Persistence of behaviours in the Forced Swim Test in 3xTg-AD mice at advanced stages of disease

Intranasal irbesartan reverts cognitive decline and activates the PI3K/AKT pathway in an LPS-induced neuroinflammation mice model

BACKGROUND

New strategies are urgently needed to manage and delay the development of Alzheimer's disease (AD). Neuroinflammation is a significant contributor to cognitive decline in neurodegenerative diseases, including AD. Angiotensin receptor blockers (ARBs) and angiotensin converting enzyme inhibitors (ACEIs) protect hypertensive patients against AD, but the cellular and molecular mechanisms underlying these effects remain unknown. In light of this, the protective effects of three ARBs and three ACEIs against neuroinflammation and cognitive decline were investigated through comprehensive pharmacologicalin vitro/in vivoscreening.

METHODS

BV-2 microglia cells were exposed tolipopolysaccharide (LPS) and treated with ARBs and ACEIs to provide initial insights into the anti-inflammatory properties of the drugs. Subsequently, irbesartan was selected, and its efficacy was evaluated inC57/BL6 male miceintranasally administered with irbesartan and injected with LPS. Long-term memory and depressive-like behavior were evaluated; dendritic spines were measured as well as neuroinflammation, neurodegeneration and cognitive decline biomarkers.

RESULTS

Irbesartan mitigated memory loss and depressive-like behavior in mice treated with LPS, probably because itincreased spine density, ameliorated synapsis dysfunction and activated the PI3K/AKT pathway. Irbesartan elevated the levels of hippocampalsuperoxide dismutase2 andglutathione peroxidaseandsuppressed LPS-induced astrogliosis.

CONCLUSIONS

Overall, this study provides compelling evidence that multiple intranasal administrations of irbesartan can effectively prevent LPS-induced cognitive decline by activating pathways involved in neuroprotection and anti-inflammatory events. These findings underscore the potential of irbesartan as a preventive strategy against the development of AD and other neurodegenerative conditions associated with neuroinflammation.

Role of TET1-mediated epigenetic modulation in Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder influenced by a complex interplay of environmental, epigenetic, and genetic factors. DNA methylation (5mC) and hydroxymethylation (5hmC) are DNA modifications that serve as tissue-specific and temporal regulators of gene expression. TET family enzymes dynamically regulate these epigenetic modifications in response to environmental conditions, connecting environmental factors with gene expression. Previous epigenetic studies have identified 5mC and 5hmC changes associated with AD. In this study, we performed targeted resequencing of TET1 on a cohort of early-onset AD (EOAD) and control samples. Through gene-wise burden analysis, we observed significant enrichment of rare TET1 variants associated with AD (p = 0.04). We also profiled 5hmC in human postmortem brain tissues from AD and control groups. Our analysis identified differentially hydroxymethylated regions (DhMRs) in key genes responsible for regulating the methylome: TET3, DNMT3L, DNMT3A, and MECP2. To further investigate the role of Tet1 in AD pathogenesis, we used the 5xFAD mouse model with a Tet1 KO allele to examine how Tet1 loss influences AD pathogenesis. We observed significant changes in neuropathology, 5hmC, and RNA expression associated with Tet1 loss, while the behavioral alterations were not significant. The loss of Tet1 significantly increased amyloid plaque burden in the 5xFAD mouse (p = 0.044) and lead to a non-significant trend towards exacerbated AD-associated stress response in 5xFAD mice. At the molecular level, we found significant DhMRs enriched in genes involved in pathways responsible for neuronal projection organization, dendritic spine development and organization, and myelin assembly. RNA-Seq analysis revealed a significant increase in the expression of AD-associated genes such as Mpeg1, Ctsd, and Trem2. In conclusion, our results suggest that TET enzymes, particularly TET1, which regulate the methylome, may contribute to AD pathogenesis, as the loss of TET function increases AD-associated pathology.

