Regulation of muscle creatine kinase by phosphorylation in normal and diabetic hearts

Area of Science:

• Biochemistry
• Molecular Biology
• Cardiology

Background:

• Protein kinase C (PKC) is a key signaling pathway in cardiac function.
• The specific targets and roles of PKC in the heart are not fully understood.
• Muscle creatine kinase (M-CK) plays a vital role in cardiac energy metabolism.

Purpose of the Study:

• To identify cardiac targets of Protein Kinase C (PKC).
• To investigate the role of M-CK phosphorylation in cardiac function, particularly in diabetes.

Main Methods:

• Utilized a PKC substrate antibody to detect phosphorylated proteins.
• Identified M-CK via tandem mass spectrometry.
• Assessed M-CK enzymatic activity following dephosphorylation by protein phosphatases (PP2A, PP2C).
• Compared M-CK phosphorylation and activity in diabetic versus control hearts.

Main Results:

• Identified a 40-kDa cardiac protein as M-CK, phosphorylated at serine 128 by PKC.
• Dephosphorylation of M-CK by PP2A or PP2C altered its forward and reverse reaction kinetics.
• Diabetic hearts showed reduced M-CK phosphorylation despite increased PKC levels.
• Observed decreased M-CK phosphorylation in diabetic hearts mirrored activity changes seen after M-CK dephosphorylation in control hearts.

Conclusions:

• PKC directly phosphorylates M-CK at serine 128, influencing its enzymatic activity.
• Reduced M-CK phosphorylation in diabetic hearts may be a compensatory mechanism to maintain ATP regeneration.
• This study elucidates a novel regulatory pathway for cardiac energy metabolism involving PKC and M-CK.