Haiyan Lou

Neuroprotective effects of linarin through activation of the PI3K/Akt pathway in amyloid-β-induced neuronal cell death.

Linarin, a natural occurring flavanol glycoside derived from Mentha arvensis and Buddleja davidii is known to have anti-acetylcholinesterase effects. The present study intended to explore the neuroprotective effects of linarin against Aβ(25-35)-induced neurotoxicity with cultured rat pheochromocytoma cells (PC12 cells) and the possible mechanisms involved. For this purpose, PC12 cells were cultured and exposed to 30 μM Aβ(25-35) in the absence or presence of linarin (0.1, 1.0 and 10 μM). In addition, the potential contribution of the PI3K/Akt neuroprotective pathway in linarin-mediated protection against Aβ(25-35)-induced neurotoxicity was also investigated. The results showed that linarin dose-dependently increased cell viability and reduced the number of apoptotic cells as measured by MTT assay, Annexin-V/PI staining, JC-1 staining and caspase-3 activity assay. Linarin could also inhibit acetylcholinesterase activity induced by Aβ(25-35) in PC12 cells. Further study revealed that linarin induced the phosphorylation of Akt dose-dependently. Treatment of PC12 cells with the PI3K inhibitor LY294002 attenuated the protective effects of linarin. Furthermore, linarin also stimulated phosphorylation of glycogen synthase kinase-3β (GSK-3β), a downstream target of PI3K/Akt. Moreover, the expression of the anti-apoptotic protein Bcl-2 was also increased by linarin treatment. These results suggest that linarin prevents Aβ(25-35)-induced neurotoxicity through the activation of PI3K/Akt, which subsequently inhibits GSK-3β and up-regulates Bcl-2. These findings raise the possibility that linarin may be a potent therapeutic compound against Alzheimers disease acting through both acetylcholinesterase inhibition and neuroprotection.

(-)-Epigallocatechin gallate protects against cerebral ischemia-induced oxidative stress via Nrf2/ARE signaling.

Abstract(−)-Epigallocatechin gallate (EGCG) has recently been shown to exert neuroprotection in a variety of neurological diseases; however, its role and the underlying mechanisms in cerebral ischemic injury are not fully understood. This study was conducted to investigate the potential neuroprotective effects of EGCG and the possible role of the nuclear factor erythroid 2-related factor 2 (Nrf2)/antioxidant response element (ARE) pathway in the putative neuroprotection against experimental stroke in rats. The results revealed that EGCG exhibit significant neuroprotection, as evidenced by reduced infarction size and the decrease in transferase dUTP nick end labeling-positive neurons. Furthermore, EGCG also enhanced levels of Nrf2 and its downstream ARE pathway genes such as heme oxygenase-1, glutamate-cysteine ligase modulatory subunit and glutamate-cysteine ligase regulatory subunit, as compared to control groups. In accordance with its induction of Nrf2 activation, EGCG exerted a robust attenuation of reactive oxygen species generation and an increase in glutathione content in ischemic cortex. Taken together, these results demonstrated that EGCG exerted significant antioxidant and neuroprotective effects following focal cerebral ischemia, possibly through the activation of the Nrf2/ARE signaling pathway.

S‐allyl cysteine activates the Nrf2‐dependent antioxidant response and protects neurons against ischemic injury in vitro and in vivo

Stroke is a devastating clinical condition for which an effective neuroprotective treatment is currently unavailable. S‐allyl cysteine (SAC), the most abundant organosulfur compound in aged garlic extract, has been reported to possess neuroprotective effects against stroke. However, the mechanisms underlying its beneficial effects remain poorly defined. The present study tests the hypothesis that SAC attenuates ischemic neuronal injury by activating the nuclear factor erythroid‐2‐related factor 2 (Nrf2)‐dependent antioxidant response in both in vitro and in vivo models. Our findings demonstrate that SAC treatment resulted in an increase in Nrf2 protein levels and subsequent activation of antioxidant response element pathway genes in primary cultured neurons and mice. Exposure of primary neurons to SAC provided protection against oxygen and glucose deprivation‐induced oxidative insults. In wild‐type (Nrf2+/+) mice, systemic administration of SAC attenuated middle cerebral artery occlusion‐induced ischemic damage, a protective effect not observed in Nrf2 knockout (Nrf2−/−) mice. Taken together, these findings provide the first evidence that activation of the Nrf2 antioxidant response by SAC is strongly associated with its neuroprotective effects against experimental stroke and suggest that targeting the Nrf2 pathway may provide therapeutic benefit for the treatment of stroke.

