A novel function of claudin-5 in maintaining the structural integrity of the heart and its implications in cardiac pathology.

This study aims to investigate the role of claudin-5 (Cldn5) in cardiac structural integrity. Proteomic analysis was performed to screen the protein profiles in enlarged left atrium from atrial fibrillation (AF) patients. Cldn5 shRNA adeno-associated virus (AAV) or siRNA was injected into the mouse left ventricle or added into HL1 cells respectively to knockdown Cldn5 in cardiomyocytes to observe whether the change of Cldn5 influences cardiac morphology and function, and affects those protein expressions stem from the proteomic analysis. Mitochondrial density and membrane potential were also measured by Mitotracker staining and JC-1 staining under the confocal microscope in HL1 cells. Cldn5 was reduced in cardiomyocytes from the left atrial appendage of AF patients compared to non-AF donors. Proteomic analysis showed 83 proteins were less abundant and 102 proteins were more abundant in AF patients. KEGG pathway analysis showed less abundant CACNA2D2, CACNB2, MYL2 and MAP6 were highly associated with dilated cardiomyopathy. Cldn5 shRNA AAV injection caused severe cardiac atrophy, dilation and myocardial dysfunction in mice. The decreases in mitochondrial numbers and mitochondrial membrane potentials in HL1 cells were observed after Cldn5 knockdown. We demonstrated for the first time the mechanism of Cldn5 downregulation-induced myocyte atrophy and myocardial dysfunction might be associated with the downregulation of CACNA2D2, CACNB2, MYL2 and MAP6, and mitochondrial dysfunction in cardiomyocytes.

A Novel Role of Claudin-5 in Prevention of Mitochondrial Fission Against Ischemic/Hypoxic Stress in Cardiomyocytes.

BACKGROUND: Downregulation of claudin-5 in the heart is associated with the end-stage heart failure. However, the underlying mechanism ofclaudin-5 is unclear. Here we investigated the molecular actions of claudin-5 in perspective of mitochondria in cardiomyocytes to better understand the role of claudin-5 in cardioprotection during ischemia. METHODS: Myocardial ischemia/reperfusion (I/R; 30 min/24 h) and hypoxia/reoxygenation (H/R; 24 h/4 h) were used in this study. Confocal microscopy and transmission electron microscope (TEM) were used to observe mitochondrial morphology. RESULTS: Claudin-5 was detected in murine heart tissue and neonatal rat cardiomyocytes (NRCM). Its protein level was severely decreased after myocardial I/R or H/R. Confocal microscopy showedclaudin-5 presented in the mitochondria of NRCM. H/R-induced claudin-5 downregulation was accompanied by mitochondrial fragmentation. The mitofusin 2 (Mfn2) expressionwas dramatically decreased while the dynamin-related protein (Drp) 1 expression was significantly increased after H/R. The TEM indicatedH/R-induced mitochondrial swelling and fission. Adenoviral claudin-5 overexpression reversed these structural disintegration of mitochondria. The mitochondria-centered intrinsic pathway of apoptosis triggered by H/R and indicated by the cytochrome c and cleaved caspase 3 in the cytoplasm of NRCMs was also reduced by overexpressing claudin-5. Claudin-5 overexpression in mouse heart also significantly decreased cleaved caspase 3 and the infarct size in ischemic heart with improved systolic function. CONCLUSION: We demonstrated for the first time the presence of claudin-5 in the mitochondria in cardiomyocytes and provided the firm evidence for the cardioprotective role of claudin-5 in the preservation of mitochondrial dynamics and cell fate against hypoxia- or ischemia-induced stress.

Olmesartan attenuates pressure-overload- or post-infarction-induced cardiac remodeling in mice.

Either angiotensin converting enzyme inhibitor (ACEI) or angiotensin receptor 1 blocker (ARB) attenuates cardiac remodeling. However, the overall molecular modulation of the reversing remodeling process in response to the ACEI or ARB treatment is not yet well determined. In this study, we examined whether gene expressions are modulated by ACEI (temocapril), ARB (olmesartan) or both in a murine model with transverse aortic constriction (TAC) and confirm whether periostin is a target gene of olmesartan in mice with myocardial infarction (MI). We detected 109 genes that were significantly up-regulated in TAC mice and a majority of these were down-regulated in response to temocapril, olmesartan or their combination which significantly attenuated cardiac remodeling at one or four weeks. Real-time RT-PCR demonstrated that olmesartan, temocapril or their combination down-regulated the expression of periostin. In MI mice treated with olmesartan for 4 weeks, the left ventricular end-diastolic and systolic dimensions measured with echocardiography were lower, whereas maximum rate of rise and fall rate of LV pressure (±dp/dt max) were greater, and Azan-staining cardiac fibrotic area was smaller. Furthermore, periostin was upregulated in response to MI, whereas olmesartan blocked this upregulation. Post-MI fibrosis was smaller in periostin knockout adult mice than in wildtype mice, while glycogen synthase kinase 3ß was increased and cyclin D1 was decreased in periostin knockout mice. These findings indicate that periostin is a target gene of ARB and olmesartan reverses cardiac remodeling at least partially through the downregulation of periostin.

