Ceramide activates a mitochondrial p38 mitogen-activated protein kinase: A potential mechanism for loss of mitochondrial transmembrane potential and apoptosis

This study examined the impact of ceramide, an intracellular mediator of apoptosis, on the mitochondria to test the hypothesis that ceramide utilized p38 MAPK in the mitochondria to alter mitochondrial potential and induce apoptosis. The capacity of ceramide to adversely affect mitochondria was demonstrated by the significant loss of mitochondrial potential (ΔΨ_m), indicated by a J-aggregate fluorescent probe, after embryonic chick cardiomyocytes were treated with the cell permeable ceramide analogue C₂-ceramide. p38 MAPK was identified in the mitochondrial fraction of the cell and p38 MAPK phosphorylation in this mitochondrial fraction of the cell occurred with ceramide treatment. In addition, SAPK phosphorylation and a decrease in ERK phosphorylation occurred in whole cell lysates after ceramide treatment. The p38 MAPK inhibitor SB 202190 but not the MEK inhibitor PD 98059 significantly inhibited ceramide-induced apoptosis and loss of ΔΨ_m. These data suggest that p38 MAPK is present in the mitochondria and its activation by ceramide indicates local signaling more directly coupled to the mitochondrial pathway in apoptosis. (Mol Cell Biochem 278: 39–51, 2005)     

Apoptosis induced by capsaicin in prostate PC-3 cells involves ceramide accumulation,neutral sphingomyelinase,and JNK activation

Numerous studies have recently focused on the anticarcinogenic, antimutagenic, or chemopreventive activities of the main pungent component of red pepper, capsaicin (N-vanillyl-8-methyl-1-nonenamide). We have previously shown that, in the androgen-independent prostate cancer PC-3 cells, capsaicin inhibits cell growth and induces apoptosis through reactive oxygen species (ROS) generation [Apoptosis 11 (2006) 89–99]. In the present study, we investigated the signaling pathways involved in the antiproliferative effect of capsaicin. Here, we report that capsaicin apoptotic effect was mediated by ceramide generation which occurred by sphingomyelin hydrolysis. Using siRNA, we demonstrated that N-SMase expression is required for the effect of capsaicin on prostate cell viability. We then investigated the role of MAP kinase cascades, extracellular signal-regulated protein kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 MAPK, in the antiproliferative effect of capsaicin, and we confirmed that capsaicin could activate ERK and JNK but not p38 MAPK. Pharmacological inhibition of JNK kinase, as well as inhibition of ROS by the reducing agent N-acetylcysteine, prevented ceramide accumulation and capsaicin-induced cell death. However, inhibition of ceramide accumulation by the SMase inhibitor D609 did not modify JNK activation. These data reveal JNK as an upstream regulator of ceramide production. Capsaicin-promoted activation of ERK was prevented with all the inhibitors tested. We conclude that capsaicin induces apoptosis in PC-3 cells via ROS generation, JNK activation, ceramide accumulation, and second, ERK activation.     

Homocysteine enhances cell proliferation in vascular smooth muscle cells: role of p38 MAPK and p47phox

Elevation of blood homocysteine levels (hyperhomocysteinemia) is a risk factor for cardiovascular disorders. One of the mechanisms by which homocysteine induces atherosclerosis is to promote the proliferation of vascular smooth muscle cells (VSMCs) in a reactive oxygen species (ROS)-dependent manner. It has been shown that homocysteine induces the production of ROS through the activation of NAD(P)H oxidases in VSMCs. In this study, we investigated the signal transduction pathways involved in the activation of NAD(P)H oxidases. Homocysteine promoted DNA synthesis in VSMCs. Inhibition of ROS by N-acetyl-L-cysteine (an antioxidant) and apocynin (an inhibitor of NAD(P)H oxidases) significantly blocked homocysteine-induced proliferation in VSMCs. Homocysteine induced a rapid increase in the phosphorylation of p38-mitogen-activated protein kinase (p38 MAPK). p38 MAPK in turn activated NAD(P)H oxidases by inducing the phosphorylation of p47phox, resulting in the generation of ROS. ROS induced the phosphorylation of Akt, which was probably responsible for proliferation in VSMCs. These findings demonstrate that homocysteine induces an increase in the activity of NAD(P)H oxidases in VSMCs by activating p38 MAPK and enhancing the phosphorylation of p47phox.     

