Cardiomyocyte NOX4 regulates resident macrophage-mediated inflammation and diastolic dysfunction in stress cardiomyopathy.

In acute sympathetic stress, catecholamine overload can lead to stress cardiomyopathy. We tested the hypothesis that cardiomyocyte NOX4 (NADPH oxidase 4)-dependent mitochondrial oxidative stress mediates inflammation and diastolic dysfunction in stress cardiomyopathy. Isoproterenol (ISO; 5 mg/kg) injection induced sympathetic stress in wild-type and cardiomyocyte (CM)-specific Nox4 knockout (Nox4CM-/-) mice. Wild-type mice treated with ISO showed higher CM NOX4 expression, H2O2 levels, inflammasome activation, and IL18, IL6, CCL2, and TNFα levels than Nox4CM-/- mice. Spectral flow cytometry and t-SNE analysis of cardiac cell suspensions showed significant increases in pro-inflammatory and pro-fibrotic embryonic-derived resident (CCR2-MHCIIhiCX3CR1hi) macrophages in wild-type mice 3 days after ISO treatment, whereas Nox4CM-/- mice had a higher proportion of embryonic-derived resident tissue-repair (CCR2-MHCIIloCX3CR1lo) macrophages. A significant increase in cardiac fibroblast activation and interstitial collagen deposition and a restrictive pattern of diastolic dysfunction with increased filling pressure was observed in wild-type hearts compared with Nox4CM-/- 7 days post-ISO. A selective NOX4 inhibitor, GKT137831, reduced myocardial mitochondrial ROS, macrophage infiltration, and fibrosis in ISO-injected wild-type mice, and preserved diastolic function. Our data suggest sympathetic overstimulation induces resident macrophage (CCR2-MHCII+) activation and myocardial inflammation, resulting in fibrosis and impaired diastolic function mediated by CM NOX4-dependent ROS.

Dual-omics reveals temporal differences in acute sympathetic stress-induced cardiac inflammation following α1 and ß-adrenergic receptors activation.

Sympathetic stress is prevalent in cardiovascular diseases. Sympathetic overactivation under strong acute stresses triggers acute cardiovascular events including myocardial infarction (MI), sudden cardiac death, and stress cardiomyopathy. α1-ARs and ß-ARs, two dominant subtypes of adrenergic receptors in the heart, play a significant role in the physiological and pathologic regulation of these processes. However, little is known about the functional similarities and differences between α1- and ß-ARs activated temporal responses in stress-induced cardiac pathology. In this work, we systematically compared the cardiac temporal genome-wide profiles of acute α1-AR and ß-AR activation in the mice model by integrating transcriptome and proteome. We found that α1- and ß-AR activations induced sustained and transient inflammatory gene expression, respectively. Particularly, the overactivation of α1-AR but not ß-AR led to neutrophil infiltration at one day, which was closely associated with the up-regulation of chemokines, activation of NF-κB pathway, and sustained inflammatory response. Furthermore, there are more metabolic disorders under α1-AR overactivation compared with ß-AR overactivation. These findings provide a new therapeutic strategy that, besides using ß-blocker as soon as possible, blocking α1-AR within one day should also be considered in the treatment of acute stress-associated cardiovascular diseases.

IMM-H007 attenuates isoprenaline-induced cardiac fibrosis through targeting TGFß1 signaling pathway.

Upon chronic stress, ß-adrenergic receptor activation induces cardiac fibrosis and leads to heart failure. The small molecule compound IMM-H007 has demonstrated protective effects in cardiovascular diseases via activation of AMP-activated protein kinase (AMPK). This study aimed to investigate IMM-H007 effects on cardiac fibrosis induced by ß-adrenergic receptor activation. Because adenosine analogs also exert AMPK-independent effects, we assessed AMPK-dependent and -independent IMM-H007 effects in murine models of cardiac fibrosis. Continual subcutaneous injection of isoprenaline for 7 days caused cardiac fibrosis and cardiac dysfunction in mice in vivo. IMM-H007 attenuated isoprenaline-induced cardiac fibrosis, diastolic dysfunction, α-smooth muscle actin expression, and collagen I deposition in both wild-type and AMPKα2-/- mice. Moreover, IMM-H007 inhibited transforming growth factor ß1 (TGFß1) expression in wild-type, but not AMPKα2-/- mice. By contrast, IMM-H007 inhibited Smad2/3 signaling downstream of TGFß1 in both wild-type and AMPKα2-/- mice. Surface plasmon resonance and molecular docking experiments showed that IMM-H007 directly interacts with TGFß1, inhibits its binding to TGFß type II receptors, and downregulates the Smad2/3 signaling pathway downstream of TGFß1. These findings suggest that IMM-H007 inhibits isoprenaline-induced cardiac fibrosis via both AMPKα2-dependent and -independent mechanisms. IMM-H007 may be useful as a novel TGFß1 antagonist.

