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Updated: Feb 24, 2026
Comparative Proteomic Analysis of Whole Kidney, Medulla, and Cortical Tubules in Diabetic Pathogenesis of Kidney Injury in Mice
Published on: May 2, 2025
Disparate phospho-Smad2 levels in advanced type 2 diabetes patients with diabetic nephropathy and early experimental
Lise Høj Thomsen1,2, Morten Fog-Tonnesen1, Lisbeth Nielsen Fink1
1a Department of Diabetes Complications Research , Novo Nordisk A/S , Måløv , Denmark.
Abstract:
Uncontrolled activation of transforming growth factor beta (TGF-β) family members is hypothesized to participate in type 2 diabetes (T2D) dependent diabetic nephropathy (DN). We evaluated and compared downstream activation of the Smad2-signaling pathway in kidney samples from T2D patients to kidneys from the T2D model of leptin receptor deficient db/db mouse. Furthermore, expression of TGF-β family members was evaluated to elucidate molecular mechanisms in the mouse model. Kidney samples from patients with advanced stages of DN showed elevated pSmad2 staining whereas db/db mouse kidneys surprisingly showed a decrease in pSmad2 in the tubular compartment. Structurally, kidney tissue showed dilated tubules and expanded glomeruli, but no clear fibrotic pattern was found in the diabetic mice. Selective TGF-β family members were up-regulated at the mRNA level. Antagonists of bone morphogenetic protein (BMP) ligands, such as Gremlin1, USAG1 and Sclerostin, were strongly up-regulated suggesting a dampening effect on BMP pathways. Together, these results indicate a lack of translation from T2D patient kidneys to the db/db model with regards to Smad signaling pathway. It is plausible that a strong up-regulation of BMP antagonizing factors account for the lack of Smad1/5/8 activation, in spite of increased expression of several BMP members.
Insights
Diabetic nephropathy (DN) involves transforming growth factor beta (TGF-β) signaling. This study found Smad2 pathway activation differs between human DN and db/db mouse models, with BMP antagonists potentially explaining discrepancies.
Area of Science:
- Nephrology
- Endocrinology
- Molecular Biology
Background:
- Transforming growth factor beta (TGF-β) signaling is implicated in type 2 diabetes (T2D) and diabetic nephropathy (DN).
- Understanding TGF-β pathway activation is crucial for developing effective DN treatments.
Purpose of the Study:
- To compare Smad2 signaling pathway activation in human DN kidney samples with the db/db mouse model.
- To investigate the expression of TGF-β family members in the db/db mouse model to elucidate molecular mechanisms of DN.
Main Methods:
- Immunohistochemical analysis of pSmad2 staining in human DN and db/db mouse kidney tissues.
- Quantitative mRNA expression analysis of TGF-β family members and BMP antagonists in db/db mouse kidneys.
- Histological examination of kidney tissue structure in db/db mice.
Main Results:
- Human DN kidneys showed elevated pSmad2, while db/db mouse kidneys exhibited decreased tubular pSmad2.
- db/db mouse kidneys displayed structural changes like dilated tubules and expanded glomeruli, but no significant fibrosis.
- Several TGF-β family members were upregulated, alongside strong upregulation of BMP antagonists (Gremlin1, USAG1, Sclerostin).
Conclusions:
- The db/db mouse model does not accurately recapitulate Smad2 signaling pathway activation seen in human T2D-dependent DN.
- Upregulation of bone morphogenetic protein (BMP) antagonists in db/db mice may inhibit BMP signaling, explaining the observed lack of Smad1/5/8 activation despite increased BMP member expression.
