Proteinase-activated receptor agonists stimulate the increase in intracellular Ca2+ in cardiomyocytes and proliferation of cardiac fibroblasts from chick embryos

Human umbilical cord mesenchymal stem cells combined with pirfenidone upregulates the expression of RGS2 in the pulmonary fibrosis in mice

Objective

The therapeutic effect of umbilical cord-derived mesenchymal stem cells (hUC-MSCs) in combination with pirfenidone (PFD) on pulmonary fibrosis in mice and its possible mechanism were investigated.

Methods

C57BL/6 mice were randomly divided into six groups: control group, model group, P₁₀ group, P₃₀ group, P₁₀₀ group, and P₃₀₀ group. Modeled by tracheal intubation with 3 mg/kg bleomycin drip, each dose of PFD was administered daily by gavage from day 7 onwards. The mice were observed continuously for 21 days and survival was recorded. Lung tissues were collected on day 21, and hematoxylin–eosin (HE) and Masson staining were performed to assess morphological changes and collagen deposition in the lungs. Collagen content was measured by the Sircol method, and fibrosis marker levels were detected by PCR and Western blot. Another batch of C57BL/6 mice was then randomly divided into five groups: hUC-MSC control group, model group, P₁₀₀ group, hUC-MSC treatment group, and hUC-MSCs + P₃₀ group. On day 7, 5 × 10⁵ hUC-MSCs were injected into the tail vein, the mice were administered PFD gavage daily from day 7 onwards, and their survival was recorded. Lung tissues were collected on day 21 to detect pathological changes, the collagen content, and the expression of regulator of G protein signaling 2 (RGS2). Pulmonary myofibroblasts (MFBs) were divided into an MFB group and an MFB + hUC-MSCs group; different doses of PFD were administered to each group, and the levels of RGS2, intracellular Ca²⁺, and fibrosis markers were recorded for each group.

Results

Compared with other PFD group doses, the P₁₀₀ group had significantly improved mouse survival and lung pathology and significantly reduced collagen and fibrosis marker levels (p < 0.05). The hUC-MSCs + P₃₀ group had significantly improved mouse survival and lung pathology, significantly reduced collagen content and fibrosis marker levels (p < 0.05), and the efficacy was better than that of the P₁₀₀ and hUC-MSCs groups (p < 0.05). RGS2 expression was significantly higher in the MSCs + P₃₀ group compared with the P₁₀₀ and hUC-MSCs groups (p < 0.05). PFD increased RGS2 expression in MFBs (p < 0.05) in a dose-dependent manner. Compared with PFD and hUC-MSCs treatment alone, combination of hUC-MSCs and PFD increased RGS2 protein levels, significantly decreased intracellular Ca²⁺ concentration, and significantly reduced fibrosis markers.

Conclusion

The findings suggest that hUC-MSCs combined with low-dose PFD have a therapeutic effect better than that of the two treatments used separately. Its effect on attenuating bleomycin-induced pulmonary fibrosis in mice is related to the increase of RGS2.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-022-02192-6.

Granzymes in cardiovascular injury and disease

Chronic inflammation and impaired wound healing play important roles in the pathophysiology of cardiovascular diseases. Moreover, the aberrant secretion of proteases plays a critical role in pathological tissue remodeling in chronic inflammatory conditions. Human Granzymes (Granule secreted enzymes - Gzms) comprise a family of five (GzmA, B, H, K, M) cell-secreted serine proteases. Although each unique in function and substrate specificities, Gzms were originally thought to share redundant, intracellular roles in cytotoxic lymphocyte-induced cell death. However, an abundance of evidence has challenged this dogma. It is now recognized, that individual Gzms exhibit unique substrate repertoires and functions both intracellularly and extracellularly. In the extracellular milieu, Gzms contribute to inflammation, vascular dysfunction and permeability, reduced cell adhesion, release of matrix-sequestered growth factors, receptor activation, and extracellular matrix cleavage. Despite these recent findings, the non-cytotoxic functions of Gzms in the context of cardiovascular disease pathogenesis remain poorly understood. Minimally detected in tissues and bodily fluids of normal individuals, GzmB is elevated in patients with acute coronary syndromes, coronary artery disease, and myocardial infarction. Pre-clinical animal models have exemplified the importance of GzmB in atherosclerosis, aortic aneurysm, and cardiac fibrosis as animals deficient in GzmB exhibit reduced tissue remodeling, improved disease phenotypes and increased survival. Although a role for GzmB in cardiovascular disease is described, further work to elucidate the mechanisms that underpin the remaining human Gzms activity in cardiovascular disease is necessary. The present review provides a summary of the pre-clinical and clinical evidence, as well as emerging areas of research pertaining to Gzms in tissue remodeling and cardiovascular disease.