Glibenclamide alleviates ß adrenergic receptor activation-induced cardiac inflammation.

ß-Adrenergic receptor (ß-AR) overactivation is a major pathological factor associated with cardiac diseases and mediates cardiac inflammatory injury. Glibenclamide has shown anti-inflammatory effects in previous research. However, it is unclear whether and how glibenclamide can alleviate cardiac inflammatory injury induced by ß-AR overactivation. In the present study, male C57BL/6J mice were treated with or without the ß-AR agonist isoprenaline (ISO) with or without glibenclamide pretreatment. The results indicated that glibenclamide alleviated ISO-induced macrophage infiltration in the heart, as determined by Mac-3 staining. Consistent with this finding, glibenclamide also inhibited ISO-induced chemokines and proinflammatory cytokines expression in the heart. Moreover, glibenclamide inhibited ISO-induced cardiac fibrosis and dysfunction in mice. To reveal the protective mechanism of glibenclamide, the NLRP3 inflammasome was further analysed. ISO activated the NLRP3 inflammasome in both cardiomyocytes and mouse hearts, but this effect was alleviated by glibenclamide pretreatment. Furthermore, in cardiomyocytes, ISO increased the efflux of potassium and the generation of ROS, which are recognized as activators of the NLRP3 inflammasome. The ISO-induced increases in these processes were inhibited by glibenclamide pretreatment. Moreover, glibenclamide inhibited the cAMP/PKA signalling pathway, which is downstream of ß-AR, by increasing phosphodiesterase activity in mouse hearts and cardiomyocytes. In conclusion, glibenclamide alleviates ß-AR overactivation-induced cardiac inflammation by inhibiting the NLRP3 inflammasome. The underlying mechanism involves glibenclamide-mediated suppression of potassium efflux and ROS generation by inhibiting the cAMP/PKA pathway.

Small molecule QF84139 ameliorates cardiac hypertrophy via activating the AMPK signaling pathway.

Cardiac hypertrophy is a common adaptive response to a variety of stimuli, but prolonged hypertrophy leads to heart failure. Hence, discovery of agents treating cardiac hypertrophy is urgently needed. In the present study, we investigated the effects of QF84139, a newly synthesized pyrazine derivative, on cardiac hypertrophy and the underlying mechanisms. In neonatal rat cardiomyocytes (NRCMs), pretreatment with QF84139 (1-10 µM) concentration-dependently inhibited phenylephrine-induced hypertrophic responses characterized by fetal genes reactivation, increased ANP protein level and enlarged cardiomyocytes. In adult male mice, administration of QF84139 (5-90 mg·kg-1·d-1, i.p., for 2 weeks) dose-dependently reversed transverse aortic constriction (TAC)-induced cardiac hypertrophy displayed by cardiomyocyte size, left ventricular mass, heart weights, and reactivation of fetal genes. We further revealed that QF84139 selectively activated the AMPK signaling pathway without affecting the phosphorylation of CaMKIIδ, ERK1/2, AKT, PKCε, and P38 kinases in phenylephrine-treated NRCMs and in the hearts of TAC-treated mice. In NRCMs, QF84139 did not show additive effects with metformin on the AMPK activation, whereas the anti-hypertrophic effect of QF84139 was abolished by an AMPK inhibitor Compound C or knockdown of AMPKα2. In AMPKα2-deficient mice, the anti-hypertrophic effect of QF84139 was also vanished. These results demonstrate that QF84139 attenuates the PE- and TAC-induced cardiac hypertrophy via activating the AMPK signaling. This structurally novel compound would be a promising lead compound for developing effective agents for the treatment of cardiac hypertrophy.

Novel roles of an intragenic G-quadruplex in controlling microRNA expression and cardiac function.

