Regulation of cardiac fibroblast-mediated maladaptive ventricular remodeling by β-arrestins

Insight into the regulatory mechanism of β-arrestin2 and its emerging role in diseases

β-arrestin2, a member of the arrestin family, mediates the desensitization and internalization of most G protein-coupled receptors (GPCRs) and functions as a scaffold protein in signalling pathways. Previous studies have demonstrated that β-arrestin2 expression is dysregulated in malignant tumours, fibrotic diseases, cardiovascular diseases and metabolic diseases, suggesting its pathological roles. Transcription and post-transcriptional modifications can affect the expression of β-arrestin2. Furthermore, post-translational modifications, such as phosphorylation, ubiquitination, SUMOylation and S-nitrosylation affect the cellular localization of β-arrestin2 and its interaction with downstream signalling molecules, which further regulate the activity of β-arrestin2. This review summarizes the structure and function of β-arrestin2 and reveals the mechanisms involved in the regulation of β-arrestin2 at multiple levels. Additionally, recent studies on the role of β-arrestin2 in some major diseases and its therapeutic prospects have been discussed to provide a reference for the development of drugs targeting β-arrestin2.

Ibrahem K. In-vivo and in-vitro toxicity evaluation of 2,3-dimethylquinoxaline: An antimicrobial found in a traditional herbal medicine

2,3-dimethylquinoxaline (DMQ) is a broad-spectrum antimicrobial phytochemical. This study aims to assess its toxicological profile. In vitro studies conducted in appropriate cell cultures, included assessment of cardiotoxicity, nephrotoxicity, and hepatotoxicity. An in vivo study was conducted in mice to determine acute oral toxicity (AOT), and subacute oral toxicity (SAOT). Acute dermal toxicity (ADT) was conducted in rats. All in-vitro toxicity studies of DMQ had negative results at concentrations ≤100 μM except for a non-significant reduction in the ATP in human hepatocellular carcinoma cell culture. The median lethal dose of DMQ was higher than 2000 mg/kg. All animals survived the scheduled necropsy and none showed any alteration in clinical signs. Biochemistry analysis revealed a significant difference between the satellite and control groups, showing an increase in platelet counts and white blood cell counts by 99.8% and 188.8%, respectively. Histology revealed enlargement of renal corpuscles; hyperplasia of testosterone-secreting cells; and dilatation of coronaries and capillaries. The present data suggests an acceptable safety profile of DMQ in rodents except for thrombocytosis, leukocytosis, and histological changes in high doses that need further investigation.

MiR-133b as a crucial regulator of TCS-induced cardiotoxicity via activating β-adrenergic receptor signaling pathway in zebrafish embryos

As a commonly used antibacterial agent in daily consumer products, triclosan (TCS) has attracted significant attention due to its potential environmental risks. In this study, we investigated the toxic effects of TCS exposure (1.4 μM) on heart development in zebrafish embryos. Our findings revealed that TCS exposure caused significant cardiac dysfunction, characterized by pericardial edema, malformations in the heart structure, and a slow heart rate. Additionally, TCS exposure induced oxidative damage and abnormal apoptosis in heart cells through the up-regulation of β-adrenergic receptor (β-AR) signaling pathway genes (adrb1, adrb2a, arrb2b), similar to the effects induced by β-AR agonists. Notably, the adverse effects of TCS exposure were alleviated by β-AR antagonists. Using high-throughput transcriptome miRNA sequencing and targeted miRNA screening, we focused on miR-133b, which targets adrb1 and was down-regulated by TCS exposure, as a potential contributor to TCS-induced cardiotoxicity. Inhibition of miR-133b produced similar toxic effects as TCS exposure, while overexpression of miR-133b down-regulated the β-AR signaling pathway and rescued heart defects caused by TCS. In summary, our findings provide new insights into the mechanisms underlying the cardiotoxic effects of TCS. We suggest that targeting the β-AR pathway and miR-133b may be effective strategies for pharmacotherapy in cardiotoxicity induced by environmental pollutants such as TCS.

