Abstract 1718: Granzyme B Co-localizes to Elastin and Plays a Major Role in Diseases Associated with Hyperlipidemia and Chronic Inflammation
Introduction: Granzyme B (GrB) is a cytotoxic serine protease that is expressed in certain subsets of T-cells, NK cells and macrophages. We have shown that GrB is lipophillic and present in lipid-rich regions of human vessels with advanced atherosclerotic plaques. In addition, it is well-known that in the presence of calcium, lipids accumulate on elastin fibres.
Hypothesis: During chronic hyperlipidemia and inflammation, GrB accumulates on elastin fibres and contributes to chronic elastin degradation, medial thinning and reduced elasticity.
Methods: To study the role of GrB in a chronic inflammatory, hyperlipidemic environment, ApoE −/− x GrB−/− double knockout (ApoE/GrB-DKO) mice were generated. Mice were fed a high fat diet for 30 weeks, sacrificed and tissues were processed. Tissues were stained with H&E to assess morphology, oil red O to assess lipid deposition, elastic van Gieson to visualize elastin, and Movat’s pentachrome to visualize extracellular matrix composition and lesion area. GrB co-localization to elastin was also assessed using confocal microscopy.
Results: ApoE−/− mice developed severe xanthomatosis, hair loss and atherosclerotic lesions by 30 weeks. The absence of the GrB gene in the ApoE/GrB-DKO mice completely abolished cutaneous xanthomatosis in addition to both the frequency and size of atherosclerotic lesions. The absence of GrB was associated with a marked reduction of elastin degradation in both the skin and blood vessels. When further examined using confocal microscopy, it was observed that GrB strongly co-localized to the shoulder regions of plaques in addition to the internal elastic lamina and medial elastin fibres. Furthermore, although ApoE −/− mice had to be sacrificed by 30 weeks for humane purposes, the ApoE/GrB DKO mice were grown for 60 weeks with minimal evidence of aging, xanthomatosis, hair graying or atherogenesis indicating that the absence of GrB may increase longevity.
Conclusions: GrB plays a key role in atherosclerotic plaque formation. Lipid accumulation on elastin fibres promotes the recruitment of GrB resulting in a slow, chronic degradation of elastin.