Activation of the Proapoptotic Unfolded Protein Response in Plaques of the Human Carotid Artery

Objective: To analyze expression of keystone markers of apoptosis and the proapoptotic signaling pathway unfolded protein response (UPR) in rupture-prone plaques of the human carotid artery. Methods: Plaque specimens were obtained during endarterectomy for high-grade carotid stenosis, and were formalin-fixed. Ten specimens were identified that exhibited criteria of advanced rupture-prone atherosclerotic plaques, and histological and immunohistological analysis of markers of apoptosis (cleaved Caspase-3, TUNEL) and UPR-(KDEL, ATF3, CHOP, CHAC-1) was performed. In addition, co-localization of apoptosis and UPR-activation was assessed by double-immunohistochemistry. Results: The mean size of the necrotic core was 44 +/- 7% and the mean minimum/representative thicknesses of the fibrous cap were 129 +/- 39 mu m/280 +/- 60 mu m, respectively. Each specimen fulfilled at least two of the criteria for rupture-prone plaques. Semi-quantitative analysis of immunohistochemistry showed a significant increase in cleaved Caspase-3-positive (1923 +/- 93 cells/mm(2)) and TUNEL-positive cells (1387 +/- 66 cells/mm(2)) when compared with control tissue. Furthermore, expression of UPR-markers KDEL, AFT3 and CHOP was significantly increased (1175 +/- 40 cells/mm(2), 1971 +/- 69 cells/mm(2) and 2173 +/- 120 cells/mm(2), respectively). Co-localization of UPR-activation with apoptosis was confirmed by double-immunohistochemistry, and lesional macrophages were identified as the primary cell-type involved. Conclusion: For the first time, activation of the proapoptotic signaling pathway UPR has been identified in advanced rupture-prone plaques of the human carotid artery. This provides additional evidence for adding UPR to the potential targets for controlling plaque apoptosis and thereby preventing plaque progression/rupture. (C) 2014 European Society for Vascular Surgery. Published by Elsevier Ltd. All rights reserved.