Cardioprotective efficacy of Xin-shu-bao tablet in heart failure with reduced ejection fraction by modulating THBD/ARRB1/FGF1/STIM1 signaling

Traditional Chinese medicine offer unique advantages in mitigating and preventing early or intermediate stage for treating heart failure (HF). The purpose of this study was to assess the in vivo therapeutic efficacy of Xin-shu-bao (XSB) at different stages of HF following induction of a myocardial infarction (MI) in mice and use mass spectrometry-based proteomics to identify potential therapeutic targets for different stages of HF based on the molecular changes following XSB treatment. XSB had high cardioprotective efficacy in the pre-HF with reduced ejection fraction (HFrEF) stages, but had a weak or no effect in the post-HFrEF stages. This was supported by echocardiographic measurements showing that XSB decreased ejection fraction and fractional shortening in HF. XSB administration improved cardiac function in the pre- and post-HFrEF mouse model, ameliorated deleterious changes to the morphology and subcellular structure of cardiomyocytes, and reduced cardiac fibrosis. Proteomics analysis showed that XSB intervention exclusively targeted thrombomodulin (THBD) and stromal interaction molecule 1 (STIM1) proteins when administered to the mice for both 8 and 6 weeks. Furthermore, XSB intervention for 8, 6, and 4 weeks after MI induction increased the expression of fibroblast growth factor 1 (FGF1) and decreased arrestin β1 (ARRB1), which are classic biomarkers of cardiac fibroblast transformation and collagen synthesis, respectively. Overall, the study suggests that early intervention with XSB could be an effective strategy for preventing HFrEF and highlights potential therapeutic targets for further investigation into HFrEF remediation strategies.

Serelaxin Inhibits Lipopolysaccharide-induced Inflammatory Response in Cardiac Fibroblasts by Activating Peroxisome Proliferator-activated Receptor-γ and Suppressing the Nuclear Factor-Kappa B Signaling Pathway

ABSTRACT

Serelaxin (sRLX) has an inhibitory effect on fibrosis. However, whether the antifibrotic effects of sRLX are achieved by inhibiting the inflammatory response has not been clarified. This study aimed to investigate the role of sRLX in lipopolysaccharide (LPS)-induced inflammation in cardiac fibroblasts and elucidate the underlying mechanisms. Cardiac fibroblasts were isolated from adult rat hearts. The effect of sRLX on the inhibition of the inflammatory response after LPS induction was examined. Cell viability was measured by MMT assay. Cell proliferation was determined using the Cell Counting Kit-8. The levels of inflammatory cytokines IL-1β, IL-6, TNF-α, and IL-10 were measured using an enzyme-linked immunosorbent assay. The mRNA levels of α-smooth muscle actin (α-SMA), collagen I/III, MMP-2, MMP-9, IL-1β, IL-6, TNF-α, IL-10, IκBα, p-IκBα, p65 subunit of nuclear factor-kappa B (NF-κB), and peroxisome proliferator-activated receptor-γ (PPAR-γ) were assessed by real-time quantitative PCR. The protein levels of α-SMA, collagen I/III, MMP-2, MMP-9, IκBα, p-IκBα, p65, p-p65, and PPAR-γ were examined by western blotting. sRLX inhibited LPS-induced IL-1β, IL-6, TNF-α, α-SMA, and collagen I/III, and elevated the expression of IL-10, MMP-2, and MMP-9. Moreover, LPS-induced activation of NF-κB pathway was suppressed by sRLX treatment. Further studies showed that sRLX did not significantly increase the expression of PPAR-γ mRNA and protein, but activated PPAR-γ activity, and the PPAR-γ inhibitor GW9662 reversed the inhibitory effect of sRLX on IL-1β, IL-6, and TNF-α production. These results suggest that sRLX alleviates cardiac fibrosis by stimulating PPAR-γ through a ligand-independent mechanism that subsequently abolish the expression of NF-κB signaling pathway.

