Lysyl oxidase expression in smooth muscle cells determines the level of intima calcification in hypercholesterolemia-induced atherosclerosis

INTRODUCTION

Cardiovascular calcification is an important public health issue with an unmeet therapeutic need. We had previously shown that lysyl oxidase (LOX) activity critically influences vascular wall smooth muscle cells (VSMCs) and valvular interstitial cells (VICs) calcification by affecting extracellular matrix remodeling. We have delved into the participation of LOX in atherosclerosis and vascular calcification, as well as in the mineralization of the aortic valve.

METHODS

Immunohistochemical and expression studies were carried out in human atherosclerotic lesions and experimental models, valves from patients with aortic stenosis, VICs, and in a genetically modified mouse model that overexpresses LOX in CMLV (TgLOXCMLV). Hyperlipemia and atherosclerosis was induced in mice through the administration of adeno-associated viruses encoding a PCSK9 mutated form (AAV-PCSK9D374Y) combined with an atherogenic diet.

RESULTS

LOX expression is increased in the neointimal layer of atherosclerotic lesions from human coronary arteries and in VSMC-rich regions of atheromas developed both in the brachiocephalic artery of control (C57BL/6J) animals transduced with PCSK9D374Y and in the aortic root of ApoE-/- mice. In TgLOXCMLV mice, PCSK9D374Y transduction did not significantly alter the enhanced aortic expression of genes involved in matrix remodeling, inflammation, oxidative stress and osteoblastic differentiation. Likewise, LOX transgenesis did not alter the size or lipid content of atherosclerotic lesions in the aortic arch, brachiocephalic artery and aortic root, but exacerbated calcification. Among lysyl oxidase isoenzymes, LOX is the most expressed member of this family in highly calcified human valves, colocalizing with RUNX2 in VICs. The lower calcium deposition and decreased RUNX2 levels triggered by the overexpression of the nuclear receptor NOR-1 in VICs was associated with a reduction in LOX.

CONCLUSIONS

Our results show that LOX expression is increased in atherosclerotic lesions, and that overexpression of this enzyme in VSMC does not affect the size of the atheroma or its lipid content, but it does affect its degree of calcification. Further, these data suggest that the decrease in calcification driven by NOR-1 in VICs would involve a reduction in LOX. These evidences support the interest of LOX as a therapeutic target in cardiovascular calcification.

Lysyl Oxidase in Ectopic Cardiovascular Calcification: Role of Oxidative Stress

Lysyl oxidase (LOX)-mediated extracellular matrix crosslinking modulates calcification in atherosclerosis and aortic valve disease; however, this enzyme also induces oxidative stress. We addressed the contribution of LOX-dependent oxidative stress to cardiovascular calcification. LOX is upregulated in human-calcified atherosclerotic lesions and atheromas from atherosclerosis-challenged LOX transgenic mice (TgLOXVSMC) and colocalized with a marker of oxidative stress (8-oxo-deoxyguanosine) in vascular smooth muscle cells (VSMCs). Similarly, in calcific aortic valves, high LOX expression was detected in valvular interstitial cells (VICs) positive for 8-oxo-deoxyguanosine, while LOX and LOXL2 expression correlated with osteogenic markers (SPP1 and RUNX2) and NOX2. In human VICs, mito-TEMPO and TEMPOL attenuated the increase in superoxide anion levels and the mineralization induced by osteogenic media (OM). Likewise, in OM-exposed VICs, β-aminopropionitrile (a LOX inhibitor) ameliorated both oxidative stress and calcification. Gain- and loss-of-function approaches in VICs demonstrated that while LOX silencing negatively modulates oxidative stress and calcification induced by OM, lentiviral LOX overexpression exacerbated oxidative stress and VIC calcification, effects that were prevented by mito-TEMPO, TEMPOL, and β-aminopropionitrile. Our data indicate that LOX-induced oxidative stress participates in the procalcifying effects of LOX activity in ectopic cardiovascular calcification, and highlight the multifaceted role played by LOX isoenzymes in cardiovascular diseases.

Lysyl oxidase-dependent extracellular matrix crosslinking modulates calcification in atherosclerosis and aortic valve disease

Extracellular matrix (ECM) is an active player in cardiovascular calcification (CVC), a major public health issue with an unmet need for effective therapies. Lysyl oxidase (LOX) conditions ECM biomechanical properties; thus, we hypothesized that LOX might impact on mineral deposition in calcific aortic valve disease (CAVD) and atherosclerosis. LOX was upregulated in calcified valves from two cohorts of CAVD patients. Strong LOX immunostaining was detected surrounding calcified foci in calcified human valves and atherosclerotic lesions colocalizing with RUNX2 on valvular interstitial cells (VICs) or vascular smooth muscle cells (VSMCs). Both LOX secretion and organized collagen deposition were enhanced in calcifying VICs exposed to osteogenic media. β-aminopropionitrile (BAPN), an inhibitor of LOX, attenuated collagen deposition and calcification. VICs seeded onto decellularized matrices from BAPN-treated VICs calcified less than cells cultured onto control scaffolds; instead, VICs exposed to conditioned media from cells over-expressing LOX or cultured onto LOX-crosslinked matrices calcified more. Atherosclerosis was induced in WT and transgenic mice that overexpress LOX in VSMC (TgLOXVSMC) by AAV-PCSK9D374Y injection and high-fat feeding. In atherosclerosis-challenged TgLOXVSMC mice both atherosclerosis burden and calcification assessed by near-infrared fluorescence (NIRF) imaging were higher than in WT mice. These animals also exhibited larger calcified areas in atherosclerotic lesions from aortic arches and brachiocephalic arteries. Moreover, LOX transgenesis exacerbated plaque inflammation, and increased VSMC cellularity, the rate of RUNX2-positive cells and both connective tissue content and collagen cross-linking. Our findings highlight the relevance of LOX in CVC and postulate this enzyme as a potential therapeutic target for CVC.

Exploration of Mediators Associated with Myocardial Remodelling in Feline Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) affects both humans and cats and exhibits considerable interspecies similarities that are exemplified by underlying pathological processes and clinical presentation to the extent that developments in the human field may have direct relevance to the feline disease. Characteristic changes on histological examination include cardiomyocyte hypertrophy and interstitial and replacement fibrosis. Clinically, HCM is characterised by significant diastolic dysfunction due to a reduction in ventricular compliance and relaxation associated with extracellular matrix (ECM) remodelling and the development of ventricular hypertrophy. Studies in rodent models and human HCM patients have identified key protein mediators implicated in these pathological changes, including lumican, lysyl oxidase and TGF-β isoforms. We therefore sought to quantify and describe the cellular location of these mediators in the left ventricular myocardium of cats with HCM and investigate their relationship with the quantity and structural composition of the ECM. We identified increased myocardial content of lumican, LOX and TGF-β2 mainly attributed to their increased expression within cardiomyocytes in HCM cats compared to control cats. Furthermore, we found strong correlations between the expressions of these mediators that is compatible with their role as important components of cellular pathways promoting remodelling of the left ventricular myocardium. Fibrosis and hypertrophy are important pathological changes in feline HCM, and a greater understanding of the mechanisms driving this pathology may facilitate the identification of potential therapies.

