THE CLINICOPATHOLOGICAL AND PROGNOSTIC SIGNIFICANCES OF C1Q EXPRESSION IN GLIOMAS: A BIOINFORMATICS ANALYSIS

Introduction. The complement system represents an important component of the inflammatory response and acts as a functional bridge between the innate and adaptive immune response. The contribution of the complement component C1q in the pathophysiology of brain cancers has been recently considered in light of its well-known involvement in carcinogenesis. Brain malignancies arise from cells of the CNS and are classified according to the tissue of phylogenetic origin. Gliomas represent the most common and aggressive form of brain tumours in adults. They derive from glial cells that help to support the functions of the other main brain cells type, the neurons (1). These are a heterogeneous group of diseases with multiple subtypes (1, 2). Glioblastoma multiforme (GBM) is the most common and fatal form of a primary brain tumour, accounting for approximately 60% of all glioma cases (3), whereas grade-II and -III gliomas are the second most common type of glioma in adults (~30%) (3). C1q molecule, together with other complement components, can be locally produced within the CNS by microglia and astrocytes, rendering it an attractive player in primary brain tumour development (4). The role of C1q in gliomas microenvironment is still poorly characterized and it is still quite puzzling whether it exerts a beneficial or a harmful activity for cancer progression. In the present study we performed a bioinformatics analysis aimed at investigating if C1q can serve as a potential prognostic marker for gliomas. Methods. The expression levels of C1qA, C1qB and C1qC genes in gliomas were analysed using Oncomine analysis. Available genomics data from The Cancer Genome Atlas project was used for Kaplan–Meier survival analysis to generate survival probability plots, using UALCAN analysis. Results. From the analysis performed on several data- sets using Oncomine, we showed a significantly higher mRNA expression levels for C1qA, C1qB and C1qC chains were detected in gliomas (different histotypes and grades) as compared to normal brain tissue (Fig. 1). We observed a positive correlation between the mRNA expression of C1qA, C1qB and C1qC mRNA poly- peptide chains and the unfavorable prognosis only in gliomas grade-II and -III, where the survival probability is indeed reduced (P <0.05) (Fig. 2). No correlation was observed in glioblastoma multiforme (Fig. 2). By immu- nohistochemical approaches we detected a high depo- sition of C1q in the tumor microenvironment of both in grade-II and -III gliomas and in GBMs examined (Fig. 3a glioma, 3b glioblastoma multiforme; 20x Magnification). Moreover, in double immunocytochemical experiments we demonstrated that CD68 positive infiltrating cells are actively synthesizing C1q in the tumor micro-envi- ronment. CD68 expression is characteristic of tumor- associated macrophages, whose enrichment in glioma has been associated with poor prognosis (5). Conclusion. In our study C1q expression was significantly correlated with poor survival probability in gliomas grade-II and -III while this is not the case for GBM. These data altogether underline how complex, multifaceted and still poorly understood is the role C1q can exert on tumor progression, and how the very same molecule can differentially affect the outcome depending on the biological context it comes to act.