Short-term recognition memory impairment is associated with decreased expression of FK506 binding protein 51 in the aged mouse brain

Disarranged neuroplastin environment upon aging and chronic stress recovery in female Sprague Dawley rats

Chronic stress produces long-term metabolic changes throughout the superfamily of nuclear receptors, potentially causing various pathologies. Sex hormones modulate the stress response and generate a sex-specific age-dependent metabolic imprint, especially distinct in the reproductive senescence of females. We monitored chronic stress recovery in two age groups of female Sprague Dawley rats to determine whether stress and/or aging structurally changed the glycolipid microenvironment, a milieu playing an important role in cognitive functions. Old females experienced memory impairment even at basal conditions, which was additionally amplified by stress. On the other hand, the memory of young females was not disrupted. Stress recovery was followed by a microglial decrease and an increase in astrocyte count in the hippocampal immune system. Since dysfunction of the brain immune system could contribute to disturbed synaptogenesis, we analyzed neuroplastin expression and the lipid environment. Neuroplastin microenvironments were explored by analyzing immunofluorescent stainings using a newly developed Python script method. Stress reorganized glycolipid microenvironment in the Cornu Ammonis 1 (CA1) and dentate gyrus (DG) hippocampal regions of old females but in a very different fashion, thus affecting neuroplasticity. The postulation of four possible neuroplastin environments pointed to the GD1a ganglioside enrichment during reproductive senescence of stressed females, as well as its high dispersion in both regions and to GD1a and GM1 loss in the CA1 region. A specific lipid environment might influence neuroplastin functionality and underlie synaptic dysfunction triggered by a combination of aging and chronic stress.

Loss of Immunohistochemical Reactivity in Association With Handling-Induced Dark Neurons in Mouse Brains

The handling-induced dark neuron is a histological artifact observed in brain samples handled before fixation with aldehydes. To explore associations between dark neurons and immunohistochemical alterations in mouse brains, we examined protein products encoded by Cav3 (neuronal perikarya/neurites), Rbbp4 (neuronal nuclei), Gfap (astroglia), and Aif1 (microglia) genes in adjacent tissue sections. Here, dark neurons were incidental findings from our prior project, studying the effects of age and high-fat diet on metabolic homeostasis in male C57BL/6N mice. Available were brains from 4 study groups: middle-aged/control diet, middle-aged/high-fat diet, old/control diet, and old/high-fat diet. Young/control diet mice were used as baseline. The hemibrains were immersion-fixed with paraformaldehyde and paraffin-embedded. In the hippocampal formation, we found negative correlations between dark neuron hyperbasophilia and immunoreactivity for CAV3, RBBP4, and glial fibrillary acidic protein (GFAP) using quantitative image analysis. There was no significant difference in dark neuron hyperbasophilia or immunoreactivity for any protein examined among all groups. In contrast, in the hippocampal fimbria, old age seemed to be associated with higher immunoreactivity for GFAP and allograft inflammatory factor-1. Our findings suggest that loss of immunohistochemical reactivity for CAV3, RBBP4, and GFAP in the hippocampal formation is an artifact associated with the occurrence of dark neurons. The unawareness of dark neurons may lead to misinterpretation of immunohistochemical reactivity alterations.

Stress-Induced Neurodegeneration: The Potential for Coping as Neuroprotective Therapy

Stress responses are essential for survival, but become detrimental to health and cognition with chronic activation. Chronic hypothalamic-pituitary-adrenal axis release of glucocorticoids induces hypothalamic-pituitary-adrenal axis dysfunction and neuronal loss, decreases learning and memory, and modifies glucocorticoid receptor/mineralocorticoid receptor expression. Elderly who report increased stress are nearly 3 times more likely to develop Alzheimer's disease, have decreased global cognition and faster cognitive decline than those reporting no stress. Patients with mild cognitive impairment are more sensitive to stress compared to healthy elderly and those with Alzheimer's disease. Stress may also transduce neurodegeneration via the gut microbiome. Coping styles determine hippocampal mineralocorticoid receptor expression in mice, indicating that coping modifies cortisol's effect on the brain. Identifying neuroprotective coping strategies that lessen the burden of stress may prevent or slow cognitive decline. Treatments and education designed to reduce stress should be recognized as neuroprotective.

Association of antiretroviral therapy with brain aging changes among HIV-infected adults

OBJECTIVE

Antiretroviral therapy (ART) is currently recommended for all persons living with HIV (PLWH), regardless of their CD4 T-cell count, and should be continued throughout life. Nonetheless, vigilance of the safety of ART, including its neurotoxicity, must continue. We hypothesized that use of certain ART drugs might be associated with aging-related cerebral degenerative changes among PLWH.

DESIGN

Clinicopathological study of PLWH who were using ART drugs at the last clinical assessment.

METHODS

Using multivariable logistic regression, we tested associations between use of each specific ART drug (with reference to use of other ART drugs) and cerebral degenerative changes including neuronal phospho-tau lesions, β-amyloid plaque deposition, microgliosis, and astrogliosis in the frontal cortex and putamen (immunohistochemistry), as well as cerebral small vessel disease (CSVD) in the forebrain white matter (standard histopathology), with relevant covariates being taken into account. The Bonferroni adjustment was applied.