Anti-Diabetic Therapy, Heart Failure and Oxidative Stress: An Update

Diabetes mellitus (DM) and heart failure (HF) are two chronic disorders that affect millions worldwide. Hyperglycemia can induce excessive generation of highly reactive free radicals that promote oxidative stress and further exacerbate diabetes progression and its complications. Vascular dysfunction and damage to cellular proteins, membrane lipids and nucleic acids can stem from overproduction and/or insufficient removal of free radicals. The aim of this article is to review the literature regarding the use of antidiabetic drugs and their role in glycemic control in patients with heart failure and oxidative stress. Metformin exerts a minor benefit to these patients. Thiazolidinediones are not recommended in diabetic patients, as they increase the risk of HF. There is a lack of robust evidence on the use of meglinitides and acarbose. Insulin and dipeptidyl peptidase-4 (DPP-4) inhibitors may have a neutral cardiovascular effect on diabetic patients. The majority of current research focuses on sodium glucose cotransporter 2 (SGLT2) inhibitors and glucagon-like peptide 1 (GLP-1) receptor agonists. SGLT2 inhibitors induce positive cardiovascular effects in diabetic patients, leading to a reduction in cardiovascular mortality and HF hospitalization. GLP-1 receptor agonists may also be used in HF patients, but in the case of chronic kidney disease, SLGT2 inhibitors should be preferred.

Human Lysyl Oxidase Over-Expression Enhances Baseline Cardiac Oxidative Stress but Does Not Aggravate ROS Generation or Infarct Size Following Myocardial Ischemia-Reperfusion

Lysyl oxidase (LOX) is an enzyme critically involved in collagen maturation, whose activity releases H₂O₂ as a by-product. Previous studies demonstrated that LOX over-expression enhances reactive oxygen species (ROS) production and exacerbates cardiac remodeling induced by pressure overload. However, whether LOX influences acute myocardial infarction and post-infarct left ventricular remodeling and the contribution of LOX to myocardial oxidative stress following ischemia-reperfusion have not been analyzed. Isolated hearts from transgenic mice over-expressing human LOX in the heart (TgLOX) and wild-type (WT) littermates were subjected to global ischemia and reperfusion. Although under basal conditions LOX transgenesis is associated with higher cardiac superoxide levels than WT mice, no differences in ROS production were detected in ischemic hearts and a comparable acute ischemia-reperfusion injury was observed (infarct size: 56.24 ± 9.44 vs. 48.63 ± 2.99% of cardiac weight in WT and TgLOX, respectively). Further, similar changes in cardiac dimensions and function were observed in TgLOX and WT mice 28 days after myocardial infarction induced by transient left anterior descending (LAD) coronary artery occlusion, and no differences in scar area were detected (20.29 ± 3.10 vs. 21.83 ± 2.83% of left ventricle). Our data evidence that, although LOX transgenesis induces baseline myocardial oxidative stress, neither ROS production, infarct size, nor post-infarction cardiac remodeling were exacerbated following myocardial ischemia-reperfusion.

Zebrafish Model to Study Angiotensin II-Mediated Pathophysiology

Hypertension, a common chronic condition, may damage multiple organs, including the kidney, heart, and brain. Thus, it is essential to understand the pathology upon ectopic activation of the molecular pathways involved in mammalian hypertension to develop strategies to manage hypertension. Animal models play a crucial role in unraveling the disease pathophysiology by allowing incisive experimental procedures impossible in humans. Zebrafish, a small freshwater fish, have emerged as an important model system to study human diseases. The primary effector, Angiotensin II of the RAS pathway, regulates hemodynamic pressure overload mediated cardiovascular pathogenesis in mammals. There are various established mammalian models available to study pathophysiology in Angiotensin II-induced hypertension. Here, we have developed a zebrafish model to study pathogenesis by Angiotensin II. We find that intradermal Angiotensin II injection every 12 h can induce cardiac remodeling in seven days. We show that Angiotensin II injection in adult zebrafish causes cardiomyocyte hypertrophy and enhances cardiac cell proliferation. In addition, Angiotensin II induces ECM protein-coding gene expression and fibrosis in the cardiac ventricles. Thus, this study can conclude that Angiotensin II injection in zebrafish has similar implications as mammals, and zebrafish can be a model to study pathophysiology associated with AngII-RAS signaling.

Oxidative stress in cardiac hypertrophy: From molecular mechanisms to novel therapeutic targets

When faced with increased workload the heart undergoes remodelling, where it increases its muscle mass in an attempt to preserve normal function. This is referred to as cardiac hypertrophy and if sustained, can lead to impaired contractile function. Experimental evidence supports oxidative stress as a critical inducer of both genetic and acquired forms of cardiac hypertrophy, a finding which is reinforced by elevated levels of circulating oxidative stress markers in patients with cardiac hypertrophy. These observations formed the basis for using antioxidants as a therapeutic means to attenuate cardiac hypertrophy and improve clinical outcomes. However, the use of antioxidant therapies in the clinical setting has been associated with inconsistent results, despite antioxidants having been shown to exert protection in several animal models of cardiac hypertrophy. This has forced us to revaluate the mechanisms, both upstream and downstream of oxidative stress, where recent studies demonstrate that apart from conventional mediators of oxidative stress, metabolic disturbances, mitochondrial dysfunction and inflammation as well as dysregulated autophagy and protein homeostasis contribute to disease pathophysiology through mechanisms involving oxidative stress. Importantly, novel therapeutic targets have been identified to counteract oxidative stress and attenuate cardiac hypertrophy but more interestingly, the repurposing of drugs commonly used to treat metabolic disorders, hypertension, peripheral vascular disease, sleep disorders and arthritis have also been shown to improve cardiac function through suppression of oxidative stress. Here, we review the latest literature on these novel mechanisms and intervention strategies with the aim of better understanding the complexities of oxidative stress for more precise targeted therapeutic approaches to prevent cardiac hypertrophy.

