Original Articles
Neuroautoantibody immunoreactivity in relation to aging and stress in apolipoprotein E-deficient mice

https://doi.org/10.1016/S0361-9230(99)00052-0Get rights and content

Abstract

Progressive disruption of both the neuroendocrine and immune systems has been correlated with age-associated pathogenesis in patients with Alzheimer’s disease and in mice lacking apolipoprotein E (ApoE). In this study, we examined neuroautoimmune and neuroendocrine activities in relation to aging and stress in ApoE-deficient mice. An elevated level of autoantibodies against brain antigens was found in sera from ApoE-deficient mice compared to that of wild-type mice as early as 7–8 weeks of age. However, there was no significant difference between the two genotypes at this age in the effect of stress on serum corticosterone or autoantibody titers. Higher titers of autoantibodies were observed in ∼12-week-old ApoE-deficient mice, especially in those exposed to chronic stress. Based on Western analysis, sera from ApoE-deficient mice showed a strong immunoreactivity with ∼78 kDa and ∼40 kDa brain abundant polypeptides, ∼58 kDa non-brain tissue abundant antigen, and others of ∼, 80–82 kDa in both the brain and non-brain tissues. Immunofluorescence confocal microscopy showed that the major cellular components recognized by the autoimmune sera from ApoE-deficient mice were associated with neuronal cell nuclei and fiber-like structures in different regions of the brain, including the frontal cortex, lateral cortex and hippocampus. These results suggest that neuroautoimmunity associated with the aging process and exposure to chronic stress may be involved in early development of neurodegeneration in mice with ApoE-deficiency.

Introduction

Apolipoprotein E (ApoE) polymorphism is a major genetic risk factor for the complex neurodegenerative disorder of Alzheimer’s disease (AD; for reviews see 7, 18). In addition to genetic factors, environmental stress and autoimmune abnormalities may play a role in the progression of AD, and it has been proposed that AD is related to the failure to adapt to chronic stress [3]. This is supported by findings of a correlation between AD and elevated levels of stress hormones [23] and with a decreased peripheral glucocorticoid sensitivity [9]. Chronic stress-induced or age-related elevation of glucocorticoid levels can lead to neuronal death and degeneration in the central nervous system (CNS) 12, 19, a major pathological feature associated with cognitive impairment in AD [18]. Another proposed mechanism contributing to the age-related neurodegeneration in AD is a cell-specific attack by autoantibodies against the CNS 8, 20, 21, 25. The age-associated pathogenesis, including autoimmunity, has been correlated with a progressive disruption in both the neuroendocrine and immune systems [14].

Studies using an animal model for investigating the role of ApoE in AD have demonstrated cognitive impairments and neurodegeneration in mice lacking ApoE 6, 10, 11, 28. In addition to memory impairment, an altered corticosterone response to stress has been observed in ApoE-deficient mice 5, 28. Mechanisms leading to memory impairment and altered stress responsiveness are still far from clear, but it has been well demonstrated in other models that cognitive impairment can result from overexposure to stress which induces an elevated level of stress hormones (for reviews see 13, 22, 24). Stress can also cause a rise in autoantibody levels in the serum [1]. In ApoE-deficient mice, memory loss is thought to be associated with early neurodegeneration due to the lack of a neurotrophic effect of ApoE [11]. A recent report has demonstrated that accumulation of β-amyloid-like protein in astrocytes in the hippocampal region can be found as early as 4 weeks of age in ApoE-deficient mice but is not observed in wild-type control mice until they are over 6 months old [17]. Such β-amyloid-induced neurotoxicity may cause neuronal cell damage and degeneration (for review [2]), leading to a disruption of neuronal functional integrity and an up-regulation of autoimmune activities. This was indirectly supported by demonstrations of a higher frequency of CD4+ T cells in ApoE-deficient mice at 9–16 weeks of age [27] and by an altered stress response and impaired memory in these mice at ∼12 weeks of age [28]. It is still unknown whether the observed abnormalities in stress response and autoimmunity occur in ApoE-deficient mice at a very young age and whether there are autoantibodies immunoreactive with the brain in the ApoE-deficient mice.

The main objective of the present study was to investigate neuroautoimmune activities in ApoE-deficient mice of different ages. We examined titers of autoantibodies in relation to stress and age, tissue distribution of the autoantigens, and major components of brain cells recognized by autoimmune sera from ApoE-deficient mice. In addition, we measured serum corticosterone concentration to determine if 7- to 8-week-old ApoE-deficient mice had the same alterations in corticosterone responses to stress as that reported for older mice 5, 28.

