Snail1 is involved in de novo cardiac fibrosis after myocardial infarction in mice

RV-specific Targeting of Snai1 Rescues Pulmonary Hypertension-induced Right Ventricular Failure by Inhibiting EndMT and Fibrosis via LOXL2 Mediated Mechanism

Background

Pulmonary hypertension (PH)-induced right ventricular (RV) failure (PH-RVF) is a significant prognostic determinant of mortality and is characterized by RV hypertrophy, endothelial-to-mesenchymal transition (EndMT), fibroblast-to-myofibroblast transition (FMT), fibrosis, and extracellular matrix (ECM)-remodeling. Despite the importance of RV function in PH, the mechanistic details of PH-RVF, especially the regulatory control of RV EndMT, FMT, and fibrosis, remain unclear. The action of transcription factor Snai1 is shown to be mediated through LOXL2 recruitment, and their co-translocation to the nucleus, during EndMT progression. We hypothesize that RV EndMT and fibrosis in PH-RVF are governed by the TGFβ1-Snai1-LOXL2 axis. Furthermore, targeting Snai1 could serve as a novel therapeutic strategy for PH-RVF.

Methods

Adult male Sprague Dawley rats (250-300g) received either a single subcutaneous injection of Monocrotaline (MCT, 60mg/kg, n=9; followed for 30-days) or Sugen (SU5416 20mg/kg, n=9; 10% O 2 hypoxia for 3-weeks followed by normoxia for 2-weeks) or PBS (CTRL, n=9). We performed secondary bioinformatics analysis on the RV bulk RNA-Seq data from MCT, SuHx, and PAB rats and human PH-PVF. We validated EndMT and FMT and their association with Snai1 and LOXL2 in the RVs of MCT and SuHx rat models and human PH-RVF using immunofluorescence, qPCR, and Western blots. For in vivo Snai1 knockdown (Snai1-KD), MCT-rats either received Snai1-siRNA (n=7; 5nM/injection every 3-4 days; 4-injections) or scramble (SCRM-KD; n=7) through tail vein from day 14-30 after MCT. Echocardiography and catheterization were performed terminally. Bulk RNASeq and differential expression analysis were performed on Snai1- and SCRM-KD rat RVs. In vitro Snai1-KD was performed on human coronary artery endothelial cells (HCAECs) and human cardiac fibroblasts (HCFs) under hypoxia+TGFβ1 for 72-hrs.

Results

PH-RVF had increased RVSP and Fulton index and decreased RV fractional area change (RVFAC %). RV RNASeq demonstrated EndMT as the common top-upregulated pathway between rat (MCT, SuHx, and PAB) and human PH-RVF. Immunofluorescence using EndMT- and FMT-specific markers demonstrated increased EndMT and FMT in RV of MCT and SuHx rats and PH-RVF patients. Further, RV expression of TGFβ1, Snai1, and LOXL2 was increased in MCT and SuHx. Nuclear co-localization and increased immunoreactivity, transcript, and protein levels of Snai1 and LOXL2 were observed in MCT and SuHx rats and human RVs. MCT rats treated with Snai1-siRNA demonstrated decreased Snai1 expression, RVSP, Fulton index, and increased RVFAC. Snai1-KD resulted in decreased RV-EndMT, FMT, and fibrosis via a LOXL2-dependent manner. Further, Snai1-KD inhibited hypoxia+TGFβ1-induced EndMT in HCAECs and FMT in HCFs in vitro by decreasing perinuclear/nuclear Snai1+LOXL2 expression and co-localization.

Conclusions

RV-specific targeting of Snai1 rescues PH-RVF by inhibiting EndMT and Fibrosis via a LOXL2-mediated mechanism.

