≡ Menu

ApoE4: This is your brain on ApoE4

At least until the CHO breaks you…

Dennis, N. a, Browndyke, J. N., Stokes, J., Need, A., Burke, J. R., Welsh-Bohmer, K. a, & Cabeza, R. (2010). Temporal lobe functional activity and connectivity in young adult APOE varepsilon4 carriers. Alzheimer’s & dementia : the journal of the Alzheimer’s Association, 6(4), 303–11. doi:10.1016/j.jalz.2009.07.003

BACKGROUND: We sought to determine if the APOE epsilon4 allele influences both the functional activation and connectivity of the medial temporal lobes (MTLs) during successful memory encoding in young adults. METHODS: Twenty-four healthy young adults, i.e., 12 carriers and 12 noncarriers of the APOE epsilon4 allele, were scanned in a subsequent-memory paradigm, using event-related functional magnetic resonance imaging. The neuroanatomic correlates of successful encoding were measured as greater neural activity for subsequently remembered versus forgotten task items, or in short, encoding success activity (ESA). Group differences in ESA within the MTLs, as well as whole-brain functional connectivity with the MTLs, were assessed. RESULTS: In the absence of demographic or performance differences, APOE epsilon4 allele carriers exhibited greater bilateral MTL activity relative to noncarriers while accomplishing the same encoding task. Moreover, whereas epsilon4 carriers demonstrated a greater functional connectivity of ESA-related MTL activity with the posterior cingulate and other peri-limbic regions, reductions in overall connectivity were found across the anterior and posterior cortices. CONCLUSIONS: These results suggest that the APOE varepsilon4 allele may influence not only functional activations within the MTL, but functional connectivity of the MTLs to other regions implicated in memory encoding. Enhanced functional connectivity of the MTLs with the posterior cingulate in young adult epsilon4 carriers suggests that APOE may be expressed early in brain regions known to be involved in Alzheimer’s disease, long before late-onset dementia is a practical risk or consideration. These functional connectivity differences may also reflect pleiotropic effects of APOE during early development.

Evans, S., Gray, M. A., Dowell, N. G., Tabet, N., Tofts, P. S., King, S. L., & Rusted, J. M. (2013). APOE E4 Carriers show prospective memory enhancement under nicotine, and evidence for specialisation within medial BA10. Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology, 38(4), 655–63. doi:10.1038/npp.2012.230

There is evidence to suggest that the APOE ɛ4 allele (which confers an increased risk of developing dementia) might be associated with cognitive advantages earlier in life. Further, nicotine might selectively benefit ɛ4 carriers. We used fMRI to explore performance on a prospective memory (PM) task in young adults (age 18-30) with and without nicotine using a within-subjects design. Participants performed an ongoing task while retaining a PM instruction to respond to specific stimuli embedded in the task. Nicotine effects varied according to APOE status. Reaction times to the PM cue were improved under nicotine in ɛ4 carriers, but not in ɛ3 carriers. In an event-related analysis, extrastriate responses to PM trials were enhanced by nicotine only in ɛ4 carriers. These differences in early visual processing may contribute to the behavioral findings. Activity in medial BA10 (previously implicated in PM) differentiated ɛ4 from ɛ3 carriers. One BA10 subregion showed greater deactivation in ɛ4 carriers during PM trials. Activity in other BA10 subregions was modulated by PM reaction time, pointing to region-specific effects within medial BA10. In addition, activity in right hippocampal formation was only seen in ɛ4 carriers receiving nicotine. These results demonstrate that cognitive enhancement by nicotine can selectively benefit APOE ɛ4 carriers, and point to genotype-specific differences in neural activity during PM. In addition, these results show that the role of medial BA10 in PM likely involves varying contributions from functionally specific subregions.

