Defining cardiac cell populations and relative cellular composition of the early fetal human heart

• Published in: PloS one 2022-11, Vol.17 (11), p.e0259477-e0259477
• Main Authors: Dewing, Jennifer M, Saunders, Vinay, O'Kelly, Ita, Wilson, David I
• Format: Article
• Language: English
• Subjects: Adult; Antibodies; Biological research; Biology and Life Sciences; Biology, Experimental; Calcium-binding protein; Cardiomyocytes; Composition; Coronary vessels; Dissection; Endothelial Cells; Fetal Heart; Fetus; Fetuses; Fibroblasts; Flow cytometry; Growth; Heart; Heart cells; Humans; Identification and classification; Immunohistochemistry; Medicine and Health Sciences; Muscles; Myocytes; Myocytes, Cardiac; Myosin; Myosin Heavy Chains - genetics; Physiological aspects; Polymerase chain reaction; Populations; Proteins; Pulmonary arteries; Research and Analysis Methods; Smooth muscle; Troponin; Troponin I; Troponin I - genetics; Veins & arteries; Ventricle; Vimentin; Vimentin - genetics
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0259477

While the adult human heart is primarily composed of cardiomyocytes, fibroblasts, endothelial and smooth muscle cells, the cellular composition during early development remains largely unknown. Reliable identification of fetal cardiac cell types using protein markers is critical to understand cardiac development and delineate the cellular composition of the developing human heart. This is the first study to use immunohistochemistry (IHC), flow cytometry and RT-PCR analyses to investigate the expression and specificity of commonly used cardiac cell markers in the early human fetal heart (8-12 post-conception weeks). The expression of previously reported protein markers for the detection of cardiomyocytes (Myosin Heavy Chain (MHC) and cardiac troponin I (cTnI), fibroblasts (DDR2, THY1, Vimentin), endothelial cells (CD31) and smooth muscle cells (α-SMA) were assessed. Two distinct populations of cTnI positive cells were identified through flow cytometry, with MHC positive cardiomyocytes showing high cTnI expression (cTnIHigh) while MHC negative non-myocytes showed lower cTnI expression (cTnILow). cTnI expression in non-myocytes was further confirmed by IHC and RT-PCR analyses, suggesting troponins are not cardiomyocyte-specific and may play distinct roles in non-muscle cells during early development. Vimentin (VIM) was expressed in cultured ventricular fibroblast populations and flow cytometry revealed VIMHigh and VIMLow cell populations in the fetal heart. MHC positive cardiomyocytes were VIMLow whilst CD31 positive endothelial cells were VIMHigh. Using markers investigated within this study, we characterised fetal human cardiac populations and estimate that 75-80% of fetal cardiac cells are cardiomyocytes and are MHC+/cTnIHigh/VIMLow, whilst non-myocytes comprise 20-25% of total cells and are MHC-/cTnILow/VIMHigh, with CD31+ endothelial cells comprising ~9% of this population. These findings show distinct differences from those reported for adult heart.