Hippocampal expression of myelin-associated inhibitors is induced with age-related cognitive decline and correlates with deficits of spatial learning and memory

Repeated Intravenous Administration of Human Neural Stem Cells Producing Choline Acetyltransferase Exerts Anti-Aging Effects in Male F344 Rats

Major features of aging might be progressive decreases in cognitive function and physical activity, in addition to withered appearance. Previously, we reported that the intracerebroventricular injection of human neural stem cells (NSCs named F3) encoded the choline acetyltransferase gene (F3.ChAT). The cells secreted acetylcholine and growth factors (GFs) and neurotrophic factors (NFs), thereby improving learning and memory function as well as the physical activity of aged animals. In this study, F344 rats (10 months old) were intravenously transplanted with F3 or F3.ChAT NSCs (1 × 106 cells) once a month to the 21st month of age. Their physical activity and cognitive function were investigated, and brain acetylcholine (ACh) and cholinergic and dopaminergic system markers were analyzed. Neuroprotective and neuroregenerative activities of stem cells were also confirmed by analyzing oxidative damages, neuronal skeletal protein, angiogenesis, brain and muscle weights, and proliferating host stem cells. Stem cells markedly improved both cognitive and physical functions, in parallel with the elevation in ACh levels in cerebrospinal fluid and muscles, in which F3.ChAT cells were more effective than F3 parental cells. Stem cell transplantation downregulated CCL11 and recovered GFs and NFs in the brain, leading to restoration of microtubule-associated protein 2 as well as functional markers of cholinergic and dopaminergic systems, along with neovascularization. Stem cells also restored muscular GFs and NFs, resulting in increased angiogenesis and muscle mass. In addition, stem cells enhanced antioxidative capacity, attenuating oxidative damage to the brain and muscles. The results indicate that NSCs encoding ChAT improve cognitive function and physical activity of aging animals by protecting and recovering functions of multiple organs, including cholinergic and dopaminergic systems, as well as muscles from oxidative injuries through secretion of ACh and GFs/NFs, increased antioxidant elements, and enhanced blood flow.

Decreased Hippocampal Neurogenesis in Aged Male Wistar Rats Is Not Associated with Memory Acquisition in a Water Maze

Brain aging is associated with a progressive decrease in learning abilities, memory, attention, decision making, and sensory perception. Age-related cognitive disturbances may be related to a decrease in the functional capacities of the hippocampus. This brain region is essential for learning and memory, and the lifelong neurogenesis occurring in the subgranular zone of the dentate gyrus may be a key event mediating the mnemonic functions of the hippocampus. In the present study, we investigated whether age-related changes in hippocampal neurogenesis are associated with learning and memory disturbances. Four- and 24-month-old rats were trained to find a hidden platform in a water maze. Though the older group showed higher latency to search the platform as compared to the younger group, both groups learned the task. However, the density of proliferating (PCNA-positive), differentiating (Dcx-positive), and new neurons (pre-labeled BrdU-positive) was significantly lower in the hippocampus of aged rats as compared to young ones. This inhibition of neurogenesis could be related to increased local production of nitric oxide since the density of neurons expressing neuronal NO-synthase was higher in the aged hippocampus. Thus, we can suggest that an age-related decrease in neurogenesis is not directly associated with place learning in aged rats.

Anti-LINGO-1 antibody protects neurons and synapses in the medial prefrontal cortex of APP/PS1 transgenic mice

The medial prefrontal cortex (mPFC), one of the most vulnerable brain regions in Alzheimer's disease (AD), plays a critical role in cognition. Leucine-rich repeat and immunoglobulin-like domain-containing nogo receptor-interacting protein-1 (LINGO-1) negatively affects nerve growth in the central nervous system; however, its role in the pathological damage to the mPFC remains to be studied in AD. In this study, an anti-LINGO-1 antibody was administered to 10-month-old APP/PS1 mice, and behavioral tests, stereological methods, immunohistochemistry and immunofluorescence were used to answer this question. Our results revealed that LINGO-1 was highly expressed in the neurons of the mPFC of AD mice, and the anti-LINGO-1 antibody improved prefrontal cortex-related function and reduced the protein level of LINGO-1, atrophy of the volume, Aβ deposition and massive losses of synapses and neurons in the mPFC of AD mice. Antagonizing LINGO-1 could effectively alleviate the pathological damage in the mPFC of AD mice, which might be an important structural basis for improving prefrontal cortex-related function. Abnormal expression of LINGO-1 in the mPFC may be one of the key targets of AD, and the effect initiated by the anti-LINGO-1 antibody may provide an important basis in the search for drugs for the prevention and treatment of AD.

Evidence for preserved insulin responsiveness in the aging rat brain

Insulin appears to exert salutary effects in the central nervous system (CNS). Thus, brain insulin resistance has been proposed to play a role in brain aging and dementia but is conceptually complex and unlikely to fit classic definitions established in peripheral tissues. Thus, we sought to characterize brain insulin responsiveness in young (4-5 months) and old (24 months) FBN male rats using a diverse set of assays to determine the extent to which insulin effects in the CNS are impaired with age. When performing hyperinsulinemic-euglycemic clamps in rats, intracerebroventricular (ICV) infusion of insulin in old animals improved peripheral insulin sensitivity by nearly two-fold over old controls and comparable to young rats, suggesting preservation of this insulin-triggered response in aging per se (p < 0.05). We next used an imaging-based approach by comparing ICV vehicle versus insulin and performed resting state functional magnetic resonance imaging (rs-fMRI) to evaluate age- and insulin-related changes in network connectivity within the default mode network. In aging, lower connectivity between the mesial temporal (MT) region and other areas, as well as reduced MT signal complexity, was observed in old rats, which correlated with greater cognitive deficits in old. Despite these stark differences, ICV insulin failed to elicit any significant alteration to the BOLD signal in young rats, while a significant deviation of the BOLD signal was observed in older animals, characterized by augmentation in regions of the septal nucleus and hypothalamus, and reduction in thalamus and nucleus accumbens. In contrast, ex vivo stimulation of hippocampus with 10 nM insulin revealed increased Akt activation in young (p < 0.05), but not old rats. Despite similar circulating levels of insulin and IGF-1, cerebrospinal fluid concentrations of these ligands were reduced with age. Thus, these data highlight the complexity of capturing brain insulin action and demonstrate preserved or heightened brain responses to insulin with age, despite dampened canonical signaling, thereby suggesting impaired CNS input of these ligands may be a feature of reduced brain insulin action, providing further rationale for CNS replacement strategies.

