Asymmetric Sensory-Motor Regeneration of Transected Peripheral Nerves Using Molecular Guidance Cues

Abstract

Neural interfaces are designed to decode motor intent and evoke sensory precepts in amputees. In peripheral nerves, recording movement intent is challenging because motor axons are only a small fraction compared to sensory fibers and are heterogeneously mixed particularly at proximal levels. We previously reported that pain and myelinated axons regenerating through a Y-shaped nerve guide with sealed ends, can be modulated by luminar release of nerve growth factor (NGF) and neurotrophin-3 (NT-3), respectively. Here, we evaluate the differential potency of NGF, glial cell line-derived neurotrophic factor (GDNF), brain-derived neurotrophic factor (BDNF), pleiotrophin (PTN), and NT-3 in asymmetrically guiding the regeneration of sensory and motor neurons. We report that, in the absence of distal target organs, molecular guidance cues can mediate the growth of electrically conductive fascicles with normal microanatomy. Compared to Y-tube compartments with bovine serum albumin (BSA), GDNF and NGF increased the motor and sensory axon content, respectively. In addition, the sensory to motor ratio was significantly increased by PTN (12.7:1) when compared to a BDNF + GDNF choice. The differential content of motor and sensory axons modulated by selective guidance cues may provide a strategy to better define axon types in peripheral nerve interfaces.

Biomimetic Approaches for Separated Regeneration of Sensory and Motor Fibers in Amputee People: Necessary Conditions for Functional Integration of Sensory–Motor Prostheses With the Peripheral Nerves

“…To achieve the differentiated regeneration also in amputee persons, the most intuitive and straightforward solution would be to reproduce in the amputated nerves the processes that naturally occur in damaged nerves with preserved epineurium and target organs, which means to create in the amputated member an artificial anatomical and biomolecular environment (a bio-hybrid medium) similar to the environment that favors the natural regeneration of the peripheral nerves. Unfortunately, and despite the enormous efforts dedicated in the last 70 years to this enterprise, differential regeneration of the sensory and motor fibers has not been yet totally achieved (Johnson et al, 2015;Anand et al, 2017;del Valle et al, 2018). Among the main reasons of this failure are the high complexity of the involved biomolecular processes and the variability of the employed experimental protocols, which make experimental data difficult to interpret.…”

“…]; (ii) cell-cell junction molecules (N-CAM, L1), which will allow the interaction between the regenerating axons and the Schwann cells present in the bands of Büngner, in the distal zone, and (iii) molecules that bind to the ECM (integrins), which will act as a support for axonal guidance to its target tissue. Gardiner, 2011;Anand et al, 2017) and molecules present in the ECM (fibrinogen, fibronectin, laminin, etc.) (Politis, 1989;Hammarberg et al, 2000;Zhang et al, 2003;Tucker and Mearow, 2008;Webber et al, 2008;Gardiner, 2011;Fudge and Mearow, 2013;Gonzalez-Perez et al, 2016; Table 1).…”

“…Conversely, inhibition of their function through the administration of antibodies against them or against their receptors normally leads to inhibition of the regeneration process and also abnormal regeneration of the fibers (Table 2 and references inside). Several cocktails of these molecules have been designed and incorporated to scaffolds for peripheral nerve regeneration and repair with deceptive up-to-day results ( Table 2; Johnson et al, 2015;Anand et al, 2017;del Valle et al, 2018). Doses of the most relevant neurotrophic factors, which have been tested to improve the molecular environment for the regenerating axons, are shown in Table 3.…”

“…Axonal growth promoters NGF, BDNF, NT3, NT4/5 Boyd and Gordon, 2003;Jin et al, 2009;Li et al, 2020 Transforming growth factors GDNF Allodi et al, 2012;Hoyng et al, 2014;Anand et al, 2017 Insulin-like growth factors IGF1 e IGF2 Di Giulio et al, 2000;Brushart et al, 2013 Fibroblast growth factors FGF2 Allodi et al, 2012;Brushart et al, 2013;Santos et al, 2016b Neuropoietic cytokines PTN, CNTF, IL6, LIF Mi et al, 2007;Gordon, 2014 Molecules integrated into the surrounding nerve tissue…”

“…Axonal growth promoters N-CAM, N-cadherin, L1, integrins, etc. Seilheimer and Schachner, 1988;Smith et al, 1994;Hammarberg et al, 2000;Franz et al, 2005;Saito et al, 2005Saito et al, , 2010Gardiner et al, 2007;Tucker and Mearow, 2008;Gardiner, 2011;Anand et al, 2017 Extracellular matrix molecules fibrinogen, fibronectin, laminin, etc. Politis, 1989;Hammarberg et al, 2000;Zhang et al, 2003;Previtali et al, 2008;Tucker and Mearow, 2008;Webber et al, 2008;Gardiner, 2011;Fudge and Mearow, 2013;Zeng et al, 2014;Santos et al, 2016b Each endoneural tube contains a specific blend of such molecules depending on the type of its axon (i.e., sensory or motor).…”