Hyaluronan (also called hyaluronic acid or hyaluronate) is a non-sulfated glycosaminoglycan
distributed widely throughout connective, epithelial, and neural tissues.
It is one of the chief components of the extracellular matrix, contributes
significantly to cell proliferation and migration, and may also be involved in
the progression of some malignant tumors. The average 70-kg man has roughly 15
grams of hyaluronan in his body, one-third of which is turned over (degraded
and synthesised) every day.
Until the late 1970s, hyaluronan was described
as a "goo" molecule, a ubiquitous carbohydrate polymer that is part of the
extracellular matrix. For example, hyaluronan is a major component of the synovial
fluid and was found to increase the viscosity of the fluid. Along with lubricin,
it is one of the fluid's main lubricating components.
Hyaluronan
is an important component of articular cartilage, where it is present as
a coat around each cell (chondrocyte). When aggrecan monomers bind to hyaluronan
in the presence of link protein, large highly negatively-charged aggregates form.
These aggregates imbibe water and are responsible for the resilience of cartilage
(its resistance to compression). The molecular weight (size) of hyaluronan
in cartilage decreases with age, but the amount increases.
Hyaluronan
is also a major component of skin, where it is involved in tissue repair.
When skin is excessively exposed to UVB rays, it becomes inflamed (sunburn) and
the cells in the dermis stop producing as much hyaluronan, and increase the rate
of its degradation. Hyaluronan degradation products also accumulate in the
skin after UV exposure.[3]
While it is abundant in extracellular matrices,
hyaluronan also contributes to tissue hydrodynamics, movement and proliferation
of cells, and participates in a number of cell surface receptor interactions,
notably those including its primary receptor, CD44. Upregulation of CD44 itself
is widely accepted as a marker of cell activation in lymphocytes. Hyaluronan's
contribution to tumor growth may be due to its interaction with CD44. Receptor
CD44 participates in cell adhesion interactions required by tumor cells. |
