[Hyaluronan: structure, metabolism, functions, and role in wound healing]

Hyaluronan (HA) is a nonsulfated nonepimerized linear glycosaminoglycan (GAG) existing in vivo as a polyanion of hyaluronic acid and composed of repeating disaccharide units of D-glucuronic acid and N-acetyl-D-glucosamine [-->4GlcAbeta1-->3GlcNAcbeta1-->]. It is a major constituent of the extracellular matrix (ECM) of the skin, joints, eye, and many other tissues and organs.The simple structure of this ubiquitous macromolecule belies the complexity of its physico-chemical properties and biological functions, which depend on HA's molecular weight and interacting molecules called "hyaladherins". HA has extraordinary hydrophilic, rheological, and signaling properties and is viscoelastic. This naturally occurring biopolymer is dynamically involved in many biological processes, such as embryogenesis, inflammation, metastasis, tumor progression, tissue turnover, and wound healing. Wound healing is a dynamic interactive process involving many precisely interrelated phases, overlapping in time and leading to the restoration of tissue integrity. The healing process reflects the complex and coordinated body response to tissue injury resulting from the interaction of different cell types and extracellular matrix components. Hyaluronan plays a key role in each phase of wound healing by stimulating cell migration, differentiation,and proliferation as well as regulating ECM organization and metabolism.