Gαq protein-biased ligand of angiotensin II type 1 receptor mediates myofibroblast differentiation through TGF-β1/ERK axis in human cardiac fibroblasts

Angiotensin II receptors are members of G protein-coupled receptor superfamily that manifest biased signals toward G protein- and β-arrestin-dependent pathways. However, the role of angiotensin II receptor-biased ligands and the mechanisms underlying myofibroblast differentiation in human cardiac fibroblasts have not been fully elucidated. Our results demonstrated that antagonism of angiotensin II type 1 receptor (AT₁ receptor) and blockade of G_αq protein suppressed angiotensin II (Ang II)-induced fibroblast proliferation, overexpression of collagen I and α-smooth muscle actin (α-SMA), and stress fibre formation, indicating the AT₁ receptor/G_αq axis is necessary for fibrogenic effects of Ang II. Stimulation of AT₁ receptors by their G_αq-biased ligand (TRV120055), but not β-arrestin-biased ligand (TRV120027), substantially exerted fibrogenic effects at a level similar to that of Ang II, suggesting that AT₁ receptor induced cardiac fibrosis in a G_αq-dependent and β-arrestin-independent manner. Valsartan prevents TRV120055-mediated fibroblast activation. TRV120055 mediated the upregulation of transforming growth factor-beta1 (TGF-β1) through the AT₁ receptor/G_αq cascade. In addition, G_αq protein and TGF-β1 were necessary for ERK1/2 activation induced by Ang II and TRV120055. Collectively, TGF-β1 and ERK1/2 are downstream effectors of the G_αq-biased ligand of AT₁ receptor for the induction of cardiac fibrosis.

Differential expression of microRNAs in bile duct obstruction-induced liver fibrosis and the identification of a novel liver fibrosis marker miR-1295b-3p

Background

Bile duct obstruction-induced liver fibrosis is mainly caused by cholestatic liver injury which stimulates liver cell inflammation and damages the liver structure, causing liver fibrosis. The differentially expressed microRNAs and the potential target genes and signal pathways that are involved in bile duct obstruction-induced liver fibrosis remain unclear. We examined the differential expression of microRNAs and the target genes in the liver tissues of patients with liver fibrosis.

Methods

High-throughput sequencing was used to detect the total microRNAs and identify the differentially expressed microRNAs. The topGO software was used to perform the Gene Ontology (GO) function enrichment analysis. The KOBAS software was used to analyze the associated biochemical metabolic pathways and signal transduction pathways. Quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot analyses were conducted to detect the expression of miR-1295b-3p, alpha smooth muscle actin (α-SMA), Bcl-2, caspase-3, Bax, and β-arrestin1 (ARRB1). Cell viability and apoptosis were detected by the Cell Counting Kit 8 (CCK-8) assay and flow cytometry. The targeting relationship between ARRB1 and miR-1295b-3p was verified using luciferase reporter assays.

Results

A total of 44 microRNAs were found to be differentially expressed, including 18 upregulated and 26 downregulated microRNAs. Five downregulated microRNAs, including miR-483-3p, miR-5589-3p, miR-1271-5p, miR-1295b-3p, and miR-7977. GO functional enrichment analysis of the target genes revealed the molecular functions, cellular location, and biological processes involved. Kyoto Encyclopedia of Genes and Genomes (KEGG) signal pathway analysis showed that the target genes are mainly involved in metabolic pathways. In addition, the results of qRT-PCR revealed that miR-1295b-3p was downregulated in human fibrotic liver tissues and TGF-β1-activated LX-2 cells (human hepatic stellate cell line). Overexpression of miR-1295b-3p alleviated liver fibrosis, decreased the α-SMA levels, and inhibited proliferation and enhanced apoptosis in LX-2 cells. Dual-luciferase assays revealed that miR-1295b-3p suppressed ARRB1 expression by binding directly to its 3' untranslated region (UTR).

Conclusions

This study identified the differentially expressed microRNAs in bile duct obstruction-induced liver fibrosis and revealed the potential target genes and signal pathways involved. Overexpression of miR-1295b-3p alleviated liver fibrosis, however, the specific targeting mechanisms warrant further clarification. Therefore, overexpressing miR-1295b-3p may be a potential treatment method for liver fibrosis.

