Avaliação molecular do risco ecotoxicológico da radiação UV

Abstract

The incidence of ultraviolet (UV) radiation poses a threat to ecosystems. Exposure to UV radiation can be lethal to organisms due to its genotoxicity. In contrast, life forms have DNA damage repair systems that minimize such adverse effects. In this way, the application of molecular approaches to assess the genotoxic potential of UV radiation and the resistance of organisms allows a more accurate characterization of the ecotoxicological risk of UV radiation. Thus, this thesis assessed the ecotoxicological risk of UV radiation related to its genotoxicity through the use of molecular experimental approaches in vitro, in vivo, and in silico. First, the development of a genomic DNA damage analysis technology named EAsy-GeL assay is presented. The technology was validated after exposing eukaryotic cells (human leukocytes), prokaryotic cells (Escherichia coli), and naked DNA samples (isolated human DNA solution) to environmentally relevant doses of UV radiation. Next, this thesis discusses the genotoxic risk of solar UV radiation in amphibians. This theme is emerging within the area of ecotoxicology and conservation, as this group of animals is suffering population declines that culminate in the extinction of many species. Resistance to UV radiation is generally correlated with DNA repair activity and levels of sunlight exposure of a species throughout evolution. However, current levels of stratospheric ozone have been decreasing and changes in ecosystems (i.e. events such as deforestation and drought) have increased in different regions, such as in southern South America, which culminate in the increased incidence of UV radiation in amphibian breeding sites. However, our understanding of how amphibians respond to solar UV-induced DNA damage in vivo is superficial. Then, this thesis presents the results of an experimental evaluation of the effects of larval exposure to UV radiation in a habitat generalist anuran speciesliving in southern South America [Odontophrynus americanus (Anura: Odontophrynidae)]. Morphological, physiological, cellular, and molecular parameters indicated that UV radiation affects the larvae and contributes to, later, impact the anuran metamorphosis even when the prevention of mortality by larval photorepair is efficient. Next, this thesis presents the results of an in silico molecular assessment of photolyase enzymes in amphibian species to shed light on the evolutionary and functional aspects of DNA photorepair in these organisms. Our main results show substitutions in amino acids relevant to the function of photolyases that repair DNA damage most frequently induced by UV radiation (cyclobutane pyrimidine dimers) in salamander and anuran species whose natural populations are decreasing. Potentially, these results may be related to interspecific variations in UV sensitivity. On the whole, this thesis highlights the importance of using molecular approaches for understanding ecological and evolutionary processes related to the genotoxic risk of UV radiation.