Functional communication between PKC-targeted cardiac troponin I phosphorylation sites

Area of Science:

• Cardiovascular Biology
• Molecular Cardiology
• Cardiac Electrophysiology

Background:

• Increased protein kinase C (PKC) activity is linked to heart failure.
• PKC phosphorylates cardiac troponin I (cTnI) at multiple sites, including S23/24, S43/45, and T144.
• Previous studies suggested communication between cTnI phosphorylation sites.

Purpose of the Study:

• To investigate the communication between cTnI phosphorylation sites.
• To evaluate the impact of combined phospho-mimetic mutations at cTnI S43/45, S23/24, and T144 on cardiac myocyte function.

Main Methods:

• Gene transfer of epitope-tagged cTnIS4D and cTnISDTD into adult cardiac myocytes.
• Assessment of myocyte contractile function, including time to peak shortening (TTP) and time to 50% re-lengthening (TTR50%).
• Analysis of secondary phosphorylation levels.

Main Results:

• Both cTnIS4D and cTnISDTD accelerated TTP and TTR50% initially.
• cTnIS4D significantly reduced peak shortening, while cTnISDTD only modestly reduced it.
• cTnIS4D led to more severe functional alterations and higher secondary phosphorylation compared to cTnISDTD.

Conclusions:

• cTnI S43/45 phosphorylation communicates with S23/24 and T144 sites.
• S23/24 exacerbates, while T144 attenuates, the functional deficits caused by S43/45D.
• Secondary phosphorylation may help maintain cardiac function during chronic PKC site phosphorylation.