For the first time, WEHI researchers have shown that a crucial subset of liver cells cannot undergo necroptosis, ruling out this kind of cell death as a cause of common liver diseases.
The surprise discovery redirects liver disease treatment efforts.
Researchers from the Walter and Eliza Hall Institute (WEHI) have demonstrated that common liver diseases are not caused by inflammatory cell death as was previously believed. This discovery settles a long-standing controversy in gastroenterology and points to a new direction for treatment.
The study team looked at hepatitis B and non-alcoholic fatty liver disease, two liver diseases that impact billions of people globally, to discover what drives their progression.
Their surprising discovery—that liver cells are incapable of undergoing an inflammatory type of cell death known as “necroptosis”—resolves key unresolved questions in the field and will direct the development of new therapeutic interventions.
A sample of liver tissue shows the typical features of liver disease, despite lacking a key gene required for necroptosis. The fat-filled hepatocytes (yellow) and collagen build-up (red) are consistent with fibrosis and fatty liver disease. Credit: WEHI
At a glance
- WEHI researchers have for the first time revealed that an important type of liver cells cannot undergo necroptosis, eliminating this type of cell death as a driver of common liver diseases
The surprise findings define the role and relevance of necroptosis in non-cancerous liver diseases, which affect billions of people worldwide
The results will help to inform new strategies for the development of treatments for these liver diseases - The findings, published in the journal Gastroenterology, offer clarity on the heavily debated role of necroptosis in the progression of liver pathologies and provide fundamental insights to guide future pre-clinical and clinical studies in a new direction.
- The study was led by chief investigator Dr. Marcel Doerflinger, former WEHI Ph.D. researcher Dr. Simon Preston and principal investigator Professor Marc Pellegrini, in collaboration with researchers from the Peter Doherty Institute for Infection and Immunity and the University of Queensland.
Liver damage
Liver diseases are a serious and rising worldwide health burden. Over 30% of the world’s population suffers from non-alcoholic fatty liver disease, the most common liver disease, whereas 296 million individuals worldwide have Hepatitis B.
Study researchers (left to right): Dr. Simon Preston, Dr. Marcel Doerflinger, Professor Marc Pellegrini. Credit: WEHI
Necroptosis has been regarded by researchers until now as being essential to the development of these diseases. It remained unclear, however, whether this kind of cell death was happening in liver cells or in immune cells that had entered the liver in response to infections or diet-related damage.
“We sought to address this research gap and define the role and relevance of necroptosis in common liver diseases,” said study lead Dr. Doerflinger.
The researchers used several preclinical genetic models of liver diseases including non-alcoholic fatty liver disease and its advanced form, non-alcoholic steatohepatitis, as well as hepatitis B.
The team deleted key genes required for necroptosis from liver cells known as ‘hepatocytes’ to observe the effects on disease development.
They found that deleting these genes had little effect, with disease progression proving comparable to normal hepatocytes. This revealed that necroptosis was not involved in the development of these liver pathologies.
“The liver is a vital organ due to its function in the body’s metabolism and detoxification,” Dr. Doerflinger said.
“It’s unclear why necroptosis is repressed in liver tissue, but we speculate it may be because the liver is constantly bathed in necroptotic signals such as gut microbial products, so limiting necroptosis could potentially protect the liver from excessive inflammation.”
Molecular mechanisms
The research also revealed the molecular mechanisms responsible for the inability of liver cells to undergo necroptosis.
After genetically profiling human liver tissue samples, the team discovered that hepatocytes cannot produce a critical protein essential for necroptosis, RIPK3.
Production of RIPK3 protein was restricted at the genetic level, where the RIPK3 gene was blocked by a type of epigenetic modification known as ‘methylation’.
“Methylation acts as a genetic blockade, preventing the body’s protein production machinery from binding to the DNA and building RIPK3 protein,” said Dr. Doerflinger.
“As a result, without this essential protein to carry out its necroptotic function, the cell death pathway can’t be initiated.”
Dr. Doerflinger said momentum had been growing in the development of inhibitors of RIPK3 for the potential treatment of liver diseases, but their potential clinical applicability had been limited by a lack of fundamental insights.
“These findings are a central piece of data that address many unanswered questions in the field that will guide future pre-clinical trials and clinical studies in this direction,” he said.
Reference: “Epigenetic Silencing of RIPK3 in Hepatocytes Prevents MLKL-mediated Necroptosis From Contributing to Liver Pathologies” by Simon P. Preston, Michael D. Stutz, Cody C. Allison, Ueli Nachbur, Quentin Gouil, Bang Manh Tran, Valerie Duvivier, Philip Arandjelovic, James P. Cooney, Liana Mackiewicz, Yanxiang Meng, Jan Schaefer, Stefanie M. Bader, Hongke Peng, Zina Valaydon, Pravin Rajasekaran, Charlie Jennison, Sash Lopaticki, Ann Farrell, Marno Ryan, Jess Howell, Catherine Croagh, Denuja Karunakaran, Carole Schuster-Klein, James M. Murphy, Theodora Fifis, Christopher Christophi, Elizabeth Vincan, Marnie E. Blewitt, Alexander Thompson, Justin A. Boddey, Marcel Doerflinger and Marc Pellegrini, 26 August 2022, Gastroenterology.
DOI: 10.1053/j.gastro.2022.08.040
The study was funded by the NHMRC and biotechnology start-up Anaxis Pharma Pty Ltd. It was performed in collaboration with Anaxis Pharma and Servier, a global pharmaceutical group.
Anaxis is a strategic joint venture established by WEHI and SYNthesis Research Pty Ltd, with a focus on necroptosis as a novel pathway of interest in human disease, developing first-in-class drug candidates for chronic inflammatory diseases including irritable bowel disease, Crohn’s disease, liver fibrosis, and reperfusion injury.