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

NGFR Gene and Single Nucleotide Polymorphisms, rs2072446 and rs11466162, Playing Roles in Psychiatric Disorders

Psychiatric disorders are a class of complex disorders characterized by brain dysfunction with varying degrees of impairment in cognition, emotion, consciousness and behavior, which has become a serious public health issue. The NGFR gene encodes the p75 neurotrophin receptor, which regulates neuronal growth, survival and plasticity, and was reported to be associated with depression, schizophrenia and antidepressant efficacy in human patient and animal studies. In this study, we investigated its association with schizophrenia and major depression and its role in the behavioral phenotype of adult mice. Four NGFR SNPs were detected based on a study among 1010 schizophrenia patients, 610 patients with major depressive disorders (MDD) and 1034 normal controls, respectively. We then knocked down the expression of NGFR protein in the hippocampal dentate gyrus of the mouse brain by injection of shRNA lentivirus to further investigate its behavioral effect in mice. We found significant associations of s2072446 and rs11466162 for schizophrenia. Ngfr knockdown mice showed social and behavioral abnormalities, suggesting that it is linked to the etiology of neuropsychiatric disorders. We found significant associations between NGFR and schizophrenia and that Ngfr may contribute to the social behavior of adult mice in the functional study, which provided meaningful clues to the pathogenesis of psychiatric disorders.

An Rtn4/Nogo-A-interacting micropeptide modulates synaptic plasticity with age

Micropeptides, encoded from small open reading frames of 300 nucleotides or less, are hidden throughout mammalian genomes, though few functional studies of micropeptides in the brain are published. Here, we describe a micropeptide known as the Plasticity–Associated Neural Transcript Short (Pants), located in the 22q11.2 region of the human genome, the microdeletion of which conveys a high risk for schizophrenia. Our data show that Pants is upregulated in early adulthood in the mossy fiber circuit of the hippocampus, where it exerts a powerful negative effect on long-term potentiation (LTP). Further, we find that Pants is secreted from neurons, where it associates with synapses but is rapidly degraded with stimulation. Pants dynamically interacts with Rtn4/Nogo-A, a well-studied regulator of adult plasticity. Pants interaction with Nogo-A augments its influence over postsynaptic AMPA receptor clustering, thus gating plasticity at adult synapses. This work shows that neural micropeptides can act as architectural modules that increase the functional diversity of the known proteome.

Fading memories in aging and neurodegeneration: Is p75 neurotrophin receptor a culprit?

Aging and age-related neurodegenerative diseases have become one of the major concerns in modern times as cognitive abilities tend to decline when we get older. It is well known that the main cause of this age-related cognitive deficit is due to aberrant changes in cellular, molecular circuitry and signaling pathways underlying synaptic plasticity and neuronal connections. The p75 neurotrophin receptor (p75^NTR) is one of the important mediators regulating the fate of the neurons in the nervous system. Its importance in neuronal apoptosis is well documented. However, the mechanisms involving the regulation of p75^NTR in synaptic plasticity and cognitive function remain obscure, although cognitive impairment has been associated with a higher expression of p75^NTR in neurons. In this review, we discuss the current understanding of how neurons are influenced by p75^NTR function to maintain normal neuronal synaptic strength and connectivity, particularly to support learning and memory in the hippocampus. We then discuss the age-associated alterations in neurophysiological mechanisms of synaptic plasticity and cognitive function. Furthermore, we also describe current evidence that has begun to elucidate how p75^NTR regulates synaptic changes in aging and age-related neurodegenerative diseases, focusing on the hippocampus. Elucidating the role that p75^NTR signaling plays in regulating synaptic plasticity will contribute to a better understanding of cognitive processes and pathological conditions. This will in turn provide novel approaches to improve therapies for the treatment of neurological diseases in which p75^NTR dysfunction has been demonstrated.

