Avaliação do potencial termogênico da oxidase alternativa mitocondrial expressa em Drosophila melanogaster
Data
2019-02-19
Autores
Garcia, Geovana Siqueira
Título da Revista
ISSN da Revista
Título de Volume
Editor
Universidade Estadual Paulista (Unesp)
Resumo
A oxidase alternativa (AOX) é uma enzima com função de química redox semelhante aos complexos III e IV da cadeia respiratória (CR), porém, sem bombeamento de prótons para o espaço intermembranas da mitocôndria. Assim, ela não contribui à força próton-motriz que leva à produção de ATP e a energia é dissipada em forma de calor. AOX está presente na maioria dos metazoários, mas ausente em vertebrados e insetos, os quais perderam independentemente ao longo da evolução o gene que a codifica. Quando foi expressa transgenicamente em Drosophila melanogaster e outros modelos experimentais, AOX de Ciona intestinalis proporcionou melhoria nas condições associadas a disfunções mitocondriais, apresentando-se com potencial terapêutico. Os efeitos benéficos, entretanto, contrastam-se com a falta de investigação aprofundada da biologia da AOX em animais, principalmente em condições laboratoriais que mimetizam as da natureza. Considerando isso e o conhecimento sobre sua função termogênica em plantas, o presente trabalho objetivou investigar os efeitos da expressão de AOX em D. melanogaster sob variação térmica, testando a hipótese de que ela gera um aumento na temperatura corpórea do organismo. Linhagens expressando AOX em diferentes níveis foram submetidas a variadas temperaturas, incluindo condições severas de estresse térmico para análises durante o desenvolvimento e a fase adulta dessas moscas. AOX promoveu um aceleramento dose-dependente no desenvolvimento, aumentou significativamente a viabilidade dos ovos/larvas em baixas temperaturas (12 e 15°C), além de maior resistência ao frio (0°C) e recuperação mais rápida após exposição a este tipo de estresse em adultos. Imagens de termografia de infravermelho em larvas também apontaram um aumento na temperatura corpórea larval. Embora os dados sejam consistentes com a hipótese de produção de calor, análises in vitro de respirometria em extratos larvais não evidenciaram efeitos bioquímicos significativos da expressão da AOX no consumo de oxigênio mitocondrial, os quais pudessem explicar qualquer mecanismo termogênico. Portanto, a AOX mitiga os efeitos do frio, através de um complexo papel no metabolismo animal, o qual ainda precisa ser melhor elucidado.
Alternative oxidase (AOX) is an enzyme that catalyzes a redox reaction similarly to complexes III and IV of the respiratory chain (RC), but without the proton pumping into the mitochondrial intermembrane space. It therefore does not contribute to the proton-motive force that leads to ATP production and so the energy is dissipated as heat. AOX is present in most metazoans, but not in vertebrates and insects, which independently lost throughout evolution its coding gene. When the enzyme was expressed transgenically in Drosophila melanogaster and other experimental models, AOX improved in the deleterious conditions associated to mitochondrial dysfunctions, presenting with a therapeutic potential. The beneficial effects, however, contrast with the lack of in-depth information about the biology of AOX in animals, especially in nature-like laboratory conditions. Considering this and the knowledge about its thermogenic function in plants, we aimed at investigating the effects of AOX expression in D. melanogaster under varying thermal conditions, testing the hypothesis that the enzyme generates an increase in organismal body temperature. We submitted different AOX-expressing lines to various temperatures, including severe stress conditions for analysis during development and during the adult stage. AOX promoted dose-dependent acceleration in development, significantly increased viability of eggs/larvae at low temperatures (12 and 15°C). It also promoted higher resistance to cold (0°C) and faster recovery after cold exposure in adults. Infrared thermography images of larvae showed an increase in larval body temperature. Although the data are consistent with the heat generation hypothesis, in vitro respirometry analysis in larval extracts did not show significant biochemical effects of AOX expression on mitochondrial oxygen consumption, which could explain any thermogenic mechanism. Therefore, AOX attenuates the effects of cold, through a complex role in animal metabolism, which warrants further investigation.
Alternative oxidase (AOX) is an enzyme that catalyzes a redox reaction similarly to complexes III and IV of the respiratory chain (RC), but without the proton pumping into the mitochondrial intermembrane space. It therefore does not contribute to the proton-motive force that leads to ATP production and so the energy is dissipated as heat. AOX is present in most metazoans, but not in vertebrates and insects, which independently lost throughout evolution its coding gene. When the enzyme was expressed transgenically in Drosophila melanogaster and other experimental models, AOX improved in the deleterious conditions associated to mitochondrial dysfunctions, presenting with a therapeutic potential. The beneficial effects, however, contrast with the lack of in-depth information about the biology of AOX in animals, especially in nature-like laboratory conditions. Considering this and the knowledge about its thermogenic function in plants, we aimed at investigating the effects of AOX expression in D. melanogaster under varying thermal conditions, testing the hypothesis that the enzyme generates an increase in organismal body temperature. We submitted different AOX-expressing lines to various temperatures, including severe stress conditions for analysis during development and during the adult stage. AOX promoted dose-dependent acceleration in development, significantly increased viability of eggs/larvae at low temperatures (12 and 15°C). It also promoted higher resistance to cold (0°C) and faster recovery after cold exposure in adults. Infrared thermography images of larvae showed an increase in larval body temperature. Although the data are consistent with the heat generation hypothesis, in vitro respirometry analysis in larval extracts did not show significant biochemical effects of AOX expression on mitochondrial oxygen consumption, which could explain any thermogenic mechanism. Therefore, AOX attenuates the effects of cold, through a complex role in animal metabolism, which warrants further investigation.
Descrição
Palavras-chave
Oxidase alternativa, Cadeia respiratória, Termogênese, Mitocôndria, Drosophila melanogaster, Oxidase alternative, Respiratory chain, Thermogenesis, Mitochondria