Segregation of motor and sensory axons regenerating through bicompartmental tubes by combining extracellular matrix components with neurotrophic factors

Abstract

Segregation of regenerating motor and sensory axons may be a good strategy to improve selective functionality of regenerative interfaces to provide closed-loop commands. Provided that extracellular matrix components and neurotrophic factors exert guidance effects on different neuronal populations, we assessed in vivo the potential of separating sensory and motor axons regenerating in a bicompartmental Y-type tube, with each branch prefilled with an adequate combination of extracellular matrix and neurotrophic factors. The severed rat sciatic nerve was repaired using a bicompartmental tube filled with a collagen matrix enriched with fibronectin (FN) and brain-derived neurotrophic factor (BDNF) encapsulated in poly-lactic co-glycolic acid microspheres (FN + MP.BDNF) in one compartment to preferentially attract motor axons and collagen enriched with laminin (LM) and nerve growth factor (NGF) and neurotrophin-3 (NT-3) in microspheres (LM + MP.NGF/NT-3) in the other compartment for promoting sensory axons regeneration. Control animals were implanted with the same Y-tube with a collagen matrix with microspheres (MP) containing PBS (Col + MP.PBS). By using retrotracer labelling, we found that LM + MP.NGF/NT-3 did not attract higher number of regenerated sensory axons compared with controls, and no differences were observed in sensory functional recovery. However, FN + MP.BDNF guided a higher number of regenerating motor axons compared with controls, improving also motor recovery. A small proportion of sensory axons with large soma size, likely proprioceptive neurons, was also attracted to the FN + MP.BDNF compartment. These results demonstrate that muscular axonal guidance can be modulated in vivo by the addition of fibronectin and BDNF.

Schwann Cell Role in Selectivity of Nerve Regeneration

“…A clear example is BDNF, a trophic factor expressed by denervated sensory SCs [ 57 , 58 ], which has been also described to specifically promote neurite outgrowth of motor neurons in vitro [ 61 , 62 , 63 ]. Although modestly, this factor also selectively enhanced motor regeneration in vivo [ 62 , 63 , 64 ]. Furthermore, the in vitro capabilities of some trophic factors to increase the neurite growth of either sensory or motor neurons are reduced when these factors are tested in vivo [ 62 , 63 , 64 ].…”

“…Although modestly, this factor also selectively enhanced motor regeneration in vivo [ 62 , 63 , 64 ]. Furthermore, the in vitro capabilities of some trophic factors to increase the neurite growth of either sensory or motor neurons are reduced when these factors are tested in vivo [ 62 , 63 , 64 ]. The discrepancies between in vitro and in vivo results when testing the ability of trophic factors to promote axonal growth highlight the limitation of the in vitro studies, in which cells grow in nonphysiological conditions.…”

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.…”

“…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.…”

“…Two main approaches have been used to guide a specific type of neuron to its originally innervating tissue: (1) use of biomaterialsbuilt devices with two separated compartments ("Y-shaped" form scaffolds) to create separate molecular environments and thus achieve a separated regeneration of the sensory and motor neurons (Anand et al, 2017;del Valle et al, 2018) and (2) replacement of the classic single lumen tube by multichanneled scaffolds, each channel resembling the endoneurium (Tran et al, 2014) and creating independent molecular environments with different neurotrophic factors (Chang et al, 2017). 3D printing is boosting the development of novel biomaterial solutions and therapeutic approaches (Dinis et al, 2015;Dixon et al, 2018;Petcu et al, 2018).…”