Protease-activated receptor 2 deficiency in hematopoietic lineage protects against myocardial infarction through attenuated inflammatory response and fibrosis

Ischaemic heart disease is one of the leading causes of death. Protease-activated receptor 2 (PAR2) is widely expressed within the cardiovascular system and is known to mediate inflammatory processes in various immunocytes, such as macrophages, mastocytes and neutrophils. Here, we investigated whether activating macrophage PAR2 modulates cardiac remodelling in a murine model of myocardial infarction. Myocardial infarction was produced by the permanent ligation of the left anterior descending coronary artery (LAD) in C57BL/6J background wild-type (WT) mice transplanted with bone marrow from WT or PAR2 knockout (PAR2 KO) mice. Hematopoietic deficiency of PAR2 had improvement of left ventricular systolic dysfunction and dilatation and decreased fibrosis deposition in remote zone at 1 week after LAD ligation. Inactivation of PAR2 also led to less recruitment of macrophages in myocardium, which was accompanied by decreased expression of pro-inflammatory cytokines. Furthermore, cultured cardiac fibroblasts (CFs) were activated and showed a fibrotic phenotype after being co-cultured in medium containing PAR2-activating macrophage, which enhances interferon-beta (INF-β) expression. The beneficial effects of macrophages with INF-β neutralisation or PAR2-deletion ameliorates the JAK/STAT3 pathway in CFs, which might be attributed to CF activation. These data suggest that macrophage-derived IFN-β plays a crucial role in adverse cardiac remodelling after myocardial infarction, at least in part, through a PAR2-dependent mechanism.

Angiotensin-II-Evoked Ca2+ Entry in Murine Cardiac Fibroblasts Does Not Depend on TRPC Channels

TRPC proteins form cation conducting channels regulated by different stimuli and are regulators of the cellular calcium homeostasis. TRPC are expressed in cardiac cells including cardiac fibroblasts (CFs) and have been implicated in the development of pathological cardiac remodeling including fibrosis. Using Ca²⁺ imaging and several compound TRPC knockout mouse lines we analyzed the involvement of TRPC proteins for the angiotensin II (AngII)-induced changes in Ca²⁺ homeostasis in CFs isolated from adult mice. Using qPCR we detected transcripts of all Trpc genes in CFs; Trpc1, Trpc3 and Trpc4 being the most abundant ones. We show that the AngII-induced Ca²⁺ entry but also Ca²⁺ release from intracellular stores are critically dependent on the density of CFs in culture and are inversely correlated with the expression of the myofibroblast marker α-smooth muscle actin. Our Ca²⁺ measurements depict that the AngII- and thrombin-induced Ca²⁺ transients, and the AngII-induced Ca²⁺ entry and Ca²⁺ release are not affected in CFs isolated from mice lacking all seven TRPC proteins (TRPC-hepta KO) compared to control cells. However, pre-incubation with GSK7975A (10 µM), which sufficiently inhibits CRAC channels in other cells, abolished AngII-induced Ca²⁺ entry. Consequently, we conclude the dispensability of the TRPC channels for the acute neurohumoral Ca²⁺ signaling evoked by AngII in isolated CFs and suggest the contribution of members of the Orai channel family as molecular constituents responsible for this pathophysiologically important Ca²⁺ entry pathway.

