Impact On Learning And Memory By Engineered Nanomaterials Through Interaction With Hippocampal Neurons

The dynamic interactions of nanoparticles with cells or cellular proteins hold one of the keys for understanding the diverse biological effects of engineered nanomaterials. In a biological environment, nanoparticles encounter and interact with thousands of proteins, forming a protein corona on the surface of the nanoparticles, but these interactions are generally perceived as non-specific protein adsorption, with protein unfolding and deactivation as the most likely consequences. The potential of a nanoparticle-protein interaction to mimic a protein-protein interaction in a cellular signaling process, characterized by stringent specificity and robust functionality, has not been demonstrated. The dissertation of part two shows that the hippocampal Ca2+/calmodulin-dependent protein kinase Ⅱ (CaMKⅡ), a multimeric intracellular serine/threonine kinase central to Ca2+signal transduction and critical for learning and memory, binds selectively and stably to distinct sites on fullerene C60nanocrystals (Nano C60). This specific interaction of CaMKⅡ with Nano C60, mediated by amino acid residues D246and K250within the catalytic domain of CaMKⅡα, but not the non-specific adsorption of CaMKⅡ to nanodiamond, causes a conformational change for CaMKⅡ and leads to some of the same biological consequences manifested by the well-documented interaction between CaMKⅡ and the NMDA (N-methyl-D-aspartate) receptor subunit NR2B protein, including generation of autonomous CaMKⅡ activity without the need for T286autophosphorylation, calmodulin trapping, CaMKⅡ translocation to post-synaptic sites, and enhancement of long-term potentiation (LTP) and spatial memory. These results underscore the critical importance of specific interactions between inorganic nanoparticles and cellular signaling proteins, and the ability to "permanently" lock CaMKⅡ in an active conformation by fullerene C60may have significant implications for both the bio-safety and the potential therapeutic applications of this classic engineered nanomaterial. The dissertation of part three shows another effect of fullerene C60on CaMKⅡ. In a reactive oxygen species (ROS)-dependent fashion, fullerene C60oxidizes the paired methionine residues within the regulatory domain of CaMKⅡβ in the CaMKⅡ holoenzyme, and cause the same active effect of H2O2on the heart CaMKⅡδ. Several different changes of CaMKII elicited by fullerene C60, work together and contribute to learning and memory enhancement. Autophagy, a cellular stress response to degrade damaged components, is tightly regulated by many moleculars. Many nanoparticles can activate autophagy in cells, and thus elicit different biological effects. The dissertation of part four show that Quantum dot (QD), widely applied in vivo for protein-labeling, has the abilities to impair synaptic transmission and synaptic plasticity in the hippocampal CA1area, and induce autophagy in neurons. Obvious LC3dot and autophagosome formation, extensive conversion of LC3-I to LC3-II, and a significant decrease of p62were observed in hippcampal neurons treated with QD. Furthermore, autophagy specific inhibitors, could suppress QD-induced autophagic flux, partly blocked QD-induced LTP impairment, abrogate QD-induced synapsin-I downregulation and synapse deficit. These results indicate elevated autophagy contributes to the synapse impairment caused by QDs. Such studies might have important implications for providing a potential clinical remedy for brain damage caused by nanomaterials and designing safer nanoparticles. The dissertation shows the biological effects of interaction between nanoparticles and proteins or cells. It may provide a theoretical basis for nanoparticles bio-safety assessment and biomedical applications.