l-Serine Deficiency Elicits Intracellular Accumulation of Cytotoxic Deoxysphingolipids and Lipid Body Formation

• Published in: The Journal of biological chemistry 2015-06, Vol.290 (23), p.14595-14609
• Main Authors: Esaki, Kayoko, Sayano, Tomoko, Sonoda, Chiaki, Akagi, Takumi, Suzuki, Takeshi, Ogawa, Takuya, Okamoto, Masahiro, Yoshikawa, Takeo, Hirabayashi, Yoshio, Furuya, Shigeki
• Format: Article
• Language: English
• Subjects: Alanine - metabolism; amino acid; Amino Acid Metabolism, Inborn Errors - genetics; Amino Acid Metabolism, Inborn Errors - metabolism; Animals; Brain - metabolism; Cells, Cultured; Female; Gene Knockout Techniques; inborn error of metabolism; Lipid Droplets - metabolism; Lipids; mass spectrometry (MS); Mice; Phosphoglycerate Dehydrogenase - genetics; Phosphoglycerate Dehydrogenase - metabolism; serine; Serine - deficiency; Serine - metabolism; sphingolipid; Sphingolipids - metabolism; Sphingosine - analogs & derivatives; Sphingosine - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M114.603860

l-Serine is required to synthesize membrane lipids such as phosphatidylserine and sphingolipids. Nevertheless, it remains largely unknown how a diminished capacity to synthesize l-serine affects lipid homeostasis in cells and tissues. Here, we show that deprivation of external l-serine leads to the generation of 1-deoxysphingolipids (doxSLs), including 1-deoxysphinganine, in mouse embryonic fibroblasts (KO-MEFs) lacking d-3-phosphoglycerate dehydrogenase (Phgdh), which catalyzes the first step in the de novo synthesis of l-serine. A novel mass spectrometry-based lipidomic approach demonstrated that 1-deoxydihydroceramide was the most abundant species of doxSLs accumulated in l-serine-deprived KO-MEFs. Among normal sphingolipid species in KO-MEFs, levels of sphinganine, dihydroceramide, ceramide, and hexosylceramide were significantly reduced after deprivation of external l-serine, whereas those of sphingomyelin, sphingosine, and sphingosine 1-phosphate were retained. The synthesis of doxSLs was suppressed by supplementing the culture medium with l-serine but was potentiated by increasing the ratio of l-alanine to l-serine in the medium. Unlike with l-serine, depriving cells of external l-leucine did not promote the occurrence of doxSLs. Consistent with results obtained from KO-MEFs, brain-specific deletion of Phgdh in mice also resulted in accumulation of doxSLs in the brain. Furthermore, l-serine-deprived KO-MEFs exhibited increased formation of cytosolic lipid bodies containing doxSLs and other sphingolipids. These in vitro and in vivo studies indicate that doxSLs are generated in the presence of a high ratio of l-alanine to l-serine in cells and tissues lacking Phgdh, and de novo synthesis of l-serine is necessary to maintain normal sphingolipid homeostasis when the external supply of this amino acid is limited. Background:l-Serine deficiency affects sphingolipid homeostasis. Results: Reduced l-serine promotes the accumulation of 1-deoxysphingolipids and the formation of lipid bodies. Conclusion: Diminished capacity for l-serine synthesis leads to a higher l-alanine to l-serine ratio and elicits the synthesis of 1-deoxysphingolipids and lipid body formation. Significance: 1-Deoxysphingolipids occur in certain disease conditions characterized by a metabolic imbalance between l-alanine and l-serine.