TY - JOUR
AU - Tsutsui,, Hiroyuki
AB - Abstract Aims Recent accumulating evidence suggests that sterile inflammation plays a crucial role in the progression of various cardiovascular diseases. However, its contribution to right ventricular (RV) dysfunction remains unknown. The aim of this study was to elucidate whether toll-like receptor 9 (TLR9)-NF-κB-mediated sterile inflammation plays a critical role in the pathogenesis of RV dysfunction. Methods and results We performed main pulmonary artery banding (PAB) in rats to induce RV pressure overload and dysfunction. On Day 14 after PAB, the pressure overload impaired RV function as indicated by increased RV end-diastolic pressure concomitant with macrophage infiltration and fibrosis, as well as maximal activation of NF-κB and TLR9. Short-term administration (days 14–16 after PAB) of a specific TLR9 inhibitor, E6446, or an NF-κB inhibitor, pyrrolidine dithiocarbamate (PDTC) significantly attenuated NF-κB activation. Furthermore, long-term administration of E6446 (treatment: days 14–28) or PDTC (prevention: days −1 to 28; treatment: days 14 to 28) improved RV dysfunction associated with mitigated macrophage infiltration and fibrosis in right ventricle and decreased serum brain natriuretic peptide levels. Conclusion Inhibition of TLR9-NF-κB pathway-mediated sterile inflammation improved PAB-induced RV dysfunction in rats. This pathway plays a major role in the progression of pressure overload-induced RV dysfunction and is potentially a novel therapeutic target for the disorder. RV dysfunction , Pressure overload , TLR9 , NF-κB , Sterile inflammation 1. Introduction Right ventricular (RV) failure is one of the leading causes of death in various cardiovascular diseases including pulmonary hypertension (PH) and congenital heart diseases.1 In the early stage of PH, RV pressure overload induces adaptive cardiac hypertrophy to maintain its performance.2 As the disease progresses, the RV dilates with fibrotic changes losing both systolic and diastolic functions and results in RV failure and death.3 However, little is known about the mechanisms of RV dysfunction, and specific therapies for RV dysfunction remain to be established. Thus, better understanding of the mechanisms of RV dysfunction is urgently needed to improve the prognosis of those patients. Nuclear factor-κB (NF-κB) is a ubiquitous transcription factor known for its roles in immunity, apoptosis, proliferation, hypertrophy, and inflammation.4 Previous reports indicated that NF-κB was activated in RV tissue samples from experimental PH models such as monocrotaline- and Sugen5416/hypoxia/normoxia-exposed rats, and that inhibition of NF-κB improved RV dysfunction in those models.5,6 However, the direct effects of NF-κB on RV dysfunction remain unclear, because its inhibition ameliorated pulmonary vascular remodelling and reduced RV afterload. Furthermore, inhibition of NF-κB deteriorated adaptive cardiac hypertrophy in mice with left ventricular (LV) pressure overload.7,8 Contrary to these results, chronic inhibition of NF-κB activation attenuated fibrosis and apoptosis, and improved cardiac function in mice with LV failure.9,10 Thus, the contribution of NF-κB activation to cardiac dysfunction remains controversial. Toll-like receptor 9 (TLR9), a key receptor modulating the innate immune system, plays an important role in activating inflammatory responses in various diseases such as interstitial pneumonia,11 systemic hypertension,12 and obesity.13 A recent study in mice has demonstrated that damaged mitochondrial DNA (mtDNA) released from pressure-overloaded cardiomyocytes activates TLR9 and induces sterile inflammation, leading to LV failure.14 Also, mtDNA triggers innate immune response via TLR9 and its down-stream NF-κB activation in cardiomyocytes.15 We, therefore, hypothesized that the TLR9-NF-κB pathway-mediated sterile inflammation might contribute to pressure overload-induced RV dysfunction. To test this hypothesis, we created RV dysfunction by performing pulmonary artery (PA) banding (PAB) in rats and evaluated subsequent changes in RV function and NF-κB activation. We employed this experimental model, because it allows us to induce RV pressure overload independent of pulmonary vascular properties, thereby making it possible to study the isolated impact of NF-κB activation on RV dysfunction. We also examined whether selective inhibition of TLR9 or NF-κB could suppress RV inflammation and improve RV function. 2. Methods The institutional animal care and use committee of the Kyushu University, Japan, approved all experimental protocols. We performed all animal procedures following the principles of the NIH Guide for the Care and Use of Laboratory Animals (NIH Publication, 8th Edition, 2011). 2.1 Pulmonary artery banding procedure in rats We performed PAB in adult male Sprague-Dawley rats weighting 180–220 g. The procedure has been reported elsewhere.16 Briefly, we anaesthetized the rat with isoflurane (isoflurane induction: 3.0% in room air; maintenance: 0.5% in room air). Through a left thoracotomy, we placed an 18-gauge needle (outer diameter, 1.3 mm) alongside the main PA, and tied the needle and the main PA together with a 3-0 nylon suture. Removal of the needle left a PA constriction with lumen size equal to the diameter of the needle. Sham operated rats underwent the same procedure without tying the PA. 2.2 Experimental protocols 2.2.1 Impact of PAB on haemodynamics and inflammation of right ventricle (protocol 1) We performed PAB on Day 0 and evaluated haemodynamics, RV histology, and NF-κB activation assay on days 1, 3, 7, 14, and 28 by euthanizing animals on each day (see Supplementary material online, Figure S1). We euthanized sham-operated rats on Day 7. 