Abstract
Background/Aim: MicroRNAs (miRNAs) have been identified as key regulators in various cancer types, including brain tumors. This study aimed to investigate the differential expression of miRNA-17 in glial tumors, cerebral metastases, and normal glial tissues. Materials and Methods: A total of 42 patients were included in this cross-sectional study. Tissue samples were obtained from patients with glial tumors or cerebral metastases and from normal glial tissues. miRNA-17 expression levels were computed by using real-time polymerase chain reaction. Receiver operating characteristics analysis was used to determine the predictive potential of miRNA-17. Results: In this study, we demonstrated a statistically significant difference in miRNA-17 expression levels between glial tumors and the control group (p=0.001), with higher miRNA-17 expression observed in glial tumors. Similarly, there was statistically higher miRNA-17 expression in metastatic cases compared with the control group (p=0.007). Conclusion: These findings suggest miRNA-17 might be a potential biomarker for differentiating glial tumors and cerebral metastases from normal glial tissue, although further research is necessary to validate these findings and investigate the potential role of miRNA-17 in the pathogenesis of these brain tumors.
MicroRNAs (miRNAs) are non-coding RNAs that participate in various biological processes, including cell proliferation, differentiation, and apoptosis. Among these, miRNA-17 has drawn significant attention in the context of neural cell biology and cancer (1-6).
In the central nervous system (CNS), miRNA-17 has been found to regulate neural stem cell expansion and their transition to intermediate progenitors, thus influencing neural development (1). Moreover, miRNA-17 has been implicated in regulating oligodendroglial cell numbers, underscoring its relevance in maintaining CNS homeostasis (7). Interestingly, miRNA-17 also exhibits neuroprotective effects, as evidenced by its role in protecting neonatal rats from hypoxic-ischemic brain damage (8).
Despite these crucial roles in normal CNS functioning, aberrant expression of miRNA-17 has been associated with pathological conditions, including glial tumors and cerebral metastases (4, 5). Glial tumors, including gliomas and glioblastomas, are the most common primary brain tumors with high morbidity and mortality rates. Cerebral metastases, on the other hand, represent the most common brain tumors and result from the spread of cancer from different parts of the body to the brain. In both these conditions, altered miRNA profiles, including dysregulation of miRNA-17, have been reported (4, 5).
Yet the precise role and potential of miRNA-17 in glial tumors and cerebral metastases still need to be understood. Previous studies have presented a complex picture, with miRNA-17 functioning as a tumor promoter and suppressor, depending on the context (2, 5). Such contradictory roles raise intriguing questions about the underlying mechanisms and potential therapeutic implications of miRNA-17 in glial tumors and cerebral metastases.
In light of these considerations, our study aimed to compare the expression miRNA-17 in glial tumors, cerebral metastases and normal glial tissue. Our findings may shed light on the role miRNA-17 in these conditions and pave the way for future research on potential therapeutic strategies.
Materials and Methods
Study design and participants. This cross-sectional study was conducted with samples collected from patients diagnosed with glial tumors or cerebral metastases and from normal glial tissue. In our study, the samples analyzed comprised 22 cases of metastasis, 20 cases of glial tumors, and 10 samples of normal tissue, providing a diverse range of specimens for a comprehensive analysis. The study received ethical approval from the Institutional Review Board (B10.1.TKH.4.34.H.GP.0.01/367), and all patients provided informed consent.
Tissue collection and storage. The tissue samples from patients diagnosed with glial tumors or cerebral metastases were obtained during neurosurgical procedures. Control samples (normal glial tissue) were obtained from patients with epilepsy undergoing surgery for seizure control, where the tissue had no histopathological abnormalities. The collected samples were immediately snap-frozen in liquid nitrogen and stored at −80°C until further use.
miRNA extraction and real-time polymerase chain reaction (PCR) analysis. miRNA was extracted from the tissue samples homogenized in QIAzol Lysis Reagent (Qiagen, Hilden, Germany) using steel beads in TissueLyser LT (Qiagen). Subsequently, miRNeasy Tissue/Cells Advanced Kit (Qiagen) was used for miRNA extraction. The concentration and purity of the extracted RNA were determined by using a NanoDrop 2000 spectrophotometer (Thermo Scientific, Waltham, MA, USA). The cDNA was synthesized from the miRNA using miScript II RT Kit (Qiagen). The protocol for real-time PCR was performed using miScript SYBR Green PCR Kit (Qiagen) on a StepOnePlus RT-PCR instrument (Applied Biosystems, Foster City, CA, USA). The RNA U6 was used as an endogenous control to compute relative expression levels of miRNA-17.
