NeuroD1-Mediated Astrocyte-to-Neuron Reprogramming for Spinal Cord Injuries

Abstract

Spinal cord injuries impact over 17,000 Americans yearly, often resulting in drastic symptoms, including loss of movement, loss/alteration of sensation, and intense pain. In the process of injury, Central Nervous System (CNS) neurons, which have limited regenerative capabilities after trauma, maintain damage. As of now, clinical treatment of these injuries focuses on rehabilitation, such as physical therapy. Success has been found with the transplantation of human embryonic pluripotent stem cells, but the ethical boundaries present as a barrier that would likely prevent this treatment from becoming widely available. Previous studies have shown cell reprogramming to be a potential treatment for SCIs. Astrocyte-to-neuron conversion can be promoted by overexpression of certain neuronal transcription factors, including NeuroD1. Astrocytes are common CNS glial cells that are known to proliferate upon injury and are proximal in lineage to neurons, making them a good target for neuronal conversion. An adeno-associated virus (AAV9) containing inverted NeuroD1 and fluorescent protein mRuby2 was injected into the spinal cord either immediately after the contusion (T1) or one-week post-contusion (T2) when reactive astrocytes are thought to be at the highest density. The control, AAV9 without NeuroD1, followed the same timeline. Histological analysis was completed in order to visualize the cell localization within the spinal cord sections 6 weeks post-injury. GFAP was used to tag astrocytes and NeuN was used for neurons. mRuby2 fluorescence is indicative of successful viral entry. Successful reprogramming would be demonstrated by similar localization of mRuby2 and neuron markers. While this localization is not perfectly indicative of reprogramming, it would provide preliminary support to these methods being effective in vivo.