Role of extracellular-regulated kinase and c-jun NH2-terminal kinase in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced neurofilament phosphorylation

Chronic exposure to low levels of aluminum alters cerebral cell signaling in response to acute MPTP administration

Two-month-old male B/6C3F1 mice were treated for 10 weeks with 100 μM aluminum lactate (Al) in drinking water. This dose of Al did not alter body weight, and there was no evidence of systemic toxicity. The degree of phosphorylation of several kinases which lead to transcription factor activation (reflecting the extent of their activation) was studied. The proportion of extracellular signal-regulated kinase (ERK) that was activated was depressed in cortex but not in the hippocampus following treatment but c-Jun N-terminal kinase (JNK), p38, IκB phosphorylation was unaltered in either tissue. Treatment of mice with 1-methyl-4-phenyl-1,2,3,6 tetrahydropyridine (MPTP) alone produced no significant changes in the degree of activation of any transcription factor studied. When MPTP dosing had been preceded by extended exposure to low levels of Al in drinking water, ERK activation was profoundly depressed in cortex and hippocampus, whereas JNK in hippocampus and IκB in cortex were greatly elevated. These changes consequent to exposure to both Al and MPTP were accompanied by an increase in NF-κB in both regions, whereas AP-1 was elevated in the hippocampus alone. Neither agent alone modulated AP-1 or NF-κB. Thus a synergistic interaction occurred between the toxicants. This interaction tended to promote the functioning of a kinase largely associated with inflammation and to depress that of ERK, which is associated with maintenance of cell survival. It is concluded that exposure to levels of Al with no evident toxicity can worsen the response to an acute challenge with MPTP. Al treatment alone was able to increase striatal 3,4-dihydroxyphenylacetic acid levels, suggesting an elevation of the rate of dopamine turnover in the striatum. However, no interaction in alteration of monoamine levels was found between Al and MPTP.

c-Jun N-terminal Kinase (JNK) Signaling as a Therapeutic Target for Alzheimer's Disease

c-Jun N-terminal kinases (JNKs) are a family of protein kinases that play a central role in stress signaling pathways implicated in gene expression, neuronal plasticity, regeneration, cell death, and regulation of cellular senescence. It has been shown that there is a JNK pathway activation after exposure to different stressing factors, including cytokines, growth factors, oxidative stress, unfolded protein response signals or Aβ peptides. Altogether, JNKs have become a focus of screening strategies searching for new therapeutic approaches to diabetes, cancer or liver diseases. In addition, activation of JNK has been identified as a key element responsible for the regulation of apoptosis signals and therefore, it is critical for pathological cell death associated with neurodegenerative diseases and, among them, with Alzheimer’s disease (AD). In addition, in vitro and in vivo studies have reported alterations of JNK pathways potentially associated with pathogenesis and neuronal death in AD. JNK’s, particularly JNK3, not only enhance Aβ production, moreover it plays a key role in the maturation and development of neurofibrillary tangles. This review aims to explain the rationale behind testing therapies based on inhibition of JNK signaling for AD in terms of current knowledge about the pathophysiology of the disease. Keeping in mind that JNK3 is specifically expressed in the brain and activated by stress-stimuli, it is possible to hypothesize that inhibition of JNK3 might be considered as a potential target for treating neurodegenerative mechanisms associated with AD.

Bisphenol A increases BeWo trophoblast survival in stress-induced paradigms through regulation of oxidative stress and apoptosis

Bisphenol A (BPA) is ubiquitous in the environment and is reported to be present at high concentrations in placental tissue, where its presence raises concerns over its potential to disrupt placental function. This report investigates how BPA interferes with the survival of human choriocarcinoma BeWo cells (a model of placental trophoblasts) under stress-induced paradigms reminiscent of pathways activated in placental development. These include conditions that promote oxidative stress (glutathione depletion) and apoptosis (serum withdrawal) or mimic hypoxia (HIF-1α accumulation via dimethyloxalylglycine treatment). Treatment of BeWo cells with BPA during stress-induced paradigms led to a consistent and significant increase in cell viability, with a concomitant increase in glutathione levels and a reduction in apoptosis. Assessment of the antioxidant capacity of BPA revealed its ability to quench reactive oxygen species and reduce the levels generated during glutathione and serum depletion. BPA was also able to reduce the activation of the antioxidant response element (ARE) through mediation of its activators, nuclear factor erythroid related factor family members (Nrf's). Indeed, the expression and nuclear translocation of Nrf2 (an important ARE activator) were impaired by BPA, while Nrf1 and Nrf3 expression levels were increased. Furthermore, BPA increased the levels of the anti-apoptotic proteins (Bcl-2 and Hsp70) and decreased HIF-1α levels during stress-induced conditions. Together, these results indicate that BPA inhibits trophoblast cell death under conditions of cellular stress. This could have implications on placental trophoblasts during development.