Data analysis. The relative expression levels of miRNA-17 in glial tumors, cerebral metastases and normal glial tissue were compared using the 2−ΔΔCt method. The data were then analyzed to identify significant differences in miRNA-17 expression across the three groups.
Statistical analysis. For the statistical analyses, The Number Cruncher Statistical System 2007 (Kaysville, UT, USA) was used. The normality of data distribution was tested with the Shapiro-Wilk test and graphical inspections for suitability of quantitative data. Normally distributed values were evaluated with Student’s t-test and Mann-Whitney U-test was used to compare two groups of quantitative variables that did not show normal distribution. Analysis of variance was used to compare more than two groups. Receiver operating characteristic (ROC) curve analysis was conducted with MedCalc software (MedCalc Software Ltd, Ostend, Belgium). Statistical significance was accepted at values of p<0.05.
Results
Our study revealed notable findings regarding miRNA-17 expression in glial tumors and cerebral metastases. The expression levels miRNA-17 were significantly elevated in both glial tumors and cerebral metastases compared to the control group. This elevation suggests a potential role for miRNA-17 as a biomarker in these conditions.
Demographic and clinical characteristics. In our study, the patient cohort exhibited a diverse age range and a balanced sex distribution. The demographic details of the patients, along with their surgical information, have been comprehensively summarized in Table I and Table II. Specifically:
Information on descriptive features of the patients with tumors (n=42).
Surgical information about the patients.
Sex distribution: Out of the total cases, 38.1% (n=16) were female. This representation provides insights into the sex-related aspects of the disease under study.
Age range and average: The ages of the patients varied significantly, ranging from 25 to 72 years. The mean age was calculated to be 51.62 years.
Expression in glial tumors. The miRNA-17 levels in the glial tumor group were markedly higher than in the control group (p=0.001). This finding aligns with the hypothesis that miRNA-17 plays a role in tumorigenesis, potentially influencing tumor growth and progression (Figure 1).
miRNA-17 expression in normal tissue (control) glial tumor and cerebral metastases (A) and according to grade of glial tumor (B). p-Values are from Mann-Whitney U-test. The boxplots show the median (line), interquartile range (box) and minimum-maximum (whiskers) values.
Expression in cerebral metastases. The cerebral metastasis group exhibited significantly higher miRNA-17 levels than controls (p=0.007). This suggests a possible role of miRNA-17 in the metastatic process, which warrants further investigation (Figure 1).
ROC analysis. The ROC analysis provided a cut-off value for miRNA-17 expression, distinguishing between glial tumor and control groups with a sensitivity of 76.472% and specificity of 76.92%. For cerebral metastases, the sensitivity was 72.22% and specificity 76.92%. These values indicate a promising diagnostic potential for miRNA-17 (Figure 2).
Receiver operating characteristics curve for miRNA-17 expression in cerebral metastases (A) and glial tumor (B) vs. normal tissue (control).
No significant difference among glial tumor grades. Interestingly, miRNA-17 values did not significantly vary across tumor grades (p>0.05). This finding suggests that while miRNA-17 is elevated in glial tumors, its expression does not correlate with tumor grade.
Clinical correlations. The clinical implications of these findings are profound. Elevated miRNA-17 levels in patients might be an early indicator of glial tumor or cerebral metastases, aiding in timely diagnosis and treatment planning.
Discussion
This study presents the differential expression patterns of miRNA-17 in glial tumors, cerebral metastases, and normal glial tissues, suggesting a potential role of miRNA-17 in the development and progression of these tumors. These findings are consistent with prior studies that have pointed to the role of miRNA-17 in neural stem cell expansion, development of the mouse neocortex (1), and regulation of oligodendroglial cell number (9). It has been established that miRNA-17 can silence P21, a key player in cell-cycle regulation, to maintain the neural progenitor pool in the developing cerebral cortex (10).