Carvedilol Selectively Stimulates βArrestin2-Dependent SERCA2a Activity in Cardiomyocytes to Augment Contractility

Heart failure (HF) carries the highest mortality in the western world and β-blockers [β-adrenergic receptor (AR) antagonists] are part of the cornerstone pharmacotherapy for post-myocardial infarction (MI) chronic HF. Cardiac β1AR-activated βarrestin2, a G protein-coupled receptor (GPCR) adapter protein, promotes Sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA)2a SUMO (small ubiquitin-like modifier)-ylation and activity, thereby directly increasing cardiac contractility. Given that certain β-blockers, such as carvedilol and metoprolol, can activate βarrestins and/or SERCA2a in the heart, we investigated the effects of these two agents on cardiac βarrestin2-dependent SERCA2a SUMOylation and activity. We found that carvedilol, but not metoprolol, acutely induces βarrestin2 interaction with SERCA2a in H9c2 cardiomyocytes and in neonatal rat ventricular myocytes (NRVMs), resulting in enhanced SERCA2a SUMOylation. However, this translates into enhanced SERCA2a activity only in the presence of the β2AR-selective inverse agonist ICI 118,551 (ICI), indicating an opposing effect of carvedilol-occupied β2AR subtype on carvedilol-occupied β1AR-stimulated, βarrestin2-dependent SERCA2a activation. In addition, the amplitude of fractional shortening of NRVMs, transfected to overexpress βarrestin2, is acutely enhanced by carvedilol, again in the presence of ICI only. In contrast, metoprolol was without effect on NRVMs’ shortening amplitude irrespective of ICI co-treatment. Importantly, the pro-contractile effect of carvedilol was also observed in human induced pluripotent stem cell (hIPSC)-derived cardiac myocytes (CMs) overexpressing βarrestin2, and, in fact, it was present even without concomitant ICI treatment of human CMs. Metoprolol with or without concomitant ICI did not affect contractility of human CMs, either. In conclusion, carvedilol, but not metoprolol, stimulates βarrestin2-mediated SERCA2a SUMOylation and activity through the β1AR in cardiac myocytes, translating into direct positive inotropy. However, this unique βarrestin2-dependent pro-contractile effect of carvedilol may be opposed or masked by carvedilol-bound β2AR subtype signaling.

Signaling pathways and targeted therapy for myocardial infarction

Although the treatment of myocardial infarction (MI) has improved considerably, it is still a worldwide disease with high morbidity and high mortality. Whilst there is still a long way to go for discovering ideal treatments, therapeutic strategies committed to cardioprotection and cardiac repair following cardiac ischemia are emerging. Evidence of pathological characteristics in MI illustrates cell signaling pathways that participate in the survival, proliferation, apoptosis, autophagy of cardiomyocytes, endothelial cells, fibroblasts, monocytes, and stem cells. These signaling pathways include the key players in inflammation response, e.g., NLRP3/caspase-1 and TLR4/MyD88/NF-κB; the crucial mediators in oxidative stress and apoptosis, for instance, Notch, Hippo/YAP, RhoA/ROCK, Nrf2/HO-1, and Sonic hedgehog; the controller of myocardial fibrosis such as TGF-β/SMADs and Wnt/β-catenin; and the main regulator of angiogenesis, PI3K/Akt, MAPK, JAK/STAT, Sonic hedgehog, etc. Since signaling pathways play an important role in administering the process of MI, aiming at targeting these aberrant signaling pathways and improving the pathological manifestations in MI is indispensable and promising. Hence, drug therapy, gene therapy, protein therapy, cell therapy, and exosome therapy have been emerging and are known as novel therapies. In this review, we summarize the therapeutic strategies for MI by regulating these associated pathways, which contribute to inhibiting cardiomyocytes death, attenuating inflammation, enhancing angiogenesis, etc. so as to repair and re-functionalize damaged hearts.

