Repair of oxidative DNA damage, cell-cycle regulation and neuronal death may influence the clinical manifestation of Alzheimer's disease.

Alzheimer's disease (AD) is characterized by progressive cognitive decline associated with a featured neuropathology (neuritic plaques and neurofibrillary tangles). Several studies have implicated oxidative damage to DNA, DNA repair, and altered cell-cycle regulation in addition to cell death in AD post-mitotic neurons. However, there is a lack of studies that systematically assess those biological processes in patients with AD neuropathology but with no evidence of cognitive impairment. We evaluated markers of oxidative DNA damage (8-OHdG, H2AX), DNA repair (p53, BRCA1, PTEN), and cell-cycle (Cdk1, Cdk4, Cdk5, Cyclin B1, Cyclin D1, p27Kip1, phospho-Rb and E2F1) through immunohistochemistry and cell death through TUNEL in autopsy hippocampal tissue samples arrayed in a tissue microarray (TMA) composed of three groups: I) "clinical-pathological AD" (CP-AD)--subjects with neuropathological AD (Braak ≥ IV and CERAD = B or C) and clinical dementia (CDR ≥ 2, IQCODE>3.8); II) "pathological AD" (P-AD)--subjects with neuropathological AD (Braak ≥ IV and CERAD = B or C) and without cognitive impairment (CDR 0, IQCODE<3.2); and III) "normal aging" (N)--subjects without neuropathological AD (Braak ≤ II and CERAD 0 or A) and with normal cognitive function (CDR 0, IQCODE<3.2). Our results show that high levels of oxidative DNA damage are present in all groups. However, significant reductions in DNA repair and cell-cycle inhibition markers and increases in cell-cycle progression and cell death markers in subjects with CP-AD were detected when compared to both P-AD and N groups, whereas there were no significant differences in the studied markers between P-AD individuals and N subjects. This study indicates that, even in the setting of pathological AD, healthy cognition may be associated with a preserved repair to DNA damage, cell-cycle regulation, and cell death in post-mitotic neurons

Staining patterns and expression levels of apoptosis marker.

<p>TUNEL staining of neurons is stronger in CP-AD (A) than in P-AD (B) or N (C). Boxplots of apoptosis scores (D). CP-AD, clinical-pathological Alzheimer’s disease (green boxes); P-AD, pathological Alzheimer’s disease (blue boxes); N, normal aging (red boxes).</p

Expression levels of markers related to progression of cell cycle.

<p>Boxplots of Cdk4 scores attributed to nuclear (A) and cytoplasmic (B) staining. Boxplots of cyclin D scores attributed to nuclear (C) and cytoplasmic (D) staining. Boxplots of phospho-Rb scores attributed to nuclear (E) and cytoplasmic (F). Boxplots of E2F1 scores attributed to nuclear (G) and cytoplasmic (H) staining. Boxplots of Cdk1 scores attributed to nuclear (I) and cytoplasmic (J) staining. Boxplots of cyclin B scores attributed to nuclear (K) and cytoplasmic (L) staining. CP-AD, clinical-pathological Alzheimer’s disease (green boxes); P-AD, pathological Alzheimer’s disease (blue boxes); N, normal aging (red boxes).</p

Summary of nuclear expression of studied markers.

<p>Expression values of nuclear staining are shown as median (min–max). Kruskal-Wallis tests were used for comparisons among the three groups (CP-AD, P-AD and N). Two-by-two group comparisons were performed by utilizing Dunn’s multiple comparisons tests. *indicates statistical significance (<i>P</i>≤0.05). CP-AD, clinical-pathological Alzheimer’s disease; P-AD, pathological Alzheimer’s disease; N, normal aging.</p

Demographic statistics.

a<p>ANOVA;</p>b<p>χ-square; PMI, Postmortem Interval; CP-AD, clinical-pathological Alzheimer’s disease; P-AD, pathological Alzheimer’s disease; N, normal aging.</p

Expression levels of markers related to DNA repair.

<p>Boxplots of p53 scores attributed to nuclear (A) and cytoplasmic (B) staining. Boxplots of BRCA1 scores attributed to nuclear (C) and cytoplasmic (D) staining. Boxplots of PTEN scores attributed to nuclear staining (E) and cytoplasmic (F) staining. Boxplots of phospho-AKT scores attributed to nuclear (G) and cytoplasmic (H) staining. CP-AD, clinical-pathological Alzheimer’s disease (green boxes); P-AD, pathological Alzheimer’s disease (blue boxes); N, normal aging (red boxes).</p

Expression levels of markers related to cell-cycle inhibition.

<p>Boxplots of p27 scores attributed to nuclear (A) and cytoplasmic (B) staining. Boxplots of Cdk5 scores attributed to nuclear (C) and cytoplasmic (D) staining. CP-AD, clinical-pathological Alzheimer’s disease (green boxes); P-AD, pathological Alzheimer’s disease (blue boxes); N, normal aging (red boxes).</p