Thrombin stimulates human endothelial arginase enzymatic activity via RhoA/ROCK pathway: implications for atherosclerotic endothelial dysfunction.
BACKGROUND
Arginase competes with endothelial nitric oxide synthase (eNOS) for the substrate l-arginine and decreases NO production. This study investigated regulatory mechanisms of arginase activity in endothelial cells and its role in atherosclerosis.


RESULTS
In human endothelial cells isolated from umbilical veins, thrombin concentration- and time-dependently stimulated arginase enzymatic activity, reaching a 1.9-fold increase (P<0.001) at 1 U/mL for 24 hours. The effect of thrombin was prevented by C3 exoenzyme or the HMG-CoA reductase inhibitor fluvastatin, which inhibit RhoA, or by the ROCK inhibitors Y-27632 and HA-1077. Adenoviral expression of constitutively active RhoA or ROCK mutants enhanced arginase activity (approximately 3-fold, P<0.001), and the effect of active RhoA mutant was inhibited by the ROCK inhibitors. Neither thrombin nor the active RhoA/ROCK mutants affected arginase II protein level, the only isozyme detectable in the cells. Moreover, a significantly higher arginase II activity (1.5-fold, not the protein level) and RhoA protein level (4-fold) were observed in atherosclerotic aortas of apoE-/- compared with wild-type mice. Interestingly, l-arginine (1 mmol/L), despite a significantly higher eNOS expression in aortas of apoE-/- mice, evoked a more pronounced contraction, which was reverted to a greater vasodilation by the arginase inhibitor l-norvaline (20 mmol/L) compared with the wild-type animals (n=5, P<0.001).


CONCLUSIONS
Thrombin enhances arginase activity via RhoA/ROCK in human endothelial cells. Higher arginase enzymatic activity is involved in atherosclerotic endothelial dysfunction in apoE-/- mice. Targeting vascular arginase may represent a novel therapeutic possibility for atherosclerosis.
Ming
Xiu-Fen
XF
Vascular Biology, Department of Medicine, Division of Physiology, University of Fribourg, Fribourg, Switzerland.
Barandier
Christine
C
Viswambharan
Hema
H
Kwak
Brenda R
BR
Mach
François
F
Mazzolai
Lucia
L
Hayoz
Daniel
D
Ruffieux
Jean
J
Rusconi
Sandro
S
Montani
Jean-Pierre
JP
Yang
Zhihong
Z
D000818:Animals; D001013:Aorta, Thoracic / Q000503:physiopathology; D001057:Apolipoproteins E / Q000235:genetics; D001119:Arginase / Q000378:metabolism*; D001161:Arteriosclerosis / Q000201:enzymology* / Q000503:physiopathology; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000201:enzymology; D004730:Endothelium, Vascular / Q000201:enzymology* / Q000503:physiopathology; D004789:Enzyme Activation; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009154:Mutation; D019001:Nitric Oxide Synthase / Q000096:biosynthesis; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction; D013917:Thrombin / Q000502:physiology*; D014471:Umbilical Veins / Q000166:cytology; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*
D001057:Apolipoproteins E; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes; C496314:NOS3 protein, human; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; C496315:Nos3 protein, mouse; D017346:Protein Serine-Threonine Kinases; D054460:rho-Associated Kinases; D013917:Thrombin; D001119:Arginase; D020742:rhoA GTP-Binding Protein