Depression-related phenotypes at early stages of Aβ and tau accumulation in inducible Alzheimer's disease mouse model: Task-oriented and concept-driven interpretations

Depression is highly prevalent in Alzheimer Disease (AD); however, there is paucity of studies that focus specifically on the assessment of depression-relevant phenotypes in AD mouse models. Conditional doxycycline-dependent transgenic mouse models reproducing amyloidosis (TetOffAPPsi) and/or tau (TetOffTauP301L) pathology starting at middle age (6 months) were used in this study. As AD patients can experience depressive symptoms relatively early in disease, testing was conducted at early, pre-pathology stages of Aβ and/or tau accumulation (starting from 45 days of transgenes expression). Tau-related differences were detected in the Novelty Suppressed Feeding task (NSF), whereas APP-related differences were observed predominantly in measures of the Open Field (OF) and Forced Swim tasks (FST). Effects of combined production of Aβ and tau were detected in immobility during the 1st half of the Tail Suspension task (TST). These data demonstrate that results from different tasks are difficult to reconcile using task/variable-centered interpretations in which a single task/variable is assigned an ad-hoc meaning relevant to depression. An alternative, concept-oriented, approach is based on multiple variables/tests, with an understanding of their possible inter-dependence and utilization of statistical approaches that handle correlated data sets. The existence of strong correlations within and between some of the tasks supported utilization of factor analyses (FA). FA explained a similar amount of variability across the genotypes (∼80%) and identified two factors stable across genotypes and representing motor activity and anxiety measures in OF. In contrast, variables related to FST, TST, and NSFT did not demonstrate a structure of factor loadings that would support the existence of a single integral factor of "depressive state" measured by these tasks. In addition, factor loadings varied between genotypes, indicating that genotype-specific between-task correlations need to be considered for interpretations of findings in any single task. In general, this study demonstrates that utilization of multiple tasks to characterize behavioral phenotypes, an approach that is finally gaining more widespread adoption, requires a step of data integration across different behavioral tests for appropriate interpretations.

Human PSEN1 Mutant Glia Improve Spatial Learning and Memory in Aged Mice

The PSEN1 ΔE9 mutation causes a familial form of Alzheimer's disease (AD) by shifting the processing of amyloid precursor protein (APP) towards the generation of highly amyloidogenic Aβ42 peptide. We have previously shown that the PSEN1 ΔE9 mutation in human-induced pluripotent stem cell (iPSC)-derived astrocytes increases Aβ42 production and impairs cellular responses. Here, we injected PSEN1 ΔE9 mutant astrosphere-derived glial progenitors into newborn mice and investigated mouse behavior at the ages of 8, 12, and 16 months. While we did not find significant behavioral changes in younger mice, spatial learning and memory were paradoxically improved in 16-month-old PSEN1 ΔE9 glia-transplanted male mice as compared to age-matched isogenic control-transplanted animals. Memory improvement was associated with lower levels of soluble, but not insoluble, human Aβ42 in the mouse brain. We also found a decreased engraftment of PSEN1 ΔE9 mutant cells in the cingulate cortex and significant transcriptional changes in both human and mouse genes in the hippocampus, including the extracellular matrix-related genes. Overall, the presence of PSEN1 ΔE9 mutant glia exerted a more beneficial effect on aged mouse brain than the isogenic control human cells likely as a combination of several factors.

Investigation of Anxiety- and Depressive-like Symptoms in 4- and 8-Month-Old Male Triple Transgenic Mouse Models of Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the most common form of dementia. Approximately 50% of AD patients show anxiety and depressive symptoms, which may contribute to cognitive decline. We aimed to investigate whether the triple-transgenic mouse (3xTg-AD) is a good preclinical model of this co-morbidity. The characteristic histological hallmarks are known to appear around 6-month; thus, 4- and 8-month-old male mice were compared with age-matched controls. A behavioral test battery was used to examine anxiety- (open field (OF), elevated plus maze, light-dark box, novelty suppressed feeding, and social interaction (SI) tests), and depression-like symptoms (forced swim test, tail suspension test, sucrose preference test, splash test, and learned helplessness) as well as the cognitive decline (Morris water maze (MWM) and social discrimination (SD) tests). Acetylcholinesterase histochemistry visualized cholinergic fibers in the cortex. Dexamethasone-test evaluated the glucocorticoid non-suppression. In the MWM, the 3xTg-AD mice found the platform later than controls in the 8-month-old cohort. The SD abilities of the 3xTg-AD mice were missing at both ages. In OF, both age groups of 3xTg-AD mice moved significantly less than the controls. During SI, 8-month-old 3xTg-AD animals spent less time with friendly social behavior than the controls. In the splash test, 3xTg-AD mice groomed themselves significantly less than controls of both ages. Cortical fiber density was lower in 8-month-old 3xTg-AD mice compared to the control. Dexamethasone non-suppression was detectable in the 4-month-old group. All in all, some anxiety- and depressive-like symptoms were present in 3xTg-AD mice. Although this strain was not generally more anxious or depressed, some aspects of comorbidity might be studied in selected tests, which may help to develop new possible treatments.

