Hydroxytyrosol (HT), an olive plant (Olea europaea L.)
polyphenol, has proven atheroprotective effects. We previously demonstrated that
heme oxygenase-1 (HO-1) is involved in the HT dependent prevention of dysfunction induced by oxidative stress in vascular endothelial cells (VECs). Here, we further investigated the signaling pathway of HT-dependent HO-1 expression in VECs. HT dose- and time-dependently increased HO-1
mRNA and
protein levels through the PI3K/Akt and ERK1/2 pathways.
Cycloheximide and
actinomycin D inhibited both increases, suggesting that HT-triggered HO-1 induction is transcriptionally regulated and that de novo
protein synthesis is necessary for this HT effect. HT stimulated nuclear accumulation of
nuclear factor E2-related factor 2 (Nrf2). This Nrf2 accumulation was blocked by
actinomycin D and
cycloheximide whereas HT in combination with the
26S proteasome inhibitor
MG132 enhanced the accumulation. HT also extended the half-life of Nrf2
proteins by decelerating its turnover. Moreover, HO-1 inhibitor, ZnppIX and CO scavenger,
hemoglobin impaired HT-dependent wound healing while
CORM-2, a CO generator, accelerated
wound closure. Together, these data demonstrate that HT upregulates HO-1 expression by stimulating the nuclear accumulation and stabilization of Nrf2, leading to the
wound repair of VECs crucial in the prevention of
atherosclerosis.