TLR7 (Toll-Like Receptor 7) Facilitates Heme Scavenging Through the BTK (Bruton Tyrosine Kinase)-CRT (Calreticulin)-LRP1 (Low-Density Lipoprotein Receptor-Related Protein-1)-Hx (Hemopexin) Pathway in Murine Intracerebral Hemorrhage

Stroke. 2018 Dec;49(12):3020-3029. doi: 10.1161/STROKEAHA.118.022155.

Abstract

Background and Purpose- Heme and iron are considered to be key factors responsible for secondary insults after intracerebral hemorrhage (ICH). Our previous study showed that LRP1 (low-density lipoprotein receptor-related protein-1)-Hx (hemopexin) facilitates removal of heme. The TLR7 (Toll-like receptor 7)-BTK (Bruton tyrosine kinase)-CRT (calreticulin) pathway regulates the expression of LRP1-Hx. This study is designed to clarify whether TLR7 activation facilitates heme scavenging and to establish the potential role of the BTK-CRT-LRP1-Hx signaling pathway in the pathophysiology of ICH. Methods- ICH was induced by stereotactic, intrastriatal injection of type VII collagenase. Mice received TLR7 agonist (imiquimod) via intraperitoneal injection after ICH induction. TLR7 inhibitor (ODN2088), BTK inhibitor (LFM-A13), and CRT agonist (thapsigargin) were given in different groups to further evaluate the underlying pathway. Mice were randomly divided into sham, ICH+vehicle (normal saline), ICH+Imiquimod (2.5, 5, and 10 μg/g), ICH+ODN2088, ICH+LFM-A13, ICH+thapsigargin, and ICH+ODN2088+thapsigargin. Imiquimod was administered twice daily starting at 6 hours after ICH; ODN2088 was administered by intracerebroventricular injection at 30 minutes, and LFM-A13 or thapsigargin was administered by intraperitoneal injection at 3 hours after ICH induction. Neurological scores, cognitive abilities, as well as brain edema, blood-brain barrier permeability, hemoglobin level, brain expression of TLR7/BTK/CRT/LRP1/Hx were analyzed. Results- Low dosage imiquimod significantly attenuated hematoma volume, brain edema, BBB permeability, and neurological deficits after ICH. Imiquimod also increased protein expressions of TLR7, BTK, CRT, LRP1, and Hx; ODN2088 reduced TLR7, BTK, CRT, LRP1, and Hx expressions. Conclusions- TLR7 plays an important role in heme scavenging after ICH by modulating the BTK-CRT-LRP1-Hx pathway. TLR7 may offer protective effects by promoting heme resolution and reduction of brain edema after ICH.

Keywords: Bruton tyrosine kinase; calreticulin; heme scavenging; imiquimod; intracerebral hemorrhage; toll-like receptor.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Agammaglobulinaemia Tyrosine Kinase / antagonists & inhibitors
  • Agammaglobulinaemia Tyrosine Kinase / drug effects
  • Agammaglobulinaemia Tyrosine Kinase / metabolism*
  • Amides / pharmacology
  • Animals
  • Blood-Brain Barrier / drug effects
  • Brain / drug effects
  • Brain / metabolism*
  • Brain Edema / metabolism
  • Calreticulin / agonists
  • Calreticulin / drug effects
  • Calreticulin / metabolism*
  • Cerebral Hemorrhage / metabolism*
  • Enzyme Inhibitors / pharmacology
  • Heme / metabolism*
  • Hemopexin / drug effects
  • Hemopexin / metabolism*
  • Imiquimod / pharmacology
  • Low Density Lipoprotein Receptor-Related Protein-1
  • Membrane Glycoproteins / agonists
  • Membrane Glycoproteins / antagonists & inhibitors
  • Membrane Glycoproteins / drug effects
  • Membrane Glycoproteins / metabolism*
  • Mice
  • Nitriles / pharmacology
  • Oligodeoxyribonucleotides / pharmacology
  • Receptors, LDL / drug effects
  • Receptors, LDL / metabolism*
  • Signal Transduction
  • Thapsigargin / pharmacology
  • Toll-Like Receptor 7 / agonists
  • Toll-Like Receptor 7 / antagonists & inhibitors
  • Toll-Like Receptor 7 / drug effects
  • Toll-Like Receptor 7 / metabolism*
  • Tumor Suppressor Proteins / drug effects
  • Tumor Suppressor Proteins / metabolism*

Substances

  • Amides
  • Calreticulin
  • Enzyme Inhibitors
  • LFM A13
  • Low Density Lipoprotein Receptor-Related Protein-1
  • Lrp1 protein, mouse
  • Membrane Glycoproteins
  • Nitriles
  • Oligodeoxyribonucleotides
  • Receptors, LDL
  • Tlr7 protein, mouse
  • Toll-Like Receptor 7
  • Tumor Suppressor Proteins
  • iCpG-ODN
  • Heme
  • Thapsigargin
  • Hemopexin
  • Agammaglobulinaemia Tyrosine Kinase
  • Btk protein, mouse
  • Imiquimod