Sex-Dependent Signatures, Time Frames and Longitudinal Fine-Tuning of the Marble Burying Test in Normal and AD-Pathological Aging Mice

The marble burying (MB) test, a classical test based on the natural tendency of rodents to dig in diverse substrates and to bury small objects, is sensitive to some intrinsic and extrinsic factors. Here, under emerging neuroethological quantitative and qualitative analysis, the MB performance of 12-month-old male and female 3xTg-AD mice for Alzheimer’s disease and age-matched counterparts of gold-standard C57BL6 strain with normal aging unveiled sex-dependent signatures. In addition, three temporal analyses, through the (1) time course of the performance, and (2) a repeated test schedule, identified the optimal time frames and schedules to detect sex- and genotype-dependent differences. Besides, a (3) longitudinal design from 12 to 16 months of age monitored the changes in the performance with aging, worsening in AD-mice, and modulation through the repeated test. In summary, the present results allow us to conclude that (1) the marble burying test is responsive to genotype, sex, aging, and its interactions; (2) the male sex was more sensitive to showing the AD-phenotype; (3) longitudinal assessment shows a reduction in females with AD pathology; (4) burying remains stable in repeated testing; (5) the time-course of marbles burying is useful; and (6) burying behavior most likely represents perseverative and/or stereotyped-like behavior rather than anxiety-like behavior in 3xTg-AD mice.

Survival Bias and Crosstalk between Chronological and Behavioral Age: Age- and Genotype-Sensitivity Tests Define Behavioral Signatures in Middle-Aged, Old, and Long-Lived Mice with Normal and AD-Associated Aging

New evidence refers to a high degree of heterogeneity in normal but also Alzheimer's disease (AD) clinical and temporal patterns, increased mortality, and the need to find specific end-of-life prognosticators. This heterogeneity is scarcely explored in very old male AD mice models due to their reduced survival. In the present work, using 915 (432 APP23 and 483 C57BL/6 littermates) mice, we confirmed the better survival curves in male than female APP23 mice and respective wildtypes, providing the chance to characterize behavioral signatures in middle-aged, old, and long-lived male animals. The sensitivity of a battery of seven paradigms for comprehensive screening of motor (activity and gait analysis), neuropsychiatric and cognitive symptoms was analyzed using a cohort of 56 animals, composed of 12-, 18- and 24-month-old male APP23 mice and wildtype littermates. Most variables analyzed detected age-related differences. However, variables related to coping with stress, thigmotaxis, frailty, gait, and poor cognition better discriminated the behavioral phenotype of male APP23 mice through the three old ages compared with controls. Most importantly, non-linear age- and genotype-dependent behavioral signatures were found in long-lived animals, suggesting crosstalk between chronological and biological/behavioral ages useful to study underlying mechanisms and distinct compensations through physiological and AD-associated aging.

