Large-scale microRNA functional high-throughput screening identifies miR-515-3p and miR-519e-3p as inducers of human cardiomyocyte proliferation

Ischemic cardiomyopathy, driven by loss of cardiomyocytes and inadequate proliferative response, persists to be a major global health problem. Using a functional high-throughput screening, we assessed differential proliferative potential of 2019 miRNAs after transient hypoxia by transfecting both miR-inhibitor and miR-mimic libraries in human iPSC-CM. Whereas miR-inhibitors failed to enhance EdU uptake, overexpression of 28 miRNAs substantially induced proliferative activity in hiPSC-CM, with an overrepresentation of miRNAs belonging to the primate-specific C19MC-cluster. Two of these miRNAs, miR-515-3p and miR-519e-3p, increased markers of early and late mitosis, indicative of cell division, and substantially alter signaling pathways relevant for cardiomyocyte proliferation in hiPSC-CM.

tRNA-like Transcripts from the NEAT1-MALAT1 Genomic Region Critically Influence Human Innate Immunity and Macrophage Functions

The evolutionary conserved NEAT1-MALAT1 gene cluster generates large noncoding transcripts remaining nuclear, while tRNA-like transcripts (mascRNA, menRNA) enzymatically generated from these precursors translocate to the cytosol. Whereas functions have been assigned to the nuclear transcripts, data on biological functions of the small cytosolic transcripts are sparse. We previously found NEAT1^-/- and MALAT1^-/- mice to display massive atherosclerosis and vascular inflammation. Here, employing selective targeted disruption of menRNA or mascRNA, we investigate the tRNA-like molecules as critical components of innate immunity. CRISPR-generated human ΔmascRNA and ΔmenRNA monocytes/macrophages display defective innate immune sensing, loss of cytokine control, imbalance of growth/angiogenic factor expression impacting upon angiogenesis, and altered cell-cell interaction systems. Antiviral response, foam cell formation/oxLDL uptake, and M1/M2 polarization are defective in ΔmascRNA/ΔmenRNA macrophages, defining first biological functions of menRNA and describing new functions of mascRNA. menRNA and mascRNA represent novel components of innate immunity arising from the noncoding genome. They appear as prototypes of a new class of noncoding RNAs distinct from others (miRNAs, siRNAs) by biosynthetic pathway and intracellular kinetics. Their NEAT1-MALAT1 region of origin appears as archetype of a functionally highly integrated RNA processing system.

A large-scale functional high-throughput screening identifies miR-515 and miR-519e as potent inducers of human iPSC-cardiomyocyte proliferation

Introduction

Ischemic heart failure persists as a global health problem despite optimized medical and adjunctive device therapies. Loss of cardiomyocytes in the absence of a proliferative response comprise a major contributor to pathological remodeling and death in this patient population. Experimental studies have shown that microRNAs (miRNAs) may be used as a therapeutic option to reinduce adult cardiomyocyte proliferation.

Purpose

This study thought to evaluate proliferative potential in human cardiomyocytes after overexpression and inhibition of 2019 miRNAs.

Methods

To identify miRNAs that regulate cardiomyocyte proliferation, we performed functional high-throughput screenings in human iPSC-derived cardiomyocytes (hiPSC-CM) after transient hypoxia. Herein, 2019 miRNA-mimics for overexpression and 2019 anti-miRs for inhibition were individually transfected to examine EdU-incorporation in hiPSC-CM. MiR-mimic-515 and miR-mimic-519e that induced the highest EdU-uptake, were further assessed by immunostaining and molecular methods for markers indicative of early and late mitosis. In addition, RNA-Sequencing in hiPSC-CM after overexpression of miR-515 and miR-519e was performed to examine differential gene expression and miRNA-modulated pathways involved in cardiomyocyte proliferation.

