Doxycycline attenuates chronic intermittent hypoxia-induced atrial fibrosis in rats

Chronic Intermittent Hypoxia-Induced Diaphragm Muscle Weakness Is NADPH Oxidase-2 Dependent

Chronic intermittent hypoxia (CIH)-induced redox alterations underlie diaphragm muscle dysfunction. We sought to establish if NADPH oxidase 2 (NOX2)-derived reactive oxygen species (ROS) underpin CIH-induced changes in diaphragm muscle, which manifest as impaired muscle performance. Adult male mice (C57BL/6J) were assigned to one of three groups: normoxic controls (sham); chronic intermittent hypoxia-exposed (CIH, 12 cycles/hour, 8 h/day for 14 days); and CIH + apocynin (NOX2 inhibitor, 2 mM) administered in the drinking water throughout exposure to CIH. In separate studies, we examined sham and CIH-exposed NOX2-null mice (B6.129S-Cybb^TM1Din/J). Apocynin co-treatment or NOX2 deletion proved efficacious in entirely preventing diaphragm muscle dysfunction following exposure to CIH. Exposure to CIH had no effect on NOX2 expression. However, NOX4 mRNA expression was increased following exposure to CIH in wild-type and NOX2 null mice. There was no evidence of overt CIH-induced oxidative stress. A NOX2-dependent increase in genes related to muscle regeneration, antioxidant capacity, and autophagy and atrophy was evident following exposure to CIH. We suggest that NOX-dependent CIH-induced diaphragm muscle weakness has the potential to affect ventilatory and non-ventilatory performance of the respiratory system. Therapeutic strategies employing NOX2 blockade may function as an adjunct therapy to improve diaphragm muscle performance and reduce disease burden in diseases characterised by exposure to CIH, such as obstructive sleep apnoea.

Mechanisms of Atrial Fibrillation in Obstructive Sleep Apnoea

Obstructive sleep apnoea (OSA) is a strong independent risk factor for atrial fibrillation (AF). Emerging clinical data cite adverse effects of OSA on AF induction, maintenance, disease severity, and responsiveness to treatment. Prevention using continuous positive airway pressure (CPAP) is effective in some groups but is limited by its poor compliance. Thus, an improved understanding of the underlying arrhythmogenic mechanisms will facilitate the development of novel therapies and/or better selection of those currently available to complement CPAP in alleviating the burden of AF in OSA. Arrhythmogenesis in OSA is a multifactorial process characterised by a combination of acute atrial stimulation on a background of chronic electrical, structural, and autonomic remodelling. Chronic intermittent hypoxia (CIH), a key feature of OSA, is associated with long-term adaptive changes in myocyte ion channel currents, sensitising the atria to episodic bursts of autonomic reflex activity. CIH is also a potent driver of inflammatory and hypoxic stress, leading to fibrosis, connexin downregulation, and conduction slowing. Atrial stretch is brought about by negative thoracic pressure (NTP) swings during apnoea, promoting further chronic structural remodelling, as well as acutely dysregulating calcium handling and electrical function. Here, we provide an up-to-date review of these topical mechanistic insights and their roles in arrhythmia.

Role of epigenetic abnormalities and intervention in obstructive sleep apnea target organs

ABSTRACT

Obstructive sleep apnea (OSA) is a common condition that has considerable impacts on human health. Epigenetics has become a rapidly developing and exciting area in biology, and it is defined as heritable alterations in gene expression and has regulatory effects on disease progression. However, the published literature that is integrating both of them is not sufficient. The purpose of this article is to explore the relationship between OSA and epigenetics and to offer better diagnostic methods and treatment options. Epigenetic modifications mainly manifest as post-translational modifications in DNA and histone proteins and regulation of non-coding RNAs. Chronic intermittent hypoxia-mediated epigenetic alterations are involved in the progression of OSA and diverse multiorgan injuries, including cardiovascular disease, metabolic disorders, pulmonary hypertension, neural dysfunction, and even tumors. This article provides deeper insights into the disease mechanism of OSA and potential applications of targeted diagnosis, treatment, and prognosis in OSA complications.

