Mitochondrial Physiology in the Major Arbovirus Vector Aedes aegypti: Substrate Preferences and Sexual Differences Define Respiratory Capacity and Superoxide Production

Abstract

Adult females of Aedes aegypti are facultative blood sucking insects and vectors of Dengue and yellow fever viruses. Insect dispersal plays a central role in disease transmission and the extremely high energy demand posed by flight is accomplished by a very efficient oxidative phosphorylation process, which take place within flight muscle mitochondria. These organelles play a central role in energy metabolism, interconnecting nutrient oxidation to ATP synthesis, but also represent an important site of cellular superoxide production. Given the importance of mitochondria to cell physiology, and the potential contributions of this organelle for A. aegypti biology and vectorial capacity, here, we conducted a systematic assessment of mitochondrial physiology in flight muscle of young adult A. aegypti fed exclusively with sugar. This was carried out by determining the activities of mitochondrial enzymes, the substrate preferences to sustain respiration, the mitochondrial bioenergetic efficiency and capacity, in both mitochondria-enriched preparations and mechanically permeabilized flight muscle in both sexes. We also determined the substrates preferences to promote mitochondrial superoxide generation and the main sites where it is produced within this organelle. We observed that respiration in A. aegypti mitochondria was essentially driven by complex I and glycerol 3 phosphate dehydrogenase substrates, which promoted distinct mitochondrial bioenergetic capacities, but with preserved efficiencies. Respiration mediated by proline oxidation in female mitochondria was strikingly higher than in males. Mitochondrial superoxide production was essentially mediated through proline and glycerol 3 phosphate oxidation, which took place at sites other than complex I. Finally, differences in mitochondrial superoxide production among sexes were only observed in male oxidizing glycerol 3 phosphate, exhibiting higher rates than in female. Together, these data represent a significant step towards the understanding of fundamental mitochondrial processes in A. aegypti, with potential implications for its physiology and vectorial capacity.

Proline as a fuel for insect flight: enhancing carbohydrate oxidation in hymenopterans

“…First, it is possible that isolated mitochondria and permeabilized muscle fibre preparations show different functional properties as reported in vertebrates [61]. A recent study on mosquitoes does not support this possibility as the two preparations responded similarly to various substrates, including proline [48]. Second, pyruvate and proline concentrations in the Campbell et al study were approximately 10-fold lower than normally used for isolated mitochondria in insects [48,60].…”

“…A recent study on mosquitoes does not support this possibility as the two preparations responded similarly to various substrates, including proline [48]. Second, pyruvate and proline concentrations in the Campbell et al study were approximately 10-fold lower than normally used for isolated mitochondria in insects [48,60]. The impact of working with such subsaturating conditions is that pyruvate-stimulated respiration could be well underestimated and that fold changes in respiration could vary widely given a typical Michaelis-Menten kinetic function.…”

“…As shown in another bee species, the oxidation of pyruvate at its highest rate is achieved by combining it with anaplerotic substrates that increase TCA cycle intermediates, regardless of whether it was malate, glutamate or proline [60]. To truly address if proline is a major oxidative fuel or mainly an anaplerotic substrate, as well as to determine the points of entry in the ETS, a combination of substrates and inhibitors will have to be used as in [48] and our study. Further work is clearly needed, but the current balance of evidence suggests that proline contributes little to energy production capacity in A. mellifera, as supported by our results on permeabilized muscle fibres.…”

“…This result is likely explained by electron convergence at the Q-junction (ubiquinone; figure 1). The enhanced respiration following complex I and II maximal respiration is typical of the contribution of other enzymes reducing ubiquinone (Q oxidoreductase), a property that has been described for proline dehydrogenase in a variety of organisms [66][67][68][69] and recently described in the dipterans Drosophila melanogaster [70] and Aedes aegypti [48]. Another Q oxidoreductase that is typically active in insects is the G3P dehydrogenase, an enzyme located on the outer face of the inner mitochondrial membrane.…”

<b><i>Aedes aegypti</b></i>: Morfologia, morfometria do ovo, desenvolvimento embrionário e aspectos relacionados à vigilância entomológica no Município de São Paulo

“…Já os machos apresentam aparelho bucal reduzido, sem potencial para romper a integridade da pele, sua alimentação é composta de néctar e seiva oriundo das plantas Considerando a relação entre a capacidade de dispersão deste inseto com o aumento do risco de dengue, Soares et al (2015), analisaram a fisiologia mitocondrial dos músculos do vôo existentes no tórax de adultos machos e fêmeas, isto foi realizado a partir da avaliação das enzimas mitocondriais após alimentação dos insetos, um dos importantes achados foi a de que a respiração mediada por oxidação prolina, um dos metabólitos da hemolinfa (análogo ao sangue para os insetos) foi notadamente maior para as fêmeas. De acordo com a pesquisa a compreensão dos processos mitocondriais são fundamentais e tem implicações potenciais para a fisiologia e capacidade vetorial do inseto.…”