Modulation of NRF2/KEAP1 Signaling by Phytotherapeutics in Periodontitis

Periodontitis affects up to 40% of adults over 60 years old and is a consequence of gingivitis. Periodontitis is characterized by a chronic inflammation, periodontal damage, and alveolar bone resorption. The nuclear factor erythroid 2-related factor 2 (NFE2L2 or NRF2)/Kelch-like ECH-Associated Protein 1 (KEAP1) (NRF2/KEAP1) signaling pathway plays a key role in periodontitis by modulating redox balance and inflammation of the periodontium. However, NRF2 expression is decreased in gingival tissues of patients with periodontitis while oxidative stress is significantly increased in this pathology. Oxidative stress and lipopolysaccharide (LPS) produced by gram-negative bacteria favor the production of inflammatory causing periodontal inflammation and favoring alveolar bone. In this review, we analyzed the current literature regarding the role of natural and synthetic compounds in modulating the NRF2/KEAP1 pathway in in vitro and in vivo models of periodontitis in order to evaluate new potential treatments of periodontitis that can improve the outcome of this disease.

A novel hydrogel containing 4-methylcatechol for skin regeneration: in vitro and in vivo study

Skin damages are usual physical injuries and different studies have been done to improve wound healing. Hydrogel due to its properties like a moist environment and cooling wound site is a good option for wound treatment. In this study, we evaluated the consequence of using alginate/chitosan hydrogel contained various dosages of 4-Methylcatechol (0, 0.1, 1% (W/W)) on wound healing. After hydrogel fabrication, different tests like SEM, swelling, release, weight loss, and hemo- and cytocompatibility were done to characterize fabricated hydrogels. Finally, the rat model was used to assess Alginate/Chitosan hydrogel's therapeutic function containing 0.1 and 1% of 4-Methylcatechol. The pore size of hydrogel was between 24.5 ± 9 and 62.1 ± 11.63 µm and about 90% of hydrogel was lost after 14 days in the weight loss test. Blood compatibility and MTT assay showed that hydrogels were nontoxic and improved cell proliferation. In vivo test showed that Alginate/Chitosan/0.1%4-Methylcatechol improved wound healing and the results were significantly better than the gauze-treated wound. Our results showed dose depending effect of 4-Methylcatechol on wound healing. This study shows the treatment effect of 4-Methylcatechol on wound healing and the possibility of using it for treating skin injuries.

Pharmacology-based molecular docking of 4-methylcatechol and its role in RANKL-mediated ROS/Keap1/Nrf2 signalling axis and osteoclastogenesis

4-Methylcatechol (4-MC) is an agonist of various neurotrophic factors, which can upregulate the expression of Heme oxygenase 1 (HO-1) protein by activating nuclear factor erythroid 2-related factor 2 (Nrf2), thereby inhibiting oxidative stress-induced neural stem cell death. During RANKL-stimulated osteoclast differentiation, intracellular reactive oxygen species (ROS) levels were increased. Nonetheless, the effect of 4-MC on osteoclast formation and bone resorption function has not been researched. In this study, we investigated the effect of HO-1 upregulation by 4-MC on RANKL-induced osteoclastogenesis and explored the molecular mechanism of HO-1 upregulation by 4-MC. We found that the small molecule compound 4-MC could bind to Keap1 amino acid residue of glycine GLY 367, isoleucine ILE 559 and valine VAL 606, with a predicted binding energy of -4.99 kcal/mol. 4-MC was found to inhibit osteoclast differentiation in vitro by activating Nrf2 to scavenge ROS, inhibiting NF-κB phosphorylation, and alleviating osteoporosis in ovariectomized (OVX) mice. Taken together, 4-MC reduces ROS by inhibiting Keap1, thereby preventing OVX-induced bone loss.

