A longitudinal multimodal in vivo molecular imaging study of the 3xTg-AD mouse model shows progressive early hippocampal and taurine loss

The understanding of the natural history of Alzheimer's disease (AD) and temporal trajectories of in vivo molecular mechanisms requires longitudinal approaches. A behavioral and multimodal imaging study was performed at 4/8/12 and 16months of age in a triple transgenic mouse model of AD (3xTg-AD). Behavioral assessment included the open field and novel object recognition tests. Molecular characterization evaluated hippocampal levels of amyloid beta (A beta) and hyperphosphorylated tau. Magnetic resonance imaging (MRI) included assessment of hippocampal structural integrity, blood-brain barrier (BBB) permeability and neurospectroscopy to determine levels of the endogenous neuroprotector taurine. Longitudinal brain amyloid accumulation was assessed using C-11 Pittsburgh compound B positron emission tomography (PET), and neuroinflammation/microglia activation was investigated using C-11-PK1195. We found altered locomotor activity at months 4/8 and 16months and recognition memory impairment at all time points. Substantial early reduction of hippocampal volume started at month 4 and progressed over 8/12 and 16months. Hippocampal taurine levels were significantly decreased in the hippocampus at months 4/8 and 16. No differences were found for amyloid and neuroinflammation with PET, and BBB was disrupted only at month 16. In summary, 3xTg-AD mice showed exploratory and recognition memory impairments, early hippocampal structural loss, increased A beta and hyperphosphorylated tau and decreased levels of taurine. In sum, the 3xTg-AD animal model mimics pathological and neurobehavioral features of AD, with early-onset recognition memory loss and MRI-documented hippocampal damage. The early-onset profile suggests temporal windows and opportunities for therapeutic intervention, targeting endogenous neuroprotectors such as taurine.