RESULTS

Darunavir use was associated with higher likelihood of neuronal phospho-tau lesions in the putamen [odds ratio (OR) 15.33, n = 93, P = 0.005]. Ritonavir use was associated with marked microgliosis in the putamen (OR 4.96, n = 101, P = 0.023). On the other hand, use of tenofovir disoproxil fumarate was associated with lower likelihood of β-amyloid plaque deposition in the frontal cortex (OR 0.13, n = 102, P = 0.012). There was a trend toward an association between emtricitabine use and CSVD (OR 13.64, n = 75, P = 0.099).

CONCLUSION

Our findings suggest that PLWH treated with darunavir and ritonavir may be at increased risk of aging-related cerebral degenerative changes.

Plasma soluble CD163 is associated with postmortem brain pathology in human immunodeficiency virus infection

OBJECTIVE

Higher plasma soluble cluster of differentiation (CD)163 (sCD163), shed by monocytes and macrophages, correlates with neurocognitive impairment in HIV infection. We hypothesized that higher antemortem plasma or cerebrospinal fluid (CSF) sCD163 would be associated with greater postmortem neurodegeneration and/or microgliosis.

DESIGN

Retrospective, postmortem observational study.

METHODS

We measured sCD163 levels in antemortem plasma (n = 54) and CSF (n = 32) samples from 74 HIV-seropositive participants (median 5 months before death) who donated their brains to research at autopsy. Postmortem, we quantified markers of synaptodendritic damage (microtubule-associated protein 2, synaptophysin), microgliosis [human leukocyte antigen DR (HLA-DR), ionized calcium-binding adaptor molecule 1], astrocytosis (glial fibrillary acidic protein), and impaired protein clearance (β-amyloid) in frontal cortex, hippocampus, putamen, and internal capsule. Multivariable least-squares regression was used to evaluate the association between plasma or CSF sCD163 and histological measures, correcting for multiple comparisons.

RESULTS

Higher plasma sCD163 was associated with lower microtubule-associated protein 2 in frontal cortex [B = -0.23, 95% confidence interval (CI) -0.41 to -0.06, P = 0.04], putamen (B = 0.32, 95% CI -0.52 to -0.12, P = 0.02), and hippocampus (B = -0.23, 95% CI -0.35 to -0.10, P = 0.01), and with lower synaptophysin in hippocampus (B = -0.25, 95% CI -0.42 to -0.03, P = 0.02) but not putamen or frontal cortex (P > 0.05). Higher plasma sCD163 was associated with higher HLA-DR in putamen (B = 0.17, 95% CI 0.08 to 0.26, P = 0.008). CSF sCD163 was not associated with any histological measure (P > 0.05).

CONCLUSION

Higher plasma sCD163 in life is associated with greater synaptodendritic damage and microglial activation in cortical and subcortical brain regions.

The FKBP5 Gene Affects Alcohol Drinking in Knockout Mice and Is Implicated in Alcohol Drinking in Humans

FKBP5 encodes FK506-binding protein 5, a glucocorticoid receptor (GR)-binding protein implicated in various psychiatric disorders and alcohol withdrawal severity. The purpose of this study is to characterize alcohol preference and related phenotypes in Fkbp5 knockout (KO) mice and to examine the role of FKBP5 in human alcohol consumption. The following experiments were performed to characterize Fkpb5 KO mice. (1) Fkbp5 KO and wild-type (WT) EtOH consumption was tested using a two-bottle choice paradigm; (2) The EtOH elimination rate was measured after intraperitoneal (IP) injection of 2.0 g/kg EtOH; (3) Blood alcohol concentration (BAC) was measured after 3 h limited access of alcohol; (4) Brain region expression of Fkbp5 was identified using LacZ staining; (5) Baseline corticosterone (CORT) was assessed. Additionally, two SNPs, rs1360780 (C/T) and rs3800373 (T/G), were selected to study the association of FKBP5 with alcohol consumption in humans. Participants were college students (n = 1162) from 21–26 years of age with Chinese, Korean or Caucasian ethnicity. The results, compared to WT mice, for KO mice exhibited an increase in alcohol consumption that was not due to differences in taste sensitivity or alcohol metabolism. Higher BAC was found in KO mice after 3 h of EtOH access. Fkbp5 was highly expressed in brain regions involved in the regulation of the stress response, such as the hippocampus, amygdala, dorsal raphe and locus coeruleus. Both genotypes exhibited similar basal levels of plasma corticosterone (CORT). Finally, single nucleotide polymorphisms (SNPs) in FKBP5 were found to be associated with alcohol drinking in humans. These results suggest that the association between FKBP5 and alcohol consumption is conserved in both mice and humans.

