Although glucocorticoids (GCs) are known to exert numerous effects in the hippocampus, their chronic regulatory functions remain poorly understood. Moreover, evidence is inconsistent regarding the longstanding hypothesis that chronic GC exposure promotes brain aging/Alzheimer's disease. Here, we adrenalectomized male F344 rats at 15-months-of-age, maintained them for 3 months with implanted corticosterone (CORT) pellets producing low or intermediate (glucocorticoid-receptor (GR)-activating) blood levels of CORT, and performed microarray/pathway analyses in hippocampal CA1. We defined the chronic GC-dependent transcriptome as 393 genes that exhibited differential expression between Intermediate- and Low-CORT groups. Short-term CORT (4 days) did not recapitulate this transcriptome. Functional processes/pathways overrepresented by chronic CORT-upregulated genes included learning/plasticity, differentiation, glucose metabolism and cholesterol biosynthesis, whereas processes overrepresented by CORT-downregulated genes included inflammatory/immune/glial responses and extracellular structure. These profiles indicate that GCs chronically activate neuronal/metabolic processes while coordinately repressing a glial axis of reactivity/inflammation. We then compared the GC-transcriptome with a previously-defined hippocampal aging transcriptome, revealing a high proportion of common genes. Although CORT and aging moved expression of some common genes in the same-direction, the majority were shifted in opposite directions by CORT and aging (e.g., glial inflammatory genes downregulated by CORT are upregulated with aging). These results contradict the hypothesis that GCs simply promote brain aging, and also suggest that the opposite-direction shifts during aging reflect resistance to CORT regulation. Therefore, we propose a new model in which aging-related GC resistance develops in some target pathways while GC overstimulation develops in others, together generating much of the brain aging phenotype.
Glucocorticoid-dependent hippocampal transcriptome in male rats: pathway-specific alterations with aging.
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Purpose: Determine if gene expression profiles in urine sediment could provide non-invasive candidate markers for painful bladder syndrome (PBS) with and/or without Hunner lesions. Materials and Methods: Fresh catheterized urine was collected and centrifuged from control (n = 5), lesion-free (n = 5), and Hunner lesion bearing (n = 3) patients. RNA was extracted from the pelleted material and quantified by gene expression microarray (Affymetrix Human Gene ST Array). Results: Three biologically likely hypotheses were tested: A) all three groups are distinct from one another; B) controls are distinct from both types of PBS patients combined, and C) Hunner lesion PBS patients are distinct from controls and non-Hunner-lesion PBS combined. For statistical parity an unlikely fourth hypothesis was included: non-Hunner-lesion PBS patients are distinct from controls and Hunner lesion PBS combined. Analyses supported selective upregulation of genes in the Hunner lesion PBS group (hypothesis C), and these were primarily associated with inflammatory function. This profile is similar to that reported in a prior microarray study of bladder biopsies in Hunner lesion PBS. Conclusions: Urine sediment gene expression from non-Hunner-lesion PBS patients lacked a clear difference from that of control subjects, while the array signatures from PBS patients with Hunner lesions showed a clear, primarily inflammatory, signature. This signature was highly similar to that seen in a prior microarray study of bladder biopsies. Thus, although sample sizes were small, this work suggests that gene expression in urine sediment may provide a non-invasive biomarker for Hunner lesion, but not non-Hunner lesion, PBS.
Gene expression analysis of urine sediment: evaluation for potential noninvasive markers of interstitial cystitis/bladder pain syndrome.
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Alzheimer's disease (AD) is a devastating neurodegenerative disorder that threatens to reach epidemic proportions as our population ages. Although much research has examined molecular pathways associated with AD, relatively few studies have focused on critical early stages. Our prior microarray study correlated gene expression in human hippocampus with AD markers. Results suggested a new model of early-stage AD in which pathology spreads along myelinated axons, orchestrated by upregulated transcription and epigenetic factors related to growth and tumor suppression (Blalock et al., 2004). However, the microarray analyses were performed on RNA from fresh frozen hippocampal tissue blocks containing both gray and white matter, potentially obscuring region-specific changes. In the present study, we used laser capture microdissection to exclude major white matter tracts and selectively collect CA1 hippocampal gray matter from formalin-fixed, paraffin-embedded (FFPE) hippoc ampal sections of the same subjects assessed in our prior study. Microarray analyses of this gray matter-enriched tissue revealed many correlations similar to those seen in our prior study, particularly for neuron-related genes. Nonetheless, in the laser-captured tissue, we found a striking paucity of the AD-associated epigenetic and transcription factor genes that had been strongly overrepresented in the prior tissue block study. In addition, we identified novel pathway alterations that may have considerable mechanistic implications, including downregulation of genes stabilizing ryanodine receptor Ca2+ release and upregulation of vascular development genes. We conclude that FFPE tissue can be a reliable resource for microarray studies, that upregulation of growth-related epigenetic/ transcription factors with incipient AD is predominantly localized to white matter, further supporting our prior findings and model, and that alterations in vascular and ryanodine receptor-relat ed pathways in gray matter are closely associated with incipient AD.
