CXCL12 and CXCR4 proteins and mRNAs were monitored in the dorsal root ganglia (DRGs) of lumbar (L4-L5) and cervical (C7-C8) spinal segments of naïve rats, rats subjected to sham operation, and those undergoing unilateral complete sciatic nerve transection (CSNT) on post-operation day 7 (POD7). Immunohistochemical, Western blot, and RT-PCR analyses revealed bilaterally increased levels of CXCR4 protein and mRNA in both lumbar and cervical DRG neurons after CSNT. Similarly, CXCL12 protein levels increased, and CXCL12 mRNA was upregulated primarily in lumbar DRGs ipsilateral to the nerve lesion. Intrathecal application of the CXCR4 inhibitor AMD3100 following CSNT reduced CXCL12 and CXCR4 protein levels in cervical DRG neurons, as well as the length of afferent axons regenerated distal to the ulnar nerve crush. Furthermore, treatment with the CXCR4 inhibitor decreased levels of activated Signal Transducer and Activator of Transcription 3 (STAT3), a critical transforming factor in the neuronal regeneration program. Administration of IL-6 increased CXCR4 levels, whereas the JAK2-dependent STAT3 phosphorylation inhibitor (AG490) conversely decreased CXCR4 levels. This indicates a link between the CXCL12/CXCR4 signaling axis and IL-6-induced activation of STAT3 in the sciatic nerve injury-induced pro-regenerative state of cervical DRG neurons. The role of CXCR4 signaling in the axon-promoting state of DRG neurons was confirmed through in vitro cultivation of primary sensory neurons in a medium supplemented with CXCL12, with or without AMD3100. The potential involvement of conditioned cervical DRG neurons in the induction of neuropathic pain is discussed.

• Keywords
• AMD3100, IL-6, STAT3, axon regeneration, pre-conditioning, sciatic nerve, transection,
• MeSH
• Benzylamines MeSH
• Chemokine CXCL12 metabolism   genetics   MeSH
• Cyclams MeSH
• Interleukin-6 metabolism   pharmacology   MeSH
• Rats MeSH
• Sciatic Neuropathy * metabolism   MeSH
• Sensory Receptor Cells * metabolism   MeSH
• Sciatic Nerve * injuries   metabolism   MeSH
• Rats, Sprague-Dawley MeSH
• Receptors, CXCR4 * metabolism   genetics   MeSH
• Nerve Regeneration * MeSH
• Signal Transduction * MeSH
• Ganglia, Spinal metabolism   MeSH
• STAT3 Transcription Factor metabolism   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Male MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Benzylamines MeSH
• Chemokine CXCL12 MeSH
• CXCL12 protein, rat MeSH Browser
• Cxcr4 protein, rat MeSH Browser
• Cyclams MeSH
• Interleukin-6 MeSH
• plerixafor MeSH Browser
• Receptors, CXCR4 * MeSH
• Stat3 protein, rat MeSH Browser
• STAT3 Transcription Factor MeSH

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

To assess the potential role of IL-6 in sciatic nerve injury-induced activation of a pro-regenerative state in remote dorsal root ganglia (DRG) neurons, we compared protein levels of SCG-10 and activated STAT3, as well as axon regeneration in IL-6 knockout (IL-6ko) mice and their wild-type (WT) counterparts. Unilateral sciatic nerve compression and transection upregulated SCG-10 protein levels and activated STAT3 in DRG neurons not only in lumbar but also in cervical segments of WT mice. A pro-regenerative state induced by prior sciatic nerve lesion in cervical DRG neurons of WT mice was also shown by testing for axon regeneration in crushed ulnar nerve. DRG neurons from IL-6ko mice also displayed bilaterally increased levels of SCG-10 and STAT3 in both lumbar and cervical segments after sciatic nerve lesions. However, levels of SCG-10 protein in lumbar and cervical DRG of IL-6ko mice were significantly lower than those of their WT counterparts. Sciatic nerve injury induced a lower level of SCG-10 in cervical DRG of IL-6ko than WT mice, and this correlates with significantly shorter regeneration of axons distal to the crushed ulnar nerve. These results suggest that IL-6 contributes, at the very least, to initiation of the neuronal regeneration program in remote DRG neurons after unilateral sciatic nerve injury.

• Keywords
• Primary sensory neuron, SCG10, STAT3, Sciatic nerve lesion, Ulnar nerve crush,
• MeSH
• Immunohistochemistry MeSH
• Interleukin-6 analysis   deficiency   metabolism   MeSH
• Intracellular Signaling Peptides and Proteins analysis   MeSH
• Mice, Inbred C57BL MeSH
• Mice, Knockout MeSH
• Mice MeSH
• Neurons chemistry   cytology   metabolism   pathology   MeSH
• Peripheral Nerve Injuries metabolism   pathology   surgery   MeSH
• Calcium-Binding Proteins MeSH
• Nerve Regeneration * MeSH
• Ganglia, Spinal cytology   metabolism   pathology   surgery   MeSH
• Stathmin MeSH
• STAT3 Transcription Factor analysis   MeSH
• Blotting, Western MeSH
• Animals MeSH
• Check Tag
• Male MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Interleukin-6 MeSH
• Intracellular Signaling Peptides and Proteins MeSH
• Calcium-Binding Proteins MeSH
• Stat3 protein, mouse MeSH Browser
• Stathmin MeSH
• Stmn2 protein, mouse MeSH Browser
• STAT3 Transcription Factor MeSH