Flexibility in energy metabolism supports hypoxia tolerance in Drosophila flight muscle: Metabolomic and computational systems analysis

Department of Bioengineering, University of California, San Diego, La Jolla, CA, USA.
Molecular Systems Biology (Impact Factor: 10.87). 02/2007; 3(1):99. DOI: 10.1038/msb4100139
Source: PubMed


The fruitfly Drosophila melanogaster offers promise as a genetically tractable model for studying adaptation to hypoxia at the cellular level, but the metabolic basis for extreme hypoxia tolerance in flies is not well known. Using (1)H NMR spectroscopy, metabolomic profiles were collected under hypoxia. Accumulation of lactate, alanine, and acetate suggested that these are the major end products of anaerobic metabolism in the fly. A constraint-based model of ATP-producing pathways was built using the annotated genome, existing models, and the literature. Multiple redundant pathways for producing acetate and alanine were added and simulations were run in order to find a single optimal strategy for producing each end product. System-wide adaptation to hypoxia was then investigated in silico using the refined model. Simulations supported the hypothesis that the ability to flexibly convert pyruvate to these three by-products might convey hypoxia tolerance by improving the ATP/H(+) ratio and efficiency of glucose utilization.

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    • "For larvae, chironomid larvae inhabiting hypoxic water are known to anaerobically convert glycogen to ethanol and acetate (Redecker and Zebe, 1988), the larval midge Chaorobus crystallinus anaerobically converts malate to succinate during anoxia (Englisch et al., 1982), the soil-living dipteran Callitroga macellaria larva anaerobically converts glycogen and amino acids to lactate, alanine and polyols (Gäde, 1985), and larval tiger beetles that experience flooding anaerobically produce lactate and alanine (Hoback et al., 2000). For adults, Drosophila are known to accumulate lactate, alanine and acetate (Feala et al., 2007), and anoxic locusts, honey bees, flies and beetles have been shown to accumulate lactate, alanine, glycerol, glycerol 3-phosphate and succinate (reviewed by Gäde, 1985; Wegener, 1987). Suppression of metabolic demand is a key aspect of long-term survival of anoxia, as generally animals must rely on internal energy stores (Guppy and Withers, 1999; Hochachka et al., 1996). "
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    ABSTRACT: Holometabolous insects undergo dramatic morphological and physiological changes during ontogeny. In particular, the larvae of many holometabolous insects are specialized to feed in soil, water or dung, inside plant structures, or inside other organisms as parasites where they may commonly experience hypoxia or anoxia. In contrast, holometabolous adults usually are winged and live with access to air. Here we show that larval Drosophila experience severe hypoxia in their normal laboratory environments; third instar larvae feed by tunneling into a medium without usable oxygen. Larvae move strongly in anoxia for many minutes, while adults (like most other adult insects) are quickly paralyzed. Adults survive anoxia nearly an order of magnitude longer than larvae (LT50: 8.3 vs. 1 h). Plausibly, the paralysis of adults is a programmed response to reduce ATP need and enhance survival. In support of that hypothesis, larvae produce lactate at 3x greater rates than adults in anoxia. However, when immobile in anoxia, larvae and adults were similarly able to decrease their metabolic rate in anoxia, to about 3% of normoxic conditions. These data suggest that Drosophila larvae and adults have been differentially selected for behavioral and metabolic responses to anoxia, with larvae exhibiting vigorous escape behavior likely enabling release from viscous anoxic media to predictably normoxic air, while the paralysis behavior of adults maximizes chances of survival of flooding events of unpredictable duration. Developmental remodeling of behavioral and metabolic strategies to hypoxia/anoxia is a previously unrecognized major attribute of holometabolism. © 2015. Published by The Company of Biologists Ltd.
    Full-text · Article · Jul 2015 · Journal of Experimental Biology
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    • "To reduce the accumulation of pyruvate, it can be transformed into acetylpyruvate using acetate (in addition to the transformation into lactate and alanine mentioned above). Although these specific end products were not known for D. cephalotes, they corroborate previous research on responses to hypoxia in Drosophila (Feala et al. 2007) and correspond to known by-products of anaerobic metabolism in other terrestrial insects (Hoback and Stanley 2001). Insects typically rely on the glycerol-3- phosphate shuttle to regenerate NADþ, which is important for maintaining glycolysis (Gilmour 1961), thus explaining the higher levels of glycerol and glyc- erol-3-phosphate. "
