or β-adrenoceptor antagonists. Thereafter, cells were exposed to physiologically elevated levels of epinephrine or epinephrine plus α- or β-adrenoceptor antagonists, and fibroblast activity was evaluated. The blockade of β1- and β2-adrenoceptors reversed the increase in fibroblast proliferation, ERK 1/2 phosphorylation, myofibroblastic differentiation and the reduction of collagen deposition induced by epinephrine. In addition, the blockade of β3-adrenoceptors reversed the increase in fibroblast proliferation and nitric oxide synthesis as well as the reduction of fibroblast migration, AKT phosphorylation and active matrix metalloproteinase-2 expression induced by epinephrine. However, the blockade of α1- and α2-adrenoceptors did not alter the effects of epinephrine on the activity of murine dermal fibroblasts. In conclusion, high levels of epinephrine directly compromise the activity of neonatal mouse skin fibroblasts through the activation of β1-, β2- and β3-adrenoceptors, but not through α1- and α2-adrenoceptors.

G protein-coupled receptor kinase-2 is a novel regulator of collagen synthesis in adult human cardiac fibroblasts

Cardiac fibroblasts (CF) make up 60-70% of the total cell number in the heart and play a critical role in regulating normal myocardial function and in adverse remodeling following myocardial infarction and the transition to heart failure. Recent studies have shown that increased intracellular cAMP can inhibit CF transformation and collagen synthesis in adult rat CF; however, mechanisms by which cAMP production is regulated in CF have not been elucidated. We investigated the potential role of G protein-coupled receptor kinase-2 (GRK2) in modulating collagen synthesis by adult human CF isolated from normal and failing left ventricles. Baseline collagen synthesis was elevated in failing CF and was not inhibited by β-agonist stimulation in contrast to normal controls. β-adrenergic receptor (β-AR) signaling was markedly uncoupled in the failing CF, and expression and activity of GRK2 were increased 3-fold. Overexpression of GRK2 in normal CF recapitulated a heart failure phenotype with minimal inhibition of collagen synthesis following β-agonist stimulation. In contrast, knockdown of GRK2 expression in normal CF enhanced cAMP production and led to greater β-agonist-mediated inhibition of basal and TGFβ-stimulated collagen synthesis versus control. Inhibition of GRK2 activity in failing CF by expression of the GRK2 inhibitor, GRK2ct, or siRNA-mediated knockdown restored β-agonist-stimulated inhibition of collagen synthesis and decreased collagen synthesis in response to TGFβ stimulation. GRK2 appears to play a significant role in regulating collagen synthesis in adult human CF, and increased activity of this kinase may be an important mechanism of maladaptive ventricular remodeling as mediated by cardiac fibroblasts.

Reduced serum content and increased matrix stiffness promote the cardiac myofibroblast transition in 3D collagen matrices

INTRODUCTION

The fibroblast-myofibroblast transition is an important event in the development of cardiac fibrosis and scar formation initiated after myocardial ischemia. The goals of the present study were to better understand the contribution of environmental factors to this transition and determine whether myofibroblasts provide equally important feedback to the surrounding environment.

METHODS

The influence of matrix stiffness and serum concentration on the myofibroblast transition was assessed by measuring message levels of a panel of cardiac fibroblast phenotype markers using quantitative reverse transcriptase polymerase chain reaction. Cell-mediated gel compaction measured the influence of environmental factors on cardiac fibroblast contractility. Immunohistochemistry characterized alpha-smooth muscle actin expression and cell morphology, while static and dynamic compression testing evaluated the effect of the cell response on the mechanical properties of the cell-seeded collagen hydrogels.

RESULTS

Both reduced serum content and increased matrix stiffness contributed to the myofibroblast transition, as indicated by contractile compaction of the gels, increased message levels of col3α1 and alpha-smooth muscle actin, and a less stellate morphology. However, the effects of serum and matrix stiffness were not additive. Mechanical testing indicated that reduced serum content increased the initial elastic modulus of cell-seeded gels and that gels lost their viscous character with time.