Oxidative-stress induced Bmp2-Smad1/5/8 signaling dependent differentiation of early cardiomyocytes from embryonic and adult epicardial cells

Heart failure has become a major life-threatening cause affecting millions globally, characterized by the permanent loss of adult functional cardiomyocytes leading to fibrosis which ultimately deprives the heart of its functional efficacy. Here we investigated the reparative property of embryonic and adult epicardial cells towards cardiomyocyte differentiation under oxidative stress-induced conditions along with the identification of a possible molecular signaling pathway. Isolated epicardial cells from embryonic chick hearts subjected to oxidative stress and hypoxia induction. Initial assessment of successful injury induction reveals hypertrophy of isolated epicardial cells. Detailed marker gene expression analyses and inhibitor studies reveal Bone morphogenic protein (Bmp)2-Smad1/5/8 signaling dependent cardiomyocyte lineage specification via epithelial to mesenchymal transition (EMT) post-injury. EMT is further confirmed by increased proliferation, migration, and differentiation towards cardiomyocyte lineage. We have also established an in-vivo model in adult male rats using Isoproterenol. Successful oxidative stress-mediated injury induction in adult heart was marked by increased activated fibroblasts followed by apoptosis of adult cardiomyocytes. The detailed characterization of adult epicardial cells reveals similar findings to our avian in-vitro data. Both in-vitro and in-vivo results show a significant increase in the expression of cardiomyocyte specific markers indicative of lineage specificity and activation of epicardial cells post oxidative stress mediated injury. Our findings suggest an EMT-induced reactivation of epicardial cells and early cardiomyocyte lineage specification following oxidative stress in a Bmp2- Smad1/5/8 dependent manner. Overall, this regulatory mechanism of cardiomyocyte differentiation induced by oxidative stress may contribute to the field of cardiac repair and regenerative therapeutics.

Differential expression of members of SOX family of transcription factors in failing human hearts

The Sry-related high-mobility-group box (SOX) gene family, with 20 known transcription factors in humans, plays an essential role during development and disease processes. Several SOX proteins (SOX4, 11, and 9) are required for normal heart morphogenesis. SOX9 was shown to contribute to cardiac fibrosis. However, differential expression of other SOXs and their roles in the failing human myocardium have not been explored. Here, we used the whole-transcriptome sequencing (RNA-seq), gene co-expression, and meta-analysis to examine whether any SOX factors might play a role in the failing human myocardium. RNA-seq analysis was performed for cardiac tissue samples from heart failure (HF) patients due to dilated cardiomyopathy (DCM), or hypertrophic cardiomyopathy (HCM) and healthy donors (NF). The RNA levels of 20 SOX genes from RNA-seq data were extracted and compared to the 3 groups. Four SOX genes whose RNA levels were significantly upregulated in DCM or HCM compared to NF. However, only SOX4 and SOX8 proteins were markedly increased in the HF groups. A moderate to strong correlation was observed between the RNA level of SOX4/8 and fibrotic genes among each individual. Gene co-expression network analysis identified genes associated and respond similarly to perturbations with SOX4 in cardiac tissues. Using a meta-analysis combining epigenetics and genome-wide association data, we reported several genomic variants associated with HF phenotype linked to SOX4 or SOX8. In summary, our results implicate that SOX4 and SOX8 have a role in cardiomyopathy, leading to HF in humans. The molecular mechanism associated with them in HF warrants further investigation.

The Epithelial-to-Mesenchymal Transition as a Possible Therapeutic Target in Fibrotic Disorders

Fibrosis is a chronic and progressive disorder characterized by excessive deposition of extracellular matrix, which leads to scarring and loss of function of the affected organ or tissue. Indeed, the fibrotic process affects a variety of organs and tissues, with specific molecular background. However, two common hallmarks are shared: the crucial role of the transforming growth factor-beta (TGF-β) and the involvement of the inflammation process, that is essential for initiating the fibrotic degeneration. TGF-β in particular but also other cytokines regulate the most common molecular mechanism at the basis of fibrosis, the Epithelial-to-Mesenchymal Transition (EMT). EMT has been extensively studied, but not yet fully explored as a possible therapeutic target for fibrosis. A deeper understanding of the crosstalk between fibrosis and EMT may represent an opportunity for the development of a broadly effective anti-fibrotic therapy. Here we report the evidences of the relationship between EMT and multi-organ fibrosis, and the possible therapeutic approaches that may be developed by exploiting this relationship.