Deficiency in FTSJ1 Affects Neuronal Plasticity in the Hippocampal Formation of Mice

Simple Summary

Neuronal plasticity refers to the brain’s ability to adapt in response to activity-dependent changes. This process, among others, allows the brain to acquire memory or to compensate for a neurocognitive deficit. We analyzed adult FTSJ1-deficient mice in order to gain insight into the role of FTSJ1 in neuronal plasticity. These mice displayed alterations in the hippocampus (a brain structure that is involved in memory and learning, among other functions) e.g., in the form of changes in dendritic spines. Changes in dendritic spines are considered to represent a morphological hallmark of altered neuronal plasticity, and thus FTSJ1 deficiency might have a direct effect upon the capacity of the brain to adapt to plastic changes. Long-term potentiation (LTP) is an electrophysiological correlate of neuronal plasticity, and is related to learning and to processes attributed to memory. Here we show that LTP in FTSJ1-deficient mice is reduced, hinting at disturbed neuronal plasticity. These findings suggest that FTSJ1 deficiency has an impact on neuronal plasticity not only morphologically but also on the physiological level.

Abstract

The role of the tRNA methyltransferase FTSJ1 in the brain is largely unknown. We analyzed whether FTSJ1-deficient mice (KO) displayed altered neuronal plasticity. We explored open field behavior (10 KO mice (aged 22–25 weeks)) and 11 age-matched control littermates (WT) and examined mean layer thickness (7 KO; 6 WT) and dendritic spines (5 KO; 5 WT) in the hippocampal area CA1 and the dentate gyrus. Furthermore, long-term potentiation (LTP) within area CA1 was investigated (5 KO; 5 WT), and mass spectrometry (MS) using CA1 tissue (2 each) was performed. Compared to controls, KO mice showed a significant reduction in the mean thickness of apical CA1 layers. Dendritic spine densities were also altered in KO mice. Stable LTP could be induced in the CA1 area of KO mice and remained stable at for at least 1 h, although at a lower level as compared to WTs, while MS data indicated differential abundance of several proteins, which play a role in neuronal plasticity. FTSJ1 has an impact on neuronal plasticity in the murine hippocampal area CA1 at the morphological and physiological levels, which, in conjunction with comparable changes in other cortical areas, might accumulate in disturbed learning and memory functions.

Anti-LINGO-1 antibody treatment alleviates cognitive deficits and promotes maturation of oligodendrocytes in the hippocampus of APP/PS1 mice

Leucine-rich repeat and immunoglobulin-like domain-containing nogo receptor-interacting protein 1 (LINGO-1), a negative regulator of oligodendrocyte differentiation and myelination, is associated with cognitive function, and its expression is highly upregulated in Alzheimer's disease (AD) patients. Anti-LINGO-1 antibody treatment can effectively antagonize the negative regulatory effect of LINGO-1. In this study, we aim to assess the effect of anti-LINGO-1 antibody treatment on cognition and hippocampal oligodendrocytes in an AD transgenic animal model. First, 10-month-old male APP/PS1 mice were administered anti-LINGO-1 antibody for 8 weeks. Then, learning and memory abilities were assessed with the Morris water maze (MWM) and Y-maze tests, and amyloid-beta (Aβ) deposition and hippocampal oligodendrocytes were investigated by immunohistochemistry, immunofluorescence, and stereology. We found that anti-LINGO-1 antibody alleviated the deficits in spatial learning and memory abilities and working and reference memory abilities, decreased the density of LINGO-1 positive cells, decreased Aβ deposition, significantly increased the number of mature oligodendrocytes and the density of myelin, reversed the abnormal increases in the number of oligodendrocyte lineage cells and the densities of oligodendrocytes precursor cells in APP/PS1 mice. Our results provide evidence that LINGO-1 might be involved in the process of oligodendrocyte dysmaturity in the hippocampus of AD mice and that antagonizing LINGO-1 can alleviate cognitive deficits in APP/PS1 mice and decrease Aβ deposition and promote oligodendrocyte differentiation and maturation in the hippocampus of these mice. Our findings suggest that changes in LINGO-1 and oligodendrocytes in the hippocampus play important roles in the pathogenesis of AD and that antagonizing LINGO-1 might be a potential therapeutic strategy for AD. This article is protected by copyright. All rights reserved.

The Clinical Significance of Cerebrospinal Fluid Reticulon 4 (RTN4) Levels in the Differential Diagnosis of Neurodegenerative Diseases

Neurodegenerative diseases (NDs) belong to the top global causes of mortality. Diagnostic approaches to improve early diagnosis and differentiation of these diseases are constantly being sought. Therefore, we aimed to assess the cerebrospinal fluid (CSF) concentrations of Reticulon 4 (RTN4) in patients with neurodegenerative diseases and evaluate the potential clinical usefulness of this protein. RTNs are transmembrane proteins mediating neuroanatomical plasticity and functional recovery after central nervous system injury or diseases. According to our best knowledge, this is the first investigation providing the data concerning the dynamic of CSF RTN4 protein levels in patients with different NDs. Methods: Overall, 77 newly diagnosed patients with neurodegenerative diseases, including Alzheimer’s disease (AD), Parkinson’s disease (PD), and multiple sclerosis (MS), as well as 21 controls, were enrolled in the study. The CSF concentrations of tested proteins were assessed using immunological assays. Results: We revealed significantly higher CSF RTN4A levels in patients with AD, PD, and MS in comparison to the controls. Moreover, the comparative analysis of RTN4 concentration between different neurodegenerative diseases revealed the highest concentration of RTN4A in AD patients and a statistically significant difference between AD vs. PD, and AD vs. MS groups. The increased CSF level of the protein correlated with Tau, and pTau181 proteins in AD as well as in PD patients. Conclusions: Our study presents a previously not identified clinical utility of RTN4 in the differential diagnosis of neurodegenerative diseases.

