Long non-coding RNA TERRA regulates DNA damage and survival of endothelial cells and cardiomyocytes: implications for aging

Introduction

Ageing is the major risk factor for cardiovascular disease. Long non-coding RNAs are emerging as novel regulators of cellular functions and contributors to cardiovascular ageing. One of the hallmarks of aging is telomere attrition. Non-coding transcripts called Telomeric repeat-containing RNA (TERRA) are molecules of 0.2–10kb in length which are transcribed from the subtelomeres and telomeres of chromosomes and might play a role in cardiovascular ageing.

Purpose

This study aims to characterize the role of TERRA in aging of the cardiovascular system.

Methods and results

TERRA molecules from different chromosomes were upregulated in the hearts of old mice compared to young mice (p=0.002). Increased TERRA expression was also shown in heart tissue of patients with ischemic heart disease compared to donors (p=0.001). In vitro an upregulation of the TERRA molecule transcribed from chromosome 20 (h20q-TERRA) was found with increasing passage in human umbilical vein endothelial cells (HUVECs) (p=0.014) and IPSC-derived cardiomyocytes (p=0.011). After h20q-TERRA knockdown with LNA GapmeRs, HUVECs show less sprout formation in a spheroid assay compared to negative control transfected HUVECs (p=0.002), without showing a change in migration (p=0.205) or proliferation (p=0.114). H20q-TERRA knockdown revealed an increase in apoptosis (p=0.015) and telomeric DNA damage (p=0.011) and a decrease in telomere length (p<0.001), while lentiviral TERRA-repeat overexpression had the opposite effect (p=0.016, p=0.031, p<0.001, resp.). Apoptosis (p=0.012) and telomeric DNA damage (p=0.007) were also increased after the knockdown of h20q-TERRA in human cardiomyocytes. An apoptosis pathway profiler array in HUVECs showed that the expression of the antioxidant PON2 was decreased after knockdown of h20q-TERRA (p=0.040). PON2 expression was increased after TERRA overexpression (p=0.003). RNA immunoprecipitation revealed that TERRA can bind to PON2. Silencing PON2 in TERRA overexpressing cells diminished the TERRA-mediated decrease in caspase activation, suggesting a detrimental role for PON2 in caspase activation and endothelial cell survival.

Conclusion

Our data demonstrates that TERRA is upregulated with ageing and plays a role in endothelial and cardiomyocyte function and survival.

Funding Acknowledgement

Type of funding sources: Public grant(s) – EU funding. Main funding source(s): Horizon 2020

The novel ageing-induced long non-coding RNA MIRIAL controls endothelial cell and mitochondrial function

 

Vascular ageing is a key risk factor for cardiovascular diseases and is characterised by a continuous decline in endothelial cell function. Despite progress in recent years, the molecular mechanisms for this deterioration remain incompletely understood. Long non-coding RNAs (lncRNAs) are a heterogeneous class of RNAs that have been shown to regulate gene expression and protein function, however, little is known about their role in the ageing-associated dysregulation of endothelial cell (EC) function. In this study, we aimed to identify and functionally characterise a novel ageing-regulated lncRNA in ECs.

