βIV-Spectrin/STAT3 complex regulates fibroblast phenotype, fibrosis, and cardiac function

Proximity Mapping of Desmosomes Reveals a Striking Shift in Their Molecular Neighborhood Associated With Maturation

Desmosomes are multiprotein adhesion complexes that link intermediate filaments to the plasma membrane, ensuring the mechanical integrity of cells across tissues, but how they participate in the wider signaling network to exert their full function is unclear. To investigate this, we carried out protein proximity mapping using biotinylation (BioID). The combined interactomes of the essential desmosomal proteins desmocollin 2a, plakoglobin, and plakophilin 2a (Pkp2a) in Madin-Darby canine kidney epithelial cells were mapped and their differences and commonalities characterized as desmosome matured from Ca2+ dependence to the mature, Ca2+-independent, hyper-adhesive state, which predominates in tissues. Results suggest that individual desmosomal proteins have distinct roles in connecting to cellular signaling pathways and that these roles alter substantially when cells change their adhesion state. The data provide further support for a dualistic concept of desmosomes in which the properties of Pkp2a differ from those of the other, more stable proteins. This body of data provides an invaluable resource for the analysis of desmosome function.

JAK/STAT3 signaling in cardiac fibrosis: a promising therapeutic target

Cardiac fibrosis is a serious health problem because it is a common pathological change in almost all forms of cardiovascular diseases. Cardiac fibrosis is characterized by the transdifferentiation of cardiac fibroblasts (CFs) into cardiac myofibroblasts and the excessive deposition of extracellular matrix (ECM) components produced by activated myofibroblasts, which leads to fibrotic scar formation and subsequent cardiac dysfunction. However, there are currently few effective therapeutic strategies protecting against fibrogenesis. This lack is largely because the molecular mechanisms of cardiac fibrosis remain unclear despite extensive research. The Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling cascade is an extensively present intracellular signal transduction pathway and can regulate a wide range of biological processes, including cell proliferation, migration, differentiation, apoptosis, and immune response. Various upstream mediators such as cytokines, growth factors and hormones can initiate signal transmission via this pathway and play corresponding regulatory roles. STAT3 is a crucial player of the JAK/STAT pathway and its activation is related to inflammation, malignant tumors and autoimmune illnesses. Recently, the JAK/STAT3 signaling has been in the spotlight for its role in the occurrence and development of cardiac fibrosis and its activation can promote the proliferation and activation of CFs and the production of ECM proteins, thus leading to cardiac fibrosis. In this manuscript, we discuss the structure, transactivation and regulation of the JAK/STAT3 signaling pathway and review recent progress on the role of this pathway in cardiac fibrosis. Moreover, we summarize the current challenges and opportunities of targeting the JAK/STAT3 signaling for the treatment of fibrosis. In summary, the information presented in this article is critical for comprehending the role of the JAK/STAT3 pathway in cardiac fibrosis, and will also contribute to future research aimed at the development of effective anti-fibrotic therapeutic strategies targeting the JAK/STAT3 signaling.

Beta IV spectrin inhibits the metastatic growth of melanoma by suppressing VEGFR2-driven tumor angiogenesis

BACKGROUND

Tumor-associated angiogenesis mediates the growth and metastasis of most solid cancers. Targeted therapies of the VEGF pathways can effectively block these processes but often fail to provide lasting benefits due to acquired resistance and complications.

RESULTS

Recently, we discovered βIV -spectrin as a powerful regulator of angiogenesis and potential new target. We previously reported that βIV -spectrin is dynamically expressed in endothelial cells (EC) to induce VEGFR2 protein turnover during development. Here, we explored how βIV -spectrin influences the tumor vasculature using the murine B16 melanoma model and determined that loss of EC-specific βIV -spectrin dramatically promotes tumor growth and metastasis. Intraperitoneally injected B16 cells formed larger tumors with increased tumor vessel density and greater propensity for metastatic spread particularly to the chest cavity and lung compared to control mice. These results support βIV -spectrin as a key regulator of tumor angiogenesis and a viable vascular target in cancer.

βIV-Spectrin in Cardiac Fibroblasts: Implications for Fibrosis and Therapeutic Targeting in Cardiac Diseases. Comment on Nassal et al. Spectrin-Based Regulation of Cardiac Fibroblast Cell-Cell Communication. Cells 2023, 12, 748

Fibroblasts in the heart, traditionally recognized as interstitial cells, have long been overlooked in the study of cardiac physiology and pathology [...].

