Brain connectivity and activity during Alzheimer’s disease progression in a mouse model by manganese‐‐enhanced MRI in living brain correlated with post‐mortem histopathology.

Abstract

Alzheimer’s disease (AD) arises from inherited mutations in genes associated with plaque formation: amyloid precursor protein (APP), tau, and presenilin, or sporadically without these mutations. Studies of mice expressing these familial Alzheimer’s disease (FAD)‐associated mutations has led to new insights into the biological processes in sporadic AD. We study a mouse model in which expression of the FAD protein, APPSwInd, can be suppressed after plaque formation. This mouse thus corresponds to sporadic Alzheimer’s disease, where plaques are present in the absence of mutated protein. We use manganese‐enhanced magnetic resonance imaging (MEMRI), an emerging technology, coupled with histopathology of serial sections to investigate how plaques affect connectivity, neural activity degeneration throughout the whole brain as the mouse ages. MEMRI can be used in two ways: to determine axonal transport dynamics and to map neural activity in living mice. Stereotactic intracranial injection of Mn2+ traces transport in hippocampus occurring over 24h in the awake behaving mouse. Systemic Mn2+ enters active neurons in the brain of freely moving mice over 24h and is imaged retrospectively. Amyloid precursor protein (APP) is the precursor to A□eta plaques. The cytoplasmic domain of APP mediates cargo‐motor attachments for axonal transport. Our results show that in APP‐KO mice, axonal transport on Mn2+ is decreased demonstrating the APP plays a role in Mn2+ transport. In old transgenic mice APPSwInd, with both over‐expression of mutated protein and plaques, axonal transport is altered, as detected by time‐lapse manganese‐enhanced magnetic resonance imaging (MEMRI) of the brain in living mice. Time‐lapse MR images were captured before and successive time points after stereotactic injection of Mn2+ (3–5nL) into CA3 of the hippocampus. Images of multiple individuals from the two groups (with plaques and no expression, or without plaques) were aligned and processed with our automated computational pipeline, and voxel‐wise statistical parametric mapping (SPM) performed. Whole brain neural activity was decreased in 3yr old mice with plaque and expressing APPSwInd compared to non‐expressing littermates, particularly in the hippocampus. Brains were harvested after MEMRI for biochemistry, or fixed, embedded and serially sectioned for histopathology. Histopathology detected mouse p‐tau–positive dystrophic neurites, decreases in the volume of septal nuclei, decrease in dentate gyrus width and cell death. Thus, plaque alone depresses transport in the important hippocampal to basal forebrain memory circuit, and decreases neural activity in the aging mouse.Support or Funding InformationSupported by NINDS RO1 NS062184 and The Harvey Family Endowment.