Differential mRNA and miRNA expression in oligodendrogliomas of different grades of malignancy

Oligodendroglial tumours originate from oligodendrocytes usually arising in the white matter and could be classified into grade-II oligodendrogliomas (OD) and anaplastic oligodendrogliomas (AOD, grade-III) according to the 2016 World Health Organization (WHO) grading scheme. ODs 1 could be diagnosed by pathological and immunohistochemical analyses, however recent evidence suggests that they could be better diagnosed on the basis of defined genetic entities, such as the combined loss of chromosome 1p and 19q arms and IDH mutation. 1p/19q co-deletion is molecular hallmark of ODs and is clinically associated with better prognosis, response to chemo/radio-therapy and overall survival. Typical oligodendroglial histological features are strongly associated with 1p/19q loss and IDH mutation, which is critically important as diagnostic point of view. The examining of exclusive molecular signatures and transcriptome expression profiles added to histological class could compliment the classification of OD subtypes. In this regard, microRNAs (miRNAs, miRs) profiles could serve classifier signatures for tumour subsets. MiRNAs are 22nt short non-coding RNAs which are expressed endogenously and regulate diverse cellular process through negative control on gene expression at the posttranscriptional level by direct or imperfect interaction with their target mRNAs. MiRNAs are involved in regulating human tumorigenesis acting as either tumour suppressors or oncogenes. During the passage of tumorigenesis miRNA expression level is significantly increased or decreased compared to corresponding normal tissue. The same is observed with their mRNAs. Therefore, transcriptome profiling of human tumours could identify signatures associated with progression, diagnosis, prognosis and response to therapy. However, until recently the information regarding the expression of miRNAs and mRNA in oligodendroglial tumours is scarce. In this study we performed miRNA and mRNA differential expression profiling between grade II and grade III ODs using microarray based expression profiling platforms (723 transcripts and 41,000 genes, respectively). 7 cases for OD grade-II, and 7 for AOD grade-III, and 15 non neoplastic white matter (nnWM) samples were used after microdissection with no previous history of treatment. We performed a systematic evaluation of miRNAs and mRNAs expressions and determined miRNAs and putative target genes that are differentially expressed in grade III AOD, but not in grade II OD and in non-neoplastic white matter (nnWM). 1 ODs when used with „s‟ will represent both OD and AOD. 50 miRNAs were overexpressed and 43 were down regulated in AOD-III, whereas 7 miRNAs showed significant reduction in expressions in OD-II group. 3 miRNAs were commonly down regulated in comparisons of both groups. The hsa-miR-23a was strongly upregulated and hsamiR-27a was strongly downregulated in AOD-III. The functions of hsa-miR-23a and hsa-miR27a were tested in human adult fibroblasts for cell proliferation assay and apoptosis detection. Cells treated with pre-miR-23a and pre-miR-27a showed 20% reduction in cell proliferation as compared with controls. Further, the functional relevance of miRNAs to their target mRNAs was validated for each group, using real time qPCR. 10 key-miRNAs from AOD were subjected to validation by qPCR. We were able to confirm 7 miRNAs (p 0.05). Among these, 5 miRs (miR193a-3p, miR-24, miR-27a, miR-30a-5p and miR-30c) showed reduced expression whose target genes (CCND1, HDAC2, PDGFA and RAB-26) were upregulated. Whereas, 2 miRNAs likewise miR-301b and miR-378 were overexpressed whose target genes BCL2, FGF2, CD44 and PPP4R4 confirmed by qPCR (p 0.05). Bioinformatics based gene ontology (GO), and networking analysis revealed that differential expression and targets are attributed to differentiation of embryonic stem cells, cell adhesion, angiogenesis and neurogenesis, resistance to apoptosis, protein-protein interactions and cell proliferation. It was possible to identify and validate miRNAs and their mRNA-targets potentially involved in the progression of oligodendrogliomas particularly in grade III-AOD. Collectively, this analysis provides new insights to malignant progression of oligodendroglial tumours and could compliment WHO-2016 diagnosis scheme and may provide predictive outcome in patients as well as decision to therapy.