Activated cGAS-STING signaling promotes malignancy in metabolic dysfunction-associated fatty liver disease via mitochondrial DNA and immune cell dysfunction

Abstract

BACKGROUND

Activated cyclic guanosine monophosphate-adenosine monophosphate synthase-stimulator of interferon genes (cGAS-STING) is associated with hepatocellular carcinoma (HCC) progression. However, its mechanisms in metabolic dysfunction-associated fatty liver disease (MAFLD) progression remain to be identified.

AIM

To investigate the dynamic alterations in cGAS-STING activation and hepatic immune cells during MAFLD malignancy.

METHODS

Approved by ethics committees, dynamic models of MAFLD were generated in Sprague-Dawley rats fed a high-fat diet supplemented with 2-fluorene acetylamino acid. Livers were grouped into MAFLD, metabolic dysfunction-associated steatohepatitis, liver cirrhosis and HCC groups on the basis of hematoxylin and eosin staining, with healthy rats used as controls. The mitochondrial ultrastructures were observed by electron microscopy. Hepatic immune cells were analyzed by single-cell sequencing. Carnitine palmitoyl transferase II (CPT-II or CPT2) and cGAS-STING were detected by enzyme-linked immunosorbent assay, real time quantitative polymerase chain reaction, immunohistochemistry, and multicolor immunofluorescence.

RESULTS

Dynamic models of MAFLD malignancy were successfully established, and hepatocytes with diffuse macrovascular steatosis, unequal nuclear sizes, disordered arrangements and damaged mitochondrial ultrastructures were identified. The activated hepatic STING expressions at the mRNA or protein levels were significantly greater (P < 0.001) in the liver cirrhosis and HCC groups. CPT2 was markedly downregulated (P < 0.001). Serum alpha-fetoprotein and Wnt3a levels were significantly increased (P < 0.001). The expression levels of vimentin-1, interferon-I, nuclear factor kappa-B, transforming growth factor-β1 and tumor necrosis factor-α progressively increased (P < 0.001). Mechanistically, accumulated lipids damage mitochondria, resulting in the downregulation of CPT2 or mitochondrial DNA expressions and the activation of the cGAS-STING pathway. Alterations in immune cells with a weak inflammatory microenvironment promoted MAFLD transformation and malignancy.

CONCLUSION

Activation of cGAS-STING in MAFLD with mitochondrial damage promoted hepatocarcinogenesis via an immune escape mechanism.

Keywords: Metabolic dysfunction-associated fatty liver disease; Cyclic guanosine monophosphate-adenosine monophosphate synthase-stimulator of interferon genes; Hepatocellular carcinoma; Mitochondrial damage; Single-cell sequencing

Core Tip: Hepatocyte cyclic guanosine monophosphate-adenosine monophosphate synthase, as a DNA sensor, recognizes damaged mitochondrial DNA with aberrant lipid metabolism to activate stimulator of interferon genes to trigger the expressions of inflammatory factors, such as type-I interferon, which might be closely related to metabolic dysfunction-associated fatty liver disease (MAFLD) progression. However, the molecular mechanisms underlying MAFLD malignancy are still unclear. In this study, the activation of the cyclic guanosine monophosphate-adenosine monophosphate synthase-stimulator of interferon genes signaling pathway was systematically evaluated in a lipid accumulation model, and the pathogenesis of MAFLD was clarified by evaluating the interactions among hepatocyte injury, inflammatory factors, and immune cells in hepatocarcinogenesis.