Increased matrix stiffness in pituitary neuroendocrine tumors invading the cavernous sinus is activated by TAFs: focus on the mechanical signatures

Abstract

Purpose: Pituitary neuroendocrine tumors (PitNETs) with invasion of the cavernous sinus (CS) are particularly challenging to treat. Tumor associated fibroblasts (TAFs) are recognized for their pivotal role in reprogramming extracellular matrix (ECM). Herein, we aimed to explore the potential involvement of TAFs in ECM reprogramming and elucidate the underlying mechanism involved.

Methods: We applied dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) to measure tumor vessel permeability and applied atomic force microscopy (AFM) to measure the matrix stiffness of PitNETs located in both CS and sella turcica (ST). Western blotting, immunofluorescence, immunohistochemistry, and quantitative RT-PCR were utilized to analyze the ECM components. Proteomic biochemical analysis was utilized to uncover potential mechanisms governing ECM dynamics.

Results: We found that PitNETs in the CS were stiffer than those in the ST. Increased ECM stiffness within the CS facilitated the acquisition of stem-like properties, enhanced proliferation, and induced epithelial-to-mesenchymal transition (EMT) of GH3 cells. Furthermore, the expression levels of lysyl oxidase (LOX), matrix metallopeptidase 2 (MMP2) and MMP9 in pituitary adenoma cells increased in the stiffer matrix. Proteomic analysis suggested TAFs were activated in the CS area and contributed enhanced matrix stiffness by secreting Col-1 and Col-3. Furthermore, mTOR pathway was activated under higher matrix stiffness and the migration and invasion of GH3 cells be repressed by mTOR inhibitor.

Conclusion: These findings demonstrated that activated TAFs contributed to stiffer matrix and increased ECM stiffness stimulating mTOR pathway in pituitary tumor cells. Our study indicated that mTOR inhibitor was a promising treatment strategy from the standpoint of PitNET biomechanical properties.

Keywords: Cavernous sinus; Matrix stiffness; Pituitary neuroendocrine tumors; Tumor associated fibroblasts; mTOR pathway.