Pharmacological Inhibition of Serine Proteases to Reduce Cardiac Inflammation and Fibrosis in Atrial Fibrillation

Systemic inflammation correlates with an increased risk of atrial fibrillation (AF) and thrombogenesis. Systemic inflammation alters vessel permeability, allowing inflammatory and immune cell migration toward target organs, including the heart. Among inflammatory cells infiltrating the atria, macrophages and mast cell have recently attracted the interest of basic researchers due to the pathogenic mechanisms triggered by their activation. This chemotactic invasion is likely implicated in short- and long-term changes in cardiac cell-to-cell communication and in triggering fibrous tissue accumulation in the atrial myocardium and electrophysiological re-arrangements of atrial cardiomyocytes, thus favoring the onset and progression of AF. Serine proteases are a large and heterogeneous class of proteases involved in several processes that are important for cardiac function and are involved in cardiac diseases, such as (i) coagulation, (ii) fibrinolysis, (iii) extracellular matrix degradation, (iv) activation of receptors (i.e., protease-activated receptors [PPARs]), and (v) modulation of the activity of endogenous signals. The recognition of serine proteases substrates and their involvement in inflammatory/profibrotic mechanisms allowed the identification of novel cardio-protective mechanisms for commonly used drugs that inhibit serine proteases. The aim of this review is to summarize knowledge on the role of inflammation and fibrosis as determinants of AF. Moreover, we will recapitulate current findings on the role of serine proteases in the pathogenesis of AF and the possible beneficial effects of drugs inhibiting serine proteases in reducing the risk of AF through decrease of cardiac inflammation and fibrosis. These drugs include thrombin and factor Xa inhibitors (used as oral anticoagulants), dipeptidyl-peptidase 4 (DPP4) inhibitors, used for type-2 diabetes, as well as novel experimental inhibitors of mast cell chymases.

Protease-activated receptor-2 regulates glial scar formation via JNK signaling

The study aimed to determine the effects of protease-activated receptor-2 (PAR-2) on glial scar formation after spinal cord injury (SCI) in Sprague-Dawley (SD) rats and the underlying mechanisms. Rivlin and Tator's acute extradural clip compression injury (CCI) model of severe SCI was established in this study. Animals were divided into four groups: 1) sham group (laminectomy only); 2) model group, treated with normal saline; 3) PAR-2 inhibitor group; 4) PAR-2 activator group. Enhanced GFAP and vimentin expression were the markers of glial scar formation. To determine whether JNK was involved in the effects of PAR-2 on GFAP and vimentin expression, we administered anisomycin (a JNK activator) in the presence of PAR-2 inhibitor and SP600125 (a JNK inhibitor) in the presence of PAR-2 activator. At 1, 7, 14 and 28 day after SCI, Basso, Beattie, and Bresnahan (BBB) locomotor score test was used to assess the locomotor functional recovery; immunofluorescence and western blot analysis were used to assess the expression level of GFAP, vimentin and p-JNK. Double immunofluorescence staining with GFAP and tubulin beta was used to assess the glial scar formation and the remaining neurons. Results suggested that PAR-2 is involved in glial scar formation and reduces neurons residues which can cause a further worsening in the functional outcomes after SCI via JNK signaling. Therefore, it may be effective to target PAR-2 in the treatment of SCI.

A current view of G protein-coupled receptor - mediated signaling in pulmonary hypertension: finding opportunities for therapeutic intervention

Pathological vascular remodeling is observed in various cardiovascular diseases including pulmonary hypertension (PH), a disease of unknown etiology that has been characterized by pulmonary artery vasoconstriction, right ventricular hypertrophy, vascular inflammation, and abnormal angiogenesis in pulmonary circulation. G protein-coupled receptors (GPCRs) are the largest family in the genome and widely expressed in cardiovascular system. They regulate all aspects of PH pathophysiology and represent therapeutic targets. We overview GPCRs function in vasoconstriction, vasodilation, vascular inflammation-driven remodeling and describe signaling cross talk between GPCR, inflammatory cytokines, and growth factors. Overall, the goal of this review is to emphasize the importance of GPCRs as critical signal transducers and targets for drug development in PH.

Evidence for functional PAR-4 thrombin receptor expression in cardiac fibroblasts and its regulation by high glucose: PAR-4 in cardiac fibroblasts

BACKGROUND

Thrombin promotes cardiac fibroblast proliferation and fibrosis via protease-activated receptor (PAR-1). PAR-4 is reportedly absent in cardiac fibroblasts. In smooth muscle cells, PAR-4 expression is also low but increases upon hyperglycemia and contributes to vascular remodelling in diabetic mice. We examined if PAR-4 is a glucose-responsive gene with remodelling-related functions in cardiac fibroblasts.

