Behavioral, endocrine and immunological characteristics of a murine model of premature aging

Skin-to-Skin Contact: Crucial for Improving Behavior, Immunity, and Redox State after Short Cohabitation of Chronologically Old Mice and Prematurely Aging Mice with Adult Mice

(1) Background: Aging is characterized by a deterioration of the homeostatic systems, namely the nervous and immune systems. The rate of aging can be modified by lifestyle factors such as social interactions. Recently, improvements in behavior, immune function, and oxidative state were observed in adult prematurely aging mice (PAM) and chronologically old mice after cohabitation with exceptional non-PAM (E-NPAM) and adult mice, respectively, for 2 months. However, the cause of this positive effect is not known. The objective of the present work was to study whether skin-to-skin contact promotes these improvements both in chronologically old mice and in adult PAM. (2) Methods: Old and adult CD1 female mice were used as well as adult PAM and E-NPAM. After cohabitation for 15 min/day for 2 months (two old mice or PAM with five adult mice or E-NPAM, respectively, with both non- and skin-to-skin contact), several behavioral tests were performed and functions and oxidative stress parameters in peritoneal leukocytes were analyzed. (3) Results: This social interaction improved behavioral responses, immune functions, redox state, and longevity, but only if the animals had skin-to-skin contact. (4) Conclusions: Physical contact seems to be crucial to experiencing the positive effects of social interaction.

The Role of Immune Cells in Oxi-Inflamm-Aging

Aging is the result of the deterioration of the homeostatic systems (nervous, endocrine, and immune systems), which preserve the organism's health. We propose that the age-related impairment of these systems is due to the establishment of a chronic oxidative stress situation that leads to low-grade chronic inflammation throughout the immune system's activity. It is known that the immune system weakens with age, which increases morbidity and mortality. In this context, we describe how the function of immune cells can be used as an indicator of the rate of aging of an individual. In addition to this passive role as a marker, we describe how the immune system can work as a driver of aging by amplifying the oxidative-inflammatory stress associated with aging (oxi-inflamm-aging) and inducing senescence in far tissue cells. Further supporting our theory, we discuss how certain lifestyle conditions (such as social environment, nutrition, or exercise) can have an impact on longevity by affecting the oxidative and inflammatory state of immune cells, regulating immunosenescence and its contribution to oxi-inflamm-aging.

Neuronal and glial region dependent changes in female mice from a model of premature aging

Adult Premature Aging Mice (PAM) show premature immunosenescence, oxidative and inflammatory stress and consequently a shorter lifespan than Exceptional Non-Prematurely Aging Mice (E-NPAM) at the same age. Indeed, adult female PAM exhibit behavioral age-related declines and abnormalities in its brain neurochemistry. Nevertheless, it is not clear whether these impairments might be accompanied by previous changes related to the neuroinflammation process in their central nervous system (CNS). Therefore, the aim of the present work was to determine if adult female PAM may show brain neuroinflammation processes comparable to those observed in chronologically old female mice. Accordingly, ICR-CD1 female mice were classified in PAM, Regular Non-Prematurely Aging Mice (R-NPAM) and E-NPAM and compared to a group of chronologically old female mice (OLD) (24±1 months). Through the application of immunohistochemical techniques we evaluated changes in the expression of NeuN (a neuronal marker), Iba-1 (a microglia marker) and GFAP (an astrocyte marker) in brain areas related to the behavioral alterations previously detected in both PAM and chronologically old mice. In general, PAM showed a lower NeuN expression and a higher GFAP and Iba1 expression mainly in the Anterior Frontal Cortex and in the Medial Hippocampal Formation, when compared to E-NPAM; similar changes were observed in OLD. Other brain areas, such as the Hypothalamic Nuclei and Motor Cortex were less affected. In conclusion, adult PAM and OLD female mice share some region-dependent neuronal and glial changes that may underlie, at least in part, some of the behavioral abnormalities previously reported in these animals.

