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: 14.1). 02/2007; 3:99. DOI: 10.1038/msb4100139
Source: PubMed

ABSTRACT 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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    • "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.
    Integrative and Comparative Biology 09/2013; 53:609-619. DOI:10.1093/icb/ict015 · 2.97 Impact Factor
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    • "Provided that the fruit fly's MR has a Q 10 of 2.2 (Schilman et al., 2011), temperature is expected to affect damage and recovery rates during anoxia and reperfusion. In the course of anoxia, low temperature probably decreases the build-up of anaerobic metabolites, like alanine, acetate and lactate (Feala et al., 2007), and possibly delays the consumption of endogenous antioxidant enzymes and energy metabolites (Zhang et al., 2011). When O 2 supply is restored, hypothermia could also reduce the build-up of reactive oxygen/nitrogen species (ROS/RNS) and slow down recovery and repair processes (e.g. "
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    ABSTRACT: Oxygen deprivation in nervous tissue depolarizes cell membranes, increasing extracellular potassium concentration ([K(+)](o)). Thus, [K(+)](o) can be used to assess neural failure. The effect of temperature (17°C, 23°C or 29°C) on the maintenance of brain [K(+)](o) homeostasis in male Drosophila melanogaster (w1118) individuals was assessed during repeated anoxic comas induced by N(2) gas. Brain [K(+)](o) was continuously monitored using K(+)-sensitive microelectrodes while body temperature was changed using a thermo electric cooler (TEC). Repetitive anoxia resulted in a loss of the ability to maintain [K(+)](o) baseline at 6.6±0.3 mM. The total [K(+)](o) baseline variation (Δ[K(+)](o)) was stabilized at 17°C (-1.1±1.3 mM), mildly rose at 23°C (17.3±1.4 mM), and considerably increased at 29°C (332.7±83.0 mM). We conclude that 1) reperfusion patterns consisting of long anoxia, short normoxia and high cycle frequency increased disruption of brain [K(+)](o) baseline maintenance, and 2) hypothermia had a protective effect on brain K(+) homeostasis during repetitive anoxia. Male flies are suggested as a useful model for examining deleterious consequences of O(2) reperfusion with possible application on therapeutical treatment of stroke or heart attack.
    Journal of Experimental Biology 08/2012; 215(23). DOI:10.1242/jeb.074468 · 3.00 Impact Factor
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    • "Higher body temperatures will increase metabolic rates of ectotherms, probably leading to increased production rates of anaerobic end-products and ROS during re-exposure to O 2 . Higher metabolic rates will increase the rate of formation of anaerobic endproducts: lactate, alanine and acetate in Drosophila (Feala et al., 2007). Higher temperatures probably also increase ion leakages that disrupt membrane electrical function. "
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    ABSTRACT: Insects in general, and Drosophila in particular, are much more capable of surviving anoxia than vertebrates, and the mechanisms involved are of considerable biomedical and ecological interest. Temperature is likely to strongly affect both the rates of damage occurring in anoxia and the recovery processes in normoxia, but as yet there is no information on the effect of this crucial variable on recovery rates from anoxia in any animal. We studied the effects of temperature, and thus indirectly of metabolic flux rates, on survival and recovery times of individual male Drosophila melanogaster following anoxia and O(2) reperfusion. Individual flies were reared at 25°C and exposed to an anoxic period of 7.5, 25, 42.5 or 60 min at 20, 25 or 30°C. Before, during and after anoxic exposure the flies' metabolic rates (MRs), rates of water loss and activity indices were recorded. Temperature strongly affected the MR of the flies, with a Q(10) of 2.21. Temperature did not affect the slope of the relationship between time to recovery and duration of anoxic exposure, suggesting that thermal effects on damage and repair rates were similar. However, the intercept of that relationship was significantly lower (i.e. recovery was most rapid) at 25°C, which was the rearing temperature. When temperatures during exposure to anoxia and during recovery were switched, recovery times matched those predicted from a model in which the accumulation and clearance of metabolic end-products share a similar dependence on temperature.
    Journal of Experimental Biology 04/2011; 214(Pt 8):1271-5. DOI:10.1242/jeb.052357 · 3.00 Impact Factor
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