Circulating autoantibodies and sex-dependent discrepancy in prevalence are unexplained phenomena of Alzheimer’s disease (AD). Using the 3xTg-AD mouse model, we reported that adult males show early manifestations of systemic autoimmunity, increased emotional reactivity, enhanced expression of the histone variant macroH2A1 in the cerebral cortex, and loss of plaque/tangle pathology. Conversely, adult females display less severe autoimmunity and retain their AD-like phenotype. This study examines the link between immunity and other traits of the current 3xTg-AD model. Young 3xTg-AD and wild-type mice drank a sucrose-laced 0.4 mg/ml solution of the immunosuppressant cyclophosphamide on weekends for 5 months. After behavioral phenotyping at 2 and 6 months of age, we assessed organ mass, serologic markers of autoimmunity, molecular markers of early AD pathology and expression of genes associated with neurodegeneration. Chronic immunosuppression prevented hematocrit drop and reduced soluble Aβ in 3xTg-AD males while normalizing the expression of histone variant macroH2A1 in 3xTg-AD females. This treatment also reduced hepatosplenomegaly, lowered autoantibody levels, and increased the effector T cell population while decreasing the proportion of regulatory T cells in both sexes. Exposure to cyclophosphamide, however, neither prevented reduced brain mass and BDNF expression nor normalized increased tau and anxiety-related behaviors. The results suggest that systemic autoimmunity increases soluble Aβ production and affects transcriptional regulation of macroH2A1 in a sex-related manner. Despite the complexity of multisystem interactions, 3xTg-AD mice can be a useful in vivo model for exploring the regulatory role of autoimmunity in the etiology of AD-like neurodegenerative disorders.

Sex-dependent discrepancies in disease prevalence and serum autoantibody levels are observed in patients and animal models of Alzheimer’s disease (AD). The present study examines whether gonadal hormones play a role in sex differences in serum autoantibody levels in the 3×Tg-AD mouse model of AD. 3×Tg-AD and wild-type (WT) mice were gonadectomised or sham-operated at 3 months of age. After behavioural phenotyping at 6 months of age, the animals were assessed for serum autoantibodies by indirect immunofluorescence for antinuclear antibodies (ANA) and by line-immunoblot assay for an additional 16 monospecific autoantibodies including anti-nucleosome antibodies. There were significant differences between the strains in ANA levels, with the major target antigens confirmed as nucleosomes. The results of ANA and anti-nucleosome assays were combined for further analysis. Further analysis revealed: 1) the level of serum autoantibodies in male 3×Tg-AD mice was higher than in female 3×Tg-AD animals, and this was not altered by orchiectomy. 2) sham-operated 3×Tg-AD female mice displayed a significantly lower level of serum autoantibodies than sham-operated WT females. 3) ovariectomy further reduced the level of serum autoantibodies in female 3×Tg-AD mice. The results suggest that dissimilar levels of serum autoantibodies in 3xTg-AD mice are a sex-dependent phenomenon and that female hormones play a role in regulation of their synthesis. Funded by grant #SVB-158618 from the Canadian Institutes of Health Research to MF.

Elevated levels of serum autoantibodies are a well-documented phenomenon in patients with Alzheimer’s disease (AD), but the nature of the autoimmunity is unclear. Triple-transgenic (3xTg-AD) mice are a well-established model that develops AD-like pathology. We observed that recent cohorts of male 3xTg-AD mice exhibit autoimmune manifestations, yet lack plaque/tangle pathology. In the current study, we identified the time course and type of autoantibodies produced during the progression and attenuation of systemic autoimmunity. Tissue samples were collected from 3xTg-AD and wild type (WT) males and females at 2, 6 and 12 months of age. Serum autoantibodies were measured by both indirect immunofluorescence and 16-antigen line immunoassay. To assess immunosuppression, serum samples from a separate cohort of mice chronically exposed to cyclophosphamide were also assessed. Several autoantibody types increased in frequency and concentration in aging 3xTg-AD mice, particularly in adult males. The most prevalent were anti-nuclear autoantibodies, particularly those targeting the nucleosomes. Among the panel of autoantibodies measured, reactivity to a single antigen (nucleosomes) was observed in the majority of samples. A few mice showed reactivity to other autoantigens, such as histones, dsDNA, RNP/Sm, AMA-M2 and rib. P. Reactivity to all autoantigens was abolished in mice exposed to the immunosuppressant cyclophosphamide. The emergence of circulating autoantibodies similar to classical autoimmune diseases (such as lupus) suggests an important, yet unreported aspect of pathology in this AD model. Future studies are aimed to elucidate the origin and role of the autoantibodies in the context of phenotype loss in 3xTg-AD males.

