MicroRNAs play important roles in post-transcriptional gene regulation. It is known to regulate many pathways involved in cell proliferation, morphogenesis and differentiation[9]. Saydam et al examined the relationship between different types of miRNAs and meningiomas and found that it altered miRNA levels in different types of meningiomas, with increased expression in some and decreased expression in others. They found an increase in the expression levels of miR-335, miR-98 and miR-181a, and a decrease in the expression levels of miRNA-200a, miRNA-373 and miRNA-575 in different meningioma cases. Moreover, miRNA-200a inhibited meningioma growth during in vitro studies[16]. Zhi et al. Various miRNAs (including miR-106a-5p, miR-219 − 5p, miR-375, miR-197, miR-224 and miR-409 − 3p) are known to be dysregulated in meningioma patients[17].
In previous studies, downregulation of miR-34a-3p in high-grade meningiomas has been reported[18; 19]. miR-34a-3p targets the Bcl-2 gene in HBL-52 cells. It has been suggested that high expression of Bcl-2 may contribute to increased cell proliferation and decreased apoptosis of tumor cells[20]. Overexpression of miR-34a-3p in meningioma inhibits cell proliferation and induces apoptosis. Therefore, it is thought that miR-34a-3p can be used as an anticancer drug in meningiomas[21]. In our study, similar results were obtained which complements previous studies on the miR-34a-3p expression in meningiomas. We found that miR-34a-3p expression was lower in the meningioma patient group compared to the healthy control group (p < 0.001).
miR-145 expression was seen in atypical and anaplastic tumours as crosschecked to benign meningiomas[22]. Moreover, meningioma cells with high miR-145 levels had impaired migratory and invasive potential in vitro and in vivo. PCR-array studies of miR145- overexpressing cells suggested that collagen type V alpha (COL5A1) expression was down regulated as a consequence of miR-145 over expression. Accordingly, COL5A1 expression was significantly upregulated in atypical and anaplastic meningiomas [23].
miR-197 has been extensively studied in the carcinogenesis progression of cancers through a variety of mechanisms, including apoptosis, proliferation, angiogenesis, metastasis, drug resistance and tumor suppressor, and has also been implicated in the prognosis of cancers[24; 25; 26]. El-Gewely et al. found that miR-197 was lowly expressed in meningioma cells, while IGFBP5 was highly expressed[19]. They demonstrated that miR-197 inhibits the pro-apoptotic IGFBP5 gene by binding to conserved binding sites in its 3′UTR[19]. In a study conducted by Zhi et al[27]. in meningiomas, it was found that miR-197 expression was lower than in healthy controls. In our study, meningioma patients showed higher expression of miR-197 than controls (p = 0.003) which is contrary to the study of Zhi et al[17]. The expression of miR-197 in our study may differ from previous studies for reasons such as sample size, study method, gender, race and environmental factors.
miR-375-5p is highly expressed in meningiomas[17]. therewithal, it is thought that miR-375-5p may be an important biomarker in meningioma patients pre- and post-operatively[17]. In our study, miR-375 expression was found to be lower in meningioma patients compared to controls (p = 0.003). We think that our results would be an important milestone for future studies, since no studies of miR-375 related to meningioma have been found in the literature till date.
There is evidence that miR-219-5p, which can individuate meningioma patients from healthy group with high sensitivity, can discriminate pre- and post-operatively from meningioma patients, can help monitor the effect of surgical resection in clinical practice[27]. The widespread use of this miRNA panel is believed to have significant potential as aa conbined diagnostic and monitoring biomarker for meningioma[27; 28]. Similar results were obtained for the miR-219a-5p in our study. It was observed that miR-219a-5p was expressed more in the meningioma patient group than in the healthy control group (p = 0.0012).
In a study investigating miR-224 expression and its relationship with histological grading and postoperative recurrence in patients with meningioma, it was found that IOMM-Lee and CH157 inhibited miR-224 expression in meningioma cells, and that miR-224 inhibition increased apoptosis and suppressed cell proliferation[29]. In addition, this study identified ERG2 as a new target of miR-224 and indicated that the miR-224-ERG2 axis played a critical role in regulating the apoptosis and proliferation of meningioma cells[29]. Considering the grades, miR-224 in grade I was found to be lower and therefore it is thought to be an important biomarker when separated by grades [17]. Wang et al.[29] studied miRNA-224 in meningioma and found significantly higher miRNA-224 expression in meningioma and a positive correlation between tumor grade and miRNA-224 expression in tissues as well as compared to normal tissues was found. Patients with low miRNA-224 expression had a significantly longer disease course and lower recurrence rate compared to other cases of meningiomas. In our study, the expression of meningioma patiens was found to be lower than healthy controls (p = 0.03) indicating that our results are consistent with the literature and expression of miR-224 has been found to be lower in grade I.
In summary, we tried to demonstrate that miRNAs can be an important potential biomarker target for meningiomas in our present study. In particular, miR-197 was expressed more than other miRNAs in this group of patients. Therefore, it may be a potential biomarker target in the pre-operative process. miR-197, miR-34a, miR-375, miR-219a and miR-224 stand out as potential biomarkers in meningiomas in human serum samples. It also strengthens the possibility that miR-197, miR-34a, miR-375 in grade I and miR-375 in grade II could be used as a potential biomarker in our meningioma.