Stem cells do not play a significant role in repopulation of adult human cardiomyocytes

Abstract

Currently, there are two points of view on the ability of adult human heart to regenerate. One of them holds that the myocardium has a poor ability to regenerate. According to the other, the myocardium can rapidly regenerate due to the presence of resident stem cells in it. The purpose of this study was to test these hypotheses by investigating the distribution of cardiomyocytes by size and ploidy in human beings of different age. Using cytofluorometry and interferometry, we determined the dry weight, volume, and ploidy of myocytes isolated from the left ventricle of a normal heart of 12 men at the age of 20–30 (n = 7) and 40–50 (n = 5) years. The mean dry weight of cardiomyocytes was 6906 ± 182 pg (10^–12 g) in the 20- to 30-yearold men and 9126 ± 263 pg in 40- to 50-year-old men; the myocyte volume was 55250 ± 1457 and 73005 ± 2106 µm³, respectively. Cells with volumes intermediate between the cells at the stage of “dividing myocytes” and mature myocytes were absent. The number of cardiomyocytes in the left ventricle was (3.18 ± 0.05) × 10⁹ in the 20–30-year-old age group and (2.06 ± 0.6) × 10⁹ in the 40–50-year-old group. The largest subset (41.3%) of the myocyte population was represented by mononuclear cells with tetraploid nuclei. The proportion of myocytes of different ploidy classes and their mean ploidy did not change in the range of 20–50 years. On the basis on these data, we concluded that stem cells do not play a significant role in restoring the number of lost myocytes. Hypertrophy of myocytes caused by the increase in their cytoplasm is the main mechanism of compensation of the function of the left ventricle of the heart in aging human beings.