Abstract
Following nerve injury, disintegrated axonal mitochondria distal to the injury site release mitochondrial formylated peptides and DNA that can induce activation and inflammatory profiling of Schwann cells via formyl peptide receptor 2 (Fpr2) and toll-like receptor 9 (TLR9), respectively. We studied RT4 schwannoma cells to investigate the regulation of Fpr2 and TLR9 after stimulation with fMLF as a prototypical formylated peptide. RT4 cells were treated with fMLF at various concentrations and times with and without pretreatment with inhibitors (chloroquine for activated TLR9, PBP10 for Fpr2). Western blots of Fpr2, TLR9, p-p38, p-NFκB, and IL-6 were compared in relation to inflammatory profiling of RT4 cells and chemokine receptors (CCR2, CXCR4) as potential co-receptors of Fpr2. fMLF stimulation upregulated Fpr2 in RT4 cells at low concentrations (10 nM and 100 nM) but higher concentrations were required (10 µM and 50 µM) when the cells were pretreated with an activated TLR9 inhibitor. Moreover, the higher concentrations of fMLF could modulate TLR9 and inflammatory markers. Upregulation of Fpr2 triggered by 10 nM and 100 nM fMLF coincided with higher levels of chemokine receptors (CCR2, CXCR4) and PKCβ. Treating RT4 cells with fMLF, as an in vitro model of Schwann cells, uncovered Schwann cells’ complex responses to molecular patterns of release from injured axonal mitochondria.
Highlights
Wallerian degeneration (WD) is a cascade of cellular and molecular events distal to a nerve injury
To investigate inflammatory profiling of RT4 cells induced by mitochondrial formyl peptides, the cells were stimulated with fMLF (Sigma-Aldrich) at final concentrations of 100 nM, 10 μM, and 50 μM for 1 and 6 h. fMLF was dissolved in dimethyl sulfoxide (DMSO), equal concentrations of DMSO were added to the medium in control cell cultures (100 nM, 0.002%; 10 μM, 0.2%; 50 μM, 1%)
In distal segments of injured axons, mitochondria are disintegrated and release mitochondrial damage-associated molecular patterns (mtDAMPs) including, among others, mitochondrial proteins and DNA (mtDNA) and formylated peptides that trigger intracellular signaling via toll-like receptor 9 (TLR9) and formyl peptide receptor 2 (Fpr2), respectively [27,28,41]
Summary
Wallerian degeneration (WD) is a cascade of cellular and molecular events distal to a nerve injury. It is considered an innate immune reaction or a sterile inflammation. Schwann cells in contact with degenerated axons are activated and reprogrammed towards axon promotion [1]. This activation of a post-injury phenotype in Schwann cells is linked to their inflammatory profiling to generate the conditions necessary for axon regeneration [2,3,4,5,6]. Inflammatory profiling of Schwann cells, exhibited as upregulation of cytokines/chemokines, [6,13] Distal segments of the injured axons contain disintegrated mitochondria [7,8,9,10] releasing both mitochondrial proteins and DNA (mtDNA), collectively characterized as mitochondrial damage-associated molecular patterns (mtDAMPs) [11,12].
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
