AICDc58 potentiates 352PHPtau, but not 352WTtau-induced cell death.

<p>Cells were transfected with AICDc58/352WTtau or AICDc58/352PHPtau in the presence (CT-GFP, check bars) or absence (GFP, black bars) of model Hirano bodies. Co-transfection of H4 cells with GFP and AICDc58/352WTtau seems to result in cell death that approximates GFP/352WTtau plus GFP/AICDc58 cells. Co-transfection of GFP and AICDc58/352PHPtau significantly enhances cell death compared to GFP/AICDc58 only (***p<0.005) or GFP/AICDc58/352WTtau (**p<0.01). The presence of model Hirano bodies significantly protected against AICDc58-, AICDc58/352WTtau-, and AICDc58/352PHPtau-induced cell death (++p<0.01 compared to cells without model Hirano bodies). Error bars represent the standard deviation.</p

Model Hirano Bodies Protect against Tau-Independent and Tau-Dependent Cell Death Initiated by the Amyloid Precursor Protein Intracellular Domain

<div><p>The main pathological hallmarks of Alzheimer’s disease are amyloid-beta plaques and neurofibrillary tangles, which are primarily composed of amyloid precursor protein (APP) and tau, respectively. These proteins and their role in the mechanism of neurodegeneration have been extensively studied. Hirano bodies are a frequently occurring pathology in Alzheimer’s disease as well as other neurodegenerative diseases. However, the physiological role of Hirano bodies in neurodegenerative diseases has yet to be determined. We have established cell culture models to study the role of Hirano bodies in amyloid precursor protein and tau-induced cell death mechanisms. Exogenous expression of APP and either of its c-terminal fragments c31 or Amyloid Precursor Protein Intracellular Domain c58 (AICDc58) enhance cell death. The presence of tau is not required for this enhanced cell death. However, the addition of a hyperphosphorylated tau mimic 352PHPtau significantly increases cell death in the presence of both APP and c31 or AICDc58 alone. The mechanism of cell death induced by APP and its c-terminal fragments and tau was investigated. Fe65, Tip60, p53, and caspases play a role in tau-independent and tau-dependent cell death. In addition, apoptosis was determined to contribute to cell death. The presence of model Hirano bodies protected against cell death, indicating Hirano bodies may play a protective role in neurodegeneration.</p> </div

Both 352PHPtau and c31 co-localize with model Hirano bodies.

<p>H4 cells were transfected with 352PHPtau or c31, and either CT-GFP to induce model Hirano bodies or GFP as a control. In control cells, tau is predominantly found in the cytoplasm while c31 is evenly diffused throughout the cell. In cells expressing CT-GFP, c31 is primarily found co-localizing with model Hirano bodies. Tau also co-localizes with model Hirano bodies, but its overall distribution is not altered. Scale bar 15 µm.</p

Model Hirano bodies protect against AICDc58 and APP/AICDc58-induced cell death.

<p>Cells were transfected with APP and/or AICDc58 in the presence (CT-GFP, check bars) or absence (GFP, black bars) of model Hirano bodies. AICDc58 causes significant cell death in H4 cells in the absence of exogenously expressed APP. Transfection of H4 cells with APP/AICDc58 causes a significant increase in cell death (* p<0.05 in comparison to GFP/AICDc58). The presence of model Hirano bodies significantly protected against AICDc58 and APP-induced cell death (+ p<.05 between with and without model Hirano bodies) and APP/AICDc58-induced cell death (++ p<0.01 between with and without model Hirano bodies). Error bars represent the standard deviation.</p

Fe65 contributes to both tau-independent and tau-dependent cell death.

<p>Cells were transfected with either APP/c31 or APP/c31/352PHP/tau in the absence (black bars) or presence of C655F Fe65 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0044996#pone.0044996-Cao1" target="_blank">[56]</a> (dotted bars). The expression of mutant C655F Fe65 significantly reduced both tau-independent and tau-dependent cell death (*** p<0.005). Error bars represent the standard deviation.</p

Model Hirano bodies protect against APP and c31-induced cell death in N2A cells.

<p>N2A cells were transfected with APP/APPc31 in the presence (CT-GFP, check bars) or absence (GFP, black bars) of model Hirano bodies. Either APP or APPc31-myc causes low amounts of cell death while the presence of both APP/c31 shows an enhanced increase in cell death. Furthermore, model Hirano bodies are able to protect against the enhanced effect of APP/c31-induced cell death (** p<0.01 between cells with and without Hirano bodies). Error bars represent the standard deviation.</p

Tip60 contributes to both tau-independent and tau-dependent cell death.

<p>Cells were transfected with either APP/c31or APP/c31/352PHPtau in the absence (black bars) or presence (dotted bars) of mutant Q377E G380E Tip60 (mTip60) <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0044996#pone.0044996-Kinoshita1" target="_blank">[53]</a>. The expression of mutant Tip60 significantly reduced both tau-independent and tau-dependent cell death (*** p<0.005). Error bars represent the standard deviation.</p