Pathogenesis of Cardiomyopathy Caused by Variants in ALPK3, an Essential Pseudokinase in the Cardiomyocyte Nucleus...

Area of Science:

• Cardiovascular Biology
• Molecular Cardiology
• Protein Biochemistry

Background:

• Alpha-kinase 3 (ALPK3) is a muscle-specific protein implicated in cardiomyopathy.
• The precise molecular function of ALPK3 and the impact of its loss-of-function variants remain largely unknown.
• Existing research highlights distinctive clinical manifestations of ALPK3-related cardiomyopathy in pediatric and adult patients.

Purpose of the Study:

• To investigate the kinase activity and functional consequences of ALPK3 variants.
• To elucidate the molecular mechanisms underlying ALPK3 loss-of-function cardiomyopathy.

Main Methods:

• Utilized isogenic human induced pluripotent stem cell-derived cardiomyocytes, mouse models, and human patient tissues.
• Performed phosphoproteomic analysis to assess ALPK3 kinase activity.
• Investigated ALPK3 localization and interactions with myomesin proteins at the nuclear envelope and sarcomere M-band.

Main Results:

• ALPK3 was identified as a pseudokinase, lacking significant catalytic activity.
• ALPK3 localizes to the nuclear envelope and sarcomere M-band, interacting with myomesins (MYOM1, MYOM2).
• Loss-of-function variants in ALPK3 lead to myomesin mislocalization and dysregulation of M-band proteins involved in sarcomere protein turnover, impairing cardiomyocyte structure and function.

Conclusions:

• ALPK3 is a crucial cardiac pseudokinase localized to the nuclear envelope and sarcomere M-band.
• ALPK3 deficiency results in mislocalization of myomesins, vital for force buffering in cardiomyocytes.
• Impaired sarcomere protein turnover and myomesin-mediated force buffering due to ALPK3 loss contribute to ventricular dilatation and hypertrophy in ALPK3 cardiomyopathy.