Advances in Molecular Pathology of Obstructive Sleep Apnea

Obstructive sleep apnea (OSA) is a common syndrome that features a complex etiology and set of mechanisms. Here we summarized the molecular pathogenesis of OSA, especially the prospective mechanism of upper? airway dilator fatigue and the current breakthroughs. Additionally, we also introduced the molecular mechanism of OSA in terms of related studies on the main signaling pathways and epigenetics alterations, such as microRNA, long non-coding RNA, and DNA methylation. We also reviewed small molecular compounds, which are potential targets for gene regulations in the future, that are involved in the regulation of OSA. This review will be beneficial to point the way for OSA research within the next decade.

Improving effects of eplerenone on atrial remodeling induced by chronic intermittent hypoxia in rats

OBJECTIVE

Atrial fibrillation (AF) is closely associated with the overactivation of the renin-angiotensin-aldosterone system. Large cohort studies and recent meta-analyses have shown that the utilization of mineralocorticoid receptor antagonists has positive effects on the prevention and development of AF. This study aimed to investigate the effects of eplerenone on atrial remodeling in AF model rats and elucidate its intrinsic mechanism.

METHODS

Ninety male Sprague-Dawley rats were randomly divided into the control group, chronic intermittent hypoxia (CIH) group, and CIH-eplerenone intervention (CIH-E) group. Rats in the CIH and CIH-E groups received CIH for 6 weeks, and rats in the CIH-E group were additionally administered eplerenone gavage (10 mg/kg/d). After modeling, the baseline parameters of each group were examined. Histopathology, molecular biology, isolated electrophysiology, and patch clamp experiments were performed after sampling.

RESULTS

Compared with the control group, rats in the CIH group showed atrial enlargement, significant aggravated fibrosis, upregulated JAK/STAT3 pathway, shortened effective refractory period (ERP), increased AF inducibility, and decreased peak current density of characteristic voltage-gated ion channels in atrial myocytes. After eplerenone intervention, rats in the CIH-E group had a smaller atrial diameter than those in the CIH group. Furthermore, downregulated JAK/STAT3 pathway, prolonged ERP, decreased AF inducibility, and increased peak current density of characteristic ion channels were also observed in the CIH-E group.

CONCLUSIONS

CIH induced significant atrial remodeling in rats and eplerenone significantly ameliorated the atrial remodeling caused by CIH. This could be attributed to the downregulation of the JAK/STAT3 pathway and the increase in the characteristic ion current density of atrial myocytes.

Ameliorative Impact of Liraglutide on Chronic Intermittent Hypoxia-Induced Atrial Remodeling

Atrial fibrillation (AF) is the most frequent form of clinical cardiac arrhythmias. Previous evidence proved that atrial anatomical remodeling (AAR) and atrial electrical remodeling (AER) are crucial for the progression and maintenance of AF. This study is aimed at investigating the impact of the glucagon-like peptide-1 (GLP-1) receptor agonist, Liraglutide (Lir), on atrial remodeling (AR) mouse model induced by chronic intermittent hypoxia (CIH). C57BL/6 mice were categorized randomly into the control, Lir, CIH, and CIH+Lir groups. CIH was performed in CIH and CIH+Lir groups for 12 weeks. Lir (0.3 mg/kg/day, s.c) was administered to the Lir and CIH+Lir groups for four weeks, beginning from the ninth week of CIH. Meanwhile, echocardiography and right atrial endocardial electrophysiology via jugular vein, as well as induction rate and duration of AF, were evaluated. Masson and Sirius red staining assays were utilized to assess the extent of fibrosis in the atrial tissue of the mice. Immunohistochemical staining, RT-qPCR, and Western blotting were performed to evaluate the marker levels of AAR and AER and the expression of genes and proteins of the miR-21/PTEN/PI3K/AKT signaling pathway, respectively. ELISA was also performed to evaluate the changes of serum inflammatory factor levels. The CIH group exhibited significant AR, increased atrial fibrosis, and a higher incidence rate of AF compared to the control group. Lir could significantly downregulate the protein expression level in the PI3K/p-AKT pathway and upregulated that of phosphatase and tensin homolog deleted on chromosome ten (PTEN). Moreover, Lir downregulated the expression of miR-21. However, the protein expressions of CACNA1C and KCNA5 in atrial tissue were not changed significantly. In addition, Lir significantly attenuated the levels of markers of inflammation (TNF-α and IL-6) in the serum. In the mouse model of CIH, Lir treatment could ameliorate AR by the miR-21/PTEN/PI3K/AKT signaling pathway and modulation of inflammatory responses.