Nogo receptor impairs the clearance of fibril amyloid-β by microglia and accelerates Alzheimer's-like disease progression

Alzheimer's disease (AD) is characterized by the progressive accumulation of β‐amyloid (Aβ)‐containing amyloid plaques, and microglia play a critical role in mediating Aβ clearance. Mounting evidence has confirmed that the ability of microglia in clearing Aβ decreased with aging and AD progress, but the underlying mechanisms are unclear. Previously, we have demonstrated that Nogo receptor (NgR), a receptor for three axon growth inhibitors associated with myelin, can decrease adhesion and migration of microglia to fibrils Aβ with aging. However, whether NgR expressed on microglia affect microglia phagocytosis of fibrils Aβ with aging remains unclear. Here, we found that aged but not young microglia showed increased NgR expression and decreased Aβ phagocytosis in APP/PS1 transgenic mice. NgR knockdown APP/PS1 mice showed simultaneous reduced amyloid burden and improved spatial learning and memory, which were associated with increased Aβ clearance. Importantly, Nogo‐P4, an agonist of NgR, enhanced the protein level of p‐Smad2/3, leading to a significant transcriptional inhibition of CD36 gene expression, which in turn decreased the microglial phagocytosis of Aβ. Moreover, ROCK accounted for Nogo‐P4‐induced activation of Smad2/3 signaling. Finally, the decreasing effect of NgR on microglial Aβ uptake was confirmed in a mouse model of intra‐hippocampal fAβ injection. Our findings suggest that NgR may play an important role in the regulation of Aβ homeostasis, and has potential as a therapeutic target for AD.

NgR1 pathway expression in cerebral ischemic Sprague-Dawley rats with cognitive impairment

Objective(s):

This study aimed to determine the effect of ischemic occlusion duration and recovery time course on motor and cognitive function, identify optimal conditions for assessing cognitive function with minimal interference from motor deficits, and elucidate the underlying mechanism of axonal inhibitors.

Materials and Methods:

Sprague-Dawley (SD) rats were randomly allocated to the transient middle cerebral artery occlusion (tMCAO) 60-min (tMCAO60min), tMCAO90min, tMCAO120min, and sham groups. We conducted forelimb grip strength, two-way shuttle avoidance task, and novel object recognition task (NORT)tests at three time points (14, 21, and 28 days). Expression of Nogo receptor-1 (NgR1), the endogenous antagonist lateral olfactory tract usher substance, ras homolog family member A (Rho-A), and RhoA-activated Rho kinase (ROCK) was examined in the ipsilateral thalamus.

Results:

There was no difference in grip strength between sham and tMCAO_90min rats at 28 days. tMCAO_90min and tMCAO_120min rats showed lower discrimination indices in the NORT than sham rats on day 28. Compared with that in sham rats, the active avoidance response rate was lower in tMCAO_90min rats on days 14, 21, and 28 and in tMCAO_120min rats on days 14 and 21. Furthermore, 50-54% of rats in the tMCAO_90min group developed significant cognitive impairment on day 28, and thalamic NgR1, RhoA, and ROCK expression were greater in tMCAO_90min rats than in sham rats.

Conclusion:

Employing 90-min tMCAO in SD rats and assessing cognitive function 28 days post-stroke could minimize motor dysfunction effects in cognitive function assessments. Axonal inhibitor deregulation could be involved in poststroke cognitive impairment.

Knockdown of Lingo-1 by short hairpin RNA promotes cognitive function recovery in a status convulsion model

The purpose of this study was to determine the dynamic changes of the Nogo-66 receptor 1 (NgR1) pathway during epileptogenesis and the potential beneficial of leucine-rich repeat and Ig-like domain-containing Nogo receptor interacting protein 1 (Lingo-1) inhibition on epilepsy rats. The hippocampal changes of the NgR1 pathway during epileptogenesis were determined by western blot analysis of multiple proteins, including neurite outgrowth inhibitor protein A (NogoA), myelin-associated glycoprotein (MAG), oligodendrocyte-myelin glycoprotein (OMgp), Lingo-1, ras homolog family member A (RhoA) and phosphorylated RhoA (p-RhoA). Lentivirus-mediated short hairpin RNA (shRNA) was used to knockdown the hippocampal expression of Lingo-1. Novel object recognition (NOR) test and Morris Water Maze (MWM) test were employed to determine the cognitive functions of rats. Hematoxylin and eosin (H&E) staining, protein expressions of RhoA, p-RhoA, and myelin basic protein (MBP), as well as convulsion susceptibility test were additionally performed. Our results showed that the NgR1 pathway was activated during epileptogenesis, characterized by up-regulation of NogoA, MAG, OMgp, and Lingo-1, which was especially significant at the chronic phase of epilepsy. The cognitive function, convulsion susceptibility and hippocampal neuronal survival of rats were impaired at the chronic phase of epileptogenesis but all improved by Lingo-1 inhibition; besides, the hippocampal protein expressions of p-RhoA and MBP were significantly decreased at the chronic phase of SC rats but increased after Lingo-1 inhibition. Our results demonstrated that Lingo-1 shRNA can improve epilepsy-induced cognitive impairment, which may be related with the pro-myelination and neuroprotection effects of Lingo-1 inhibition.