Anti-LINGO-1 antibody ameliorates cognitive impairment, promotes adult hippocampal neurogenesis, and increases the abundance of CB1R-rich CCK-GABAergic interneurons in AD mice

In view of the negative regulatory effect of leucine-rich repeat and immunoglobulin-like domain-containing nogo receptor-interacting protein 1 (LINGO-1) on neurons, an antibody against LINGO-1 (anti-LINGO-1 antibody) was herein administered to 10-month-old APP/PS1 transgenic Alzheimer's disease (AD) mice for 2 months as an experimental intervention. Behavioral, stereology, immunohistochemistry and immunofluorescence analyses revealed that the anti-LINGO-1 antibody significantly improved the cognitive abilities, promoted adult hippocampal neurogenesis (AHN), decreased the amyloid beta (Aβ) deposition, enlarged the hippocampal volume, and increased the numbers of total neurons and GABAergic interneurons, including GABAergic and CCK-GABAergic interneurons rich in cannabinoid type 1 receptor (CB1R), in the hippocampus of AD mice. In contrast, this intervention significantly reduced the number of GABAergic interneurons expressing LINGO-1 and CB1R in the hippocampus of AD mice. More importantly, we also found a negative correlation between LINGO-1 and CB1R on GABAergic interneurons in the hippocampus of AD mice, while the anti-LINGO-1 antibody reversed this relationship. These results indicated that LINGO-1 plays an important role in the process of hippocampal neuron loss in AD mice and that antagonizing LINGO-1 can effectively prevent hippocampal neuron loss and promote AHN. The improvement in cognitive abilities may be attributed to the improvement in AHN, and in the numbers of GABAergic interneurons and CCK-GABAergic interneurons rich in CB1Rs in the hippocampus of AD mice induced by the anti-LINGO-1 antibody. Collectively, the double target effect (LINGO-1 and CB1R) initiated by the anti-LINGO-1 antibody may provide an important basis for the study of drugs for the prevention and treatment of AD in the future.

LOTUS, an endogenous Nogo receptor antagonist, is involved in synapse and memory formation

The Nogo signal is involved in impairment of memory formation. We previously reported the lateral olfactory tract usher substance (LOTUS) as an endogenous antagonist of the Nogo receptor 1 that mediates the inhibition of axon growth and synapse formation. Moreover, we found that LOTUS plays an essential role in neural circuit formation and nerve regeneration. However, the effects of LOTUS on synapse formation and memory function have not been elucidated. Here, we clearly showed the involvement of LOTUS in synapse formation and memory function. The cultured hippocampal neurons derived from lotus gene knockout (LOTUS-KO) mice exhibited a decrease in synaptic density compared with those from wild-type mice. We also found decrease of dendritic spine formation in the adult hippocampus of LOTUS-KO mice. Finally, we demonstrated that LOTUS deficiency impairs memory formation in the social recognition test and the Morris water maze test, indicating that LOTUS is involved in functions of social and spatial learning and memory. These findings suggest that LOTUS affects synapse formation and memory function.

The ZiBuPiYin recipe regulates proteomic alterations in brain mitochondria-associated ER membranes caused by chronic psychological stress exposure: Implications for cognitive decline in Zucker diabetic fatty rats

Chronic psychological stress (PS) cumulatively affects memory performance through the deleterious effects on hypothalamic-pituitary-adrenal axis regulation. Several functions damaged in cognitive impairment-related diseases are regulated by mitochondria-associated ER membranes (MAMs). To elucidate the role of ZiBuPiYin recipe (ZBPYR) in regulating the MAM proteome to improve PS-induced diabetes-associated cognitive decline (PSD), differentially expressed MAM proteins were identified among Zucker diabetic fatty rats, PSD rats, and PS combined with ZBPYR administration rats via iTRAQ with LC-MS/MS. Proteomic analysis revealed that the expressions of 85 and 33 proteins were altered by PS and ZBPYR treatment, respectively. Among these, 21 proteins were differentially expressed under both PS and ZBPYR treatments, whose functional categories included energy metabolism, lipid and protein metabolism, and synaptic dysfunction. Furthermore, calcium signaling and autophagy-related proteins may play roles in the pathogenesis of PSD and the mechanism of ZBPYR, respectively. Notably, KEGG pathway analysis suggested that ‘Alzheimer's disease’ and ‘oxidative phosphorylation’ pathways may be impaired in PSD pathogenesis, while ZBPYR could play a neuroprotective role through regulating the above pathways. Overall, exposure to chronic PS contributes to the evolution of diabetes-associated cognitive decline and ZBPYR might prevent and treat PSD by regulating the MAM proteome.

Effect of ladostigil treatment of aging rats on gene expression in four brain areas associated with regulation of memory

Episodic and spatial memory decline in aging and are controlled by the hippocampus, perirhinal, frontal and parietal cortices and the connections between them. Ladostigil, a drug with antioxidant and anti-inflammatory activity, was shown to prevent the loss of episodic and spatial memory in aging rats. To better understand the molecular effects of aging and ladostigil on these brain regions we characterized the changes in gene expression using RNA-sequencing technology in rats aged 6 and 22 months. We found that the changes induced by aging and chronic ladostigil treatment were brain region specific. In the hippocampus, frontal and perirhinal cortex, ladostigil decreased the overexpression of genes regulating calcium homeostasis, ion channels and those adversely affecting synaptic function. In the parietal cortex, ladostigil increased the expression of several genes that provide neurotrophic support, while reducing that of pro-apoptotic genes and those encoding pro-inflammatory cytokines and their receptors. Ladostigil also decreased the expression of axonal growth inhibitors and those impairing mitochondrial function. Together, these actions could explain the protection by ladostigil against age-related memory decline.

