Abstract 343: Endothelial Regulator of G-Protein Signaling-5 Maintains Endothelial Permeability and Controls Vascular Smooth Muscle Cell Migration in vitro

Abstract

GAP-inhibitor, RGS5 has been described as a VSMC marker and is associated with plaque stability. Its role in endothelial cells (EC) is unclear. We examined RGS5 expression patterns in human vasculature and hypothesized that loss of RGS5 alters EC biology and crosstalk with VSMC such, that it could promote atherogenesis.

Methods: Human internal mammary artery (IMA), saphenous vein (SV) and failing myocardium (MYO) samples were stained for RGS5, αSMA and vWF. RGS5 or scrambled siRNA knocked down (RGS5-KD) HUVECs were used. oxLDL or TNFα induced THP1-adhesion to HUVECs was assessed. The 2h diffusion rate of Evans-blue bound to 0.1%-BSA/DPBS through a HUVEC monolayer was spectrophotometrically measured in the presence of PTX. HUVECs were also subjected to spheroid sprouting in collagen/methylcellulose. qRT-PCR using the Δ(ΔCT) method with HPRT as house-keeper was used to assess MMP-9, VEGF-A and caveolin-1 expression in transfected cells. To test RGS5-dependent paracrine effects of EC-secreted factors on VSMC, isotonic buffer was conditioned for 2h by transfected HUVECs (CB). CB was added to VSMC during a scratch assay.

Results: RGS5 signal was enhanced in the endothelium of SV compared to IMA (63±9 vs 22±4 %vessel perimeter, p<0.05, n=4). Similar patterns were observed in myocardium. In IMA plaques RGS5 was prominently reduced in medial VSMC underlying and in the endothelium covering the plaque compared to non-diseased vessels. No effect on TNFα- or oxLDL-induced adhesion was observed in RGS5-KD HUVECs. HUVEC permeability increased in RGS5-KD cells (1 vs 2.5± 0.2 normalized OD, n=4, p<0.05), which was reduced by PTX (1.4±0.25). MMP-9 (1.0±0.03 vs 2.5±0.54, p<0.05, n=5), VEGF-A (1.0±0.02 vs 2.8±0.76, p<0.05, n=5) and Caveolin-1 (1.0±0.01 vs 1.6±0.17, n=3) expression (2-Δ (ΔCT)) were increased in RGS5-KD HUVECs. RGS5-KD increased the number of spheroid sprouts (2.1± 0.5 vs 3.5± 0.3,n=4, p<0.05). CB of RGS5-KD HUVECs increased VSMC migration (49±2.2 vs 67±2.6 %coverage, p<0.05, n=7).

Conclusion: In conclusion, RGS5 levels could be involved in vascular differentiation. Its effects on permeability and VSMC migration point towards a prominent role in angiogenesis and atherogenesis. Atherosclerosis studies in RGS5-deficient animals are warranted.