Nox4 and HO‐1 Mediate Effects of Fluid Shear Stress on PLGF in an In Vitro Model of the Vessel Wall

Abstract

Fluid shear stress (FSS) is a key stimulus for arteriogenesis (remodeling of collateral arterioles after upstream occlusion) and placental growth factor (PLGF) is an important arteriogenic mediator. We previously showed that elevated FSS increases PLGF via reactive oxygen species (ROS) in vitro, and that NADP(H) oxidases (Nox) are a likely source of ROS in this pathway. In this study, we tested the hypotheses that 1) Nox4 contributes to this pathway and 2) heme oxygenase 1 (HO-1) is downstream of Nox4. We tested these hypotheses in a model consisting of human coronary artery endothelial cells (EC) and smooth muscle cells (SMC) cultured on either side of Transwell inserts. EC were exposed to pulsatile FSS of 0.07 Pa (normal shear, NS), 1.24 Pa (high shear, HS), or 0.00 Pa (control) for 2 h. Nox-4 was the dominant isoform in both cell types. After 4 h, Nox-4 was increased ~64% by HS relative to NS and control (n=3, p<0.01). Nox-4 siRNA attenuated the effect of HS on PLGF (n=5, p<0.05). Heme oxygenase-1 (HO-1) was also increased by HS (~50%, n=5, p<0.01). Inhibition of HO-1 with zinc protoporphyrin (30 µM, n=5, p<0.01) or HO-1 siRNA (n=3, p<0.01) abolished the effect of HS on PLGF. Conversely, induction of HO-1 with hemin increased PLGF ~60% (n=3, p<0.01). Lastly, the effects of the individual enzymatic products of HO-1 on PLGF were tested by treating cells with a CO donor (CORM-A1), biliverdin, or ferric ammonium citrate (FAC). Both CORM-A1 (0-400 µM) and biliverdin (0-100 µM) dose-dependently decreased PLGF to ~50% of control (n=3, p<0.01). In contrast, FAC (10-200 µg/ml) increased PLGF ~2-fold (n=3, p<0.01). We conclude that Nox4, HO-1 and iron mediate upregulation of PLGF by FSS. Support: R01 HL084494 (PL).