Rolipram Prevents the Formation of Abdominal Aortic Aneurysm (AAA) in Mice: PDE4B as a Target in AAA

Abdominal aortic aneurysm (AAA) is a common life-threatening condition characterized by exacerbated inflammation and the generation of reactive oxygen species. Pharmacological treatments to slow AAA progression or to prevent its rupture remain a challenge. Targeting phosphodiesterase 4 (PDE4) has been verified as an effective therapeutic strategy for an array of inflammatory conditions; however, no studies have assessed yet PDE4 in AAA. Here, we used angiotensin II (AngII)-infused apolipoprotein E deficient mice to study the involvement of the PDE4 subfamily in aneurysmal disease. PDE4B but not PDE4D was upregulated in inflammatory cells from both experimental and human AAA. The administration of the PDE4 selective inhibitor rolipram (3 mg/kg/day) to AngII-challenged mice (1000 ng/kg bodyweight/min) protected against AAA formation, limiting the progressive increase in the aortic diameter without affecting the blood pressure. The drug strongly attenuated the rise in vascular oxidative stress (superoxide anion) induced by AngII, and decreased the expression of inflammatory markers, as well as the recruitment of macrophages (MAC3+), lymphocytes (CD3+), and neutrophils (ELANE+) into the vessel wall. Rolipram also normalized the vascular MMP2 expression and MMP activity, preserving the elastin integrity and improving the vascular remodelling. These results point to PDE4B as a new therapeutic target for AAA.

Cross your heart? Collagen cross-links in cardiac health and disease

Extracellular matrix (ECM) remodeling occurs in response to various cardiac insults including infarction, pressure overload and dilated myopathies. Each type of remodeling necessitates distinct types of ECM turnover and deposition yet an increase in myocardial fibrillar collagen content is appreciated as a contributing feature to cardiac dysfunction in each of these pathologies. In addition, aging, is also associated with increases in cardiac collagen content. The importance of characterizing differences in ECM composition and processes used by cardiac fibroblasts in the assembly of fibrotic collagen accumulation is critical for the design of strategies to reduce and ultimately regress cardiac fibrosis. Collagen cross-linking is one factor that influences collagen deposition and insolubility with direct implications for tissue properties such as stiffness. In this review, three different types of collagen cross-links shown to be important in cardiac fibrosis will be discussed; those catalyzed by lysyl oxidases, those catalyzed by transglutaminases, and those that result from non-enzymatic modification by the addition of advanced glycation end products. Insight into cellular mechanisms that govern collagen cross-linking in the myocardium will provide novel pathways for exploring new treatments to treat diseases associated with cardiac fibrosis.

Resistin induces cardiac fibroblast-myofibroblast differentiation through JAK/STAT3 and JNK/c-Jun signaling

Cardiac fibrosis is characterized by excessive deposition of extracellular matrix proteins and myofibroblast differentiation. Our previous findings have implicated resistin in cardiac fibrosis; however, the molecular mechanisms underlying this process are still unclear. Here we investigated the role of resistin in fibroblast-to-myofibroblast differentiation and elucidated the pathways involved in this process. Fibroblast-to-myofibroblast transdifferentiation was induced with resistin or TGFβ1 in NIH-3T3 and adult cardiac fibroblasts. mRNA and protein expression of fibrotic markers were analyzed by qPCR and immunoblotting. Resistin-knockout mice, challenged with a high-fat diet (HFD) for 20 weeks to stimulate cardiac impairment, were analyzed for cardiac function and fibrosis using histologic and molecular methods. Cardiac fibroblasts stimulated with resistin displayed increased fibroblast-to-myofibroblast conversion, with increased levels of αSma, col1a1, Fn, Ccn2 and Mmp9, with remarkable differences in the actin network appearance. Mechanistically, resistin promotes fibroblast-to-myofibroblast transdifferentiation and fibrogenesis via JAK2/STAT3 and JNK/c-Jun signaling pathways, independent of TGFβ1. Resistin-null mice challenged with HFD showed an improvement in cardiac function and a decrease in tissue fibrosis and reduced mRNA levels of fibrogenic markers. These findings are the first to delineate the role of resistin in the process of cardiac fibroblast-to-myofibroblast differentiation via JAK/STAT3 and JNK/c-Jun pathways, potentially leading to stimulation of cardiac fibrosis.

Collagen Cross-Linking Is Associated With Cardiac Remodeling in Hypertrophic Obstructive Cardiomyopathy

Background Collagen cross-linking is covalent bonds among collagen fibers from catalysis of lysyl oxidase (LOX) and advanced glycation end products (AGEs). We aimed to evaluate the formation of enzymatic and nonenzymatic collagen cross-linking and its clinical significance in patients with hypertrophic obstructive cardiomyopathy. Methods and Results Forty-four patients with hypertrophic obstructive cardiomyopathy who underwent surgical myectomy were consecutively enrolled. Cardiovascular magnetic resonance parameters of left atrial/left ventricular function were measured, including peak filling rate (PFR) and early peak emptying rate (PER-E). Total collagen was the sum of soluble and insoluble collagen, which were assessed by collagen assay. The myocardial LOX and AGEs expression were measured by molecular and biochemical methods. Compared with patients without atrial fibrillation, insoluble collagen (P=0.018), insoluble collagen fraction (P=0.017), and AGEs (P=0.039) were higher in patients with atrial fibrillation, whereas LOX expression was similar (P=0.494). The insoluble collagen fraction was correlated with PFR index (PFR normalized by left ventricular filling volume) (r=-0.44, P=0.005), left atrial diameters (r=0.36, P=0.021) and PER-E index (PER-E normalized by left ventricular filling volume) (r=-0.49, P=0.001).Myocardial LOX was positively correlated with total collagen (r=0.37, P=0.025) and insoluble collagen fraction (r=0.53, P < 0.001), but inversely correlated with PFR index (r=-0.43, P=0.006) and PER-E index (r=-0.35, P=0.027). In multiple regression analysis, myocardial LOX was independently associated with PFR, while insoluble collagen fraction showed independent correlation with PER-E after adjustment for clinical confounders. Conclusions Collagen cross-linking plays an important role on heart remodeling in hypertrophic obstructive cardiomyopathy. Myocardial LOX expression is independently correlated with left ventricular stiffness, while accumulation of AGEs cross-links might be associated with the occurrence of atrial fibrillation in patients with hypertrophic obstructive cardiomyopathy.