Eriodictyol-7-O- glucoside activates Nrf2 and protects against cerebral ischemic injury.

Stroke is a complex disease that may involve oxidative stress-related pathways in its pathogenesis. The nuclear factor erythroid-2-related factor 2/antioxidant response element (Nrf2/ARE) pathway plays an important role in inducing phase II detoxifying enzymes and antioxidant proteins and thus has been considered a potential target for neuroprotection in stroke. The aim of the present study was to determine whether eriodictyol-7-O-glucoside (E7G), a novel Nrf2 activator, can protect against cerebral ischemic injury and to understand the role of the Nrf2/ARE pathway in neuroprotection. In primary cultured astrocytes, E7G increased the nuclear localization of Nrf2 and induced the expression of the Nrf2/ARE-dependent genes. Exposure of astrocytes to E7G provided protection against oxygen and glucose deprivation (OGD)-induced oxidative insult. The protective effect of E7G was abolished by RNA interference-mediated knockdown of Nrf2 expression. In vivo administration of E7G in a rat model of focal cerebral ischemia significantly reduced the amount of brain damage and ameliorated neurological deficits. These data demonstrate that activation of Nrf2/ARE signaling by E7G is directly associated with its neuroprotection against oxidative stress-induced ischemic injury and suggest that targeting the Nrf2/ARE pathway may be a promising approach for therapeutic intervention in stroke.

Novel FTY720-Based Compounds Stimulate Neurotrophin Expression and Phosphatase Activity in Dopaminergic Cells.

α-Synuclein is a chaperone-like protein implicated in Parkinsons disease (PD). Among α-synucleins normal functions is an ability to bind to and stimulate the activity of the protein phosphatase 2A (PP2A) catalytic subunit in vitro and in vivo. PP2A activity is impaired in PD and in dementia with Lewy Bodies in brain regions harboring α-synuclein aggregates. Using PP2A as the readout, we measured PP2A activity in response to α-synuclein, ceramides, and FTY720, and then on the basis of those results, we created new FTY720 compounds. We then measured the effects of those compounds in dopaminergic cells. In addition to stimulating PP2A, all three compounds stimulated the expression of brain derived neurotrophic factor and protected MN9D cells against tumor-necrosis-factor-α-associated cell death. FTY720-C2 appears to be more potent while FTY720-Mitoxy targets mitochondria. Importantly, FTY720 is already FDA approved for treating multiple sclerosis and is used clinically worldwide. Our findings suggest that FTY720 and our new FTY720-based compounds have considerable potential for treating synucleinopathies such as PD.

FTY720 Attenuates 6-OHDA-Associated Dopaminergic Degeneration in Cellular and Mouse Parkinsonian Models

FTY720 (fingolimod) is the first oral drug approved for treating relapsing-remitting forms of multiple sclerosis. It is also protective in other neurological models including ischemia, Alzheimer’s disease, Huntington disease and Rett syndrome. However, whether it might protect in a 6-hydroxydopamine (6-OHDA) mouse model associated with the dopaminergic pathology of Parkinson’s disease (PD), has not been explored. Therefore, in the present study, we investigated the effects of FTY720 on 6-OHDA-induced neurotoxicity in cell cultures and mice. Here we show that FTY720 protected against 6-OHDA cytotoxicity and apoptosis in SH-SY5Y cells. We also show that prior administration of FTY720 to 6-OHDA lesioned mice ameliorated both motor deficits and nigral dopaminergic neurotoxicity, while also reducing 6-OHDA-associated inflammation. The protective effects of FTY720 were associated with activation of AKT and ERK1/2 pro-survival pathways and an increase in brain derived neurotrophic factor (BDNF) expression in vitro and in vivo. These findings suggest that FTY720 holds promise as a PD therapeutic acting, at least in part, through AKT/ERK1/2/P-CREB-associated BDNF expression.

