Nuclear matrix protein (NRP/B) modulates the nuclear factor (Erythroid-derived 2)-related 2 (NRF2)-dependent oxidative stress response

The emerging role of ectodermal neural cortex 1 in cancer

Ectodermal neural cortex 1 (ENC1) is a protein that plays a crucial role in the regulation of various cellular processes such as cell proliferation, differentiation, and apoptosis. Numerous studies have shown that ENC1 is overexpressed in various types of cancers, including breast, lung, pancreatic, and colorectal cancer, and its upregulation is correlated with a poorer prognosis. In addition to its role in cancer growth and spreading, ENC1 has also been linked to neuronal process development and neural crest cell differentiation. In this review, we provide an overview of the current knowledge on the relationship between ENC1 and cancer. We discuss the molecular mechanisms by which ENC1 contributes to tumorigenesis, including its involvement in multiple oncogenic signaling pathways. We also summarize the potential of targeting ENC1 for cancer therapy, as its inhibition has been shown to significantly reduce cancer cell invasion, growth, and metastasis. Finally, we highlight the remaining gaps in our understanding of ENC1's role in cancer and propose potential directions for future research.

Impact of NQO1 dysregulation in CNS disorders

NAD(P)H Quinone Dehydrogenase 1 (NQO1) plays a pivotal role in the regulation of neuronal function and synaptic plasticity, cellular adaptation to oxidative stress, neuroinflammatory and degenerative processes, and tumorigenesis in the central nervous system (CNS). Impairment of the NQO1 activity in the CNS can result in abnormal neurotransmitter release and clearance, increased oxidative stress, and aggravated cellular injury/death. Furthermore, it can cause disturbances in neural circuit function and synaptic neurotransmission. The abnormalities of NQO1 enzyme activity have been linked to the pathophysiological mechanisms of multiple neurological disorders, including Parkinson's disease, Alzheimer's disease, epilepsy, multiple sclerosis, cerebrovascular disease, traumatic brain injury, and brain malignancy. NQO1 contributes to various dimensions of tumorigenesis and treatment response in various brain tumors. The precise mechanisms through which abnormalities in NQO1 function contribute to these neurological disorders continue to be a subject of ongoing research. Building upon the existing knowledge, the present study reviews current investigations describing the role of NQO1 dysregulations in various neurological disorders. This study emphasizes the potential of NQO1 as a biomarker in diagnostic and prognostic approaches, as well as its suitability as a target for drug development strategies in neurological disorders.

Regulation of Cell Proliferation and Nrf2-Mediated Antioxidant Defense: Conservation of Keap1 Cysteines and Nrf2 Binding Site in the Context of the Evolution of KLHL Family

Keap1 (Kelch-like ECH-associated protein 1) is one of the major negative regulators of the transcription factor Nrf2 (nuclear factor erythroid-2-related factor 2), which induces the expression of numerous proteins defending the cell against different stress conditions. Keap1 is generally negatively regulated by post-translational modification (mostly via its cysteine residues) and interaction with other proteins that compete with Nrf2 for binding. Cysteine residues in Keap1 have different effects on protein regulation, as basic residues (Lys, Arg, and His) in close proximity to them increase cysteine modification potential. In this paper, we present an evolutionary analysis of residues involved in both mechanisms of Keap1 regulation in the broader context of the KLHL protein family in vertebrates. We identified the typical domain structure of the KLHL protein family in several proteins outside of this family (namely in KBTBD proteins 2, 3, 4, 6, 7, 8, 12 and 14). We found several cysteines that are flanked by basic residues (namely, C14, C38, C151, C226, C241, C273, C288, C297, C319, and C613) and, therefore, may be considered more susceptible to regulatory modification. The Nrf2 binding site is completely conserved in Keap1 in vertebrates but is absent or located in nonaligned DA and BC loops of the Kelch domain within the KLHL family. The development of specific substrate binding regions could be an evolutionary factor of diversification in the KLHL protein family.

