Smooth muscle cell FTO regulates contractile function.

The fat mass and obesity gene (FTO) is a N6-methyladenosine RNA demethylase that was initially linked by Genome-wide association studies to increased rates of obesity. Subsequent studies have revealed multiple mass-independent effects of the gene, including cardiac myocyte contractility. We created a mouse with a conditional and inducible smooth muscle cell deletion of Fto (Myh11 Cre+ Ftofl/fl) and did not observe any changes in mouse body mass or mitochondrial metabolism. However, the mice had significantly decreased blood pressure (hypotensive), despite increased heart rate and sodium, and significantly increased plasma renin. Remarkably, the third-order mesenteric arteries from these mice had almost no myogenic tone or capacity to constrict to smooth muscle depolarization or phenylephrine. Microarray analysis from Fto-/--isolated smooth muscle cells demonstrated a significant decrease in serum response factor (Srf) and the downstream effectors Acta2, Myocd, and Tagln; this was confirmed in cultured human coronary arteries with FTO siRNA. We conclude Fto is an important component to the contractility of smooth muscle cells.NEW & NOTEWORTHY We show a key role for the fat mass obesity (FTO) gene in regulating smooth muscle contractility, possibly by methylation of serum response factor (Srf).

A venous-specific purinergic signaling cascade initiated by Pannexin 1 regulates TNFα-induced increases in endothelial permeability.

The endothelial cell barrier regulates the passage of fluid between the bloodstream and underlying tissues, and barrier function impairment exacerbates the severity of inflammatory insults. To understand how inflammation alters vessel permeability, we studied the effects of the proinflammatory cytokine TNFα on transendothelial permeability and electrophysiology in ex vivo murine veins and arteries. We found that TNFα specifically decreased the barrier function of venous endothelium without affecting that of arterial endothelium. On the basis of RNA expression profiling and protein analysis, we found that claudin-11 (CLDN11) was the predominant claudin in venous endothelial cells and that there was little, if any, CLDN11 in arterial endothelial cells. Consistent with a difference in claudin composition, TNFα increased the permselectivity of Cl- over Na+ in venous but not arterial endothelium. The vein-specific effects of TNFα also required the activation of Pannexin 1 (Panx1) channels and the CD39-mediated hydrolysis of ATP to adenosine, which subsequently stimulated A2A adenosine receptors. Moreover, the increase in vein permeability required the activation of the Ca2+ channel TRPV4 downstream of Panx1 activation. Panx1-deficient mice resisted the pathologic effects of sepsis induced by cecal ligation and puncture on life span and lung vascular permeability. These data provide a targetable pathway with the potential to promote vein barrier function and prevent the deleterious effects of vascular leak in response to inflammation.

Loss of Endothelial FTO Antagonizes Obesity-Induced Metabolic and Vascular Dysfunction.

RATIONALE: Increasing prevalence of obesity and its associated risk with cardiovascular diseases demands a better understanding of the contribution of different cell types within this complex disease for developing new treatment options. Previous studies could prove a fundamental role of FTO (fat mass and obesity-associated protein) within obesity; however, its functional role within different cell types is less understood. OBJECTIVES: We identify endothelial FTO as a previously unknown central regulator of both obesity-induced metabolic and vascular alterations. METHODS AND RESULTS: We generated endothelial Fto-deficient mice and analyzed the impact of obesity on those mice. While the loss of endothelial FTO did not influence the development of obesity and dyslipidemia, it protected mice from high-fat diet-induced glucose intolerance and insulin resistance by increasing AKT (protein kinase B) phosphorylation in endothelial cells and skeletal muscle. Furthermore, loss of endothelial FTO prevented the development of obesity-induced hypertension by preserving myogenic tone in resistance arteries. In Fto-deficient arteries, microarray analysis identified upregulation of L-Pgds with significant increases in prostaglandin D2 levels. Blockade of prostaglandin D2 synthesis inhibited the myogenic tone protection in resistance arteries of endothelial Fto-deficient mice on high-fat diet; conversely, direct addition of prostaglandin D2 rescued myogenic tone in high-fat diet-fed control mice. Myogenic tone was increased in obese human arteries with FTO inhibitors or prostaglandin D2 application. CONCLUSIONS: These data identify endothelial FTO as a previously unknown regulator in the development of obesity-induced metabolic and vascular changes, which is independent of its known function in regulation of obesity.

Leptin promotes neointima formation and smooth muscle cell proliferation via NADPH oxidase activation and signalling in caveolin-rich microdomains.

AIMS: Apolipoprotein E (apoE) may act as a vasculoprotective factor by promoting plasma lipid clearance and cholesterol efflux. Moreover, apoE accumulates at sites of vascular injury and modulates the effect of growth factors on smooth muscle cells (SMCs). Experimental data suggested that hypothalamic apoE expression is reduced in obesity and associated with leptin resistance. In this study, we examined the role of apoE in mediating the effects of leptin on vascular lesion formation. METHODS AND RESULTS: Leptin was administered to apoE knockout (apoE-/-) mice via osmotic pumps to increase its circulating levels. Morphometric analysis revealed that leptin did not alter neointima formation and failed to increase α-actin- or PCNA-immunopositive SMCs after vascular injury. Similar findings were obtained after analysis of atherosclerotic lesions. Comparison of apoE-/-, wild-type, or LDL receptor-/- mice and functional analyses in aortic SMCs from WT or apoE-/- mice or human arterial SMCs after treatment with small interfering (si)RNA or heparinase revealed that leptin requires the presence of apoE, expressed, secreted and bound to the cell surface, to fully activate leptin receptor signalling and to promote SMC proliferation and neointima formation. Mechanistically, leptin induced the phosphorylation and membrane translocation of caveolin (cav)-1, and apoE down-regulation or caveolae disruption inhibited the leptin-induced p47phox activation, ROS formation and SMC proliferation. Finally, leptin failed to increase neointima formation in mice lacking cav-1. CONCLUSION: Our findings suggest that apoE mediates the effects of leptin on vascular lesion formation by stabilizing cav-1-enriched cell membrane microdomains in SMCs, thus allowing NADPH oxidase assembly and ROS-mediated mitogenic signalling.