Locus-Conserved Circular RNA cZNF292 Controls Endothelial Cell Flow Responses.

BACKGROUND: Circular RNAs (circRNAs) are generated by back splicing of mostly mRNAs and are gaining increasing attention as a novel class of regulatory RNAs that control various cellular functions. However, their physiological roles and functional conservation in vivo are rarely addressed, given the inherent challenges of their genetic inactivation. Here, we aimed to identify locus conserved circRNAs in mice and humans, which can be genetically deleted due to retained intronic elements not contained in the mRNA host gene to eventually address functional conservation. METHODS AND RESULTS: Combining published endothelial RNA-sequencing data sets with circRNAs of the circATLAS databank, we identified locus-conserved circRNA retaining intronic elements between mice and humans. CRISPR/Cas9 mediated genetic depletion of the top expressed circRNA cZfp292 resulted in an altered endothelial morphology and aberrant flow alignment in the aorta in vivo. Consistently, depletion of cZNF292 in endothelial cells in vitro abolished laminar flow-induced alterations in cell orientation, paxillin localization and focal adhesion organization. Mechanistically, we identified the protein SDOS (syndesmos) to specifically interact with cZNF292 in endothelial cells by RNA-affinity purification and subsequent mass spectrometry analysis. Silencing of SDOS or its protein binding partner Syndecan-4, or mutation of the SDOS-cZNF292 binding site, prevented laminar flow-induced cytoskeletal reorganization thereby recapitulating cZfp292 knockout phenotypes. CONCLUSIONS: Together, our data reveal a hitherto unknown role of cZNF292/cZfp292 in endothelial flow responses, which influences endothelial shape.

Aging impairs the neurovascular interface in the heart.

Aging is a major risk factor for impaired cardiovascular health. Because the aging myocardium is characterized by microcirculatory dysfunction, and because nerves align with vessels, we assessed the impact of aging on the cardiac neurovascular interface. We report that aging reduces nerve density in the ventricle and dysregulates vascular-derived neuroregulatory genes. Aging down-regulates microRNA 145 (miR-145) and derepresses the neurorepulsive factor semaphorin-3A. miR-145 deletion, which increased Sema3a expression or endothelial Sema3a overexpression, reduced axon density, mimicking the aged-heart phenotype. Removal of senescent cells, which accumulated with chronological age in parallel to the decline in nerve density, rescued age-induced denervation, reversed Sema3a expression, preserved heart rate patterns, and reduced electrical instability. These data suggest that senescence-mediated regulation of nerve density contributes to age-associated cardiac dysfunction.

The hydrogen-peroxide producing NADPH oxidase 4 does not limit neointima development after vascular injury in mice.

OBJECTIVE: The NADPH oxidase Nox4 is an important source of H2O2. Nox4-derived H2O2 limits vascular inflammation and promotes smooth muscle differentiation. On this basis, the role of Nox4 for restenosis development was determined in the mouse carotid artery injury model. METHODS AND RESULTS: Genetic deletion of Nox4 by a tamoxifen-activated Cre-Lox-system did not impact on neointima formation in the carotid artery wire injury model. To understand this unexpected finding, time-resolved single-cell RNA-sequencing (scRNAseq) from injured carotid arteries of control mice and massive-analysis-of-cDNA-ends (MACE)-RNAseq from the neointima harvested by laser capture microdissection of control and Nox4 knockout mice was performed. This revealed that resting smooth muscle cells (SMCs) and fibroblasts exhibit high Nox4 expression, but that the proliferating de-differentiated SMCs, which give rise to the neointima, have low Nox4 expression. In line with this, the first weeks after injury, gene expression was unchanged between the carotid artery neointimas of control and Nox4 knockout mice. CONCLUSION: Upon vascular injury, Nox4 expression is transiently lost in the cells which comprise the neointima. NADPH oxidase 4 therefore does not interfere with restenosis development after wire-induced vascular injury.

Deletion of NoxO1 limits atherosclerosis development in female mice.

OBJECTIVE: Oxidative stress is a risk factor for atherosclerosis. NADPH oxidases of the Nox family produce ROS but their contribution to atherosclerosis development is less clear. Nox2 promotes and Nox4 rather limits atherosclerosis. Although Nox1 with its cytosolic co-factors are largely expressed in epithelial cells, a role for Nox1 for atherosclerosis development was suggested. To further define the role of this homologue, the role of its essential cytosolic cofactor, NoxO1, was determined for atherosclerosis development with the aid of knockout mice. METHODS AND RESULTS: Wildtype (WT) and NoxO1 knockout mice were treated with high fat diet and adeno-associated virus (AAV) overexpressing pro-protein convertase subtilisin/kexin type 9 (PCSK9) to induce hepatic low-density lipoprotein (LDL) receptor loss. As a result, massive hypercholesterolemia was induced and spontaneous atherosclerosis developed within three month. Deletion of NoxO1 reduced atherosclerosis formation in brachiocephalic artery and aortic arch in female but not male NoxO1-/- mice as compared to WT littermates. This was associated with a reduced pro-inflammatory cytokine signature in the plasma of female but not male NoxO1-/- mice. MACE-RNAseq of the vessel did not reveal this signature and the expression of the Nox1/NoxO1 system was low to not detectable. CONCLUSIONS: The scaffolding protein NoxO1 plays some role in atherosclerosis development in female mice probably by attenuating the global inflammatory burden.

The polarity protein Scrib limits atherosclerosis development in mice.

AIMS: The protein Scrib (Scribble 1) is known to control apico-basal polarity in epithelial cells. The role of polarity proteins in the vascular system remains poorly characterized; however, we previously reported that Scrib maintains the endothelial phenotype and directed migration. On this basis, we hypothesized that Scrib has anti-atherosclerotic functions. METHODS AND RESULTS: Tamoxifen-induced Scrib-knockout mice were crossed with ApoE-/- knockout mice and spontaneous atherosclerosis under high-fat diet (HFD), as well as accelerated atherosclerosis in response to partial carotid artery ligation and HFD, was induced. Deletion of Scrib resulted in increased atherosclerosis development in both models. Mechanistically, flow- as well as acetylcholine-induced endothelium-dependent relaxation and AKT phosphorylation was reduced by deletion of Scrib, whereas vascular permeability and leucocyte extravasation were increased after Scrib knockout. Scrib immune pull down in primary carotid endothelial cells and mass spectrometry identified Arhgef7 (Rho Guanine Nucleotide Exchange Factor 7, ßPix) as interaction partner. Scrib or Arhgef7 down-regulation by siRNA reduced the endothelial barrier function in human umbilical vein endothelial cells. Gene expression analysis from murine samples and from human biobank material of carotid endarterectomies indicated that loss of Scrib resulted in endothelial dedifferentiation with a decreased expression of endothelial signature genes. CONCLUSIONS: By maintaining a quiescent endothelial phenotype, the polarity protein Scrib elicits anti-atherosclerotic functions.