Using RNA sequencing data of cardiac ECs derived from 12 weeks young and 20 months old mice, we identified Mirial as an ageing-induced lncRNA (1.32-fold, p=0.00005). Mirial is conserved between mice and humans and has no obvious coding potential. GapmeR-mediated silencing of MIRIAL in human umbilical vein ECs (HUVECs) decreased cell proliferation by 50%, migration by 24% (p=0.045) and basal angiogenic sprouting by 53% (p=0.0029), without affecting apoptosis or senescence. Additionally, silencing of MIRIAL increases mitochondrial mass (1.8-fold, p<0.01) and spare respiratory capacity (1.95-fold). Preliminary data from the hearts of Mirial knockout mice confirm the elevated mitochondrial mass after Mirial ablation (1.26-fold, p=0.05). In HUVECS, MIRIAL is mainly associated with the chromatin (80%), suggesting a role in the regulation of gene expression. Pathway analysis showed an overrepresentation of p53 target genes that were upregulated upon MIRIAL knockdown, which was validated using qRT-PCR (1.8–5.2-fold increases). Interestingly, this effect is fully dependent on the presence of p53. Moreover, p53 and phospho-p53 (Ser15) were both increased (1.8-fold, p=0.01 and 2.9-fold, p=0.02, respectively) after MIRIAL silencing. Pulldown of MIRIAL identified DDX5 and MRPL41 as direct p53 interactors and RNA immunoprecipitation revealed that MIRIAL physically interacts with p53 (3.75-fold enrichment, p<0.01). Gene set enrichment analysis of RNA sequencing data revealed that 10% of deregulated genes after MIRIAL knockdown have a binding site for Forkhead Box O (FoxO) transcription factors. In particular, FoxO1 is known as one of the key players in endothelial proliferation and regulation of angiogenesis as well as in mitochondrial biogenesis.

Taken together, MIRIAL is an ageing-induced lncRNA in endothelial cells acting as a key regulator of metabolic and cellular function. MIRIAL promotes cell proliferation, migration and basal angiogenic sprouting while decreasing mitochondrial function. We hypothesise that MIRIAL influences these cellular functions by affecting the p53 pathway and mitochondrial respiration through FoxO signalling. The results from the present study suggest that modulation of cellular MIRIAL expression may be a promising strategy to prevent or even reverse ageing-induced functional decline of ECs, both in vitro and in vivo.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Deutsche Forschungsgemeinschaft - Collaborative Research Centre (SFB) 834 - Project B9Deutsche Forschungsgemeinschaft - Collaborative Research Centre/Transregio (TRR) 267 - Project B4

The endothelial-enriched lncRNA LINC01235 regulates hypoxia response via HIF-3a

Background

Cardiovascular diseases (CVDs) remain the leading cause of death worldwide. Hypoxia induces significant changes in cardiovascular control mechanisms potentially resulting in pathophysiology. Recently, an increasing number of long non-coding RNAs (lncRNAs) was reported to participate in the regulation of Hypoxia-inducible factors (HIF). Analysis of single-cell RNA-sequencing of human Abdominal Aortic Aneurysms pinpointed the endothelial-enriched lncRNA LINC01235. LINC01235 was previously correlated with tumour progression in gastric cancer and worse patient prognosis in breast cancer. Globally, the role of LINC01235 in the cardiovascular system remains unknown.

Purpose

The objective of this study is to unravel the function of LINC01235 in endothelial cells (ECs).

Methods and results

LINC01235 levels were elevated in human umbilical vein ECs (7.66 fold, p<0.05), human aortic ECs (16.84 fold, p<0.05) and human dermal microvascular ECs (639.73 fold, p<0.05) over other human cardiovascular cells like vascular smooth muscle cells, aortic fibroblasts and cardiomyocytes. Severe hypoxia (0.2% O2 for 24h) reduced LINC01235 expression significantly (0.33 fold, p<0.05). SiRNA-mediated LINC01235 silencing in HUVECs (0.12, p<0.05) resulted in decreased proliferation (0.76 fold, p<0.05) and vascular endothelial growth factor A (VEGFA)-stimulated angiogenic sprouting (0.39 fold, p<0.05). Loss of LINC01235 did not affect apoptosis, metabolism or barrier function. Analysis of RNA-sequencing data revealed that many hypoxia-responsive genes were downregulated after knockdown of LINC01235 (siCtrl vs. siLINC01235). These included HIF-3α (0.24 fold, p<5.86e-28) as a potential key regulator of the cellular feedback to hypoxia. Phenotypically, knockdown of HIF3A using siRNAs (0.07 fold, p<0.05) resulted in decreased proliferation (0.82 fold, p<0.05) and VEGFA-stimulated angiogenic sprouting (0.50 fold, p<0.05). Accordingly, hypoxia response and LINC01235 knockdown exhibit a negative correlation based on transcriptomics data (R=−0.157, p<2.2e-16), further emphasizing a role of LINC01235 in hypoxia response.