BackgroundSex‐dependent discrepancies in prevalence and autoimmune markers are characteristics of Alzheimer’s disease (AD). Using the 3xTg‐AD mouse model, we previously reported that adult males show early systemic autoimmunity along with behavioural dysfunction, altered epigenetic factors, and lack of plaque/tangle pathology. Conversely, adult females display less severe autoimmunity and retain AD‐like pathology and behaviour. The present study examines whether gonadal hormones play a role in the etiology of these traits in current cohorts of 3xTg‐AD mice.Method3xTg‐AD and wild‐type mice were gonadectomized or sham‐operated at 3 months of age. After behavioural phenotyping at 6 months of age, the animals were assessed for serologic markers of autoimmunity, T splenocyte distribution, molecular markers of AD pathology, and expression of genes and histone variants associated with neurodegeneration.ResultIn female transgenic (AD) mice, gonadectomy resulted in reduced levels of circulating antinuclear/nucleosome autoantibodies and poorer spatial learning performance, but did not affect the T cell population. In contrast, in transgenic male animals, gonadectomy improved spatial memory and cognitive flexibility, diminished splenic CD8+ T cells, yet had no impact on anti‐nuclear/nucleosome autoantibodies. Sex hormone‐related effects on anti‐nucleosome autoantibodies led us to focus on histones. Gonadectomized AD females exhibited enhanced expression of mouse (m) and transgenic Mapt genes, consistent with reduced binding activity of the repressive histone variant macroH2A1 at the mMapt gene body, compared to their sham counterparts. In contrast, gonadectomized AD males showed reduced expression of App and H2afy genes, reduced cortical soluble Aβ42 levels, and increased macroH2A1 binding at the mPsen1 promoter, compared to sham‐operated AD males.ConclusionFemale sex hormones enhance autoimmunity and spatial learning, whereas male sex hormones may be detrimental to spatial memory, cognitive flexibility, and autoimmunity in young adulthood. Furthermore, female sex hormones increase expression of the Mapt gene, but have no effect on App expression or Aβ42 levels. Conversely, male sex hormones increase App expression and Aβ42 levels, but have no effect on tau expression. Our work suggests that gonadal hormones contribute to sex differences in autoimmunity, AD‐like pathology, and “cognitive” function in this model. Moreover, histone variants may contribute to sex‐specific differences in AD pathology.

Background: Circulating autoantibodies and sex-dependent discrepancy in prevalence are unexplained phenomena of Alzheimer’s disease (AD). Using the 3xTg-AD mouse model, we reported that adult males show early manifestations of systemic autoimmunity, increased emotional reactivity, enhanced expression of the histone variant macroH2A1 in the cerebral cortex, and loss of plaque/tangle pathology. Conversely, adult females display less severe autoimmunity and retain their AD-like phenotype. This study examines the link between immunity and other traits of the current 3xTg-AD model. Methods: Young 3xTg-AD and wild-type mice drank a sucrose-laced 0.4 mg/ml solution of the immunosuppressant cyclophosphamide on weekends for 5 months. After behavioral phenotyping at 2 and 6 months of age, we assessed organ mass, serologic markers of autoimmunity, molecular markers of early AD pathology and expression of genes associated with neurodegeneration. Results: Chronic immunosuppression prevented hematocrit drop and reduced soluble Aβ in 3xTg-AD males while normalizing the expression of histone variant macroH2A1 in 3xTg-AD females. This treatment also reduced hepatosplenomegaly, lowered autoantibody levels, and increased the effector T cell population while decreasing the proportion of regulatory T cells in both sexes. Exposure to cyclophosphamide, however, neither prevented reduced brain mass and BDNF expression nor normalized increased tau and anxiety-related behaviors. Conclusion: The results suggest that systemic autoimmunity increases soluble Aβ production and affects transcriptional regulation of macroH2A1 in a sex-related manner. Despite the complexity of multisystem interactions, 3xTg-AD mice can be a useful in vivo model for exploring the regulatory role of autoimmunity in the etiology of AD-like neurodegenerative disorders.