Transient receptor potential vanilloid (TRPV) channel expression in meningiomas: prognostic and predictive significance.

The TRPV1-4 members of TRPV cation channel subfamily are mainly regarded as polymodal receptors that may be activated by diverse changes in cellular microenvironment and endogenous and exogenous agents. Abnormal expression of these channels has been reported in various tumors but not in meningiomas. Meningioma cells are thought to originate from arachnoid cap cells due to cytological and functional similarities between the two types of cells. To investigate the expression profile of TRPV1-4 channels in meningiomas and compare with TRPV1-4 channel expression in leptomeninges, we used immunohistochemistry in formalin-fixed, paraffin-embedded semi-serial tissue sections from 175 meningiomas with different grades and histological subtypes, and normal brain or meningioma specimens that contained leptomeninges. The labeling index (LI), defined as the percentage of positive (labeled) cells out of the total number of tumor cells counted, was determined. Leptomeninges were TRPV1-4 immunonegative. A significant percentage of tumors exhibited TRPV1-4 channel expression which was independent of the proliferation index of the tumors but was significantly associated with histopathological subtypes. The TRPV1 and TRPV3 immunoexpression was decreased whereas TRPV4 immunoexpression was significantly greater in high-grade (WHO, grade II and III) as compared with low-grade (WHO, grade I) meningiomas. Additionally, TRPV4 emerged as an independent predictor for the degree of malignancy using the binary logistic regression model [dependent variable: grade I versus higher grades (II and III)]. Kaplan-Meier analysis for 102 patients showed no significant association of TRPV1-4 expression with overall survival. The above data support that TRPV1-4 channels are implicated in meningioma pathogenesis, and TRPV4 has predictive significance in the disease.