Plasminogen activator inhibitor-1 (PAI-1) is cardioprotective in mice by maintaining microvascular integrity and cardiac architecture

Cardiomyocyte PAI-1 influences the cardiac transcriptome and limits the extent of cardiac fibrosis in response to left ventricular pressure overload

Plasminogen activator inhibitor-1 (PAI-1) is a specific and rapid-acting inhibitor of endogenous plasminogen activators (uPA and tPA). The global PAI-1 knockout mice (PAI-1KO) develop age-dependent cardiac-selective fibrosis, and young global PAI-1KO mice exhibit augmented susceptibility to developing cardiac fibrosis in response to hypertension. Here, we tested the hypothesis that cardiomyocyte PAI-1 is necessary to provide cardioprotective effects in a left ventricular pressure overload-induced murine model of cardiac hypertrophy and fibrosis using cardiomyocyte-specific PAI-1 knockout (cmPAI-1KO) mice. The results revealed that cmPAI-1KO mice display significantly worse cardiac fibrosis than controls. To investigate the molecular mechanisms responsible for these effects, genome-wide cardiac transcriptome analysis was performed. Loss of cardiomyocyte PAI-1 led to differential expression of 978 genes compared to controls in response to left ventricular pressure overload. Pathway enrichment analysis identified the inflammatory response, cell substrate adhesion, regulation of cytokine production, leukocyte migration, extracellular matrix organization, and cytokine-mediated signaling pathways as being significantly upregulated in cmPAI-1KO hearts. Conversely, specific epigenetic repressors, cation transmembrane transport, muscle system processes, and nitric oxide signaling were significantly downregulated in cmPAI-1KO hearts compared to control hearts in response to left ventricular pressure overload. Collectively, the present study provides strong evidence of the impact of cardiomyocyte PAI-1 in regulation of the transcriptome network involved in the cardiac stress response. In response to stress, the deregulatory impact of cardiomyocyte PAI-1 loss on the cardiac transcriptome may be the underlying cause of cardiac-selective accelerated fibrogenesis in global PAI-1-deficient mice.

Eosinophils protect pressure overload- and β-adrenoreceptor agonist-induced cardiac hypertrophy

AIMS

Blood eosinophil (EOS) counts and EOS cationic protein (ECP) levels associate positively with major cardiovascular disease (CVD) risk factors and prevalence. This study investigates the role of EOS in cardiac hypertrophy.

METHODS AND RESULTS

A retrospective cross-section study of 644 consecutive inpatients with hypertension examined the association between blood EOS counts and cardiac hypertrophy. Pressure overload- and β-adrenoreceptor agonist isoproterenol-induced cardiac hypertrophy was produced in EOS-deficient ΔdblGATA mice. This study revealed positive correlations between blood EOS counts and left ventricular (LV) mass and mass index in humans. ΔdblGATA mice showed exacerbated cardiac hypertrophy and dysfunction, with increased LV wall thickness, reduced LV internal diameter, and increased myocardial cell size, death, and fibrosis. Repopulation of EOS from wild-type (WT) mice, but not those from IL4-deficient mice ameliorated cardiac hypertrophy and cardiac dysfunctions. In ΔdblGATA and WT mice, administration of ECP mEar1 improved cardiac hypertrophy and function. Mechanistic studies demonstrated that EOS expression of IL4, IL13, and mEar1 was essential to control mouse cardiomyocyte hypertrophy and death and cardiac fibroblast TGF-β signalling and fibrotic protein synthesis. The use of human cardiac cells yielded the same results. Human ECP, EOS-derived neurotoxin, human EOS, or murine recombinant mEar1 reduced human cardiomyocyte death and hypertrophy and human cardiac fibroblast TGF-β signalling.

CONCLUSION

Although blood EOS counts correlated positively with LV mass or LV mass index in humans, this study established a cardioprotective role for EOS IL4 and cationic proteins in cardiac hypertrophy and tested a therapeutic possibility of ECPs in this human CVD.

Lifetime Evaluation of Left Ventricular Structure and Function in Male C57BL/6J Mice after Gamma and Space-Type Radiation Exposure

The lifetime effects of space irradiation (IR) on left ventricular (LV) function are unknown. The cardiac effects induced by space-type IR, specifically 5-ion simplified galactic cosmic ray simulation (simGCRsim), are yet to be discovered. Three-month-old, age-matched, male C57BL/6J mice were irradiated with 137Cs gamma (γ; 100, 200 cGy) and simGCRsim (50 and 100 cGy). LV function was assessed via transthoracic echocardiography at 14 and 28 days (early), and at 365, 440, and 660 (late) days post IR. We measured the endothelial function marker brain natriuretic peptide in plasma at three late timepoints. We assessed the mRNA expression of the genes involved in cardiac remodeling, fibrosis, inflammation, and calcium handling in LVs harvested at 660 days post IR. All IR groups had impaired global LV systolic function at 14, 28, and 365 days. At 660 days, 50 cGy simGCRsim-IR mice exhibited preserved LV systolic function with altered LV size and mass. At this timepoint, the simGCRsim-IR mice had elevated levels of cardiac fibrosis, inflammation, and hypertrophy markers Tgfβ1, Mcp1, Mmp9, and βmhc, suggesting that space-type IR may induce the cardiac remodeling processes that are commonly associated with diastolic dysfunction. IR groups showing statistical significance were modeled to calculate the Relative Biological Effectiveness (RBE) and Radiation Effects Ratio (RER). The observed dose-response shape did not indicate a lower threshold at these IR doses. A single full-body IR at doses of 100-200 cGy for γ-IR, and 50-100 cGy for simGCRsim-IR decreases the global LV systolic function in WT mice as early as 14 and 28 days after exposure, and at 660 days post IR. Interestingly, there is an intermediate time point (365 days) where the impairment in LV function is observed. These findings do not exclude the possibility of increased acute or degenerative cardiovascular disease risks at lower doses of space-type IR, and/or when combined with other space travel-associated stressors such as microgravity.

PAI-1: A Major Player in the Vascular Dysfunction in Obstructive Sleep Apnea?

Obstructive sleep apnea is a chronic and prevalent condition that is associated with endothelial dysfunction, atherosclerosis, and imposes excess overall cardiovascular risk and mortality. Despite its high prevalence and the susceptibility of CVD patients to OSA-mediated stressors, OSA is still under-recognized and untreated in cardiovascular practice. Moreover, conventional OSA treatments have yielded either controversial or disappointing results in terms of protection against CVD, prompting the need for the identification of additional mechanisms and associated adjuvant therapies. Plasminogen activator inhibitor-1 (PAI-1), the primary inhibitor of tissue-type plasminogen activator (tPA) and urinary-type plasminogen activator (uPA), is a key regulator of fibrinolysis and cell migration. Indeed, elevated PAI-1 expression is associated with major cardiovascular adverse events that have been attributed to its antifibrinolytic activity. However, extensive evidence indicates that PAI-1 can induce endothelial dysfunction and atherosclerosis through complex interactions within the vasculature in an antifibrinolytic-independent matter. Elevated PAI-1 levels have been reported in OSA patients. However, the impact of PAI-1 on OSA-induced CVD has not been addressed to date. Here, we provide a comprehensive review on the mechanisms by which OSA and its most detrimental perturbation, intermittent hypoxia (IH), can enhance the transcription of PAI-1. We also propose causal pathways by which PAI-1 can promote atherosclerosis in OSA, thereby identifying PAI-1 as a potential therapeutic target in OSA-induced CVD.

Loureirin B Alleviates Myocardial Ischemia/Reperfusion Injury via Inhibiting PAI-1/TGF-β1/Smad Signaling Pathway

Myocardial ischemia/reperfusion (MI/R) injury is a common clinical problem after myocardial infarction without effective therapy. Loureirin B (LrB) is a kind of flavonoid with anti-inflammatory and antifibrotic activities. However, the effect of LrB on MI/R and its underlying mechanism remains elusive. In the present study, a mouse model of MI/R was established by coronary artery occlusion. Administration of LrB (0.5 mg/kg or 1 mg/kg) for 4 weeks effectively improved left ventricular (LV) function and reduced myocardial infarction in MI/R mice. MI/R-induced expression of IL-6, TNF-α, and IL-1β in the hearts was reduced by LrB treatment. Histological analysis showed that LrB attenuated myocardial collagen deposition. LrB downregulated fibronectin, collagen I, collagen III, and α-SMA expression. Notably, LrB inhibited the expression of profibrotic plasminogen activator inhibitor-1 (PAI-1), transforming growth factor (TGF)-β1, TGF-β1R, and p-Smad2/3. Consistently, LrB inhibited the activation of TGF-β1/Smad signaling pathway and the expression of fibrosis-related proteins in angiotensin (Ang) II-treated cardiac fibroblasts (CFs). Overexpression of PAI-1 abolished the effects of LrB on Ang II-treated CFs, suggesting that LrB may function through regulating PAI-1. These results indicated that LrB may alleviate MI/R-induced myocardial fibrosis by inhibiting PAI-1/TGF-β1/Smad signaling pathway. Thus, LrB may be a potential drug in the treatment of MI/R injury.

