Nicotine-mediated Neuroprotection Research Articles

Polyamine regulation of ion channel assembly and implications for nicotinic acetylcholine receptor pharmacology

Small molecule polyamines are abundant in all life forms and participate in diverse aspects of cell growth and differentiation. Spermidine/spermine acetyltransferase (SAT1) is the rate-limiting enzyme in polyamine catabolism and a primary genetic risk factor for suicidality. Here, using genome-wide screening, we find that SAT1 selectively controls nicotinic acetylcholine receptor (nAChR) biogenesis. SAT1 specifically augments assembly of nAChRs containing α7 or α4β2, but not α6 subunits. Polyamines are classically studied as regulators of ion channel gating that engage the nAChR channel pore. In contrast, we find polyamine effects on assembly involve the nAChR cytosolic loop. Neurological studies link brain polyamines with neurodegenerative conditions. Our pharmacological and transgenic animal studies find that reducing polyamines enhances cortical neuron nAChR expression and augments nicotine-mediated neuroprotection. Taken together, we describe a most unexpected role for polyamines in regulating ion channel assembly, which provides a new avenue for nAChR neuropharmacology.

The Age-Related Effect of Nicotine on the Expression of Neuroprotective Genes in Ventral Tegmental Area and Substantia Nigra

Selective degeneration of dopaminergic neurons, which are predominantly located in the substantia nigra (SN) of the midbrain, is one of the hallmarks of Parkinson’s disease (PD). Large-scale microarray experimental data revealed several genes with significantly differential expression between the ventral tegmental area (VTA) and the SN dopamine (DA) neurons. Several epidemiological studies have additionally indicated nicotine-mediated neuroprotection in PD patients. Based on the strong evidence implicating lipoprotein lipase (LPL), pituitary adenylate cyclase-activating polypeptide and gastrin-releasing peptide genes in neuroprotection, this letter investigates area- and age-specific nicotine regulation of these genes’ expression in the VTA and SN of different age groups (3 months, 12 months, and 24 months) in an in vivo animal model. Our in vivo rat model results suggest that out of these genes, only the LPL gene has significantly differential expression between the VTA and SN in the senior age group (24 months). Nicotine treatment did not upregulate the neuroprotective genes in adult and senior groups (12 and 24 months). Differential expression of the LPL gene in the senior population may contribute to the different survival rates of DA neurons within the VTA and SN. However, downregulation by nicotine suggests that these genes may not be related to the nicotine-mediated neuroprotection known to reduce the risks of PD. Our results suggest that nicotine may not play an important role in the regulation of neuroprotective gene expressions, while providing new insights into the role of nicotine in PD.

ER-stress and autophagy regulation of nicotine-mediated neuroprotection in a mouse model of Parkinson's disease

ER-stress and autophagy regulation of nicotine-mediated neuroprotection in a mouse model of Parkinson's disease

The Expression of CYP2D22, An Ortholog of Human CYP2D6, in Mouse Striatum and Its Modulation in 1-Methyl 4-Phenyl-1,2,3,6-Tetrahydropyridine-Induced Parkinson's Disease Phenotype and Nicotine-Mediated Neuroprotection

