Extracellular signal-regulated kinase as an inducer of non-apoptotic neuronal death

Paraquat and Parkinson's Disease: The Molecular Crosstalk of Upstream Signal Transduction Pathways Leading to Apoptosis

Parkinson's disease (PD) is a heterogeneous disease involving a complex interaction between genes and the environment that affects various cellular pathways and neural networks. Several studies have suggested that environmental factors such as exposure to herbicides, pesticides, heavy metals, and other organic pollutants are significant risk factors for the development of PD. Among the herbicides, paraquat has been commonly used, although it has been banned in many countries due to its acute toxicity. Although the direct causational relationship between paraquat exposure and PD has not been established, paraquat has been demonstrated to cause the degeneration of dopaminergic neurons in the substantia nigra pars compacta. The underlying mechanisms of the dopaminergic lesion are primarily driven by the generation of reactive oxygen species, decrease in antioxidant enzyme levels, neuroinflammation, mitochondrial dysfunction, and ER stress, leading to a cascade of molecular crosstalks that result in the initiation of apoptosis. This review critically analyses the crucial upstream molecular pathways of the apoptotic cascade involved in paraquat neurotoxicity, including mitogenactivated protein kinase (MAPK), phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K)/AKT, mammalian target of rapamycin (mTOR), and Wnt/β-catenin signaling pathways.

Endoplasmic Reticulum Stress Signaling and Neuronal Cell Death

Besides protein processing, the endoplasmic reticulum (ER) has several other functions such as lipid synthesis, the transfer of molecules to other cellular compartments, and the regulation of Ca²⁺ homeostasis. Before leaving the organelle, proteins must be folded and post-translationally modified. Protein folding and revision require molecular chaperones and a favorable ER environment. When in stressful situations, ER luminal conditions or chaperone capacity are altered, and the cell activates signaling cascades to restore a favorable folding environment triggering the so-called unfolded protein response (UPR) that can lead to autophagy to preserve cell integrity. However, when the UPR is disrupted or insufficient, cell death occurs. This review examines the links between UPR signaling, cell-protective responses, and death following ER stress with a particular focus on those mechanisms that operate in neurons.

Rhinacanthin-C but Not -D Extracted from Rhinacanthus nasutus (L.) Kurz Offers Neuroprotection via ERK, CHOP, and LC3B Pathways

Neurodegenerative diseases present an increasing problem as the world's population ages; thus, the discovery of new drugs that prevent diseases such as Alzheimer's, and Parkinson's diseases are vital. In this study, Rhinacanthin-C and -D were isolated from Rhinacanthus nasustus, using ethyl acetate, followed by chromatography to isolate Rhinacanthin-C and -D. Both compounds were confirmed using NMR and ultra-performance-LCMS. Using glutamate toxicity in HT-22 cells, we measured cell viability and apoptosis, ROS build-up, and investigated signaling pathways. We show that Rhinacanthin-C and 2-hydroxy-1,4-naphthoquinone have neuroprotective effects against glutamate-induced apoptosis in HT-22 cells. Furthermore, we see that Rhinacanthin-C resulted in autophagy inhibition and increased ER stress. In contrast, low concentrations of Rhinacanthin-C and 2-hydroxy-1,4-naphthoquinone prevented ER stress and CHOP expression. All concentrations of Rhinacanthin-C prevented ROS production and ERK1/2 phosphorylation. We conclude that, while autophagy is present in HT-22 cells subjected to glutamate toxicity, its inhibition is not necessary for cryoprotection.

Mycobacterium tuberculosis effector PPE36 attenuates host cytokine storm damage via inhibiting macrophage M1 polarization

Tuberculosis caused by Mycobacterium tuberculosis remains a serious global public health threat. Macrophage polarization is crucial for the innate immunity against M. tuberculosis. However, how M. tuberculosis interferes with macrophage polarization is elusive. We demonstrated here that M. tuberculosis PPE36 (Rv2108) blocked macrophage M1 polarization, preventing the cytokine storm, and alleviating inflammatory damage to mouse immune organs. PPE36 inhibited the polarization of THP-1 cell differentiation to M1 macrophages, reduced mitochondrial dehydrogenase activity, inhibited the expression of CD16, and repressed the expression of pro-inflammatory cytokines IL-6 and TNF-α, as well as chemokines CXCL9, CXCL10, CCL3, and CCL5. Intriguingly, in the mouse infection model, PPE36 significantly alleviated the inflammatory damage of immune organs caused by a cytokine storm. Furthermore, we found that PPE36 inhibited the polarization of macrophages into mature M1 macrophages by suppressing the ERK signaling. The study provided novel insights into the function and mechanism of action of M. tuberculosis effector PPE36 both at the cellular and animal level.

Reversible Changes in BDNF Expression in MK-801-Induced Hippocampal Astrocytes Through NMDAR/PI3K/ERK Signaling

Dizocilpine (MK-801), a non-competitive N-methyl-D-aspartic acid receptor (NMDA-R) antagonist, can induce schizophrenia-like symptoms in healthy individuals, implicating NMDA-R hypofunction in disease pathogenesis. Brain-derived neurotrophic factor (BDNF) is also implicated in schizophrenia, and expression is regulated by NMDA-R activity, suggesting a functional link. We previously found that BDNF signaling was upregulated by MK-801 in cultured hippocampal astrocytes, but the underlying mechanism is not clear. To address this issue, the levels of BDNF expression and secretion were evaluated in hippocampal astrocytes incubated with MK-801 by ELISA and qPCR, with and without NMDA co-incubation or pretreatment of either the ERK1/2 inhibitor, PD98059 or the PI3K inhibitor, LY294002. The apoptosis, viability, and proliferation of the astrocytes were also examined. In the current study, we demonstrate that MK-801 treatment (20 μM for 5 days) enhances the proliferation of rat cultured hippocampal astrocytes. Expression of BDNF mRNA was enhanced after 24 h in MK-801, but returned to near baseline over the next 24 h in the continued presence of MK-801. However, two successive 24-h treatments enhanced BDNF expression. These application regimens had no effect on apoptosis or proliferation rate. Co-addition of NMDA significantly inhibited MK-801-induced upregulation of BDNF. Similarly, MK-801-induced BDNF upregulation was blocked by pretreatment with inhibitors of PI3K and ERK1/2, but not by inhibitors of p38 and JNK. These findings suggested that astrocytes may contribute to the acute neurological and behavioral response to MK-801 treatment via a transient increase in BDNF expression involving NMDA-R–PI3K–ERK signaling.

Cytoplasmic phosphorylated ERK1/2 expression in patients with melanoma is associated with tumor stage and metastasis

Melanoma is the cause of most deaths from skin cancer. The extracellular signal-regulated kinase 1/2 (ERK1/2) pathway has been reported to participate in progression of melanoma in fair skinned populations. ERK1/2 is found in both the cytoplasm and nucleus of cells, and phosphorylated ERK1/2 has been implicated in tumor progression. We investigated the relation between melanoma progression and expression of cytoplasmic and nuclear phosphorylated ERK1/2. We examined 34 surgically resected melanomas and investigated their clinicopathologic characteristics. We found immunostaining of phosphorylated ERK1/2 in all melanomas and faint staining in benign nevi. We found expression of cytoplasmic phosphorylated ERK1/2 in most melanomas; however, nuclear phosphorylated ERK1/2 expression was found in only five melanomas. Expression of cytoplasmic phosphorylated ERK1/2 was related to the tumor stage in melanoma. Nine of 10 cases of distant metastasis were positive for cytoplasmic phosphorylated ERK1/2. Our findings suggest that phosphorylated ERK1/2 expression is relevant to clinical pathology and that in melanoma patients, phosphorylated ERK1/2 expression is found in both the cytoplasm and nucleus. Our findings suggest that cytoplasmic phosphorylated ERK1/2 participates in progression of melanoma and that it could be a useful target for clinical treatment of melanoma.