Role of the lysyl oxidase enzyme family in cardiac function and disease

Heart diseases are a major cause of morbidity and mortality world-wide. Lysyl oxidase (LOX) and related LOX-like (LOXL) isoforms play a vital role in remodelling the extracellular matrix (ECM). The LOX family controls ECM formation by cross-linking collagen and elastin chains. LOX/LOXL proteins are copper-dependent amine oxidases that catalyse the oxidation of lysine, causing cross-linking between the lysine moieties of lysine-rich proteins. Dynamic changes in LOX and LOXL protein-expression occur in a variety of cardiac pathologies; these changes are believed to be central to the associated tissue-fibrosis. An awareness of the potential pathophysiological importance of LOX has led to the evaluation of interventions that target LOX/LOXL proteins for heart-disease therapy. The purposes of this review article are: (i) to summarize the basic biochemistry and enzyme function of LOX and LOXL proteins; (ii) to consider their tissue and species distribution; and (iii) to review the results of experimental studies of the roles of LOX and LOXL proteins in heart disease, addressing involvement in the mechanisms, pathophysiology and therapeutic responses based on observations in patient samples and relevant animal models. Therapeutic targeting of LOX family enzymes has shown promising results in animal models, but small-molecule approaches have been limited by non-specificity and off-target effects. Biological approaches show potential promise but are in their infancy. While there is strong evidence for LOX-family protein participation in heart failure, myocardial infarction, cardiac hypertrophy, dilated cardiomyopathy, atrial fibrillation and hypertension, as well as potential interest as therapeutic targets, the precise involvement of LOX-family proteins in heart disease requires further investigation.

Lysyl Oxidase (LOX): Functional Contributions to Signaling Pathways

Cu-dependent lysyl oxidase (LOX) plays a catalytic activity-related, primary role in the assembly of the extracellular matrix (ECM), a dynamic structural and regulatory framework which is essential for cell fate, differentiation and communication during development, tissue maintenance and repair. LOX, additionally, plays both activity-dependent and independent extracellular, intracellular and nuclear roles that fulfill significant functions in normal tissues, and contribute to vascular, cardiac, pulmonary, dermal, placenta, diaphragm, kidney and pelvic floor disorders. LOX activities have also been recognized in glioblastoma, diabetic neovascularization, osteogenic differentiation, bone matrix formation, ligament remodeling, polycystic ovary syndrome, fetal membrane rupture and tumor progression and metastasis. In an inflammatory context, LOX plays a role in diminishing pluripotent mesenchymal cell pools which are relevant to the pathology of diabetes, osteoporosis and rheumatoid arthritis. Most of these conditions involve mechanisms with complex cell and tissue type-specific interactions of LOX with signaling pathways, not only as a regulatory target, but also as an active player, including LOX-mediated alterations of cell surface receptor functions and mutual regulatory activities within signaling loops. In this review, we aim to provide insight into the diverse ways in which LOX participates in signaling events, and explore the mechanistic details and functional significance of the regulatory and cross-regulatory interactions of LOX with the EGFR, PDGF, VEGF, TGF-β, mechano-transduction, inflammatory and steroid signaling pathways.

Neuron-derived orphan receptor-1 modulates cardiac gene expression and exacerbates angiotensin II-induced cardiac hypertrophy

Hypertensive cardiac hypertrophy (HCH) is a common cause of heart failure (HF), a major public health problem worldwide. However, the molecular bases of HCH have not been completely elucidated. Neuron-derived orphan receptor-1 (NOR-1) is a nuclear receptor whose role in cardiac remodelling is poorly understood. The aim of the present study was to generate a transgenic mouse over-expressing NOR-1 in the heart (TgNOR-1) and assess the impact of this gain-of-function on HCH. The CAG promoter-driven transgenesis led to viable animals that over-expressed NOR-1 in the heart, mainly in cardiomyocytes and also in cardiofibroblasts. Cardiomyocytes from TgNOR-1 exhibited an enhanced cell surface area and myosin heavy chain 7 (Myh7)/Myh6 expression ratio, and increased cell shortening elicited by electric field stimulation. TgNOR-1 cardiofibroblasts expressed higher levels of myofibroblast markers than wild-type (WT) cells (α 1 skeletal muscle actin (Acta1), transgelin (Sm22α)) and were more prone to synthesise collagen and migrate. TgNOR-1 mice experienced an age-associated remodelling of the left ventricle (LV). Angiotensin II (AngII) induced the cardiac expression of NOR-1, and NOR-1 transgenesis exacerbated AngII-induced cardiac hypertrophy and fibrosis. This effect was associated with the up-regulation of hypertrophic (brain natriuretic peptide (Bnp), Acta1 and Myh7) and fibrotic markers (collagen type I α 1 chain (Col1a1), Pai-1 and lysyl oxidase-like 2 (Loxl2)). NOR-1 transgenesis up-regulated two key genes involved in cardiac hypertrophy (Myh7, encoding for β-myosin heavy chain (β-MHC)) and fibrosis (Loxl2, encoding for the extracellular matrix (ECM) modifying enzyme, Loxl2). Interestigly, in transient transfection assays, NOR-1 drove the transcription of Myh7 and Loxl2 promoters. Our findings suggest that NOR-1 is involved in the transcriptional programme leading to HCH.

Isovaleroylbinankadsurin A ameliorates cardiac ischemia/reperfusion injury through activating GR dependent RISK signaling

Ischemia/reperfusion (I/R) injury is a pathological process caused by reperfusion. The prevention of I/R injury is of great importance as it would enhance the efficacy of myocardial infarction treatment in patients. Isovaleroylbinankadsurin A (ISBA) has been demonstrated to possess multiple bioactivities for treating diseases. However, its protective effect on myocardial I/R injury remains unknown. In this study, the cardiomyocytes hypoxia/reoxygenation (H/R) in vitro model and coronary artery ligation in vivo model were used to examine the protective effect of ISBA. Apoptosis was determined by flow cytometry and Caspase 3 activity. Protein level was determined by Western blot. The mitochondrial viability was examined with mitochondrial viability stain assay. Mitochondrial membrane potential was detected by JC-1 staining and reactive oxygen species (ROS) was stained with 2',7'-dichlorodihydrofluorescein diacetate (DCF-DA). The binding interactions between ISBA and receptors was simulated by molecular docking. Results showed that ISBA effectively protected cardiomyocytes from I/R injury in in vitro and in vivo models. It remarkably blocked the apoptosis induced by H/R injury through the mitochondrial dependent pathway. Activation of the reperfusion injury salvage kinase (RISK) pathway was demonstrated to be essential for ISBA to exert its protective effect on cardiomyocytes. Moreover, molecular docking indicated that ISBA could directly bind to glucocorticoid receptor (GR) and thus induce its activation. Furthermore, the treatment of GR inhibitor RU486 partially counteracted the protective effect of ISBA on cardiomyocytes, consistent with the results of docking.Most attractively, by activating GR dependent RISK pathway, ISBA significantly elevated the cellular anti-oxidative capacity and hence alleviated oxidative damage induced by I/R injury. In conclusion, our study proved that ISBA protected the heart from myocardial I/R injury through activating GR dependent RISK pathway and consequently inhibiting the ROS generation. It provides a valuable reference for ISBA to be developed as a candidate drug for cardiovascular diseases.

