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

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.