Abstract 380: Aging Enhances Endoplasmic Reticulum Stress-Induced Apoptosis in Murine Macrophages

Introduction and hypothesis

Aging enhances atherosclerosis for unclear reasons. As macrophage apoptosis and endoplasmic reticulum (ER) stress contribute to atherosclerosis, we examined if aging sensitizes these cells to apoptosis during ER stress.

Methods and Results

Peritoneal macrophages were isolated from young (aged 2-4 months) and aged (aged 16-18 months) mice, exposed to the ER stress inducer tunicamycin (TM) in vitro, and apoptosis was measured by Annexin V staining via fluorescent microscopy. We found that aged macrophages exhibited significantly more apoptosis than young macrophages (see Figure). We next measured key ER stress proteins in macrophages by Western blot to determine the underlying molecular pathways impacted by aging. With aging, we found reduced activation of inositol-requiring enzyme-1 (IRE1α), a key ER stress transducer. We next examined if augmenting activated IRE1α levels in aged macrophages reduced apoptosis during ER stress. We employed siRNA to knock down x-box binding protein 1 (XBP1), a downstream effector of IRE1α, which has been shown to induce feedback activation of IRE1α in hepatocytes. siRNA to XBP1 significantly reduced tunicamycin-induced cell apoptosis in aged macrophages from 26.1±0.408% to 5.48±1.38% (p<0.05) but not in young macrophages.

Conclusions

Our study has uncovered a novel, age-dependent interaction by which macrophages undergo apoptosis upon ER stress, and suggests that enhancing IRE1α activation will alleviate aging-augmented ER stress and subsequent apoptosis. This novel interaction may have important implications for the pathogenesis of atherosclerosis with aging.