Modulating the functional contributions of c-Myc to the human endothelial cell cyclic strain response.

This study addresses whether pathological levels of cyclic strain activate the c-Myc promoter, leading to c-Myc transcription and downstream gene induction in human umbilical vein endothelial cells (HUVEC) or human aortic endothelial cells (HAEC). mRNA and protein expression of c-Myc under physiological (6-10%) and pathological cyclic strain conditions (20%) were studied. Both c-Myc mRNA and protein expression increased 2-3-fold in HUVEC cyclically strained at 20%. c-Myc protein increased 4-fold in HAEC. In HUVEC, expression of mRNA peaked at 1.5-2 h. Subsequently, the effect of modulating c-Myc on potential downstream gene targets was determined. A small molecular weight compound that binds to and stabilizes the silencer element in the c-Myc promoter attenuates cyclic strain-induced c-Myc transcription by about 50%. This compound also modulates c-Myc downstream gene targets that may be instrumental in induction of vascular disease. Cyclic strain-induced gene expression of vascular endothelial growth factor, proliferating cell nuclear antigen and heat shock protein 60 are attenuated by this compound. These results offer a possible mechanism and promising clinical treatment for vascular diseases initiated by increased cyclic strain.

Gene expression of endothelial cells under pulsatile non-reversing vs. steady shear stress; comparison of nitric oxide production.

Pulsations in arterial blood flow expose the endothelium to diverse mechanical forces that may differentially regulate endothelial cell (EC) phenotype. We postulated that pulsatile non-reversing shear stress (typical of the common carotid artery), would produce a more "athero-protective" gene expression pattern compared with steady shear stress of the same mean value. Transcriptional analysis of human umbilical vein endothelial cells (HUVEC) subjected to 24 h of pulsatile shear stress (average = 13 dyne/cm(2), range = 7-25 dyne/cm(2); 1 Hz) or steady shear stress (13 dyne/cm(2)) identified approximately 200 differentially expressed genes. Hierarchical cluster analysis indicated that HUVEC respond similarly to both types of shear stress (Pearson correlation coefficient = 0.785). However, categorization of the differentially expressed genes with Ingenuity Pathways Analysis and with Expression Analysis Systematic Explorer revealed possible differences in nitric oxide (NO) production and signaling. Consistent with gene expression analysis, pulsatile shear stress significantly attenuated NO production relative to steady shear stress (0.77 +/- 0.08, p < 0.01) in HUVEC without significantly altering the levels of intracellular reactive oxygen species (0.95 +/- 0.14, p = 0.65). These results demonstrate that the common carotid flow waveform elicits subtle changes in HUVEC responses to arterial levels of shear stress, which lead to differences in NO production.