Abstract
Spinal cord edema, mainly including vasogenic and cytotoxic edema, influences neurological outcome after spinal cord contusion (SCC). Aquaporin 4 (AQP4) is the most ubiquitous water channel in the central nervous system (CNS), which is a rate-limiting factor in vasogenic edema expressing in brain injury, and it contributes to the formation of cytotoxic edema locating in astrocytes. However, little is known about the regulatory mechanism of AQP4 within vasogenic and cytotoxic edema in SCC, and whether the regulation mechanism of AQP4 is related to Cytochrome coxidase (COX5A) affecting energy metabolism. Therefore, the SCC model is established by Allen’s method, and the degree of edema and neuronal area is measured. The motor function of rats is evaluated by the Basso, Beattie, and Bresnahan (BBB) scoring system. Meanwhile, AQP4 and COX5A are detected by real-time quantitative PCR (qRT-PCR) and western blot (WB). The localization of targeted protein is exhibited by immunohistochemical staining (IHC) and immunofluorescence (IF). Additionally, the methodology of AQP4 lentivirus-mediated RNA interference (AQP4-RNAi) is used to reveal the effect on edema of SCC and the regulating molecular mechanism. Firstly, we observe that the tissue water content increases after SCC and decreases after the peak value of tissue water content at 3 days (P < 0.05) with abundant expression of AQP4 protein locating around vascular endothelial cells (VECs), which suggests that the increasing AQP4 promotes water reabsorption and improves vasogenic edema in the early stage of SCC. However, the neuronal area is larger than in the sham group in the 7 days (P < 0.05) with the total water content of spinal cord decrease. Meanwhile, AQP4 migrates from VECs to neuronal cytomembrane, which indicates that AQP4 plays a crucial role in aggravating the formation and development of cytotoxic edema in the middle stages of SCC. Secondly, AQP4-RNAi is used to elucidate the mechanism of AQP4 to edema of SCC. The neuronal area shrinks and the area of cytotoxic edema reduces after AQP4 downregulation. The BBB scores are significantly higher than in the vector group after AQP4-RNAi at 5, 7, and 14 (P < 0.05). There is a relationship between AQP4 and COX5A shown by bioinformatics analysis. After AQP4 inhibition, the expression of COX5A is significantly upregulated in the swelling astrocytes. Therefore, the inhibition of AQP4 expression reduces cytotoxic edema in SCC and improves motor function, which may be associated with upregulation of COX5A via affecting energy metabolism. Moreover, it is not clear how the inhibition of AQP4 directly causes the upregulation of COX5A.
Highlights
Spinal cord injury (SCI) is currently an irreversible pathological condition that is characterized by devastating loss of functions in motor and sensory abilities of victims for life (Trgovcevic et al, 2014; Ahuja et al, 2017)
Identification of Oligonucleotide Sequences for Lentivirus-Mediated Aquaporin 4 (AQP4) Inhibition In order to elucidate the mechanism of AQP4 in rats with spinal cord contusion (SCC), we constructed the recombinant of AQP4
Immunofluorescent staining showed that the expression of AQP4 was labeled by red fluorescent protein (RFP) in cells, which suggested that the AQP4-RNA interference (RNAi)-LV had been successfully transfected into the host cells in vitro (Figure 3C)
Summary
Spinal cord injury (SCI) is currently an irreversible pathological condition that is characterized by devastating loss of functions in motor and sensory abilities of victims for life (Trgovcevic et al, 2014; Ahuja et al, 2017). The initial symptom is usually a series of secondary injuries characteristic of inflammation, apoptosis and edema in the cell These secondary injuries result in consequential motor and sensory dysfunctions after SCI (Fujii et al, 1993; Flanders et al, 1999; McDonald and Sadowsky, 2002; Liu and Xu, 2012; Zhang et al, 2015). One of the consequences of spinal cord contusion (SCC) has been found to induce the expression of various genes relating to edema and inflammation, including Aquaporin 4 (AQP4) and cytokines (Schwab et al, 1998; Yuan et al, 2000; Schubert et al, 2008), and evidence shows that cellular water entry during cytotoxic edema is mediated by AQP4 channels in astroglial cells in traumatic brain injury (TBI) (Benfenati et al, 2011; Thrane et al, 2011; Hsu et al, 2015; Sturdivant et al, 2016)
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