A novel role for the immunophilin FKBP52 in motor coordination

FKBP52 is a ubiquitously distributed immunophilin that has been associated with wide-ranging functions in cell signalling as well as hormonal and stress responses. Amongst other pathways, it acts via complex-formation with corticosteroid receptors and has consequently been associated with stress- and age- related neurodegenerative disorders including Alzheimer's and Parkinson's diseases. Reduced levels of FKBP52 have been linked to tau dysfunction and amyloid beta toxicity in AD. However, FKBP52's role in cognition and neurodegenerative disorder-like phenotypes remain to be elucidated. The present study aimed therefore at investigating the cognitive and behavioural effects of reduced FKBP52 levels of genetically modified mice during ageing. Female and male FKBP52(+/+), FKBP52(+/-) and FKBP52(-/-) mice were compared at two-, ten-, twelve-, fifteen- and eighteen-months-of-age in a series of behavioural tests covering specie-specific behaviour, motor activity and coordination, fear-, spatial and recognition memory as well as curiosity and emotionality. Whilst cognitively unimpaired, FKBP52(+/-) mice performed worse on an accelerating rotating rod than FKBP52(+/+) littermates across all age-groups suggesting that FKBP52 is involved in processes controlling motor coordination. This deficit did not exacerbate with age but did worsen with repeated testing; pointing towards a role for FKBP52 in learning of tasks requiring motor coordination abilities. This study contributes to the knowledge base of FKBP52's implication in neurodegenerative diseases by demonstrating that FKBP52 by itself does not directly affect cognition and may therefore rather play an indirect, modulatory role in the functional pathology of AD, whereas it directly affects motor coordination, an early sign of neurodegenerative damages to the brain.

Neuroprotective effects of the immunomodulatory drug FK506 in a model of HIV1-gp120 neurotoxicity

Background

HIV-associated neurocognitive disorders (HAND) continue to be a common morbidity associated with chronic HIV infection. It has been shown that HIV proteins (e.g., gp120) released from infected microglial/macrophage cells can cause neuronal damage by triggering inflammation and oxidative stress, activating aberrant kinase pathways, and by disrupting mitochondrial function and biogenesis. Previous studies have shown that FK506, an immunophilin ligand that modulates inflammation and mitochondrial function and inhibits calcineurin, is capable of rescuing the neurodegenerative pathology in models of Parkinson’s disease, Alzheimer’s disease, and Huntington’s disease. In this context, the main objective of this study was to evaluate if FK506 could rescue the neuronal degeneration and mitochondrial alterations in a transgenic (tg) animal model of HIV1-gp120 neurotoxicity.

Methods

GFAP-gp120 tg mice were treated with FK506 and analyzed for neuropathology, behavior, mitochondrial markers, and calcium flux by two-photon microscopy.

Results

We found that FK506 reduced the neuronal cell loss and neuro-inflammation in the gp120 tg mice. Moreover, while vehicle-treated gp120 tg mice displayed damaged mitochondria and increased neuro-inflammatory markers, FK506 rescued the morphological mitochondrial alterations and neuro-inflammation while increasing levels of optic atrophy 1 and mitofusin 1. By two-photon microscopy, calcium levels were not affected in the gp120 tg mice and no effects of FK506 were detected. However, at a functional level, FK506 ameliorated the gp120 tg mice hyperactivity in the open field.

Conclusions

Together, these results suggest that FK506 might be potentially neuroprotective in patients with HAND by mitigating inflammation and mitochondrial alterations.

Lifetime methamphetamine dependence is associated with cerebral microgliosis in HIV-1-infected adults

Methamphetamine (Meth) use is common among HIV-infected persons. It remains unclear whether Meth dependence is associated with long-lasting degenerative changes in the brain parenchyma and microvasculature of HIV-infected individuals. We examined the postmortem brains of 78 HIV-infected adults, twenty of whom were diagnosed with lifetime Meth dependence (18 past and two current at the final follow-up visit). Using logistic regression models, we analyzed associations of Meth with cerebral gliosis (immunohistochemistry for ionized calcium-binding adapter molecule-1 (Iba1) and glial fibrillary acidic protein (GFAP) in frontal, temporo-parietal, and putamen-internal capsule regions), synaptodendritic loss (confocal microscopy for synaptophysin (SYP) and microtubule-associated protein-2 (MAP2) in frontal cortex), β-amyloid plaque deposition (immunohistochemistry in frontal and temporo-parietal cortex and putamen), and arteriolosclerosis (histopathology in forebrain white matter). We found that Meth was associated with marked Iba1 gliosis in the temporo-parietal region (odds ratio, 4.42 (95 % confidence interval, 1.36, 14.39), p = 0.014, n = 62), which remained statistically significant after adjusting for HIV encephalitis, white matter lesions, and opportunistic diseases (n = 61); hepatitis C virus seropositivity (n = 54); and lifetime dependence on alcohol, opiates, and cannabis (n = 62). There was no significant association of Meth with GFAP gliosis, SYP or MAP2 loss, β-amyloid plaque deposition, or arteriolosclerosis. In conclusion, we found lifetime Meth dependence to be associated with focal cerebral microgliosis among HIV-infected adults, but not with other brain degenerative changes examined. Some of the changes in select brain regions might be reversible following extended Meth abstinence or, alternatively, might have not been induced by Meth initially.