Filippini, N., MacIntosh, B. J., Hough, M. G., Goodwin, G. M., Frisoni, G. B., Smith, S. M., … Mackay, C. E. (2009). Distinct patterns of brain activity in young carriers of the APOE-epsilon4 allele. Proceedings of the National Academy of Sciences of the United States of America, 106(17), 7209–14. doi:10.1073/pnas.0811879106

The APOE epsilon4 allele is a risk factor for late-life pathological changes that is also associated with anatomical and functional brain changes in middle-aged and elderly healthy subjects. We investigated structural and functional effects of the APOE polymorphism in 18 young healthy APOE epsilon4-carriers and 18 matched noncarriers (age range: 20-35 years). Brain activity was studied both at rest and during an encoding memory paradigm using blood oxygen level-dependent fMRI. Resting fMRI revealed increased “default mode network” (involving retrosplenial, medial temporal, and medial-prefrontal cortical areas) coactivation in epsilon4-carriers relative to noncarriers. The encoding task produced greater hippocampal activation in epsilon4-carriers relative to noncarriers. Neither result could be explained by differences in memory performance, brain morphology, or resting cerebral blood flow. The APOE epsilon4 allele modulates brain function decades before any clinical or neurophysiological expression of neurodegenerative processes.

Mondadori, C. R. A., de Quervain, D. J.-F., Buchmann, A., Mustovic, H., Wollmer, M. A., Schmidt, C. F., … Henke, K. (2007). Better memory and neural efficiency in young apolipoprotein E epsilon4 carriers. Cerebral cortex (New York, N.Y. : 1991), 17(8), 1934–47. doi:10.1093/cercor/bhl103

The apolipoprotein E (APOE) epsilon4 allele is the major genetic risk factor for Alzheimer’s disease, but an APOE effect on memory performance and memory-related neurophysiology in young, healthy subjects is unknown. We found an association of APOE epsilon4 with better episodic memory compared with APOE epsilon2 and epsilon3 in 340 young, healthy persons. Neuroimaging was performed in a subset of 34 memory-matched individuals to study genetic effects on memory-related brain activity independently of differential performance. E4 carriers decreased brain activity over 3 learning runs, whereas epsilon2 and epsilon3 carriers increased activity. This smaller neural investment of epsilon4 carriers into learning reappeared during retrieval: epsilon4 carriers exhibited reduced retrieval-related activity with equal retrieval performance. APOE isoforms had no differential effects on cognitive measures other than memory, brain volumes, and brain activity related to working memory. We suggest that APOE epsilon4 is associated with good episodic memory and an economic use of memory-related neural resources in young, healthy humans.

Moreau, P.-H., Bott, J.-B., Zerbinatti, C., Renger, J. J., Kelche, C., Cassel, J.-C., & Mathis, C. (2013). ApoE4 confers better spatial memory than apoE3 in young adult hAPP-Yac/apoE-TR mice. Behavioural brain research, 243, 1–5. doi:10.1016/j.bbr.2012.12.043

The APOE-ɛ4 allele is associated with increased cognitive decline during normal aging and Alzheimer’s disease. However, several studies intriguingly found a beneficial effect on cognition in young adult human APOE-ɛ4 carriers. Here, we show that 3-month old bigenic hAPP-Yac/apoE4-TR mice outperformed their hAPP-Yac/apoE3-TR counterparts on learning and memory performances in the highly hippocampus-dependent, hidden-platform version of the Morris water maze task. The two mouse lines did not differ in a non-spatial visible-platform version of the task. This hAPP-Yac/apoE-TR model may thus provide a useful tool to study the mechanisms involved in the antagonistic pleiotropic effects of APOE-ɛ4 on cognitive functions.

Rusted, J. M., Evans, S. L., King, S. L., Dowell, N., Tabet, N., & Tofts, P. S. (2013). APOE e4 polymorphism in young adults is associated with improved attention and indexed by distinct neural signatures. NeuroImage, 65, 364–73. doi:10.1016/j.neuroimage.2012.10.010

The APOE e4 allele, which confers an increased risk of developing dementia in older adulthood, has been associated with enhanced cognitive performance in younger adults. An objective of the current study was to compare task-related behavioural and neural signatures for e4 carriers (e4+) and non-e4 carriers (e4-) to help elucidate potential mechanisms behind such cognitive differences. On two measures of attention, we recorded clear behavioural advantages in young adult e4+ relative to e4-, suggesting that e4+ performed these tasks with a wider field of attention. Behavioural advantages were associated with increased task-related brain activations detected by fMRI (BOLD). In addition, behavioural measures correlated with structural measures derived from a former DTI analysis of white matter integrity in our cohort. These data provide clear support for an antagonistic pleiotropy hypothesis–that the e4 allele confers some cognitive advantage in early life despite adverse consequences in old age. The data implicate differences in both structural and functional signatures as complementary mediators of the behavioural advantage.

0 comments… add one

Leave a Comment