Cardiomyocyte proliferation contributes to heart growth in young humans

Abstract

The human heart is believed to grow by enlargement but not proliferation of cardiomyocytes (heart muscle cells) during postnatal development. However, recent studies have shown that cardiomyocyte proliferation is a mechanism of cardiac growth and regeneration in animals. Combined with evidence for cardiomyocyte turnover in adult humans, this suggests that cardiomyocyte proliferation may play an unrecognized role during the period of developmental heart growth between birth and adolescence. We tested this hypothesis by examining the cellular growth mechanisms of the left ventricle on a set of healthy hearts from humans aged 0-59 y (n = 36). The percentages of cardiomyocytes in mitosis and cytokinesis were highest in infants, decreasing to low levels by 20 y. Although cardiomyocyte mitosis was detectable throughout life, cardiomyocyte cytokinesis was not evident after 20 y. Between the first year and 20 y of life, the number of cardiomyocytes in the left ventricle increased 3.4-fold, which was consistent with our predictions based on measured cardiomyocyte cell cycle activity. Our findings show that cardiomyocyte proliferation contributes to developmental heart growth in young humans. This suggests that children and adolescents may be able to regenerate myocardium, that abnormal cardiomyocyte proliferation may be involved in myocardial diseases that affect this population, and that these diseases might be treatable through stimulation of cardiomyocyte proliferation.heart failure | pediatrics H eart failure, a leading public health problem worldwide (1), is linked to the loss of cardiomyocytes (2-4). The only currently available, definitive therapy-heart transplantation-is limited by donor availability. New approaches, such as cell transplantation, have shown encouraging results in clinical trials (5, 6). However, a third, complementary strategy has emerged, based on stimulating endogenous regenerative mechanisms. One approach for developing such regeneration strategies is to examine the cellular mechanisms of myocardial growth, since mechanisms of regeneration should be similar to the mechanisms of development.Although stem and progenitor cells are important for morphogenesis of the myocardium, developmental growth in a number of nonhuman species is largely driven by cardiomyocyte proliferation (7-9). In biological models that, unlike adult humans, regenerate myocardium, cardiomyocyte proliferation is important for regeneration as well as postnatal heart growth (10, 11). For example, in mice, developmental cardiomyocyte proliferation continues for up to day 7 after birth, which coincides with the loss of regenerative capacity (11,12). The close temporal relationship between cardiomyocyte proliferation and heart regeneration in animals raises the question of whether and to what age and extent cardiomyocyte proliferation plays a role in humans. The answer may help us understand the endogenous regenerative potential of the human heart and possibly indicate strategies for stimulating cardiomyocyte proliferation to reg...

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