Protective Effects of Hepatocyte Stress Defenders, Nrf1 and Nrf2, Against MASLD Progression

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Background: Progression of metabolic dysfunction associated steatotic liver disease (MASLD) to steatohepatitis (MASH) is driven by stress-inducing lipids that promote liver inflammation and fibrosis, and MASH can lead to cirrhosis and hepatocellular carcinoma. Previously, we showed coordinated defenses regulated by transcription factors, nuclear factor erythroid 2 related fac-tor-1 (Nrf1) and -2 (Nrf2), protect against hepatic lipid stress. Here, we investigated protective effects of hepatocyte Nrf1 and Nrf2 against MASH-linked liver fibrosis and tumorigenesis. Methods: Male and female mice with flox alleles for genes encoding Nrf1 (Nfe2l1), Nrf2 (Nfe2l2), or both were fed a MASH-inducing diet enriched with high fat, fructose, and cholesterol (HFFC) or control diet for 24-52 weeks. During this period, hepatocyte Nrf1, Nrf2, or combined deficien-cy for ~7-days, ~7-weeks, and ~35-weeks was induced by administering mice hepatocyte target-ing adeno-associated virus (AAV) expressing Cre recombinase. The effect on MASH, markers of liver fibrosis and proliferation, and liver tumorigenesis was compared to control mice receiving AAV expressing green fluorescent protein. Also, to assess the impact of Nrf1 and Nrf2 induction on liver fibrosis, HFFC diet fed C57bl/6J mice received weekly injections of carbon tetrachloride, and from week 16-24, mice were treated with Nrf2 activating drug bardoxolone, hepatocyte overexpression of human NRF1 (hNRF1), or both, and these groups were compared to control. Results: Compared to control diet, 24-week feeding with HFFC diet increased bodyweight as well as liver weight, steatosis, and inflammation. It also increased hepatocyte proliferation and a marker of liver damage, p62. Hepatocyte Nrf1 and combined deficiency increased liver steatosis in control diet fed but not HFFC diet fed mice, and increased liver inflammation under both diet conditions. Hepatocyte Nrf1 deficiency also increased hepatocyte proliferation, whereas com-bined deficiency did not, and this also occurred for p62 level in control diet fed conditions. In 52-week HFFC diet fed mice, 35 weeks of hepatocyte Nrf1 deficiency, but not combined deficien-cy, resulted in more liver tumors in male mice, but not in female mice. In contrast, hepatocyte Nrf2 deficiency had no effect on any of these parameters. However, in the 15-week CCL4 exposed and 24-week HFFC diet fed mice, Nrf2 induction with bardoxolone reduced liver steatosis, inflam-mation, fibrosis, and proliferation. Induction of hepatic Nrf1 activity with hNRF1 enhanced the effect of bardoxolone on steatosis and may have stimulated liver progenitor cells. Conclusion: Physiologic Nrf1 delays MASLD progression, Nrf2-induction alleviates MASH, and combined enhancement synergistically protects against steatosis and may facilitate liver re-pair.

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