Secreted Phospholipase A2-IIA Modulates Transdifferentiation of Cardiac Fibroblast through EGFR Transactivation: An Inflammation-Fibrosis Link

Secreted phospholipase A₂-IIA (sPLA₂-IIA) is a pro-inflammatory protein associated with cardiovascular disorders, whose functions and underlying mechanisms in cardiac remodelling are still under investigation. We herein study the role of sPLA₂-IIA in cardiac fibroblast (CFs)-to-myofibroblast differentiation and fibrosis, two major features involved in cardiac remodelling, and also explore potential mechanisms involved. In a mice model of dilated cardiomyopathy (DCM) after autoimmune myocarditis, serum and cardiac sPLA₂-IIA protein expression were found to be increased, together with elevated cardiac levels of the cross-linking enzyme lysyl oxidase (LOX) and reactive oxygen species (ROS) accumulation. Exogenous sPLA₂-IIA treatment induced proliferation and differentiation of adult rat CFs. Molecular studies demonstrated that sPLA₂-IIA promoted Src phosphorylation, shedding of the membrane-anchored heparin-binding EGF-like growth factor (HB-EGF) ectodomain and EGFR phosphorylation, which triggered phosphorylation of ERK, P70S6K and rS6. This was also accompanied by an up-regulated expression of the bone morphogenic protein (BMP)-1, LOX and collagen I. ROS accumulation were also found to be increased in sPLA₂-IIA-treated CFs. The presence of inhibitors of the Src/ADAMs-dependent HB-EGF shedding/EGFR pathway abolished the CF phenotype induced by sPLA₂-IIA. In conclusion, sPLA₂-IIA may promote myofibroblast differentiation through its ability to modulate EGFR transactivation and signalling as key mechanisms that underlie its biological and pro-fibrotic effects.

Morphological and Functional Characteristics of Animal Models of Myocardial Fibrosis Induced by Pressure Overload

Myocardial fibrosis is characterized by excessive deposition of myocardial interstitial collagen, abnormal distribution, and excessive proliferation of fibroblasts. According to the researches in recent years, myocardial fibrosis, as the pathological basis of various cardiovascular diseases, has been proven to be a core determinant in ventricular remodeling. Pressure load is one of the causes of myocardial fibrosis. In experimental models of pressure-overload-induced myocardial fibrosis, significant increase in left ventricular parameters such as interventricular septal thickness and left ventricular posterior wall thickness and the decrease of ejection fraction are some of the manifestations of cardiac damage. These morphological and functional changes have a serious impact on the maintenance of physiological functions. Therefore, establishing a suitable myocardial fibrosis model is the basis of its pathogenesis research. This paper will discuss the methods of establishing myocardial fibrosis model and compare the advantages and disadvantages of the models in order to provide a strong basis for establishing a myocardial fibrosis model.

NFATc3-dependent expression of miR-153-3p promotes mitochondrial fragmentation in cardiac hypertrophy by impairing mitofusin-1 expression

Mitochondrial dysfunction is involved in the pathogenesis of various cardiovascular disorders. Although mitochondrial dynamics, including changes in mitochondrial fission and fusion, have been implicated in the development of cardiac hypertrophy, the underlying molecular mechanisms remain mostly unknown. Here, we show that NFATc3, miR-153-3p, and mitofusion-1 (Mfn1) constitute a signaling axis that mediates mitochondrial fragmentation and cardiomyocyte hypertrophy.

Methods: Isoprenaline (ISO) was used to stimulate the hypertrophic response and mitochondrial fragmentation in cultured cardiomyocytes and in vivo. We performed immunoblotting, immunofluorescence, and quantitative real-time PCR to validate the function of Mfn1 in cardiomyocyte hypertrophy. Bioinformatic analyses, a luciferase reporter assay, and gain- and loss-of-function studies were used to demonstrate the biological function of miR-153-3p, which regulates mitochondrial fragmentation and hypertrophy by targeting Mfn1. Moreover, ChIP-qPCR and a luciferase reporter assay were performed to identify transcription factor NFATc3 as an upstream regulator to control the expression of miR-153-3p.

Results: Our results show that ISO promoted mitochondrial fission and enhanced the expression of miR-153-3p in cardiomyocytes. Knockdown of miR-153-3p attenuated ISO-induced mitochondrial fission and hypertrophy in cultured primary cardiomyocytes. miR-153-3p suppression inhibited mitochondrial fragmentation in ISO-induced cardiac hypertrophy in a mouse model. We identified direct targeting of Mfn1, a key protein of the mitochondrial fusion process, by miR-153-3p. Also, miR-153-3p promoted ISO-induced mitochondrial fission by suppressing the translation of Mfn1. We further found that NFATc3 activated miR-153-3p expression. Knockdown of NFATc3 inhibited miR-153-3p expression and blocked mitochondrial fission and hypertrophic response in cardiomyocytes.

Conclusions: Our data revealed a novel signaling pathway, involving NFATc3, miR-153-3p, and Mfn1, which could be a therapeutic target for the prevention and treatment of cardiac hypertrophy.

The Role of Lysyl Oxidase Enzymes in Cardiac Function and Remodeling

Lysyl oxidase (LOX) proteins comprise a family of five copper-dependent enzymes (LOX and four LOX-like isoenzymes (LOXL1-4)) critical for extracellular matrix (ECM) homeostasis and remodeling. The primary role of LOX enzymes is to oxidize lysyl and hydroxylysyl residues from collagen and elastin chains into highly reactive aldehydes, which spontaneously react with surrounding amino groups and other aldehydes to form inter- and intra-catenary covalent cross-linkages. Therefore, they are essential for the synthesis of a mature ECM and assure matrix integrity. ECM modulates cellular phenotype and function, and strikingly influences the mechanical properties of tissues. This explains the critical role of these enzymes in tissue homeostasis, and in tissue repair and remodeling. Cardiac ECM is mainly composed of fibrillar collagens which form a complex network that provides structural and biochemical support to cardiac cells and regulates cell signaling pathways. It is now becoming apparent that cardiac performance is affected by the structure and composition of the ECM and that any disturbance of the ECM contributes to cardiac disease progression. This review article compiles the major findings on the contribution of the LOX family to the development and progression of myocardial disorders.

