title: Overexpression of the monocyte chemokine CCL2 in dorsal root ganglion neurons causes a conditioning-like increase in neurite outgrowth and does so via a STAT3 dependent mechanism.
abstract: Neuroinflammation plays a critical role in the regeneration of peripheral nerves following axotomy. An injury to the sciatic nerve leads to significant macrophage accumulation in the L5 DRG, an effect not seen when the dorsal root is injured. We recently demonstrated that this accumulation around axotomized cell bodies is necessary for a peripheral conditioning lesion response to occur. Here we asked whether overexpression of the monocyte chemokine CCL2 specifically in DRG neurons of uninjured mice is sufficient to cause macrophage accumulation and to enhance regeneration or whether other injury-derived signals are required. AAV5-EF1α-CCL2 was injected intrathecally, and this injection led to a time-dependent increase in CCL2 mRNA expression and macrophage accumulation in L5 DRG, with a maximal response at 3 weeks post-injection. These changes led to a conditioning-like increase in neurite outgrowth in DRG explant and dissociated cell cultures. This increase in regeneration was dependent upon CCL2 acting through its primary receptor CCR2. When CCL2 was overexpressed in CCR2-/- mice, macrophage accumulation and enhanced regeneration were not observed. To address the mechanism by which CCL2 overexpression enhances regeneration, we tested for elevated expression of regeneration-associated genes in these animals. Surprisingly, we found that CCL2 overexpression led to a selective increase in LIF mRNA and neuronal phosphorylated STAT3 (pSTAT3) in L5 DRGs, with no change in expression seen in other RAGs such as GAP-43. Blockade of STAT3 phosphorylation by each of two different inhibitors prevented the increase in neurite outgrowth. Thus, CCL2 overexpression is sufficient to induce macrophage accumulation in uninjured L5 DRGs and increase the regenerative capacity of DRG neurons via a STAT3-dependent mechanism.
authors.affiliation: Department of Neurosciences, Case Western Reserve University, Cleveland, OH 44106-4975, USA.
authors.forename: Jon P
authors.initials: JP
authors.lastname: Niemi
authors.affiliation: Department of Neurosciences, Case Western Reserve University, Cleveland, OH 44106-4975, USA.
authors.forename: Alicia
authors.initials: A
authors.lastname: DeFrancesco-Lisowitz
authors.affiliation: Department of Neurosciences, Case Western Reserve University, Cleveland, OH 44106-4975, USA.
authors.forename: Jared M
authors.initials: JM
authors.lastname: Cregg
authors.affiliation: Department of Neurosciences, Case Western Reserve University, Cleveland, OH 44106-4975, USA.
authors.forename: Madeline
authors.initials: M
authors.lastname: Howarth
authors.affiliation: Department of Neurosciences, Case Western Reserve University, Cleveland, OH 44106-4975, USA. Electronic address: rez@case.edu.
authors.forename: Richard E
authors.initials: RE
authors.lastname: Zigmond
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D018932:Chemokine CCL2 / Q000235:genetics / Q000378:metabolism*; D005727:Ganglia, Spinal / Q000166:cytology / Q000378:metabolism*; D008264:Macrophages / Q000378:metabolism; D051379:Mice; D009416:Nerve Regeneration / Q000502:physiology*; D016501:Neurites / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D059348:Peripheral Nerve Injuries / Q000378:metabolism; D010766:Phosphorylation; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D012584:Sciatic Nerve / Q000293:injuries / Q000378:metabolism
chemical_list: D018932:Chemokine CCL2; D050796:STAT3 Transcription Factor
keywords: CCL2; DRG; MCP-1; Macrophage; Neuroinflammation; Regeneration; STAT3