Anti-Lingo-1 antibody ameliorates spatial memory and synapse loss induced by chronic stress

Chronic stress can induce cognitive impairment, and synapse number was significantly decreased in the hippocampus of rats suffering from chronic stress. Lingo-1 is a potent negative regulator of axonal outgrowth and synaptic plasticity. In the current study, the effects of anti-Lingo-1 antibody on the spatial learning and memory abilities and hippocampal synapses of stressed rats were investigated. After 4 weeks of stress exposure, the model group was randomly divided into a chronic stress group and an anti-Lingo-1 group. Then, the anti-Lingo-1 group rats were treated with anti-Lingo-1 antibody (8 mg/kg) for 3 weeks. The effects of anti-Lingo-1 antibody on the spatial learning and memory abilities were investigated with the Morris water maze test. Immunohistological staining and an unbiased stereological method were used to estimate the total number of dendritic spine synapses in the hippocampus. At the behavioral level, after 3 weeks of treatment, the anti-Lingo-1 group rats displayed significantly more platform location crossings in the Morris water maze test than the chronic stress group rats. Anti-Lingo-1 significantly prevented the declines in dendritic spine synapses and postsynaptic density protein-95 (PSD-95) expression in the dentate gyrus and the CA1 and CA3 regions of the hippocampus. The present results indicated that anti-Lingo-1 antibody may be a safe and effective drug for alleviating memory impairment in rats after chronic stress and protecting synapses in the hippocampus of stressed rats.

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.

Age-related changes in hippocampal-dependent synaptic plasticity and memory mediated by p75 neurotrophin receptor

The plasticity mechanisms in the nervous system that are important for learning and memory are greatly impacted during aging. Notably, hippocampal-dependent long-term plasticity and its associative plasticity, such as synaptic tagging and capture (STC), show considerable age-related decline. The p75 neurotrophin receptor (p75NTR ) is a negative regulator of structural and functional plasticity in the brain and thus represents a potential candidate to mediate age-related alterations. However, the mechanisms by which p75NTR affects synaptic plasticity of aged neuronal networks and ultimately contribute to deficits in cognitive function have not been well characterized. Here, we report that mutant mice lacking the p75NTR were resistant to age-associated changes in long-term plasticity, associative plasticity, and associative memory. Our study shows that p75NTR is responsible for age-dependent disruption of hippocampal homeostatic plasticity by modulating several signaling pathways, including BDNF, MAPK, Arc, and RhoA-ROCK2-LIMK1-cofilin. p75NTR may thus represent an important therapeutic target for limiting the age-related memory and cognitive function deficits.

The Influence of Neuron-Extrinsic Factors and Aging on Injury Progression and Axonal Repair in the Central Nervous System

In the aging western population, the average age of incidence for spinal cord injury (SCI) has increased, as has the length of survival of SCI patients. This places great importance on understanding SCI in middle-aged and aging patients. Axon regeneration after injury is an area of study that has received substantial attention and made important experimental progress, however, our understanding of how aging affects this process, and any therapeutic effort to modulate repair, is incomplete. The growth and regeneration of axons is mediated by both neuron intrinsic and extrinsic factors. In this review we explore some of the key extrinsic influences on axon regeneration in the literature, focusing on inflammation and astrogliosis, other cellular responses, components of the extracellular matrix, and myelin proteins. We will describe how each element supports the contention that axonal growth after injury in the central nervous system shows an age-dependent decline, and how this may affect outcomes after a SCI.