Many studies have documented the active role of various miRNAs in metastatic processes. For instance, the work by Zhao et al. focused on the effects of celastrol, an anti-inflammatory drug, on oxygen-induced retinopathy and demonstrated that celastrol inhibits pathological neovascularization by targeting the miRNA-17-5p/hypoxia-inducible factor 1-alpha/vascular endothelial growth factor pathway (11). Likewise, the research conducted by Zhang et al. established that the long non-coding RNA MIR17HG promotes neuronal damage and microglial activation in Parkinson’s disease by targeting the miRNA-153-3p/alpha-synuclein axis (12). These findings underscore the significant roles of various miRNAs in regulating cell proliferation, apoptosis, and angiogenesis, which are critical aspects of the metastatic process.
Similarly, several miRNAs have been implicated in glial tumorigenesis. For instance, the study by Li et al. showed that astrocyte elevated gene-1 (AEG1) serves as a target of miR542 to promote glioblastoma proliferation and invasion (13). In another study by Yuan et al., a 4-miRNA signature, including miR-17, was found to predict survival in glioblastoma multiforme, highlighting the potential role of miRNAs as biomarkers in patients with glial tumors (5). Moreover, studies such as those conducted by Billur et al. (6) and Ozdogan et al. (6, 7) have shed light on the potential of miRNAs, such as miR-582-5p and miR-221, respectively, as potential non-invasive biomarkers for glioblastoma multiforme. These findings emphasize the relevance of miRNAs in the pathogenesis, diagnosis, and prognosis of glial tumors.
Notably, miRNA-17-5p was found to play a crucial role in protecting neonatal rats from hypoxic-ischemic brain damage, further signifying its neuroprotective function (8). In contrast, other studies have reported its role in promoting cell growth and chemoresistance, implying its oncogenic nature (2).
Our results showing higher expression of miRNA-17 in glial tumors and cerebral metastases are consistent with studies suggesting that miRNA-17-5p may contribute to glial scar formation after spinal cord injuries (14), astrocyte proliferation after spinal cord injury (15), and increased survival of astrocytes under hypoxic conditions (3). In glioblastoma multiforme, a complex interplay between miRNA-17-5p and other miRNAs has been demonstrated, leading to survival prediction (5).
The elevated expression of miRNA-17 in cerebral metastases is supported by evidence from studies indicating its involvement in axon-myelin remodeling and functional recovery after stroke (4, 16). Other studies demonstrated that miRNA-17-5p facilitated neuronal differentiation of transplanted neural stem/precursor cells under neuroinflammatory conditions (17).
The limitations of our study are primarily related to the sample size and the sole focus on the expression of miRNA-17. Further studies should explore the mechanistic pathways of how miRNA-17 contributes to the development and progression of glial tumors and cerebral metastases while considering the influence of other miRNAs (6, 7, 18-20).
In conclusion, the significantly higher expression of miRNA-17 in glial tumors and cerebral metastases, compared to normal glial tissue, highlights its potential role as a biomarker for these conditions. Our findings underline the need for further research to investigate the precise role and therapeutic potential of miRNA-17 in glial tumors and cerebral metastases.
Footnotes
Authors’ Contributions
Okan Türk, Nail Demirel: Organized and coordinated the research. Cumhur Kaan Yaltirik: Led the article writing. Seda Güleç Yılmaz, Fatma Tuba Akdeniz: Carried out the laboratory work. Mustafa Kaya: Contributed to the design and implementation of the research methodology. Ömer Faruk Şahin: Assisted in data collection and preliminary data analysis. Turgay İsbir: Supervised the study and contributed to data analysis.
Conflicts of Interest
The Authors declare no conflicts of interest in relation to this study.
- Received November 10, 2023.
- Revision received December 29, 2023.
- Accepted January 10, 2024.
- Copyright © 2024 The Author(s). Published by the International Institute of Anticancer Research.
This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY-NC-ND) 4.0 international license (https://creativecommons.org/licenses/by-nc-nd/4.0).
References
In this issue
Jump to section
Related Articles
Cited By...
- No citing articles found.