Increased matrix stiffness in pituitary neuroendocrine tumors invading the cavernous sinus is activated by CAFs through the mTOR pathway

Abstract

Purpose Pituitary neuroendocrine tumors (PitNETs) with invasion of the cavernous sinus (CS) are particularly challenging to treat. Cancer associated fibroblasts (CAFs) are recognized for their pivotal role in reprogramming extracellular matrix (ECM). Herein, we aimed to explore the potential involvement of CAFs 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 saddle area (SDL). 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 SDL. Increased ECM stiffness within the CS facilitated the acquisition of stem-like properties, enhanced proliferation, and induced epithelial-to-mesenchymal transition (EMT). 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 a potential role for CAFs in ECM reprogramming, which was validated in tumor tissues and primary CAFs from pituitary adenomas in both the CS and SDL. Importantly, the stiffer ECM environment promoted the progression of PitNETs via the mTOR pathway. Conclusion These findings demonstrated the significant contribution of activated CAFs to the stiffening of matrix. Therefore, targeting the mTOR pathway to alter mechanical properties emerges as a promising approach to enhance treatment efficacy.