Functions of RNA-Binding Proteins in Cardiovascular Disease.

Gene expression is under tight regulation from the chromatin structure that regulates gene accessibility by the transcription machinery to protein degradation. At the transcript level, this regulation falls on RNA-binding proteins (RBPs). RBPs are a large and diverse class of proteins involved in all aspects of a transcript's lifecycle: splicing and maturation, localization, stability, and translation. In the past few years, our understanding of the role of RBPs in cardiovascular diseases has expanded. Here, we discuss the general structure and function of RBPs and the latest discoveries of their role in pulmonary and systemic cardiovascular diseases.

Sex Differences in Therapies against Myocardial Ischemia-Reperfusion Injury: From Basic Science to Clinical Perspectives.

Mortality from myocardial infarction (MI) has declined over recent decades, which could be attributed in large part to improved treatment methods. Early reperfusion is the cornerstone of current MI treatment. However, reoxygenation via restored blood flow induces further damage to the myocardium, leading to ischemia-reperfusion injury (IRI). While experimental studies overwhelmingly demonstrate that females experience greater functional recovery from MI and decreased severity in the underlying pathophysiological mechanisms, the outcomes of MI with subsequent reperfusion therapy, which is the clinical correlate of myocardial IRI, are generally poorer for women compared with men. Distressingly, women are also reported to benefit less from current guideline-based therapies compared with men. These seemingly contradicting outcomes between experimental and clinical studies show a need for further investigation of sex-based differences in disease pathophysiology, treatment response, and a sex-specific approach in the development of novel therapeutic methods against myocardial IRI. In this literature review, we summarize the current knowledge on sex differences in the underlying pathophysiological mechanisms of myocardial IRI, including the roles of sex hormones and sex chromosomes. Furthermore, we address sex differences in pharmacokinetics, pharmacodynamics, and pharmacogenetics of current drugs prescribed to limit myocardial IRI. Lastly, we highlight ongoing clinical trials assessing novel pharmacological treatments against myocardial IRI and sex differences that may underlie the efficacy of these new therapeutic approaches.

Myocardial fibrosis and calcification are attenuated by microRNA-129-5p targeting Asporin and Sox9 in cardiac fibroblasts.

Myocardial fibrosis and calcification associate with adverse outcomes in nonischemic heart failure. Cardiac fibroblasts (CF) transition into myofibroblasts (MF) and osteogenic fibroblasts (OF) to promote myocardial fibrosis and calcification. However, common upstream mechanisms regulating both CF-to-MF transition and CF-to-OF transition remain unknown. microRNAs are promising targets to modulate CF plasticity. Our bioinformatics revealed downregulation of miR-129-5p and upregulation of its targets small leucine-rich proteoglycan Asporin (ASPN) and transcription factor SOX9 as common in mouse and human heart failure (HF). We experimentally confirmed decreased miR-129-5p and enhanced SOX9 and ASPN expression in CF in human hearts with myocardial fibrosis and calcification. miR-129-5p repressed both CF-to-MF and CF-to-OF transition in primary CF, as did knockdown of SOX9 and ASPN. Sox9 and Aspn are direct targets of miR-129-5p that inhibit downstream ß-catenin expression. Chronic Angiotensin II infusion downregulated miR-129-5p in CF in WT and TCF21-lineage CF reporter mice, and it was restored by miR-129-5p mimic. Importantly, miR-129-5p mimic not only attenuated progression of myocardial fibrosis, calcification marker expression, and SOX9 and ASPN expression in CF but also restored diastolic and systolic function. Together, we demonstrate miR-129-5p/ASPN and miR-129-5p/SOX9 as potentially novel dysregulated axes in CF-to-MF and CF-to-OF transition in myocardial fibrosis and calcification and the therapeutic relevance of miR-129-5p.

HNRNPA2B1: RNA-Binding Protein That Orchestrates Smooth Muscle Cell Phenotype in Pulmonary Arterial Hypertension.