Histamine is involved in the regulation of collagen content in cultured heart myofibroblasts via H2, H3 and H4 histamine receptors

Histamine is involved in the regulation of collagen metabolism during healing following a myocardial infarction; however, its effects on the intact heart tissue is unknown. The aim of the present study was to determine whether histamine may influence collagen content in cells isolated from intact heart, and to identify the histamine receptor involved in the regulation of collagen deposition. Cells were isolated from intact rat hearts and subjected to identification by flow cytometry. The effects of histamine and its receptor agonists and antagonists were investigated. The heart cells were found to be actin, desmin and vimentin positive. Histamine (used at a concentrations of 1x10-10-1x10-5 M) increased collagen content within the culture and increased the expression of α1 chain of the procollagen type III gene. The H2, H3 and H4 receptor inhibitors ranitidine, ciproxifan and JNJ 7777120 blocked the effect of histamine on collagen content. All tested histamine receptor agonists, viz. 2-pyridylethylamine dihydrochloride (H1 receptor agonist), amthamine dihydrobromide (H2 receptor agonist), imetit (H3 receptor agonist) and 4-methylhistamine hydrochloride (H4 receptor agonist), elevated collagen content within the heart myofibroblast cultures. The cells isolated from the intact heart were identified as myofibroblasts. Thus, the results of the present study showed that histamine augmented collagen content in the heart myofibroblast culture by activation of three histamine receptors (H2, H3 and H4). The effect of the amine was also dependent on the activation of collagen type III gene expression.

Alarin alleviated cardiac fibrosis via attenuating oxidative stress in heart failure rats

The present study was to explore whether alarin could alleviate heart failure (HF) and attenuate cardia fibrosis via inhibiting oxidative stress. The fibrosis of cardiac fibroblasts (CFs) was induced by angiotensin (Ang) II. HF models were induced by ligation of the left anterior descending artery to cause ischemia myocardial infarction (MI) in Sprague–Dawley rats. Alarin (1.0 nM/kg/d) was administrated by intraperitoneal injection for 28 days. The decreases of left ventricular (LV) ejection fraction (EF), fractional shortening (FS), the maximum of the first differentiation of LV pressure (LV ± dp/dt_max) and LV systolic pressure (LVSP), and the increases of LV volume in systole (LVVS), LV volume in diastole (LVVD), LV end-systolic diameter (LVESD) and LV end-diastolic diameter (LVEDD) in MI rats were improved by alarin treatment. The increases in the expression levels of collagen I, collagen III, and transforming growth factor (TGF)-β were inhibited by alarin treatment in CFs and in the hearts of MI rats. The levels of NADPH oxidase (Nox) activity, superoxide anions and malondialdehyde (MDA) levels were increased, and the level of superoxide dismutase (SOD) activity was reduced in Ang II-treated CFs, which were reversed by alarin. Nox1 overexpression reversed the effects of alarin on attenuating the increases of collagen I, collagen III and TGF-β expression levels induced by Ang II in CFs. These results indicated that alarin improved HF and cardiac fibrosis via inhibiting oxidative stress in HF rats. Nox1 played important roles in the regulation of alarin effects on attenuating CFs fibrosis induced by Ang II.

Apelin-13 alleviated cardiac fibrosis via inhibiting the PI3K/Akt pathway to attenuate oxidative stress in rats with myocardial infarction-induced heart failure

The present study aimed to determine whether apelin-13 could attenuate cardiac fibrosis via inhibiting the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) pathway to inhibit reactive oxygen species in heart failure (HF) rats. HF models were established by inducing ischemia myocardial infarction (MI) through ligation of the left anterior descending artery in Sprague–Dawley (SD) rats. MI-induced changes in hemodynamics and cardiac function were reversed by apelin-13 administration. The increases in the levels of collagen I, collagen III, α-smooth muscle actin (SMA), and transforming growth factor-β (TGF-β) in the heart of MI rats and cardiac fibroblasts (CFs) treated with angiotensin (Ang) II were inhibited by apelin-13. The levels of PI3K and p-Akt increased in Ang II-treated CFs, and these increases were blocked by apelin-13. The PI3K overexpression reversed the effects of apelin-13 on Ang II-induced increases in collagen I, collagen III, α-SMA, and TGF-β, NADPH oxidase activity and superoxide anions in CFs. Apelin-13 reduced the increases in the levels of NADPH oxidase activity and superoxide anions in the heart of MI rats and CFs with Ang II treatment. The results demonstrated that apelin-13 improved cardiac dysfunction, impaired cardiac hemodynamics, and attenuated fibrosis of CFs induced by Ang II via inhibiting the PI3K/Akt signaling pathway to inhibit oxidative stress.