Thrombin in complex with dabigatran can still interact with PAR-1 via exosite-I and instigate loss of vascular integrity

BACKGROUND

Atrial fibrillation (AF) can lead to the loss of microvascular integrity thereby enhancing AF progression. Mechanistically, the pro-coagulant state that drives the risk of stroke in patients with AF may also play a causal role in microvascular loss. Direct oral anticoagulants (DOACs), the preferred anticoagulants for AF, can target factors upstream (factor Xa [FXa]) or downstream (thrombin) in the coagulation cascade and mediate differential vascular effects through interaction with protease-activated receptors (PARs).

OBJECTIVE

To investigate the potential effect of different DOACs on vascular integrity.

METHODS

To model the impact of DOACs on vascular integrity, we utilized platelet-free plasma in thrombin generation assays and endothelial barrier assays under identical experimental conditions. These multifactorial systems provide all coagulation factors and their respective natural inhibitors in physiological ratios in combination with the pro-coagulant endothelial surface on which coagulation is initiated. Furthermore, the system provides pro- and anti-barrier factors and monitoring both assays simultaneously permits coupling of thrombin kinetics to endothelial barrier dynamics.

RESULTS

We provide evidence that the anti-FXa DOAC rivaroxaban and the anti-thrombin DOAC dabigatran are efficient in blocking their target proteases. However, while rivaroxaban could preserve endothelial barrier function, dabigatran failed to protect endothelial integrity over time, which could be prevented in the presence of a custom-made peptide that blocks thrombin's exosite-I.

CONCLUSIONS

Proteolytically inactive thrombin in complex with dabigatran evokes loss of barrier function that can be prevented by a protease-activated receptor-1 mimicking peptide blocking thrombin's exosite-I.

Interconnections between Inflammageing and Immunosenescence during Ageing

Acute inflammation is a physiological response to injury or infection, with a cascade of steps that ultimately lead to the recruitment of immune cells to clear invading pathogens and heal wounds. However, chronic inflammation arising from the continued presence of the initial trigger, or the dysfunction of signalling and/or effector pathways, is harmful to health. While successful ageing in older adults, including centenarians, is associated with low levels of inflammation, elevated inflammation increases the risk of poor health and death. Hence inflammation has been described as one of seven pillars of ageing. Age-associated sterile, chronic, and low-grade inflammation is commonly termed inflammageing-it is not simply a consequence of increasing chronological age, but is also a marker of biological ageing, multimorbidity, and mortality risk. While inflammageing was initially thought to be caused by "continuous antigenic load and stress", reports from the last two decades describe a much more complex phenomenon also involving cellular senescence and the ageing of the immune system. In this review, we explore some of the main sources and consequences of inflammageing in the context of immunosenescence and highlight potential interventions. In particular, we assess the contribution of cellular senescence to age-associated inflammation, identify patterns of pro- and anti-inflammatory markers characteristic of inflammageing, describe alterations in the ageing immune system that lead to elevated inflammation, and finally assess the ways that diet, exercise, and pharmacological interventions can reduce inflammageing and thus, improve later life health.

Identification of Cardiac Fibrosis in Young Adults With a Homozygous Frameshift Variant in SERPINE1

Importance

Cardiac fibrosis is exceedingly rare in young adults. Identification of genetic variants that cause early-onset cardiomyopathy may inform novel biological pathways. Experimental models and a single case report have linked genetic deficiency of plasminogen activator inhibitor-1 (PAI-1), a downstream target of cardiac transforming growth factor β, with cardiac fibrosis.

Objective

To perform detailed cardiovascular phenotyping and genotyping in young adults from an Amish family with a frameshift variant (c.699_700dupTA) in SERPINE1, the gene that codes for PAI-1.

Design, Setting, and Participants

This observational study included participants from 3 related nuclear families from an Amish community in the primary analysis and participants from the extended family in the secondary analysis. Participants were recruited from May 2015 to December 2016, and analysis took place from June 2015 to June 2020.

Main Outcomes and Measures

(1) Multimodality cardiovascular imaging (transthoracic echocardiography and cardiac magnetic resonance imaging), (2) whole-exome sequencing, and (3) induced pluripotent stem cell-derived cardiomyocytes.

Results

Among 17 participants included in the primary analysis, the mean (interquartile range) age was 23.7 (20.9-29.9) years and 9 individuals (52.9%) were confirmed to be homozygous for the SERPINE1 c.699_700dupTA variant. Late gadolinium enhancement was present in 6 of 9 homozygous participants (67%) with absolute PAI-1 deficiency vs 0 of 8 in the control group (P = .001). Late gadolinium enhancement patterns tended to be dense and linear, usually subepicardial but also midmyocardial and transmural with noncoronary distributions. Targeted whole-exome sequencing analysis identified that homozygosity for c.699_700dupTA SERPINE1 was the only shared pathogenic variant or variant of uncertain significance after examination of cardiomyopathy genes among those with late gadolinium enhancement. Induced pluripotent stem cell-derived cardiomyocytes from participants homozygous for the SERPINE1 c.699_700dupTA variant exhibited susceptibility to cardiomyocyte injury in response to angiotensin II (increased transforming growth factor β1 secretion and release of lactate dehydrogenase) compared with control induced pluripotent stem cell-derived cardiomyocytes. In a secondary analysis based on echocardiography in 155 individuals across 3 generations in the extended family, no difference in global longitudinal strain was observed in carriers for the SERPINE1 c.699_700dupTA variant compared with wild-type participants, supporting an autosomal recessive inheritance pattern.

Conclusions and Relevance

In this study, a highly penetrant, autosomal recessive, cardiac fibrosis phenotype among young adults with homozygous frameshift variant for SERPINE1 was identified, suggesting an optimal range of PAI-1 levels are needed for cardiac homeostasis.

A Narrative Review on Plasminogen Activator Inhibitor-1 and Its (Patho)Physiological Role: To Target or Not to Target?

Plasminogen activator inhibitor-1 (PAI-1) is the main physiological inhibitor of plasminogen activators (PAs) and is therefore an important inhibitor of the plasminogen/plasmin system. Being the fast-acting inhibitor of tissue-type PA (tPA), PAI-1 primarily attenuates fibrinolysis. Through inhibition of urokinase-type PA (uPA) and interaction with biological ligands such as vitronectin and cell-surface receptors, the function of PAI-1 extends to pericellular proteolysis, tissue remodeling and other processes including cell migration. This review aims at providing a general overview of the properties of PAI-1 and the role it plays in many biological processes and touches upon the possible use of PAI-1 inhibitors as therapeutics.

Plasminogen activator inhibitor-1 reduces cardiac fibrosis and promotes M2 macrophage polarization in inflammatory cardiomyopathy

Plasminogen activator inhibitor-1 (PAI-1) has a cardioprotective function in mice by repressing cardiac fibrosis through TGF-β and plasminogen-mediated pathways. In addition it is known to be involved in the recruitment and polarization of monocytes/macrophages towards a M2 phenotype in cancer. Here, we investigated the expression of PAI-1 in human dilated cardiomyopathy (DCM) and inflammatory dilated cardiomyopathy (DCMi) and its effect on cardiac fibrosis and macrophage polarization. We retrospectively analyzed endomyocardial biopsies (EMBs) of patients with DCM or DCMi for PAI-1 expression by immunohistochemistry. Furthermore, EMBs were evaluated for the content of fibrotic tissue, number of activated myofibroblasts, TGF-β expression, as well as for M1 and M2 macrophages. Patients with high-grade DCMi (DCMi-high, CD3⁺ lymphocytes > 30 cells/mm²) had significantly increased PAI-1 levels compared to DCM and low-grade DCMi patients (DCMi-low, CD3⁺ lymphocytes = 14-30 cells/mm²) (15.5 ± 0.4% vs. 1.0 ± 0.1% and 4.0 ± 0.1%, p ≤ 0.001). Elevated PAI-1 expression in DCMi-high subjects was associated with a diminished degree of cardiac fibrosis, decreased levels of TGF-β and reduced number of myofibroblasts. In addition, DCMi-high patients revealed an increased proportion of non-classical M2 macrophages towards classical M1 macrophages, indicating M2 macrophage-favoring properties of PAI-1 in inflammatory cardiomyopathies. Our findings give evidence that elevated expression of cardiac PAI-1 in subjects with high-grade DCMi suppresses fibrosis by inhibiting TGF-β and myofibroblast activation. Moreover, our data indicate that PAI-1 is involved in the polarization of M2 macrophages in the heart. Thus, PAI-1 could serve as a potential prognostic biomarker and as a possible therapeutic target in inflammatory cardiomyopathies.