TREM2 overexpression attenuates neuroinflammation and protects dopaminergic neurons in experimental models of Parkinson's disease

ABSTRACT Triggering receptor expressed on myeloid cells‐2 (TREM2) was a newly identified receptor expressed on microglia. Several observations support the hypothesis that TREM2 variation may confer susceptibility to Parkinsons disease (PD). Therefore, in this paper, we explored the role of TREM2 in the 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) mouse model of PD. Our results revealed that overexpression of TREM2 remarkably reduced MPTP‐induced neuropathology including the dopaminergic neurodegeneration and neuroinflammation in vivo. Further mechanistic study revealed that TREM2 inhibited neuroinflammation by negatively regulating the TRAF6/TLR4‐mediated activation of the MAPK and NF‐&kgr;B signaling pathways. Taken together, our data suggest that TREM2 may have important neuroprotective effects against PD by critically modulating neuroinflammatory responses. These findings provide insights into the role of TREM2 in PD pathogenesis, and highlight TREM2 as a potential therapeutic target for this kind of disease. HIGHLIGHTSTREM2 protects against MPTP‐induced dopaminergic neurotoxicity in vivo.TREM2 inhibits MPTP‐induced neuroinflammatory program in vivo.TREM2‐induced anti‐inflammatory effects are associated with reduced astrogliosis and microgliosis.TREM2 suppresses TLR4‐mediated inflammatory responses in MPTP PD mouse model.

Contributions of triggering-receptor-expressed-on-myeloid-cells-2 to neurological diseases

ABSTRACT Recent laboratory and gene sequencing data suggest that variations in receptors called the “triggering-receptors-expressed-on-myeloid-cells” (TREMs) are implicated in Alzheimers disease, Parkinsons disease, multiple sclerosis, and frontotemporal lobar degeneration. TREM receptors are thought to play a critical role in regulating the immune system, inflammation, and certain cellular functions. One TREM, in particular, TREM2, is highly expressed on cells of the myeloid lineage. The binding of TREM2 to the adapter protein, DNAX activating protein of 12 kD (DAP12), in microglial cells has been shown to modulate phagocytosis within the nervous system. This review highlights the role of TREM2 in neurological diseases. Moreover, here we consider potential contributions of TREM2 and mechanisms underlying TREM2 activity as contributing to neurodegeneration. These findings may provide novel insights and opportunities to consider, especially for clinicians, as they diagnose and treat certain neurological diseases.

Inhibition of HDAC6 increases acetylation of peroxiredoxin1/2 and ameliorates 6-OHDA induced dopaminergic injury

OBJECTIVE Histone deacetylase 6 (HDAC6) has been regarded as an unusual HDAC because of its unique properties. It contains two deacetylase catalytic domains and one ubiquitin-binding domain, thus exerting both enzymatic and non-enzymatic actions on cellular function. To date, the ubiquitin-binding activity of HDAC6 has been implicated in several neurodegenerative disorders including Parkinsons disease (PD). However, the deacetylation effect of HDAC6 in PD has not been fully illustrated. Therefore, the aim of the present study was to explore the role of deacetyation activity of HDAC6 in PD. METHODS We used an in vivo 6-OHDA induced PD model and a specific HDAC6 inhibitor tubastatin A to investigate the acetylation levels of peroxiredoxin1 (Prx1) and peroxiredoxin2 (Prx2) and to explore the effects of tubastain A on nigrostriatal dopaminergic system. RESULTS Our results showed that expression of HDAC6 significantly increased in dopaminergic neurons after 6-OHDA injury. Acetylation levels of Prx1 and Prx2 decreased. Pharmacological inhibition of HDAC6 with specific inhibitor tubastatin A increased acetylation of Prx1 and Prx2, reduced ROS production and ameliorated dopaminergic neurotoxicity. CONCLUSION Our results for the first time provide evidence that HDAC6 medicated deacetylation of Prx1 and Prx2 contributes to oxidative injury in PD, suggesting that the development of specific HDAC6 inhibitor is required to develop more effective therapeutic strategies to treat PD.

Polysorbate 80‐coated PLGA nanoparticles improve the permeability of acetylpuerarin and enhance its brain‐protective effects in rats

Acetylpuerarin (AP) is an acetylated derivative of puerarin (PUE). The study aimed to prepare polysorbate 80‐coated poly(lactic‐co‐glycolic acid) (PLGA) nanoparticles to improve the permeability of AP across the blood–brain barrier (BBB) and enhance its brain‐protective effects.