New findings on SNP variants of human protein L-isoaspartyl methyltransferase that affect catalytic activity, thermal stability, and aggregation.

Protein L-isoaspartyl methyltransferase (PIMT/PCMT1), a product of the pcmt1 gene, catalyzes repair of abnormal L-isoaspartyl linkages in age-damaged proteins. Pcmt1 knockout mice exhibit a profound neuropathology and die 30-60 days postnatal from an epileptic seizure. Here we characterize four new SNP variants of human PIMT with respect to enzymatic activity, thermal stability, and propensity to aggregation. Under standard assay conditions, L191S, A150V, P174H and A65V showed activity losses of 72%, 64%, 61%, and 11% respectively. By differential scanning fluorimetry, melting temperature deviations were -5.2, -4.5, +0.5, and -3.4°C. SDS-PAGE of purified protein reveal significant aggregation of L191S, A150V, and P174H, but not A65V. We also report new data on three unusual PIMT variants among the 13 recently characterized by our laboratory. A7P and I58V were previously found to have 1.8-2.0 times the activity of WT PIMT in the standard assay; however, upon kinetic analysis, we find both variants exhibit reduced catalytic efficiency (Vmax/Km) due to weak isoaspartyl substrate binding. The near complete loss of activity (<1%) seen in R36C was investigated by comparing activity of two artificial variants. R36K shows 4.6X the activity of R36C, while R36A shows no improvement, suggesting the guanidino nitrogens of the R36 play a key role in binding the methyl donor S-adenosyl-L-methionine (AdoMet). The new findings reported here extend the list of human PIMT variants that may contribute to neurological diseases in the young and the decline of CNS function in the aged.

Trimetazidine Protects Cardiomyocytes Against Hypoxia/Reoxygenation Injury by Promoting AMP-activated Protein Kinase-dependent Autophagic Flux.

Trimetazidine (TMZ), a metabolic agent, may protect against myocardial ischemia/reperfusion injury. Because of the critical role of autophagy in cardioprotection, we aimed to evaluate whether autophagy was involved in TMZ-induced protection during hypoxia/reoxygenation (H/R). Neonatal rat cardiomyocytes were subjected to H/R injury, and they were divided into 7 groups: control, control+TMZ, control+chloroquine (Cq)/compound C (com C), H/R, H/R+TMZ, H/R+Cq/com C, and H/R+TMZ+Cq/com C. Autophagic flux was primarily assessed by Western blot and tandem fluorescent mRFP-GFP-LC3. Assays for MTS, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling, and lactate dehydrogenase release were performed to assess cell injury. Our results showed that TMZ pretreatment had a cardioprotective effect against H/R injury. The H/R+TMZ group had an increased ratio of LC3-II to LC3-I and increased autophagic flux (degradation of p62 and increases in autophagosomes and autolysosomes). TMZ also reduced apoptosis and enhanced cell survival while inducing autophagy. Correspondingly, autophagy inhibition with Cq blocked this protective effect. Furthermore, TMZ-induced enhancement of autophagy could be related to increased AMP-activated protein kinase (AMPK) phosphorylation and decreased Mammalian target of rapamycin (mTOR) phosphorylation, which was abolished by an AMPK-specific inhibitor (com C). Our data provide evidence that TMZ pretreatment protects against H/R injury by promoting autophagic flux through the AMPK signaling pathway.

Polymorphic Variants of Human Protein l-Isoaspartyl Methyltransferase Affect Catalytic Activity, Aggregation, and Thermal Stability: IMPLICATIONS FOR THE ETIOLOGY OF NEUROLOGICAL DISORDERS AND COGNITIVE AGING.

