Granzyme B contributes to impaired wound healing during chronic inflammation in apolipoprotein E knockout mice (P3036)

Abstract

Abstract Granzyme B (GzmB) is a serine protease expressed by immune cells during chronic inflammation and is capable of degrading extracellular matrix (ECM) proteins such as fibronectin (FN). Apolipoprotein E (ApoE) is a protein known to suppress inflammation and is expressed in skin. ApoE knockout (KO) mice develop an inflammatory skin phenotype when fed a high fat diet leading to impaired wound healing. We hypothesized that excessive GzmB activity contributes to impaired healing in ApoE KO mice through the degradation of ECM. Wild type (WT), ApoE KO and ApoE/GzmB double knockout (DKO) mice were fed a high fat diet for 30 weeks and given a 1 cm diameter skin wound on their mid dorsum. Wounds were allowed to heal for 16 days at which point the wounded tissue was harvested. All WT mouse wounds showed complete closure after 16 days while only 40% achieved closure in ApoE KO mice. Wound contraction was also slower in ApoE KO mice compared to WT controls (P<0.05). Histological analysis demonstrated persistent inflammation in ApoE KO mouse wounds at Day 16 featuring neutrophils, macrophages, T cells and GzmB. Wounded skin from ApoE KO mice also contained a FN fragment of similar size to that produced by GzmB in vitro. Compared to ApoE KO mice, DKO mice showed faster contraction (P<0.05) and better healing with 80% of wounds achieving closure by Day 16. These results suggest GzmB contributes to impaired wound healing in ApoE KO mouse wounds, possibly through excessive degradation of FN.