The ratio of prematurely aging to non-prematurely aging mice cohabiting, conditions their behavior, immunity and lifespan

Adult prematurely aging mice (PAM) show behavioral deterioration, premature immunosenescence and increased oxidative stress, impairments that are associated with their shorter lifespan, compared to the corresponding exceptional non-prematurely aging mice (ENPAM). When PAM live in a predominantly ENPAM environment (2/5, respectively) they exhibit an improvement of immunity and redox state in their spleen and thymus leukocytes, and an increased lifespan. Nevertheless, it is unknown if other PAM/ENPAM ratios could affect behavioral and peritoneal leukocyte functions of PAM and change their lifespan. ENPAM and PAM were divided into the following groups: C-ENPAM (8 ENPAM in the cage); C-PAM (8 PAM in the cage); ENPAM>50% and PAM<50% (5 ENPAM/2 PAM in each cage); ENPAM = 50% and PAM = 50% (4 ENPAM/4 PAM in each cage), and PAM>50% and ENPAM<50% (5 PAM/2 ENPAM in each cage). After two months, mice were submitted to a battery of behavioral tests. Several functions and oxidative stress parameters were then assessed in their peritoneal leukocytes. Animals were maintained in these conditions to analyze their lifespan. The results showed that PAM>50%, PAM = 50% and PAM<50% exhibited better behavioral responses, immunity and redox states in their peritoneal leukocytes than C-PAM. This improvement was higher when the number of ENPAM in the cage was increased, with most of the parameters in PAM<50% reaching similar values to those in C-ENPAM, and an increased lifespan. However, ENPAM that cohabited with PAM showed, in general, an impairment of parameters studied. In conclusion, the PAM/ENPAM cohabitation ratio is relevant to behavior and immunity.

Frailty Quantified by the "Valencia Score" as a Potential Predictor of Lifespan in Mice

The development of frailty scores suitable for mice and which resemble those used in the clinical scenario is of great importance to understand human frailty. The aim of the study was to determine an individual frailty score for each mouse at different ages and analyze the association between the frailty score and its lifespan. For this purpose, the "Valencia Score" for frailty was used. Thus, a longitudinal study in mice was performed analyzing weight loss, running time and speed, grip strength and motor coordination at the late-adult, mature and old ages (40, 56 and 80 weeks old, respectively). These parameters are equivalent to unintentional weight loss, poor endurance, slowness, weakness, and low activity level, respectively, in humans. A cut-off point was used to identify frail mice for each criterion. All the measurements were also performed on chronologically adult prematurely aging mice. The results show that by using the "Valencia Score" for frailty a prematurely aged phenotype can be identified even during the adulthood of animals. This opens up the possibility of carrying out preventive long-term interventions. Moreover, the individual frailty score of a given mouse at the late-adult, mature and old ages is shown to be a relevant predictor of its lifespan.

Sexual Dimorphism in the Behavioral Responses and the Immunoendocrine Status in d-Galactose-Induced Aging

For almost 20 years, chronic systemic d-galactose, a monosaccharide abundantly present in milk products, fruits, and vegetables, has been used as a tool to achieve models of accelerated aging. Its neurotoxicity, induced by abnormal accumulation of reactive oxygen species and advanced glycation end products, has been widely reported. However, behavioral outcomes are still controversial and little is known about sex-dependent vulnerability. We performed a comprehensive behavioral and multifunctional screening of the chronic effects of low (50 mg/kg) and high (100 mg/kg) doses of d-galactose in 6-month-old male and female gold-standard C57BL/6 mice. Twelve classical tests with convergent validity analyzed sensorimotor, emotional and cognitive domains, indicating the existence of thresholds of response. Distinct vulnerability patterns were found in a selective sex- and dose-dependent manner. In males, d-galactose induced sensorimotor impairment and immunoendocrine senescence, but the low dose resulted in improved learning and memory. Oppositely, d-galactose-treated females exhibited a dose-dependent worse motor and spatial learning, but improved memory. Behavioral outcome items point at distinct neuronal substrates underlying the functional capacity of d-galactose-treated animals to meet task-dependent performance demands. They support that males and females can be regarded as two exceptional natural scenarios to study the functional interplay in the cross talk of homeostatic networks in aging.

