Toll-like receptor 4 knockout protects against anthrax lethal toxin-induced cardiac contractile dysfunction: Role of autophagy

MacHender R. Kandadi, Arthur E. Frankel, Jun Ren

Research output: Contribution to journalArticle

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Abstract

Background And Purpose Anthrax lethal toxin (LeTx) is known to induce circulatory shock and death, although the underlying mechanisms have not been elucidated. This study was designed to evaluate the role of toll-like receptor 4 (TLR4) in anthrax lethal toxin-induced cardiac contractile dysfunction. Experimental Approach Wild-type (WT) and TLR4 knockout (TLR-/-) mice were challenged with lethal toxin (2 μg·g-1, i.p.), and cardiac function was assessed 18 h later using echocardiography and edge detection. Small interfering RNA (siRNA) was employed to knockdown TLR4 receptor or class III PI3K in H9C2 myoblasts. GFP-LC3 puncta was used to assess autophagosome formation. Western blot analysis was performed to evaluate autophagy (LC3, Becline-1, Agt5 and Agt7) and endoplasmic reticulum (ER) stress (BiP, eIF2α and calreticulin). Key Results In WT mice, lethal toxin exposure induced cardiac contractile dysfunction, as evidenced by reduced fractional shortening, peak shortening, maximal velocity of shortening/re- lengthening, prolonged re-lengthening duration and intracellular Ca2+ derangement. These effects were significantly attenuated or absent in the TLR4 knockout mice. In addition, lethal toxin elicited autophagy in the absence of change in ER stress. Knockdown of TLR4 or class III PI3 kinase using siRNA but not the autophagy inhibitor 3-methyladenine significantly attenuated or inhibited lethal toxin-induced autophagy in H9C2 cells. Conclusion And Implications Our results suggest that TLR4 may be pivotal in mediating the lethal cardiac toxicity induced by anthrax possibly through induction of autophagy. These findings suggest that compounds that negatively modulate TLR4 signalling and autophagy could be used to treat anthrax infection-induced cardiovascular complications.

Original languageEnglish (US)
Pages (from-to)612-626
Number of pages15
JournalBritish Journal of Pharmacology
Volume167
Issue number3
DOIs
StatePublished - Oct 2012

Fingerprint

Toll-Like Receptor 4
Autophagy
Anthrax
Endoplasmic Reticulum Stress
Phosphatidylinositol 3-Kinases
Knockout Mice
Small Interfering RNA
Cardiovascular Infections
Calreticulin
Myoblasts
anthrax toxin
Echocardiography
Shock
Western Blotting

Keywords

  • anthrax
  • autophagy
  • cardiac function
  • ER stress
  • intracellular Ca
  • lethal toxin

ASJC Scopus subject areas

  • Pharmacology

Cite this

Toll-like receptor 4 knockout protects against anthrax lethal toxin-induced cardiac contractile dysfunction : Role of autophagy. / Kandadi, MacHender R.; Frankel, Arthur E.; Ren, Jun.

In: British Journal of Pharmacology, Vol. 167, No. 3, 10.2012, p. 612-626.

Research output: Contribution to journalArticle

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abstract = "Background And Purpose Anthrax lethal toxin (LeTx) is known to induce circulatory shock and death, although the underlying mechanisms have not been elucidated. This study was designed to evaluate the role of toll-like receptor 4 (TLR4) in anthrax lethal toxin-induced cardiac contractile dysfunction. Experimental Approach Wild-type (WT) and TLR4 knockout (TLR-/-) mice were challenged with lethal toxin (2 μg·g-1, i.p.), and cardiac function was assessed 18 h later using echocardiography and edge detection. Small interfering RNA (siRNA) was employed to knockdown TLR4 receptor or class III PI3K in H9C2 myoblasts. GFP-LC3 puncta was used to assess autophagosome formation. Western blot analysis was performed to evaluate autophagy (LC3, Becline-1, Agt5 and Agt7) and endoplasmic reticulum (ER) stress (BiP, eIF2α and calreticulin). Key Results In WT mice, lethal toxin exposure induced cardiac contractile dysfunction, as evidenced by reduced fractional shortening, peak shortening, maximal velocity of shortening/re- lengthening, prolonged re-lengthening duration and intracellular Ca2+ derangement. These effects were significantly attenuated or absent in the TLR4 knockout mice. In addition, lethal toxin elicited autophagy in the absence of change in ER stress. Knockdown of TLR4 or class III PI3 kinase using siRNA but not the autophagy inhibitor 3-methyladenine significantly attenuated or inhibited lethal toxin-induced autophagy in H9C2 cells. Conclusion And Implications Our results suggest that TLR4 may be pivotal in mediating the lethal cardiac toxicity induced by anthrax possibly through induction of autophagy. These findings suggest that compounds that negatively modulate TLR4 signalling and autophagy could be used to treat anthrax infection-induced cardiovascular complications.",
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