The adhesion and migration of microglia to β-amyloid (Aβ) is decreased with aging and inhibited by Nogo/NgR pathway

Background

Alzheimer’s disease is characterized by progressive accumulation of β-amyloid (Aβ)-containing amyloid plaques, and microglia play a critical role in internalization and degradation of Aβ. Our previous research confirmed that Nogo-66 binding to Nogo receptors (NgR) expressed on microglia inhibits cell adhesion and migration in vitro.

Methods

The adhesion and migration of microglia isolated from WT and APP/PS1 mice from different ages were measured by adhesion assays and transwells. After NEP1-40 (a competitive antagonist of Nogo/NgR pathway) was intracerebroventricularly administered via mini-osmotic pumps for 2 months in APP/PS1 transgenic mice, microglial recruitment toward Aβ deposits and CD36 expression were determined.

Results

In this paper, we found that aging led to a reduction of microglia adhesion and migration to fAβ_1–42 in WT and APP/PS1 mice. The adhesion and migration of microglia to fAβ_1–42 were downregulated by the Nogo, which was mediated by NgR, and the increased inhibitory effects of the Nogo could be observed in aged mice. Moreover, Rho GTPases contributed to the effects of the Nogo on adhesion and migration of microglia to fAβ_1–42 by regulating cytoskeleton arrangement. Furthermore, blocking the Nogo/NgR pathway enhanced recruitment of microglia toward Aβ deposits and expression of CD36 in APP/PS1 mice.

Conclusion

Taken together, Nogo/NgR pathway could take part in Aβ pathology in AD by modulating microglial adhesion and migration to Aβ and the Nogo/NgR pathway might be an important target for treating AD.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1250-1) contains supplementary material, which is available to authorized users.

Simultaneous assessment of cognitive function, circadian rhythm, and spontaneous activity in aging mice

Cognitive function declines substantially with age in both humans and animal models. In humans, this decline is associated with decreases in independence and quality of life. Although the methodology for analysis of cognitive function in human models is relatively well established, similar analyses in animal models have many technical issues (e.g., unintended experimenter bias, motivational issues, stress, and testing during the light phase of the light dark cycle) that limit interpretation of the results. These caveats, and others, potentially bias the interpretation of studies in rodents and prevent the application of current tests of learning and memory as part of an overall healthspan assessment in rodent models of aging. The goal of this study was to establish the methodology to assess cognitive function in aging animals that addresses many of these concerns. Here, we use a food reward-based discrimination procedure with minimal stress in C57Bl/6J male mice at 6, 21, and 27 months of age, followed by a reversal task to assess behavioral flexibility. Importantly, the procedures minimize issues related to between-experimenter confounds and are conducted during both the dark and light phases of the light dark cycle in a home-cage setting. During cognitive testing, we were able to assess multiple measures of spontaneous movement and diurnal activity in young and aged mice including, distance moved, velocity, and acceleration over a 90-h period. Both initial discrimination and reversal learning significantly decreased with age and, similar to rats and humans, not all old mice demonstrated impairments in learning with age. These results permitted classification of animals based on their cognitive status. Analysis of movement parameters indicated decreases in distance moved as well as velocity and acceleration with increasing age. Based on these data, we developed preliminary models indicating, as in humans, a close relationship exists between age-related movement parameters and cognitive ability. Our results provide a reliable method for assessing cognitive performance with minimal stress and simultaneously provide key information on movement and diurnal activity. These methods represent a novel approach to developing non-invasive healthspan measures in rodent models that allow standardization across laboratories.

LINGO-1 antibody ameliorates myelin impairment and spatial memory deficits in the early stage of 5XFAD mice

AIMS

Multiple evidence has indicated that myelin injury is common in Alzheimer's disease (AD). However, whether myelin injury is an early event in AD and the relationship between it and cognitive function is still elusive.

METHODS

Spatial memory of 5XFAD mice was determined by Morris water maze at 1 and 3 months old. Meanwhile, the deposition of Aβ, the expression of myelin basic protein (MBP), LINGO-1, NgR, and myelin ultrastructure in many memory-associated brain regions were detected in one-month-old and three-month-old mice (before and after LINGO-1 antibody administration) using immunostaining, Western blot (WB), and transmission electron microscopy (TEM), respectively.

RESULTS

No abnormal Aβ deposition was found in one-month-old 5XFAD mice. However, spatial memory deficits were proved in accordance with an obvious demyelination in memory-associated brain regions in one-month-old mice and both deteriorated with age. Administration of LINGO-1 antibody could obviously restore the myelin impairments in CA1 and DG region and partially ameliorate spatial memory deficits.

