The tyrosine phosphatase, SHP-1, is a negative regulator of endothelial superoxide formation

We investigated the role of SH2-domain containing phosphatase-1 (SHP-1) in endothelial reduced nicotinamide adenine dinucleotide (phosphate) (NAD[P]H)-oxidase-dependent oxidant production.

Superoxide (O2*-) generation by endothelial NAD(P)H-oxidase promotes endothelial dysfunction and atherosclerosis. Signaling pathways that regulate NAD(P)H-oxidase activity are, however, poorly understood.

SH2-domain containing phosphatase-1 was inhibited using site-directed magnetofection of antisense oligodesoxynucleotides (AS-ODN) or short interfering ribonucleic acid (siRNA) in vitro in human umbilical vein endothelial cells (HUVEC) and in isolated hamster arteries; O2*- was measured by cytochrome c reduction in vitro. Activities of NAD(P)H-oxidase activity, phosphatidyl-inositol-3-kinase (PI3K), and SHP-1 were assessed by specific assays; Rac1 activation was assessed by a pull-down assay.

Basal endothelial O2*- release was enhanced after inhibition of endothelial SHP-1 (p < 0.01), which could be prevented by specific inhibition of NAD(P)H-oxidase (p < 0.01); SHP-1 activity was high under basal conditions, further increased by vascular endothelial growth factor (10 ng/ml, p < 0.05), and abolished by SHP-1 AS-ODN treatment (p < 0.01), which also increased NAD(P)H-oxidase activity 3.3-fold (p < 0.01). Vascular endothelial growth factor also induced O2*- release (p < 0.01), which was even more enhanced when SHP-1 was knocked down (p < 0.05). The effect of SHP-1 was mediated by inhibition of PI3K/Rac1-dependent NAD(P)H-oxidase activation (p < 0.01); SHP-1 AS-ODN augmented tyrosine phosphorylation of the p85 regulatory subunit of PI3K (p < 0.05) and Rac1 activation. The latter was prevented by wortmannin, a blocker of PI3K.

In HUVEC, SHP-1 counteracts basal and stimulated NAD(P)H-oxidase activity by negative regulation of PI3K-dependent Rac1 activation; SHP-1 thus seems to be an important part of endothelial antioxidative defense controlling the activity of the O2(*-)-producing NAD(P)H-oxidase.