Role of Kalirin and mouse strain in retention of spatial memory training in an Alzheimer's disease model mouse line

Spatiotemporal development of the neuronal accumulation of amyloid precursor protein and the amyloid plaque formation in the brain of 3xTg-AD mice

The amyloid plaque is a hallmark of Alzheimer's disease. The accumulation of the amyloid precursor protein (APP) in the neuronal structure is assumed to lead to amyloid plaque formation through the excessive production of β-amyloid protein. To study the relationship between the neuronal accumulation of APP and amyloid plaque formation, we histologically analyzed their development in the different brain regions in 3xTg-AD mice, which express Swedish mutated APP (APPSWE) in the neurons. Observation throughout the brain revealed APPSWE-positive somata in the broad regions. Quantitative model analysis showed that the somatic accumulation of APPSWE developed firstly in the hippocampus from a very early age (<1 month) and proceeded slower in the isocortex. In line with this, the hippocampus was the first region to form amyloid plaques at the age of 9-12 months, while amyloid plaques were rarely observed in the isocortex. Females had more APPSWE-positive somata and plaques than males. Furthermore, amyloid plaques were observed in the lateral septum and pontine grey, which did not contain APPSWE-positive somata but only the APPSWE-positive fibers. These results suggested that neuronal accumulation of APPSWE, both in somatodendritic and axonal domains, is closely related to the formation of amyloid plaques.

Nervonic acid reduces the cognitive and neurological disturbances induced by combined doses of D-galactose/AlCl3 in mice

Nervonic acid (NA) is a kind of ultra-long-chain monounsaturated fatty acid, which can repair nerve cell damage caused by oxidative stress. Alzheimer's disease (AD) is a nervous system disease and often accompanied by the decline of learning and memory capacity. In this study, the combined dose of D-galactose/AlCl3 was used to establish a mouse model of AD. Meanwhile, the mice were treated with different doses of NA (10.95 and 43.93 mg/kg). The results showed that NA delayed the decline of locomotion and learning ability caused by D-galactose/AlCl3, increased the activity of total superoxide dismutase, catalase, glutathione peroxidase, and reduced the content of malondialdehyde in vivo. Besides, NA reduced the levels of interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), aspartate aminotransferase, alanine aminotransferase, increased the levels of 5-hydroxytryptamine, dopamine, γ-aminobutyric acid, alleviated the cell morphology damage induced by D-galactose/AlCl3 in hippocampus and liver tissue. Furthermore, the intervention of NA upregulated the expression levels of PI3K, AKT, and mTOR genes and downregulated the expression levels of TNF-α, IL-6, and IL-1β genes. Therefore, we speculate the intervention of NA could be an effective way in improving cognitive impairment through the activation of PI3K signaling pathway. These results suggest that NA has the potential to be developed as antioxidant drug for the prevention and early therapy of AD.

Kalirin is involved in epileptogenesis by modulating the activity of the Rac1 signaling pathway

BACKGROUND AND OBJECTIVE

Epilepsy is a common chronic brain disease. Despite the availability of various anti-seizure drugs, approximately 30 % of patients do not respond to treatment. Recent research suggests that Kalirin plays a role in regulating neurological function. However, the pathogenesis of Kalirin in epileptic seizures remains unclear. This study aims to investigate the role and mechanism of Kalirin in epileptogenesis.

MATERIALS AND METHODS

An epileptic model was induced by intraperitoneal injection of pentylenetetrazole (PTZ). Endogenous Kalirin was inhibited using shRNA. The expression of Kalirin, Rac1, and Cdc42 in the hippocampal CA1 region was measured using Western blotting. Spine and synaptic structures were examined using Golgi staining and electron microscopy. Moreover, the necrotic neurons in CA1 were examined using HE staining.

RESULTS

The results indicated that the epileptic score increased in epileptic animals, while inhibition of Kalirin decreased the epileptic scores and increased the latent period of the first seizure attack. Inhibition of Kalirin attenuated the increases in Rac1 expression, dendritic spine density, and synaptic vesicle number in the CA1 region induced by PTZ. However, the increase in Cdc42 expression was not affected by the inhibition of Kalirin.

