Despite some advances in surgical and adjuvant treatments, GBM patients still suffer from poor prognoses32.MiRNA-based biomarkers have some advantages to touch upon being easily obtainable in a non-invasive manner12 and representing throughout the disease course and tumor status33.Recently, miRNAs have been identified as promising noninvasive biomarkers that can show tumor development in early stages and so improves GBM diagnosis and prognosis34. Herein, under the literature reviews and data mining using in silico tools, we chose three miRNAs including hsa-let-7c-5p, hsa-miR-206-5p, and hsa-miR-1909-5p that may contribute to GBM development.Different miRNAs have been detected that can successfully discriminate GBM, thus, we conducted an investigation into whether asignature of these candidate miRNAs can be a new diagnostic biomarker. To fill this yawning gap, the expression of each candidate miRNA was determined using RT-qPCR and their associations with clinicopathological features were analyzed.
Hsa-let-7c is a vital tumor suppressor miRNA playing a proactive role in the inhibition of proliferation, migration, and invasion of lung cancer cells 35; this miRNA is somehow linked to the etiology of recurrent lung cancer, although the exact mechanism yet still is blanketed in mystery. Recently, Luo et al. showed that hsa-let-7c-5p may regulate CyclinD1 expression via the Wnt/β-catenin signaling pathway in osteoblasts 36, suggesting that this miRNA may have a hand in cell cycling of tumor cells as well. Hsa-let-7c-5p is down-regulated in recurrent GBM than primary GBM samples 37. Also, hsa-let-7c inhibits metastasis in colorectal cancer and its down-regulation stimulates the expression of K-RAS, MMP11, and PBX3 that leads to the promoted cell migration and invasion 38,39. Therefore, hsa-let-7c-5p down-regulation may make a contribution to GBM recurrence via triggering GBM cell migration and invasion. Although there are many studies showing different roles of this miRNA in cellular and molecular events, its functions in GBM are still shrouded in mystery. Herein, we showed that this miRNA is downregulated in patients’ samples than the control tissues and this was consistent with the data derived from GEO database (Fig. 4a-c); this verifies the tumor suppressor roles of this miRNA. The AUC-ROC curve analysis proposed that this miRNA is a reliable biomarker with good sensitivity and specificity that in turn is capable of distinguishing between GBM and healthy tissues, however, the prognostic potentiality was not detected in silico.
Zhang et al. showed that hsa-miR-206suppressed cell proliferation in gastric cancer at least partially by targeting the CyclinD240. Similarly, the expression of this miRNA is downregulated in breast cancer 41, laryngeal cancer 42, rhabdomyosarcoma 43, colorectal cancer 44, and prostate cancer45. These findings bestowed a tumor-suppressive role to hsa-miR-206-5p.This miRNA activates apoptosis and inhibits tumor cell migration46.Overexpression of hsa-miR-206-5pgives rise to the decreased expression of metabolicgenes,NADPHproduction, and ribose synthesis in mouse models 47. Furthermore, Hao et al. showed that the expression ofhsa-miR-206 was decreased in GBM tumor samples and pertinent cell models than in control tissues/cells48.They demonstrated that hsa-miR-206 is a tumor suppressor and its inhibitionsets stages for GBM development and progression. Our findings were in line with these results. Using AUC-ROC curve analysis, we showed that hsa-miR-206-5p is a promising biomarker that can discriminate the GBM from healthy tissues. Also, using in silico data, we showed that this miRNA is a probable prognostic biomarker for GBM, however, further studies are required in order to showthe exact molecular mechanisms whereby this miRNA functions in GBM development/progression.
Hsa-miR-1909-5p isup-regulated in pediatric dysembryoplastic neuroepithelial tumors, casting light on its oncogenic functions49. Braoudakiet al. showed that this miRNA is a potential biomarker distinguishing between the tumor types and the normal tissues49. Furthermore, it has been identified that hsa-miR-1909-5p was significantly up-regulated in less aggressive rectal cancer patients 50.Hsa-miR-1909 is expressed in the early stages of gastric cancer51, however, regarding GBM, there is a snippet of information about the roles of this miRNA in the development or progression; for instance, Li et al.elucidated that miR-1909-5p was significantly upregulated in a GBM patient52. Using a high-throughput technique, it has been identified that miR-1909-5p was upregulated in GBM tumors53. Our results underscored that miR-1909-5p functions oncogenic roles in GBM development, however, further studies are needed to arrive at a conclusion and to unearth the detailed underlying molecular mechanisms. On the other side, it has been recently demonstrated that miR-1909-5p may play a tumor-suppressive role in the etiology of Parkinson's disease, i.e., its downregulation was identified in postmortem samples of patients with Parkinson's disease54. This study can per se show what complications are expectable when it comes to miRNAs. In a nutshell, we demonstrated that hsa-miR-1909-5p is a diagnostic biomarker in GBM and is upregulated in GBM patients, proved by in silico tools. Long term follow-ups did not show any prognostic biomarker potentiality for this miRNA.
In this study, we also showed that hsa-let-7c-5p, hsa-miR-206-5p, and hsa-miR-1909-5p target different genes that most of which are involved in cell cycle, IGF signaling, cell proliferation/growth, and cell migration.This may substantiate that the signature of these miRNA may represent different cellular processes that are often dysregulated in GBM.
There are some limitations in this study; for example, as obtaining direct samples from GBM tumors needs surgery, it would be feasible and more convenient if we did check the expression of the signature in serum, plasma, or cerebrospinal fluids. Therefore, further studies seem to beimperative to determine the exosomal levels of this signature to show whether this can be used as a non-invasive method to discriminate tumor and healthy samples or not. Likewise, as in silico analysis showed, the signature targets a substantial number of genes; so, miRNA and gene expression profiling isnecessary to determine which genes are targeted by the signature. Thirdly, to confirm our findings, conducting larger investigations with more diverse samples would be helpful.