Extracellular superoxide released from mitochondria mediates mast cell death by advanced glycation end products

Advanced glycation end products (AGEs) accumulate during aging and to higher extents under pathological conditions such as diabetes. Since we previously showed that mast cells expressed the AGE-binding protein, receptor for AGEs (RAGE) on their cell surface, we examined whether AGE affected mast cell survival. Herein, we demonstrate that mast cells undergo apoptosis in response to AGE. Glycated albumin (GA), an AGE, but not stimulation with the high-affinity IgE receptor (FcepsilonRI), can induce mast cell death, as measured by annexin V/propidium iodide double-staining. GA (> or =0.1 mg/ml) exhibited this pro-apoptotic activity in a concentration-dependent manner. GA and FcepsilonRI stimulation increased the cytosolic Ca(2+) levels to a similar extent, whereas GA, but not FcepsilonRI stimulation, caused mitochondrial Ca(2+) overload and membrane potential collapse, resulting in mitochondrial integrity disruption, cytochrome c release and caspase-3/7 activation. In addition, GA, but not FcepsilonRI stimulation, induced extracellular release of superoxide from mitochondria, and this release played a key role in the disruption of Ca(2+) homeostasis. Knockdown of RAGE expression using small interfering RNA abolished GA-induced apoptosis, mitochondrial Ca(2+) overload, and superoxide release, demonstrating that RAGE mediates the GA-induced mitochondrial death pathway. AGE-induced mast cell apoptosis may contribute to the immunocompromised and inflammatory conditions.