Simultaneous dysregulation of multiple microRNAs (miRs) affects various pathological pathways related to cardiac failure. In addition to being potential cardiac disease-specific markers, miR-23b/27b/24-1 were reported to be responsible for conferring cardiac pathophysiological processes. In this study, we identified a conserved guanine-rich RNA motif within the miR-23b/27b/24-1 cluster that can form an RNA G-quadruplex (rG4) in vitro and in cells. Disruption of this intragenic rG4 significantly increased the production of all three miRs. Conversely, a G4-binding ligand tetrandrine (TET) stabilized the rG4 and suppressed miRs production in human and rodent cardiomyocytes. Our further study showed that the rG4 prevented Drosha-DGCR8 binding and processing of the pri-miR, suppressing the biogenesis of all three miRs. Moreover, CRISPR/Cas9-mediated G4 deletion in the rat genome aberrantly elevated all three miRs in the heart in vivo, leading to cardiac contractile dysfunction. Importantly, loss of the G4 resulted in reduced targets for the aforementioned miRs critical for normal heart function and defects in the L-type Ca2+ channel-ryanodine receptor (LCC-RyR) coupling in cardiomyocytes. Our results reveal a novel mechanism for G4-dependent regulation of miR biogenesis, which is essential for maintaining normal heart function.

Membrane nanotubes facilitate the propagation of inflammatory injury in the heart upon overactivation of the ß-adrenergic receptor.

Acute sympathetic stress quickly induces cardiac inflammation and injury, suggesting that pathogenic signals rapidly spread among cardiac cells and that cell-to-cell communication may play an important role in the subsequent cardiac injury. However, the underlying mechanism of this response is unknown. Our previous study demonstrated that acute ß-adrenergic receptor (ß-AR) signaling activates inflammasomes in the heart, which triggers the inflammatory cascade. In the present study, ß-AR overactivation induced inflammasome activation in both the cardiomyocytes and cardiac fibroblasts (CFs) of mice hearts following a subcutaneous injection of isoproterenol (ISO, 5 mg/kg body weight), a selective agonist of ß-AR. In isolated cardiac cells, ISO treatment only activated the inflammasomes in the cardiomyocytes but not the CFs. These results demonstrated that inflammasome activation was propagated from cardiomyocytes to CFs in the mice hearts. Further investigation revealed that the inflammasomes were activated in the cocultured CFs that connected with cardiomyocytes via membrane nanotubes (MNTs), a novel membrane structure that mediates distant intercellular connections and communication. Disruption of the MNTs with the microfilament polymerization inhibitor cytochalasin D (Cyto D) attenuated the inflammasome activation in the cocultured CFs. In addition, the MNT-mediated inflammasome activation in the CFs was blocked by deficiency of the inflammasome component NOD-like receptor protein 3 (NLRP3) in the cardiomyocytes, but not NLRP3 deficiency in the CFs. Moreover, ISO induced pyroptosis in the CFs cocultured with cardiomyocytes, and this process was inhibited by disruption of the MNTs with Cyto D or by the NLRP3 inhibitor MCC950 and the caspase-1 inhibitor Z-YVAD-FMK (FMK). Our study revealed that MNTs facilitate the rapid propagation of inflammasome activation among cardiac cells to promote pyroptosis in the early phase of ß-adrenergic insult. Therefore, preventing inflammasome transfer is a potential therapeutic strategy to alleviate acute ß-AR overactivation-induced cardiac injury.

Author Correction: Increased circulating ß2-adrenergic receptor autoantibodies are associated with smoking-related emphysema.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

α1-AR overactivation induces cardiac inflammation through NLRP3 inflammasome activation.

Acute sympathetic stress causes excessive secretion of catecholamines and induces cardiac injuries, which are mainly mediated by ß-adrenergic receptors (ß-ARs). However, α1-adrenergic receptors (α1-ARs) are also expressed in the heart and are activated upon acute sympathetic stress. In the present study, we investigated whether α1-AR activation induced cardiac inflammation and the underlying mechanisms. Male C57BL/6 mice were injected with a single dose of α1-AR agonist phenylephrine (PE, 5 or 10 mg/kg, s.c.) with or without pretreatment with α-AR antagonist prazosin (5 mg/kg, s.c.). PE injection caused cardiac dysfunction and cardiac inflammation, evidenced by the increased expression of inflammatory cytokine IL-6 and chemokines MCP-1 and MCP-5, as well as macrophage infiltration in myocardium. These effects were blocked by prazosin pretreatment. Furthermore, PE injection significantly increased the expression of NOD-like receptor protein 3 (NLRP3) and the cleavage of caspase-1 (p20) and interleukin-18 in the heart; similar results were observed in both Langendorff-perfused hearts and cultured cardiomyocytes following the treatment with PE (10 µM). Moreover, PE-induced NLRP3 inflammasome activation and cardiac inflammation was blocked in Nlrp3-/- mice compared with wild-type mice. In conclusion, α1-AR overactivation induces cardiac inflammation by activating NLRP3 inflammasomes.

