Sustained Toll-Like Receptor 9 Activation Promotes Systemic and Cardiac Inflammation, and Aggravates Diastolic Heart Failure in SERCA2a KO Mice

Increased levels of circulating oxidized mitochondrial DNA contribute to chronic inflammation in metabolic syndrome, and MitoQ-based antioxidant therapy alleviates this DNA-induced inflammation

Here, the aim was to investigate the role of circulating oxidized mitochondrial DNA (ox-mtDNA) in metabolic syndrome (MetS)-associated chronic inflammation and evaluate the effect of Mito-Quinone (MitoQ)-based antioxidant therapy on inflammation. A total of 112 MetS patients and 111 healthy control individuals (HCs) were recruited. Peripheral blood was collected, and mononuclear cells (PBMCs) were separated. In a preclinical study, MitoQ, a mitochondrial-targeted antioxidant, was administered to Sprague-Dawley (SD) rats fed a high-fat diet (HFD). In vitro, H₂O₂- or MitoQ-treated HUVECs served as the oxidative or antioxidative cell models to detect the cell-free ox-mtDNA level. Plasma or cell-free ox-mtDNA levels were measured by qPCR. Additionally, THP-1 cells were incubated with plasma cell-free DNA (cfDNA) from MetS patients and HCs or cell-free ox-mtDNA to detect TLR9-NF-κB pathway activation. Plasma ox-mtDNA levels and TLR9 expression levels in PBMCs were increased in MetS patients. In vivo, HFD-fed rats showed elevated plasma ox-mtDNA and TLR9 expression levels in cardiac-residing immune cells, but MitoQ administration attenuated these increases. In vitro, a significant lower level of cell-free ox-mtDNA was detected in MitoQ-treated cells, compared with H₂O₂-treated cells. Coincubation of plasma cfDNA from MetS patients or cell-free ox-mtDNA and THP-1 cells increased TLR9-NF-κB p65 expression, and promoted IL-1β, IL-6 and IL-8 secretion in THP-1 cells. In conclusion, increased circulating ox-mtDNA contributes to chronic inflammation in MetS by activating the TLR9-NF-κB pathway. MitoQ-based antioxidant therapy effectively alleviates inflammation by reducing ox-mtDNA release.

Impact of myeloid differentiation protein 1 on cardiovascular disease

Cardiovascular disease remains the leading cause of disability and mortality worldwide and a significant global burden. Many lines of evidence suggest complex remodeling responses to cardiovascular disease, such as myocardial ischemia, hypertension and valve disease, which lead to poor clinical outcomes, including heart failure, arrhythmia and sudden cardiac death (SCD). The mechanisms underlying cardiac remodeling are closely related to reactive oxygen species (ROS) and inflammation. Myeloid differentiation protein 1 (MD1) is a secreted glycoprotein known as lymphocyte antigen 86. The complex of MD1 and radioprotective 105 (RP105) is an important regulator of inflammation and is involved in the modulation of vascular remodeling and atherosclerotic plaque development. A recent study suggested that the expression of MD1 in hypertrophic cardiomyopathy (HCM) patients is decreased compared with that in donor hearts. Therefore, MD1 may play an important role in the pathological processes of cardiovascular disease and have potential clinical value. Here, this review aims to discuss the current knowledge regarding the role of MD1 in the regulation of cardiac pathophysiology.

Insight into the Pro-inflammatory and Profibrotic Role of Macrophage in Heart Failure With Preserved Ejection Fraction

The prevalence of heart failure (HF) with preserved ejection fraction (HFpEF) is higher than that of HF with reduced/midrange ejection fraction (HFrEF/HFmrEF). However, no evidence-based guidelines for managing HFpEF have been generated. The current body of knowledge indicates that fibrosis and inflammation are important components of the cardiac remodeling process in HFpEF. In addition, macrophages potentially play an important role in pro-inflammatory and profibrotic processes in HFpEF patients, whereas HFpEF comorbidities could be a driving force for systemic microvascular inflammation and endothelial dysfunction. Under such circumstances, macrophages reportedly contribute to inflammation and fibrosis through 3 phases namely, inflammation, repair, and resolution. Signal transduction pathway-targeted therapies using animal experiments have generated important discoveries and breakthroughs for understanding the underlying mechanisms of HFpEF. However, only a handful of studies have reported promising results using human trials. Further investigations are therefore needed to elucidate the exact mechanisms underlying HFpEF and immune-pathogenesis of cardiac fibrosis.