What’s in a name? On fibroblast phenotype and nomenclature

Fibroblasts have long been recognized as important stromal cells, playing key roles in synthesizing and maintaining the extracellular matrix, but historically were treated as a relatively uniform cell type. Studies in recent years have revealed a surprising level of heterogeneity of fibroblasts across tissues, and even within organs such as the skin and heart. This heterogeneity may have functional consequences, including during stress and disease. While the field has moved forward quickly to begin to address the scientific import of this heterogeneity, the descriptive language used for these cells has not kept pace, particularly when considering the phenotype changes that occur as fibroblasts convert to myofibroblasts in response to injury. We discuss here the nature and sources of the heterogeneity of fibroblasts, and review how our understanding of the complexity of the fibroblast to myofibroblast phenotype conversion has changed with increasing scrutiny. We propose that the time is opportune to reevaluate how we name and describe these cells, particularly as they transition to myofibroblasts through discrete stages. A standardized nomenclature is essential to address the confusion that currently exists in the literature as to the usage of terms like myofibroblast and the description of fibroblast phenotype changes in disease.

Novel molecular therapeutic targets in cardiac fibrosis: a brief overview 1

Cardiac fibrosis, characterized by excessive accumulation of extracellular matrix, abolishes cardiac contractility, impairs cardiac function, and ultimately leads to heart failure. In recent years, significant evidence has emerged that supports the highly dynamic and responsive nature of the cardiac extracellular matrix. Although our knowledge of cardiac fibrosis has advanced tremendously over the past decade, there is still a lack of specific therapies owing to an incomplete understanding of the disease etiology and process. In this review, we attempt to highlight some of the recently investigated molecular determinants of ischemic and non-ischemic fibrotic remodeling of the myocardium that present as promising avenues for development of anti-fibrotic therapies.

MiR-30e Attenuates Isoproterenol-induced Cardiac Fibrosis Through Suppressing Snai1/TGF-β Signaling

Background:

MicroRNAs are a class of small RNA molecules that inhibit protein expression through either degradation of messenger RNA or interference with protein translation. Our previous work suggested an involvement of miR-30e in myocardial fibrosis; however, the exact role of miR-30e in the pathogenesis of cardiac fibrosis and the underlying mechanisms are not known.

Methods:

Male Sprague Dawley rats were treated with isoproterenol (ISO) to induce cardiac remodeling and fibrosis and treated with either miR-30e agomir (AG) or antagomir and respective controls. The expression of miR-30e was evaluated by reverse transcription and quantitative polymerase chain reaction. Myocardial fibrosis was assessed by Masson's trichrome staining, and the level of oxidative stress and the expression of Snai1 and transforming growth factor-beta (TGF-β) were detected using Western blots.

Results:

A significant downregulation of miR-30e was found in the hearts of ISO-treated rats with cardiac fibrosis compared with nontreated controls. In vivo administration of miR-30e AG increased the survival of ISO-treated rats compared with AG-negative control administration, which was associated with reduced oxidative stress. We further identified Snai1 as a novel miR-30e target. Snai1 expression was significantly increased in hearts from ISO-treated rats, which coincided with decreased miR-30e expression and increased TGF-β expression. An miR-30e putative target sequence was identified in the 3′-untranslated region (UTR) Snai1. In a reporter assay, miR-30e greatly suppressed the activity of wild-type 3′-UTR–fused luciferase reporter, but showed no significant effect with the mutated 3′-UTR–fused reporter.

Conclusion:

MiR-30e attenuated ISO-induced cardiac dysfunction and cardiac fibrosis in a rat cardiac remodeling model. Mechanistically, miR-30e suppressed Snai1/TGF-β pathway which was involved in ISO-induced cardiac remodeling.

Snail1 is positively correlated with atrial fibrosis in patients with atrial fibrillation and rheumatic heart disease