The Antiplatelet Effect of 4-Methylcatechol in a Real Population Sample and Determination of the Mechanism of Action

A polyphenol-rich diet has beneficial effects on cardiovascular health. However, dietary polyphenols generally have low bioavailability and reach low plasma concentrations. Small phenolic metabolites of these compounds formed by human microbiota are much more easily absorbable and could be responsible for this effect. One of these metabolites, 4-methylcatechol (4-MC), was suggested to be a potent anti-platelet compound. The effect of 4-MC was tested ex vivo in a group of 53 generally healthy donors using impedance blood aggregometry. The mechanism of action of this compound was also investigated by employing various aggregation inducers/inhibitors and a combination of aggregometry and enzyme linked immunosorbent assay (ELISA) methods. 4-MC was confirmed to be more potent than acetylsalicylic acid on both arachidonic acid and collagen-triggered platelet aggregation. Its clinically relevant effect was found even at a concentration of 10 μM. Mechanistic studies showed that 4-MC is able to block platelet aggregation caused by the stimulation of different pathways (receptors for the von Willebrand factor and platelet-activating factor, glycoprotein IIb/IIIa, protein kinase C, intracellular calcium elevation). The major mechanism was defined as interference with cyclooxygenase-thromboxane synthase coupling. This study confirmed the strong antiplatelet potential of 4-MC in a group of healthy donors and defined its mechanism of action.

[Search for Neuroprotective Compounds -From 4-Methycatechol to Citrus Compounds]

In the 1980s, the authors developed the enzyme immunoassay (EIA) system for mouse nerve growth factor (NGF) to clarify its important physiological roles. Our EIA system was a new and powerful tool for measurement of extremely low levels of NGF in vitro and in vivo, and it contributed to investigation into the regulatory mechanism of NGF synthesis. After that, we demonstrated that the compounds with a low molecular weight, such as 4-methylcatechol, which elicit stimulatory activity toward NGF synthesis, were useful and practical for therapeutic purposes; as NGF has potent activity on neuronal degeneration in both the central nervous system (CNS) and the peripheral nervous system. Since 2008, we have been searching for and isolating neuroprotective component(s) from citrus peels. As a result, our study revealed that 1) 3,5,6,7,8,3',4'-heptamethoxyflavone (HMF) has neuroprotective ability in the CNS by inducing brain-derived neurotrophic factor (BDNF) and by suppressing inflammation; 2) auraptene (AUR) also has neuroprotective ability in the CNS by suppressing inflammation and by probably inducing neurotrophic factor(s). As the content of AUR in the peels of Kawachi Bankan is exceptionally high, 1) we found this peel powder to exert neuroprotective effects in the brain of various pathological model mice; 2) some of the AUR transited from the peel to the juice during the squeezing process to obtain the juice. Therefore, K. Bankan juice, which is enriched in AUR by adding peel paste to the raw juice, was shown to be practical for suppression of cognitive dysfunction of aged healthy volunteers.

Beneficial Effects of Spirulina Aqueous Extract on Vasodilator Function of Arteries from Hypertensive Rats

Hypertension is a multifactorial disorder considered one of the major causes of premature death worldwide. This pathology is associated with vascular functional/structural alterations in which nitric oxide (NO) and oxygen reactive species participate. On the other hand, the use of microalgae extracts in the treatment of cardiovascular diseases is increasing. Based on the antioxidant and antihypertensive properties of Spirulina, this study aims to investigate the effect of an aqueous extract of Spirulina on the vasodilator function of the aorta from spontaneously hypertensive rats (SHR), analyzing the functional role of NO. For this, aortic segments from male SHR were divided into two groups, one control and the other exposed to an Spirulina aqueous extract (0.1% w/v, for 3 hours), to analyze (i) the production of NO, superoxide anion, and hydrogen peroxide; (ii) the vasodilator response induced by acetylcholine (ACh), by the NO donor and sodium nitroprusside (SNP), and by the KATP channel opener and pinacidil; and (iii) the expression of the p-Akt, p-eNOS, and HO-1 proteins. The results showed that the aqueous Spirulina extract (i) increased the production of NO, did not significantly modify that of superoxide, while decreased that of hydrogen peroxide; (ii) increased the vasodilatory responses induced by ACh, NPS, and pinacidil; and (iii) increased the expression of p-Akt and HO-1. These results suggest that incubation with the aqueous Spirulina extract improves the vascular function of arteries from SHR by increasing the release/bioavailability/function of NO. Increased KATP channel activation and expression of pAkt and HO-1 appear to be participating in these actions.

