Synthesis of IL-6 by hepatocytes is a normal response to common hepatic stimuli

PLoS One. 2014 Apr 24;9(4):e96053. doi: 10.1371/journal.pone.0096053. eCollection 2014.

Abstract

Exogenous interleukin 6 (IL-6), synthesized at the initiation of the acute phase response, is considered responsible for signaling hepatocytes to produce acute phase proteins. It is widely posited that IL-6 is either delivered to the liver in an endocrine fashion from immune cells at the site of injury, or alternatively, in a paracrine manner by hepatic immune cells within the liver. A recent publication showed there was a muted IL-6 response in lipopolysaccharide (LPS)-injured mice when nuclear NFκB was specifically inactivated in the hepatocytes. This indicates hepatocellular signaling is also involved in regulating the acute phase production of IL-6. Herein, we present extensive in vitro and in vivo evidence that normal hepatocytes are directly induced to synthesize IL-6 mRNAs and protein by challenge with LPS, a bacterial hepatotoxin, and by HGF, an important regulator of hepatic homeostasis. As the IL-6 receptor is found on the hepatocyte, these results reveal that induction of the acute phase response can be regulated in an autocrine as well as endocrine/paracrine fashion. Further, herein we provide data indicating that following partial hepatectomy (PHx), HGF differentially regulates IL-6 production in hepatocytes (induces) versus immune cells (suppresses), signifying disparate regulation of the cell sources involved in IL-6 production is a biologically relevant mechanism that has previously been overlooked. These findings have wide ranging ramifications regarding how we currently interpret a variety of in vivo and in vitro biological models involving elements of IL-6 signaling and the hepatic acute phase response.

Publication types

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

MeSH terms

  • Animals
  • Autocrine Communication
  • Cells, Cultured
  • Culture Media, Serum-Free
  • Hepatocyte Growth Factor / metabolism
  • Hepatocyte Growth Factor / pharmacology
  • Hepatocytes / drug effects
  • Hepatocytes / metabolism*
  • Interleukin-6 / biosynthesis*
  • Interleukin-6 / genetics
  • Interleukin-6 / metabolism
  • Lipopolysaccharides / pharmacology
  • Liver / drug effects
  • Liver / immunology
  • Liver / metabolism
  • Macrophages / metabolism
  • Mice, Inbred C57BL
  • RNA, Messenger / metabolism
  • Rats, Inbred F344

Substances

  • Culture Media, Serum-Free
  • Interleukin-6
  • Lipopolysaccharides
  • RNA, Messenger
  • Hepatocyte Growth Factor