Fractalkine depresses cardiomyocyte contractility

Area of Science:

• Cardiovascular Biology
• Molecular Cardiology
• Prostaglandin Signaling

Background:

• Cardiomyocyte-specific knockout of prostaglandin E2 EP4 receptor (EP4 KO) in male mice leads to reduced cardiac function.
• Gene array analysis revealed increased fractalkine, a chemokine linked to heart failure, in the left ventricles (LV) of EP4 KO mice.
• This suggests a potential role for fractalkine, regulated by PGE2, in depressed cardiac contractility.

Purpose of the Study:

• To investigate the regulation of fractalkine by prostaglandin E2 (PGE2).
• To determine the effect of fractalkine on cardiomyocyte contractility and intracellular calcium.
• To elucidate the mechanisms by which fractalkine influences cardiac function.

Main Methods:

• Measurement of fractalkine levels in the LV of EP4 KO and wild-type (WT) mice using ELISA.
• Assessment of PGE2's effect on fractalkine secretion in cultured neonatal cardiomyocytes and fibroblasts.
• Evaluation of fractalkine's impact on cardiomyocyte contractility and intracellular calcium using Fura-2 AM loading and electrical field stimulation.

Main Results:

• Elevated LV fractalkine was observed in EP4 KO mice; however, PGE2 only regulated fractalkine secretion in fibroblasts.
• Fractalkine treatment of cardiomyocytes reduced contraction and relaxation speeds under basal and isoproterenol-stimulated conditions.
• Fractalkine increased Ca(2+) transient amplitude but decreased cardiac troponin I phosphorylation, indicating direct effects on the contractile apparatus.

Conclusions:

• Fractalkine significantly depresses cardiomyocyte contractility.
• These effects occur through mechanisms downstream of intracellular calcium handling.
• The study identifies fractalkine as a key mediator in EP4 receptor-associated cardiac dysfunction.