Project description:We examined the use of toxicogenomics data to 1) elucidate the underlying mechanisms of pulmonary responses following exposures to titanium dioxide (TiO2) nanoparticles (NPs) of different size and surface charge, and 2) determine if such responses are influenced by embedding particles in complex paint matrix. Adult C57BL/6 mice were exposed via single intratracheal instillation to three doses of free forms of NRCWE-030 (10.5 nm), NRCWE-025 (38 nm), NRCWE-001 (10 nm, neutral charge) NRCWE-002 (10 nm, positive charge) or to sanding dusts of paint consisting of NRCWE-030+NRCWE-025 or NRCWE-025 alone. Controls were exposed to dispersion medium without NPs. TiO2NPs were characterized for size, surface area, and agglomeration status in the exposure medium. Hyperspectral microscopy was performed to detect TiO2NPs in lungs and to determine the in vivo status of matrix-embedded TiO2NPs. Pulmonary gene expression profiles were generated using DNA microarrays on lung tissues collected at 24 h and 28 d post exposure time points. Bioinformatics tools were used to characterize size and surface property-pertinent effects. The data from 360 individual arrays were collapsed into 567 differentially expressed genes (False discovery rate adjusted P ≤ 0.05 and fold change ≥ 1.5 in any one condition). Unsupervised hierarchical clustering of the 567 genes revealed that TiO2NPs clustered mainly based on the post-exposure time points and then by the particle types. A meta analysis using pathway tools showed that the combination of smaller size and positive surface charge contributes to the potency of TiO2NPs. Although embedding in matrix dampens the overall toxicity of TiO2NPs, the smaller size positively influences the toxicity. Paint matrix itself did not induce any response. Finally, the observed differences in response reflected the differences in severity of the response and not the underlying mechanisms. Thus, transcriptional profiling is an effective tool to determine the important properties responsible for eliciting a response.

Project description:Fluorescence spectroscopy techniques like Förster resonance energy transfer (FRET) and fluorescence correlation spectroscopy (FCS) have become important tools for the in vitro and in vivo investigation of conformational dynamics in biomolecules. These methods rely on the distance-dependent quenching of the fluorescence signal of a donor fluorophore either by a fluorescent acceptor fluorophore (FRET) or a non-fluorescent quencher, as used in FCS with photoinduced electron transfer (PET). The attachment of fluorophores to the molecule of interest can potentially alter the molecular properties and may affect the relevant conformational states and dynamics especially of flexible biomolecules like intrinsically disordered proteins (IDP). Using the intrinsically disordered S-peptide as a model system, we investigate the impact of terminal fluorescence labeling on the molecular properties. We perform extensive molecular dynamics simulations on the labeled and unlabeled peptide and compare the results with in vitro PET-FCS measurements. Experimental and simulated timescales of end-to-end fluctuations were found in excellent agreement. Comparison between simulations with and without labels reveal that the ?-stacking interaction between the fluorophore labels traps the conformation of S-peptide in a single dominant state, while the unlabeled peptide undergoes continuous conformational rearrangements. Furthermore, we find that the open to closed transition rate of S-peptide is decreased by at least one order of magnitude by the fluorophore attachment. Our approach combining experimental and in silico methods provides a benchmark for the simulations and reveals the significant effect that fluorescence labeling can have on the conformational dynamics of small biomolecules, at least for inherently flexible short peptides. The presented protocol is not only useful for comparing PET-FCS experiments with simulation results but provides a strategy to minimize the influence on molecular properties when chosing labeling positions for fluorescence experiments.

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The distribution of physical, chemical and conformational properties in signal and nascent peptides.

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