Spectrin-Based Regulation of Cardiac Fibroblast Cell-Cell Communication

Cardiac fibroblasts (CFs) maintain the fibrous extracellular matrix (ECM) that supports proper cardiac function. Cardiac injury induces a transition in the activity of CFs to promote cardiac fibrosis. CFs play a critical role in sensing local injury signals and coordinating the organ level response through paracrine communication to distal cells. However, the mechanisms by which CFs engage cell-cell communication networks in response to stress remain unknown. We tested a role for the action-associated cytoskeletal protein βIV-spectrin in regulating CF paracrine signaling. Conditioned culture media (CCM) was collected from WT and βIV-spectrin deficient (qv4J) CFs. WT CFs treated with qv4J CCM showed increased proliferation and collagen gel compaction compared to control. Consistent with the functional measurements, qv4J CCM contained higher levels of pro-inflammatory and pro-fibrotic cytokines and increased concentration of small extracellular vesicles (30-150 nm diameter, exosomes). Treatment of WT CFs with exosomes isolated from qv4J CCM induced a similar phenotypic change as that observed with complete CCM. Treatment of qv4J CFs with an inhibitor of the βIV-spectrin-associated transcription factor, STAT3, decreased the levels of both cytokines and exosomes in conditioned media. This study expands the role of the βIV-spectrin/STAT3 complex in stress-induced regulation of CF paracrine signaling.

Inflammatory Glycoprotein 130 Signaling Links Changes in Microtubules and Junctophilin-2 to Altered Mitochondrial Metabolism and Right Ventricular Contractility

BACKGROUND

Right ventricular dysfunction (RVD) is the leading cause of death in pulmonary arterial hypertension (PAH), but no RV-specific therapy exists. We showed microtubule-mediated junctophilin-2 dysregulation (MT-JPH2 pathway) causes t-tubule disruption and RVD in rodent PAH, but the druggable regulators of this critical pathway are unknown. GP130 (glycoprotein 130) activation induces cardiomyocyte microtubule remodeling in vitro; however, the effects of GP130 signaling on the MT-JPH2 pathway and RVD resulting from PAH are undefined.

METHODS

Immunoblots quantified protein abundance, quantitative proteomics defined RV microtubule-interacting proteins (MT-interactome), metabolomics evaluated the RV metabolic signature, and transmission electron microscopy assessed RV cardiomyocyte mitochondrial morphology in control, monocrotaline, and monocrotaline-SC-144 (GP130 antagonist) rats. Echocardiography and pressure-volume loops defined the effects of SC-144 on RV-pulmonary artery coupling in monocrotaline rats (8-16 rats per group). In 73 patients with PAH, the relationship between interleukin-6, a GP130 ligand, and RVD was evaluated.

RESULTS

SC-144 decreased GP130 activation, which normalized MT-JPH2 protein expression and t-tubule structure in the monocrotaline RV. Proteomics analysis revealed SC-144 restored RV MT-interactome regulation. Ingenuity pathway analysis of dysregulated MT-interacting proteins identified a link between microtubules and mitochondrial function. Specifically, SC-144 prevented dysregulation of electron transport chain, Krebs cycle, and the fatty acid oxidation pathway proteins. Metabolomics profiling suggested SC-144 reduced glycolytic dependence, glutaminolysis induction, and enhanced fatty acid metabolism. Transmission electron microscopy and immunoblots indicated increased mitochondrial fission in the monocrotaline RV, which SC-144 mitigated. GP130 antagonism reduced RV hypertrophy and fibrosis and augmented RV-pulmonary artery coupling without altering PAH severity. In patients with PAH, higher interleukin-6 levels were associated with more severe RVD (RV fractional area change 23±12% versus 30±10%, P=0.002).

CONCLUSIONS

GP130 antagonism reduces MT-JPH2 dysregulation, corrects metabolic derangements in the RV, and improves RVD in monocrotaline rats.

Emerging therapeutic targets for cardiac hypertrophy

INTRODUCTION

Cardiac hypertrophy is associated with adverse outcomes across cardiovascular disease states. Despite strides over the last three decades in identifying molecular and cellular mechanisms driving hypertrophy, the link between pathophysiological stress stimuli and specific myocyte/heart growth profiles remains unclear. Moreover, the optimal strategy for preventing pathology in the setting of hypertrophy remains controversial.

