In the present study, 47 DEmiRNAs and 38 FRGs were identified in SCI. These FRGs were found to be related to the response to lipids, inflammation, and some signal transduction pathways. Subsequently, the top five hub FRGs—PPARG, IL-1β, PTGS2, IFNG, and MAPK3—were screened out. Target relationships between DEmiRNAs and the five hub FRGs were predicted. And then ceRNA network and TF-miRNA-mRNA network were constructed through ENCORI dataset and TransmiR v2.0 database, respectively. Moreover, potential drugs that could target the top five hub FRGs were predicted using DGIdb. Finally,combined with the prediction results, miR-326 and its target gene IL-1β were selected and validated in rat SCI model via RT-qPCR testing. Our verification demonstrated that the expression levels of miR-326 and IL-1β were consistent with the results of our bioinformatics analysis. Our findings may contribute to further studies exploring the mechanisms of ferroptosis after SCI, as well as provide novel diagnostic and therapeutic targets for SCI.
Ferroptosis is a form of nonapoptotic cell death, which was first reported by Dixon et al. in 2012 [10]. Subsequent studies have reported that this mode of cell death occurs in SCI [13, 16, 30]. The latest view of the mechanism of ferroptosis in SCI proposed that the accumulation of iron occurs as the first step [12]. Excessive iron in cells will induce mitochondrial damage and reactive oxygen species (ROS) production via the Fenton reaction [31, 32]. In addition, ferrous iron has high reactivity and increases the cytotoxicity of ROS. The primary role of ROS is to cause oxidative damage to biofilms by targeting polyunsaturated fatty acids [12]. Large amounts of ROS will trigger lipid peroxidation that damages the plasma membrane and leads to ferroptosis [33]. Moreover, the critical role of the inflammatory response in a secondary injury caused by SCI has been widely considered and demonstrated [34, 35]. Interestingly, ferroptosis has been linked to inflammation and immunity [36]. It was reported that inhibiting ferroptosis helps reduce the toxicity of inflammation and enhances neuronal survival after SCI [37]. The results of GO enrichment analysis in the present study were consistent with the current understanding of the biological processes of ferroptosis. However, there have been few reports of the pathways associated with ferroptosis in SCI. A recent study showed that the HIF-1 signaling pathway might play a central role in ferroptosis after SCI [38]. In our study, along with the HIF-1 signaling pathway, we also found other important pathways to be enriched, including the IL-7, TNF, and NOD-like receptor signaling pathways. This suggests that these pathways may be involved in ferroptosis after SCI, though the reports to date are rare. Further studies are needed to improve our understanding of the roles of these pathways in the pathophysiological process of SCI.
Among the five hub genes, IL-1β is an important inflammatory cytokine, and it is also a critical driver of ferroptosis [19]. It has been reported that IL-1β was significantly up-regulated [39] and had a deleterious effect on the plasticity of CNS axons after SCI [40]. Another study demonstrated that IL-1β inhibits the recovery of SCI by inducing NF-κB and up-regulating microRNA-372 expression [41]. On the contrary, down-regulating IL-1β will reduce secondary injury after SCI, protect neurons, and improve the prognosis [39, 42]. Research has proven that the molecular mechanism of down-regulating IL-1β can significantly reduce the expression of TNF-α, Bax, and caspase-3, and increase the expression of Bcl-2 [39]. Furthermore, IL-1β was reported to be involved in the pathogenesis of neuropathic pain [43], and it can be used as a molecular biomarker for the degree of such pain [44]. Given the strong link between ferroptosis and inflammation, scholars are interested in determining whether abnormal expression of IL-1β is associated with ferroptosis. An in vitro experiment demonstrated that up-regulating IL-1β expression induced ferroptosis in an osteoarthritis model [45]. However, there are not yet reports on whether this positive relationship between IL-1β and ferroptosis also exists in SCI. The results of our bioinformatics analysis showed that IL-1β was up-regulated in ferroptosis induced by SCI. We then verified the expression levels of IL-1β in vitro, and the results were consistent with the bioinformatics analysis. This indicates that IL-1β may be a core gene related to ferroptosis after SCI. What’s more, we predicted the target relationship between DEmiRNAs and ferroptosis-related DEmRNAs, thereby making a preliminary identification of miRNA-326 as the sponge gene of IL-1β.
MicroRNAs (miRNAs) are small non-coding RNAs widely involved in and influencing cellular and physiological functions in all multicellular organisms [46]. It has been revealed that miRNAs may perform their biological functions by directly interacting with target mRNAs [47]. It was reported that miR-326 was down-regulated and targeted TNFSF14 to promote pulmonary inflammation in the fibrotic lung tissues of silica-treated mice [48]. miR-326 was also discovered to inhibit the neddylation process and alleviate inflammatory bowel disease by targeting NEDD8 [49]. Recently, various reports have shown that the down-regulation of miR-326 promotes lung cellular inflammatory damage induced by lipopolysaccharide [50, 51]. The latest study reported that miR-326 expression was down-regulated in sevofluraneinduced human hippocampal neuron injury and promoted neuronal inflammation and apoptosis [52]. Furthermore, some scholars have found miRNA-326 to be highly expressed in multiple sclerosis patients[2, 53]. However, the expression of miR-326 in ferroptosis induced by SCI, and its specific functions in that scenario, remain unclear. In the present study, we verified the miRNA-326 expression level in vitro using an RT-qPCR assay and found the result was consistent with our prediction and most previous findings. Additionally, our study revealed that the target regulatory relationship of miR-326–IL-1β may be among the molecular mechanisms of ferroptosis induced by SCI.
However, this study had certain limitations that must be addressed in future research. First, only one human dataset was found to be available for biological analysis, whereas future research should seek to use multiple sequencing data. Second, certain clinical data were lacking due to the difficulty of obtaining blood samples from patients with acute SCI. Furthermore, it has been reported that gene expression varies at different time points after SCI [54], a variable that was not accounted for in this research design. Therefore, clinical studies with large samples and multiple time points are needed in the future. Third, only the miR-326–IL-1β expression levels were detected by RT-qPCR in our study, meaning further research is required to verify the specific mechanism of ferroptosis induced by SCI.
In sum, we investigated the expression of ferroptosis-related genes after SCI, analyzed the biological processes and signaling pathways of ferroptosis-related genes, and predicted the regulatory relationship between DEmiRNA and key genes. Our study revealed that the target regulatory relationship of miR-326–IL-1β may be among the molecular mechanisms of ferroptosis after SCI. Our results provide a basis for further investigation of those molecular mechanisms. In addition, our research also provides novel diagnostic and therapeutic targets for SCI, though a range of molecular experiments is needed to validate our findings in the future.