Increased mitochondrial NADPH oxidase 4 (NOX4) expression in aging is a causative factor in aortic stiffening.

Aging is characterized by increased aortic stiffness, an early, independent predictor and cause of cardiovascular disease. Oxidative stress from excess reactive oxygen species (ROS) production increases with age. Mitochondria and NADPH oxidases (NOXs) are two major sources of ROS in cardiovascular system. We showed previously that increased mitochondrial ROS levels over a lifetime induce aortic stiffening in a mouse oxidative stress model. Also, NADPH oxidase 4 (NOX4) expression and ROS levels increase with age in aortas, aortic vascular smooth muscle cells (VSMCs) and mitochondria, and are correlated with age-associated aortic stiffness in hypercholesterolemic mice. The present study investigated whether young mice (4 months-old) with increased mitochondrial NOX4 levels recapitulate vascular aging and age-associated aortic stiffness. We generated transgenic mice with low (Nox4TG605; 2.1-fold higher) and high (Nox4TG618; 4.9-fold higher) mitochondrial NOX4 expression. Young Nox4TG618 mice showed significant increase in aortic stiffness and decrease in phenylephrine-induced aortic contraction, but not Nox4TG605 mice. Increased mitochondrial oxidative stress increased intrinsic VSMC stiffness, induced aortic extracellular matrix remodeling and fibrosis, a leftward shift in stress-strain curves, decreased volume compliance and focal adhesion turnover in Nox4TG618 mice. Nox4TG618 VSMCs phenocopied other features of vascular aging such as increased DNA damage, increased premature and replicative senescence and apoptosis, increased proinflammatory protein expression and decreased respiration. Aortic stiffening in young Nox4TG618 mice was significantly blunted with mitochondrial-targeted catalase overexpression. This demonstration of the role of mitochondrial oxidative stress in aortic stiffness will galvanize search for new mitochondrial-targeted therapeutics for treatment of age-associated vascular dysfunction.

[The biological functions of cell-to-cell connection over long distance--membrane nanotube].

Cell-to-cell connections provide conduits for signal exchanges, and play important functional roles in physiological and pathological processes of multicellular organisms. Membrane nanotubes are common long-distance connections between cells, not only transfer molecule signals and mitochondria, but also cooperate with gap junction and other cell-to-cell communications to transfer signals. During the last decade, there are many studies about membrane nanotubes, which focus on the similarities and differences between membrane nanotubes and other cell-to-cell communications, as well as their biological functions. In the present review, we summarized the latest findings about the structural diversity, the similarities and differences in signal transmission with other types of cell-to-cell communications, and physiological and pathological roles of membrane nanotubes.

[Research advances of autonomic nervous system in the regulation of cardiac inflammation].

The autonomic nervous system consists of the sympathetic nervous system and the parasympathetic nervous system. These two systems control the heart and work in a reciprocal fashion to modulate myocardial energy metabolism, heart rate as well as blood pressure. Multiple cardiac pathological conditions are accompanied by autonomic imbalance, characterized by sympathetic overactivation and parasympathetic inhibition. Studies have shown that overactive sympathetic nervous system leads to increased cardiac inflammatory reaction. Orchestrated inflammatory response serves to clear dead cardiac tissue and activate reparative process, whereas excessive inflammation may result in pathological cardiac remodeling. Since the discovery of the α7 nicotinic acetylcholine receptor (α7nAChR)-mediated cholinergic anti-inflammatory pathway (CAP), the protective effects of the parasympathetic nervous system in cardiac inflammation have attracted more attention recently. In this review, we summarized the role and underlying mechanisms of the sympathetic and parasympathetic nervous systems in cardiac inflammation, in order to provide new insight into cardiac inflammatory response in cardiovascular diseases.

