Background/Aims: Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related mortality worldwide and is driven by metabolic reprogramming that supports tumor growth and progression. A common missense genetic variant (rs2642438, p.A165T) in mitochondrial amidoxime reducing component 1 (MTARC1), identified as protective against liver disease, has been recently associated with lower prevalence of steatosis, cirrhosis, and HCC. However, the mechanistic role of MTARC1 in HCC is unclear. Therefore, we sought to decipher the role of MTARC1 in HCC. Methods: We investigated the role of MTARC1 in HCC by performing siRNA-mediated knockdown across human immortalized HCC cell lines (Hep3B2, HuH7, HepG2 and HepaRG) homozygous for the risk allele (p.A165) and by generating stable CRISPR-Cas9 knockout (KO) models. Next, we assessed the effect of MTARC1 loss on cell proliferation, migration, lipid metabolism, and fatty acid oxidation in vitro, as well as tumor aggressiveness in a subcutaneous xenograft mouse model. Additionally, we performed global proteomics in both in vitro and xenograft models. Results: Transient knockdown of MTARC1 p.A165 reduced proliferation in HCC cell lines. CRISPR-Cas9-mediated stable MTARC1 p.A165 KO in Hep3B2 cells led to decreased neutral lipid intracellular accumulation, enhanced β-oxidation and reduced cell migration. An MTARC1 KO xenograft model had reduced tumor volume. Proteomic analyses of both in vitro HCC cells and xenograft tumors revealed inhibition of oncogenic pathways and activation of anti-proliferative proteins. Conclusions Downregulation of MTARC1 p.A165 inhibits lipid accumulation, dampens tumor-promoting pathways and restricts tumor growth, highlighting MTARC1 as a promising therapeutic target for HCC.

Background/Aims: Metabolic dysfunction-associated steatotic liver disease (MASLD) is a global epidemic. The disease has a strong genetic component, and a common missense variant (rs2642438) in the mitochondrial amidoxime-reducing component 1 (MARC1) gene confers protection against its onset and severity. However, there are contrasting results regarding the mechanisms that promote this protection. Methods: We downregulated MARC1 in primary human hepatocytes (PHHs) using short interfering RNA (siRNA). We measured neutral lipid content by Oil-Red O staining and fatty acid oxidation by radiolabeled tracers. We also performed RNA-sequencing and proteomic analysis using LC-MS. Additionally, we analyzed data from 239,075 participants from the UK Biobank. Results: Downregulation of MARC1 reduced neutral lipid content in PHHs homozygous for the wild type (p.A165, risk), but not for the mutant (p.T165, protective), allele. We found that this reduction was mediated by increased fatty acid utilization via β-oxidation. Consistent with these results, we found that the levels of 3-hydroxybutyrate, a by-product of β-oxidation, were higher in carriers of the rs2642438 minor allele among samples from the UK biobank, indicating higher β-oxidation in these individuals. Moreover, downregulation of the MARC1 p.A165 variant resulted in a more favorable phenotype by reducing ferroptosis and reactive oxygen species levels. Conclusions MARC1 downregulation in carriers of the risk allele results in lower hepatocyte neutral lipids content due to higher β-oxidation, while upregulating beneficial pathways involved in cell survival.

Background/Aims: Metabolic dysfunction-associated steatotic liver disease (MASLD) is a global epidemic. The disease has a strong genetic component, and a common missense variant (rs2642438) in the mitochondrial amidoxime-reducing component 1 (MARC1) gene confers protection against its onset and severity. However, there are contrasting results regarding the mechanisms that promote this protection. Methods: We downregulated MARC1 in primary human hepatocytes (PHHs) using short interfering RNA (siRNA). We measured neutral lipid content by Oil-Red O staining and fatty acid oxidation by radiolabeled tracers. We also performed RNA-sequencing and proteomic analysis using LC-MS. Additionally, we analyzed data from 239,075 participants from the UK Biobank. Results: Downregulation of MARC1 reduced neutral lipid content in PHHs homozygous for the wild type (p.A165, risk), but not for the mutant (p.T165, protective), allele. We found that this reduction was mediated by increased fatty acid utilization via β-oxidation. Consistent with these results, we found that the levels of 3-hydroxybutyrate, a by-product of β-oxidation, were higher in carriers of the rs2642438 minor allele among samples from the UK biobank, indicating higher β-oxidation in these individuals. Moreover, downregulation of the MARC1 p.A165 variant resulted in a more favorable phenotype by reducing ferroptosis and reactive oxygen species levels. Conclusions MARC1 downregulation in carriers of the risk allele results in lower hepatocyte neutral lipids content due to higher β-oxidation, while upregulating beneficial pathways involved in cell survival.

Background/Aims: Metabolic dysfunction-associated steatotic liver disease (MASLD) is a global epidemic. The disease has a strong genetic component, and a common missense variant (rs2642438) in the mitochondrial amidoxime-reducing component 1 (MARC1) gene confers protection against its onset and severity. However, there are contrasting results regarding the mechanisms that promote this protection. Methods: We downregulated MARC1 in primary human hepatocytes (PHHs) using short interfering RNA (siRNA). We measured neutral lipid content by Oil-Red O staining and fatty acid oxidation by radiolabeled tracers. We also performed RNA-sequencing and proteomic analysis using LC-MS. Additionally, we analyzed data from 239,075 participants from the UK Biobank. Results: Downregulation of MARC1 reduced neutral lipid content in PHHs homozygous for the wild type (p.A165, risk), but not for the mutant (p.T165, protective), allele. We found that this reduction was mediated by increased fatty acid utilization via β-oxidation. Consistent with these results, we found that the levels of 3-hydroxybutyrate, a by-product of β-oxidation, were higher in carriers of the rs2642438 minor allele among samples from the UK biobank, indicating higher β-oxidation in these individuals. Moreover, downregulation of the MARC1 p.A165 variant resulted in a more favorable phenotype by reducing ferroptosis and reactive oxygen species levels. Conclusions MARC1 downregulation in carriers of the risk allele results in lower hepatocyte neutral lipids content due to higher β-oxidation, while upregulating beneficial pathways involved in cell survival.