Sung Min Nam

Melatonin improves D-galactose-induced aging effects on behavior, neurogenesis, and lipid peroxidation in the mouse dentate gyrus via increasing pCREB expression.

Abstract:  Melatonin (N‐acetyl‐5‐methoxytryptamine) has multiple functions. In this study, we investigated the effects of melatonin on memory, cell proliferation, and neuroblast differentiation in the dentate gyrus of a mouse model of d‐galactose‐induced aging. d‐galactose was subcutaneously administered to 7‐wk‐old mice for 10 wk, and age‐matched mice were used as controls. Seven weeks after d‐galactose administration, vehicle (water) or melatonin (6 mg/L in water) was administered ad libitum to the mice for 3 wk. The administration of d‐galactose significantly increased the escape latency compared with that in the control mice on days 1–3. In addition, cells in the subgranular zone and in the granule cell layer of the dentate gyrus showed severe damage (cytoplasmic condensation) in the d‐galactose‐treated mice. However, melatonin supplementation to these mice for 3 wk significantly ameliorated the d‐galactose‐induced increase in escape latency and neuronal damage compared with the vehicle‐treated group. The administration of melatonin also significantly restored the d‐galactose‐induced reduction of proliferating cells (Ki67‐positive cells) and differentiating neuroblasts (doublecortin‐positive neuroblasts) in the dentate gyrus. Furthermore, the administration of melatonin significantly increased Ser133‐phosphorylated cyclic AMP response element binding protein in the dentate gyrus. The administration of melatonin significantly reduced d‐galactose‐induced lipid peroxidation in the dentate gyrus. These results suggest that melatonin may be helpful in reducing age‐related phenomena in the brain.

Effects of Curcumin (Curcuma longa) on Learning and Spatial Memory as Well as Cell Proliferation and Neuroblast Differentiation in Adult and Aged Mice by Upregulating Brain-Derived Neurotrophic Factor and CREB Signaling

Aging is a progressive process, and it may lead to the initiation of neurological diseases. In this study, we investigated the effects of wild Indian Curcuma longa using a Morris water maze paradigm on learning and spatial memory in adult and D-galactose-induced aged mice. In addition, the effects on cell proliferation and neuroblast differentiation were assessed by immunohistochemistry for Ki67 and doublecortin (DCX) respectively. The aging model in mice was induced through the subcutaneous administration of D-galactose (100 mg/kg) for 10 weeks. C. longa (300 mg/kg) or its vehicle (physiological saline) was administered orally to adult and D-galactose-treated mice for the last three weeks before sacrifice. The administration of C. longa significantly shortened the escape latency in both adult and D-galactose-induced aged mice and significantly ameliorated D-galactose-induced reduction of cell proliferation and neuroblast differentiation in the subgranular zone of hippocampal dentate gyrus. In addition, the administration of C. longa significantly increased the levels of phosphorylated CREB and brain-derived neurotrophic factor in the subgranular zone of dentate gyrus. These results indicate that C. longa mitigates D-galactose-induced cognitive impairment, associated with decreased cell proliferation and neuroblast differentiation, by activating CREB signaling in the hippocampal dentate gyrus.

Effects of luteolin on spatial memory, cell proliferation, and neuroblast differentiation in the hippocampal dentate gyrus in a scopolamine-induced amnesia model

Abstract Objectives: Luteolin, a common flavonoid from many plants, has various pharmacological activities, including a memory-improving effect. In this study, we investigated the effects of luteolin on spatial memory, cell proliferation, and neuroblast differentiation in the hippocampal dentate gyrus in a rat model of scopolamine (SCO)-induced amnesia. Methods: Scopolamine was subcutaneously administered for 28 days via an Alzet minipump (44 mg/ml delivered at 2·5 μl/h) along with a daily intraperitoneal administration of vehicle (saline) 10 mg/kg luteolin or 5 mg/kg galantamine (GAL) (a control drug for acetylcholinesterase (AChE) inhibitor) for 28 days. Results: The administration of SCO significantly decreased the spatial alteration percentage in the Y-maze test compared to that in the vehicle (saline)-treated group. The administration of luteolin or GAL significantly improved the spatial alteration percentage compared to that in the SCO-treated group. Similarly, the administration of SCO significantly decreased the cell proliferation (Ki67-positive cells) and neuroblast differentiation (doubleocortin-positive cells) in the dentate gyrus. The administration of luteolin or GAL significantly mitigated the SCO-induced reduction of Ki67- and doublecortin-immunoreactive cells in the dentate gyrus. In addition, the administration of luteolin significantly decreased the lipid peroxidation (malondialdehyde (MDA) levels) and increased the brain-derived neurotrophic factor (BDNF) and AChE levels in the hippocampal homogenates compared to the SCO-treated group. Conclusion: These results suggest that the luteolin treatment improves the SCO-induced reduction of cell proliferation and neuroblast differentiation in the dentate gyrus. The mechanism underlying the amelioration of SCO-induced amnesia by luteolin may be associated with the increase in BDNF, acetylcholine, and the decrease in lipid peroxidation.

