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Differential effects of Smad3 targeting in a murine model of chronic kidney disease
Terese Kellenberger1, Søren Krag1, Carl Christian Danielsen2
1Research Laboratory for Biochemical Pathology, Aarhus University Hospital, Institute of Clinical Medicine, University of Aarhus, Aarhus, Denmark.
Abstract:
Transforming growth factor (TGF)-β1 has a pivotal role in the pathogenesis of progressive kidney diseases that are characterized by fibrosis. The main intracellular signaling pathway of TGF-β1 is the Smad system, where Smad2 and Smad3 play a central role in transcriptional regulation of target genes involved in extracellular matrix (ECM) metabolism. This study analyzes the hypothesis that blockade of Smad3 attenuates the development of TGF-β1-driven renal fibrosis. This was examined in vivo in a transgenic model of TGF-β1-induced chronic kidney disease with Smad3 or without Smad3 expression and in vitro in mesangial cells and glomerular endothelial cells with Smad2/3 inhibitors or Smad3-knockdown. Electron microscopy was used for evaluation of morphological changes, real-time polymerase chain reaction for detection of RNA expression, and immunohistochemistry for localization of ECM components. Matrix metalloproteinase (MMP) level was assessed by gelatin zymography electrophoresis and located by in situ zymography. The results show TGF-β1-induced mesangial matrix expansion, tubulointerstitial fibrosis, and tubular basement membrane thickening that are attenuated by Smad3 deletion, whereas TGF-β1-induced glomerular basement membrane thickening is not shown. The amount and distribution profile of MMP-2 may suggest a role of the enzyme herein. We conclude that Smad3 targeting is not exclusively beneficial as Smad3 has diverse transcriptional regulatory effects in different cell types in the kidney.
Insights
Blocking Smad3 partially reduces kidney fibrosis caused by transforming growth factor (TGF)-β1. However, Smad3 has varied roles in different kidney cells, indicating complex effects in treating kidney disease.
Area of Science:
- Nephrology
- Molecular Biology
- Cell Biology
Background:
- Transforming growth factor (TGF)-β1 drives progressive kidney diseases and fibrosis.
- The Smad intracellular signaling pathway, particularly Smad2 and Smad3, regulates extracellular matrix (ECM) metabolism.
- Smad3's role in TGF-β1-induced renal fibrosis requires further investigation.
Purpose of the Study:
- To test if blocking Smad3 attenuates TGF-β1-driven renal fibrosis.
- To analyze the in vivo and in vitro effects of Smad3 deletion or inhibition on kidney fibrosis.
Main Methods:
- In vivo studies using a transgenic model of TGF-β1-induced chronic kidney disease with and without Smad3.
- In vitro studies using mesangial and glomerular endothelial cells with Smad2/3 inhibitors or Smad3 knockdown.
- Morphological analysis via electron microscopy, gene expression via real-time PCR, ECM localization via immunohistochemistry, and matrix metalloproteinase (MMP) assessment.
Main Results:
- Smad3 deletion attenuated TGF-β1-induced mesangial matrix expansion, tubulointerstitial fibrosis, and tubular basement membrane thickening.
- TGF-β1-induced glomerular basement membrane thickening was not affected by Smad3 deletion.
- MMP-2 levels and distribution suggested a potential role in the observed fibrotic changes.
Conclusions:
- Smad3 deletion partially ameliorates TGF-β1-induced renal fibrosis, particularly affecting mesangial matrix and tubulointerstitial tissue.
- Smad3's role in TGF-β1-induced glomerular basement membrane thickening is limited.
- Targeting Smad3 may not be exclusively beneficial due to its diverse regulatory effects across different kidney cell types.