The environmental endocrine disruptor p-nitrophenol interacts with FKBP51, a positive regulator of androgen receptor and inhibits androgen receptor signaling in human cells

The compound p-nitrophenol, which shows the anti-androgenic activity, can easily become anthropogenic pollutants and pose a threat to the environment and human health. Previous work indicates that the anti-androgenic mechanism of p-nitrophenol is complex and may involve several components in the AR signaling pathway, but the molecular details of how p-nitrophenol inhibits AR signaling are still not quite clear. Here, we characterized p-nitrophenol binds to the FK1 domain of an AR positive regulator FKBP51 with micromolar affinity and structural analysis of FK1 domain in complex with p-nitrophenol revealed that p-nitrophenol occupies a hydrophobic FK1 pocket that is vital for AR activity enhancement. Molecular dynamics simulation indicated that p-nitrophenol is stably bound to the FK1 pocket and the hotspot residues that involved p-nitrophenol binding are mainly hydrophobic and overlap with the AR interaction site. Furthermore, we showed that p-nitrophenol inhibits the androgen-dependent growth of human prostate cancer cells, possibly through down-regulating the expression levels of AR activated downstream genes. Taken together, our data suggests that p-nitrophenol suppresses the AR signaling pathway at least in part by blocking the interaction between AR and its positive regulator FKBP51. We believe that our findings could provide new guidelines for assessing the potential health effects of p-nitrophenol.

Microstructural changes to the brain of mice after methamphetamine exposure as identified with diffusion tensor imaging

Methamphetamine (METH) is an addictive psychostimulant inducing neurotoxicity. Human magnetic resonance imaging and diffusion tensor imaging (DTI) of METH-dependent participants find various structural abnormities. Animal studies demonstrate immunohistochemical changes in multiple cellular pathways after METH exposure. Here, we characterized the long-term effects of METH on brain microstructure in mice exposed to an escalating METH binge regimen using in vivo DTI, a methodology directly translatable across species. Results revealed four patterns of differential fractional anisotropy (FA) and mean diffusivity (MD) response when comparing METH-exposed (n=14) to saline-treated mice (n=13). Compared to the saline group, METH-exposed mice demonstrated: 1) decreased FA with no change in MD [corpus callosum (posterior forceps), internal capsule (left), thalamus (medial aspects), midbrain], 2) increased MD with no change in FA [posterior isocortical regions, caudate-putamen, hypothalamus, cerebral peduncle, internal capsule (right)], 3) increased FA with decreased MD [frontal isocortex, corpus callosum (genu)], and 4) increased FA with no change or increased MD [hippocampi, amygdala, lateral thalamus]. MD was negatively associated with calbindin-1 in hippocampi and positively with dopamine transporter in caudate-putamen. These findings highlight distributed and differential METH effects within the brain suggesting several distinct mechanisms. Such mechanisms likely change brain tissue differentially dependent upon neural location.

Age and High-Fat Diet Effects on Glutamine Synthetase Immunoreactivity in Liver and Hippocampus and Recognition Memory in Mice

BACKGROUND

High-Fat Diet (HFD)-induced obesity may promote agerelated memory impairment via disturbances of ammonia-glutamine metabolism.

OBJECTIVE

We studied the effects of age and long-term HFD exposure on Glutamine Synthetase (GS) expression in the liver and hippocampus and recognition memory in mice.

METHODS

Adult (5-month-old) and aged (15-month-old) male C57BL/6 mice were exposed to control diet (CD, 14% calories from fat) or HFD (60% fat). Novel place recognition testing was conducted and tissue was collected after 4 and 5 months on HFD, respectively. Tissue GS expression levels were assessed using immunohistochemistry and image analysis.

RESULTS

The obese mice developed moderate/severe hepatic steatosis. GS immunoreactivity was observed in perivenous hepatocytes and in hippocampal astrocytes and neuropil. Hepatic GS immunoreactivity density was higher in aged mice on HFD (n = 8) than CD (n = 13, P = 0.004). In aged mice, hippocampal GS immunoreactivity density was higher with HFD than CD (P = 0.037). In the novel place recognition test, aged mice were classified into impaired (n = 7) and unimpaired (n = 12), relative to adult mice (n = 22). Hippocampal GS immunoreactivity density was higher in impaired than unimpaired aged mice (P < 0.05).

CONCLUSION

Long-term exposure of aged mice to HFD was associated with increased GS expression in the liver and hippocampus. Novel place recognition impairment in aged mice was associated with increased hippocampal GS expression. These findings suggest that excess ammonia is involved in the age-related effects of HFD exposure and in neurotoxicity.

