178 Expression of active matrix metalloproteinase-1 in dermal fibroblasts: A novel mouse model of accelerated human dermal aging

Abstract

Fragmentation, disorganization, and depletion of the collagen-rich dermal extracellular matrix (ECM) are characteristic features of aged human skin. These deleterious alterations are thought to critically mediate many of the prominent clinical attributes of aged skin including thinning, fragility, impaired wound healing, and propensity for carcinoma. Matrix metalloproteinase-1 (MMP1), which is a secreted enzyme that initiates cleavage of collagen fibrils, is significantly increased in dermal fibroblasts in aged human skin. To investigate the potential role of elevated MMP1 in skin aging, we have generated a Cre-inducible mouse model, using CRISPR/Cas9 technology, that expresses full-length, catalytically-active human MMP1 (MMP1*) in dermal fibroblasts, driven by a Pdgfra-Cre transgene. Immunohistology of Pdgfra;MMP1* bitransgenic mice revealed MMP1* expression by fibroblasts throughout the dermis in dorsal, ear, tail, and volar skin. MMP1 activity in dorsal skin, measured by ELISA, was significantly greater (39-fold, n=6, p<0.01) in Pdgfra;MMP1* mice than littermate controls. MMP1* protein was similarly increased (7.6ng/g, n=6) vs. not detectable in controls. Importantly, by the age of six months, dorsal skin of Pdgfra;MMP1* mice revealed physical, histological, and molecular alterations that closely resembled those seen in aged human skin. These features included increased fragility, thinning of the dermis (reduced 35%, n=5, p<0.01), fragmentation and disorganization of collagen fibrils, visualized multiphoton confocal second harmonic generation microscopy, reduced fibroblast spreading, and altered gene expression, including reductions of type I, III, IV, and V collagens and upregulation of IL1-beta and IL-6. The above data demonstrate that elevated dermal expression of MMP1 is a key driver of many aspects of skin aging. Therapeutic intervention to reduce/inhibit MMP1 activity during aging may help to prolong skin health throughout life.