Characterization and functional analysis of BmSR-B1 for phytosterol uptake

• Published in: Steroids Vol. 184; p. 109039
• Main Authors: Takeshima, Mika, Ogihara, Mari H., Kataoka, Hiroshi
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.08.2022
• Subjects: Lipophorin; Phytophagous insects; Phytosterol; Silkworm; SR-B1; Sterol uptake; 20E; MRM; ninaD; SR-B1; DHCR24; Phytophagous insects; LpR; rpl3; HDL; LC-MS/MS; Sterol uptake; Phytosterol; 7dC; Cameo 2; Silkworm; Lipophorin
• ISSN: 0039-128X; 1878-5867
• DOI: 10.1016/j.steroids.2022.109039

[Display omitted] •Two of silkworm SR-B1 were associated with phytosterol uptake from lipophorin.•BmSR-B1_3 and BmSR-B1_4 highly expressed in phytosterol-rich midgut and fat body.•BmSR-B1_3 and BmSR-B1_4 enhanced accumulation of specific phytosterols. Insects cannot synthesize sterols, such as cholesterol, and require sterols in their diet. Phytophagous insects use dietary phytosterols as a source of cholesterol. Sterols are transported from the midgut by the insect lipoprotein, lipophorin (Lp), although mechanisms for uptake of phytosterols into tissues are unclear. This study characterizes Scavenger Receptor class B type1 (SR-B1) from Bombyx mori (BmSR-B1) as molecules related to phytosterol uptake. According to sterol quantification using LC-MS/MS analysis, the midgut and fat body were phytosterol-rich relative to cholesterol-rich brain and prothoracic glands. Gene expression analysis of Bmsr-b1 in silkworm tissues showed that the genes Bmsr-b1_2, 3, 4, 6, and 10 were expressed in the midgut and fat body. To characterize the function of BmSR-B1, 11 BmSR-B1 homologs expressed in Bombyx ovary-derived BmN cells and Drosophila melanogaster embryo-derived Schneider 2 (S2) cells were incubated with purified Lp. Our analysis showed that BmSR-B1_3 induced the accumulation of campesterol and BmSR-B1_4 induced the accumulation of β-sitosterol and campesterol in culture cells. BmSR-B1 incorporated specific phytosterols into insect cells by selective uptake across the cell membrane where BmSR-B1 was localized. In conclusion, our study demonstrated that one function of BmSR-B1 is the uptake of phytosterols into silkworm tissues.