Elsevier

The Spine Journal

Volume 14, Issue 2, 1 February 2014, Pages 353-360
The Spine Journal

Basic Science
Spatial and temporal expression levels of specific microRNAs in a spinal cord injury mouse model and their relationship to the duration of compression

https://doi.org/10.1016/j.spinee.2013.08.015Get rights and content

Abstract

Background context

MicroRNAs, a class of small nonprotein-coding RNAs, are thought to control gene translation into proteins. The latter are the ultimate effectors of the biochemical cascade occurring in any physiological and pathological process. MicroRNAs have been shown to change their expression levels during injury of spinal cord in contusion rodent models. Compression is the most frequent mode of damage of neural elements in spinal cord injury. The cellular and molecular changes occurring in the spinal cord during prolonged compression are not very well elucidated. Understanding the underlying molecular events that occur during sustained compression is paramount in building new therapeutic strategies.

Purpose

The purpose of our study was to probe the relationship between the expression level changes of different miRNAs and the timing of spinal cord decompression in a mouse model.

Study design

A compression spinal cord injury mouse model was used for the study.

Methods

A laminectomy was performed in the thoracic spine of C57BL/6 mice. Then, the thecal sac was compressed to create the injury. Decompression was performed early for one group and it was delayed in the second group. The spinal cord at the epicenter of the injury and one level rostral to it were removed at 3, 6, and 24 hours after trauma, and RNA was extracted. Expression levels of six different microRNAs and the relationship to the duration of compression were analyzed. This work was supported in part by the University Research Council Grants Program at the University of Texas Health Science Center San Antonio (Grant 130267). There are no specific conflicts of interest to be disclosed for this work.

Results

Expression levels of microRNAs in the prolonged compression of spinal cord model were significantly different compared with the expression levels in the short duration of compression spinal cord injury model. Furthermore, microRNAs show a different expression pattern in different regions of the injured spinal cord.

Conclusions

Our findings demonstrate that spinal cord compression causes alterations in the expression of different miRNAs in the acute phase of injury. Their expression is related to the duration of the compression of the spinal cord. These findings suggest that early decompression of the spinal cord may have an important modulating effect on the molecular cascade triggered during secondary injury through the changes in expression levels of specific microRNAs.

Introduction

Spinal cord injury (SCI) affects approximately 12,000 individuals every year and causes devastating life-long disability as the result of poor neurologic recovery [1], [2]. The primary mechanical insult to the spinal cord initiates a deleterious cascade of events, leading to secondary injury including ischemia, edema, inflammation, and cellular necrosis [3], [4], [5], [6], which causes additional damage to neural elements by activating destructive pathophysiologic and pathobiochemical cascades [7], [8]. Compression is the most frequent mode of damage in traumatic SCI [9]. It has been shown that persistent compression of spinal cord causes potentially reversible processes of secondary injury [10], [11], [12]. Because the cellular and molecular mechanisms underlying secondary spinal cord injury are still not completely understood, the current treatments in the acute phase of compressive SCI are limited, with surgical decompression being the main stream of therapy. Although studies in animals have shown that early decompression, and as such shorter compression time, improves functional recovery, studies in humans have not been as successful [9], [10], [11]. Understanding the underlying molecular events that occur during prolonged compression is paramount in building new therapeutic strategies that can promote neurologic recovery [13], [14], [15], [16]. Several studies have demonstrated that duration of compression of spinal cord is directly correlated with significant physiological, histologic, and genetic alterations at a cellular level [8], [9], [14], [15]. After SCI, there is a down-regulation of genes related to synapses, cytoskeletal rearrangement, and neurotransmission, whereas genes involved in inflammation, ischemia, cell death, angiogenesis, and neurigenesis are up-regulated [15], [17].

MicroRNAs (miRNAs) are a class of small, nonprotein-coding RNA molecules [18], [19]. They modulate translation of specific genes, allowing them to fine-tune protein expression and thus regulate different physiologic and pathologic cellular processes [20], [21], [22], [23], [24], [25], [26]. Because the expression of many different gene products can be regulated by an individual miRNA, they are attractive candidates for effective interventions aimed to suppress pathophysiologic cellular responses to injury and environmental changes [27], [28]. It has been recently shown that miRNAs expression is altered in an SCI model [29], [30]. Furthermore, it has been shown that some miRNAs may play a role in the pathologic processes of secondary injury to the spinal cord [31], [32]. The majority of these studies have been performed on contusion models of SCI, which involve a single moment mechanical impact injury to the spinal cord. Hence, it is largely unknown whether the expression of miRNAs is altered with prolonged compression of the spinal cord. Furthermore, it is unknown whether miRNA expression is related to the duration of compression of spinal cord.

The goal of our study was to probe the relationship between the expression of six specific miRNAs and the timing of spinal cord decompression in a mouse model. Specifically we analyzed the changes in expression patterns of miR-29b, miR-30, miR-107, miR-148, miR-137, and miR-210 as related to the duration of spinal cord compression in an SCI mouse model. Furthermore we studied the expression changes of these specific miRNAs across two different spinal cord regions: at the injury level and rostral to the injury site.

Section snippets

SCI model

All work on animals was carried out at the animal facility of the University of Texas Health Science Center in San Antonio after being approved by the Animal Care and Use Committee at the UTHSCSA and complied with the National Institute of Health principles of laboratory animal care (NIH publication No. 80–23).

C57BL/6 male mice of 28 to 30 g of weight were used for these experiments. The surgical procedure was performed with animals under general anesthesia. Anesthesia was induced with a

Results

We evaluated expression patterns of six different miRNAs in a compressive spinal cord injury mouse model. It is known that the vascular injury plays an important role in SCI. Hence the majority of the miRNAs chosen for our study have been shown to change their expression levels in neuron and astrocytes placed in ischemic conditions [46]. To determine whether the length of compression influences the expression pattern of miRNAs we used two mouse models and compared the time-dependent expression

Discussion

The degree of neurologic disability after spinal cord trauma primarily depends on the extent of neural element loss and the remaining function of the residual neural tissue. Hence, it is important to reduce the loss of neurons induced by the secondary damage that occurs after the primary mechanical injury to the spine. Neurons and other cells in the central nervous system respond to injury by altering their gene and protein expression patterns and activating several molecular pathways that

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    Author disclosures: MZ: Nothing to disclose. LF: Nothing to disclose. JGS: Nothing to disclose. DFJ: Nothing to disclose. MD: Nothing to disclose. VB: Nothing to disclose.

    This work was supported in part by the University Research Council Grants Program at the University of Texas Health Science Center San Antonio (Grant 130267) and by the Department of Neurosurgery at the University of Texas Health Science Center at San Antonio, San Antonio, Texas. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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