CONCLUSIONS

The results suggest that reduced serum and increased matrix stiffness promote the myofibroblast phenotype in the myocardium. This transition both enhances and is promoted by matrix stiffness, indicating the presence of positive feedback that may contribute to the pathogenesis of cardiac fibrosis.

Angiotensin1-9 antagonises pro-hypertrophic signalling in cardiomyocytes via the angiotensin type 2 receptor

The renin–angiotensin system (RAS) regulates blood pressure mainly via the actions of angiotensin (Ang)II, generated via angiotensin converting enzyme (ACE). The ACE homologue ACE2 metabolises AngII to Ang1-7, decreasing AngII and increasing Ang1-7, which counteracts AngII activity via the Mas receptor. However, ACE2 also converts AngI to Ang1-9, a poorly characterised peptide which can be further converted to Ang1-7 via ACE. Ang1-9 stimulates bradykinin release in endothelium and has antihypertrophic actions in the heart, attributed to its being a competitive inhibitor of ACE, leading to decreased AngII, rather than increased Ang1-7. To date no direct receptor-mediated effects of Ang1-9 have been described. To further understand the role of Ang1-9 in RAS function we assessed its action in cardiomyocyte hypertrophy in rat neonatal H9c2 and primary adult rabbit left ventricular cardiomyocytes, compared to Ang1-7. Cardiomyocyte hypertrophy was stimulated with AngII or vasopressin, significantly increasing cell size by approximately 1.2-fold (P < 0.05) as well as stimulating expression of the hypertrophy gene markers atrial natriuretic peptide, brain natriuretic peptide, β-myosin heavy chain and myosin light chain (2- to 5-fold, P < 0.05). Both Ang1-9 and Ang1-7 were able to block hypertrophy induced by either agonist (control, 186.4 μm; AngII, 232.8 μm; AngII+Ang1-7, 198.3 μm; AngII+Ang1-9, 195.9 μm; P < 0.05). The effects of Ang1-9 were not inhibited by captopril, supporting previous evidence that Ang1-9 acts independently of Ang1-7. Next, we investigated receptor signalling via angiotensin type 1 and type 2 receptors (AT1R, AT2R) and Mas. The AT1R antagonist losartan blocked AngII-induced, but not vasopressin-induced, hypertrophy. Losartan did not block the antihypertrophic effects of Ang1-9, or Ang1-7 on vasopressin-stimulated cardiomyocytes. The Mas antagonist A779 efficiently blocked the antihypertrophic effects of Ang1-7, without affecting Ang1-9. Furthermore, Ang1-7 activity was also inhibited in the presence of the bradykinin type 2 receptor antagonist HOE140, without affecting Ang1-9. Moreover, we observed that the AT2R antagonist PD123,319 abolished the antihypertrophic effects of Ang1-9, without affecting Ang1-7, suggesting Ang1-9 signals via the AT2R. Radioligand binding assays demonstrated that Ang1-9 was able to bind the AT2R (pKi = 6.28 ± 0.1). In summary, we ascribe a direct biological role for Ang1-9 acting via the AT2R. This has implications for RAS function and identifying new therapeutic targets in cardiovascular disease.

Effects of arginine vasopressin on differentiation of cardiac fibroblasts into myofibroblasts

BACKGROUND

Differentiation of cardiac fibroblasts (CFs) into myofibroblasts is a critical event in the initiation of myocardial fibrosis (MF). Previous studies have shown that arginine vasopressin (AVP) facilitates MF. However, the effects of AVP on CFs-myofibroblasts transformation, and its possible mechanisms are still unknown.

