# MicroRNA-133b Dysregulation in a Mouse Model of Cervical Contusion Injury

## TL;DR

This study explores how microRNA-133b levels change in the spinal cord and brain after a cervical injury in mice, suggesting a longer therapeutic window for treatment.

## Contribution

The study reveals the temporal and spatial dynamics of endogenous miR133b after spinal cord injury in mice.

## Key findings

- Most miR133b changes occurred at the injury site with minimal effects in rostral and caudal regions.
- Acute miR133b changes were specific to the lesion site, with delayed changes in the motor cortex.
- Ipsilateral and contralateral brain hemispheres showed different responses to unilateral spinal injury.

## Abstract

Our previous research studies have demonstrated the role of microRNA133b (miR133b) in healing the contused spinal cord when administered either intranasally or intravenously 24 h following an injury. While our data showed beneficial effects of exogenous miR133b delivered within hours of a spinal cord injury (SCI), the kinetics of endogenous miR133b levels in the contused spinal cord and rostral/caudal segments of the injury were not fully investigated. In this study, we examined the miR133b dysregulation in a mouse model of moderate unilateral contusion injury at the fifth cervical (C5) level. Between 30 min and 7 days post-injury, mice were euthanized and tissues were collected from different areas of the spinal cord, ipsilateral and contralateral prefrontal motor cortices, and off-targets such as lung and spleen. The endogenous level of miR133b was determined by RT-qPCR. We found that after SCI, (a) most changes in miR133b level were restricted to the injured area with very limited alterations in the rostral and caudal parts relative to the injury site, (b) acute changes in the endogenous levels were predominantly specific to the lesion site with delayed miR133b changes in the motor cortex, and (c) ipsilateral and contralateral hemispheres responded differently to unilateral SCI. Our results suggest that the therapeutic window for exogenous miR133b therapy begins earlier than 24 h post-injury and potentially lasts longer than 7 days.