Premature aging in behavior and immune functions in tyrosine hydroxylase haploinsufficient female mice. A longitudinal study

Aging is accompanied by impairment in the nervous, immune, and endocrine systems as well as in neuroimmunoendocrine communication. In this context, there is an age-related alteration of the physiological response to acute stress, which is modulated by catecholamine (CA), final products of the sympathetic-adreno-medullary axis. The involvement of CA in essential functions of the nervous system is consistent with the neuropsychological deficits found in mice with haploinsufficiency (hemizygous; HZ) of tyrosine hydroxylase (TH) enzyme (TH-HZ). However, other possible alterations in regulatory systems have not been studied in these animals. The aim of the present work was to analyze whether adult TH-HZ female mice presented the impairment of behavioral traits and immunological responses that occurs with aging and whether they had affected their mean lifespan. ICR-CD1 female TH-HZ and wild type (WT) mice were used in a longitudinal study. Behavioral tests were performed on adult and old mice in order to evaluate their sensorimotor abilities and exploratory capacity, as well as anxiety-like behaviors. At the ages of 2 ± 1, 4 ± 1, 9 ± 1, 13 ± 1 and 20 ± 1 months, peritoneal leukocytes were extracted and several immune functions were assessed (phagocytic capacity, Natural Killer (NK) cytotoxicity, and lymphoproliferative response to lipopolysaccharide (LPS) and concanavalin A (ConA)). In addition, several oxidative stress parameters (catalase, glutathione reductase and glutathione peroxidase activities, and reduced glutathione (GSH) concentrations as antioxidant compounds as well as xanthine oxidase activity, oxidized glutathione (GSSG) concentrations, and GSSG/GSH ratio as oxidants) were analyzed. As inflammatory stress parameters TNF-alpha and IL-10 concentrations, and TNF-alpha/IL-10 ratios as inflammatory/anti-inflammatory markers, were measured. Animals were maintained in standard conditions until their natural death. The results indicate that adult TH-HZ mice presented worse sensorimotor abilities and exploratory capacity than their WT littermates as well as greater anxiety-like behaviors. With regards to the immune system, adult TH-HZ animals exhibited lower values of phagocytic capacity, NK cytotoxicity, and lymphoproliferative response to LPS and ConA than WT mice. Moreover, immune cells of TH-HZ mice showed higher oxidative and inflammatory stress than those of WT animals. Although these differences between TH-HZ and WT, in general, decreased with aging, this premature immunosenescence and impairment of behavior of TH-HZ mice was accompanied by a shorter mean lifespan in comparison to WT counterparts. In conclusion, haploinsufficiency of th gene in female mice appears to provoke premature aging of the regulatory systems affecting mean lifespan.

Prolonged lifespan with enhanced exploratory behavior in mice overexpressing the oxidized nucleoside triphosphatase hMTH1

The contribution that oxidative damage to DNA and/or RNA makes to the aging process remains undefined. In this study, we used the hMTH1-Tg mouse model to investigate how oxidative damage to nucleic acids affects aging. hMTH1-Tg mice express high levels of the hMTH1 hydrolase that degrades 8-oxodGTP and 8-oxoGTP and excludes 8-oxoguanine from both DNA and RNA. Compared to wild-type animals, hMTH1-overexpressing mice have significantly lower steady-state levels of 8-oxoguanine in both nuclear and mitochondrial DNA of several organs, including the brain. hMTH1 overexpression prevents the age-dependent accumulation of DNA 8-oxoguanine that occurs in wild-type mice. These lower levels of oxidized guanines are associated with increased longevity and hMTH1-Tg animals live significantly longer than their wild-type littermates. Neither lipid oxidation nor overall antioxidant status is significantly affected by hMTH1 overexpression. At the cellular level, neurospheres derived from adult hMTH1-Tg neural progenitor cells display increased proliferative capacity and primary fibroblasts from hMTH1-Tg embryos do not undergo overt senescence in vitro. The significantly lower levels of oxidized DNA/RNA in transgenic animals are associated with behavioral changes. These mice show reduced anxiety and enhanced investigation of environmental and social cues. Longevity conferred by overexpression of a single nucleotide hydrolase in hMTH1-Tg animals is an example of lifespan extension associated with healthy aging. It provides a link between aging and oxidative damage to nucleic acids.

