Figure 3. Diminished hepatic TG secretion and lipid synthesis, but normal turnover of apoB in the absence of XBP1.

(A) Mice were injected with Tyloxapol after a four-hour fast and plasma triglyceride levels measured over time. N=4/group. Primary hepatocytes were labeled with [¹⁴C]-acetate. Radiolabeled fatty acids (B) and sterols (C) extracted from equal numbers of cells were measured by scintillation counting. (D) Primary hepatocytes from WT and Xbp1Δ mice were labeled with ³⁵S-methionine/cysteine for 30 min and then chased for indicated times. Radiolabeled apoB protein species were immunoprecipitated from cells and media and revealed by SDS-PAGE followed by fluorography. (E) The disappearance from cells and the accumulation in media of radiolabeled apoB protein species were determined by plotting relative radioactivity of each band (normalized to initial level in cells or final level in media) versus chase time. (F) Western blot analysis of plasma apoB protein.