Abstract
BACKGROUND: Fragmentation of collagen fibrils, the major structure protein in skin, is a hallmark of dermal ageing. Matrix metalloproteinases (MMPs) are largely responsible for the fragmentation of collagen fibrils. OBJECTIVES: To quantify gene expression of all 23 known mammalian MMPs in sun-protected young and aged human skin in vivo and to investigate the potential mechanism underlying age-related alteration of multiple MMPs. METHODS: MMP mRNA expression levels and MMP activity in sun-protected young and aged human skin in vivo were determined by real-time reverse transcription polymerase chain reaction (RT-PCR) and in situ zymography, respectively. The relative contributions to elevated MMPs in epidermis and dermis were quantified by laser capture microdissection coupled real-time RT-PCR. Dermal fibroblast morphology and collagen fibril fragmentation in human skin in vivo were assessed by second-harmonic generation microscopy and atomic force microscopy, respectively. In vitro cell morphology was assessed by CellTracker® fluorescent dye (Molecular Probes, Eugene, OR, U.S.A.) and phalloidin staining. Protein levels were determined by ProteinSimple capillary electrophoresis immunoassay (ProteinSimple, Santa Clare, CA, U.S.A.). RESULTS: Multiple MMPs are elevated in aged human skin dermis. Increased MMP activity and collagen fibril fragmentation were observed in aged skin dermis. As dermal fibroblasts are the major MMP-producing cells in the dermis, reduction of dermal fibroblast size, which is observed in aged human skin, contributes to the elevation of age-related multiple MMPs. Reduction of fibroblast size upregulates c-Jun/c-Fos and activates AP-1. CONCLUSIONS: Combined actions of the wide variety of MMPs that are constitutively elevated in aged dermis may be involved in the progressive degradation of dermal collagen fibrils. Age-related elevations of multiple MMPs are likely to be a result of the reduction of fibroblast size via activation of AP-1.