levels on the plasma membrane play a key role in regulating the CD44 binding capacity to HA by sequestering this receptor
within specialized membrane domains called lipid rafts.62 Finally, interactions between HA and CD44 are also partially responsible
for the anti-allergic effects linked to HA.63
EPIDERMAL AND DERMAL HYALURONIC ACID IN GOOD AND BAD TIMES
Highest HA concentrations are detected in developing skin.64,65 Adult skin HA accounts for approximately 50% of the total body HA. Most of the cutaneous HA is localized in the dermis reaching
concentrations of 0.5 mg/kg, while epidermal HA has been estimated to be around 0.1 mg/kg. Dermal HA plays a critical role in skin hydration by sequestering water as well as maintaining water balance with the aqueous component of the internal milieu (water associated with HA comprises a separate non-circulating aqueous compartment within the skin). Changes in HA amounts, level of fragmentation, and organization, as well as decreased expression of CD44, have been reported in both intrinsic and extrinsic aging. Disruptions of HA-homeostasis is linked to loss of skin moisture as well as impaired age-related wound healing and the delayed resolution of a variety of skin diseases.66-68 In addition, non-fragmented HA fails to organize into normal structures
such as the pericellular coats in photoaged skin.69