Protein l-isoaspartyl methyltransferase (PIMT/PCMT1), a product of the human pcmt1 gene, catalyzes repair of abnormal l-isoaspartyl linkages in age-damaged proteins. Pcmt1 knock-out mice exhibit a profound neuropathology and die 30-60 days postnatal from an epileptic seizure. Here we express 15 reported variants of human PIMT and characterize them with regard to their enzymatic activity, thermal stability, and propensity to aggregation. One mutation, R36C, renders PIMT completely inactive, whereas two others, A7P and I58V, exhibit activity that is 80-100% higher than wild type. G175R is highly prone to aggregation and has greatly reduced activity. R17S and R17H show markedly enhanced sensitivity to thermal denaturation. Based on previous studies of moderate PIMT variation in humans and mice, we predict that heterozygosity for R36C, G175R, R17S, and R17H will prove detrimental to cognitive function and successful aging, whereas homozygosity (if it ever occurs) will lead to severe neurological problems in the young.

4-PBA prevents pressure overload-induced myocardial hypertrophy and interstitial fibrosis by attenuating endoplasmic reticulum stress.

Our previous study indicated that attenuation of endoplasmic reticulum (ER) stress by administration of 4-phenylbutyric acid (4-PBA) could prevent cardiac rupture and remodeling in a mouse model of myocardial infarction (MI). However, whether 4-PBA is protective in hypertrophic heart disease is unclear. Thus, we tested the therapeutic effect of 4-PBA on pressure-overload induced myocardial hypertrophy. Transverse aortic constriction (TAC) was used to create myocardial hypertrophy in C57BL/6 male mice for 4 weeks. Immediately after surgery, the mice were administrated either 4-PBA (20 mg/kg/day) or 0.9% NaCl by intraperitoneal injection. At the end of 4 weeks, the mice underwent high-resolution echocardiographic imaging. Our results showed that both the left ventricular posterior wall thickness at end systole (LVPWs) and diastole (LVPWd) were increased in the TAC group, compared to control. 4-PBA administration attenuated hypertrophy and decreased the heart weight over body weight ratio. Masson's trichrome staining showed that myocardial interstitial fibrosis and collagen deposition were also decreased by 4-PBA. We next detected the ER stress response in the heart tissues of TAC mice in different time points. Western blotting showed that the expression of ER stress marker, GRP78, CHOP and phosphor-PERK, were persistently increased 4 weeks after TAC. The treatment of 4-PBA inhibited the expression of ER stress markers. We also demonstrated that the 4-PBA at 20 mg/kg/day had no effect on histone 3 deacetylation inhibition, while attenuating ER stress and TAC-induced hypertrophy. These findings suggest that 4-PBA may be a therapeutic strategy to consider in preventing pressure-overload induced myocardial hypertrophy and interstitial fibrosis by selectively attenuating ER stress.

Attenuation of ER stress prevents post-infarction-induced cardiac rupture and remodeling by modulating both cardiac apoptosis and fibrosis.

Endoplasmic reticulum (ER) stress is implicated in the pathophysiology of various cardiovascular diseases, but the role of ER stress in cardiac rupture and/or remodeling after myocardial infarction (MI) is still unclear. Here we investigated whether ER stress plays a major role for these processes in mice. We ligated the left coronary artery (LCA) without reperfusion in mice and administered either NaCl or 4-phenylbutyric acid (4-PBA, 20 mg/kg/d) intraperitoneally for 4 weeks. Cardiac rupture rates during the first week of MI were 37.5% and 18.2% in the control and 4-PBA groups, respectively. The extent of ventricular aneurysm and fibrosis was less, and the cardiac function better, in the 4-PBA group compared with the control group. The protein levels of ER stress markers in the heart tissues of the control group remained elevated during the entire 4-week period after MI, while pro-apoptotic proteins mainly increased in the early phase, and the pro-fibrotic proteins markedly increased in the late phase post MI; 4-PBA decreased all of these protein levels. In the primary cultured neonatal rat cardiomyocytes or fibroblasts, hypoxia (3% O2) increased the number of apoptotic cardiomyocytes and promoted the proliferation and migration of fibroblasts, all of which were attenuated by 4-PBA (0.5 mM). These findings indicate that MI induces ER stress and provokes cardiac apoptosis and fibrosis, culminating in cardiac rupture and remodeling, and that the attenuation of ER stress could be an effective therapeutic target to prevent post-MI complications.

Olmesartan prevents cardiac rupture in mice with myocardial infarction by modulating growth differentiation factor 15 and p53.

