Neutrophils are rapidly recruited to infarct site in response to cardiomyocyte death. Apoptosis and phagocytosis by macrophages prevents further damage to host tissues, but can also polarise macrophages towards an anti-inflammatory phenotype, potentially enhancing repair and reducing infarct expansion after myocardial infarction. Pharmacological induction of neutrophil apoptosis by cyclin-dependent kinase inhibitor drugs (CDKi) has been shown to enhance resolution of inflammation in the murine lung (Rossi et al ., 2006). The present study study investigated the in vitro effects of a CDKi (AT7519) on mouse neutrophil apoptosis and determined its effects on agonist-induced Ca2+ flux.
Immature bone marrow-derived neutrophils (BMDNs) were isolated and inflammatory neutrophils obtained from the lavage of thioglycollate-induced peritonitis (TGNs). Apoptosis was assessed by flow-cytometric analysis of annexinV/propidium iodide (PI) binding, DNA incorporation of PI into permeablised cells (hyplodiploid peak) and morphological assessment of cyto-centrifuge preparations. Intracellular Ca2+ flux was assessed by spectrofluorimetric analysis of Fura-2 loaded cells.
BMDNs and TGNs underwent constitutive apoptosis at 6 and 20h, an effect enhanced by AT7519 in a concentration, time and caspase-dependent manner. For example, at 6h, apoptosis assessed by hypodiploid peak quantification was 6.7% in control BMDNs vs 15.2% in 1 μM AT7519 treated cells. In TGNs, apoptosis as assessed by annexinV/PI binding at 6 h were 6.2% in control vs 12.0% in 1μM AT7519 treated cells (n = 6). Interestingly, AT7519 did not directly induce Ca2+ fluxes in BMDNs or TGNs nor did it affect Ca2+ fluxes triggered by neutrophil agonists (fMLF and PAF).
Thus AT7519 enhances mouse neutrophil apoptosis without affecting early activation responses such as agonist-induced Ca2+ flux and therefore suggests that CDKi induce apoptosis even in the presence of stimuli found at inflammatory sites, which make it a promising anti-inflammatory agent to be used in the setting of MI.
This study was supported by a Chinese Scholarship Council/University of Edinburgh Fellowship to XZ and by a BHF Centre of Research Excellence Award.
Reference Rossi AG, et al. Cyclin-dependent kinase inhibitors enhance the resolution of inflammation by promoting inflammatory cell apoptosis. Nature Med 2006;12:1056–1064
- neutrophil apoptosis
- myocardial infarct
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