A cardiac mitochondrial cAMP signaling pathway regulates calcium accumulation, permeability transition and cell death

Area of Science:

• Cardiology
• Mitochondrial Biology
• Cell Signaling

Background:

• Cytosolic cyclic adenosine monophosphate (cAMP) is crucial for cardiac function, but its role within mitochondria is largely unknown.
• Mitochondria are key regulators of cardiac cell death, metabolism, and energy production.

Purpose of the Study:

• To investigate the presence and function of cAMP signaling components within cardiac mitochondria.
• To determine the role of mitochondrial cAMP in regulating mitochondrial function and cell death in cardiomyocytes.

Main Methods:

• Utilized cellular and subcellular approaches in primary cardiomyocytes and isolated mitochondria.
• Investigated the expression of soluble adenylyl cyclase (sACt) and exchange protein directly activated by cAMP 1 (Epac1) within mitochondria.
• Assessed mitochondrial function, including oxygen consumption, membrane potential (ΔΨm), ATP production, and calcium handling.

Main Results:

• Demonstrated the local expression and activity of sACt and Epac1 within cardiac mitochondria.
• Showed that sACt produces mitochondrial cAMP upon stimulation with bicarbonate (HCO3(-)) and Ca(2+).
• Found that mitochondrial cAMP enhances oxygen consumption, increases ΔΨm and ATP production, and prevents mitochondrial permeability transition (MPT) by regulating Ca(2+) entry.
• Observed that this pathway is independent of protein kinase A and Epac2.
• Demonstrated that stimulating mitochondrial cAMP signaling in failing rat hearts rescued mitochondria from Ca(2+)-induced MPT.

Conclusions:

• Identified a novel, mitochondria-specific cAMP signaling pathway in the heart.
• Established a direct link between mitochondrial cAMP, enhanced mitochondrial metabolism, and protection against cell death.
• Highlighted the potential of targeting mitochondrial cAMP for therapeutic interventions in cardiac pathologies.