CapZ integrates several signaling pathways in response to mechanical stiffness

Area of Science:

• Muscle physiology
• Cellular mechanotransduction
• Cytoskeletal dynamics

Background:

• Muscle adaptation to physiological demand involves cytoskeletal remodeling.
• Actin-binding proteins, such as actin-capping protein (CapZ), are thought to regulate thin filament formation.
• CapZ's role in integrating signaling pathways for muscle growth is not fully understood.

Purpose of the Study:

• To investigate the hypothesis that CapZ integrates signaling pathways (phosphorylation, PIP2 binding) to regulate muscle fiber growth.
• To assess how CapZ function is modulated by mechanical load and specific signaling molecules.

Main Methods:

• Cultured neonatal rat ventricular myocytes on substrates of varying stiffness (10 kPa, 100 kPa, glass).
• Utilized neomycin (PIP2 sequestering agent) and PMA (PKC activator) to manipulate signaling.
• Employed molecular simulations, Fluorescence Recovery After Photobleaching (FRAP), and Förster Resonance Energy Transfer (FRET) to analyze CapZ behavior and interactions.

Main Results:

• Molecular simulations indicated phosphorylation at T267 modifies PIP2 interactions with CapZ's β-tentacle.
• FRAP showed CapZ binding to thin filaments increases with stiffness or PMA but decreases with PIP2 reduction.
• CapZ lacking the β-tentacle and T267 phosphorylation site showed altered sensitivity to PMA and PIP2.

Conclusions:

• CapZ integrates mechanical load and signaling pathways (PIP2, phosphorylation) to regulate muscle fiber growth.
• CapZ binding to actin is modulated by these signals, loosening in growth states.
• Findings may have implications for understanding fibrotic heart disease.