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MTORC1 stimulates phosphatidylcholine synthesis to promote triglyceride secretion.

ABSTRACT: Liver triacylglycerol (TAG) synthesis and secretion are closely linked to nutrient availability. After a meal, hepatic TAG formation from fatty acids is decreased, largely due to a reduction in circulating free fatty acids (FFA). Despite the postprandial decrease in FFA-driven esterification and oxidation, VLDL-TAG secretion is maintained to support peripheral lipid delivery and metabolism. The regulatory mechanisms underlying the postprandial control of VLDL-TAG secretion remain unclear. Here, we demonstrated that the mTOR complex 1 (mTORC1) is essential for this sustained VLDL-TAG secretion and lipid homeostasis. In murine models, the absence of hepatic mTORC1 reduced circulating TAG, despite hepatosteatosis, while activation of mTORC1 depleted liver TAG stores. Additionally, mTORC1 promoted TAG secretion by regulating phosphocholine cytidylyltransferase ? (CCT?), the rate-limiting enzyme involved in the synthesis of phosphatidylcholine (PC). Increasing PC synthesis in mice lacking mTORC1 rescued hepatosteatosis and restored TAG secretion. These data identify mTORC1 as a major regulator of phospholipid biosynthesis and subsequent VLDL-TAG secretion, leading to increased postprandial TAG secretion.

SUBMITTER: Quinn WJ

PROVIDER: S-EPMC5663357 | biostudies-literature | 2017 Nov

REPOSITORIES: biostudies-literature

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mTORC1 stimulates phosphatidylcholine synthesis to promote triglyceride secretion.

Quinn William J WJ Wan Min M Shewale Swapnil V SV Gelfer Rebecca R Rader Daniel J DJ Birnbaum Morris J MJ Titchenell Paul M PM

The Journal of clinical investigation 20171016 11

Liver triacylglycerol (TAG) synthesis and secretion are closely linked to nutrient availability. After a meal, hepatic TAG formation from fatty acids is decreased, largely due to a reduction in circulating free fatty acids (FFA). Despite the postprandial decrease in FFA-driven esterification and oxidation, VLDL-TAG secretion is maintained to support peripheral lipid delivery and metabolism. The regulatory mechanisms underlying the postprandial control of VLDL-TAG secretion remain unclear. Here, ...[more]

PMID: 29035283

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Project description:Background and Aims: Inflammasome-mediated caspase-1 activity regulates the maturation and release of the pro-inflammatory cytokines interleukin (IL)-1M-CM-^_ and IL-18. Recently, we showed that caspase-1 deficiency strongly reduces high fat diet-induced adiposity although the mechanism is still unclear. We now aimed to elucidate the mechanism by which caspase-1 deficiency reduces modulates resistance to high fat diet-feeding fat accumulation in adipose tissue by focusing on the role of caspase-1 in the regulation of triglyceride (TG)-rich lipoprotein metabolism. Methods: Caspase-1 deficient and wild-type mice (both C57Bl/6 background) were used to determine postprandial TG kinetics, intestinal TG absorption, VLDL-TG production as well as TG clearance, all of which strongly contribute to the supply of TG for storage in adipose tissue. Micro-array and qPCR analysis were used to unravel intestinal and hepatic metabolic pathways involved. Results: Caspase-1 deficiency reduced the postprandial response to an oral lipid load, while tissue specific clearance of TG-rich lipoproteins was not changed. Indeed, an oral olive oil gavage containing [3H]TG revealed that caspase-1 deficiency significantly decreased intestinal chylomicron-TG production and reduced the uptake of [3H]TG-derived FA by liver, muscle, and adipose tissue. Similarly, caspase-1 deficiency reduced the hepatic VLDL-TG production without reducing VLDL-apoB production, despite an elevated hepatic TG content. Pathway analysis revealed that caspase-1 deficiency reduces intestinal and hepatic expression of genes involved in lipogenesis. Conclusions: Absence of caspase-1 reduces assembly and secretion of TG-rich lipoproteins, thereby reducing the availability of TG-derived FA for uptake by peripheral organs including adipose tissue. We anticipate that caspase-1 represents a novel link between innate immunity and lipid metabolism. Keywords: Expression profiling by array Wild-type (WT) and Casp1-null mice were maintained at lab chow. Animals, aged between 14 and 16 weeks (n=3 per genotype), were killed and liver and intestinal segments were removed. Livers were isolated from mice that were fasted over night, whereas intesines were removed from mice 2 hrs after they received an oral lipid load.Total RNA was isolated and subjected to gene expression profiling.

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MTORC1 stimulates phosphatidylcholine synthesis to promote triglyceride secretion.

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mTORC1 stimulates phosphatidylcholine synthesis to promote triglyceride secretion.

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