Mechanisms underlying Nrf2 nuclear translocation by non-lethal levels of hydrogen peroxide: p38 MAPK-dependent neutral sphingomyelinase2 membrane trafficking and ceramide/PKCζ/CK2 signaling

Hydrogen peroxide is an aerobic metabolite playing a central role in redox signaling and oxidative stress. H₂O₂ could activate redox sensitive transcription factors, such as Nrf2, AP-1 and NF-κB by different manners. In some cells, treatment with non-lethal levels of H₂O₂ induces rapid activation of Nrf2, which upregulates expression of a set of genes involved in glutathione (GSH) synthesis and defenses against oxidative damage. It depends on two steps, the rapid translational activation of Nrf2 and facilitation of Nrf2 nuclear translocation. We review the molecular mechanisms by which H₂O₂ induces nuclear translocation of Nrf2 in cultured cells by highlighting the role of neutral sphingomyelinase 2 (nSMase2), a GSH sensor. H₂O₂ enters cells through aquaporin channels in the plasma membrane and is rapidly reduced to H₂O by GSH peroxidases to consume cellular GSH, resulting in nSMase2 activation to generate ceramide. H₂O₂ also activates p38 MAP kinase, which enhances transfer of nSMase2 from perinuclear regions to plasma membrane lipid rafts to accelerate ceramide generation. Low levels of ceramide activate PKCζ, which then activates casein kinase 2 (CK2). These protein kinases are able to phosphorylate Nrf2 to stabilize and activate it. Notably, Nrf2 also binds to caveolin-1 (Cav1), which protects Nrf2 from Keap1-mediated degradation and limits Nrf2 nuclear translocation. We propose that Cav1serves as a signaling hub for the control of H₂O₂-mediated phosphorylation of Nrf2 by kinases, which results in release of Nrf2 from Cav1 to facilitate nuclear translocation. In summary, H₂O₂ induces GSH depletion which is recovered by Nrf2 activation dependent on p38/nSMase2/ceramide signaling.

Regulation of the Expression of Heme Oxygenase-1: Signal Transduction, Gene Promoter Activation, and Beyond

Significance: Heme oxygenase-1 (HO-1) is a ubiquitous 32-kDa protein expressed in many tissues and highly inducible. They catalyze the degradation of the heme group and the release of free iron, carbon monoxide, and biliverdin; the latter converted to bilirubin by biliverdin reductase. Its role in the regulation of cellular homeostasis is widely documented. Studying regulation of HO-1 expression is important not only to understand the life of healthy cells but also the unbalances in cell metabolism that lead to disease. Recent Advances: The regulation of its enzymatic activity depends heavily upon changes in expression studied mainly at the transcriptional level. Current knowledge regarding HO-1 gene expression focuses primarily on transcription factors such as Nrf2 (nuclear factor erythroid 2-related factor 2), AP-1 (activator protein-1), and hypoxia-inducible factor, which collect signal transduction pathway information at the HO-1 gene promoter. Understanding of gene expression regulation is not limited to transcription factor activity but also involves an extended range of post- or cotranscriptional regulated events. Critical Issues: In addition to the regulation of gene promoter activity, alternative splicing, alternative polyadenylation, and regulation of messenger RNA stability play critical roles in changes in HO-1 gene expression levels, involving specific factors, proteins, and microRNAs. All potential targets for diagnosis or treatment of diseases are related to HO-1 dysregulation. Future Directions: Unbalances in the tightly regulated gene expression mechanisms lead to cell transformation and cancer development. Knowledge of these events and signal transduction cascades triggered by oncogenes in which HO-1 plays a critical role is of upmost importance for research in this field.

Bardoxolone methyl analog attenuates proteinuria-induced tubular damage by modulating mitochondrial function

