Identification of the receptor scavenging hemopexin-heme complexes

Blood. 2005 Oct 1;106(7):2572-9. doi: 10.1182/blood-2005-03-1185. Epub 2005 Jun 9.

Abstract

Heme released from heme-binding proteins on internal hemorrhage, hemolysis, myolysis, or other cell damage is highly toxic due to oxidative and proinflammatory effects. Complex formation with hemopexin, the high-affinity heme-binding protein in plasma and cerebrospinal fluid, dampens these effects and is suggested to facilitate cellular heme metabolism. Using a ligand-affinity approach, we purified the human hemopexin-heme receptor and identified it as the low-density lipoprotein receptor-related protein (LRP)/CD91, a receptor expressed in several cell types including macrophages, hepatocytes, neurons, and syncytiotrophoblasts. Binding experiments, including Biacore analysis, showed that hemopexin-heme complex formation elicits the high receptor affinity. Uptake studies of radio-labeled hemopexin-heme complex in LRP/CD91-expressing COS cells and confocal microscopy of the cellular processing of fluorescent hemopexin-heme complex established the ability of LRP/CD91 to mediate hemopexin-heme internalization resulting in cellular heme uptake and lysosomal hemopexin degradation. Uptake of hemopexin-heme complex induced LRP/CD91-dependent heme-oxygenase 1 mRNA transcription in cultured monocytes. In conclusion, hemopexin-heme complexes are removed by a receptor-mediated pathway showing striking similarities to the CD163-mediated haptoglobin-hemoglobin clearance in macrophages. Furthermore, the data indicate a hitherto unknown role of LRP/CD91 in inflammation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antigens, CD / biosynthesis
  • Antigens, CD / metabolism
  • Antigens, Differentiation, Myelomonocytic / biosynthesis
  • COS Cells
  • Chlorocebus aethiops
  • Electrophoresis, Polyacrylamide Gel
  • Endocytosis
  • Heme / chemistry*
  • Heme Oxygenase (Decyclizing) / metabolism
  • Hemoglobins / metabolism
  • Hemopexin / chemistry*
  • Hemorrhage / metabolism
  • Humans
  • Inflammation
  • Ligands
  • Low Density Lipoprotein Receptor-Related Protein-1
  • Macrophages / metabolism
  • Microscopy, Confocal
  • Models, Biological
  • Monocytes / metabolism
  • Oxygen / metabolism
  • Protein Binding
  • RNA, Messenger / metabolism
  • Receptors, Cell Surface / biosynthesis
  • Time Factors
  • alpha-Macroglobulins / metabolism

Substances

  • Antigens, CD
  • Antigens, Differentiation, Myelomonocytic
  • CD163 antigen
  • Hemoglobins
  • LRP1 protein, human
  • Ligands
  • Low Density Lipoprotein Receptor-Related Protein-1
  • RNA, Messenger
  • Receptors, Cell Surface
  • alpha-Macroglobulins
  • Heme
  • Hemopexin
  • Heme Oxygenase (Decyclizing)
  • heme oxygenase-2
  • Oxygen