Investigation of Toll-Like Receptor Family Expression in Glioblastoma: a Comparative Analysis of qPCR and Cell Culture

Aim: Glioblastoma is the most frequent, and fatal brain cancer in adults. Toll-like receptors are cell surface receptors comprised of 10 receptors (Toll-like receptor 1−10) related to triggering innate immunity by recognizing pathogens. However, some studies suggested that the expression of Toll-like receptors might be related to cancer cell proliferation and progression in some tumors including glioblastoma with some contradictory results. Thus, we aimed to investigate all ten members of the Toll-like receptor expression profile in glioblastoma for the first time in the literature to contribute additional data to the literature.

Patients and Methods: Quantitative real-time polymerase chain reaction was applied to formalin-fixed paraffin-embedded tissues of 25 glioblastoma patients, diagnosed between January and December 2018, to evaluate the mRNA expression of Toll-like receptors. Also, the expression of each Toll-like receptor was investigated by cell culture analysis using five different cell lines of human glioblastoma (T98G, U87-MG, U373, LN18, and A172). The results were compared statistically.

Results: Toll-like receptor 1, Toll-like receptor 6, and Toll-like receptor 7 mRNA levels were significantly increased in the formalin-fixed paraffin-embedded tissues of the glioblastoma group (p<0.001, each) whereas the expression of Toll-like receptor 4 and Toll-like receptor 10 was downregulated compared to the control group (p=0.023, p<0.001, respectively), by qPCR analysis.  Additionally, Toll-like receptor mRNA expression profiles differed among the cell lines.

Conclusion: In our study, many Toll-like receptor members seemed to display different expression level in the glioblastoma microenvironment and affect it diversely.  Further comprehensive studies are required to confirm the endogenous protein level of each Toll-like receptor in glioblastoma, to clarify their precise role in the pathogenesis and prognosis of glioblastoma, and to shed light on new target therapies.