Self-beating Atypically Shaped Cardiomyocytes Survive a Long-term Postnatal Development While Preserving the Expression of Fetal Cardiac Genes in Mice

Abstract

S U M M A R Y The present study was designed to examine the postnatal developmental changes of atypically shaped cardiomyocytes (ACMs) prepared from the heart of newborn [postnatal day 1 (day-1)] through aged (12-month-old) mice. ACMs were identified as a novel type of self-beating cardiomyocyte with a peculiar morphology in mouse cardiac ventricles. The cell length of ACMs significantly increased during the first three postnatal months and further increased over the following 9 months. In contrast, the population of ACMs was significantly decreased within the first 5 weeks and reached a plateau in the adult stage. ACMs obtained from newborn and adult mice exhibited similar spontaneous action potentials. The expression of the fetal cardiac gene products atrial natriuretic peptide and voltage-gated T-type Ca 21 channel Ca V 3.2 was confirmed by immunostaining in ACMs obtained from both newborn and aged mice. These observations provide evidence that ACMs that exhibit spontaneous beating survive the long-term postnatal development of cardiac ventricles while preserving the expression of fetal cardiac genes. This manuscript contains online supplemental material at http://www.jhc.org. Please visit this article online to view these materials. (J Histochem Cytochem 58:543-551, 2010)

Identification of cardiac progenitors that survive in the ischemic human heart after ventricular myocyte death

“…However, the endogenous behavior and physiological role or importance of these cells remains unknown. ACMs are likely distinct cell populations from these previous reported cells, given their lack of stem cell markers and their ability to spontaneously develop into beating cells in the absence of stimuli and lack of any appreciable proliferation in culture1213. However, several characteristics of ACMs, such as their spontaneous beating and expression of cardiac-specific proteins, suggest that they are “progeny” of cardiomyocytes.…”

“…S1) indicate that the degradation mechanisms for HIF-1α are somewhat inhibited or absent in ACMs, which may also support the view that ACMs are more resistant to ischemia than cardiomyocytes. ACMs are present in neonatal to aged hearts while preserving the expressing of fetal cardiac gene products, such as atrial natriuretic peptide (ANP) and voltage-gated T-type Ca 2+ channel Ca V 3.213. Since HIF-1α is a master regulator of cellular and developmental O 2 homeostasis during the fetal stage45, the constitutive presence of HIF-1α protein in ACMs may be an additional fetal characteristics of these cells.…”

“…Atypically-shaped cardiomyocytes (ACMs) are a type of cardiac progenitors identified in the cultures of cardiomyocyte-removed fraction obtained from mouse cardiac ventricles that spontaneously develop into beating cells within 3–5 days culture121314. Beating ACMs possess a peculiar morphology far different from a typical cardiomyocytes and the electrophysiological properties similar to those of sino-atrial (SA) nodal pace maker cells12.…”

“…Beating ACMs possess a peculiar morphology far different from a typical cardiomyocytes and the electrophysiological properties similar to those of sino-atrial (SA) nodal pace maker cells12. ACMs can be obtained from neonatal to aged heart, while preserving the expression of the fetal cardiac gene products, such as atrial natriuretic peptide (ANP) and T-type Ca 2+ channel Ca V 3.213, and are more ischemic resistant compared with the ventricular myocytes14. ACMs are thus thought to be not classified into stem cells but some kinds of cardiac progenitors that already entered into a cardiomyocyte lineage.…”

A simple antegrade perfusion method for isolating viable single cardiomyocytes from neonatal to aged mice

“…We have used a Langendorff‐based technique, using simple devices without the addition of BDM or nonphysiological chemicals to the solutions described by Shioya (), to isolate mouse ventricular myocytes (Omatsu‐Kanbe et al. ; Hoshino et al. ), atrial myocytes (Nakamura et al.…”