Smoking exposure induces human lung endothelial cell adaptation to apoptotic stress

Am J Respir Cell Mol Biol. 2014 Mar;50(3):513-25. doi: 10.1165/rcmb.2013-0023OC.


Prolonged exposure to cigarette smoking is the main risk factor for emphysema, a component of chronic obstructive pulmonary diseases (COPDs) characterized by destruction of alveolar walls. Moreover, smoking is associated with pulmonary artery remodeling and pulmonary hypertension, even in the absence of COPD, through as yet unexplained mechanisms. In murine models, elevations of intra- and paracellular ceramides in response to smoking have been implicated in the induction of lung endothelial cell apoptosis, but the role of ceramides in human cell counterparts is yet unknown. We modeled paracrine increases (outside-in) of palmitoyl ceramide (Cer16) in primary human lung microvascular cells. In naive cells, isolated from nonsmokers, Cer16 significantly reduced cellular proliferation and induced caspase-independent apoptosis via mitochondrial membrane depolarization, apoptosis-inducing factor translocation, and poly(ADP-ribose) polymerase cleavage. In these cells, caspase-3 was inhibited by ceramide-induced Akt phosphorylation, and by the induction of autophagic microtubule-associated protein-1 light-chain 3 lipidation. In contrast, cells isolated from smokers exhibited increased baseline proliferative features associated with lack of p16(INK4a) expression and Akt hyperphosphorylation. These cells were resistant to Cer16-induced apoptosis, despite presence of both endoplasmic reticulum stress response and mitochondrial membrane depolarization. In cells from smokers, the prominent up-regulation of Akt pathways inhibited ceramide-triggered apoptosis, and was associated with elevated sphingosine and high-mobility group box 1, skewing the cell's response toward autophagy and survival. In conclusion, the cell responses to ceramide are modulated by an intricate cross-talk between Akt signaling and sphingolipid metabolites, and profoundly modified by previous cigarette smoke exposure, which selects for an apoptosis-resistant phenotype.

Publication types

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

MeSH terms

  • Adaptation, Physiological
  • Apoptosis / drug effects*
  • Apoptosis Regulatory Proteins / metabolism
  • Autophagy / drug effects
  • Cell Proliferation / drug effects
  • Cells, Cultured
  • Ceramides / toxicity*
  • Dose-Response Relationship, Drug
  • Endothelial Cells / drug effects*
  • Endothelial Cells / metabolism
  • Endothelial Cells / pathology
  • HMGB1 Protein / metabolism
  • Humans
  • Lung / blood supply*
  • Membrane Potential, Mitochondrial / drug effects
  • Palmitic Acids / toxicity*
  • Paracrine Communication / drug effects
  • Phenotype
  • Proto-Oncogene Proteins c-akt / metabolism
  • Signal Transduction / drug effects
  • Smoke / adverse effects*
  • Smoking / adverse effects*
  • Stress, Physiological / drug effects*
  • Time Factors


  • Apoptosis Regulatory Proteins
  • Ceramides
  • HMGB1 Protein
  • HMGB1 protein, human
  • Palmitic Acids
  • Smoke
  • Proto-Oncogene Proteins c-akt