Disruption of Abcc6 Transporter in Zebrafish Causes Ocular Calcification and Cardiac Fibrosis

Pseudoxanthoma elasticum (PXE), caused by ABCC6/MRP6 mutation, is a heritable multisystem disorder in humans. The progressive clinical manifestations of PXE are accompanied by ectopic mineralization in various connective tissues. However, the pathomechanisms underlying the PXE multisystem disorder remains obscure, and effective treatment is currently available. In this study, we generated zebrafish abcc6a mutants using the transcription activator-like effector nuclease (TALEN) technique. In young adult zebrafish, abcc6a is expressed in the eyes, heart, intestine, and other tissues. abcc6a mutants exhibit extensive calcification in the ocular sclera and Bruch's membrane, recapitulating part of the PXE manifestations. Mutations in abcc6a upregulate extracellular matrix (ECM) genes, leading to fibrotic heart with reduced cardiomyocyte number. We found that abcc6a mutation reduced levels of both vitamin K and pyrophosphate (PPi) in the serum and diverse tissues. Vitamin K administration increased the gamma-glutamyl carboxylated form of matrix gla protein (cMGP), alleviating ectopic calcification and fibrosis in vertebrae, eyes, and hearts. Our findings contribute to a comprehensive understanding of PXE pathophysiology from zebrafish models.

Transplantation of adipose tissue lacking PAI-1 improves glucose tolerance and attenuates cardiac metabolic abnormalities in high-fat diet-induced obesity

Adipose tissue is an important metabolic organ, and transplantation of white adipose tissue plays crucial roles in glucose homoeostasis and energy metabolism. However, how adipose tissue affects glucose utilization is poorly understood. PAI-1-knockout (PAI-1KO) mice were previously shown to be resistant to a high-fat diet and obesity. We used microPET/CT (positron emission tomography/computed tomography), gene microarray, and biochemical assays to measure changes in systemic and myocardial glucose metabolism in mice subjected to transplantation of adipose tissue from PAI-1KO and wild-type mice. Here, we show that transplanting subcutaneous white adipose tissue (scWAT) from PAI-1KO mice into high-fat diet (HFD)-fed mice reduced levels of serum total cholesterol and triglycerides, and improved glucose tolerance in the HFD-fed mice. microPET/CT imaging revealed that cardiac glucose uptake was increased in the heart but not in the liver, hindlimb muscles, or abdominal subcutaneous white adipose tissue in HFD-fed mice transplanted with PAI-1KO scWAT, suggesting that the transplanted PAI-1KO scWAT exerted endocrine effects in the heart. In addition, transplantation of scWAT from PAI-1KO mice upregulated mitochondrial gene expression in cardiac muscle, increased the expression of glucose transporters 1 and 4 in cardiac tissues and was associated with an increased NAD⁺/NADH ratio. Together, these findings suggest that modulating PAI-1 in scWAT may provide a promising approach for intervening in glucose metabolism.

Myeloperoxidase instigates proinflammatory responses in a cecal ligation and puncture rat model of sepsis

Myeloperoxidase (MPO)-derived hypochlorous (HOCl) reacts with membrane plasmalogens to yield α-chlorofatty aldehydes such as 2-chlorofatty aldehyde (2-ClFALD) and its metabolite 2-chlorofatty acid (2-ClFA). Recent studies showed that 2-ClFALD and 2-ClFA serve as mediators of the inflammatory responses to sepsis by as yet unknown mechanisms. Since no scavenger for chlorinated lipids is available and on the basis of the well-established role of the MPO/HOCl/chlorinated lipid axis in inflammatory responses, we hypothesized that treatment with MPO inhibitors (N-acetyl lysyltyrosylcysteine amide or 4-aminobenzoic acid hydrazide) would inhibit inflammation and proinflammatory mediator expression induced by cecal ligation and puncture (CLP). We used intravital microscopy to quantify in vivo inflammatory responses in Sham and CLP rats with or without MPO inhibition. Small intestines, mesenteries, and lungs were collected to assess changes in MPO-positive staining and lung injury, respectively, as well as free 2-ClFA and proinflammatory mediators levels. CLP caused neutrophil infiltration, 2-ClFA generation, acute lung injury, leukocyte-/platelet-endothelium interactions, mast cell activation (MCA), plasminogen activator inhibitor-1 (PAI-1) production, and the expression of several cytokines, chemokines, and vascular endothelial growth factor, changes that were reduced by MPO inhibition. Pretreatment with a PAI-1 inhibitor or MC stabilizer prevented CLP-induced leukocyte-endothelium interactions and MCA, and abrogated exogenous 2-ClFALD-induced inflammatory responses. Thus, we provide evidence that MPO instigates these inflammatory changes in CLP and that chlorinated lipids may serve as a mechanistic link between the enzymatic activity of MPO and PAI-1- and mast cell-dependent adhesive interactions, providing a rationale for new therapeutic interventions in sepsis.NEW & NOTEWORTHY Using two distinct myeloperoxidase (MPO) inhibitors, we show for the first time that MPO plays an important role in producing increases in free 2-chlorofatty aldehyde (2-ClFALD)-a powerful proinflammatory chlorinated lipid in plasma and intestine-a number of cytokines and other inflammatory mediators, leukocyte and platelet rolling and adhesion in postcapillary venules, and lung injury in a cecal ligation and puncture model of sepsis. In addition, the use of a plasminogen activator inhibitor-1 (PAI-1) inhibitor or a mast cell stabilizer prevented inflammatory responses in CLP-induced sepsis. PAI-1 inhibition also prevented the proinflammatory responses to exogenous 2-ClFALD superfusion. Thus, our study provides some of the first evidence that MPO-derived free 2-ClFA plays an important role in CLP-induced sepsis by a PAI-1- and mast cell-dependent mechanism.

Drospirenone-containing contraceptive exerts positive effects on cardiac uric acid and PAI-1 but not GSK-3: Improved safety profiles in contraception?

The use of combined oral contraceptives (COC) have been associated with increased risk of adverse cardiovascular events and elevated cardiac and circulating plasminogen activator inhibitor-1 (PAI-1) and glycogen synthase kinase-3 (GSK-3) have been implicated in these events. Contraceptives containing drospirenone, a progestin with anti-androgenic actions may have a positive or neutral effect on cardiac PAI-1 and GSK-3 levels. Studies on the favorable effects of oral contraceptives containing drospirenone when compared with other androgenic contraceptives have not been fully elucidated. We therefore sought to compare the effect of a contraceptive containing ethinyl estradiol and drospirenone (DSP) with a contraceptive containing ethinyl estradiol and levonorgestrel (LVG) on cardiac uric acid (UA), PAI-1, GSK-3 and some hematological parameters. Ten weeks old female Wistar rats were divided into three groups; control (CON), LVG or DSP treated rats. The treatment lasted for 8 weeks. Results showed that LVG and not DSP treatment led to increase in plasma and cardiac tissue UA, plasma and cardiac PAI-1 as well as granulocyte-lymphocyte ratio (GLR) and platelet-lymphocyte ratio (PLR). However, the DSP treatment affected the circulating GSK-3. Taken together, the findings showed that LVG and not DSP affected cardiac UA and PAI-1. These results suggest that COC containing drospirenone appears to have positive effects on cardiac UA and PAI-1 levels but do not affect GSK-3, hence, COC containing drospirenone may be a better and safer means of contraception compared to androgenic contraceptives.

Platelets inhibit apoptotic lung epithelial cell death and protect mice against infection-induced lung injury

Thrombocytopenia is associated with worse outcomes in patients with acute respiratory distress syndrome, which is most commonly caused by infection and marked by alveolar-capillary barrier disruption. However, the mechanisms by which platelets protect the lung alveolar-capillary barrier during infectious injury remain unclear. We found that natively thrombocytopenic Mpl ^-/- mice deficient in the thrombopoietin receptor sustain severe lung injury marked by alveolar barrier disruption and hemorrhagic pneumonia with early mortality following acute intrapulmonary Pseudomonas aeruginosa (PA) infection; barrier disruption was attenuated by platelet reconstitution. Although PA infection was associated with a brisk neutrophil influx, depletion of airspace neutrophils failed to substantially mitigate PA-triggered alveolar barrier disruption in Mpl ^-/- mice. Rather, PA cell-free supernatant was sufficient to induce lung epithelial cell apoptosis in vitro and in vivo and alveolar barrier disruption in both platelet-depleted mice and Mpl ^-/- mice in vivo. Cell-free supernatant from PA with genetic deletion of the type 2 secretion system, but not the type 3 secretion system, mitigated lung epithelial cell death in vitro and lung injury in Mpl ^-/- mice. Moreover, platelet releasates reduced poly (ADP ribose) polymerase cleavage and lung injury in Mpl ^-/- mice, and boiling of platelet releasates, but not apyrase treatment, abrogated PA supernatant-induced lung epithelial cell cytotoxicity in vitro. These findings indicate that while neutrophil airspace influx does not potentiate infectious lung injury in the thrombocytopenic host, platelets and their factors protect against severe pulmonary complications from pathogen-secreted virulence factors that promote host cell death even in the absence of overt infection.

