Heat shock factor 1 in brain tumors: a link with transient receptor potential channels TRPV1 and TRPA1.

Novel data report a "cross-talk" between Heat-Shock Factor 1 (HSF1) and the transient receptor potential vanilloid 1 cation channel (TRPV1) located in the cell membrane, introducing these channels as possible drug targets for the regulation of HSF1 activation. This study aims to investigate the co-expression of TRPV1 and HSF1 in human brain tumors. Additionally, the expression of the transient receptor potential ankyrin 1 channel (TRPA1), which is co-operated with TRPV1 in a plethora of cells, was studied. Immunohistochemical staining for HSF1, TRPV1 and TRPA1 expression was quantitatively analyzed in paraffin-embedded semi-serial tissue sections from 74 gliomas and 71 meningiomas. mRNA levels of HSF1, TRPV1 and TRPA1 were evaluated using real-time PCR. Although HSF1 was significantly increased compared with TRPV1/TRPA1 (p ≤ 0.001) in both gliomas and meningiomas, high co-expression levels for HSF1, TRPV1 and TRPA1 were found in 62.50% of diffuse fibrillary astrocytomas (WHO, grade II), 37.50% of anaplastic astrocytomas (WHO, grade III), 16.32% of glioblastomas multiforme (WHO, grade IV), and 42.25% of meningiomas (WHO, grade I and II). Correlation analysis revealed a relationship of HSF1 with TRPV1/TRPA1 in diffuse fibrillary astrocytomas (WHO, grade II) and benign meningiomas (WHO, grade I) contrary to glioblastomas multiforme (WHO, grade IV) and high grade meningiomas (WHO, grade II). Importantly, TRPA1 and TRPV1 expression levels were significantly increased in meningiomas compared with astrocytic tumors (p < 0.05). In conclusion, HSF1 and TRPV1/TRPA1 co-expression may be implicated in the pathogenesis of human brain tumors and should be considered for the therapeutic approaches for these tumors.

Evaluation of AQP4/TRPV4 Channel Co-expression, Microvessel Density, and its Association with Peritumoral Brain Edema in Intracranial Meningiomas.

Apart from VEGF-A pathway activation, the existence of peritumoral edema (PTBE) in meningiomas has been correlated with the expression levels of water transporter aquaporin 4 (AQP4). A novel cooperation of AQP4 with the transient receptor potential isoform 4 (TRPV4), a polymodal swelling-sensitive cation channel, has been proposed for regulating cell volume in glial cells. We investigated AQP4/TRPV4 channel co-expression in meningiomas along with the neovascularization of tumors and associate with PTBE. Immunohistochemical staining for AQP4 and TRPV4 expression was quantitatively analyzed in semi-serial sections of archival tissue from 174 patients. Microvessel density was expressed as microvessel count (MVC). PTBE was measured and edema index (EI) was assessed in 23 patients, based on magnetic resonance images (MRI) whereas mRNA levels of AQP4 and TRPV4 were evaluated in these patients using quantitative real-time PCR. High AQP4 was associated with lower-tumor grade (p < 0.05). AQP4 and TRPV4 were correlated in benign (WHO, grade I) (p < 0.0001) but not in high-grade (WHO, grades II and III) meningiomas (p > 0.05). AQP4/TRPV4 levels were independent of EI and MVC (p > 0.05). In contrast, EI was correlated to MVC (p = 0.02). AQP4/TRPV4 co-expression was detected in both edematous and non-edematous meningiomas. However, most of tumors with larger edema (EI ≥ 2) demonstrated increased levels of AQP4 and TRPV4. Importantly, peri-meningioma tissue of edematous meningiomas demonstrated significantly increased expression for AQP4 (p = 0.007) but not for TRPV4 (p > 0.05) compared with the main tumor. AQP4 and TRPV4 expression is rather associated with a response to vasogenic edema of meningiomas than with edema formation.

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.