2.2.2 Effects of short-term (3-day) TLR9 inhibition on NF-κB activation in PAB rats (protocol 2) To determine the direct effects of short-term TLR9 inhibition on NF-κB activation, we used a selective TLR9 inhibitor (E6446 provided by Eisai, Brazil),17 and an NF-κB inhibitor, pyrrolidine dithiocarbamate (PDTC; Sigma, Japan).6,18 We measured NF-κB activity on Day 14 in the following four groups: (i) age-matched sham-operated rats (Sham), (ii) PAB alone rats (Vehicle), (iii) PAB rats administered PDTC (200 mg/kg/day as dietary admix, from days 14 to 16), and (iv) PAB rats administered E6446 (10 mg/kg/day in drinking water, from days 14 to 16). Compared with other TLR inhibitors, E6446 is a highly selective, orally active TLR9 inhibitor in vitro (IC50 for TLR9, 7, and 4 are 0.01, 1.78, and 10.58 µM, respectively, in human embryonic kidney cells),19 and the specificity is also maintained in vivo (up to 20 mg/kg/day).17 E6446 was also reported to diminish Il6 production in response to a TLR9 ligand, unmethylated CpG, in human peripheral blood mononuclear cells at concentrations ranging from 0.05 to 0.5 µM.17 In addition, we observed that E6446 at concentrations ranging from 1.0 to 3.0 µM) concentration-dependently and markedly inhibited the expression of Il6 mRNA in rat peritoneal macrophages pretreated with unmethylated CpG treatment (data not shown). 2.2.3 Effects of long-term NF-κB or TLR9 inhibition on RV function in PAB rats (protocol 3) In the preventive protocol, we administered PDTC to animals from 1 day prior to PAB (Day −1) to Day 28. In the treatment protocol, we administered PDTC or E6446 from days 14 to 28 after PAB. In each protocol, we performed echocardiography on Day 27 and catheterization on Day 28 in five groups of rats: (i) age-matched sham-operated (Sham), (ii) PAB alone (Vehicle), (iii) PAB with PDTC (200 mg/kg/day as dietary admix, from days −1 to 28) (PDCT-P), (iv) PAB with PDTC (200 mg/kg/day as dietary admix, from days 14 to 28) (PDCT-T), and (v) PAB with E6446 (10 mg/kg/day in drinking water, from days 14 to 28) (E6446-T). 2.3 Evaluation of RV function, haemodynamic parameters, and RV hypertrophy Under isoflurane (1.5% in room air) anaesthesia, we performed echocardiography (Vevo2100; VISUALSONICS, Fujifilm, Japan) and measured RV end-diastolic diameter and RV end-systolic diameter at the level of the papillary muscle using the two-dimensional parasternal short-axis view.20 We estimated tricuspid annular plane systolic excursion (TAPSE) and base-to-apex shortening of RV during systole using M-mode in the four-chamber view. On the following day after the echocardiography, we conducted open-chest RV catheterization under general anaesthesia (isoflurane induction: 3.0% in room air; maintenance: 0.5% in room air). We inserted a 2-Fr micro-tip catheter (SPR-320; Millar Instruments, Houston, TX, USA) into right ventricle to measure high fidelity RV pressure. We measured aortic pressure (AP) via the carotid artery using a fluid filled system (DX-300; Nihon-Kohden, Japan). We attached a flow probe (2.5 PS; Transonic Systems, Ithaca, NY, USA) around the aortic root to measure aortic flow. We digitized instantaneous RVP, AP, and aortic flow at 1000 Hz with 16-bit resolution (Power Lab 16/30, AD Instruments, Sydney, Australia) and stored in a dedicated laboratory computer system. Real-time digital data analysis yielded RV systolic pressure (RVSP), RV end-diastolic pressure (RVEDP), maximum time derivative of RV pressure normalized by RVEDP (Max + dP/dt/RVEDP), mean AP (mAP), and cardiac output (CO). We obtained cardiac index (CI) by normalizing CO with body weight. After haemodynamic measurements, the heart was removed and weighed. We graded RV hypertrophy by the weight ratio of RV free wall to the sum of LV free wall and septum (RV/LV+S).21 2.4 Measurement of NF-κB activity NF-κB activation, which indicates the DNA binding ability of p65, was determined by enzyme-linked immunosorbent assay (ELISA). RV tissues were excised and immediately frozen. We extracted the nuclear protein samples from RV tissues using NE-PER Nuclear and Cytoplasmic Extraction Reagents (Thermo Fisher Scientific, USA) according to the manufacturer’s instruction. We quantified NF-κB activity as reported previously using TransAM NFκB p65 (Active Motif, USA).22 Briefly, we incubated the nuclear protein samples for 1 h in a 96-well plate coated with an oligonucleotide containing the NF-κB consensus sequence (5′-GGGACTTTCC-3′). After washing, we added NF-κB antibody (1:1000 dilution) to these wells. After 1-h incubation with a secondary horseradish peroxidase-conjugated antibody (1:1000 dilution), we estimated the specific binding by colorimetry at 450 nm with reference wavelength at 655 nm and standard curves. 