Ontogenetic changes in protein level of amyloid precursor protein (APP) in growth cones and synaptosomes from rat...

To elucidate the functional role of the amyloid precursor protein (APP) during brain ontogeny, developmental changes of APP levels in growth cones and synaptosomes were studied from embryonic day 14 up to postnatal day (PD) 400 using Western analysis. APP level in growth cones was low during prenatal stages of development, but demonstrating a continuous increase from PD 3 up to PD 10. Highest concentration of APP in synaptosomes was found between PD 7 and 10, followed by a considerable decrease up to PD 30 and persisting at this level up to PD 400. In situ hybridization to differentiate between APP695 mRNA, APP751 mRNA and APP770 mRNA revealed distinct age-related expression pattern of various APP isoforms. During prenatal brain development APP695 mRNA is maximally expressed in brain structures, containing differentiating nerve cells. APP751 and APP770 mRNA isoforms are diffusely distributed in the embryo throughout the prenatal period examined and their expression is higher in peripheral organs such as skin, lung, liver and bones as compared to the brain. The increase of APP level during synaptogenesis suggests a functional role of APP in the processes of neurite outgrowth and cell targeting as well as in the maintenance of the functional integrity of synapses in the mature brain. The APP695 isoform seems to be the major form involved in embryonic brain maturation.