MicroRNA-146a protects against Hepatocellular Carcinoma through suppression of CCL5

The microRNA miR-146a regulates several aspects of chronic inflammation, including the Hepatocellular Carcinoma (HCC) risk factor hepatosteatosis. Here, we find that loss of miR-146a leads to significantly increased tumor burden in a mouse model of HCC. Notably, this miR-146a-/- phenotype is most pronounced in females, who are typically not sensitive to this model. Mechanistically, we identified increases in dysfunctional CD8+ T-cells that express high levels of CCL5 and resemble Taa cells, as well as elevated levels of myeloid cells that resemble monocytic myeloid-derived suppressor cells (M-MDSCs), a class of myeloid cells that suppress tumor immunity. Deletion of Ccl5 from miR-146a-deficient mice returned tumor growth and the aberrant myeloid cell population to wild-type (WT) levels. Surprisingly, deletion of Ccl5 did not rescue the gross metabolic phenotype observed in miR-146a-/- mice subjected to HCC induction, indicating independent roles for miR-146a in its regulation of HCC and metabolic disease. Taken together, this work reveals a critical host protective role for miR-146a in HCC through suppression of CCL5, providing an impetus for targeting these pathways as a means to combat HCC. Further, the correlations with disease and Taa cells suggest that aging may increase HCC risk through the accumulation of Taa cells.