On the Relationship between Diabetes and Obstructive Sleep Apnea: Evolution and Epigenetics

This review offers an overview of the relationship between diabetes, obstructive sleep apnea (OSA), obesity, and heart disease. It then addresses evidence that the traditional understanding of this relationship is incomplete or misleading. In the process, there is a brief discussion of the evolutionary rationale for the development and retention of OSA in light of blood sugar dysregulation, as an adaptive mechanism in response to environmental stressors, followed by a brief overview of the general concepts of epigenetics. Finally, this paper presents the results of a literature search on the epigenetic marks and changes in gene expression found in OSA and diabetes. (While some of these marks will also correlate with obesity and heart disease, that is beyond the scope of this project). We conclude with an exploration of alternative explanations for the etiology of these interlinking diseases.

The effect of long-term doxycycline treatment in a mouse model of cigarette smoke-induced emphysema and pulmonary hypertension

Chronic obstructive pulmonary disease (COPD) is a major cause of death and a still incurable disease, comprising emphysema and chronic bronchitis. In addition to airflow limitation, patients with COPD can suffer from pulmonary hypertension (PH). Doxycycline, an antibiotic from the tetracycline family, in addition to its pronounced antimicrobial activity, acts as a matrix metalloproteinase (MMP) inhibitor and has anti-inflammatory properties. Furthermore, doxycycline treatment exhibited a beneficial effect in several preclinical cardiovascular disease models. In preclinical research, doxycycline is frequently employed for gene expression modulation in Tet-On/Tet-Off transgenic animal models. Therefore, it is crucial to know whether doxycycline treatment in Tet-On/Tet-Off systems has effects independent of gene expression modulation by such systems. Against this background, we assessed the possible curative effects of long-term doxycycline administration in a mouse model of chronic CS exposure. Animals were exposed to cigarette smoke (CS) for 8 mo and then subsequently treated with doxycycline for additional 3 mo in room air conditions. Doxycycline decreased the expression of MMPs and general pro-inflammatory markers in the lungs from CS-exposed mice. This downregulation was, however, insufficient to ameliorate CS-induced emphysema or PH. Tet-On/Tet-Off induction by doxycycline in such models is a feasible genetic approach to study curative effects at least in established CS-induced emphysema and PH. However, we report several parameters that are influenced by doxycycline and use of a Tet-On/Tet-Off system when evaluating those parameters should be interpreted with caution.

MicroRNA-21 Mediates a Positive Feedback on Angiotensin II-Induced Myofibroblast Transformation

Objective

Post myocardial infarction (MI) fibrosis has been identified as an important factor in the progression of heart failure. Previous studies have revealed that microRNA-21 (miR-21) plays an important role in the pathogenesis of fibrosis. The purpose of this study was to explore the role of miR-21 in post-MI cardiac fibrosis.

Material and Methods

MI was established in wild-type (WT) and miR-21 knockout (KO) mice. Primary mice cardiac fibroblasts (CFs) were isolated from WT and miR-21 KO mice and were treated with angiotensin II (Ang II) or Sprouty1 (Spry1) siRNA. Histological analysis and echocardiography were used to determine the extent of fibrosis and cardiac function.

Results

Compared with WT mice, miR-21 KO mice displayed smaller fibrotic areas and decreased expression of fibrotic markers and inflammatory cytokines. In parallel, Ang II-induced myofibroblasts transformation was partially inhibited upon miR-21 KO in primary CFs. Mechanistically, we found that the expression of Spry1, a previously reported target of miR-21, was markedly increased in miR-21 KO mice post MI, further inhibiting ERK1/2 activation. In vitro studies showed that Ang II activated ERK1/2/TGF-β/Smad2/3 pathway. Phosphorylated Smad2/3 further enhanced the expression of α-SMA and FAP and may promote the maturation of miR-21, thereby downregulating Spry1. Additionally, these effects of miR-21 KO on fibrosis were reversed by siRNA-mediated knockdown of Spry1.