AREAS COVERED

This review discusses molecular mechanisms underlying cardiac hypertrophy with a focus on factors driving the orientation of myocyte growth and the impact on heart function. We highlight recent work showing a novel role for the spectrin-based cytoskeleton, emphasizing regulation of myocyte dimensions but not hypertrophy per se. Finally, we consider opportunities for directing the orientation of myocyte growth in response to hypertrophic stimuli as an alternative therapeutic approach. Relevant publications on the topic were identified through Pubmed with open-ended search dates.

EXPERT OPINION

To define new therapeutic avenues, more precision is required when describing changes in myocyte and heart structure/function in response to hypertrophic stimuli. Recent developments in computational modeling of hypertrophic networks, in concert with more refined experimental approaches will catalyze translational discovery to advance the field and further our understanding of cardiac hypertrophy and its relationship with heart disease.

Mechanisms of Fibroblast Activation and Myocardial Fibrosis: Lessons Learned from FB-Specific Conditional Mouse Models

Heart failure (HF) is a leading cause of morbidity and mortality across the world. Cardiac fibrosis is associated with HF progression. Fibrosis is characterized by the excessive accumulation of extracellular matrix components. This is a physiological response to tissue injury. However, uncontrolled fibrosis leads to adverse cardiac remodeling and contributes significantly to cardiac dysfunction. Fibroblasts (FBs) are the primary drivers of myocardial fibrosis. However, until recently, FBs were thought to play a secondary role in cardiac pathophysiology. This review article will present the evolving story of fibroblast biology and fibrosis in cardiac diseases, emphasizing their recent shift from a supporting to a leading role in our understanding of the pathogenesis of cardiac diseases. Indeed, this story only became possible because of the emergence of FB-specific mouse models. This study includes an update on the advancements in the generation of FB-specific mouse models. Regarding the underlying mechanisms of myocardial fibrosis, we will focus on the pathways that have been validated using FB-specific, in vivo mouse models. These pathways include the TGF-β/SMAD3, p38 MAPK, Wnt/β-Catenin, G-protein-coupled receptor kinase (GRK), and Hippo signaling. A better understanding of the mechanisms underlying fibroblast activation and fibrosis may provide a novel therapeutic target for the management of adverse fibrotic remodeling in the diseased heart.

Ca2+/calmodulin kinase II-dependent regulation of βIV-spectrin modulates cardiac fibroblast gene expression, proliferation, and contractility

Fibrosis is a pronounced feature of heart disease and the result of dysregulated activation of resident cardiac fibroblasts (CFs). Recent work identified stress-induced degradation of the cytoskeletal protein β_IV-spectrin as an important step in CF activation and cardiac fibrosis. Furthermore, loss of β_IV-spectrin was found to depend on Ca²⁺/calmodulin-dependent kinase II (CaMKII). Therefore, we sought to determine the mechanism for CaMKII-dependent regulation of β_IV-spectrin and CF activity. Computational screening and MS revealed a critical serine residue (S2250 in mouse and S2254 in human) in β_IV-spectrin phosphorylated by CaMKII. Disruption of β_IV-spectrin/CaMKII interaction or alanine substitution of β_IV-spectrin Ser2250 (β_IV-S2254A) prevented CaMKII-induced degradation, whereas a phosphomimetic construct (β_IV-spectrin with glutamic acid substitution at serine 2254 [β_IV-S2254E]) showed accelerated degradation in the absence of CaMKII. To assess the physiological significance of this phosphorylation event, we expressed exogenous β_IV-S2254A and β_IV-S2254E constructs in β_IV-spectrin-deficient CFs, which have increased proliferation and fibrotic gene expression compared with WT CFs. β_IV-S2254A but not β_IV-S2254E normalized CF proliferation, gene expression, and contractility. Pathophysiological targeting of β_IV-spectrin phosphorylation and subsequent degradation was identified in CFs activated with the profibrotic ligand angiotensin II, resulting in increased proliferation and signal transducer and activation of transcription 3 nuclear accumulation. While therapeutic delivery of exogenous WT β_IV-spectrin partially reversed these trends, β_IV-S2254A completely negated increased CF proliferation and signal transducer and activation of transcription 3 translocation. Moreover, we observed β_IV-spectrin phosphorylation and associated loss in total protein within human heart tissue following heart failure. Together, these data illustrate a considerable role for the β_IV-spectrin/CaMKII interaction in activating profibrotic signaling.