METHODS

CFs obtained from neonatal Sprague-Dawley rats were stimulated with AVP in the absence or presence of AVP V1a receptor specific antagonist [d(CH2)5Tyr(Me)]AVP. CFs-myofibroblast transformation was detected by expression of alpha-smooth muscle actin (alpha-SMA) and collagen synthesis. Western bolt and immunofluorescent staining were used to detect expression of alpha-SMA, [H]Proline incorporation was used to detect collagen synthesis. AVP-induced transforming growth factor-beta1 (TGF-beta1) secretion was detected by enzyme-linked immunosorbent assay. CFs was also stimulated with exogenous TGF-beta1 to find out the required dose to induce CFs-myofibroblast transformation.

RESULTS

10 mol/L AVP increased alpha-SMA expression and collagen synthesis significantly, and this effect was blocked by [d(CH2)5Tyr(Me)]AVP at the concentration of 10 mol/L. Meanwhile, AVP significantly increased TGF-beta1 secretion of CFs in a dose-dependent manner, and this effect was also blocked by 10 mol/L [d(CH2)5Tyr(Me)]AVP. However, the maximum production of biologic active TGF-beta1 induced by AVP is far less than the dose of exogenous TGF-beta1 needed to induce CFs-myofibroblast transformation.

CONCLUSIONS

AVP can induce CFs-myofibroblast transformation via its V1a receptor, AVP-induced increase of TGF-beta1 synthesis, which also is mediated by V1a receptor, may play a minor role in the transformation. Inducing differentiation of CFs into myofibroblasts may be a mechanism of AVP contributing to MF.

Estrogen receptor-beta prevents cardiac fibrosis

Development of cardiac fibrosis portends the transition and deterioration from hypertrophy to dilation and heart failure. Here we examined how estrogen blocks this important development. Angiotensin II (AngII) and endothelin-1 induce cardiac hypertrophy and fibrosis in humans. and we find that these agents directly stimulate the transition of the cardiac fibroblast to a myofibroblast. AngII and endothelin-1 stimulated TGFβ1 synthesis in the fibroblast, an inducer of fibrosis that signaled via c-jun kinase to Sma- and Mad-related protein 3 phosphorylation and nuclear translocation in myofibroblasts. As a result, mesenchymal proteins fibronectin and vimentin were produced, as were collagens I and III, the major forms found in fibrotic hearts. 17β-Estradiol (E2) or dipropylnitrile, an estrogen receptor (ER)β agonist, comparably blocked all these events, reversed by estrogen receptor (ER)β small interfering RNA. E2 and dipropylnitrile signaling through cAMP and protein kinase A prevented myofibroblast formation and blocked activation of c-jun kinase and important events of fibrosis. In the hearts of ovariectomized female mice, cardiac hypertrophy and fibrosis were induced by AngII infusion and prevented by E2 administration to wild type but not ERβ knockout rodents. Our results establish the cardiac fibroblast as an important target for hypertrophic/fibrosis-inducing peptides the actions of which were mitigated by E2/ERβ acting in these stromal cells.

A novel, orally active LPA(1) receptor antagonist inhibits lung fibrosis in the mouse bleomycin model

BACKGROUND AND PURPOSE

The aim of this study was to assess the potential of an antagonist selective for the lysophosphatidic acid receptor, LPA(1), in treating lung fibrosis We evaluated the in vitro and in vivo pharmacological properties of the high affinity, selective, oral LPA(1)-antagonist (4'-{4-[(R)-1-(2-chloro-phenyl)-ethoxycarbonylamino]-3-methyl-isoxazol-5-yl}-biphenyl-4-yl)-acetic acid (AM966).

EXPERIMENTAL APPROACH

The potency and selectivity of AM966 for LPA(1) receptors was determined in vitro by calcium flux and cell chemotaxis assays using recombinant and native cell cultures. The in vivo efficacy of AM966 to reduce tissue injury, vascular leakage, inflammation and fibrosis was assessed at several time points in the mouse bleomycin model.

