TGF-beta is a key mediator in renal
fibrosis. Kidney-targeted gene therapy with anti-
TGF-beta strategies is expected to have therapeutic potential, but this has been hampered by concerns over the safety and practicability of viral vectors and the inefficiency of nonviral transfection techniques. The present study explored the potential role of
TGF-beta/Smad signaling in renal
fibrosis in vivo and developed a safe and effective gene therapy to specifically block
TGF-beta signaling and renal
fibrosis in a rat unilateral
ureteral obstruction (UUO) model by transferring a
doxycycline-regulated Smad7 gene or control empty vectors using an ultrasound-
microbubble (
Optison)-mediated system. The Smad7 transgene expression was tightly controlled by addition of
doxycycline in the daily
drinking water. Groups of six rats were sacrificed at day 7, and the transfection rate, Smad7 transgene expression, and tubulointerstitial
fibrosis including alpha-smooth muscle actin and
collagen matrix
mRNA and
protein expression were determined. Compared with the non-ultrasound treatment, the combination of ultrasound with
Optison largely increased the transfection rate of
FITC-ODN and Smad7 transgene expression up to a 1000-fold, and this was found in all kidney tissues. Compared with normal rats, Smad7 expression within the UUO kidney was significantly reduced, and this was associated with up to a sixfold increase in Smad2 and Smad3 activation and severe tubulointerstitial
fibrosis. In contrast, treatment with inducible Smad7 resulted in a fivefold increase in Smad7 expression with complete inhibition of Smad2 and Smad3 activation and tubulointerstitial
fibrosis in terms of tubulointerstitial myofibroblast accumulation (85% downward arrow ) and
collagen I and III
mRNA and
protein expression (60 to 70% downward arrow ). In conclusion, the ultrasound-mediated inducible Smad7 gene transfer is a safe, effective, and controllable gene therapy.
TGF-beta-mediated renal
fibrosis is regulated positively by Smad2/3, but negatively by Smad7. Target blockade of
TGF-beta/Smad signaling by expression of Smad7 may provide a new therapeutic potential for renal
fibrosis.