A key role for the novel coronary artery disease gene JCAD in atherosclerosis via shear stress mechanotransduction.

AIMS: Genome-wide association studies (GWAS) have consistently identified an association between coronary artery disease (CAD) and a locus on chromosome 10 containing a single gene, JCAD (formerly KIAA1462). However, little is known about the mechanism by which JCAD could influence the development of atherosclerosis. METHODS AND RESULTS: Vascular function was quantified in subjects with CAD by flow-mediated dilatation (FMD) and vasorelaxation responses in isolated blood vessel segments. The JCAD risk allele identified by GWAS was associated with reduced FMD and reduced endothelial-dependent relaxations. To study the impact of loss of Jcad on atherosclerosis, Jcad-/- mice were crossed to an ApoE-/- background and fed a high-fat diet from 6 to16 weeks of age. Loss of Jcad did not affect blood pressure or heart rate. However, Jcad-/-ApoE-/- mice developed significantly less atherosclerosis in the aortic root and the inner curvature of the aortic arch. En face analysis revealed a striking reduction in pro-inflammatory adhesion molecules at sites of disturbed flow on the endothelial cell layer of Jcad-/- mice. Loss of Jcad lead to a reduced recovery perfusion in response to hind limb ischaemia, a model of altered in vivo flow. Knock down of JCAD using siRNA in primary human aortic endothelial cells significantly reduced the response to acute onset of flow, as evidenced by reduced phosphorylation of NF-КB, eNOS, and Akt. CONCLUSION: The novel CAD gene JCAD promotes atherosclerotic plaque formation via a role in the endothelial cell shear stress mechanotransduction pathway.

Platelet endothelial cell adhesion molecule-1 mediates endothelial-cardiomyocyte communication and regulates cardiac function.

BACKGROUND: Dilated cardiomyopathy is characterized by impaired contractility of cardiomyocytes, ventricular chamber dilatation, and systolic dysfunction. Although mutations in genes expressed in the cardiomyocyte are the best described causes of reduced contractility, the importance of endothelial-cardiomyocyte communication for proper cardiac function is increasingly appreciated. In the present study, we investigate the role of the endothelial adhesion molecule platelet endothelial cell adhesion molecule (PECAM-1) in the regulation of cardiac function. METHODS AND RESULTS: Using cell culture and animal models, we show that PECAM-1 expressed in endothelial cells (ECs) regulates cardiomyocyte contractility and cardiac function via the neuregulin-ErbB signaling pathway. Conscious echocardiography revealed left ventricular (LV) chamber dilation and systolic dysfunction in PECAM-1(-/-) mice in the absence of histological abnormalities or defects in cardiac capillary density. Despite deficits in global cardiac function, cardiomyocytes isolated from PECAM-1(-/-) hearts displayed normal baseline and isoproterenol-stimulated contractility. Mechanistically, absence of PECAM-1 resulted in elevated NO/ROS signaling and NRG-1 release from ECs, which resulted in augmented phosphorylation of its receptor ErbB2. Treatment of cardiomyocytes with conditioned media from PECAM-1(-/-) ECs resulted in enhanced ErbB2 activation, which was normalized by pre-treatment with an NRG-1 blocking antibody. To determine whether normalization of increased NRG-1 levels could correct cardiac function, PECAM-1(-/-) mice were treated with the NRG-1 blocking antibody. Echocardiography showed that treatment significantly improved cardiac function of PECAM-1(-/-) mice, as revealed by increased ejection fraction and fractional shortening. CONCLUSIONS: We identify a novel role for PECAM-1 in regulating cardiac function via a paracrine NRG1-ErbB pathway. These data highlight the importance of tightly regulated cellular communication for proper cardiac function.

Natural aminoacyl tRNA synthetase fragment enhances cardiac function after myocardial infarction.