BACKGROUND AND PURPOSE: Cardiac rupture is a catastrophic complication that occurs after acute myocardial infarction (MI) and, at present, there are no effective pharmacological strategies for preventing this condition. Here we investigated the effect of the angiotensin II receptor blocker olmesartan (Olm) on post-infarct cardiac rupture and its underlying mechanisms of action. EXPERIMENTAL APPROACH: C57Bl/6 mice with MI were treated with Olm, aldosterone (Aldo) or vehicle. Cultured neonatal cardiomyocytes and fibroblasts were exposed to normoxia or anoxia and treated with angiotensin II (Ang II), RNH6270 (active ingredient of Olm) or Aldo. KEY RESULTS: The mortality rate and incidence of cardiac rupture in MI mice during the first week in the Olm-treated group were significantly lower than in the vehicle-treated group. Olm or RNH6270 reduced myeloperoxidase staining in the infarcted myocardium, decreased apoptosis in cultured cardiomyocytes and fibroblasts, as assessed by Hoechst staining and TUNEL assay, attenuated the accumulation of p53 and phosphorylated p53 and cleaved caspase 3 induced by MI or Ang II, as assessed by Western blotting, and up-regulated growth differentiation factor-15 (GDF-15). In cultured cardiomyocytes and fibroblasts, treatment with Ang II, Aldo or anoxia significantly down-regulated the expression of GDF-15. CONCLUSIONS AND IMPLICATIONS: Olm prevents cardiac rupture through inhibition of apoptosis and inflammation, which is attributable to the down-regulation of p53 activity and up-regulation of GDF-15. Our findings suggest that early administration of an AT1 receptor anatagonist to patients with acute MI is a potential preventive approach for cardiac rupture.

Histamine H2 receptor activation exacerbates myocardial ischemia/reperfusion injury by disturbing mitochondrial and endothelial function.

There is evidence that H2R blockade improves ischemia/reperfusion (I/R) injury, but the underlying cellular mechanisms remain unclear. Histamine is known to increase vascular permeability and induce apoptosis, and these effects are closely associated with endothelial and mitochondrial dysfunction, respectively. Here, we investigated whether activation of the histamine H2 receptor (H2R) exacerbates myocardial I/R injury by increasing mitochondrial and endothelial permeability. Serum histamine levels were measured in patients with coronary heart disease, while the influence of H2R activation was assessed on mitochondrial and endothelial function in cultured cardiomyocytes or vascular endothelial cells, and myocardial I/R injury in mice. The serum histamine level was more than twofold higher in patients with acute myocardial infarction than in patients with angina or healthy controls. In neonatal rat cardiomyocytes, histamine dose-dependently reduced viability and induced apoptosis. Mitochondrial permeability and the levels of p-ERK1/2, Bax, p-DAPK2, and caspase 3 were increased by H2R agonists. In cultured human umbilical vein endothelial cells (HUVECs), H2R activation increased p-ERK1/2 and p-moesin levels and also enhanced permeability of HUVEC monolayer. All of these effects were abolished by the H2R blocker famotidine or the ERK inhibitor U0126. After I/R injury or permanent ischemia, the infarct size was reduced by famotidine and increased by an H2R agonist in wild-type mice. In H2R KO mice, the infarct size was smaller; myocardial p-ERK1/2, p-DAPK2, and mitochondrial Bax were downregulated. These findings indicate that H2R activation exaggerates myocardial I/R injury by promoting myocardial mitochondrial dysfunction and by increasing cardiac vascular endothelial permeability.

Resveratrol improves myocardial ischemia and ischemic heart failure in mice by antagonizing the detrimental effects of fractalkine*.

