Impaired Infarct Healing in Atherosclerotic Mice With Ly-6ChiMonocytosis

Objective To test if blood monocytosis in mice with atherosclerosis affects infarct healing. Background Monocytes are cellular protagonists of tissue repair and their specific subtypes regulate the healing program after MI. Inflammatory Ly-6Chi monocytes dominate on day 1-4 and digest damaged tissue; reparative Ly-6Clo monocytes dominate on day 5-10 and promote angiogenesis and scar formation. However, the monocyte repertoire is disturbed in atherosclerotic mice: Ly-6Chi monocytes expand selectively, which may disrupt the resolution of inflammation. Methods and Results Ex vivo analysis of 5 day-old infarcts showed >10-times more Ly-6Chi monocytes in atherosclerotic (apoE-/-) mice compared to wild type mice. The injured tissue in apoE-/- mice also showed a more pronounced inflammatory gene expression profile (e.g. increased TNF-α and MPO and decreased TGF-β) and a higher abundance of proteases, which are associated with the activity of Ly-6Chi monocytes. To relate inflammatory activity to left ventricular remodeling, we used a combination of noninvasive molecular and physiologic imaging. FMT-CT on day 5 post MI showed higher proteolysis and phagocytosis in infarcts of atherosclerotic mice. Serial MRI showed accelerated deterioration of EF between day 1 and 21 after MI in apoE-/-. Finally, we could recapitulate these features in wild-type mice with artificially–induced Ly-6Chi monocytosis. Conclusion Ly-6Chi monocytosis disturbs resolution of inflammation in murine infarcts and consequently enhances left ventricular remodeling. These findings position monocyte subsets as potential therapeutic targets to augment tissue repair after infarction and to prevent post-MI heart failure.