Characterization of skeletal alterations in a model of prematurely aging mice

An age-related bone loss occurs, apparently associated with the concomitant increase in an oxidative stress situation. However, the underlying mechanisms of age-related osteopenia are ill defined since these studies are time consuming and require the use of many animals (mainly rodents). Here, we aimed to characterize for the first time the bone status of prematurely aging mice (PAM), which exhibit an increased oxidative stress. Tibiae from adult (6 months) PAM show an increase in bone mineral density (BMD) and bone mineral content (assessed by bone densitometry) versus those in their normal counterparts (non-prematurely aging mice, NPAM) and similarly decreased in both kinds of mouse with age. However, at this bone site, trabecular BMD (determined by μ-computerized tomography) was similar in both adult PAM and old (18 months) NPAM. Femurs from these groups of mice present an increase in oxidative stress, inflammation, osteoclastogenic, and adipogenic markers, but a decrease in the gene expression of osteoblastic differentiation markers and of the Wnt/β-catenin pathway. Our findings show that adult PAM recapitulate various age-related bone features, and thus are a suitable model for premature bone senescence studies.

Stable behavioral inhibition and glucocorticoid production as predictors of longevity

Several personality/temperament traits have been linked to health outcomes in humans and animals but underlying physiological mechanisms for these differential outcomes are minimally understood. In this paper, we compared the strength of a behavioral trait (behavioral inhibition) and an associated physiological trait (glucocorticoid production) in predicting life span. In addition, we examined the relative stability of both the behavioral and physiological traits within individuals over a significant portion of adulthood, and tested the hypothesis that a stable behavioral trait is linked with a stable physiological bias. In a sample of 60 Sprague-Dawley male rats, we found that stable inhibition/neophobia was a stronger predictor of life span than stably elevated glucocorticoid production. In addition, these predictors appeared to have an additive influence on life span in that males with both risk factors (stable inhibition and consistently high glucocorticoid production) had the shortest life spans of all, suggesting both traits are important predictors of life span. Across a 4-month period in young adulthood, inhibition and glucocorticoid reactivity were relatively stable traits, however these two traits were not highly correlated with one another. Interestingly, baseline glucocorticoid production was a better predictor of life span than reactivity levels. The results indicate that glucocorticoid production in young adulthood is an important predictor of life span, although not as strong a predictor as inhibition, and that other physiological processes may further explain the shortened life span in behaviorally-inhibited individuals.

Female temperament, tumor development and life span: relation to glucocorticoid and tumor necrosis factor alpha levels in rats

Behavioral characteristics closely associated with specific physiological profiles present an important area of research in understanding health disparities. In particular, glucocorticoid overproduction may be an important factor moderating disease progression; natural variance in production of this steroid has been proposed as one mechanism underlying individual differences in health and disease. In the current paper, we examined immune parameters in female rats of two different behavioral types previously shown to have differential glucocorticoid production and life spans. We categorized young female rats according to their behavioral response to novelty (high- or low-locomotion), and compared their glucocorticoid production, adrenal size, thymus size, tumor necrosis factor-alpha (TNF-alpha) production, tumor development and life span. As expected, high-locomotion females produced more glucocorticoids and had larger adrenal glands during young adulthood than did low-locomotion females. High-locomotion females had significantly smaller thymuses and reduced TNF-alpha levels compared to low-locomotion, suggesting altered immune function in young adulthood. Finally, high-locomotion females had shorter life spans than did low-locomotion females, and this was particularly true in females that developed pituitary tumors, but not in those that developed mammary tumors. These results, along with other published findings, suggest that high-locomotion rodent females experience life-long elevations in glucocorticoid responses to novelty, and that these elevated levels may be comparable to chronic stress. This naturally occurring endocrine profile may influence immune responses which in turn could affect disease susceptibility. Variance in immune function across personality types may be partially moderated by natural variance in glucocorticoid production.

