Elsevier

Brain Research

Volume 1486, 27 November 2012, Pages 14-26
Brain Research

Research Report
Role of stereotaxically injected IgG from db/db mice in the phosphorylation of the microtubule-associated protein tau in hippocampus

https://doi.org/10.1016/j.brainres.2012.08.049Get rights and content

Abstract

People with type 2 diabetes (T2DM) mellitus are high risk for dementia and Alzheimer's disease (AD) via several plausible pathways. However, the underlying mechanisms have been still unclear, and the relation of immune injury to the pathogenesis of T2DM-related AD is not yet completely understood. Our present study aimed to elucidate the possible role of immunoglobulin IgG in the immune process of AD associated with T2DM in db/db mice. Hippocampi of 20 db/db mice and 20 C57BL/6 mice were subjected to immunohistochemistry and immunofluorescence assays. The phosphorylation of tau, glycogen synthase kinase (GSK)-3β and AKT activity was examined by Western blot analysis. IgG purified from the sera of IgG deposit-positive db/db mice was stereotaxically injected into the hippocampi of another 12 db/db mice and 12 C57BL/6 mice. The phosphorylation of tau, Abeta, GSK-3β and AKT activity was analyzed. Compared with the C57BL/6 control, 13 of the 20 db/db mice exhibited high levels of IgG deposits in the hippocampus. Treatment with IgG triggered tau hyperphosphorylations and Abeta deposition, which are likely major factors in AD. Meanwhile, IgG inhibited AKT phosphorylation and promoted GSK-3β activity. The IgG deposits observed in some db/db mice were possibly related to the impairment of T2DM-related AD development. Some autoimmune processes may be involved in AD in type 2 diabetes mellitus development at the level of the hippocampus.

Highlights

► We discuss role of IgG in immune process of AD associated with T2DM in db/db mice. ► The IgG were possibly related to the impairment of T2DM-related AD development. ► Some autoimmune processes involved in AD in type 2 diabetes mellitus development.

Introduction

Type 2 diabetes mellitus (T2DM) is a common metabolic disease with increasing prevalence. It is associated with slow, progressive organ damages, such as nephropathy, angiopathy, retinopathy, and peripheral neuropathy. T2DM is also often considered to have deleterious effects on the brain. T2DM has been demonstrated to affect cognition and cause central nervous system functional disturbance, such as hypomnesia (Arvanitakis et al., 2004, Okereke et al., 2008, Strachan et al., 1997, Sinclair et al., 2000, Yaffe et al., 2004). T2DM is also associated as well with increased incidence of dementia including Alzheimer's disease (AD)(Ott et al., 1996, Ott et al., 1999, Pasquier et al., 2006, Strachan et al., 2008, Whitmer, 2007, Xu et al., 2004).

AD is heterogeneous and involves more than one aetiopathogenisis. AD, the cause of one of the most common types of dementia, is a brain disorder affecting the elderly. AD is characterized by the formation of two main protein aggregates namely, senile plaques and neurofibrillary tangles. These aggregates are involved in the process leading to progressive neuronal degeneration and death. Senile plaques are generated by the deposition of fibrils of the beta-amyloid peptide in the human brain. Beta-amyloid peptide (Abeta) is a fragment derived from the proteolytic processing of the amyloid precursor protein (Sima and Li, 2006). Tau protein is the major component of paired helical filaments (PHFs), which form a compact filamentous network described as neurofibrillary tangles (NFTs). Abnormally hyperphosphorylated tau is the primary and pivotal pathological characteristic of AD (Iqbal et al., 2002, 2005; Wang et al., 2007). Glycogen synthase kinase-3 (GSK-3) is a key signaling molecule that induces AD-related neurodegeneration and deficits in memory formation (Balaraman et al., 2006, Iqbal and Grundke-Iqbal, 2008, Takashima, 2006).

Recently, some studies have revealed that immune inflammatory reaction is related to the development of AD. The activation of microglia resulted in the secretion of proinflammatory molecules, such as IL-1beta, TNF-alpha (Bamberger et al., 2003, Giovannini et al., 2002, Li et al., 2003). Immunotherapy aiming at Abeta for AD has been developed. Both active immunization and passive transferring of Abeta-specific antibodies are studied to attenuate amyloid deposits and improve cognitive deficits (Cribbs, 2010, Kim et al., 2007, Orgogozo et al., 2003).

Studies have suggested that T2DM is associated with AD, the most devastating progressive neurodegenerative disease that causes dementia, and eventually, death. However, the underlying mechanism has not yet been identified (Irie et al., 2008, Messier, 2003, Nicolls, 2004, Xu et al., 2009). Pancreatic beta-cell dysfunction and insulin resistance are two interrelated defects in the pathophysiology of T2DM (Meece, 2007, Spellman, 2010). Pancreatic beta-cell dysfunction is central to the progression of T2DM, where there is a reduction in islet cell number and/or beta-cell mass (Harris et al., 2008, Meier, 2008). Pancreatic beta-cell mass is regulated by cell proliferation, neogenesis, and apoptosis. T2DM can also have islet-related antibodies (Horton et al., 1999). Studies have demonstrated that some antibodies have existed in T2DM (Baudouin et al., 1988, Gleichmann et al., 1984, Nicoloff et al., 2004). These lead to the formation of circulating immune complexes (CIC). CIC is associated with diabetic complications, such as diabetic nephropathy (Nicoloff et al., 2004). In our present study, immune activity in hippocampal tissue from db/db mice model of T2DM was established. Changes in tau phosphorylation, Abeta deposition, tau-related protein kinase GSK-3β and AKT in the mice brain were examined. These changes were induced by the stereotaxic injection of IgG from IgG deposit-positive db/db mice into their hippocampi. These findings may be potential new insight into the mechanism by which T2DM increases the risk for AD.

Section snippets

Clinical observations

When the mice were 20 weeks, the type 2 diabetic db/db mice were heavier (p<0.01) than the C57BL/6 control mice. Type 2 diabetic db/db mice showed significantly (p<0.01) elevated FBG levels (Table 1).

IgG deposition

Immunohistochemical staining for IgG on the hippocampus specimens obtained from the 20 db/db mice and 20 C57BL/6 mice were performed. Frozen sections were treated with anti-IgG. Sparse conspicuous deposition was found in the C57BL/6 mice and in 7 of the 20 db/db mice. Hippocampus sections from 13

Discussion

Type 1 diabetes mellitus is an autoimmune disease caused by the autoimmune destruction of islet beta-cell in the pancreas. Such cells include the islet cell autoantibody (ICA), insulin autoantibody, glutamic acid decarboxylase, and protein tyrosine phosphatise (Taplin and Barker, 2008). T2DM is a heterogeneous disorder including at least two major subgroups, which can be further characterized by HLA-DR antigens and organ-specific antibodies. Some studies have demonstrated that pancreatic islet

Reagent

Anti-IgG antibody was purchased from SouthernBiotech. Anti-total tau antibody (monoclonal antibody) was purchased from Epitomics. Anti-pS396 antibody (phosphoserine 396, polyclonal antibody) for Western blot and Anti-pT212 antibody (phosphothreonine 212, polyclonal antibody) for Western blot were from BioSource International. Anti-p202 antibody (phosphoserine 202, monoclonal antibody) was from epitomics. Anti-total tau antibody and anti-pS396 antibody for immunohistochemistry were from Bioss

Acknowledgments

We thank Dr. Yuzhen Liang and Mei Lin for helpful experimental design suggestions and expert technical assistance.

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    These authors contributed equally to this work.

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