Caenorhabditis elegans deep lipidome profiling by using integrative mass spectrometry acquisitions reveals significantly altered lipid networks

Combined matrix-assisted laser desorption/ionisation-mass spectrometry imaging with liquid chromatography-tandem mass spectrometry for observing spatial distribution of lipids in whole Caenorhabditis elegans

RATIONALE

Matrix-assisted laser desorption/ionisation-mass spectrometry imaging (MALDI-MSI) is a powerful label-free technique for biomolecule detection (e.g., lipids), within tissue sections across various biological species. However, despite its utility in many applications, the nematode Caenorhabditis elegans is not routinely used in combination with MALDI-MSI. The lack of studies exploring spatial distribution of biomolecules in nematodes is likely due to challenges with sample preparation.

METHODS

This study developed a sample preparation method for whole intact nematodes, evaluated using cryosectioning of nematodes embedded in a 10% gelatine solution to obtain longitudinal cross sections. The slices were then subjected to MALDI-MSI, using a RapifleX Tissuetyper in positive and negative polarities. Samples were also prepared for liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis using an Exploris 480 coupled to a HPLC Vanquish system to confirm the MALDI-MSI results.

RESULTS

An optimised embedding method was developed for longitudinal cross-sectioning of individual worms. To obtain longitudinal cross sections, nematodes were frozen at -80°C so that all worms were rod shaped. Then, the samples were defrosted and transferred to a 10% gelatine matrix in a cryomold; the worms aligned, and the whole cryomold submerged in liquid nitrogen. Using MALDI-MSI, we were able to observe the distribution of lipids within C. elegans, with clear differences in their spatial distribution at a resolution of 5 μm. To confirm the lipids from MALDI-MSI, age-matched nematodes were subjected to LC-MS/MS. Here, 520 lipids were identified using LC-MS/MS, indicating overlap with MALDI-MSI data.

CONCLUSIONS

This optimised sample preparation technique enabled (un)targeted analysis of spatially distributed lipids within individual nematodes. The possibility to detect other biomolecules using this method thus laid the basis for prospective preclinical and toxicological studies on C. elegans.

Anti-aging activities of neutral and acidic polysaccharides from Polygonum multiflorum Thunb in Caenorhabditis elegans

Polygonum multiflorum Thunb (PM) is used to slow the aging process. Although polysaccharides are a major constituent of PM, their anti-aging properties have not been thoroughly investigated. Therefore, this study aimed to examine the anti-aging effects of polysaccharides extracted from PM using the Caenorhabditis elegans (C. elegans) model. Two types of water-soluble heteropolysaccharides, namely a neutral polysaccharide (RPMP-N) and an acidic polysaccharide (RPMP-A), were obtained from PM. Their structures were elucidated by various methods. The effects of these polysaccharides on the lifespan, levels of antioxidants, and activities of antioxidant-related enzymes in C. elegans were also evaluated. The results showed that RPMP-A had higher GalA content compared with RPMP-N. The average molecular weights of RPMP-N and RPMP-A were 245.30 and 28.45 kDa, respectively. RPMP-N is a α-1,4-linked dextran as the main chain, and contains a small amount of branched dextran with O-6 as the branched linkage site；RPMP-A may be a complex of α-1,4-linked dextran, HG and RG-I. Treatment with RPMP-N and RPMP-A increased the mean lifespan of C. elegans, and significantly regulated oxidative stress. RPMP-A exhibited stronger anti-aging effects compared with RPMP-N. These findings suggest that RPMP-A may be a potent antioxidant and anti-aging component that can be used for developing functional food products and effective dietary supplements.

Development of an Efficient On-Tissue Epoxidation Reaction Mediated by Urea Hydrogen Peroxide for MALDI MS/MS Imaging of Lipid C═C Location Isomers

Unsaturated lipids containing different numbers and locations of C═C bonds are significantly associated with a variety of cellular and metabolic functions. Although matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) has been used to visualize the spatial distribution patterns of various lipids in biological tissues, in situ identification, discrimination, and visualization of lipid C═C location isomers remain challenging. Herein, an efficient and fast on-tissue chemical derivatization (OTCD) approach was developed to pinpoint the locations of C═C bonds in complex lipids in situ via methyltrioxorhenium (MTO)-catalyzed epoxidation of C═C with a urea hydrogen peroxide (UHP)/hexafluoroisopropanol (HFIP) system. The efficiency of OTCD could reach 100% via one-step spray deposition of the solution mixture of MTO/UHP/HFIP at room temperature. The developed OTCD method provided rich structural information on lipid C═C location isomers, and their accurate spatial distribution patterns were resolved in mouse brain tissues. Tissue-specific distributions and changes of lipid C═C location isomers in the liver sections of obese ob/ob and diabetic db/db mice were further investigated, and their correlation in two animal models was revealed. The simplicity and high efficiency of the OTCD method developed for MALDI tandem MSI of lipid C═C location isomers possess great potential for functional spatial lipidomics.

Unveiling potentially convergent key events related to adverse outcome pathways induced by silver nanoparticles via cross-species omics-scale analysis

The adverse effects of silver nanoparticles (AgNPs) have been studied in various models. However, there has been discordance between molecular responses across the literature, attributed to methodological biases and the physicochemical variability of AgNPs. In this study, a gene pathway meta-analysis was conducted to identify convergent and divergent key events (KEs) associated with AgNPs and explore common patterns of these KEs across species. We performed a cross-species analysis of transcriptomic data from multiple studies involving various AgNPs exposure. Pathway enrichment analysis revealed a set of pathways linked to oxidative stress, apoptosis, and metabolite and lipid metabolism, which are considered potentially conserved KEs across species. Subsequently, experiments confirmed that oxidative stress responses could be early KEs in both Caenorhabditis elegans and HepG2 cells. Moreover, AgNPs preferentially impaired the mitochondria, as evidenced by mitochondrial fragmentation and dysfunction. Furthermore, disruption of amino acids, nucleotides, sulfur compounds, glycerolipids, and glycerophospholipids metabolism were in good agreement with gene pathway shreds of evidence. Our findings imply that, although there may be organism-specific responses, potentially conserved events could exist regardless of species and physicochemical factors. These results provide valuable insights into the development of adverse outcome pathways of AgNPs across species and the regulatory toxicity of AgNPs.

Lipid class-dependent alterations of Caenorhabditis elegans under harmane exposure

Altered lipid patterns in Caenorhabditis elegans (C. elegans) resulting from exposure to harmane remain to be explored. In this study, untargeted lipidomics was carried out to elucidate the effects of acute exposure to harmane on the lipidome of C. elegans. Exposure to the compound was evaluated based on the reproduction ability of the worms at 0.1 and 1 μg/mL. No significant effects of harmane were observed at these concentrations. Furthermore, we found that the modulatory effects of harmane on the lipidome of C. elegans at 1 μg/mL were lipid class dependent. In particular, harmane-treated worms were enriched in triglycerides and fatty acids, regardless of the degree of saturation. Glycerophospholipids were generally down-regulated. Furthermore, functional analyses suggested that there was a reduction in lipid membrane bilayer-related terms, and in some related to the mitochondria, and endoplasmic reticulum of C. elegans when treated with harmane. Lipid droplets and storage appeared to be up-regulated. In conclusion, our findings suggest that harmane exposure affects the lipidome of C. elegans in a sophisticated manner. Further investigations are required to elucidate the molecular mechanisms underlying these lipid pattern changes.