Abstract 255: Modulation Of Cardiac Macrophages As A Strategy For Infarct Healing
Heart failure is the leading cause of death in the developed world and myocardial infarction (MI) is the most common cause. Macrophages are key cells that orchestrate the initial inflammatory as well as later stage wound healing responses following MI. These functions are carried out by pro-inflammatory (M1) and reparative (M2) macrophages respectively. Optimal healing response after MI requires a balancing act of the biphasic macrophage response, so as to not prolong inflammatory signals detrimental to wound healing. Taking advantage of the fact that interleukin-4 (IL-4) activates macrophages towards M2, we hypothesize that delivering IL-4 to the post-MI heart can alter the ratio of M2 to M1 macrophages in the infarct area and induce a better healing response. In this study, we validate our approach in vitro and perform in vitro optimization of a suitable delivery system.
RAW 264.7 macrophages were stimulated with IL-4 (10ng/uL) or LPS/IFN-γ (100ng/mL and 10ng/mL) for 24h and gene expression markers (qPCR) and Nitric Oxide (NO) levels (Griess assay) analyzed as indication of M1or M2 activation. Mouse aortic endothelial cells were treated with conditioned media from these cells for 24h and tube formation assessed on matrigel. A bioactive, protease-cleavable polyethylene glycol (PEG) hydrogel delivery system was evaluated for release of functional IL-4 to LPS-activated macrophages. Empty or IL-4 encapsulating hydrogel was placed on a trans-well above LPS-stimulated macrophages. Collagenase I at 0.1mg/mL was applied over 48h to degrade the gels and release IL-4 (n≥3 and p<0.05 considered significant by one-way ANOVA).
We demonstrate that IL-4 significantly upregulates M2 markers (MRC-1 and Arg-1) while IFN-γ and LPS upregulate M1 markers (NO and TNF-alpha). We observe enhanced tube density in endothelial cells treated with M2 media while M1 inhibited tube formation. Hydrogel release study shows a significant reduction in NO levels of LPS-stimulated macrophages when IL-4 is released, demonstrating that IL-4 is released from the gel in its bioactive form. In conclusion, we show that macrophages can indeed respond to changing stimuli and adopt distinct activation types and our PEG based hydrogel could be a potential delivery system for in vivo IL-4 delivery.
- © 2013 by American Heart Association, Inc.