Metabolic oxidation regulates embryonic stem cell differentiation.

Metabolites offer an important unexplored complementary approach to understanding the pluripotency of stem cells. Using MS-based metabolomics, we show that embryonic stem cells are characterized by abundant metabolites with highly unsaturated structures whose levels decrease upon differentiation. By monitoring the reduced and oxidized glutathione ratio as well as ascorbic acid levels, we demonstrate that the stem cell redox status is regulated during differentiation. On the basis of the oxidative biochemistry of the unsaturated metabolites, we experimentally manipulated specific pathways in embryonic stem cells while monitoring the effects on differentiation. Inhibition of the eicosanoid signaling pathway promoted pluripotency and maintained levels of unsaturated fatty acids. In contrast, downstream oxidized metabolites (for example, neuroprotectin D1) and substrates of pro-oxidative reactions (for example, acyl-carnitines), promoted neuronal and cardiac differentiation. We postulate that the highly unsaturated metabolome sustained by stem cells allows them to differentiate in response to in vivo oxidative processes such as inflammation.

Proteomic profiling of the prechylomicron transport vesicle involved in the assembly and secretion of apoB-48-containing chylomicrons in the intestinal enterocytes.

Intracellular assembly of chylomicrons (CM) occurs in intestinal enterocytes through a series of complex vesicular interactions. CM are transported from the ER to the Golgi using a specialized vesicular compartment called the prechylomicron transport vesicle (PCTV). In this study, PCTVs were isolated from the enteric ER of the Syrian Golden hamster, and characterized using 2-DE and MS. Proteomic profiles of PCTV-associated proteins were developed with the intention of identifying proteins involved in the formation, transport, lipidation, and assembly of CM particles. Positively identified proteins included those involved in lipoprotein assembly, namely microsomal triglyceride transfer protein and apolipoprotein B-48, as well as proteins involved in vesicular transport, such as Sar1 and vesicle-associated membrane protein 7. Other groups of proteins found were chaperones, intracellular vesicular trafficking proteins, fatty acid-binding proteins, and lipid-related proteins. These findings have increased our understanding of the transport vesicle involved in the intracellular assembly and transport of CM and can provide insight into potential cellular factors responsible for dysregulation of intestinal CM production.

Microsomal proteomics.

Proteomic profiling of subcellular compartments has many advantages over traditional proteomic approaches using whole cell lysates as it allows for detailed proteome analysis of a specific organelle and corresponding functional characteristics. The microsome is a critical, membranous compartment involved in the synthesis, sorting, and secretion of proteins as well as other metabolic functions. This chapter will describe detailed methods for the isolation of microsomal organelles including the ER, Golgi, and prechylomicron transport vesicle (PCTV), a recently identified vesicular system involved in intestinal lipoprotein assembly and secretion. Particular focus is given to the isolation of microsomes from primary hepatocytes and enterocytes freshly isolated from rodent liver and intestinal tissue, and their proteomic profiling using a combination of two-dimensional gel electrophoresis and mass spectrometry.

The induction of hepatocellular neoplasia by trichloroacetic acid administered in the drinking water of the male B6C3F1 mouse.

The prevalence (percent of animals with a tumor) and multiplicity (number of tumors per animal) of hepatocellular neoplasia in the male B6C3F1 mouse exposed to trichloroacetic acid (TCA) in the drinking water were determined. Male mice were exposed to 0.05, 0.5, and 5 g/L TCA for 60 wk (Study 1), to 4.5 g/L TCA for 104 wk (Study 2) and to 0.05 and 0.5 g/L TCA for 104 wk (Study 3). Time-weighted mean daily doses measured for the low, medium, and high dose groups were consistent over the three studies, 6-8, 58-68, and 572-602 mg/kg-d for the 0.05, 0.5, and the 4.5-5 g/L treatment groups, respectively. No significant changes in animal survival were noted across the studies. A significant increase in the prevalence and multiplicity of hepatocellular tumors was found in the 58-68 and 572-602 mg/kg/d TCA dose groups. Nonhepatoproliferative changes (cytoplasmic alterations, inflammation, and necrosis) in mice treated with TCA were mild and dose related. A TCA-induced increase in liver palmitoyl CoA oxidase activity, a marker of peroxisome proliferation, correlated with tumor induction. A linear association was found between peroxisome proliferation and tumor induction. Sporadic increases in the labeling index of nuclei outside of proliferative lesions were observed at carcinogenic doses throughout the studies. Given that there are no compelling data demonstrating genotoxic activity of either TCA or any metabolite, data are consistent with an epigenetic mode of action. The studies provide dose-response data on the development of hepatocellular neoplasia in male mice over a lifetime exposure to TCA. A no-observed-effect-level (NOEL) of 6 mg/kg/d was calculated for neoplastic and nonproliferative liver pathology.