Inhibitory effect of catecholic colonic metabolites of rutin on fatty acid hydroperoxide and hemoglobin dependent lipid peroxidation in Caco-2 cells

To determine the preventive effect of dietary rutin on oxidative damages occurring in the digestive tract, 13-hydroperoxyoctadecadienoic acid and hemoglobin were exposed to Caco-2 intestinal cells after the pretreatment with colonic rutin metabolites. Among four catechol-type metabolites, quercetin and 3,4-dihydroxytoluene exerted significant protection on 13-hydroperoxyoctadecadienoic and hemoglobin-dependent lipid peroxidation of this epithelial cell. Compared with quercetin, a much lower concentration allowed 3,4-dihydroxytoluene to maximize the protective effect, though it needed a longer pre-incubation period. Neither quercetin nor 3,4-dihydroxytoluene affected the expression of peroxiredoxin-6 protein, which comprises the cellular antioxidant defense system. It is concluded that 3,4-dihydroxytoluene is a plausible rutin colonic metabolite that can suppress oxidative damages of intestinal epithelial cells by directly inhibiting lipid peroxidation. This result may illuminate the preventive role of dietary rutin against colorectal cancer incidence in relation to the consumption of red and processed meat.

Anti-inflammatory and antioxidant properties of Schisandrin C promote mitochondrial biogenesis in human dental pulp cells

AIM

To examine the properties of Schisandrin C as an anti-inflammatory and antioxidant compound, and whether its characteristics promote mitochondrial biogenesis in human dental pulp cells (HDPCs).

METHODOLOGY

HDPCs were extracted from fresh third molars and cultured for experiments. Reactive oxidative stress (ROS) and nitric oxide (NO) formation were analysed by a Muse cell analyser. Western blotting and gelatin zymography were used to identify the presence of antioxidants, as well as anti-inflammatory and mitochondrial biogenesis with specific antibody. An unpaired Student's t-test was used for statistical analysis.

RESULTS

Schisandrin C inhibited lipopolysaccharide-stimulated inflammatory molecules; interleukin 1 beta, tumour necrosis factor alpha, intracellular adhesion molecule-1, vascular cell adhesion molecule-1, matrix metalloproteinase-2 and -9, NO production, ROS formation, nuclear factor kappa B translocation (P < 0.05) through the mitogen-activated protein kinase pathway. Schisandrin C increased the expression of superoxide dismutase enzymes as well as haem oxygenase-1 and peroxisome proliferator-activated receptor gamma coactivator 1-alpha through the phosphorylated-protein kinase B (p-Akt) and nuclear factor erythroid 2-related factor-2 pathways (P < 0.05). The anti-inflammatory and antioxidant properties of Schisandrin C promoted mitochondrial biogenesis.

CONCLUSIONS

Schisandrin C has the potential to reduce inflammation and oxidation and to promote mitochondrial biogenesis. Therefore, Schisandrin C may be considered for use as an anti-inflammatory compound for oral inflammation through mitochondrial biogenesis.

