Nicotine Rescues Depressive-like Behaviors via α7-type Nicotinic Acetylcholine Receptor Activation in CaMKIV Null Mice

Research advances on CaMKs-mediated neurodevelopmental injury

Calcium/calmodulin-dependent protein kinases (CaMKs) are important proteins in the calcium signaling cascade response pathway, which can broadly regulate biological functions in vivo. Multifunctional CaMKs play key roles in neural development, including neuronal circuit building, synaptic plasticity establishment, and neurotrophic factor secretion. Currently, four familial proteins, calcium/calmodulin-dependent protein kinase I (CaMKI), calcium/calmodulin-dependent protein kinase II (CaMKII), eukaryotic elongation factor 2 kinase (eEF2K, popularly known as CaMKIII) and calcium/calmodulin-dependent protein kinase IV (CaMKIV), are thought to have been the most extensively studied during neurodevelopment. Although their spatial structures are extremely similar, as well as the initial starting point of activation, both require the activation of calcium and calmodulin (CaM) complexes to be involved in the process, and the phosphorylation sites and modes of each member are different. Furthermore, due to the high structural similarity of CaMKs, their members may play synergistic roles in the regulation of neural development, but different CaMKs also have their own means of regulating neural development. In this review, we first describe the visualized protein structural forms of CaMKI, CaMKII, eEF2K and CaMKIV, and then describe the functions of each kinase in neurodevelopment. After that, we focus on four main mechanisms of neurodevelopmental damage caused by CaMKs: CaMKI/ERK/CREB pathway inhibition leading to dendritic spine structural damage; Ca2+/CaM/CaMKII through induction of mitochondrial kinetic disorders leading to neurodevelopmental damage; CaMKIII/eEF2 hyperphosphorylation affects the establishment of synaptic plasticity; and CaMKIV/JNK/NF-κB through induction of an inflammatory response leading to neurodevelopmental damage. In conclusion, we briefly discuss the pathophysiological significance of aberrant CaMK family expression in neurodevelopmental disorders, as well as the protective effects of conventional CaMKII and CaMKIII antagonists against neurodevelopmental injury.

α7 nicotinic acetylcholine receptor in memory processing

Information storage in the brain involves different memory types and stages that are processed by several brain regions. Cholinergic pathways through acetylcholine receptors actively participate on memory modulation, and their disfunction is associated with cognitive decline in several neurological disorders. During the last decade, the role of α7 subtype of nicotinic acetylcholine receptors in different memory stages has been studied. However, the information about their role in memory processing is still scarce. In this review, we attempt to identify brain areas where α7 nicotinic receptors have an essential role in different memory types and stages. In addition, we discuss recent work implicating-or not-α7 nicotinic receptors as promising pharmacological targets for memory impairment associated with neurological disorders.

Hydroxynorketamine, but not ketamine, acts via α7 nicotinic acetylcholine receptor to control presynaptic function and gene expression

Ketamine is clinically used fast-acting antidepressant. Its metabolite hydroxynorketamine (HNK) shows a robust antidepressant effect in animal studies. It is unclear, how these chemically distinct compounds converge on similar neuronal effects. While KET acts mostly as N-methyl-d-aspartate receptor (NMDAR) antagonist, the molecular target of HNK remains enigmatic. Here, we show that KET and HNK converge on rapid inhibition of glutamate release by reducing the release competence of synaptic vesicles and induce nuclear translocation of pCREB that controls expression of neuroplasticity genes connected to KET- and HNK-mediated antidepressant action. Ro25-6981, a selective antagonist of GluN2B, mimics effect of KET indicating that GluN2B-containing NMDAR might mediate the presynaptic effect of KET. Selective antagonist of α7 nicotinic acetylcholine receptors (α7nAChRs) or genetic deletion of Chrna7, its pore-forming subunit, fully abolishes HNK-induced synaptic and nuclear regulations, but leaves KET-dependent cellular effects unaffected. Thus, KET or HNK-induced modulation of synaptic transmission and nuclear translocation of pCREB can be mediated by selective signaling via NMDAR or α7nAChRs, respectively. Due to the rapid metabolism of KET to HNK, it is conceivable that subsequent modulation of glutamatergic and cholinergic neurotransmission affects circuits in a cell-type-specific manner and contributes to the therapeutic potency of KET. This finding promotes further exploration of new combined medications for mood disorders.