Vitamin C-induced activation of phospholipase D in lung microvascular endothelial cells: regulation by MAP kinases

Our earlier studies have shown that vitamin C at pharmacological doses (mM) induces loss of redox-dependent viability in bovine lung microvascular endothelial cells (BLMVECs) that is mediated by oxidative stress. Therefore, here, we investigated the vitamin C-induced activation of the lipid signaling enzyme, phospholipase D (PLD) in BLMVECs. Monolayer cultures of BLMVECs were treated with vitamin C (0-10 mM) for different time periods (0-2 h) and the activity of PLD was determined. Vitamin C induced activation of PLD in BLMVECs in a time- and dose-dependent fashion that was significantly attenuated by antioxidants, p38 mitogen-activated protein kinase (p38 MAPK)-specific inhibitor (SB203580), extracellular signal-regulated protein kinase (ERK)-specific inhibitor (PD98059), and transient transfection of cells with dominant-negative (DN)-p38 MAPK and DN-ERK1/ERK2. Vitamin C also induced phosphorylation and enhanced the activities of p38 MAPK and ERK in BLMVECs in a time-dependent fashion. It was also evident that vitamin C induced translocation of PLD(1) and PLD(2), association of p38 MAPK and ERK with PLD(1) and PLD(2), threonine phosphorylation of PLD(1) and PLD(2) and SB203580- and PD98059-inhibitable threonine phosphorylation of PLD(1) in BLMVECs. Transient transfection of BLMVECs with DN-p38 MAPK and DN-ERK1/ERK2 resulted in marked attenuation of vitamin C-induced phosphorylation of threonine in PLD(1) and PLD(2). We, for the first time, showed that vitamin C at pharmacological doses, activated PLD in the lung microvascular ECs through oxidative stress and MAPK activation.     

Involvement of the endocannabinoid system in periodontal healing

Endocannabinoids including anandamide (AEA) and 2-arachidonoylglycerol (2-AG) are important lipid mediators for immunosuppressive effects and for appropriate homeostasis via their G-protein-coupled cannabinoid (CB) receptors in mammalian organs and tissues, and may be involved in wound healing in some organs. The physiological roles of endocannabinoids in periodontal healing remain unknown. We observed upregulation of the expression of CB1/CB2 receptors localized on fibroblasts and macrophage-like cells in granulation tissue during wound healing in a wound-healing model in rats, as well as an increase in AEA levels in gingival crevicular fluid after periodontal surgery in human patients with periodontitis. In-vitro, the proliferation of human gingival fibroblasts (HGFs) by AEA was significantly attenuated by AM251 and AM630, which are selective antagonists of CB1 and CB2, respectively. CP55940 (CB1/CB2 agonist) induced phosphorylation of the extracellular-regulated kinases (ERK) 1/2, p38 mitogen-activated protein kinase (p38MAPK), and Akt in HGFs. Wound closure by CP55940 in an in-vitro scratch assay was significantly suppressed by inhibitors of MAP kinase kinase (MEK), p38MAPK, and phosphoinositol 3-kinase (PI3-K). These findings suggest that endocannabinoid system may have an important role in periodontal healing.     

