Abstract 535: Shear Stress Upregulates Placental Growth Factor in an in vitro Model of the Vessel Wall in a Reactive Oxygen Species Dependent Manner
Arteriogenesis is the process by which mature arteries form from collateral arterioles after upstream arterial stenosis or occlusion. During collateral remodeling, monocytes are recruited to the vessel wall. Placental growth factor (PLGF) is a potent stimulator of arteriogenesis via monocyte recruitment. Although fluid shear stress is thought to be the primary signal for arteriogenesis, its role in regulating PLGF expression is unknown. However, PLGF is increased in collaterals by upstream arterial ligation. Therefore, we hypothesized that PLGF expression is regulated by shear stress. To test this hypothesis, we created an in vitro model of coronary vessels, consisting of human coronary artery endothelial cells (HCAEC) and human coronary artery smooth muscle cells (HCASMC) cocultured on porous Transwell inserts. HCAEC were then exposed to normal (low) shear stress (LSS) (time average 0.7 dyne/cm2), high shear stress (HSS) (time average 12.4 dyne/cm2), or no shear (static) for 2 hours. HSS significantly increased secreted PLGF protein compared to LSS (~25%, n= 5, p < 0.05) as determined by ELISA. Knockdown of PLGF by siRNA in HCAEC significantly reduced secreted PLGF protein while knockdown in HCASMC had no significant effect, suggesting HCAEC are the primary source of PLGF protein (n=4, p<0.01). Both H2O2 and nitrite (an index of NO production) were significantly increased by shear stress compared to static control (~35%, n= 5, p < 0.05). Treatment with catalase (500 U/mL) attenuated the effects of HSS on PLGF protein levels, whereas L-NAME (100 μM) had no significant effect. Treatment with 5 μM diphenyleneiodonium mimicked the effects of catalase on PLGF protein levels, implicating NADPH oxidase (Nox) as the source of H2O2. PCR analysis revealed Nox-4 as the predominant isoform present in both cell types. Relative Nox-4 mRNA was increased by HSS in HCAEC compared to both LSS and control. Relative gene expression of heme oxygenase-1 (HO-1), which is regulated by Nox-4, was also increased in both cell types by HSS, suggesting the possibility that HO-1 may contribute to the regulation of PLGF expression. These data demonstrate that redox signaling plays a role in the mechanotransduction of shear stress into a regulatory signal for PLGF expression.
- © 2013 by American Heart Association, Inc.