Enhanced Autophagy in GAB1-Deficient Vascular Endothelial Cells Is Responsible for Atherosclerosis Progression

Autophagy is a host machinery that controls cellular health. Dysfunction of autophagy is responsible for the pathogenesis of many human diseases that include atherosclerosis obliterans (ASO). Physiologically, host autophagy removes aging organelles and delays the formation of atherosclerotic plaque. However, in ischemia event, dysregulated autophagy can be induced to trigger autosis, leading to an inevitable cellular death. Grb2-associated binder 1 (GAB1) is a docking/scaffolding adaptor protein that regulates many cell processes including autophagy. Our study first reported that the protein expression of GAB1 significantly decreased in ASO. Mechanically, our results showed that inhibition of Akt (protein kinase B), the upstream of mTOR (mechanistic target of rapamycin), significantly enhanced autophagy by demonstrating the downregulation of p62/Sequestosome 1 expression and the upregulation of the ratio of LC3II/LC3I. Conversely, we found that the inhibition of ERK1/2 (extracellular signal-regulated kinases1/2), p38, and JNK (c-Jun N-terminal kinase) signaling pathway, respectively, significantly inhibited autophagy by demonstrating the upregulation of p62 expression and the downregulation of the ratio of LC3II/LC3I. Further, we demonstrated that knockdown of GAB1 significantly increased autophagy in HUVECs (human umbilical vein endothelial cells) via activation of MAPK (mitogen-activated protein kinase) pathways that include ERK1/2, p38, and JNK. Moreover, we found that knockdown of GAB1 profoundly inhibited HUVEC proliferation, migration, and tube formation. Taken together, this study first suggests that GAB1 is a key regulator of autophagy in HUVECs. Targeting GAB1 may serve as a potential strategy for the atherosclerosis treatment.

Molecular Regulation in Dopaminergic Neuron Development. Cues to Unveil Molecular Pathogenesis and Pharmacological Targets of Neurodegeneration

The relatively few dopaminergic neurons in the mammalian brain are mostly located in the midbrain and regulate many important neural functions, including motor integration, cognition, emotive behaviors and reward. Therefore, alteration of their function or degeneration leads to severe neurological and neuropsychiatric diseases. Unraveling the mechanisms of midbrain dopaminergic (mDA) phenotype induction and maturation and elucidating the role of the gene network involved in the development and maintenance of these neurons is of pivotal importance to rescue or substitute these cells in order to restore dopaminergic functions. Recently, in addition to morphogens and transcription factors, microRNAs have been identified as critical players to confer mDA identity. The elucidation of the gene network involved in mDA neuron development and function will be crucial to identify early changes of mDA neurons that occur in pre-symptomatic pathological conditions, such as Parkinson’s disease. In addition, it can help to identify targets for new therapies and for cell reprogramming into mDA neurons. In this essay, we review the cascade of transcriptional and posttranscriptional regulation that confers mDA identity and regulates their functions. Additionally, we highlight certain mechanisms that offer important clues to unveil molecular pathogenesis of mDA neuron dysfunction and potential pharmacological targets for the treatment of mDA neuron dysfunction.

Thiamine Deficiency Modulates p38MAPK and Heme Oxygenase-1 in Mouse Brain: Association with Early Tissue and Behavioral Changes

Thiamine deficiency (TD) produces severe neurodegenerative lesions. Studies have suggested that primary neurodegenerative events are associated with both oxidative stress and inflammation. Very little is known about the downstream effects on intracellular signaling pathways involved in neuronal death. The primary aim of this work was to evaluate the modulation of p38^MAPK and the expression of heme oxygenase 1 (HO-1) in the central nervous system (CNS). Behavioral, metabolic, and morphological parameters were assessed. Mice were separated into six groups: control (Cont), TD with pyrithiamine (Ptd), TD with pyrithiamine and Trolox (Ptd + Tr), TD with pyrithiamine and dimethyl sulfoxide (Ptd + Dmso), Trolox (Tr) and DMSO (Dmso) control groups and treated for 9 days. Control groups received standard feed (AIN-93M), while TD groups received thiamine deficient feed (AIN-93DT). All the groups were subjected to behavioral tests, and CNS samples were collected for cell viability, histopathology and western blot analyses. The Ptd group showed a reduction in weight gain and feed intake, as well as a reduction in locomotor, grooming, and motor coordination activities. Also, Ptd group showed a robust increase in p38^MAPK phosphorylation and mild HO-1 expression in the cerebral cortex and thalamus. The Ptd group showed a decreased cell viability, hemorrhage, spongiosis, and astrocytic swelling in the thalamus. Groups treated with Trolox and DMSO displayed diminished p38^MAPK phosphorylation in both the structures, as well as attenuated thalamic lesions and behavioral activities. These data suggest that p38^MAPK and HO-1 are involved in the TD-induced neurodegeneration in vivo, possibly modulated by oxidative stress and neuroinflammation.

The Role of PI3K/Akt and ERK in Neurodegenerative Disorders

Disruption of Akt and Erk-mediated signal transduction significantly contributes in the pathogenesis of various neurodegenerative diseases (NDs), such as Parkinson's disease, Alzheimer's diseases, Huntington's disease, and many others. These regulatory proteins serve as the regulator of cell survival, motility, transcription, metabolism, and progression of the cell cycle. Therefore, targeting Akt and Erk pathway has been proposed as a reasonable approach to suppress ND progression. This review has emphasized on involvement of Akt/Erk cascade in the neurodegeneration. Akt has been reported to regulate neuronal toxicity through its various substrates like FOXos, GSK3β, and caspase-9 etc. Akt is also involved with PI3K in signaling pathway to mediate neuronal survival. ERK is another kinase which also regulates proliferation, differentiation, and survival of the neural cell. There has also been much progress in developing a therapeutic molecule targeting Akt and Erk signaling. Therefore, improved understanding of the molecular mechanism behind the regulatory aspect of Akt and Erk networks can make strong impact on exploration of the neurodegenerative disease pathogenesis.

Interleukin-1β induces apoptosis in annulus fibrosus cells through the extracellular signal-regulated kinase pathway

PURPOSE

The loss of intervertebral disc (IVD) cells due to excessive apoptosis induced by inflammatory cytokines is a major cause of IVD degeneration. This study aims to explore the mechanism of interleukin-1β (IL-1β)-induced apoptosis of annulus fibrosus cells (AFCs). It's hypothesized that IL-1β induces apoptosis through the extracellular signal-regulated kinase (ERK) pathway in AFCs.

METHODS

The mRNA and protein expression levels of apoptosis-associated genes were analyzed by quantitative real-time PCR and Western blotting. The apoptotic rate was measured by flow cytometry. Three experimental groups were established, including Control, IL-1β, and IL-1β+U0126 groups, respectively.

RESULTS

Increase in the expression of apoptosis-associated genes including B-cell lymphoma-2 associated X (Bax), caspase-3, and caspase-9, and meanwhile, decrease in the expression of B-cell lymphoma-2 (Bcl-2) gene were found in patients with degenerative IVDs. In in vitro tests, both apoptosis and phosphorylated ERK expression in rat AFCs decreased in the IL-1β+U0126 group compared with the IL-1β group. The expression levels of Bax, caspase-3, and caspase-9 in AFCs decreased significantly in the IL-1β+U0126 group compared with those in the IL-1β group. The expression level of Bcl-2, on the other hand, significantly increased.

CONCLUSIONS

Findings from this study suggest that IL-1β induces apoptosis in AFCs through the ERK pathway, and therefore, ERK inhibition may provide certain protection against the adverse effects of IL-1β.