Microarray analyses of laser-captured hippocampus reveal distinct gray and white matter signatures associated with incipient Alzheimer's disease.
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For these data, we analyzed hippocampal gene expression of nine control and 22 AD subjects of varying severity on 31 separate microarrays. We then tested the correlation of each gene's expression with MiniMental Status Examination (MMSE) and neurofibrillary tangle (NFT) scores across all 31 subjects regardless of diagnosis. These tests revealed a major transcriptional response comprising thousands of genes significantly correlated with AD markers. Several hundred of these genes were also correlated with AD markers across only control and incipient AD subjects (MMSE > 20).
Incipient Alzheimer's disease: microarray correlation analyses reveal major transcriptional and tumor suppressor responses.
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Background: Age-related cognitive deficits negatively affect quality of life and can presage serious neurodegenerative disorders. Despite sleep disruptions well-recognized negative influence on cognition, and its prevalence with age, surprisingly few studies have tested sleeps relationship to cognitive aging.
Deep sleep and parietal cortex gene expression changes are related to cognitive deficits with age.
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Studies of aging and longevity are revealing how diseases that shorten life can be controlled to improve the quality of life and lifespan itself. Two strategies under intense study to accomplish this goal are rapamycin treatment and calorie restriction. New strategies are being discovered including one that uses low-dose myriocin treatment. Myriocin inhibits the first enzyme in sphingolipid synthesis in all eukaryotes and we showed recently that low-dose myriocin treatment increases yeast lifespan at least in part by down-regulating the sphingolipid-controlled Pkh1/2-Sch9 (ortholog of mammalian S6 kinase) signaling pathway.
Reducing sphingolipid synthesis orchestrates global changes to extend yeast lifespan.
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Recent microarray studies in the hippocampus of rodents or Alzheimers disease (AD) subjects have identified a substantial number of cellular pathways/processes correlated with aging and cognitive decline. However, the temporal relationships among these expression changes or with cognitive impairment have not been studied in depth. Here, using Affymetrix microarrays, immunohistochemistry and Morris water maze cognitive testing across 5 age groups of male F344 rats (n=9-15/group, one microarray per animal), we systematically analyzed the temporal sequence and cellular localization of aging changes in expression. These were correlated with performance scores on the hippocampus-dependent Morris Water Maze task. Significant microarray results were sorted in to Early, Intermediate, Midlife, and Late patterns of expression, and functionally categorized (Early- downregulated neural development, lipid synthesis and energy-utilization; upregulated ribosomal synthesis, growth, stress/inflammatory, lysosome and protein/lipid degradation. Intermediate- increased defense/inflammatory activation and decreased transporter activity; Midlife- downregulated energy-dependent signaling and neurite growth, upregulated astroglial activation, Ca2+-binding, cholesterol/lipid trafficking, myelinogenic processes and additional lysosome/inflammation; Late- further recruitment of genes in already-altered pathways). Immunohistochemistry revealed a primarily astrocytic localization of the processes upregulated in midlife, as well as increased density of myelin proteins. Evidence of cognitive impairment first appeared in the 12-month-old group (midlife) and was increased further in the 23-month-old group, exhibiting the highest correlations with some upregulated genes related to cholesterol transport (e.g., Apoe, Abca2), protein management and ion binding. Some upregulated genes for inflammation (Il6st) and myelinogenesis (Pmp22) also correlated with impairment. Together, the data are consistent with a novel sequential cascade model of brain aging in which metabolic alterations early in maturity are followed by inflammation and midlife activation of an astrocyte-centered cholesterol trafficking pathway that stimulates oligodendrocyte remyelination programs. Importantly, this cholesterol trafficking pathway also may compete for astroglial bioenergetic support of neurons, in turn, leading to downregulation of energy-dependent pathways needed to sustain cognitive functions.