Multiple clinical studies have shown that bardoxolone methyl, a potent activator of nuclear factor erythroid 2–related factor 2 (Nrf2), is effective in increasing glomerular filtration rate in patients with chronic kidney disease. However, whether an Nrf2 activator can protect tubules from proteinuria-induced tubular damage via anti-inflammatory and antioxidative stress mechanisms is unknown. Using an Institute of Cancer Research–derived glomerulonephritis (ICGN) mouse model of nephrosis, we examined the effects of dihydro-CDDO-trifluoroethyl amide (dh404), a rodent-tolerable bardoxolone methyl analog, in protecting the tubulointerstitium; dh404 markedly suppressed tubular epithelial cell damage in the renal interstitium of ICGN mice. The tubular epithelial cells of ICGN mice showed a decrease in the size and number of mitochondria, as well as the breakdown of the crista structure, whereas the number and ultrastructure of mitochondria were maintained by the dh404 treatment. To further determine the effect of dh404 on mitochondrial function, we used human proximal tubular cells in vitro. Stimulation with albumin and free fatty acid increased mitochondrial reactive oxygen species (ROS). However, dh404 administration diminished mitochondrial ROS. Our data show that dh404 significantly reduced proteinuria-induced tubular cell mitochondrial damage, suggesting that improved redox balance and mitochondrial function and suppression of inflammation underlie the cytoprotective mechanism of Nrf2 activators, including bardoxolone methyl, in diabetic kidney disease.—Nagasu, H., Sogawa, Y., Kidokoro, K., Itano, S., Yamamoto, T., Satoh, M., Sasaki, T., Suzuki, T., Yamamoto, M., Wigley, W. C., Proksch, J. W., Meyer, C. J., Kashihara, N. Bardoxolone methyl analog attenuates proteinuria-induced tubular damage by modulating mitochondrial function.

Low expression of ENC1 predicts a favorable prognosis in patients with ovarian cancer

Ectodermal-neural cortex 1 (ENC1) belongs to a member of the kelch family of genes. It is an actin-binding protein and plays a pivotal role in neuronal and adipocyte differentiation. Here, we found that lower expression of ENC1 in the ovarian cancer patients was associated with favorable prognosis. In addition, ENC1 was heterogeneously expressed in various ovarian cancer cells. The messenger RNA and protein expression levels of ENC1 in HO-8910PM and NIH:OVCAR-3 cells were obviously higher than that in the other types of ovarian cancer cells. Knockdown of ENC1 in HO-8910PM or NIH:OVCAR-3 cells could significantly increase the reactive oxygen species levels, resulting in inhibition of in vitro proliferation, migration, and invasion. Our findings suggest that decreasing expression of ENC1 may be a new approach that can be used for ovarian cancer treatment.

Combining mouse embryonic stem cells and zebrafish embryos to evaluate developmental toxicity of chemical exposure

The assays in this study utilize mouse embryonic stem cells (mESCs) and zebrafish embryos to evaluate the potential developmental toxicity of industrial and pharmaceutical chemicals. A set of eleven chemicals of known mammalian in vivo teratogenicity were tested in the assays and correlations to mammalian data. Using mESCs, proliferation, differentiation, and cytotoxicity of the chemicals were measured. In zebrafish embryos, lethality and the lowest effect level concentrations for morphological malformations were determined. Clustering of the assays based on frequency of affected assays resulted in a ranking of the test compounds that correlated to in vivo rodent data (R = 0.88, P < 0.001). We conclude that the combination of ESC- and zebrafish-based assays provides a valuable platform for the prioritization of pharmaceutical and industrial chemicals for further testing of developmental toxicity in rodents.

Infiltration of M1, but not M2, macrophages is impaired after unilateral ureter obstruction in Nrf2-deficient mice

Chronic inflammation can be a major driver of the failure of a variety of organs, including chronic kidney disease (CKD). The NLR family pyrin domain-containing 3 (NLRP3) inflammasome has been shown to play a pivotal role in inflammation in a mouse kidney disease model. Nuclear factor erythroid 2-related factor 2 (Nrf2), the master transcription factor for anti-oxidant responses, has also been implicated in inflammasome activation under physiological conditions. However, the mechanism underlying inflammasome activation in CKD remains elusive. Here, we show that the loss of Nrf2 suppresses fibrosis and inflammation in a unilateral ureter obstruction (UUO) model of CKD in mice. We consistently observed decreased expression of inflammation-related genes NLRP3 and IL-1β in Nrf2-deficient kidneys after UUO. Increased infiltration of M1, but not M2, macrophages appears to mediate the suppression of UUO-induced CKD symptoms. Furthermore, we found that activation of the NLRP3 inflammasome is attenuated in Nrf2-deficient bone marrow–derived macrophages. These results demonstrate that Nrf2-related inflammasome activation can promote CKD symptoms via infiltration of M1 macrophages. Thus, we have identified the Nrf2 pathway as a promising therapeutic target for CKD.