Prostaglandin E2 receptors differentially regulate the output of proinflammatory cytokines in myometrial cells from term pregnant women.

Prostaglandin (PG) E2 plays critical roles during pregnancy and parturition. Emerging evidence indicates that human labour is an inflammatory event. We sought to investigate the effect of PGE2 on the output of proinflammatory cytokines in cultured human uterine smooth muscle cells (HUSMCs) from term pregnant women and elucidate the role of subtypes of PGE2 receptors (EP1, EP2, EP3 and EP4). After drug treatment and/or transfection of each receptor siRNA, the concentrations of inflammatory secreting factors in HUSMCs culture medium were detected by the corresponding ELISA kits. The results showed that, PGE2 increased interleukin 6 (IL-6) and tumor necrosis factor alpha (TNFα) output, decreased chemokine (c-x-c motif) ligand 8 (CXCL8) output in a dose-dependent manner, but had no effect on IL-1ß and chemokine (c-c motif) ligand 2 (CCL-2) secretion of HUSMCs. EP1/EP3 agonist 17-phenyl-trinor-PGE2 stimulated IL-6 and TNFα whilst suppressing IL-1ß and CXCL8 output. The effects of 17-phenyl-trinor-PGE2 on IL-1ß and CXCL8 secretion were remained whereas its effect on IL-6 and TNFα output did not occur in the cells with EP3 knockdown. The stimulatory effects of 17-phenyl-trinor-PGE2 on IL-6 and TNFα were remained whereas the inhibitory effects of 17-phenyl-trinor-PGE2 on IL-1ß secretion was blocked in the cells with EP1 knockdown. Either of EP2 and EP4 agonists stimulated IL-1ß and TNFα output, which was reversed by EP2 and EP4 siRNA, respectively. The inhibitors of phospholipase C (PLC) and protein kinase C (PKC) blocked EP1/EP3 modulation of TNFα and CXCL8 output. PI3K inhibitor LY294002 and P38 inhibitor SB202190 blocked 17-phenyl-trinor-PGE2-induced IL-1ß and IL-6 output, respectively. The inhibitors of adenylyl cyclase and PKA prevented EP2 and EP4 stimulation of IL-1ß and TNFα output, whereas PLC and PKC inhibitors blocked EP2- and EP4-induced TNFα output but not IL-1ß output. Our data suggest that PGE2 receptors exhibit different effects on the output of various cytokines in myometrium, which can subtly modulate the inflammatory microenvironment in myometrium during pregnancy.

ß­estradiol alleviates hypertension­ and concanavalin A­mediated inflammatory responses via modulation of connexins in peripheral blood lymphocytes.

Gap junctions (GJs) formed by connexins (Cxs) in T lymphocytes have been reported to have important roles in the T lymphocyte­driven inflammatory response and hypertension­mediated inflammation. Estrogen has a protective effect on cardiovascular diseases, including hypertension and it attenuates excessive inflammatory responses in certain autoimmune diseases. However, the mechanisms involved in regulating the pro­inflammatory response are complex and poorly understood. The current study investigated whether ß­estradiol suppresses hypertension and pro­inflammatory stimuli­mediated inflammatory responses by regulating Cxs and Cx­mediated GJs in peripheral blood lymphocytes. Male, 16­week­old spontaneously hypertensive rats (SHR) and Wistar­Kyoto rats (WKY) rats were randomly divided into the following three groups: WKY rats, vehicle (saline)­treated SHRs, and ß­estradiol (20 µg/kg/day)­treated SHRs. ß­estradiol was administered subcutaneously for 5 weeks. Hematoxylin and eosin staining was performed to evaluate target organ injury. Flow cytometry and ELISA were used to measure the populations of T lymphocyte subtypes in the peripheral blood, and expression of Cx40/Cx43 in T cell subtypes, and pro­inflammation cytokines levels, respectively. ELISA, a dye transfer technique, immunofluorescence and immunoblotting were used to analyze the effect of ß­estradiol on pro­inflammatory cytokine secretion, Cx­mediated GJs and the expression of Cxs in concanavalin A (Con A)­stimulated peripheral blood lymphocytes isolated from WKY rat. ß­estradiol significantly decreased blood pressure and inhibited hypertension­induced target organ injury in SHRs. Additionally, ß­estradiol treatment significantly improved the immune homeostasis of SHRs, as demonstrated by the decreased percentage of cluster of differentiation (CD)4+/CD8+ T­cell subset ratio, reduced serum levels of pro­inflammatory cytokines and increased the percentage of CD4+CD25+ T cells. ß­estradiol also markedly reduced the expression of Cx40/Cx43 in T lymphocytes from SHRs. In vitro, ß­estradiol significantly suppressed the production of pro­inflammatory cytokines, reduced communication via Cx­mediated gap junctions and decreased the expression of Cx40/Cx43 in Con A­stimulated lymphocytes. These results indicate that ß­estradiol attenuates inflammation and end organ damage in hypertension, which may be partially mediated via downregulated expression of Cxs and reduced function of Cx­mediated GJ.