Results

Using a functional high-throughput screening, we assessed differential proliferative potential of 2019 miRNAs after transient hypoxia by transfecting both miR-inhibitor and miR-mimic libraries in human iPSC-derived cardiomyocytes (hiPSC-CM). Overexpression of 28 miRNAs substantially induced proliferative activity in hiPSC-CM, with an overrepresentation of miRNAs belonging to the C19MC-cluster and adjacent miR-371–373 family. Two of these miRNAs, miR-515 and miR-519e increased markers of early and late mitosis, with an additive cardiomyocyte turnover after transient hypoxia and substantially increased Aurora B-kinase activity in midbodies, indicative of cell division. These findings were supported by molecular studies using qRT-PCR, Western blot, and RNA-Sequencing after overexpression of miR-515 and miR-519e showing substantial alterations of signaling pathways relevant for cardiomyocytes proliferation in human iPSC-CM.

Conclusion

Collectively, these results support a critical role of miR-515 and miR-519e for induction of proliferation in human cardiomyocytes under hypoxic conditions, such as present in patients with ischemia-driven cardiomyopathy.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): This work was supported by the German Centre for Cardiovascular Research (DZHK), Deutsche Stiftung für Herzforschung (DSHF) and OPO Foundation.

Atheroprone fluid shear stress-regulated ALK1-Endoglin-SMAD signaling originates from early endosomes

BACKGROUND

Fluid shear stress enhances endothelial SMAD1/5 signaling via the BMP9-bound ALK1 receptor complex supported by the co-receptor Endoglin. While moderate SMAD1/5 activation is required to maintain endothelial quiescence, excessive SMAD1/5 signaling promotes endothelial dysfunction. Increased BMP signaling participates in endothelial-to-mesenchymal transition and inflammation culminating in vascular diseases such as atherosclerosis. While the function of Endoglin has so far been described under picomolar concentrations of BMP9 and short-term shear application, we investigated Endoglin under physiological BMP9 and long-term pathophysiological shear conditions.

RESULTS

We report here that knock-down of Endoglin leads to exacerbated SMAD1/5 phosphorylation and atheroprone gene expression profile in HUVECs sheared for 24 h. Making use of the ligand-trap ALK1-Fc, we furthermore show that this increase is dependent on BMP9/10. Mechanistically, we reveal that long-term exposure of ECs to low laminar shear stress leads to enhanced Endoglin expression and endocytosis of Endoglin in Caveolin-1-positive early endosomes. In these endosomes, we could localize the ALK1-Endoglin complex, labeled BMP9 as well as SMAD1, highlighting Caveolin-1 vesicles as a SMAD signaling compartment in cells exposed to low atheroprone laminar shear stress.

CONCLUSIONS

We identified Endoglin to be essential in preventing excessive activation of SMAD1/5 under physiological flow conditions and Caveolin-1-positive early endosomes as a new flow-regulated signaling compartment for BMP9-ALK1-Endoglin signaling axis in atheroprone flow conditions.

A novel class of small tRNA-like noncoding transcripts arising from the human NEAT1-MALAT1 region critically influences innate immunity and angiogenesis

Background

The evolutionary conserved NEAT1-MALAT1 gene cluster encounters high interest in cardiovascular medicine and oncology. The cluster generates large primary transcripts which remain nuclear, whereas novel tRNA-like transcripts (mascRNA, menRNA) enzymatically generated from these precursors translocate to the cytosol. We previously found that NEAT1 and MALAT1 deficient mice display accelerated atherosclerosis and vascular inflammation due to immune dysfunctions.

Methods

While the previously investigated mice were deficient in the entire NEAT1 or MALAT1 locus, here we aimed to selectively disrupt only tRNA-like transcripts “menRNA” arising from NEAT1, or “mascRNA” arising from MALAT1. To none of these a biological function has been assigned so far. Both lncRNAs give rise to transcripts of vastly different size (NEAT1: 23kb MENb, 3.7kb MENe, 59nt “menRNA”; MALAT1: 8.3 kb primary, 59nt “mascRNA”), and traditional knockout methods are unable to selectively inactivate one of the small transcripts only. Through CRISPR/Cas9 editing we therefore developed human monocyte-macrophage cell lines with short deletions in the respective tRNA-encoding sequences to disrupt normal menRNA or mascRNA formation, respectively. These editing procedures do not affect transcription of the respective lncRNA parent transcripts, and also not disturb regular formation of the triple-helix structures at their 3'-ends which support stabilization of the respective lncRNAs (Fig. 1).

