In vivo imaging reveals a phase-specific role of STAT3 during central and peripheral nervous system axon regeneration

Abstract

In the peripheral nervous system (PNS), damaged axons regenerate successfully, whereas axons in the CNS fail to regrow. In neurons of the dorsal root ganglia (DRG), which extend branches to both the PNS and CNS, only a PNS lesion but not a CNS lesion induces axonal growth. How this differential growth response is regulated in vivo is only incompletely understood. Here, we combine in vivo timelapse fluorescence microscopy with genetic manipulations in mice to reveal how the transcription factor STAT3 regulates axonal regeneration. We show that selective deletion of STAT3 in DRG neurons of STAT3-floxed mice impairs regeneration of peripheral DRG branches after a nerve cut. Further, overexpression of STAT3 induced by viral gene transfer increases outgrowth and collateral sprouting of central DRG branches after a dorsal column lesion by more than 400%. Notably, repetitive in vivo imaging of individual fluorescently labeled PNS and CNS axons reveals that STAT3 selectively regulates initiation but not later perpetuation of axonal growth. With STAT3, we thus identify a phase-specific regulator of axonal outgrowth. Activating STAT3 might provide an opportunity to "jumpstart" regeneration, and thus prime axons in the injured spinal cord for application of complementary therapies that improve axonal elongation.in vivo microscopy | spinal cord injury | peripheral nerve lesion | intrinsic growth program L esioned peripheral nervous system (PNS) axons regenerate successfully, whereas lesioned CNS axons fail to regrow. This differential behavior is exemplified by neurons located in the dorsal root ganglia (DRG), which extend one branch into the PNS and another into the CNS. In these neurons, a cut in the PNS but not in the CNS is followed by neuronal outgrowth (1). If, however, the DRG neuron is "conditioned" by a transection of its peripheral branch, a subsequent central lesion can be followed by extensive outgrowth (2,3). This suggests the existence of a common intrinsic neuronal growth program that can, in principle, support both PNS and CNS growth but is normally initiated only after a PNS lesion. In recent years, several intracellular components that might regulate this intrinsic growth program have been identified (4, 5). They include a number of transcriptional regulators such as the transcription factors cJun (6), SMAD1 (7), ATF3 (8), AKRD1 (9), NFIL3 (10), and several KLF family members (11). One particularly interesting transcriptional regulator is STAT3, which is activated as part of the JAK-STAT signaling pathway (12). The following findings make STAT3 a good candidate for regulating axon growth: first, increased levels of STAT3 expression and phosphorylation are associated with axonal regeneration (13-15) and axonal remodelling (16). Second, molecules that can affect STAT3 signaling such as the neuropoietic cytokines IL-6, ciliary neurotrophic factor, and leukemia inhibitory factor, as well as the intracellular regulator SOCS3, have been shown to influence axonal regeneration (17-20). Third, STAT3 expression prom...

Ready, STAT, go: transcription factors on the move

“…This is in contrast to previous reports showing that transduction of an active STAT3 increases neurite outgrowth (Miao et al, 2006) and central DRG branches (Bareyre et al, 2011) and that deletion of STAT3 leads to reduced neurite outgrowth and sensory neuron regeneration (Qiu et al, 2005;Bareyre et al, 2011). These differences may result from the type of assays used to assess axon outgrowth and regeneration.…”

In-vivo single neuron axotomy triggers axon regeneration to restore synaptic density in specific cortical circuits

“…4a). The average speed of regrowing axons in the adult brain was 20 ± 5 mm per day (n ¼ 5 axons from 5 mice) and the fastest rate detected wasB700 mm per day, which was comparable to peripheral nerve regrowth 24 .…”

NGL-2 Regulates Pathway-Specific Neurite Growth and Lamination, Synapse Formation, and Signal Transmission in the Retina

“…AAV-CAG-CFP viruses were a generous gift from Drs. F. M. Bareyre and M. Kerschensteiner (Institute of Clinical Neuroimmunology, Ludwig-Maximilians Universität München, Munich, Germany) (Bareyre et al, 2011). Before injection, mice were placed on ice for ϳ2 min.…”

“…Presynaptic ribbons are assembled from electron dense precursor spheres (Blanks et al, 1974;Regus-Leidig et al, 2009). In WT mice, the number of anchored ribbons reaches a maximum ϳP30 and precursor spheres or club-shaped intermediates of ribbon assembly are rarely observed at this age (Regus-Leidig et al, 2009).…”