Accelerated epigenetic aging in brain is associated with pre-mortem HIV-associated neurocognitive disorders

HIV infection leads to age-related conditions in relatively young persons. HIV-associated neurocognitive disorders (HAND) are considered among the most prevalent of these conditions. To study the mechanisms underlying this disorder, researchers need an accurate method for measuring biological aging. Here, we apply a recently developed measure of biological aging, based on DNA methylation, to the study of biological aging in HIV+ brains. Retrospective analysis of tissue bank specimens and pre-mortem data was carried out. Fifty-eight HIV+ adults underwent a medical and neurocognitive evaluation within 1 year of death. DNA was obtained from occipital cortex and analyzed with the Illumina Infinium Human Methylation 450K platform. Biological age determined via the epigenetic clock was contrasted with chronological age to obtain a measure of age acceleration, which was then compared between those with HAND and neurocognitively normal individuals. The HAND and neurocognitively normal groups did not differ with regard to demographic, histologic, neuropathologic, or virologic variables. HAND was associated with accelerated aging relative to neurocognitively normal individuals, with average relative acceleration of 3.5 years. Age acceleration did not correlate with pre-mortem neurocognitive functioning or HAND severity. This is the first study to demonstrate that the epigenetic age of occipital cortex samples is associated with HAND status in HIV+ individuals pre-mortem. While these results suggest that the increased risk of a neurocognitive disorder due to HIV might be mediated by an epigenetic aging mechanism, future studies will be needed to validate the findings and dissect causal relationships and downstream effects.

HIV-1 Infection Accelerates Age According to the Epigenetic Clock

Background. Infection with human immunodeficiency virus type 1 (HIV) is associated with clinical symptoms of accelerated aging, as evidenced by the increased incidence and diversity of age-related illnesses at relatively young ages and supporting findings of organ and cellular pathologic analyses. But it has been difficult to detect an accelerated aging effect at a molecular level.

Methods. Here, we used an epigenetic biomarker of aging based on host DNA methylation levels to study accelerated aging effects due to HIV infection. DNA from brain and blood tissue was assayed via the Illumina Infinium Methylation 450 K platform.

Results. Using 6 novel DNA methylation data sets, we show that HIV infection leads to an increase in epigenetic age both in brain tissue (7.4 years) and blood (5.2 years). While the observed accelerated aging effects in blood may reflect changes in blood cell composition (notably exhausted cytotoxic T cells), it is less clear what explains the observed accelerated aging effects in brain tissue.

Conclusions. Overall, our results demonstrate that the epigenetic clock is a useful biomarker for detecting accelerated aging effects due to HIV infection. This tool can be used to accurately determine the extent of age acceleration in individual tissues and cells.

Mouse Models of Huntington's Disease

In this review, we explore the similarities and differences in the behavioural neurobiology found in the mouse models of Huntington's disease (HD) and the human disease state. The review is organised with a comparative focus on the functional domains of motor control, cognition and behavioural disturbance (akin to psychiatric disturbance in people) and how our knowledge of the underlying physiological changes that are manifest in the HD mouse lines correspond to those seen in the HD clinical population. The review is framed in terms of functional circuitry and neurotransmitter systems and how abnormalities in these systems impact on the behavioural readouts across the mouse lines and how these may correspond to the deficits observed in people. In addition, interpretational issues associated with the data from animal studies are discussed.

Expression and localization of type II diacylglycerol kinase isozymes δ and η in the developing mouse brain

The functions of type II diacylglycerol kinase (DGK) δ and -η in the brain are still unclear. As a first step, we investigated the spatial and temporal expression of DGKδ and -η in the brains of mice. DGKδ2, but not DGKδ1, was highly expressed in layers II-VI of the cerebral cortex; CA-CA3 regions and dentate gyrus of hippocampus; mitral cell, glomerular and granule cell layers of the olfactory bulb; and the granule cell layer in the cerebellum in 1- to 32-week-old mice. DGKδ2 was expressed just after birth, and its expression levels dramatically increased from weeks 1 to 4. A substantial amount of DGKη (η1/η2) was detected in layers II-VI of the cerebral cortex, CA1 and CA2 regions and dentate gyrus of the hippocampus, mitral cell and glomerular layers of the olfactory bulb, and Purkinje cells in the cerebellum of 1- to 32-week-old mice. DGKη2 expression reached maximum levels at P5 and decreased by 4 weeks, whereas DGKη1 increased over the same time frame. These results indicate that the expression patterns of DGK isozymes differ from each other and also from other isozymes, and this suggests that DGKδ and -η play distinct and specific roles in the brain.

Prenatal alcohol exposure is associated with altered subcellular distribution of glucocorticoid and mineralocorticoid receptors in the adolescent mouse hippocampal formation

Background

Accumulating evidence indicates that several of the long-term consequences of prenatal alcohol exposure (PAE) are the result of changes in the development and function of cortico-limbic structures, including the hippocampal formation. The glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) are key regulators of hippocampal formation development, structure, and functioning and, thus, are potential mediators of PAE’s effects on this brain region. In the present studies, we assessed the impact of PAE on components of corticosteroid signaling pathways in the mouse hippocampal formation.

