Altered cytoskeletal structure of smooth muscle cells in ureteropelvic junction obstruction.

Purpose: Ureteropelvic junction obstruction is one of the most common causes of hydronephrosis in children. A malfunction of smooth muscle cells is believed to be the underlying mechanism causing obstruction. We investigated the expression of some integrins, talin and -dystroglycan, considered the main compound of smooth muscle cell cytoskeleton, and active caspase 3 at the level of the ureteropelvic junction obstruction. Materials and Methods: Specimens were obtained at pyeloplasty in 12 children with ureteropelvic junction obstruction. Six control specimens were obtained during organ explantation. Specimens were divided into renal pelvis, ureteropelvic junction and ureter below the obstruction. Western blot analysis of active caspase 3, and immunofluorescence and polymerase chain reaction analysis were performed for 7A, 1A, 7B and 1D integrins, talin and -dystroglycan. Results: Talin and -dystroglycan were slightly impaired in ureteropelvic junction obstruction, while 7B and 1D integrins were severely reduced, and 7A, 1A and active caspase 3 were significantly enhanced compared to controls. Conclusions: We demonstrated activation of apoptosis and a critical alteration of cytoskeleton that might explain the altered function and the increased apoptosis in smooth muscle cells in ureteropelvic junction obstruction. The delayed rearrangement of the cytoskeleton of smooth muscle cells in ureteropelvic junction obstruction might be linked to a postnatal splicing from 7A and 1A to 7B and 1D integrins, respectively. This relationship could explain the common clinical scenario of spontaneous improvement of hydronephrosis in children with suspected ureteropelvic junction obstruction.