Abstract 638: Flow Modulates the Endothelial Expression of Neuronal Guidance Cues

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Disturbed hemodynamic conditions lead to impaired homeostasis of the vascular endothelium and, subsequently, influx and retention of monocytes in the arterial wall. Emerging data suggest that, aside from a role in the development and maintenance of the nervous system, neuronal guidance cues (NGCs) are also required for physiological and pathological immune responses. We recently reported that NGCs are differentially expressed in atherosclerosis-prone and -resistant aortic sites in LDLR-/-mice during early atherogenesis. Here, we detail our investigation of the role of shear stress on the expression levels of NGCs (ephrins, slits, netrins and semaphorins) in human umbilical vein endothelial cells (ECs) under atherosclerosis-prone (static) and -protective (laminar flow) conditions. To gain insight into the consequences of laminar flow on the mRNA expression levels of NGCs in ECs, the cells were exposed to 0, 1 or 7 days of laminar flow (shear stress 10 dynes/cm2, IBIDI-flow system). The mRNA levels of the leukocyte attractant NGCs EphrinA1, B1 and B2 were all reduced by laminar flow, in particular for EphrinB2 (52%[[Unable to Display Character: ]], p=0.02). In contrast, the potentially anti-inflammatory Slit2 displayed a striking early response to flow, with a marked increase in mRNA expression after 1day (2.2-fold, p=0.02), but was not sustained at Day 7. Interestingly, the expression levels of netrin-4, semaphorin 3F and semaphorin 4B were upregulated in ECs exposed to laminar flow for 1 and 7 days (2.1-fold, p=0.05; 3.0-fold, p=0.04; 2.1-fold, p=0.05; respectively), suggesting these NGCs as potentially athero-protective anti-inflammatory leukocyte repellent. Moreover, overexpression of the shear-induced transcription factor Krüppel-like factor 2 (KLF2) in static cultured ECs induced the expression of both semaphorin3F mRNA and protein (3.8 fold and 3.9 fold, respectively), while netrin-4 mRNA and protein upregulation appeared to be independent of KLF2. Taken together, our study provides novel insight into regulation of the endothelial NGC expression profile by flow, which could implicate NGCs as mediators of the EC function by facilitating repulsion or attraction of monocytes under varying hemodynamic conditions.