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Spatially Resolved Activity-based Proteomic Profiles of the Murine Small Intestinal Lipases.

ABSTRACT: Despite the crucial function of the small intestine in nutrient uptake our understanding of the molecular events underlying the digestive function is still rudimentary. Recent studies demonstrated that enterocytes do not direct the entire dietary triacylglycerol toward immediate chylomicron synthesis. Especially after high-fat challenges, parts of the resynthesized triacylglycerol are packaged into cytosolic lipid droplets for transient storage in the endothelial layer of the small intestine. The reason for this temporary storage of triacylglycerol is not completely understood. To utilize lipids from cytosolic lipid droplets for chylomicron synthesis in the endoplasmic reticulum, stored triacylglycerol has to be hydrolyzed either by cytosolic lipolysis or lipophagy. Interestingly, triacylglycerol storage and chylomicron secretion rates are unevenly distributed along the small intestine, with the proximal jejunum exhibiting the highest intermittent storage capacity. We hypothesize that correlating hydrolytic enzyme activities with the reported distribution of triacylglycerol storage and chylomicron secretion in different sections of the small intestine is a promising strategy to determine key enzymes in triacylglycerol remobilization. We employed a serine hydrolase specific activity-based labeling approach in combination with quantitative proteomics to identify and rank hydrolases based on their relative activity in 11 sections of the small intestine. Moreover, we identified several clusters of enzymes showing similar activity distribution along the small intestine. Merging our activity-based results with substrate specificity and subcellular localization known from previous studies, carboxylesterase 2e and arylacetamide deacetylase emerge as promising candidates for triacylglycerol mobilization from cytosolic lipid droplets in enterocytes.

SUBMITTER: Schittmayer M

PROVIDER: S-EPMC7710144 | biostudies-literature | 2020 Dec

REPOSITORIES: biostudies-literature

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Spatially Resolved Activity-based Proteomic Profiles of the Murine Small Intestinal Lipases.

Schittmayer Matthias M Vujic Nemanja N Darnhofer Barbara B Korbelius Melanie M Honeder Sophie S Kratky Dagmar D Birner-Gruenberger Ruth R

Molecular & cellular proteomics : MCP 20201006 12

Despite the crucial function of the small intestine in nutrient uptake our understanding of the molecular events underlying the digestive function is still rudimentary. Recent studies demonstrated that enterocytes do not direct the entire dietary triacylglycerol toward immediate chylomicron synthesis. Especially after high-fat challenges, parts of the resynthesized triacylglycerol are packaged into cytosolic lipid droplets for transient storage in the endothelial layer of the small intestine. Th ...[more]

PMID: 33023980

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Project description:Despite the crucial function of the small intestine for nutrient uptake our understanding of the molecular events underlying the digestive function is very rudimentary. For example, it has only recently become evident that not all absorbed triacylglycerol (TAG) is immediately secreted in the form of chylomicrons (CM) by enterocytes. Instead, especially after high-fat challenges, parts of the re-synthesized TAG can be packaged into cytosolic lipid droplets (CLD) for transient storage in the endothelial layer of the small intestine. The reasons for this intermediate storage of TAGs are currently not completely understood. Several mechanisms, including alleviating lipotoxicity to enterocytes, limits in the rate of CM assembly or smoothening of the post-prandial peaks of blood hypertriglyceridemia have been suggested to explain this intermediate storage of TAG in CLD. Interestingly, rather than being evenly distributed across the small intestine, the proximal jejunum exhibits the highest TAG storage and CM secretion. Once stored in CLD, lipids are either remobilized in the inter-prandial phase or by various stimuli, e.g. a sequential meal containing either lipids or glucose. After remobilization, a triglyceride peak can be observed in the form of plasma CM well before lipids from the second meal have been digested in the intestinal lumen. To synthesize CM with lipids from CLD, CLD TAG have to be hydrolyzed to be transported across the ER membrane which can either be achieved by cytoplasmic TAG lipolysis or lipophagy. We hypothesize that correlating enzymatic activities of hydrolases with the reported distribution of TAG storage and chylomicron secretion in different sections of the small intestine is a promising strategy to pinpoint the key players in TAG remobilization. To rank hydrolases based on their relative activity in the different sections of the small intestine we have harnessed a serine hydrolase specific activity-based labeling strategy to label active hydrolases in freshly harvested enterocytes. Enrichment of activity labeled enzymes over control samples and abundance of enriched hydrolases from individual small intestine sections was analyzed using quantitative proteomics, resulting in a ranking of the most active hydrolases in 11 fractions of murine small intestine. Moreover, several clusters of enzymes showing similar activity distribution along the small intestine were identified.

Dataset Information

Spatially Resolved Activity-based Proteomic Profiles of the Murine Small Intestinal Lipases.

Publications

Spatially Resolved Activity-based Proteomic Profiles of the Murine Small Intestinal Lipases.

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