The present study investigated the association between Snail1 and atrial fibrosis in patients with atrial fibrillation (AF) and rheumatic heart disease (RHD) and to determine the possible mechanism underlying this interrelation. A total of 19 patients were included in the current study and were divided into two groups: A sinus rhythm (SR) group (n=9) and an AF group (n=10). All patients underwent heart valve replacement surgery, during which ~200 mg right atrium tissue was obtained. Hematoxylin and eosin and Masson's trichrome-stained sections were used to evaluate the morphological changes of cardiomyocytes and the level of fibrosis. Immunohistochemistry was applied to observe the location and expression of Snail1. Reverse transcription-quantitative polymerase chain reaction was used to measure Snail1 mRNA levels. Western blotting was used to determine changes in the expression of Snail1, as well as in the expression of proteins involved in the Wnt pathway, including Wnt1, Wnt 3a, Wnt8a, Wnt5a and Wnt11. Compared with the SR group, expanded cardiomyocytes and higher collagen deposition was detected in the atrial tissue of the AF group. The expression of Snail1 mRNA and protein was significantly higher in the AF group than in the SR group (P<0.05). Additionally, the expression of Wnt1, 3a and 8a in the canonical Wnt signaling pathway, and Wnt5a and 11 in the noncanonical Wnt signaling pathway were significantly increased in the AF group. Furthermore, the phosphorylation level of glycogen synthase kinase 3β (GSK3β) and the levels of β-catenin and GSK3β were significantly increased in the AF group compared with the SR group (P<0.05). Snail1 may be involved in the development and maintenance of atrial fibrosis in patients with atrial fibrillation and rheumatic heart disease and may be developed as a novel biomarker to evaluate myocardial fibrosis in the future. Additionally, the current study suggests that the Wnt signaling pathway may participate in the process of increased Snail1 expression and atrial fibrosis in patients with AF and RHD.

Epithelial-to-mesenchymal transition transcription factors in cancer-associated fibroblasts

Beyond inducing epithelial‐to‐mesenchymal transcription (EMT), transcriptional factors of the Snail, ZEB and Twist families (EMT‐TFs) control global plasticity programmes affecting cell stemness and fate. Literature addressing the reactivation of these factors in adult tumour cells is very extensive, as they enable cancer cell plasticity and fuel both tumour initiation and metastatic spread. Incipient data reveal that EMT‐TFs are also expressed in fibroblasts, providing these with additional properties. Here, I will review recent reports on the expression of EMT‐TFs in cancer‐associated fibroblasts (CAFs). The new model suggests that EMT‐TFs can be envisioned as essential metastasis and chemoresistance‐promoting molecules, thereby enabling coordinated plasticity programmes in parenchyma and stroma–tumour compartments.

Age-dependent down-regulation of hyperpolarization-activated cyclic nucleotide-gated channel 4 causes deterioration of canine sinoatrial node function

The activity of pacemaker cells in the sinoatrial node (SAN) is an indicator of normal sinus rhythm. Clinical studies have revealed that the dysfunction of the SAN progressively increases with aging. In this study, we determined the changes in hyperpolarization-activated cyclic nucleotide-gated channel 4 (HCN4) expression and the relationship between aging and canine SAN dysfunction. The results of cardiac electrophysiological determination revealed that the intrinsic heart rate decreased from 168 ± 11 beats min-1 in young canines to 120 ± 9 beats min-1 in adults and to 88 ± 9 beats min-1 in aged canines. The sinus node recovery time (SNRT) increased from 412 ± 32 ms in young canines to 620 ± 56 ms in adults and to 838 ± 120 ms in aged canines. Corrected SNRT (CSNRT) increased from 55 ± 12 ms in young canines to 117 ± 27 ms in adults and to 171 ± 37 ms in aged canines. These results indicated that SAN function deteriorated with aging in the canine heart. However, histological staining illustrated that fibrosis was not significantly increased with aging in canine SAN. Real-time polymerase chain reaction indicated that the expression of HCN4 mRNA was downregulated in the elderly canine SAN. Similarly, we also verified that HCN4 protein expression within the SAN declined with aging via immunofluorescence staining and western blot analysis. Taken together, our data show that electrical remodeling, related to the down-regulation of HCN4, is responsible for the gradually increased incidence of SAN dysfunction with aging. Our results provide further evidence for explaining the mechanisms of age-related deterioration in the SAN.

