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

Gaiqing Wang, Zhenni Guo, Lusha Tong, Fang Xue, Paul R. Krafft, Enkhjargal Budbazar, John H. Zhang, Jiping Tang

Research output: Contribution to journalArticlepeer-review

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.

Original languageEnglish
Pages (from-to)3020-3029
Number of pages10
JournalStroke
Volume49
Issue number12
DOIs
StatePublished - Dec 2018

ASJC Scopus Subject Areas

  • Clinical Neurology
  • Cardiology and Cardiovascular Medicine
  • Advanced and Specialized Nursing

Keywords

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

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