Translational Modeling of Psychomotor Function in Normal and AD-Pathological Aging With Special Concerns on the Effects of Social Isolation

Phenotypical, Behavioral, and Systemic Hallmarks in End-Point Mouse Scenarios

The state of frailty is a clinical-biological syndrome that affects the older population with a higher risk of functional dependence. Animal models can provide a tool to study this complex scenario. In the present work, we analyzed the physical and behavioral hallmarks of end-point status in 16-month-old mice (C57BL/6J) according to animal welfare regulations compared to age-matched counterparts with normal aging. A group of 6-month-old mice was added to control for age bias. First, we identified 'structural kyphosis' (visible and unmodifiable deformation in locomotion) correlated with piloerection as the hallmarks of the physical frailty phenotype compared to the 'postural kyphosis' (adjustment to counteract increased visceral volume but attenuated during locomotion) of old mice with normal aging. Alopecia (barbering) was presented in both old groups. Normal levels of exploratory activity in the corner test for neophobia and triceps surae muscle weight but an increased latency of rearing indicated the poorest emotional phenotype, with a possible contribution of structural kyphosis. The presence of hepatomegaly and splenomegaly counteracted the significant WAT loss commonly associated with end-of-life traits, which should have a normal body weight but preserved muscle mass.

Clasping, ledge-score coordination and early gait impairments as primary behavioural markers of functional impairment in Alzheimer's disease

Motor performance facilitates the understanding of the functional state related to the progression of Alzheimer's disease (AD). At the translational level, this brief report refines the characterization of the motor dysfunction of the 3xTg-AD mouse model in different motor tasks, focusing on the abnormal clasping reflex and coordination impairments measured through the Phenotype Scoring System four items screening originally developed for models of ataxia. We studied male 3xTg-AD mice at 6, 12, and 16 months of age (mimicking the early, advanced, and late stages of the disease, respectively) and their age-matched non-transgenic counterparts with normal aging. According to the score, incidence, or severity of the four items and the total score, the 3xTg-AD mice showed deficiencies in all score elements. Clasping was increased independently of age, and its severity worsened with repeated testing. In contrast, the impairment of coordination worsened with the progress of the disease. The gait score was sensitive to genotype since early stages, and the worse ledge score was evident at 16 months. Kyphosis and ledge scores were sensitive to age. The impairments and functional limitations of male 3xTg-AD mice related to the stages of AD provide a scenario that allows understanding the heterogeneity of non-cognitive symptoms.

Abnormal whisker movements in the 3xTg-AD mouse model of Alzheimer's disease

Alzheimer's disease is the most frequent form of dementia in elderly people. The triple transgenic (3xTg-AD) mouse model of Alzheimer's Disease is important in biomedical research as these mice develop both neuropathological and behavioural phenotypes. However, their behavioural phenotype is variable, with findings depending on the specific task, as well as the age and sex of the mice. Whisker movements show motor, sensory and cognitive deficits in mouse models of neurodegenerative disease. Therefore, we examined whisker movements in 3, 12.5 and 17-month-old female 3xTg-AD mice and their B6129S/F2 wildtype controls. Mice were filmed using a high-speed video camera (500 fps) in an open arena during a novel object exploration task. Genotype and age differences were found in mice exploring the arena prior to object contact. Prior to whisker contact, the 3-month-old 3xTg-AD mice had smaller whisker angles compared with the wildtype controls, suggesting an early motor phenotype in these mice. Pre-contact mean angular position at 3 months and whisking amplitude at 17 months of age differed between the 3xTg-AD and wildtype mice. During object contact 3xTg-AD mice did not reduce whisker spread as frequently as the wildtype mice at 12.5 and 17 months, which may suggest sensory or attentional deficits. We show that whisker movements are a powerful behavioural measurement tool for capturing behavioural deficits in mouse models that show complex phenotypes, such as the 3xTg-AD mouse model.

Impact of Behavioral Assessment and Re-Test as Functional Trainings That Modify Survival, Anxiety and Functional Profile (Physical Endurance and Motor Learning) of Old Male and Female 3xTg-AD Mice and NTg Mice with Normal Aging

Longitudinal approaches for disease-monitoring in old animals face survival and frailty limitations, but also assessment and re-test bias on genotype and sex effects. The present work investigated these effects on 56 variables for behavior, functional profile, and biological status of male and female 3xTg-AD mice and NTg counterparts using two designs: (1) a longitudinal design: naïve 12-month-old mice re-tested four months later; and (2) a cross-sectional design: naïve 16-month-old mice compared to those re-tested. The results confirmed the impact as (1) improvement of survival (NTg rested females), variability of gait (3xTg-AD 16-month-old re-tested and naïve females), physical endurance (3xTg-AD re-tested females), motor learning (3xTg-AD and NTg 16-month-old re-tested females), and geotaxis (3xTg-AD naïve 16-month-old males); but (2) worse anxiety (3xTg-AD 16-month-old re-tested males), HPA axis (3xTg-AD 16-month-old re-tested and naïve females) and sarcopenia (3xTg-AD 16-month-old naïve females). Males showed more functional correlations than females. The functional profile, biological status, and their correlation are discussed as relevant elements for AD-pathology. Therefore, repetition of behavioral batteries could be considered training by itself, with some variables sensitive to genotype, sex, and re-test. In the AD-genotype, females achieved the best performance in physical endurance and motor learning, while males showed a deterioration in most studied variables.

