Mesenchymal cells infiltrating a bladder acellular matrix gradually lose smooth muscle characteristics in intraperitoneally regenerated urothelial lining tissue in rats.
OBJECTIVE
To characterize serial long-term histological changes in mesenchymal cells infiltrating a collagen-based matrix, as in a hollow organ with differentiated urothelial lining created intraperitoneally by grafting cultured urothelial cells, mesenchymal cells with smooth-muscle immunohistochemical characteristics infiltrated into the scaffold, despite no mesenchymal cells being seeded into the scaffold before grafting.


METHODS
To regenerate a urothelial lining tissue intraperitoneally, rat urothelial cells were cultured and seeded with the feeder-layer technique onto bladder acellular matrix (BAM). After 7 days of cultivation to attach urothelial cells on the BAM, the matrix was folded with the urothelial cells inside and grafted onto the mesentery of the previously partially cystectomized rat.


RESULTS
The grafted urothelial cells on the BAM, which formed a monolayer before grafting, stratified into three to four layers as early as 4 days after grafting. Although the regenerated urothelium became thinner with time, there was urothelial stratification and a peculiar angular appearance on the apical surface of the regenerated urothelium even after 56 days. The mesenchymal cells infiltrating the BAM showed positive immunohistochemical staining to alpha-smooth muscle actin or desmin at 7 days. Subsequently, the number of actin- or desmin-positive cells gradually decreased with time. On transmission electron microscopy, the infiltrating mesenchymal cells were characterized as myofibroblasts at 7 days. Smooth muscle-like cells were identified at 14 and 28 days, and fibrocytes were the main population at 56 days.


CONCLUSIONS
Although epithelial-mesenchymal interactions have been assumed to be one of the most critical factors in smooth-muscle development, mesenchymal cells infiltrating the scaffold in this intraperitoneal regeneration model gradually lost smooth muscle characteristics with time. These results suggest that interactions between cultured urothelial cells and infiltrating mesenchymal cells alone could not maintain the smooth muscle character of infiltrating mesenchymal cells.
Moriya
Kimihiko
K
Department of Urology, Hokkaido University Graduate School of Medicine, Sapporo, Japan. k-moriya@med.hokudai.ac.jp
Kakizaki
Hidehiro
H
Watanabe
Satoshi
S
Sano
Hiroshi
H
Nonomura
Katsuya
K
D000818:Animals; D005260:Female; D009130:Muscle, Smooth / Q000166:cytology*; D051381:Rats; D017208:Rats, Wistar; D001743:Urinary Bladder / Q000166:cytology*; D019459:Urothelium / Q000166:cytology