RNA isolation from fetal and adult human tissues for transcriptional profiling

Endocardial-to-mesenchymal transformation and mesenchymal cell colonization at the onset of human cardiac valve development

The elucidation of mechanisms in semilunar valve development might enable the development of new therapies for congenital heart disorders. Here, we found differences in proliferation-associated genes and genes repressed by VEGF between human semilunar valve leaflets from first and second trimester hearts. The proliferation of valve interstitial cells and ventricular valve endothelial cells (VECs) and cellular density declined from the first to the second trimester. Cytoplasmic expression of NFATC1 was detected in VECs (4 weeks) and, later, cells in the leaflet/annulus junction mesenchyme expressing inactive NFATC1 (5.5-9 weeks) were detected, indicative of endocardial-to-mesenchymal transformation (EndMT) in valvulogenesis. At this leaflet/annulus junction, CD44(+) cells clustered during elongation (11 weeks), extending toward the tip along the fibrosal layer in second trimester leaflets. Differing patterns of maturation in the fibrosa and ventricularis were detected via increased fibrosal periostin content, which tracked the presence of the CD44(+) cells in the second trimester. We revealed that spatiotemporal NFATC1 expression actively regulates EndMT during human valvulogenesis, as early as 4 weeks. Additionally, CD44(+) cells play a role in leaflet maturation toward the trilaminar structure, possibly via migration of VECs undergoing EndMT, which subsequently ascend from the leaflet/annulus junction.

Strategies in tissue engineering and regenerative medicine

"Strategies in Tissue Engineering": this special issue is edited by Prof. Katja Schenke-Layland and Prof. Heike Walles and covers many salient aspects of tissue engineering and regenerative medicine. The issue includes articles on Raman spectroscopy and its application in tissue engineering; bioreactor design and surface functionalization for tissue culture applications; improved method for RNA isolation from tissue samples and much more.

Elastogenesis at the onset of human cardiac valve development

Semilunar valve leaflets have a well-described trilaminar histoarchitecture, with a sophisticated elastic fiber network. It was previously proposed that elastin-containing fibers play a subordinate role in early human cardiac valve development; however, this assumption was based on data obtained from mouse models and human second and third trimester tissues. Here, we systematically analyzed tissues from human fetal first (4-12 weeks) and second (13-18 weeks) trimester, adolescent (14-19 years) and adult (50-55 years) hearts to monitor the temporal and spatial distribution of elastic fibers, focusing on semilunar valves. Global expression analyses revealed that the transcription of genes essential for elastic fiber formation starts early within the first trimester. These data were confirmed by quantitative PCR and immunohistochemistry employing antibodies that recognize fibronectin, fibrillin 1, 2 and 3, EMILIN1 and fibulin 4 and 5, which were all expressed at the onset of cardiac cushion formation (~week 4 of development). Tropoelastin/elastin protein expression was first detectable in leaflets of 7-week hearts. We revealed that immature elastic fibers are organized in early human cardiovascular development and that mature elastin-containing fibers first evolve in semilunar valves when blood pressure and heartbeat accelerate. Our findings provide a conceptual framework with the potential to offer novel insights into human cardiac valve development and disease.