Indexes for flotation and circling, two non-search behaviors in the water maze, sensitive to d-galactose-induced accelerated aging and Alzheimer's disease

The study of behavioral and psychological symptoms of dementia (BPSD) has been largely neglected in most experimental research on Alzheimer's disease (AD) classically focused on cognitive symptoms. The aquatic environment of the Morris water maze (MWM) implies a stressful condition for mice leading to cognitive performances with presence of other behaviors related to emotionality. This can be critical in models such as the 3xTg-AD mice that exhibit a noticeable BPSD-like profile. The present work is aimed to provide a quantitative (number of episodes and duration) and qualitative (prevalence) analysis of flotation and circling, the most common 'non-searching behaviors' elicited in the MWM. We studied the expression of these behaviors in 6-month-old gold-standard wildtype C57BL/6 mice (genetic background) and 3xTg-AD mice (onset of disease) and when both genotypes were submitted to chronic d-galactose induced accelerated aging. Elicitation of floating and circling was recorded during three standard MWM paradigms: visual perceptual learning, place task for spatial reference memory and a final probe trial for short-term memory. In view of the results, we demonstrate that the index of 'flotation', characteristic of non-transgenic performance, is sensitive (reduction) to accelerated aging and AD. Conversely, circling behavior, characteristic of 3xTg-AD mice, can be an additional tool for evaluating BPSD-like symptoms in AD-models while its index unveils bizarre behavior induced by d-galactose induced aging. These results can be useful in relation to preventive and/or therapeutical interventions targeting AD but they may also be suitable in the evaluation of the potential risk factors in animals with normal aging.

Comorbid sensorimotor and emotional profiles in the forced swim test immobility and predictive value of a single assay in very old female mice

The increase of prevalence of mental health problems in the elderly due to the aging of the population becomes an outstanding issue since in most individuals it happens in an already complex multimorbid scenario that may include frailty and age-related medical conditions. Depression, soon the major cause of global disease burden, can be found as an age-related comorbidity and frailty, or as part of neurodegenerative diseases and where females are more vulnerable to it. Thought the multifactorial aetiology and heterogeneous nature of depression render it difficult to be modelled in animals, active behaviours elicited in the Forced Swimming Test (FST) are used to screen antidepressant treatments. However, interpretation of immobility remains controversial. The present work addressed this issue in very-old (21 months) female C57bl/6 × 129 mice, also with the concern that a '6 minutes × 2 days' protocol can result demanding for a very-old animal and confounding factors may also arise. Animals were behaviourally assessed for sensorimotor functions, emotionality and anxiety-like behaviours, novelty seeking, and immobility in a 2-days FST. The predictive value of the first day evidenced that one single assay as sufficient for the assessment of immobility, and that the repeated test did not increase the immobility response. Moreover, sensorimotor tasks, neophobia in the corner test and emotional behaviour in the dark-light box correlated with FST immobility, contributing to the response. The results support the concern of geroscience on the relevance of using aged animals but also aware about taking into account the complexity of their comorbid scenario.

Long-term Treatment with Low-Dose Caffeine Worsens BPSD-Like Profile in 3xTg-AD Mice Model of Alzheimer's Disease and Affects Mice with Normal Aging

Coffee or caffeine has recently been suggested as prophylaxis for dementia. Although memory problems are hallmarks of Alzheimer's disease, this dementia is also characterized by neuropsychiatric symptoms called Behavioral and Psychological Symptoms of Dementia (BPSD). The impact of preventive/therapeutic strategies on both cognitive and non-cognitive symptoms can be addressed in the 3xTg-AD mice, since they exhibit cognitive but also BPSD-like profiles. Here, we studied the long-term effects of a low dose of caffeine in male 3xTg-AD mice and as compared to age-matched non-transgenic (NTg) counterparts with normal aging. Animals were treated (water or caffeine in drinking water) from adulthood (6 months of age) until middle-aged (13 months of age), that in 3xTg-AD mice correspond to onset of cognitive impairment and advanced stages, respectively. The low caffeine dosing used (0.3 mg/ml) was previously found to give a plasma concentration profile in mice roughly equivalent to that of a human coffee drinker. There were significant effects of caffeine on most behavioral variables, especially those related to neophobia and other anxiety-like behaviors, emotionality, and cognitive flexibility. The 3xTg-AD and NTg mice were differently influenced by caffeine. Overall, the increase of neophobia and other anxiety-related behaviors resulted in an exacerbation of BPSD-like profile in 3xTg-AD mice. Learning and memory, strongly influenced by anxiety in 3xTg-AD mice, got little benefit from caffeine, only shown after a detailed analysis of navigation strategies. The worsened pattern in NTg mice and the use of search strategies in 3xTg-AD mice make both groups more similar. Circadian motor activity showed genotype differences, which were found to be enhanced by caffeine. Selective effects of caffeine on NTg were found in the modulation of behaviors related to emotional profile and risk assessment. Caffeine normalized splenomegaly of 3xTg-AD mice, a physical indicator of their impaired peripheral immune system, and trended to increase their corticosterone levels. Our observations of adverse caffeine effects in an Alzheimer's disease model together with previous clinical observations suggest that an exacerbation of BPSD-like symptoms may partly interfere with the beneficial cognitive effects of caffeine. These results are relevant when coffee-derived new potential treatments for dementia are to be devised and tested.