Mechanism of ERK/CREB pathway in pain and analgesia

Research has long centered on the pathophysiology of pain. The Transient Receiver Potential (TRP) protein family is well known for its function in the pathophysiology of pain, and extensive study has been done in this area. One of the significant mechanisms of pain etiology and analgesia that lacks a systematic synthesis and review is the ERK/CREB (Extracellular Signal-Regulated Kinase/CAMP Response Element Binding Protein) pathway. The ERK/CREB pathway-targeting analgesics may also cause a variety of adverse effects that call for specialized medical care. In this review, we systematically compiled the mechanism of the ERK/CREB pathway in the process of pain and analgesia, as well as the potential adverse effects on the nervous system brought on by the inhibition of the ERK/CREB pathway in analgesic drugs, and we suggested the corresponding solutions.

Neuroprotective effect of alpha-pinene is mediated by suppression of the TNF-α/NF-κB pathway in Alzheimer's disease rat model

Monoterpene alpha-pinene possesses antioxidant, cardioprotective, and neuroprotective properties. We evaluated the effect of alpha-pinene on oxidative/nitrosative stress, neuroinflammation, and molecular and behavioral changes induced by beta-amyloid (Aβ)_1-42 in rats and investigated the possible mechanisms of these outcomes. Male Wistar rats received alpha-pinene (50 mg/kg intraperitoneally) for 14 consecutive days after intrahippocampal injection of Aβ_1-42 . Alpha-pinene decreased malondialdehyde and nitric oxide levels, increased glutathione content, and enhanced catalase activity in Aβ-injected rats. Also, messenger RNA expression of tumor necrosis factor-α, interleukin-1β, interleukin-6, nuclear factor κB, and N-methyl- d-aspartate receptor subunits 2A and 2B reduced in the hippocampus of these animals. Besides this, alpha-pinene repressed the Aβ_1-42 -induced reduction of nicotinic acetylcholine receptor α7 subunit and brain-derived neurotrophic factor expression. Treatment with alpha-pinene caused Aβ-receiving rats to spend more time in the target quadrant in the Morris water maze test and led to an increase in percentages of open arm entrance and time spent in the open arm in the elevated plus-maze test. We concluded that alpha-pinene strengthens the antioxidant system and prevents neuroinflammation in the hippocampus of rats receiving Aβ. It improves spatial learning and memory and reduces anxiety-like behavior in these animals. Consequently, alpha-pinene alleviates Aβ-induced oxidative/nitrosative stress, neuroinflammation, and behavioral deficits. It is probably a suitable candidate for the treatment of neurodegenerative diseases.

Role of the Cholinergic Anti-Inflammatory Reflex in Central Nervous System Diseases

In several central nervous system diseases, it has been reported that inflammation may be related to the etiologic process, therefore, therapeutic strategies are being implemented to control inflammation. As the nervous system and the immune system maintain close bidirectional communication in physiological and pathological conditions, the modulation of inflammation through the cholinergic anti-inflammatory reflex has been proposed. In this review, we summarized the evidence supporting chemical stimulation with cholinergic agonists and vagus nerve stimulation as therapeutic strategies in the treatment of various central nervous system pathologies, and their effect on inflammation.

Homomeric and Heteromeric α7 Nicotinic Acetylcholine Receptors in Health and Some Central Nervous System Diseases

Nicotinic acetylcholine receptors (nAChRs) are pentameric ligand-gated ion channels involved in the modulation of essential brain functions such as memory, learning, and attention. Homomeric α7 nAChR, formed exclusively by five identical α7 subunits, is involved in rapid synaptic transmission, whereas the heteromeric oligomers composed of α7 in combination with β subunits display metabotropic properties and operate in slower time frames. At the cellular level, the activation of nAChRs allows the entry of Na⁺ and Ca²⁺; the two cations depolarize the membrane and trigger diverse cellular signals, depending on the type of nAChR pentamer and neurons involved, the location of the intervening cells, and the networks of which these neuronal cells form part. These features make the α7 nAChR a central player in neurotransmission, metabolically associated Ca²⁺-mediated signaling, and modulation of diverse fundamental processes operated by other neurotransmitters in the brain. Due to its ubiquitous distribution and the multiple functions it displays in the brain, the α7 nAChR is associated with a variety of neurological and neuropsychiatric disorders whose exact etiopathogenic mechanisms are still elusive.

