Mitochondria in Memory Retrieval in Wild‐Type Mice and in the Impairment of Memory Retrieval in Amyloid Precursor Protein Transgenic Mice

Abstract

AbstractBackgroundTreatment of Alzheimer’s disease (AD) would benefit from earlier diagnosis and a better understanding of the biochemical and cellular events underlying memory loss. This study, which follows our previous work identifying early deficits in long‐term memory retrieval and memory‐associated glucose uptake in amyloid precursor protein transgenic (APPtg) mice, aims to a) test our hypothesis of stimulus‐dependent synaptic mitochondrial activity as a mechanism underlying memory retrieval, and b) investigate any mitochondrial abnormalities possibly associated with the impairment of memory retrieval in APPtg mice (and possibly in presymptomatic AD).MethodThe J20 APPtg mouse line has been used. Two genotypes (APPtg and wild‐type) and two behavioral groups have been analysed, a) a group subject to criterion‐based watermaze training, sacrificed 20 sec following a probe trial seven days after learning the task (the memory retrieval group), and b) a group with no behavioral training (the basal levels group). Synaptosome forebrain samples (enriched in synapses) from 16 mice (four mice from each of the genotype/behavioral combinations) have been subjected to proteomics, Western blot and electron microscopy analyses. Oxygen consumption and enzymatic activity assay analyses are ongoing.ResultOur previous behavioral result of significantly impaired 7‐day memory retrieval has been reproduced. Our proteomics analysis has suggested higher synaptic levels of mitochondrial proteins during memory retrieval, compared to basal levels in wild‐type mice, a phenotype also present but less evident in APPtg mice. Western analysis has indicated lower synaptic levels of proteins involved in mitochondrial fusion and fission during memory retrieval, compared to basal levels. No difference was identified by electron microscopy in a) numbers of synaptic mitochondria or b) synaptic mitochondrial area. Our oxygen consumption and enzymatic activity assay results are planned to be collected on time for this presentation.ConclusionOur data provide evidence supporting our hypothesis of mitochondrial involvement a) in memory retrieval and b) in the impairment of memory retrieval in APPtg mice and possibly in early AD. They also provide some clues on the exact mitochondrial mechanisms, which is the focus of our current research.