Up-regulation of the inflammatory cytokines IFN-γ and IL-12 and down-regulation of IL-4 in cerebral cortex regions of APPSWE transgenic mice
Introduction
Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the most common cause of dementia. AD is characterized neuropathologically by the deposition of extracellular amyloid plaques containing aggregates of the β-amyloid (Aβ) peptide, as well as by intracellular aggregations of neurofibrillary tangles consisting of paired helical filaments of hyperphosphorylated tau protein Glenner et al., 1984, Braak and Braak, 1998, Selkoe, 1998. AD patholgy also involves selective neuronal cell loss accompanied by cerebrovascular amyloidosis. The mechanisms behind AD have not been completely defined.
An abnormal immunological response and inflammatory cytokines are proposed to be involved in the pathogenesis of a number of neurodegenerative processes Benveniste, 1992, Du, 1999. In AD, immune and inflammatory process related proteins have been implicated as mediators in responses to brain injury. Elevated levels of major histocompatibility complex (MHC) antigen class II (MHC II) molecules and a number of inflammatory mediators associated with β-amyloid deposits have been detected in brains from AD patients. The latter include up-regulation of cytokines, such as interleukin-1 (IL-1) (Griffin et al., 1989), IL-6 (Bauer et al., 1991) and tumor necrosis factor-α (TNF-α) (Dickson et al., 1993). Acute phase proteins, such as α1-antichymotrypsin (Abraham et al., 1990), α2-macroglobulin Bauer et al., 1991, Strauss et al., 1992, and up-regulation of several complement proteins are also thought to be involved in the pathogenesis of AD Eikelenboom et al., 1989, Eikelenboom et al., 2000, Eikelenboom and Hoogendijk, 1999, Zhan et al., 1994. Moreover, microglia and astroglial cells surrounding mature plaques in AD brains may further lead to inflammatory neurotoxin production resulting in cell death (Cotter et al., 1999). The neuroimmunological cascade produced by the local immune reaction may play a major contribution to neuronal dysfunction and neurodegeneration.
Although the majority of AD cases occur spontaneously, respectively sporadic, the study of inherited familial cases has provided much insight as to the genetic factors that contribute to the development of AD neurodegeneration. Various mutations in the amyloid protein precursor (APP) and the presenilin genes can lead to early onset, autosomal dominant AD (Hardy, 1997). The presenilin 1 and presenilin 2 genes have been identified as pathogenic loci involved in the majority of early onset AD (Hutton and Hardy 1997).
One of the most widely used animal models for β-amyloid plaques in the cortical regions of the brain is that of the Tg (HuApp695.K670-M671L) 2576 transgenic mouse, which over-expresses human APP with the Swedish double mutation (Hsiao et al., 1996). The Tg2576 transgenic mice reflect in part AD pathology including elevated levels of Aβ1–40 and Aβ1–42, the presence of amyloid plaques, neuropil abnormalities and microglial activation Irizarry et al., 1997, Frautschy et al., 1998.
We used Tg2576 mice to elucidate the mechanisms underlying the hypothesis that β-amyloid induces immune activation, as well as to improve the understanding of the role of cytokines in the disease processes of AD. The expression of the cytokines, IFN-γ, IL-12 and IL-4 by immunocytochemistry and in situ hybridization was examined in brain sections from cortical regions of transgenic Tg2576 mice at various postnatal ages ranging between 3 and 19 months.
Section snippets
Transgenic animal
Two female Tg (HuAPP695SWE) 2576 mice (a kind gift from Dr. K. Hsiao) in a hybrid background of C57BL6/SJL and C57B6 males (Bomice and Mollegaard Breeding Laboratories, Ejby, Denmark) were employed to breed a colony of experimental animals. The animals were individually housed in Plexiglas cages (25×20×15 cm) with free access to rodent chow and water and were maintained on a 12-h light/dark cycle.
Studies were performed on male Tg2576 mice and age-matched male non-transgenic littermates as
Results
IFN-γ and IL-12 mRNA and protein positive cells were scattered within the cortex region of the brain sections of Tg2576 mice and produced mainly in cells with the size and morphology corresponding to microglia (Fig. 1). After double staining, the brain sections of 17–19-month-old Tg2576 mice revealed a co-localization of IFN-γ or IL-12 and ED1 (microglia) (Fig. 2a) or GFAP (activated astrocytes) (Fig. 2b) immunoreactivity, indicating that IFN-γ and IL-12 are expressed by reactive microglia and
Discussion
In this study, we show that both IFN-γ and IL-12 transcription and production are markedly enhanced with increased age in the cortical brain regions of Tg2576 mice in reactive microglia and astrocytes surrounding β-amyloid deposits. Therefore, IFN-γ and IL-12 may play an inflammatory role in amyloid plaque formation and microglial as well as astrocyte activation. The increase of the difference and degree of significance between transgenic Tg2576 mice and wild-type control mice suggests a
Acknowledgments
This study was supported by grants from Konung Gustaf V:s och Drottning Victorias foundation, Gamla tjänarinnor foundation, Loo och Hans Ostermans foundation, Gun och Bertil Stohnes foundation, Eirs 50-year foundation, Alzheimer foundation, SADF foundation and funds from the Swedish Municipal Pension Institute, the Swedish Medical Research Council and the Karolinska Institute.
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