bp(MESH:Neuroprotection)

Entity

Name

Neuroprotection

Namespace

mesh

Namespace Version

20181007

Namespace URL

https://raw.githubusercontent.com/pharmacome/terminology/8ccfed235e418e4c8aa576f9a5ef0f838e794c7f/external/mesh-names.belns

Nicotine protection of cultured rat cortical neu- rons against Abeta toxicity is blocked by the alpha4beta2 antagonist, dihydro-beta-erythroidine (Kihara et al., 1998). PubMed:19293145

Donepezil, which protects cultured rat cortical neurons, when applied for 4 days resulted in an up-regulation of alpha4 and alpha7 nAChRs with the result that donepezil was even more potently protective (Kume et al., 2005). PubMed:19293145

In SHSY5Y cells, RNA interference (RNAi) knockdown of alpha7 enhanced Abeta toxicity (Qi et al., 2007), and alpha7 antagonists, but not alpha4beta2 antagonists, block galantamine protection of cultured rat neurons (Kihara et al., 2004). Donepezil protects cultured rat cortical neurons against Abeta toxicity through both alpha7 and non-alpha7 nAChRs (Takada et al., 2003). It is therefore likely that alpha7 nAChRs are the primary mediators of nicotine neuroprotection, but in some cells, non-alpha7 subtypes are also likely to contribute. PubMed:19293145

The discovery that nicotine, a ligand acting at nAChRs, and its mimetics can protect neurons against Abeta toxicity (Kihara et al., 1998) is of interest, especially in view of the observation that nicotine also enhances cognition (Rusted et al., 2000). Nicotinic receptors play a particularly prominent role in nicotine protection. The protective effect is blocked by the nicotinic antagonists dihydro-beta-erythroidine and mecamylamine (Kihara et al., 2001; Takada- Takatori et al., 2006). PubMed:19293145

The neuroprotective effects of nicotine are blocked by inhibitors of either PI3K or SRC family kinases, and nicotine evokes an increase in levels of phosphorylated AKT, B-cell chronic lymphocytic leukemia/lymphoma (BCL2), and BCL-2-like protein (Shimohama and Kihara, 2001), which are further downstream in the PI3K/AKT pathway (Fig. 3). PubMed:19293145

JAK-2, another early target in the nicotine neuroprotection pathway that may mediate signaling between the nAChR and the PI3K pathway (Shaw et al., 2002), may link nAChR activation with the JAK/signal transducer and activator of transcription 3 (STAT-3) protective pathway. JAK-2 is also activated by nicotine in non-neuronal cells such as nAChR-bearing keratinocytes (Arredondo et al., 2006). In a microarray study, expression of 8 of 33 JAK/STAT pathway genes was altered when human bronchial epithelial cells were exposed to 5 microM nicotine for 4 to 10 h (Tsai et al., 2006). Thus, the JAK-2/STAT-3 pathway is activated by exposure to nicotine. PubMed:19293145

There is evidence that nicotine’s neuroprotective effects can be mediated through tumor necrosis factor-alpha (TNF-alpha). Application of either nicotine or TNF-alpha protects cultured mouse embryonic cortical neurons from N-methyl-D-aspartate (NMDA) toxicity, but coapplication of both does not. PubMed:19293145

It has been shown that the alpha7 receptors, but not the alpha3beta2 receptors, specifically trigger calcium release from intracellular stores by activating ryanodine receptors. Such a specific functional coupling of alpha7 receptors and ryanodine-sensitive stores may provide another site of therapeutic intervention. However, the sustained calcium rise seen in these cells upon prolonged nicotine administration, which is more likely to be of relevance to neuroprotection than short-term responses, is more dependent upon the activation of inositol 1,4,5-triphosphate receptors (Dajas-Bailador et al., 2002a), which are also a target for phosphorylation by FYN (Cui et al., 2004). PubMed:19293145

Likewise, blocking the PI3K-AKT pathway inhibits the protective effects of AChE inhibitors on neuroblastoma cells or neuronal cells against Abeta (Arias et al., 2005) or L-glutamate neurotoxicity (Takada-Takatori et al., 2006). In all these studies, protection was also inhibited by nAChR blockers, suggesting that these effects are mediated by nAChRs. PubMed:19293145

Stevens et al. (2003) showed that calcineurin is involved in nicotine neuroprotection. Abeta, through alpha7 nAChRs, increases Ca2+, which phosphorylates NMDARs via calcineurin and protein tyrosine phosphatase, nonreceptor type 5 (striatum-enriched) (Snyder et al., 2005). PubMed:19293145