The p38 mitogen-activated protein kinase mediates cytoskeletal remodeling in pulmonary microvascular endothelial cells upon intracellular adhesion molecule-1 ligation

Changes in the cytoskeleton of endothelial cells (ECs) play important roles in mediating neutrophil migration during inflammation. Previous studies demonstrated that neutrophil adherence to TNF-alpha-treated pulmonary microvascular ECs induced cytoskeletal remodeling in ECs that required ICAM-1 ligation and oxidant production and was mimicked by cross-linking ICAM-1. In this study, we examined the role of ICAM-1-induced signaling pathways in mediating actin cytoskeletal remodeling. Cross-linking ICAM-1 induced alterations in ICAM-1 distribution, as well as the filamentous actin rearrangements and stiffening of ECs shown previously. ICAM-1 cross-linking induced phosphorylation of the p38 mitogen-activated protein kinase (MAPK) that was inhibited by allopurinol and also induced an increase in the activity of the p38 MAPK that was inhibited by SB203580. However, SB203580 had no effect on oxidant production in ECs or ICAM-1 clustering. ICAM-1 cross-linking also induced phosphorylation of heat shock protein 27, an actin-binding protein that may be involved in filamentous actin polymerization. The time course of heat shock protein 27 phosphorylation paralleled that of p38 MAPK phosphorylation and was completely inhibited by SB203580. In addition, SB203580 blocked the EC stiffening response induced by either neutrophil adherence or ICAM-1 cross-linking. Moreover, pretreatment of ECs with SB203580 reduced neutrophil migration toward EC junctions. Taken together, these data demonstrate that activation of p38 MAPK, mediated by xanthine oxidase-generated oxidant production, is required for cytoskeletal remodeling in ECs induced by ICAM-1 cross-linking or neutrophil adherence. These cytoskeletal changes in ECs may in turn modulate neutrophil migration toward EC junctions.     

Protein kinase C-induced activation of a ceramide/protein phosphatase 1 pathway leading to dephosphorylation of p38 MAPK

Recently we showed that, in human breast cancer cells, activation of protein kinase C by 4beta-phorbol 12-myristate 13-acetate (PMA) produced ceramide formed from the salvage pathway (Becker, K. P., Kitatani, K., Idkowiak-Baldys, J., Bielawski, J., and Hannun, Y. A. (2005) J. Biol. Chem. 280, 2606-2612). In this study, we investigated intracellular signaling events mediated by this novel activated pathway of ceramide generation. PMA treatment resulted in transient activation of mitogen-activated protein kinases (ERK1/2, JNK1/2, and p38) followed by dephosphorylation/inactivation. Interestingly, fumonisin B1 (FB1), an inhibitor of the salvage pathway, attenuated loss of phosphorylation of p38, suggesting a role for ceramide in p38 dephosphorylation. This was confirmed by knock-down of longevity-assurance homologue 5, which partially suppressed the formation of C(16)-ceramide induced by PMA and increased the phosphorylation of p38. These results demonstrate a role for the salvage pathway in feedback inhibition of p38. To determine which protein phosphatases act in this pathway, specific knock-down of serine/threonine protein phosphatases was performed, and it was observed that knock-down of protein phosphatase 1 (PP1) catalytic subunits significantly increased p38 phosphorylation, suggesting activation of PP1 results in an inhibitory effect on p38. Moreover, PMA recruited PP1 catalytic subunits to mitochondria, and this was significantly suppressed by FB1. In addition, phospho-p38 resided in PMA-stimulated mitochondria. Upon PMA treatment, a mitochondria-enriched/purified fraction exhibited significant increases in C(16)-ceramide, a major ceramide specie, which was suppressed by FB1. Taken together, these data suggest that accumulation of C(16)-ceramide in mitochondria formed from the protein kinase C-dependent salvage pathway results at least in part from the action of longevity-assurance homologue 5, and the generated ceramide modulates the p38 cascade via PP1.     