Section snippets

Animals and serum collection

Male, ApoE-deficient (C57BL/6J homozygous mice for Apoetm1Unc mutation; knockout) and their wild-type control mice were purchased from Jackson Laboratory (Bar Harbor, ME, USA). In this study, adequate measures were taken to minimize pain and discomfort of animals, and the experiments were conducted in accordance with national legislation and with the National Institutes of Health guide regarding the care and use of animals for experimental procedures. All mice were singly housed and given 7

Results

Autoimmune reactivities of the sera from both age groups of mice against brain antigens determined by ELISA are shown in Fig. 1. Both age groups of ApoE-deficient mice appeared to have higher titers of autoantibodies than wild-type controls, based on differences in the normalized absorbance using the two-way ANOVA of overall effects of genotypes (Age-Group 1: df = 24, F = 6.818, p = 0.014; Age-Group 2: df = 24, F = 7.007, p = 0.014). There was no overall effect of stress on antibody titers

Discussion

The ApoE-deficient mouse has been used as an animal model for studying the relationship between ApoE and AD. It has been shown that ApoE-deficiency in mice results in cognitive impairments and CNS neurodegeneration, which are pathological features seen in patients with AD 6, 10, 11, 28. In a previous study, we reported an impaired spatial memory and an altered corticosterone response to stress in young ApoE-deficient mice at ∼12 weeks of age, suggesting a disruption of functional integrity of

Acknowledgements

This study was supported by a grant from the US Army (DAMD 17-97-2-7013).

References (28)

  • P.E. Stokes

    The potential role of excessive cortisol induced by HPA hyperfunction in the pathogenesis of depression

    Eur. Neuropsychopharmacol

    (1995)
  • D. Storga et al.

    Monoaminergic neurotransmitters, their precursors and metabolites in brains of Alzheimer patients

    Neurosci. Lett.

    (1996)
  • S. Andrejevic et al.

    Stress-induced rise in serum anti-brain autoantibody levels in the rat

    Intl J. Neurosci.

    (1997)
  • C.W. Cotman et al.

    A potential role for apoptosis in neurodegeneration and Alzheimer’s

    Mol. Neurobiol.

    (1995)
  • Cited by (13)

    • Unique B-1 cells specific for both N-pyrrolated proteins and DNA evolve with apolipoprotein E deficiency

      2022, Journal of Biological Chemistry
      Citation Excerpt :

      The results of this study suggest the potential role of pyrP in promoting B-1a cell proliferation and the production of bispecific IgM Abs for pyrP/DNA. An apoE deficiency has been reported to be associated with the production of autoAbs to innate antigens, such as oxidized low-density lipoproteins and numerous self-proteins (28–30). Notably, consistent with the previous studies showing the enhanced production of anti-DNA autoAbs in the apoE−/− mice (15, 31), a progressive increase in the IgM response to both pyrBSA and DNA and expansion of the B-1a cells in the PerC of apoE−/− mice were observed (Figs. 2 and 3A).

    • Apolipoprotein E binds to and reduces serum levels of DNA-mimicking, pyrrolated proteins

      2019, Journal of Biological Chemistry
      Citation Excerpt :

      The data led us to speculate that apoE may bind pyrrolated proteins generated within the lipoprotein fraction. apoE deficiency is associated with the production of autoantibodies against antigens including neuronal nuclei, cardiolipin, and oxidized LDL (28, 29). The most likely scenario is that the altered lipid and lipoprotein metabolism caused by the deficiency of apoE may accelerate the immune response, leading to the overproduction of these autoantibodies.

    • Effects of environmental enrichment and regrouping on natural autoantibodies-binding danger and neural antigens in healthy pigs with different individual characteristics

      2017, Animal
      Citation Excerpt :

      A large part of the NAb repertoire is directed to self-antigens, and these antibodies are referred to as NAAb. Blood levels of autoantibodies-binding neural antigens have been related to acute and chronic stress (Andrejević et al., 1997; Zhou et al., 1999), and could both reflect and affect neuronal functioning (Gold et al., 2012). Myelin basic protein (MBP) is an important protein in the process of myelination of nerves in the nervous system, and it has been found that high levels of autoantibodies to MBP and other neural antigens were associated with neurological damage (Abou-Donia et al., 2013).

    • Differential sensitivity of the perioculomotor urocortin-containing neurons to ethanol, psychostimulants and stress in mice and rats

      2009, Neuroscience
      Citation Excerpt :

      Since the magnitude of the Fos response after cocaine was substantially weaker than after ethanol, we questioned whether the effect of cocaine in pIIIu was pharmacologically-specific or, alternatively, produced by the stress of being injected with cocaine. To examine this, we tested the effect of restraint stress, a treatment known to produce a robust glucocorticoid response (Zhou et al., 1999; Lund et al., 2006), and a significant increase in Fos-ir in the rat pIIIu (Gaszner et al., 2004). We compared Fos-ir in the C57BL/6 J mice following 2.5 g/kg of ethanol, 30 mg/kg of cocaine or 2 h of restraint stress (Fig. 4).

    View all citing articles on Scopus
    View full text