Curiously, although most studies are in agreement that nAChRs need to be activated to mediate their protective effects, mouse cortical neurons are protected by the alpha7 antagonist methyllycaconitine (Martin et al., 2004), raising the possibility that neuroprotection by alpha7 agonists may be through desensitization rather than activation of this rapidly desensitizing receptor. This would be consistent with the alpha7- dependent activation of intracellular signaling pathways by Abeta (Bell et al., 2004), but the opposite effects on cell survival exerted by Abeta and nicotine means that other mechanisms must be sought, such as ligand-specific coupling to downstream signaling pathways. PubMed:19293145

Calcium signaling pathways are involved both in the toxic action of Abeta and in the protection against that toxicity offered by nicotinic ligands. Given that alpha7 homomeric nAChRs are much more permeable to calcium ions than are most other nAChRs (Bertrand et al., 1993), it is to be expected that nicotinic neuroprotection mediated by nAChRs, notably alpha7, would depend upon the activation of calcium signaling pathways. ABT-418 is a nicotinic agonist that protects primary rat cortical neurons from glutamate toxicity through its activation of alpha7 nAChRs, and this is blocked when calcium is removed from the extracellular medium (Donnelly-Roberts et al., 1996). PubMed:19293145

Likewise, blocking the PI3K-AKT pathway inhibits the protective effects of AChE inhibitors on neuroblastoma cells or neuronal cells against Abeta (Arias et al., 2005) or L-glutamate neurotoxicity (Takada-Takatori et al., 2006). In all these studies, protection was also inhibited by nAChR blockers, suggesting that these effects are mediated by nAChRs. PubMed:19293145

From these findings, it would seem that FYN plays a neuroprotective role. However, FYN may also play a paradoxical role in Abeta toxicity. Indeed, Abeta activates both FYN and the PI3K cascade (Williamson et al., 2002), whereas germline knockout of FYN is neuroprotective in mice (Lambert et al., 1998; Chin et al., 2004). FYN knockout protects mature mouse neurons in organotypic central nervous system cultures (Lambert et al., 1998). PubMed:19293145

Furthermore, inhibitors of SRC, a closely related tyrosine kinase, also prevent nicotinic protection of differentiated PC12 cells against serum-deprivation-induced cell death (Li et al., 1999b), and inhibitors of FYN or Janus kinase-2 (JAK-2) block the neuroprotection against Abeta toxicity of therapeutic AChE inhibitors (Takada-Takatori et al., 2006). PubMed:19293145

Furthermore, inhibitors of SRC, a closely related tyrosine kinase, also prevent nicotinic protection of differentiated PC12 cells against serum-deprivation-induced cell death (Li et al., 1999b), and inhibitors of FYN or Janus kinase-2 (JAK-2) block the neuroprotection against Abeta toxicity of therapeutic AChE inhibitors (Takada-Takatori et al., 2006). PubMed:19293145

JAK-2, also implicated in the neuroprotective pathway, may play a role in linking nAChR action with calcium signaling, because JAK-2 phosphorylates inositol 1,4,5-triphosphate receptors through its activation of FYN (Wallace et al., 2005). PubMed:19293145

Furthermore, inhibitors of SRC, a closely related tyrosine kinase, also prevent nicotinic protection of differentiated PC12 cells against serum-deprivation-induced cell death (Li et al., 1999b), and inhibitors of FYN or Janus kinase-2 (JAK-2) block the neuroprotection against Abeta toxicity of therapeutic AChE inhibitors (Takada-Takatori et al., 2006). PubMed:19293145

From these findings, it would seem that FYN plays a neuroprotective role. However, FYN may also play a paradoxical role in Abeta toxicity. Indeed, Abeta activates both FYN and the PI3K cascade (Williamson et al., 2002), whereas germline knockout of FYN is neuroprotective in mice (Lambert et al., 1998; Chin et al., 2004). FYN knockout protects mature mouse neurons in organotypic central nervous system cultures (Lambert et al., 1998). PubMed:19293145

Abeta, an important player in AD, is derived from beta-amyloid precursor protein (APP) through sequential cleavages by beta- and gamma-secretases: APP is cleaved by beta-secretase (BACE1) to generate the large secreted derivative sAPPbeta and the membrane-bound APP C-terminal fragment-beta; the latter can be further cleaved by gamma-secretase to generate Abeta and APP intracellular domain. Alternatively, APP can be cleaved by alpha-secretase within the Abeta domain, which precludes Abeta production and instead generates secreted sAPPalpha that has been shown to be neuroprotective PubMed:24590577