Action of SNAIL1 in Cardiac Myofibroblasts Is Important for Cardiac Fibrosis following Hypoxic Injury

Hypoxic injury to the heart results in cardiac fibrosis that leads to cardiac dysfunction and heart failure. SNAIL1 is a zinc finger transcription factor implicated in fibrosis following organ injury and cancer. To determine if the action of SNAIL1 contributed to cardiac fibrosis following hypoxic injury, we used an endogenous SNAIL1 bioluminescence reporter mice, and SNAIL1 knockout mouse models. Here we report that SNAIL1 expression is upregulated in the infarcted heart, especially in the myofibroblasts. Utilizing primary cardiac fibroblasts in ex vivo cultures we find that pro-fibrotic factors and collagen I increase SNAIL1 protein level. SNAIL1 is required in cardiac fibroblasts for the adoption of myofibroblast fate, collagen I expression and expression of fibrosis-related genes. Taken together this data suggests that SNAIL1 expression is induced in the cardiac fibroblasts after hypoxic injury and contributes to myofibroblast phenotype and a fibrotic scar formation. Resultant collagen deposition in the scar can maintain elevated SNAIL1 expression in the myofibroblasts and help propagate fibrosis.

Notch in fibrosis and as a target of anti-fibrotic therapy

The Notch pathway represents a highly conserved signaling network with essential roles in regulation of key cellular processes and functions, many of which are critical for development. Accumulating evidence indicates that it is also essential for fibrosis and thus the pathogenesis of chronic fibroproliferative diseases in diverse organs and tissues. Different effects of Notch activation are observed depending on cellular and tissue context as well as in both physiologic and pathologic states. Close interactions of Notch signaling pathway with other signaling pathways have been identified. In this review, current knowledge on the role of the Notch signaling with special focus on fibrosis and its potential as a therapeutic target is summarized.

Snail1-driven plasticity of epithelial and mesenchymal cells sustains cancer malignancy

The transcription factor Snail1 induces epithelial-to-mesenchymal transition (EMT) in tumor epithelial cells, a process associated with the emergence of stemness, invasion and cancer malignancy. Here, we review recent reports indicating that Snail1 also regulates mesenchymal plasticity and paracrine signaling and propose that Snail1 orchestrates the generation of cancer stem cells (CSCs) and cancer-associated fibroblasts (CAFs). Our view supports the current models for tumorigenesis that consider stemness and tumor microenvironment as retroactive actors for metastasis formation, revealing Snail1 as a regulator of these metastatic forces. This view offers new perspectives for understanding and targeting metastasis.

Nrf2 and Snail-1 in the prevention of experimental liver fibrosis by caffeine

AIM: To determine the molecular mechanisms involved in experimental hepatic fibrosis prevention by caffeine (CFA).

METHODS: Liver fibrosis was induced in Wistar rats by intraperitoneal thioacetamide or bile duct ligation and they were concomitantly treated with CFA (15 mg/kg per day). Fibrosis and inflammatory cell infiltrate were evaluated and classified by Knodell index. Inflammatory infiltrate was quantified by immunohistochemistry (anti-CD11b). Gene expression was analyzed by quantitative reverse transcription-polymerase chain reaction for collagen I (Col-1), connective tissue growth factor (CTGF), transforming growth factor β1 (TGF-β1), tumor necrosis factor alpha (TNF-α), interleukin-1 (IL-1), IL-6, superoxide dismutase (SOD) and catalase (CAT). Activation of Nrf2 and Snail-1 was analyzed by Western-blot. TNF-α expression was proved by enzyme-linked immunosorbant assay, CAT activity was performed by zymography.

RESULTS: CFA treatment diminished fibrosis index in treated animals. The Knodell index showed both lower fibrosis and necroinflammation. Expression of profibrogenic genes CTGF, Col-1 and TGF-β1 and proinflammatory genes TNF-α, IL-6 and IL-1 was substantially diminished with CFA treatment with less CD11b positive areas. Significantly lower values of transcriptional factor Snail-1 were detected in CFA treated rats compared with cirrhotic rats without treatment; in contrast Nrf2 was increased in the presence of CFA. Expression of SOD and CAT was greater in animals treated with CFA showing a strong correlation between mRNA expression and enzyme activity.

CONCLUSION: Our results suggest that CFA inhibits the transcriptional factor Snail-1, down-regulating profibrogenic genes, and activates Nrf2 inducing antioxidant enzymes system, preventing inflammation and fibrosis.