Antitumor Efficacy of Huqizhengxiao (HQZX) Decoction Based on Inhibition of Telomerase Activity in Nude Mice of Hepatocarcinoma Xenograft

Objective: Huqizhengxiao (HQZX) decoction is a mixture of traditional Chinese medicines comprising 10 herbs, with inhibitory effects on hepatocarcinoma. The aim of the study is to observe the antitumor efficacy and mechanism of HQZX decoction in nude mice with hepatocellular carcinoma xenografts. Methods: HepG2-luc subcutaneous hepatocarcinoma was established in nude mice. The mice were divided into 5 groups: control, cinobufagin, HQZXS, HQZXM, and HQZXH with doses 13.52, 27.03, and 54.06 g/kg, respectively. HQZX decoction was prepared for intraperitoneal intragastric administration for 3 weeks. Tumor growth was measured with Vernier calipers and in vivo imaging system. α-Fetoprotein (AFP) was determined by radioimmunoassay. Tumor necrosis factor–α (TNF-α) was measured with enzyme-linked immunosorbent assay (ELISA) assay. Telomerase activity was measured with polymerase chain reaction–ELISA. Nuclear mitosis and necrosis were observed with hematoxylin-eosin stain. Apoptotic proteins of caspase-3, Bcl-2, and Bax were examined by Western blot. Signaling molecules of ERK, mTOR, and STAT3 were measured with Luminex assay. Results: HQZX decoction showed good inhibition of HepG2-luc xenografts. Compared with control group, the relative tumor proliferation rate was less than 60% in the HQZXH and HQZXS. The tumor inhibition rate of HQZXH group reached 52% ± 15%. Relative average optical density values of the HQZXS and HQZXH groups decreased significantly. The mitotic index in HQZXS, HQZXM, and HQZXH groups decreased greatly. Telomerase activity of HQZXS was clearly reduced, and, the caspase-3 expression upregulated in HQZXH group. Bcl-2 expression was downregulated in HQZXS and HQZXH. The ratios of p-ERK/ERK and p-STAT3/STAT3 in HQZXS group were significantly downregulated. Conclusion: HQZX decoction can clearly inhibit the growth of hepatocellular carcinoma and induce tumor apoptosis. Its antitumor mechanism may be related to reducing telomerase activity and regulating the STAT3 and ERK signal pathway.

Critical Roles of Dual-Specificity Phosphatases in Neuronal Proteostasis and Neurological Diseases

Protein homeostasis or proteostasis is a fundamental cellular property that encompasses the dynamic balancing of processes in the proteostasis network (PN). Such processes include protein synthesis, folding, and degradation in both non-stressed and stressful conditions. The role of the PN in neurodegenerative disease is well-documented, where it is known to respond to changes in protein folding states or toxic gain-of-function protein aggregation. Dual-specificity phosphatases have recently emerged as important participants in maintaining balance within the PN, acting through modulation of cellular signaling pathways that are involved in neurodegeneration. In this review, we will summarize recent findings describing the roles of dual-specificity phosphatases in neurodegeneration and offer perspectives on future therapeutic directions.

Active targeting co-delivery system based on hollow mesoporous silica nanoparticles for antitumor therapy in ovarian cancer stem-like cells

The combination of nanocarriers and chemotherapy drugs can release the chemotherapy drugs to the tumor tissue, which can enhance the antitumor effect and reduce the adverse reactions at the same time. In this study, a co-delivery system based on hollow mesoporous silica nanoparticles (HMSN) was developed and characterized. We also investigated the in vitro effect of this system on CD117+CD44+A2780 cell line. HMSN was selected as the nanocarrier, with -COOH modified on the surface and doxorubicin (DOX), NVP-AEW 541 (NVP) loaded inside. IGF‑1R was chosen as the drug target, apoptosis rate and expression of cyclin B1, Bax, Bcl-xl, p-Akt were used to evaluate the antitumor effect of HMSN‑COOH@DOX fluorescence NVP. The HMSN co-delivery system was successfully synthesized with encapsulation efficiency of 37% (DOX) and 44% (NVP), and high PH-sensitive property was observed. The apoptosis rate of CD117+CD44+A2780 ovarian cancer stem-like cells treated by HMSN co-delivery system were almost 3 times higher than those of the free drugs group. The expression of Bax was significantly increased while Bcl-xl, and p-Akt reduced (P≤0.05). These data indicate that the co-delivery system demonstrated a high efficiency in promoting apoptosis in ovarian cancer stem-like cells by targeting IGF‑1R, but further study is still needed.

Periplaneta americana Extracts Promote Skin Wound Healing via Nuclear Factor Kappa B Canonical Pathway and Extracellular Signal-Regulated Kinase Signaling

Periplaneta americana extracts (PAEs) exhibit wound healing properties. However, the underlying molecular mechanisms are not well understood. Here, we treated human skin fibroblasts (HSF) with PAE and the proliferation was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The wound healing and transwell migration assays were used to detect cell migration. Nuclear factor kappa B (NF-κB) and extracellular signal-regulated kinase (ERK) pathways were analyzed by Western blot (WB). Immunofluorescence staining was used to detect the key molecular localization in the cells. The results showed that PAE enhanced the proliferation and migration of HSF cells. The expression and activation of key proteins such as RelA and p-ERK were increased in NF-κB and ERK pathways followed by nuclear translocation. In vivo, both WB and immunohistochemical (IHC) staining showed that PAE enhanced p-IκBα and p-ERK activation and the nuclear translocation of RelA. Our study suggests that the protective function of PAE is mediated via enhanced NF-κB and ERK signaling.

Conditional ablation of myeloid TNF increases lesion volume after experimental stroke in mice, possibly via altered ERK1/2 signaling

Microglia are activated following cerebral ischemia and increase their production of the neuro- and immunomodulatory cytokine tumor necrosis factor (TNF). To address the function of TNF from this cellular source in focal cerebral ischemia we used TNF conditional knock out mice (LysMcreTNF^fl/fl) in which the TNF gene was deleted in cells of the myeloid lineage, including microglia. The deletion reduced secreted TNF levels in lipopolysaccharide-stimulated cultured primary microglia by ~93%. Furthermore, phosphorylated-ERK/ERK ratios were significantly decreased in naïve LysMcreTNF^fl/fl mice demonstrating altered ERK signal transduction. Micro-PET using ¹⁸[F]-fluorodeoxyglucose immediately after focal cerebral ischemia showed increased glucose uptake in LysMcreTNF^fl/fl mice, representing significant metabolic changes, that translated into increased infarct volumes at 24 hours and 5 days compared to littermates (TNFfl/fl). In naïve LysMcreTNF^fl/fl mice cytokine levels were low and comparable to littermates. At 6 hours, TNF producing microglia were reduced by 56% in the ischemic cortex in LysMcreTNF^fl/fl mice compared to littermate mice, whereas no TNF⁺ leukocytes were detected. At 24 hours, pro-inflammatory cytokine (TNF, IL-1β, IL-6, IL-5 and CXCL1) levels were significantly lower in LysMcreTNF^fl/fl mice, despite comparable infiltrating leukocyte populations. Our results identify microglial TNF as beneficial and neuroprotective in the acute phase and as a modulator of neuroinflammation at later time points after experimental ischemia, which may contribute to regenerative recovery.

