Multiple sclerosis (MS) is a chronic disease with neurodegeneration and inflammation comprising a complex immune mechanism . While there is still insufficient information about its exact underlying genetic factors, many studies showed that transcriptional dysregulation may have a role in MS pathogenesis .
Studies show the imperative regulatory role of long non-coding RNA (lncRNA) in the immune system and pathogenesis of different CNS disorders, including MS . These factors are vital regulators of CNS function and would be used in the diagnosis and treatment of CNS disorders . LncRNAs are described in different autoimmune, neurodegenerative, and oncologic diseases. The wide variations in their expression throughout innate immune response and during immune cell differentiation determine their directive role in immunity . Therefore, we aimed to investigate, for the first time, the serum-relative expression levels of lincR-Ccr2-5′AS and lncRNA THRIL in patients with RRMS and SPMS.
Our results showed that lincR-Ccr2-5′AS was significantly downregulated in MS patients compared to the controls. There is still insufficient data about lincR-Ccr2-5′AS in other autoimmune diseases. However, Hu et al. revealed that lincR-Ccr2-5′AS is expressed in Th2 lineage . It is well-known that Th1 and Th2 lymphocytes and their related cytokines are involved in MS pathogenesis . It was found that the ratio of CD4+CCR3+/CD4+CCR4+ (which represents Th1/Th2 balance) was higher in MS patients , which indicates that there is a shift from Th2 to Th1 in the pathogenesis of MS . Besides, GATA3 “the master regulator of Th2” is the transcription factor for lincR-Ccr2-5′AS in Th2 . It was previously found downregulated in MS patients . Previous studies, which support and explain our findings, showed that downregulation of lincR-Ccr2-5′AS decreases the expression of Ccr1, Ccr3, Ccr2, and Ccr5 genes in Th2 lineage . This affects the enrollment of T lymphocytes and macrophages into the CNS which was believed to be involved in the pathogenesis of MS .
In our study, a higher relative expression level of lincR-Ccr2-5′AS was reported in patients with sensory manifestations. However, patients with motor manifestations (ataxia) had significantly lower expression levels of lincR-Ccr2-5′AS. To explain this finding, Miller et al. showed that the initial presentation of sensory symptoms is correlated with a decreased risk of conversion of the clinically isolated syndrome (CIS) to MS compared to symptoms that influence movement . A related point to consider is that GATA3 “the master regulator of Th2” is the transcription factor for lincR-Ccr2-5′AS in Th2 . Besides, the GATA3 expression level was found low in MS patients . Fernando et al. found that the overexpression of GATA3 could reduce the severity of disease and delay the onset of Experimental Autoimmune Encephalomyelitis: an animal model for MS (EAE), and with GATA3 overexpression, a few mice had ataxia .
We found that the relative expression level of lincR-Ccr2-5′AS was significantly low in patients with EDSS score ≥5 when compared to those with EDSS<5. To explain these results, Khoury et al. showed that the activation of T-lymphocyte is linked to the disease activity in patients with multiple sclerosis .
We found a significant increase in the relative expression level of lincR-Ccr2-5′AS after interferon treatment. This increase could be explained by the “steady-state” of chemokine receptor expression (CCR4) in CD4+T-cell surface during treatment with interferon (IFN), since CCR4 mRNA expression is associated with GATA-3 expression . This confers the effect of interferon with the expression of Th2 chemokine receptors in MS patients toward the normalization .
Taking these points together, we can assume the potential role of lincR-Ccr2-5AS' in the genetic susceptibility to MS and its impact on the clinical presentation and the disease course.
Our results showed that lncRNA THRIL was upregulated among MS patients. Besides, it was significantly upregulated in patients with RRMS compared to those with SPMS (p=0.04). In addition, binary logistic regression showed that THRIL could be a predictor of MS with p-value <0.05, OR = 6.45. In agreement with our results, Eftekharian et al.  detected a significant THRIL upregulation in MS patients. However, they did not find a significant correlation between THRIL expression levels and EDSS. In contrary to our findings, Li et al. showed reduced THRIL expression levels in the acute phase of Kawasaki disease . This contradiction may be attributed to the altered roles of TNF in the pathogenesis of MS and other autoimmune disorders. Besides, it was reported to induce a pro-inflammatory effect in lipopolysaccharide (LPS)-induced osteoarthritis cell injury model .
THRIL was demonstrated to control the expression of the innate immune response genes . THRIL is crucial for TNF-α expression. Obradovic et al. demonstrated the role of TNF-α in MS ; they found that MS patients had a higher concentration of TNF-α in CSF and plasma during relapse and SPMS compared to MS patients during remission. The increased TNF-α expression in SPMS may suppress levels of THRIL by the negative feedback inhibition to regulate TNF-α levels expressed by cells in response to inflammatory stimuli . This negative feedback loop could explain the decreased level of THRIL in our SPMS patients. It is well-known that TNF-α could prompt inflammation, affect the recruitment of the immune cells in tissues, and increase tissue destruction. However, its role in MS needs to be elucidated .
Our data showed the potential role of THRIL as a biomarker for genetic susceptibility to MS. Besides, it could have a role as a prognostic biomarker for the prediction of conversion of RRMS to SPMS.
A higher serum level of THRIL was found in patients with EDSS scores ≤5 when compared to those with EDSS≥5.5. We may attribute the variation of its level among different EDSS groups to the conversion of patients from inflammation to neurodegeneration in a severe state of the disease, which is accompanied by a drop in several inflammatory biomarkers .
In our study, we found a significantly higher expression level of THRIL in patients treated with interferon. This high THRIL level might reflect a continuous subclinical immune activity that interferon could not suppress. Despite the role of TNF in MS pathogenesis, TNF inhibitors worsen the disease condition . On the other hand, TNF antagonisms were shown to cause demyelinating lesions. In general, these findings suggest a diverse TNF role in autoimmunity within CNS .
This study has some limitations; there were deficient data for both long non-coding RNAs in different autoimmune diseases. Another limitation is the small number of MS patients. Thus, further large-scale studies should be applied. Previous study demonstrated long non-coding RNAs in peripheral blood mononuclear cells in MS patients . We have tried to use another type of samples in order to estimate long non-coding RNAs; comparative studies could be then performed. Finally, due to the nature of case-control studies, some recall and selection bias could not be avoided.