Plasminogen Activator Inhibitor-1 Promotes Neutrophil Infiltration and Tissue Injury on Ischemia-Reperfusion

OBJECTIVE

Ischemia-reperfusion (I/R) injury significantly contributes to organ dysfunction and failure after myocardial infarction, stroke, and transplantation. In addition to its established role in the fibrinolytic system, plasminogen activator inhibitor-1 has recently been implicated in the pathogenesis of I/R injury. The underlying mechanisms remain largely obscure.

APPROACH AND RESULTS

Using different in vivo microscopy techniques as well as ex vivo analyses and in vitro assays, we identified that plasminogen activator inhibitor-1 rapidly accumulates on microvascular endothelial cells on I/R enabling this protease inhibitor to exhibit previously unrecognized functional properties by inducing an increase in the affinity of β2 integrins in intravascularly rolling neutrophils. These events are mediated through low-density lipoprotein receptor-related protein-1 and mitogen-activated protein kinase-dependent signaling pathways that initiate intravascular adherence of these immune cells to the microvascular endothelium. Subsequent to this process, extravasating neutrophils disrupt endothelial junctions and promote the postischemic microvascular leakage. Conversely, deficiency of plasminogen activator inhibitor-1 effectively reversed leukocyte infiltration, microvascular dysfunction, and tissue injury on experimental I/R without exhibiting side effects on microvascular hemostasis.

CONCLUSIONS

Our experimental data provide novel insights into the nonfibrinolytic properties of the fibrinolytic system and emphasize plasminogen activator inhibitor-1 as a promising target for the prevention and treatment of I/R injury.

Statins Promote Cardiac Infarct Healing by Modulating Endothelial Barrier Function Revealed by Contrast-Enhanced Magnetic Resonance Imaging

OBJECTIVE

The endothelium has a crucial role in wound healing, acting as a barrier to control transit of leukocytes. Endothelial barrier function is impaired in atherosclerosis preceding myocardial infarction (MI). Besides lowering lipids, statins modulate endothelial function. Here, we noninvasively tested whether statins affect permeability at the inflammatory (day 3) and the reparative (day 7) phase of infarct healing post-MI using contrast-enhanced cardiac magnetic resonance imaging (MRI).

APPROACH AND RESULTS

Noninvasive permeability mapping by MRI after MI in C57BL/6, atherosclerotic ApoE^-/-, and statin-treated ApoE^-/- mice was correlated to subsequent left ventricular outcome by structural and functional cardiac MRI. Ex vivo histology, flow cytometry, and quantitative polymerase chain reaction were performed on infarct regions. Increased vascular permeability at ApoE^-/- infarcts was observed compared with C57BL/6 infarcts, predicting enhanced left ventricular dilation at day 21 post-MI by MRI volumetry. Statin treatment improved vascular barrier function at ApoE^-/- infarcts, indicated by reduced permeability. The infarcted tissue of ApoE^-/- mice 3 days post-MI displayed an unbalanced Vegfa(vascular endothelial growth factor A)/Angpt1 (angiopoetin-1) expression ratio (explaining leakage-prone vessels), associated with higher amounts of CD45⁺ leukocytes and inflammatory LY6C^hi monocytes. Statins reversed the unbalanced Vegfa/Angpt1 expression, normalizing endothelial barrier function at the infarct and blocking the augmented recruitment of inflammatory leukocytes in statin-treated ApoE^-/- mice.

CONCLUSIONS

Statins lowered permeability and reduced the transit of unfavorable inflammatory leukocytes into the infarcted tissue, consequently improving left ventricular outcome.

Mechanisms of plasminogen activator inhibitor 1 action in stromal remodeling and related diseases

Plasminogen activator inhibitor type 1 (PAI-1) is the main physiologic inhibitor of fibrinolysis. However, it is also involved in many physiological processes such as extracellular matrix (ECM) proteolysis and remodeling, cell adhesion, motility, and apoptosis, angiogenesis, etc. The aim of the study was to summarize current knowledge and gain insights into the mechanisms of PAI-1 action in the processes of stromal remodeling and diseases with considerable matrix pathologies (atherosclerosis, tissue fibrosis, cancer metastasis, pregnancy related complications, etc). As a component of an early cellular response to injury, PAI-1 reacts with membrane surface proteins and participates in the initiation of intracellular signaling, specifically cytoskeletal reorganization and motility. Complexity of ECM homeostasis resides in varying relation of the plasminogen system components and other matrix constituents. Inflammatory mediators (transforming growth factor-β and interferon-γ) and hormones (angiotensin II) are in the close interdependent relation with PAI-1. Also, special attention is devoted to the role of increased PAI-1 concentrations due to the common 4G/5G polymorphism. Some of the novel mechanisms of ECM modification consider PAI-1 dependent stabilization of urokinase mediated cell adhesion, control of the vascular endothelial cadherin trafficking and interaction with endothelial cells proteasome, its relation to matrix metalloproteinase 2 and osteopontin, and oxidative inhibition by myeloperoxidase. Targeting and/or alteration of PAI-1 functions might bring benefit to the future therapeutic approaches in diseases where ECM undergoes substantial remodeling.

Plasminogen Activator Inhibitor Type-1 as a Regulator of Fibrosis

Fibrosis is known as a frequent and irreversible pathological condition which is associated with organ failure. Tissue fibrosis is a central process in a variety of chronic progressive diseases such as diabetes, hypertension, and persistent inflammation. This state could contribute to chronic injury and the initiation of tissue repair. Fibrotic disorders represent abnormal wound healing with defective matrix turnover and clearance that lead to excessive accumulation of extracellular matrix components. A variety of identified growth factors, cytokines, and persistently activated myofibroblasts have critical roles in the pathogenesis of fibrosis. Irrespective of etiology, the transforming growth factor-β pathway is the major driver of fibrotic response. Plasminogen activator inhibitor-1 (PAI-1) is a crucial downstream target of this pathway. Transforming growth factor-β positively regulates PAI-1 gene expression via two main pathways including Smad-mediated canonical and non-canonical pathways. Overexpression of PAI-1 reduces extracellular matrix degradation via perturbing the plasminogen activation system. Indeed, elevated PAI-1 levels inhibit proteolytic activity of tissue plasminogen activator and urokinase plasminogen activator which could contribute to a variety of inflammatory elements in the injury site and to excessive matrix deposition. This review summarizes the current knowledge of critical pathways that regulate PAI-1 gene expression and suggests effective approaches for the treatment of fibrotic disease. J. Cell. Biochem. 119: 17-27, 2018. © 2017 Wiley Periodicals, Inc.

Plasminogen Activator Inhibitor Type I Controls Cardiomyocyte Transforming Growth Factor-β and Cardiac Fibrosis

BACKGROUND

Fibrosis is the pathological consequence of stress-induced tissue remodeling and matrix accumulation. Increased levels of plasminogen activator inhibitor type I (PAI-1) have been shown to promote fibrosis in multiple organ systems. Paradoxically, homozygous genetic deficiency of PAI-1 is associated with spontaneous age-dependent, cardiac-selective fibrosis in mice. We have identified a novel PAI-1-dependent mechanism that regulates cardiomyocyte-derived fibrogenic signals and cardiac transcriptional pathways during injury.

METHODS

Cardiac fibrosis in subjects with homozygous mutation in SERPINE-1 was evaluated with late gadolinium-enhanced cardiac magnetic resonance imaging. A murine cardiac injury model was performed by subcutaneous infusion of either saline or Angiotensin II by osmotic minipumps. We evaluated blood pressure, cardiac function (by echocardiography), fibrosis (with Masson Trichrome staining), and apoptosis (with TUNEL staining), and we performed transcriptome analysis (with RNA sequencing). We further evaluated fibrotic signaling in isolated murine primary ventricular myocytes.

RESULTS

Cardiac fibrosis was detected in 2 otherwise healthy humans with complete PAI-1 deficiency because of a homozygous frameshift mutation in SERPINE-1. In addition to its suppressive role during spontaneous cardiac fibrosis in multiple species, we hypothesized that PAI-1 also regulates fibrosis during cardiac injury. Treatment of young PAI-1^-/- mice with Angiotensin II induced extensive hypertrophy and fibrotic cardiomyopathy, with increased cardiac apoptosis and both reactive and replacement fibrosis. Although Angiotensin II-induced hypertension was blunted in PAI-1^-/- mice, cardiac hypertrophy was accelerated. Furthermore, ventricular myocytes were found to be an important source of cardiac transforming growth factor-β (TGF-β) and PAI-1 regulated TGF-β synthesis by cardiomyocytes in vitro as well as in vivo during cardiac injury. Transcriptome analysis of ventricular RNA after Angiotensin II treatment confirmed that PAI-1 deficiency significantly enhanced multiple TGF-β signaling elements and transcriptional targets, including genes for extracellular matrix components, mediators of extracellular matrix remodeling, matricellular proteins, and cardiac integrins compared with wild-type mice.

CONCLUSIONS

PAI-1 is an essential repressor of cardiac fibrosis in mammals. We define a novel cardiomyocyte-specific regulatory mechanism for TGF-β production by PAI-1, which explains the paradoxical effect of PAI-1 deficiency in promoting cardiac-selective fibrosis. Thus, PAI-1 is a molecular switch that controls the cardiac TGF-β axis and its early transcriptional effects that lead to myocardial fibrosis.