Necrotic cell death occur via JNK pathway with the activity of transcription factor c-Jun by 4-MC in INS-1 cell line

In this study, it was aimed to determine the doses of 4-methylcatechol causing cell death in rat insulinoma β-cells (INS-1), to find out the type of cellular death at these doses, and to investigate the molecular mechanism of cellular death occurring. More necrotic cells were observed than apoptosis with the administration of 350, 400, and 450 μM 4-methylcatechol. Lactate dehydrogenase levels, reactive oxygen species, mitochondrial potential loss, ATP, and GTP losses increased at these doses. The JNK and ERK cellular pathway were screened. We observed an increase in p-RAF1 activity, the active JNK amount, the total c-Jun amount, while a decrease in p-RAF1 expression, the total JNK amount, JNK expression, ATF2 expression, active ERK, and its expression and Elk1 expression. It was concluded that cells perform necrotic death by the following options: i) phosphorylated RAF1 activates the JNK pathway with the activity of transcription factor c-Jun; ii) Hsp 70 and Hsp 90 do not show a change inside the cell, rendering the JNK pathway active.

Involvement of Nrf2-mediated heme oxygenase-1 expression in anti-inflammatory action of chitosan oligosaccharides through MAPK activation in murine macrophages

Chitosan and its derivatives have been reported to have anti-inflammatory effects in vitro and in vivo. It is also suggested that chitosan and its derivatives could be up-regulating heme oxygenase-1 (HO-1) in different models. However, the up-regulation of HO-1 by chitosan oligosaccharides (COS) remains unexplored in regard to anti-inflammatory action in lipopolysaccharide (LPS)-stimulated murine macrophages (RAW264.7 cells). Treatment with COS induced HO-1 expression in LPS-stimulated RAW264.7 cells, whereas the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) was decreased. Pretreatment with ZnPP, a HO-1 inhibitor, reduced the COS-mediated anti-inflammatory action. HO-1 induction is mediated by activating the nuclear translocation of NF-E2-related factor 2 (Nrf2) using COS. Moreover, COS increased the phosphorylation of extracellular signal regulated kinase (ERK1/2), c-Jun N-terminal kinase/stress-activated protein kinase (JNK), and p38 MAPK. However, specific inhibitors of ERK, JNK, and p38 reduced COS-mediated nuclear translocation of Nrf2. Therefore, HO-1 induction also decreased in RAW264.7 cells. Collectively, COS exert an anti-inflammatory effect through Nrf2/MAPK-mediated HO-1 induction.

Activation of Nrf2/HO-1signaling pathway involves the anti-inflammatory activity of magnolol in Porphyromonas gingivalis lipopolysaccharide-stimulated mouse RAW 264.7 macrophages

Magnolol isolated from Magnolia officinalis, a Chinese medical herb, exhibits an anti-inflammatory activity and a protective effect against periodontitis. The inflammation caused by lipopolysaccharide (LPS) from Porphyromonas gingivalis (P. gingivalis) has been considered a key inducer in the development of periodontitis. In this study, we investigated whether magnolol inhibits P. gingivalis LPS-evoked inflammatory responses in RAW 264.7 macrophages and the involvement of heme oxygenase-1 (HO-1). Magnolol significantly activated p38 MAPK, Nrf-2/HO-1 cascade and reactive oxygen species (ROS) formation. Notably, the Nrf-2 activation and HO-1 induction by magnolol were greatly diminished by blocking p38 MAPK activity and ROS production. Furthermore, in P. gingivalis LPS-stimulated macrophages, magnolol treatment remarkably inhibited the inflammatory responses evidenced by suppression of pro-inflammatory cytokine, prostaglandin E2, nitrite formation, and the expression of inducible nitric oxide synthase and cyclooxygenase-2, as well as NF-κB activation accompanied by a significant elevation of Nrf-2 nuclear translocation and HO-1 expression/activity. However, inhibiting HO-1 activity with tin protoporphyrin IX markedly reversed the anti-inflammatory effects of magnolol. Collectively, these findings provide a novel mechanism by which magnolol inhibits P. gingivalis LPS-induced inflammation in macrophages is at least partly mediated by HO-1 activation, and thereby promoting its clinical use in periodontitis.

