Effects of SMAD7 Overexpression on Peritoneal Inflammation in a Rat Peritoneal Dialysis Model

Abstract

Objective

Transforming growth factor-beta (TGF-β) has been shown to play a role in peritoneal complications due to long-term peritoneal dialysis (PD). In this study, we examined the effects of the TGF-β signaling pathway on peritoneal inflammation associated with PD in rats by over-expressing Smad7, an inhibitor of TGF-β/Smad signaling.

Methods

Peritoneal inflammation was induced in male Sprague-Dawley rats by intraperitoneal injections of 4.25% glucose dialysate (100 mg/kg body weight) daily for 4 weeks, with the addition of lipopolysaccharides (0.6 mg/kg body weight) on days 8, 10, 12, 22, 24, and 26. Peritoneal Smad7 gene transfer was achieved using an ultrasound microbubble mediated, doxycycline regulated, Smad7-expressing plasmid on day 0 and day 14 after initiation of PD. An empty vector was used as control. All rats were sacrificed after 4 weeks of PD. Peritoneal inflammatory response, including infiltration of total leukocytes (OX-1 positive) and macrophages (ED-1 positive) and expression of interleukin (IL)-1β) and tumor necrosis factor-alpha (TNF-α), was examined by immunofluorescence and RT-PCR.

Results

After PD, peritoneal inflammation developed in control animals, as demonstrated by an increase in the number of OX-1-positive and ED-1-positive cells and upregulation of IL-1β and TNF-α mRNA and protein expression. In contrast, in animals treated with Smad7 gene transfer, IL-1β and TNF-α expression and OX-1-positive and ED-1-positive cell infiltration were significantly inhibited. Furthermore, prevention of peritoneal inflammation by overexpression of Smad7 was associated with inhibition of phosphorylation of Smad2/3, a downstream of the TGF-β signaling pathway, as well as TGF-β1 expression.

Conclusion

Overexpression of Smad7 suppresses peritoneal inflammation induced by high glucose and lipopolysaccharides. The ability of Smad7 gene transfer to inhibit peritoneal inflammation indicates that targeting TGF-β/Smad signaling may represent a new therapeutic strategy for the treatment of peritoneal complications associated with PD.