Ectodermal-Neural Cortex 1 Isoforms Have Contrasting Effects on MC3T3-E1 Osteoblast Mineralization and Gene Expression

The importance of Wnt pathway signaling in development of bone has been well established. Here we investigated the role of a known Wnt target, ENC1 (ectodermal-neural cortex 1; NRP/B), in osteoblast differentiation. Enc1 expression was detected in mouse osteoblasts, chondrocytes, and osteocytes by in situ hybridization, and osteoblastic expression was verified in differentiating primary cultures and MC3T3-E1 pre-osteoblast cells, with 57 kDa and 67 kDa ENC1 protein isoforms detected throughout differentiation. Induced knockdown of both ENC1 isoforms reduced alkaline phosphatase staining and virtually abolished MC3T3-E1 mineralization. At culture confluence, Alpl (alkaline phosphatase liver/bone/kidney) expression was markedly reduced compared with control cells, and there was significant and coordinated alteration of other genes involved in cellular phosphate biochemistry. In contrast, with 67 kDa-selective knockdown mineralized nodule formation was enhanced and there was a two-fold increase in Alpl expression at confluence. There was enhanced expression of Wnt/β-catenin target genes with knockdown of both isoforms at this time-point and a five-fold increase in Frzb (Frizzled related protein) with 67 kDa-selective knockdown at mineralization, indicating possible ENC1 interactions with Wnt signaling in osteoblasts. These results are the first to demonstrate a role for ENC1 in the control of osteoblast differentiation. Additionally, the contrasting mineralization phenotypes and transcriptional patterns seen with coordinate knockdown of both ENC1 isoforms vs selective knockdown of 67 kDa ENC1 suggest opposing roles for the isoforms in regulation of osteoblastic differentiation, through effects on Alpl expression and phosphate cellular biochemistry. This study is the first to report differential roles for the ENC1 isoforms in any cell lineage. J. Cell. Biochem. 118: 2141-2150, 2017. © 2016 Wiley Periodicals, Inc.

Neonatal ventral hippocampus lesion changes nuclear restricted protein/brain (NRP/B) expression in hippocampus, cortex and striatum in developmental periods of rats

Schizophrenia is conceptualized as a neurodevelopmental disorder in which developmental alterations in immature brain systems are not clear. Rats with neonatal ventral hippocampal lesions (NVHL) can exhibit schizophrenia-like behaviors, and these rats have been widely used to study the developmental mechanisms of schizophrenia. The nuclear restricted protein/brain (NRP/B) is a nuclear matrix protein that is critical for the normal development of the neuronal system. This study assessed the effect of NVHL induced by the administration of ibotenic acid on the protein expression of NRP/B in the hippocampus, cortex and striatum in pre- and post-pubertal rats. The expressions of NeuN in various developmental periods were assessed accordingly. Sprague-Dawley rat pups were administered ibotenic acid at postnatal day (PD) 7. Western blotting and an immunofluorescence staining analysis showed that the expression of NRP/B was significantly decreased in the hippocampus, cortex and striatum of the NVHL rats at PD14, 28 and 42. The expressions of NeuN were decreased accordingly. In vitro experiment showed the NRP/B knockdown can decrease the Tuj1 expression in cultured cortical neurons. The data suggest that NVHL induces a change in NRP/B expression that affects neurons in the developmental period.

Metallothionein plays a prominent role in the prevention of diabetic nephropathy by sulforaphane via up-regulation of Nrf2

