The antimicrobial peptide LL-37 triggers release of apoptosis-inducing factor and shows direct effects on mitochondria

Elisabeth Bankell; Xiaoyan Liu; Martin Lundqvist; Daniel Svensson; Karl Swärd; Emma Sparr; Bengt-Olof Nilsson

doi:10.1016/j.bbrep.2021.101192

The antimicrobial peptide LL-37 triggers release of apoptosis-inducing factor and shows direct effects on mitochondria

Biochem Biophys Rep. 2021 Dec 20:29:101192. doi: 10.1016/j.bbrep.2021.101192. eCollection 2022 Mar.

Authors

Elisabeth Bankell¹, Xiaoyan Liu², Martin Lundqvist³, Daniel Svensson¹, Karl Swärd¹, Emma Sparr², Bengt-Olof Nilsson¹

Affiliations

¹ Department of Experimental Medical Science, Lund University, BMC D12, SE-22184, Lund, Sweden.
² Division of Physical Chemistry, Department of Chemistry, Lund University, SE-22100, Lund, Sweden.
³ Division of Biochemistry and Structural Biology, Department of Chemistry, Lund University, SE-22100, Lund, Sweden.

Abstract

The human antimicrobial peptide LL-37 permeabilizes the plasma membrane of host cells, but LL-37-induced direct effects on mitochondrial membrane permeability and function has not been reported. Here, we demonstrate that LL-37 is rapidly (within 20 min) internalized by human osteoblast-like MG63 cells, and that the peptide co-localizes with MitoTracker arguing for accumulation in mitochondria. Subcellular fractionation and Western blot disclose that stimulation with LL-37 (8 μM) for 2 h triggers release of the mitochondrial protein apoptosis-inducing factor (AIF) to the cytosol, whereas LL-37 causes no release of cytochrome C oxidase subunit IV of the inner mitochondrial membrane, suggesting that LL-37 affects mitochondrial membrane permeability in a specific manner. Next, we investigated release of AIF and cytochrome C from isolated mitochondria by measuring immunoreactivity by dot blot. The media of mitochondria treated with LL-37 (8 μM) for 2 h contained 50% more AIF and three times more cytochrome C than that of control mitochondria, showing that LL-37 promotes release of both AIF and cytochrome C. Moreover, in vesicles reflecting mitochondrial membrane lipid composition, LL-37 stimulates membrane permeabilization and release of tracer molecules. We conclude that LL-37 is rapidly internalized by MG63 cells and accumulates in mitochondria, and that the peptide triggers release of pro-apoptotic AIF and directly affects mitochondrial membrane structural properties.

Keywords: Apoptosis; Cathelicidin; Innate immunity; Mitochondria; Mitochondria model membranes.