Opposite Effects of Moderate and Extreme Cx43 Deficiency in Conditional Cx43-Deficient Mice on Angiotensin II-Induced Cardiac Fibrosis

Connexin 43 (Cx43) is essential for cardiac electrical coupling, but its effects on myocardial fibrosis is controversial. Here, we analyzed the role of Cx43 in myocardial fibrosis caused by angiotensin II (AngII) using Cx43^fl/fl and Cx43^Cre-ER(T)/fl inducible knock-out (Cx43 content: 50%) mice treated with vehicle or 4-hydroxytamoxifen (4-OHT) to induce a Cre-ER(T)-mediated global deletion of the Cx43 floxed allele. Myocardial collagen content was enhanced by AngII in all groups (n = 8–10/group, p < 0.05). However, animals with partial Cx43 deficiency (vehicle-treated Cx43^Cre-ER(T)/fl) had a significantly higher AngII-induced collagen accumulation that reverted when treated with 4-OHT, which abolished Cx43 expression. The exaggerated fibrotic response to AngII in partially deficient Cx43^Cre-ER(T)/fl mice was associated with enhanced p38 MAPK activation and was not evident in Cx43 heterozygous (Cx43^+/-) mice. In contrast, normalization of interstitial collagen in 4-OHT-treated Cx43^Cre-ER(T)/fl animals correlated with enhanced MMP-9 activity, IL-6 and NOX2 mRNA expression, and macrophage content, and with reduced α-SMA and SM22α in isolated fibroblasts. In conclusion, our data demonstrates an exaggerated, p38 MAPK-dependent, fibrotic response to AngII in partially deficient Cx43^Cre-ER(T)/fl mice, and a paradoxical normalization of collagen deposition in animals with an almost complete Cx43 ablation, an effect associated with increased MMP-9 activity and inflammatory response and reduced fibroblasts differentiation.

Emerging Roles of Lysyl Oxidases in the Cardiovascular System: New Concepts and Therapeutic Challenges

Lysyl oxidases (LOX and LOX-likes (LOXLs) isoenzymes) belong to a family of copper-dependent enzymes classically involved in the covalent cross-linking of collagen and elastin, a pivotal process that ensures extracellular matrix (ECM) stability and provides the tensile and elastic characteristics of connective tissues. Besides this structural role, in the last years, novel biological properties have been attributed to these enzymes, which can critically influence cardiovascular function. LOX and LOXLs control cell proliferation, migration, adhesion, differentiation, oxidative stress, and transcriptional regulation and, thereby, their dysregulation has been linked to a myriad of cardiovascular pathologies. Lysyl oxidase could modulate virtually all stages of the atherosclerotic process, from endothelial dysfunction and plaque progression to calcification and rupture of advanced and complicated plaques, and contributes to vascular stiffness in hypertension. The alteration of LOX/LOXLs expression underlies the development of other vascular pathologies characterized by a destructive remodeling of the ECM, such as aneurysm and artery dissections, and contributes to the adverse myocardial remodeling and dysfunction in hypertension, myocardial infarction, and obesity. This review examines the most recent advances in the study of LOX and LOXLs biology and their pathophysiological role in cardiovascular diseases with special emphasis on their potential as therapeutic targets.

Induction of LOX by TGF-β1/Smad/AP-1 signaling aggravates rat myocardial fibrosis and heart failure

This study aims to evaluate the efficacy of lysyl oxidase (LOX) inhibition in regulating rat myocardial fibrosis and chronic heart failure (CHF) and to validate the regulation of LOX by TGF-β1/Smad2/3 signaling in this process. A rat model of CHF was established by abdominal aortic coarctation. The renin-angiotensin-aldosterone system (RAAS) indexes (PRA, ACE2, Ang II, and ALD), cardiac function indicators (LVEF, LVFS, SAP, DAP, and LVEDP), ventricular remodeling- and fibrosis-related indicators (hydroxyproline, collagen deposition,and MMP-2/9), and morphological changes of myocardial tissues were examined. Rat cardiac fibroblasts (RCFs) were used in vitro assays. CHF patients showed increased LOX activity, accompanied by activated RAAS and TGF-β1. Furthermore, inhibition of LOX by β-aminopropionitrile (BAPN) mitigated the RAAS activation and attenuated cardiac dysfunction, ventricular remodeling, myocardial fibrosis, and collagen deposition in CHF rats. Moreover, TGF-β1 signaling diminished the LOX inhibition-mediated antiheart failure effect. Further assays showed that TGF-β1/Smad2/3 signaling increased expression of c-jun (AP-1 transcription factor subunit), which transcriptionally induced LOX expression. Additionally, BAPN abrogated the TGF-β1-mediated increase in cell proliferation and levels of MMP-2/9 and collagen I/III in RCFs. In conclusion, LOX can be induced by TGF-β1/Smad/AP-1 signaling and LOX inhibition attenuates rat myocardial fibrosis and CHF.

MicroRNA-19a/b-3p protect the heart from hypertension-induced pathological cardiac hypertrophy through PDE5A

AIM

PDE5A is a leading factor contributing to cGMP signaling and cardiac hypertrophy. However, microRNA-mediated posttranscriptional regulation of PDE5A has not been reported. The aim of this study is to screen the microRNAs that are able to regulate PDE5A and explore the function of the microRNAs in cardiac hypertrophy and remodeling.

METHODS AND RESULTS

Although miR-19a/b-3p (microRNA-19a-3p and microRNA-19b-3p) have been reported to be differentially expressed during cardiac hypertrophy, the direct targets and the functions of this microRNA family for regulation of cardiac hypertrophy have not yet been investigated. The present study identified some direct targets and the underlying functions of miR-19a/b-3p by using bioinformatics tools and gene manipulations within mouse neonatal cardiomyocytes. Transfection of miR-19a/b-3p down-regulated endogenous expressions of PDE5A at both mRNA and protein levels with real-time PCR and western blot. Luciferase reporter assays showed that PDE5A was a direct target of miR-19a/b-3p. In mouse models of cardiac hypertrophy, we found that miR-19a/b-3p was expressed in cardiomyocytes and that its expression was reduced in pressure overload-induced hypertrophic hearts. miR-19a/b-3p transgenic mice prevented the progress of cardiac hypertrophy and cardiac remodeling in response to angiotensin II infusion with echocardiographic assessment and pressure-volume relation analysis.