The main contributory factors of Parkinson's disease (PD) are aging, genetic factors, and environmental exposure to pesticides and heavy metals. CYP2D22, a mouse ortholog of human CYP2D6, is expected to participate in a chemically induced PD phenotype due to its structural resemblance with CYP2D6. Despite its expected participation in PD, its expression in the nigrostriatal tissues and modulation by the chemicals that induce PD or offer neuroprotection have not yet been investigated. The present study was undertaken to investigate CYP2D22 expression in mouse striatum and to assess its involvement in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD phenotype and nicotine-mediated neuroprotection. The animals were treated intraperitoneally daily with nicotine (1 mg/kg) for 8 weeks, followed by MPTP (20 mg/kg) + nicotine (1 mg/kg) for 2-4 weeks and vice versa, along with respective controls. In some sets of experiments, the animals were treated with ketoconazole (300 mg/kg), a CYP3AH/CYP2D22 inhibitor, along with nicotine and/or MPTP. Tyrosine hydroxylase (TH)-immunoreactivity in the substantia nigra, the expression of nicotinic acetylcholine receptors (nAChRs) alpha6 and alpha4, dopamine content, and 1-methyl-4-phenylpyridinium ion (MPP(+)) level in the striatum were measured to confirm the MPTP-induced PD phenotype and nicotine-mediated neuroprotection. CYP2D22 and nAChRs expressions were measured in the striatum by RT-PCR/western blotting and dopamine level; CYP2D22 catalytic activity and MPP(+) content were determined by high-performance liquid chromatography (HPLC). MPTP increased dopaminergic neuronal degeneration and the striatal MPP(+) level and reduced striatal dopamine content; it attenuated expression/activity of CYP2D22 and nAChRs that were significantly restored in nicotine-treated animals. Ketoconazole reduced the nicotine-mediated increase in CYP2D22 expression and activity, dopamine content, and TH-immunoreactivity. The results indicate the expression of CYP2D22 in mouse striatum and its possible role in the MPTP-induced PD phenotype and nicotine-mediated neuroprotection.

Neuroprotection via nAChRs: the role of nAChRs in neurodegenerative disorders such as Alzheimer's and Parkinson's disease

Epidemiological studies have identified a negative correlation between smoking and the development of neurodegenerative disorders such as Parkinson's disease, and in some studies, Alzheimer's disease. These findings have been attributed to the ability of nicotine to act as a neuroprotective agent. A large number of studies demonstrate that nicotine can protect against neuronal death in vitro and in vivo, and the mechanisms underlying the ability of nicotine to protect against excitotoxicity and amyloid-? toxicity are beginning to be elucidated. Despite the compelling evidence that nicotine is neuroprotective, it is clear that nicotine can be toxic under some circumstances. The balance between nicotine neuroprotection and toxicity depends on dose, developmental stage and regimen of administration. Therefore, a full understanding of the molecular and cellular effects of nicotine on signaling pathways relevant to neuronal survival is critical for informed drug discovery of nicotinic compounds to combat human neurodegeneration. This review summarizes recent studies related to the mechanisms underlying nicotine-mediated neuroprotection, and addresses issues that are relevant to use of nicotine as a neuroprotective agent in vivo.

Dissecting the signaling pathway of nicotine‐mediated neuroprotection in a mouse Alzheimer disease model

Nicotine has a therapeutic benefit in treating Alzheimer's disease (AD). In the present study we show that nicotine decreases accumulation of beta-amyloid (Abeta) in the cortex and hippocampus of APP (V717I) transgenic mice. Nicotine prevents activation of NF-kappaB and c-Myc by inhibiting the activation of MAP kinases (MAPKs). As a result, the activity of inducible NOS and the production of NO are down-regulated. RNA interference experiments show that the above nicotine-mediated process requires alpha7 nAChR. Nicotine decreases Abeta via the activation of alpha7nAChRs through MAPK, NF-kappaB, and c-myc pathways. Nicotine also inhibits apoptosis and cell cycle progression in this mouse line. The dissected signaling pathway of nicotine-mediated neuroprotection in the present study provides a mechanistic basis for the potential development of drug targets for treating AD.

Angiotensin II Blocks Nicotine-Mediated Neuroprotection against β-Amyloid (1-42) via Activation of the Tyrosine Phosphatase SHP-1

We showed recently that nicotine activates the growth-promoting enzyme Janus kinase 2 (JAK2) in PC12 cells and that preincubation of these cells with the JAK2-specific inhibitor AG-490 blocked the nicotine-induced neuroprotection against beta-amyloid (1-42) [Abeta (1-42)]. These results provided direct evidence for linkage between JAK2 and the alpha7 nicotinic acetylcholine receptor-induced neuroprotection in PC12 cells. We also showed that preincubation with angiotensin II (Ang II), functioning via the angiotensin II type 2 (AT2) receptor, blocked both the nicotine-induced activation of JAK2 and its neuroprotection against Abeta (1-42). Recently growth-inhibitory effects of the AT2 receptor have been reported to be mediated by the activation of protein tyrosine phosphatases (PTPases) and that AT2 receptor stimulation is associated with a rapid activation of the PTPase SHP-1 (the cytoplasmic tyrosine phosphatase that contains Src homology 2 domains), a negative regulator of JAK2 signaling. Therefore, the potential biological significance of AT2 receptor-induced effects on both the nicotine-induced activation of JAK2 and its neuroprotection against Abeta (1-42) led us to investigate whether SHP-1 activation could be involved in this process. We found that Ang II induced the activation of SHP-1 and that an antisense against SHP-1 not only augmented the nicotine-induced tyrosine phosphorylation of JAK2 but also blocked the Ang II neutralization of the nicotine-induced neuroprotection. These results demonstrate that nicotine-induced tyrosine phosphorylation of JAK2 and neuroprotection against Abeta (1-42) in PC12 cells are blocked by Ang II via AT2 receptor-induced activation of SHP-1.

