Milk fat globule-EGF factor 8 mediates the enhancement of apoptotic cell clearance by glucocorticoids

Cell Death Differ. 2013 Sep;20(9):1230-40. doi: 10.1038/cdd.2013.82. Epub 2013 Jul 5.

Abstract

The phagocytic clearance of apoptotic cells is essential to prevent chronic inflammation and autoimmunity. The phosphatidylserine-binding protein milk fat globule-EGF factor 8 (MFG-E8) is a major opsonin for apoptotic cells, and MFG-E8(-/-) mice spontaneously develop a lupus-like disease. Similar to human systemic lupus erythematosus (SLE), the murine disease is associated with an impaired clearance of apoptotic cells. SLE is routinely treated with glucocorticoids (GCs), whose anti-inflammatory effects are consentaneously attributed to the transrepression of pro-inflammatory cytokines. Here, we show that the GC-mediated transactivation of MFG-E8 expression and the concomitantly enhanced elimination of apoptotic cells constitute a novel aspect in this context. Patients with chronic inflammation receiving high-dose prednisone therapy displayed substantially increased MFG-E8 mRNA levels in circulating monocytes. MFG-E8 induction was dependent on the GC receptor and several GC response elements within the MFG-E8 promoter. Most intriguingly, the inhibition of MFG-E8 induction by RNA interference or genetic knockout strongly reduced or completely abolished the phagocytosis-enhancing effect of GCs in vitro and in vivo. Thus, MFG-E8-dependent promotion of apoptotic cell clearance is a novel anti-inflammatory facet of GC treatment and renders MFG-E8 a prospective target for future therapeutic interventions in SLE.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antigens, Surface / genetics*
  • Antigens, Surface / metabolism*
  • Apoptosis / immunology*
  • Cell Line, Tumor
  • Glucocorticoids / metabolism*
  • Humans
  • Lupus Erythematosus, Systemic / genetics
  • Lupus Erythematosus, Systemic / immunology
  • Lupus Erythematosus, Systemic / metabolism
  • Macrophages / immunology
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Milk Proteins / genetics*
  • Milk Proteins / metabolism*
  • Opsonin Proteins / genetics
  • Opsonin Proteins / metabolism
  • Phagocytosis / immunology*
  • Promoter Regions, Genetic
  • RNA Interference
  • RNA, Small Interfering
  • Receptors, Glucocorticoid / metabolism
  • Response Elements / genetics
  • U937 Cells

Substances

  • Antigens, Surface
  • Glucocorticoids
  • MFGE8 protein, human
  • Milk Proteins
  • Opsonin Proteins
  • RNA, Small Interfering
  • Receptors, Glucocorticoid