The emerging role of YAP/TAZ in mechanotransduction

In this review, we discuss new emerging medical applications of the rapidly evolving field of mammalian synthetic biology. We start with simple mammalian synthetic biological components and move towards more complex and therapy-oriented gene circuits. A comprehensive list of ON–OFF switches, categorized into transcriptional, post-transcriptional, translational and post-translational, is presented in the first sections. Subsequently, Boolean logic gates, synthetic mammalian oscillators and toggle switches will be described. Several synthetic gene networks are further reviewed in the medical applications section, including cancer therapy gene circuits, immuno-regulatory networks, among others. The final sections focus on the applicability of synthetic gene networks to drug discovery, drug delivery, receptor-activating gene circuits and mammalian biomanufacturing processes.

Studies in animals and patients indicate that rapamycin affects vasodilatation differently in outer and inner curvatures of blood vessels. We evaluated in this study whether rapamycin affects endothelial nitric oxide synthase (eNOS) responsiveness to shear stress under normo- and hypercholesteraemic conditions to explain these findings. Shear stress levels were varied over a large range of values in carotid arteries of transgenic mice expressing human eNOS fused to enhanced green fluorescence protein. The mice were divided into control, low-dose rapamycin (3 µg/kg/day), and high-dose rapamycin (3 mg/kg/day) groups and into normocholesteraemic and hypercholesteraemic (ApoE−/− on high cholesterol diet for 3–4 weeks) groups. The effect of rapamycin treatment on eNOS was evaluated by quantification of eNOS expression and of intracellular protein levels by en face confocal microscopy. A sigmoid curve fit was used to described these data. The efficacy of treatment was confirmed by measurement of rapamycin serum levels (2.0 ± 0.5 ng/mL), and of p27^kip1 expression in vascular tissue (increased by 2.4 ± 0.5-fold). In control carotid arteries, eNOS expression increased by 1.8 ± 0.3-fold in response to rapamycin. In the treated vessels, rapamycin reduced maximal eNOS expression at high shear stress levels (>5 Pa) in a dose-dependent way and shifted the sigmoid curve to the right. Hypercholesteraemia had a tendency to increase the leftward shift and the reduction in maximal eNOS expression (P = 0.07). Rapamycin is associated with high eNOS in low shear regions, i.e. in atherogenic regions, protecting these regions against atherosclerosis, and is associated with a reduction of eNOS at high shear stress affecting vasomotion in these regions.

In this review, we summarized the effect of mechanical factors (shear and wall stress) on thin-cap fibroatheroma formation and rupture. To make this review understandable for a biology-oriented audience, we start with detailed definitions of relevant mechanical metrics. We then describe how biomechanics has supported histopathologic efforts to understand the basis of plaque rupture. In addition to plaque rupture, biomechanics also contributes toward the progression of thin-cap fibroatheroma through a multitude of reported mechanobiological mechanisms. We thus propose a new mechanism whereby both shear stress and wall stress interact to create thin-cap fibroatheromas. Specifically, when regions of certain blood flow and wall mechanical stimuli coincide, they synergistically create inflammation within the cellular environment that can lead to thin-cap fibroatheroma rupture. A consequence of this postulate is that local shear stress is not sufficient to cause rupture, but it must coincide with regions of local tissue stiffening and stress concentrations that can occur during plaque progression. Because such changes to the wall mechanics occur over a micrometer scale, high spatial resolution imaging techniques will be necessary to evaluate this hypothesis and ultimately predict plaque rupture in a clinical environment.

Background. The chemokine CXCL10 is specifically upregulated during experimental development of plaque with an unstable phenotype. In this study we evaluated the functional consequences of these findings in mice and humans.Methods and Results. InApoE-/-mice, we induced unstable plaque with using a flow-altering device around the carotid artery. From week 1 to 4, mice were injected with a neutralizing CXCL10 antibody. After 9 weeks, CXCL10 inhibition resulted in a more stable plaque phenotype: collagen increased by 58% (P=0.002), smooth muscle cell content increased 2-fold (P=0.03), while macrophage MHC class II expression decreased by 50% (P=0.005). Also, the size of necrotic cores decreased by 41% (P=0.01). In 106 human carotid endarterectomy specimens we found that increasing concentrations of CXCL10 strongly associate with an increase in atheromatous plaque phenotype (ANOVA,P=0.003), with high macrophage, low smooth muscle cell, and low collagen content.Conclusions. In the present study we showed that CXCL10 is associated with the development of vulnerable plaque in human and mice. We conclude that CXCL10 might provide a new lead towards plaque-stabilizing therapy.