HAF Prevents Hepatocyte Apoptosis and Hepatocellular Carcinoma through Transcriptional Regulation of the NF-κB pathway

Background: Hepatocellular carcinoma (HCC) incidence is increasing worldwide due to the obesity epidemic, which drives metabolic dysfunction-associated steatohepatitis (MASH) that can lead to HCC. However, the molecular pathways that lead to MASH-HCC are poorly understood. We have previously reported that male mice with global haploinsufficiency of hypoxia-associated factor, HAF ( SART1 ^{+/ -} ) spontaneously develop MASH/HCC. However, the cell type(s) responsible for HCC associated with HAF loss are unclear.

Results: SART1 -floxed mice were crossed with mice expressing Cre-recombinase within hepatocytes (Alb-Cre; hepS ^-/- ) or macrophages (LysM-Cre, macS ^-/- ). Only hepS ^-/- mice (both male and female) developed HCC suggesting that HAF protects against HCC primarily within hepatocytes. HAF-deficient macrophages showed decreased P-p65 and P-p50 and in many major components of the NF-κB pathway, which was recapitulated using HAF siRNA in vitro . HAF depletion increased Apoptosis both in vitro and in vivo , suggesting that HAF mediates a tumor suppressor role by suppressing hepatocyte Apoptosis. We show that HAF regulates NF-κB activity by controlling transcription of TRADD and RIPK1 . Mice fed a high-fat diet (HFD) showed marked suppression of HAF, P-p65 and TRADD within their livers after 26 weeks, but manifest profound upregulation of HAF, P-65 and TRADD within their livers after 40 weeks of HFD, implicating deregulation of the HAF-NF-κB axis in the progression to MASH. In humans, HAF was significantly decreased in livers with simple steatosis but significantly increased in HCC compared to normal liver.

Conclusions: HAF is novel transcriptional regulator of the NF-κB pathway that protects against hepatocyte Apoptosis and is a key determinant of cell fate during progression to MASH and MASH-HCC.