BACKGROUND: RNA-binding proteins are master orchestrators of gene expression regulation. They regulate hundreds of transcripts at once by recognizing specific motifs. Thus, characterizing RNA-binding proteins targets is critical to harvest their full therapeutic potential. However, such investigation has often been restricted to a few RNA-binding protein targets, limiting our understanding of their function. In cancer, the RNA-binding protein HNRNPA2B1 (heterogeneous nuclear ribonucleoprotein A2B1; A2B1) promotes the pro-proliferative/anti-apoptotic phenotype. The same phenotype in pulmonary arterial smooth muscle cells (PASMCs) is responsible for the development of pulmonary arterial hypertension (PAH). However, A2B1 function has never been investigated in PAH. METHOD: Through the integration of computational and experimental biology, the authors investigated the role of A2B1 in human PAH-PASMC. Bioinformatics and RNA sequencing allowed them to investigate the transcriptome-wide function of A2B1, and RNA immunoprecipitation and A2B1 silencing experiments allowed them to decipher the intricate molecular mechanism at play. In addition, they performed a preclinical trial in the monocrotaline-induced pulmonary hypertension rat model to investigate the relevance of A2B1 inhibition in mitigating pulmonary hypertension severity. RESULTS: They found that A2B1 expression and its nuclear localization are increased in human PAH-PASMC. Using bioinformatics, they identified 3 known motifs of A2B1 and all mRNAs carrying them. In PAH-PASMC, they demonstrated the complementary nonredundant function of A2B1 motifs because all motifs are implicated in different aspects of the cell cycle. In addition, they showed that in PAH-PASMC, A2B1 promotes the expression of its targets. A2B1 silencing in PAH-PASMC led to a decrease of all tested mRNAs carrying an A2B1 motif and a concomitant decrease in proliferation and resistance to apoptosis. Last, in vivo A2B1 inhibition in the lungs rescued pulmonary hypertension in rats. CONCLUSIONS: Through the integration of computational and experimental biology, the study revealed the role of A2B1 as a master orchestrator of the PAH-PASMC phenotype and its relevance as a therapeutic target in PAH.

Y-Chromosome Gene, Uty, Protects Against Pulmonary Hypertension by Reducing Proinflammatory Chemokines.

Rationale: Idiopathic pulmonary arterial hypertension (PAH) is a terminal pulmonary vascular disease characterized by increased pressure, right ventricular failure, and death. PAH exhibits a striking sex bias and is up to four times more prevalent in females. Understanding the molecular basis behind sex differences could help uncover novel therapies. Objectives: We previously discovered that the Y chromosome is protective against hypoxia-induced experimental pulmonary hypertension (PH), which may contribute to sex differences in PAH. Here, we identify the gene responsible for Y-chromosome protection, investigate key downstream autosomal genes, and demonstrate a novel preclinical therapy. Methods: To test the effect of Y-chromosome genes on PH development, we knocked down each Y-chromosome gene expressed in the lung by means of intratracheal instillation of siRNA in gonadectomized male mice exposed to hypoxia and monitored changes in right ventricular and pulmonary artery hemodynamics. We compared the lung transcriptome of Uty knockdown mouse lungs to those of male and female PAH patient lungs to identify common downstream pathogenic chemokines and tested the effects of these chemokines on human pulmonary artery endothelial cells. We further inhibited the activity of these chemokines in two preclinical pulmonary hypertension models to test the therapeutic efficacy. Measurements and Main Results: Knockdown of the Y-chromosome gene Uty resulted in more severe PH measured by increased right ventricular pressure and decreased pulmonary artery acceleration time. RNA sequencing revealed an increase in proinflammatory chemokines Cxcl9 and Cxcl10 as a result of Uty knockdown. We found CXCL9 and CXCL10 significantly upregulated in human PAH lungs, with more robust upregulation in females with PAH. Treatment of human pulmonary artery endothelial cells with CXCL9 and CXCL10 triggered apoptosis. Inhibition of Cxcl9 and Cxcl10 expression in male Uty knockout mice and CXCL9 and CXCL10 activity in female rats significantly reduced PH severity. Conclusions:Uty is protective against PH. Reduction of Uty expression results in increased expression of proinflammatory chemokines Cxcl9 and Cxcl10, which trigger endothelial cell death and PH. Inhibition of CLXC9 and CXLC10 rescues PH development in multiple experimental models.