KEY RESULTS

AM966 was a potent antagonist of LPA(1) receptors, with selectivity for this receptor over the other LPA receptors. In vitro, AM966 inhibited LPA-stimulated intracellular calcium release (IC(50)= 17 nM) from Chinese hamster ovary cells stably expressing human LPA(1) receptors and inhibited LPA-induced chemotaxis (IC(50)= 181 nM) of human IMR-90 lung fibroblasts expressing LPA(1) receptors. AM966 demonstrated a good pharmacokinetic profile following oral dosing in mice. In the mouse, AM966 reduced lung injury, vascular leakage, inflammation and fibrosis at multiple time points following intratracheal bleomycin instillation. AM966 also decreased lactate dehydrogenase activity and tissue inhibitor of metalloproteinase-1, transforming growth factor beta1, hyaluronan and matrix metalloproteinase-7, in bronchoalveolar lavage fluid.

CONCLUSIONS AND IMPLICATIONS

These findings demonstrate that AM966 is a potent, selective, orally bioavailable LPA(1) receptor antagonist that may be beneficial in treating lung injury and fibrosis, as well as other diseases that are characterized by pathological inflammation, oedema and fibrosis.

New insights into the mechanism of fibroblast to myofibroblast transformation and associated pathologies

Myofibroblasts are a differentiated cell type essential for wound healing, participating in tissue remodeling following insult. Myofibroblasts are typically activated fibroblasts, although they can also be derived from other cell types, including epithelial cells, endothelial cells, and mononuclear cells. In most organ systems, cell signals initiated following tissue-specific insult or during the metastatic process lead to differentiation of fibroblasts or other precursor cells to the myofibroblast phenotype. In addition to their beneficial and necessary role in wound healing, myofibroblasts also contribute to a number of pathologies, primarily fibrotic processes and tumor invasiveness. This review explores both traditional and nontraditional concepts of myofibroblast differentiation in the cornea, skin, heart, and other tissues, as well as some of the pathologies associated with myofibroblast activities.

Adenylyl cyclase 6 deletion reduces left ventricular hypertrophy, dilation, dysfunction, and fibrosis in pressure-overloaded female mice

OBJECTIVES

This study sought to test the hypothesis that pressure stress of the adenylyl cyclase 6-deleted (AC6-KO) heart would result in excessive hypertrophy, early dilation and dysfunction, and increased fibrosis.

BACKGROUND

Cardiac-directed AC6 expression attenuates left ventricular (LV) hypertrophy and dysfunction in cardiomyopathy.

METHODS

AC6-KO and control (CON) mice underwent transverse aortic constriction (TAC) to induce pressure overload. Measures of LV hypertrophy, function, and fibrosis were obtained 3 weeks after TAC, and LV samples were assessed for alterations in expression of FHL1 and periostin.

RESULTS

Three weeks after TAC, female AC6-KO mice had preserved left ventricular (LV) ejection fraction (CON: 22+/-2%; AC6-KO: 52+/-4%; p<0.001) and reduced LV end-diastolic dimension (CON: 4.6+/-0.1 mm; AC6-KO: 3.6+/-0.1 mm; p<0.001). Reduced LV/tibial length ratio (CON: 10.4+/-1.5 mg/mm; AC6-KO: 7.5+/-2.3 mg/mm; p<0.001) and reduced LV expression of atrial natriuretic factor (p<0.05), alpha-skeletal muscle actin (p<0.05), and beta-myosin heavy chain (p<0.05) were observed in AC6-KO mice. In addition, AC6 deletion was associated with less LV fibrosis (p<0.01) and reduced collagen types I (p<0.05) and III (p<0.05) expression 3 weeks after TAC. LV protein expression of FHL1 (p<0.02) and periostin (p=0.04) were reduced after TAC in AC6-KO mice. The roles of AC6 deletion in cardiac myocytes and fibroblasts were examined in vitro using pharmacological hypertrophy and AC6 knockdown (small interfering ribonucleic acid), which recapitulated in vivo findings.

CONCLUSIONS

The deleterious effects of LV pressure overload were reduced in female mice with AC6 deletion. Reductions in FHL1 and periostin expression, direct consequences of reduced AC6 in cardiac myocytes and fibroblasts, appear to be of mechanistic importance for these unanticipated beneficial effects.

