Mitochondrial-dependent apoptosis in experimental rodent abdominal aortic aneurysms

OBJECTIVES: While extrinsic mechanisms of apoptosis in abdominal aortic aneurysms (AAAs) are recognized, this project hypothesizes that an intrinsic, mitochondrial-dependent, mechanism of apoptosis also contributes to experimental AAA formation. METHODS: Rat aortas were perfused with either saline or elastase (N = 5 per group) and harvested 7 days postperfusion. The aortas were placed in gluteraldehyde for subsequent transmission electron microscopy, Bouin's solution for TUNEL, or paraformaldehyde for immunohistochemical staining for caspase-9, caspase-3, and Bid. RESULTS: Abdominal aortic diameters increased 168 +/- 25% (mean +/- SEM) after elastase perfusion. compared with 30 +/- 5% after saline perfusion (P < .001). Apoptosis of aortic smooth muscle cells, macrophages, and neutrophils was evidenced by transmission electron microscopy and TUNEL in the elastase-perfused aneurysmal aortas. Quantitative analysis of the apoptotic cells revealed a significant (P < .01) increase in the number of total apoptotic cells in the elastase-perfused aortas (12 +/- 3 cells per high-power field), compared with that of saline-infused controls (1.3 +/- 0.2). Caspase-9, the key initiator in the mitochondrial-dependent apoptotic pathway, stained positively in only elastase-perfused aortas. Bid staining was not detected in either the elastase-perfused aortas or the saline controls. CONCLUSIONS: Apoptosis is evident in multiple cell lines in elastase-perfused aneurysmal aortas, but rarely observed in control aortas. Caspase-9, the key initiator of intrinsic apoptosis, was documented only in elastase-perfused aortas. These results suggest that mitochondrial-dependent apoptosis is associated with abdominal aortic aneurysm formation.