Behavioural Effects of Adult Vitamin D Deficiency in BALB/c Mice Are not Associated with Proliferation or Survival of Neurons in the Adult Hippocampus

Epidemiological studies have shown that up to one third of adults have insufficient levels of vitamin D and there is an association between low vitamin D concentrations and adverse brain outcomes, such as depression. Vitamin D has been shown to be involved in processes associated with neurogenesis during development. Therefore, the aim of this study was to test the hypothesis that adult vitamin D (AVD) deficiency in BALB/c mice was associated with (a) adult hippocampal neurogenesis at baseline, b) following 6 weeks of voluntary wheel running and (c) a depressive-like phenotype on the forced swim test (FST), which may be linked to alterations in hippocampal neurogenesis. We assessed proliferation and survival of adult born hippocampal neurons by counting the number of cells positive for Ki67 and doublecortin (DCX), and incorporation of 5-Bromo-2’-Deoxyuridine (BrdU) within newly born mature neurons using immunohistochemistry. There were no significant effects of diet on number of Ki67⁺, DCX⁺ or BrdU⁺ cells in the dentate gyrus. All mice showed significantly increased number of Ki67⁺ cells and BrdU incorporation, and decreased immobility time in the FST, after voluntary wheel running. A significant correlation was found in control mice between immobility time in the FST and level of hippocampal neurogenesis, however, no such correlation was found for AVD-deficient mice. We conclude that AVD deficiency was not associated with impaired proliferation or survival of adult born neurons in BALB/c mice and that the impact on rodent behaviour may not be due to altered neurogenesis per se, but to altered function of new hippocampal neurons or processes independent of adult neurogenesis.

Early postnatal handling and environmental enrichment improve the behavioral responses of 17-month-old 3xTg-AD and non-transgenic mice in the Forced Swim Test in a gender-dependent manner

Forced Swimming Test (FST) models behavioural despair in animals by loss of motivation to respond or the refusal to escape. The present study was aimed at characterizing genetic (genotype and gender) and environmental factors (age/stage of disease and rearing conditions: C, standard; H, early postnatal handling; EE, environmental enrichment consisting in physical exercise as well as social and object enrichment) that may modulate the poor behavioural and cognitive flexibility response we have recently described in 12-month-old male 3xTg-AD mice in the FST. The comprehensive analysis of the ethogram shown in the FST considered the intervals of the test (0-2 and 2-6min), all the elicited behavioural responses (immobility, swimming and climbing) and their features (total duration and frequency of episodes). The long persistence of behaviours found in 17-month-old (late-stages of disease) 3xTg-AD mice was comparable to that recently described in males at 12 months of age (beginning of advanced stages) but also suggested increased age-dependent frailty in both genotypes. The poor behavioral flexibility of 3xTg-AD mice to elicit the behavioural despair shown by the NTg mice, was also found in the female gender. Finally, the present work demonstrates that early-life interventions were able to improve the time and frequency of episodes of immobility, being more evident in the female gender of both old NTg and 3xTg-AD mice. Ontogenic modulation by early-postnatal handling resulted in a more effective long-term improvement of the elicited behaviours in the FST than that achieved by environmental enrichment. The results talk in favor of the beneficence of early-life interventions on ageing in both healthy and disease conditions.