Altered Hippocampal Epigenetic Regulation Underlying Reduced Cognitive Development in Response to Early Life Environmental Insults

The hippocampus is involved in learning and memory and undergoes significant growth and maturation during the neonatal period. Environmental insults during this developmental timeframe can have lasting effects on brain structure and function. This study assessed hippocampal DNA methylation and gene transcription from two independent studies reporting reduced cognitive development stemming from early life environmental insults (iron deficiency and porcine reproductive and respiratory syndrome virus (PRRSv) infection) using porcine biomedical models. In total, 420 differentially expressed genes (DEGs) were identified between the reduced cognition and control groups, including genes involved in neurodevelopment and function. Gene ontology (GO) terms enriched for DEGs were associated with immune responses, angiogenesis, and cellular development. In addition, 116 differentially methylated regions (DMRs) were identified, which overlapped 125 genes. While no GO terms were enriched for genes overlapping DMRs, many of these genes are known to be involved in neurodevelopment and function, angiogenesis, and immunity. The observed altered methylation and expression of genes involved in neurological function suggest reduced cognition in response to early life environmental insults is due to altered cholinergic signaling and calcium regulation. Finally, two DMRs overlapped with two DEGs, VWF and LRRC32, which are associated with blood brain barrier permeability and regulatory T-cell activation, respectively. These results support the role of altered hippocampal DNA methylation and gene expression in early life environmentally-induced reductions in cognitive development across independent studies.

Treatment With Nilvadipine Mitigates Inflammatory Pathology and Improves Spatial Memory in Aged hTau Mice After Repetitive Mild TBI

Mild traumatic brain injury (mTBI) is the most common form of brain trauma worldwide. The effects of mTBI are not well-studied within the elderly population, yet older adults constitute a significant portion of all mTBI patients. Few preclinical studies have focused on the effects of mTBI, or mTBI treatments, in the aged brain, and none have explored repetitive mTBI (r-mTBI). In this study, we have administered our well-characterized 5-injury model (5 r-mTBI) to hTau mice aged 24 months to explore the neurobehavioral and neuropathological outcomes, and the effects of treatment with the dihydropyridine, Nilvadipine. Our previous studies have shown that Nilvadipine inhibits spleen tyrosine kinase (Syk), is effective at reducing inflammation, tau hyperphosphorylation, and amyloid production, and it has recently been investigated in a European Phase III clinical trial for Alzheimer’s disease (AD). In our 24-month-old r-mTBI mice, we observed increased neuroinflammation and a trend toward impaired cognitive performance compared to sham controls. Treatment with Nilvadipine mitigated the TBI-induced inflammatory response in aged r-mTBI animals and significantly improved spatial memory. To our knowledge, this is the only preclinical study focusing on the treatment of r-mTBI in aged, and these results suggest a therapeutic potential of Nilvadipine for consequences of mTBI.

[Inhibitors of CNS regeneration, their physiological role and participation in pathogenesis of diseases]

The review is devoted to axon growth inhibitors in the CNS, including a physiological role of myelin-associated proteins (Nogo-A, MAG, OMgp) and their involvement in the pathogenesis of various diseases (spinal injuries, stroke, neurodegenerations).

Nogo-66 Restricts Synaptic Strengthening via Lingo1 and the ROCK2-Cofilin Pathway to Control Actin Dynamics

Nogo-A restricts long-term potentiation (LTP) at the Schaffer collateral-CA1 pathway in the adult hippocampus via 2 extracellular domains: Nogo-A-Δ20 and Nogo-66. Nogo-66 signals via Nogo Receptor 1 (NgR1) to regulate synaptic function. Whether the NgR1 coreceptors Lingo1 and p75NTR are involved in the signaling in this context is still not known. Moreover, the intracellular cascade mediating the activity of Nogo-66 in restricting LTP is unexplored. We combine electrophysiology and biochemistry in acute hippocampal slices and demonstrate that a loss of function for Lingo1 results in a significant increase in LTP levels at the Schaffer collateral-CA1 pathway, and that Lingo1 is the NgR1 coreceptor mediating the role of Nogo-66 in restricting LTP. Our data show that p75NTR is not involved in mediating the Nogo-66 effect on LTP. Moreover, loss of function for p75NTR and NgR1 equally attenuate LTD, suggesting that p75NTR might mediate the NgR1-dependent regulation of LTD, independently of Nogo-66. Finally, our results indicate that Nogo-66 signaling limits LTP via the ROCK2-Cofilin pathway to control the dynamics of the actin cytoskeleton. The present results elucidate the signaling pathway activated by Nogo-66 to control LTP and contribute to the understanding of how Nogo-A stabilizes the neural circuits to limit activity-dependent plasticity events in the mature hippocampus.

Three-dimensional visualization and a deep-learning model reveal complex fungal parasite networks in behaviorally manipulated ants

Some microbes possess the ability to adaptively manipulate host behavior. To better understand how such microbial parasites control animal behavior, we examine the cell-level interactions between the species-specific fungal parasite Ophiocordyceps unilateralis sensu lato and its carpenter ant host (Camponotus castaneus) at a crucial moment in the parasite's lifecycle: when the manipulated host fixes itself permanently to a substrate by its mandibles. The fungus is known to secrete tissue-specific metabolites and cause changes in host gene expression as well as atrophy in the mandible muscles of its ant host, but it is unknown how the fungus coordinates these effects to manipulate its host's behavior. In this study, we combine techniques in serial block-face scanning-electron microscopy and deep-learning-based image segmentation algorithms to visualize the distribution, abundance, and interactions of this fungus inside the body of its manipulated host. Fungal cells were found throughout the host body but not in the brain, implying that behavioral control of the animal body by this microbe occurs peripherally. Additionally, fungal cells invaded host muscle fibers and joined together to form networks that encircled the muscles. These networks may represent a collective foraging behavior of this parasite, which may in turn facilitate host manipulation.

A proteomic analysis of contextual fear conditioned rats reveals dynamic modifications in neuron and oligodendrocyte protein expression in the dentate gyrus

Contextual memory is an intricate process involving synaptic plasticity and network rearrangement. Both are governed by many molecular processes including phosphorylation and modulation of protein expression. However, little is known about the molecules involved in it. Here, we exploited the advantages of a quantitative proteomic approach to identify a great number of molecules in the rat dentate gyrus after a contextual fear conditioning session. Our results allowed us to highlight protein expression patterns, not only related to neuroplasticity, but also to myelin structure, such as myelin basic protein and myelin proteolipid protein showing a decrease in expression. Validation of the modification in protein expression reveals a dynamic profile during the 48 h following the fear conditioning session. The expression of proteins involved in neurite outgrowth, such as BASP-1 and calcineurin B1, and in synaptic structure and function, VAMP2 and RAB3C, was increased in the dentate gyrus of rats submitted to fear conditioning compared to controls. We showed that the increase in BASP-1 protein was specific to fear conditioning learning as it was not present in immediate-shock rats, neither in rats exposed to a novel environment without being shocked. As myelin is known to stabilise synaptic network, the decrease in myelin proteins suggests a neuroglia interactive process taking place in the dentate gyrus in the 24 h following contextual fear learning, which has never been demonstrated before. These results therefore open the way to the study of new plasticity mechanisms underlying learning and memory.