Role of miRNA-1 and miRNA-21 in Acute Myocardial Ischemia-Reperfusion Injury and Their Potential as Therapeutic Strategy.

Coronary artery disease remains the leading cause of death. Acute myocardial infarction (MI) is characterized by decreased blood flow to the coronary arteries, resulting in cardiomyocytes death. The most effective strategy for treating an MI is early and rapid myocardial reperfusion, but restoring blood flow to the ischemic myocardium can induce further damage, known as ischemia-reperfusion (IR) injury. Novel therapeutic strategies are critical to limit myocardial IR injury and improve patient outcomes following reperfusion intervention. miRNAs are small non-coding RNA molecules that have been implicated in attenuating IR injury pathology in pre-clinical rodent models. In this review, we discuss the role of miR-1 and miR-21 in regulating myocardial apoptosis in ischemia-reperfusion injury in the whole heart as well as in different cardiac cell types with special emphasis on cardiomyocytes, fibroblasts, and immune cells. We also examine therapeutic potential of miR-1 and miR-21 in preclinical studies. More research is necessary to understand the cell-specific molecular principles of miRNAs in cardioprotection and application to acute myocardial IR injury.

Nuclear Receptor Nur77 Controls Cardiac Fibrosis through Distinct Actions on Fibroblasts and Cardiomyocytes.

Fibrosis is a hallmark of adverse cardiac remodeling, which promotes heart failure, but it is also an essential repair mechanism to prevent cardiac rupture, signifying the importance of appropriate regulation of this process. In the remodeling heart, cardiac fibroblasts (CFs) differentiate into myofibroblasts (MyoFB), which are the key mediators of the fibrotic response. Additionally, cardiomyocytes are involved by providing pro-fibrotic cues. Nuclear receptor Nur77 is known to reduce cardiac hypertrophy and associated fibrosis; however, the exact function of Nur77 in the fibrotic response is yet unknown. Here, we show that Nur77-deficient mice exhibit severe myocardial wall thinning, rupture and reduced collagen fiber density after myocardial infarction and chronic isoproterenol (ISO) infusion. Upon Nur77 knockdown in cultured rat CFs, expression of MyoFB markers and extracellular matrix proteins is reduced after stimulation with ISO or transforming growth factor-ß (TGF-ß). Accordingly, Nur77-depleted CFs produce less collagen and exhibit diminished proliferation and wound closure capacity. Interestingly, Nur77 knockdown in neonatal rat cardiomyocytes results in increased paracrine induction of MyoFB differentiation, which was blocked by TGF-ß receptor antagonism. Taken together, Nur77-mediated regulation involves CF-intrinsic promotion of CF-to-MyoFB transition and inhibition of cardiomyocyte-driven paracrine TGF-ß-mediated MyoFB differentiation. As such, Nur77 provides distinct, cell-specific regulation of cardiac fibrosis.

Single-Cell Study of Two Rat Models of Pulmonary Arterial Hypertension Reveals Connections to Human Pathobiology and Drug Repositioning.

Rationale: The cellular and molecular landscape and translational value of commonly used models of pulmonary arterial hypertension (PAH) are poorly understood. Single-cell transcriptomics can enhance molecular understanding of preclinical models and facilitate their rational use and interpretation.Objectives: To determine and prioritize dysregulated genes, pathways, and cell types in lungs of PAH rat models to assess relevance to human PAH and identify drug repositioning candidates.Methods: Single-cell RNA sequencing was performed on the lungs of monocrotaline (MCT), Sugen-hypoxia (SuHx), and control rats to identify altered genes and cell types, followed by validation using flow-sorted cells, RNA in situ hybridization, and immunofluorescence. Relevance to human PAH was assessed by histology of lungs from patients and via integration with human PAH genetic loci and known disease genes. Candidate drugs were predicted using Connectivity Map.Measurements and Main Results: Distinct changes in genes and pathways in numerous cell types were identified in SuHx and MCT lungs. Widespread upregulation of NF-κB signaling and downregulation of IFN signaling was observed across cell types. SuHx nonclassical monocytes and MCT conventional dendritic cells showed particularly strong NF-κB pathway activation. Genes altered in SuHx nonclassical monocytes were significantly enriched for PAH-associated genes and genetic variants, and candidate drugs predicted to reverse the changes were identified. An open-access online platform was developed to share single-cell data and drug candidates (http://mergeomics.research.idre.ucla.edu/PVDSingleCell/).Conclusions: Our study revealed the distinct and shared dysregulation of genes and pathways in two commonly used PAH models for the first time at single-cell resolution and demonstrated their relevance to human PAH and utility for drug repositioning.

