FIGURE 1:
Saturated but not unsaturated free fatty acids induce the UPR before lipotoxicity in human hepatocytes. (A–C) Mouse primary hepatocytes (MPHs), rat primary hepatocytes (RPHs), HepG2 cells, and primary human hepatocytes (HPHs) were treated with the indicated concentrations of palmitate, stearate, or oleate for 24 h. Cell death was measured by LDH release. (D) LC50 values (micromoles) from LDH release assay were calculated in XLfit using four-parameter curve fits. (E) HepG2 cells were stained for neutral lipid accumulation using LipidTox Deep Red imaging for up to 24 h. Neutral lipid was quantified by counting total spot counts in PerkinElmer's Columbus software package and normalized to vehicle. (F–H) Cell death was measured by LDH release in HepG2 cells incubated with 600 μM palmitate, stearate, or oleate for the indicated times. (I, J) Immunoblot analysis of HepG2 lysates treated with 600 μM palmitate, 2 μM tunicamycin, 600 μM stearate, or 600 μM oleate for up to 24 h, as indicated. Measured proteins are indicated to the right. (K–N) Changes in gene transcripts from HepG2 cells incubated with 600 μM palmitate or oleate for up to 24 h, as indicated. The XBP1s/t is a ratio of the spliced XBP1 mRNA relative to total XBP1 transcript, and the measured transcript and length of FFA treatment are also shown.