Plasminogen Activator Inhibitor-1 Protects Mice Against Cardiac Fibrosis by Inhibiting Urokinase-type Plasminogen Activator-mediated Plasminogen Activation

Plasminogen activator inhibitor-1 (PAI-1) is known to protect mice against cardiac fibrosis. It has been speculated that PAI-1 may regulate cardiac fibrosis by inactivating urokinase-type plasminogen activator (uPA) and ultimately plasmin (Pm) generation. However, the in vivo role of PAI-1 in inactivating uPA and limiting the generation of Pm during cardiac fibrosis remains to be established. The objective of this study was to determine if the cardioprotective effect of PAI-1 is mediated through its ability to directly regulate urokinase -mediated activation of plasminogen (Pg). An Angiotensin II (AngII)-aldosterone (Ald) infusion mouse model of hypertension was utilised in this study. Four weeks after AngII-Ald infusion, PAI-1-deficient (PAI-1^-/-) mice developed severe cardiac fibrosis. However, a marked reduction in cardiac fibrosis was observed in PAI-1^-/-/uPA^-/- double knockout mice that was associated with reduced inflammation, lower expression levels of TGF-β and proteases associated with tissue remodeling, and diminished Smad2 signaling. Moreover, total ablation of cardiac fibrosis was observed in PAI-1^-/- mice that express inactive plasmin (Pm) but normal levels of zymogen Pg (PAI-1^-/-/Pg^S743A/S743A). Our findings indicate that PAI-1 protects mice from hypertension-induced cardiac fibrosis by inhibiting the generation of active Pm.

Overlapping and Divergent Actions of Structurally Distinct Histone Deacetylase Inhibitors in Cardiac Fibroblasts

Inhibitors of zinc-dependent histone deacetylases (HDACs) profoundly affect cellular function by altering gene expression via changes in nucleosomal histone tail acetylation. Historically, investigators have employed pan-HDAC inhibitors, such as the hydroxamate trichostatin A (TSA), which simultaneously targets members of each of the three zinc-dependent HDAC classes (classes I, II, and IV). More recently, class- and isoform-selective HDAC inhibitors have been developed, providing invaluable chemical biology probes for dissecting the roles of distinct HDACs in the control of various physiologic and pathophysiological processes. For example, the benzamide class I HDAC-selective inhibitor, MGCD0103 [N-(2-aminophenyl)-4-[[(4-pyridin-3-ylpyrimidin-2-yl)amino]methyl] benzamide], was shown to block cardiac fibrosis, a process involving excess extracellular matrix deposition, which often results in heart dysfunction. Here, we compare the mechanisms of action of structurally distinct HDAC inhibitors in isolated primary cardiac fibroblasts, which are the major extracellular matrix-producing cells of the heart. TSA, MGCD0103, and the cyclic peptide class I HDAC inhibitor, apicidin, exhibited a common ability to enhance histone acetylation, and all potently blocked cardiac fibroblast cell cycle progression. In contrast, MGCD0103, but not TSA or apicidin, paradoxically increased expression of a subset of fibrosis-associated genes. Using the cellular thermal shift assay, we provide evidence that the divergent effects of HDAC inhibitors on cardiac fibroblast gene expression relate to differential engagement of HDAC1- and HDAC2-containing complexes. These findings illustrate the importance of employing multiple compounds when pharmacologically assessing HDAC function in a cellular context and during HDAC inhibitor drug development.

The Transcription Profile Unveils the Cardioprotective Effect of Aspalathin against Lipid Toxicity in an In Vitro H9c2 Model

Aspalathin, a C-glucosyl dihydrochalcone, has previously been shown to protect cardiomyocytes against hyperglycemia-induced shifts in substrate preference and subsequent apoptosis. However, the precise gene regulatory network remains to be elucidated. To unravel the mechanism and provide insight into this supposition, the direct effect of aspalathin in an isolated cell-based system, without the influence of any variables, was tested using an H9c2 cardiomyocyte model. Cardiomyocytes were exposed to high glucose (33 mM) for 48 h before post-treatment with or without aspalathin. Thereafter, RNA was extracted and RT2 PCR Profiler Arrays were used to profile the expression of 336 genes. Results showed that, 57 genes were differentially regulated in the high glucose or high glucose and aspalathin treated groups. Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) analysis revealed lipid metabolism and molecular transport as the biological processes altered after high glucose treatment, followed by inflammation and apoptosis. Aspalathin was able to modulate key regulators associated with lipid metabolism (Adipoq, Apob, CD36, Cpt1, Pparγ, Srebf1/2, Scd1 and Vldlr), insulin resistance (Igf1, Akt1, Pde3 and Map2k1), inflammation (Il3, Il6, Jak2, Lepr, Socs3, and Tnf13) and apoptosis (Bcl2 and Chuk). Collectively, our results suggest that aspalathin could reverse metabolic abnormalities by activating Adipoq while modulating the expression of Pparγ and Srebf1/2, decreasing inflammation via Il6/Jak2 pathway, which together with an observed increased expression of Bcl2 prevents myocardium apoptosis.

Identification of nondiabetic heart failure-associated genes by bioinformatics approaches in patients with dilated ischemic cardiomyopathy

Heart failure (HF) is a common pathological condition affecting 4% of the worldwide population. However, approaches for predicting or treating nondiabetic HF (ND-HF) progression are insufficient. In the current study, the gene expression profile GSE26887 was analyzed, which contained samples from 5 healthy controls, 7 diabetes mellitus-HF patients and 12 ND-HF patients with dilated ischemic cardiomyopathy. The dataset of 5 healthy controls and 12 ND-HF patients was normalized with robust multichip average analysis and the differentially expressed genes (DEGs) were screened by unequal variance t-test and multiple-testing correction. In addition, the protein-protein interaction (PPI) network of the upregulated and downregulated genes was constructed using the Search Tool for the Retrieval of Interacting Genes/Proteins database and the Cytoscape software platform. Subsequently, gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were performed. A total of 122 upregulated and 133 downregulated genes were detected. The most significantly up- and downregulated genes were EIF1AY and SERPINE1, respectively. In addition, 38 and 77 nodes were obtained in the up- and downregulated PPI network. DEGs that owned the highest connectivity degree were USP9Y and UTY in the upregulated network, and CD44 in the downregulated networks, respectively. NPPA and SERPINE1 were also found to be hub genes in the PPI network. Several GO terms and pathways that were enriched by DEGs were identified, and the most significantly enriched KEGG pathways were drug metabolism and extracellular matrix-receptor interaction. In conclusion, the two DEGs, NPPA and SERPINE1, may be important in the pathogenesis of HF and may be used for the diagnosis and treatment of HF.

Systems Chemo-Biology and Transcriptomic Meta-Analysis Reveal the Molecular Roles of Bioactive Lipids in Cardiomyocyte Differentiation

Lipids, which are essential constituents of biological membranes, play structural and functional roles in the cell. In recent years, certain lipids have been identified as regulatory signaling molecules and have been termed "bioactive lipids". Subsequently, the importance of bioactive lipids in stem cell differentiation and cardiogenesis has gained increasing recognition. Therefore, the aim of this study was to identify the biological processes underlying murine cardiac differentiation and the mechanisms by which bioactive lipids affect these processes. For this purpose, a transcriptomic meta-analysis of microarray and RNA-seq data from murine stem cells undergoing cardiogenic differentiation was performed. The differentially expressed genes identified via this meta-analysis, as well as bioactive lipids, were evaluated using systems chemo-biology tools. These data indicated that bioactive lipids are associated with the regulation of cell motility, cell adhesion, cytoskeletal rearrangement, and gene expression. Moreover, bioactive lipids integrate the signaling pathways involved in cell migration, the secretion and remodeling of extracellular matrix components, and the establishment of the cardiac phenotype. In conclusion, this study provides new insights into the contribution of bioactive lipids to the induction of cellular responses to various stimuli, which may originate from the extracellular environment and morphogens, and the manner in which this contribution directly affects murine heart morphogenesis.

