Abstract 241: MicroRNA-24 Controls Macrophage Survival in Murine Abdominal Aortic Aneurysm Via Chi3l1
Abdominal aortic aneurysm (AAA) is a major source of vascular mortality, and effective treatments remain elusive. MicroRNAs (miRs) are key regulators of vascular homeostasis and pathology. Array profiling and qRT-PCR of aneurysmal aortic tissue in two murine AAA models (elastase-infused C57/Bl6, and angiotensin II(AngII)-treated ApoE-/- mice) showed significant down-regulation of miR-24. Levels of a recently identified inflammatory mediator and predicted target of miR-24, YKL-40/Chi3l1 (chitinase 3 like-1), were inversely correlated with miR-24 expression in both models. Previously we showed that aortic over-expression of miR-24 significantly reduced inflammatory activity and macrophage survival, leading to a dramatic decrease in AAA expansion in both mouse models.
We explored the roles of miR-24 and Chi3l1 in macrophages in vitro. Specifically, we examined peritoneal macrophages obtained from AngII-treated ApoE-/- mice and RAW (mouse leukemic monocyte/macrophage) cells, stimulated with interleukin-6 (IL6) to trigger inflammation and apoptosis. In both cell types, modulation of miR-24 through transfection with anti-miR-24 (to inhibit) or pre-miR-24 (to overexpress) altered apoptotic response to IL6 by caspase and annexin assays. Pre-24 significantly decreased macrophage survival, while anti-24 abrogated the pro-apoptotic effects of IL6. Again, Chi3l1 was inversely correlated with miR-24 expression, and treatment with recombinant Chi3l1 led to dose-dependent attenuation of apoptosis. As expected, IL6 treatment decreased miR-24, and increased Chi3l1. This effect was mediated by the NF-kB pathway. Prior to IL6 treatment, macrophages were transfected with siRNA against either RelA (p65) or Nfkb1 (p50) (key components of NF-kB signaling). Knock-down was >75% by qRT-PCR, and both demonstrated significant decreases in resultant NF-kB activity. Both methods attenuated the impact of IL6 treatment on miR-24 (vs. neg. control siRNA). These results suggest that the apoptotic effects of inflammatory stimuli on macrophages in AAA are opposed by a drop in miR-24 and a rise in its target Chi3l1, permitting macrophage infiltration and survival. This would explain in part the positive effects of pre-miR-24 on AAA progression in vivo.
- © 2013 by American Heart Association, Inc.