CONCLUSION

This study suggests that Kalirin is involved in the development of seizures by modulating the activity of Rac1, providing a novel anti-epileptic target.

The Labyrinthine Landscape of APP Processing: State of the Art and Possible Novel Soluble APP-Related Molecular Players in Traumatic Brain Injury and Neurodegeneration

Amyloid Precursor Protein (APP) and its cleavage processes have been widely investigated in the past, in particular in the context of Alzheimer’s Disease (AD). Evidence of an increased expression of APP and its amyloidogenic-related cleavage enzymes, β-secretase 1 (BACE1) and γ-secretase, at the hit axon terminals following Traumatic Brain Injury (TBI), firstly suggested a correlation between TBI and AD. Indeed, mild and severe TBI have been recognised as influential risk factors for different neurodegenerative diseases, including AD. In the present work, we describe the state of the art of APP proteolytic processing, underlining the different roles of its cleavage fragments in both physiological and pathological contexts. Considering the neuroprotective role of the soluble APP alpha (sAPPα) fragment, we hypothesised that sAPPα could modulate the expression of genes of interest for AD and TBI. Hence, we present preliminary experiments addressing sAPPα-mediated regulation of BACE1, Isthmin 2 (ISM2), Tetraspanin-3 (TSPAN3) and the Vascular Endothelial Growth Factor (VEGFA), each discussed from a biological and pharmacological point of view in AD and TBI. We finally propose a neuroprotective interaction network, in which the Receptor for Activated C Kinase 1 (RACK1) and the signalling cascade of PKCβII/nELAV/VEGF play hub roles, suggesting that vasculogenic-targeting therapies could be a feasible approach for vascular-related brain injuries typical of AD and TBI.

Klotho Regulated by Estrogen Plays a Key Role in Sex Differences in Stress Resilience in Rats

Klotho (KL) is a glycosyl hydrolase and aging-suppressor gene. Stress is a risk factor for depression and anxiety, which are highly comorbid with each other. The aim of this study is to determine whether KL is regulated by estrogen and plays an important role in sex differences in stress resilience. Our results showed that KL is regulated by estrogen in rat hippocampal neurons in vivo and in vitro and is essential for the estrogen-mediated increase in the number of presynaptic vesicular glutamate transporter 1 (Vglut1)-positive clusters on the dendrites of hippocampal neurons. The role of KL in sex differences in stress response was examined in rats using 3-week chronic unpredictable mild stress (CUMS). CUMS produced a deficit in spatial learning and memory, anhedonic-like behaviors, and anxiety-like behaviors in male but not female rats, which was accompanied by a reduction in KL protein levels in the hippocampus of male but not female rats. This demonstrated the resilience of female rats to CUMS. Interestingly, the knockdown of KL protein levels in the rat hippocampus of both sexes caused a decrease in stress resilience in both sexes, especially in female rats. These results suggest that the regulation of KL by estrogen plays an important role in estrogen-mediated synapse formation and that KL plays a critical role in the sex differences in cognitive deficit, anhedonic-like behaviors, and anxiety-like behaviors induced by chronic stress in rats, highlighting an important role of KL in sex differences in stress resilience.

Adiponectin Ameliorates Cognitive Behaviors and in vivo Synaptic Plasticity Impairments in 3xTg-AD Mice

BACKGROUND

Cognitive deficit is mainly clinical characteristic of Alzheimer's disease (AD). Recent reports showed adiponectin and its analogues could reverse cognitive impairments, lower amyloid-β protein (Aβ) deposition, and exert anti-inflammatory effects in different APP/PS1 AD model mice mainly exhibiting amyloid plaque pathology. However, the potential in vivo electrophysiological mechanism of adiponectin protecting against cognitive deficits in AD and the neuroprotective effects of adiponectin on 3xTg-AD mice including both plaque and tangle pathology are still unclear.

OBJECTIVE

To observe the effects of adiponectin treatment on cognitive deficits in 3xTg-AD mice, investigate its potential in vivo electrophysiological mechanism, and testify its anti-inflammatory effects.

