CD73 Promotes Age-Dependent Accretion of Atherosclerosis.

OBJECTIVE: CD73 is an ectonucleotidase which catalyzes the conversion of AMP (adenosine monophosphate) to adenosine. Adenosine has been shown to be anti-inflammatory and vasorelaxant. The impact of ectonucleotidases on age-dependent atherosclerosis remains unclear. Our aim was to investigate the role of CD73 in age-dependent accumulation of atherosclerosis. Approach and results: Mice doubly deficient in CD73 and ApoE (apolipoprotein E; (cd73-/-/apoE-/-) were generated, and the extent of aortic atherosclerotic plaque was compared with apoE-/- controls at 12, 20, 32, and 52 weeks. By 12 weeks of age, cd73-/-/apoE-/- mice exhibited a significant increase in plaque (1.4±0.5% of the total vessel surface versus 0.4±0.1% in apoE-/- controls, P<0.005). By 20 weeks of age, this difference disappeared (2.9±0.4% versus 3.3±0.7%). A significant reversal in phenotype emerged at 32 weeks (9.8±1.2% versus 18.3±1.4%; P<0.0001) and persisted at the 52 week timepoint (22.4±2.1% versus 37.0±2.1%; P<0.0001). The inflammatory response to aging was found to be comparable between cd73-/-/apoE-/- mice and apoE-/- controls. A reduction in lipolysis in CD73 competent mice was observed, even with similar plasma lipid levels (cd73-/-/apoE-/- versus apoE-/- at 12 weeks [16.2±0.7 versus 9.5±1.4 nmol glycerol/well], 32 weeks [24.1±1.5 versus 7.4±0.4 nmol/well], and 52 weeks [13.8±0.62 versus 12.7±2.0 nmol/well], P<0.001). CONCLUSIONS: At early time points, CD73 exerts a subtle antiatherosclerotic influence, but with age, the pattern reverses, and the presence of CD73 promoted suppression of lipid catabolism.

Compartmentalized Actions of the Plasminogen Activator Inhibitors, PAI-1 and Nsp, in Ischemic Stroke.

Tissue plasminogen activator (tPA) is a multifunctional protease. In blood tPA is best understood for its role in fibrinolysis, whereas in the brain tPA is reported to regulate blood-brain barrier (BBB) function and to promote neurodegeneration. Thrombolytic tPA is used for the treatment of ischemic stroke. However, its use is associated with an increased risk of hemorrhagic transformation. In blood the primary regulator of tPA activity is plasminogen activator inhibitor 1 (PAI-1), whereas in the brain, its primary inhibitor is thought to be neuroserpin (Nsp). In this study, we compare the effects of PAI-1 and Nsp deficiency in a mouse model of ischemic stroke and show that tPA has both beneficial and harmful effects that are differentially regulated by PAI-1 and Nsp. Following ischemic stroke Nsp deficiency in mice leads to larger strokes, increased BBB permeability, and increased spontaneous intracerebral hemorrhage. In contrast, PAI-1 deficiency results in smaller infarcts and increased cerebral blood flow recovery. Mechanistically, our data suggests that these differences are largely due to the compartmentalized action of PAI-1 and Nsp, with Nsp deficiency enhancing tPA activity in the CNS which increases BBB permeability and worsens stroke outcomes, while PAI-1 deficiency enhances fibrinolysis and improves recovery. Finally, we show that treatment with a combination therapy that enhances endogenous fibrinolysis by inhibiting PAI-1 with MDI-2268 and reduces BBB permeability by inhibiting tPA-mediated PDGFRα signaling with imatinib significantly reduces infarct size compared to vehicle-treated mice and to mice with either treatment alone.

Calcineurin initiates smooth muscle differentiation in neural crest stem cells.

The process of vascular smooth muscle cell (vSMC) differentiation is critical to embryonic angiogenesis. However, despite its importance, the vSMC differentiation program remains largely undefined. Murine gene disruption studies have identified several gene products that are necessary for vSMC differentiation, but these methodologies cannot establish whether or not a factor is sufficient to initiate the differentiation program. A gain-of-function system consisting of normal vSMC progenitor cells would serve as a useful complement to whole animal loss-of-function studies. We use such a system here, namely freshly isolated rat neural crest stem cells (NCSCs), to show that activation of the calcineurin signaling pathway is sufficient to drive these cells toward a smooth muscle fate. In addition, we present data suggesting that transforming growth factor (TGF)-beta1, which also causes NCSCs to differentiate into smooth muscle, activates calcineurin signaling in NCSCs, leading to a model in which activation of calcineurin signaling is the mechanism by which TGF-beta1 causes SMC differentiation in these cells.