Impact of neonatal iron deficiency on hippocampal DNA methylation and gene transcription in a porcine biomedical model of cognitive development

BACKGROUND

Iron deficiency is a common childhood micronutrient deficiency that results in altered hippocampal function and cognitive disorders. However, little is known about the mechanisms through which neonatal iron deficiency results in long lasting alterations in hippocampal gene expression and function. DNA methylation is an epigenetic mark involved in gene regulation and altered by environmental factors. In this study, hippocampal DNA methylation and gene expression were assessed via reduced representation bisulfite sequencing and RNA-seq on samples from a previous study reporting reduced hippocampal-based learning and memory in a porcine biomedical model of neonatal iron deficiency.

RESULTS

In total 192 differentially expressed genes (DEGs) were identified between the iron deficient and control groups. GO term and pathway enrichment analysis identified DEGs associated with hypoxia, angiogenesis, increased blood brain barrier (BBB) permeability, and altered neurodevelopment and function. Of particular interest are genes previously implicated in cognitive deficits and behavioral disorders in humans and mice, including HTR2A, HTR2C, PAK3, PRSS12, and NETO1. Altered genome-wide DNA methylation was observed across 0.5 million CpG and 2.4 million non-CpG sites. In total 853 differentially methylated (DM) CpG and 99 DM non-CpG sites were identified between groups. Samples clustered by group when comparing DM non-CpG sites, suggesting high conservation of non-CpG methylation in response to neonatal environment. In total 12 DM sites were associated with 9 DEGs, including genes involved in angiogenesis, neurodevelopment, and neuronal function.

CONCLUSIONS

Neonatal iron deficiency leads to altered hippocampal DNA methylation and gene regulation involved in hypoxia, angiogenesis, increased BBB permeability, and altered neurodevelopment and function. Together, these results provide new insights into the mechanisms through which neonatal iron deficiency results in long lasting reductions in cognitive development in humans.

Cognitive differences between Sprague-Dawley rats selectively bred for sensitivity or resistance to diet induced obesity

Epidemiological studies have shown strong correlations between high fat diets, diet-induced obesity and cognitive impairment, primarily focusing on cognitive defects after the onset of obesity. A remaining question is whether cognitive impairment precedes obesity in individuals metabolically prone to diet-induced obesity. The inbred diet-induced obesity sensitive (DIO) and resistant (DR) strains of Sprague-Dawley rats serve as models for human polygenic obesity. DIO rats become overweight on a standard rat chow and have metabolic symptoms similar to overweight humans. We hypothesized that cognitive impairment pre-exists in adult male DIO rats prior to exposure to high fat diet. Male DIO and DR rats were fed a standard rat chow diet from 4 through 20 weeks of age and subjected to the Morris water maze at 12 weeks of age. At 5 and 20 weeks of age, brains of DIO and DR males were examined for indices of inflammation, lipid peroxidation and neuroproliferation. DIO rats showed significant memory impairment on water maze and increased indices of hippocampal inflammation at 20 weeks of age compared to DR rats. At 5 weeks of age, DIO rats exhibited significantly less neural progenitor cell (NPCs) proliferation in the dentate gyrus and increased hippocampal lipid peroxidation compared to DR rats. Therefore, we conclude that DIO rats exhibit early post-weaning indices of hippocampal inflammation, lipid peroxidation and decreased NPC proliferation, as well as impaired hippocampal dependent memory by early adulthood suggesting that inherent metabolic differences predispose the DIO strain to cognitive deficit prior to exposure to high fat diet and/or obesity.

CNS-wide Sexually Dimorphic Induction of the Major Histocompatibility Complex 1 Pathway With Aging

The major histocompatibility complex I (MHCI) pathway, which canonically functions in innate immune viral antigen presentation and detection, is functionally pleiotropic in the central nervous system (CNS). Alternative roles include developmental synapse pruning, regulation of synaptic plasticity, and inhibition of neuronal insulin signaling; all processes altered during brain aging. Upregulation of MHCI components with aging has been reported; however, no systematic examination of MHCI cellular localization, expression, and regulation across CNS regions, life span, and sexes has been reported. In the mouse, MHCI is expressed by neurons and microglia, and MHCI components and receptors (H2-K1, H2-D1, β2M, Lilrb3, Klra2, CD247) display markedly different expression profiles across the hippocampus, cortex, cerebellum, brainstem, and retina. MHCI components, receptors, associated inflammatory transcripts (IL1α, IL1β, IL6, TNFα), and TAP (transporter associated with antigen processing) components are induced with aging and to a greater degree in female than male mice across CNS regions. H2-K1 and H2-D1 expression is associated with differential CG and non-CG promoter methylation across CNS regions, ages, and between sexes, and concomitant increased expression of proinflammatory genes. Meta-analysis of human brain aging data also demonstrates age-related increases in MHCI. Induction of MHCI signaling could contribute to altered synapse regulation and impaired synaptic plasticity with aging.

Non-canonical actions of Nogo-A and its receptors

Nogo-A is a myelin associated protein and one of the most potent neurite growth inhibitors in the central nervous system. Interference with Nogo-A signaling has thus been investigated as therapeutic target to promote functional recovery in CNS injuries. Still, the finding that Nogo-A presents a fairly ubiquitous expression in many types of neurons in different brain regions, in the eye and even in the inner ear suggests for further functions besides the neurite growth repression. Indeed, a growing number of studies identified a variety of functions including regulation of neuronal stem cells, modulation of microglial activity, inhibition of angiogenesis and interference with memory formation. Aim of the present commentary is to draw attention on these less well-known and sometimes controversial roles of Nogo-A. Furthermore, we are addressing the role of Nogo-A in neuropathological conditions such as ischemic stroke, schizophrenia and neurodegenerative diseases.