Post-conditioning with sevoflurane induces heme oxygenase-1 expression via the PI3K/Akt pathway in lipopolysaccharide-induced acute lung injury

The aim of the present study was to explore the regulatory mechanism of heme oxygenase-1 (HO-1) expression induced by sevoflurane (Sevo) in lipopolysaccharide (LPS)‑induced acute lung injury (ALI). Sprague-Dawley rats were divided randomly into six groups: (A) Control, (B) 2.4% Sevo only, (C) LY294002 (PI3K inhibitor) only, (D) LPS + 2.4% Sevo, (E) LY294002 + LPS + 2.4% Sevo and (F) LPS only. The pathological changes in wet/dry weight ratio (W/D), the activities of superoxide dismutase, myeloperoxidase (MPO), malondialdehyde, and HO-1, as well as the expression of intercellular adhesion molecule (ICAM-1), HO-1, phospho-phosphatidylinositol 3-kinase (pPI3K) and phospho-Akt (pAkt) were recorded. Sevo post-conditioning was able to effectively protect from ALI with decreasing pathomorphological scores, MPO activity, W/D and the mRNA and protein expression levels of ICAM-1. Sevo promotes HO-1 expression via the PI3K/protein kinase B (PI3K/Akt) pathway with activation of pPI3K and pAkt. Inhibition of the PI3K/Akt pathway by LY294002 partly eliminates the protective effects of Sevo. It is concluded that Sevo post-conditioning has a vital role in inducing the upregulation of HO-1 expression via the PI3K/Akt pathway to alleviate ALI.

Neuroprotective effects of Hu-Yi-Neng, a diet supplement, on SH-SY5Y human neuroblastoma cells

OBJECTIVES

Oxidative stress is considered the potential risk to the development of dementia. Some medicines, vitamins, and diet supplements have been suggested to have possible benefits via the antioxidative effects to slow the decline of cognitive function in demented and non-demented individuals. However, few studies were conducted to examine their functions, especially in composite diet supplements. Hu-Yi-Neng is a composite diet supplement, including ginkgo biloba, extract of pine bark, phosphatidyl serine, docosahexaenoic acid, and folic acid, used extensively in Taiwan. Therefore, our aim is to investigate the potential protective effects of Hu-Yi-Neng on human neuron cells. MATERALS AND METHODS: H2O2-induced neuronal toxicity was characterized in SH-SY5Y human neuroblastoma cells by the decrease of cell viability using PrestoBlue™ assay and by the increase of intracellular reactive oxygen species (ROS) level using DCFH-DA (2', 7'-dichlorodihydrofluorescin diacetate) assays. HO-1 mRNA expression was detected by real-time PCR. Akt and Erk 1/2 proteins were detected by western blotting.

RESULTS

Pretreatment with Hu-Yi-Neng significantly reversed the decrease in cell viability induced by H2O2 in SH-SY5Y cells. Furthermore, Hu-Yi-Neng dose-dependently suppressed the elevation of intracellular reactive oxygen species (ROS) level. Hu-Yi-Neng protected SH-SY5Y cells from oxidative stress may via the increase in mRNA expression of heme oxygenase-1 (HO-1), an antioxidant enzyme. In addition, Hu-Yi-Neng inhibited H2O2-induced phosphorylation of Akt kinase but further increased the phosphorylation of Erk 1/2.

CONCLUSION

Our results suggest that Hu-Yi-Neng has protective effect against oxidative stress-induced neuron cell loss and it could be an ideal composite diet supplement for preventing neurodegenerative diseases.

Anti-inflammatory activity of Bambusae Caulis in Taeniam through heme oxygenase-1 expression via Nrf-2 and p38 MAPK signaling in macrophages

