Transforming growth factor-β1 mediates migration in cultured human control and exstrophy bladder smooth muscle cells

Transforming growth factor-β1 regulates extracellular matrix composition, and impacts function and proliferation in multiple cell types, including bladder smooth muscle cells. In this study we evaluated the response to transforming growth factor-β1 in cultured exstrophy and control bladder smooth muscle cells.

Primary bladder smooth muscle cell cultures were established from patients with bladder exstrophy or vesicoureteral reflux. Smooth muscle specific α-actin and heavy chain myosin expression was determined using immunohistochemistry. Cell migration, intracellular calcium concentration and proliferation were determined after incubation for 24 to 48 hours in basal media, with or without transforming growth factor-β1 (0.001 to 3 nM) or transforming growth factor-β1 receptor inhibitor SB 431542 (10 μM).

Cultured exstrophy and control smooth muscle cells stained positive for α-actin and heavy chain myosin. Exstrophy smooth muscle cells demonstrated increased migration compared to control smooth muscle cells at baseline (38% vs 20%, p = 0.01). Transforming growth factor-β1 increased control smooth muscle cell migration while SB 431542 decreased exstrophy smooth muscle cell migration. Control cells had a higher intracellular calcium concentration, which decreased significantly when exposed to SB 431542. Transforming growth factor-β1 did not cause significant changes in intracellular calcium concentration. Inhibition of transforming growth factor-β1 receptors decreased proliferation in exstrophy and control smooth muscle cells, but exogenous transforming growth factor-β1 did not impact proliferation.

Our results suggest that there are distinct differences in bladder smooth muscle cell function between control and exstrophy cases which persist in culture. Although resting intracellular calcium concentration was higher in control cells, proliferation rates were similar in both cell types, indicating that lower intracellular calcium concentration did not impact growth potential. In contrast, enhanced migration was observed in exstrophy cells, possibly due to excess transforming growth factor-β1 signaling, but seemingly independent of increases in intracellular calcium concentration.