Sodium butyrate, a histone deacetylase Inhibitor, ameliorates SIRT2-induced memory impairment, reduction of cell proliferation, and neuroblast differentiation in the dentate gyrus

Abstract Objectives: Histone deacetylases (HDACs) play a key role in synaptic plasticity and learning and memory. Sirtuin 2 (SIRT2), a class III HDAC, is abundantly expressed in neurons and functions as a mitotic exit regulator in dividing cells. In this study, we investigated the role of SIRT2 in cell proliferation and neuroblast differentiation in the mouse dentate gyrus. Methods: To facilitate the delivery of SIRT2 into neurons, we constructed a PEP-1-SIRT2 fusion protein. Mice were divided into three groups: vehicle (PEP-1), SIRT2, and SIRT2 with sodium butyrate (an HDAC inhibitor). PEP-1 or PEP-1-SIRT2 fusion protein was administered intraperitoneally to 7-week-old mice once a day for 3 weeks, and the mice were killed 2 h after the last administration. Sodium butyrate, an HDAC inhibitor, was subcutaneously administered in parallel with PEP-1-SIRT2 once a day for 3 weeks. Results: The administration of PEP-1-SIRT2 alone significantly reduced the time spent exploring a new object in the novel object recognition test, whereas treatment with sodium butyrate increased the time spent exploring a new object. Results of Ki67 and doublecortin immunohistochemistry revealed that the administration of PEP-1-SIRT2 significantly reduced cell proliferation and neuroblast differentiation, respectively, in the dentate gyrus. However, the administration of sodium butyrate significantly ameliorated the SIRT2-induced reduction in cell proliferation and neuroblast differentiation. Conclusion: This result suggests that histone acetylation and deacetylation are key factors modulating hippocampal functions such as memory formation, cell proliferation, and neuroblast differentiation in the dentate gyrus.

Valeriana officinalis extract and its main component, valerenic acid, ameliorate D-galactose-induced reductions in memory, cell proliferation, and neuroblast differentiation by reducing corticosterone levels and lipid peroxidation.

Valeriana officinalis is used in herbal medicine of many cultures as mild sedatives and tranquilizers. In this study, we investigated the effects of extract from valerian root extracts and its major component, valerenic acid on memory function, cell proliferation, neuroblast differentiation, serum corticosterone, and lipid peroxidation in adult and aged mice. For the aging model, D-galactose (100 mg/kg) was administered subcutaneously to 6-week-old male mice for 10 weeks. At 13 weeks of age, valerian root extracts (100 mg/kg) or valerenic acid (340 μg/kg) was administered orally to control and D-galactose-treated mice for 3 weeks. The dosage of valerenic acid (340 μg/kg), which is the active ingredient of valerian root extract, was determined by the content of valerenic acid in valerian root extract (3.401±0.066 mg/g) measured by HPLC. The administration of valerian root extract and valerenic acid significantly improved the preferential exploration of new objects in novel object recognition test and the escape latency, swimming speeds, platform crossings, and spatial preference for the target quadrant in Morris water maze test compared to the D-galactose-treated mice. Cell proliferation and neuroblast differentiation were significantly decreased, while serum corticosterone level and lipid peroxidation in hippocampus were significantly increased in the D-galactose-treated group compared to that in the control group. The administration of valerian root extract significantly ameliorated these changes in the dentate gyrus of both control and D-galactose-treated groups. In addition, valerenic acid also mitigated the D-galactose-induced reduction of these changes. These results indicate that valerian root extract and valerenic acid enhance cognitive function, promote cell proliferation and neuroblast differentiation, and reduce serum corticosterone and lipid peroxidation in aged mice.