Results

We found the tRNA-like transcripts menRNA and mascRNA critically influence innate immunity and angiogenesis. In addition to common anomalies resulting from their selective CRISPR-Cas9 mediated deletion (Fig. 1), there are specific disturbances associated with either Δmasc or Δmen cells (Fig. 2).

Both ΔmascRNA and ΔmenRNA human monocytes show profoundly altered ribosomal RNA/protein and tRNA-modifying enzyme expression, display anomalous growth/ angiogenetic factor expression, fundamentally change angiogenetic patterns in co-cultures with human endothelial cells, and have gravely disturbed innate immune responses (LPS, DNA and RNA viruses) (Fig. 1).

CRISPR-engineered ΔmenRNA cells share remakable similarities with human post-MI PBMCs, suggesting the NEAT1-menRNA system may significantly contribute to post-MI residual inflammatory risk despite optimal standard therapy (Fig. 2).

Conclusions

Beyond prior work in knockout mice documenting immune function of the NEAT1-MALAT1 cluster, the current study identifies menRNA and mascRNA as important novel components of human innate immunity with relevance for angiogenetic processes. These data provide a second mechanistic link for the apparent relevance of the NEAT1-MALAT1 gene cluster in cardiovascular and malignant diseases. As prototypes of a novel class of small noncoding RNAs (distinct from miRNAs and siRNAs) they may constitute cytosolic therapeutic targets.

Funding Acknowledgement

Type of funding sources: Other. Main funding source(s): DZHK Shared Expertise Project/B19-006_SE/FKZ 81X2100257/Transcriptome analysis of circulating immune cells to improve the assessment of prognosis and the response to novel anti-inflammatory treatments after myocardial infarction Figure 1. Common anomaliesFigure 2. Specific anomalies

Propionate attenuates atherosclerosis by immune-dependent regulation of intestinal cholesterol metabolism

AIMS

Atherosclerotic cardiovascular disease (ACVD) is a major cause of mortality and morbidity worldwide, and increased low-density lipoproteins (LDLs) play a critical role in development and progression of atherosclerosis. Here, we examined for the first time gut immunomodulatory effects of the microbiota-derived metabolite propionic acid (PA) on intestinal cholesterol metabolism.

METHODS AND RESULTS

Using both human and animal model studies, we demonstrate that treatment with PA reduces blood total and LDL cholesterol levels. In apolipoprotein E-/- (Apoe-/-) mice fed a high-fat diet (HFD), PA reduced intestinal cholesterol absorption and aortic atherosclerotic lesion area. Further, PA increased regulatory T-cell numbers and interleukin (IL)-10 levels in the intestinal microenvironment, which in turn suppressed the expression of Niemann-Pick C1-like 1 (Npc1l1), a major intestinal cholesterol transporter. Blockade of IL-10 receptor signalling attenuated the PA-related reduction in total and LDL cholesterol and augmented atherosclerotic lesion severity in the HFD-fed Apoe-/- mice. To translate these preclinical findings to humans, we conducted a randomized, double-blinded, placebo-controlled human study (clinical trial no. NCT03590496). Oral supplementation with 500 mg of PA twice daily over the course of 8 weeks significantly reduced LDL [-15.9 mg/dL (-8.1%) vs. -1.6 mg/dL (-0.5%), P = 0.016], total [-19.6 mg/dL (-7.3%) vs. -5.3 mg/dL (-1.7%), P = 0.014] and non-high-density lipoprotein cholesterol levels [PA vs. placebo: -18.9 mg/dL (-9.1%) vs. -0.6 mg/dL (-0.5%), P = 0.002] in subjects with elevated baseline LDL cholesterol levels.

