Toll-like Receptor (TLR) Signaling Interacts with CREBH to Modulate High-density Lipoprotein (HDL) in Response to Bacterial Endotoxin.

Bacterial endotoxin can induce inflammatory and metabolic changes in the host. In this study, we revealed a molecular mechanism by which a stress-inducible, liver-enriched transcription factor, cAMP-responsive element-binding protein hepatic-specific (CREBH), modulates lipid profiles to protect the liver from injuries upon the bacterial endotoxin lipopolysaccharide (LPS). LPS challenge can activate CREBH in mouse liver tissues in a toll-like receptor (TLR)/MyD88-dependent manner. Upon LPS challenge, CREBH interacts with TNF receptor-associated factor 6 (TRAF6), an E3 ubiquitin ligase that functions as a key mediator of TLR signaling, and this interaction relies on MyD88. Further analysis demonstrated that TRAF6 mediates K63-linked ubiquitination of CREBH to facilitate CREBH cleavage and activation. CREBH directly activates expression of the gene encoding Apolipoprotein A4 (ApoA4) under LPS challenge, leading to modulation of high-density lipoprotein (HDL) in animals. CREBH deficiency led to reduced production of circulating HDL and increased liver damage upon high-dose LPS challenge. Therefore, TLR/MyD88-dependent, TRAF6-facilitated CREBH activation represents a mammalian hepatic defense response to bacterial endotoxin by modulating HDL.