Nano-pulling stimulates axon regeneration in dorsal root ganglia by inducing stabilization of axonal microtubules and activation of local translation

Axonal plasticity is a phenomenon strongly related to neuronal development as well as regeneration. Recently, it has been demonstrated that active mechanical tension, intended as an extrinsic factor, is a valid contribution to the modulation of axonal plasticity. In previous publications, our team validated a method, the "nano-pulling", for applying mechanical forces on developing axons of isolated primary neurons using magnetic nanoparticles (MNP) actuated by static magnetic fields. This method was found to promote axon growth and synaptic maturation. Here, we explore the possibility to use nano-pulling as an extrinsic factor to promote axon regeneration in a neuronal tissue explant. Having this in mind, whole dorsal root ganglia (DRG) have been dissected from mouse spinal cord, incubated with MNPs, and then stretched. We found that particles were able to penetrate the ganglion and to localise both into the somas and in sprouting axons. Our results point that the nano-pulling doubles the regeneration rate, documented by an increase in the arborizing capacity of axons, and an accumulation of cellular organelles related to mass addition (endoplasmic reticulum and mitochondria) with respect to spontaneous regeneration. In line with the previous results on isolated hippocampal neurons, we observed an increase in the density of stable microtubules and activation of local translation in stretched ganglions. The collected data demonstrate that the nano-pulling is able to enhance axon regeneration in whole spinal ganglia exposed to MNPs and external magnetic fields. The preliminary data represent an encouraging starting point for proposing the nano-pulling as biophysical tool to design novel therapies based on the use of force as an extrinsic factor for promoting nerve regeneration.