Contrasting features of ERK1/2 activity and synapsin I phosphorylation at the ERK1/2-dependent site in the rat brain in status epilepticus induced by kainic acid in vivo

Extracellular signal-regulated kinase 1/2 (ERK1/2) plays diverse roles in the central nervous system. Activation of ERK1/2 has been observed in various types of neuronal excitation, including seizure activity in vivo and in vitro. However, studies examining ERK1/2 activity and its substrate phosphorylation in parallel are scarce especially in seizure models. We have been studying the phosphorylation state of the presynaptic protein, synapsin I at ERK1/2-dependent and -independent sites in various types of seizure models and showed that ERK1/2-dependent phosphorylation of synapsin I was indeed under control of ERK1/2 activity in vivo. To further expand our study, here we examined the effects of prolonged seizure activity on ERK1/2 activity and synapsin I phosphorylation by using status epilepticus induced by kainic acid (KA-SE) in rats in vivo. In KA-SE, robust ERK1/2 activation was observed in the hippocampus, a representative limbic structure, with lesser activation in the parietal cortex, a representative non-limbic structure. In contrast, the phosphorylation level of synapsin I at ERK1/2-dependent phospho-site 4/5 was profoundly decreased, the extent of which was much larger in the hippocampus than in the parietal cortex. In addition, phosphorylation at other ERK1/2-independent phospho-sites in synapsin I also showed an even larger decrease. All these changes disappeared after recovery from KA-SE. These results indicate that the phosphorylation state of synapsin I is dynamically regulated by the balance between kinase and phosphatase activities. The contrasting features of robust ERK1/2 activation yet synapsin I dephosphorylation may be indicative of an irreversible pathological outcome of the epileptic state in vivo.

Upregulated Ras/Raf/ERK1/2 signaling pathway: a new hope in the repair of spinal cord injury

An increasing number of studies report that the Ras/Raf/extracellular signal-regulated kinase 1/2 (ERK1/2) signaling pathway has a death-promoting apoptotic function in neural cells. We hypothesized that the Ras/Raf/ERK1/2 signaling pathway may be abnormally regulated in rat injured spinal cord models. The weight drop method was used to establish rat spinal cord injury at T₉. Western blot analysis and immunohistochemical staining revealed Ras expression was dramatically elevated, and the phosphorylations of A-Raf, B-Raf and C-Raf were all upregulated in the injured spinal cord. Both mitogen-activated protein kinase kinase 1/2 and ERK1/2, which belong to the Ras/Raf signaling kinases, were upregulated. These results indicate that Ras/Raf/ERK1/2 signaling may be upregulated in injured spinal cord and are involved in recovery after spinal cord injury.

BRAF-mutated colorectal cancer: clinical implications for a distinct subset of the disease

SUMMARY 

Colorectal cancer (CRC) is many diseases, with each case defined by the underlying genetic and molecular changes of that particular tumor. The heterogeneity of CRC emphasizes the need to understand this disease within the context of genetic subsets. BRAF mutations mark a subpopulation that arises through the serrated pathway to carcinogenesis. This subset of cancers is associated with unique clinical and histopathologic characteristics. BRAF-mutated CRCs have a worse prognosis compared with their wild-type counterparts, and may not be as responsive to chemotherapy. Target therapies specifically against BRAF and its related signaling pathways are under both scientific and clinical investigation. This article highlights the clinical relevance of the subset of BRAF-mutated CRCs.

Sigma-1 receptor stimulation protects retinal ganglion cells from ischemia-like insult through the activation of extracellular-signal-regulated kinases 1/2

Sigma-1 receptor (σ-1) activation and mitogen-activated protein kinases (MAPKs) have been shown to protect retinal ganglion cells (RGCs) from cell death. The purpose of this study was to determine if σ-1 receptor stimulation with pentazocine could promote neuroprotection under conditions of an ischemia-like insult (oxygen glucose deprivation (OGD)) through the phosphorylation of extracellular signal regulated kinase (pERK)1/2. Primary RGCs were isolated from P3-P7 Sprague-Dawley rats and purified by sequential immunopanning using Thy1.1 antibodies. RGCs were cultured for 7 days before subjecting the cells to an OGD insult (0.5% oxygen in glucose-free medium) for 6 h. During the OGD, RGCs were treated with pentazocine (σ-1 receptor agonist) with or without BD 1047 (σ-1 receptor antagonist). In other experiments, primary RGCs were treated with pentazocine in the presence or absence of an MEK1/2 inhibitor, PD098059. Cell survival/death was assessed by staining with the calcein-AM/ethidium homodimer reagent. Levels of pERK1/2, total ERK1/2, and beta tubulin expression were determined by immunoblotting and immunofluorescence staining. RGCs subjected to OGD for 6 h induced 50% cell death in primary RGCs (p < 0.001) and inhibited pERK1/2 expression by 65% (p < 0.001). Cell death was attenuated when RGCs were treated with pentazocine under OGD (p < 0.001) and pERK1/2 expression was increased by 1.6 fold (p < 0.05) compared to OGD treated RGCs without pentazocine treatment. The co-treatment of PD098059 (MEK1/2 inhibitor) with pentazocine significantly abolished the protective effects of pentazocine on the RGCs during this OGD insult. Activation of the σ-1 receptor is a neuroprotective target that can protect RGCs from an ischemia-like insult. These results also established a direct relationship between σ-1 receptor stimulation and the neuroprotective effects of the ERK1/2 pathway in purified RGCs subjected to OGD. These findings suggest that activation of the σ-1 receptor may be a therapeutic target for neuroprotection particularly relevant to ocular neurodegenerative diseases that effect RGCs.

Activation of Erk and p53 regulates copper oxide nanoparticle-induced cytotoxicity in keratinocytes and fibroblasts

Copper oxide nanoparticles (CuONP) have attracted increasing attention due to their unique properties and have been extensively utilized in industrial and commercial applications. For example, their antimicrobial capability endows CuONP with applications in dressings and textiles against bacterial infections. Along with the wide applications, concerns about the possible effects of CuONP on humans are also increasing. It is crucial to evaluate the safety and impact of CuONP on humans, and especially the skin, prior to their practical application. The potential toxicity of CuONP to skin keratinocytes has been reported recently. However, the underlying mechanism of toxicity in skin cells has remained unclear. In the present work, we explored the possible mechanism of the cytotoxicity of CuONP in HaCaT human keratinocytes and mouse embryonic fibroblasts (MEF). CuONP exposure induced viability loss, migration inhibition, and G₂/M phase cycle arrest in both cell types. CuONP significantly induced mitogen-activated protein kinase (extracellular signal-regulated kinase [Erk], p38, and c-Jun N-terminal kinase [JNK]) activation in dose- and time-dependent manners. U0126 (an inhibitor of Erk), but not SB 239063 (an inhibitor of p38) or SP600125 (an inhibitor of JNK), enhanced CuONP-induced viability loss. CuONP also induced decreases in p53 and p-p53 levels in both cell types. Cyclic pifithrin-α, an inhibitor of p53 transcriptional activity, enhanced CuONP-induced viability loss. Nutlin-3α, a p53 stabilizer, prevented CuONP-induced viability loss in HaCaT cells, but not in MEF cells, due to the inherent toxicity of nutlin-3α to MEF. Moreover, the experiments on primary keratinocytes are in accordance with the conclusions acquired from HaCaT and MEF cells. These data demonstrate that the activation of Erk and p53 plays an important role in CuONP-induced cytotoxicity, and agents that preserve Erk or p53 activation may prevent CuONP-induced cytotoxicity.

Superparamagnetic iron oxide nanoparticles exacerbate the risks of reactive oxygen species-mediated external stresses

Superparamagnetic iron oxide nanoparticles (IONPs) have been widely applied in numerous biomedical fields. The evaluation of the toxicity of IONPs to the environment and human beings is indispensable to guide their applications. IONPs are usually considered to have good biocompatibility; however, some literatures have reported the toxicity of IONPs in vitro and in vivo. The controversy surrounding the biocompatibility of IONPs prompted us to carefully consider the biological effects of IONPs, especially under stress conditions. However, the potential risks of IONPs under stress conditions have not yet been evaluated in depth. Acrolein is widespread in the environment and modulates stress-induced gene activation and cell death in many organs and tissues. In this study, we assessed the sensitivity of H9c2 cardiomyocyte cells embedded with IONPs to acrolein and investigated the possible molecular mechanisms involved in this sensitivity. IONPs, which alone exhibited no toxicity, sensitized the H9c2 cardiomyocytes to acrolein-induced dysfunction. The IONP/acrolein treatment induced a loss of viability, membrane disruption, reactive oxygen species (ROS) generation, Erk activation, mitochondrial and lysosomal dysfunction, and necrosis in H9c2 cells. Treatment with an ROS generation inhibitor (diphenyleneiodonium) or an iron chelator (deferoxamine) prevented the IONP/acrolein-induced loss of viability, suggesting that ROS and IONP degradation facilitated the toxicity of the IONP/acrolein treatment in H9c2 cells. Our data suggest that cells embedded in IONPs are more vulnerable to oxidative stress, which confirms the hypothesis that nanoparticles can sensitize cells to the adverse effects of external stimulation. The present work provides a new perspective from which to evaluate the interactions between nanoparticles and cells.