A naturally-occurring fragment of tyrosyl-tRNA synthetase (TyrRS) has been shown in higher eukaryotes to 'moonlight' as a pro-angiogenic cytokine in addition to its primary role in protein translation. Pro-angiogenic cytokines have previously been proposed to be promising therapeutic mechanisms for the treatment of myocardial infarction. Here, we show that systemic delivery of the natural fragment of TyRS, mini-TyrRS, improves heart function in mice after myocardial infarction. This improvement is associated with reduced formation of scar tissue, increased angiogenesis of cardiac capillaries, recruitment of c-kitpos cells and proliferation of myocardial fibroblasts. This work demonstrates that mini-TyrRS has beneficial effects on cardiac repair and regeneration and offers support for the notion that elucidation of the ever expanding repertoire of noncanonical functions of aminoacyl tRNA synthetases offers unique opportunities for development of novel therapeutics.

Haemodynamic and extracellular matrix cues regulate the mechanical phenotype and stiffness of aortic endothelial cells.

Endothelial cells (ECs) lining blood vessels express many mechanosensors, including platelet endothelial cell adhesion molecule-1 (PECAM-1), that convert mechanical force into biochemical signals. While it is accepted that mechanical stresses and the mechanical properties of ECs regulate vessel health, the relationship between force and biological response remains elusive. Here we show that ECs integrate mechanical forces and extracellular matrix (ECM) cues to modulate their own mechanical properties. We demonstrate that the ECM influences EC response to tension on PECAM-1. ECs adherent on collagen display divergent stiffening and focal adhesion growth compared with ECs on fibronectin. This is because of protein kinase A (PKA)-dependent serine phosphorylation and inactivation of RhoA. PKA signalling regulates focal adhesion dynamics and EC compliance in response to shear stress in vitro and in vivo. Our study identifies an ECM-specific, mechanosensitive signalling pathway that regulates EC compliance and may serve as an atheroprotective mechanism that maintains blood vessel integrity in vivo.

A novel pathway spatiotemporally activates Rac1 and redox signaling in response to fluid shear stress.

Hemodynamic forces regulate embryonic organ development, hematopoiesis, vascular remodeling, and atherogenesis. The mechanosensory stimulus of blood flow initiates a complex network of intracellular pathways, including activation of Rac1 GTPase, establishment of endothelial cell (EC) polarity, and redox signaling. The activity of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase can be modulated by the GTP/GDP state of Rac1; however, the molecular mechanisms of Rac1 activation by flow are poorly understood. Here, we identify a novel polarity complex that directs localized Rac1 activation required for downstream reactive oxygen species (ROS) production. Vav2 is required for Rac1 GTP loading, whereas, surprisingly, Tiam1 functions as an adaptor in a VE-cadherin-p67phox-Par3 polarity complex that directs localized activation of Rac1. Furthermore, loss of Tiam1 led to the disruption of redox signaling both in vitro and in vivo. Our results describe a novel molecular cascade that regulates redox signaling by the coordinated regulation of Rac1 and by linking components of the polarity complex to the NADPH oxidase.

Endothelial Shc regulates arteriogenesis through dual control of arterial specification and inflammation via the notch and nuclear factor-κ-light-chain-enhancer of activated B-cell pathways.

RATIONALE: Arteriogenesis, the shear stress-driven remodeling of collateral arteries, is critical in restoring blood flow to ischemic tissue after a vascular occlusion. Our previous work has shown that the adaptor protein Shc mediates endothelial responses to shear stress in vitro. OBJECTIVE: To examine the role of the adaptor protein Shc in arteriogenesis and endothelial-dependent responses to shear stress in vivo. METHODS AND RESULTS: Conditional knockout mice in which Shc is deleted from endothelial cells were subjected to femoral artery ligation. Hindlimb perfusion recovery was attenuated in Shc conditional knockout mice compared with littermate controls. Reduced perfusion was associated with blunted collateral remodeling and reduced capillary density. Bone marrow transplantation experiments revealed that endothelial Shc is required for perfusion recovery because loss of Shc in bone marrow-derived hematopoietic cells had no effect on recovery. Mechanistically, Shc deficiency resulted in impaired activation of the nuclear factor κ-light-chain-enhancer of activated B-cell-dependent inflammatory pathway and reduced CD45⁺ cell infiltration. Unexpectedly, Shc was required for arterial specification of the remodeling arteriole by mediating upregulation of the arterial endothelial cell marker ephrinB2 and activation of the Notch pathway. In vitro experiments confirmed that Shc was required for shear stress-induced activation of the Notch pathway and downstream arterial specification through a mechanism that involves upregulation of Notch ligands delta-like 1 and delta-like 4. CONCLUSIONS: Shc mediates activation of 2 key signaling pathways that are critical for inflammation and arterial specification; collectively, these pathways contribute to arteriogenesis and the recovery of blood perfusion.

