Targeting TFAM downregulation mediated mtDNA-NLRP3 pathway suppresses TAM infiltration and HCC progression

The infiltration of TAMs mediates an immunosuppressive tumor microenvironment, which plays a crucial role in the malignant progression of HCC. TFAM is a key molecule that regulates mtDNA replication and transcription, and its expression frequently downregulated in various tumors, including HCC. Our previous study indicated that the downregulation of TFAM triggers mtDNA stress, thereby inducing autophagy and promoting ESCC survival through the STING pathway. However, it remains unclear whether cytosolic mtDNA stress, mediated by TFAM downregulation, is implicated in microenvironment regulation, particularly in the infiltration of TAMs in HCC. In this study, we found that TFAM expression was significantly decreased and correlated with CD163 expression in HCC tissues. The downregulated expression of TFAM in HCC cells contributed to TAM infiltration. Mechanistically, the downregulation of TFAM induced cytosolic mtDNA stress, which activated the NLRP3 inflammasome and promoted the expression of IL-18 and IL-1β in HCC cells, thereby inducing macrophage recruitment and M2 polarization. Depleting cytosolic mtDNA using DNase I or blocking NLRP3 inflammasome activation with an NLRP3 antagonist in HCC cells with TFAM downregulation significantly suppresses the infiltration of M2-TAMs. Moreover, blocking the mtDNA-NLRP3 pathway significantly inhibited TAM infiltration and orthotopic mouse HCC model progression. Taken together, our results reveal a novel mechanism by which cytosolic mtDNA stress mediates TAM infiltration in HCC.