Activation of microglia and induction of pro-inflammatory cytokines in the hippocampus of type 2 diabetic rats

Abstract Objectives: The majority of immune cells in the brain are comprised of microglia, which undergo morphological changes when activated to remove damaged neurons and infectious agents from the brain tissue. In this study, we investigated the effects of type 2 diabetes on microglial activation and the subsequent secretion of pro-inflammatory cytokines, such as interferon-gamma (IFN-gamma) and interleukin-1beta (IL-1beta), in the hippocampus using Zucker diabetic fatty (ZDF) rats and Zucker lean control (ZLC) rats at various diabetic stages. Methods: Zucker lean control and Zucker diabetic fatty rats were sacrificed at 12 (early diabetic stage), 20, or 30 weeks of age (chronic diabetic stage), and the hippocampus was obtained via transcardiac perfusion or dissection for immunohistochemistry and western blot analysis, respectively. Results: Zucker diabetic fatty rats demonstrated significantly higher glucose levels at 12 and 30 weeks of age compared to ZLC rats. Microglia immunoreactive to ionized calcium-binding adapter molecule 1 (Iba-1) had hypertrophied cytoplasm with retracted processes at 30 weeks of age. In contrast, Iba-1-immunoreactive microglia displayed similar morphology in ZDF and ZLC rats at 12 and 20 weeks of age. Similarly, IFN-gamma and IL-1beta protein levels were significantly increased in ZDF rats compared to ZLC rats at 30 weeks of age, but not at 12 and 20 weeks of age. Interleukin-1beta immunoreactivity in the ZDF rats predominantly increased in the dentate gyrus and CA1 region of the hippocampus compared to that of ZLC rats at 30 weeks of age. In addition, IL-1beta immunoreactive structures in ZDF rats at 30 weeks of age were detected near the astrocytes and microglia. Conclusion: These results suggest that chronic diabetes activates microglia and significantly increases pro-inflammatory cytokine levels in the hippocampus.

Chronic type 2 diabetes reduces the integrity of the blood-brain barrier by reducing tight junction proteins in the hippocampus.

In the present study, we investigated the effects of type 2 diabetes-induced hyperglycemia on the integrity of the blood–brain barrier and tight junction markers in the rat hippocampus. Forty-week-old diabetic (Zucker diabetic fatty, ZDF) rats and littermate control (Zucker lean control, ZLC) rats were used in this study. We evaluated the integrity of the blood–brain barrier by measuring sodium fluorescein extravasation and blood vessel ultrastructure. In addition, tight junction markers, such as zona occludens-1, occludin and claudin-5, were quantified by western blot analysis. ZDF rats showed significantly increased sodium fluorescein leakage in the hippocampus. Tight junction markers, such as occludin and claudin-5, were significantly decreased in the hippocampi of ZDF rats compared to those of ZLC rats. In addition, ZDF rats showed ultrastructural changes with phagocytic findings in the blood vessels. These results suggest that chronic untreated diabetes impairs the permeability of the hippocampal blood–brain barrier by down-regulating occludin and claudin-5, indicating that chronic untreated diabetes may cause hippocampus-dependent dysfunction.

Physical exercise ameliorates the reduction of neural stem cell, cell proliferation and neuroblast differentiation in senescent mice induced by D-galactose

BackgroundAging negatively affects adult hippocampal neurogenesis, and exercise attenuates the age-related reduction in adult hippocampal neurogenesis. In the present study, we used senescent mice induced by D-galactose to examine neural stem cells, cell proliferation, and neuronal differentiation with or without exercise treatment. D-galactose (100 mg/kg) was injected to six-week-old C57BL/6 J mice for 6 weeks to induce the senescent model. During these periods, the animals were placed on a treadmill and acclimated to exercise for 1 week. Then treadmill running was conducted for 1 h/day for 5 consecutive days at 10-12 m/min for 5 weeks.ResultsBody weight and food intake did not change significantly after D-galactose administration with/without treadmill exercise, although body weight and food intake was highest after treadmill exercise in adult animals and lowest after treadmill exercise in D-galactose-induced senescent model animals. D-galactose treatment significantly decreased the number of nestin (a neural stem cell marker), Ki67 (a cell proliferation marker), and doublecortin (DCX, a differentiating neuroblast marker) positive cells compared to those in the control group. In contrast, treadmill exercise significantly increased Ki67- and DCX-positive cell numbers in both the vehicle- and D-galactose treated groups. In addition, phosphorylated cAMP-response element binding protein (pCREB) and brain derived neurotrophic factor (BDNF) was significantly decreased in the D-galactose treated group, whereas exercise increased their expression in the subgranular zone of the dentate gyrus in both the vehicle- and D-galactose-treated groups.ConclusionThese results suggest that treadmill exercise attenuates the D-galactose-induced reduction in neural stem cells, cell proliferation, and neuronal differentiation by enhancing the expression of pCREB and BDNF in the dentate gyrus of the hippocampus.