2.5 Measurement of serum brain natriuretic peptide levels We measured serum brain natriuretic peptide (BNP) using the Rat BNP 45 ELISA Kit (ab108816; Abcam, Cambridge, England).23 Briefly, serum samples (50 μL) were applied to wells containing primary capture antibody and incubated. We added 50 μL of Biotinylated BNP 45 antibody to each well. After incubation, we added 50 μL of SP Conjugate and 50 μL of Chromogen Substrate to each well. After 10-min incubation, we added 50 μL of Stop Solution to each well and read the absorbance at 450 nm with reference at 655 nm. 2.6 Reverse transcription-polymerase chain reaction (RT-PCR) analysis We extracted total RNAs from RV and cells using the RNeasy Mini Kit (QIAGEN, Hilden, Germany) and determined mRNA expression levels by real-time polymerase chain reaction (PCR).24 For reverse transcription and amplification, we used the ReverTra Ace qPCR Kit (TOYOBO, Japan) and SYBR Premix Ex Taq (TaKaRa, Tokyo, Japan), respectively. We obtained the PCR primers and probes from TaKaRa. A 10-μL RT reaction mixture containing 200 ng of total RNA, oligo dT primer, random primer, and Moloney murine leukaemia virus reverse transcriptase was subjected to transverse transcription. The aliquot of RT product was diluted with water, and 25 μg of the cDNA was subjected to real-time PCR analysis using a FastStart SYBR Green Master kit and a LightCycler (Roche, Basel, Switzerland). The thermal cycle was composed of an initial denaturation at 95°C, for 30 s followed by 40 cycles of denaturation at 95°C for 5 s and annealing at 60°C for 34 s. We analysed the melting curve of the PCR product at the end of the real-time PCR analysis and confirmed the single peak of the melting profile. Electrophoresis confirmed that each PCR product showed a single band with the expected molecular size. We employed the ΔΔCt method to analyse the fluorescence data using 18s (5′-CCC TGA ACT CAA CTG TGA AAT AGC A-3′, 5′-CCC AAG TCA AGG GCT TGG AA-3′) as an internal control. 2.7 Histopathological analysis After catheterization, the rat was euthanized (by exsanguination under isoflurane). The heart was harvested, immediately fixed in buffered 10% paraformaldehyde, embedded in paraffin, and cut into 5-μm thick sections. We stained serial sections with haematoxylin and eosin or Masson Trichrome. Myocyte hypertrophy: We measured myocyte cross-sectional area by tracing the outline of 80 to 120 myocytes stained by haematoxylin and eosin in each section.25 Fibrotic area: We quantified fibrotic area on digitized images of Masson Trichrome stained sections. We expressed the blue stained tissue areas as a percentage of total RV surface area.25 2.8 Immunohistochemical analysis We used 5-μm thick sections for immunohistochemical staining. All sections were blocked with 5% skim milk in PBS, and incubated with primary antibody at 4°C overnight. The antibodies used were anti-mouse p65 (1:200 dilution; MAB3026; Millipore, MA, USA), anti-mouse CD68 (1:400 dilution; ab31630; Abcam, Cambridge, England) and anti-CD34 antibody (1:100 dilution; LS-C150289; LS Bio, WA, USA). We incubated each section with biotinylated secondary antibody prior to horseradish peroxidase-labelled streptavidin. We acquired images with an upright microscope (BX63, Olympus, Japan). CD68-positive macrophage count: Number of CD68-positive cells in RV tissue section was counted and normalized by area (cell/mm2).26 Capillary density: We identified capillary epithelium by CD34 antibody. Capillary density was expressed as the number of CD34-positive capillaries per section area, measured in at least three randomly chosen areas per ventricle, where cardiomyocytes were transversally sectioned at a magnification of ×400.27 Apoptosis: We labelled apoptotic cells using a TdT-mediated dUTP-biotin nick end labelling in situ Apoptosis Detection Kit (MK500, TaKaRa, Tokyo, Japan). In brief, 5-μm sections were deparaffinized, rehydrated and treated with 20 μg/mL Proteinase-K (9034, Clontech, CA, USA) for 15 min before in situ hybridization, and labelled following the manufacturer’s protocol. The lacteal grand in rats served as positive control. We counterstained each section with haematoxylin and examined by light microscopy at ×400. 2.9 Immunofluorescent analysis Stable TLR9 locates in endoplasmic reticulum (ER).28 When TLR9 senses its specific agonist in subcellular ligand such as unmethylated CpG, it translocates from ER to the endosome, and subsequently ligates to the agonist and activates the down-stream signalling such as MyD88 and TRAF6 in the endosome.29,30 To evaluate TLR9 activation in right ventricle of Sham and PAB rats on Day 14 after the surgery, we used immunofluorescent analysis to trace TLR9 translocation from ER to endosome. Briefly, we embedded the heart in OCT compound (Sakura, Japan) at −80°C. After slicing the heart into 8-μm thick sections, we fixed them in acetone (Sigma, Japan). Each section was washed with PBS containing 0.1% Triton X-100 (Sigma-Aldrich, MO, USA), then blocked with 5% skim milk in PBS. We incubated the sections at 4°C overnight with the following antibodies: anti-TLR9 antibody (1:50 dilution; ab12121; Abcam), EEA1 antibody (a marker of endosome, 1:50 dilution; #2411; Cell Signaling, MA USA) and calnexin antibody (a marker of ER, 1:100 dilution; #2433; Cell Signaling). Each section was washed with PBS and incubated with fluorescence-conjugated secondary antibodies (1:1000 dilution; Alexa fluor 488- or 555-coupled; Invitrogen, CA, USA). We acquired images with a confocal microscope (FV1000-D; Olympus, Japan). Negative control sections for immunofluorescent experiments were treated with normal IgG (normal mouse IgG: sc-2025, and normal rabbit IgG: sc-2027; both from Santa Cruz Biotechnology, TX, USA) instead of primary antibody, and all sections showed no specific staining (data not shown). 