An Arrhythmic Mutation E7K Facilitates TRPM4 Channel Activation via Enhanced PIP₂ Interaction.

Area of Science:

• Cardiovascular Physiology
• Molecular Biology
• Ion Channel Function

Background:

• TRPM4 channels are Ca2+-activated and selective for monovalent cations, crucial in cardiac function.
• A gain-of-function mutation (E7K) in the TRPM4 channel's N-terminus is linked to cardiac arrhythmias due to increased membrane expression.

Purpose of the Study:

• To investigate the functional consequences of the TRPM4 E7K mutation beyond cell membrane expression.
• To elucidate the role of phosphatidylinositol 4,5-bisphosphate (PIP2) in TRPM4 channel activity and how the E7K mutation affects this interaction.

Main Methods:

• Utilized patch clamping and Förster Resonance Energy Transfer (FRET) based measurements in an expression system.
• Employed diC8PIP2 for channel activity recovery and Danio rerio voltage-sensing phosphatase (DrVSP) for endogenous PIP2 level manipulation.
• Tested the effects of N-terminal polypeptides (WT and E7K) on TRPM4 channel activation.

Main Results:

• Intracellular diC8PIP2 restored TRPM4 channel activity, with higher potency for the E7K mutant.
• Reduced endogenous PIP2 levels decreased TRPM4 activity, an effect less pronounced in the E7K mutant, indicating altered PIP2 modulation of voltage dependence.
• N-terminal polypeptides inhibited TRPM4 activation, with greater inhibition by the E7K sequence.

Conclusions:

• N-terminal interaction with PIP2 is essential for TRPM4 channel function.
• The E7K mutation strengthens PIP2 interaction, potentially by modulating voltage-dependent activation, contributing to its arrhythmogenic potential.