PLK2 is a novel regulator of osteopontin-driven fibrosis and diastolic dysfunction in permanent atrial fibrillation

Abstract

Background and aim Atrial fibrillation (AF) is frequently accompanied by cardiac fibrosis and diastolic heart failure. Due to the heterogeneous nature and complexity of fibrosis, the knowledge of the underlying pathomechanisms is limited. Thus, effective antifibrotic pharmacotherapy is missing. The objective of this study was to decipher the role of polo-like kinase 2 (PLK2) in the pathogenesis of cardiac fibrosis and left ventricular diastolic dysfunction. We put particular emphasis on the identification of profibrotic downstream targets of PLK2, which can serve as therapeutic targets. Methods and results This study was based on human atrial tissue biopsies and peripheral blood samples, a PLK2 knockout mouse model, a canine tachy-pacing model and specific pharmacological interventions on cardiac fibroblasts. In human atrial AF tissue samples, PLK2 was 50% downregulated by hypoxia-induced promoter methylation compared to sinus rhythm (SR) control. Confirmatory analysis of a canine tachy-pacing model showed PLK2 downregulation exclusively in the atria but not in the ventricles. Specific pharmacological inhibition as well as genetic deletion of PLK2 led to a striking myofibroblast phenotype. Discovery proteomics revealed that the global knockout of PLK2 resulted in de novo secretion of the inflammatory cytokine osteopontin (OPN) in cardiac fibroblasts and concomitant ventricular fibrosis in the PLK2 knockout mouse model. An ELISA analysis of peripheral blood samples of AF patients with electrophysiologically proven fibrosis, confirmed significantly increased OPN plasma concentrations compared to SR and non-fibrosis AF controls. Consequently, echocardiography on PLK2 KO mice revealed left ventricular diastolic dysfunction, tachycardia and fibrosis-typical surface ECG anomalies (PQ and QRS prolongation). Mechanistically, we identified the ERK1/2 signaling pathway as the molecular link between reduced expression of PLK2 and elevated osteopontin transcription. In a reverse translational attempt, we successfully tested the capability of 5-amino-salicylic acid (5-ASA) to inhibit osteopontin transcription and to reverse a TGF-β-induced myofibroblast phenotype in vitro. Currently the long-term administration of 5-ASA is tested in PLK2 knockout mice to evaluate the therapeutic potential to prevent cardiac fibrosis and diastolic heart failure development. Conclusion and clinical impact We identified PLK2 as an epigenetically regulated kinase involved in the pathophysiology of fibrosis in AF. PLK2 knockout mice can serve as a model of diastolic heart failure wherein OPN is a promising therapeutic target. Our results strengthen the current hypothesis that atrial fibrillation is not only an ion channel disease but a complex systemic disorder. Restoration of physiological PLK2 expression and blockade of osteopontin release with 5-ASA may constitute valuable new drug targets for the prevention and treatment of fibrosis and diastolic heart failure in AF. Funding Acknowledgement Type of funding source: Public Institution(s). Main funding source(s): Faculty of Medicine, Carl Gustav Carus, Dresden, “MeDDrive Start” Grant

Genetic Deletion of Polo-Like Kinase 2 Induces a Pro-Fibrotic Pulmonary Phenotype

“…Accordingly, SMAD2/3 phosphorylation was significantly elevated in KO compared to WT ( Figure 1 f). These results are in line with our previous finding, that genetic deletion and pharmacological inhibition of PLK2 stimulate ERK1/2 phosphorylation in cardiac fibroblasts [ 13 ]. Although the mechanisms by which PLK2 modulates these pathways are little understood, there is data demonstrating that neuronal PLK2 regulates the Ras pathway by phosphorylation-dependent degradation of RasGRF1, a guanidine exchange factor that stimulates Ras activity [ 39 , 40 ].…”

“…Nonetheless, the observed trend is in agreement with published data, demonstrating a disease-driving role of OPN in IPF [ 17 , 45 , 46 ]. Additionally, these results support previous findings that both genetic deletion and pharmacological inhibition of PLK2 lead to a significant increase in OPN protein expression in cardiac fibroblasts [ 13 ]. However, as of now, it remains the subject of future research whether fibroblasts, alveolar epithelial cells, immune cells or their specific interactions are accountable for the observed increase of OPN and IL18 expression in PLK2 KO lungs.…”

“…Pulmonary fibrosis comprises a particularly heterogeneous group of fibroproliferative disease, which can be the sequelae of multiple triggering stimuli [ 1 , 24 ]. Recent findings suggest that PLK2 is involved in non-pulmonary fibrosis regulation[ 13 ] and differential PLK2 expression has been demonstrated in pulmonary fibroblasts upon stimulation with TGFβ [ 14 ]. To ascertain whether PLK2 and its downstream targets are differentially regulated in pulmonary fibrosis, we analyzed gene expression in lung tissue samples from different fibrotic entities such as idiopathic pulmonary fibrosis (IPF), alveolar fibroelastosis (AFE), organizing pneumonia (OP) and systemic sclerosis (SSC).…”

“…Polo-like kinase 2 (PLK2) is a serine-threonine kinase that regulates cell cycle progression, cell proliferation, mitochondrial respiration and apoptosis [ 9 , 10 , 11 , 12 ]. There is first evidence that PLK2 regulates fibrosis formation in cardiovascular disease [ 13 ] and differential regulation of PLK2 gene expression was found in Transforming Growth Factor beta 1 (TGF-β) treated adult lung fibroblasts [ 14 ]. However, the function of PLK2 in pulmonary fibrosis development remains unclear.…”

Polo-Like Kinase 2: From Principle to Practice

“…PLK2 may also play a key role in dynamic compression enhanced chondrogenesis ( 51 ). In fibrotic diseases, the loss of PLK2 function leads to the transformation of fibroblasts into myofibroblasts, thus promoting the occurrence and development of the disease, the specific mechanism of which will be discussed later ( 22 , 23 , 52 , 53 ).…”