Uridine triphosphate (UTP) induces profibrotic responses in cardiac fibroblasts by activation of P2Y2 receptors

Cardiac fibroblasts (CFs) play a key role in response to injury and remodeling of the heart. Nucleotide (P2) receptors regulate the heart but limited information is available regarding such receptors in CFs. We thus sought to determine if extracellular nucleotides regulate fibrotic responses (e.g., proliferation, migration and expression of profibrotic markers) of CFs in primary culture. UTP increased rat CF migration 3-fold (p<0.001), proliferation by 30% (p<0.05) and mRNA expression of profibrotic markers: alpha smooth muscle actin (alpha-SMA), plasminogen activator inhibitor-1 (PAI-1), transforming growth factor beta, soluble ST2, interleukin-6 and monocyte chemoattractant protein-1 (MCP-1) by 3.0-, 15-, 2.0-, 7.6-, 11-, and 6.1-fold, respectively (p<0.05). PAI-1 protein expression induced by UTP was dependent on protein kinase C (PKC) and extracellular signal-regulated kinase (ERK), based on blockade by the PKC inhibitor Ro-31-8220 and the ERK inhibitor U0126, respectively. The rank order for enhanced expression of PAI-1 and alpha-SMA by nucleotides (UTPgammaS>>UDPbetaS>>ATPgammaS), the expression of P2Y2 receptors as the most abundantly expressed P2Y receptor in rat CFs and a blunted response to UTP in P2Y2(-/-) mice all implicate P2Y2 as the predominant P2Y receptor that mediates nucleotide-promoted profibrotic responses. Additional results indicate that P2Y2 receptor-promoted profibrotic responses in CFs are transient, perhaps as a consequence of receptor desensitization. We conclude that P2Y2 receptor activation is profibrotic in CFs; thus inhibition of P2Y2 receptors may provide a novel means to diminish fibrotic remodeling and turnover of extracellular matrix in the heart.

Inhibition of calcium-calmodulin-dependent kinase II suppresses cardiac fibroblast proliferation and extracellular matrix secretion

Calcium-calmodulin-dependent protein kinase II (CaMKII) is one of the main protein kinases mediating intracellular Ca changes. It is also involved in the process of cardiac diseases, such as cardiac hypertrophy, but its effects on myocardial fibrosis remain unclear. The present study investigates whether CaMKII is involved in cardiac fibroblast proliferation and extracellular matrix (ECM) secretion induced by angiotensin II (AngII) or electrical field stimulation (EFS) in cultured neonatal rat cardiac fibroblasts. Cardiac fibroblast proliferation was assessed by a cell survival assay (MTT) and manual cell enumeration. Cellular matrix production was demonstrated by matrix metalloproteinases (MMP) 1, 2, 9, and collagen I/III messenger RNA expression, MMP-2, 9 protein expression, and secretion of transforming growth factor beta1 and tumor necrosis factor alpha. Either AngII or EFS promoted cardiac fibroblast proliferation and ECM secretion, while also up-regulating expression of CaMKII deltaB and deltaC. More importantly, CaMKII inhibitors, autocamtide-2-related inhibitory peptide (AIP 5 microM) or KN93 (0.5 microM), suppressed cardiac fibroblast proliferation, inhibited the excretion of transforming growth factor beta1 and tumor necrosis factor alpha, decreased the messenger RNA expression of MMP-1, 2, 9 and collagen I/III, and decreased the protein expression of MMP-2, 9. These results suggest that CaMKII mediates cardiac fibroblast proliferation and ECM secretion induced by either AngII or EFS.