Recently, it has been reported that several natural extracts have anti-inflammatory effects through HO-1 induction. In this study, we used the ethyl acetate fraction of Bambusae Caulis in Taeniam (BCE) to investigate its anti-inflammatory effect on macrophages stimulated with LPS from Porphyromonas gingivalis. BCE inhibited the production of pro-inflammatory cytokines in P. gingivalis LPS-stimulated RAW264.7 cells. BCE also suppressed the nuclear translocation of NF-κB and AP-1. A selective inhibitor of HO-1 attenuated BCE's inhibitory effects on the production of pro-inflammatory cytokines. BCE also dose-dependently increased HO-1 expression at both the mRNA and the protein levels. BCE increased nuclear translocation of Nrf-2. Finally, a specific inhibitor of p38 reduced BCE-induced HO-1 expression and BCE-induced phosphorylation of p38 MAPK. BCE induced anti-inflammatory effects by activating Nrf-2-mediated HO-1 induction via p38 signaling in P. gingivalis LPS-stimulated macrophages. This result indicates that BCE is a promising therapeutic agent for combating periodontitis.

Schisandra chinensis α-iso-cubebenol induces heme oxygenase-1 expression through PI3K/Akt and Nrf2 signaling and has anti-inflammatory activity in Porphyromonas gingivalis lipopolysaccharide-stimulated macrophages

Heme oxygenase-1 (HO-1) is a potent anti-inflammatory molecule that regulates pro-inflammatory mediators. Several studies have indicated that HO-1 expression is induced by a variety of stimuli such as lipopolysaccharide (LPS), cytokines, oxidative stress, and antioxidant phytochemicals. In this study, we assessed the anti-inflammatory effects of a novel α-iso-cubebenol isolated from dried fruits of Schisandra chinensis in human macrophage THP-1 cells and investigated the involvement of HO-1 signaling. We first observed that α-iso-cubebenol induced HO-1 mRNA and protein expression in a dose- and time-dependent manner via activation of erythroid-specific nuclear factor-regulated factor 2 (Nrf2). We also found that α-iso-cubebenol induced phosphorylation of phosphoinositide 3-kinase (PI3K)/Akt and extracellular-regulated kinase (ERK) in a time-dependent manner. Furthermore, treatment of THP-1 cells with inhibitors and siRNA specific for PI3K/Akt and ERK decreased the expression of HO-1. These results suggested that α-iso-cubebenol induced HO-1 expression through the activation of PI3K/Akt, ERK, and Nrf2 signaling. Next, α-iso-cubebenol strongly inhibited Porphyromonas gingivalis LPS-stimulated pro-inflammatory cytokines (tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, and IL-12). Moreover, we observed that α-iso-cubebenol treatment inhibited nuclear levels and activity of NF-κB in a dose-dependent manner. Additionally, treatment with tin-protoporphyrin (SnPP), a selective inhibitor of HO-1, reversed the α-iso-cubebenol-mediated inhibition of P. gingivalis LPS-induced pro-inflammatory cytokines. Hence, α-iso-cubebenol might induce anti-inflammatory effects on P. gingivalis LPS-stimulated human THP-1 macrophages by mediating the activation of PI3k/Akt and ERK that leads to over-expression of HO-1 and Nrf-2. These findings suggest that α-iso-cubebenol may be considered as a novel therapeutic agent to ameliorate periodontitis.

Hydroxytyrosol induces proliferation and cytoprotection against oxidative injury in vascular endothelial cells: role of Nrf2 activation and HO-1 induction

Hydroxytyrosol (HT), a phenolic compound in olive oil and leaves, has been reported to prevent various human pathologies including cardiovascular diseases. This study investigated the effects of HT on proliferation and protection against oxidative stress-induced damage in vascular endothelial cells (VECs) and the molecular mechanism(s) involved. Treatment of VECs with HT increased cell proliferation, promoted wound repair, and protected cells against H(2)O(2) cytotoxicity through the activation of Akt and ERK1/2, but not p38 MAPK. HT increased the expression and nuclear translocation of nuclear factor-E2-related factor-2 (Nrf2). Nrf2 expression was attenuated by LY294002 and U0126, inhibitors of phosphatidylinositol-3-kinase and MEK1/2, respectively. Nrf2 siRNA decreased both proliferative and cytoprotective effects of HT and abrogated HO-1 induction. Moreover, HO-1 inhibition with HO-1 siRNA or zinc protoporphyrin IX significantly prevented HT-induced cell proliferation, cytoprotection, and reduction in intracellular reactive oxygen species (ROS), suggesting that HO-1 is involved in these HT functions. The findings demonstrate that HT positively regulates the antioxidant defense system in VECs through the activation of Nrf2 followed by cell proliferation and resistance to vascular injury. The present study provides a molecular basis for the contribution of HT in the Mediterranean diet to the prevention of cardiovascular diseases.

