In acute and chronic inflammation, neutrophils and platelets, both of which promote monocyte recruitment, are often activated simultaneously. We investigated how secretory products of neutrophils and platelets synergize to enhance the recruitment of monocytes. We found that neutrophil-borne human neutrophil peptide 1 (HNP1, α-defensin) and platelet-derived CCL5 form heteromers. These heteromers stimulate monocyte adhesion through CCR5 ligation. We further determined structural features of HNP1-CCL5 heteromers and designed a stable peptide that could disturb proinflammatory HNP1-CCL5 interactions. This peptide attenuated monocyte and macrophage recruitment in a mouse model of myocardial infarction. These results establish the in vivo relevance of heteromers formed between proteins released from neutrophils and platelets and show the potential of targeting heteromer formation to resolve acute or chronic inflammation.

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Background: Ischemic heart diseases are classified among the leading cause of death and reduced life quality worldwide. Although revascularization strategies significantly reduce mortality after acute myocardial infarction (MI), a significant number of MI patients develop chronic heart failure over time. We previously reported that a fragment of the extra cellular matrix (ECM) protein Agrin promotes cardiac regeneration following MI in adult mice. Methods: To test the therapeutic potential of Agrin in a preclinical porcine model we performed ischemia reperfusion (I/R) injuries using balloon occlusion for 60 minutes followed by either 3, 7 or 28 days reperfusion period. Results: We first demonstrate that local (antegrade) delivery of recombinant human Agrin (rhAgrin) to the infarcted pig heart can target the affected regions in an efficient and clinically-relevant manner. Single dose of recombinant human Agrin improved heart function, infarct size, fibrosis and adverse remodeling parameters 28 days post MI. Short-term MI experiments along with complementary murine studies revealed myocardial protection, improved angiogenesis, inflammatory suppression and cell cycle re-entry, as Agrin's mechanisms of action. Conclusions: We show that a single dose of Agrin is capable of reducing ischemia reperfusion injury and improving heart function, demonstrating that Agrin could serve as a therapy for patients with acute MI and potentially heart failure.

CCR2 surface expression on Ly6C monocytes changes in a time-of-day-dependent manner, which crucially affects cardiac monocyte recruitment after an acute ischemic event.