Pulmonary hypertension secondary to pulmonary fibrosis: clinical data, histopathology and molecular insights.

Pulmonary hypertension (PH) developing secondarily in pulmonary fibrosis (PF) patients (PF-PH) is a frequent co-morbidity. The high prevalence of PH in PF patients is very concerning since the presence of PH is a strong predictor of mortality in PF patients. Until recently, PH was thought to arise solely from fibrotic destruction of the lung parenchyma, leading to hypoxic vasoconstriction and loss of vascular bed density. Thus, potential cellular and molecular dysregulation of vascular remodeling as a driver of PF-PH has been under-investigated. The recent demonstrations that there is no correlation between the severity of the fibrosis and development of PH, along with the finding that significant vascular histological and molecular differences exist between patients with and without PH have shifted the etiological paradigm of PF-PH. This review aims to provide a comprehensive translational overview of PH in PF patients from clinical diagnosis and outcome to the latest understanding of the histology and molecular pathophysiology of PF-PH.

The Role of MicroRNAs in Acute Respiratory Distress Syndrome and Sepsis, From Targets to Therapies: A Narrative Review.

Acute respiratory distress syndrome (ARDS) is a significant cause of morbidity and mortality in the intensive care unit (ICU) and is characterized by lung epithelial and endothelial cell injury, with increased permeability of the alveolar-capillary membrane, leading to pulmonary edema, severe hypoxia, and difficulty with ventilation. The most common cause of ARDS is sepsis, and currently, treatment of ARDS and sepsis has consisted mostly of supportive care because targeted therapies have largely been unsuccessful. The molecular mechanisms behind ARDS remain elusive. Recently, a number of microRNAs (miRNAs) identified through high-throughput screening studies in ARDS patients and preclinical animal models have suggested a role for miRNA in the pathophysiology of ARDS. miRNAs are small noncoding RNAs ranging from 18 to 24 nucleotides that regulate gene expression via inhibition of the target mRNA translation or by targeting complementary mRNA for early degradation. Unsurprisingly, some miRNAs that are differentially expressed in ARDS overlap with those important in sepsis. In addition, circulatory miRNA may be useful as biomarkers or as targets for pharmacologic therapy. This can be revolutionary in a syndrome that has neither a measurable indicator of the disease nor a targeted therapy. While there are currently no miRNA-based therapies targeted for ARDS, therapies targeting miRNA have reached phase II clinical trials for the treatment of a wide range of diseases. Further studies may yield a unique miRNA profile pattern that serves as a biomarker or as targets for miRNA-based pharmacologic therapy. In this review, we discuss miRNAs that have been found to play a role in ARDS and sepsis, the potential mechanism of how particular miRNAs may contribute to the pathophysiology of ARDS, and strategies for pharmacologically targeting miRNA as therapy.

Sex differences underlying preexisting cardiovascular disease and cardiovascular injury in COVID-19.

The novel 2019 coronavirus disease (COVID-19), resulting from severe acute respiratory syndrome coronarvirus-2 (SARS-CoV-2) infection, typically leads to respiratory failure in severe cases; however, cardiovascular injury is reported to contribute to a substantial proportion of COVID-19 deaths. Preexisting cardiovascular disease (CVD) is among the most common risk factors for hospitalization and death in COVID-19 patients, and the pathogenic mechanisms of COVID-19 disease progression itself may promote the development of cardiovascular injury, increasing risk of in-hospital death. Sex differences in COVID-19 are becoming more apparent as mounting data indicate that males seem to be disproportionately at risk of severe COVID-19 outcome due to preexisting CVD and COVID-19-related cardiovascular injury. In this review, we will provide a basic science perspective on current clinical observations in this rapidly evolving field and discuss the interplay sex differences, preexisting CVD and COVID-19-related cardiac injury.

