Broad scale proteomic analysis of heat-destabilised symbiosis in the hard coral Acropora millepora

Coral reefs across the globe are threatened by warming oceans. The last few years have seen the worst mass coral bleaching events recorded, with more than one quarter of all reefs irreversibly impacted. Considering the widespread devastation, we need to increase our efforts to understanding the physiological and metabolic shifts underlying the breakdown of this important symbiotic ecosystem. Here, we investigated the proteome (PRIDE accession # PXD011668) of both host and symbionts of the reef-building coral Acropora millepora exposed to ambient (~ 28 °C) and elevated temperature (~ 32 °C for 2 days, following a five-day incremental increase) and explored associated biomolecular changes in the symbiont, with the aim of gaining new insights into the mechanisms underpinning the collapse of the coral symbiosis. We identified 1,230 unique proteins (774 host and 456 symbiont) in the control and thermally stressed corals, of which 107 significantly increased and 125 decreased in abundance under elevated temperature relative to the control. Proteins involved in oxidative stress and proteolysis constituted 29% of the host proteins that increased in abundance, with evidence of impairment to endoplasmic reticulum and cytoskeletal regulation proteins. In the symbiont, we detected a decrease in proteins responsible for photosynthesis and energy production (33% of proteins decreased in abundance), yet minimal signs of oxidative stress or proteolysis. Lipid stores increased > twofold despite reduction in photosynthesis, suggesting reduced translocation of carbon to the host. There were significant changes in proteins related to symbiotic state, including proteins linked to nitrogen metabolism in the host and the V-ATPase (-0.6 fold change) known to control symbiosome acidity. These results highlight key differences in host and symbiont proteomic adjustments under elevated temperature and identify two key proteins directly involved in bilateral nutrient exchange as potential indicators of symbiosis breakdown.

A day in the life of winter plankton: under-ice community dynamics during 24 h in a eutrophic lake

Although diel vertical migration (DVM) in aquatic systems may account for the largest daily migration of biomass globally, our understanding of this process under ice cover is limited, particularly in fresh water. The date of lake ice onset and duration of ice cover is declining globally, therefore determining the extent of plankton migrations under ice is imperative to inform our baseline understanding of seasonal differences in community structure and function, and how conditions may change over time. We investigated whether plankton exhibit DVM under ice and explored interactions between phytoplankton and zooplankton at highly resolved space–time scales across 24 h in a eutrophic system. Despite the dominance of motile taxa, phytoplankton remained vertically segregated based on morpho-functional groups throughout the sampling period. Daphnia mendotae exhibited size-structured DVM with an upward migration at sunset and sunrise, and midnight sinking, presumably to avoid the rise of predatory Chaoborus. We hypothesize that because overwintering daphnids require rich lipid stores, D. mendotae migrated to access small, lipid-rich phytoplankton that were limited to surface waters. Given our study took place during an unusually warm winter in a eutrophic system, our results may represent future under-ice dynamics under increasing eutrophication pressure and climate warming in shallow lakes.

The role of trematode parasites as a nutritional food source for higher trophic level consumers

Recently, there has been a call for the inclusion of free-living stages of trematode parasites in food web models as they are present in high numbers in aquatic ecosystems and serve as prey for higher trophic levels. I investigated the presence of lipids in cercariae, specifically neutral energy reserve lipid stores and long-chain polyunsaturated fatty acids (LC-PUFA), as they are considered the primary energy currency in aquatic ecosystems. Cercariae of all investigated taxa contained distinct neutral lipid compositions and Ribeiroia ondatrae cercariae had significant quantities of total lipids, as well as essential fatty acids (EFA). I also investigated the viability of cercariae as prey items for dragonfly larvae (Leucorrhinia intacta) and detected indistinguishable proportions of EFA in larvae subsisting on equivalent quantities of R. ondatrae and Daphnia spp. This suggests that cercariae may contribute to nutrient subsidies in aquatic ecosystems, thereby supporting aquatic organism growth and fitness.

The role of trematode parasites as a nutritional food source for higher trophic level consumers

Recently, there has been a call for the inclusion of free-living stages of trematode parasites in food web models as they are present in high numbers in aquatic ecosystems and serve as prey for higher trophic levels. I investigated the presence of lipids in cercariae, specifically neutral energy reserve lipid stores and long-chain polyunsaturated fatty acids (LC-PUFA), as they are considered the primary energy currency in aquatic ecosystems. Cercariae of all investigated taxa contained distinct neutral lipid compositions and Ribeiroia ondatrae cercariae had significant quantities of total lipids, as well as essential fatty acids (EFA). I also investigated the viability of cercariae as prey items for dragonfly larvae (Leucorrhinia intacta) and detected indistinguishable proportions of EFA in larvae subsisting on equivalent quantities of R. ondatrae and Daphnia spp. This suggests that cercariae may contribute to nutrient subsidies in aquatic ecosystems, thereby supporting aquatic organism growth and fitness.

Lipid metabolism in Calanus finmarchicus is sensitive to variations in predation risk and food availability

Late developmental stages of the marine copepods in the genus Calanus can spend extended periods in a dormant stage (diapause) that is preceded by the accumulation of large lipid stores. We assessed how lipid metabolism during development from the C4 stage to adult is altered in response to predation risk and varying food availability, to ultimately understand more of the metabolic processes during development in Calanus copepods. We used RNA sequencing to assess if perceived predation risk in combination with varied food availability affects expression of genes associated with lipid metabolism and diapause preparation in C. finmarchicus. The lipid metabolism response to predation risk differed depending on food availability, time and life stage. Predation risk caused upregulation of lipid catabolism with high food, and downregulation with low food. Under low food conditions, predation risk disrupted lipid accumulation. The copepods showed no clear signs of diapause preparation, supporting earlier observations of the importance of multiple environmental cues in inducing diapause in C. finmarchicus. This study demonstrates that lipid metabolism is a sensitive endpoint for the interacting environmental effects of predation pressure and food availability. As diapause may be controlled by lipid accumulation, our findings may contribute towards understanding processes that can ultimately influence diapause timing.

