In the PNAS Early Edition this week, investigators in Japan show that miR-33, encoded by an intron of Srebp2, regulates HDL cholesterol in vivo. Using miR-33-deficient mice, the team found that "miR-33 repressed the expression of ATP-binding cassette transporter A1 protein, a key regulator of HDL synthesis, by mediating cholesterol efflux from cells to apolipoprotein A-I," they write.