Methods

Throughout pregnancy, mouse dams were offered either 10% (w/v) ethanol sweetened with 0.066% (w/v) saccharin (SAC) or 0.066% (w/v) SAC alone using a limited (4-hour) access, drinking-in-the-dark paradigm. The hippocampal formation was isolated from naïve postnatal day 40 to 50 offspring, and subcellular fractions were prepared. Using immunoblotting techniques, we measured the levels of GR, MR, 11-β-hydroxysteroid dehydrogenase 1 (11β-HSD1), and the FK506-binding proteins 51 (FKBP51, FKBP5) and 52 (FKBP52, FKBP4). Finally, we determined the effect of PAE on context discrimination, a hippocampal-dependent learning/memory task.

Results

PAE was associated with reduced MR and elevated GR nuclear localization in the hippocampal formation, whereas cytosolic levels of both receptors were not significantly altered. FKBP51 levels were reduced, while FKBP52 levels were unaltered, and 11β-HSD1 levels were increased in postnuclear fractions isolated from PAE mouse hippocampal formation. These neurochemical alterations were associated with reduced context discrimination.

Conclusions

The data support a model in which PAE leads to increased nuclear localization of GRs secondary to reductions in FKBP51 and increases in 11β-HSD1 levels in the adolescent mouse hippocampal formation. Persistent dysregulation of GR subcellular distribution is predicted to damage the hippocampal formation and may underlie many of the effects of PAE on hippocampal-dependent functioning.

Short-term recognition memory correlates with regional CNS expression of microRNA-138 in mice

OBJECTIVES

We hypothesized that microRNA (miR) expression may be involved in memory function because it controls local protein translation at synapses and dendritic spines.

DESIGN

Case-control animal study.

METHODS

We assessed the miR repertoire in the hippocampus of young, 6-month-old (N = 18) mice compared with aged, 26-month-old (N = 23) mice and compared miR quantity to memory scores as determined by the novel object recognition task. We performed a histological brain regional analysis of miR-138, acyl protein thioesterase 1 (APT1) mRNA, and APT1 protein.

RESULTS

We found that higher miR-138 expression in the mouse hippocampus is correlated with better memory performance. We also found that APT1 (a depalmytoylation enzyme expressed at dendritic spines whose translation is controlled by miR-138) mRNA is increased in the mouse hippocampal CA1 and dentate gyrus in aged mice compared with young mice, but not in mice with memory impairment. We found APT1 protein distribution to be lower in cells with high miR-138 expression.

CONCLUSIONS

These results suggest that increased miR-138 is associated with better memory and increased APT1 gene transcription occurs with aging. The role of miR-138 and APT1 protein function in memory and aging warrants further investigation.

The developing, aging neocortex: how genetics and epigenetics influence early developmental patterning and age-related change

A hallmark of mammalian development is the generation of functional subdivisions within the nervous system. In humans, this regionalization creates a complex system that regulates behavior, cognition, memory, and emotion. During development, specification of neocortical tissue that leads to functional sensory and motor regions results from an interplay between cortically intrinsic, molecular processes, such as gene expression, and extrinsic processes regulated by sensory input. Cortical specification in mice occurs pre- and perinatally, when gene expression is robust and various anatomical distinctions are observed alongside an emergence of physiological function. After patterning, gene expression continues to shift and axonal connections mature into an adult form. The function of adult cortical gene expression may be to maintain neocortical subdivisions that were established during early patterning. As some changes in neocortical gene expression have been observed past early development into late adulthood, gene expression may also play a role in the altered neocortical function observed in age-related cognitive decline and brain dysfunction. This review provides a discussion of how neocortical gene expression and specific patterns of neocortical sensori-motor axonal connections develop and change throughout the lifespan of the animal. We posit that a role of neocortical gene expression in neocortex is to regulate plasticity mechanisms that impact critical periods for sensory and motor plasticity in aging. We describe results from several studies in aging brain that detail changes in gene expression that may relate to microstructural changes observed in brain anatomy. We discuss the role of altered glucocorticoid signaling in age-related cognitive and functional decline, as well as how aging in the brain may result from immune system activation. We describe how caloric restriction or reduction of oxidative stress may ameliorate effects of aging on the brain.

Hippocampal calbindin-1 immunoreactivity correlate of recognition memory performance in aged mice

Aging-related dysregulation of neuronal calcium metabolism, which not only involves the control of calcium fluxes but also the cytosolic calcium buffering system such as calbindin-1 (Calb1), may disturb synaptic plasticity and thereby memory functioning. Calb1 expression has been shown to affect hippocampal long-term potentiation and learning and to play a neuroprotective role in animal models of ischemic brain injury and neurodegenerative disorders. We hypothesize that memory performance in aged mice correlates with neuronal Calb1 protein expression in the hippocampal formation. We studied a set of 18 aged and 22 young male C57BL/6N mice, in which the aged group performed poorer than the young in single-trial novel object recognition testing (two-tailed p=0.005, U test). Apparent decreases in the Calb1 immunoreactivity (measured by quantitative immunohistochemistry) in aged mice compared to that in young mice were not statistically significant either in the hippocampal CA1 subfield or dentate gyrus. In the aged mouse group, levels of Calb1 immunoreactivity both in the CA1 subfield and dentate gyrus correlated directly with the measure of recognition memory performance (Spearman rank correlation r(s)=0.47 and 0.48, two-tailed p=0.047 and 0.044, respectively). Our results suggest that hippocampal Calb1 expression affects memory performance in aged mice probably via its role in maintaining neuronal calcium homeostasis. Alternatively, our finding of lower Calb1 immunoreactivity with poorer memory performance in aged mice might be attributed to saturation of Calb1 protein by higher levels of intracellular calcium, due to aging-related dysregulation of neuronal calcium fluxes.