Plasminogen activator inhibitor-1 suppresses profibrotic responses in fibroblasts from fibrotic lungs

Idiopathic pulmonary fibrosis (IPF) is a fatal lung disease characterized by progressive interstitial scarification. A hallmark morphological lesion is the accumulation of myofibroblasts or fibrotic lung fibroblasts (FL-fibroblasts) in areas called fibroblastic foci. We previously demonstrated that the expression of both urokinase-type plasminogen activator (uPA) and the uPA receptor are elevated in FL-fibroblasts from the lungs of patients with IPF. FL-fibroblasts isolated from human IPF lungs and from mice with bleomycin-induced pulmonary fibrosis showed an increased rate of proliferation compared with normal lung fibroblasts (NL-fibroblasts) derived from histologically "normal" lung. Basal expression of plasminogen activator inhibitor-1 (PAI-1) in human and murine FL-fibroblasts was reduced, whereas collagen-I and α-smooth muscle actin were markedly elevated. Conversely, alveolar type II epithelial cells surrounding the fibrotic foci in situ, as well as those isolated from IPF lungs, showed increased activation of caspase-3 and PAI-1 with a parallel reduction in uPA expression. Transduction of an adenovirus PAI-1 cDNA construct (Ad-PAI-1) suppressed expression of uPA and collagen-I and attenuated proliferation in FL-fibroblasts. On the contrary, inhibition of basal PAI-1 in NL-fibroblasts increased collagen-I and α-smooth muscle actin. Fibroblasts isolated from PAI-1-deficient mice without lung injury also showed increased collagen-I and uPA. These changes were associated with increased Akt/phosphatase and tensin homolog proliferation/survival signals in FL-fibroblasts, which were reversed by transduction with Ad-PAI-1. This study defines a new role of PAI-1 in the control of fibroblast activation and expansion and its role in the pathogenesis of fibrosing lung disease and, in particular, IPF.

Microinflammation factors in the common diseases of the heart and kidneys

Aim. To determine levels of interleukin-8 (IL-8) and plasminogen activator inhibitor-1 (PAI-1) in different cardiorenal syndrome (CRS) modalities and to compare findings to some already investigated direct and indirect parameters of inflammation and atherosclerosis. Materials and Methods. Testing involved 114 examinees, divided into control and clinical groups suffering from different modalities and were formed according to the basis of a valid classification for CRS. Results. C-reactive protein (CRP) was significantly higher in all CRSs in comparison to the control group (P < 0.05). PAI-1 in CRSs was statistically higher than in the control group. IL-8 was increased in all CRSs, and especially in CRS-5, where no significance was found. PAI-1 correlated with IL-8 in all CRSs, with significant value in CRS-2 and CRS-5. Correlation for PAI-1 and high-density lipoproteins (HDL) was found in CRS-4, while IL-8 was found to be related to CRP level in all CRSs, with significance only in CRS-1 (P < 0.001). Conclusions. C-reactive protein, IL-8, and PAI-1 could be useful for clinical differentiation of chronic modalities of CRSs. Inflammation was the most pronounced in CRS-4. Lipid status parameters could be useful for differentiation of CRSs. Furthermore, HDL in chronic primary kidney diseases and triglycerides and total cholesterol in CRS-5 could be valuable.

PAI-1 inhibits development of chronic otitis media and tympanosclerosis in a mouse model of otitis media

CONCLUSION

Bullae of type 1 plasminogen activator inhibitor (PAI-1) knockout (KO) mice showed low levels of inflammation against nontypable Haemophilus influenzae (NTHi) at the early stage of otitis media (OM). However, PAI-1 KO mice fail to terminate inflammation, which may significantly contribute to the development of tympanosclerosis in PAI-1 KO mice.

OBJECTIVE

To investigate the role of PAI-1 in the pathogenesis of OM and subsequent tympanosclerosis.

METHODS

OM was induced with NTHi in PAI-1 KO and background control C57BL/6 mice. mRNA expression of PAI-1, tissue-type plasminogen activator (tPA), and urokinase-type plasminogen activator (uPA) was measured in the bullae of C57BL/6 mice. mRNA expression of interleukin (IL)-1β, tumor necrosis factor (TNF) α, macrophage inflammatory protein (MIP-2), tPA, and uPA in PAI-1 KO and C57BL/6 mice was compared. Histological changes produced by OM were compared at 1, 3, and 7 days after NTHi inoculation.

RESULTS

NTHi up-regulated the expression of PAI-1 and tPA in the bullae of C57BL/6 mice, but not uPA. mRNA expression of IL-1β, TNFα, and MIP-2 was low in PAI-1 KO mice at early time points, but significantly higher at the later stage of OM. Similarly to the gene expression results, histological changes associated with OM were less at days 1 and 3 in PAI-1 KO mice. However, unlike the gradual resolution of OM pathologies in C57BL/6 mice, PAI-1 KO mice showed significant pathological changes of tympanosclerosis.

Plasminogen activator inhibitor 1, fibroblast apoptosis resistance, and aging-related susceptibility to lung fibrosis

Idiopathic pulmonary fibrosis (IPF) is a fatal lung disorder with unknown cause and no effective treatment. The incidence of and mortality from IPF increase with age, suggesting that advanced age is a major risk factor for IPF. The mechanism underlying the increased susceptibility of the elderly to IPF, however, is unknown. In this study, we show for the first time that the protein level of plasminogen activator inhibitor 1 (PAI-1), a protease inhibitor which plays an essential role in the control of fibrinolysis, was significantly increased with age in mouse lung homogenate and lung fibroblasts. Upon bleomycin challenge, old mice experienced augmented PAI-1 induction and lung fibrosis as compared to young mice. Most interestingly, we show that fewer (myo)fibroblasts underwent apoptosis and more (myo)fibroblasts with increased level of PAI-1 accumulated in the lung of old than in young mice after bleomycin challenge. In vitro studies further demonstrate that fibroblasts isolated from lungs of old mice were resistant to H2O2 and tumor necrosis factor alpha-induced apoptosis and had augmented fibrotic responses to TGF-β1, compared to fibroblasts isolated from young mice. Inhibition of PAI-1 activity with a PAI-1 inhibitor, on the other hand, eliminated the aging-related apoptosis resistance and TGF-β1 sensitivity in isolated fibroblasts. Moreover, we show that knocking down PAI-1 in human lung fibroblasts with PAI-1 siRNA significantly increased their sensitivity to apoptosis and inhibited their responses to TGF-β1. Together, the results suggest that increased PAI-1 expression may underlie the aging-related sensitivity to lung fibrosis in part by protecting fibroblasts from apoptosis.

Global gene expression profiling in PAI-1 knockout murine heart and kidney: molecular basis of cardiac-selective fibrosis

Fibrosis is defined as an abnormal matrix remodeling due to excessive synthesis and accumulation of extracellular matrix proteins in tissues during wound healing or in response to chemical, mechanical and immunological stresses. At present, there is no effective therapy for organ fibrosis. Previous studies demonstrated that aged plasminogen activator inhibitor-1 (PAI-1) knockout mice develop spontaneously cardiac-selective fibrosis without affecting any other organs. We hypothesized that differential expressions of profibrotic and antifibrotic genes in PAI-1 knockout hearts and unaffected organs lead to cardiac selective fibrosis. In order to address this prediction, we have used a genome-wide gene expression profiling of transcripts derived from aged PAI-1 knockout hearts and kidneys. The variations of global gene expression profiling were compared within four groups: wildtype heart vs. knockout heart; wildtype kidney vs. knockout kidney; knockout heart vs. knockout kidney and wildtype heart vs. wildtype kidney. Analysis of illumina-based microarray data revealed that several genes involved in different biological processes such as immune system processing, response to stress, cytokine signaling, cell proliferation, adhesion, migration, matrix organization and transcriptional regulation were affected in hearts and kidneys by the absence of PAI-1, a potent inhibitor of urokinase and tissue-type plasminogen activator. Importantly, the expressions of a number of genes, involved in profibrotic pathways including Ankrd1, Pi16, Egr1, Scx, Timp1, Timp2, Klf6, Loxl1 and Klotho, were deregulated in PAI-1 knockout hearts compared to wildtype hearts and PAI-1 knockout kidneys. While the levels of Ankrd1, Pi16 and Timp1 proteins were elevated during EndMT, the level of Timp4 protein was decreased. To our knowledge, this is the first comprehensive report on the influence of PAI-1 on global gene expression profiling in the heart and kidney and its implication in fibrogenesis and several other biological processes. The significance of these observations in the light of heart-specific profibrotic signaling and fibrogenesis are discussed.

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.

Lack of haptoglobin results in unbalanced VEGFα/angiopoietin-1 expression, intramural hemorrhage and impaired wound healing after myocardial infarction

Decreased haptoglobin (Hp) functionality due to allelic variations is associated with worsened outcome in patients after myocardial infarction (MI). However, mechanisms through which haptoglobin deficiency impairs cardiac repair remain to be elucidated. In the present study, we identified novel molecular alterations mediated by Hp involved in early and late cardiac repair responses after left coronary artery ligation in Hp(-/-) and wild-type (WT) mice. We observed a higher mortality rate in Hp(-/-) mice despite similar infarct size between groups. Deaths were commonly caused by cardiac rupture in Hp(-/-) animals. Histological analysis of 3 and 7days old non-ruptured infarcted hearts revealed more frequent and more severe intramural hemorrhage and increased leukocyte infiltration in Hp(-/-) mice. Analyses of non-ruptured hearts revealed increased oxidative stress, reduced PAI-1 activity and enhanced VEGFα transcription in Hp(-/-) mice. In line with these observations, we found increased microvascular permeability in Hp(-/-) hearts 3days after infarction. In vitro, haptoglobin prevented hemoglobin-induced oxidative stress and restored VEGF/Ang-1 balance in endothelial cell cultures. During long-term follow-up of the surviving animals, we observed altered matrix turnover, impaired scar formation and worsened cardiac function and geometry in Hp(-/-)mice. In conclusion, haptoglobin deficiency severely deteriorates tissue repair and cardiac performance after experimental MI. Haptoglobin plays a crucial role in both short- and long-term cardiac repair responses by reducing oxidative stress, maintaining microvascular integrity, myocardial architecture and proper scar formation.