METHODS AND RESULTS

Cardiac PAR-4 increased in mice with streptozotocin- or diabetogenic diet (DD)-induced diabetes. PAR-4 mRNA and protein were detectable in cardiac fibroblasts from chow-fed mice and increased in high (HG, 25mM) vs. low glucose (LG; 5.5mM) cultures. Conversely PAR-4 mRNA was higher in fibroblasts from DD-fed mice but reduced in LG cultures. Cardiac fibroblasts in HG culture responded more strongly to thrombin or PAR-4 activating peptide in terms of migration (wound-scratch assay), remodelling-associated gene expression (interleukin 6, alpha smooth muscle actin) and oxidative stress (dihydroethidium fluorescence).

CONCLUSION

PAR-4 is expressed in mouse cardiac fibroblasts and is dynamically regulated by extracellular glucose in vitro and diabetes in vivo, thereby impacting on fibroblast functions relevant for cardiac remodelling. These findings add further evidence for the usefulness of the recently developed PAR-4 antagonists in clinical settings.

Coagulation and non-coagulation effects of thrombin

Thrombin is a multifunctional serine protease produced from prothrombin, and is a key regulator in hemostatic and non-hemostatic processes. It is the main effector protease in primary hemostasis by activating platelets, and plays a key role in secondary hemostasis. Besides its well-known functions in hemostasis, thrombin also plays a role in various non-hemostatic biological and pathophysiologic processes, predominantly mediated through activation of protease-activated receptors (PARs). Depending on several factors, such as the concentration of thrombin, the duration of activation, the location of PARs, the presence of coreceptors, and the formation of PAR heterodimers, activation of the receptor by thrombin can induce different cellular responses. Moreover, thrombin can have opposing effects in the same cell; it can induce both inflammatory and anti-inflammatory signals. Owing to the complexity of thrombin's signal transduction pathways, the exact mechanism behind the dichotomy of thrombin is yet still unknown. In this review, we highlight the hemostatic and non-hemostatic functions of thrombin, and specifically focus on the non-hemostatic dual role of thrombin under various conditions and in relation to cardiovascular disease.

Upregulation of RGS2: a new mechanism for pirfenidone amelioration of pulmonary fibrosis

BACKGROUND

Pirfenidone was recently approved for treatment of idiopathic pulmonary fibrosis. However, the therapeutic dose of pirfenidone is very high, causing side effects that limit its doses and therapeutic effectiveness. Understanding the molecular mechanisms of action of pirfenidone could improve its safety and efficacy. Because activated fibroblasts are critical effector cells associated with the progression of fibrosis, this study investigated the genes that change expression rapidly in response to pirfenidone treatment of pulmonary fibroblasts and explored their contributions to the anti-fibrotic effects of pirfenidone.

METHODS

We used the GeneChip microarray to screen for genes that were rapidly up-regulated upon exposure of human lung fibroblast cells to pirfenidone, with confirmation for specific genes by real-time PCR and western blots. Biochemical and functional analyses were used to establish their anti-fibrotic effects in cellular and animal models of pulmonary fibrosis.

RESULTS

We identified Regulator of G-protein Signaling 2 (RGS2) as an early pirfenidone-induced gene. Treatment with pirfenidone significantly increased RGS2 mRNA and protein expression in both a human fetal lung fibroblast cell line and primary pulmonary fibroblasts isolated from patients without or with idiopathic pulmonary fibrosis. Pirfenidone treatment or direct overexpression of recombinant RGS2 in human lung fibroblasts inhibited the profibrotic effects of thrombin, whereas loss of RGS2 exacerbated bleomycin-induced pulmonary fibrosis and mortality in mice. Pirfenidone treatment reduced bleomycin-induced pulmonary fibrosis in wild-type but not RGS2 knockout mice.

CONCLUSIONS

Endogenous RGS2 exhibits anti-fibrotic functions. Upregulated RGS2 contributes significantly to the anti-fibrotic effects of pirfenidone.

