Impacts Of PICALM And CLU Variants Associated With Alzheimer’s Disease On The Functional Connectivity Of The Hippocampus In Healthy Young Adults

Background:The rs3851179single nucleotide polymorphism (SNP) in the PICALM gene and rs11136000SNP in the CLU gene are recently associated with Alzheimer’s disease (AD). Investigating the effects of these genetic variants on the resting-state functional connectivity (rsFC) of the hippocampus might provide new insight into AD pathogenesis. In this study, we investigated the main and interaction effects of these two genetic variants on the hippocampal rsFC in healthy young adults.Methods:A total of283healthy young Chinese Han adults underwent genotyping and resting-state functional MRI examinations. Both the main and interaction effects of these two genetic variants (PICALM and CLU) on the hippocampal rsFC were analyzed.1. Genotyping We extracted genomic DNA from3000μl of whole blood using the EZgeneTM Blood gDNA Miniprep Kit (Biomiga Inc, San Diego, CA, USA). Then, we genotyped the PICALM rs3851179and CLU rs11136000in each subject using the PCR and ligation detection reaction (LDR) method.2. All preprocessing steps were carried out using the statistical parametric mapping (SPM8, http://www.fil.ion.ucl.ac.uk/spm) based on Matlab.3. The preprocessing of high resolution structural data including segmentation of gray and white matter, spatial normalization and smooth with a4mm full width at half maximum; while the preprocessing of rs-fMRI data including slice timing, realignment, spatial normalization to the MNI, resampling to3×3×3mm3cubic voxels, and smoothed with a4mm full width at half maximum.4. Functional connectivity was calculated using the DPARSF software based on Matlab; and the rsFC differences were investigated between the two genotypes with the age, gender and education years as covariates of no interest.5. Voxel-based morphometry (VBM) analysis of structural MRI data was performed to investigate group differences of grey matter volume.6. Multiple comparisons were statistically corrected by Monte Carlo simulation. Finally, the corrected statistical parameter mapping was overlapped onto MNI standard template and the coordinate, size and peak t values of each significant cluster were recorded.Results:The hippocampus showed positive rsFC with the default mode network and negative rsFC with the fronto-parietal network. Risk PICALM G-allele carriers showed weaker negative rsFC compared to AA carriers, whereas risk CLU-CC carriers exhibited stronger positive and negative rsFC than T-allele carriers. There existed complex interactions between PICALM and CLU on the negative rsFC of the hippocampus.Conclusions:Our results suggest that the PICALM and CLU risk genotypes exert differential impacts on the hippocampal rsFC in healthy young subjects. The complex interactions between the PICALM and CLU should be considered when investigating the impact of these two genetic variants on the brain.