Effective treatment of edema and endothelial barrier dysfunction with imatinib

BACKGROUND

Tissue edema and endothelial barrier dysfunction as observed in sepsis and acute lung injury carry high morbidity and mortality, but currently lack specific therapy. In a recent case report, we described fast resolution of pulmonary edema on treatment with the tyrosine kinase inhibitor imatinib through an unknown mechanism. Here, we explored the effect of imatinib on endothelial barrier dysfunction and edema formation.

METHODS AND RESULTS

We evaluated the effect of imatinib on endothelial barrier function in vitro and in vivo. In human macro- and microvascular endothelial monolayers, imatinib attenuated endothelial barrier dysfunction induced by thrombin and histamine. Small interfering RNA knock-downs of the imatinib-sensitive kinases revealed that imatinib attenuates endothelial barrier dysfunction via inhibition of Abl-related gene kinase (Arg/Abl2), a previously unknown mediator of endothelial barrier dysfunction. Indeed, Arg was activated by endothelial stimulation with thrombin, histamine, and vascular endothelial growth factor. Imatinib limited Arg-mediated endothelial barrier dysfunction by enhancing Rac1 activity and enforcing adhesion of endothelial cells to the extracellular matrix. Using mouse models of vascular leakage as proof-of-concept, we found that pretreatment with imatinib protected against vascular endothelial growth factor-induced vascular leakage in the skin, and effectively prevented edema formation in the lungs. In a murine model of sepsis, imatinib treatment (6 hours and 18 hours after induction of sepsis) attenuated vascular leakage in the kidneys and the lungs (24 hours after induction of sepsis).

CONCLUSIONS

Thus, imatinib prevents endothelial barrier dysfunction and edema formation via inhibition of Arg. These findings identify imatinib as a promising approach to permeability edema and indicate Arg as novel target for edema treatment.

Infrared fluorescence for vascular barrier breach in vivo--a novel method for quantitation of albumin efflux

Vascular hyperpermeability contributes to morbidity in inflammation. Current methodologies for in vivo assessment of permeability based on extravasation of Evans Blue (EB)-bound albumin are cumbersome and often lack sensitivity. We developed a novel infrared fluorescence (IRF) methodology for measurement of EB-albumin extravasation to quantify vascular permeability in murine models. Vascular permeability induced by endotoxaemia was examined for all solid organs, brain, skin and peritoneum by IRF and the traditional absorbance-based measurement of EB in tissue extracts. Organ IRF increased linearly with increasing concentrations of intravenous EB (2.5-25 mg/kg). Tissue IRF was more sensitive for EB accumulation compared to the absorbance-based method. Accordingly, differences in vascular permeability and organ EB accumulation between lipopolysaccharide-treated and saline-treated mice were often significant when analysed by IRF-based detection but not by absorbance-based detection. EB was detected in all 353 organs analysed with IRF but only in 67% (239/353) of organs analysed by absorbance-based methodology, demonstrating improved sensitivity of EB detection in organs with IRF. In contrast, EB in plasma after EB administration was readily measured by both methods with high correlation between the two methods (n=116, r2=0.86). Quantitation of organ-specific EB-IRF differences due to endotoxin was optimal when IRF was compared between mice matched for weight, gender, and age, and with appropriate corrections for organ weight and EB plasma concentrations. Notably, EB-IRF methodology leaves organs intact for subsequent histopathology. In summary, EB-IRF is a novel, highly sensitive, rapid, and convenient method for the relative quantification of EB in intact organs of treatment versus control mice.

Fibrosis in Atrial Fibrillation - Role of Reactive Species and MPO

Atrial fibrosis with enhanced turnover and deposition of matrix proteins leads to inhomogeneous atrial electrical conduction and gives rise to electrical reentry circuits resulting in atrial fibrillation. The multifactorial pathogenesis of atrial fibrosis involves resident cardiac cells as well as infiltrating leukocytes, both generating and sequestering matrix metalloproteinases (MMPs), a key enzyme family involved in fibrosis. A growing body of evidence points toward an important role of reactive oxygen species (ROS) in the release and activation of pro-MMPs and the stimulation of pro-fibrotic cascades. Myeloperoxidase (MPO), a bactericidal enzyme released from activated polymorphonuclear neutrophils (PMN) is not only associated with a variety of cardiovascular diseases, but has also been shown to be mechanistically linked to atrial fibrosis and fibrillation. MPO catalyzes the generation of reactive species like hypochlorous acid, which affect intracellular signaling cascades in various cells and advance activation of pro-MMPs and deposition of atrial collagen resulting in atrial arrhythmias. Thus, inflammatory mechanisms effectively promote atrial structural remodeling and importantly contribute to the initiation and perpetuation of atrial fibrillation.

Effects of altered plasminogen activator inhibitor-1 expression on cardiovascular disease

Plasminogen Activator Inhibitor-1 (PAI-1) is a multifunctional protein with the ability to not only regulate fibrinolysis through inhibition of plasminogen activation, but also cell signaling events which have direct downstream effects on cell function. Elevated plasma levels of this protein have been shown to have profound effects on the development and progression of cardiovascular diseases. However, results from a number of studies, especially those using PAI-1 deficient mouse models, have demonstrated that its function is ambiguous, with evidence of both preventing and enhancing various disease states. A number of lifestyle changes and pharmacological reagents have been identified that can regulate PAI-1 levels or function. Those reagents that target function are focused on its ability to regulate plasmin formation, and have been studied in in vivo models of thrombosis. Further investigations involving regulation of cell function could potentially resolve paradoxical issues associated with the function of this protein in regulating cardiovascular disease.

Estrogen regulates endothelial migration via plasminogen activator inhibitor (PAI-1)

Endothelial plasminogen activator inhibitor (PAI-1) controls vascular remodeling, angiogenesis and fibrinolysis. PAI-1 blood levels in women are related to estrogen. The aim of this study was to characterize the signaling pathways through which estrogen regulates PAI-1 in endothelial cells. Furthermore, we aimed to investigate whether PAI-1 is implicated in the control of endothelial migration by estrogen. Cultured human umbilical vein endothelial cells (HUVECs) and ovariectomized rats were used to test the effects of 17β-estradiol (E(2)) on PAI-1 expression and its role on endothelial migration. At physiological concentrations, E(2) increases the expression of PAI-1 in HUVEC within 6-12 h through activation of a signaling cascade initiated by estrogen receptor α and involving G proteins, phosphatidylinositol-3-OH kinase and Rho-associated kinase II. ROCK-II activation turns into an over-expression of c-Jun and c-Fos that is required for E(2)-induced expression of PAI-1. Estrogen-induced PAI-1 expression is implicated in HUVEC horizontal migration. PAI-1 regulation is found also in vivo, in female rats, where ovariectomy is associated with reduced PAI-1 expression, while estrogen replacement counteracts this change. In conclusion, E(2) increases PAI-1 synthesis in human endothelial cells and in rodent aorta through a G protein-initiated signaling that targets early-immediate gene expression. This regulatory pathway is implicated in endothelial cell migration. These findings describe new mechanisms of action of estrogens in the vessels, which may be important for vascular remodeling and hemostasis.

Cellular plasticity: the good, the bad, and the ugly? Microenvironmental influences on progenitor cell therapy

Progenitor cell based therapies have emerged for the treatment of ischemic cardiovascular diseases where there is insufficient endogenous repair. However, clinical success has been limited, which challenges the original premise that transplanted progenitor cells would orchestrate repair. In this review, we discuss the basics of endothelial progenitor cell therapy and describe how microenvironmental changes (i.e., trophic and mechano-structural factors) in the damaged myocardium influence progenitor cell plasticity and hamper beneficial therapeutic outcome. Further understanding of these microenvironmental clues will enable optimization of cell therapy at all levels. We discuss current concepts and provide future perspectives for the enhancement of progenitor cell therapy, and merge these advances into a combined approach for ischemic tissue repair.

PAI-1, progress in understanding the clinical problem and its aetiology

Plasminogen activator inhibitor-1 (PAI-1, also known as SERPINE1) is a member of the serine protease inhibitor (SERPIN) superfamily and is the primary physiological regulator of urokinase-type plasminogen activator (uPA) and tissue-type plasminogen activator (tPA) activity. Although the principal function of PAI-1 is the inhibition of fibrinolysis, PAI-1 possesses pleiotropic functions besides haemostasis. In the quarter century since its discovery, a number of studies have focused on improving our understanding of PAI-1 functions in vivo and in vitro. The use of Serpine1-deficient mice has particularly enhanced our understanding of the functions of PAI-1 in various physiological and pathophysiological conditions. In this review, the results of recent studies on PAI-1 and its role in clinical conditions are discussed.