Adrenal angiotensin II type 1 receptor biased signaling: The case for "biased" inverse agonism for effective aldosterone suppression

Angiotensin II (AngII) uses two distinct G protein-coupled receptor (GPCR) types, AT₁R and AT₂R, to exert a plethora of physiologic effects in the body and to significantly affect cardiovascular homeostasis. Although not much is known about the signaling of the AT₂R, AT₁R signaling is known to be quite pleiotropic, mobilizing a variety of signal transducers inside cells to produce a biological outcome. When the outcome in question is aldosterone production from the adrenal cortex, the main transducers activated specifically by the adrenocortical AT₁R to signal toward that cellular effect are the G_q/11 protein alpha subunits and the β-arrestins (also known as Arrestin-2 and -3). The existence of various downstream pathways the AT₁R signal can travel down on has led to the ever-expanding filed of GPCR pharmacology termed "biased" signaling, which refers to a ligand preferentially activating one signaling pathway over others downstream of the same receptor in the same cell. However, "biased" signaling or "biased" agonism is therapeutically desirable only when the downstream pathways lead to different or opposite cellular outcomes, so the pathway promoting the beneficial effect can be selectively activated over the pathway that leads to detrimental consequences. In the case of the adrenal AT₁R, both G_q/11 proteins and β-arrestins mediate signaling to the same end-result: aldosterone synthesis and secretion. Therefore, both pathways need to remain inactive in the adrenal cortex to fully suppress the production of aldosterone, which is one of the culprit hormones elevated in chronic heart failure, hypertension, and various other cardiovascular diseases. Variations in the effectiveness of the AT₁R antagonists, which constitute the angiotensin receptor blocker (ARB) class of drugs (also known as sartans), at the relative blockade of these two pathways downstream of the adrenal AT₁R opens the door to the flip term "biased" inverse agonism at the AT₁R. ARBs that are unbiased and equipotent inverse agonists for both G proteins and β-arrestins at this receptor, like candesartan and valsartan, are the most preferred agents with the best efficacy at reducing circulating aldosterone, thereby ameliorating heart failure. In the present review, the biased signaling of the adrenal AT₁R, particularly in relation to aldosterone production, is examined and the term "biased" inverse agonism at the AT₁R is introduced and explained, as a means of pharmacological categorization of the various agents within the ARB drug class.

β-Arrestin as a Therapeutic Target in Heart Failure

Heart failure is a major source of morbidity and mortality, driven, in part, by maladaptive sympathetic hyperactivity in response to poor cardiac output. Current therapies target β-adrenergic and angiotensin II G protein-coupled receptors to reduce adverse cardiac remodeling and improve clinical outcomes; however, there is a pressing need for new therapeutic approaches to preserve cardiac function. β-arrestin is a multifunctional protein which has come under analysis in recent years as a key player in G protein-coupled receptor signal transduction and a potential therapeutic target in heart failure. β-arrestin attenuates β-adrenergic and angiotensin II receptor signaling to limit the deleterious response to excessive sympathetic stimulation while simultaneously transactivating cardioprotective signaling cascades that preserve cardiac structure and function in response to injury. β-arrestin signaling may provide unique advantages compared to classic heart failure treatment approaches, but a number of challenges currently limit clinical applications. In this review, we discuss the role and functions of β-arrestin and the current attempts to develop G protein-coupled receptor agonists biased towards β-arrestin activation. Furthermore, we examine the functional diversity of cardiac β-arrestin isotypes to explore key considerations in the promise of β-arrestin as a pharmacotherapeutic target in heart failure.