Inactivation of MTOR promotes autophagy-mediated epithelial injury in particulate matter-induced airway inflammation

Autophagy. 2020 Mar;16(3):435-450. doi: 10.1080/15548627.2019.1628536. Epub 2019 Jun 16.

Abstract

Particulate matter (PM) is able to induce airway epithelial injury, while the detailed mechanisms remain unclear. Here we demonstrated that PM exposure inactivated MTOR (mechanistic target of rapamycin kinase), enhanced macroautophagy/autophagy, and impaired lysosomal activity in HBE (human bronchial epithelial) cells and in mouse airway epithelium. Genetic or pharmaceutical inhibition of MTOR significantly enhanced, while inhibition of autophagy attenuated, PM-induced IL6 expression in HBE cells. Consistently, club-cell-specific deletion of Mtor aggravated, whereas loss of Atg5 in bronchial epithelium reduced, PM-induced airway inflammation. Interestingly, the augmented inflammatory responses caused by MTOR deficiency were markedly attenuated by blockage of downstream autophagy both in vitro and in vivo. Mechanistically, the dysregulation of MTOR-autophagy signaling was partially dependent on activation of upstream TSC2, and interacted with the TLR4-MYD88 to orchestrate the downstream NFKB activity and to regulate the production of inflammatory cytokines in airway epithelium. Moreover, inhibition of autophagy reduced the expression of EPS15 and the subsequent endocytosis of PM. Taken together, the present study provides a mechanistic explanation for how airway epithelium localized MTOR-autophagy axis regulates PM-induced airway injury, suggesting that activation of MTOR and/or suppression of autophagy in local airway might be effective therapeutic strategies for PM-related airway disorders.Abbreviations: ACTB: actin beta; AKT: AKT serine/threonine kinase; ALI: air liquid interface; AP2: adaptor related protein complex 2; ATG: autophagy related; BALF: bronchoalveolar lavage fluid; COPD: chronic obstructive pulmonary disease; CXCL: C-X-C motif chemokine ligand; DOX: doxycycline; EGF: epidermal growth factor; EGFR: epidermal growth factor receptor; EPS15: epidermal growth factor receptor pathway substrate 15; HBE: human bronchial epithelial; H&E: hematoxylin & eosin; IKK: IKB kinase; IL: interleukin; LAMP2: lysosomal-associated membrane protein 2; LPS: lipopolysaccharide; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; MTEC: mouse tracheal epithelial cells; MTOR: mechanistic target of rapamycin kinase; MYD88: MYD88 innate immune signal transduction adaptor; NFKB: nuclear factor of kappa B; NFKBIA: NFKB inhibitor alpha; PM: particulate matter; PtdIns3K: phosphatidylinositol 3-kinase; Rapa: rapamycin; RELA: RELA proto-oncogene, NFKB subunit; SCGB1A1: secretoglobin family 1A member 1; siRNA: small interfering RNAs; SQSTM1: sequestosome 1; TEM: transmission electronic microscopy; TLR4: toll like receptor 4; TSC2: TSC complex subunit 2.

Keywords: Airway epithelial injury; MTOR; airway inflammation; autophagy; particulate matter.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / metabolism
  • Animals
  • Autophagy*
  • Autophagy-Related Protein 5 / metabolism
  • Bronchi / pathology
  • Cell Line
  • Cytokines / metabolism
  • Endocytosis / drug effects
  • Epithelial Cells / drug effects
  • Epithelial Cells / metabolism
  • Epithelial Cells / pathology*
  • Gene Deletion
  • Humans
  • Lysosomes / drug effects
  • Lysosomes / metabolism
  • Mice
  • Microtubule-Associated Proteins / deficiency
  • Microtubule-Associated Proteins / metabolism
  • Models, Biological
  • Myeloid Differentiation Factor 88 / metabolism
  • NF-kappa B / metabolism
  • Particulate Matter / toxicity*
  • Pneumonia / chemically induced*
  • Pneumonia / pathology*
  • Protein Binding / drug effects
  • Proto-Oncogene Mas
  • Signal Transduction
  • TOR Serine-Threonine Kinases / metabolism*
  • Toll-Like Receptor 4 / metabolism
  • Tuberous Sclerosis Complex 2 Protein / metabolism

Substances

  • Adaptor Proteins, Signal Transducing
  • Autophagy-Related Protein 5
  • Cytokines
  • EPS15 protein, human
  • MAS1 protein, human
  • Map1lc3b protein, mouse
  • Microtubule-Associated Proteins
  • Myeloid Differentiation Factor 88
  • NF-kappa B
  • Particulate Matter
  • Proto-Oncogene Mas
  • TSC2 protein, human
  • Toll-Like Receptor 4
  • Tuberous Sclerosis Complex 2 Protein
  • TOR Serine-Threonine Kinases

Grants and funding

This work was supported by the National Key R&D Program of China (Grant 2016YFA0501602 to Z.-H. C.), Key Project of Chinese National Programs for Fundamental Research and Development (973 program, 2015CB553405 to Z.-H. C.), the Major Project (81490532 to H.-H. S.) and the General Projects (81670031 to Z.-H. C., 81370126 to W. L., and 81570021 to H.-Q. H.) from the National Natural Science Foundation of China, and the Precision Medicine Research of the National Key Research and Development Plan of China (2016YFC0905800).