Aberrant Deactivation-Induced Gain of Function in TRPM4 Mutant Is Associated with Human Cardiac Conduction Block

Area of Science:

• Cardiovascular Physiology
• Ion Channel Function
• Molecular Cardiology

Background:

• Gain-of-function mutations in Ca2+-activated transient receptor potential melastatin member 4 (TRPM4) are linked to severe cardiac conduction defects.
• The precise molecular mechanisms underlying TRPM4-associated cardiac channelopathies remain incompletely understood.

Purpose of the Study:

• To elucidate the functional and mechanistic basis of the TRPM4 A432T gain-of-function mutation.
• To investigate the impact of TRPM4 A432T on channel gating, expression, and ion current in cardiac cells.

Main Methods:

• Utilized photolysis of caged calcium (Ca2+) for precise calcium ion manipulation.
• Performed quantitative Ca2+ measurements and detailed electrophysiological analyses.
• Employed rational mutagenesis of TRPM4 at position 432 to assess amino acid effects.

Main Results:

• The TRPM4 A432T mutation resulted in a 2-fold increase in membrane current, despite a 50% decrease in plasma membrane expression.
• Kinetic analysis revealed a 4-fold slower deactivation rate for TRPM4 A432T, leading to progressively rising currents during cardiac action potentials.
• Amino acid bulkiness at position 432 was critical for aberrant gating; charged amino acids rendered the channel non-functional.

Conclusions:

• Slowed deactivation of TRPM4 channels due to specific amino acid substitutions (e.g., alanine to threonine at position 432) is a key mechanism driving gain-of-function.
• This study identifies a novel mechanistic link between TRPM4 channel dysfunction and the pathogenesis of human cardiac channelopathies.