Increased hippocampal accumulation of autophagosomes predicts short-term recognition memory impairment in aged mice

Constitutive macroautophagy involved in the turnover of defective long-lived proteins and organelles is crucial for neuronal homeostasis. We hypothesized that macroautophagic dysregulation in selective brain regions was associated with memory impairment in aged mice. We used the single-trial object recognition test to measure short-term memory in 18 aged mice compared to 22 young mice and employed immunohistochemistry to assess cellular distribution of proteins involved in the selective degradation of ubiquitinated proteins via macroautophagy. Values of the discrimination ratio (DR, a measure of short-term recognition memory performance) in aged mice were significantly lower than those in young mice (median, 0.54 vs. 0.67; p = 0.005, U test). Almost exclusively in aged mice, there were clusters of puncta immunoreactive for microtubule-associated protein 1 light chain 3 (LC3), ubiquitin- and LC3-binding protein p62, and ubiquitin in neuronal processes predominantly in the hippocampal formation, olfactory bulb/tubercle, and cerebellar cortex. The hippocampal burden of clustered puncta immunoreactive for LC3 and p62 exhibited inverse linear correlations with DR in aged mice (ρ = -0.48 and -0.55, p = 0.044 and 0.018, respectively, Spearman's rank correlation). These findings suggest that increased accumulation of autophagosomes within neuronal processes in selective brain regions is characteristic of aging. The dysregulation of macroautophagy can adversely affect the turnover of aggregate-prone proteins and defective organelles, which may contribute to memory impairment in aged mice.

Antioxidant sestrin-2 redistribution to neuronal soma in human immunodeficiency virus-associated neurocognitive disorders

Sestrin-2 is involved in p53-dependent antioxidant defenses and in the maintenance of metabolic homeostasis. We hypothesize that sestrin-2 expression is altered in the brains of subjects diagnosed with human immunodeficiency virus (HIV)-associated neurocognitive disorders (HAND) due to neuronal oxidative stress. We studied sestrin-2 immunoreactivity in 42 isocortex sections from HIV-1-infected subjects compared to 18 age-matched non-HIV controls and 19 advanced Alzheimer's disease (AD) cases. With HIV infection, the sestrin-2 immunoreactivity pattern shifted from neuropil predominance (N) to neuropil and neuronal-soma co-dominance (NS) and neuronal-soma predominance (S; P < 0.0001, Chi-square test for linear trend). Among HIV cases showing the NS or S pattern, HAND cases were preferentially associated with the S pattern (n = 10 of 20) compared to cognitively intact cases (n = 1 of 11; P = 0.047, Fisher's exact test). In AD brains, sestrin-2 immunoreactivity was mostly intense in the neuropil and co-localized with phospho-Tau immunoreactivity in a subset of neurofibrillary lesions. Phospho-Tau-immunoreactive neurofibrillary lesions were rare in HIV cases and their occurrence was not associated with HAND. Levels of isocortical 8-hydroxy-deoxyguanosine (marker of nucleic acid oxidation) immunoreactivity were not significantly altered in HAND cases compared to cognitively intact HIV cases. In conclusion, the sestrin-2 immunoreactivity redistribution to neuronal soma in HAND suggests unique involvement of sestrin-2 in the pathophysiology of HAND, which is different from the role of sestrin-2 in AD pathogenesis. Alternatively, the difference in sestrin-2 immunoreactivity distribution between HAND and AD may be related to different degrees of severity or stages of oxidative stress.

Increased cortical expression of FK506 binding protein-51 in HIV-associated neurocognitive disorders

FK506 binding protein (FKBP)-51 and FKBP52 act as molecular chaperones to control glucocorticoid receptor (GR) sensitivity. Dysregulation of proteins involved in GR-mediated signaling can lead to maladaptive stress response and aging-related cognitive decline. As HIV infection is related to chronic stress, we hypothesized that altered cortical expression of these proteins was associated with HIV-associated neurocognitive disorders (HAND). We used quantitative immunohistochemistry to assess expression levels of these proteins in the mid-frontal gyrus of 55 HIV-infected subjects free of cerebral opportunistic diseases compared to 20 age-matched non-HIV controls. The immunoreactivity normalized to the neuroanatomic area measured (IRn) for FKBP51 was increased in HIV subjects both in the cortex and subcortical white matter (p < 0.0001, U test), while no significant alterations were observed for GR or FKBP52. Notably, the cortical FKBP51 IRn was higher in HAND subjects than in cognitively normal HIV subjects (p = 0.02, U test). There was also a trend for increasing cortical FKBP51 IRn with the increasing severity of HAND (p = 0.08, Kruskal-Wallis test). No significant changes in FKBP51 IRn were found with respect to hepatitis C virus infection, lifetime methamphetamine use, or antiretroviral treatment in HIV subjects. In conclusion, the increased cortical expression of FKBP51 (an inhibitor for GR activity) might represent negative feedback in an attempt to reduce GR sensitivity in the setting of chronic stress-induced elevation of GR-mediated signaling inherent in HIV infection. The further increased FKBP51 expression might lead to maladaptive stress response and HAND.

