Granzyme B Mediates Both Direct and Indirect Cleavage of Extracellular Matrix in Skin After Chronic Low‐Dose Ultraviolet Light Irradiation

Abstract

Extracellular matrix (ECM) degradation is a hallmark of tissue aging, as well as many other chronic inflammatory diseases that can lead to a loss of function. Granzyme B (GzmB), a serine protease that is expressed by a variety cells, has been shown to accumulate in the extracellular space during chronic inflammation and cleave a number of proteins. Using a chronic low‐grade UV‐irradiation murine model, we hypothesized that GzmB contributes to skin damage and ECM degradation through processes involving both direct ECM cleavage and indirect ECM cleavage through the induction of other proteinases. Wild‐type and GzmB‐knockout (KO) mice were repeatedly exposed to minimal erythemal doses of solar simulated UV‐irradiation for up to 20 weeks. GzmB expression was significantly increased in wild‐type UV‐treated skin compared to non‐irradiated controls. GzmB deficiency significantly protected against the formation of wrinkles and the loss of dermal collagen density. GzmB‐KO mice were also protective against the loss of fibronectin (FN) in vivo, and FN fragments were released from the cell‐derived matrix of cultured fibroblasts after GzmB treatment. GzmB‐mediated FN fragments increased the release of metalloproteinase (MMP)‐1 and MMP‐3 from fibroblasts. Furthermore, GzmB cleavage of decorin predisposed collagen fibrils more susceptible to attack by MMP‐1. Finally, GzmB reduced the barrier function of a monolayer of keratinocytes in vitro as measured by electrical impedance. Collectively, these findings indicate a significant role for GzmB in ECM degradation, which may have implications in many aged‐related dermatological indications.