Estrogen receptors and lesion-induced response of striatal dopamine receptors

Neuroprotection by 17β-estradiol and an estrogen receptor (ER) agonist against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) lesion were shown to implicate protein kinase B (Akt) signaling in mice. In order to evaluate the associated mechanisms, this study compared estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ) intact or knockout (KO) and wild-type (WT) C57Bl/6 male mice following MPTP treatment of 7, 9, 11mg/kg and/or 17β-estradiol. Striatal D1 and D2 dopamine (DA) receptors were measured by autoradiography with the specific ligands [(3)H]-SCH 23390 and [(3)H]-raclopride, respectively and signaling by Western blot for Akt, glycogen synthase kinase 3β (GSK3β) and extracellular-regulated signal kinases (ERK1 and ERK2). Control ERKOβ mice had lower striatal [(3)H]-SCH 23390 specific binding than WT and ERKOα mice; both KO mice had lower [(3)H]-raclopride specific binding. Striatal D1 receptors decreased with increasing doses of MPTP in correlation with striatal DA concentrations in ERKOα mice and remained unchanged in WT and ERKOβ mice. Striatal D2 receptors decreased with increasing doses of MPTP in correlation with striatal DA concentrations in WT and ERKOα mice and increased in ERKOβ mice. In MPTP-lesioned mice, 17β-estradiol treatment increased D1 receptors in ERKOα and ERKOβ mice and D2 receptors in WT and ERKOβ mice. MPTP did not affect striatal pAkt/Akt and pGSK3β/GSK3β levels in WT and ERKOα mice, while in vehicle-treated ERKOβ mice these levels were higher and increased with MPTP lesioning. Striatal pERK1/ERK1 and pERK2/ERK2 levels showed to a lesser extent a similar pattern. In conclusion, ERs affected the response of striatal DA receptors to a MPTP lesion and post receptor signaling.

Moderate superoxide production is an early promoter of mitochondrial biogenesis in differentiating N2a neuroblastoma cells

Reactive oxygen species (ROS) have been widely considered as harmful for cell development and as promoters of cell aging by increasing oxidative stress. However, ROS have an important role in cell signaling and they have been demonstrated to be beneficial by triggering hormetic signals, which could protect the organism from later insults. In the present study, N2a murine neuroblastoma cells were used as a paradigm of cell-specific (neural) differentiation partly mediated by ROS. Differentiation was triggered by the established treatments of serum starvation, forskolin or dibutyryl cyclic AMP. A marked differentiation, expressed as the development of neurites, was detected by fixation and staining with coomassie brilliant blue after 48 h treatment. This was accompanied by an increase in mitochondrial mass detected by mitotracker green staining, an increased expression of the peroxisome proliferator-activated receptor gamma (PPARγ) coactivator 1-alpha (PGC-1α) and succinate dehydrogenase activity as detected by MTT. In line with these results, an increase in free radicals, specifically superoxide anion, was detected in differentiating cells by flow cytometry. Superoxide scavenging by MnTBAP and MAPK inhibition by PD98059 partially reversed differentiation and mitochondrial biogenesis. In this way, we demonstrated that mitochondrial biogenesis and differentiation are mediated by superoxide and MAPK cues. Our data suggest that differentiation and mitochondrial biogenesis in N2a cells are part of a hormetic response which is triggered by a modest increase of superoxide anion concentration within the mitochondria.

Loss of ATF2 function leads to cranial motoneuron degeneration during embryonic mouse development

The AP-1 family transcription factor ATF2 is essential for development and tissue maintenance in mammals. In particular, ATF2 is highly expressed and activated in the brain and previous studies using mouse knockouts have confirmed its requirement in the cerebellum as well as in vestibular sense organs. Here we present the analysis of the requirement for ATF2 in CNS development in mouse embryos, specifically in the brainstem. We discovered that neuron-specific inactivation of ATF2 leads to significant loss of motoneurons of the hypoglossal, abducens and facial nuclei. While the generation of ATF2 mutant motoneurons appears normal during early development, they undergo caspase-dependent and independent cell death during later embryonic and foetal stages. The loss of these motoneurons correlates with increased levels of stress activated MAP kinases, JNK and p38, as well as aberrant accumulation of phosphorylated neurofilament proteins, NF-H and NF-M, known substrates for these kinases. This, together with other neuropathological phenotypes, including aberrant vacuolisation and lipid accumulation, indicates that deficiency in ATF2 leads to neurodegeneration of subsets of somatic and visceral motoneurons of the brainstem. It also confirms that ATF2 has a critical role in limiting the activities of stress kinases JNK and p38 which are potent inducers of cell death in the CNS.

Cell type-specific anti-cancer properties of valproic acid: independent effects on HDAC activity and Erk1/2 phosphorylation

Background

The anti-epileptic drug valproic acid (VPA) has attracted attention as an anti-cancer agent.

