Nai-Hong Chen

Osthole improves chronic cerebral hypoperfusion induced cognitive deficits and neuronal damage in hippocampus.

This study is to investigate the effects of osthole on cognitive impairment and neuronal degeneration in hippocampus induced by chronic cerebral hypoperfusion in rats, as well as the potential mechanism. Permanent occlusion of bilateral common carotid arteries (2VO) induced severe cognitive deficits tested by the water maze task, along with oxidative stress and neuronal loss in hippocampus. Oral administration of osthole for 3 weeks markedly attenuated cognitive deficits and neuronal damage. Biochemical experiments revealed that osthole decreased the production of malondialdehyde (MDA) and significantly increased the activities of Glutathione Peroxidase (GPx) and Catalase. Western blot analyses indicated that osthole prevented the downregulation of bcl-2 expression and upregulation of bax expression, which resulted in decreasing bax/bcl-2 ratio in hippocampus of 2VO rats. Additionally, osthole effectively alleviated the activation of caspase-3 induced by permanent occlusion of bilateral common carotid arteries. The observed results in present study suggest that osthole exhibits therapeutic potential for vascular dementia, which is most likely related, at least in part, to its antioxidation and anti-apoptotic actions.

Triterpenoid saponins with neuroprotective effects from the roots of Polygala tenuifolia.

The methanol fraction of an ethanolic extract from the roots of Polygala tenuifolia Willd. showed antagonistic action on neurotoxicity induced by glutamate and serum deficiency in PC12 cells. Bioassay-guided fractionation led to the isolation of six new triterpenoid saponins, onjisaponins V - Z, and Vg ( 1 - 6), together with ten known saponins ( 7 - 16). The structures of 1 - 6 were elucidated by spectroscopic and chemical methods. Screening results indicated that compounds 1 - 16 showed neuroprotective effects against serum deficiency and glutamate at the concentration of 10 (-5) mol/L.

Overexpression of α-Synuclein Down-Regulates BDNF Expression

Parkinson’s disease (PD) is a chronic progressive neurodegenerative movement disorder characterized by the selective loss of nigrostriatal dopaminergic neurons. However, the molecular pathways leading to the dopaminergic neuron degeneration have remained obscure until recently. Reports demonstrated that reduction of brain-derived neurotrophic factor (BDNF) was involved in the etiology and pathogenesis of PD, but its mechanism has not been elucidated. α-Synuclein has a causal role in Parkinson’s disease, and could interfere with transcriptional regulation of dopamine neurons. In this study, α-synuclein overexpression was found to decrease the expression of BDNF, and also to suppress the transactivation of nuclear factors of activated T-cells (NFAT) and cAMP response element binding protein (CREB), both of which regulate BDNF expression. Furthermore, overexpressed α-synuclein could associate with protein kinase C (PKC) and impair its activity. Meanwhile glycogen synthase kinase-3β (GSK3β) was activated and extracellular signal-regulated protein kinase (ERK) activity was inhibited by overexpression of α-synuclein; both of them were downstream kinases of PKC. Therefore, the impaired PKC signal pathway caused by α-synuclein overexpression might account at least partially for the down-regulation of BDNF.

Protective effect of (−)clausenamide against Aβ-induced neurotoxicity in differentiated PC12 cells

The neurotoxicity of aggregated beta-amyloid (Abeta) has been implicated as a critical cause in the pathogenesis of Alzheimers disease (AD). In the present study, we investigated the effect of (-)clausenamide ((-)Clau), an aqueous extract of leaves of Clausena lassium (lour) skeel, on the neurotoxicity of Abeta(25-35). The viability of differentiated PC12 cells was determined by MTT assay. Apoptosis was detected by flow cytometry. DCFH-DA was used for assessment of intracellular ROS generation, JC-1 and Rhodamine 123 for measurement of mitochondrial transmembrane potential (MMP). The intracellular calcium was determined with Fluo-3. The phosphorylation of p38 MAPK and the expression of Bcl-2, Bax, P53, Caspase 3 were examined by Western blot. The results showed that (-)Clau significantly elevated cell viability. Furthermore, (-)Clau arrested the apoptotic cascade by reversing overload of calcium, preventing ROS generation, moderated the dissipation of MMP and the misbalance of Bcl-2 and Bax, inhibiting the activation of p38 MAPK and the expression of P53 and cleaved Caspase 3. Our results suggested that (-)Clau may be a therapeutic agent for AD.

Effects of Glucocorticoids on Age-Related Impairments of Hippocampal Structure and Function in Mice

Effects of glucocorticoids (GCs) on maze-learning performances and hippocampal morphology were observed in male C57BL/6Cr mice. Correlations between aging, GCs and maze-learning performances were also studied. (2) Eight-arm radial maze was used in maze-learning tests. Learning performance was assessed by the parameters of time of getting all the bait, number of reentry errors into the already-entered arm with bait, and number of missed entries into an unbaited arm. Brain sections, 8xa0μm thick, were Nissl-stained with cresyl violet or stained immunocytochemically with antibodies against neurofilaments. (3) With aging, normal pyramidal cells decreased gradually in amount, and degenerating cells increased since the age of 18xa0months, accompanied with the maze-learning deficit. Here we have suggested that these changes were associated with the age-related deficits in adaptation tolerance of neurons to stress. In addition, the age-related deficits in plasticity of hippocampal neurons to GCs in young mice (3xa0months of age) resulted in an increase in plasma corticosterone (CORT) concentrations, degeneration of hippocampal pyramidal cells, as well as maze-learning deficits. (4) In conclusion, our data indicated that CORT caused the degeneration of hippocampal pyramidal cells and the impairment of memory.

