In vitro cytotoxicity study of superparamagnetic iron oxide and silica nanoparticles on pneumocyte organelles.

Inhalation is the main route of nanoparticles (NP) exposure during manufacturing. Although many mechanisms of toxicity have been described, the interaction of NP with relevant pneumocytes organelles is not widely understood. Considering that the physicochemical properties of NP influence their toxicological responses, the objective of this study was to evaluate whether exposure to different NP, crystalline Fe3O4 NP and amorphous SiO2 NP could alter pneumocytes organelles in alveolar epithelial cells. To achieve this goal, cell viability, ultrastructural changes, lysosomal damage, mitochondrial membrane potential (MMP), lipid droplets (LD) formation and cytokines production were evaluated by MTT, electron microscopy, lysotracker red staining, JC-1, Oil Red staining and Milliplex® assay respectively. Both NP were observed within lamellar bodies (LB), lysosomes, and cytoplasm causing morphological changes. Exposure to SiO2 NP at 6 h induced lysosomal activation, but not Fe3O4 NP. MMP decreased and LD increased at the highest concentrations after both NP exposure. Pro-inflammatory cytokines were released only after SiO2 NP exposure at 48 h. These results indicate that SiO2 NP have a greater impact than Fe3O4 NP on organelles responsible for energy, secretion, degradation and metabolism in pneumocytes leading to the development of respiratory disorders or the exacerbation of preexisting conditions. Therefore, the established biocompatibility for amorphous NP has to be reconsidered.

The Growth arrest specific 1 (Gas1) gene is transcriptionally regulated by NeuroD1 via two distal E-boxes.

Growth arrest specific 1 (GAS1) is a signaling mediator for the development of the central nervous system that works as a co-receptor for sonic hedgehog (SHH) to induce the amplification of neural progenitors during the patterning of the mammalian neural tube and establishing granular cells in the cerebellum. Recently, we confirmed that Gas1 is also expressed by neural progenitors of the developing cortex and the dentate gyrus of the hippocampus. The presence of GAS1 in progenitor stages indicates that one of its principal roles is the maintenance of these cells during neurogenic events. However, the signals responsible for the expression of Gas1 in progenitor cells are unknown, an aspect that is relevant to understand its functions during neurogenesis. Here, we focused on elucidating the mechanisms of the transcriptional regulation of Gas1 and using comparative genomics methods found two highly conserved E-boxes in the Gas1 promoter which mediate its up-regulation by NeuroD1. Additionally, we found that GAS1 and NeuroD1 co-localize in the neocortex, the dentate gyrus of the hippocampus and the external granular layer of the cerebellum, suggesting a previously unsuspected regulatory relationship. Our data indicate that Gas1 is a direct target of NeuroD1 during the induction of the neurogenic program.