Ac-SDKP inhibits transforming growth factor-beta1-induced differentiation of human cardiac fibroblasts into myofibroblasts

N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) inhibits collagen production and cell proliferation in cultured rat cardiac fibroblasts, but its effect on differentiation of fibroblasts into myofibroblasts is not known. High amounts of transforming growth factor-beta1 (TGF-beta1) have been found in fibrotic cardiac tissue. TGF-beta1 converts fibroblasts into myofibroblasts, which produce more extracellular matrix proteins than fibroblasts. We hypothesized that 1) Ac-SDKP inhibits TGF-beta1-induced differentiation of fibroblasts into myofibroblasts; and 2) this effect is mediated in part by blocking phosphorylation of small-mothers-against-decapentaplegic (Smad) 2 and extracellular signal-regulated kinase (ERK) 1/2. For this study, we used human fetal cardiac fibroblasts (HCFs), which do not spontaneously become myofibroblasts when cultured at low passages. We investigated the effect of Ac-SDKP on TGF-beta1-induced HCF transformation into myofibroblasts, Smad2 and ERK1/2 phosphorylation, Smad7 expression, cell proliferation, and collagen production. We also investigated TGF-beta1 production by HCFs stimulated with endothelin-1 (ET-1). As expected, HCFs treated with TGF-beta1 transformed into myofibroblasts as indicated by increased expression of alpha-smooth muscle actin and a higher proportion of the embryonic isoform of smooth muscle myosin compared with untreated cells. TGF-beta1 also increased Smad2 and ERK1/2 phosphorylation but did not affect Smad7 expression. In addition, TGF-beta1 stimulated HCF proliferation as indicated by an increase in mitochondrial dehydrogenase activity and collagen production (hydroxyproline assay). Ac-SDKP significantly inhibited all of the effects of TGF-beta1. It also inhibited ET-1-stimulated TGF-beta1 production. We concluded that Ac-SDKP markedly suppresses differentiation of human cardiac fibroblasts into myofibroblasts, probably by inhibiting the TGF-beta/Smad/ERK1/2 signaling pathway, and thus mediating its anti-fibrotic effects.

Mineralocorticoid receptor inhibits CREB signaling by calcineurin activation

We investigated the interaction of MR with cAMP-response element binding protein (CREB) and provide a mechanistic explanation and insights into the cellular relevance. MR --> CREB crosstalk was assessed in vascular smooth muscle cells and heterologous expression systems. Experiments were designed in a way that only one variable changed at a time and the respective vehicles served as controls. MR, but not GR, activation (aldosterone or hydrocortisone, IC(50), approximately 0.3 nM) inhibits CREB transcriptional activity induced by stimulation of beta1/2-adrenoceptors and adenylyl cyclase or addition of membrane-permeable cAMP up to 70% within 2 h after addition. The MR DNA-binding domain is not required for this inhibition. cAMP formation is virtually unchanged, whereas MR exerts a robust inhibition of CREB(S133) phosphorylation via calcineurin/PP2B activation without changes in PP2B-Aalpha or beta expression. In parallel, the PP2B-sensitive NFaT-pathway is activated. The inhibitory crosstalk attenuates CREB-induced glucose-6-phosphate dehydrogenase expression. Overall, transcriptional relevant MR --> CREB crosstalk occurs at the level of CREB phosphorylation by enhanced calcineurin activity, enables GRE-independent genomic signaling of MR, and is of potential pathophysiological relevance.

Mechanism of the transforming growth factor-beta induction of fibronectin expression in hepatic stem-like cells