2.10 Statistical analysis All data were verified for normal distribution. We presented data as mean ± SEM. A P-value less than 0.05 was considered statistically significant. For haemodynamic and remodelling studies, we tested the differences among six groups by one-way analysis of variance (ANOVA) followed by a post hoc Dunnett test (vs. Sham group as control). For protocols 2 and 3, we tested the differences among five groups by one-way ANOVA followed by a post hoc Tukey–Kramer test. 3. Results 3.1 Impact of PAB on haemodynamic parameters, RV hypertrophy and wall thickening and inflammation (protocol 1) RVSP increased time-dependently following PAB reaching a maximum on Day 14 (Figure 1A). RVEDP initially increased on Day 1 but declined thereafter indicating activation of compensatory mechanisms. RVEDP re-increased on Days 14 and 28 suggesting possible worsening of RV function (Figure 1B). Mean AP and heart rate (HR) remained unchanged (Figure 1C and D). RV hypertrophy (RV/LV+S: weight ratio of RV free wall to the sum of LV free wall and septum) developed after PAB and progressed over time (Figure 1E). Haematoxylin and eosin staining revealed that RV wall thickening and dilatation (Figure 1F). These results suggested that PAB activated compensatory mechanisms including RV hypertrophy until Day 7, which successfully lowered RVEDP. However, after Day 14, the compensatory mechanisms were no longer sufficient to prevent RV dysfunction. Figure 1 View largeDownload slide Impact of pulmonary artery banding (PAB) on haemodynamic parameters and right ventricular hypertrophy in rats. (A) Right ventricular systolic pressure (RVSP). (B) Right ventricular end-diastolic pressure (RVEDP). (C) Heart rate (HR). (D) Mean arterial pressure (mAP). (E) Right ventricular hypertrophy (RV/LV+S: weight ratio of RV free wall to the sum of LV free wall and septum). Rats underwent PAB or sham operation (Sham). N = 4–5 in each group for A to D, and N = 6–9 in each group for E. Values are expressed as mean ± SEM. Differences were tested by one-way analysis of variance, followed by post hoc Dunnet test. **P < 0.01 vs. Sham. (F) Representative low-magnification photomicrographs of whole heart cross-sections. Haematoxylin and eosin stained. Scale bars indicate 1 mm. Figure 1 View largeDownload slide Impact of pulmonary artery banding (PAB) on haemodynamic parameters and right ventricular hypertrophy in rats. (A) Right ventricular systolic pressure (RVSP). (B) Right ventricular end-diastolic pressure (RVEDP). (C) Heart rate (HR). (D) Mean arterial pressure (mAP). (E) Right ventricular hypertrophy (RV/LV+S: weight ratio of RV free wall to the sum of LV free wall and septum). Rats underwent PAB or sham operation (Sham). N = 4–5 in each group for A to D, and N = 6–9 in each group for E. Values are expressed as mean ± SEM. Differences were tested by one-way analysis of variance, followed by post hoc Dunnet test. **P < 0.01 vs. Sham. (F) Representative low-magnification photomicrographs of whole heart cross-sections. Haematoxylin and eosin stained. Scale bars indicate 1 mm. Immunostaining showed increased expression of p65 in the nuclei of cardiomyocytes and interstitial inflammatory cells following PAB (Figure 2A). ELISA showed a significant increase in NF-κB activity on Day 14 (PAB: 14.3 ± 4.1 vs. Sham: 4.3 ± 0.9 pg/mg, P < 0.05) (Figure 2B). Figure 2 View largeDownload slide Temporal changes in right ventricle NF-κB activity in rats that underwent pulmonary artery banding (PAB). (A) Representative photomicrographs of p65 immunostaining of right ventricle cross-sections of rats that underwent sham operation (Sham) or PAB at various time points. Arrow heads indicate p65-positive cells. Scale bars indicate 200 μm. (B) NF-κB activity evaluated by ELISA. N = 5 in each group. Values are expressed as mean ± SEM. Differences were tested by one-way analysis of variance, followed by post hoc Dunnet test. *P < 0.05 vs. Sham. Figure 2 View largeDownload slide Temporal changes in right ventricle NF-κB activity in rats that underwent pulmonary artery banding (PAB). (A) Representative photomicrographs of p65 immunostaining of right ventricle cross-sections of rats that underwent sham operation (Sham) or PAB at various time points. Arrow heads indicate p65-positive cells. Scale bars indicate 200 μm. (B) NF-κB activity evaluated by ELISA. N = 5 in each group. Values are expressed as mean ± SEM. Differences were tested by one-way analysis of variance, followed by post hoc Dunnet test. *P < 0.05 vs. Sham. 3.2 Translocation of TLR9 from ER to endosome in the right ventricle To clarify the up-stream molecular mechanism of NF-κB in the right ventricle of PAB rats, we examined the activity of TLR9 that plays a key role in NF-κB-mediated sterile inflammation.29 Immunofluorescent images showed co-localization of TLR9 with calnexin (ER marker) in the right ventricle of Sham and PAB rats on Day 14 (Figure 3A). On the other hand, TLR9 co-localized with EEA1 (endosome marker) in PAB but not in Sham rats (Figure 3B). These results indicate the translocation of TLR9 from ER to endosomes, suggesting TLR9 activation in the right ventricle of PAB rats on Day 14. Figure 3 View largeDownload slide Activity of toll-like receptor 9 (TLR9) in right ventricle of rats that underwent pulmonary artery banding (PAB). Representative immunofluorescent images of TLR9 in RV tissues of sham-operated (Sham) rats or rats on Day 14 after PAB. (A) Calnexin (green) and TLR9 (red). (B) EEA1 (green) and TLR9 (red). DAPI, 4′,6-diamidino-2-phenylindole for nuclear staining. Arrow heads indicate double positive deposits. Scale bars indicate 20 μm. Figure 3 View largeDownload slide Activity of toll-like receptor 9 (TLR9) in right ventricle of rats that underwent pulmonary artery banding (PAB). Representative immunofluorescent images of TLR9 in RV tissues of sham-operated (Sham) rats or rats on Day 14 after PAB. (A) Calnexin (green) and TLR9 (red). (B) EEA1 (green) and TLR9 (red). DAPI, 4′,6-diamidino-2-phenylindole for nuclear staining. Arrow heads indicate double positive deposits. Scale bars indicate 20 μm. 3.3 Effects of short-term TLR9 inhibition on NF-κB activation in the right ventricle (protocol 2) As shown in Figure 4A, p65 was highly expressed in the nuclei of cardiomyocytes and interstitial inflammatory cells in the right ventricle of PAB rats (Vehicle) on Day 16. Short-term administration (days 14–16) of PDTC or E6446 remarkably decreased p65-positive cells in not only in the nuclei of cardiomyocytes but also interstitial inflammatory cells in the right ventricle of PAB rats (Figure 4B and C). ELISA showed that short-term administration of PDTC or E6446 significantly and similarly attenuated the activation of NF-κB in PAB rats (Figure 4D). Figure 4 View largeDownload slide Right ventricular (RV) NF-κB activity after short-term treatment with pyrrolidine dithiocarbamate (PDTC) or E6446 in rats that underwent pulmonary artery banding (PAB). (A) Representative photomicrographs of p65-imunostained RV tissues of sham-operated rats (Sham) or rats on Day 16 after PAB. Higher magnification images are shown in insets. Arrow heads indicate p65-positive cells. Scale bars indicates 50 μm. (B and C) Statistical analyses of the counting results for p65-positive cells in cardiomyocytes (B) and interstitial cells (C). (D) NF-κB activation evaluated by ELISA. N = 4 in each group. Values are expressed as mean ± SEM. Differences were tested by one-way analysis of variance, followed by post hoc Tukey–Kramer test. ‡P < 0.01 vs. Sham; *P < 0.05 and **P < 0.01 vs. PAB alone (Vehicle). Figure 4 View largeDownload slide Right ventricular (RV) NF-κB activity after short-term treatment with pyrrolidine dithiocarbamate (PDTC) or E6446 in rats that underwent pulmonary artery banding (PAB). (A) Representative photomicrographs of p65-imunostained RV tissues of sham-operated rats (Sham) or rats on Day 16 after PAB. Higher magnification images are shown in insets. Arrow heads indicate p65-positive cells. Scale bars indicates 50 μm. (B and C) Statistical analyses of the counting results for p65-positive cells in cardiomyocytes (B) and interstitial cells (C). (D) NF-κB activation evaluated by ELISA. N = 4 in each group. Values are expressed as mean ± SEM. Differences were tested by one-way analysis of variance, followed by post hoc Tukey–Kramer test. ‡P < 0.01 vs. Sham; *P < 0.05 and **P < 0.01 vs. PAB alone (Vehicle). 3.4 Effect of chronic NF-κB or TLR9 inhibition on RV function and serum BNP (protocol 3) PAB did not change mAP or HR in Vehicle, PDTC-P, PDTC-T, and E6446 groups, except for HR in Vehicle group on Day 28 (see Supplementary material online, Figure S2A and B). Compared with the PAB alone (Vehicle) group, PDTC or E6446 increased RVSP (Figure 5A), CI (Figure 5B) and Max + dP/dt/RVEDP (Figure 5D), and decreased RVEDP (Figure 5C). In addition, TAPSE significantly increased in PDTC groups (Figure 5E). Other echocardiography derived parameters were shown in Supplementary material online, Figure S3A–C. PDTC or E6446 significantly decreased the elevated serum BNP level in PAB rats (Figure 5F). All these data indicated that chronic inhibition of NF-κB or TLR9 improved RV dysfunction in PAB rats. Figure 5 View largeDownload slide Effects of long-term treatment with pyrrolidine dithiocarbamate (PDTC) or E6446 on haemodynamic and right ventricular (RV) functional parameters and serum brain natriuretic peptide (BNP) level in rats that underwent pulmonary artery banding (PAB). (A) RV systolic pressure (RVSP). (B) Cardiac index (CI). (C) RV end-diastolic pressure (RVEDP). (D) RV Max positive dP/dt divided by RVEDP (Max + dP/dt/RVEDP). (E) Tricuspid annular plane systolic excursion (TAPSE). (F) Serum BNP level. Measurements were performed on Day 28 after PAB in the following groups: sham-operated (Sham), PAB alone (Vehicle), PAB with PDTC on days −1 to 28 (prevention: PDTC-P), PAB with PDTC on days 14–28 (treatment: PDTC-T), and PAB with E6446 on days 14–28 (treatment: E6446-T). N = 4–6 in each group. Values are expressed as mean ± SEM. Differences were tested by one-way analysis of variance, followed by post hoc Tukey–Kramer test. †P < 0.05 and ‡P < 0.01 vs. Sham; *P < 0.05 and **P < 0.01 vs. Vehicle. Figure 5 View largeDownload slide Effects of long-term treatment with pyrrolidine dithiocarbamate (PDTC) or E6446 on haemodynamic and right ventricular (RV) functional parameters and serum brain natriuretic peptide (BNP) level in rats that underwent pulmonary artery banding (PAB). (A) RV systolic pressure (RVSP). (B) Cardiac index (CI). (C) RV end-diastolic pressure (RVEDP). (D) RV Max positive dP/dt divided by RVEDP (Max + dP/dt/RVEDP). (E) Tricuspid annular plane systolic excursion (TAPSE). (F) Serum BNP level. Measurements were performed on Day 28 after PAB in the following groups: sham-operated (Sham), PAB alone (Vehicle), PAB with PDTC on days −1 to 28 (prevention: PDTC-P), PAB with PDTC on days 14–28 (treatment: PDTC-T), and PAB with E6446 on days 14–28 (treatment: E6446-T). N = 4–6 in each group. Values are expressed as mean ± SEM. Differences were tested by one-way analysis of variance, followed by post hoc Tukey–Kramer test. †P < 0.05 and ‡P < 0.01 vs. Sham; *P < 0.05 and **P < 0.01 vs. Vehicle. 