RT Journal Article
SR Electronic
T1 Injury-free priming: induction of Primary Afferent Collateral Sprouting in uninjured sensory neurons <em>in vivo</em> primes them for enhanced axon outgrowth <em>in vitro</em>
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 463935
DO 10.1101/463935
A1 Sara Soleman
A1 Jeffrey C. Petruska
A1 Lawrence D.F. Moon
YR 2018
UL http://biorxiv.org/content/early/2018/11/14/463935.abstract
AB Prior “conditioning” nerve lesions can prime DRG neurons for enhanced axon regeneration. We tested the hypothesis that adult DRG neurons can be similarly primed for axon elongation without axonal injury through induction of Primary Afferent Collateral Sprouting (PACS). PACS was induced in uninjured T11 DRG neurons by denervating dermatomes rostrally and caudally. In this model uninjured adult DRG neurons extend uninjured axons into denervated skin in vivo. Collateral sprouting by the spared T11 DRG neurons was confirmed by mapping the expansion of its responsive zones of skin up to 14 days. At 7 or 14 days after induction of PACS, DRG neurons were dissociated and cultured without growth factors for 18 hours. Neurons from T11 PACS DRG had longer mean neurite lengths than neurons from naïve DRG. A larger proportion of neurons from T11 PACS DRG showed an elongating or arborizing phenotype than neurons from naïve DRG. DRGs serving nerves transected to create the denervated dermatomes contained large numbers of neurons expressing Activating Transcription Factor 3 (ATF3), a marker of the injury response. In contrast, T11 DRG from both unoperated rats and PACS rats contained very few neurons expressing ATF3. Microarray analyses and qRTPCR of T11 DRG and denervated/reinnervated skin reveal regulation of receptor/ligand systems as well as additional potential regulators of growth during PACS. We suggest that extracellular cues in denervated skin modify the intrinsic growth program of uninjured DRG neurons that enhances their ability to elongate or arborize even after explantation. Collectively, these data indicate that induction of PACS does not induce an injury response, yet primes many of these uninjured neurons for in vitro axon growth.Graphical abstract; please use Figure 1C.Highlights: (for separate editable file)Others have shown that a prior conditioning lesion enhances the regeneration of DRG axons in vivo and predisposes them to elongate rather than arborize after dissociation of ganglia and culturing in vitro.We now show that inducing uninjured DRG neurons to undergo Primary Afferent Collateral Sprouting (PACS) into zones of denervation in the skin in vivo primes them for subsequent axon elongation or arborization in vitro.Transection of thoracic cutaneous nerves (T9, T10, T12, T13) created zones of denervated skin with concomitant loss of the sensory drive of the cutaneous muscle trunci (CTM) reflex.Over time, neurons from the uninjured T11 DRG underwent collateral sprouting within the skin which reduced the size of the zone of denervation and restored sensory drive of the CTM reflex.T11 DRG were dissociated either 7 or 14 days after induction of PACS and cultured in defined media lacking neurotrophins and growth factors: these neurons elongated or arborized more than naive neurons from unoperated rats.Microarray analysis and qRTPCR showed that that the GDNF family ligands artemin and persephin were upregulated in denervated skin at 7 and/or 14 days after induction of PACS.We suggest that exposure of uninjured DRG neurons to neurotrophins and growth factors in denervated skin primes them for enhanced outgrowth after explantation.