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SULFORAPHANE ACUTELY ACTIVATES MULTIPLE STARVATION RESPONSE PATHWAYS

ABSTRACT: Sulforaphane (SFN) is an isothiocyanate present in cruciferous vegetables that ameliorates various disease models in rodents (e.g., cancer, diabetes, seizures) that are likewise mitigated by dietary restriction leading us to test the hypothesis that this compound elicits cellular responses consistent with being a fasting mimetic. Using untransformed human retinal pigment epithelial (RPE-1) cells, we report that SFN impacted multiple nutrient-sensing pathways consistent with a fasting state. SFN treatment (i) increased mitochondrial resistance to oxidative stress, (ii) acutely suppressed markers of mTORC1/2 activity via inhibition of insulin signaling, (iii) upregulated autophagy and further amplified autophagic flux induced by rapamycin or nutrient deprivation while concomitantly promoting lysosomal and mitochondrial biogenesis, (iv) acutely decreased glucose uptake and lactate secretion followed by an adaptive rebound that coincided with suppressed protein levels of thioredoxin-interacting protein (TXNIP) due to early transcriptional down-regulation. This early suppression of TXNIP mRNA expression could be overcome with exogenous glucosamine consistent with SFN inhibiting glutamine F6P amidotransferase (GFAT), the rate limiting enzyme of the hexosamine biosynthetic pathway. SFN also altered multiple glycolytic and tricarboxylic acid (TCA) cycle intermediates while reducing the inhibitory phosphorylation on pyruvate dehydrogenase, indicative of an adaptive cellular starvation response directing pyruvate into acetyl coenzyme A for uptake by the TCA cycle. RNA-seq of cells treated for 4hrs with SFN confirmed the activation of signature starvation-responsive transcriptional programs. Concomitant with stabilizing and activating the transcription factor NF-E2-related factor 2, we posit that the fasting-mimetic properties of SFN underlie both the therapeutic efficacy and potential toxicity of this phytochemical.

ORGANISM(S): Homo sapiens

PROVIDER: GSE275316 | GEO | 2024/11/28

REPOSITORIES: GEO

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Project description:Malic enzymes decarboxylate the tricarboxylic acid (TCA) cycle intermediate malate to the glycolytic end-product pyruvate and are well positioned to regulate metabolic flux in central carbon metabolism. The bacterium Sinorhizobium meliloti has a NAD(P)-malic enzyme (DME) and a NADP-malic enzyme (TME) and DME is required for symbiotic N2-fixation. To help understand the role of these enzymes, we examined growth, metabolic and transcriptional consequences resulting from the deletion of these enzymes. Few effects were observed upon growth with glucose, whereas growth with the gluconeogenic substrate, succinate, resulted in transcriptional and metabolic effects particularly in the dme mutant strains. When grown with succinate, DME mutant cells accumulated hexose sugar phosphates and trehalose, while TME mutants accumulated putrescine. Succinate-grown DME mutant cells also showed increased transcription of genes for gluconeogenesis and for pathways such as amino acid and fatty acid synthesis that divert metabolites away from the TCA cycle. These data suggested that, DME is required to regulate the levels of TCA cycle intermediates and that the activity of TME is insufficient to prevent the accumulation of TCA cycle intermediates in cells utilizing succinate as carbon source. Consistent with this, in short-1-3 hour incubations with succinate, dme mutant cells excreted large amounts of malate whereas little malate was excreted from tme or wild-type cells. These results support the suggestion that DME is required for N2-fixation in alfalfa because it is required for synthesis of pyruvate and acetyl-CoA and the rapid metabolism of C4-dicarboxylates supplied by the plant. RNA expression was measured for S. meliloti in exponential phase grown in MOPS (morpholinpropanesulfonic acid) buffered minimal media under 2 growth conditions: 1) 15 mM succinate, 2) 15 mM glucose; using wild type cells as well as dme and tme mutant strains (6 experiments, 2 replicates: total 12 samples)

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SULFORAPHANE ACUTELY ACTIVATES MULTIPLE STARVATION RESPONSE PATHWAYS

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