CONCLUSIONS

Our results demonstrated that myelin injury was an early event in 5XFAD mice even prior to emergence of deposition of Aβ. Intervention with the LINGO-1 antibody could attenuate impaired spatial memory deficits by remyelination, which suggested that myelin injury was involved in spatial memory deficits and remyelination may be a potential therapeutic strategy in early stage of AD or mild cognitive impairments.

The blockage of the Nogo/NgR signal pathway in microglia alleviates the formation of Aβ plaques and tau phosphorylation in APP/PS1 transgenic mice

Background

Alzheimer’s disease (AD) is characterized by extracellular β-amyloid (Aβ) plaques, neurofibrillary tangles (NFTs), and microglia-dominated neuroinflammation. The Nogo/NgR signal pathway is involved in AD pathological features, but the detailed mechanism needs further investigation. Our previous studies have confirmed that the activation of NgR on microglia by Nogo promotes the expression of proinflammatory cytokines and inhibits cell adhesion and migration behaviors. In the present study, we investigated the effects of Nogo/NgR signaling pathway on the pathological features of AD and possible mechanisms.

Methods

After NEP1-40 (a competitive antagonist of Nogo/NgR pathway) was intracerebroventricularly administered via mini-osmotic pumps for 2 months in amyloid precursor protein (APP)/PS1 transgenic mice, plaque load, tau phosphorylation, and inflammatory responses were determined. After primary mouse neurons were exposed to the conditioned medium from BV-2 microglia stimulated by Nogo, the production of Aβ and phosphorylation of tau was quantified by ELISA and western blot.

Results

Inhibition of the Nogo/NgR signaling pathway ameliorated pathological features including amyloid plaques and phosphorylated levels of tau in APP/PS1 mice. In addition, after treatment with the conditioned medium from BV-2 microglia stimulated by Nogo, Aβ production and tau phosphorylation in cultured neurons were increased. The conditioned medium also increased the expression of APP, its amyloidogenic processing, and the activity of GSK3β in neurons. The conditioned medium was also proinflammatory medium, and the blockage of the Nogo/NgR pathway improved the neuroinflammatory environment in APP/PS1 mice.

Conclusions

Taken together, the neuroinflammation mediated by Nogo/NgR pathway in microglia could directly take part in the pathological process of AD by influencing the amyloidogenesis and tau phosphorylation. These results contribute to a better understanding of AD pathogenesis and could offer a new therapeutic option for delaying the progression of AD.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0522-x) contains supplementary material, which is available to authorized users.

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.

Dynamic nature of the p75 neurotrophin receptor in response to injury and disease

Neurotrophins and their respective tropomyosin related kinase (Trk) receptors (TrkA, TrkB, and TrkC) and the p75 neurotrophin receptor (p75(NTR)) play a fundamental role in the development and maintenance of the nervous system making them important targets for treatment of neurodegenerative diseases. Whereas Trk receptors are directly activated by specific neurotrophins, the p75(NTR) is a multifunctional receptor that exerts its effects via heterodimeric interactions with TrkA, TrkB, TrkC, sortilin or the Nogo receptor to regulate a wide array of cellular functions. By partnering with different receptors the p75(NTR) regulates binding of mature versus pro-neurotrophins and activation of different signaling pathways with outcomes ranging from growth and survival to cell death. While the developmental downregulation of the p75(NTR) has raised questions regarding its role in the mature nervous system, recent data have revealed widespread expression of low levels, a role in synaptic plasticity and adult neurogenesis and upregulation in response to injury or disease. Studies are needed to better understand these processes, particularly in the damaged nervous system, but will be complicated by expression of p75(NTR) on immune cells including macrophages and microglia that are intimately involved in disease and repair processes. Recent approaches that regulate p75(NTR) function with small non-peptide ligands have demonstrated potent neuroprotection in models of injury and neurodegenerative diseases that highlight the importance of the p75(NTR) as a therapeutic target. Future studies hold the promise of revealing a wealth of information on the multifaceted actions of the p75(NTR) that will inform the design of new neurotrophin-based therapies.

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.

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.

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.