Mitochondrial metabolism and body condition of naturally infected sunfish

Parasites can affect host behavior, cognition, locomotion, body condition and 18 many other physiological traits. Changes to host aerobic metabolism are likely 19 responsible for these parasite-induced performance alterations. Whole-organism 20 metabolic rate is underpinned by cellular energy metabolism driven most prominently by 21 the mitochondria. However, few studies have explored how mitochondrial enzymatic 22 activity relates to body condition and parasite infection despite being a putative site for 23 metabolic disruptions related to health status. We studied correlations among natural 24 parasite infection, host body condition and the activity of key mitochondrial enzymes in 25 target organs from wild-caught pumpkinseed sunfish ( Lepomis gibbosus ) to better 26 understand the cellular responses of fish hosts to endoparasite infection. Enzymatic 27 activities in the gills, spleen, and brain of infected fish were not significantly related to 28 parasite infection or host body condition. However, the activity of cytochrome C oxidase, 29 an enzyme involved in oxidative phosphorylation, in fish hearts was higher in individuals 30 with lower body condition. Activities of citrate synthase, complexes I and III and 31 carnitine palmitoyltransferase were also significantly different among organ types. These 32 results provide preliminary information regarding the likely mitochondrial pathways 33 affecting host body condition, the maintenance energetic requirements of different organs 34 and their specific dependency on particular mitochondrial pathways. These results help 35 pave the way for future studies on the effects of parasite infection on mitochondrial 36 metabolism. measure the mitochondrial metabolism of a freshwater naturally parasitized with helminth endoparasites and to explore relationships among intensity, enzymatic activity, and body condition in four key We hypothesize the in intensities.


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Most wild animals are infected with parasites (Dobson et al. 2008 organisms living in or on another specie, the host, that they exploit for resources (shelter 4 0 and/or energy) (Lewin 1982). However, quantifying parasite-induced damages and/or 1 9 4 negligeable and thus not corrected for. The corrected fish mass was used to calculate the  Le Cren's body condition index was calculated for each fish. This index uses the 1 9 8 log relation between the corrected mass and the total length of the fish to estimate a slope  Once the organs were extracted from the fish, they were diluted 20 times their Enzymatic assays were performed at room temperature in 96-well plates using a were performed by adding 10 mM of sodium azide to the sample and background 2 3 6 activities were done by omitting DTT then deducted to the activity of the assay. The 2 3 7 reaction solution was bubbled for 5 minutes and the absorbance ratio of 550nm/565nm 2 3 8 was determined. If the ratio was higher than 9, the solution was used (Thibault et al.  A different situation was seen with CS activity. There was no significance in the 3 0 7 models that included the parasite density and organ type (see table S1) and no significant including both factors (figure 1B-2B-3B). However, a significant difference between 3 1 0 organs was detected (p-value = < 2e -16 ) in the model including body condition and organ 3 1 1 type without interactions. These differences are between the spleen (0.013 ± 0.00071 U 3 1 2 mg protein -1 ) and the brain (0.063 ± 0.003 U mg protein -1 ) (p-value < 2e -16 ); between the 3 1 3 heart (0.087 ± 0.0051 U mg protein -1 ) and the gills (0.026 ± 0.0014 U mg protein -1 ) (p-3 1 4 value < 2e -16 ); between the spleen and the heart (p-value = < 2e -16 ); between the brain and 3 1 5 the gills (p-value < 2e -16 ); between the heart and the brain (p-value< 3.52e -12 ); and 3 1 6 between the gills and the spleen (p-value< 1,04e -12 ) (figure 4A).