Drosophila PDGF/VEGF signaling from muscles to hepatocyte-like cells protects against obesity

PDGF/VEGF ligands regulate a plethora of biological processes in multicellular organisms via autocrine, paracrine, and endocrine mechanisms. We investigated organ-specific metabolic roles of Drosophila PDGF/VEGF-like factors (Pvfs). We combine genetic approaches and single-nuclei sequencing to demonstrate that muscle-derived Pvf1 signals to the Drosophila hepatocyte-like cells/oenocytes to suppress lipid synthesis by activating the Pi3K/Akt1/TOR signaling cascade in the oenocytes. Functionally, this signaling axis regulates expansion of adipose tissue lipid stores in newly eclosed flies. Flies emerge after pupation with limited adipose tissue lipid stores and lipid level is progressively accumulated via lipid synthesis. We find that adult muscle-specific expression of pvf1 increases rapidly during this stage and that muscle-to-oenocyte Pvf1 signaling inhibits expansion of adipose tissue lipid stores as the process reaches completion. Our findings provide the first evidence in a metazoan of a PDGF/VEGF ligand acting as a myokine that regulates systemic lipid homeostasis by activating TOR in hepatocyte-like cells.

FLCN Gene Ablation Reduces Fibrosis and Inflammation in a Diet-Induced NASH Model

Non-alcoholic steatohepatitis (NASH) represents a major economic burden and is characterized by triglyceride accumulation, inflammation, and fibrosis. No pharmacological agents are currently approved to treat this condition. Emerging data suggests an important role of autophagy in this condition, which serves to degrade intracellular lipid stores, reduce hepatocellular damage, and dampen inflammation. Autophagy is primarily regulated by the transcription factors TFEB and TFE3, which are negatively regulated by mTORC1. Given that FLCN is an mTORC1 activator via its GAP activity towards RagC/D, we generated a liver specific Flcn knockout mouse model to study its role in NASH progression. We demonstrate that loss of FLCN results in reduced triglyceride accumulation, fibrosis, and inflammation in mice exposed to a NASH-inducing diet. Hence, the GAP activity of FLCN could a promising target for small molecule drugs to treat NASH progression by specifically activating autophagy and lysosomal biogenesis while leaving mRNA translation machinery unperturbed. Collectively, these results show an unexpected role for FLCN in NASH progression and highlight new possibilities for treatment strategies through its role in hepatocyte homeostasis.

Impacts of Dietary Nutritional Composition on Larval Development and Adult Body Composition in the Yellow Fever Mosquito (Aedes aegypti)

Background: the mosquito Aedes aegypti (Ae. aegypti) is an important vector of arboviruses, including Zika, Dengue, and Chikungunya. The dietary requirements of larval Ae. aegypti are not well understood and likely impact developmental and physiological parameters knowledge of which could be important for vector control. This study examines the effects nutrition has on growth and development of larval Ae. aegypti of laboratory-reared Rockefeller strain mosquitoes. Methods: mosquito larvae were split into five feeding groups with diets providing different ratios of protein and carbohydrates. Each group received autolyzed Brewer’s yeast (AY - high-protein), and/or rice flour (RF—high-carbohydrate). The groups were monitored to record larval developmental times, adult sizes and nutritional stores. Results: the 100% AY group failed to pupate, suggesting the AY alone is either lacking in critical nutrients or is toxic at higher concentrations. The 100% RF group resulted in the smallest adults that took the longest time to reach pupation. Of the remaining groups, the 25% AY/75% RF (Med–low) diet yielded adult mosquitoes with highest average weight, wing length, and lipid stores relative to the other diets. Conclusions: the dietary requirements for development, body size, and nutrient stores of Ae. aegypti mosquitoes appear to be dependent on a relatively low but essential proportion of dietary protein to carbohydrates to achieve optimal developmental outcomes.

Impact of high-fat diet on lifespan, metabolism, fecundity and behavioral senescence in Drosophila

Excess consumption of high-fat diet (HFD) is likely to result in obesity and increases the predisposition to associated health disorders. Drosophila melanogaster has emerged as an important model to study the effects of HFD on metabolism, gut function, behavior, and ageing. In this study, we investigated the effects of HFD on physiology and behavior of female flies at different time-points over several weeks. We found that HFD decreases lifespan, and also with age leads to accelerated decline of climbing ability in both virgins and mated flies. In virgins HFD also increased sleep fragmentation with age. Furthermore, long-term exposure to HFD results in elevated adipokinetic hormone (AKH) transcript levels and an enlarged crop with increased lipid stores. We detected no long-term effects of HFD on body mass, or levels of triacylglycerides (TAG), glycogen or glucose, although fecundity was diminished. However, one week of HFD resulted in decreased body mass and elevated TAG levels in mated flies. Finally, we investigated the role of AKH in regulating effects of HFD during aging. Both with normal diet (ND) and HFD, Akh mutant flies displayed increased longevity compared to control flies. However, both mutants and controls showed shortened lifespan on HFD compared to ND. In flies exposed to ND, fecundity is decreased in Akh mutants compared to controls after one week, but increased after three weeks. However, HFD leads to a similar decrease in fecundity in both genotypes after both exposure times. Thus, long-term exposure to HFD increases AKH signaling, impairs lifespan and fecundity and augments age-related behavioral senescence.