Capriello, Teresa (2021) Neurobehavioural, histological, physiological and gene expression analyses in zebrafish exposed to aluminium. [Tesi di dottorato]

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Aluminium (Al) is a ubiquitous element, naturally occurring in the soil, air, and water. Its presence in the environment has been increasing due to anthropogenic activities and the consequent pollution, especially in water bodies. Accordingly, this study aimed to find out more about its toxic effects on aquatic organisms. For this reason, the research was conducted using Danio rerio, commonly called zebrafish, like model organism, both as adult and during the embryonic stage. Zebrafish embryos, at 6 hpf, were exposed for 72 hours at increasing Al concentrations of 1.40, 2.80 and 5.60 mg/L. Phenotypic alterations, the time of hatching, swimming ability, but also apoptosis and oxidative stress responses have been assessed for all tested concentrations. The mRNA expression level of c-fos, appa and appb as marker genes of neural development and function were analysed for the highest used concentration. Instead, the adults were exposed to 11 mg/L of Al and the behavioural and locomotor responses were assessed at 10, 15 and 20 days of exposure. Moreover, particular attention was paid to the main organs involved in these activities, as brain and musculature and gills for which the changes in the oxidative state and the histological alterations induced by Al were assessed. The data showed that Al significantly affected the development of zebrafish inducing morphological alterations, changes of motility and cell death. The oxidative state of larvae was altered, although the formation of reactive oxygen species and the levels of metallothioneins, and the activity of some antioxidant enzymes, decreased at the maximum concentration tested. In addition, at this concentration, the expression of the evaluated genes increased. For the adults, the behavioural and locomotory responses, suggested an increase in the anxiety state, especially observed in animals exposed to Al for 15 days with a compromising the histology and functionality of several organs analysed after Al short-term exposures and an improvement/stabilization of their conditions with increasing exposure time. In particular, the neurotoxic role of Al was investigated, understanding the correlation between exposure to this metal and induced neurodegeneration, myelin alteration and changed in the expression of the GFAP protein, marker of glial cells. Finally, the evaluation of markers involved in the parkinsonism by RT-qPCR, allowed to better understand also the role of Al in the regulation of genes related to Parkinson's neurodegenerative disease. The overall information gives a realistic snapshot of Al toxicity and provides new information on the mechanism of action of this metal, as widespread as dangerous for environmental and human health.

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