Palm Oil-Rich Diet Affects Murine Liver Proteome and S-Palmitoylome

Palmitic acid (C16:0) is the most abundant saturated fatty acid in animals serving as a substrate in synthesis and β-oxidation of other lipids, and in the modification of proteins called palmitoylation. The influence of dietary palmitic acid on protein S-palmitoylation remains largely unknown. In this study we performed high-throughput proteomic analyses of a membrane-enriched fraction of murine liver to examine the influence of a palm oil-rich diet (HPD) on S-palmitoylation of proteins. HPD feeding for 4 weeks led to an accumulation of C16:0 and C18:1 fatty acids in livers which disappeared after 12-week feeding, in contrast to an accumulation of C16:0 in peritoneal macrophages. Parallel proteomic studies revealed that HPD feeding induced a sequence of changes of the level and/or S-palmitoylation of diverse liver proteins involved in fatty acid, cholesterol and amino acid metabolism, hemostasis, and neutrophil degranulation. The HPD diet did not lead to liver damage, however, it caused progressing obesity, hypercholesterolemia and hyperglycemia. We conclude that the relatively mild negative impact of such diet on liver functioning can be attributed to a lower bioavailability of palm oil-derived C16:0 vs. that of C18:1 and the efficiency of mechanisms preventing liver injury, possibly including dynamic protein S-palmitoylation.

Endoplasmic reticulum stress as a key mechanism in stunted growth of seawater rainbow trout (Oncorhynchus mykiss)

Background Rainbow trout (Oncorhynchus mykiss) is a salmonid species with a complex life-history. Wild populations are naturally divided into freshwater residents and sea-run migrants. Migrants undergo an energy-demanding adaptation for life in seawater, known as smoltification, while freshwater residents display these changes in an attenuated magnitude and rate. Despite this, in seawater rainbow trout farming all fish are transferred to seawater. Under these circumstances, weeks after seawater transfer, a significant portion of the fish die (around 10%) or experience growth stunting (GS; around 10%), which represents an important profitability and welfare issue. The underlying causes leading to GS in seawater-transferred rainbow trout remain unknown. In this study, we aimed at characterising the GS phenotype in seawater-transferred rainbow trout using untargeted and targeted approaches. To this end, the liver proteome (LC-MS/MS) and lipidome (LC-MS) of GS and fast-growing phenotypes were profiled to identify molecules and processes that are characteristic of the GS phenotype. Moreover, the transcription, abundance or activity of key proteins and hormones related to osmoregulation (Gill Na+, K + –ATPase activity), growth (plasma IGF-I, and liver igf1, igfbp1b, ghr1 and ctsl) and stress (plasma cortisol) were measured using targeted approaches. Results No differences in Gill Na+, K + –ATPase activity and plasma cortisol were detected between the two groups. However, a significant downregulation in plasma IGF-I and liver igf1 transcription pointed at this growth factor as an important pathomechanism for GS. Changes in the liver proteome revealed reactive-oxygen-species-mediated endoplasmic reticulum stress as a key mechanism underlying the GS phenotype. From the lipidomic analysis, key observations include a reduction in triacylglycerols and elevated amounts of cardiolipins, a characteristic lipid class associated with oxidative stress, in GS phenotype. Conclusion While the triggers to the activation of endoplasmic reticulum stress are still unknown, data from this study point towards a nutritional deficiency as an underlying driver of this phenotype.

The liver proteome response to torpor in a basoendothermic mammal, Tenrec ecaudatus, provides insights into the evolution of homeothermy

Many mammals use adaptive heterothermy (e.g. torpor, hibernation) to reduce metabolic demands of maintaining high body temperature (Tb). Torpor is typically characterized by coordinated declines in Tb and metabolic rate (MR) followed by active rewarming. Most hibernators experience periods of euthermy between bouts of torpor during which homeostatic processes are restored. In contrast, the common tenrec, a basoendothermic Afrotherian mammal, hibernates without interbout arousals and displays extreme flexibility in Tb and MR. We investigated the molecular basis of this plasticity in tenrecs by profiling the liver proteome of animals that were active or torpid with high and more stable Tb (~32°C) or lower Tb (~14°C). We identified 768 tenrec liver proteins, of which 50.9% were differentially abundant between torpid and active animals. Protein abundance was significantly more variable in active cold and torpid compared to active warm animals, suggesting poor control of proteome abundance. Our data suggest that torpor in tenrecs may lead to mismatches in protein pools due to poor coordination of anabolic and catabolic processes. We propose that the evolution of endothermy leading to a more realized homeothermy of boreoeutherians likely led to greater coordination of homeostatic processes and reduced mismatches in thermal sensitivities of metabolic pathways.

Chronic temperature stress effects on the liver proteome of two threespine stickleback (Gasterosteus aculeatus) populations using a novel DIA assay library

A data-independent acquisition (DIA) assay library was generated for the liver of threespine sticklebacks to evaluate alterations in protein abundance and functional enrichment of molecular pathways following either chronic warm (25°C) or cold (7°C) three-week temperature challenge in two estuarine populations. The DIA assay library was created from a data-dependent acquisition (DDA) based raw spectral library that was filtered to remove low quality or ambiguous peptides. Functional enrichment analyses using STRING identified larger networks that were significantly enriched by examining both the entire liver proteome and only significantly elevated or depleted proteins from the various comparisons. These systems level analyses revealed the unique liver proteomic signatures of two populations of threespine sticklebacks acclimated to chronic temperature stress. The Big lagoon population (BL) had a stronger response than the Klamath river population (KL). At 7°C, BL showed alterations in protein homeostasis that likely fueled a higher demand for energy, but both populations successfully acclimated to this temperature. The warm acclimation induced major increases in proteins involved in chromatin structure and transcription, while there were decreases in proteins related to translation and fatty acid metabolism. Functional enrichment analyses of the entire liver proteome uncovered differences in glycolysis and carbohydrate metabolism between the two populations and between the cold acclimated and control groups. We conclude that the synchronous regulatory patterns of many proteins observed in the liver of threespine sticklebacks provide more comprehensive insight into population-specific responses to thermal stress than the use of less specific pre-determined biomarkers.