%0 Generic
%A Gehrs, Stephanie
%C Heidelberg
%D 2026
%F heidok:36162
%R 10.11588/heidok.00036162
%T Epigenetic regulation of the endothelial cell transcriptome during angiogenesis and quiescence
%U https://archiv.ub.uni-heidelberg.de/volltextserver/36162/
%X Epigenetic mechanisms play a crucial role in determining endothelial cell (EC) states during development and disease. Investigating the epigenetic regulation of ECs during development and EC-associated diseases is essential for understanding downstream transcriptomic changes and phenotypes. In recent years, studies have incorporated DNA methylation and/or chromatin analysis to gain insights into how epigenetic modifications regulate endothelial gene expression. However, the genome-wide integration of epigenetic layers, such as chromatin accessibility, DNA methylation, and histone tail modifications, and their impact on gene expression during the EC state transition remain largely unexplored. Additionally, no hierarchical order of epigenetic layers has been identified.   This thesis therefore aimed to I) uncover the epigenetic landscape of ECs in vivo during physiological state transition, II) elucidate the epigenetic reprogramming that occurs during pathological EC transition, and III) functionally characterize the role of the DNA methyltransferase DNMT3A during embryonic and postnatal vasculature development.  During developmental transitions, ECs in the murine lung vasculature undergo significant transcriptomic changes to adapt to environmental cues. This state transition is driven by epigenetic modifications, particularly at enhancer regions, which are selectively accessible near state-specific genes. Developmental enhancer regions that lost their active histone modification during state transition sustained accessible chromatin and their non-methylated DNA, potentially serving as epigenetic memory. Under pathological conditions such as lung tumor development and metastasis progression, vascular reactivation requires the reestablishment of angiogenic enhancers, enabling the hijacking of developmental transcriptional programs, such as cell proliferation and migration. This process may be facilitated by chromatin-modifying enzymes, along with the preservation of DNA hypomethylation and chromatin accessibility at these enhancers.  In the murine endothelium, DNA methylation is specifically mediated by DNMT3A and plays a fundamental role in shaping the endothelial enhancer landscape. Longitudinal postnatal EC analysis revealed that significant alterations in DNA methylation occurred as ECs transitioned from an angiogenic state to a quiescent state. Once vascular quiescence is established, these methylation marks remain mostly stable throughout aging. Interestingly, the edges of regulatory elements in angiogenic ECs showed reduced DNA methylation compared with those in quiescent ECs, indicating the need for active DNA methylation upon state transition. The absence of DNMT3A-dependent DNA methylation, analyzed in ECs isolated from Dnmt3a knockout mice, resulted in the loss of active enhancers, leading to subtle transcriptional changes, likely due to alterations in enhancer integrity.  In the context of the murine placental vasculature, single-cell transcriptome analysis revealed that the spatial zonation of the murine placental labyrinth vasculature is controlled by flow-regulated epigenetic mechanisms. The identified blood flow-dependent zonation is crucial for proper fetal nourishment, and disruptions in this process can lead to placental insufficiency. Since DNMT3A introduces DNA methylation in ECs, its loss results in global DNA hypomethylation, impaired angiogenic capacity, and fetal growth retardation. Furthermore, a meta-analysis identified a link between reduced DNMT3A expression in the human placental endothelium and preeclampsia, highlighting its clinical relevance in placental dysfunction. Collectively, these findings underline the importance of DNMT3A as a critical regulator of endothelial cell gene expression and function across different vascular beds, with significant implications for developmental biology and disease.