Conclusion

In summary, the EC-enriched lncRNA LINC01235 is likely required for the suppression of hypoxia-induced gene expression under normoxic conditions potentially mediated by HIF-3α. Functionally, loss of LINC01235 decreased proliferation and VEGFA-stimulated angiogenic sprouting without an effect on cell death, metabolism or barrier integrity.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): DFG - TRR267

The novel ageing-induced long non-coding RNA MIRIAL controls endothelial cell and mitochondrial function

 

Vascular ageing is a key risk factor for cardiovascular diseases and is characterised by a continuous decline in endothelial function. Despite progress in recent years, the molecular mechanisms for this deterioration remain incompletely understood. Long non-coding RNAs (lncRNAs) are a heterogeneous class of RNAs that have been shown to regulate gene expression and protein function, however, little is known about their role in the ageing-associated dysregulation of endothelial cell (EC) function.

In this study, we aimed to identify and functionally characterise a novel ageing-regulated lncRNA in ECs.

Using RNA sequencing data of cardiac ECs from 12 weeks young and 20 months old mice, we identified Mirial as an ageing-induced lncRNA (1.32-fold, p=0.ehab724.33565). MIRIAL is conserved between mice and humans and has no obvious coding potential. GapmeR-mediated silencing of MIRIAL in human umbilical vein ECs (HUVECs) decreased cell proliferation by 50%, migration by 24% (p=0.045) and basal angiogenic sprouting by 53% (p=0.0029), while increasing VEGF-A-stimulated sprouting by 50% (p=0.0139) and not affecting apoptosis or senescence. Subcellular fractionation of HUVECs revealed that MIRIAL was predominantly associated with the chromatin (80%). Pathway analysis of RNA sequencing data showed an overrepresentation of upregulated p53 target genes upon MIRIAL knockdown in HUVECs which was validated using qRT-PCR (1.8–5.2-fold increased). Using siRNA against p53 we showed that this effect is fully dependent on the presence of p53. Moreover, p53 and its phosphorylated form (Ser15) were both increased (1.8-fold, p=0.01 and 2.9-fold, p=0.02) after MIRIAL silencing. Intriguingly, RNA immunoprecipitation revealed that MIRIAL physically interacts with p53 (3.75-fold enriched, p=0.0067). To further study the interactome of MIRIAL, we performed RNA pulldown assays followed by mass spectrometry analysis of bound proteins, which identified the ageing-associated prohibitin (PHB) 1 and 2 to potentially interact with MIRIAL. Similar to MIRIAL knockdown, siRNA-mediated PHB 1 or 2 silencing caused proliferative defects. Further, PHBs are known to physically interact with p53 and control mitochondrial metabolism, a key factor in cellular ageing. Interestingly, silencing of MIRIAL in HUVECs increased mitochondrial mass (1.8-fold, p=0.0008) and spare respiratory capacity (1.95-fold) with the latter being decreased in isolated aged murine ECs.

Taken together, MIRIAL is an ageing-induced lncRNA in ECs acting as a key regulator of metabolic and cellular function. MIRIAL promotes cell proliferation, migration and basal angiogenic sprouting while decreasing mitochondrial function and VEGF-A-stimulated sprouting. We hypothesise that MIRIAL influences p53 signalling and mitochondrial respiration through PHB 1 and 2. The present study suggests that modulation of MIRIAL expression may be a promising strategy to prevent or even reverse ageing-induced functional decline of ECs.