A role of the subdiaphragmatic vagus nerve in depression-like phenotypes in mice after fecal microbiota transplantation from Chrna7 knock-out mice with depression-like phenotypes

The α7 subtype of the nicotinic acetylcholine receptor (α7 nAChR: coded by Chrna7) regulates the cholinergic ascending anti-inflammatory pathway involved in depression. We previously reported that Chrna7 knock-out (KO) mice show depression-like phenotypes through systemic inflammation. In this study, we investigated whether fecal microbiota transplantation (FMT) from Chrna7 KO mice causes depression-like phenotypes in mice treated with an antibiotic cocktail (ABX). Chrna7 KO mice with depression-like phenotypes show an abnormal gut microbiota composition, although the alpha diversity and beta diversity were not altered. FMT from Chrna7 KO mice caused depression-like phenotypes, systemic inflammation, and downregulation of synaptic proteins in the prefrontal cortex (PFC) in the ABX-treated mice compared to FMT from the control mice. The Principal component analysis based on the OTU level showed that the FMT group from the KO mice were different from the FMT group from the control mice. We found differences in abundance for several bacteria in the FMT group from the KO mice at the taxonomic level when compared with the other group. Interestingly, subdiaphragmatic vagotomy significantly blocked the development of depression-like phenotypes in the ABX-treated mice after FMT from Chrna7 KO mice. These data suggest that FMT from Chrna7 KO mice produce depression-like phenotypes in ABX-treated mice via the subdiaphragmatic vagus nerve. The brain-gut-microbiota axis association with the subdiaphragmatic vagus nerve plays an important role in the development of depression.

The Calcium/Calmodulin-Dependent Kinases II and IV as Therapeutic Targets in Neurodegenerative and Neuropsychiatric Disorders

CaMKII and CaMKIV are calcium/calmodulin-dependent kinases playing a rudimentary role in many regulatory processes in the organism. These kinases attract increasing interest due to their involvement primarily in memory and plasticity and various cellular functions. Although CaMKII and CaMKIV are mostly recognized as the important cogs in a memory machine, little is known about their effect on mood and role in neuropsychiatric diseases etiology. Here, we aimed to review the structure and functions of CaMKII and CaMKIV, as well as how these kinases modulate the animals’ behavior to promote antidepressant-like, anxiolytic-like, and procognitive effects. The review will help in the understanding of the roles of the above kinases in the selected neurodegenerative and neuropsychiatric disorders, and this knowledge can be used in future drug design.

α7 Nicotinic Acetylcholine Receptor Agonist PNU-282987 Ameliorates Cognitive Impairment Induced by Chronic Intermittent Hypoxia

PURPOSE

Cognitive impairment is an important complication of obstructive sleep apnea (OSA). Chronic intermittent hypoxia (CIH), the main pathophysiological characteristics of OSA, is closely related to cognitive dysfunction and may be mediated by alpha-7 nicotinic acetylcholine receptors (α7nAChR). This study investigated the effects and clarified the mechanisms of α7nAChR on the cognitive function of mice with CIH.

METHODS

Thirty CD-1 mice were randomly divided into room air (RA), CIH-2 weeks (CIH2W), and CIH-4 weeks (CIH4W) groups. Cognitive function was evaluated by novel object recognition (NOR) and Morris water maze (MWM) tests after exposure. Then, 104 CD-1 mice were exposed to CIH for 4 weeks and randomly divided into four groups: CIH4W (control), with dimethyl sulfoxide (DMSO) (sham), with α7nAChR-specific agonist PNU-282987 (PNU), and with α7nAChR-specific inhibitor methyllycaconitine and PNU-282987 (MLA+PNU). In addition to the evaluation of cognitive function, apoptotic bodies in the hippocampus were detected by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining, changes in p-CREB and BDNF were detected by immunohistochemistry, while those of ERK1/2, CREB, PGC-1α, FNDC5, and BDNF were detected by Western blotting in the hippocampal tissues of the mice.

RESULTS

Compared to the CIH2W and RA groups, the CIH4W group showed cognitive dysfunction in the NOR and MWM tests. The changes in cognitive dysfunction were alleviated by PNU-282987; furthermore, MLA pretreatment offset the effect. In hippocampal tissues, TUNEL assays showed decreased apoptotic cells, immunohistochemical staining showed increased expressions of p-CREB and BDNF. The expression levels of p-ERK1/2/t-ERK1/2, p-CREB/t-CREB, PGC-1α, FNDC5, and BDNF were increased after PNU-282987 injection.

CONCLUSION

Four weeks of CIH caused cognitive dysfunction in mice. Activating α7nAChR might ameliorate this dysfunction by upregulating the ERK1/2/CREB signaling pathway; enhancing PGC-1α, FNDC5, and BDNF expression levels; and reducing cell apoptosis in the hippocampal tissue of mice.