Decrease in prosaposin in the Dystrophic mdx mouse brain

BACKGROUND

Duchenne muscular dystrophy caused by a mutation in the X-linked dystrophin gene induces metabolic and structural disorders in the brain. A lack of dystrophin in brain structures is involved in impaired cognitive function. Prosaposin (PS), a neurotrophic factor, is abundant in the choroid plexus and various brain regions. We investigated whether PS serves as a link between dystrophin loss and gross and/or ultrastructural brain abnormalities.

METHODOLOGY/PRINCIPAL FINDINGS

The distribution of PS in the brains of juvenile and adult mdx mice was investigated by immunochemistry, Western blotting, and in situ hybridization. Immunochemistry revealed lower levels of PS in the cytoplasm of neurons of the cerebral cortex, hippocampus, cerebellum, and choroid plexus in mdx mice. Western blotting confirmed that PS levels were lower in these brain regions in both juveniles and adults. Even with low PS production in the choroids plexus, there was no significant PS decrease in cerebrospinal fluid (CSF). In situ hybridization revealed that the primary form of PS mRNA in both normal and mdx mice was Pro+9, a secretory-type PS, and the hybridization signals for Pro+9 in the above-mentioned brain regions were weaker in mdx mice than in normal mice. We also investigated mitogen-activated protein kinase signalling. Stronger activation of ERK1/2 was observed in mdx mice, ERK1/2 activity was positively correlated with PS activity, and exogenous PS18 stimulated both p-ERK1/2 and PS in SH-SY5Y cells.

CONCLUSIONS/SIGNIFICANCE

Low levels of PS and its receptors suggest the participation of PS in some pathological changes in the brains of mdx mice.

ERK pathway is activated in bare-FeNPs-induced autophagy

Iron oxide nanoparticles (FeNPs) are known to be one of the most biocompatible and safe nanoparticles. However, their long-term persistence remains a problem, and macrophages play as an important mediator in continuous stimulation of the immune system due to biopersistence of nanoparticles. In the present study, we identified the mechanisms underlying the uptake and toxicity of bare-FeNPs using RAW264.7 cells, a mouse peritoneal macrophage cell line. The bare-FeNPs penetrated the cell membrane through electrostatic interactions together with the general phagocytic pathway. At 24 h after exposure, they distributed freely in the cytosol or within autophagosome-like vacuoles. Bare-FeNPs induced decrease in the cell viability along with the cell cycle arrest in G1 phase. In addition, they increased the generation of ROS and the secretion of NO and TNF alpha as well as the expression of SOD-1 and SOD-2 proteins, which are an antioxidant. While the mitochondrial calcium level, the intensity of labeled mitochondria, and ATP production decreased, the levels of autophagy-related proteins such as p62, beclin 1, ATG5, and LC3B increased in a dose-dependent manner together with the levels of ATF 3, p-EGFR, and p-ERK proteins. However, the level of p-JNK protein clearly decreased. TEM images also showed that damaged organelle exist within autophagosome-like vacuoles with bare-FeNPs. On the basis of these results, we suggest that bare-FeNPs induce autophagy by initiating oxidative stress in RAW264.7 cells. Furthermore, ERK, but not JNK, pathway is activated in bare-FeNPs-induced autophagy.

Adiponectin modulates oxidative stress-induced autophagy in cardiomyocytes

Diastolic heart failure (HF) i.e., "HF with preserved ejection fraction" (HF-preserved EF) accounts for up to 50% of all HF presentations; however there have been no therapeutic advances. This stems in part from an incomplete understanding about HF-preserved EF. Hypertension is the major cause of HF-preserved EF whilst HF-preserved EF is also highly associated with obesity. Similarly, excessive reactive oxygen species (ROS), i.e., oxidative stress occurs in hypertension and obesity, sensitizing the heart to the renin-angiotensin-aldosterone system, inducing autophagic type-II programmed cell death and accelerating the propensity to adverse cardiac remodeling, diastolic dysfunction and HF. Adiponectin (APN), an adipokine, mediates cardioprotective actions but it is unknown if APN modulates cardiomyocyte autophagy. We tested the hypothesis that APN ameliorates oxidative stress-induced autophagy in cardiomyocytes. Isolated adult rat ventricular myocytes were pretreated with recombinant APN (30 µg/mL) followed by 1mM hydrogen peroxide (H2O2) exposure. Wild type (WT) and APN-deficient (APN-KO) mice were infused with angiotensin (Ang)-II (3.2 mg/kg/d) for 14 days to induced oxidative stress. Autophagy-related proteins, mTOR, AMPK and ERK expression were measured. H2O2 induced LC3I to LC3II conversion by a factor of 3.4±1.0 which was abrogated by pre-treatment with APN by 44.5±10%. However, neither H2O2 nor APN affected ATG5, ATG7, or Beclin-1 expression. H2O2 increased phospho-AMPK by 49±6.0%, whilst pretreatment with APN decreased phospho-AMPK by 26±4%. H2O2 decreased phospho-mTOR by 36±13%, which was restored by APN. ERK inhibition demonstrated that the ERK-mTOR pathway is involved in H2O2-induced autophagy. Chronic Ang-II infusion significantly increased myocardial LC3II/I protein expression ratio in APN-KO vs. WT mice. These data suggest that excessive ROS caused cardiomyocyte autophagy which was ameliorated by APN by inhibiting an H2O2-induced AMPK/mTOR/ERK-dependent mechanism. These findings demonstrate the anti-oxidant potential of APN in oxidative stress-associated cardiovascular diseases, such as hypertension-induced HF-preserved EF.

An endogenously produced fragment of cardiac myosin-binding protein C is pathogenic and can lead to heart failure

RATIONALE

A stable 40-kDa fragment is produced from cardiac myosin-binding protein C when the heart is stressed using a stimulus, such as ischemia-reperfusion injury. Elevated levels of the fragment can be detected in the diseased mouse and human heart, but its ability to interfere with normal cardiac function in the intact animal is unexplored.

OBJECTIVE

To understand the potential pathogenicity of the 40-kDa fragment in vivo and to investigate the molecular pathways that could be targeted for potential therapeutic intervention.

METHODS AND RESULTS

We generated cardiac myocyte-specific transgenic mice using a Tet-Off inducible system to permit controlled expression of the 40-kDa fragment in cardiomyocytes. When expression of the 40-kDa protein is induced by crossing the responder animals with tetracycline transactivator mice under conditions in which substantial quantities approximating those observed in diseased hearts are reached, the double-transgenic mice subsequently experience development of sarcomere dysgenesis and altered cardiac geometry, and the heart fails between 12 and 17 weeks of age. The induced double-transgenic mice had development of cardiac hypertrophy with myofibrillar disarray and fibrosis, in addition to activation of pathogenic MEK-ERK pathways. Inhibition of MEK-ERK signaling was achieved by injection of the mitogen-activated protein kinase (MAPK)/ERK inhibitor U0126. The drug effectively improved cardiac function, normalized heart size, and increased probability of survival.

CONCLUSIONS

These results suggest that the 40-kDa cardiac myosin-binding protein C fragment, which is produced at elevated levels during human cardiac disease, is a pathogenic fragment that is sufficient to cause hypertrophic cardiomyopathy and heart failure.