CONCLUSION

Our study elucidates that PDE5A is a novel direct target of miR-19a/b-3p, and demonstrates that antihypertrophic roles of the miR-19a/b-3p family in Ang II-induced hypertrophy and cardiac remodeling, suggests that endogenous miR-19a/b-3p might have clinical potential to suppress cardiac hypertrophy and heart failure.

The role and mechanism of transforming growth factor beta 3 in human myocardial infarction-induced myocardial fibrosis

Transforming growth factor beta (TGFβ) plays a crucial role in tissue fibrosis. A number of studies have shown that TGFβ3 significantly attenuated tissue fibrosis. However, the mechanism involved in this effect is poorly understood. In this study we found that the expression level of TGFβ3 was higher in human myocardial infarction (MI) tissues than in normal tissues, and interestingly, it increased with the development of fibrosis post‐myocardial infarction (post‐MI). In vitro, human cardiac fibroblasts (CFs) were incubated with angiotensin II (Ang II) to mimic the ischaemic myocardium microenvironment and used to investigate the anti‐fibrotic mechanism of TGFβ3. Then, fibrosis‐related proteins were detected by Western blot. It was revealed that TGFβ3 up‐regulation attenuated the proliferation, migration of human CFs and the expression of collagens, which are the main contributors to fibrosis, promoted the phenotype shift and the cross‐linking of collagens. Importantly, the expression of collagens was higher in the si‐smad7 groups than in the control groups, while silencing smad7 increased the phosphorylation level of the TGFβ/smad signalling pathway. Collectively, these results indicated that TGFβ3 inhibited fibrosis via the TGFβ/smad signalling pathway, possibly attributable to the regulation of smad7, and that TGFβ3 might serve as a potential therapeutic target for myocardial fibrosis post‐MI.

Thrombospondin-2 regulates extracellular matrix production, LOX levels, and cross-linking via downregulation of miR-29

Collagen fibrillogenesis and crosslinking have long been implicated in extracellular matrix (ECM)-dependent processes such as fibrosis and scarring. However, the extent to which matricellular proteins influence ECM protein production and fibrillar collagen crosslinking has yet to be determined. Here we show that thrombospondin 2 (TSP2), an anti-angiogenic matricellular protein, is an important modulator of ECM homeostasis. Specifically, through a fractionated quantitative proteomics approach, we show that loss of TSP2 leads to a unique ECM phenotype characterized by a significant decrease in fibrillar collagen, matricellular, and structural ECM protein production in the skin of TSP2 KO mice. Additionally, TSP2 KO skin displays decreased lysyl oxidase (LOX), which manifests as an increase in fibrillar collagen solubility and decreased levels of LOX-mediated fibrillar collagen crosslinking. We show that these changes are indirectly mediated by miR-29, a major regulator of ECM proteins and LOX, as miR-29 expression is increased in the TSP2 KO. Altogether, these findings indicate that TSP2 contributes to ECM production and assembly by regulating miR-29 and LOX.

Cardiomyocyte calcineurin is required for the onset and progression of cardiac hypertrophy and fibrosis in adult mice

Previous studies have demonstrated that activation of calcineurin induces pathological cardiac hypertrophy (CH). In these studies, loss-of-function was mostly achieved by systemic administration of the calcineurin inhibitor cyclosporin A. The lack of conditional knockout models for calcineurin function has impeded progress toward defining the role of this protein during the onset and the development of CH in adults. Here, we exploited a mouse model of CH based on the infusion of a hypertensive dose of angiotensin II (AngII) to model the role of calcineurin in CH in adulthood. AngII-induced CH in adult mice was reduced by treatment with cyclosporin A, without affecting the associated increase in blood pressure, and also by induction of calcineurin deletion in adult mouse cardiomyocytes, indicating that cardiomyocyte calcineurin is required for AngII-induced CH. Surprisingly, cardiac-specific deletion of calcineurin, but not treatment of mice with cyclosporin A, significantly reduced AngII-induced cardiac fibrosis and apoptosis. Analysis of profibrotic genes revealed that AngII-induced expression of Tgfβ family members and Lox was not inhibited by cyclosporin A but was markedly reduced by cardiac-specific calcineurin deletion. These results show that AngII induces a direct, calcineurin-dependent prohypertrophic effect in cardiomyocytes, as well as a systemic hypertensive effect that is independent of calcineurin activity.

Intermittent Hypoxia Mimicking Sleep Apnea Increases Passive Stiffness of Myocardial Extracellular Matrix. A Multiscale Study

Background: Tissue hypoxia-reoxygenation characterizes obstructive sleep apnea (OSA), a very prevalent respiratory disease associated with increased cardiovascular morbidity and mortality. Experimental studies indicate that intermittent hypoxia (IH) mimicking OSA induces oxidative stress and inflammation in heart tissue at the cell and molecular levels. However, it remains unclear whether IH modifies the passive stiffness of the cardiac tissue extracellular matrix (ECM). Aim: To investigate multiscale changes of stiffness induced by chronic IH in the ECM of left ventricular (LV) myocardium in a murine model of OSA. Methods: Two-month and 18-month old mice (N = 10 each) were subjected to IH (20% O₂ 40 s-6% O₂ 20 s) for 6 weeks (6 h/day). Corresponding control groups for each age were kept under normoxia. Fresh LV myocardial strips (∼7 mm × 1 mm × 1 mm) were prepared, and their ECM was obtained by decellularization. Myocardium ECM macroscale mechanics were measured by performing uniaxial stress-strain tensile tests. Strip macroscale stiffness was assessed as the stress value (σ) measured at 0.2 strain and Young's modulus (E_M) computed at 0.2 strain by fitting Fung's constitutive model to the stress-strain relationship. ECM stiffness was characterized at the microscale as the Young's modulus (E_m) measured in decellularized tissue slices (∼12 μm tick) by atomic force microscopy. Results: Intermittent hypoxia induced a ∼1.5-fold increase in σ (p < 0.001) and a ∼2.5-fold increase in E_M (p < 0.001) of young mice as compared with normoxic controls. In contrast, no significant differences emerged in E_m among IH-exposed and normoxic mice. Moreover, the mechanical effects of IH on myocardial ECM were similar in young and aged mice. Conclusion: The marked IH-induced increases in macroscale stiffness of LV myocardium ECM suggests that the ECM plays a role in the cardiac dysfunction induced by OSA. Furthermore, absence of any significant effects of IH on the microscale ECM stiffness suggests that the significant increases in macroscale stiffening are primarily mediated by 3D structural ECM remodeling.

