Hyaluronan and Renal Fluid Handling : Studies during Normal and Pathological Conditions of Renal Function

The kidney is the major organ responsible for the regulation of the composition and volume of the body fluids, which is essential for homeostasis. The glycosaminoglycan hyaluronan (HA), with extreme water-binding capacity, is present in the interstitium of the kidney with a heterogenous distribution. The importance of HA in renal water-handling is unknown and was the focus of the present investigation. Acute water-loading in rats caused the amount of papillary HA to increase and during water deprivation, the amount was reduced. Gerbils, with extreme urine concentrating capacity, have less HA in the renal papilla in normal conditions and responded diametrically different to water-loading (reduction in HA). Renomedullary interstitial cells (RMICs), which are probably the main producers of HA in the renal medulla, were cultured at different media osmolalities to mimic the milieu of the medulla during variations in the water balance. The amount of HA found in the media was decreased at high osmolalities and increased at low osmolalities, thereby strengthening the in vivo results. CD44, an HA-receptor involved in the uptake and degradation of HA, was expressed on RMICs in an osmolality dependent manner. During high media osmolality, the CD44 expression increased and at lower osmolalities, the opposite occurred, probably due to the need for uptake and degradation of HA. Renal ischemia-reperfusion injury causes a cortical accumulation of HA, up-regulation of CD44, and a depression of functional parameters. The time periods of ischemia correlated with the accumulation of HA which, in turn, was inversely correlated to GFR. Hyaluronidase injections in this setting failed to reduce HA levels and significantly improve renal function. In conclusion, the results from the present study suggest an important role for HA and RMICs in renal water-handling and that the intrarenal distribution of HA is altered after ischemia-reperfusion injury, which correlates with renal dysfunction