Deletion of Extra Domain A of Fibronectin Reduces Acute Myocardial Ischaemia/Reperfusion Injury in Hyperlipidaemic Mice by Limiting Thrombo-Inflammation.

Background:  Fibronectin splicing variant containing extra domain A (Fn-EDA), which is an endogenous ligand for Toll-like receptor 4 (TLR4), is present in negligible amounts in the plasma of healthy humans, but markedly elevated in patients with co-morbid conditions including diabetes and hyperlipidaemia, which are risk factors for myocardial infarction (MI). Very little is known about the role of Fn-EDA in the pathophysiology of acute MI under these co-morbid conditions.

Materials And Methods:  We determined the role of Fn-EDA in myocardial ischaemia/reperfusion (I/R) injury in the hyperlipidaemic apolipoprotein E-deficient (ApoE) mice. Infarct size, plasma cardiac troponin I (cTnI) levels, intravascular thrombosis (CD41-positive), neutrophil infiltration (Ly6 B.2-positive), neutrophil extracellular traps (citrullinated H3-positive) and myocyte apoptosis (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling-positive) were assessed in myocardial I/R injury model (1-hour ischaemia/23 hours of reperfusion).

Results:  Irrespective of gender, Fn-EDAApoE mice exhibited smaller infarct size and decreased cTnI levels concomitant with reduced post-ischaemic intra-vascular thrombi, neutrophils influx, neutrophil extracellular traps and myocyte apoptosis (< 0.05 vs. ApoE mice). Genetic deletion of TLR4 attenuated myocardial I/R injury in ApoE mice (< 0.05 vs. ApoE mice), but did not further reduce in Fn-EDA ApoE mice suggesting that Fn-EDA requires TLR4 to mediate myocardial I/R injury. Bone marrow transplantation experiments revealed that Fn-EDA exacerbates myocardial I/R injury through TLR4 expressed on the haematopoietic cells. Infusion of a specific inhibitor of Fn-EDA, 15 minutes post-reperfusion, into ApoE mice attenuated myocardial I/R injury.

Conclusion:  Fn-EDA exacerbates TLR4-dependent myocardial I/R injury by promoting post-ischaemic thrombo-inflammatory response. Targeting Fn-EDA may reduce cardiac damage following coronary artery re-canalization after acute MI.