Age-related changes in anxiety are task-specific in the senescence-accelerated prone mouse 8

In the senescence-accelerated prone mouse 8 (SAMP8), an excellent model of brain aging, aged individuals have impairments in learning and memory. One study has indicated that the anxiety is also reduced in those mice. However, increased anxiety with aging has been observed in other models, such as C57BL mice and rats. Altered emotion is linked to impairments in learning and memory. Thus, we were interested in further characterizing the pattern of age-related changes in anxiety in this strain. In the present study, a battery of tasks (i.e., elevated plus maze, open field, black-white alley, food neophobia and hole-board) was used to determine the age-related alterations in anxiety in the SAMP8 mice. Three age groups (2, 6, and 10 months of age) of SAMP8 mice and their control SAMR1 (senescence-accelerated resistant mouse 1) mice were used. The results showed that the effect of age was significant only in the elevated plus maze and black-white alley tasks. The SAMP8 showed a tendency toward increased anxiety with age as measured by the time spent on the open arms of elevated plus maze. When the sexes were separated for analysis, the increased anxiety was significant in the old (10-month-old) male SAMP8. In the black-white alley task, however, anxiety levels in the old male SAMP8 mice were lower than those of the middle-aged (6-month-old) mice, but similar to those in the young (2-month-old) mice. These results suggested that the age-related anxiety levels of SAMP8 mice are sex- and task-specific.

Behavioral inhibition and glucocorticoid dynamics in a rodent model

Behavioral inhibition (i.e. avoidance of unfamiliar) has been linked to significant differences in stress physiology and health. Developing an animal model of this common temperament provides a means to experimentally study the development and physiology of this trait as it relates to stress-related health processes. To elaborate such an animal model, we studied individual rat responses to two novel situations that mimic behavioral inhibition tests for humans (one non-social and one social). We measured individual consistency of behavioral responses across tests and time, and examined the relationship between behavior and glucocorticoid levels in outbred Sprague-Dawley male rats. Individuals were consistent in their behavioral responses to the same novel environment over time, but not in their responses across two different environments (i.e. non-social vs. social). A third of males were slow to approach novelty in both arenas (INHIBITED) and another third were fast to approach in both arenas (NON-INHIBITED). Behavioral inhibition was relatively stable across time and was associated with increased glucocorticoid production at baseline and in response to novelty but not during a post-novelty recovery period. Glucocorticoid levels were more closely related to their responses to the social novel arena than the non-social arena. Thus, behavioral inhibition is associated with acute and basal glucocorticoid over production and social inhibition is a more important predictor of adrenal activity than non-social inhibition. These preliminary observations provide strong support for an animal model of human behavioral inhibition and identify specific aspect of glucocorticoid production dynamics to examine in behaviorally inhibited children.

Early maternal deprivation and neonatal single administration with a cannabinoid agonist induce long-term sex-dependent psychoimmunoendocrine effects in adolescent rats

Maternal deprivation [24h on postnatal day 9] might represent an animal model of schizophrenia and behavioural and neurochemical alterations observed in adulthood may be mediated by hippocampal impairments induced by abnormally increased glucocorticoids due to neonatal stress. We aimed to provide new data for psychoimmunoendocrine characterization of this animal model by evaluating its effects in adolescent rats of both genders. In previous studies we found that cannabinoid compounds counteracted the enhanced impulsivity of maternally deprived animals and that the cannabinoid receptor agonist WIN 55,212-2 showed neuroprotective properties in neonatal rats. So, we hypothesised that this compound could counteract at least some of the detrimental effects that we expected to find in maternally deprived animals. Accordingly, the drug was administered immediately after the maternal deprivation period. Maternally deprived males showed significantly decreased motor activity in the holeboard and the plus-maze. The cannabinoid agonist induced, exclusively in males, a significant anxiogenic-like effect, which was reversed by maternal deprivation. In the forced swimming test, both treatments independently induced depressive-like responses. Maternal deprivation reduced immunological function whereas the drug exerted tissue-dependent effects on the immune parameters analysed. Maternally deprived females showed reduced corticosterone levels whereas the cannabinoid agonist increased hormone concentration in all groups. In general, the results show detrimental effects of both treatments as well as intriguing interactions, notably in relation to emotional behaviour and certain immunological responses.

