Alzheimer's disease (AD)
dementia impacts all facets of higher order cognitive function and is characterized by the presence of distinctive pathological lesions in the gray matter (GM). The profound alterations in GM structure and function have fostered the view that AD impacts are primarily a consequence of GM damage. However, the white matter (WM) represents about 50% of the cerebrum and this area of the brain is substantially atrophied and profoundly abnormal in both sporadic AD (SAD) and familial AD (
FAD). We examined the WM biochemistry by ELISA and Western blot analyses of key
proteins in 10
FAD cases harboring mutations in the
presenilin genes PSEN1 and PSEN2 as well as in 4 non-demented control (NDC) individuals and 4 subjects with SAD. The molecules examined were direct substrates of PSEN1 such as Notch-1 and
amyloid precursor
protein (APP). In addition,
apolipoproteins, axonal transport molecules, cytoskeletal and structural
proteins,
neurotrophic factors and synaptic
proteins were examined. PSEN-
FAD subjects had, on average, higher amounts of WM
amyloid-beta (Aβ)
peptides compared to SAD, which may play a role in the devastating dysfunction of the brain. However, the PSEN-
FAD mutations we examined did not produce uniform increases in the relative proportions of Aβ42 and exhibited substantial variability in total Aβ levels. These observations suggest that neurodegeneration and
dementia do not depend solely on enhanced Aβ42 levels. Our data revealed additional complexities in PSEN-
FAD individuals. Some direct substrates of γ-
secretase, such as Notch,
N-cadherin, Erb-B4 and APP, deviated substantially from the NDC group baseline for some, but not all, mutation types.
Proteins that were not direct γ-
secretase substrates, but play key structural and functional roles in the WM, likewise exhibited varied concentrations in the distinct PSEN mutation backgrounds. Detailing the diverse biochemical pathology spectrum of PSEN mutations may offer valuable insights into
dementia progression and the design of effective therapeutic interventions for both SAD and
FAD.