Insights into the physiological role of CNS regeneration inhibitors

The growth inhibitory nature of injured adult mammalian central nervous system (CNS) tissue constitutes a major barrier to robust axonal outgrowth and functional recovery following trauma or disease. Prototypic CNS regeneration inhibitors are broadly expressed in the healthy and injured brain and spinal cord and include myelin-associated glycoprotein (MAG), the reticulon family member NogoA, oligodendrocyte myelin glycoprotein (OMgp), and chondroitin sulfate proteoglycans (CSPGs). These structurally diverse molecules strongly inhibit neurite outgrowth in vitro, and have been most extensively studied in the context of nervous system injury in vivo. The physiological role of CNS regeneration inhibitors in the naïve, or uninjured, CNS remains less well understood, but has received growing attention in recent years and is the focus of this review. CNS regeneration inhibitors regulate myelin development and axon stability, consolidate neuronal structure shaped by experience, and limit activity-dependent modification of synaptic strength. Altered function of CNS regeneration inhibitors is associated with neuropsychiatric disorders, suggesting crucial roles in brain development and health.

Glatiramer acetate guards against rapid memory decline during relapsing-remitting experimental autoimmune encephalomyelitis

Cognitive decline presents a therapeutic challenge for patients with multiple sclerosis (MS), a disease characterized by recurrent autoimmune demyelination and by progressive CNS degeneration. Glatiramer acetate (GA, also known as Copolymer 1, Cop-1, or Copaxone), commonly used to treat MS, reduces the frequency of relapses; it has both anti-inflammatory and neuroprotective properties. However, clinical trials have not definitively shown that GA improves cognitive impairment during MS. Using an in vivo animal model of autoimmune demyelination, i.e., relapsing-remitting experimental autoimmune encephalomyelitis (EAE), we tested short-term memory in EAE mice (EAE), in EAE mice treated with GA for 10 days starting at the time of immunization (EAE + GA), and in age-matched healthy, naïve mice (Naïve). Short-term memory was assessed using the cross-maze test at 10, 20, and 30 days post-immunization (d.p.i.); data were analyzed at each time point and over time. At 10 d.p.i., EAE and EAE + GA mice had better memory function than Naïve mice. However, at the later time points, EAE mice had a steep negative slope of memory function (indicating decline), whereas EAE + GA mice had a flatter, less-negative slope of memory function. Notably, the memory function of EAE mice significantly decreased over time compared with that of Naïve mice, indicating that EAE had a negative impact on cognitive ability. In contrast, there was no statistically significant difference between the slopes of memory function in mice with EAE treated with GA versus Naïve mice, which revealed effective, albeit partial, protection by GA treatment against progressive memory decline during EAE disease. Of particular interest, although EAE mice had memory decline over 30 d.p.i., their clinical disease scores improved during that time. Thus, our results suggest that EAE mice had a significant progressive memory decline and that GA, administered at the time of immunization, partially guards against rapid memory decline.

Age-dependent decline of nogo-a protein in the mouse cerebrum

Nogo-A, a myelin-associated neurite growth inhibitory protein, is implicated in synaptic plasticity. It binds to its receptor namely the Nogo-66 receptor1 (NgR1) and regulates filamentous (F) actin dynamics via small GTPases of the Rho family, RhoA kinase (ROCK), LimK and cofilin. These proteins are associated with the structural plasticity, one of the components of synaptic plasticity, which is known to decline with normal aging. So, the level of Nogo-A and its receptor NgR1 are likely to vary during normal brain aging. However, it is not clearly understood how the levels of Nogo-A and its receptor NgR1 change in the cerebrum during aging. Several studies show an age- and gender-dependent decline in synaptic plasticity. Therefore, the present study was planned to analyze the relative changes in the mRNA and protein levels of Nogo-A and NgR1 in both male and female mice cerebrum during normal aging. Western blot analysis has shown decrease in Nogo-A protein level during aging in both male and female mice cerebrum. This was further confirmed by immunofluorescence analysis. RT-PCR analysis of Nogo-A mRNA showed no significant difference in the above-mentioned groups. This was also supported by in situ hybridization. NgR1 protein and its mRNA expression levels showed no significant alteration with aging in the cerebrum of both male and female mice. Taken together, we speculate that the downregulation of Nogo-A protein might have a role in the altered synaptic plasticity during aging.

Effects of YC-1 on learning and memory functions of aged rats

Background

The aim of this study was to investigate the effects of a potent nitric oxide-guanylate cyclase activator, 3-(5′-hydroxymethyl-2′-furyl)-1-benzylindazole (YC-1), on learning and memory functions in aged rats.

Material/Methods

Rats were divided into 2 groups as 4-month-old and 24-month-old rats. Rats received YC-1 (1 mg/kg/day) for 2 weeks long-term. Morris water maze (MWM) and passive avoidance (PA) tests were used to determine learning and memory functions.

Results

In the MWM test, there is a significant increase in the acquisition latency (1–4 days) of 24-month-old rats. There is a significant reduction in the “time spent in the escape platform’s quadrant” in 24-month-old rats compared to 4-month-old rats in the probe trial of the MWM test. YC-1 treatment reversed the reduction of the “time spent in the escape platform’s quadrant” of 24-month-old rats. In the PA test, there was no significant difference in the 1^st-day latency of rats in all groups. On the 2nd day, retention latency significantly decreased in the 24-month-old rats compared to 4-month-olds. YC-1 reversed the diminished retention latency in 24-month-old rats. YC-1 treatment and aging did not affect results of the locomotor activity test or the foot-shock sensitivity test, suggesting our results were not due to a change in motor activity or disability of the animals.

Conclusions

Our findings suggest that activation of the NO-sGC-cGMP pathway plays an important role in spatial and emotional learning and memory functions in aged rats.