The adaptor protein Shc integrates growth factor and ECM signaling during postnatal angiogenesis.

Angiogenesis requires integration of cues from growth factors, extracellular matrix (ECM) proteins, and their receptors in endothelial cells. In the present study, we show that the adaptor protein Shc is required for angiogenesis in zebrafish, mice, and cell-culture models. Shc knockdown zebrafish embryos show defects in intersegmental vessel sprouting in the trunk. Shc flox/flox; Tie2-Cre mice display reduced angiogenesis in the retinal neovascularization model and in response to VEGF in the Matrigel plug assay in vivo. Functional studies reveal a model in which Shc is required for integrin-mediated spreading and migration specifically on fibronectin, as well as endothelial cell survival in response to VEGF. Mechanistically, Shc is required for activation of the Akt pathway downstream of both integrin and VEGF signaling, as well as for integration of signals from these 2 receptors when cells are grown on fibronectin. Therefore, we have identified a unique mechanism in which signals from 2 critical angiogenic signaling axes, integrins and VEGFR-2, converge at Shc to regulate postnatal angiogenesis.

Role of PECAM-1 in arteriogenesis and specification of preexisting collaterals.

RATIONALE: Hemodynamic forces caused by the altered blood flow in response to an occlusion lead to the induction of collateral remodeling and arteriogenesis. Previous work showed that platelet endothelial cell adhesion molecule (PECAM)-1 is a component of a mechanosensory complex that mediates endothelial cell responses to shear stress. OBJECTIVE: We hypothesized that PECAM-1 plays an important role in arteriogenesis and collateral remodeling. METHODS AND RESULTS: PECAM-1 knockout (KO) and wild-type littermates underwent femoral artery ligation. Surprisingly, tissue perfusion and collateral-dependent blood flow were significantly increased in the KO mice immediately after surgery. Histology confirmed larger caliber of preexisting collaterals in the KO mice. Additionally, KO mice showed blunted recovery of perfusion from hindlimb ischemia and reduced collateral remodeling, because of deficits in shear stress-induced signaling, including activation of the nuclear factor κB pathway and inflammatory cell accumulation. Partial recovery was associated with normal responses to circumferential wall tension in the absence of PECAM-1, as evidenced by the upregulation of ephrin B2 and monocyte chemoattractant protein-1, which are 2 stretch-induced regulators of arteriogenesis, both in vitro and in vivo. CONCLUSIONS: Our findings suggest a novel role for PECAM-1 in arteriogenesis and collateral remodeling. Furthermore, we identify PECAM-1 as the first molecule that determines preexisting collateral diameter.

Inhibition of tumor angiogenesis by a natural fragment of a tRNA synthetase.

Human tyrosyl- and tryptophanyl-tRNA synthetases (TyrRS and TrpRS, respectively) link protein synthesis to signal-transduction pathways, including angiogenesis. Fragments of TyrRS stimulate angiogenesis, whereas those of TrpRS (T2-TrpRS) inhibit angiogenesis. Thus, these two synthetases acquired opposing activities during evolution, possibly as a coordinated mechanism for regulating angiogenesis. The recent identification of the cellular target of T2-TrpRS sheds light into the mechanism of angiogenesis inhibition. This mechanism provides a molecular basis for the lack of effect of T2-TrpRS on the normal vasculature. With these features, we suggest that this fragment of a tRNA synthetase might safely be used to arrest neovascularization of tumors. In particular, an anti-angiogenesis agent that stops the growth of tumor vessels without affecting normal vessels might serve as an adjunct to cytotoxic therapy.