Hypercoagulability causes atrial fibrosis and promotes atrial fibrillation

AIMS

Atrial fibrillation (AF) produces a hypercoagulable state. Stimulation of protease-activated receptors by coagulation factors provokes pro-fibrotic, pro-hypertrophic, and pro-inflammatory responses in a variety of tissues. We studied the effects of thrombin on atrial fibroblasts and tested the hypothesis that hypercoagulability contributes to the development of a substrate for AF.

METHODS AND RESULTS

In isolated rat atrial fibroblasts, thrombin enhanced the phosphorylation of the pro-fibrotic signalling molecules Akt and Erk and increased the expression of transforming growth factor β1 (2.7-fold) and the pro-inflammatory factor monocyte chemoattractant protein-1 (6.1-fold). Thrombin also increased the incorporation of ³H-proline, suggesting enhanced collagen synthesis by fibroblasts (2.5-fold). All effects could be attenuated by the thrombin inhibitor dabigatran. In transgenic mice with a pro-coagulant phenotype (TM^pro/pro), the inducibility of AF episodes lasting >1 s was higher (7 out of 12 vs. 1 out of 10 in wild type) and duration of AF episodes was longer compared with wild type mice (maximum episode duration 42.8 ± 68.4 vs. 0.23 ± 0.39 s). In six goats with persistent AF treated with nadroparin, targeting Factor Xa-mediated thrombin generation, the complexity of the AF substrate was less pronounced than in control animals (LA maximal activation time differences 23.3 ± 3.1 ms in control vs. 15.7 ± 2.1 ms in nadroparin, P < 0.05). In the treated animals, AF-induced α-smooth muscle actin expression was lower and endomysial fibrosis was less pronounced.

CONCLUSION

The hypercoagulable state during AF causes pro-fibrotic and pro-inflammatory responses in adult atrial fibroblasts. Hypercoagulability promotes the development of a substrate for AF in transgenic mice and in goats with persistent AF. In AF goats, nadroparin attenuates atrial fibrosis and the complexity of the AF substrate. Inhibition of coagulation may not only prevent strokes but also inhibit the development of a substrate for AF.

c-Src/Pyk2/EGFR/PI3K/Akt/CREB-activated pathway contributes to human cardiomyocyte hypertrophy: Role of COX-2 induction

Thrombin and COX-2 regulating cardiac hypertrophy are via various signaling cascades. Several transcriptional factors including CREB involve in COX-2 expression. However, the interplay among thrombin, CREB, and COX-2 in primary human neonatal ventricular cardiomyocytes remains unclear. In this study, thrombin-induced COX-2 promoter activity, mRNA and protein expression, and PGE2 synthesis were attenuated by pretreatment with the inhibitors of c-Src (PP1), Pyk2 (PF431396), EGFR (AG1478), PI3K/Akt (LY294002/SH-5), and p300 (GR343), or transfection with siRNAs of c-Src, Pyk2, EGFR, p110, Akt, CREB, and p300. Moreover, thrombin-stimulated phosphorylation of c-Src, Pyk2, EGFR, Akt, CREB and p300 was attenuated by their respective inhibitors. These results indicate that thrombin-induced COX-2 expression is mediated through PAR-1/c-Src/Pyk2/EGFR/PI3K/Akt linking to CREB and p300 cascades. Functionally, thrombin-induced hypertrophy and ANF/BNP release were, at least in part, mediated through a PAR-1/COX-2-dependent pathway. We uncover the importance of COX-2 regarding human cardiomyocyte hypertrophy that will provide a therapeutic intervention in cardiovascular diseases.