Transforming growth factor-beta1 (TGF-beta1) plays an important role in the fibrogenic process in the liver. The aim of the present study was to explore the action of TGF-beta1 on fibronectin expression in rat hepatic stem-like cells and the underlying mechanisms. The level of fibronectin expression was determined in hepatic stem-like cells (WB cells) before and after TGF-beta1 stimulation by RT-PCR and Western blot methods. Using immunogold transmission electron microscopy and the Western blot method, we observed the result of the expression and the distribution of cAMP, phosphorylated Smad3 and Smad7 before and after TGF-beta1 treatment. The levels of fibronectin expression in both mRNA and protein increased 4- to 5-fold after TGF-beta1 stimulation, reaching an optimum level after 8 h and then gradually falling back. Similarly, TGF-beta1 stimulation resulted in an increase of cAMP in WB cells, peaking at 8 h. After treatment with TGF-beta1 for 24 h, the expression of cAMP gradually decreased. In addition, we found that TGF-beta1 treatment also contributed to the increased expression and to changes in cellular distribution of phosphorylated Smad3 (translocation from the cytoplasm to the nucleus) and Smad7 (translocation from the nucleus to the cytoplasm) in WB cells. The present study demonstrates that TGF-beta is involved in the fibrogenic process in hepatic stem cells through up-regulation of fibronectin expression, and the mechanisms underlying this process may be associated with the activation of cAMP and Smad pathways.

Cyclic GMP kinase and RhoA Ser188 phosphorylation integrate pro- and antifibrotic signals in blood vessels

Vascular fibrosis is a major complication of hypertension and atherosclerosis, yet it is largely untreatable. Natriuretic peptides (NPs) repress fibrogenic activation of vascular smooth muscle cells (VSMCs), but the intracellular mechanism mediating this effect remains undetermined. Here we show that inhibition of RhoA through phosphorylation at Ser188, the site targeted by the NP effector cyclic GMP (cGMP)-dependent protein kinase I (cGK I), is critical to fully exert antifibrotic potential. cGK I(+/-) mouse blood vessels exhibited an attenuated P-RhoA level and concurrently increased RhoA/ROCK signaling. Importantly, cGK I insufficiency caused dynamic recruitment of ROCK into the fibrogenic programs, thereby eliciting exaggerated vascular hypertrophy and fibrosis. Transgenic expression of cGK I-unphosphorylatable RhoA(A188) in VSMCs augmented ROCK activity, vascular hypertrophy, and fibrosis more prominently than did that of wild-type RhoA, consistent with the notion that RhoA(A188) escapes the intrinsic inhibition by cGK I. Additionally, VSMCs expressing RhoA(A188) became refractory to the antifibrotic effects of NPs. Our results identify cGK I-mediated Ser188 phosphorylation of RhoA as a converging node for pro- and antifibrotic signals and may explain how diminished cGMP signaling, commonly associated with vascular malfunction, predisposes individuals to vascular fibrosis.

Coupled calcium and zinc dyshomeostasis and oxidative stress in cardiac myocytes and mitochondria of rats with chronic aldosteronism

A dyshomeostasis of extra- and intracellular Ca(2+) and Zn(2+) occurs in rats receiving chronic aldosterone/salt treatment (ALDOST). Herein, we hypothesized that the dyshomeostasis of intracellular Ca(2+) and Zn(2+) is intrinsically coupled that alters the redox state of cardiac myocytes and mitochondria, with Ca(2+) serving as a pro-oxidant and Zn(2+) as an antioxidant. Toward this end, we harvested hearts from rats receiving 4 weeks of ALDOST alone or cotreatment with either spironolactone (Spiro), an aldosterone receptor antagonist, or amlodipine (Amlod), an L-type Ca(2+) channel blocker, and from age/sex-matched untreated controls. In each group, we monitored cardiomyocyte [Ca(2+)]i and [Zn(2+)]i and mitochondrial [Ca(2+)]m and [Zn(2+)]m; biomarkers of oxidative stress and antioxidant defenses; expression of Zn transporters, Zip1 and ZnT-1; metallothionein-1, a Zn(2+)-binding protein; and metal response element transcription factor-1, a [Zn(2+)]i sensor and regulator of antioxidant defenses. Compared with controls, at 4-week ALDOST, we found the following: (a) increased [Ca(2+)]i and [Zn(2+)]i, together with increased [Ca(2+)]m and [Zn(2+)]m, each of which could be prevented by Spiro and attenuated with Amlod; (b) increased levels of 3-nitrotyrosine and 4-hydroxy-2-nonenal in cardiomyocytes, together with increased H(2)O(2) production, malondialdehyde, and oxidized glutathione in mitochondria that were coincident with increased activities of Cu/Zn superoxide dismutase and glutathione peroxidase; and (c) increased expression of metallothionein-1, Zip1 and ZnT-1, and metal response element transcription factor-1, attenuated by Spiro. Thus, an intrinsically coupled dyshomeostasis of intracellular Ca(2+) and Zn(2+) occurs in cardiac myocytes and mitochondria in rats receiving ALDOST, where it serves to alter their redox state through a respective induction of oxidative stress and generation of antioxidant defenses. The importance of therapeutic strategies that can uncouple these two divalent cations and modulate their ratio in favor of sustained antioxidant defenses is therefore suggested.

