Enforced expression of miR-342 promotes an inflammatory phenotype in liver metastasis-associated macrophages [miRNAseq_1510]

Liver macrophages are crucial to maintain liver homeostasis. However, upon metastatic seeding, cancer cells co-opt these macrophages to act as tumor-associated macrophages (TAMs), facilitating tumor growth and invasiveness. MicroRNAs (miRNAs) are key regulators of TAM pro-tumoral functions, thus modulating their expression in liver macrophages may constitute a novel approach for liver metastasis immunotherapy. In this study, we identify a myeloid specific miRNA, miR-342-3p, and investigate its anti-tumoral function in liver macrophages in the context of colorectal cancer liver metastasis (CRLM). To this aim, we harnessed lentiviral vectors (LV) to infer and modulate miRNA activity in liver macrophages in vitro and in vivo. We found that miR-342-3p was highly active in macrophages in the healthy liver, but downregulated in proximity to CRLM. Rescuing miR-342-3p activity through enforced miRNA expression induced a pro-inflammatory phenotype in liver macrophages, which was associated to reduced CRLM growth. Transcriptomic analysis revealed Slc7a11, a cysteine-glutamate antiporter associated with TAM pro-tumoral functions, as a major miR-342-3p target. Overall, our findings highlight the potential of miR-342-3p in TAM reprogramming to enhance anti-tumoral immunity. To identify genes differentially expressed among cell populations targeted by systemic lentiviral vector (LV) delivery, we injected mice with a PGK.GFP LV and FACS sorted preferentially transduced cell populations, namely Kupffer cells (KCs) and liver sinusoidal endothelial cells (LSECs) from liver and B cells, red pulp macrophages (RPM), classical dendritic cells type 1 and 2 (cDC1, cDC2) from spleen. Bulk RNAseq of small RNA fraction was performed for all samples.