Another-regulin regulates cardiomyocyte calcium handling via integration of neuroendocrine signaling with SERCA2a...

Area of Science:

• Cardiovascular Biology
• Molecular Cardiology
• Calcium Signaling

Background:

• Calcium (Ca²⁺) dysregulation is central to cardiovascular disease.
• Intracellular Ca²⁺ homeostasis is critical for cardiac function, primarily regulated by the sarco/endoplasmic reticulum Ca²⁺ ATPase (SERCA2a).
• Another-regulin (ALN) is a novel cardiomyocyte protein that inhibits SERCA2a, indicating a more complex Ca²⁺ regulatory network.

Purpose of the Study:

• To investigate the role of ALN in cardiomyocyte Ca²⁺ handling and contractility.
• To elucidate the post-translational modifications of ALN and their impact on SERCA2a activity.
• To determine how neuroendocrine signaling influences ALN activity in the heart.

Main Methods:

• Generation and analysis of ALN knockout (KO) mice and wildtype (WT) littermates.
• In vitro and in vivo studies involving immunoprecipitation, FRET analysis, and adeno-associated virus (AAV)-mediated gene delivery.
• Assessment of cardiomyocyte Ca²⁺ cycling, contractility, and SERCA2a activity under various conditions, including stimulation with Gα_q agonists.

Main Results:

• ALN KO cardiomyocytes exhibited enhanced Ca²⁺ cycling and contractility, suggesting increased SERCA2a activity.
• ALN is phosphorylated at Serine 19 (S19), and this modification alters its inhibitory interaction with SERCA2a, with S19 phosphorylation relieving inhibition.
• Expression of phospho-deficient ALN (S19A) in KO mice led to increased SERCA2a inhibition and reduced Ca²⁺ clearance, while phosphomimetic ALN (S19D) did not.
• Gα_q-agonist stimulation increased ALN phosphorylation in WT cardiomyocytes, leading to augmented Ca²⁺ cycling, an effect absent in ALN KO mice.

Conclusions:

• ALN plays a significant role in regulating cardiomyocyte Ca²⁺ handling and contractility.
• Post-translational modification of ALN via S19 phosphorylation is a key mechanism controlling its interaction with SERCA2a and modulating cardiac function.
• ALN integrates neuroendocrine signaling pathways with SERCA2a activity, providing a novel regulatory node for cardiac Ca²⁺ handling.