Various aspects of inflammation in heart failure

Despite significant advances in the prevention and treatment of heart failure (HF), the prognosis in patients who have been hospitalised on at least one occasion due to exacerbation of HF is still poor. Therefore, a better understanding of the underlying pathophysiological mechanisms of HF is crucial in order to achieve better results in the treatment of this clinical syndrome. One of the areas that, for years, has aroused the interest of researchers is the activation of the immune system and the elevated levels of biomarkers of inflammation in patients with both ischaemic and non-ischaemic HF. Additionally, it is intriguing that the level of circulating pro-inflammatory biomarkers correlates with the severity of the disease and prognosis in this group of patients. Unfortunately, clinical trials aimed at assessing interventions to modulate the inflammatory response in HF have been disappointing, and the modulation of the inflammatory response has had either no effect or even a negative effect on the HF prognosis. The article presents a summary of current knowledge on the role of immune system activation and inflammation in the pathogenesis of HF. Understanding the immunological mechanisms pathogenetically associated with left ventricular remodelling and progression of HF may open up new therapeutic possibilities for HF.

NETosis as a Pathogenic Factor for Heart Failure

Heart failure threatens the lives of patients and reduces their quality of life. Heart failure, especially heart failure with preserved ejection fraction, is closely related to systemic and local cardiac persistent chronic low-grade aseptic inflammation, microvascular damage characterized by endothelial dysfunction, oxidative stress, myocardial remodeling, and fibrosis. However, the initiation and development of persistent chronic low-grade aseptic inflammation is unexplored. Oxidative stress-mediated neutrophil extracellular traps (NETs) are the main immune defense mechanism against external bacterial infections. Furthermore, NETs play important roles in noninfectious diseases. After the onset of myocardial infarction, atrial fibrillation, or myocarditis, neutrophils infiltrate the damaged tissue and aggravate inflammation. In tissue injury, damage-related molecular patterns (DAMPs) may induce pattern recognition receptors (PRRs) to cause NETs, but whether NETs are directly involved in the pathogenesis and development of heart failure and the mechanism is still unclear. In this review, we analyzed the markers of heart failure and heart failure-related diseases and comorbidities, such as mitochondrial DNA, high mobility box group box 1, fibronectin extra domain A, and galectin-3, to explore their role in inducing NETs and to investigate the mechanism of PRRs, such as Toll-like receptors, receptor for advanced glycation end products, cGAS-STING, and C-X-C motif chemokine receptor 2, in activating NETosis. Furthermore, we discussed oxidative stress, especially the possibility that imbalance of thiol redox and MPO-derived HOCl promotes the production of 2-chlorofatty acid and induces NETosis, and analyzed the possibility of NETs triggering coronary microvascular thrombosis. In some heart diseases, the deletion or blocking of neutrophil-specific myeloperoxidase and peptidylarginine deiminase 4 has shown effectiveness. According to the results of current pharmacological studies, MPO and PAD4 inhibitors are effective at least for myocardial infarction, atherosclerosis, and certain autoimmune diseases, whose deterioration can lead to heart failure. This is essential for understanding NETosis as a therapeutic factor of heart failure and the related new pathophysiology and therapeutics of heart failure.

TLR9 deficiency alleviates doxorubicin-induced cardiotoxicity via the regulation of autophagy

Doxorubicin is a commonly used anthracycline chemotherapeutic drug. Its application for treatment has been impeded by its cardiotoxicity as it is detrimental and fatal. DNA damage, cardiac inflammation, oxidative stress and cell death are the critical links in DOX-induced myocardial injury. Previous studies found that TLR9-related signalling pathways are associated with the inflammatory response of cardiac myocytes, mitochondrial dysfunction and cardiomyocyte death, but it remains unclear whether TLR9 could influence DOX-induced heart injury. Our current data imply that DOX-induced cardiotoxicity is ameliorated by TLR9 deficiency both in vivo and in vitro, manifested as improved cardiac function and reduced cardiomyocyte apoptosis and oxidative stress. Furthermore, the deletion of TLR9 rescued DOX-induced abnormal autophagy flux in vivo and in vitro. However, the inhibition of autophagy by 3-MA abolished the protective effects of TLR9 deletion on DOX-induced cardiotoxicity. Moreover, TLR9 ablation suppressed the activation of p38 MAPK during DOX administration and may promote autophagy via the TLR9-p38 MAPK signalling pathway. Our study suggests that the deletion of TLR9 exhibits a protective effect on doxorubicin-induced cardiotoxicity by enhancing p38-dependent autophagy. This finding could be used as a basis for the development of a prospective therapy against DOX-induced cardiotoxicity.

Reporting animal research: Explanation and elaboration for the ARRIVE guidelines 2.0

Improving the reproducibility of biomedical research is a major challenge. Transparent and accurate reporting is vital to this process; it allows readers to assess the reliability of the findings and repeat or build upon the work of other researchers. The ARRIVE guidelines (Animal Research: Reporting In Vivo Experiments) were developed in 2010 to help authors and journals identify the minimum information necessary to report in publications describing in vivo experiments. Despite widespread endorsement by the scientific community, the impact of ARRIVE on the transparency of reporting in animal research publications has been limited. We have revised the ARRIVE guidelines to update them and facilitate their use in practice. The revised guidelines are published alongside this paper. This explanation and elaboration document was developed as part of the revision. It provides further information about each of the 21 items in ARRIVE 2.0, including the rationale and supporting evidence for their inclusion in the guidelines, elaboration of details to report, and examples of good reporting from the published literature. This document also covers advice and best practice in the design and conduct of animal studies to support researchers in improving standards from the start of the experimental design process through to publication.

