Colorectal cancer-derived small extracellular vesicles induce TGFβ1-mediated epithelial to mesenchymal transition of normal hepatocytes: new insights on pre-metastatic niche formation in the liver

More than 50% of patients affected by colorectal cancer (CRC) present liver metastasis, which is the most frequent cause of CRC-associated death. Numerous studies have shown that metastatic cascade is the result of complex mechanisms based on two-way interactions between invasive CRC cells and liver resident cells. In recent years, several findings have demonstrated that small extracellular vesicles (SEVs) released by cancer cells play a crucial role in the formation of pre-metastatic niche in the liver, specifically affecting the activities of non-parenchymal cells as Kupffer cells and hepatic stellate cells. However, although hepatocytes (heps) are the most conspicuous in the liver, their involvement in pre-metastatic niche formation remains still unknown. This study shows for the first time that SEVs derived from CRC cells (CRC_SEVs) carrying TGFβ1 impair the morphological and functional properties of human normal heps and trigger their TGFβ1-dependent epithelial to mesenchymal transition (EMT). Moreover, SEVs were also isolated from the plasma and biopsies of CRC patients. Heps treated with patients-derived SEVs underwent an EMT, thus confirming previous results. Since it is known that the EMT of heps led to the formation of a fibrotic environment, which can promote metastasis, the obtained results indicate for the first time that heps can have an active role in regulating the pre-metastatic niche formation. Uveal melanoma (UM) is rare cancer originating from the uveal tract within the eye. Fifty percent of UM patients will develop metastatic disease, mainly in the liver; however, the reasons why the metastatic site is almost exclusively the liver are still unknown. Moreover, the role of UM-derived SEVs in initiating liver metastasis is still unknown. Similarly, to CRC-SEVs, it was found that UM-SEVs induce EMT in human normal heps. Finally, to investigate the establishment of a fibrotic environment in CRC-SEVs-conditioned liver, a three-dimensional (3D) model, represented by liver spheroids was developed. Once characterized, liver spheroids were treated with CRC-SEVs, which decreased functional and structural markers expression, thus confirming the data obtained in 2D. Moreover, CRC-SEVs treatment increased the production of fibronectin, a known marker of fibrosis, in liver spheroids. By co-culturing metastatic CRC cells with liver spheroids, it was demonstrated that the pre-conditioning with SEVs derived by CRC cells isolated from the primary tumor strongly increased the ability of metastatic cells to invade liver spheroids. Collectively these data shed the light on mechanisms involved in the formation of the pre-metastatic niche in the liver, demonstrating that heps actively participate in this process. This evidence may help to find new therapeutic opportunities to counteract liver metastasis of CRC.