Ultrasound Stimulation Increases Neurite Regeneration in Injured Dorsal Root Ganglion Neurons through Mammalian Target of Rapamycin Activation

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

Introduction

Axonal plasticity is strongly related to neuronal development as well as regeneration. It was recently demonstrated that active mechanical tension, intended as an extrinsic factor, is a valid contribution to the modulation of axonal plasticity.

Methods

In previous publications, our team validated a the "nano-pulling" method used to apply mechanical forces to 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 use of nano-pulling as an extrinsic factor to promote axon regeneration in a neuronal tissue explant.

Results

Whole dorsal root ganglia (DRG) were thus dissected from a mouse spinal cord, incubated with MNPs, and then stretched. We found that particles were able to penetrate the ganglion and thus become localised both in the somas and in sprouting axons. Our results highlight that nano-pulling doubles the regeneration rate, and this is accompanied by an increase in the arborizing capacity of axons, an accumulation of cellular organelles related to mass addition (endoplasmic reticulum and mitochondria) and pre-synaptic proteins with respect to spontaneous regeneration. In line with the previous results on isolated hippocampal neurons, we observed that this process is coupled to an increase in the density of stable microtubules and activation of local translation.

Discussion

Our data demonstrate that nano-pulling enhances axon regeneration in whole spinal ganglia exposed to MNPs and external magnetic fields. These preliminary data represent an encouraging starting point for proposing nano-pulling as a biophysical tool for the design of novel therapies based on the use of force as an extrinsic factor for promoting nerve regeneration.

Low-intensity pulsed ultrasound enhances neurite growth in serum-starved human neuroblastoma cells

Introduction

Low-intensity pulsed ultrasound (LIPUS) is a recognized tool for promoting nerve regeneration and repair; however, the intracellular mechanisms of LIPUS stimulation remain underexplored.

Method

The present study delves into the effects of varying LIPUS parameters, namely duty cycle, spatial average-temporal average (SATA) intensity, and ultrasound amplitude, on the therapeutic efficacy using SK-N-SH cells cultured in serum-starved conditions. Four distinct LIPUS settings were employed: (A) 50 mW/cm2, 40%, (B) 25 mW/cm2, 10%, (C) 50 mW/cm2, 20%, and (D) 25 mW/cm2, 10%.

Results

Immunochemistry analysis exhibited neurite outgrowth promotion in all LIPUS-treated groups except for Group D. Further, LIPUS treatment was found to successfully promote brain-derived neurotrophic factor (BDNF) expression and enhance the phosphorylation of extracellular signal-regulated kinase (ERK)1/2, protein kinase B (Akt), and mammalian target of rapamycin (mTOR) signaling pathways, as evidenced by western blot analysis.

Discussion

The study suggests that the parameter combination of LIPUS determines the therapeutic efficacy of LIPUS. Future investigations should aim to optimize these parameters for different cell types and settings and delve deeper into the cellular response mechanism to LIPUS treatment. Such advancements may aid in tailoring LIPUS treatment strategies to specific therapeutic needs.

Cavitation-assisted sonothrombolysis by asymmetrical nanostars for accelerated thrombolysis

Sonothrombolysis with recombinant tissue plasminogen activator (rtPA) and microbubbles has been widely studied to enhance thrombolytic potential. Here, we report different sonothrombolysis strategy in nanoparticles using microbubbles cavitation. We found that different particles in shape exhibited different reactivity toward the cavitation, leading to a distinct sonothrombolytic potential. Two different gold nanoparticles in shape were functionalized with the rtPA: rtPA-functionalized gold nanospheres (NPt) and gold nanostars (NSt). NPt could not accelerate the thrombolytic potential with a sole acoustic stimulus. Importantly, NSt enhanced the potential with acoustic stimulus and microbubble-mediated cavitation, while NPt were not reactive to cavitation. Coadministration of NSt and microbubbles resulted in a dramatic reduction of the infarcts in a photothrombotic model and recovery in the cerebral blood flow. Given the synergistic effect and in vivo feasibility of this strategy, cavitation-assisted sonothrombolysis by asymmetrical NSt might be useful for treating acute ischemic stroke.

Photoacoustic Carbon Nanotubes Embedded Silk Scaffolds for Neural Stimulation and Regeneration

Neural interfaces using biocompatible scaffolds provide crucial properties, such as cell adhesion, structural support, and mass transport, for the functional repair of nerve injuries and neurodegenerative diseases. Neural stimulation has also been found to be effective in promoting neural regeneration. This work provides a generalized strategy to integrate photoacoustic (PA) neural stimulation into hydrogel scaffolds using a nanocomposite hydrogel approach. Specifically, polyethylene glycol (PEG)-functionalized carbon nanotubes (CNT), highly efficient photoacoustic agents, are embedded into silk fibroin to form biocompatible and soft photoacoustic materials. We show that these photoacoustic functional scaffolds enable nongenetic activation of neurons with a spatial precision defined by the area of light illumination, promoting neuron regeneration. These CNT/silk scaffolds offered reliable and repeatable photoacoustic neural stimulation, and 94% of photoacoustic-stimulated neurons exhibit a fluorescence change larger than 10% in calcium imaging in the light-illuminated area. The on-demand photoacoustic stimulation increased neurite outgrowth by 1.74-fold in a rat dorsal root ganglion model, when compared to the unstimulated group. We also confirmed that promoted neurite outgrowth by photoacoustic stimulation is associated with an increased concentration of neurotrophic factor (BDNF). As a multifunctional neural scaffold, CNT/silk scaffolds demonstrated nongenetic PA neural stimulation functions and promoted neurite outgrowth, providing an additional method for nonpharmacological neural regeneration.