Effects of a new synthetic butyrylcholinesterase inhibitor, HBU-39, on cell proliferation and neuroblast differentiation in the hippocampal dentate gyrus in a scopolamine-induced amnesia animal model

In this study, we synthesized [1-(4-(benzo[d][1,3]dioxol-5-ylmethyl)piperazin-1-yl)-5-(1,2-dithiolan-3-yl)pentan-1-one, HBU-39], a (α)-lipoic acid derivative, and found this compound strongly inhibited butyrylcholinesterase (BuChE) in an in vitro experiment. We also examined the effects of HBU-39 on cell proliferation and neuroblast differentiation using the specific markers Ki67 and doublecortin (DCX), respectively, in the hippocampal dentate gyrus of a rat model of scopolamine-induced amnesia. For this, scopolamine was subcutaneously administered for 28 days by an ALzet osmotic minipump (44 mg/mL delivered at 2.5 μL/h). HBU-39 (1mg/kg per day) and galantamine (an acetylcholinesterase inhibitor used as a control; 5mg/kg per day) were intraperitoneally administered for 28 days. The administration of scopolamine significantly decreased the mean number of Ki67- and DCX-immunoreactive cells in the dentate gyrus. However, treatment with both HBU-39 and galantamine significantly ameliorated the reductions in cell proliferation and neuroblast differentiation. In particular, the mean number of Ki67- and DCX-immunoreactive cells was prominently abundant in the HBU-treated group compared to that in the galantamine-treated group. These results suggest that the BuChE inhibitor, HBU-39, can ameliorate the scopolamine-induced reductions of cell proliferation and neuroblast differentiation, and HBU-39 may be applicable to amnesia patients to promote memory functions.

Treadmill exercise is associated with reduction of reactive microgliosis and pro-inflammatory cytokine levels in the hippocampus of type 2 diabetic rats

Abstract Objectives: In the present study, we investigated the effects of treadmill exercise on microglial activation and the subsequent release of tumour necrosis factor-alpha (TNF-alpha), interleukin (IL)-6 and IL-1-beta in the hippocampus in a rat model of type 2 diabetes. Methods: At 30 weeks of age, diabetic (Zucker diabetic fatty, ZDF) rats and their littermate control (Zucker lean control, ZLC) rats were either placed on a stationary treadmill or made to run for 1 hour/day at 12–16 m/minute on five consecutive days, for 10 weeks. Once the rats reached 40 weeks, they were perfused and their hippocampus collected for immunohistochemistry or hippocampus collected fresh for the Western blotting or enzyme-linked immunosorbent assay (ELISA). Results: The whole blood glucose levels in exercised ZDF rats were significantly higher than in the sedentary or exercised ZLC rats, but were significantly lower than in the sedentary ZDF rats. In the sedentary ZLC and exercised ZLC rats, ionised calcium-binding adapter molecule 1 (Iba-1) immunoreactive microglia showed normal morphology which had small cytoplasm with ramified processes. In the sedentary ZDF rats, some Iba-1 immunoreactive microglia showed abnormal morphology which had hypertrophied cytoplasm with retracted processes. However, exercised ZDF rats had small cytoplasm with highly ramified processes. Levels of TNF-alpha, IL-6 and IL-1beta in the hippocampal homogenates were significantly increased in sedentary ZDF rats compared to sedentary ZLC rats, respectively. However, TNF-alpha, IL-6 and IL-1beta levels in the exercised ZDF rats were significantly decreased compared with those of sedentary ZDF rats, respectively. Discussion: These results suggest that exercise in type 2 diabetic rats reduces microglial activation and the subsequent increase of pro-inflammatory cytokine levels in the hippocampus.