We evaluated the effect of miRNAs on inflammatory factors, including IL-1β, IL-6, TNF-α, and hs-CRP, in developing MS. Analysis of miRNA dysfunction and changes in inflammatory factors can help better understand the cause of MS and new alternative methods of diagnosing and treating the disease. This study found that the association between IL-1β, IL-6, TNF-α, and hs-CRP and miRNAs that are involved in developing MS. We selected several miRNAs to investigate their association with inflammatory factors: miRNA-21, miRNA-155, miRNA-182, and miRNA-437. We examined the levels of IL-1β, IL-6, TNF-α, hs-CRP, and miRNAs in the cerebrospinal fluid of MS patients and healthy individuals.
Studies have examined the expression of miRNAs in cell-free cerebrospinal fluid [28–30], a biological fluid reflecting events in the central nervous system. However, no study has examined the association with active multiple sclerosis lesions. The differential miRNA expression in CSF from MS patients is a valuable indication of CNS inflammation. One study discovered miRNAs in the CSF and serum of dogs having neurological disorders. It was found that microRNA-21 levels in the CSF of dogs with MUO were higher than in dogs with OND and normal CSF NCC . Fenoglio et al. discovered that miRNA-21 was overrepresented in the PBMCs of patients with recurrent MS compared to control subjects. They hypothesized that this increase occurs entirely in the acute phase of MS and provides to producing and controlling CD4+ T cells involved in the inflammatory processes affecting the central nervous system associated with MS [32, 33]. miRNA-21 is involved in T cell activation and death, Treg cell activity and growth, and Th17 cell differentiation . miRNA-155 is an essential regulator of inflammation and contributes to the modulation of the autoimmune response in MS. miRNA-155 is involved in Blood-Brain Barrier (BBB) breakdown under inflammatory conditions by downregulating critical junctional proteins . Additionally, one study found that MS patients had higher expression of miRNA-182-5p than the control group . Another study found that individuals with depression had increased miRNA-182-5p expression in blood . These results confirm our observations.
Changes in miRNAs in CSF reflect changes in miRNAs in diseased brain tissue more accurately than changes in blood or postmortem brain samples . This event can be explained by one of 2 different mechanisms: (1) Due to the inherent difficulties in sampling brain tissue in vivo, miRNA expression in human research is predominantly studied using postmortem samples. However, prolonged postmortem delay and previous drug use affect the study of postmortem brain tissue;(2) Peripheral blood cannot accurately represent the gene expression level in the brain. Because the brain is closely related to the CSF, CSF markers allow the discovery of new CNS biomarkers. Wan et al. identified several miRNAs in cerebrospinal fluid (CSF) from patients with MDD [39, 40]. Results showed that the relationship between inflammatory cytokines and miRNA-21, miRNA-155, and miRNA-182 was statistically significant. Still, between miRNA-182 and TNF-α between case and control patients, there was a direct and moderate correlation. There was an indirect and moderate correlation between miRNA-437 and hs-CRP, which were also statistically significant. MiRNA-155 is an essential regulator of inflammation and contributes to the modulation of the autoimmune response in MS. Emerging evidence suggests that neuropathic pain is a neuro-immune dysfunction associated with increased immune system activity. miRNA-155 has a well-characterized effect on inflammatory variables associated with neuropathic pain, including interleukin-1, interleukin-6, TNF-, NF-B, and p38 mitogen-activated protein kinase (MAPK) [41–43]. The miRNA-155 expression has been increased in the prefrontal cortex of rats suffering from inflammatory pain . MicroRNAs affect the differentiation and function of inflammatory cells. MiRNA-182 is a transcription factor that regulates FOXO1 expression in T cells and influences cell differentiation and activation. Additionally, miRNA-21 promotes T cell progression to Th1, IFN production, and Foxp3 expression. In astrocyte cells, miRNA-155 controls the production of pro-inflammatory genes . In our study, an increase in miRNA-155 was associated with an increase in inflammatory variables. Further results revealed a statistical relationship between pro-inflammatory cytokines and miRNA-182 and miRNA-437. Our results suggest that these microRNAs could be used as therapeutic targets in the future.
Many studies have shown that miRNA-21 plays a critical role in terminating inflammation and negatively limits the pro-inflammatory response elicited by many of the same triggers that increase miRNA-21. In macrophages, miRNA-21 is a critical modulator of the anti-inflammatory response . In individuals with Gd+ MS, a steady increase in miRNA-21 was observed over time. There was a positive correlation between this increase and the frequency of Gd+ lesions and neurofilament light chain (NF-L) concentration . However, Yang et al . demonstrated that mice lacking miRNA-21 had worse survival rates, more severe cardiac dysfunction, and more extensive infarct and scar regions after myocardial infarction) (MI) compared with WT mice. MiRNA-21 knockout mice had higher levels of pro-inflammatory cytokines such as IL-1, IL-6, and TNF–in cardiac tissue and increased infiltration of CD11b+ monocytes/macrophages with pro-inflammatory cytokine production. In our study, miRNA-21 expression was increased in the CSF of MS patients. This increase in expression increased the level of inflammatory factors. Comparison of the results of our study with other studies showed that changes in miRNA-21 expression are different in different tissues and diseases.
The results of ROC analysis show that the highest area under the curve was obtained for miRNA-21 (97), miRNA-182 (97), miRNA-155 (96), and miRNA-437(66). Based on the high values under the curve, it can be concluded that biomarkers have excellent performance in distinguishing people with MS from people without MS. They can be used to follow the healing process . Which miRNAs were associated with the highest rate of correct MS diagnoses compared with misdiagnoses? MiRNA-155 in CSF was associated with the highest percentage of accurate MS diagnoses compared with misdiagnoses.