Hormonal regulation of cardiac fibroblast function

Area of Science:

• Cardiovascular Biology
• Molecular Cardiology
• Fibrosis Research

Background:

• Myocardial fibrosis, an accumulation of collagen in heart tissue, is linked to activated renin-angiotensin-aldosterone system (RAAS) in conditions like hypertension and heart failure.
• This fibrosis appears driven by hormonal factors rather than hemodynamic load.
• Cardiac fibroblasts produce collagen and the enzyme matrix metalloproteinase 1 (MMP 1) for collagen degradation.

Purpose of the Study:

• To investigate if RAAS hormones angiotensin II (Ang II) and aldosterone (Aldo) directly stimulate collagen synthesis or inhibit MMP 1 production in cardiac fibroblasts.
• To determine the role of mineralocorticoid and Ang II receptors in mediating these effects.

Main Methods:

• Adult rat cardiac fibroblasts were cultured under serum-free conditions.
• Cells were incubated with varying concentrations of Ang II, Aldo, dexoycorticosterone (DOC), or PGE2 for 24 hours.
• Collagen synthesis was measured by 3H-proline incorporation, normalized to total protein synthesis.
• MMP 1 activity was assessed by 14C-collagen degradation.
• Receptor antagonists were used to block specific pathways.

Main Results:

• Ang II and mineralocorticoids (Aldo, DOC) significantly increased collagen synthesis in a dose-dependent manner compared to controls.
• Prostaglandin E2 (PGE2) significantly decreased collagen synthesis.
• The increase in collagen synthesis induced by Ang II and Aldo was blocked by their respective receptor antagonists (Ang II type 1 and mineralocorticoid receptor antagonists).

Conclusions:

• Angiotensin II and aldosterone directly stimulate collagen synthesis in cardiac fibroblasts.
• These RAAS hormones play a significant role in promoting myocardial fibrosis.
• Targeting RAAS pathways may be a therapeutic strategy to reduce cardiac fibrosis.