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Updated: Apr 6, 2026
Unilateral Ureteral Obstruction Model for Investigating Kidney Interstitial Fibrosis
Published on: April 25, 2025
The Smad3/Smad4/CDK9 complex promotes renal fibrosis in mice with unilateral ureteral obstruction
Xinli Qu1, Mengjie Jiang2, Yu Bo Yang Sun1
1Department of Anatomy and Developmental Biology, School of Biomedical Sciences, Monash University, Clayton, Victoria, Australia.
Abstract:
Transforming growth factor-β1 (TGF-β1)/Smad signaling has a central role in the pathogenesis of renal fibrosis. Smad3 and Smad4 are pro-fibrotic, while Smad2 is anti-fibrotic. However, these Smads form heterogeneous complexes, the functions of which are poorly understood. Here we studied Smad complex function in renal fibrosis using the mouse model of unilateral ureteric obstruction. Mice heterozygous for Smad3/4 (Smad3/4+/-) exhibited substantial protection from renal fibrosis through day 7 of obstruction, whereas Smad2/3+/- and Smad2/4+/- mice showed only modest protection. Formation of Smad3/Smad4/CDK9 complexes was an early event following obstruction in wild-type mice, which involved nuclear phosphorylation of the linker regions of Smad3. Significantly, Smad3 or Smad4 deficiency decreased the formation of Smad4/CDK9 or Smad3/CDK9 complex, Smad3 linker phosphorylation, and fibrosis but at different degrees. In vitro, TGF-β1 stimulation of collagen I promoter activity involved formation of Smad3/Smad4/CDK9 complexes, and overexpression of each component gave additive increases in collagen promoter activity. Co-administration of a CDK9 inhibitor and Smad3-specific inhibition achieved better protection from TGF-β1-induced fibrotic response in vitro and renal interstitial fibrosis in vivo. Thus formation of Smad3/Smad4/CDK9 complex drives renal fibrosis during ureteral obstruction. Formation of this complex represents a novel target for antifibrotic therapies.
Insights
The Smad3/Smad4/CDK9 complex drives renal fibrosis by promoting transforming growth factor-β1 (TGF-β1) signaling. Inhibiting this complex offers a promising new therapeutic target for kidney fibrosis.
Area of Science:
- Nephrology
- Molecular Biology
- Cell Signaling
Background:
- Renal fibrosis pathogenesis involves transforming growth factor-β1 (TGF-β1)/Smad signaling.
- Smad proteins (Smad2, Smad3, Smad4) have complex roles, with Smad3 and Smad4 being pro-fibrotic and Smad2 anti-fibrotic.
- The function of heterogeneous Smad complexes in renal fibrosis remains poorly understood.
Purpose of the Study:
- To investigate the role of Smad complex formation in renal fibrosis.
- To identify specific Smad complexes involved in the pathogenesis of kidney fibrosis.
- To explore the potential of targeting Smad complexes for antifibrotic therapies.
Main Methods:
- Utilized a mouse model of unilateral ureteric obstruction to study renal fibrosis.
- Analyzed Smad complex formation, including Smad3/Smad4/CDK9 complexes, and Smad3 linker phosphorylation.
- Employed in vitro cell culture and in vivo experiments with inhibitors targeting CDK9 and Smad3.
Main Results:
- Mice with Smad3/4 deficiency showed significant protection against renal fibrosis.
- Formation of Smad3/Smad4/CDK9 complexes was an early event in obstruction-induced fibrosis, involving Smad3 linker phosphorylation.
- Inhibition of CDK9 and Smad3 synergistically reduced TGF-β1-induced fibrotic responses in vitro and in vivo.
Conclusions:
- The formation of Smad3/Smad4/CDK9 complexes is a key driver of renal interstitial fibrosis during ureteral obstruction.
- Targeting the Smad3/Smad4/CDK9 complex represents a novel therapeutic strategy for treating kidney fibrosis.
