Hideaki Tagashira

Magnolol and honokiol prevent learning and memory impairment and cholinergic deficit in SAMP8 mice

The therapeutic use of neurotrophic factors to treat neurodegenerative disorders, including Alzheimers disease, is considered feasible. Magnolol and honokiol, constituents of the Magnolia plant, are small organic compounds with neurotrophic activity. We investigated whether magnolol and honokiol can prevent age-related learning and memory impairment and cholinergic deficits in senescence-accelerated mice (SAM). Magnolol (1, 10 mg/kg) or honokiol (0.1, 1 mg/kg) were orally administered to SAMP8 mice once a day for 14 days in 2-month-old mice. Learning and memory performance were evaluated by passive avoidance tests and location and object novelty recognition tests. SAMP8 mice showed significant impairment of learning and memory at 4 and 6 months of age. This age-related learning and memory impairment was prevented by pretreatment with either magnolol (10 mg/kg) or honokiol (1 mg/kg). Cholinergic neuron densities in the medial septum and vertical limb of the diagonal band of the forebrain were evaluated by an immunohistochemical analysis of choline acetyltransferase (ChAT). SAMP8 mice showed a significant cholinergic deficit at 6 months of age. These age-related cholinergic deficits were prevented by treatment with either magnolol (10 mg/kg) or honokiol (1 mg/kg). Moreover, SAMP8 mice showed decreased activity of Akt, a member of the prosurvival pathway, in the forebrain at 2 months of age. A 14-day treatment with either magnolol (10 mg/kg) or honokiol (1 mg/kg) enhanced phosphorylation of Akt in the forebrain at 2 months of age. These results suggest that magnolol and honokiol prevent age-related learning and memory impairment by preserving cholinergic neurons in the forebrain. These compounds may have potential therapeutic applications to various neurodegenerative disorders.

Expression of a Truncated Form of the Endoplasmic Reticulum Chaperone Protein, σ1 Receptor, Promotes Mitochondrial Energy Depletion and Apoptosis

Background: An ER-associated chaperone protein, σ1 receptor (σ1R), regulates ER/mitochondrial Ca2+ mobilization through the IP3 receptor. Results: We identify a novel short splicing variant of σ1R, termed σ1SR, and demonstrate its dominant negative function. Conclusion: σ1SR interferes with σ1R function in mitochondrial Ca2+ mobilization and ATP production under ER stress conditions. Significance: In contrast to σ1R function, σ1SR has detrimental effects on cell survival. The σ1 receptor (σ1R) regulates endoplasmic reticulum (ER)/mitochondrial interorganellar Ca2+ mobilization through the inositol 1,4,5-trisphosphate receptor (IP3R). Here, we observed that expression of a novel splice variant of σ1R, termed short form σ1R (σ1SR), has a detrimental effect on mitochondrial energy production and cell survival. σ1SR mRNA lacks 47 ribonucleotides encoding exon 2, resulting in a frameshift and formation of a truncated receptor. σ1SR localizes primarily in the ER at perinuclear regions and forms a complex with σ1R but not with IP3R in the mitochondrion-associated ER membrane. Overexpression of both σ1R and the truncated isoform promotes mitochondrial elongation with increased ER mitochondrial contact surface. σ1R overexpression increases the efficiency of mitochondrial Ca2+ uptake in response to IP3R-driven stimuli, whereas σ1SR overexpression reduces it. Most importantly, σ1R promotes ATP production via increased mitochondrial Ca2+ uptake, promoting cell survival in the presence of ER stress. By contrast, σ1SR suppresses ATP production following ER stress, enhancing cell death. Taken together, the newly identified σ1SR isoform interferes with σ1R function relevant to mitochondrial energy production under ER stress conditions, promoting cellular apoptosis.

Stimulation of the Sigma-1 Receptor by DHEA Enhances Synaptic Efficacy and Neurogenesis in the Hippocampal Dentate Gyrus of Olfactory Bulbectomized Mice