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None of the previously mentioned models including parasite density were found 3 1 8 to be significant in the case of CPT (see table S1), but trends were present for body a significant effect (p-value = < 2e -16 ) with the brain having a higher enzymatic activity 3 2 1 (0,0034 ± 0,00021 U mg protein -1 ) compared to the gills (0,0016 ± 0,000046 U mg 3 2 2 protein -1 ) (p-value = 4,41e -14 ), the heart (0,0016 ± 0,000010 U mg protein -1 ) (p-value = 3 2 3 3,83e -15 ) and the spleen (0,0013 ± 0,00010 U mg protein -1 ) (p-value = < 2e -16 ). Also, the spleen had a significantly different CPT activity compared to the gills (p-value = 0,0087) and to the heart (p-value = 0,041) ( Figure 4B). These results were obtained using the 3 2 6 statistical model including only body condition and organ type without their interaction. For ETS, there was no significant relationship between any of the tested factors 3 2 8 and enzymatic activity for models with either cestode density or black spot density (see table S1) (figure 1D-2D-3D) except for the organ type (p-value= 0,00078) in the model including cestode density and organ type without interactions. Cestode density 3 3 1 approached significance (p-value = 0.093) and the gills ETS activity (0,011 ± 0,00065 U 3 3 2 mg protein -1 ) was found to be significantly different of the brain activity (0,0082 ± 3 3 3 0,00041 U mg protein -1 ) (p-value = 0,00051) and the spleen (0,0084 ± 0,00082 U mg 3 3 4 protein -1 ) (p-value= 0,00031) ( Figure 4C). The goal of this study was to explore the mitochondrial metabolism of parasitized 3 3 7 L. gibbosus. We found no significant relationship between parasite density and host 3 3 8 mitochondrial enzymatic activity in any of the tested enzymes in the four organs we 3 3 9 studied. However, there was a significant negative relationship between body condition 3 4 0 and CCO activity of the heart. Indeed, the heart's activity was higher when an individual 3 4 1 had lower body condition. The activity of CS varied significantly among organs with 3 4 2 brain and heart activity being significantly higher than the spleen, and heart activity also 3 4 3 being higher than that of the gills. The activities of ETS and CPT were also found to be 3 4 4 significantly different between organs: the gills and the brain had the highest activity respectively.

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Parasites and host body condition We found no correlation between parasite density and host body condition, 3 4 8 despite a negative trend with both types of parasites (figure S1). Although parasites tend 3 4 9 to be negatively related to host body condition, some studies have also found positive or Lemly and Esch (1984) explored these relationships in a semi-controlled experimental set-up (cages placed in a lake), as opposed to our wild-caught fish. In our case, it is 3 5 6 impossible to know when parasite infections occurred in hosts, and thus whether fish were experiencing acute stages of infection that are more likely to be associated with 3 5 8 increased energetic costs (Lemly and Esch 1984). Given that the cestodes we study are 3 5 9 known to damage the liver, an important glycogen reserve, we expected to find a 3 6 0 significant negative relationship between parasite infection and host body condition. (Anodonta) woodiana) had an altered energy metabolism that could not be explained by directly, this is difficult since the liver tissue was often so heavily damaged in our 3 6 8 population of fish that uninfected tissue was difficult to discriminate and collect properly Enzymatic activity and host body condition Our results showed that CCO activity is correlated with a decreasing body activity in the heart means increased overall capacity for energy production and muscular 3 9 6 activity. Since the heart is responsible for the circulation of the blood throughout the 3 9 7 body, increased energy production may lead to increased blood circulation to tissues. It is 3 9 8 possible that fish in poor body condition experience increased nutrient demand, and thus have greater heart activity. Alternatively, heart morphology may be modified by general, we tend to see a non-significant negative trend between enzymatic activity and 4 1 0 body condition for all organs. Some of these trends are close to being significant 4 1 1 especially in CPT's case, justifying increasing the sample size to clarify these trends.

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Enzymatic activity and organ type 4 1 3 Although activities of most tested enzymes did not change in response to parasite 4 1 4 or body condition, they all differed significantly between organs. One notable example is coincides with the fact that the heart and the brain are two highly energy depending 4 1 9 organs. Increased TCA activity and/or mitochondrial density leads to more reducing 4 2 0 equivalent feeding the OXPHOS pathway, which may further increase ATP production. The heart has high baseline energetic demand (Laurent et al. 1983). By undergoing interesting observation was carnitine palmitoyltransferase activity, which was highest in 4 2 6 the brain ( Figure 4B). This organ has stored lipid that can be used by neuronal cells to that the brain potentially tends to consume more of its lipid reserve then other organs, 4 2 9 possibly to compensate for a lack of substrates coming from the digestive system, a 4 3 0 consequence of parasitism.

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The spleen is a small organ with a low energetic demand when not mounting an 4 3 2 immune reaction, and we found low activity in this organ for all tested enzymes. More  Linnaeus: how many parasites? How many hosts? Proceedings of the National Academy  Environment 408: 3746-3762.  Physiology 76: 525-542. the Q-junction in permeabilized fibers. Scientific reports 7: 1-13.  Magistretti, P., and I. Allaman. 2013. Brain energy metabolism. pp. 1591-1620.

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Neuroscience in the 21st century: from basic to clinical. Springer New York. Margolis, L., and J.R. Arthur. 1979. Synopsis of the parasites of fishes of Canada.

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Bulletin of the Fisheries Research Board of Canada. immunity. Nat Immunol 18: 488-498. to widespread glucocorticoid hormone increases in vertebrate hosts: A meta analysis.