CONCLUSION

Our findings reveal a novel immune-mediated pathway linking the gut microbiota-derived metabolite PA with intestinal Npc1l1 expression and cholesterol homeostasis. The results highlight the gut immune system as a potential therapeutic target to control dyslipidaemia that may introduce a new avenue for prevention of ACVDs.

Sirtuin 5 promotes arterial thrombosis by blunting the fibrinolytic system

AIMS

Arterial thrombosis as a result of plaque rupture or erosion is a key event in acute cardiovascular events. Sirtuin 5 (SIRT5) belongs to the lifespan-regulating sirtuin superfamily and has been implicated in acute ischaemic stroke and cardiac hypertrophy. This project aims at investigating the role of SIRT5 in arterial thrombus formation.

METHODS AND RESULTS

Sirt5 transgenic (Sirt5Tg/0) and knock-out (Sirt5-/-) mice underwent photochemically induced carotid endothelial injury to trigger arterial thrombosis. Primary human aortic endothelial cells (HAECs) were treated with SIRT5 silencing-RNA (si-SIRT5) as well as peripheral blood mononuclear cells from acute coronary syndrome (ACS) patients and non-ACS controls (case-control study, total n = 171) were used to increase the translational relevance of our data. Compared to wild-type controls, Sirt5Tg/0 mice displayed accelerated arterial thrombus formation following endothelial-specific damage. Conversely, in Sirt5-/- mice, arterial thrombosis was blunted. Platelet function was unaltered, as assessed by ex vivo collagen-induced aggregometry. Similarly, activation of the coagulation cascade as assessed by vascular and plasma tissue factor (TF) and TF pathway inhibitor expression was unaltered. Increased thrombus embolization episodes and circulating D-dimer levels suggested augmented activation of the fibrinolytic system in Sirt5-/- mice. Accordingly, Sirt5-/- mice showed reduced plasma and vascular expression of the fibrinolysis inhibitor plasminogen activator inhibitor (PAI)-1. In HAECs, SIRT5-silencing inhibited PAI-1 gene and protein expression in response to TNF-α. This effect was mediated by increased AMPK activation and reduced phosphorylation of the MAP kinase ERK 1/2, but not JNK and p38 as shown both in vivo and in vitro. Lastly, both PAI-1 and SIRT5 gene expressions are increased in ACS patients compared to non-ACS controls after adjustment for cardiovascular risk factors, while PAI-1 expression increased across tertiles of SIRT5.

CONCLUSION

SIRT5 promotes arterial thrombosis by modulating fibrinolysis through endothelial PAI-1 expression. Hence, SIRT5 may be an interesting therapeutic target in the context of atherothrombotic events.

Endothelial SIRT6 blunts stroke size and neurological deficit by preserving blood-brain barrier integrity: a translational study

AIMS

Aging is an established risk factor for stroke; genes regulating longevity are implicated in the pathogenesis of ischaemic stroke where to date, therapeutic options remain limited. The blood-brain barrier (BBB) is crucially involved in ischaemia/reperfusion (I/R) brain injury thus representing an attractive target for developing novel therapeutic agents. Given the role of endothelial cells in the BBB, we hypothesized that the endothelial-specific expression of the recently described longevity gene SIRT6 may exhibit protective properties in stroke.

METHODS AND RESULTS

SIRT6 endothelial expression was reduced following stroke. Endothelial-specific Sirt6 knockout (eSirt6-/-) mice, as well as animals in which Sirt6 overexpression was post-ischaemically induced, underwent transient middle cerebral artery occlusion (tMCAO). eSirt6-/- animals displayed increased infarct volumes, mortality, and neurological deficit after tMCAO, as compared to control littermates. Conversely, post-ischaemic Sirt6 overexpression decreased infarct size and neurological deficit. Analysis of ischaemic brain sections revealed increased BBB damage and endothelial expression of cleaved caspase-3 in eSIRT6-/- mice as compared to controls. In primary human brain microvascular endothelial cells (HBMVECs), hypoxia/reoxygenation (H/R) reduced SIRT6 expression and SIRT6 silencing impaired the barrier function (transendothelial resistance) similar to what was observed in mice exposed to I/R. Further, SIRT6-silenced HBMVECs exposed to H/R showed reduced viability, increased cleaved caspase-3 expression and reduced activation of the survival pathway Akt. In ischaemic stroke patients, SIRT6 expression was higher in those with short-term neurological improvement as assessed by NIHSS scale and correlated with stroke outcome.