C188-9 reduces TGF-β1-induced fibroblast activation and alleviates ISO-induced cardiac fibrosis in mice

Cardiac fibrosis is the final event of heart failure and is associated with almost all forms of cardiovascular disease. Cardiac fibroblasts (CFs), a major cell type in the heart, are responsible for regulating normal myocardial function and maintaining extracellular matrix homeostasis in adverse myocardial remodeling. In this study, we found that C188‐9, a small‐molecule inhibitor of signal transducer and activator of transcription 3 (STAT3), exhibited an antifibrotic function, both in vitro and in vivo. C188‐9 decreased transforming growth factor‐β1‐induced CF activation and fibrotic gene expression. Moreover, C188‐9 treatment alleviated heart injury and cardiac fibrosis in an isoproterenol‐induced mouse model by suppressing STAT3 phosphorylation and activation. These findings may help us better understand the role of C188‐9 in cardiac fibrosis and facilitate the development of new treatments for cardiac fibrosis and other cardiovascular diseases.

Regulation of Cardiac Conduction and Arrhythmias by Ankyrin/Spectrin-Based Macromolecular Complexes

The cardiac conduction system is an extended network of excitable tissue tasked with generation and propagation of electrical impulses to signal coordinated contraction of the heart. The fidelity of this system depends on the proper spatio-temporal regulation of ion channels in myocytes throughout the conduction system. Importantly, inherited or acquired defects in a wide class of ion channels has been linked to dysfunction at various stages of the conduction system resulting in life-threatening cardiac arrhythmia. There is growing appreciation of the role that adapter and cytoskeletal proteins play in organizing ion channel macromolecular complexes critical for proper function of the cardiac conduction system. In particular, members of the ankyrin and spectrin families have emerged as important nodes for normal expression and regulation of ion channels in myocytes throughout the conduction system. Human variants impacting ankyrin/spectrin function give rise to a broad constellation of cardiac arrhythmias. Furthermore, chronic neurohumoral and biomechanical stress promotes ankyrin/spectrin loss of function that likely contributes to conduction disturbances in the setting of acquired cardiac disease. Collectively, this review seeks to bring attention to the significance of these cytoskeletal players and emphasize the potential therapeutic role they represent in a myriad of cardiac disease states.

Severe Form of ßIV-Spectrin Deficiency With Mitochondrial Dysfunction and Cardiomyopathy-A Case Report

ßIV-spectrin is a protein of the spectrin family which is involved in the organization of the cytoskeleton structure and is found in high quantity in the axon initial segment and the nodes of Ranvier. Together with ankyrin G, ßIV-spectrin is responsible for the clustering of KCNQ2/3-potassium channels and NaV-sodium channels. Loss or reduction of ßIV-spectrin causes a destabilization of the cytoskeleton and an impairment in the generation of the action potential, which leads to neuronal degeneration. Furthermore, ßIV-spectrin has been described to play an important role in the maintenance of the neuronal polarity and of the diffusion barrier. ßIV-spectrin is also located in the heart where it takes an important part in the structural organization of ion channels and has also been described to participate in cell signaling pathways through binding of transcription factors. We describe two patients with a severe form of ßIV-spectrin deficiency. Whole-exome sequencing revealed the homozygous stop mutation c.6016C>T (p.R2006^*) in the SPTBN4 gene. The phenotype of these patients is characterized by profound psychomotor developmental arrest, respiratory insufficiency and deafness. Additionally one of the patients presents with cardiomyopathy, optical nerve atrophy, and mitochondrial dysfunction. This is the first report of a severe form of ßIV-spectrin deficiency with hypertrophic cardiomyopathy and mitochondrial dysfunction.

Emerging therapeutic targets for cardiac arrhythmias: role of STAT3 in regulating cardiac fibroblast function