Pregnancy-associated cardiac dysfunction and the regulatory role of microRNAs.

Many crucial cardiovascular adaptations occur in the body during pregnancy to ensure successful gestation. Maladaptation of the cardiovascular system during pregnancy can lead to complications that promote cardiac dysfunction and may lead to heart failure (HF). About 12% of pregnancy-related deaths in the USA have been attributed to HF and the detrimental effects of cardiovascular complications on the heart can be long-lasting, pre-disposing the mother to HF later in life. Indeed, cardiovascular complications such as gestational diabetes mellitus, preeclampsia, gestational hypertension, and peripartum cardiomyopathy have been shown to induce cardiac metabolic dysfunction, oxidative stress, fibrosis, apoptosis, and diastolic and systolic dysfunction in the hearts of pregnant women, all of which are hallmarks of HF. The exact etiology and cardiac pathophysiology of pregnancy-related complications is not yet fully deciphered. Furthermore, diagnosis of cardiac dysfunction in pregnancy is often made only after clinical symptoms are already present, thus necessitating the need for novel diagnostic and prognostic biomarkers. Mounting data demonstrates an altered expression of maternal circulating miRNAs during pregnancy affected by cardiovascular complications. Throughout the past decade, miRNAs have become of growing interest as modulators and biomarkers of pathophysiology, diagnosis, and prognosis in cardiac dysfunction. While the association between pregnancy-related cardiovascular complications and cardiac dysfunction or HF is becoming increasingly evident, the roles of miRNA-mediated regulation herein remain poorly understood. Therefore, this review will summarize current reports on pregnancy-related cardiovascular complications that may lead to cardiac dysfunction and HF during and after pregnancy in previously healthy women, with a focus on the pathophysiological role of miRNAs.

Experimental Pulmonary Hypertension Is Associated With Neuroinflammation in the Spinal Cord.

RATIONALE: Pulmonary hypertension (PH) is a rare but fatal disease characterized by elevated pulmonary pressures and vascular remodeling, leading to right ventricular failure and death. Recently, neuroinflammation has been suggested to be involved in the sympathetic activation in experimental PH. Whether PH is associated with neuroinflammation in the spinal cord has never been investigated. METHODS/RESULTS: PH was well-established in adult male Wistar rats 3-week after pulmonary endothelial toxin Monocrotaline (MCT) injection. Using the thoracic segments of the spinal cord, we found a 5-fold increase for the glial fibrillary acidic protein (GFAP) in PH rats compared to controls (p < 0.05). To further determine the region of the spinal cord where GFAP was expressed, we performed immunofluorescence and found a 3 to 3.5-fold increase of GFAP marker in the gray matter, and a 2 to 3-fold increase in the white matter in the spinal cord of PH rats compared to controls. This increase was due to PH (MCT vs. Control; p < 0.01), and there was no difference between the dorsal versus ventral region. PH rats also had an increase in the pro-inflammatory marker chemokine (C-C motif) ligand 3 (CCL3) protein expression (∼ 3-fold) and (2.8 to 4-fold, p < 0.01) in the white matter. Finally, angiogenesis was increased in PH rat spinal cords assessed by the adhesion molecule CD31 expression (1.5 to 2.3-fold, p < 0.01). CONCLUSION: We report for the first time evidence for neuroinflammation in the thoracic spinal cord of pulmonary hypertensive rats. The impact of spinal cord inflammation on cardiopulmonary function in PH remains elusive.

Connecting sex differences, estrogen signaling, and microRNAs in cardiac fibrosis.