3.5 Effects of chronic NF-κB or TLR9 inhibition on RV hypertrophy, macrophage infiltration and fibrosis Compared with Sham group, PAB significantly increased CSA, RV/LV+S, infiltration of CD68-positive macrophages and RV fibrosis (Figure 6A–D), and significantly decreased RV capillary density without changing apoptotic ratio (see Supplementary material online, Figure S4A–C) on Day 28. PDTC or E6446 did not affect CSA or RV/LV+S compared with Vehicle group. In contrast, either treatment significantly and markedly suppressed PAB-induced infiltration of CD68-positive macrophages and RV fibrosis (Figure 6A, D, E), but preserved RV capillary density and had no impact on apoptosis (see Supplementary material online, Figure S4A–C). These results suggested that chronic inhibition of the NF-κB-TLR9 pathway ameliorated pressure overload-induced RV inflammation and fibrosis, but not RV hypertrophy itself. Figure 6 View largeDownload slide Effects of long-term treatment with pyrrolidine dithiocarbamate (PDTC) or E6446 on cardiomyocyte size, inflammation and fibrosis in right ventricle of rats that underwent pulmonary artery banding (PAB). (A) Representative haematoxylin and eosin (HE, scale bars = 20 μm), CD68 (arrow heads indicate CD68-positive macrophages, scale bars = 50 μm), and Masson trichrome stained right ventricle tissue (MT, scale bars = 200 μm). (B) Cross-sectional area (CSA) evaluated by HE staining. (C) Right ventricular hypertrophy (RV/LV+S = weight ratio of RV free wall to the sum of LV free wall and septum). Statistical analysis of the results for CD68-positive macrophages (D) and for fibrosis (E). Measurements were performed on Day 28 after PAB in the following groups: sham-operated (Sham), PAB alone (Vehicle), PAB with PDTC on days −1 to 28 (prevention: PDTC-P), PAB with PDTC on days 14–28 (treatment: PDTC-T), and PAB with E6446 on days 14–28 (treatment: E6446-T). N = 4–6 in each group. Values are expressed as mean ± SEM. Differences were tested by one-way analysis of variance, followed by post hoc Tukey–Kramer test. ‡P < 0.01 vs. Sham; **P < 0.01 vs. Vehicle. Figure 6 View largeDownload slide Effects of long-term treatment with pyrrolidine dithiocarbamate (PDTC) or E6446 on cardiomyocyte size, inflammation and fibrosis in right ventricle of rats that underwent pulmonary artery banding (PAB). (A) Representative haematoxylin and eosin (HE, scale bars = 20 μm), CD68 (arrow heads indicate CD68-positive macrophages, scale bars = 50 μm), and Masson trichrome stained right ventricle tissue (MT, scale bars = 200 μm). (B) Cross-sectional area (CSA) evaluated by HE staining. (C) Right ventricular hypertrophy (RV/LV+S = weight ratio of RV free wall to the sum of LV free wall and septum). Statistical analysis of the results for CD68-positive macrophages (D) and for fibrosis (E). Measurements were performed on Day 28 after PAB in the following groups: sham-operated (Sham), PAB alone (Vehicle), PAB with PDTC on days −1 to 28 (prevention: PDTC-P), PAB with PDTC on days 14–28 (treatment: PDTC-T), and PAB with E6446 on days 14–28 (treatment: E6446-T). N = 4–6 in each group. Values are expressed as mean ± SEM. Differences were tested by one-way analysis of variance, followed by post hoc Tukey–Kramer test. ‡P < 0.01 vs. Sham; **P < 0.01 vs. Vehicle. 4. Discussion This study has demonstrated that PAB increased NF-κB activity via TLR9 in the pressure-overloaded RV in rats. Short-term treatment with E6446 significantly attenuated the increased NF-κB activity in PAB rats, suggesting that TLR9 plays a major role in regulating the NF-κB activation. Chronic inhibition of the TLR9-NF-κB pathway improved RV function in PAB rats associated with attenuating macrophage infiltration and RV fibrosis. These results suggest that inhibition of the TLR9-NF-κB pathway-mediated sterile inflammation could be a novel therapeutic target for pressure overload-induced RV dysfunction. Although previous studies have demonstrated the activation of NF-κB in established RV dysfunction in experimental PH models such as monocrotaline- and Sugen5416/hypoxia/normoxia-exposed rats,6,31 little is known about its temporal roles and up-stream mechanisms of activation in this process. In this study, PAB did not significantly activate NF-κB from days 1 to 7, during which RV showed the simple compensatory adaptive mechanism of cardiac hypertrophy as evidenced by the increase in RVSP with relatively low RVEDP. On the other hand, on Day 14, RV pressure overload significantly activated NF-κB, and concomitantly increased RVEDP and decreased CI, suggesting the decreased slope of CO-preload (RVEDP) relation, thereby impaired RV function. In addition, we found that chronic treatment with PDTC for both prevention (from days −1 to 28) and treatment (from days 14 to 28) protocols strikingly reduced RVEDP and increased CI despite preserved or further increased RVSP, suggesting that the inhibitors steepened the slope of CO-preload relation and improved RV function without any effect on RV hypertrophy on Day 28. Taken together, these data suggest that (i) pressure overload alone is sufficient to activate NF-κB, (ii) NF-κB activation at a later time point (from Day 