Vibrio vulnificus-induced death of Jurkat T-cells requires activation of p38 mitogen-activated protein kinase by NADPH oxidase-derived reactive oxygen species

Vibrio vulnificus, a pathogenic bacterium causing primary septicemia, exhibited cytotoxicity towards Jurkat cells of T-lymphocytes through intracellular reactive oxygen species (ROS) production. Pretreatment of Jurkat T-cells with diphenyleneiodonium chloride (DPI) abolished V. vulnificus-induced ROS generation and bacterial ability to cause cell death. Jurkat T-cells expressing dominant-negative protein of Rac subunit of NADPH oxidase (NOX) did not show increased ROS production and cell death by V. vulnificus. Vibrio vulnificus also triggered phosphorylation of mitogen-activated protein kinases (MAPKs) including p38 and ERK1/2 in Jurkat T-cells. Experiments using inhibitors or small interfering RNAs for each MAPK showed that both MAPKs are involved in V. vulnificus-induced cell death. DPI only blocked the phosphorylation of p38 MAPK in Jurkat T-cells exposed by V. vulnificus. This study demonstrates that V. vulnificus induces death of Jurkat T-cells via ROS-dependent activation of p38 MAPK, and that NOX plays a major role in ROS generation in V. vulnificus-exposed cells.     

Sodium nitroprusside activates p38 mitogen activated protein kinase through a cGMP/PKG independent mechanism

The objective of this study was to understand the mechanism of action of nitric oxide (NO) in the heart by determining whether nitric oxide (NO) released from sodium nitroprusside (SNP) induces p38 mitogen activated protein kinase (p38 MAPK) phosphorylation and whether this is mediated through a cyclic GMP (cGMP)/protein kinase G (PKG) pathway. p38 MAPK activation was examined by Western blotting of whole cell lysates of embryonic chick cardiomyocytes with antibodies specific to the native or phosphorylated forms of p38 MAPK. SNP, 1 mM, which released significant amounts of NO as determined by Griess reaction, induced p38 MAPK phosphorylation that was apparent within 10 min, was significantly (p<0.05) greater than control at 60 min and remained higher than initial levels up to the 4 h end point of the experiment. This could not be attributed to hydrogen peroxide release from SNP as catalase did not affect SNP-induced p38 MAPK phosphorylation. SB202190, a relatively selective inhibitor of p38 MAPK, mainly p38alpha MAPK, inhibited SNP-induced p38 MAPK phosphorylation. SNP-induced p38 MAPK phosphorylation was not altered by pre-treatment with the PKG inhibitor KT 5823 or by ODQ a potent and selective inhibitor of NO-sensitive guanylyl cyclase. p38 MAPK phosphorylation was not induced by the cell permeable cGMP analogue, 8-Br-cGMP. In summary, considering that new therapeutic strategies aimed at NO and p38 MAPK are being considered for myocardial injury and heart failure, these data demonstrate that SNP induces p38 MAPK phosphorylation through a pathway that is independent of NO-induced activation of cGMP/PKG pathways and suggest that non cGMP/PKG regulatory proteins leading to p38 MAPK phosphorylation merit further investigation to address this therapeutic target.     

Activation of SRC tyrosine kinases in response to ICAM-1 ligation in pulmonary microvascular endothelial cells

Previous studies demonstrated that ICAM-1 ligation on human pulmonary microvascular endothelial cells (ECs) sequentially induces activation of xanthine oxidase and p38 MAPK. Inhibition of these signaling events reduces neutrophil migration to the EC borders. This study examined the role of SRC tyrosine kinases in ICAM-1-initiated signaling within these ECs. Cross-linking ICAM-1 on tumor necrosis factor-alpha-pretreated ECs induced an increase in the activity of SRC tyrosine kinases. This increase was inhibited by allopurinol (a xanthine oxidase inhibitor), Me2SO (a hydroxyl radical scavenger), or deferoxamine (an iron chelator). Phenylarsine oxide, a tyrosine phosphatase inhibitor, reduced the base-line activity of SRC as well as the increase in SRC activity induced by ICAM-1 cross-linking. Specific inhibition of the protein expression of the SRC homology 2-containing protein-tyrosine phosphatase-2 (SHP-2) by an antisense oligonucleotide prevented the induced SRC activation but had no effect on the basal SRC activity. Activation of SRC tyrosine kinases was accompanied by tyrosine phosphorylation of ezrin at Tyr-146, which was inhibited by PP2, an SRC tyrosine kinase inhibitor. Moreover, PP2 completely inhibited p38 activation, suggesting a role for SRC tyrosine kinases in p38 activation. These data demonstrate that ICAM-1 ligation activates SRC tyrosine kinases and that this activation requires SHP-2 as well as production of reactive oxygen species generated from xanthine oxidase. Activation of SRC tyrosine kinases in turn leads to tyrosine phosphorylation of ezrin, as well as activation of p38, a kinase previously identified to be required for cytoskeletal changes induced by ICAM-1 ligation and for neutrophil migration along the EC surface.     