METHODS

Barnes maze test, Morris water maze test, and fear conditioning test were used to evaluate the memory-ameliorating effects of adiponectin on 3xTg-AD mice. In vivo hippocampal electrophysiological recording was used to observe the change of basic synaptic transmission, long-term potentiation, and long-term depression. Immunohistochemistry staining and western blot were used to observe the activation of microglia and astroglia, and the expression levels of proinflammatory factors and anti-inflammtory factor IL-10.

RESULTS

Adiponectin treatment could alleviate spatial memory and conditioned fear memory deficits observed in 3xTg-AD mice, improve in vivo LTP depression and LTD facilitation, inhibit overactivation of microglia and astroglia, decrease the expression of proinflammatory factors NF- κB and IL-1β, and increase the expression level of IL-10 in the hippocampus of 3xTg-AD mice.

CONCLUSION

Adiponectin could ameliorate cognitive deficits in 3xTg-AD mice through improving in vivo synaptic plasticity impairments and alleviating neuroinflammation in the hippocampus of 3xTg-AD mice.

Multiple roles for peptidylglycine α-amidating monooxygenase in the response to hypoxia

The biosynthesis of many of the peptides involved in homeostatic control requires peptidylglycine α-amidating monooxygenase (PAM), an ancient, highly conserved copper- and ascorbate-dependent enzyme. Using the production of amidated chromogranin A to monitor PAM function in tumor cells, physiologically relevant levels of hypoxia were shown to inhibit this monooxygenase. The ability of primary pituitary cells exposed to hypoxic conditions for 4 h to produce amidated chromogranin A was similarly inhibited. The affinity of the purified monooxygenase for oxygen (K_m  = 99 ± 19 μM) was consistent with this result. The ability of PAM to alter secretory pathway behavior under normoxic conditions required its monooxygenase activity. Under normoxic conditions, hypoxia-inducible factor 1a levels in dense cultures of corticotrope tumor cells expressing high levels of PAM exceeded those in control cells; expression of inactive monooxygenase did not have this effect. The effects of hypoxia on levels of two PAM-regulated genes (activating transcription factor 3 [Atf3] and FK506 binding protein 2 [Fkbp2]) differed in cells expressing high versus low levels of PAM. Putative hypoxia response elements occur in both human and mouse PAM, and hPAM has consistently been identified as one of the genes upregulated in response to hypoxia. Expression of PAM is also known to alter gene expression. A quarter of the genes consistently upregulated in response to hypoxia were downregulated following increased expression of PAM. Taken together, our data suggest roles for PAM and amidated peptide secretion in the coordination of tissue-specific responses to hypoxia.

Sexual Dimorphism in the 3xTg-AD Mouse Model and Its Impact on Pre-Clinical Research

Female sex is a leading risk factor for developing Alzheimer’s disease (AD). Sexual dimorphism in AD is gaining attention as clinical data show that women are not only more likely to develop AD but also to experience worse pathology and faster cognitive decline. Pre-clinical AD research in animal models often neglects to address sexual dimorphism in evaluation of behavioral or molecular characteristics and outcomes. This can compromise its translation to a clinical setting. The triple-transgenic AD mouse model (3xTg-AD) is a commonly used but unique AD model because it exhibits both amyloid and tau pathology, essential features of the human AD phenotype. Mounting evidence has revealed important sexually dimorphic characteristics of this animal model that have yet to be reviewed and thus, are often overlooked in studies using the 3xTg-AD model. In this review we conduct a thorough analysis of reports of sexual dimorphism in the 3xTg-AD model including findings of molecular, behavioral, and longevity-related sex differences in original research articles through August 2020. Importantly, we find results to be inconsistent, and that strain source and differing methodologies are major contributors to lack of consensus regarding traits of each sex. We first touch on the nature of sexual dimorphism in clinical AD, followed by a brief summary of sexual dimorphism in other major AD murine models before discussing the 3xTg-AD model in depth. We conclude by offering four suggestions to help unify pre-clinical mouse model AD research inspired by the NIH expectations for considering sex as a biological variable.