Dehydroepiandrosterone (DHEA) is the most abundant neurosteroid synthesized de novo in the central nervous system. We previously reported that stimulation of the sigma-1 receptor by DHEA improves cognitive function by activating calcium/calmodulin-dependent protein kinase II (CaMKII), protein kinase C and extracellular signal-regulated kinase in the hippocampus in olfactory bulbectomized (OBX) mice. Here, we asked whether DHEA enhances neurogenesis in the subgranular zone of the hippocampal dentate gyrus (DG) and improves depressive-like behaviors observed in OBX mice. Chronic treatment with DHEA at 30 or 60 mg/kg p.o. for 14 days significantly improved hippocampal LTP impaired in OBX mice concomitant with increased CaMKII autophosphorylation and GluR1 (Ser-831) phosphorylation in the DG. Chronic DHEA treatment also ameliorated depressive-like behaviors in OBX mice, as assessed by tail suspension and forced swim tests, while a single DHEA treatment had no affect. DHEA treatment also significantly increased the number of BrdU-positive neurons in the subgranular zone of the DG of OBX mice, an increase inhibited by treatment with NE-100, a sigma-1 receptor antagonist. DHEA treatment also significantly increased phosphorylation of Akt (Ser-473), Akt (Ser-308) and ERK in the DG. Furthermore, GSK-3β (Ser-9) phosphorylation increased in the DG of OBX mice possibly accounting for increased neurogenesis through Akt activation. Finally, we confirmed that DHEA treatment of OBX mice increases the number of BrdU-positive neurons co-expressing β-catenin, a downstream GSK-3βtarget. Overall, we conclude that sigma-1 receptor stimulation by DHEA ameliorates OBX-induced depressive-like behaviors by increasing neurogenesis in the DG through activation of the Akt/GSK-3β/β-catenin pathway.

The T-type voltage-gated calcium channel as a molecular target of the novel cognitive enhancer ST101: enhancement of long-term potentiation and CaMKII autophosphorylation in rat cortical slices

J. Neurochem. (2012) 121, 44–53.

Methyl pyruvate rescues mitochondrial damage caused by SIGMAR1 mutation related to amyotrophic lateral sclerosis.

BACKGROUND Amyotrophic lateral sclerosis (ALS) is a disease caused by motor neuron degeneration. Recently, a novel SIGMAR1 gene variant (p.E102Q) was discovered in some familial ALS patients. METHODS We address mechanisms underlying neurodegeneration caused by the mutation using Neuro2A cells overexpressing σ1R(E102Q), a protein of a SIGMAR1 gene variant (p.E102Q) and evaluate potential amelioration by ATP production via methyl pyruvate (MP) treatment. RESULTS σ1R(E102Q) overexpression promoted dissociation of the protein from the endoplasmic reticulum (ER) membrane and cytoplasmic aggregation, which in turn impaired mitochondrial ATP production and proteasome activity. Under ER stress conditions, overexpression of wild-type σ1R suppressed ER stress-induced mitochondrial injury, whereas σ1R(E102Q) overexpression aggravated mitochondrial damage and induced autophagic cell death. Moreover, σ1R(E102Q)-overexpressing cells showed aberrant extra-nuclear localization of the TAR DNA-binding protein (TDP-43), a condition exacerbated by ER stress. Treatment of cells with the mitochondrial Ca(2+) transporter inhibitor Ru360 mimicked the effects of σ1R(E102Q) overexpression, indicating that aberrant σ1R-mediated mitochondrial Ca(2+) transport likely underlies TDP-43 extra-nuclear localization, segregation in inclusion bodies, and ubiquitination. Finally, enhanced ATP production promoted by methyl pyruvate (MP) treatment rescued proteasome impairment and TDP-43 extra-nuclear localization caused by σ1R(E102Q) overexpression. CONCLUSIONS Our observations suggest that neurodegeneration seen in some forms of ALS are due in part to aberrant mitochondrial ATP production and proteasome activity as well as TDP-43 mislocalization resulting from the SIGMAR1 mutation. GENERAL SIGNIFICANCE ATP supplementation by MP represents a potential therapeutic strategy to treat ALS caused by SIGMAR1 mutation.

σ1-Receptor stimulation with fluvoxamine ameliorates transverse aortic constriction-induced myocardial hypertrophy and dysfunction in mice