Admission macrophage migration inhibitory factor predicts long-term prognosis in patients with ST-elevation myocardial infarction.

Aims: We previously showed in patients with ST-segment elevated myocardial infarction (STEMI) that admission levels of macrophage migration inhibitory factor (MIF) predict infarct size. We studied whether admission MIF alone or in combination with other biomarkers is useful for risk assessment of acute and chronic clinical outcomes in STEMI patients. Methods and results: A total of 658 STEMI patients treated with primary percutaneous coronary intervention (PCI) were consecutively recruited. MIF level was determined at admission and echocardiography performed on day-3 and then 12 months post-MI. Patients were followed for a median period of 64 months. Major endpoints included ST-segment resolution, all-cause mortality, and major adverse cardiovascular events (MACE). High MIF level was associated with larger enzymatic infarct size, incomplete resolution of ST-segment elevation post-PCI, impaired left ventricular ejection fraction (LVEF), and poorer improvement of LVEF (all P < 0.001). After adjustment for classical risk factors standard biomarkers and day-3 LVEF, admission MIF remained independently prognostic for all-cause mortality [hazard ratio (HR) 2.27, 95% confidence interval (CI) 1.43-3.22], and MACE (HR 1.39, 95% CI 1.12-1.71, both P < 0.05). MIF was a significant additive predictor of all-cause mortality with a net reclassification improvement of 0.34 (P = 0.02). Furthermore, patients in high tertile of both admission MIF and day-3 Nt-proBNP had the highest mortality risk relative to other tertile groups (HR 11.28, 95% CI 4.82-26.94; P < 0.001). Conclusion: STEMI patients with high admission MIF level experienced a poorer recovery of cardiac function and worse long-term adverse outcomes. Combination of Nt-proBNP with MIF further improves prognostic capability.

RNA-binding protein HuR regulates hsa-let-7c expression by its RNA recognition motif.

MicroRNAs (miRNAs) are small noncoding RNAs that control diverse cellular and developmental events through repression of large sets of target mRNAs. miRNAs expressions were mainly regulated at two levels: transcriptional and post-transcriptional. Transcriptional regulation of miRNA-encoding genes produce specific expression patterns of individual miRNA. However, the mechanism of post-transcriptional regulation of miRNAs remains largely unknown. The present study was aimed to clarify whether HuR, an evolutionary conserved AU-rich binding protein, could regulate miRNAs expressions. By means of a computational screen for AUUUA motifs within pri-miRNAs, we found that the downstream of hsa-let-7c but not hsa-miR-21 was enriched of AUUUA motifs. Then we transfected HuR and mutant HuR lacking RNA recognition motif 3 (RRM3) respectively into HEK293T cells. And HuR protein and miRNAs expressions were detected by Western blot and real-time PCR, respectively. The results showed that the overexpression of HuR promoted mature hsa-let-7c expression but not hsa-miR-21 expression. Furthermore, overexpression of HuR deletion mutant lacking RRM3 did not promote hsa-let-7c expression. These results suggest that RRM3 is crucial for HuR mediating mature hsa-let-7c expression. Collectively, these findings proposed a novel role of HuR in biogenesis of miRNAs, possibly by way of post-transcriptional regulation of miRNAs.

Mitochondria are transported along microtubules in membrane nanotubes to rescue distressed cardiomyocytes from apoptosis.

