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The hyaluronic acid receptor RHAMM is induced by stretch injury of rat bladder in vivo and influences smooth muscle cell contraction in vitro [corrected].

PURPOSE
Loss of bladder compliance from hypercontractility and fibrosis may represent an injury response to excessive intravesical pressure. Together, interactions between cell and extracellular matrix components regulate cell response to injury and extracellular matrix remodeling. The receptor for hyaluronic acid mediated motility (RHAMM) is a recently described hyaluronic acid binding protein known to influence multiple types of cell extracellular matrix interaction in development, injury and cancer. We evaluate the role of RHAMM in mediating early events in bladder stretch injury.


MATERIALS AND METHODS
An acute stretch injury model was used. The rat bladder was injured by hydrodistention inducing gross hematuria. Tissues were analyzed for temporal and spatial expression of RHAMM in the mucosa and detrusor regions by immunostaining, western and reverse transcriptase polymerase chain reaction analyses. The contractile activity of smooth muscle cell primary cultures was analyzed using a gel contraction assay in the presence of peptide fragments known to block RHAMM function.


RESULTS
Acute hydrodistention caused immediate and significant injury to the bladder, with fracturing of smooth muscle cell bundles, edema and hemorrhage. RHAMM immunolocalized to the mucosa and detrusor within 2 hours of injury, peaking by 5 to 10 hours. A shift from low molecular weight (55 kD.) to high (120 kD.) receptor isoforms was prominent during the peak expression period noted by immunolocalization. RHAMM messenger ribonucleic acid increased only slightly (40%) by 5 hours after injury. Smooth muscle cell primary cultures actively initiated and maintained the contraction of collagen gels by more than 75% of baseline in vitro. Blocking RHAMM function significantly inhibited the ability to less than 25% of smooth muscle cells to contract the gels in vitro.


CONCLUSIONS
Increased expression of RHAMM is an early event precipitated by stretch injury to the bladder. Since extracellular matrix hyaluronic acid is found early in tissue repair responses, its receptor RHAMM may be mediating initial bladder responses to stretch injury, some of which (contraction) may be experimentally blocked in vitro. Since the receptor directly regulates protein kinase signaling which in turn mediates smooth muscle cell contraction and collagen synthesis, further studies of RHAMM function in bladder pathology are warranted.