Behavioural effects of PNU-282987 and stress in an animal model of Alzheimer's disease

Life Experience Matters: Enrichment and Stress Can Influence the Likelihood of Developing Alzheimer's Disease via Gut Microbiome

Alzheimer's disease (AD) is a chronic neurodegenerative disease, characterized by the presence of β-amyloid (Aβ) plaques and neurofibrillary tangles (NFTs) formed from abnormally phosphorylated tau proteins (ptau). To date, there is no cure for AD. Earlier therapeutic efforts have focused on the clinical stages of AD. Despite paramount efforts and costs, pharmaceutical interventions including antibody therapies targeting Aβ have largely failed. This highlights the need to alternate treatment strategies and a shift of focus to early pre-clinical stages. Approximately 25-40% of AD cases can be attributed to environmental factors including chronic stress. Gut dysbiosis has been associated with stress and the pathogenesis of AD and can increase both Aβ and NFTs in animal models of the disease. Both stress and enrichment have been shown to alter AD progression and gut health. Targeting stress-induced gut dysbiosis through probiotic supplementation could provide a promising intervention to delay disease progression. In this review, we discuss the effects of stress, enrichment, and gut dysbiosis in AD models and the promising evidence from probiotic intervention studies.

G-Protein-Coupled Receptors in CNS: A Potential Therapeutic Target for Intervention in Neurodegenerative Disorders and Associated Cognitive Deficits

Neurodegenerative diseases are a large group of neurological disorders with diverse etiological and pathological phenomena. However, current therapeutics rely mostly on symptomatic relief while failing to target the underlying disease pathobiology. G-protein-coupled receptors (GPCRs) are one of the most frequently targeted receptors for developing novel therapeutics for central nervous system (CNS) disorders. Many currently available antipsychotic therapeutics also act as either antagonists or agonists of different GPCRs. Therefore, GPCR-based drug development is spreading widely to regulate neurodegeneration and associated cognitive deficits through the modulation of canonical and noncanonical signals. Here, GPCRs’ role in the pathophysiology of different neurodegenerative disease progressions and cognitive deficits has been highlighted, and an emphasis has been placed on the current pharmacological developments with GPCRs to provide an insight into a potential therapeutic target in the treatment of neurodegeneration.

Positive Allosteric Modulation of Alpha7 Nicotinic Acetylcholine Receptors Transiently Improves Memory but Aggravates Inflammation in LPS-Treated Mice

Neuroinflammation accompanies or even precedes the development of cognitive changes in many brain pathologies, including Alzheimer’s disease. Therefore, dampening inflammatory reactions within the brain is a promising strategy for supporting cognitive functions in elderly people and for preventing the development of neurodegenerative disorders. Nicotinic acetylcholine receptors containing α7 subunits (α7 nAChRs) are involved in regulating cell survival, inflammation, and memory. The aim of our study was to evaluate the efficiency of α7-specific therapy at different stages of inflammation and to compare the effects of orthosteric agonist PNU282987 and type 2 positive allosteric modulator (PAM) PNU120596 in mice after a single injection of lipopolysaccharide (LPS). The data presented demonstrate that PNU282987 protected mice from LPS-induced impairment of episodic memory by decreasing IL-6 levels in the blood, stabilizing the brain mitochondria and up-regulating the brain α7-, α3-, and α4-containing nAChRs. Such treatment was efficient when given simultaneously with LPS or a week after LPS injection and was not efficient if LPS had been injected 2 months before. PNU120596 also decreased IL-6, stabilized mitochondria and up-regulated the brain nAChRs. However, its memory-improving effect was transient and disappeared after the end of the injection cycle. Moreover, cessation of PNU120596 treatment resulted in a sharp increase in IL-1β and IL-6 levels in the blood. It is concluded that activating α7 nAChRs protects the mouse brain from the pathogenic effect of LPS in the early stages of inflammation but is not efficient when irreversible changes have already occurred. The use of a PAM does not improve the effect of the agonist, possibly potentiates the effect of endogenous agonists, and results in undesirable effects after treatment cessation.

Activation of Nicotinic Acetylcholine α7 Receptor Attenuates Progression of Monocrotaline-Induced Pulmonary Hypertension in Rats by Downregulating the NLRP3 Inflammasome

Background: Inflammation and altered immunity contribute to the development of pulmonary arterial hypertension (PH). The alpha 7 nicotinic acetylcholine receptor (α7nAChR) possesses anti-inflammatory activities. The current study was performed to investigate the effects of a selective α7nAChR agonist, PNU-282987, on controlling a monocrotaline (MCT)-induced rat model of PH and explored the underlying mechanisms.

Methods: Sprague-Dawley rats were injected with MCT and treated with PNU-282987 at the prevention (starting 1 week before MCT) and treatment (starting 2 weeks after MCT) settings. Four weeks after MCT injection, hemodynamic changes, right ventricular structure, and lung morphological features were assessed. Enzyme-linked immunosorbent assay, Western blot and qRT-PCR were performed to assess levels of inflammatory cytokines and NLRP3 (Nod-like receptor family pyrin domain-containing 3) inflammasome pathway in the rat lung tissues. In addition, the lung macrophage line NR8383 was used to confirm the in vivo data.

