Cardiomyocyte nuclear remodeling after mechanical unloading

Area of Science:

• Cardiovascular Biology
• Cellular Biology
• Heart Failure Pathophysiology

Background:

• Cardiomyocytes (heart muscle cells) can increase DNA content under stress.
• Mechanical unloading via left ventricular assist devices (LVADs) has been linked to decreased DNA content and increased proliferation markers in cardiomyocytes.
• Cardiac recovery leading to LVAD explantation is infrequent, limiting studies on long-term effects.

Purpose of the Study:

• To investigate if changes in cardiomyocyte DNA content during mechanical unloading occur independently of cardiomyocyte proliferation.
• To quantify nuclear number, cell size, DNA content, and cell-cycling markers in cardiomyocytes from unloaded and loaded hearts.

Main Methods:

• Utilized a novel imaging flow cytometry technique.
• Compared human subjects undergoing LVAD implantation versus primary heart transplantation.
• Quantified cardiomyocyte nuclear number, cell size, DNA content, and cell-cycle markers (Ki67, H3P).

Main Results:

• Cardiomyocyte size was 15% smaller in unloaded hearts compared to loaded controls.
• No significant differences were observed in mono-, bi-, or multinucleated cells.
• DNA content per nucleus significantly decreased in unloaded hearts.
• Cell-cycle markers Ki67 and phospho-histone H3 were not elevated in unloaded samples.

Conclusions:

• Mechanical unloading of failing hearts is associated with decreased cardiomyocyte DNA content per nucleus.
• These changes occur independently of the cell's nucleation state.
• The findings suggest a regression of hypertrophic nuclear remodeling rather than cardiomyocyte proliferation during unloading.