Investigation On The Role And Mechanism Of Neutral Sphingomyelinase 2 Inhibits Colorectal Cancer Liver Metastasis By Exosomal Regulation Of Intercellular Ceramide Transfer Ceramide Transfer In Regenerative Liver Tissues

Background and aimsPartial hepatectomy(PH)is currently the preferred method for the treatment of colorectal cancer liver metastasis(CRLM).At present,the effect of PH-induced liver regeneration(LR)on CRLM remains unclear.Most studies show that LR can promote the progress of CRLM,while a few studies show that LR can inhibit the progress of CRLM.The machinery that prevents colorectal cancer liver metastasis(CRLM)in the context of LR remains elusive.Ceramide(CER)is a potent anti-cancer lipid involved in intercellular interaction.Here,we investigated the role of CER metabolism in mediating the interaction between hepatocytes and metastatic colorectal cancer(CRC)cells to regulate CRLM in the context of LR.MethodsMice were intrasplenically injected with CRC cells,LR was induced by 70%partial hepatectomy(PH)to mimic the CRLM in the context of LR.The alteration of CER metabolizing enzymes in CRLM cancer tissue and adjacent liver tissue were detected by qPCR,immunohistochemical staining and western blotting,and the content of CER in CRLM cancer tissue and CRLM adjacent liver tissue were detected by targeted lipomics.The biological roles of CER metabolism in vitro and in vivo were examined by performing a series of functional experiments.ResultsWe found that induction of LR augmented apoptosis but promoted matrix metalloproteinase 2(MMP2)expression and epithelial-mesenchymal transition(EMT)to increase the invasiveness of metastatic CRC cells,resulting in aggressive CRLM.Upregulation of neutral sphingomyelinase 2(nSMase2,SMPD3)was determined in the regenerating hepatocytes after LR induction and persisted in the CRLM-adjacent hepatocytes after CRLM formation.However,there was no significant change of CER metabolizing enzyme in CRLM tissues.Hepatic Smpd3 knockdown was found to further promote CRLM after LR induction by abolishing mitochondrial apoptosis and augmenting the invasiveness in metastatic CRC cells by upregulating MMP2 and EMT through promoting the nuclear translocation of β-catenin(CANTB).Serum exosones extracted from mice on day 3 after partial hatectomy can enhance the migration and invasion of CRC cells.Serum exosomes extracted from Smpd3 knockdown mice on day 3 after partial hepatectomy can inhibition of apoptosis and enhance the invasion of metastatic CRC cells,resulting in aggressive CRLM.Treatment with SMPD3 inhibitor GW4869 significantly inhibited the secretion of exosomes in mice,reduced the mitochondrial apoptosis and enhanced the invasion of metastatic CRC cells,further promoting the progression of CRLM in the context of LR.Mechanistically,we found that hepatic SMPD3 controlled the generation of exosomal CER in the regenerating hepatocytes and the CRLM-adjacent hepatocytes.The SMPD3-produced exosomal CER critically conducted the intercellular transfer of CER from the hepatocytes to metastatic CRC cells and impeded CRLM by inducing mitochondrial apoptosis and restricting the invasiveness in metastatic CRC cells.The administration of nanoliposomal CER was found to suppress CRLM by inducing mitochondrial apoptosis and attenuating the invasiveness of metastatic CRC cells in the context of LR substantially.ConclusionSMPD3-produced exosomal CER constitutes a critical anti-CRLM mechanism in LR to impede CRLM,offering the promise of utilizing CER as a therapeutic agent to prevent the recurrence of CRLM after PH.