Resveratrol and cellular / nuclear targets − Rakyat Biologi

Specific non-antioxidant effects of resveratrol in cellular signaling and regulation of gene expression have been studied and have an important impact on atherosclerosis development.

Resveratrol was able to act on the MAPK cascade. Downstream targets for the action of MAPKs comprise mitogenic/pro-inflammatory enzymes and nuclear transcription factors (figure 5). Resveratrol is able to act at different levels. Indeed, resveratrol is able to act on upstream pathway by inhibiting the phosphorylation and the activity of PKC [127, 139, 140]. Resveratrol inhibits PKC-catalyzed phosphorylation of arginin-rich protein substrate in a non competitive manner [141]. The potency of resveratrol depends on the nature of the substrate and cofactors [141]. As diacylglycerol, resveratrol interacts with the C1 domains and induces the association of PKCa with membrane vesicles. Resveratrol can also inhibit other kinases such as Src which activates MAPK cascade [102]. Resveratrol inhibits also the PI3K phosphorylation and prevents the Akt / protein kinase B (PKB) phosphorylation. Consistent with this action, resveratrol attenuates the phosphorylation of p70^S6K which was shown in VSMC to require both the Akt / PKB and the ERK signaling cascades [86]. Consequently, resveratrol disturbs the protein synthesis because p70^S6K plays a critical role in regulating the translation of mRNAs. Resveratrol downregulates MAPK cascade by inhibiting the tyrosine phosphorylation of ERK1/2/JNK/p38 and the translocation into nucleus in the vascular cells [47, 84, 142]. This inhibition of phosphorylation and of translocation into nucleus from cytoplasm, reduces the expression of various genes implicated in the vasoconstriction, angiogenesis, proliferation, differenciation. In addition to its action on MAPK cascade, the polyphenol affects nuclear factors and consequently the gene expression. Its affects NFkB which activates the transcription of several target genes implicated in initiation and progression of pathogenesis in atherosclerosis, in inflammation, as well as in cancer [143]. Many stimuli such as oxLDL, ROS, PKC, have the potency to activate the NFkB pathway. NFkB is located in the cytoplasm as an inactive complex when associated with the inhibitor of kB (IkB). In response to stimuli, the catalytic subunits of IkB kinase (IKK) complex phosphorylate IkBa at two conserved serines. This phosphorylation event triggers the ubiquitin-dependent degradation of IkB by the 26S proteasome. Active p50/p65 complex is subsequently activated by phosphorylation of IKK a and PKC resulting in nuclear translocation of p50/p65 heterodimers (figure 5). The nuclear NFkB then binds to specific kB DNA motifs and modulates the transcription of target genes (e.g. COX, iNOS, cytokines, ...).

The first study on the effect of resveratrol on NFkB showed that treatment with oxLDL and VLDL activate NFkB binding activity and that resveratrol attenuates the activation of NFkB in PC-12 cells [144]. Furthermore, thanks to its properties of ROS scavenger and PKC inhibitor, resveratrol blocks stimuli-mediated phosphorylation and degradation of IkBa as well as the activation of IKKa (figure 5) [58, 145, 146]. Resveratrol inhibits the phosphorylation of p65 and its transactivation [137] by inhibiting kinases such as IKKa [145], PKC [127] and the intrinsic kinase of PKCd [147]. A recent study shows that a long treatment with resveratrol in human umbilical vein endothelial cells increases tyrosine phosphorylation of IkBa, p50-NFkB and p65- NFkB suggesting the involvement of such alterations in the modulation of NFkB transcription activity [148]. It has been also reported that resveratrol is a potent inhibitor of NFkB nuclear translocation and IkB degradation [58]. Resveratrol blocks the translocation of the p65 subunit of NFkB in inflammatory agents (TNFa, PMA, LPS, H₂O₂)-stimulated cells resulting in reduced transcriptional activity [146]. GATA and AP-1 are also affected by resveratrol. Indeed, the suppression of NFkB by resveratrol coincides with the inhibition of activator protein-1 (AP-1) [149]. In fact, resveratrol inhibits stimuli-induced AP-1-mediated activity [146, 150, 151] through the inhibition of c-Src non-receptor tyrosine kinase [152] and MAPK pathways such as MEKK1 and JNK [146, 152], which can activate both AP-1 and NFkB pathways [153, 154]. Moreover, resveratrol reduces the DNA binding activity and transcriptional activities of AP-1 and its composition [60, 84, 155]. The disturbing of the nuclear factors (e.g. NFkB, AP-1, GATA,...) by resveratrol affects the genes expression. In particular two genes, iNOS and COX-2, are involved in the CHD process. Concerning the iNOS gene, its expression is controlled, in part, by NFkB [156]. So, resveratrol is able to inhibit iNOS expression in various cell types [157-162], in particular in macrophages regulating blood pressure where resveratrol inhibits iNOS and down-regulates NFkB [161]. Concerning COX-2, various reports demonstrate the presence of COX-2 expression by SMCs in human atherosclerotic lesions [163, 164], and its expression is also regulated by various nuclear factors such as NFkB, AP-1, c-Jun [165]. Many studies demonstrated that resveratrol inhibits COX expression via an action on the nuclear factor such as AP-1, c-Jun [150, 151, 166, 167]. Moreover, docking studies on both COX-1 and COX-2 protein structures also revealed that hydroxylated but not methoxylated resveratrol analogues are able to bind to the previously identified binding sites of the enzymes [168]. This down-regulation of COX-1/2 genes expression by resveratrol is correlated with a decrease of inflammation [122]. Indeed, the inflammatory aspect of atherosclerosis include the COX-dependent prostaglandin cascade, and so resveratrol decreases the level of prostaglandin by a reduction of COX-2 activity. Resveratrol can also act on COX-1/2 via the peroxisome proliferator-activated receptor (PPAR). In human VSMC a PPARa agonist has been shown to decrease NFkB activity [169]. Decreased NFkB activity reduces COX-2, so PPARa can depress the COX-1/2 induction in human. Activation of this PPAR may contribute to the anti-inflammatory activity of the pharmacological ligands that influence the development of atherosclerosis [170]. Resveratrol is able to activate PPARa in vascular EC and its consumption (20 mg/kg, 3 days) reduces infarct volume by 36% at 24 hours after middle cerebral artery occlusion in mice [171]. In fact, resveratrol is a dual activator of PPARa and PPARg [171]. So, by this activation of PPARs, resveratrol could contribute to the lipid metabolism modulation and prevent the inflammatory activation of SMCs. Moreover, PPARa shifts the human liver fatty-acid oxidation/glycerolipid esterification balance towards the catabolic route, thereby reducing TGs supply for VLDL synthesis and contributing to the antihypertriglyceridaemic action of resveratrol.

By attenuation of nuclear factors binding activity (e.g. NFkB, AP-1, GATA), resveratrol perturbs the control of the expression of various genes (e.g. ET-1, MCP-1, VCAM-1, ICAM-1, SR-A, IL-1, IL-6) involved in atherosclerosis and inflammatory response [58, 65, 84, 172].

Caloric

Among the polyphenol with benefics properties, resveratrol, a phytoalexin of grapewine, can acts on the aging phenomena as well as caloric restriction which reduces atherosclerosis [173], inflammation [174] and deleters effects of aging [175].