Sulforaphane (SFN) prevents diabetic nephropathy (DN) in type 1 diabetes via up-regulation of nuclear factor (erythroid-derived 2)-like 2 (Nrf2). However, it has not been addressed whether SFN also prevents DN from type 2 diabetes or which Nrf2 downstream gene(s) play(s) the key role in SFN renal protection. Here we investigated whether Nrf2 is required for SFN protection against type 2 diabetes-induced DN and whether metallothionein (MT) is an Nrf2 downstream antioxidant using Nrf2 knockout (Nrf2-null) mice. In addition, MT knockout mice were used to further verify if MT is indispensable for SFN protection against DN. Diabetes-increased albuminuria, renal fibrosis, and inflammation were significantly prevented by SFN, and Nrf2 and MT expression was increased. However, SFN renal protection was completely lost in Nrf2-null diabetic mice, confirming the pivotal role of Nrf2 in SFN protection from type 2 diabetes-induced DN. Moreover, SFN failed to up-regulate MT in the absence of Nrf2, suggesting that MT is an Nrf2 downstream antioxidant. MT deletion resulted in a partial, but significant attenuation of SFN renal protection from type 2 diabetes, demonstrating a partial requirement for MT for SFN renal protection. Therefore, the present study demonstrates for the first time that as an Nrf2 downstream antioxidant, MT plays an important, though partial, role in mediating SFN renal protection from type 2 diabetes.

Impact of the phosphatidylinositide 3-kinase signaling pathway on the cardioprotection induced by intermittent hypoxia

BACKGROUND

Exposure to intermittent hypoxia (IH) may enhance cardiac function and protects heart against ischemia-reperfusion (I/R) injury. To elucidate the underlying mechanisms, we developed a cardioprotective IH model that was characterized at hemodynamic, biochemical and molecular levels.

METHODS

Mice were exposed to 4 daily IH cycles (each composed of 2-min at 6-8% O2 followed by 3-min reoxygenation for 5 times) for 14 days, with normoxic mice as controls. Mice were then anesthetized and subdivided in various subgroups for analysis of contractility (pressure-volume loop), morphology, biochemistry or resistance to I/R (30-min occlusion of the left anterior descending coronary artery (LAD) followed by reperfusion and measurement of the area at risk and infarct size). In some mice, the phosphatidylinositide 3-kinase (PI3K) inhibitor wortmannin was administered (24 µg/kg ip) 15 min before LAD.

RESULTS

We found that IH did not induce myocardial hypertrophy; rather both contractility and cardiac function improved with greater number of capillaries per unit volume and greater expression of VEGF-R2, but not of VEGF. Besides increasing the phosphorylation of protein kinase B (Akt) and the endothelial isoform of NO synthase with respect to control, IH reduced the infarct size and post-LAD proteins carbonylation, index of oxidative damage. Administration of wortmannin reduced the level of Akt phosphorylation and worsened the infarct size.

CONCLUSION

We conclude that the PI3K/Akt pathway is crucial for IH-induced cardioprotection and may represent a viable target to reduce myocardial I/R injury.

Combustion-derived flame generated ultrafine soot generates reactive oxygen species and activates Nrf2 antioxidants differently in neonatal and adult rat lungs

BACKGROUND

Urban particulate matter (PM) has been epidemiologically correlated with multiple cardiopulmonary morbidities and mortalities, in sensitive populations. Children exposed to PM are more likely to develop respiratory infections and asthma. Although PM originates from natural and anthropogenic sources, vehicle exhaust rich in polycyclic aromatic hydrocarbons (PAH) can be a dominant contributor to the PM2.5 and PM0.1 fractions and has been implicated in the generation of reactive oxygen species (ROS).

OBJECTIVES

Current studies of ambient PM are confounded by the variable nature of PM, so we utilized a previously characterized ethylene-combusted premixed flame particles (PFP) with consistent and reproducible physiochemical properties and 1) measured the oxidative potential of PFP compared to ambient PM, 2) determined the ability of PFPs to generate oxidative stress and activate the transcription factor using in vitro and ex vivo models, and 3) we correlated these responses with antioxidant enzyme expression in vivo.

METHODS

We compared oxidative stress response (HMOX1) and antioxidant enzyme (SOD1, SOD2, CAT, and PRDX6) expression in vivo by performing a time-course study in 7-day old neonatal and young adult rats exposed to a single 6-hour exposure to 22.4 μg/m3 PFPs.

RESULTS

We showed that PFP is a potent ROS generator that induces oxidative stress and activates Nrf2. Induction of the oxidative stress responsive enzyme HMOX1 in vitro was mediated through Nrf2 activation and was variably upregulated in both ages. Furthermore, antioxidant enzyme expression had age and lung compartment variations post exposure. Of particular interest was SOD1, which had mRNA and protein upregulation in adult parenchyma, but lacked a similar response in neonates.