Membrane nanotubes (MNTs) act as "highways" between cells to facilitate the transfer of multiple signals and play an important role in many diseases. Our previous work reported on the transfer of mitochondria via MNTs between cardiomyocytes (CMs) and cardiac myofibroblasts (MFs); however, the elucidation of the underlying mechanism and pathophysiological significance of this transfer requires additional study. In this study, we determined that the mean movement velocity of mitochondria in MNTs between CMs and MFs was approximately 17.5 ± 2.1 nm/s. Meanwhile, treatment with microtubule polymerisation inhibitors nocodazole or colcemid in cell culture decreased mitochondrial velocity, and knockdown of the microtubule motor protein kinesin family member 5B (KIF5B) led to a similar effect, indicating that mitochondrial movement was dependent on microtubules and the motor protein KIF5B. Furthermore, we showed that hypoxia/reoxygenation-induced CM apoptosis was attenuated by coculture with intact or hypoxia/reoxygenation-treated MFs, which transferred mitochondria to CMs. This rescue was prevented either by separating the cells using Transwell culture or by impairing mitochondrial transfer with nocodazole or colcemid treatment. In conclusion, as a novel means of intercellular communication, MNTs rescue distressed CMs from apoptosis by transporting mitochondria along microtubules via KIF5B.

IL-18 cleavage triggers cardiac inflammation and fibrosis upon ß-adrenergic insult.

Aims: Rapid over-activation of ß-adrenergic receptor (ß-AR) upon stress leads to cardiac inflammation, a prevailing factor that underlies heart injury. However, mechanisms by which acute ß-AR stimulation induce cardiac inflammation still remain unknown. Here, we set out to identify the crucial role of inflammasome/interleukin (IL)-18 in initiating and maintaining cardiac inflammatory cascades upon ß-AR insult. Methods and results: Male C57BL/6 mice were injected with a single dose of ß-AR agonist, isoproterenol (ISO, 5 mg/kg body weight) or saline subcutaneously. Cytokine array profiling demonstrated that chemokines dominated the initial cytokines upregulation specifically within the heart upon ß-AR insult, which promoted early macrophage infiltration. Further investigation revealed that the rapid inflammasome-dependent activation of IL-18, but not IL-1ß, was the critical up-stream regulator for elevated chemokine expression in the myocardium upon ISO induced ß1-AR-ROS signalling. Indeed, a positive correlation was observed between the serum levels of norepinephrine and IL-18 in patients with chest pain. Genetic deletion of IL-18 or the up-stream inflammasome component NLRP3 significantly attenuated ISO-induced chemokine expression and macrophage infiltration. In addition, IL-18 neutralizing antibodies selectively abated ISO-induced chemokines, proinflammatory cytokines and adhesion molecules but not growth factors. Moreover, blocking IL-18 early after ISO treatment effectively attenuated cardiac inflammation and fibrosis. Conclusion: Inflammasome-dependent activation of IL-18 within the myocardium upon acute ß-AR over-activation triggers cytokine cascades, macrophage infiltration and pathological cardiac remodelling. Blocking IL-18 at the early stage of ß-AR insult can successfully prevent inflammatory responses and cardiac injuries.

[AMP-activated kinase activation inhibits transforming growth factor-ß1 production in cardiac fibroblasts via targeting C/EBPß].

AMP-activated protein kinase (AMPK) activation has been shown to protect against fibrosis. However, the underlying mechanism remains unclear. Here we explored the effect of AMPK activation on transforming growth factor-ß1 (TGFß1) production induced by angiotensin II (AngII) in cardiac fibroblasts and the underlying mechanisms. Adult mouse cardiac fibroblasts were isolated. TGFß1 and AMPK activity were determined by ELISA and Western blots, respectively. Pretreatment of AMPK activator AICAR inhibited TGFß1 production induced by AngII in cardiac fibroblasts, which was reversed by AMPK inhibitor compound C. Furthermore, bioinformatics predicted a potential CCAAT/enhancer-binding protein ß (C/EBPß) binding site in the promoter region of the mouse Tgfb1 gene. Luciferase reporter with wild type, but not deleted, C/EBPß binding sites transfection in mouse embryonic fibroblasts showed increased TGFß1 transcriptional activity induced by AngII, indicating that C/EBPß mediates AngII-induced TGFß1 transcript expression. Pretreatment of AICAR inhibited C/EBPß expression induced by AngII. In conclusion, AMPK activation inhibited TGFß1 production induced by AngII in cardiac fibroblasts through targeting C/EBPß. This finding provides a new mechanism underlying the anti-fibrogenic effects of AMPK activation.