Preventing Diabetic Cardiomyopathy through Suppressing TGR5-Mediated Fatty Acid Uptake

Background and Problem Statement

Diabetic Cardiomyopathy (DBCM) is a severe complication frequently faced by diabetic patients, characterized by lipid accumulation in the myocardium and cardiac dysfunction. Bile acid metabolism plays a crucial role in cardiovascular and metabolic diseases. Among them, TGR5 (Takeda G protein-coupled receptor 5), a major bile acid receptor, has been shown to be associated with metabolic regulation and myocardial protection. However, the specific role of the bile acid-TGR5 pathway in maintaining cardiac metabolic balance remains unclear.

Research Source

This article is a collaborative work by multiple research institutions, including Peking University. This research was completed on June 23, 2023, and accepted for publication in Nature Metabolism on March 26, 2024.

Research Methods

Experimental Procedures

The study used cardiomyocyte-specific TGR5 knockout mice (TGR5fl/fl, TGR5δcm) to explore the role of TGR5 in cardiac lipid metabolism by inducing cardiotoxicity through a diabetic model:

1. Diabetic Model Establishment:

   • High-fat diet (HFD) combined with streptozotocin (STZ) treatment was used for TGR5fl/fl and TGR5δcm mice, which were fed for 24 weeks.
   • A genetic model of T2DM, db/db TGR5δcm mice, was established by crossbreeding db/+ mice with αMHC-GPbar1fl/fl mice.

2. Cardiac Function Assessment:

   • Echocardiography was used to evaluate cardiac contractility and diastolic function, with measurements and comparisons of parameters such as GLS, EF, and FS.

3. Histological and Molecular Biology Detection:

   • Oil Red O staining and Bodipy ⁴⁹³⁄₅₀₃ staining were used to assess lipid accumulation, and Masson’s trichrome staining was used to evaluate myocardial fibrosis.
   • Levels of markers such as ANP, BNP, and β-MHC were detected.

4. Lipid Metabolism Analysis:

   • Transmission electron microscopy was used to observe the number and size of lipid droplets.
   • Lipidomic analysis was performed to compare differences in lipid species and content between TGR5 knockout and non-knockout mice.

5. Relationship between TGR5 and CD36:

   • Immunoprecipitation (IP) and Western blot experiments were used to verify the palmitoylation relationship between TGR5 and CD36 and its effect on fatty acid uptake.

6. Drug Intervention and Functional Validation:

   • The effects of TGR5 agonist INT-777 or bile acids DCA and TCA on cardiac function and lipid metabolism were observed.

Subject Processing

• Cardiomyocyte-specific TGR5 Knockout Mice: All groups of mice were fed a high-fat diet and induced with diabetes by STZ injection.
• Drug Intervention Experiments: db/db mice were treated with INT-777 or bile acids DCA and TCA, and cardiac function was monitored continuously.

Data Analysis Algorithms

ANOVA, t-test, and Mann-Whitney test were mainly used to analyze the experimental data, ensuring statistical significance.

Main Results

Cardiomyocyte-specific TGR5 Knockout Exacerbates Cardiac Dysfunction

After 24 weeks of high-fat diet/streptozotocin treatment, cardiomyocyte-specific TGR5 knockout mice exhibited significant cardiac function impairment, including worsening of contractility and diastolic function, with significant decreases in GLS, EF, and FS parameters. Additionally, cardiac hypertrophy, fibrosis, and lipid accumulation were significantly increased.

TGR5 Inhibits Myocardial Lipid Accumulation

Further mechanistic studies revealed that TGR5 knockout upregulated the palmitoyl acyltransferase DHHC4-mediated CD36 palmitoylation, promoting CD36 localization on the membrane and increasing lipid uptake. This excessive activity of CD36 led to exacerbated lipid accumulation in cardiomyocytes.

Drug Intervention Results

After treatment with the TGR5 agonist INT-777 or bile acids DCA and TCA, DBCM mice showed significant improvement in cardiac function and reduced myocardial lipid accumulation, indicating that TGR5 activation could reverse the metabolic dysregulation and cardiac injury caused by TGR5 deficiency.

Research Conclusions and Significance

1. Scientific Significance:

   • This study is the first to reveal the critical regulatory role of TGR5 in myocardial lipid metabolism, elucidating the mechanism of the TGR5-DHHC4 pathway in cardiac fatty acid uptake and CD36 palmitoylation.
   • The research data supports TGR5 as a potential therapeutic target by regulating myocardial lipid metabolism, thereby preventing and reversing the progression of diabetic cardiomyopathy.

2. Application Value:

   • TGR5 agonists such as INT-777 and specific bile acids (DCA and TCA) have potential applications in the prevention and treatment of diabetic cardiomyopathy.

3. Research Highlights:

   • The study innovatively combined genetic and pharmacological models, systematically exploring the role of TGR5 in cardiac function and lipid metabolism from multiple angles.
   • Through detailed molecular and cellular studies, the importance of CD36 palmitoylation and its membrane localization in lipid metabolism was revealed.

Supplementary Information

Analysis of bile acid levels in human samples revealed that bile acids preferentially bound to the TGR5 receptor (such as DCA) were significantly reduced in diabetic subjects, suggesting that the TGR5 signaling pathway may be a key node in the development of diabetic cardiomyopathy.

This study provides important evidence for a comprehensive understanding of the role of TGR5 in myocardial metabolic regulation and reveals the potential of TGR5 in the treatment of diabetic cardiomyopathy. Future research can further explore the clinical application of TGR5 agonists and related optimizations.