Funding Acknowledgement

Type of funding sources: Public grant(s) – EU funding. Main funding source(s): European Research Council (ERC) Starting Grant: Non-coding RNA in Vascular Ageing (NOVA)

Key transcriptional regulators of the vasoprotective effects of shear stress

Atherosclerotic plaque rupture and subsequent thrombosis is the main cause of sudden coronary death. Remarkably, atherosclerosis only develops in certain predisposed areas of the vasculature. Endothelial cells in these predisposed areas experience low or oscillatory shear stress, which activates the proinflammatory and procoagulant transcription factors activator protein 1 (AP-1) and nuclear factor B (NFB), thus inducing a proinflammatory, procoagulant surface. In contrast, healthy endothelial cells that are exposed to prolonged high laminar shear stress, express antiinflammatory and anticoagulant genes. The key shear stress-induced transcription factors that govern the expression of these genes are Krüppel-like factor 2 (KLF2) and nuclear factor erythroid 2-like 2 (Nrf2). Together KLF2 and Nrf2 govern ~70% of the shear stress-elicited gene sets. Nrf2 potently induces anti-inflammatory/antioxidant enzymes, while KLF2 induces anti-inflammatory and anticoagulant proteins, most specifically endothelial Nitric oxide synthase (eNOS) and thrombomodulin (TM). KLF2 also inhibits proinflammatory and antifibrinolytic genes through inhibition of the proinflammatory transcription factors AP-1 and NFB. The widespread beneficial effects of the key transcription factors KLF2 and Nrf2 on endothelial phenotype, holds the promise that their targeted modulation might lead to a new class of cardiovascular drugs.

Key transcriptional regulators of the vasoprotective effects of shear stress

Atherosclerotic plaque rupture and subsequent thrombosis is the main cause of sudden coronary death. Remarkably, atherosclerosis only develops in certain predisposed areas of the vasculature. Endothelial cells in these predisposed areas experience low or oscillatory shear stress, which activates the proinflammatory and procoagulant transcription factors activator protein 1 (AP-1) and nuclear factor kappaB (NFkappaB), thus inducing a proinflammatory, procoagulant surface. In contrast, healthy endothelial cells that are exposed to prolonged high laminar shear stress, express anti-inflammatory and anticoagulant genes. The key shear stress-induced transcription factors that govern the expression of these genes are Krüppel-like factor 2 (KLF2) and nuclear factor erythroid 2-like 2 (Nrf2). Together KLF2 and Nrf2 govern approximately 70% of the shear stress-elicited gene sets. Nrf2 potently induces anti-inflammatory/antioxidant enzymes, while KLF2 induces anti-inflammatory and anticoagulant proteins, most specifically endothelial Nitric oxide synthase (eNOS) and thrombomodulin (TM). KLF2 also inhibits proinflammatory and antifibrinolytic genes through inhibition of the proinflammatory transcription factors AP-1 and NFkappaB. The widespread beneficial effects of the key transcription factors KLF2 and Nrf2 on endothelial phenotype, holds the promise that their targeted modulation might lead to a new class of cardiovascular drugs.

The social impact of haemophilia

Haemophilia, one of the oldest known genetic disorders, imposes varying degrees of disability on those affected. A survey of 137 haemophiliacs, seventy-eight adults and fifty-nine children, in the north of England was conducted to discover the extent of social, educational and employment problems created by the disease, while investigation of sixty-nine mothers of patients provided information on its impact on family life.

Some problems are adequately met, others not; those of education and employment are the most serious. Educational deficiencies are due to incomplete and interrupted schooling. Choice of employment is severely restricted for them, and stability of employment is adversely affected by episodes of ill-health. But with improved methods of medical treatment the children are losing less school time than the adults did, fewer of them attend schools for the physically handicapped, and this should result in the attainment of better educational standards, and therefore more hope for permanent and satisfactory employment in the future.

The birth of a haemophilic child markedly affects the family, particularly the mother, but again there is a difference in response between the present and the older generation of mothers.