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    ABSTRACT: Thermal limits in ectotherms may arise through a mismatch between supply and demand of oxygen. At higher temperatures, the ability of their cardiac and ventilatory activities to supply oxygen becomes insufficient to meet their elevated oxygen demand. Consequently, higher levels of oxygen in the environment are predicted to enhance tolerance of heat, whereas reductions in oxygen are expected to reduce thermal limits. Here, we extend previous research on thermal limits and oxygen limitation in aquatic insect larvae and directly test the hypothesis of increased anaerobic metabolism and lower energy status at thermal extremes. We quantified metabolite profiles in stonefly nymphs under varying temperatures and oxygen levels. Under normoxia, the concept of oxygen limitation applies to the insects studied. Shifts in the metabolome of heat-stressed stonefly nymphs clearly indicate the onset of anaerobic metabolism (e.g., accumulation of lactate, acetate, and alanine), a perturbation of the tricarboxylic acid cycle (e.g., accumulation of succinate and malate), and a decrease in energy status (e.g., ATP), with corresponding decreases in their ability to survive heat stress. These shifts were more pronounced under hypoxic conditions, and negated by hyperoxia, which also improved heat tolerance. Perturbations of metabolic pathways in response to either heat stress or hypoxia were found to be somewhat similar but not identical. Under hypoxia, energy status was greatly compromised at thermal extremes, but energy shortage and anaerobic metabolism could not be conclusively identified as the sole cause underlying thermal limits under hyperoxia. Metabolomics proved useful for suggesting a range of possible mechanisms to explore in future investigations, such as the involvement of leaking membranes or free radicals. In doing so, metabolomics provided a more complete picture of changes in metabolism under hypoxia and heat stress.
    Full-text · Article · Sep 2013 · Integrative and Comparative Biology
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    • "Altering the metabolic pathways to produce more ATP is a common strategy to cope with hypoxia for living organisms. For example, metabolomic and computational analyses of fruitfly flight muscles under 0.5% oxygen levels showed that conversion of pyruvate from lactate to alanine and acetate could convey hypoxia tolerance by improving ATP-producing efficiency per glucose [33]. Flux-balance analyses showed that flies adapted to 4% oxygen levels produced more ATP per glucose by lowering pyruvate carboxylase flux and preferring the usage of Complex I to Complex II [26,34]. "
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    ABSTRACT: Responses to hypoxia have been investigated in many species; however, comparative studies between conspecific geographical populations at different altitudes are rare, especially for invertebrates. The migratory locust, Locusta migratoria, is widely distributed around the world, including on the high-altitude Tibetan Plateau (TP) and the low-altitude North China Plain (NP). TP locusts have inhabited Tibetan Plateau for over 34,000 years and thus probably have evolved superior capacity to cope with hypoxia. Here we compared the hypoxic responses of TP and NP locusts from morphological, behavioral, and physiological perspectives. We found that TP locusts were more tolerant of extreme hypoxia than NP locusts. To evaluate why TP locusts respond to extreme hypoxia differently from NP locusts, we subjected them to extreme hypoxia and compared their transcriptional responses. We found that the aerobic metabolism was less affected in TP locusts than in NP locusts. RNAi disruption of PDHE1beta, an entry gene from glycolysis to TCA cycle, increased the ratio of stupor in TP locusts and decreased the ATP content of TP locusts in hypoxia, confirming that aerobic metabolism is critical for TP locusts to maintain activity in hypoxia. Our results indicate that TP and NP locusts have undergone divergence in hypoxia tolerance. These findings also indicate that insects can adapt to hypoxic pressure by modulating basic metabolic processes.
    Full-text · Article · Sep 2013 · BMC Genomics
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