Hippocampal and cognitive aging across the lifespan: a bioenergetic shift precedes and increased cholesterol trafficking parallels memory impairment.
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Male Fischer 344 rats aged 4 months (young, n=10), 14 months (mid-aged, n=10), and 24 months (aged, n=10) were trained sequentially on two tasks: Morris Spatial Water Maze (SWM) and Object Memory Task (OMT). The training/testing sequence lasted 7 d, and hippocampal tissue was collected 24 hr later. Training and testing occured on each day except for days 2 and 3 of the 7 d sequence.
Gene microarrays in hippocampal aging: statistical profiling identifies novel processes correlated with cognitive impairment.
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Hippocampal overexpression of FK506-binding protein 12.6/1b (FKBP1b), a negative regulator of ryanodine receptor Ca2+ release, reverses aging-induced memory impairment and neuronal Ca2+ dysregulation. Here, we test the hypothesis that FKBP1b also can protect downstream transcriptional networks from aging-induced dysregulation. We gave hippocampal microinjections of FKBP1b-expressing viral vector to male rats at either 13-months-of-age (long-term) or 19-months-of-age (short-term) and tested memory performance in the Morris water maze at 21-months-of-age. Aged rats treated short- or long-term with FKBP1b substantially outperformed age-matched vector controls and performed similarly to each other and young controls. Transcriptional profiling in the same animals identified 2342 genes whose hippocampal expression was up-/down-regulated in aged controls vs. young controls (the aging effect). Of these aging-dependent genes, 876 (37%) also showed altered expression in aged FKBP1b-treated rats compared to aged controls, with FKBP1b restoring expression of essentially all such genes (872/876, 99.5%) in the direction opposite the aging effect and closer to levels in young controls. This inverse relationship between the aging and FKBP1b effects suggests that the aging effects arise from FKBP1b deficiency. Functional category analysis revealed that genes downregulated with aging and restored by FKBP1b associated predominantly with diverse brain structure categories, including cytoskeleton, membrane channels and extracellular region. Conversely, genes upregulated with aging but not restored by FKBP1b associated primarily with glial-neuroinflammatory, ribosomal and lysosomal categories. Immunohistochemistry confirmed aging-induced rarefaction, and FKBP1b-mediated restoration, of neuronal microtubular structure. Thus, a previously-unrecognized genomic network modulating diverse brain structural processes is dysregulated by aging and restored by FKBP1b overexpression.
FK506-Binding Protein 12.6/1b, a Negative Regulator of [Ca<sup>2+</sup>], Rescues Memory and Restores Genomic Regulation in the Hippocampus of Aging Rats.
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We used Au nanoparticles (Au-NPs) as a model for studying particle specific effects of manufactured nanomaterials (MNMs) by examining the toxicogenomic responses in a model soil organism, free living nematode Caenorhabditis elegans. Global genome expression for nematodes exposed to 4-nm citrate-coated Au-NPs at the LC10 (5.9 mg L-1) revealed significant differential expression of 797 genes. The levels of expression for five genes (apl-1, dyn-1, act-5, abu-11, and hsp-4) were confirmed independently with qRT-PCR. Seven common biological pathways associated with 38 of these genes were identified. Activation of 26 pqn/abu genes from noncanonical Unfolded Protein Response (UPR) pathway and up-regulation of molecular chaperones (hsp-16.1, hsp-70, hsp-3 and hsp-4) were observed and are likely indicative of endoplasmic reticulum stress. Inhibition of abu-11 with RNAi showed increase in mortality in Au-NP exposed nematodes suggesting possible involvement of abu-11 (a gene associated with specific to C. elegans UPR) in a protective mechanism against Au-NPs. Exposure to Au-NPs also caused activation of genes involved in apoptosis and necrosis and resulted ultimately in 10% mortality. These results demonstrate that Au-NPs are bioavailable and cause adverse effects to a model ecoreceptor which activate both general and specific biological pathways.
Toxicogenomic responses of the model organism Caenorhabditis elegans to gold nanoparticles.