The nuclear receptor NOR-1 modulates redox homeostasis in human vascular smooth muscle cells

The nuclear receptor NOR-1 (Neuron-derived Orphan Receptor-1) has recently been involved in vascular remodeling and coronary artery disease, however, to date, only a few NOR-1 target genes have been described. We aimed to identify genes regulated by NOR-1 in human vascular smooth muscle cells (VSMC). Lentiviral overexpression of NOR-1 increases reactive oxygen species (ROS) in human VSMC. In accordance, NOR-1 strongly increased NADPH oxidase NOX1 mRNA and protein levels, while NOR-1 silencing significantly reduced NOX1 expression. Luciferase reporter, site-directed mutagenesis and EMSA studies identified two nerve growth factor-induced clone B (NGFI-B)-response elements (NBREs) in NOX1 promoter as essential elements for NOR-1 responsiveness. NOR-1 and NOX1 were co-expressed by VSMC in human atherosclerotic lesions, and NOX1 knockdown counteracted the increased ROS production and cell migration induced by NOR-1 overexpression. NOR-1 also modulated the expression of other enzymes involved in cellular redox status, in particular, upregulated superoxide dismutase-1 (SOD1) and SOD3 while downregulated SOD2 and NOX4. NOR-1 induced SOD1 and SOD3 transcriptional activity and participated in the modulation of SOD3 by inflammatory stimuli. By contrast, NOR-1 impaired SOD2 transcription antagonizing NFκB signaling. These results indicate that NOR-1 induces NOX1 in human VSMC and participates in the complex gene networks regulating oxidative stress and redox homeostasis in the vasculature.

Inhibitor of lysyl oxidase improves cardiac function and the collagen/MMP profile in response to volume overload

The cardiac extracellular matrix is a complex architectural network that serves many functions, including providing structural and biochemical support to surrounding cells and regulating intercellular signaling pathways. Cardiac function is directly affected by extracellular matrix (ECM) composition, and alterations of the ECM contribute to the progression of heart failure. Initially, collagen deposition is an adaptive response that aims to preserve tissue integrity and maintain normal ventricular function. However, the synergistic effects of proinflammatory and profibrotic responses induce a vicious cycle, which causes excess activation of myofibroblasts, significantly increasing collagen deposition and accumulation in the matrix. Furthermore, excess synthesis and activation of the enzyme lysyl oxidase (LOX) during disease increases collagen cross-linking, which significantly increases collagen resistance to degradation by matrix metalloproteinases (MMPs). In the present study, the aortocaval fistula model of volume overload (VO) was used to determine whether LOX inhibition could prevent adverse changes in the ECM and subsequent cardiac dysfunction. The major findings from this study were that LOX inhibition 1) prevented VO-induced increases in left ventricular wall stress; 2) partially attenuated VO-induced ventricular hypertrophy; 3) completely blocked the increases in fibrotic proteins, including collagens, MMPs, and their tissue inhibitors; and 4) prevented the VO-induced decline in cardiac function. It remains unclear whether a direct interaction between LOX and MMPs exists; however, our experiments suggest a potential link between the two because LOX inhibition completely attenuated VO-induced increases in MMPs. Overall, our study demonstrated key cardioprotective effects of LOX inhibition against adverse cardiac remodeling due to chronic VO. NEW & NOTEWORTHY Although the primary role of lysyl oxidase (LOX) is to cross-link collagens, we found that elevated LOX during cardiac disease plays a key role in the progression of heart failure. Here, we show that inhibition of LOX in volume-overloaded rats prevented the development of cardiac dysfunction and improved ventricular collagen and matrix metalloproteinase/tissue inhibitor of metalloproteinase profiles.

Overexpression of integrin α11 induces cardiac fibrosis in mice

AIM

To understand the role of the collagen-binding integrin α11 in vivo, we have used a classical approach of creating a mouse strain overexpressing integrin α11. A transgenic mouse strain overexpressing α11 in muscle tissues was analysed in the current study with special reference to the heart tissue.

METHODS

We generated and phenotyped integrin α11 transgenic (TG) mice by echocardiography, magnetic resonance imaging and histology. Wild-type (WT) mice were subjected to aortic banding (AB) and the expression of integrin α11 was measured in flow cytometry-sorted cardiomyocytes and non-myocytes.

RESULTS

TG mice developed left ventricular concentric hypertrophy by 6 months, with increased collagen deposition and reactivation of mRNA encoding foetal genes associated with cardiovascular pathological remodelling compared to WT mice. Masson's trichrome staining revealed interstitial fibrosis, confirmed additionally by magnetic resonance imaging and was found to be most prominent in the cardiac septum of TG but not WT mice. TG hearts expressed increased levels of transforming growth factor-β2 and transforming growth factor-β3 and upregulated smooth muscle actin. Macrophage infiltration coincided with increased NF-κB signalling in TG but not WT hearts. Integrin α11 expression was increased in both cardiomyocytes and non-myocyte cells from WT AB hearts compared to sham-operated animals.

CONCLUSION

We report for the first time that overexpression of integrin α11 induces cardiac fibrosis and left ventricular hypertrophy. This is a result of changes in intracellular hypertrophic signalling and secretion of soluble factors that increase collagen production in the heart.

TMEM16A regulates portal vein smooth muscle cell proliferation in portal hypertension

The aim of the present study was to elucidate the effect of transmembrane protein 16A (TMEM16A) on portal vein smooth muscle cell (PVSMC) proliferation associated with portal vein remodeling in portal hypertension (PHT). Sprague-Dawley rats were subjected to bile duct ligation to establish a rat model of liver cirrhosis and PHT. Sham-operated animals served as controls. At 8 weeks after bile duct ligation, the extent of liver fibrosis and the portal vein wall thickness were assessed using hematoxylin-eosin staining. The protein expression levels of TMEM16A, extracellular signal-regulated kinase 1 and 2 (ERK1/2) and phosphorylated ERK1/2 (p-ERK1/2) in the portal vein were detected by immunohistochemistry and western blotting. In vitro, the lentivirus vectors were constructed and transfected into PVSMCs to upregulate the expression of TMEM16A. Isolated rat primary PVSMCs were treated with a small molecule inhibitor of TMEM16A, T16A-inhA01. Cell cycle was detected by flow cytometry. The activity of TMEM16A in the portal vein isolated from bile duct ligated rats was decreased, while the expression level of p-ERK1/2 was increased. However, in vitro, upregulation of TMEM16A promoted the proliferation PVSMCs, while inhibition of TMEM16A channels inhibited the proliferation of PVSMCs. The results indicated that TMEM16A contributes to PVSMCs proliferation in vitro, but in vivo, it may be a negative regulator of cell proliferation influenced by numerous factors.