Axotomy Induces Phasic Alterations in Luman/CREB3 Expression and Nuclear Localization in Injured and Contralateral Uninjured Sensory Neurons: Correlation With Intrinsic Axon Growth Capacity

Abstract

Luman/CREB3 is an important early retrograde axotomy signal regulating acute axon outgrowth in sensory neurons through the adaptive unfolded protein response. As the injury response is transcriptionally multiphasic, a spatiotemporal analysis of Luman/ CREB3 localization in rat dorsal root ganglion (DRG) with unilateral L4-L6 spinal nerve injury was conducted to determine if Luman/CREB3 expression was similarly regulated. Biphasic alterations in Luman/CREB3 immunofluorescence and nuclear localization occurred in neurons ipsilateral to 1-hour, 1-day, 2-day, 4-day, and 1-week injury, with a largely parallel, but less avid response contralaterally. This biphasic response was not observed at the transcript level. To assess whether changes in neuronal Luman expression corresponded with an altered intrinsic capacity to grow an axon/neurite in vitro, injury-conditioned and contralateral uninjured DRG neurons underwent a 24-hour axon growth assay. Two-day injury-conditioned neurons exhibited maximal outgrowth capacity relative to naïve, declining at later injury-conditioned timepoints. Only neurons contralateral to 1-week injury exhibited significantly higher axon growth capacity than naïve. In conclusion, alterations in neuronal injury-associated Luman/CREB3 expression support that a multiphasic cell body response occurs and reveal a novel contralateral plasticity in axon growth capacity at 1-week post-injury. These adaptive responses have the potential to inform when repair or therapeutic intervention may be most effective.

CREB3 Transcription Factors: ER-Golgi Stress Transducers as Hubs for Cellular Homeostasis

“…In dorsal root ganglion sensory neurons CREB3 localizes to the soma and the axonal ER. In response to nerve injury, CREB3 is synthesized in axons and transported to the nuclei of injured neurons via importin-dependent retrograde transport (Hasmatali et al, 2019). Interestingly, immunoprecipitation assays indicated that CREB3 interacts with importin, but CREB3-target genes involved in axon growth were not identified.…”

The Conditioning Lesion Response in Dorsal Root Ganglion Neurons Is Inhibited in Oncomodulin Knock-Out Mice

“…It should be noted that in our experiments, we have performed a unilateral conditioning lesion and then compared the effects in the ipsilateral to those in the contralateral DRGs. This comparison may underestimate the magnitude of the effect on the ipsilateral ganglia, as in recent studies in the rat, it has been shown that, after spinal nerve transection, some stimulation of gene expression and neurite outgrowth occurs not only in the ipsilateral DRGs but also, though to a lesser extent, in the contralateral DRGs (Hasmatali et al, 2019;Hasmatali et al, 2020;Verge et al, 2020).…”

The Mechanisms of Peripheral Nerve Preconditioning Injury on Promoting Axonal Regeneration

“…Notably, CREB3 synthesis and releasing from the axonal endoplasmic reticulum was induced by axotomy and then transferred to the cell nucleus in an importin-mediated manner [ 39 ], which regulates the unfolded protein response (UPR ER ) and cholesterol biosynthesis that are crucially associating with the acute stress response in axonal growth [ 39 , 40 ]. The authors also show that upregulation and nuclear localization of Luman coordinate with the increased transcriptional activity in injured neurons, achieving maximal outgrowth capacity at two-day injury-conditioned neurons relative to naïve [ 41 ].…”