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Inhibition of receptor-interacting protein kinase 1 improves experimental non-alcoholic fatty liver disease
Amine Majdi1, Lynda Aoudjehane1, Vlad Ratziu2
1Sorbonne Université, Inserm, Centre de Recherche Saint-Antoine (CRSA), Paris, France; Institute of Cardiometabolism and Nutrition (ICAN), Paris, France.
Background & Aims:
In non-alcoholic fatty liver disease (NAFLD), hepatocytes can undergo necroptosis: a regulated form of necrotic cell death mediated by the receptor-interacting protein kinase (RIPK) 1. Herein, we assessed the potential for RIPK1 and its downstream effector mixed lineage kinase domain-like protein (MLKL) to act as therapeutic targets and markers of activity in NAFLD.
Methods:
C57/BL6J-mice were fed a normal chow diet or a high-fat diet (HFD). The effect of RIPA-56, a highly specific inhibitor of RIPK1, was evaluated in HFD-fed mice and in primary human steatotic hepatocytes. RIPK1 and MLKL concentrations were measured in the serum of patients with NAFLD.
Results:
When used as either a prophylactic or curative treatment for HFD-fed mice, RIPA-56 caused a downregulation of MLKL and a reduction of liver injury, inflammation and fibrosis, characteristic of non-alcoholic steatohepatitis (NASH), as well as of steatosis. This latter effect was reproduced by treating primary human steatotic hepatocytes with RIPA-56 or necrosulfonamide, a specific inhibitor of human MLKL, and by knockout (KO) of Mlkl in fat-loaded AML-12 mouse hepatocytes. Mlkl-KO led to activation of mitochondrial respiration and an increase in β-oxidation in steatotic hepatocytes. Along with decreased MLKL activation, Ripk3-KO mice exhibited increased activities of the liver mitochondrial respiratory chain complexes in experimental NASH. In patients with NAFLD, serum concentrations of RIPK1 and MLKL increased in correlation with activity.
Conclusion:
The inhibition of RIPK1 improves NASH features in HFD-fed mice and reverses steatosis via an MLKL-dependent mechanism that, at least partly, involves an increase in mitochondrial respiration. RIPK1 and MLKL are potential serum markers of activity and promising therapeutic targets in NAFLD.
Lay Summary:
There are currently no pharmacological treatment options for non-alcoholic fatty liver disease (NAFLD), which is now the most frequent liver disease. Necroptosis is a regulated process of cell death that can occur in hepatocytes during NAFLD. Herein, we show that RIPK1, a gatekeeper of the necroptosis pathway that is activated in NAFLD, can be inhibited by RIPA-56 to reduce not only liver injury, inflammation and fibrosis, but also steatosis in experimental models. These results highlight the potential of RIPK1 as a therapeutic target in NAFLD.
Insights
Targeting RIPK1 (receptor-interacting protein kinase 1) with RIPA-56 effectively reduced liver injury and fat accumulation in non-alcoholic fatty liver disease (NAFLD) models. This approach also identified RIPK1 and MLKL as potential biomarkers for NAFLD activity.
Area of Science:
- Hepatology
- Cell Death Pathways
- Biomarker Discovery
Background:
- Non-alcoholic fatty liver disease (NAFLD) is a prevalent condition with limited treatment options.
- Hepatocytes in NAFLD can undergo necroptosis, a regulated form of cell death.
- Receptor-interacting protein kinase 1 (RIPK1) mediates necroptosis and is implicated in NAFLD pathogenesis.
Purpose of the Study:
- To investigate RIPK1 and its downstream effector MLKL as potential therapeutic targets in NAFLD.
- To assess RIPK1 and MLKL as markers of disease activity in NAFLD.
Main Methods:
- Utilized high-fat diet (HFD) induced mouse models of NAFLD.
- Administered RIPA-56, a specific RIPK1 inhibitor, to HFD-fed mice and primary human steatotic hepatocytes.
- Measured RIPK1 and MLKL serum concentrations in patients with NAFLD.
- Employed MLKL knockout (KO) and RIPK3 KO in experimental models.
Main Results:
- RIPA-56 treatment reduced liver injury, inflammation, fibrosis, and steatosis in HFD-fed mice.
- Inhibition of MLKL or RIPK1 also reversed steatosis in human hepatocytes and mouse models.
- MLKL deficiency enhanced mitochondrial respiration and beta-oxidation in steatotic hepatocytes.
- Serum RIPK1 and MLKL levels correlated with NAFLD activity in patients.
Conclusions:
- RIPK1 inhibition ameliorates non-alcoholic steatohepatitis (NASH) features and steatosis through an MLKL-dependent mechanism involving mitochondrial respiration.
- RIPK1 and MLKL show promise as therapeutic targets and serum biomarkers for NAFLD activity.