Platelet endothelial cell adhesion molecule-1 (PECAM-1) inhibits low density lipoprotein-induced signaling in platelets

At physiological concentrations, low density lipoprotein (LDL) increases the sensitivity of platelets to aggregation- and secretion-inducing agents without acting as an independent activator of platelet functions. LDL sensitizes platelets by inducing a transient activation of p38MAPK, a Ser/Thr kinase that is activated by the simultaneous phosphorylation of Thr180 and Tyr182 and is an upstream regulator of cytosolic phospholipase A2 (cPLA2). A similar transient phosphorylation of p38MAPK is induced by a peptide mimicking amino acids 3359-3369 in apoB100 called the B-site. Here we report that the transient nature of p38MAPK activation is caused by platelet endothelial cell adhesion molecule 1 (PECAM-1), a receptor with an immunoreceptor tyrosine-based inhibitory motif. PECAM-1 activation by cross-linking induces tyrosine phosphorylation of PECAM-1 and a fall in phosphorylated p38MAPK and cPLA2. Interestingly, LDL and the B-site peptide also induce tyrosine phosphorylation of PECAM-1, and studies with immunoprecipitates indicate the involvement of c-Src. Inhibition of the Ser/Thr phosphatases PP1/PP2A (okadaic acid) makes the transient p38MAPK activation by LDL and the B-site peptide persistent. Inhibition of Tyr-phosphatases (vanadate) increases Tyr-phosphorylated PECAM-1 and blocks the activation of p38MAPK. Together, these findings suggest that, following a first phase in which LDL, through its B-site, phosphorylates and thereby activates p38MAPK, a second phase is initiated in which LDL activates PECAM-1 and induces dephosphorylation of p38MAPK via activation of the Ser/Thr phosphatases PP1/PP2A.     

Activation of p38MAPK by TGF-beta in fetal rat hepatocytes requires radical oxygen production, but is dispensable for cell death.

We have previously found that transforming growth factor-beta (TGF-beta) induces an increase in radical oxygen species (ROS) production that mediates its apoptotic effects in fetal hepatocytes. In this paper we show that TGF-beta activates p38 mitogen-activated protein kinase (p38MAPK) and ROS may be responsible for this activation. Activation of p38MAPK occurs late, coincident with the maximal production of ROS, it is inhibited by radical scavengers and it is accentuated by the presence of glutathione synthesis inhibitors. However, p38MAPK does not appear to be involved in any of the apoptotic events: loss of Bcl-x(L) levels, cytochrome c release, cleavage of caspase substrates and loss of cell viability.     

