Mild Cognitive Impairment and Asymptomatic Alzheimer Disease Subjects: Equivalent β-Amyloid and Tau Loads With Divergent Cognitive Outcomes

• Published in: Journal of neuropathology and experimental neurology Vol. 73; no. 4; pp. 295 - 304
• Main Authors: Iacono, Diego, Resnick, Susan M., O’Brien, Richard, Zonderman, Alan B., An, Yang, Pletnikova, Olga, Rudow, Gay, Crain, Barbara, Troncoso, Juan C.
• Format: Journal Article
• Language: English
• Published: England by American Association of Neuropathologists, Inc 01.04.2014
• Subjects: Aged, 80 and over; Alzheimer Disease - metabolism; Alzheimer Disease - pathology; Alzheimer Disease - physiopathology; Amyloid beta-Peptides - metabolism; Autopsy; Brain - metabolism; Brain - pathology; Cognitive Dysfunction - pathology; Cognitive Dysfunction - physiopathology; Female; Humans; Male; Neuropsychological Tests; Postmortem Changes; Stereotaxic Techniques; tau Proteins - metabolism
• ISSN: 0022-3069; 1554-6578; 1554-6578
• DOI: 10.1097/NEN.0000000000000052

ABSTRACTOlder adults with intact cognition before death and substantial Alzheimer disease (AD) lesions at autopsy have been termed “asymptomatic AD subjects” (ASYMAD). We previously reported hypertrophy of neuronal cell bodies, nuclei, and nucleoli in the CA1 of the hippocampus (CA1), anterior cingulate gyrus, posterior cingulate gyrus, and primary visual cortex of ASYMAD versus age-matched Control and mild cognitive impairment (MCI) subjects. However, it was unclear whether the neuronal hypertrophy could be attributed to differences in the severity of AD pathology. Here, we performed quantitative analyses of the severity of β-amyloid (Aβ) and phosphorylated tau (tau) loads in the brains of ASYMAD, Control, MCI, and AD subjects (n = 15 per group) from the Baltimore Longitudinal Study of Aging. Tissue sections from CA1, anterior cingulate gyrus, posterior cingulate gyrus, and primary visual cortex were immunostained for Aβ and tau; the respective loads were assessed using unbiased stereology by measuring the fractional areas of immunoreactivity for each protein in each region. The ASYMAD and MCI groups did not differ in Aβ and tau loads. These data confirm that ASYMAD and MCI subjects have comparable loads of insoluble Aβ and tau in regions vulnerable to AD pathology despite divergent cognitive outcomes. These findings imply that cognitive impairment in AD may be caused or modulated by factors other than insoluble forms of Aβ and tau.