Selective serotonin reuptake inhibitors (SSRIs) are known to reduce post-myocardial infarction-induced morbidity and mortality. However, the molecular mechanism underlying SSRI-induced cardioprotection remains unclear. Here, we investigated the role of σ(1)-receptor (σ(1)R) stimulation with fluvoxamine on myocardial hypertrophy and cardiac functional recovery. Male ICR mice were subjected to transverse aortic constriction (TAC) in the cardiac aortic arch. To confirm the cardioprotective role of fluvoxamine by σ(1)R stimulation, we treated mice with fluvoxamine (0.5 or 1 mg/kg) orally once per day for 4 wk after the onset of aortic banding. Interestingly, in untreated mice, σ(1)R expression in the left ventricle (LV) decreased significantly over the 4 wk as TAC-induced hypertrophy increased. In contrast, fluvoxamine administration significantly attenuated TAC-induced myocardial hypertrophy concomitant with recovery of σ(1)R expression in the LV. Fluvoxamine also attenuated hypertrophy-induced impaired LV fractional shortening. The fluvoxamine cardioprotective effect was nullified by treatment with a σ(1)R antagonist [NE-100 (1 mg/kg)]. Importantly, another SSRI with very low affinity for σ(1)Rs, paroxetine, did not elicit antihypertrophic effects in TAC mice and cultured cardiomyocytes. Fluvoxamine treatment significantly restored TAC-induced impaired Akt and endothelial nitric oxide synthase (eNOS) phosphorylation in the LV. Our findings suggest that fluvoxamine protects against TAC-induced cardiac dysfunction via upregulated σ(1)R expression and stimulation of σ(1)R-mediated Akt-eNOS signaling in mice. This is the first report of a potential role for σ(1)R stimulation by fluvoxamine in attenuating cardiac hypertrophy and restoring contractility in TAC mice.

Dehydroepiandrosterone‐Mediated Stimulation of Sigma‐1 Receptor Activates Akt‐eNOS Signaling in the Thoracic Aorta of Ovariectomized Rats with Abdominal Aortic Banding

OBJECTIVE Decreased dehydroepiandrosterone (DHEA) levels are associated with endothelial dysfunction and increased cardiovascular mortality in postmenopausal women. Using ovariectomized rats, we first defined whether expression of sigma-1 receptor (Sig-1R) in the aorta is regulated following pressure overload (PO) and also after DHEA treatment. We also investigated effects of DHEA known as Sig-1R agonist on impaired Akt/endothelial nitric oxide synthase (eNOS) signaling in the thoracic aorta under PO. RESEARCH DESIGN/METHODS Wistar rats subjected to bilateral ovariectomy (OVX) were further treated with abdominal aortic stenosis 2 weeks later. DHEA (15 and 30 mg/kg) was administered orally once a day for 14 days starting from 2 weeks after the aortic banding. RESULTS Time course study indicated that expression of Sig-1R expression and eNOS decreased time dependently in the thoracic aorta from 1 to 4 weeks after PO. DHEA treatment significantly inhibited the decreased Sig-1R expression in the thoracic aorta. The DHEA treatment also significantly restored PO-induced impaired Akt phosphorylation and stimulated eNOS protein expression with concomitant increased Akt-mediated eNOS phosphorylation (Ser1177). We did not find any changes in the phosphorylation of ERK1/2 and PKCα in the aorta following PO and after treatment with DHEA. CONCLUSION We here reported, for the first time, that DHEA treatment induces the upregulation and stimulation of Sig-1R in the thoracic aorta that stimulate Sig-1R-mediated Akt-eNOS signaling pathways in ovariectomized rats under PO.

Targeting sigma-1 receptor with fluvoxamine ameliorates pressure-overload-induced hypertrophy and dysfunctions

Objective: We here investigated the effect of sigma-1 receptor (Sig-1R) stimulation with fluvoxamine on myocardial hypertrophy, cardiac functional recovery and defined mechanisms underlying its cardioprotective action. Methods: Wistar rats subjected to bilateral ovariectomy (OVX) were treated with abdominal aortic banding between the right and left renal arteries. To confirm the cardioprotective role of Sig-1R stimulation, we treated the rats with Sig-1R agonist (fluvoxamine, 0.5 and 1 mg/kg) orally once a day for 4 weeks after the onset of aortic banding. Results: Interestingly, the expression of Sig-1R in the left ventricle (LV) decreased significantly 4 weeks after pressure overload (PO)-induced hypertrophy in OVX rats. The fluvoxamine administration significantly attenuated PO-induced myocardial hypertrophy with concomitant increase in the expression of Sig-1R in LV. Fluvoxamine also attenuated hypertrophy-induced impaired LV functions. The cardioprotective effect of fluvoxamine was nullified by treatment with Sig-1R antagonist (NE-100; 1 mg/kg). Fluvoxamine treatment significantly restored PO-induced impaired eNOS and Akt activity in the LV. Conclusion: We here found, for the first time, the potential role of Sig-1R expression in the heart in attenuating PO-induced hypertrophy in OVX rats. Fluvoxamine treatment protects PO-induced cardiac injury via upregulation of Sig-1R and stimulation of Sig-1R-mediated Akt-eNOS signaling in ovariectomized rats.