CONCLUSION

Endothelial SIRT6 exerts a protective role in ischaemic stroke by blunting I/R-mediated BBB damage and thus, it may represent an interesting novel therapeutic target to be explored in future clinical investigation.

Apold1 deficiency associates with increased arterial thrombosis in vivo

BACKGROUND

Endothelial cells regulate the formation of blood clots; thus, genes selectively expressed in these cells could primarily determine thrombus formation. Apold1 (apolipoprotein L domain containing 1) is a gene expressed by endothelial cells; whether Apold1 directly contributes to arterial thrombosis has not yet been investigated. Here, we assessed the effect of Apold1 deletion on arterial thrombus formation using an in vivo model of carotid thrombosis induced by photochemical injury.

MATERIAL AND METHODS

Apold1 knockout (Apold1^-/- ) mice and wild-type (WT) littermates underwent carotid thrombosis induced by photochemical injury, and time to occlusion was recorded. Tissue factor (TF) activity and activation of mitogen-activated protein kinases (MAPKs) and phosphatidyl-inositol-3 kinase (PI3K)/Akt pathways were analysed by colorimetric assay and Western blotting in both Apold1^-/- and WT mice. Finally, platelet reactivity was assessed using light transmission aggregometry.

RESULTS

After photochemical injury, Apold1^-/- mice exhibited shorter time to occlusion as compared to WT mice. Moreover, TF activity was increased in carotid arteries of Apold1^-/- when compared to WT mice. Underlying mechanistic markers such as TF mRNA and MAPKs activation were unaffected in Apold1^-/- mice. In contrast, phosphorylation of Akt was reduced in Apold1^-/- as compared to WT mice. Additionally, Apold1^-/- mice displayed increased platelet reactivity to stimulation with collagen compared with WT animals.

CONCLUSIONS

Deficiency of Apold1 results in a prothrombotic phenotype, accompanied by increased vascular TF activity, decreased PI3K/Akt activation and increased platelet reactivity. These findings suggest Apold1 as an interesting new therapeutic target in the context of arterial thrombosis.

2182Sirtuin 5 regulates arterial thrombosis by modulating endothelial plasminogen activator inhibitor-1

Introduction

Arterial thrombosis as a result of plaque rupture or erosion is a crucial event in myocardial infarction and stroke. Oxidative stress and inflammation promote endothelial dysfunction and play a pivotal role in destabilization of the atherosclerotic plaque. Sirtuin 5 (SIRT5) is a member of the sirtuin protein family with function as a NAD+-dependent protein desuccinylase and demalonylase. Being implicated in the regulation of different pathophysiological processes among which production of reactive oxygen species and transcription of inflammatory mediators, SIRT5 plays a role in the development of several cardiovascular diseases such as myocardial infarction and stroke. To date, the possible involvement of SIRT5 as a mediator of arterial thrombosis remains to be investigated.

Purpose

In this study we investigate the putative role of this protein in arterial thrombosis by using an established in vivo mouse model. The translational value of animal findings as well as the molecular mechanism underlying the observed effect will be investigated also in primary human aortic endothelial cells (HAECs).

Methods

SIRT5 knockout (KO) as well as SIRT5 transgenic (TG) animals were used for in vivo experiments. HAECs treated with SIRT5 silencing RNA (si-SIRT5) and stimulated with tumor necrosis factor (TNF)-α were used for in vitro assays.