Coagulation and coagulation signalling in fibrosis

Following tissue injury, a complex and coordinated wound healing response comprising coagulation, inflammation, fibroproliferation and tissue remodelling has evolved to nullify the impact of the original insult and reinstate the normal physiological function of the affected organ. Tissue fibrosis is thought to result from a dysregulated wound healing response as a result of continual local injury or impaired control mechanisms. Although the initial insult is highly variable for different organs, in most cases, uncontrolled or sustained activation of mesenchymal cells into highly synthetic myofibroblasts leads to the excessive deposition of extracellular matrix proteins and eventually loss of tissue function. Coagulation was originally thought to be an acute and transient response to tissue injury, responsible primarily for promoting haemostasis by initiating the formation of fibrin plugs to enmesh activated platelets within the walls of damaged blood vessels. However, the last 20years has seen a major re-evaluation of the role of the coagulation cascade following tissue injury and there is now mounting evidence that coagulation plays a critical role in orchestrating subsequent inflammatory and fibroproliferative responses during normal wound healing, as well as in a range of pathological contexts across all major organ systems. This review summarises our current understanding of the role of coagulation and coagulation initiated signalling in the response to tissue injury, as well as the contribution of uncontrolled coagulation to fibrosis of the lung, liver, kidney and heart. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.

Aspirin suppresses cardiac fibroblast proliferation and collagen formation through downregulation of angiotensin type 1 receptor transcription

Aspirin (acetyl salicylic acid, ASA) is a common drug used for its analgesic and antipyretic effects. Recent studies show that ASA not only blocks cyclooxygenase, but also inhibits NADPH oxidase and resultant reactive oxygen species (ROS) generation, a pathway that underlies pathogenesis of several ailments, including hypertension and tissue remodeling after injury. In these disease states, angiotensin II (Ang II) activates NADPH oxidase via its type 1 receptor (AT1R) and leads to fibroblast growth and collagen synthesis. In this study, we examined if ASA would inhibit NADPH oxidase activation, upregulation of AT1R transcription, and subsequent collagen generation in mouse cardiac fibroblasts challenged with Ang II. Mouse heart fibroblasts were isolated and treated with Ang II with or without ASA. As expected, Ang II induced AT1R expression, and stimulated cardiac fibroblast growth and collagen synthesis. The AT1R blocker losartan attenuated these effects of Ang II. Similarly to losartan, ASA, and its SA moiety suppressed Ang II-mediated AT1R transcription and fibroblast proliferation as well as expression of collagens and MMPs. ASA also suppressed the expression of NADPH oxidase subunits (p22(phox), p47(phox), p67(phox), NOX2 and NOX4) and ROS generation. ASA did not affect total NF-κB p65, but inhibited its phosphorylation and activation. These observations suggest that ASA inhibits Ang II-induced NADPH oxidase expression, NF-κB activation and AT1R transcription in cardiac fibroblasts, and fibroblast proliferation and collagen expression. The critical role of NADPH oxidase activity in stimulation of AT1R transcription became apparent in experiments where ASA also inhibited AT1R transcription in cardiac fibroblasts challenged with H2O2. Since SA had similar effect as ASA on AT1R expression, we suggest that ASA's effect is mediated by its SA moiety.

Activation of protease activated receptor 1 increases the excitability of the dentate granule neurons of hippocampus

Protease activated receptor-1 (PAR1) is expressed in multiple cell types in the CNS, with the most prominent expression in glial cells. PAR1 activation enhances excitatory synaptic transmission secondary to the release of glutamate from astrocytes following activation of astrocytically-expressed PAR1. In addition, PAR1 activation exacerbates neuronal damage in multiple in vivo models of brain injury in a manner that is dependent on NMDA receptors. In the hippocampal formation, PAR1 mRNA appears to be expressed by a subset of neurons, including granule cells in the dentate gyrus. In this study we investigate the role of PAR activation in controlling neuronal excitability of dentate granule cells. We confirm that PAR1 protein is expressed in neurons of the dentate cell body layer as well as in astrocytes throughout the dentate. Activation of PAR1 receptors by the selective peptide agonist TFLLR increased the intracellular Ca²⁺ concentration in a subset of acutely dissociated dentate neurons as well as non-neuronal cells. Bath application of TFLLR in acute hippocampal slices depolarized the dentate gyrus, including the hilar region in wild type but not in the PAR1-/- mice. PAR1 activation increased the frequency of action potential generation in a subset of dentate granule neurons; cells in which PAR1 activation triggered action potentials showed a significant depolarization. The activation of PAR1 by thrombin increased the amplitude of NMDA receptor-mediated component of EPSPs. These data suggest that activation of PAR1 during normal function or pathological conditions, such as during ischemia or hemorrhage, can increase the excitability of dentate granule cells.