Inhibition of PTPs by H(2)O(2) regulates the activation of distinct MAPK pathways

It has been shown that endogenous production of reactive oxygen species (ROS) during T cell activation regulates signaling events including MAPK activation. Protein tyrosine phosphatases (PTPs) have been regarded as targets of ROS which modify the catalytic cysteine residues of the enzymes. We have analyzed the interplay between the inhibition of PTPs and the activation of MAPK by H(2)O(2). Stimulation of Jurkat T cells with H(2)O(2) induces the phosphorylation of ERK, p38, and JNK members of MAPK family. H(2)O(2) stimulation of T cells was found to inhibit the PTP activity of CD45, SHP-1, and HePTP. Transfection of cells with wtSHP-1 decreased H(2)O(2)-induced ERK and JNK phosphorylation without affecting p38 phosphorylation. Transfection with wtHePTP inhibited H(2)O(2)-induced ERK and p38 phosphorylation without inhibiting JNK phosphorylation. The Src-family kinase inhibitor, PP2, inhibited the H(2)O(2)-induced phosphorylation of ERK, p38, and JNK. The phospholipase C (PLC) inhibitor, U73122, or the protein kinase C (PKC) inhibitor, Ro-31-8425, blocked H(2)O(2)-induced ERK phosphorylation, whereas the same treatment did not inhibit p38 or JNK phosphorylation. Taken together, these results suggest that inhibition of PTPs by H(2)O(2) contributes to the induction of distinct MAPK activation profiles via differential signaling pathways.     

MAPKAPK-2-mediated LIM-kinase activation is critical for VEGF-induced actin remodeling and cell migration

Vascular endothelial growth factor-A (VEGF-A) induces actin reorganization and migration of endothelial cells through a p38 mitogen-activated protein kinase (MAPK) pathway. LIM-kinase 1 (LIMK1) induces actin remodeling by phosphorylating and inactivating cofilin, an actin-depolymerizing factor. In this study, we demonstrate that activation of LIMK1 by MAPKAPK-2 (MK2; a downstream kinase of p38 MAPK) represents a novel signaling pathway in VEGF-A-induced cell migration. VEGF-A induced LIMK1 activation and cofilin phosphorylation, and this was inhibited by the p38 MAPK inhibitor SB203580. Although p38 phosphorylated LIMK1 at Ser-310, it failed to activate LIMK1 directly; however, MK2 activated LIMK1 by phosphorylation at Ser-323. Expression of a Ser-323-non-phosphorylatable mutant of LIMK1 suppressed VEGF-A-induced stress fiber formation and cell migration; however, expression of a Ser-323-phosphorylation-mimic mutant enhanced these processes. Knockdown of MK2 by siRNA suppressed VEGF-A-induced LIMK1 activation, stress fiber formation, and cell migration. Expression of kinase-dead LIMK1 suppressed VEGF-A-induced tubule formation. These findings suggest that MK2-mediated LIMK1 phosphorylation/activation plays an essential role in VEGF-A-induced actin reorganization, migration, and tubule formation of endothelial cells.     

Reactive oxygen species are involved in the IFN‐γ‐stimulated production of Th2 chemokines in HaCaT keratinocytes

The increased generation of reactive oxygen species (ROS) induces inflammation in different cell types. However, it is unclear whether ROS play an essential role in the production of thymus and activation‐regulated chemokine (TARC/CCL17) and macrophage‐derived chemokine (MDC/CCL22) in keratinocytes. Here, we investigated the function of ROS in the production of these two Th2 chemokines in interferon‐gamma (IFN‐γ)‐treated HaCaT keratinocytes. We found that IFN‐γ‐induced production of both chemokines in parallel with the increased generation of intracellular ROS. A ROS scavenger, N‐acetyl cysteine (NAC), significantly inhibited the IFN‐γ‐induced production of chemokines as well as the activation of I kappa‐B (IκB)–nuclear factor‐kappa B (NF‐κB). Inhibitors of Janus family kinases (JAKs), p38 mitogen‐activated kinase (MAPK), and NF‐κB suppressed IFN‐γ‐induced production of TARC and MDC. NF‐κB activation was inhibited by both inhibitors of JAKs and p38 MAPK. Importantly, IFN‐γ‐stimulated phosphorylation of p38 MAPK was significantly suppressed by JAKs inhibitors, but not significantly affected by NAC or L ‐buthionine sulfoximine (L‐BSO). However, IFN‐γ‐stimulated activation of IκB and NF‐κB was suppressed by NAC but enhanced by BSO. Furthermore, inhibition of p38 MAPK and JAKs did not affect ROS generation in IFN‐γ‐stimulated HaCaT cells. These results indicate that intracellular ROS and JAKs/p38 MAPK both contribute independently to IFN‐γ‐stimulated production of TARC and MDC in HaCaT keratinocytes, by increasing NF‐κB activation. J. Cell. Physiol. 226: 58–65, 2010. © 2010 Wiley‐Liss, Inc.     