Conclusion

Our findings suggest that miR-21 promotes post-MI fibrosis by targeting Spry1. Furthermore, it mediates a positive feedback on Ang II, thereby inducing the ERK/TGF-β/Smad pathway. Therefore, targeting the miR-21–Spry1 axis may be a promising therapeutic option for ameliorating post-MI cardiac fibrosis.

Role of ion channels in chronic intermittent hypoxia-induced atrial remodeling in rats

AIMS

Atrial remodeling, including structural and electrical remodeling, is considered as the substrate in the development of atrial fibrillation (AF). Structural remodeling mainly involves atrial fibrosis, and electrical remodeling is closely related to the changes of ion channels in atrial myocytes. In this study, we aimed to investigate the changes of ion channels in atrial remodeling induced by CIH in rats, which provide the explication for the mechanisms of AF.

MATERIALS AND METHODS

80 male Sprague-Dawley rats were randomized into two groups: Control and CIH group (n = 40). CIH rats were subjected to CIH 8 h/d for 30 days. Atrial epicardial conduction velocity, conduction inhomogeneity and AF inducibility were examined. Masson's trichrome staining was used to evaluate the extent of atrial fibrosis, and the expression levels of ion channel subunits were measured by RT-qPCR, Western blot, and IHC, respectively. The remaining 40 rats were used for whole-cell patch clamp experiments. Action potential, I_Na, I_Ca-L, I_to were recorded and compared between two groups.

KEY FINDINGS

CIH rats showed increased AF inducibility, atrial interstitial collagen deposition, APD, expression levels of RyR2, p-RyR2, CaMKII, p-CaMKII, and decreased atrial epicardial conduction velocity, expression levels of Na_v1.5, Ca_v1.2, K_v1.5, K_v4.2, K_v4.3 compared to the Control rats, and the current density of I_Na, I_Ca-L, I_to were significantly decreased in CIH group.

SIGNIFICANCE

We observed significant atrial remodeling induced by CIH in our rat model, which was characterized by changes in ion channels. These changes may be the mechanisms of CIH promoting AF.

Epigenetics: A Potential Mechanism Involved in the Pathogenesis of Various Adverse Consequences of Obstructive Sleep Apnea

Epigenetics is defined as the heritable phenotypic changes which do not involve alterations in the DNA sequence, including histone modifications, non-coding RNAs, and DNA methylation. Recently, much attention has been paid to the role of hypoxia-mediated epigenetic regulation in cancer, pulmonary hypertension, adaptation to high altitude, and cardiorenal disease. In contrast to sustained hypoxia, chronic intermittent hypoxia with re-oxygenation (IHR) plays a major role in the pathogenesis of various adverse consequences of obstructive sleep apnea (OSA), resembling ischemia re-perfusion injury. Nevertheless, the role of epigenetics in the pathogenesis of OSA is currently underexplored. This review proposes that epigenetic processes are involved in the development of various adverse consequences of OSA by influencing adaptive potential and phenotypic variability under conditions of chronic IHR. Improved understanding of the interaction between genetic and environmental factors through epigenetic regulations holds great value to give deeper insight into the mechanisms underlying IHR-related low-grade inflammation, oxidative stress, and sympathetic hyperactivity, and clarify their implications for biomedical research.

Matrix metalloproteinases as possible biomarkers of obstructive sleep apnea severity - A systematic review

Obstructive sleep apnea is an underdiagnosed sleep-related breathing disorder affecting millions of people. Recurrent episodes of apnea/hypopnea result in intermittent hypoxia leading to oxidative stress. Obstructive sleep apnea is considered an independent risk factor for cardiovascular disease but the exact pathophysiology of adverse cardiovascular outcomes of obstructive sleep apnea has not been fully elucidated. Matrix metalloproteinases (MMPs) have been associated with both oxidative stress and cardiovascular diseases. Hypoxic conditions were shown to influence MMP expression, secretion and activity. Moreover, matrix metalloproteinases contribute to ischemia/reperfusion injury. Therefore, action of matrix metalloproteinases can provide a possible molecular mechanism linking obstructive sleep apnea with oxidative stress and cardiovascular disease. The aim of this paper was to review the current evidence of association between matrix metalloproteinases and obstructive sleep apnea with focus on hypoxemia and severity of obstructive sleep apnea.