Tanshinone IIA induces autophagic cell death via activation of AMPK and ERK and inhibition of mTOR and p70 S6K in KBM-5 leukemia cells

Although tanshinone IIA (Tan IIA) from Salviae miltiorrhizae was known to induce apoptosis in various cancers, its underlying mechanism of autophagic cell death was not reported yet. Thus, in the present study, the molecular mechanism of autophagic cell death by Tan IIA was investigated in KBM-5 leukemia cells. Tan IIA significantly increased the expression of microtubule-associated protein light chain 3 (LC3) II as a hallmark of autophagy in western blotting and immunofluorescence staining. Tan IIA augmented the phosphorylation of adenosine monophosphate-activated protein kinase (AMPK) and attenuated the phosphorylation of mammalian target of rapamycin (mTOR) and p70 S6K in a dose-dependent manner. Conversely, autophagy inhibitor 3-methyladenine partly reversed the cytotoxicity and the phosphorylation of AMPK, mTOR and p70 S6K induced by Tan IIA in KBM-5 leukemia cells. In addition, Tan IIA dramatically activated the extracellular signal regulated kinase (ERK) signaling pathway including Raf, ERK and p90 RSK in a dose-dependent and time-dependent manner. Consistently, ERK inhibitor PD184352 suppressed LC3-II activation induced by Tan IIA, whereas PD184352 and PD98059 did not affect poly (ADP-ribose) polymerase cleavage and sub-G1 accumulation induced by Tan IIA in KBM-5 leukemia cells. Furthermore, Tan IIA could induce autophagy via LC3-II activation in various cancer cells such as prostate (PC-3), multiple myeloma (U266), lung (NCI-H460), and breast (MDA-MB-231) cells. Overall, these findings suggest that Tan IIA induces autophagic cell death via activation of AMPK and ERK and inhibition of mTOR and p70 S6K in KBM-5 cells as a potent natural compound for leukemia treatment.

Oxidative stress and mitogen-activated protein kinase pathways involved in cadmium-induced BRL 3A cell apoptosis

In this study, BRL 3A cells were treated with different Cd concentrations (0, 10, 20, and 40 μmol/L) for 12 h and preincubated with or without N-acetyl-L-cysteine (NAC) (2 mmol/L) for 30 min, and cells were treated with Cd (0 and 20 μmol/L), pretreated with p38 inhibitor (SB203580), JNK (c-Jun NH2-terminal kinases) inhibitor (SP600125), and extracellular signal-regulated kinase (ERK) inhibitor (U0126) for 30 min, and then treated with 20 μmol/L Cd for 12 h. Cd decreased cell viability, SOD, and GSH-Px activity in a concentration-dependent manner. Increased MDA level, ROS generation, nuclear condensation, shrinkage, and fragmentation in cell morphology were inhibited by NAC. Cd-induced apoptosis was attenuated by pretreatment with SB203580, SP600125, and U0126. The results of western blot showed that NAC preincubation affected Cd-activated MAPK pathways, p38 and ERK phosphorylation. Cd treatment elevated the mRNA levels of Bax and decreased the mRNA levels of Bcl-2, respectively. The same effect was found in their protein expression levels. These results suggest that oxidative stress and MAPK pathways participate in Cd-induced apoptosis and that the balance between pro- and antiapoptotic genes (Bax and Bcl-2) is important in Cd-induced apoptosis.

High glucose induces apoptosis and suppresses proliferation of adult rat neural stem cells following in vitro ischemia

Background

Post-stroke hyperglycemia appears to be associated with poor outcome from stroke, greater mortality, and reduced functional recovery. Focal cerebral ischemia data support that neural stem cells (NSCs) play an important role in post-ischemic repair. Here we sought to evaluate the negative effects of hyperglycemia on the cellular biology of NSCs following anoxia, and to test whether high glucose affects NSC recovery from ischemic injury.

Results

In this study, we used immortalized adult neural stem cells lines and we induced in vitro ischemia by 6 h oxygen and glucose deprivation (OGD) in an anaerobic incubator. Reperfusion was performed by returning cells to normoxic conditions and the cells were then incubated in experimental medium with various concentrations of glucose (17.5, 27.75, 41.75, and 83.75 mM) for 24 h. We found that high glucose (≥27.75 mM) exposure induced apoptosis of NSCs in a dose-dependent manner after exposure to OGD, using an Annexin V/PI apoptosis detection kit. The cell viability and proliferative activity of NSCs following OGD in vitro, evaluated with both a Cell Counting kit-8 (CCK-8) assay and a 5-ethynyl-2’-deoxyuridine (EdU) incorporation assay, were inhibited by high glucose exposure. Cell cycle analysis showed that high glucose exposure increased the percentage of cells in G0/G1-phase, and reduced the percentage of cells in S-phase. Furthermore, high glucose exposure was found to significantly induce the activation of c-Jun N-terminal protein kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) and suppress extracellular signal-regulated kinase 1/2 (ERK1/2) activity.

Conclusions

Our results demonstrate that high glucose induces apoptosis and inhibits proliferation of NSCs following OGD in vitro, which may be associated with the activation of JNK/p38 MAPK pathways and the delay of G1-S transition in the cells.

Regulation of ERK1/2 mitogen-activated protein kinase by NMDA-receptor-induced seizure activity in cortical slices

Extracellular signal-regulated kinase 1/2 (ERK1/2) that belongs to a subfamily of mitogen-activated protein kinases (MAPKs) plays diverse roles in the central nervous system. Activation of ERK1/2 has been observed in various types of neuronal excitation, including seizure activity in vivo and in vitro, as well as in NMDA-receptor (NMDA-R)-dependent long-term potentiation in the hippocampus. On the other hand, recent studies in cultured neurons have shown that NMDA-R stimulation could result in either ERK1/2 activation or non-activation, depending on the pharmacological manipulations. To assess NMDA-R-dependent regulation of ERK1/2 activity in vivo, here we examined the effect of NMDA-R-induced seizure activity on ERK1/2 activation by using rat cortical slice preparations. NMDA-R-dependent seizure activity introduced by Mg2+ -free condition did not cause ERK1/2 activation. On the other hand, when picrotoxin was added to concurrently suppress GABAA-receptor-mediated inhibition, profound ERK1/2 activation occurred, which was accompanied by strong phospho-ERK1/2-staining in the superficial and deep cortical layer neurons. In this case, prolonged membrane depolarization and enhanced burst action potential firings, both of which were much greater than those in Mg2+ -free condition alone, were observed. Differential ERK1/2 activation was supported by the concurrent selective increase in phosphorylation of a substrate protein, phospho-site 4/5 of synapsin I. These results indicate that NMDA-R activation through a release from Mg2+ -blockade, which accompanies enhancement of both excitatory and inhibitory synaptic transmission, was not enough, but concurrent suppression of GABAergic inhibition, which leads to a selective increase in excitatory synaptic transmission, was necessary for robust ERK1/2 activation to occur within the cortical network.

Knockdown of RAB25 promotes autophagy and inhibits cell growth in ovarian cancer cells

RAB25 belongs to the Rab family of small GTPases and is implicated in the development of various types of human cancer. To evaluate the role of RAB25 in ovarian cancer, RAB25 was knocked down by siRNA in HEY and ES‑2 human ovarian cancer cells. Autophagy, cell growth and cell apoptosis were evaluated. The results showed that knockdown of RAB25 increased acidic vesicle organelles and GFP-microtubule-associated protein 1 light chain 3 punctate fluorescence in ovarian cancer cells. Autophagy that promoted by knockdown of RAB25 was not observed in cells where the ERK1/2 signaling pathway had been inhibited by U0126. Knockdown of RAB25 reduced cell cycle progression and cell growth. Apoptosis of ovarian cancer cells could be induced by knockdown of RAB25. These results support the tumorigenic role of RAB25 in ovarian cancer cells.

