Fibroblast-Specific TGF-β Signaling Mediates Cardiac Dysfunction, Fibrosis, and Hypertrophy in Obese Diabetic Mice
New Mechanism of Diabetic Cardiomyopathy: The Role of Fibroblast-Specific TGF-β/Smad3 Signaling Pathway
Research Background
Diabetes is a significant risk factor for cardiovascular diseases and heart failure (HF) globally. Diabetic patients not only face risks of macrovascular complications such as hypertension and atherosclerosis but are also prone to developing a unique myocardial condition known as diabetic cardiomyopathy (DCM). The main features of DCM include myocardial interstitial and perivascular fibrosis, which may lead to diastolic dysfunction and subsequently increase the incidence of heart failure. Although the clinical significance of DCM has been widely recognized, its molecular mechanisms remain unclear.
Transforming growth factor-beta (TGF-β) is a key fibrogenic mediator that promotes collagen synthesis and extracellular matrix (ECM) deposition by activating fibroblasts. The TGF-β signaling pathway is significantly activated in various tissues of diabetic patients, including the heart, kidneys, and liver. However, whether the TGF-β signaling pathway mediates fibrosis and dysfunction in DCM through fibroblast-specific mechanisms has not been thoroughly investigated.
Research Source
This study was conducted by a team from Albert Einstein College of Medicine, including Izabela Tuleta, Anis Hanna, Claudio Humeres, and others, and was published in Cardiovascular Research in 2024. The research was funded by the National Institutes of Health (NIH) and the U.S. Department of Defense.
Research Process and Results
1. Construction and Treatment of Animal Models
The research team constructed two mouse models: one with fibroblast-specific knockout of the TGF-β receptor 2 (TBR2) and the other with fibroblast-specific knockout of Smad3. These mice were in lean and obese diabetic (db/db) backgrounds. By injecting tamoxifen to induce gene knockout, the researchers evaluated heart function, fibrosis, and myocardial hypertrophy in these mice at 6 months of age.
2. Assessment of Heart Function
Two-dimensional echocardiography (2D echocardiography) and speckle-tracking echocardiography were used to assess heart function in the mice. The results showed that db/db mice exhibited significant systolic and diastolic dysfunction. Fibroblast-specific knockout of TBR2 or Smad3 significantly improved heart function in db/db mice, as evidenced by the recovery of systolic and diastolic function. In lean mice, knockout of TBR2 or Smad3 led to a slight deterioration in heart function, indicating that the TGF-β signaling pathway plays a role in maintaining normal heart function.
3. Assessment of Fibrosis and Myocardial Hypertrophy
Through histological analysis, the researchers found that myocardial interstitial fibrosis and hypertrophy were significantly increased in db/db mice. Fibroblast-specific knockout of TBR2 or Smad3 significantly reduced fibrosis and hypertrophy in db/db mice. These results suggest that the TGF-β signaling pathway mediates fibrosis and hypertrophy in DCM by activating fibroblasts.
4. Transcriptomic Analysis
The researchers performed RNA sequencing (RNA-seq) on fibroblasts from db/db and lean mice and found that genes related to oxidative stress, ECM organization, and cholesterol metabolism were significantly upregulated in db/db fibroblasts. In particular, thbs4 (encoding thrombospondin-4, TSP-4) was significantly upregulated in db/db fibroblasts and significantly downregulated after Smad3 knockout. However, in vitro experiments showed that stimulation or overexpression of TSP-4 did not significantly activate the fibrogenic phenotype of fibroblasts, suggesting that TSP-4 may be a marker of fibroblast activation rather than a direct driver.
5. Signaling Pathway Analysis
Using Ingenuity Pathway Analysis (IPA), the researchers found that the TGF-β, p53, MYC, PDGF-BB, EGFR, and Wnt3a/β-catenin signaling pathways were significantly activated in db/db fibroblasts. These signaling pathways may be key regulators of fibroblast activation in DCM.
Conclusions and Significance
This study is the first to reveal the central role of fibroblast-specific TGF-β/Smad3 signaling in DCM. By activating the TGF-β/Smad3 signaling pathway, fibroblasts in diabetic hearts promote fibrosis and hypertrophy, leading to cardiac dysfunction. The study also found that TSP-4 is a marker of fibroblast activation, but its direct role in fibrosis is limited. These findings provide new therapeutic targets for DCM, suggesting that the TGF-β signaling pathway may be a potential target for treating diabetes-associated heart failure.
Research Highlights
- First to reveal the role of fibroblast-specific TGF-β signaling in DCM: The study directly demonstrated the key role of the TGF-β signaling pathway in fibroblasts using gene knockout models.
- Multilayered experimental design: Combining in vivo animal models, in vitro cell experiments, and transcriptomic analysis, the study comprehensively revealed the molecular mechanisms of DCM.
- TSP-4 as a marker of fibroblast activation: Although TSP-4 has a limited direct role in fibrosis, its role as a marker of fibroblast activation provides a new direction for future research.
Application Value
The findings of this study provide new insights for the treatment of DCM. Targeting the TGF-β/Smad3 signaling pathway may effectively alleviate fibrosis and dysfunction in diabetic hearts. Additionally, TSP-4, as a marker of fibroblast activation, may be used for diagnosing and monitoring the progression of DCM.
Other Valuable Information
The study also pointed out that the TGF-β signaling pathway plays a role in maintaining normal heart function, so precise regulation of TGF-β signaling activity is necessary in treatment to avoid deterioration of heart function due to excessive inhibition. This finding suggests that future treatment strategies may need to be individualized, tailored to the specific conditions of different patients.
This study provides important clues for understanding the molecular mechanisms of DCM and lays the foundation for developing new treatment methods.