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

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 Ca2+ concentration assessed by laser-scanning confocal microscopy of Fluo-4-AM-loaded MG63 cells. LL-37 increased Ca2+ also in the presence of the respective L- and T-type voltage-sensitive Ca2+ channel blockers nifedipine and NiCl2. LL-37 had no effect on Ca2+ in cells incubated with Ca2+-free solution. LL-37 (4 and 8 μM) reduced the MG63 cell number both in the presence and absence of Ca2+ in the medium. In conclusion, LL-37 reduces the osteoblast cell number by promoting apoptosis, and furthermore, LL-37 stimulates Ca2+ inflow via a mechanism independent of voltage-sensitive Ca2+ channels. Interestingly, LL-37-induced lowering of the cell number seems to be mediated via a mechanism independent of Ca2+. Copyright © 2013 S. Karger AG, Basel.