Endothelial TRPV4 channels prevent tumor growth and metastasis via modulation of tumor angiogenesis and vascular integrity.

Transient receptor potential vanilloid 4 (TRPV4) is a ubiquitously expressed polymodally activated ion channel. TRPV4 has been implicated in tumor progression; however, the cell-specific role of TRPV4 in tumor growth, angiogenesis, and metastasis is unknown. Here, we generated endothelial-specific TRPV4 knockout (TRPV4ECKO) mice by crossing TRPV4lox/lox mice with Tie2-Cre mice. Tumor growth and metastasis were significantly increased in a syngeneic Lewis lung carcinoma tumor model of TRPV4ECKO mice compared to TRPV4lox/lox mice. Multiphoton microscopy, dextran leakage, and immunohistochemical analysis revealed increased tumor angiogenesis and metastasis that were correlated with aberrant leaky vessels (increased width and reduced pericyte and VE-cadherin coverage). Mechanistically, increases in VEGFR2, p-ERK, and MMP-9 expression and DQ gelatinase activity were observed in the TRPV4ECKO mouse tumors. Our results demonstrated that endothelial TRPV4 is a critical modulator of vascular integrity and tumor angiogenesis and that deletion of TRPV4 promotes tumor angiogenesis, growth, and metastasis.

Extracellular Vesicles From Pathological Microenvironment Induce Endothelial Cell Transformation and Abnormal Angiogenesis via Modulation of TRPV4 Channels.

The soluble and mechanical microenvironment surrounding endothelial cells influences and instructs them to form new blood vessels. The cells in the pathological tumor microenvironment release extracellular vesicles (EVs) for paracrine signaling. EVs have been shown to induce angiogenesis by communicating with endothelial cells, but the underlying molecular mechanisms are not well known. We have recently shown that the mechanosensitive ion channel transient receptor vanilloid 4 (TRPV4) expression and activity is significantly reduced in tumor endothelial cells (TEC), and that activation of TRPV4 normalized the tumor vasculature and improved cancer therapy. However, whether and how the tumor microenvironment downregulates TRPV4 and transforms the normal endothelial cell phenotype remains unknown. To explore this, we exposed normal human endothelial cells (hNEC) to human lung tumor cell conditioned media (TCM) and measured phenotypic changes and angiogenesis. We found that treatment with TCM transformed hNEC to a TEC-like phenotype (hTEC) as evidenced by increased expression of tumor endothelial cell marker 8 (TEM8) and exhibition of abnormal angiogenesis on 2D-Matrigels compared to normal hNEC. Mechanistically, expression and activity of TRPV4 was decreased in hTEC. Further, when pre-treated with exosome inhibitor GW4869, TCM failed to induce hNEC transformation to hTEC. Finally, addition of purified EVs from TCM induced transformation of hNEC to hTEC as evidenced by abnormal angiogenesis in vitro. Taken together, our results suggest that the pathological (tumor) microenvironment transforms normal endothelial cells into a tumor endothelial cell-like phenotype through EVs via the downregulation of TRPV4.