HYALURONAN - ITS NATURE, DISTRIBUTION, FUNCTIONS AND TURNOVER

Hyaluronan is a polysaccharide found in all tissues and body fluids of vertebrates as well as in some bacteria. It is a linear polymer of ex ceptional molecular weight, especially abundant in loose connective ti ssue. Hyaluronan is synthesized in the cellular plasma membrane. It ex ists as a pool associated with the cell surface, another bound to othe r matrix components, and a largely mobile pool. A number of proteins, the hyaladherins, specifically recognize the hyaluronan structure. Int eractions of this kind bind hyaluronan with proteoglycans to stabilize the structure of the matrix, and with cell surfaces to modify cell be haviour. Because of the striking physicochemical properties of hyaluro nan solutions, various physiological functions have been assigned to i t, including lubrication, water homeostasis, filtering effects and reg ulation of plasma protein distribution. In animals and man, the half-l ife of hyaluronan in tissues ranges from less than 1 to several days. It is catabolized by receptor-mediated endocytosis and lysosomal degra dation either locally or after transport by lymph to lymph nodes which degrade much of it. The remainder enters the general circulation and is removed from blood, with a half-life of 2-5 min, mainly by the endo thelial cells of the liver sinuoids.