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UBC Theses and Dissertations

Granzyme B in skin aging, injury and repair Hiebert, Paul Ryan

Abstract

Granzyme B (GzmB) is a serine protease that can be released into the extracellular spaces by immune cells during chronic inflammation where it is capable of degrading several components of the extracellular matrix (ECM). Several chronic inflammatory skin diseases have demonstrated elevated levels of GzmB however the exact role of GzmB in the skin remains poorly understood. Apolipoprotein E (ApoE) is a protein highly expressed in the skin, where it can regulate inflammation through its anti-oxidative and anti-inflammatory properties. Mice deficient in ApoE develop an inflammatory skin phenotype when fed a high fat diet indicative of premature aging featuring ECM remodeling, hair graying, hair loss and frailty. I therefore hypothesized that GzmB contributes to skin aging, injury and impaired healing in ApoE knockout (ApoE-KO) mice through the degradation of ECM proteins. In the present dissertation, I identified the high fat diet-fed ApoE-KO mouse as a model that displays several characteristic features of skin aging including skin thinning and collagen disorganization. Further investigations also identified that high fat diet-fed ApoE-KO mice show defects in cutaneous wound healing such as delayed wound closure, reduced contraction and altered collagen content. These changes became worse with age and high fat diet. To test the role of GzmB in this process, GzmB/ApoE double knockout (DKO) mice were generated. These DKO mice were protected from skin thinning and collagen disorganization even when fed a high fat diet, suggesting that GzmB plays a role in ECM remodeling during aging of the skin in ApoE-KO mice. Further investigation revealed that GzmB-mediated degradation of the proteoglycan decorin is likely to be a key mechanism by which GzmB contributes to collagen disorganization and skin aging in ApoE-KO mice. Furthermore, DKO mice showed improved wound healing compared to ApoEKO mice featuring faster wound closure, increased contraction and reduced fibronectin degradation. In vitro cleavage assays revealed that fibronectin fragments generated by GzmB matched those identified in non-healing ApoE-KO mouse wounds. In summary, my findings suggest that extracellular GzmB contributes to skin aging and impaired healing in ApoE-KO mouse skin through the degradation of ECM components such as decorin and fibronectin.

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