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.

Project description:The sterol regulatory element binding proteins (SREBPs) are transcription factors that govern cholesterol and fatty acid metabolism. Owing to their central role in controlling hepatic lipid and lipoprotein metabolism their activity is tightly coordinated, and accordingly dysregulation of the SREBP pathway is associated with development of dyslipidemia and non-alcoholic fatty liver disease. Using a suite of genome-wide genetic screens we have recently identified SPRING (C12ORF49) as a novel post-transcriptional regulator of SREBP activation in vitro. Our previous work demonstrated that constitutive ablation of Spring in mice is embryonically lethal. Here we show that inducible global deletion of Spring is also untolerated, and therefore to interrogate the physiological role of SPRING in controlling hepatic lipid metabolism we developed liver-specific Spring knockout mice (LKO). Liver transcriptomics and proteomics analysis revealed severely attenuated SREBP signaling in livers and in hepatocytes of LKO mice, which was associated with marked effects on both plasma and hepatic lipid levels. In plasma, total cholesterol levels were dramatically reduced in both male and female LKO mice, apparent in both the LDL and HDL fractions, while triglyceride levels remained largely unaffected. In liver, loss of Spring diminished cholesterol and triglyceride biosynthesis resulting in decreased hepatic cholesterol and triglyceride content. This coincided with reduced secretion of VLDL into the circulation. Consistent with diminished hepatic de novo lipogenesis, LKO mice were protected from developing hepatosteatosis when challenged with a fructose-rich diet. Supporting the significance of our findings in mice, we identified common and rare SPRING genetic variants that are strongly associated with circulating HDL-c and ApoA1 levels in humans. Collectively, our study positions SPRING as a core component of hepatic SREBP signaling, and consequently of systemic lipid metabolism in mice and humans.

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Mus musculus

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