Beneficial effects of tolvaptan on atrial remodeling induced by chronic intermittent hypoxia in rats

INTRODUCTION

Atrial remodeling in the form of fibrosis is considered as the substrate for the development of atrial fibrillation (AF). The aim of this study was to investigate the effects of tolvaptan on chronic intermittent hypoxia (CIH) induced atrial remodeling and the mechanisms underlying such changes.

METHODS

A total of 45 Sprague-Dawley rats were randomized into three groups: Control group, CIH group, CIH with tolvaptan treatment (CIH-T) group (n = 15). CIH rats were subjected to CIH 6 hour/d for 30 days, and CIH-T rats were administrated tolvaptan while they received CIH. After the echocardiography examination, rats were sacrificed in the 31 days. In each group, 5 rats were randomly selected for isolated heart electrophysiology testing, for other 10 rats, the tissues of atria were sampled for histological and molecular biological experiments, Masson's trichrome staining was used to evaluate the extent of atrial fibrosis, expression levels of microRNA-21 (miR-21), Sprouty-1 (Spry1), phosphatase, and tensin homolog (PTEN), extracellular regulated protein kinase (ERK), phospho-extracellular regulated protein kinase (p-ERK), matrix metalloprotein 9 (MMP-9), phosphoinositide 3-kinase (PI3K), protein kinase B (AKT), phospho-protein kinase B (p-AKT), nuclear factor-k-gene binding (NF-κB), phosphor-nuclear factor-k-gene binding (p-NF-κB) were measured.

RESULTS

Compared to the Control rats, CIH rats showed higher atrial interstitial collagen deposition and AF inducibility, mRNA levels of miR-21, MMP-9, PI3K, AKT, and protein levels of ERK, p-ERK, MMP-9, NF-κB, p-NF-κB were significantly increased, whereas mRNA levels of Spry1, ERK, and protein levels of Spry1, PTEN, PI3K, AKT, p-AKT were significantly decreased. Treatment with tolvaptan attenuated CIH-induced atrial fibrosis, reduced AF inducibility, expression levels of miR-21 and its downstream factors were also improved.

CONCLUSIONS

CIH-induced significant atrial remodeling in our rat model, which was attenuated by tolvaptan. These changes may be explained due to alterations in miR-21/Spry1/ERK/MMP-9, miR-21/PTEN/PI3K/AKT, and NF-κB pathways by tolvaptan.

Doxycycline Attenuates Atrial Remodeling by Interfering with MicroRNA-21 and Downstream Phosphatase and Tensin Homolog (PTEN)/Phosphoinositide 3-Kinase (PI3K) Signaling Pathway

BACKGROUND Atrial remodeling especially in the form of fibrosis is the most important substrate of atrial fibrillation (AF). The aim of this study was to investigate the effects of doxycycline on chronic intermittent hypoxia (CIH)-induced atrial remodeling and the pathophysiological mechanisms underlying such changes. MATERIAL AND METHODS A total of 30 Sprague-Dawley rats were randomized into 3 groups: Control group, CIH group, and CIH with doxycycline treatment group. CIH rats were subjected to CIH 6 h/d for 30 days and treatment rats were administrated doxycycline while they received CIH. After the echocardiography examination, rats were sacrificed at 31 days. The tissues of atria were collected for histological and molecular biological experiments, Masson staining was used to evaluate the extent of atrial fibrosis, microRNA-21, and its downstream target phosphatase and tensin homolog (PTEN), phosphoinositide 3-kinase (PI3K) were assessed. RESULTS Compared to the control group, the CIH rats showed higher atrial interstitial collagen fraction, increased microRNA-21, PI3K levels, and decreased PTEN levels. Doxycycline treatment attenuated CIH-induced atrial fibrosis, reduced microRNA-21 and PI3K, and increased PTEN. CONCLUSIONS CIH induced significant atrial remodeling, which was attenuated by doxycycline in our rat model. These changes may be explained due to alterations in the microRNA-21-related signaling pathways by doxycycline.