Abstract 18001: Shear Stress-Induced Endothelium-Dependent Dilation of Mouse Coronary Arteries is Caveolae-Dependent

Abstract

BACKGROUND: Shear stress-induced dilation (SSD) is an important vascular endothelial function that is impaired in diseases such as diabetes mellitus. Caveolin-1 is the major structural protein required for the formation of endothelial caveolae, where signaling molecules and pathways are assembled. In this study, we hypothesized that SSD of mouse small coronary arteries (MCA) is caveolae-dependent. METHODS: MCA (80-130 μm) freshly isolated from WT and Cav-1 knockout (KO) mice were mounted in a vessel chamber, pressurized at 80 mmHg, pre-contracted to 60-80% baseline diameter with endothelin-1, and subjected to physiological levels of shear stress at 25 dyn/cm 2 using a microinjection pump coupled to a pressure servo controller. SSD was measured by videomicroscopy and expressed as % of maximum diameter measured in the absence of Ca 2+ . Donor (intact WT or KO) and detector (WT with no endothelium) vessels were mounted in separate chambers connected by a micropipette. Diabetes mellitus was produced by streptozotocin (STZ) injection. RESULTS: SSD of MCA is significantly diminished in KO mice. 25 dyn/cm 2 produced 92.9±1.2% SSD in WT but only 42.0±0.7% in KO (n=10 for both, *p<0.05). Removal of endothelium reduced SSD to 22.3±3.3% in WT and to 14.9±1.3% in KO (n=8 for both, * vs. intact vessels but not WT vs. KO). Inhibition of eNOS (L-NAME), PGIS (Indocin), and CYP monooxygenase (SKF525A) reduced endothelial-dependent SSD by 44%, 34%, and 21% respectively in WT (all * vs control) but had no effect in KO, suggesting deficiency in shear stress-induced generation of vasodilators in KO. This is confirmed by the significant reduction in SSD in detector vessels with KO serving as donors (*42.0±0.7%, n=6 vs. 64.3±6.4% n=4, WT donor). With diabetes, MCA from WT and KO lost the ability for SSD (WT 25.9±2.4%, n=6 and KO 24.4±2.3%, n=5), which was similar to the effects of endothelium denudation. CONCLUSION: Integrity of caveolae is critical for endothelium-dependent SSD in MCA. KO endothelium is deficient in shear stress-mediated generation of vasodilators including NO, PGI 2 , and EET. Diabetic MCA have impaired endothelial function with loss of SSD. Caveolae plays a critical role in endothelial signal transduction from shear stress to vasodilator production and release.