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Understanding bladder regeneration: smooth muscle ontogeny
1Department of Urology, University of California-San Francisco, USA.
Purpose:
We determined the origin of smooth muscle cells in acellular bladder matrix grafts.
Materials And Methods:
A total of 15 female Sprague-Dawley rats underwent partial cystectomy and grafting with an acellular matrix derived from rat bladder. The grafts were examined 1, 2, 3 and 4 weeks after grafting by immunohistochemical studies for smooth muscle markers and by transmission electron microscopy for smooth muscle morphology. Bladder matrix and bladder epithelium recombinants were created and grafted subcutaneously and under the renal capsule in nude mice. Recombinants were examined 1, 2, 3 and 4 weeks postoperatively by immunohistochemical studies for bladder epithelium and bladder smooth muscle.
Results:
Smooth muscle ingrowth into acellular matrix was initially seen at 2 weeks. The immunohistochemical and electron microscopic characteristics of the cells were similar to those of fetal smooth muscle 2 weeks and newborn smooth muscle 4 weeks after grafting. Matrix epithelium recombinants displayed mature bladder epithelium with 3 to 7 layers but they did not support the ingrowth of smooth muscle cells.
Conclusions:
Mature bladder smooth muscle cells undergo dedifferentiation, migration and redifferentiation to repopulate an acellular matrix graft. It is unlikely that adult fibroblasts from the surrounding tissue are induced by epithelium and matrix to form smooth muscle. The contractile behavior of bladder substitute materials likely reflects the properties of the host bladder.