34 The synthesis of HA increases during tissue injury and wound healing 25, 44, 45 and HA regulates several aspects of tissue repair, including activation of inflammatory cells to enhance immune response 46 - 48 and the response to injury of fibroblasts 49, 50 and epithelial cells. Over the past 2 decades there was considerable evidence presented that unraveled the functional role of HA in molecular mechanisms and indicated the potential role of HA for the development of novel therapeutic strategies for many diseases.įunctions of HA include the following: hydration, lubrication of joints, a space filling capacity, and the framework through which cells migrate.
Half life 1 skins skin#
16 This review presents in brief recent knowledge in HA biology and function and focuses on its involvement in skin aging. Recent reviews have described the involvement of HA with respect to its role in angiogenesis, 7 reactive oxygen species, 8 chondrocytes, 9 cancer, 10, 11 lung injury, 12, 13 immune regulation 14, 15 and skin. Yet, the predominant component of the skin ECM is HA. These ECM molecules, although they appear amorphous by light microscopy, they form a highly organized structure, comprising mainly of GAG, proteoglycans, growth factors and structural proteins such as collagens. Recently, it is appreciated that ECM molecules that lie between cells, in addition to providing a constructive framework, they exert major effects on cellular function.
In the beginning, most of the studies focused on the cells that comprise the skin layers, such as the epidermis, the dermis and the underlying subcutis. During the past decades the constituents of the skin have been well characterized. 6 HA belongs to the extracellular matrix (ECM) molecules. The key molecule involved in skin moisture is hyaluronan or hyaluronic acid (HA), a glycosaminoglycan (GAG) with a unique capacity to bind and retain water molecules. Skin aging is also associated with loss of skin moisture. 5 Therefore, elevated levels of degraded collagen and reduced collagen synthesis are pathologies occurring in intrinsically aged as well as photoaged skin. 4 ROS in extrinsic or intrinsic skin aging induce the transcription factor c-Jun via mitogen-activated protein kinases (MAPK), leading to overexpression of matrix metalloproteinase (MMP)-1, MMP-3 and MMP-9 and prevention of the expression of procollagen-1. For example, reactive oxygen species (ROS), arising from oxidative cell metabolism, play a major role in both processes. 3Įven though intrinsic and extrinsic skin aging are distinctive processes, they share similarities in molecular mechanisms. It is well established that the deficiency in estrogens and androgens results in collagen degradation, dryness, loss of elasticity, epidermal atrophy and wrinkling of the skin. 1 Intrinsic skin aging is influenced by hormonal changes that occur with age, 2 such as the gradual decreased production of sex hormones from the mid-twenties and the diminution of estrogens and progesterone associated with menopause. The second is extrinsic aging, which is the result of exposure to external factors, mainly ultraviolet (UV) irradiation, that is also referred to as photoaging. The first is intrinsic or innate aging, an unpreventable process, which affects the skin in the same pattern as it affects all internal organs. It is the result of two biologically independent processes.
Human skin aging is a complex biological process, not yet fully understood.