Defects in CYB5A and CYB5B impact sterol-C4 oxidation in cholesterol biosynthesis and demonstrate regulatory roles of dimethyl sterols
Mei-Yan Ma,
Gang Deng,
Wen-Zhuo Zhu,
Ming Sun,
Lu-Yi Jiang,
Wei-Hui Li,
Yuan-Bin Liu,
Lin Guo,
Bao-Liang Song,
Xiaolu Zhao
Affiliations
Mei-Yan Ma
Hubei Key Laboratory of Cell Homeostasis, College of Life Sciences, Taikang Center for Life and Medical Sciences, Wuhan University, Wuhan 430000, China
Gang Deng
Hubei Key Laboratory of Cell Homeostasis, College of Life Sciences, Taikang Center for Life and Medical Sciences, Wuhan University, Wuhan 430000, China
Wen-Zhuo Zhu
Hubei Key Laboratory of Cell Homeostasis, College of Life Sciences, Taikang Center for Life and Medical Sciences, Wuhan University, Wuhan 430000, China
Ming Sun
Hubei Key Laboratory of Cell Homeostasis, College of Life Sciences, Taikang Center for Life and Medical Sciences, Wuhan University, Wuhan 430000, China
Lu-Yi Jiang
Hubei Key Laboratory of Cell Homeostasis, College of Life Sciences, Taikang Center for Life and Medical Sciences, Wuhan University, Wuhan 430000, China
Wei-Hui Li
Hubei Key Laboratory of Cell Homeostasis, College of Life Sciences, Taikang Center for Life and Medical Sciences, Wuhan University, Wuhan 430000, China
Yuan-Bin Liu
Hubei Key Laboratory of Cell Homeostasis, College of Life Sciences, Taikang Center for Life and Medical Sciences, Wuhan University, Wuhan 430000, China
Lin Guo
Hubei Key Laboratory of Cell Homeostasis, College of Life Sciences, Taikang Center for Life and Medical Sciences, Wuhan University, Wuhan 430000, China
Bao-Liang Song
Hubei Key Laboratory of Cell Homeostasis, College of Life Sciences, Taikang Center for Life and Medical Sciences, Wuhan University, Wuhan 430000, China; Corresponding author
Xiaolu Zhao
Hubei Key Laboratory of Cell Homeostasis, College of Life Sciences, Taikang Center for Life and Medical Sciences, Wuhan University, Wuhan 430000, China; Corresponding author
Summary: Cytochrome b5 (CYB5) is a hemoprotein crucial for electron transfer to oxygenases. Although microsomal CYB5A is required for sterol C4-demethylation in vitro, cholesterol biosynthesis remains intact in Cyb5a knockout mice. Here, we show that knockout of mitochondrial CYB5B, rather than CYB5A, blocks cholesterol biosynthesis at the sterol-C4 oxidation step in HeLa cells, causing an accumulation of testis meiosis-activating sterol (T-MAS) and dihydro-T-MAS. Surprisingly, liver-specific Cyb5b knockout (L-Cyb5b−/−) mice exhibit normal cholesterol metabolism. Further knockdown of Cyb5a in L-Cyb5b−/− (L-Cyb5b−/−/short hairpin [sh]Cyb5a) mice leads to a marked accumulation of T-MAS and dihydro-T-MAS, indicating that either CYB5A or CYB5B is required for sterol C4-demethylation. The L-Cyb5b−/−/shCyb5a mice are largely normal, with lower sterol regulatory element-binding protein (SREBP)-target gene expression during refeeding and higher liver triglyceride levels while fasting, as T-MAS and dihydro-T-MAS inhibit the SREBP pathway and activate the PPARγ pathway. In summary, CYB5A and CYB5B compensate for sterol C4-demethylation, and T-MAS and dihydro-T-MAS can modulate the SREBP and PPARγ pathways.