Introduction : Cardiac fibrosis contributes to the development of cardiovascular disease (CVD) and arrhythmia. Cardiac fibroblasts (CFs) are collagen-producing cells that regulate extracellular matrix (ECM) homeostasis. A complex signaling network has been defined linking environmental stress to changes in CF function and fibrosis. Signal Transducer and Activator of Transcription 3 (STAT3) has emerged as a critical integrator of pro-fibrotic signals in CFs downstream of several established signaling networks. Areas covered : This article provides an overview of STAT3 function in CFs and its involvement in coordinating a vast web of intracellular pro-fibrotic signaling molecules and transcription factors. We highlight recent work elucidating a critical role for the fibroblast cytoskeleton in maintaining spatial and temporal control of STAT3-related signaling . Finally, we discuss potential opportunities and obstacles for therapeutic targeting of STAT3 to modulate cardiac fibrosis and arrhythmias. Relevant publications on the topic were identified through Pubmed. Expert opinion : Therapeutic targeting of STAT3 for CVD and arrhythmias presents unique challenges and opportunities. Thus, it is critical to consider the multimodal and dynamic nature of STAT3 signaling. Going forward, it will be beneficial to consider ways to maintain balanced STAT3 function, rather than large-scale perturbations in STAT3 function.

Identification of transcription factors MYC and C/EBPβ mediated regulatory networks in heart failure based on gene expression omnibus datasets

Background

Heart failure is one of leading cause of death worldwide. However, the transcriptional profiling of heart failure is unclear. Moreover, the signaling pathways and transcription factors involving the heart failure development also are largely unknown. Using published Gene Expression Omnibus (GEO) datasets, in the present study, we aim to comprehensively analyze the differentially expressed genes in failing heart tissues, and identified the critical signaling pathways and transcription factors involving heart failure development.

Methods

The transcriptional profiling of heart failure was identified from previously published gene expression datasets deposited in GSE5406, GSE16499 and GSE68316. The enriched signaling pathways and transcription factors were analyzed using Database for Annotation, Visualization and Integrated Discovery (DAVID) website and gene set enrichment analysis (GSEA) assay. The transcriptional networks were created by Cytoscape.

Results

Compared with the normal heart tissues, 90 genes were particularly differentially expressed in failing heart tissues, and those genes were associated with multiple metabolism signaling pathways and insulin signaling pathway. Metabolism and insulin signaling pathway were both inactivated in failing heart tissues. Transcription factors MYC and C/EBPβ were both negatively associated with the expression profiling of failing heart tissues in GSEA assay. Moreover, compared with normal heart tissues, MYC and C/EBPβ were down regulated in failing heart tissues. Furthermore, MYC and C/EBPβ mediated downstream target genes were also decreased in failing heart tissues. MYC and C/EBPβ were positively correlated with each other. At last, we constructed MYC and C/EBPβ mediated regulatory networks in failing heart tissues, and identified the MYC and C/EBPβ target genes which had been reported involving the heart failure developmental progress.

Conclusions

Our results suggested that metabolism pathways and insulin signaling pathway, transcription factors MYC and C/EBPβ played critical roles in heart failure developmental progress.

Fibroblast growth factor-inducible 14 mediates macrophage infiltration in heart to promote pressure overload-induced cardiac dysfunction

AIMS

Heart failure (HF) is characterized by compromised cardiac structure and function. Previous work has identified a link between upregulation of pro-inflammatory cytokines and HF. Tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) is a pro-inflammatory cytokine, which binds to fibroblast growth factor inducible 14 (Fn14), a ubiquitously expressed cell-surface receptor. The objective of this study was to investigate the role of TWEAK/Fn14 pathway in promoting cardiac inflammation under non ischemic stress conditions.

MAIN METHODS

Wild type (WT) and Fn14 knock out (Fn14^-/-) mice were subjected to pressure overload [transaortic constriction (TAC)] for 1 or 6 weeks. A subset of WT TAC animals were treated with the Fn14 antagonist L524-0366. Cardiac function was measured by echocardiography. Cardiac fibrosis and macrophage infiltration were quantified using immunohistochemistry and flow cytometry, respectively. Cardiac fibroblasts were isolated for quantifying TWEAK-induced chemokine release.

KEY FINDINGS

Fn14^-/- mice displayed improved cardiac function, reduced fibrosis and lower macrophage infiltration in heart compared to WT following TAC. L524-0366 mitigated maladaptive remodeling with TAC. TWEAK induced secretion of the pro-inflammatory chemokine, monocyte chemoattractant protein 1 from WT but not Fn14^-/- fibroblasts in vitro, in part through activation of non-canonical NF-κB signaling. Finally, Fn14 expression was increased in mouse following TAC and in human failing hearts.

SIGNIFICANCE

Our findings support an important role for the TWEAK/Fn14 promoting macrophage infiltration and fibrosis in heart under non-ischemic stress, with potential for therapeutic intervention to improve cardiac function in the setting of HF.