Protease-activated receptors and myocardial infarction

Protease-activated receptors (PARs) are widely expressed within the heart. They are activated by a myriad of proteases, including coagulation proteases. In vitro studies showed that activation of PAR-1 and PAR-2 on cardiomyocytes induced hypertrophy. In addition, PAR-1 stimulation on cardiac fibroblasts induced proliferation. Genetic and pharmacologic approaches have been used to investigate the role of the different PARs in cardiac ischemia/reperfusion (I/R) injury. In mice and rats, PAR-1 is reported to play a role in inflammation, infarct size, and remodeling after cardiac I/R injury. However, there are notable differences between the effect of a deficiency in PAR-1 and inhibition of PAR-1. For instance, inhibition of PAR-1 reduced infarct size whereas there was no effect of a deficiency of PAR-1. These differences maybe due to off-target effects of the inhibitor or PAR-4 compensation of PAR-1 deficiency. Similarly, a deficiency of PAR-2 was associated with reduced cardiac inflammation and improved heart function after I/R injury, whereas pharmacologic activation of PAR-2 was found to be protective due to increased vasodilatation. These differences maybe due to different signaling responses induced by an endogenous protease versus an exogenous agonist peptide. Surprisingly, PAR-4 deficiency resulted in increased cardiac injury and increased mortality after I/R injury. In contrast, a pharmacological study indicated that inhibition of PAR-4 was cardioprotective. It is possible that the major cellular target of the PAR-4 inhibitor is platelets, which have been shown to contribute to inflammation in the injured heart, whereas PAR-4 signaling in cardiomyocytes may be protective. These discrepant results between genetic and pharmacological approaches indicate that further studies are needed to determine the role of different PARs in the injured heart.

MMP-9 gene ablation and TIMP-4 mitigate PAR-1-mediated cardiomyocyte dysfunction: a plausible role of dicer and miRNA

Although matrix metalloproteinase-9 (MMP-9) is involved in cardiomyocytes contractility dysfunction, tissue inhibitor of metalloproteinase-4 (TIMP-4) mitigates the effect of MMP-9, and proteinase-activated receptor-1 (PAR-1, a G-protein couple receptor, GPCR) is involved in the signaling cascade of MMP-9-mediated cardiac dysfunction, the mechanism(s) are unclear. To test the hypothesis that induction of dicer and differential expression of microRNAs (miRNAs) contribute, in part, to the down regulation of sarcoplasmic reticulum calcium ATPase isoform 2a (serca-2a) in MMP-9 and PAR-1-mediated myocytes dysfunction, ventricular cardiomyocytes were isolated from C57BL/6J mice and treated with 3 ng/ml of MMP-9, 12 ng/ml of TIMP-4, and 10 and 100 microM of PAR-1 antagonist with MMP-9. Specific role of MMP-9 was determined by using MMP-9 knock out (MMP-9KO) and their corresponding control (FVB) mice. Ion Optics video-edge detection system and Fura 2-AM loading were used for determining the contractility and calcium release from cardiomyocytes. Quantitative and semi-quantitative PCR were used to determine the expression of dicer, TIMP-4 and serca-2a. miRNA microarrays were used for assessing the expression of different miRNAs between MMP-9KO and FVB cardiomyocytes. The results suggest that MMP-9 treatment attenuates the voltage-induced contraction of primary cardiomyocytes while TIMP-4, an inhibitor of MMP-9, reverses the inhibition. MMP-9 treatment is also associated with reduced Ca(2+) transients. This effect is blocked by a PAR-1 antagonist, suggesting that PAR-1 mediates this effect. The effect is not as great at high concentrations (100 microM) perhaps due to mild toxicity. The PAR-1 antagonist effect did not affect calcium transients unlike TIMP-4. Interestingly, we show that MMP-KO myocytes contract more rapidly and release more Ca(2+) than FVB. The relevant RNA species serca-2a is induced and dicer is inhibited. There is selective inhibition of miR-376b and over-expression of miR-1, miR-26a, miR-30d, and miR-181c in MMP-9KO that are implicated in regulation of G-PCR and calcium handling.