A novel flow cytometric high throughput assay for a systematic study on molecular mechanisms underlying T cell receptor-mediated integrin activation

Lymphocyte function-associated antigen 1 (LFA-1), a member of β2-integrin family, exerts multiple roles in host T cell immunity and has been identified as a useful drug-development target for inflammatory and autoimmune diseases. Applying the findings that primary resting T cells absorb nanometric membrane vesicles derived from antigen presenting cells (APC) via dual receptor/ligand interactions of T cell receptor (TCR) with cognate peptide-major histocompatibility complex (MHC) complex (pMHC) and LFA-1 with its ligand, intercellular adhesion molecule-1 (ICAM-1), and that signaling cascades triggered by TCR/pMHC interaction take a part in the vesicle-absorption, we established a cell-based high throughput assay for systematic investigation, via isolation of small molecules modulating the level of vesicle-absorption, of molecular mechanisms underlying the T cell absorption of APC-derived vesicles, i.e., structural basis of TCR/pMHC and LFA-1/ICAM-1 interactions and TCR-mediated LFA-1 activation. As primary T cells along with physiological ligands expressed in biological membrane are used and also individual cells in assay samples are analyzed by flow cytometry, results obtained using the assay system hold superior physiological and therapeutic relevance as well as statistical precision.

LFA-1-dependent Ca2+ entry following suboptimal T cell receptor triggering proceeds without mobilization of intracellular Ca2+

A surge in cytosolic calcium ion concentration by entry of extracellular Ca2+ is a hallmark of T cell activation. According to store-operated Ca2+ entry mechanism, the Ca2+ entry is preceded by activation of phospholipase C-gamma1 (PLC-gamma1) and the consequent mobilization of intracellular Ca2+. Using membrane vesicles expressing the mouse class I major histocompatibility complex, i.e. Ld plus costimulatory ligands, i.e. B7-1 and intercellular adhesion molecule-1 along with 2C T cell receptor transgenic T cells, we investigated the roles of CD28 and LFA-1 (lymphocyte function-associated antigen-1) in the activation of PLC-gamma1 and Ca2+ signaling. Both CD28 and LFA-1 made significant and comparable contributions to the activation of PLC-gamma1 as gauged by the level of its phosphorylation at tyrosine 783. In contrast, their roles in Ca2+ signaling were quite distinct so that LFA-1/intercellular adhesion molecule-1 interaction exerted a determining role, whereas CD28/B7-1 interaction played only a minimal role. In particular, when the T cells were activated by suboptimal T cell receptor stimulation, LFA-1 played an indispensable role in the Ca2+ signaling. Further experiments using Ca2+-free medium demonstrated that the entry of extracellular Ca2+ was not always accompanied by mobilization of intracellular Ca2+. Thus, intracellular Ca2+ mobilization was hardly detected under the condition that LFA-1 played the indispensable role in the entry of extracellular Ca2+, while a distinct level of intracellular Ca2+ mobilization was readily detected under the condition that LFA-1 played only the supporting role. These results ensure the unique role of LFA-1 in T cell Ca2+ signaling and reveal that LFA-1-dependent Ca2+ entry proceeds via a mechanism separate from store-operated Ca2+ entry.