B-Raf is required for normal murine cardiac development and function.

Area of Science:

• Cardiovascular Biology
• Developmental Biology
• Molecular Cardiology

Background:

• Cardiomyocyte growth involves proliferative and hypertrophic pathways, often mediated by the RAF/MEK/ERK (MAPK) pathway.
• Raf-1 dysregulation is linked to myocardial hypertrophy, but the role of B-Raf in cardiomyocyte development and maturation is less understood.

Purpose of the Study:

• To investigate the hypothesis that B-Raf loss accelerates neonatal cardiomyocyte maturation and impairs cardiac function in adulthood.
• To determine the impact of B-Raf deletion on cardiomyocyte proliferation, hypertrophy, and cell cycle regulation.
• To explore potential sex differences in response to B-Raf deficiency.

Main Methods:

• Utilized conditional knockout (KO) mice lacking B-Raf, studying hearts at postnatal days 1, 3, 8, and 14.
• Performed primary cardiomyocyte cultures, Western blotting for B-Raf and phosphorylated ERK1/2, histology, and echocardiography.
• Assessed markers of hypertrophy (mTOR, SERC2A), cell cycle inhibitors (p21, p27, p53), and cyclin levels.

Main Results:

• B-Raf KO hearts showed reduced B-Raf and phosphorylated ERK1/2 by postnatal day 3.
• Increased cardiomyocyte volume, elevated hypertrophy and maturation markers, and upregulated cell cycle inhibitors were observed in KO hearts.
• KO mice developed dilated cardiomyopathy with thinned walls and enlarged left chamber volume by 3 months; male hearts exhibited adaptive remodeling.

Conclusions:

• B-Raf is crucial for normal neonatal cardiomyocyte proliferation and maturation.
• Loss of B-Raf leads to accelerated maturation, impaired cardiac structure, and dilated cardiomyopathy.
• While male hearts show adaptive remodeling, the long-term consequences and response to stress require further investigation.