Modeling Functional Limitations, Gait Impairments, and Muscle Pathology in Alzheimer's Disease: Studies in the 3xTg-AD Mice

Gait impairments in Alzheimer's disease (AD) result from structural and functional deficiencies that generate limitations in the performance of activities and restrictions in individual's biopsychosocial participation. In a translational way, we have used the conceptual framework proposed by the International Classification of Disability and Health Functioning (ICF) to classify and describe the functioning and disability on gait and exploratory activity in the 3xTg-AD animal model. We developed a behavioral observation method that allows us to differentiate qualitative parameters of psychomotor performance in animals' gait, similar to the behavioral patterns observed in humans. The functional psychomotor evaluation allows measuring various dimensions of gait and exploratory activity at different stages of disease progression in dichotomy with aging. We included male 3xTg-AD mice and their non-transgenic counterpart (NTg) of 6, 12, and 16 months of age (n = 45). Here, we present the preliminary results. The 3xTg-AD mice show more significant functional impairment in gait and exploratory activity quantitative variables. The presence of movement limitations and muscle weakness mark the functional decline related to the disease severity stages that intensify with increasing age. Motor performance in 3xTg-AD is accompanied by a series of bizarre behaviors that interfere with the trajectory, which allows us to infer poor neurological control. Additionally, signs of physical frailty accompany the functional deterioration of these animals. The use of the ICF as a conceptual framework allows the functional status to be described, facilitating its interpretation and application in the rehabilitation of people with AD.

Kyphosis and bizarre patterns impair spontaneous gait performance in end-of-life mice with Alzheimer's disease pathology while gait is preserved in normal aging

The shorter life spans of mice provide an exceptional experimental gerontology scenario. We previously described increased bizarre (disruptive) behaviors in the 6-month-old 3xTg-AD mice model for Alzheimer's disease (AD), compared to C57BL/6J wildtype (NTg), when confronting new environments. In the present work, we evaluated spontaneous gait and exploratory activity at old age, using 16-month-old mice. Male sex was chosen since sex-dependent psychomotor effects of aging are stronger in NTg males than females and, at this age, male 3 × Tg-AD mice are close to an end-of-life status due to increased mortality rates. Mice's behavior was evaluated in a transparent test box during the neophobia response. Stretching, jumping, backward movements and bizarre circling were identified during the gait and exploratory activity. The results corroborate that in the face of novelty and recognition of places, old 3xTg-AD mice exhibit increased bizarre behaviors than mice with normal aging. Furthermore, bizarre circling and backward movements delayed the elicitation of locomotion and exploration, in an already frail scenario, as shown by highly prevalent kyphosis in both groups. Thus, the translational study of co-occurrence of psychomotor impairments and anxiety-like behaviors can be helpful for understanding and managing the progressive functional deterioration shown in aging, especially in AD.

Fine-Tuning the PI3K/Akt Signaling Pathway Intensity by Sex and Genotype-Load: Sex-Dependent Homozygotic Threshold for Somatic Growth but Feminization of Anxious Phenotype in Middle-Aged PDK1 K465E Knock-In and Heterozygous Mice

According to the Research Domain Criteria (RDoC), phenotypic differences among disorders may be explained by variations in the nature and degree of neural circuitry disruptions and/or dysfunctions modulated by several biological and environmental factors. We recently demonstrated the in vivo behavioral translation of tweaking the PI3K/Akt signaling, an essential pathway for regulating cellular processes and physiology, and its modulation through aging. Here we describe, for the first time, the in vivo behavioral impact of the sex and genetic-load tweaking this pathway. The anxiety-like phenotypes of 61 mature (11-14-month-old) male and female PDK1 K465E knock-in, heterozygous, and WT mice were studied. Forced (open-field) anxiogenic environmental conditions were sensitive to detect sex and genetic-load differences at middle age. Despite similar neophobia and horizontal activity among the six groups, females exhibited faster ethograms than males, with increased thigmotaxis, increased wall and bizarre rearing. Genotype-load unveiled increased anxiety in males, resembling female performances. The performance of mutants in naturalistic conditions (marble test) was normal. Homozygotic-load was needed for reduced somatic growth only in males. Factor interactions indicated the complex interplay in the elicitation of different negative valence system's items and the fine-tuning of PI3K/Akt signaling pathway intensity by genotype-load and sex.