CONCLUSIONS

We conclude that PFPs are effective ROS generators, comparable to urban ambient PM2.5, that induce oxidative stress in neonatal and adult rat lungs. PFPs upregulate a select set of antioxidant enzymes in young adult animals, that are unaffected in neonates. We conclude that the inability of neonatal animals to upregulate the antioxidant response may, in part, explain enhanced their susceptibility to ultrafine particles, such as PFP.

Ischemic injury promotes Keap1 nitration and disturbance of antioxidative responses in endothelial cells: a potential vasoprotective effect of melatonin

Clinical epidemiology has indicated that the endothelial injury is a potential contributor to the pathogenesis of ischemic neurovascular damage. In this report, we assessed S-nitrosylation and nitration of Keap1 to identify downstream nitric oxide redox signaling targets into endothelial cells during ischemia. Here, oxygen-glucose deprivation (OGD) exposure initiates the nuclear import of Keap1 in endothelial cells, which interacted with nuclear-localized Nrf2, as demonstrated through co-immunoprecipitation and immunocytochemical assay. Paralleling the ischemia-induced nuclear import of Keap1, increased nitrotyrosine immunoreactivity in endothelial cells was also observed. Consistently, the addition of peroxynitrite provoked nuclear import of Keap1 and a concomitant Nrf2 nuclear import in the endothelial cells. Importantly, pharmacological inhibition of nitrosative stress by melatonin partially inhibited the OGD-induced constitutive nuclear import of Keap1 and subsequently disturbance of Nrf2/Keap1 signaling. Moreover, the effect of melatonin on nitration and S-nitrosylation of keap1 was examined in endothelial cells with 6 hr OGD exposure. Here, we demonstrated that OGD induced tyrosine nitration of Keap1, which was blocked by melatonin treatment, while there were no significant changes in S-nitrosylation of Keap1. The specific amino acid residues of Keap1 involved in tyrosine nitration were identified as Y473 by mass spectrometry. Moreover, the protective role of melatonin against damage to endothelial tight junction integrity was addressed by ZO-1 expression, paralleled with the restored heme oxygenase-1 levels during OGD. Together, our results emphasize that upon nitrosative stress, the protective effect of melatonin on endothelial cells is likely mediated at least in part by inhibition of ischemia-evoked protein nitration of Keap1, hence contributing to relieve the disturbance of Nrf2/Keap1 antioxidative signaling.

Aldo-keto reductases mediate constitutive and inducible protection against aldehyde toxicity in human neuroblastoma SH-SY5Y cells

Reactive aldehydes including methyl glyoxal, acrolein and 4-hydroxy-2-nonenal (4-HNE) have been implicated in the progression of neurodegenerative diseases. The reduction of aldehydes to alcohols by the aldo-keto reductase (AKR) family of enzymes may represent an important detoxication route within neuronal cells. In this study, the ability of AKR enzymes to protect human neuroblastoma SH-SY5Y cells against reactive aldehydes was assessed. Using gene-specific RNA interference (RNAi), we report that AKR7A2 makes a significant contribution to the reduction of methyl glyoxal in SH-SY5Y cells, with its knockdown altering the IC(50) from 410 to 25.8μM, and that AKR1C3 contributes to 4-HNE reduction, with its knockdown lowering the IC(50) from 1.25 to 0.58μM. In addition, we have shown that pretreatment of cells with sub-lethal concentrations of 4-HNE or methyl glyoxal leads to a significant increase in IC(50) when cells are exposed to higher concentrations of the toxic aldehyde. The IC(50) for methyl glyoxal increased from 410μM to 1.9mM, and the IC(50) for 4-HNE increased from 120 to 690nM. To investigate this protection, we show that pretreatment of cells with the AKR inhibitor sorbinil lead to decreased resistance to aldehydes. We show that AKR1C can be induced 8-fold in SH-SY5Y cells by treatment with sub-lethal concentrations of methyl glyoxal, and 5-fold by 4-HNE treatment. AKR1B is not induced by methyl glyoxal but is induced 10-fold by 4-HNE treatment. Furthermore, we have shown that this adaptive response can also be induced using the chemoprotective agent tert-butyl hydroquinone (t-BHQ), and that this also evokes an increase in the expression and activity of AKR1B and AKR1C. These findings highlight the potential for the interventional upregulation of AKR via non-toxic derivatives or natural compounds as a novel therapeutic approach towards the detoxication of aldehydes, with the aim of halting the progression of aldehyde-dependent neurodegenerative diseases.