Results: Monocrotaline injection produced PH in rats and downregulated α7nAChR mRNA and protein expression in rat lung tissues compared to sham controls. Pharmacological activation of α7nAChR by PNU-282987 therapy improved the rat survival rate, attenuated the development of PH as assessed by remodeling of pulmonary arterioles, reduced the right ventricular (RV) systolic pressure, and ameliorated the hypertrophy and fibrosis of the RV in rats with MCT-induced PH. The expression of TNF-α, IL-6, IL-1β, and IL-18 were downregulated in rat lung tissues, which implied that PNU-282987 therapy may help regulate inflammation. These protective effects involved the inhibition of the NLRP3 inflammasome. In vitro assays of cultured rat lung macrophages confirmed that the anti-inflammation effect of PNU-282987 therapy may contribute to the disturbance of NLRP3 inflammasome activation.

Conclusion: Targeting α7nAChR with PNU-282987 could effectively prevent and treat PH with benefits for preventing ongoing inflammation in the lungs of rats with MCT-induced PH by inhibiting NLRP3 inflammasome activation.

Nicotinic acetylcholine receptor α7 subunit improves energy homeostasis and inhibits inflammation in nonalcoholic fatty liver disease

OBJECTIVE

Nonalcoholic fatty liver disease (NAFLD) is one of the most common liver diseases worldwide; yet, the pathogenesis of the disorder is not completely understood. The nicotinic acetylcholine receptor α7 subunit (α7nAChR) plays an indispensable role in the vagus nerve-regulated cholinergic anti-inflammatory pathway.

METHODS

In the present study, we investigated the key role of α7nAChR in NAFLD development. Male wild-type (WT) and α7nAChR knockout (α7nAChR^-/-) mice were fed a normal chow or a high-fat diet (HFD) for 16weeks to induce NAFLD.

RESULTS

We found that both the mRNA and protein levels of α7nAChR in the liver tissue of NAFLD mice were significantly higher than those in mice fed normal chow. There were no differences in food intake, body weight, hepatic cholesterol and triglyceride contents, and insulin sensitivity between WT and α7nAChR^-/- mice under normal condition. When the WT and α7nAChR^-/- mice were challenged with HFD, the body weight of α7nAChR^-/- mice became higher than that of WT mice. The oxygen consumption and energy expenditure in HFD-fed α7nAChR^-/- mice were significantly lower than that in HFD-fed WT mice. The HFD-fed α7nAChR^-/- mice also showed more aggravated hepatic lipid accumulation, steatosis and oxidative stress than HFD-fed WT mice. Macrophage infiltration; mRNA levels of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and IL-1β; and liver fibrosis were significantly accelerated in HFD-fed α7nAChR^-/- mice compared to that in HFD-fed WT mice. In addition, the bolus insulin injection-activated insulin signaling pathway, which was reflected by the phosphorylation of insulin receptor at Tyr1162/Tyr1163 site (p-IR^{Tyr1162/Tyr1163}), insulin receptor substrate-1 at Tyr612 site (p-IRS-1^Tyr612) and Akt at Ser473 (p-Akt^Ser473), was significantly compromised in liver tissues of HFD-fed α7nAChR^-/- mice relative to HFD-fed WT mice. Finally, pharmacologically activation of α7nAChR in HFD-fed mice, with a selective agonist PNU-282987, remarkably ameliorated the hepatic steatosis, inflammatory cell infiltration and fibrosis.

CONCLUSION

In conclusion, our results demonstrate that activation of α7nAChR improves energy homeostasis and inhibits inflammation in nonalcoholic fatty liver disease.

Therapeutic potential of α7 nicotinic receptor agonists to regulate neuroinflammation in neurodegenerative diseases

Neurodegenerative diseases, such as Alzheimer's, Parkinson's and Huntington's diseases, are all characterized by a component of innate immunity called neuroinflammation. Neuronal loss and neuroinflammation are two phenomena closely linked. Hence, the neuroinflammation is a relevant target for the management of the neurodegenerative diseases given that, to date, there is no treatment to stop neuronal loss. Several studies have investigated the potential effects of activators of alpha 7 nicotinic acetylcholine receptors in animal models of neurodegenerative diseases. These receptors are widely distributed in the central nervous system. After activation, they seem to mediate the cholinergic anti-inflammatory pathway in the brain. This anti-inflammatory pathway, first described in periphery, regulates activation of microglial cells considered as the resident macrophage population of the central nervous system. In this article, we shortly review the agonists of the alpha 7 nicotinic acetylcholine receptors that have been evaluated in vivo and we focused on the selective positive allosteric modulators of these receptors. These compounds represent a key element to enhance receptor activity only in the presence of the endogenous agonist.