Axonal plasticity in response to active forces generated through magnetic nanopulling

Abstract

Mechanical force is crucial in guiding axon outgrowth, before and after synapse formation. This process is referred to as stretch-growth. However, how neurons transduce mechanical inputs into signaling pathways remains poorly understood. Another open question is how stretch-growth is coupled in time with the intercalated addition of new mass along the entire axon. Here, we demonstrate that active mechanical force generated by magnetic nano-pulling induces a remodeling of the axonal cytoskeleton. Specifically, the increase in the axonal density of microtubules leads to an accumulation of organelles and signaling vesicles which, in turn, promotes local translation by increasing the probability of assembly of the translation factories. The modulation of axonal transport and local translation sustains enhanced axon outgrowth and synapse maturation.

Low forces push the maturation of neural precursors into neurons

“…In fact, ultrastructural analyses of immature neural processes of stretched NES cells showed an increase in the linear density of MTs, in the number of tubular ER, and the number of mitochondria. These data are similar findings previously reported for the stretched axons of mouse hippocampal primary neurons (de Vincentiis et al, 2020; Falconieri et al, 2021; Falconieri Alessandro et al, 2022)…”

“…This analogy across different stages of neural development raises the question as to how mechanical stimuli represent a well-conserved mechanism to shape the formation of the CNS during development. The observations collected in different models (de Vincentiis et al, 2020; Falconieri Alessandro et al, 2022; V. Raffa et al, 2018) and with different stretching modalities (de Vincentiis et al, 2020; Falconieri et al, 2021) consistently indicate the importance of MTs as a node in signal transduction.…”

“…Although the picture is not yet complete, a crucial point arising from current and previous studies (de Vincentiis et al, 2020; Falconieri et al, 2021; Falconieri Alessandro et al, 2022; V. Raffa et al, 2018) is that mechanical stimulation is a well-conserved mechanism that induces a local remodeling in the neural process cytoskeleton.…”

“…Magnetic nano-pulling allows the in vitro chronic stimulation of cells with extremely low forces (<1 nN) and continuous load application for days or weeks, mimicking in vivo developmental conditions. This process is named stretch growth (SG) (Pfister et al, 2004) and is accompanied by the addition of new mass and axonal cytoskeleton remodeling (de Vincentiis et al, 2020; Falconieri Alessandro et al, 2022). In developing neurons, nano-pulling is associated with axonal elongation, sprouting, and neuron maturation (de Vincentiis et al, 2020; Falconieri et al, 2021; Falconieri Alessandro et al, 2022; Pita-Thomas et al, 2015; Steketee et al, 2011; Wang et al, 2020).…”

“…This process is named stretch growth (SG) (Pfister et al, 2004) and is accompanied by the addition of new mass and axonal cytoskeleton remodeling (de Vincentiis et al, 2020; Falconieri Alessandro et al, 2022). In developing neurons, nano-pulling is associated with axonal elongation, sprouting, and neuron maturation (de Vincentiis et al, 2020; Falconieri et al, 2021; Falconieri Alessandro et al, 2022; Pita-Thomas et al, 2015; Steketee et al, 2011; Wang et al, 2020). This suggests that SG may also influence neurogenesis.…”