OBJECTIVES: To test the hypothesis that resveratrol would improve cardiac remodeling by inhibiting the detrimental effects of fractalkine. We previously reported that fractalkine exacerbates heart failure. Furthermore, this study sought to determine whether resveratrol targets fractalkine to improve myocardial ischemia and cardiac remodeling. DESIGN: Randomized and controlled laboratory investigation. SETTING: Research laboratory. SUBJECTS: Neonatal rat cardiac cells and C57BL/6 mice. INTERVENTIONS: Cardiac cells were treated with recombinant mouse soluble fractalkine for 24 hrs or pretreated with 25 µM resveratrol. Cardiomyocytes were exposed to anoxia/reoxygenation, H2O2, or pretreatment with resveratrol. Ex vivo murine hearts were perfusioned with soluble fractalkine or pretreated with resveratrol after global ischemia. Mice were subjected to the left coronary artery ligation to induce myocardial infarction and randomized to treatment with resveratrol or vehicle alone for 42 days. MEASUREMENTS AND MAIN RESULTS: In a murine myocardial infarction model, we found that resveratrol increased survival and delayed the progression of cardiac remodeling evaluated by serial echocardiography. At 6 wks, the heart weight/body weight ratio, lung weight/body weight ratio, and old infarct size were significantly smaller in resveratrol-treated mice than in untreated myocardial infarction mice. In cultures of neonatal rat cells, exposure to soluble fractalkine increased the atrial natriuretic peptide expression by cardiomyocytes, matrix metalloproteinase-9 and procollagen expression by fibroblasts, and intercellular adhesion molecule-1 expression by microvascular endothelial cells, while it decreased autophagy in cardiomyocytes. All these effects were blocked by coculture with resveratrol. The methyl thiazolyl tetrazolium assay showed that soluble fractalkine reduced the viability of cultured cardiomyocytes during exposure to anoxia/reoxygenation or H2O2, while pretreatment with resveratrol blocked this effect. Perfusion of ex vivo murine hearts with soluble fractalkine after global ischemia led to an increase of infarct size, which was prevented by pretreatment with resveratrol. CONCLUSION: Resveratrol alleviates the deleterious effects of fractalkine on myocardial ischemia and thus reduces subsequent cardiac remodeling.

Deficiency of type 1 cannabinoid receptors worsens acute heart failure induced by pressure overload in mice.

AIMS: We investigated the influence of type one cannabinoid receptor (CB1) deficiency on acute heart failure (AHF) and the underlying mechanism. Acute heart failure syndrome is an important clinical problem because of its high morbidity and mortality rates. Activation of CB1 induces vascular dilation and reinforces the properties of morphine, long-standing therapies for AHF syndrome, but the effect of endogenous CB1 activation on AHF is largely unknown. METHODS AND RESULTS: Acute heart failure mouse model characterized by hypertension and pulmonary oedema was created by using transverse aortic constriction (TAC). Mortality, echocardiography, haemodynamic, morphology, and circulatory catecholamine levels in response to TAC were evaluated in CB1 knockout (KO) and wild-type mice. Type one cannabinoid receptor KO mice had a much higher mortality rate at 1 week after TAC attributable to AHF (65 vs. 11%, P< 0.001). One hour after TAC, CB1 KO mice had significant larger lung weight to body weight ratio (LW/BW, 14.53 + 1.09 mg/g in KO vs. 10.42 + 0.36 mg/g in WT, P < 0.01) and higher plasma epinephrine levels (9720 + 1226 pg/mL vs. 6378 + 832 pg/mL, P < 0.05). Pharmacological activation of CB1 reduced LW/BW in wild-type mice. Administration of epinephrine to wild-type TAC mice significantly increased left ventricular end-diastolic pressure and LW/BW, while CB1 agonists reduced the LW/BW and the plasma levels of catecholamine and increased myocardial activity of AMP-activated protein kinase. CONCLUSION: Endogenous activation of CB1 in mice has cardiac protection in AHF, which is attributable to the inhibition of excessive sympathetic activation.

Detrimental effect of fractalkine on myocardial ischaemia and heart failure.

AIMS: Fractalkine (FKN) is a newly identified membrane-bound chemokine; its role in myocardial ischaemia and heart failure is largely unknown. We attempted to investigate the role of FKN in myocardial ischaemia and ischaemia or pressure overload-induced ventricular remodelling and heart failure. METHODS AND RESULTS: FKN-induced changes of heart failure-related genes in cultured rat cardiac cells and the effect of FKN on cultured cardiomyocyte injury during anoxia/reoxygenation (A/R) were examined. The direct influence of FKN neutralization on heart failure and the potential mechanism was also investigated. In mice with failing hearts, myocardial FKN expression was correlated with the lung weight/body weight ratio, left ventricular fractional shortening, and brain natriuretic peptide expression. In cultured rat cells, exposure to FKN increased natriuretic peptide A expression in cardiomyocytes, matrix metalloproteinase-9 expression in fibroblasts, and intercellular adhesion molecule-1 expression in microvascular endothelial cells. FKN also promoted cardiomyocyte damage during A/R and neutralizing FKN antibody treatment improved heart failure induced by myocardial infarction or pressure overload. Neutralizing FKN or its receptor inhibited the activation of mitogen-activated protein kinases (MAPKs) in hypoxic cardiomyocytes or ischaemic myocardium. CONCLUSION: FKN promotes myocardial injury and accelerates the progress of heart failure, which is associated with the activation of MAPKs.