The microenvironment of freeze-injured mouse urinary bladders enables successful tissue engineering.

Mouse bone marrow-derived cells implanted into freeze-injured bladder walls form smooth muscle layers, but not in intact walls. We determined if the microenvironment within injured urinary bladders was supportive of smooth muscle layer development. The urinary bladders of female nude mice were freeze-injured for 30 s. Three days later, the rate of blood flow in the wounded areas and in comparable areas of intact control urinary bladders was observed by charge-coupled device (CCD) video microscopy. Injured and control bladder walls were also analyzed histologically and cytologically. Growth factor mRNA expression was determined by real-time reverse transcription polymerase chain reaction arrays. The injured regions maintained a partial microcirculation in which blood flow velocity was significantly less than in controls. The injured bladder walls had few typical smooth muscle layers, and blood vessels in the walls had reduced smooth muscle content. The loss of smooth muscle cells in the bladder walls may have resulted in the formation of large porous spaces seen by scanning electron microscopy of the injured areas. The expression of nineteen growth-related mRNAs, including secreted phosphoprotein 1, inhibin beta-A, glial cell line-derived neurotrophic factor, and transforming growth factor beta1, were significantly upregulated in the injured urinary bladders. In conclusion, the microenvironment in freeze-injured urinary bladders enables successful tissue engineering.