Serpina3n attenuates granzyme B-mediated decorin cleavage and rupture in a murine model of aortic aneurysm

L S Ang,S J Williams,W A Boivin,K Carmine-Simmen,T Abraham,R C Bleackley,D J Granville,H Zhao,B M Mcmanus

doi:10.1038/cddis.2011.88

Abstract

Granzyme B (GZMB) is a proapoptotic serine protease that is released by cytotoxic lymphocytes. However, GZMB can also be produced by other cell types and is capable of cleaving extracellular matrix (ECM) proteins. GZMB contributes to abdominal aortic aneurysm (AAA) through an extracellular, perforin-independent mechanism involving ECM cleavage. The murine serine protease inhibitor, Serpina3n (SA3N), is an extracellular inhibitor of GZMB. In the present study, administration of SA3N was assessed using a mouse Angiotensin II-induced AAA model. Mice were injected with SA3N (0–120 μg/kg) before pump implantation. A significant dose-dependent reduction in the frequency of aortic rupture and death was observed in mice that received SA3N treatment compared with controls. Reduced degradation of the proteoglycan decorin was observed while collagen density was increased in the aortas of mice receiving SA3N treatment compared with controls. In vitro studies confirmed that decorin, which regulates collagen spacing and fibrillogenesis, is cleaved by GZMB and that its cleavage can be prevented by SA3N. In conclusion, SA3N inhibits GZMB-mediated decorin degradation leading to enhanced collagen remodelling and reinforcement of the adventitia, thereby reducing the overall rate of rupture and death in a mouse model of AAA.

Highlights

Granzyme B (GZMB) is a 32 kDa serine protease that is released by cytotoxic lymphocytes.[5]
Recently a perforinindependent, extracellular role for GZMB has been proposed.[6,7]. In support of the latter, we have shown, using apolipoprotein E (ApoE) Â GZMB-double knockout (GDKO) and ApoE Â perforin-double knockout (PDKO) mice, that GZMB contributes to Abdominal aortic aneurysms (AAAs) through an extracellular, perforinindependent mechanism.[7]
Necropsy was performed on all mice that died prematurely before the 28-day time point and in all cases confirmed the presence of large ruptured aortic dissections and extensive blood clots in the abdominal cavity suggesting that death was caused by exsanguination following AAA rupture

Summary

Introduction

Granzyme B (GZMB) is a 32 kDa serine protease that is released by cytotoxic lymphocytes.[5]. Decorin-deficient mice exhibit skin fragility because of reduced collagen tensile strength.[8] In previous work, we identified decorin as a substrate of GZMB and demonstrated that GZMB deficiency prevents the loss of decorin degradation and collagen disorganization in the skin of aging mice.[6] With respect to aneurysm pathology, deficient decorin expression is associated with lethal forms of Marfan’s syndrome[9] and a three-fold downregulation of decorin expression is observed in patients with acute aortic dissection.[10]. As decorin functions to regulate matrix assembly by modulating collagen spacing and organization,[13] GZMB likely contributes to the loss of adventitial collagen architecture through the cleavage of decorin

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