Exploiting the unique regenerative capacity of the liver to underpin cell and gene therapy strategies for genetic and acquired liver disease

Role of the FOXM1/CMA/ER stress axis in regulating the progression of nonalcoholic steatohepatitis

BACKGROUND/AIMS

The molecular mechanisms driving nonalcoholic steatohepatitis (NASH) progression are poorly understood. This research examines the involvement of chaperone-mediated autophagy (CMA) in NASH progression.

METHODS

Hepatic CMA activity was analysed in NASH mice and patients. Lysosome-associated membrane protein 2A (LAMP2A) was knocked down or overexpressed to assess the effects of hepatocyte-specific CMA on NASH progression. Mice received a high-fat diet or a methionine and choline-deficient diet to induce NASH. Palmitic acid was employed to mimic lipotoxicity-induced hepatocyte damage in vitro. The promoter activity of FOXM1 was evaluated via ChIP and dual-luciferase reporter assays.

RESULTS

Hepatic CMA activity was substantially low in NASH mice and patients. LAMP2A knockdown resulted in hepatocyte-specific CMA deficiency, which promoted fibrosis and hepatic inflammation in NASH mice. Both in vitro and in vivo, CMA deficiency also exacerbated hepatocyte damage and endoplasmic reticulum (ER) stress. Mechanistically, CMA deficiency in hepatocytes increased cholesterol accumulation by blocking the degradation of 3-hydroxy-3-methylglutaryl coenzyme A (HMGCR), a key cholesterol synthesis-related enzyme, and the accumulated cholesterol subsequently induced ER stress and hepatocyte damage. The restoration of hepatocyte-specific CMA activity effectively ameliorated diet-induced NASH and ER stress in vivo and in vitro. FOXM1 directly bound to LAMP2A promoter and negatively regulated its transcription. The upregulation of FOXM1 expression impaired CMA and enhanced ER stress, which in turn increased FOXM1 expression, resulting in a vicious cycle and promoting NASH development.

CONCLUSIONS

This study highlights the significance of the FOXM1/CMA/ER stress axis in NASH progression and proposes novel therapeutic targets for NASH.

KEY POINTS

Chaperone-mediated autophagy (CMA) deficiency in hepatocytes promotes hepatic inflammation and fibrosis in mice with nonalcoholic steatohepatitis (NASH) by inducing cholesterol accumulation and endoplasmic reticulum (ER) stress. Upregulated FOXM1 impairs CMA by suppressing the transcription of lysosome-associated membrane protein 2A (LAMP2A), a rate-limiting component of CMA. ER stress increases FOXM1 expression and cholesterol accumulation. FOXM1/CMA/ER stress axis forms a vicious circle and promotes the development of NASH.

FOXM1: Functional Roles of FOXM1 in Non-Malignant Diseases

Forkhead box (FOX) proteins are a wing-like helix family of transcription factors in the DNA-binding region. By mediating the activation and inhibition of transcription and interactions with all kinds of transcriptional co-regulators (MuvB complexes, STAT3, β-catenin, etc.), they play significant roles in carbohydrate and fat metabolism, biological aging and immune regulation, development, and diseases in mammals. Recent studies have focused on translating these essential findings into clinical applications in order to improve quality of life, investigating areas such as diabetes, inflammation, and pulmonary fibrosis, and increase human lifespan. Early studies have shown that forkhead box M1 (FOXM1) functions as a key gene in pathological processes in multiple diseases by regulating genes related to proliferation, the cell cycle, migration, and apoptosis and genes related to diagnosis, therapy, and injury repair. Although FOXM1 has long been studied in relation to human diseases, its role needs to be elaborated on. FOXM1 expression is involved in the development or repair of multiple diseases, including pulmonary fibrosis, pneumonia, diabetes, liver injury repair, adrenal lesions, vascular diseases, brain diseases, arthritis, myasthenia gravis, and psoriasis. The complex mechanisms involve multiple signaling pathways, such as WNT/β-catenin, STAT3/FOXM1/GLUT1, c-Myc/FOXM1, FOXM1/SIRT4/NF-κB, and FOXM1/SEMA3C/NRP2/Hedgehog. This paper reviews the key roles and functions of FOXM1 in kidney, vascular, lung, brain, bone, heart, skin, and blood vessel diseases to elucidate the role of FOXM1 in the development and progression of human non-malignant diseases and makes suggestions for further research.

Alternative oxidase-mediated respiration prevents lethal mitochondrial cardiomyopathy

Alternative oxidase (AOX) is a non‐mammalian enzyme that can bypass blockade of the complex III‐IV segment of the respiratory chain (RC). We crossed a Ciona intestinalis AOX transgene into RC complex III (cIII)‐deficient Bcs1l^p.S78G knock‐in mice, displaying multiple visceral manifestations and premature death. The homozygotes expressing AOX were viable, and their median survival was extended from 210 to 590 days due to permanent prevention of lethal cardiomyopathy. AOX also prevented renal tubular atrophy and cerebral astrogliosis, but not liver disease, growth restriction, or lipodystrophy, suggesting distinct tissue‐specific pathogenetic mechanisms. Assessment of reactive oxygen species (ROS) production and damage suggested that ROS were not instrumental in the rescue. Cardiac mitochondrial ultrastructure, mitochondrial respiration, and pathological transcriptome and metabolome alterations were essentially normalized by AOX, showing that the restored electron flow upstream of cIII was sufficient to prevent cardiac energetic crisis and detrimental decompensation. These findings demonstrate the value of AOX, both as a mechanistic tool and a potential therapeutic strategy, for cIII deficiencies.

Sodium butyrate ameliorates S100/FCA-induced autoimmune hepatitis through regulation of intestinal tight junction and toll-like receptor 4 signaling pathway

BACKGROUND AND AIM

Recent investigation revealed that dysbiosis in the gut flora and disruption of permeability of intestinal barrier are possible causes for the development of autoimmune hepatitis. Supplementation of sodium butyrate has been suggested to protect liver injury from disrupted permeability of small intestine. In current study, we employed S100/Freund's complete adjuvant induced autoimmune hepatitis to investigate therapeutic efficacy of sodium butyrate and its mechanism in the liver and upper small intestine.

METHODS

C57BL/6 mice were employed and divided into three groups - control group (n=8), autoimmune hepatitis group (n=12) and autoimmune hepatitis with treatment of sodium butyrate group (n=12). Histological staining and western blot analyses were employed to evaluate liver and upper small intestine morphology and gene expression respectively.

RESULTS

The findings revealed that S100/Freund's complete adjuvant caused liver injury and disruption of upper small intestine villi. Sodium butyrate attenuated the injuries and prevented migration of Escherichia coli into the liver. Moreover, the effect of sodium butyrate on protection of injuries of the liver and upper small intestine could be due to inhibition of toll-like receptor 4 signaling pathway, as well as its down-regulation of inflammatory cytokines - interleukin-6 and tumor necrosis factor-a.

CONCLUSIONS

Sodium butyrate can prevent liver injury by maintaining the integrity of small intestine and inhibiting inflammatory response in S100/Freund's complete adjuvant induced autoimmune hepatitis.