One of the changes brought about by Wallerian degeneration distal to nerve injury is disintegration of axonal mitochondria and consequent leakage of mitochondrial DNA (mtDNA)-the natural ligand for the toll-like receptor 9 (TLR9). RT-PCR and immunohistochemical or Western blot analyses were used to detect TLR9 mRNA and protein respectively in the lumbar (L4-L5) and cervical (C7-C8) dorsal root ganglia (DRG) ipsilateral and contralateral to a sterile unilateral sciatic nerve compression or transection. The unilateral sciatic nerve lesions led to bilateral increases in levels of both TLR9 mRNA and protein not only in the lumbar but also in the remote cervical DRG compared with naive or sham-operated controls. This upregulation of TLR9 was linked to activation of the Nuclear Factor kappa B (NFκB) and nuclear translocation of the Signal Transducer and Activator of Transcription 3 (STAT3), implying innate neuronal immune reaction and a pro-regenerative state in uninjured primary sensory neurons of the cervical DRG. The relationship of TLR9 to the induction of a pro-regenerative state in the cervical DRG neurons was confirmed by the shorter lengths of regenerated axons distal to ulnar nerve crush following a previous sciatic nerve lesion and intrathecal chloroquine injection compared with control rats. The results suggest that a systemic innate immune reaction not only triggers the regenerative state of axotomized DRG neurons but also induces a pro-regenerative state further along the neural axis after unilateral nerve injury.

• Keywords
• axon regeneration, compression, early endosomes, mitochondrial DNA, sciatic nerve, the endoplasmic reticulum, transection,
• MeSH
• Rats MeSH
• Sciatic Neuropathy immunology   metabolism   pathology   therapy   MeSH
• Neurons cytology   immunology   MeSH
• Rats, Wistar MeSH
• Immunity, Innate immunology   MeSH
• Ganglia, Spinal cytology   MeSH
• Toll-Like Receptor 9 genetics   metabolism   MeSH
• STAT3 Transcription Factor genetics   metabolism   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Male MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Stat3 protein, rat MeSH Browser
• Tlr9 protein, rat MeSH Browser
• Toll-Like Receptor 9 MeSH
• STAT3 Transcription Factor MeSH

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.

• Keywords
• Wallerian degeneration, chemokines, cytokines, damage-associated molecular patterns, disintegration, mitochondria, receptors,
• MeSH
• Chloroquine pharmacology   MeSH
• Rats MeSH
• N-Formylmethionine Leucyl-Phenylalanine pharmacology   MeSH
• Cell Line, Tumor MeSH
• Neurilemmoma metabolism   pathology   MeSH
• Receptors, CCR2 genetics   metabolism   MeSH
• Receptors, CXCR4 genetics   metabolism   MeSH
• Receptors, Formyl Peptide antagonists & inhibitors   genetics   metabolism   MeSH
• Schwann Cells cytology   drug effects   metabolism   MeSH
• Signal Transduction drug effects   MeSH
• Toll-Like Receptor 9 antagonists & inhibitors   genetics   metabolism   MeSH
• Up-Regulation drug effects   MeSH
• Inflammation metabolism   pathology   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Chloroquine MeSH
• N-Formylmethionine Leucyl-Phenylalanine MeSH
• Receptors, CCR2 MeSH
• Receptors, CXCR4 MeSH
• Receptors, Formyl Peptide MeSH
• Toll-Like Receptor 9 MeSH