Sex differences are evident in the pathophysiology of heart failure (HF). Progression of HF is promoted by cardiac fibrosis and no fibrosis-specific therapies are currently available. The fibrotic response is mediated by cardiac fibroblasts (CFs), and a central event is their phenotypic transition to pro-fibrotic myofibroblasts. These myofibroblasts may arise from various cellular origins including resident CFs and epicardial and endothelial cells. Both female subjects in clinical studies and female animals in experimental studies generally present less cardiac fibrosis compared with males. This difference is at least partially considered attributable to the ovarian hormone 17ß-estradiol (E2). E2 signals via estrogen receptors to regulate genes are involved in the fibrotic response and myofibroblast transition. Besides protein-coding genes, E2 also regulates transcription of microRNA that modulate cardiac fibrosis. Sex dimorphism, E2, and miRNAs form multi-level regulatory networks in the pathophysiology of cardiac fibrosis, and the mechanism of these networks is not yet fully deciphered. Therefore, this review is aimed at summarizing current knowledge on sex differences, E2, and estrogen receptors in cardiac fibrosis, emphasizing on microRNAs and myofibroblast origins. KEY MESSAGES: • E2 and ERs regulate cardiac fibroblast function. • E2 and ERs may distinctly affect male and female cardiac fibrosis pathophysiology. • Sex, E2, and miRNAs form multi-level regulatory networks in cardiac fibrosis. • Sex-dimorphic and E2-regulated miRNAs affect mesenchymal transition.

NR4A nuclear receptors in cardiac remodeling and neurohormonal regulation.

Heart failure is characterized by the constant interplay between the underlying cardiac insult, degree of myocardial dysfunction and the activity of compensatory neurohormonal mechanisms. The sympathetic nervous system (SNS) and renin-angiotensin-aldosterone system (RAAS) become activated to maintain cardiac output; however, their chronic hyperactivity will eventually become deleterious. Several nuclear hormone receptors, including the mineralocorticoid receptor and estrogen receptor, are well-known to modulate cardiac disease. Recently, the subfamily of NR4A nuclear receptors i.e. Nur77, Nurr1 and NOR-1, are emerging as key players in cardiac stress responses, as well as pivotal regulators of neurohormonal mechanisms. In this review, we summarize current literature on NR4A nuclear receptors in the heart and in various components of the SNS, RAAS and immune system and discuss the functional implications for NR4As in cardiac function and disease.

Nuclear Receptor Nur77 Limits the Macrophage Inflammatory Response through Transcriptional Reprogramming of Mitochondrial Metabolism.

Activation of macrophages by inflammatory stimuli induces reprogramming of mitochondrial metabolism to support the production of pro-inflammatory cytokines and nitric oxide. Hallmarks of this metabolic rewiring are downregulation of α-ketoglutarate formation by isocitrate dehydrogenase (IDH) and accumulation of glutamine-derived succinate, which enhances the inflammatory response via the activity of succinate dehydrogenase (SDH). Here, we identify the nuclear receptor Nur77 (Nr4a1) as a key upstream transcriptional regulator of this pro-inflammatory metabolic switch in macrophages. Nur77-deficient macrophages fail to downregulate IDH expression and accumulate higher levels of succinate and other TCA cycle-derived metabolites in response to inflammatory stimulation in a glutamine-independent manner. Consequently, these macrophages produce more nitric oxide and pro-inflammatory cytokines in an SDH-dependent manner. In vivo, bone marrow Nur77 deficiency exacerbates atherosclerosis development and leads to increased circulating succinate levels. In summary, Nur77 induces an anti-inflammatory metabolic state in macrophages that protects against chronic inflammatory diseases such as atherosclerosis.

Nur77 variants solely comprising the amino-terminal domain activate hypoxia-inducible factor-1α and affect bone marrow homeostasis in mice and humans.

Gene targeting via homologous recombination can occasionally result in incomplete disruption of the targeted gene. Here, we show that a widely used Nur77-deficient transgenic mouse model expresses a truncated protein encoding for part of the N-terminal domain of nuclear receptor Nur77. This truncated Nur77 protein is absent in a newly developed Nur77-deficient mouse strain generated using Cre-Lox recombination. Comparison of these two mouse strains using immunohistochemistry, flow cytometry, and colony-forming assays shows that homologous recombination-derived Nur77-deficient mice, but not WT or Cre-Lox-derived Nur77-deficient mice, suffer from liver immune cell infiltrates, loss of splenic architecture, and increased numbers of bone marrow hematopoietic stem cells and splenic colony-forming cells with age. Mechanistically, we demonstrate that the truncated Nur77 N-terminal domain protein maintains the stability and activity of hypoxia-inducible factor (HIF)-1, a transcription factor known to regulate bone marrow homeostasis. Additionally, a previously discovered, but uncharacterized, human Nur77 transcript variant that encodes solely for its N-terminal domain, designated TR3ß, can also stabilize and activate HIF-1α. Meta-analysis of publicly available microarray data sets shows that TR3ß is highly expressed in human bone marrow cells and acute myeloid leukemia samples. In conclusion, our study provides evidence that a transgenic mouse model commonly used to study the biological function of Nur77 has several major drawbacks, while simultaneously identifying the importance of nongenomic Nur77 activity in the regulation of bone marrow homeostasis.

