The antimicrobial peptide LL-37 alters human osteoblast Ca2+ handling and induces Ca2+-independent apoptosis

J Innate Immun. 2013;5(3):290-300. doi: 10.1159/000346587. Epub 2013 Feb 13.

Abstract

The human antimicrobial peptide cathelicidin LL-37 has, besides its antimicrobial properties, also been shown to regulate apoptosis in a cell type-specific manner. Mechanisms involved in LL-37-regulated apoptotic signaling are not identified. Here, we show that LL-37 reduces the human osteoblast-like MG63 cell number and cell viability in the micromolar concentration range with an IC50 value of about 5 µM. Treatment with 4 µM LL-37 increased the number of annexin V-positive cells and stimulated activation of caspase 3 showing that LL-37 promotes apoptosis. Treatment with 4 µM LL-37 caused an acute and sustained rise in intracellular Ca(2+) concentration assessed by laser-scanning confocal microscopy of Fluo-4-AM-loaded MG63 cells. LL-37 increased Ca(2+) also in the presence of the respective L- and T-type voltage-sensitive Ca(2+) channel blockers nifedipine and NiCl2. LL-37 had no effect on Ca(2+) in cells incubated with Ca(2+)-free solution. LL-37 (4 and 8 µM) reduced the MG63 cell number both in the presence and absence of Ca(2+) in the medium. In conclusion, LL-37 reduces the osteoblast cell number by promoting apoptosis, and furthermore, LL-37 stimulates Ca(2+) inflow via a mechanism independent of voltage-sensitive Ca(2+) channels. Interestingly, LL-37-induced lowering of the cell number seems to be mediated via a mechanism independent of Ca(2+).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Annexin A5 / immunology
  • Annexin A5 / metabolism
  • Antimicrobial Cationic Peptides / immunology
  • Antimicrobial Cationic Peptides / pharmacology*
  • Apoptosis / drug effects*
  • Apoptosis / immunology
  • Calcium / immunology*
  • Calcium / metabolism
  • Calcium Channels, L-Type / immunology
  • Calcium Channels, L-Type / metabolism
  • Calcium Channels, T-Type / immunology
  • Calcium Channels, T-Type / metabolism
  • Cell Line
  • Dose-Response Relationship, Drug
  • Humans
  • Osteoblasts / immunology*
  • Osteoblasts / metabolism

Substances

  • Annexin A5
  • Antimicrobial Cationic Peptides
  • Calcium Channels, L-Type
  • Calcium Channels, T-Type
  • ropocamptide
  • Calcium