Cognitive decline is sexually dimorphic in Alzheimer's disease (AD). Men show higher incidences of amnestic mild cognitive impairment yet women disproportionally phenoconvert to AD. It is hypothesized that men maintain greater cognitive reserve than women under comparable amyloid-ß (Aß) challenge. One behavioral aspect of cognitive reserve in mice is the capacity to cope with Aß-associated stereotypies by switching to increasingly effective navigational search strategies in the Morris water maze. To explore inherent sex differences in this paradigm, however, we require an AßPP mouse model wherein behavioral flexibility is impaired earlier in females than males despite equivalent Aß load. Here, we show that when F1 C57Bl/6×C3H/HeJ TgCRND8 mice are placed on C57Bl/6 background, N5 Tg males and females exhibit equivalent Aß pathologies at 2, 4, 6, and 8 months of age yet females display learning and memory deficits earlier than males. We further show that this N5 line does not carry the autosomal recessive pde6brd1 mutation that impairs visual acuity and that the estrous cycle is not disrupted on this genetic background. At 5.5 months of age, Tg males, but not females, compensate for Aß-associated stereotypic behaviors (i.e., hyperactive tight circling) by alternating navigational search strategies and adopting increasingly productive spatial search strategies. Females fail to overcome Aß-associated stereotypies and do not efficiently switch from systematic to spatial learning strategies. Together, these data identify a novel AßPP mouse model that can be used for preclinical testing of interventions targeting sexual dimorphisms in behavioral indices of cognitive reserve.
Alzheimer Disease/physiopathology , Alzheimer Disease/psychology , Cognitive Reserve , Disease Models, Animal , Sex Characteristics , Alzheimer Disease/genetics , Alzheimer Disease/pathology , Amyloid beta-Protein Precursor/genetics , Amyloid beta-Protein Precursor/metabolism , Animals , Brain/pathology , Brain/physiopathology , Cyclic Nucleotide Phosphodiesterases, Type 6/genetics , Cyclic Nucleotide Phosphodiesterases, Type 6/metabolism , Female , Humans , Male , Maze Learning/physiology , Mice, Inbred C3H , Mice, Inbred C57BL , Mice, Transgenic , Plaque, Amyloid/genetics , Plaque, Amyloid/pathology , Plaque, Amyloid/physiopathology , Plaque, Amyloid/psychology , Psychomotor Performance/physiology , Spatial Memory/physiology , Spatial Navigation/physiology , Survival Analysis
Not all of the mysteries of life lie in our genetic code. Some can be found buried in our membranes. These shells of fat, sculpted in the central nervous system into the cellular (and subcellular) boundaries of neurons and glia, are themselves complex systems of information. The diversity of neural phospholipids, coupled with their chameleon-like capacity to transmute into bioactive molecules, provides a vast repertoire of immediate response second messengers. The effects of compositional changes on synaptic function have only begun to be appreciated. Here, we mined 29 neurolipidomic datasets for changes in neuronal membrane phospholipid metabolism in Alzheimer's Disease (AD). Three overarching metabolic disturbances were detected. We found that an increase in the hydrolysis of platelet activating factor precursors and ethanolamine-containing plasmalogens, coupled with a failure to regenerate relatively rare alkyl-acyl and alkenyl-acyl structural phospholipids, correlated with disease severity. Accumulation of specific bioactive metabolites [i.e., PC(O-16:0/2:0) and PE(P-16:0/0:0)] was associated with aggravating tau pathology, enhancing vesicular release, and signaling neuronal loss. Finally, depletion of PI(16:0/20:4), PI(16:0/22:6), and PI(18:0/22:6) was implicated in accelerating Aß42 biogenesis. Our analysis further suggested that converging disruptions in platelet activating factor, plasmalogen, phosphoinositol, phosphoethanolamine (PE), and docosahexaenoic acid metabolism may contribute mechanistically to catastrophic vesicular depletion, impaired receptor trafficking, and morphological dendritic deformation. Together, this analysis supports an emerging hypothesis that aberrant phospholipid metabolism may be one of multiple critical determinants required for Alzheimer disease conversion.