Synergistic and multidimensional regulation of plasminogen activator inhibitor type 1 expression by transforming growth factor type β and epidermal growth factor

The major physiological inhibitor of plasminogen activator, type I plasminogen activator inhibitor (PAI-1), controls blood clotting and tissue remodeling events that involve cell migration. Transforming growth factor type β (TGFβ) and epidermal growth factor (EGF) interact synergistically to increase PAI-1 mRNA and protein levels in human HepG2 and mink Mv1Lu cells. Other growth factors that activate tyrosine kinase receptors can substitute for EGF. EGF and TGFβ regulate PAI-1 by synergistically activating transcription, which is further amplified by a decrease in the rate of mRNA degradation, the latter being regulated only by EGF. The combined effect of transcriptional activation and mRNA stabilization results in a rapid 2-order of magnitude increase in the level of PAI-1. TGFβ also increases the sensitivity of the cells to EGF, thereby recruiting the cooperation of EGF at lower than normally effective concentrations. The contribution of EGF to the regulation of PAI-1 involves the MAPK pathway, and the synergistic interface with the TGFβ pathway is downstream of MEK1/2 and involves phosphorylation of neither ERK1/2 nor Smad2/3. Synergism requires the presence of both Smad and AP-1 recognition sites in the promoter. This work demonstrates the existence of a multidimensional cellular mechanism by which EGF and TGFβ are able to promote large and rapid changes in PAI-1 expression.

PAI-1 in tissue fibrosis

Fibrosis is defined as a fibroproliferative or abnormal fibroblast activation-related disease. Deregulation of wound healing leads to hyperactivation of fibroblasts and excessive accumulation of extracellular matrix (ECM) proteins in the wound area, the pathological manifestation of fibrosis. The accumulation of excessive levels of collagen in the ECM depends on two factors: an increased rate of collagen synthesis and or decreased rate of collagen degradation by cellular proteolytic activities. The urokinase/tissue type plasminogen activator (uPA/tPA) and plasmin play significant roles in the cellular proteolytic degradation of ECM proteins and the maintenance of tissue homeostasis. The activities of uPA/tPA/plasmin and plasmin-dependent MMPs rely mostly on the activity of a potent inhibitor of uPA/tPA, plasminogen activator inhibitor-1 (PAI-1). Under normal physiologic conditions, PAI-1 controls the activities of uPA/tPA/plasmin/MMP proteolytic activities and thus maintains the tissue homeostasis. During wound healing, elevated levels of PAI-1 inhibit uPA/tPA/plasmin and plasmin-dependent MMP activities, and, thus, help expedite wound healing. In contrast to this scenario, under pathologic conditions, excessive PAI-1 contributes to excessive accumulation of collagen and other ECM protein in the wound area, and thus preserves scarring. While the level of PAI-1 is significantly elevated in fibrotic tissues, lack of PAI-1 protects different organs from fibrosis in response to injury-related profibrotic signals. Thus, PAI-1 is implicated in the pathology of fibrosis in different organs including the heart, lung, kidney, liver, and skin. Paradoxically, PAI-1 deficiency promotes spontaneous cardiac-selective fibrosis. In this review, we discuss the significance of PAI-1 in the pathogenesis of fibrosis in multiple organs.

Effect of the plasminogen-plasmin system on hypertensive renal and cardiac damage

BACKGROUND

The plasminogen-plasmin system affects tissue fibrosis, presumably by interacting with metalloproteinases (MMPs) and macrophage recruitment. This study tests the influence of plasminogen activator inhibitor-1 (PAI-1) and tissue-type plasminogen activator (tPa) on angiotensin II-mediated hypertensive kidney and heart injury.

METHOD

Hypertension was induced by continuous angiotensin II (Ang II) infusion via osmotic mini-pumps over 4 weeks. The effects of Ang II infusion were determined in mice lacking PAI-1 (PAI-1), mice lacking tPa (tPa), and wild-type mice. Normotensive mice of the respective genotype served as controls. Blood pressure was recorded by continuous radiotelemetric intra-arterial measurements.

RESULTS

Ang II infusion significantly enhanced arterial blood pressure in all groups. However, the increase in blood pressure was more pronounced in the tPa group. Albuminuria was highest in hypertensive wild-type compared to the other Ang II-infused groups. Hypertensive PAI-1 mice exhibited less glomerulosclerosis, higher nephrin immunostaining, and lower renal interstitial collagen I deposition. Gelatin zymography revealed higher activity of MMP-2 in hypertensive PAI-1, whereas no differences were observed in macrophage infiltration. tPa deficiency did not alter kidney fibrosis, although hypertensive tPa revealed less renal expression of fibrotic genes, less macrophage infiltration, and reduced MMP-2 activity. On the other hand, hypertension-induced fibrosis as well as macrophage infiltration in the heart was profoundly enhanced in PAI-1 mice. Fibrin staining revealed perivascular exudations in the myocardium of hypertensive PAI-1 suggesting vascular leakage.

CONCLUSION

These findings underscore the unexpectedly complex role of plasminogen activation for hypertensive target organ damage.

Target cell movement in tumor and cardiovascular diseases based on the epithelial-mesenchymal transition concept

Epithelial-mesenchymal transition (EMT) is a fundamental mechanism in development driving body plan formation. EMT describes a transition process wherein polarized epithelial cells lose their characteristics and acquire a mesenchymal phenotype. The apico-basal polarity of epithelial cells is replaced by a front-rear polarity in mesenchymal cells which favor cell-extracellular matrix than intercellular adhesion. These events serve as a prerequisite to the context-dependent migratory and invasive functions of mesenchymal cells. In solid tumors, carcinoma cells undergoing EMT not only invade and metastasize but also exhibit cancer stem cell-like properties, providing resistance to conventional and targeted therapies. In cardiovascular systems, epicardial cells engaged in EMT contribute to myocardial regeneration. Conversely, cardiovascular endothelial cells undergoing EMT cause cardiac fibrosis. Growing evidence has shed light on the potential development of novel therapeutics that target cell movement by applying the EMT concept, and this may provide new therapeutic strategies for the treatment of cancer and heart diseases.

Life-threatening hemorrhage and prolonged wound healing are remarkable phenotypes manifested by complete plasminogen activator inhibitor-1 deficiency in humans

BACKGROUND

 Plasminogen activator inhibitor-1 (PAI-1) is the primary physiological regulator of urokinase plasminogen activator (uPA) and tissue plasminogen activator (tPA) activity. A number of studies have shown that elevated levels of PAI-1 are related to pathological states such as an increased risk of arterial thrombotic events and a poor prognosis for cancer patients; however, there are few reports about PAI-1 deficiency in humans because the disorder is very rare.

OBJECTIVE

 To understand the in vivo impact of a complete PAI-1 deficiency, Serpine1(-/-) mice were generated; a number of in vivo studies have been conducted to elucidate the function of PAI-1 using Serpine1(-/-) mice. The phenotypes demonstrated in Serpine1(-/-) mice, however, were quite different from those in humans. Therefore, it is necessary to find out and analyze SERPINE1 deficiency in humans.

PATIENT AND METHODS

 The patient is a 47-year-old woman who has had multiple episodes of major bleeding. Although most of the patient's blood coagulation factors were functionally normal, her PAI-1 antigen levels were undetectable. Therefore, DNA sequencing of the SERPINE1 gene were analyzed.

RESULTS

 The proband had a homozygous 1-bp duplication (C) at exon 3 (c.356dupC; p.Ile120AspfsX42). Both wild-type PAI-1 (42.7 kDa) and mutated (Mut) PAI-1 (14.7kDa) were expressed in COS-1 cells, although the level of Mut PAI-1 expressed in the cell lysates was much lower. Wild-type PAI-1 was observed in the culture supernatant, whereas no Mut PAI-1 was detected in the supernatant.

CONCLUSIONS

 Considering the results of the present study, the translation of mouse studies to humans must be performed with great care.

This is not Dr. Conn's aldosterone anymore

In 1955, Dr. Jerome Conn described a patient with severe hypertension and hypokalemia and an aldosterone-secreting adenoma. The prevalence of hyperaldosteronism is increased among patients with obesity or resistant hypertension. Angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers reduce the secretion of aldosterone, but with chronic treatment aldosterone concentrations "escape" back to baseline values. Mineralocorticoid receptor (MR) antagonism reduces mortality in patients with heart disease who are already taking an ACE inhibitor and diuretic. In addition to affecting sodium and potassium homeostasis via classical MR-dependent pathways, aldosterone induces inflammation and causes cardiovascular remodeling and renal injury. Some of these effects involve MR-independent pathways. At the same time, ligands other than aldosterone can activate the MR. This paper reviews mechanism(s) for the proinflammatory and profibrotic effects of aldosterone and presents data indicating that endogenous aldosterone, acting at the MR, contributes to many of the pro-inflammatory and pro-fibrotic effects of angiotensin II in vivo.