Role of ERK1/2 activation and nNOS uncoupling on endothelial dysfunction induced by lysophosphatidylcholine.

Background and Aims: Lysophosphatidylcholine (LPC) - a main component of oxidized LDL - is involved in endothelial dysfunction that precedes atherosclerosis, with an increased superoxide anions and a reduced NO production via endothelial NO synthase (eNOS) uncoupling. However, there is no evidence about the mechanisms involved in neuronal NOS (nNOS) uncoupling. Extracellular signal-regulated kinase (ERK) is related to the control of NO production and inflammatory gene transcription activation in atherosclerosis. Our aim was to investigate the role of nNOS/ERK1/2 pathway on endothelial dysfunction induced by LPC, in mouse aorta and human endothelial cells.
Methods: Thoracic aorta from wild type mice was used to perform vascular reactivity studies in the presence or absence of LPC. Human endothelial cells were used to investigate the effect of LPC on expression of nNOS and his products NO and H ₂ O ₂ .
Results: LPC reduced acetylcholine (ACh)-induced vasodilation in mouse aorta (Emax _CT/LPC  = ∼95 ± 2/62 ± 3%, p = 0.0004) and increased phenylephrine-induced vasoconstriction (Emax _CT/LPC  = ∼4 ± 0,1/6 ± 0,1 mN/mm, p = 0.0002), with a reduction in NO (fluorescence intensity _CT/LPC  = 91 ± 3/62±2 × 10 ³ , p = 0.0002) and H ₂ O ₂ (fluorescence intensity _CT/LPC  = ∼16 ± 0,8/10 ± 0,7 × 10 ³ , p = 0.0041) production evocated by ACh. An inhibition of nNOS by TRIM (Emax _CT/CT+TRIM  = ∼93 ± 1/43 ± 3%, p = 0,0048; Emax _LPC/LPC+TRIM  = ∼62 ± 3/65 ± 3%) or H ₂ O ₂ degradation by catalase (Emax _CT/CT+cat  = ∼93 ± 1/46 ± 2%, p < 0,001; Emax _LPC/LPC+cat  = ∼62,8 ± 3,2/60,5 ± 4,7%) reduced the relaxation in the control but not in LPC group. PD98059, an ERK1/2 inhibitor, abolished the increase in vasoconstriction in LPC-treated vessels (Emax _LPC/LPC+PD  = ∼6 ± 0,1/3 ± 0,1 mN/mm, p = 0.0001). LPC also reduced the dimer/monomer proportion and increased nNOS ^ser852 phosphorylation.
Conclusions: LPC induced nNOS uncoupling and nNOS ^Ser852 phosphorylation, reduced NO and H ₂ O ₂ production and improved superoxide production by modulating ERK1/2 activity in human and murine endothelial cells.
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