Neuroprotection by Nicotine in Mouse Primary Cortical Cultures Involves Activation of Calcineurin and L-Type Calcium Channel Inactivation

Regulation of intracellular calcium influences neuronal excitability, synaptic plasticity, gene expression, and neurotoxicity. In this study, we investigated the role of calcium in mechanisms underlying nicotine-mediated neuroprotection from glutamate excitotoxicity. Neuroprotection by nicotine in primary cortical cultures was not seen in knock-out mice lacking the beta2 subunit of the nicotinic acetylcholine receptor (nAChR). Neuroprotection was partially blocked in wild-type cultures by alpha-bungarotoxin, an antagonist of the alpha7 nAChR subtype, suggesting a potential cooperative role for these subtypes. Pretreatment with nicotine decreased glutamate-mediated calcium influx in primary cortical cultures by 41%, an effect that was absent in cultures from knock-out mice lacking the beta2 subunit of the nAChR. This effect was dependent on calcium entry through L-type channels during nicotine pretreatment in wild-type cultures. The ability of nicotine to decrease glutamate-mediated calcium influx was occluded by cotreatment with nifedipine during glutamate application, suggesting that nicotine pretreatment decreased subsequent activity of L-type calcium channels. Treatment with the calcineurin antagonists FK506 and cyclosporine during pretreatment eliminated both nicotine-mediated neuroprotection and the effects of nicotine on L-type channels. We conclude that neuroprotective effects of nicotine in cortical neurons involve both beta2- and alpha7-containing nAChRs, activation of calcineurin, and decreased intracellular calcium via L-type channels.

Nicotine‐induced neuroprotection against N‐methyl‐d‐aspartic acid or β‐amyloid peptide occur through independent mechanisms distinguished by pro‐inflammatory cytokines

Nicotine, the causative agent of addiction to tobacco, can also be a neuroprotectant. Nicotine-induced neuroprotection against different toxins is imparted through pharmacologically distinct neuronal nicotinic acetylcholine receptors (nAChR) where protection against chronic N-methyl-d-aspartic acid (NMDA) exposure is through nAChRalpha7 but protection against the toxic peptide of amyloid precursor protein, Abeta25-35, is through nAChRalpha4beta2. The inflammatory cytokine tumor necrosis factor alpha (TNFalpha) is also neuroprotective, however, in the presence of nicotine, neuroprotection against NMDA is abolished. The specificity of nicotine-TNFalpha antagonism was further refined using a mouse transgenic dominant negative of nAChRalpha7 in which nicotine failed to induce neuroprotection against NMDA and antagonism of TNFalpha was absent. However, nicotine-mediated neuroprotection against Abeta25-35 was unaffected and, therefore, did not require the expression of functional nAChRalpha7s. The mechanism of TNFalpha-mediated neuroprotection and antagonism by nicotine was independent of caspase 8 activation or nuclear factor kappa B translocation in neurons but C6-ceramide addition to neuronal cultures subsequently exposed to NMDA mimicked the neuroprotective effect of TNFalpha and, like TNFalpha, it was antagonized by cotreatment with nicotine. Therefore, the neuroprotective effects of nicotine against differing toxic assaults requires distinct nAChR subtypes and proceeds through intracellular pathways that overlap with similarly different mechanisms initiated by pro-inflammatory cytokines. These results provide insight into how nicotine imparts neuroprotection and modulates inflammatory responses.