Functional expression of carnitine/organic cation transporter OCTN1 in mouse brain neurons: possible involvement in neuronal differentiation

The aim of the present study is to clarify the functional expression and physiological role in brain neurons of carnitine/organic cation transporter OCTN1/SLC22A4, which accepts the naturally occurring antioxidant ergothioneine (ERGO) as a substrate in vivo. After intracerebroventricular administration, the distribution of [(3)H]ERGO in several brain regions of octn1(-/-) mice was much lower than that in wild-type mice, whereas extracellular marker [(14)C]mannitol exhibited similar distribution in the two strains. The [(3)H]ERGO distribution in wild-type mice was well correlated with the amount of ERGO derived from food intake and the OCTN1 mRNA level in each brain region. Immunohistochemical analysis revealed colocalization of OCTN1 with neuronal cell markers microtubule-associated protein 2 (MAP2) and βIII-tubulin in mouse brain and primary cultured cortical neurons, respectively. Moreover, cultured cortical neurons exhibited time-dependent and saturable uptake of [(3)H]ERGO. These results demonstrate that OCTN1 is functionally expressed in brain neurons. The addition of ERGO simultaneously with serum to culture medium of cortical neurons attenuated mRNA and protein expressions of MAP2, βIII-tubulin and synapse formation marker synapsin I, and induced those of sex determining region Y-box 2 (Sox2), which is required to maintain the properties of undifferentiated neural stem cells. In neuronal model Neuro2a cells, knockdown of OCTN1 by siRNA reduced the uptake of [(3)H]ERGO with concomitant up-regulation of oxidative stress marker HO-1 and Sox2, and down-regulation of neurite outgrowth marker GAP43. Interestingly, the siRNA knockdown decreased the number of differentiated Neuro2a cells showing long neurites, but increased the total number of cells. Thus, OCTN1 is involved in cellular differentiation, but inhibits their proliferation, possibly via the regulation of cellular oxidative stress. This is the first evidence that OCTN1 plays a role in neuronal differentiation and proliferation, which are required for brain development.

Molecular characterization, expression analysis, and role of ALDH3B1 in the cellular protection against oxidative stress

Aldehyde dehydrogenase (ALDH) enzymes are critical in the detoxification of aldehydes. The human genome contains 19 ALDH genes, mutations in which are the basis of several diseases. The expression, subcellular localization, enzyme kinetics, and role of ALDH3B1 in aldehyde- and oxidant-induced cytotoxicity were investigated. ALDH3B1 was purified from Sf9 cells using chromatographic methods, and enzyme kinetics were determined spectrophotometrically. ALDH3B1 demonstrated high affinity for hexanal (K(m)=62 μM), octanal (K(m)=8 μM), 4-hydroxy-2-nonenal (4HNE; K(m)=52 μM), and benzaldehyde (K(m)=46 μM). Low affinity was seen toward acetaldehyde (K(m)=23.3 mM), malondialdehyde (K(m)=152 mM), and the ester p-nitrophenyl acetate (K(m)=3.6 mM). ALDH3B1 mRNA was abundant in testis, lung, kidney, and ovary. ALDH3B1 protein was highly expressed in these tissues and the liver. Immunofluorescence microscopy of ALDH3B1-transfected human embryonic kidney (HEK293) cells and subcellular fractionation of mouse kidney and liver revealed a cytosolic protein localization. ALDH3B1-transfected HEK293 cells were significantly protected from the lipid peroxidation-derived aldehydes trans-2-octenal, 4HNE, and hexanal and the oxidants H(2)O(2) and menadione. In addition, ALDH3B1 protein expression was up-regulated by 4HNE in ARPE-19 cells. The results detailed in this study support a pathophysiological role for ALDH3B1 in protecting cells from the damaging effects of oxidative stress.