Abstract
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.
Highlights
Inflammation and autoimmunity are involved in the progression of many heart diseases.Myocarditis is a precursor of dilated cardiomyopathy (DCM) and represents the most common cause of chronic heart failure or even sudden death; little is known about the mechanismsCells 2020, 9, 396; doi:10.3390/cells9020396 www.mdpi.com/journal/cellsCells 2020, 9, 396 involved in post-inflammatory cardiac remodelling leading to DCM [1,2,3]
We focused on cardiac fibroblast (CFs) because of its key role during the pathological remodelling of the heart and we examined whether sPLA2 -IIA could induce the transition of quiescent fibroblasts towards synthetic and proliferative myofibroblasts
The antioxidants, NAC and DPI, did not affect the increased collagen expression levels triggered by sPLA2 -IIA to further investigate the relationship among sPLA2 -IIA and factors involved in the maturation of collagen fibers, we studied the expression of bone morphogenic protein (BMP)-1 and lysyl oxidase (LOX) in CFs treated with sPLA2 -IIA for 24 h
Summary
Inflammation and autoimmunity are involved in the progression of many heart diseases.Myocarditis is a precursor of dilated cardiomyopathy (DCM) and represents the most common cause of chronic heart failure or even sudden death; little is known about the mechanismsCells 2020, 9, 396; doi:10.3390/cells9020396 www.mdpi.com/journal/cellsCells 2020, 9, 396 involved in post-inflammatory cardiac remodelling leading to DCM [1,2,3]. Significant steps in the progression from myocarditis to DCM and heart failure involve extracellular matrix (ECM) remodelling and fibrosis, which is characterised by the abundant production of ECM proteins resulting in a change of the structure and architecture of the myocardium, impairing the ventricular contractility and functionality [4,5]. In experimental autoimmune myocarditis (EAM), a mouse model of myocarditis, it has been demonstrated that overproduction of pro-inflammatory proteins such as TNFα, TGFβ and IL-1β play important roles by affecting the production of ECM proteins and ECM-regulatory proteins [6,7,8]. Among the ECM macromolecules produced by activated CFs, periostin, bone morphogenetic protein-1 (BMP-1) and lysyl oxidase (LOX) play a key role in promoting collagen cross-linking, which determined mechanical properties of the ECM, making it less prone to degradation [12,13]
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