Toll-like receptor 4 deficiency causes pulmonary emphysema

J Clin Invest. 2006 Nov;116(11):3050-9. doi: 10.1172/JCI28139. Epub 2006 Oct 19.

Abstract

TLRs have been studied extensively in the context of pathogen challenges, yet their role in the unchallenged lung is unknown. Given their direct interface with the external environment, TLRs in the lungs are prime candidates to respond to air constituents, namely particulates and oxygen. The mechanism whereby the lung maintains structural integrity in the face of constant ambient exposures is essential to our understanding of lung disease. Emphysema is characterized by gradual loss of lung elasticity and irreversible airspace enlargement, usually in the later decades of life and after years of insult, most commonly cigarette smoke. Here we show Tlr4(-/-) mice exhibited emphysema as they aged. Adoptive transfer experiments revealed that TLR4 expression in lung structural cells was required for maintaining normal lung architecture. TLR4 deficiency led to the upregulation of what we believe to be a novel NADPH oxidase (Nox), Nox3, in lungs and endothelial cells, resulting in increased oxidant generation and elastolytic activity. Treatment of Tlr4(-/- )mice or endothelial cells with chemical NADPH inhibitors or Nox3 siRNA reversed the observed phenotype. Our data identify a role for TLR4 in maintaining constitutive lung integrity by modulating oxidant generation and provide insights into the development of emphysema.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antioxidants / metabolism
  • Cells, Cultured
  • Elastin / metabolism
  • Mice
  • Mice, Knockout
  • Myeloid Differentiation Factor 88 / deficiency
  • Myeloid Differentiation Factor 88 / genetics
  • Myeloid Differentiation Factor 88 / metabolism
  • NADPH Oxidases / metabolism
  • Oxidants / metabolism
  • Pancreatic Elastase / metabolism
  • Pulmonary Emphysema / genetics
  • Pulmonary Emphysema / metabolism*
  • Pulmonary Emphysema / pathology*
  • Toll-Like Receptor 4 / deficiency*
  • Toll-Like Receptor 4 / genetics
  • Toll-Like Receptor 4 / metabolism*

Substances

  • Antioxidants
  • Myd88 protein, mouse
  • Myeloid Differentiation Factor 88
  • Oxidants
  • Tlr4 protein, mouse
  • Toll-Like Receptor 4
  • Elastin
  • NADPH Oxidases
  • Nox3 protein, mouse
  • Pancreatic Elastase