New insights into SERCA2a gene therapy in heart failure: pay attention to the negative effects of B-type natriuretic peptides

Sarcoplasmic/endoplasmic reticulum calcium ATPase 2a (SERCA2a) is a target of interest in gene therapy for heart failure with reduced ejection fraction (HFrEF). However, the results of an important clinical study, the Calcium Upregulation by Percutaneous Administration of Gene Therapy in Cardiac Disease (CUPID) trial, were controversial. Promising results were observed in the CUPID 1 trial, but the results of the CUPID 2 trial were negative. The factors that caused the controversial results remain unclear. Importantly, enrolled patients were required to have a higher plasma level of B-type natriuretic peptide (BNP) in the CUPID 2 trial. Moreover, BNP was shown to inhibit SERCA2a expression. Therefore, it is possible that high BNP levels interact with treatment effects of SERCA2a gene transfer and accordingly lead to negative results of CUPID 2 trial. From this point of view, effects of SERCA2a gene therapy should be explored in heart failure with preserved ejection fraction, which is characterised by lower BNP levels compared with HFrEF. In this review, we summarise the current knowledge of SERCA2a gene therapy for heart failure, analyse potential interaction between BNP levels and therapeutic effects of SERCA2a gene transfer and provide directions for future research to solve the identified problems.

The Role of Toll-Like Receptor Signaling in the Progression of Heart Failure

Medical systems worldwide are being faced with a growing need to understand mechanisms behind the pathogenesis of heart failure (HF) that is considered as a leading cause of morbidity and mortality around the world. Elevated levels of inflammatory mediators have been identified in patients with HF, which are primarily manifestations of innate immune responses mediated by pattern recognition receptors (PRRs). Toll-like receptors (TLRs), which belong to PRRs, are subjected to the release of pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs) to generate innate immune responses. More and more emerging data indicate that TLR signaling pathway molecules are involved in the progression of HF. Herein, we present new data with regard to the activation of TLRs in the failing heart, focusing on TLR2, TLR3, TLR4, and TLR9, and suggest the potential use of TLRs in target therapy.

Toll-Like Receptor 9 Promotes Survival in SERCA2a KO Heart Failure Mice

Aim. Inflammation is important in heart failure (HF). The role of the immune receptor toll-like receptor 9 (TLR9) in HF is not understood and not investigated in diastolic HF. We investigated the role of TLR9 in a murine diastolic HF model caused by cardiomyocyte SERCA2a excision. Methods and Results. We crossed SERCA2a KO and TLR9 KO mice to generate four mouse lines. Tamoxifen-induced cardiomyocyte SERCA2a gene excision was carried out in mice, causing diastolic HF. After 7.6 weeks, cardiac functions and dimensions were analyzed by echocardiography and heart tissues were processed. HF mice depleted of TLR9 demonstrated reduced survival compared to SERC2a KO mice, with a median life expectancy of 58 days compared to 63 days. Both HF groups displayed increased left atrium size, lung weight, fetal gene expressions, monocyte/macrophage infiltration, and fibrosis. However, there were no significant differences between the groups. Conclusion. In mice with SERCA2a KO-induced diastolic HF, the absence of TLR9 reduced median life expectancy. The cause remains elusive, as all investigated HF parameters were unaltered. Still, these findings support a salutary role of TLR9 in some subsets of HF conditions and underline the importance for future studies on the mechanisms of TLR9 in diastolic HF.

Low Circulating Levels of Mitochondrial and High Levels of Nuclear DNA Predict Mortality in Chronic Heart Failure

BACKGROUND

Mitochondrial DNA (mtDNA) and possibly nuclear DNA (nDNA) are released as danger-associated molecular patterns during cardiac stress, and may activate several innate immune receptors. The purpose of this study was to investigate the regulation of these danger-associated molecular patterns during human heart failure (HF).

METHODS AND RESULTS

Plasma levels of mtDNA and nDNA from HF patients (n = 84) were analyzed by reverse transcriptase-polymerase chain reaction and compared with controls (n = 72). Increased levels of mtDNA were found in New York Heart Association (NYHA) I-II and NYHA III-IV. There was evidence of increased nDNA in NYHA III-IV compared with controls and NYHA I-II. Kaplan-Meier analysis revealed higher mortality in patients with high nDNA levels, whereas high levels of mtDNA were associated with survival.

CONCLUSIONS

Plasma levels of mtDNA and nDNA are elevated in human HF associated with increased and decreased mortality, respectively. This study may suggest a rationale for exploring interventions within inflammatory signaling pathways activated by nucleic acids as novel targets in treatment of HF.