Low-Intensity Pulsed Ultrasound Enhanced Neurite Guidance Growth through Netrin-1/DCC Signal Pathway in Primary Cultured Cortical Neurons of Rats

Low-intensity pulsed ultrasound is found to be effective in axonal regeneration, while the role of ultrasound in axonal growth guidance is still unclear. This study was performed to explore the neuroprotective role of low-intensity pulsed ultrasound (US) both in vitro and in vivo. Primary cultured rat cortical neurons were subjected to 1.0 MHz ultrasound for 5 min every day at intensity of 0, 0.008, 0.12, and 0.21 W/cm². Our results demonstrated that low-intensity pulsed ultrasound significantly increased neuronal cell viability and inhibited neuronal apoptosis in vitro as determined by fluorescein diacetate assay (FDA) and a TdT-mediated biotin-dUTP nicked-end labeling (TUNEL) assay. Moreover, low-intensity pulsed ultrasound at 0.12 W/cm² significantly enhanced the axonal growth guidance by activation of netrin-1 and DCC (deleted in colorectal carcinoma) expression as determined by Western blots assay. More interestingly, we further found that low-intensity pulsed ultrasound treatment at 0.21 W/cm² promoted the functional restoration of rat injured nerves in vivo, decreased hemorrhage, and reversed the injury process by activating positive netrin-1 expression as seen in the immunohistochemistry (IHC) assay. Thus, our study strongly demonstrated that low-intensity pulsed ultrasound activated netrin-1/DCC signaling and further mediated neurite outgrowth. It would be a new approach to nerve regeneration in the future.

Magnetic Force-Driven Graphene Patterns to Direct Synaptogenesis of Human Neuronal Cells

Precise control of axonal growth and synaptic junction formation are incredibly important to repair and/or to mimic human neuronal network. Here, we report a graphene oxide (GO)-based hybrid patterns that were proven to be excellent for guiding axonal growth and its consequent synapse formation of human neural cells. Unlike the previous method that utilized micro-contacting printing technique to generate GO patterns, here, GO-encapsulated magnetic nanoparticles were first synthesized and utilized as core materials wherein the external magnetic force facilitated the transfer of GO film to the desired substrate. Owing to the intrinsic property of GO that provides stable cell attachment and growth for long-term culture, human neuronal cells could be effectively patterned on the biocompatible polymer substrates with different pattern sizes. By using magnetic force-driven GO hybrid patterns, we demonstrated that accumulation and expression level of Synaptophysin of neurons could be effectively controlled with varying sizes of each pattern. The synaptic network between each neuron could be precisely controlled and matched by guiding axonal direction. This work provides treatment and modeling of brain diseases and spinal cord injuries.