Interactions between SIRT1 and MAPK/ERK regulate neuronal apoptosis induced by traumatic brain injury in vitro and in vivo

Traumatic brain injury (TBI) is a serious insult that frequently leads to neurological dysfunction or death. Silent information regulator family protein 1 (SIRT1), as the founding member of nicotinamide adenine dinucleotide (NAD)-dependent deacetylases, has recently been demonstrated to have neuroprotective effect in several models of neurodegenerative diseases. The present study attempts to determine whether SIRT1 has a neuroprotective effect in the model of TBI, and further to investigate the possible regulatory mechanism of neuron death. Thus, we employ transection model in vitro and weight-drop model in vivo to mimic the insults of TBI. The study shows that the expressions of SIRT1, phosphorylation extracellular signal-regulated kinase (p-ERK) and cleaved Caspase-3 are induced after trauma injury in vitro or in vivo. Furthermore, inhibiting SIRT1 by pharmacological inhibitor salermide or SIRT1 siRNA significantly promotes apoptotic neuron death and reduces ERK1/2 activation induced by mechanical injury in vitro and in vivo. Inhibition of ERK1/2 activation with PD98059 or U0126 (two mitogen activated protein kinase kinase inhibitors) in vitro and in vivo significantly attenuates the SIRT1 and cleaved Caspase-3 expression to protect neuron against TBI-induced apoptosis. These results reveal that SIRT1 plays a neuroprotective effect against neuronal apoptosis induced by TBI. The interactions between SIRT1 and MAPK/ERK pathway regulate neuronal apoptosis induced by mechanical trauma injury in vitro and in vivo.

Adaptor protein LNK is a negative regulator of brain neural stem cell proliferation after stroke

Ischemic stroke causes transient increase of neural stem and progenitor cell (NSPC) proliferation in the subventricular zone (SVZ), and migration of newly formed neuroblasts toward the damaged area where they mature to striatal neurons. The molecular mechanisms regulating this plastic response, probably involved in structural reorganization and functional recovery, are poorly understood. The adaptor protein LNK suppresses hematopoietic stem cell self-renewal, but its presence and role in the brain are poorly understood. Here we demonstrate that LNK is expressed in NSPCs in the adult mouse and human SVZ. Lnk(-/-) mice exhibited increased NSPC proliferation after stroke, but not in intact brain or following status epilepticus. Deletion of Lnk caused increased NSPC proliferation while overexpression decreased mitotic activity of these cells in vitro. We found that Lnk expression after stroke increased in SVZ through the transcription factors STAT1/3. LNK attenuated insulin-like growth factor 1 signaling by inhibition of AKT phosphorylation, resulting in reduced NSPC proliferation. Our findings identify LNK as a stroke-specific, endogenous negative regulator of NSPC proliferation, and suggest that LNK signaling is a novel mechanism influencing plastic responses in postischemic brain.

In vivo manganese exposure modulates Erk, Akt and Darpp-32 in the striatum of developing rats, and impairs their motor function

Manganese (Mn) is an essential metal for development and metabolism. However, exposures to high Mn levels may be toxic, especially to the central nervous system (CNS). Neurotoxicity is commonly due to occupational or environmental exposures leading to Mn accumulation in the basal ganglia and a Parkinsonian-like disorder. Younger individuals are more susceptible to Mn toxicity. Moreover, early exposure may represent a risk factor for the development of neurodegenerative diseases later in life. The present study was undertaken to investigate the developmental neurotoxicity in an in vivo model of immature rats exposed to Mn (5, 10 and 20 mg/kg; i.p.) from postnatal day 8 (PN8) to PN12. Neurochemical analysis was carried out on PN14. We focused on striatal alterations in intracellular signaling pathways, oxidative stress and cell death. Moreover, motor alterations as a result of early Mn exposure (PN8-12) were evaluated later in life at 3-, 4- and 5-weeks-of-age. Mn altered in a dose-dependent manner the activity of key cell signaling elements. Specifically, Mn increased the phosphorylation of DARPP-32-Thr-34, ERK1/2 and AKT. Additionally, Mn increased reactive oxygen species (ROS) production and caspase activity, and altered mitochondrial respiratory chain complexes I and II activities. Mn (10 and 20 mg/kg) also impaired motor coordination in the 3^rd, 4^th and 5^th week of life. Trolox™, an antioxidant, reversed several of the Mn altered parameters, including the increased ROS production and ERK1/2 phosphorylation. However, Trolox™ failed to reverse the Mn (20 mg/kg)-induced increase in AKT phosphorylation and motor deficits. Additionally, Mn (20 mg/kg) decreased the distance, speed and grooming frequency in an open field test; Trolox™ blocked only the decrease of grooming frequency. Taken together, these results establish that short-term exposure to Mn during a specific developmental window (PN8-12) induces metabolic and neurochemical alterations in the striatum that may modulate later-life behavioral changes. Furthermore, some of the molecular and behavioral events, which are perturbed by early Mn exposure are not directly related to the production of oxidative stress.

Upregulation of Ras/Raf/ERK1/2 signaling and ERK5 in the brain of autistic subjects

Autism is a neurodevelopmental disorder characterized by impairments in social interaction, verbal communication and repetitive behaviors. A number of studies have shown that the Ras/Raf/ERK1/2 (extracellular signal-regulated kinase) signaling pathway plays important roles in the genesis of neural progenitors, learning and memory. Ras/Raf/ERK1/2 and ERK5 have also been shown to have death-promoting apoptotic roles in neural cells. Recent studies have shown a possible association between neural cell death and autism. In addition, two recent studies reported that a deletion of a locus on chromosome 16, which included the mitogen-activated protein kinase 3 (MAPK3) gene that encodes ERK1, is associated with autism. Most recently, our laboratory detected that Ras/Raf/ERK1/2 signaling activities were significantly enhanced in the brain of BTBR mice that model autism, as they exhibit many autism-like behaviors. We thus hypothesized that Ras/Raf/ERK1/2 signaling and ERK5 could be abnormally regulated in the brain of autistic subjects. In this study, we show that the expression of Ras protein was significantly elevated in the frontal cortex of autistic subjects. C-Raf phosphorylation was increased in the frontal cortex, while both C-Raf and A-Raf activities were enhanced in the cerebellum of autistic subjects. We also detected that both the protein expression and activities of ERK1/2 were significantly upregulated in the frontal cortex of autistic subjects, but not in the cerebellum. Furthermore, we showed that ERK5 protein expression is upregulated in both frontal cortex and cerebellum of autistic subjects. These results suggest that the upregulation of Ras/Raf/ERK1/2 signaling and ERK5 activities mainly found in the frontal cortex of autistic subjects may be critically involved in the pathogenesis of autism.

Neurotoxic effects of the HCV core protein are mediated by sustained activation of ERK via TLR2 signaling

Hepatitis C virus (HCV) infection is a serious problem among those co-infected with human immunodeficiency virus; however, its impact in the central nervous system (CNS) remains unclear. This study aimed to investigate the mechanisms underlying HCV core protein-mediated neurodegeneration. Analysis of human HCV seropositive cases demonstrated widespread damage to neuronal dendritic processes and sustained activation of extracellular signal-related kinase (ERK); analogous pathologies were observed in wild type injected with HCV core protein into the hippocampus. In vitro analysis in neuronal cells exposed to HCV core demonstrated retraction of the neuronal processes in an ERK/Signal Transducer and Activator of Transcription 3 (STAT3)-dependent manner dependent on toll-like receptor 2 (TLR2) signaling activation. These results indicate that HCV core protein neurotoxicity may be mediated by the sustained activation of ERK/STAT3 via TLR2-IRAK1 signaling pathway. These pathways provide novel targets for development of neuroprotective treatments for HCV involvement of the CNS.

