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The glucosylceramide synthase inhibitor PDMP causes lyso-somal lipid accumulation and mTOR inactivation

ABSTRACT: We investigated subcellular sphingolipid distribution using a functionalized sphingosine analogue (pacSph) by confocal microscopy in control, PDMP and NB-DNJ (Miglustat) treated WT and SGPL1 knock-out cells (experimentA; channel 1: pacSph, channel 2: Lamp1). We studied lysosomal sphingolipid (pacSph) export using pulse-chase experiments in control and PDMP treated SGPL1 knock-out cells (experimentB; channel 1: pacSph, channel 2: Lamp1). We analyzed other lipids such as LBPA (immunofluorescence staining) and cholesterol (filipin staining) at the lysosome in control, PDMP and NB-DNJ (Miglustat) treated WT cells by microscopy (experimentC). We investigated a timeline of lipid accumulating effects arising from PDMP treatment by confocal microscopy. Therefore, we investigated LBPA (immunofluorescence staining in WT cells; channel 1: LBPA, channel 2: Lamp1), sphingolipids (using pacSph in SGPL1 knock-out cells; channel 1: pacSph, channel 2: Lamp1) and cholesterol (filipin staining in WT cells; channel 1: Filipin, channel 2: Lamp1) (experimentD). We analysed the timeline of mTOR (channel 1: mTOR, channel 2: Lamp1) and TFEB (channel 1: DAPI, channel 2: TFEB) subcellular translocation arising from PDMP treatment in WT cells by immunofluorescence microscopy (experimentE).

ORGANISM(S): Homo sapiens (human)

SUBMITTER: Pia Hartwig

PROVIDER: S-BIAD144 | bioimages |

REPOSITORIES: bioimages

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Project description:Background & aimsHepatocyte cellular dysfunction and death induced by lipids and macrophage-associated inflammation are characteristics of nonalcoholic steatohepatitis (NASH). The fatty acid palmitate can activate death receptor 5 (DR5) on hepatocytes, leading to their death, but little is known about how this process contributes to macrophage-associated inflammation. We investigated whether lipid-induced DR5 signaling results in the release of extracellular vesicles (EVs) from hepatocytes, and whether these can induce an inflammatory macrophage phenotype.MethodsPrimary mouse and human hepatocytes and Huh7 cells were incubated with palmitate, its metabolite lysophosphatidylcholine, or diluent (control). The released EV were isolated, characterized, quantified, and applied to macrophages. C57BL/6 mice were placed on chow or a diet high in fat, fructose, and cholesterol to induce NASH. Some mice also were given the ROCK1 inhibitor fasudil; 2 weeks later, serum EVs were isolated and characterized by immunoblot and nanoparticle-tracking analyses. Livers were collected and analyzed by histology, immunohistochemistry, and quantitative polymerase chain reaction.ResultsIncubation of primary hepatocytes and Huh7 cells with palmitate or lysophosphatidylcholine increased their release of EVs, compared with control cells. This release was reduced by inactivating mediators of the DR5 signaling pathway or rho-associated, coiled-coil-containing protein kinase 1 (ROCK1) inhibition. Hepatocyte-derived EVs contained tumor necrosis factor-related apoptosis-inducing ligand and induced expression of interleukin 1β and interleukin 6 messenger RNAs in mouse bone marrow-derived macrophages. Activation of macrophages required DR5 and receptor-interacting protein kinase 1. Administration of the ROCK1 inhibitor fasudil to mice with NASH reduced serum levels of EVs; this reduction was associated with decreased liver injury, inflammation, and fibrosis.ConclusionsLipids, which stimulate DR5, induce release of hepatocyte EVs, which activate an inflammatory phenotype in macrophages. Strategies to inhibit ROCK1-dependent release of EVs by hepatocytes might be developed for the treatment of patients with NASH.

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The glucosylceramide synthase inhibitor PDMP causes lyso-somal lipid accumulation and mTOR inactivation

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