Hippocampal subregions exhibit both distinct and shared transcriptomic responses to aging and nonneurodegenerative cognitive decline

Impairment of hippocampal-dependent spatial learning and memory with aging affects a large segment of the aged population. Hippocampal subregions (CA1, CA3, and DG) have been previously reported to express both common and specific morphological, functional, and gene/protein alterations with aging and cognitive decline. To comprehensively assess gene expression with aging and cognitive decline, transcriptomic analysis of CA1, CA3, and DG was conducted using Adult (12M) and Aged (26M) F344xBN rats behaviorally characterized by Morris water maze performance. Each subregion demonstrated a specific pattern of responses with aging and with cognitive performance. The CA1 and CA3 demonstrating the greatest degree of shared gene expression changes. Analysis of the pathways, processes, and regulators of these transcriptomic changes also exhibit a similar pattern of commonalities and differences across subregions. Gene expression changes between Aged cognitively Intact and Aged cognitively Impaired rats often showed an inversion of the changes between Adult and Aged rats. This failure to adapt rather than an exacerbation of the aging phenotype questions a conventional view that cognitive decline is exaggerated aging. These results are a resource for investigators studying cognitive decline and also demonstrate the need to individually examine hippocampal subregions in molecular analyses of aging and cognitive decline.

Nogo-A-deficient Transgenic Rats Show Deficits in Higher Cognitive Functions, Decreased Anxiety, and Altered Circadian Activity Patterns

Decreased levels of Nogo-A-dependent signaling have been shown to affect behavior and cognitive functions. In Nogo-A knockout and knockdown laboratory rodents, behavioral alterations were observed, possibly corresponding with human neuropsychiatric diseases of neurodevelopmental origin, particularly schizophrenia. This study offers further insight into behavioral manifestations of Nogo-A knockdown in laboratory rats, focusing on spatial and non-spatial cognition, anxiety levels, circadian rhythmicity, and activity patterns. Demonstrated is an impairment of cognitive functions and behavioral flexibility in a spatial active avoidance task, while non-spatial memory in a step-through avoidance task was spared. No signs of anhedonia, typical for schizophrenic patients, were observed in the animals. Some measures indicated lower anxiety levels in the Nogo-A-deficient group. Circadian rhythmicity in locomotor activity was preserved in the Nogo-A knockout rats and their circadian period (tau) did not differ from controls. However, daily activity patterns were slightly altered in the knockdown animals. We conclude that a reduction of Nogo-A levels induces changes in CNS development, manifested as subtle alterations in cognitive functions, emotionality, and activity patterns.

Aged rats are hypo-responsive to acute restraint: implications for psychosocial stress in aging

Cognitive processes associated with prefrontal cortex and hippocampus decline with age and are vulnerable to disruption by stress. The stress/stress hormone/allostatic load hypotheses of brain aging posit that brain aging, at least in part, is the manifestation of life-long stress exposure. In addition, as humans age, there is a profound increase in the incidence of new onset stressors, many of which are psychosocial (e.g., loss of job, death of spouse, social isolation), and aged humans are well-understood to be more vulnerable to the negative consequences of such new-onset chronic psychosocial stress events. However, the mechanistic underpinnings of this age-related shift in chronic psychosocial stress response, or the initial acute phase of that chronic response, have been less well-studied. Here, we separated young (3 month) and aged (21 month) male F344 rats into control and acute restraint (an animal model of psychosocial stress) groups (n = 9–12/group). We then assessed hippocampus-associated behavioral, electrophysiological, and transcriptional outcomes, as well as blood glucocorticoid and sleep architecture changes. Aged rats showed characteristic water maze, deep sleep, transcriptome, and synaptic sensitivity changes compared to young. Young and aged rats showed similar levels of distress during the 3 h restraint, as well as highly significant increases in blood glucocorticoid levels 21 h after restraint. However, young, but not aged, animals responded to stress exposure with water maze deficits, loss of deep sleep and hyperthermia. These results demonstrate that aged subjects are hypo-responsive to new-onset acute psychosocial stress, which may have negative consequences for long-term stress adaptation and suggest that age itself may act as a stressor occluding the influence of new onset stressors.

Insulin-like growth factor-1 in CNS and cerebrovascular aging

Insulin-like growth factor-1 (IGF-1) is an important anabolic hormone that decreases with age. In the past two decades, extensive research has determined that the reduction in IGF-1 is an important component of the age-related decline in cognitive function in multiple species including humans. Deficiency in circulating IGF-1 results in impairment in processing speed and deficiencies in both spatial and working memory. Replacement of IGF-1 or factors that increase IGF-1 to old animals and humans reverses many of these cognitive deficits. Despite the overwhelming evidence for IGF-1 as an important neurotrophic agent, the specific mechanisms through which IGF-1 acts have remained elusive. Recent evidence indicates that IGF-1 is both produced by and has important actions on the cerebrovasculature as well as neurons and glia. Nevertheless, the specific regulation and actions of brain- and vascular-derived IGF-1 is poorly understood. The diverse effects of IGF-1 discovered thus far reveal a complex endocrine and paracrine system essential for integrating many of the functions necessary for brain health. Identification of the mechanisms of IGF-1 actions will undoubtedly provide critical insight into regulation of brain function in general and the causes of cognitive decline with age.

Increased neuroplasticity may protect against cardiovascular disease

Neuroplasticity refers to the capacity of the nervous system to modify its organization such that the brain can be shaped by environmental input. Individuals exhibit different degrees of neuroplasticity because of their different courses of growth. Neuroplasticity may thus play a role in individual differences in the treatment of neuropsychiatric diseases. The nervous system monitors and coordinates internal organ function. Thus neuroplasticity may also be associated with the pathogenesis and the treatment of some other diseases besides neuropsychiatric diseases. The cardiovascular system is controlled by the nervous system, mainly by the autonomic nervous system. Stress may lead to depression and cardiovascular disease (CVD). CVD is associated with depression, which is a disorder of decreased neuroplasticity. And the mechanisms of depression and CVD are related. So we conclude that decreased neuroplasticity causes the coexistence of depression with CVD, and increased neuroplasticity may be beneficial against the development of CVD. This theory provides another angle that can explain some of the reported phenomena related to CVD and neuropsychiatry and provide a potential treatment to protect against CVD.