Regardless of the exact effect of Abeta1–42 on receptor activity, it does seem to block the activation by nicotine and, consistent with the cytoprotective nature of this interaction, amyloid deposition limits neuroprotection151. This phenomenon may explain at least part of the neurotoxicity that is associated with Abeta1–42 (ReF. 156). PubMed:19721446

Choline, like nicotine, can protect neural cells from cytotoxicity that is induced by growth factor deprivation152 or exposure to the glutamate analogue AMPA (alpha-amino-3-hydroxy-5-methyl-4- isoxazole propionic acid)153. PubMed:19721446

The alpha7 nAChR has previously been implicated in the in vitro neuroprotective effects of nicotine, using PC12 cells151. PubMed:19721446

As with nicotine, the weak alpha7 nAChR agonist GTS-21 is neuroprotective, specifically protecting against Abeta1–42-elicited neurotoxicity154. This effect is probably due to small, protracted increases in receptor-mediated Ca2+ influx. importantly, high concentrations of GTS-21 reduced cell survival, underlining the possible risk of over-stimulation152 PubMed:19721446

The alpha7 nAChR has previously been implicated in the in vitro neuroprotective effects of nicotine, using PC12 cells151. PubMed:19721446

By contrast, deleting the alpha7 nAChR subunit in a mouse model of Alzheimer’s disease that overexpresses a mutated form of the human amyloid precursor protein confers protection against memory loss and synaptic dysfunction, supporting a crucial role for alpha7 nAChR as a target288. PubMed:19721446

The astrocyte protein GFAP was unchanged, while microglia Iba1 expression was elevated (Iba1: 40%, P = 0.0013; Figure S6b-d) suggesting that DQ-mediated neuroprotection and decreased SASP was not derived from a reduction in pro-inflammatory glia (astrocytes or microglia) but instead associated with fewer NFT-containing neurons PubMed:30126037

NF-κB induction and activation mediates the neuroprotection bestowed by pre-conditioning with a sub-optimal dose of kainic acid and linolenic acid against severe ischemia PubMed:28745240

NF-κB induction and activation mediates the neuroprotection bestowed by pre-conditioning with a sub-optimal dose of kainic acid and linolenic acid against severe ischemia PubMed:28745240

Decoy κB nucleotides mediate cell death by blocking neurotrophins and anti-apoptotic factors supporting an essential role for NF-κB in the neuroprotective process PubMed:25652642

These NF-κB mediated neuroprotective effects have been largely observed in early stages of neuronal regeneration in AD PubMed:25652642

From these findings, it would seem that FYN plays a neuroprotective role. However, FYN may also play a paradoxical role in Abeta toxicity. Indeed, Abeta activates both FYN and the PI3K cascade (Williamson et al., 2002), whereas germline knockout of FYN is neuroprotective in mice (Lambert et al., 1998; Chin et al., 2004). FYN knockout protects mature mouse neurons in organotypic central nervous system cultures (Lambert et al., 1998). PubMed:19293145

Calcium signaling pathways are involved both in the toxic action of Abeta and in the protection against that toxicity offered by nicotinic ligands. Given that alpha7 homomeric nAChRs are much more permeable to calcium ions than are most other nAChRs (Bertrand et al., 1993), it is to be expected that nicotinic neuroprotection mediated by nAChRs, notably alpha7, would depend upon the activation of calcium signaling pathways. ABT-418 is a nicotinic agonist that protects primary rat cortical neurons from glutamate toxicity through its activation of alpha7 nAChRs, and this is blocked when calcium is removed from the extracellular medium (Donnelly-Roberts et al., 1996). PubMed:19293145

Stevens et al. (2003) showed that calcineurin is involved in nicotine neuroprotection. Abeta, through alpha7 nAChRs, increases Ca2+, which phosphorylates NMDARs via calcineurin and protein tyrosine phosphatase, nonreceptor type 5 (striatum-enriched) (Snyder et al., 2005). PubMed:19293145

JAK-2, also implicated in the neuroprotective pathway, may play a role in linking nAChR action with calcium signaling, because JAK-2 phosphorylates inositol 1,4,5-triphosphate receptors through its activation of FYN (Wallace et al., 2005). PubMed:19293145

The alpha7 nAChR has previously been implicated in the in vitro neuroprotective effects of nicotine, using PC12 cells151. PubMed:19721446

The alpha7 nAChR has previously been implicated in the in vitro neuroprotective effects of nicotine, using PC12 cells151. PubMed:19721446