SAR1B GTPase is necessary to protect intestinal cells from disorders of lipid homeostasis, oxidative stress, and inflammation

Genetic defects in SAR1B GTPase inhibit chylomicron (CM) trafficking to the Golgi and result in a huge intraenterocyte lipid accumulation with a failure to release CMs and liposoluble vitamins into the blood circulation. The central aim of this study is to test the hypothesis that SAR1B deletion (SAR1B(-/-)) disturbs enterocyte lipid homeostasis (e.g., FA beta-oxidation and lipogenesis) while promoting oxidative stress and inflammation. Another issue is to compare the impact of SAR1B(-/-) to that of its paralogue SAR1A(-/-) and combined SAR1A(-/-)/B-/-. To address these critical issues, we have generated Caco-2/15 cells with a knockout of SAR1A, SAR1B, or SAR1A/B genes. SAR1B(-/-) results in lipid homeostasis disruption, reflected by enhanced mitochondrial FA beta-oxidation and diminished lipogenesis in intestinal absorptive cells via the implication of PPAR alpha and PGC1 alpha transcription factors. Additionally, SAR1B(-/-)cells, which mimicked enterocytes of CM retention disease, spontaneously disclosed inflammatory and oxidative characteristics via the implication of NF-kappa B and NRF2. In most conditions, SAR1A(-/-) cells showed a similar trend, albeit less dramatic, but synergetic effects were observed with the combined defects of the two SAR1 paralogues. In conclusion, SAR1B and its paralogue are needed not only for CM trafficking but also for lipid homeostasis, prooxidant/antioxidant balance, and protection against inflammatory processes.