Endotoxin suppresses mouse hepatic low-density lipoprotein-receptor expression via a pathway independent of the toll-like receptor 4.

Endotoxin provokes an inflammatory state in the infected host. C3H/HeJ mice are tolerant to endotoxin because of an Lps gene mutation. Recent studies have identified that this gene encodes the Toll-like receptor 4. Endotoxin also induces hyperlipidemia and suppresses hepatic low-density lipoprotein (LDL)-receptor expression. In the current study, we investigated whether a defective Lps gene would impair the hepatic LDL-receptor response to endotoxin in C3H/HeJ mice. Eighteen hours after an intraperitoneal injection of endotoxin, the hepatic LDL-receptor expression and the plasma lipoprotein pattern were analyzed. Endotoxin increased plasma triglyceride and apoE in very low-density lipoproteins (VLDL) and intermediate-density lipoproteins, and decreased apoAI in high-density lipoproteins (HDL) in the endotoxin-sensitive mice (C3H/HeN), but not in the endotoxin-resistant mice (C3H/HeJ). These data indicate that a defective Lps gene impairs the endotoxin signaling to alter these lipoproteins. However, the hepatic LDL-receptor response to endotoxin in the endotoxin-resistant mice was similar to that in the endotoxin-sensitive mice. Thus, at a dose of 5 microg/mouse, endotoxin reduced hepatic LDL-receptor expression by 35% in C3H/HeN mice and by 52% in C3H/HeJ mice. At a dose of 50 microg/mouse, endotoxin reduced hepatic LDL-receptor expression by 61% in C3H/HeN mice and by 63% in C3H/HeJ mice. It is concluded that endotoxin suppresses hepatic LDL-receptor expression in vivo via a pathway independent of the Toll-like receptor 4.