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Arachidonate 5 Lipoxygenase is Essential for Biosynthesis of Specialized Pro-resolving Mediators and Cardiac Repair in Heart Failure.

Arachidonate 5 lipoxygenase-derived leukotrienes are primary signals of leukocyte activation and inflammation in response to ischemic cardiac injury (MI; myocardial infarction). Using risk-free male C57BL/6J and arachidonate 5-lipoxygenase (ALOX5) null mice (8-12 weeks), we quantitated leukocytes and ALOX5-derived bioactive lipids of the infarcted left ventricle (LV) and spleen to measure the physiological inflammation and cardiac repair. Our results showed that ALOX5 endogenously generates specialized pro-resolving mediators (SPMs) that facilitate cardiac repair post-MI. Deficiency of ALOX5 lead to increase cyclooxygenase gene expression, 6-keto prostaglandin F1α, and neutrophil abundance with signs of unresolved inflammation post-MI. Consequently, ALOX5 deficiency impaired the resolution of inflammation and cardiac repair, including increased myocardium rupture post-MI in acute heart failure. On-time ALOX5 activation is critical for leukocyte abundance from the infarcted heart, indicating an essential role of ALOX5 in the resolution of inflammation. In addition, to balance the inflammatory responses, ALOX5 is also necessary for fibroblast signaling, as the ALOX5-deficient fibroblast are prone to fibroblast-to-myofibroblast differentiation leading to defective scar formation in post-MI cardiac repair. Consistent with these findings, ALOX5-null mice showed an overly inflammatory response, defective fibrotic signaling, and unresolved inflammation. These findings are indicative of a critical role of ALOX5 in myocardium healing, inflammation-resolution signaling, cardiac repair, and fibroblast pathophysiology.