A comparison of lipid storage in Phaeodactylum tricornutum and Tetraselmis suecica using laser scanning confocal microscopy.

Microalgae contain lipid bodies (LBs) composed of triacylglycerols, which can be converted to biodiesel. Here we demonstrate a method to study the accumulation patterns of LBs in different microalgae strains and culture conditions utilizing laser scanning confocal microscopy (LSCM) with BODIPY 505/515 (4,4-difluoro-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene) staining, in parallel with Nile Red (9-diethylamino-5H-benzo-a-phenoxazine-5-one) fluorescence analysis of intracellular lipids in microplates. Phaeodactylum tricornutum and Tetraselmis suecica were selected as model organisms and monitored throughout the growth phases in standard and nitrogen-deficient growth conditions. Utilizing image quantification techniques, the number and morphology of LBs suggest that P. tricornutum accumulates lipids by merging with existing LBs, while T. suecica synthesizes new LBs. We observed that T. suecica accumulates a higher number of LBs and total volume of lipids per cell, while P. tricornutum accumulates only 1-2 LBs with a larger volume per LB. LSCM analysis complements Nile Red (NR) methods because LSCM provides three-dimensional images of lipid accumulation at a cellular level, while NR analysis can quickly monitor the total levels of intracellular lipids for phenotypic screening. Using NR analysis, we have observed that the optimal harvest date for P. tricornutum and T. suecica in standard cultivation conditions is 24 and 42 days, respectively. Comparison with nitrogen-deficient growth conditions is utilized as a model to confirm that LSCM and NR analysis can be used to study lipid storage and productivity for diverse growth conditions and various strains of microalgae.

Phenotypic screening with oleaginous microalgae reveals modulators of lipid productivity.

Here we describe the first phenotypic screening with microalgae to study lipid metabolism and to discover organic small molecules as chemical triggers that increase growth and lipid production. A microplate assay has been developed for analysis of intracellular lipids using Nile Red fluorescence in order to screen a collection of diverse bioactive organic molecules (e.g., kinase inhibitors) with four strains of oleaginous microalgae (Nannochloropsis salina, Nannochloropsis oculata, Nannochloris sp., and Phaeodactylum tricornutum). Several small molecules identified in microplate screening increased lipid productivity >200% without decreasing growth and biomass production. Selected compounds were further investigated in the context of larger batch culture experiments (e.g., 500 mL) and demonstrated to increase lipid levels (up to 84%) while maintaining or increasing the specific growth rate. Bioactive molecules such as forskolin and quinacrine were identified as promising probes of microalgae lipid pathways. We have also determined that common antioxidants such as epigallocatechin gallate and butylated hydroxyanisole (BHA) increase lipid productivity and may represent new probes of oxidative signaling pathways for photooxidative protection.

Proteomic profiling of intestinal prechylomicron transport vesicle (PCTV)-associated proteins in an animal model of insulin resistance (94 char).

Intestinal overproduction of apolipoprotein B (apoB)-48-containing chylomicrons is increasingly recognized as an underlying factor in metabolic dyslipidemia commonly observed in insulin-resistant states. Enhanced chylomicron assembly and secretion has been documented in animal models of insulin resistance, but the underlying mechanistic factors are unknown. Chylomicron assembly occurs through a series of complex vesicular interactions involving prechylomicron transport vesicles (PCTVs), which transport lipids from the endoplasmic reticulum (ER) to the Golgi. We report proteomic profiles of PCTVs isolated from the enteric ER in the small intestine of the fructose-fed hamster, an established model of diet-induced insulin resistance. Using 2D gel electrophoresis and tandem mass spectrometry, PCTVs were characterized and proteomic profiles of PCTV-associated proteins from insulin-resistant and control enterocytes were developed, with the intention of identifying proteins involved in insulin signaling attenuation and lipoprotein overproduction. A number of PCTV-associated proteins were found to be differentially expressed including microsomal triglyceride transfer protein (MTP), apoB-48, Sar1 and VAMP7. We postulate that altered expression of Sar1 and MTP may contribute to increased chylomicron assembly in the fructose-fed hamster. These findings have increased our understanding of the intracellular assembly and transport of nascent chylomicrons and potential cellular factors responsible for lipoprotein overproduction in insulin-resistant states.