Succinate modulates Ca(2+) transient and cardiomyocyte viability through PKA-dependent pathway

Area of Science:

• Cardiology
• Molecular Biology
• Biochemistry

Background:

• G-protein-coupled receptor 91 (GPR91) is a receptor for succinate, a citric acid cycle intermediate.
• The function of succinate in the heart remains largely unknown.
• GPR91 is an orphan receptor, meaning its endogenous ligand was not initially identified.

Purpose of the Study:

• To investigate the expression and function of GPR91 in rat ventricular cardiomyocytes.
• To determine the role of succinate in cardiac calcium handling and cardiomyocyte viability.
• To elucidate the signaling pathway by which succinate exerts its effects in the heart.

Main Methods:

• Quantitative real-time PCR to confirm GPR91 expression in cardiomyocytes.
• Measurement of intracellular calcium transients using fluorescent indicators.
• Western blotting to assess protein phosphorylation levels (ryanodine receptor, phospholamban).
• Pharmacological inhibition of adenylyl cyclase and protein kinase A (PKA).
• Use of a FRET-based biosensor to monitor PKA activity.
• Caspase-3 activity assays to evaluate apoptosis.

Main Results:

• Rat ventricular cardiomyocytes express GPR91.
• Succinate, acting via GPR91, significantly increased the amplitude and rate of decline of global Ca(2+) transients.
• Succinate enhanced the phosphorylation of ryanodine receptor and phospholamban.
• The effects of succinate on Ca(2+) transients were blocked by adenylyl cyclase and PKA inhibitors.
• Succinate directly activated PKA, confirmed by FRET-based assays.
• Succinate reduced cardiomyocyte viability through caspase-3 activation, an effect prevented by PKA inhibition.

Conclusions:

• Succinate functions as a signaling molecule in cardiomyocytes through GPR91.
• Succinate modulates cardiac Ca(2+) handling and cell viability via a PKA-dependent pathway.
• These findings highlight a novel role for succinate in regulating cardiac physiology and pathology.