Chemokine-like factor 1, a novel cytokine, induces nerve cell migration through the non-extracellular Ca2+-dependent tyrosine kinases pathway

Chemokine-like factor 1 (CKLF1) is a newly cloned chemotactic cytokine. The roles of CKLF1 in the immune system and the respiratory system have been reported, but its function in the nervous system is still remaining unclear. We aimed to investigate the role of CKLF1 in the nerve cell migration and its regulatory mechanisms. By chemotaxis assays and wound-healing assays, CKLF1 stimulated the migration of SH-SY5Y cells dose-dependently. By immunofluorescence staining, CKLF1 induced actin polymerization. By western blotting, proline-rich tyrosine kinase 2 (PYK2) was phosphorylated at Tyr-402 in response to CKLF1 and this phosphorylation was apparently suppressed by phospholipase C-gamma inhibitor U73122, but not extracellular Ca(2+) chelator EGTA. Furthermore, after transfection of dominant-negative mutant PYK2 plasmid, the chemotaxis upon CKLF1 was significantly attenuated in SH-SY5Y cells. Concluding, CKLF1 stimulates the migration of SH-SY5Y cells dose-dependently by activating non-extracellular Ca(2+)-dependent tyrosine kinases pathway and inducing actin polymerization.

Coumarin Glycosides and Iridoid Glucosides with Neuroprotective Effects from Hydrangea paniculata

Five new coumarin glycosides, umbelliferone 7-O-sophoroside (1), umbelliferone 7-O-β-D-glucopyranosyl(1u2009→u20093)-β-D-glucopyranoside (2), umbelliferone 7-O-β-D-glucopyranosyl(1u2009→u20093)-[β-D-apiofuranosyl(1u2009→u20096)]-β-D-glucopyranoside (3), umbelliferone 7-O-β-D-glucopyranosyl(1u2009→u20092)-β-D-apiofuranosyl(1u2009→u20096)-β-D-glucopyranoside (4), and umbelliferone 7-O-β-D-glucopyranosyl(1u2009→u20095)-β-D-apiofuranosyl(1u2009→u20096)-β-D-glucopyranoside (5), and two new iridoid glucosides, 7-O-E-isoferuloyl loganic acid (6) and 7-O-β-D-glucopyranosyl loganin (7), together with eight known compounds (8-15) were isolated from the stems of Hydrangea paniculata. Their structures were established by spectroscopic analysis and chemical methods. At 10u2009µM, compounds 1, 3, 5, 6, 8, 9, and 13 showed neuroprotective effects against serum deprivation-induced PC12 cell damage.

Ginsenoside Rg1 promotes glutamate release via a calcium/calmodulin-dependent protein kinase II-dependent signaling pathway.

Ginseng is one of most extensively used traditional oriental medicines worldwide with beneficial efficacy on cognitive function disorders. Pharmacological researches on its active ingredient--ginsenoside Rg1 revealed that it can improve learning and memory potentially via modulating neurotransmission in the central nervous system, whereas the specific mechanism involved has not been elucidated yet. Our previous studies have indicated that ginsenoside Rb1 could enhance glutamate release via PKA-dependent signaling pathway whereas Rg1 could enhance glutamate release via PKA-independent signaling pathway. In this work we sought to determine the role of another key mediator in neurotransmitter release--calcium/calmodulin-dependent protein kinase II (CaMKII) in the mechanism of Rg1-enhanced glutamate release. Pre-treatment with CaMKII inhibitor KN93 blocked Rg1-induced glutamate release in primary hippocampal neurons. To investigate how CaMKII was involved in this process, the effect of Rg1 on CaMKII was further studied. Rg1 activated CaMKII and subsequently increased phosphorylation level of Synapsin I (Serine(603), a substrate site of CaMKII)--an abundant phosphoprotein essential for regulating neurotransmitter release, which could be blocked by pre-treatment with CaMKII inhibitor KN93. In conclusion, the present study suggests that Rg1 promotes glutamate release potentially via a CaMKII-dependent signaling pathway in which Synapsin I may potentially act as a downstream effector. Combined with our previous study on Rb1, these two studies altogether indicated that different ginsenosides may promote neurotransmitter release via differential signaling pathways.

Three triterpenoid saponins from the roots of Polygala japonica Houtt.

Three new triterpenoid saponins polygalasaponins LI-LIII (1-3) with two acylation groups in oligosaccharide chain, together with three known saponins were isolated from the roots of Polygala japonica Houtt. (4-6). The neuroprotective effects of these compounds on neuron-like PC12 cells were evaluated in vitro. Compounds 5 and 6 show neuroprotective effects in Aβ₂₅₋₃₅ model at the concentration of 10 μM.

A new perspective in Parkinson’s disease, chaperone-mediated autophagy

Parkinsons disease (PD) is an age-related neurodegenerative disease characterized by loss of dopaminergic neurons and aggregation of alpha-synuclein. Although the role of alpha-synuclein in the pathology of PD is still unclear, the fact that its aggregation contributes to the loss of dopaminergic neurons has been confirmed. Therefore, controlling the alpha-synuclein protein level may be critical for PD pathogenesis and may provide potential therapeutics. Wild-type alpha-synuclein is physiologically degraded by chaperone-mediated autophagy (CMA), and dysfunction of CMA results in alpha-synuclein aggregation and compensative macroautophagy activation which finally leads to cell death. Therefore, CMA may participate in PD pathogenesis as a very important factor, and up-regulating CMA activity could degrade overloaded alpha-synuclein. In view of potential compensative effects, maintenance of the balance of CMA activity will be another major challenge in the future development of the therapeutic strategy. Herein we review the current knowledge of the role of CMA in PD.