14) contributes to the development of RV dysfunction, and (iii) NF-κB activation may not be involved in the adaptive cardiac hypertrophy in response to sustained pressure overload. The third observation agrees with a previous study looking at RV hypertrophy in Sugen5416/hypoxia/normoxia-exposed rats6 but contradicts another study that examined LV hypertrophy in transverse aortic constriction (TAC) mice.8 The reason for this discrepancy is unclear, however, differences in ventricle studied, method of NF-κB inhibition and/or animal species might be responsible, and further investigations are needed to clarify this issue. Recent studies have indicated that haemodynamic stress-induced mtDNA damage and the resultant inflammation via activation of TLR9 play an important role in the pathogenesis of LV failure.14 This study demonstrated that PAB caused NF-κB activation, macrophage infiltration, and fibrosis in the pressure-overloaded RV. In addition, we observed translocation of TLR9 from ER to endosomes suggesting activation of TLR9 on Day 14 when NF-κB was maximally activated. These data suggest that haemodynamic stress contributes to the inflammatory process via activation of the TLR9-NF-κB pathway in the pressure-overloaded RV. This interpretation is further supported by the results of short-term inhibition of TLR9, in which the selective TLR9 inhibitor E6446 attenuated NF-κB activation in PAB rats. Although technical difficulties prevented us from measuring DAMPs levels in the RV myocytes, Oka et al.14 reported that deposits of mtDNA co-localized with TLR9 in autolysosomes from pressure-overloaded LV in Dnase2a−/− mice on Day 2 after TAC. Based on their observations, it is reasonable to speculate that the ligand of TLR9 is mtDNA in the RV after PAB, and that pressure overload-induced mtDNA damage together with subsequent sterile inflammation via activation of TLR9 may be responsible for the development of RV fibrosis and dysfunction without the further changes of RV hypertrophy. We found that long-term treatment with either PDTC or E6446 increased Max + dP/dt/RVEDP, TAPSE and CI and decreased RVEDP, resulting in reduced serum BNP level, an index of RV failure without changes of RV hypertrophy. These data indicate that chronic inhibition of the TLR9-NF-κB pathway improved RV function at least in part by reducing RV fibrosis in PAB (Figure 5). Our results provide novel evidence that TLR9-NF-κB-mediated inflammation may contribute to the pathogenesis of RV dysfunction (or failure) induced by pressure overload. Regarding the specificity of E6446 on TLR9 in vivo, Franklin et al.17 reported that 20 mg/kg (5 days) of E6446 completely inhibited increases of cytokine levels in response to the TLR9 agonist (CpG ODN1668) but not to the synthetic non-nucleic acid agonists of TLR7 (i.e. CL097, R848) or LPS in the spleen cells harvested from mice. Another study demonstrated that 20 or 60 mg/kg/day of E6446 markedly and dose-dependently inhibited a key down-stream cytokine of TLR9, serum Il6 levels 2 h after the challenge with CpG ODN1668 in C57BL/6 mice.19 These data suggest that the specificity of E6446 (up to 20 mg/kg/day) for TLR9 appears to be maintained in this dose range in vivo. In our preliminary study, we also measured Il6 mRNA levels in the RVs of following rat groups; sham, PAB and PAB with E6446 (10 mg/kg/day, days 14 to 16) on Day 16. We found PAB increased the tissue Il6 level (9.3 ± 3.6, n = 4, respectively), which was markedly suppressed by a short-term administration of E6446 (4.9 ± 2.3, n = 4, respectively). We did not assess the translocation of TLR9 from ER to the endosome in the RVs of PAB rats with E6446 treated rats, because E6446 reduces the endosomal activation of nucleic acid-sensing TLR9 by inhibiting the link between the agonist and TLR9 after its translocation to the endosome.17,19 However, based on the data of inhibitory effects of E6446 on Il6 mRNA, we thought 10 mg/kg/day of E6446 as a selective TLR9 inhibitor in PAB rats. Regarding the specificity of PDTC in vivo, Liu et al.32 reported that pretreatment of rats with 200 mg/kg of PDTC suppressed LPS-induced NF-κB/DNA-binding activity but not AP-1–binding activity in rats. This dose of PDTC had no effect on DNA-binding activities of the other transcription factors AP-2, CREB or Sp-1. These data suggest that 200 mg/kg of PDTC is within the range of specific inhibitory doses on NF-κB in rats. In our study, short-term administration of PDTC (200 mg/kg/day, days 14 to 16) significantly decreased p65-positive cells and NF-κB activities in the right ventricle of PAB rats (Figure 4A–D). Regarding the cell type with TLR9-NF-κB mediated sterile inflammation, we demonstrated that short-term inhibition of TLR9 with a selective TLR9 inhibitor E6446 or an NF-κB inhibitor PDTC attenuated NF-κB activation not only in the nuclei of cardiomyocytes but also interstitial inflammatory cells (Figure 4B and C). In our preliminary study, we found little positive cells for T or B cell markers in right ventricles of PAB. We observed that these inflammatory cells were predominantly CD68-positive macrophages, and that both inhibitors significantly suppressed their expressions in right ventricles with PAB (Figure 6D). We speculate that the pressure overload initially damages mtDNA and then activate following TLR9-NF-κB pathway activation cardiomyocytes. The fragmented mtDNA spilled out from the cardiomyocytes may activate the TLR9-NF-κB pathway in resident