Tyrosine kinase B protein expression is reduced in the cerebellum of patients with bipolar disorder

BACKGROUND

The role of the cerebellum in coordinating mental activity is supported by its connections with cerebral regions involved in cognitive/affective functioning, with decreased activities on functional neuroimaging observed in the cerebellum of schizophrenia patients performing mental tasks. Brain-derived neurotrophic factor (BDNF)-induced activation of tyrosine kinase B (TrkB) is essential to synaptic plasticity. We hypothesized that alterations in BDNF and TrkB expression in the cerebellum were associated with schizophrenia and affective disorders.

METHODS

We employed immunohistochemistry and immunoblotting to quantify protein expression of BDNF and TrkB in the cerebellum of patients with schizophrenia, bipolar disorder, and major depression compared to controls (n=15 each).

RESULTS

While TrkB immunoreactivity in each of the molecular and granule-cell layers was reduced in all 3 disease groups (12-34%) compared to the control (P=0.018 and 0.038, respectively, ANOVA), only the reduction in bipolar disorder remained statistically significant upon Tukey-Kramer post hoc analyses (P=0.019 and 0.021, respectively). Apparent decreases in BDNF immunoreactivity in all 3 disease groups (12-30%) compared to the control were not statistically significant. TrkB immunoreactivity was not significantly associated with any of the demographic, clinical, and postmortem variables. Immunoblotting displayed an 85-kDa TrkB-immunoreactive band, consistent with a truncated isoform, in all 60 cases.

LIMITATIONS

On immunoblotting, apparent decreases in 85-kDa-TrkB levels in all 3 disease groups compared to the control were not statistically significant.

CONCLUSIONS

Our finding of reduced TrkB expression in bipolar disorder suggests that dysregulation of TrkB-mediated neurotrophin signaling in the cerebellum may play a role in the pathophysiology of this disease.

11beta-hydroxysteroid dehydrogenase type 1 deficiency prevents memory deficits with aging by switching from glucocorticoid receptor to mineralocorticoid receptor-mediated cognitive control

Local brain amplification of glucocorticoids (GCs) by 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) plays a pivotal role in age-related memory deficits. 11β-HSD1 deficient mice are protected from spatial memory impairments with aging, but the underlying mechanisms are unknown. To determine which brain receptors [high-affinity mineralocorticoid receptors (MRs) or low-affinity glucocorticoid receptors (GRs)] are involved, spatial memory was measured in aged 11β-HSD1(-/-) mice before and during intracerebroventricular infusion (10 d) of spironolactone (MR antagonist) or RU486 (GR antagonist). Aged C57BL/6J control mice showed impaired spatial memory in the Y-maze; this improved with GR blockade, while MR blockade had no effect. In contrast, aged 11β-HSD1(-/-) mice showed intact spatial memory that became impaired with MR blockade, but not GR blockade. Hippocampal MR and GR mRNA expression and plasma corticosterone levels were not significantly altered with spironolactone or RU486 in either genotype. These data support the notion that 11β-HSD1 deficiency in aging mice leads to lower intracellular GC concentrations in brain, particularly in the hippocampus, which activate predominantly MRs to enhance memory, while in aging C57BL/6J controls, the increased intracellular GCs saturate MRs and activate predominantly GRs, thus impairing memory, an effect reversed by GR blockade.

Hippocampal dysfunction effects on context memory: possible etiology for posttraumatic stress disorder

Hippocampal volume reductions and functional impairments are reliable findings in posttraumatic stress disorder (PTSD) imaging studies. However, it is not clear if and how hippocampal dysfunction contributes to the etiology and maintenance of PTSD. Individuals with PTSD are often described as showing fear responses to trauma reminders outside of contexts in which these cues would reasonably predict danger. Animal studies suggest that the hippocampus is required to form and recall associations between contextual stimuli and aversive events. For example, the hippocampus is critical for encoding memories in which a complex configuration of multiple cues is associated with the aversive event. Conversely, the hippocampus is not required for associations with discrete cues. In animal studies, if configural memory is disrupted, learning strategies using discrete cue associations predominate. These data suggest poor hippocampal function could bias the organism toward forming multiple simple cue associations during trauma, thus increasing the chances of fear responses in multiple environments (or contexts) in which these cues may be present. Here we will examine clinical and preclinical literature to support a theory of hippocampal dysfunction as a primary contributory factor to the etiology of PTSD, and discuss future research required to test these hypotheses. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.