Rivastigmine improves hippocampal neurogenesis and depression-like behaviors via 5-HT1A receptor stimulation in olfactory bulbectomized mice.

Rivastigmine is a non-competitive inhibitor of both acetylcholinesterase (AChE) and butylcholinesterase (BuChE) used to treat mild to moderate dementia in Alzheimers disease (AD) patients. Although rivastigmine reportedly ameliorates cognitive dysfunction in these patients, its ability to improve Behavioral and Psychological Symptoms of Dementia (BPSD) remains unclear. To determine whether rivastigmine treatment antagonizes depression-like behaviors, we chronically administered rivastigmine (0.1-1.0mg/kg) to olfactory bulbectomized (OBX) mice once a day for 2weeks, starting 2weeks after bulbectomy. Chronic treatment at 0.3 or 1.0mg/kg dose dependently and significantly improved depression-like behaviors, as assessed by tail suspension (TST), forced swim (FST), locomotion and novelty-suppressed feeding (NSFT) tests. Importantly, co-administration with WAY-100635 (1.0mg/kg), a 5-HT1A receptor antagonist, but not ketanserin (1.0mg/kg,), a 5-HT2A receptor antagonist, completely blocked rivastigmine-induced anti-depressive effects, suggesting that 5-HT1A receptor stimulation mediates this activity. Consistent with this observation, rivastigmine treatment significantly rescued impaired neurogenesis observed in OBX mice in a 5-HT1A receptor-dependent manner. Furthermore, enhanced protein kinase B (Akt) and extracellular signal-regulated kinase (ERK) phosphorylation seen following rivastigmine treatment was closely associated with improved neurogenesis. These effects were blocked by WAY-100635 but not ketanserin treatment. Finally, we confirmed that 5-HT1A but not 5-HT2A receptor stimulation by specific agonists mimicked rivastigmine-induced anti-depression activity and promoted hippocampal neurogenesis. We conclude that, in addition to enhancing the cholinergic system, rivastigmine treatment restores normal function of the hippocampal serotonergic system, an activity that likely ameliorates depressive behaviors in AD patients.

Distinct cardioprotective effects of 17β-estradiol and dehydroepiandrosterone on pressure overload-induced hypertrophy in ovariectomized female rats.

ObjectiveWe recently reported decreased &sgr;1 receptor expression in the heart after abdominal aortic stenosis in bilateral ovariectomized rats. Here, we use ovariectomized female rats to investigate the distinct cardioprotective effects of 17&bgr;-estradiol (E2) and dehydroepiandrosterone (DHEA) in pressure overload (PO)–induced cardiac dysfunction. MethodsE2 (0.1 mg/kg) and DHEA (30 mg/kg) were administered to rats subcutaneously and orally, respectively, for 14 days starting 2 weeks after aortic banding. ResultsBoth E2 and DHEA treatments significantly inhibited PO-induced increases both in heart weight/body weight ratio and lung weight/body weight ratios. Both E2 and DHEA also ameliorated hypertrophy-induced impairment of left ventricular end-diastolic pressure, left ventricular–developed pressure, left ventricular contraction and relaxation (±dp/dt) rates, heart rate, and mean arterial blood pressure. Notably, DHEA but not E2 administration rescued decreased PO-induced &sgr;1 receptor reduction in the heart. Coadministration with N,N-Dipropyl-2-[4-methoxy-3-(2-phenylethoxy) phenyl]-ethylamine monohydrochloride, an &sgr;1 receptor antagonist, inhibited DHEA-induced amelioration of heart dysfunction without altering E2-induced cardioprotection. Mechanistically, both E2 and DHEA treatments significantly restored PO-induced decreases in protein kinase B (Akt) phosphorylation and Akt-mediated endothelial nitric oxide synthase (eNOS) phosphorylation (Ser1179). N,N-Dipropyl-2-[4-methoxy-3-(2-phenylethoxy) phenyl]-ethylamine monohydrochloride treatment totally abolished DHEA-induced Akt and eNOS phosphorylation without altering E2-induced Akt-eNOS activation. ConclusionsTaken together, these results from an ovariectomized rat model of PO-induced cardiac dysfunction show that DHEA but not E2 elicits a cardioprotective action through &sgr;1 receptor activation. DHEA-induced Akt-eNOS activation through &sgr;1 receptors is probably associated with its cardioprotective activity.