inflammatory cells, mainly macrophages. This speculation is supported by our immunohistochemical observations that the p65-positive cells were expressed predominantly in cardiomyocytes on Day 3 after PAB and in both cardiomyocytes and inflammatory cells on Day 14 (Figure 2A). We, therefore, conjecture that the initial inflammatory response via TLR9 takes place in cardiomyocytes, which is followed by activation of the TLR9-NF-κB pathway in cells in close vicinity. Further temporal examinations with techniques such as electronic microscopy using cell-specific antibodies for cardiomyocytes, interstitial macrophages or fibroblasts are needed to confirm our speculation especially cell types contributing to the TLR9-NF-κB-mediated inflammation in the pressure-overloaded right ventricle in the future studies. Various studies demonstrated the involvement of inflammatory cells in the development of RV dysfunction in rats with monocrotaline-induced PH27 or with acute pulmonary embolism.33 Also, a report indicated that transient PAB in dogs resulted in overexpression of pro-inflammatory cytokines including IL-1β and IL-6.34 Another paper showed that increased expressions of inflammatory genes such as TNF-α and ICAM-2 in right ventricle with advanced RV failure, which was induced by systemic-to-pulmonary shunting 6 months after the surgery in piglets.35 On the other hand, the roles of inflammatory cells and mediators in the development of RV failure in patients remain largely unknown. One of the reasons is that most data were obtained using tissue/organ samples from patients at autopsy or heart transplantation when the disorder has advanced to end-stage.2 These patients likely receive multiple treatments including mechanical support to achieve haemodynamic unloading, which further complicates the interpretation of the findings. The findings in this study indicate that inhibition of the TLR9-NF-κB pathway attenuates inflammatory cell infiltration and fibrosis in PAB rats. Further studies are needed to identify detailed regulatory relationship of the TLR9-NF-κB pathway with its downstream pro-inflammatory signalling and fibrosis in the development of RV dysfunction. In addition, it has been reported that TLR9-NF-κB directly reduces cardiac contractility in vitro and in vivo studies.36 These data suggest that the inhibition of TLR9-NF-κB not only causes interstitial fibrosis but also reduces cardiac contractility in the pressure-overloaded right ventricle. The effects of TLR9 on inflammatory signalling in systemic arteries remain controversial. In contrast to in vitro data describing CpG DNA-mediated activation of macrophages stimulating foam cell formation,37 Koulis et al.,38 have reported that genetic ablation of TLR9 worsened atherosclerosis via activation of CD4+ T cells in ApoE−/− mice with a high-fat diet.39 They demonstrated that CpG oligodeoxynucleotide TLR9 agonist reduced the severity of atherosclerotic lesions. We speculate that mechanisms of inflammatory cell types or cytokines between atherosclerosis and RV dysfunction might be different. However, the underlying mechanisms remain unclear. For translation of our present findings into clinical medicine, further studies are needed to evaluate the adverse effects of a specific TLR9 inhibitor, E6446 on systemic arteries in patients with RV dysfunction. 5. Conclusion In conclusion, we demonstrated that the TLR9-NF-κB pathway-mediated sterile inflammation contributed to the development of RV dysfunction in rats with RV pressure overload. Considering that RV failure is a leading cause of death in various cardiovascular diseases including PH and congenital heart diseases, and there are no effective therapeutic agents for RV dysfunction, our novel finding that E6446, an orally active selective TLR9 inhibitor, attenuated TLR9-NF-κB-mediated inflammation and improved RV dysfunction is potentially of major clinical importance for the treatment of this disorder. For translation of our present findings into clinical medicine, further studies are needed to investigate whether TLR9-NF-κB-mediated inflammation is activated in patients with RV dysfunction, and whether E6446 selectively and safely inhibits inflammation and improves RV function in those patients. Footnotes Time for primary review: 36 days Acknowledgements We thank Akiko Ando for technical assistance. Conflict of interest: K.A. worked in a department endowed by Actelion Pharmaceuticals Japan and received a research grant from Mochida Pharmaceutical Co., Ltd. K.S. works in a department endowed by Actelion Pharmaceuticals Japan and received research funding from Actelion Pharmaceuticals Japan. H.T. received honoraria from Daiichi Sankyo, Inc., Otsuka Pharmaceutical Co., Ltd., Takeda Pharmaceutical Co. Ltd., Mitsubishi Tanabe Pharma Corporation, Boehringer Ingelheim Japan, Inc., Novartis Pharma K.K., Bayer Yakuhin, Ltd., Bristol-Myers Squibb KK, and Astellas Pharma Inc. and research funds from Actelion Pharmaceuticals Japan, Daiichi Sankyo, Inc., and Astellas Pharma Inc. 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TI - Inhibition of TLR9-NF-κB-mediated sterile inflammation improves pressure overload-induced right ventricular dysfunction in rats
JF - Cardiovascular Research
DO - 10.1093/cvr/cvy209
DA - 2019-03-01
UR - https://www.deepdyve.com/lp/oxford-university-press/inhibition-of-tlr9-nf-b-mediated-sterile-inflammation-improves-A6tUnVWutS
SP - 658
VL - 115
IS - 3
DP - DeepDyve
ER -