Results

When compared to WT animals, SIRT5 KO mice display blunted carotid artery thrombus formation as underlined by delayed time to occlusion in a photochemical injury model. Oppositely, in SIRT5 TG mice the formation of an occlusive thrombus is accelerated (Fig 1). Mechanistically, SIRT5 KO and WT animals show no difference in terms of vascular tissue factor (TF) activity, TF concentration in plasma and expression of TF pathway inhibitor (TFPI) in the aorta. In line with the observed reduced thrombogenicity, SIRT5 KO animal express reduced level of the pro-thrombotic plasminogen activator-1 (PAI-1), as assessed by western blot in aorta lysate. Of interest, SIRT5 genetic deletion does not affect platelet aggregation, as assessed by ex-vivo collagen-induced aggregometry. In HAECs, SIRT5-silencing inhibits PAI-1 expression in response to TNF-α. Real-time polymerase chain reaction revealed that inhibition of PAI-1 expression occurs at the mRNA level. This effect is mediated by reduced activation of the MAP kinase Erk 1/2, but not JNK (Fig 1).

Conclusions

SIRT5 mediates arterial thrombosis by increasing endothelial PAI-1 expression. Hence, SIRT5 may be an effective therapeutic target in the context of atherothrombosis.

2287Endothelial SIRT6 exerts a beneficial role in cerebral ischemia/reperfusion injury by preserving blood-brain barrier integrity

Introduction

Stroke is a major cause of mortality and morbidity worldwide. Yet, therapeutic strategies are limited to the early reperfusion which can, on the other hand, worsen the brain damage trough ischemia/reperfusion (I/R) injury. Post-stroke blood-brain barrier (BBB) impairment is associated with worsened outcome. Aging is a major risk factor for stroke and genes regulating lifespan also contribute to the determination of cerebral damage during I/R injury.

Purpose

Given the pivotal role of endothelial cells in BBB, we hypothesized that the endothelial-specific expression of the longevity gene SIRT6 may protect the BBB from ischemia/reperfusion damage thus having a beneficial role on stroke outcome.

Methods

Endothelial-specific SIRT6 knockout (eSIRT6−/−) mice and control littermates (CTRL) underwent transient middle cerebral artery occlusion (tMCAO) for 45 min followed by 48 hours of reperfusion. Immunohistochemistry (IHC) was used to investigate BBB permeability by IgG extravasation and molecular mechanisms. Primary human brain microvascular endothelial cells (HBMVECs) transfected with either SIRT6 (siSIRT6) or scrambled (siSCR) small interfering RNA were subjected to hypoxia/reoxygenation (H/R). An in vitro BBB model consisting of a monolayer of siRNA-treated HBMVECs was established and barrier function was assessed by 48 h-lasting transendothelial electrical resistance measurement. SIRT6 expression in monocytes from stroke patients was correlated with the short-term neurological outcome [ΔNIHSS% = (NIHSS discharge-NIHSS admission)/ NIHSS admission*100].

Results

eSIRT6−/− displayed higher infarct volumes and lower survival rate compared to WT mice 48 h after tMCAO. The increased infarct volume was functionally relevant as eSIRT6−/− also showed worse post-stroke neurological impairment. Analysis of brain sections revealed increased BBB damage and increased endothelial expression of cleaved caspase-3 in eSIRT6−/− as compared to control littermates. In vitro, H/R reduced SIRT6 expression in HBMVECs. Mirroring the animal results, SIRT6 silencing impaired the barrier function of HBMVECs 48 h after exposure to H/R. In line with this, SIRT6-silenced HBMVECs showed reduced viability, increased cleaved caspase-3 expression and reduced activation of the anti-apoptotic survival pathway Akt as compared to control cells after H/R. The direct interaction between SIRT6 and Akt was confirmed by co-immunoprecipitation. In ischemic stroke patients, SIRT6 expression was higher in those with short-term neurological improvement (ΔNIHSS% >0) and negatively correlated with ΔNIHSS%.

Conclusion

Endothelial SIRT6 exerts a beneficial role in ischemic stroke by blunting I/R-mediated BBB damage. Specifically, SIRT6 reduces endothelial I/R-induced apoptotic death through activation of the protective Akt pathway. The longevity gene SIRT6 may represent a novel therapeutic target for the treatment of ischemic stroke.

Acknowledgement/Funding

Swiss National Science Foundation