Impairment of oxidative stress-induced heme oxygenase-1 expression by the defect of Parkinson-related gene of PINK1

Parkinson's disease (PD) is one of the most common neurodegenerative diseases. Mutation in the phosphatase and tensin homolog (PTEN)-induced putative kinase 1 (PINK1) gene causes an autosomal recessive form of PD. However, the etiology related to PINK1 is still not clear. Here, we examined the effect of PINK1 on heme oxygenase (HO)-1 induction in SH-SY5Y neuronal cells following H(2)O(2) or 1-methyl-4-phenylpyridinium (MPP(+)) treatment. The HO-1 induction in response to H(2)O(2) and MPP(+) treatment was impaired by the expression of recombinant PINK1 G309D mutant. PINK1 G309D mutation increased the apoptosis of SH-SY5Y cells following H(2)O(2) treatment and cell survival was rescued by the over-expression of HO-1 using adenovirus (Ad) infection. In addition, knockdown of tumor necrosis factor receptor-associated protein-1 (TRAP1), which is the substrate of PINK1 kinase, in SH-SY5Y cells also inhibited the expression of HO-1 in response to oxidative stress. The up-regulation of TRAP1 expression following H(2)O(2) treatment was inhibited by the expression of recombinant PINK1 G309D mutant. The H(2)O(2)-induced HO-1 induction was Akt- and ERK-dependent. The phosphorylation of ERK and Akt but not p38 was inhibited in cells expressing the PINK1 G309D mutant and knockdown of TRAP1. These results indicate a novel pathway by which the defect of PINK1 inhibits the oxidative stress-induced HO-1 production. Impairment of HO-1 production following oxidative stress may accelerate the dopaminergic neurodegeneration in Parkinson patients with PINK1 defect.

Estrogen stimulates proliferation and differentiation of neural stem/progenitor cells through different signal transduction pathways

Our previous study indicated that both 17β-estradiol (E2), known to be an endogenous estrogen, and bisphenol A (BPA), known to be a xenoestrogen, could positively influence the proliferation or differentiation of neural stem/progenitor cells (NS/PCs). The aim of the present study was to identify the signal transduction pathways for estrogenic activities promoting proliferation and differentiation of NS/PCs via well known nuclear estrogen receptors (ERs) or putative membrane-associated ERs. NS/PCs were cultured from the telencephalon of 15-day-old rat embryos. In order to confirm the involvement of nuclear ERs for estrogenic activities, their specific antagonist, ICI-182,780, was used. The presence of putative membrane-associated ER was functionally examined as to whether E2 can activate rapid intracellular signaling mechanism. In order to confirm the involvement of membrane-associated ERs for estrogenic activities, a cell-impermeable E2, bovine serum albumin-conjugated E2 (E2-BSA) was used. We showed that E2 could rapidly activate extracellular signal-regulated kinases 1/2 (ERK 1/2), which was not inhibited by ICI-182,780. ICI-182,780 abrogated the stimulatory effect of these estrogens (E2 and BPA) on the proliferation of NS/PCs, but not their effect on the differentiation of the NS/PCs into oligodendroglia. Furthermore, E2-BSA mimicked the activity of differentiation from NS/PCs into oligodendroglia, but not the activity of proliferation. Our study suggests that (1) the estrogen induced proliferation of NS/PCs is mediated via nuclear ERs; (2) the oligodendroglial generation from NS/PCs is likely to be stimulated via putative membrane-associated ERs.