Influence of Aging and Enriched Environment on Motor Activity and Emotional Responses in Mice

We have evaluated different behavioral parameters in ICR (CD1) female mice of three different ages (38-39 weeks: mature; 62 weeks: late mature; 90 weeks: old), and addressed the effects of an enriched housing condition. We employed the following battery of tests: Holeboard, open field, elevated plus-maze (EPM), and forced swimming test (FST). The results suggest that aging process differentially affects diverse aspects of behavior. With respect to motor activity, late mature animals were more affected by enrichment, whereas old animals appeared to be more affected when emotional responses were considered. We propose that the diminished percentage of time in the open arms of the EPM showed by enriched mice may be indicative of decreased novelty seeking, whereas their decreased climbing behavior may indicate a reduced escape-related behavior in an inescapable situation.

A model of premature aging in mice based on altered stress-related behavioral response and immunosenescence

The intensity of behavioral and neuroendocrine responses to stressful stimuli in rodent strains seems to be inversely related to their life span. We have previously shown that interindividual differences in members of outbred Swiss and inbred BALB/c mouse populations, both male and female, may be related to their behavior in a simple T-maze test. The animals that explore the maze slowly show impaired neuromuscular vigor and coordination, decreased locomotor activity, increased level of emotionality/anxiety, decreased levels of brain biogenic amines as well as immunosenescence and decreased life span, when compared to their control counterparts, which quickly explore the maze. These traits are similar to some of the alterations previously observed in aging animals and therefore we proposed that those 'slow mice' are biologically older than the fast animals and may be a model of prematurely aging mice (PAM). Although most of our work on this model has been performed on chronologically adult-mature animals, we have also shown that certain characteristics of PAM, such as increased anxiety and deficient immune response, are already present in chronologically young animals. Thus, it is tempting to hypothesize that chronic hyperreactivity to stress (trait anxiety) leading to immune dysfunction may have a causal relationship with impaired health and premature aging. In view of the link between oxidative stress and the aging process, the redox state of peritoneal leukocytes from PAM has been studied, showing an oxidative stress situation. In the present work we have determined the levels of a key antioxidant, reduced glutathione (GSH), and the oxidant malondialdehyde (MDA), a marker of lipid peroxidation, both in the spleen and brain of male and female PAM and non-PAM (NPAM). We found that GSH and MDA are decreased and increased, respectively, in PAM with respect to NPAM. Moreover, diet supplementation with antioxidants showed to be an effective strategy for protection against early immune and behavioral decline, altered redox state of leukocytes and premature mortality in PAM, which supports the validity of this model of premature aging as well as its link with oxidative stress.

Oxidative stress in leukocytes from young prematurely aging mice is reversed by supplementation with biscuits rich in antioxidants

Aging is associated with a progressive dysregulation of immune responses as a result of increased oxidative stress. Therefore, we have assessed the oxidative stress status of peritoneal leukocytes from young prematurely aging mice (PAM) as compared with non-prematurely aging mice (NPAM), as well as the effects on this oxidative stress of a dietary supplementation with biscuits rich in antioxidants (vitamin C, vitamin E, beta-carotenes, zinc and selenium). We found that, in the peritoneal leukocytes, the levels of several parameters of oxidation such as extracellular superoxide anion (O(2)(-)), Prostaglandin E(2) (PGE(2)), nitric oxide, oxidized glutathione (GSSG) and lipid peroxidation (malondialdehyde, MDA) were higher in PAM as compared with NPAM, whereas the antioxidant defences such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione reductase (GR) activities, as well as reduced glutathione (GSH) levels, were decreased. Consequently, young PAM showed an oxidative stress in their leukocytes, which is characteristic of mice of an older chronological age. Antioxidant diet supplementation was able to restore redox homeostasis, increasing the antioxidant and decreasing the oxidant levels. Accordingly, supplementation with adequate levels of antioxidants, from an early age, could be useful to preserve health, especially in prematurely aging populations.