Neuromuscular Activity Induces Paracrine Signaling and Triggers Axonal Regrowth after Injury in Microfluidic Lab-On-Chip Devices

Abstract

Peripheral nerve injuries, including motor neuron axonal injury, often lead to functional impairments. Current therapies are mostly limited to surgical intervention after lesion, yet these interventions have limited success in restoring functionality. Current activity-based therapies after axonal injuries are based on trial-error approaches in which the details of the underlying cellular and molecular processes are largely unknown. Here we show the effects of the modulation of both neuronal and muscular activity with optogenetic approaches to assess the regenerative capacity of cultured motor neuron (MN) after lesion in a compartmentalized microfluidic-assisted axotomy device. With increased neuronal activity, we observed an increase in the ratio of regrowing axons after injury in our peripheral-injury model. Moreover, increasing muscular activity induces the liberation of leukemia inhibitory factor and glial cell line-derived neurotrophic factor in a paracrine fashion that in turn triggers axonal regrowth of lesioned MN in our 3D hydrogel cultures. The relevance of our findings as well as the novel approaches used in this study could be useful not only after axotomy events but also in diseases affecting MN survival.

Genetic control of neuronal activity enhances axonal growth only on permissive substrates

“…Consistent with previous works [23, 33–35], we showed that increasing neuronal activity on DRG sensory neurons enhanced axonal growth in non-inhibitory in vitro and in vivo peripheral injury models. Additionally, and still accordingly to previous studies [36], we also demonstrated these effects in embryonic cortical cells in vitro, highlighting the presence of similar mechanisms among different neuronal types.…”

“…The design used for microfluidic devices was a modification of a previously published device(Taylor et al, 2005; Sala-Jarque et al, 2020). The resulting device consists in 4 receptacles of 7mm diameter, connected in pairs by a longitudinal compartment (cell body and axonal compartments) which are in turn interconnected by 100 microchannels (10μm x 10μm x 900μm).…”

“…The design used for microfluidic devices were a modification of a previously published device [23,24].…”

Genetic control of neuronal activity enhances axonal growth only on permissive substrates

“…The designs used for microfluidic devices were modifications of previously published devices (Sala-Jarque et al 2020 ; Taylor et al 2005 ). One of the devices consists in 4 reservoirs of 7 mm diameter, connected in pairs by a longitudinal compartment (cell body and axonal compartments) which are in turn interconnected by 100 microchannels (10 μm × 10 μm × 900 μm).…”

A Brief Review of In Vitro Models for Injury and Regeneration in the Peripheral Nervous System

“…Similarly, microfluidic vacuum aspiration followed by introducing air bubbles within the axonal compartment resulted in features linked to acute axonal degeneration, delayed bulb formation, and impairment of axonal mitochondrial transport [ 63 ]. A recent study used these techniques to mimic the role of myotubular contractility on axonal regeneration, where axons from motor neurons co-cultured with myotubes were injured using fluidic aspiration along with bubble introduction [ 64 ].…”