Conference Agenda

The Peripheral Nervous System is endowed by regenerative capacity after a damage that could be either due to trauma or toxic injuries. However, this process is often incomplete and normally the system does not reach full recovery. Key steps to the creation of a permissive environment for axonal regrowth, are the trans-differentiation of Schwann cells coupled to the remodelling of the extracellular matrix. Among the molecules involved, the activation of proteases and secretases is instructive for nerve regeneration and remyelination. Indeed, the concerted action of alpha, beta and gamma secretases cooperates to balance activating and inhibitory signals necessary for physiological myelination and remyelination upon injury. These molecules actively regulate the composition of extra cellular matrix component, in addition to processing factors essential for nerve regeneration. Further, both proteases and metalloproteases modulate the blood coagulation cascade, whose factors participate in forming newly synthetized myelin and in regulating axonal regeneration.

We recently demonstrated that the alpha secretase ADAM17, in addition to its role during myelination, is implicated also during the nerve regeneration process. Indeed, we showed that ADAM17 cleaves p75NTR, regulates fibrin clearance, and eventually fine-tunes remyelination. In mutant mice specifically lacking ADAM 17 in Schwann cells, p75NTR abnormally accumulates, leading to a downregulation of tissue plasminogen activator (tPA) expression, excessive fibrin accumulation over time, and delayed remyelination. These mutants also present impaired macrophage recruitment and defective nerve conduction velocity. Thus, ADAM17 expressed in Schwann cells, controls the whole regeneration process, and its absence hampers effective nerve repair.

These results provide important insights into the complex regulation of remyelination following nerve injury, identifying in ADAM17 and p75NTR a new signalling axis implicated in these events. Modulation of this pathway could effectively promote nerve remyelination, an often-inefficient process, with the aim of restoring a functional axo-glial unit.

The peripheral nervous system can regenerate after injury. Regeneration relies on an intrinsic ability of motor neurons on one hand, and on the contribution of different cell types in the milieu on the other. At the neuromuscular junction (NMJ), the synapse that governs locomotion, an important axis that drives functional recovery after a damage to the motor axon terminal is that of the chemokine CXCL12α, released by Schwann cells, and its neuronal receptor CXCR4. Importantly, CXCR4 expression increases upon nerve injury, and its inhibition delays the process of nerve repair. Our hypothesis is that in Amyotrophic lateral sclerosis (ALS), a severe neurodegenerative condition whose first signs of impairment originate at the NMJ even before symptoms manifestation, regeneration competence is progressively lost, overwhelmed by degenerative events, but can be revived through CXCR4 stimulation.

This paper will describe conditions and parameters to be considered for limb replantation after traumatic amputation. In previous years we have extensively worked on the development of chitosan based nerve guides. We have learned from pre-clinical models comparing acute and delayed nerve repair strategies that bioartificial nerve guides may support better the regeneration after delayed nerve repair. We have also learned that chitosan has a stimulatory effect on the pro-regenerative macrophages. We therefore hypothesize that chitosan material can also provide an optimal bridge for replantation approaches after traumatic limb amputation. In order to identify the conditions of peripheral nerve tissue in amputated limbs over 6 hours after amputation, we have performed a histomorphometric analysis of a porcine peripheral nerves after hind limb amputation under different storage conditions.

Methods: Semithin cross sections of the (1) proximal muscle branch of the sciatic nerve, (2) peroneal nerve, (3) tibial nerve, and (4) caudal sural cutaneous nerve were analyzed for myelinated nerve fiber density, fiber diameter, axon diameter, thickness of the myelin sheath, and g-ratio. Values were compared to non-amputated healthy control nerves. Further, corresponding nerve segments were cultured and the outgrowth behaviour of Schwann cells quantified in vitro.

Results: Preliminary results indicate that on the histomorphometrical level no significant differences are detectable between more proximal and more distal nerve segments along the limb. In vitro investigations are still on their way.

Conclusions: Peripheral nerve tissue in amputated hind limbs does not show significant changes in histomorphometric degeneration related parameters in comparison to non-amputated healthy controls after 6 hours of amputation. Schwann cells need to be further characterized for elucidating their regenerative potential also in contact to chitosan materials.

The recent opioid crisis in the USA has demonstrated the limitations in pain management options available at the moment. Therefore, investigating the biology of pain perception is vital to promote the development of more specific and non-addictive analgesic drugs, especially in the context of chronic pain.

Altered skin and muscle innervation, as a result of an unbalance of internal and external growth signals in neurons, is one of the causes of neuropathic pain.

Peripheral neurons survive and grow in response to neurotrophins, released by surrounding cells. It has been speculated that intracellular growth factors also contribute to and regulate neurotrophin signaling, but the current knowledge on this topic is severely lacking. Intriguingly, this signaling axis could be relevant in shaping nociception in the peripheral neurons.

In a recently published article (Marvaldi et al., 2020), knockout of importin α3 in dorsal root ganglia (DRG) neurons was shown to reduce neuropathic pain perception. Importin α3 is a shuttle protein of the karyopherin family that acts as an adaptor protein of KPNB1 for the delivery of transcription factors to the nucleus. Indeed, analysis has shown that importin α3 null mice have altered gene expression upon injury.

Our research aims to investigate which genes, found to have altered expressions in importin α3 null mice, are relevant for pain perception. In particular, we are planning to look for those genes that are differently modulated at the early and late stages of chronic pain. By comparing our findings to data collected from previously published articles, we will identify candidate proteins that may more likely be involved in the nociception pathways and then further characterize their roles through biochemical assays (both in vitro and in vivo).

Finally, we hope to unravel novel transcriptional networks controlling nociception, which could become new therapeutic targets to manage chronic pain patients.