Inhibition of PCSK9 Attenuates Liver Endothelial Cell Activation Induced by Colorectal Cancer Stem Cells During Liver Metastasis

<b>Background:</b> Colorectal cancer (CRC) is among the most prevalent and lethal cancers globally, with liver metastasis representing the leading cause of CRC-related mortality. Proprotein convertase subtilisin/kexin type 9 (PCSK9) has recently gained attention due to its overexpression in colorectal tumor tissues and its potential role in driving metastatic progression. This aims to investigate the involvement of PCSK9 in the liver metastatic niche, focusing on its effects on liver sinusoidal endothelial cells (LSECs), key components of the liver microenvironment. <b>Methods:</b> LSECs were stimulated with conditioned media derived from differentiated colorectal cancer cells and cancer stem cells (CSCs), the latter generated by reprogramming SW620 and CT26 cell lines. RNA sequencing was used to profile gene expression in LSECs. PCSK9 mRNA and protein levels were quantified by qPCR and Western blotting, respectively. PCSK9 expression in CRC liver metastases was evaluated by immunofluorescent staining. <b>Results</b>: PCSK9 was detected in both human and murine LSECs and significantly upregulated following exposure to CSC-conditioned media. Immunofluorescent staining confirmed PCSK9 expression in LSECs within CRC liver metastases. Total RNA sequencing revealed that a pre-treatment of LSECs with the PCSK9 inhibitor PF-06446864 prior to CSC stimulation seems to reduce the expression of microRNAs linked to cell migration and proliferation. Functional assays demonstrated that CSC-conditioned media enhanced LSEC proliferation and migration, effects reversed by PCSK9 inhibition. <b>Conclusions:</b> PCSK9 promotes the activation of LSECs in response to colorectal CSCs, contributing to a pro-metastatic phenotype. These findings highlight PCSK9 as a potential therapeutic target in colorectal liver metastasis.