Methods

The present study investigated effects of VPA exposure on histone deacetylase (HDAC) inhibition, cell growth, cell speed, and the degree of Erk1/2 phosphorylation in 10 cell lines (BT4C, BT4Cn, U87MG, N2a, PC12-E2, CSML0, CSML100, HeLa, L929, Swiss 3T3).

Results

VPA induced significant histone deacetylase (HDAC) inhibition in most of the cell lines, but the degree of inhibition was highly cell type-specific. Moreover, cell growth, motility and the degree of Erk1/2 phosphorylation were inhibited, activated, or unaffected by VPA in a cell type-specific manner. Importantly, no relationship was found between the effects of VPA on HDAC inhibition and changes in the degree of Erk1/2 phosphorylation, cell growth, or motility. In contrast, VPA-induced modulation of the MAPK pathway downstream of Ras but upstream of MEK (i.e., at the level of Raf) was important for changes in cell speed.

Conclusions

These results suggest that VPA can modulate the degree of Erk1/2 phosphorylation in a manner unrelated to HDAC inhibition and emphasize that changes in the degree of Erk1/2 phosphorylation are also important for the anti-cancer properties of VPA.

MPP+-induced neuronal death in rats involves tyrosine 33 phosphorylation of WW domain-containing oxidoreductase WOX1

WW domain-containing oxidoreductase (named WWOX, FOR or WOX1) is a pro-apoptotic protein and tumor suppressor. Animals treated with dopaminergic neurotoxin 1-methyl-4-phenyl-pyridinium (MPP+) develop Parkinson's disease (PD)-like symptoms. Here we investigated whether WOX1 is involved in MPP+-induced neurodegeneration. Upon insult with MPP+ in rat brains, WOX1 protein was upregulated and phosphorylated at Tyr33 (or activated) in the injured neurons in the striatum and cortex ipsilaterally to intoxication, as determined by immunohistochemistry and Western blotting. Also, WOX1 was present in the condensed nuclei and damaged mitochondria of degenerative neurons, as revealed by transmission immunoelectron microscopy. Time-lapse microscopy revealed that MPP+ induced membrane blebbing and shrinkage of neuroblastoma SK-N-SH cells. Dominant-negative WOX1, a potent inhibitor of Tyr33 phosphorylation, abolished this event, indicating a critical role of the phosphorylation in apoptosis. c-Jun N-terminal kinase (JNK1) is known to bind and counteract the apoptotic function of WOX1. Suppression of JNK1 function by a dominant-negative spontaneously induced WOX1 activation. WOX1 physically interacted with JNK1 in SK-N-SH cells and rat brain extracts. MPP+ rapidly increased the binding, followed by dissociation, which is probably needed for WOX1 to exert apoptosis. We synthesized a short Tyr33-phosphorylated WOX1 peptide (11 amino acid residues). Interestingly, this peptide blocked MPP+-induced neuronal death in the rat brains, whereas non-phospho-WOX1 peptide had no effect. Together, activated WOX1 plays an essential role in the MPP+-induced neuronal death. Our synthetic phospho-WOX1 peptide prevents neuronal death, suggestive of its therapeutic potential in mitigating the symptoms of PD.

ATP-sensitive potassium channel opener iptakalim protects against MPP+-induced astrocytic apoptosis via mitochondria and mitogen-activated protein kinase signal pathways

Inhibition of astrocytic apoptosis has been regarded as a novel prospective strategy for treating neurodegenerative disorders such as Parkinson's disease. In the present study, we demonstrated that iptakalim (IPT), an ATP-sensitive potassium channel (K(ATP) channel) opener, exerted protective effect on MPP(+)-induced astrocytic apoptosis, which was reversed by selective mitochondrial K(ATP) channel blocker 5-hydroxydecanoate. Further study revealed that IPT inhibited glutathione (GSH) depletion, mitochondrial membrane potential loss and subsequent release of pro-apoptotic factors (cytochrome c and apoptosis-inducing factor (AIF), and c-Jun NH(2)-terminal kinase/mitogen-activated protein kinases (MAPK) phosphorylation induced by MPP(+). Meanwhile, extracellular signal-regulated kinase (ERK) 1/2 inhibitor PD98059 inhibited the protective effect of IPT on MPP(+)-induced astrocytic apoptosis. Furthermore, IPT could also activate ERK/MAPK and maintain increased phospho-ERK1/2 level after MPP(+) exposure. Taken together, these findings reveal for the first time that IPT protects against MPP(+)-induced astrocytic apoptosis via inhibition of mitochondria apoptotic pathway and regulating the MAPK signal transduction pathways by opening mitochondrial ATP-sensitive potassium (mitoK(ATP)) channels in astrocytes. And targeting K(ATP) channels expressed in astrocytes may provide a novel therapeutic strategy for neurodegenerative disorders.