Expression of NgR1-antagonizing proteins decreases with aging and cognitive decline in rat hippocampus

The myelin-associated inhibitor/Nogo-66 receptor 1 (NgR1) pathway directly functions in negative modulation of structural and electrophysiological synaptic plasticity. A previous study has established an important role of NgR1 pathway signaling in cognitive function, and we have demonstrated that multiple components of this pathway, including ligands, NgR1 co-receptors, and RhoA, are upregulated at the protein level specifically in cognitively impaired, but not age-matched cognitively intact aged rats. Recent studies have identified two novel endogenous NgR1 antagonists, LOTUS and LGI1, and an alternative co-receptor, ADAM22, which act to suppress NgR1 pathway signaling. To determine whether these endogenous NgR1-inhibiting proteins may play a compensatory role in age-related cognitive impairment by counteracting overexpression of NgR1 agonists and co-receptors, we quantified the expression of LOTUS, LGI1, and ADAM22 in hippocampal CA1, CA3 and DG subregions dissected from mature adult and aged rats cognitively phenotyped for spatial learning and memory by Morris water maze testing. We have found that endogenous inhibitors of NgR1 pathway action decrease significantly with aging and cognitive decline and that lower expression levels correlate with declining cognitive ability, particularly in CA1 and CA3. These data suggest that decreased expression of NgR1-antagonizing proteins may exert a combinatorial effect with increased NgR1 signaling pathway components to result in abnormally strong suppression of synaptic plasticity in age-related cognitive impairment.

Immune marker CD68 correlates with cognitive impairment in normally aged rats

The relationship between heightened neuroinflammation and cognitive decline in the normally aged brain is still debatable, as most data are derived from insult-related models. Accordingly, the aim of the current study was to determine whether a link could be established for 2 immune markers at the post-transcriptional level; CD68 and MHC-II, in a normally aged (24-month-old) rat population discriminated for their learning abilities. Using the Morris Water Maze (MWM) task, aged rats were divided into aged learning-impaired (AI) or -unimpaired (AU) groups. Western immunoblots of hippocampal tissue revealed a significant increase of CD68 in AI rats compared to the AU group. Moreover, up-regulated CD68 expression correlated with increased latency times in the MWM task. Immunofluorescence for CD68 revealed intense staining in the white matter regions and CA3 subregion of the hippocampus in the AI group. Despite expression of MHC-II in the AI group, no correlation was found. Overall, these data suggest that CD68 could play a role associated with cognitive decline in a subgroup of the normally aged population.

Increased hippocampal NgR1 signaling machinery in aged rats with deficits of spatial cognition

Myelin-associated inhibitor/NgR1 signaling has important roles in modulation of synaptic plasticity, with demonstrated effects on cognitive function. We have previously demonstrated that NgR1 and its ligands are upregulated in the hippocampus of aged rats with impaired spatial learning and memory, but it is unknown whether increased expression of these proteins indicates a potential increase in pathway signaling because NgR1 requires co-receptors for signal transduction through RhoA. Two co-receptor complexes have been identified to date, comprised of NgR1 and LINGO-1, and either p75 or TROY. In this study, we assessed the expression of LINGO-1, p75 and TROY, and the downstream effector RhoA in mature adult (12 months) and aged (26 months) male Fischer 344/Brown Norway hybrid rats classified as cognitively impaired or cognitively intact by Morris water maze testing. The hippocampal distribution of NgR1 and its co-receptors was assessed to determine whether receptor/co-receptor interaction, and therefore signaling through this pathway, is possible. Protein expression of LINGO-1, p75, TROY and RhoA was significantly elevated in cognitively impaired, but not intact, aged rats compared with mature adults, and expression levels correlated significantly with water maze performance. Co-localization of NgR1 with LINGO-1, p75 and TROY was observed in hippocampal neurons of aged, cognitively impaired rats. Further, expression profiles of NgR1 pathway components were demonstrated to classify rats as cognitively intact or cognitively impaired with high accuracy. Together, this suggests that hippocampal induction of this pathway is a conserved phenomenon in cognitive decline that may impair learning and memory by suppressing neuronal plasticity.

Aging, synaptic dysfunction, and insulin-like growth factor (IGF)-1

Insulin-like growth factor (IGF)-1 is an important neurotrophic hormone. Deficiency of this hormone has been reported to influence the genesis of cognitive impairment and dementia in the elderly patients. Nevertheless, there are studies indicating that cognitive function can be maintained into old age even in the absence of circulating IGF-1 and studies that link IGF-1 to an acceleration of neurological diseases. Although IGF-1 has a complex role in brain function, synaptic effects appear to be central to the IGF-1-induced improvement in learning and memory. In this review, synaptic mechanisms of learning and memory and the effects of IGF-1 on synaptic communication are discussed. The emerging data indicate that synaptic function decreases with age and that IGF-1 contributes to information processing in the brain. Further studies that detail the specific actions of this important neurotrophic hormone will likely lead to therapies that result in improved cognitive function for the elderly patients.

Neuroglial expression of the MHCI pathway and PirB receptor is upregulated in the hippocampus with advanced aging

The hippocampus undergoes changes with aging that impact neuronal function, such as synapse loss and altered neurotransmitter release. Nearly half of the aged population also develops deficits in spatial learning and memory. To identify age-related hippocampal changes that may contribute to cognitive decline, transcriptomic analysis of synaptosome preparations from adult (12 months) and aged (28 months) Fischer 344-Brown Norway rats assessed for spatial learning and memory was performed. Bioinformatic analysis identified the MHCI pathway as significantly upregulated with aging. Age-related increases in mRNAs encoding the MHCI genes RT1-A1, RT1-A2, and RT1-A3 were confirmed by qPCR in synaptosomes and in CA1 and CA3 dissections. Elevated levels of the MHCI cofactor (B2m), antigen-loading components (Tap1, Tap2, Tapbp), and two known MHCI receptors (PirB, Klra2) were also confirmed. Protein expression of MHCI was elevated with aging in synaptosomes, CA1, and DG, while PirB protein expression was induced in both CA1 and DG. MHCI expression was localized to microglia and neuronal excitatory postsynaptic densities, and PirB was localized to neuronal somata, axons, and dendrites. Induction of the MHCI antigen processing and presentation pathway in hippocampal neurons and glia may contribute to age-related hippocampal dysfunction by increasing neuroimmune signaling or altering synaptic homeostasis.