The Content and Size of Hyaluronan in Biological Fluids and Tissues

Abstract

Hyaluronan is a simple repeating disaccharide polymer, synthesized at the cell surface by integral membrane synthases. The repeating sequence is perfectly homogeneous, and is the same in all vertebrate tissues and fluids. The polymer molecular mass is more variable. Most commonly, hyaluronan is synthesized as a high-molecular mass polymer, with an average molecular mass of approximately 1000-8000 kDa. There are a number of studies showing increased hyaluronan content, but reduced average molecular mass with a broader range of sizes present, in tissues or fluids when inflammatory or tissue-remodeling processes occur. In parallel studies, exogenous hyaluronan fragments of low-molecular mass (generally, <200 kDa) have been shown to affect cell behavior through binding to receptor proteins such as CD44 and RHAMM (gene name HMMR), and to signal either directly or indirectly through toll-like receptors. These data suggest that receptor sensitivity to hyaluronan size provides a biosensor of the state of the microenvironment surrounding the cell. Sensitive methods for isolation and characterization of hyaluronan and its fragments have been developed and continue to improve. This review provides an overview of the methods and our current state of knowledge of hyaluronan content and size distribution in biological fluids and tissues.

Keywords: assay; hyaluronan; molecular mass; molecular weight; quantification.

Figure 1

Example molecular mass distributions of human synovial fluid (SF) HA determined by agarose gel electrophoresis. From top to bottom: (A) normal human SF obtained from young healthy volunteers. (B–D) Representative osteoarthritis (OA) patient SF. The dashed vertical line corresponds to the migration position of 4000 kDa HA. The fraction of HA having slower electrophoretic migration, and thus higher M than 4000 kDa, is a measure of the high M HA content. In normal human SF, the portion of HA with M > 4000 kDa averaged 61%. OA patients varied in the extent of HA degradation. The OA-HIGH profile, similar to that seen in normal SF and representative of OA samples with more than 60% of HA having M > 4000 kDa, was found for 26% of patients. The OA-MEDIUM profile, representative of OA samples with approximately 41–60% of HA having M > 4000 kDa, was found for 41% of patients. The OA-LOW profile, representative of OA samples with <40% of HA having M > 4000 kDa, was found for 33% of patients. From Lee (90).