Proinflammatory Cytokines Impair Vitamin D-Induced Host Defense in Cultured Airway Epithelial Cells

Am J Respir Cell Mol Biol. 2017 Jun;56(6):749-761. doi: 10.1165/rcmb.2016-0289OC.

Abstract

Vitamin D is a regulator of host defense against infections and induces expression of the antimicrobial peptide hCAP18/LL-37. Vitamin D deficiency is associated with chronic inflammatory lung diseases and respiratory infections. However, it is incompletely understood if and how (chronic) airway inflammation affects vitamin D metabolism and action. We hypothesized that long-term exposure of primary bronchial epithelial cells to proinflammatory cytokines alters their vitamin D metabolism, antibacterial activity, and expression of hCAP18/LL-37. To investigate this, primary bronchial epithelial cells were differentiated at the air-liquid interface for 14 days in the presence of the proinflammatory cytokines, TNF-α and IL-1β (TNF-α/IL-1β), and subsequently exposed to vitamin D (inactive 25(OH)D3 and active 1,25(OH)2D3). Expression of hCAP18/LL-37, vitamin D receptor, and enzymes involved in vitamin D metabolism (CYP24A1 and CYP27B1) was determined using quantitative PCR, Western blot, and immunofluorescence staining. Furthermore, vitamin D-mediated antibacterial activity was assessed using nontypeable Haemophilus influenzae. We found that TNF-α/IL-1β treatment reduced vitamin D-induced expression of hCAP18/LL-37 and killing of nontypeable H. influenzae. In addition, CYP24A1 (a vitamin D-degrading enzyme) was increased by TNF-α/IL-1β, whereas CYP27B1 (that converts 25(OH)D3 to its active form) and vitamin D receptor expression remained unaffected. Furthermore, we have demonstrated that the TNF-α/IL-1β-mediated induction of CYP24A1 was, at least in part, mediated by the transcription factor specific protein 1, and the epidermal growth factor receptor-mitogen-activated protein kinase pathway. These findings indicate that TNF-α/IL-1β decreases vitamin D-mediated antibacterial activity and hCAP18/LL-37 expression via induction of CYP24A1 and suggest that chronic inflammation impairs protective responses induced by vitamin D.

Keywords: airway epithelial cells; hCAP18/LL-37; host defense; proinflammatory mediators; vitamin D.

MeSH terms

  • Acute Lung Injury / pathology
  • Antimicrobial Cationic Peptides
  • Bronchi / cytology*
  • Calcifediol / pharmacology
  • Cathelicidins / metabolism
  • Cell Differentiation / drug effects
  • Cells, Cultured
  • Cytokines / metabolism*
  • Epithelial Cells / drug effects
  • Epithelial Cells / immunology*
  • Epithelial Cells / metabolism
  • ErbB Receptors / metabolism
  • Extracellular Signal-Regulated MAP Kinases / metabolism
  • Haemophilus influenzae / drug effects
  • Humans
  • Inflammation Mediators / metabolism*
  • Interleukin-17 / pharmacology
  • Interleukin-1beta / pharmacology
  • Microbial Viability / drug effects
  • Mucins / metabolism
  • Sp1 Transcription Factor / metabolism
  • Time Factors
  • Tumor Necrosis Factor-alpha / pharmacology
  • Vitamin D / pharmacology*
  • Vitamin D3 24-Hydroxylase / metabolism

Substances

  • Antimicrobial Cationic Peptides
  • Cathelicidins
  • Cytokines
  • Inflammation Mediators
  • Interleukin-17
  • Interleukin-1beta
  • Mucins
  • Sp1 Transcription Factor
  • Tumor Necrosis Factor-alpha
  • Vitamin D
  • Vitamin D3 24-Hydroxylase
  • ErbB Receptors
  • Extracellular Signal-Regulated MAP Kinases
  • Calcifediol