PXR and LXR in hepatic steatosis: a new dog and an old dog with new tricks

Mol Pharm. 2008 Jan-Feb;5(1):60-6. doi: 10.1021/mp700121u. Epub 2007 Dec 12.

Abstract

PXR was isolated as a "xenobiotic receptor" that regulates drug-metabolizing enzymes and transporters, whereas LXR is known to promote hepatic lipogenesis by activating the lipogenic transcriptional factor sterol regulatory element-binding protein (SREBP). We have recently shown that PXR can mediate a SREBP-independent lipogenic pathway by activating the free fatty acid (FFA) uptake transporter CD36, PPARgamma, and several accessory lipogenic enzymes, such as stearoyl CoA desaturase-1 (SCD-1) and long-chain free fatty acid elongase (FAE). More recently, we found activation of LXR also induced the expression of CD36. Promoter analysis established CD36 as a novel transcriptional target of LXRalpha. Moreover, the steatotic effect of LXR agonists was largely abolished in CD36 null mice, suggesting an essential role for CD36 and FFA uptake in LXR-mediated steatosis. We also showed that PPARgamma, a positive regulator of CD36, is also a transcriptional target of PXR. Thus, PXR can regulate CD36 directly or through its activation of PPARgamma. Interestingly, PXR- and LXR-mediated CD36 activation and PXR-mediated PPARgamma activation are all liver-specific. We conclude that CD36 is a shared target of LXR, PXR, and PPARgamma. The network of CD36 regulation controlled by LXR, PXR, and PPARgamma establishes this FFA transporter as a common target of orphan nuclear receptors in their mediation of hepatic steatosis. It is hoped that the nuclear receptor-mediated CD36 regulation may offer novel targets for the therapeutic management of alcoholic and nonalcoholic steatosis.

Publication types

  • Research Support, N.I.H., Extramural
  • Review

MeSH terms

  • Animals
  • CD36 Antigens / metabolism
  • DNA-Binding Proteins / metabolism*
  • Fatty Liver / metabolism
  • Fatty Liver / pathology*
  • Humans
  • Liver X Receptors
  • Orphan Nuclear Receptors
  • Pregnane X Receptor
  • Receptors, Cytoplasmic and Nuclear / metabolism*
  • Receptors, Steroid / metabolism*

Substances

  • CD36 Antigens
  • DNA-Binding Proteins
  • Liver X Receptors
  • NR1H3 protein, human
  • Nr1h3 protein, mouse
  • Orphan Nuclear Receptors
  • Pregnane X Receptor
  • Receptors, Cytoplasmic and Nuclear
  • Receptors, Steroid