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The role of granzyme B and perforin in atheromatous diseases

University of British Columbia

Atheromatous diseases, such as atherosclerosis and transplant vascular disease (TVD), are inflammatory vascular diseases that carry an important health burden for the North American population. Although the adaptive immune response contributes to the pathogenesis of atherosclerosis and TVD , the mechanisms of the cellular cytotoxic immune response in these diseases is poorly understood. To date, both cellular and biochemical effectors of the cytotoxic immune response have been observed in atherosclerosis and TVD . Two such effector molecules, granzyme B and perforin, are key components of cellular cytotoxic immunity that act in concert to induce cell death of virus-infected and foreign cells through the granule exocytosis pathway. In this dissertation I hypothesize that granzyme B and perforin contribute to the pathogenesis of inflammatory vascular diseases by inducing endothelial and smooth muscle cell death. Granzyme B was shown to localize to lipid-rich regions in human advanced atherosclerotic and TVD lesions. In these lesions, granzyme B was observed in and around vascular smooth muscle cells (VSMC) in the intima and media, and also localized to TdT UTP Nick End Labeling (TUNEL)-positive cells suggesting that this protein was inducing apoptosis in these lesions. In support of the latter notion, granzyme B induced VSMC apoptosis in vitro. Surprisingly, granzyme B-induced VSMC death did not depend on perforin as it could induce VSMC death through the proteolysis of extracellular proteins and initiated the cleavage of a number of VSMC-derived extracellular proteins, one of which was fibronectin. Importantly, activated T cells induced VSMC apoptosis through a perforin-independent granzyme B-mediated pathway. To investigate the contribution of the granule exocytosis pathway to vascular damage of allograft coronary arteries and in the resultant initiation of TVD, cardiac heterotopic transplantation was performed into perforin-knockout (PKO) mice. Although granzyme B can induce VSMC death through a perforin-independent mechanism, T cell-induced endothelial cell (EC) death has been shown to depend on perforin. Because EC death is an initiating event in TVD, while VSMC death may contribute to lesion remodeling and augmentation of atheromatous diseases, perforin-mediated cytotoxicity was investigated in these experiments to determine its role in the initiation of TVD. Allograft coronary arteries from PKO recipients contained significantly less EC damage and death at 12 days post-transplantation as compared to wild type recipients. Also, there was significantly less intimal thickening in allograft arteries from PKO (13.4 ± 5.1% luminal narrowing) as compared to wild type (54.2 ± 6.7% luminal narrowing) recipients at 30 days post-transplantation (p<0.00002). In summary, the results obtained in this work provide valuable insights into the contribution of granule exocytosis-mediated cell death in the pathogenesis of TVD. In particular, granzyme B induces VSMC death through a perforin-independent pathway and this may contribute to atheromatous lesion growth. In addition, perforin-mediated EC death is an important process in allograft vascular damage and resultant TVD, and blockade of this pathway can attenuate TVD.

Text

2009-12-16

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http://hdl.handle.net/2429/16885

Pathology

University of British Columbia

UBCV

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