Endothelial cell-expressed long non-coding RNAs in cardiac regeneration

Abstract

Abstract Endothelial cells (ECs) are the most abundant non-myocyte cell types in the heart. Upon cardiac injury, revascularization can occur through proliferation and migration of ECs from existing blood vessels in the surrounding myocardium. In animal models, revascularization is crucial to stimulate cardiomyocyte survival and regeneration. In the human heart, establishing blood flow could improve outcomes of tissue engineering or cell based therapy to regenerate the heart after injury. In addition to establishing blood flow, EC also secrete factors in a paracrine manner which can act on neighbouring cardiomyocytes. We investigate a role for non-coding RNA in the regulation of endothelial cell function and their potential role in neovascularization and cardiac regeneration. A large portion of the genome is transcribed into non-coding RNA, which does not encode protein. Many long non-coding RNAs (lncRNAs) have been shown to be involved in important regulatory processes such as genomic imprinting and chromatin modification. To identify lncRNAs which could be involved in cardiac regeneration, we isolated ECs from neonatal mice at postnatal day 1 and 5.5. The potential for cardiac regeneration was observed in mice at postnatal day 1, but this capacity is lost by day 5.5. Differential expression of lncRNAs in ECs was assessed by RNA sequencing. Three potential target lncRNAs, which also have a human homologue, were selected. NR2F2-AS1 and HAND2-AS1 were upregulated at postnatal day 1, whereas FOXD2-AS1 was upregulated at day 5.5. These genes were selected for further validation in human cardiac microvascular endothelial cells (CMEC). Knockdown of NR2F2-AS1 resulted in a decrease in proliferation but did not affect angiogenic sprouting. Loss of HAND2-AS1 resulted in a trend to impaired sprouting but did not affect proliferation. FOXD2-AS1 knockdown resulted in a significant decrease in angiogenic sprouting. We observed no change in the rate of migration after knockdown of any of the three genes. Knockdown of the lncRNAs did not affect expression of the antisense protein coding transcripts, therefore the effects we observe are likely mediated by the lncRNAs. In conclusion, lncRNAs NR2F2-AS1, HAND2-AS1 and FOXD2-AS1 regulate different aspects of EC function such as proliferation and sprouting. Modulation of expression of these transcripts therefore may be considered as a therapeutic tool to promote cardiac regeneration.