Advanced Glycation End Products Induce Human Corneal Epithelial Cells Apoptosis through Generation of Reactive Oxygen Species and Activation of JNK and p38 MAPK Pathways

Advanced Glycation End Products (AGEs) has been implicated in the progression of diabetic keratopathy. However, details regarding their function are not well understood. In the present study, we investigated the effects of intracellular reactive oxygen species (ROS) and JNK, p38 MAPK on AGE-modified bovine serum albumin (BSA) induced Human telomerase-immortalized corneal epithelial cells (HUCLs) apoptosis. We found that AGE-BSA induced HUCLs apoptosis and increased Bax protein expression, decreased Bcl-2 protein expression. AGE-BSA also induced the expression of receptor for advanced glycation end product (RAGE). AGE-BSA-RAGE interaction induced intracellular ROS generation through activated NADPH oxidase and increased the phosphorylation of p47phox. AGE-BSA induced HUCLs apoptosis was inhibited by pretreatment with NADPH oxidase inhibitors, ROS quencher N-acetylcysteine (NAC) or neutralizing anti-RAGE antibodies. We also found that AGE-BSA induced JNK and p38 MAPK phosphorylation. JNK and p38 MAPK inhibitor effectively blocked AGE-BSA-induced HUCLs apoptosis. In addition, NAC completely blocked phosphorylation of JNK and p38 MAPK induced by AGE-BSA. Our results indicate that AGE-BSA induced HUCLs apoptosis through generation of intracellular ROS and activation of JNK and p38 MAPK pathways.     

Luteolin and Apigenin Attenuate 4-Hydroxy-2-Nonenal-Mediated Cell Death through Modulation of UPR,Nrf2-ARE and MAPK Pathways in PC12 Cells

Luteolin and apigenin are dietary flavones and exhibit a broad spectrum of biological activities including antioxidant, anti-inflammatory, anti-cancer and neuroprotective effects. The lipid peroxidation product 4-hydroxy-2-nonenal (4-HNE) has been implicated as a causative agent in the development of neurodegenerative disorders. This study investigates the cytoprotective effects of luteolin and apigenin against 4-HNE-mediated cytotoxicity in neuronal-like catecholaminergic PC12 cells. Both flavones restored cell viability and repressed caspase-3 and PARP-1 activation in 4-HNE-treated cells. Luteolin also mitigated 4-HNE-mediated LC3 conversion and reactive oxygen species (ROS) production. Luteolin and apigenin up-regulated 4-HNE-mediated unfolded protein response (UPR), leading to an increase in endoplasmic reticulum chaperone GRP78 and decrease in the expression of UPR-targeted pro-apoptotic genes. They also induced the expression of Nrf2-targeted HO-1 and xCT in the absence of 4-HNE, but counteracted their expression in the presence of 4-HNE. Moreover, we found that JNK and p38 MAPK inhibitors significantly antagonized the increase in cell viability induced by luteolin and apigenin. Consistently, enhanced phosphorylation of JNK and p38 MAPK was observed in luteolin- and apigenin-treated cells. In conclusion, this result shows that luteolin and apigenin activate MAPK and Nrf2 signaling, which elicit adaptive cellular stress response pathways, restore 4-HNE-induced ER homeostasis and inhibit cytotoxicity. Luteolin exerts a stronger cytoprotective effect than apigenin possibly due to its higher MAPK, Nrf2 and UPR activation, and ROS scavenging activity.