Régénération des nerfs
Chaque année au Canada, plus de 25 000 personnes sont victimes d'accidents ou de maladies qui endommagent le système cérébrovasculaire et 1 000 autres subissent des lésions à la moelle épinière. La capacité de régénération du corps adulte est limitée. (Les os et les nerfs des enfants, par contre, ont plus de plasticité jusqu’à l’âge de 18 ans environ.) Bon nombre de tissus adultes réagissent mal aux lésions traumatiques. Le système nerveux est particulièrement vulnérable, car il n’est pas en mesure de rétablir les connexions qui contrôlent les fonctions du corps humain. Mais des chercheurs de l'École Polytechnique de Montréal poursuivent l’une des plus ardentes quêtes de la médecine : la réparation et la régénération des tissus, des neurones et des fonctions perturbés par des lésions traumatiques.
L'ingénierie tissulaire recouvre l'ensemble des techniques qui allient la biologie cellulaire et moléculaire avec l'ingénierie mécanique, chimique et des matériaux dans le but de créer ou de reconstituer un tissu. Afin de régénérer un nerf périphérique sectionné, l'utilisation d'une prothèse tubulaire, appelée guide de régénérescence nerveuse, reliée aux deux extrémités du nerf lésé et capable d'interagir avec le tissu.
It is known that injured neurons in the central nervous system (CNS) do not regenerate, but it is not clear why. Adult CNS neurons may lack an intrinsic capacity for rapid regeneration, and CNS glia create an inhibitory environment for growth after injury (http://www.sciencedaily.com/releases/2007/05/070520091842.htm).
Peripheral nerve injury, which affects 2.8% of all trauma patients, results quite often in lifelong disability. Since peripheral nerves relay signals between the brain and the rest of the body, injury to these nerves results in loss of sensory and motor function. Upper extremity paralysis alone affects more than 300,000 individuals annually in the US. The most serious form of peripheral nerve injury is complete severance of the nerve.
The severed nerve can regenerate; the nerve fibers from the nerve end closest to the spinal cord have to grow across the injury gap, enter the other nerve segment and then work their way through to their end targets (skin, muscle, etc). Usually, when the gap between the severed nerve endings is larger than a few millimeters, the nerve does not regenerate on its own. If left untreated, the end result is permanent sensory and motor paralysis. A few hundred thousand people suffer from this debilitating condition annually in the US.
Currently, the most successful form of treatment is to take a section of healthy nerve (autograft) from another part of the patient's body to bridge the damaged one. This autograft then serves as a guide for nerve fibers to cross the injury gap. Although successful, this autograft procedure has major drawbacks including loss of function at the donor site, multiple surgeries and, quite often, it's just not possible to find a suitable nerve to use as a graft. Various synthetic nerve grafts are currently available but none work better than the autograft and can't bridge gaps larger than 4 centimeters.
Researchers at the Laboratory for Innovation & Bioperformance (LIAB) of the Ecole Polytechnique of Montreal, Quebec (Canada) are developing a technology that has the potential to serve as a better alternative than currently available synthetic nerve grafts. The graft material is composed entirely of biocompatible and biodegradable carbon nanotube-based fibers . These fibers act as physical guides for regenerating nerve fibers. They are also developed a way to make these nanotube-based fibers bioactive by attaching various biochemicals directly onto the surfaces of the nanofibers. Thus, the bioactive nanofiber technology mimics the nerve autograft by providing both physical and biochemical cues to enhance and direct nerve growth.
This technology is now patented by the LIAB researchers (http://www.faqs.org/patents/app/20090169594)
Another ongoing project at the LIAB of the Ecole Polytechnique of Montreal is using superparamagnetic nanoparticles and MRI magnetic fields for addressing the challenges associated with regeneration for Central Nervous System Axon after injury. By providing mechanical tension to the regrowing axon, it is possible to enhance the regenerative axon growth in vivo. This mechanically induced neurite outgrowth may provide a possible method for bypassing the inhibitory interface and the tissue beyond a CNS related injury.
Using vivo and in vitro models, LIAB's researchers are currently investigating how these superparamagnetic nanoparticles (SPMNPs) can be incorporated into neurons and axons at the site of injury. SPMNPs could open the frontiers for new therapies based on the exploitation of the mechanical forces acting on SPMNP-bound neurons to promote axonal elongation/growth.