Lipopolysaccharide signaling in the carotid chemoreceptor pathway of rats with sepsis syndrome

In addition to their role in cardiorespiratory regulation, carotid body (CB) chemoreceptors serve as sensors for inflammatory status and as a protective factor during sepsis. However, lipopolysaccharide-induced sepsis (LPS) reduces CB responsiveness to excitatory or depressant stimuli. We tested whether LPS exerts a direct effect on the carotid chemoreceptor pathway, the CB and its sensory ganglion. We determined that the rat CB and nodose-petrosal-jugular ganglion complex (NPJgc) express TLR4, TNF-α and its receptors (TNF-R1 and TNF-R2). LPS administration (15mg/kg intraperitoneally) evoked MyD88-mechanism pathway activation in CB and NPJgc, with NF-κB p65, p38 MAPK, and ERK activation. Consistently, LPS increased TNF-α and TNF-R2. Double-labeling studies showed that the aforementioned pathway occurs in TH-containing glomus cells and NPJgc neurons, components of the chemosensitive neural pathway. Thus, our results suggest that LPS acting directly through TLR4/MyD88-mechanism pathways increases TNF-α and TNF-R2 expression in the carotid chemoreceptor pathway. These results show a novel afferent pathway to the central nervous system during endotoxemia, and could be relevant in understanding sepsis pathophysiology and therapy.

6-Hydroxydopamine-induced PC12 cell death is mediated by MEF2D down-regulation

Recently, it was reported that in a 4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model, neuronal cell death is associated with the cdk5-mediated hyperphosphorylation of myocyte enhancer factor 2 (MEF2), a transcription factor that is critically required for neuronal survival. In the present study, we investigated the possible involvement of cdk5-mediated MEF2D down-regulation on 6-hydroxydopamine (6-OHDA)-induced PC12 cell death. 6-OHDA was found to significantly increase nitric oxide (NO) production and to induce apoptosis in a time-dependent manner in PC12 cells. Furthermore, 6-OHDA was found to markedly reduce MEF2D levels under conditions that could induce PC12 cell apoptosis. In addition, PC12 cell death and MEF2D degradation by 6-OHDA were prevented by the cdk5 inhibitor roscovitine, but roscovitine could not restore the 6-OHDA-induced inactivation of Akt. These results suggest that the cell death and MEF2D degradation caused by 6-OHDA are dependent on cdk5 activity. On the other hand, roscovitine enhanced the 6-OHDA-induced activations of ERK1/2 and JNK, but reduced the 6-OHDA-induced activation of p38. These results suggest that PC12 cell death by 6-OHDA appears to be regulated by the down-regulation of MEF2D via some interaction between cdk5 and MAP kinase.

Differences in activation of ERK1/2 and p38 kinase in Jnk3 null mice following KA treatment

The MAPK family is formed by extracellular signal-regulated kinases p38 kinase and stress-activated protein kinases (SAPK/JNK). There are three genes that encode for three JNK proteins. JNK3 is mainly expressed in the central nervous system and has been related to various processes in that tissue. Specifically, JNK3 plays a crucial role in neuronal death in several neurodegenerative diseases. The activation of this kinase has been described in epilepsy, Alzheimer's disease, Parkinson's disease and Huntington's disease. Different studies have shown that the lack of the Jnk3 gene confers neuroprotection. However, the specific mechanism involved in such neuroprotection has not yet been elucidated. Therefore, in the present study, we analyzed the neuroprotection in mice lacking Jnk3 against neuronal death induced by kainic acid. Moreover, we analyzed the activation of different MAPKs. The results revealed that neuronal death was attenuated and different activation/inactivation of p38 and extracellular signal-regulated kinases 1/2 was reported with respect to control. Therefore, the data indicate that the lack of the JNK3 protein modulates other MAPKs and these changes could also have a pivotal role in neuroprotection.

CD99 inhibits neural differentiation of human Ewing sarcoma cells and thereby contributes to oncogenesis

Ewing sarcoma (EWS) is an aggressive bone tumor of uncertain cellular origin. CD99 is a membrane protein that is expressed in most cases of EWS, although its function in the disease is unknown. Here we have shown that endogenous CD99 expression modulates EWS tumor differentiation and malignancy. We determined that knocking down CD99 expression in human EWS cell lines reduced their ability to form tumors and bone metastases when xenografted into immunodeficient mice and diminished their tumorigenic characteristics in vitro. Further, reduction of CD99 expression resulted in neurite outgrowth and increased expression of beta-III tubulin and markers of neural differentiation. Analysis of a panel of human EWS cells revealed an inverse correlation between CD99 and H-neurofilament expression, as well as an inverse correlation between neural differentiation and oncogenic transformation. As knockdown of CD99 also led to an increase in phosphorylation of ERK1/2, we suggest that the CD99-mediated prevention of neural differentiation of EWS occurs through MAPK pathway modulation. Together, these data indicate a new role for CD99 in preventing neural differentiation of EWS cells and suggest that blockade of CD99 or its downstream molecular pathway may be a new therapeutic approach for EWS.

The impact of erythropoietin on short-term changes in phosphorylation of brain protein kinases in a rat model of traumatic brain injury

We found that recombinant human erythropoietin (rhEPO) reduced significantly the development of brain edema in a rat model of diffuse traumatic brain injury (TBI) (impact-acceleration model). In this study, we investigated the molecular and intracellular changes potentially involved in these immediate effects. Brain tissue nitric oxide (NO) synthesis, phosphorylation level of two protein kinases (extracellular-regulated kinase (ERK)-1/-2 and Akt), and brain water content were measured 1 (H1) and 2 h (H2) after insult. Posttraumatic administration of rhEPO (5,000 IU/kg body weight, intravenously, 30 mins after injury) reduced TBI-induced upregulation of ERK phosphorylation, although it increased Akt phosphorylation at H1. These early molecular changes were associated with a reduction in brain NO synthesis at H1 and with an attenuation of brain edema at H2. Intraventricular administration of the ERK-1/-2 inhibitor, U0126, or the Akt inhibitor, LY294002, before injury showed that ERK was required for brain edema formation, and that rhEPO-induced reduction of edema could involve the ERK pathway. These results were obtained in the absence of any evidence of blood-brain barrier damage on contrast-enhanced magnetic resonance images. The findings of our study indicate that the anti edematous effect of rhEPO could be mediated through an early inhibition of ERK phosphorylation after diffuse TBI.

Posttranslational regulation of BCL2 levels in cerebellar granule cells: A mechanism of neuronal survival

Apoptosis can be modulated by K(+) and Ca(2+) inside the cell and/or in the extracellular milieu. In murine organotypic cultures, membrane potential-regulated Ca(2+) signaling through calcineurin phosphatase has a pivotal role in development and maturation of cerebellar granule cells (CGCs). P8 cultures were used to analyze the levels of expression of B cell lymphoma 2 (BCL2) protein, and, after particle-mediated gene transfer in CGCs, to study the posttranslational modifications of BCL2 fused to a fluorescent tag in response to a perturbation of K(+)/Ca(2+) homeostasis. There are no changes in Bcl2 mRNA after real time PCR, whereas the levels of the fusion protein (monitored by calculating the density of transfected CGCs under the fluorescence microscope) and of BCL2 (inWestern blotting) are increased. After using a series of agonists/antagonists for ion channels at the cell membrane or the endoplasmic reticulum (ER), and drugs affecting protein synthesis/degradation, accumulation of BCL2 was related to a reduction in posttranslational cleavage by macroautophagy. The ER functionally links the [K(+)](e) and [Ca(2+)](i) to the BCL2 content in CGCs along two different pathways. The first, triggered by elevated [K(+)](e) under conditions of immaturity, is independent of extracellular Ca(2+) and operates via IP3 channels. The second leads to influx of extracellular Ca(2+) following activation of ryanodine channels in the presence of physiological [K(+)](e), when CGCs are maintained in mature status. This study identifies novel mechanisms of neuroprotection in immature and mature CGCs involving the posttranslational regulation of BCL2.