Nur77 protects against adverse cardiac remodelling by limiting neuropeptide Y signalling in the sympathoadrenal-cardiac axis.

Aims: Cardiac remodelling and heart failure are promoted by persistent sympathetic activity. We recently reported that nuclear receptor Nur77 may protect against sympathetic agonist-induced cardiac remodelling in mice. The sympathetic co-transmitter neuropeptide Y (NPY) is co-released with catecholamines and is a known cardiac modulator and predictor of heart failure mortality. Recently, transcriptome analyses revealed NPY as a putative target of Nur77. In this study, we assess whether Nur77 modulates adverse cardiac remodelling via NPY signalling. Methods and results: Nur77 represses NPY expression in the PC12 adrenal chromaffin cell line. Accordingly, NPY levels are higher in adrenal gland, plasma, and heart from Nur77-KO compared to wild-type mice. Conditioned medium from Nur77-silenced chromaffin cells and serum from Nur77-KO mice induce marked hypertrophy in cultured neonatal rat cardiomyocytes, which is inhibited by the NPY type 1 receptor (NPY1R) antagonist BIBO3304. In cardiomyocytes from Nur77-KO mice, intracellular Ca2+ is increased partially via the NPY1R. This is independent from elevated circulating NPY since cardiomyocyte-specific Nur77-deficient mice (CM-KO) do not have elevated circulating NPY, but do exhibit BIBO3304-sensitive, increased cardiomyocyte intracellular Ca2+. In vivo, this translates to NPY1R antagonism attenuating cardiac calcineurin activity and isoproterenol-induced cardiomyocyte hypertrophy and fibrosis in full-body Nur77-KO mice, but not in CM-KO mice. Conclusions: The cardioprotective action of Nur77 can be ascribed to both inhibition of circulating NPY levels and to cardiomyocyte-specific modulation of NPY-NPY1R signalling. These results reveal the underlying mechanism of Nur77 as a promising modifier gene in heart failure.

Thrombospondin-4 mediates cardiovascular remodelling in angiotensin II-induced hypertension.

Thrombospondin 4 (TSP-4) expression is induced in the heart and vasculature under pathological conditions, including myocardial infarction, myocardial pressure overload, and hypertension. TSP-4 is linked to remodelling processes, where it may affect extracellular matrix protein organization. In previous work, we studied the role of TSP-4 in small arteries during hypertension using Ang II-treated Thrombospondin 4 knockout (Thbs4-/-) mice. We reported increased heart weight, as well as the occurrence of aortic aneurysms in the Ang II-treated Thbs4-/- animals. In the present study, we further characterized the hearts and aortas from these animals. Hypertrophy of cardiomyocytes, together with perivascular fibrosis and inflammation was observed in the Ang II-treated Thbs4-/- hearts. In the aortas, an increase in the aortic wall cross-sectional area (CSA) and wall thickness of the Ang II-treated Thbs4-/- mice was found. More detailed investigation of the Ang II-treated Thbs4-/- aortas also revealed the appearance of aortic dissections in the outer medial layer of the arteries, as well as pronounced inflammation. No differences were found in several other extracellular matrix-related parameters, such as number of elastin breaks or stress-strain relationships. However, at the ultrastructural level, collagen fibers showed alterations in diameter in the media and adventitia of the Ang II-treated Thbs4-/- mice, in the area prone to dissection. In conclusion, we identified TSP-4 as an important protein in the development of cardiac hypertrophy and aortic dissections in Ang II-induced hypertension.