New Liver Cell Discovery Offers Hope for Treating Severe MASH
Researchers have uncovered a previously unknown type of liver cell that could be the key to treating metabolic dysfunction-associated steatohepatitis (MASH), a severe form of liver disease. This discovery, detailed in the Journal of Clinical Investigation, reveals a specific signaling pathway that may protect the liver from damage and inflammation.
MASH is a critical progression of metabolic dysfunction-associated steatotic liver disease (MASLD). It currently affects between 5% and 10% of the adult population in the United States and can lead to life-threatening complications, including cirrhosis and liver cancer.
Uncovering the “Disease-Associated” Hepatocyte
The liver is a complex organ comprising over a dozen different cell types, including immune cells, stromal cells, and hepatocytes (the primary liver cells). Traditionally, scientists categorized hepatocytes into three distinct zones based on their location and the specific genes they expressed to perform specialized functions.
However, a research team led by Jiandie Lin, a professor of cell and developmental biology at the University of Michigan Life Sciences Institute, found that this traditional model doesn’t tell the whole story. By analyzing gene expression signatures from individual hepatocytes in both healthy and MASH-afflicted livers, the team identified a new cluster of cells with a unique identity.
Crucially, this specific group of cells only appeared in livers with MASH. These cells displayed signatures of cellular senescence—a state where cells stop dividing but do not die. While it sounds benign, senescent cells are often problematic; they interfere with normal tissue function and trigger harmful inflammation that drives disease progression.
The Role of the Themis Gene
While investigating these senescent cells, the researchers noticed unusual activity from a gene called Themis. Under normal conditions, the Themis gene—which encodes the THEMIS protein—is active in T cells (a type of immune cell) but remains dormant in healthy hepatocytes.
The study found that in both human and mouse MASH livers, Themis expression was strongly increased, ranking as one of the most activated genes in these diseased cells. This led the researchers to ask a pivotal question: was this increase damaging the liver, or was the body attempting to protect itself?
Protective Effects and Therapeutic Potential
To test the function of THEMIS, the team used mouse models to observe what happened when the protein was manipulated:
- When THEMIS was deleted: Hepatocytes without the protein fared significantly worse. The livers showed increased signs of injury, higher levels of senescence, and more severe inflammation and fibrosis.
- When THEMIS was increased: The researchers observed a decrease in cellular senescence and improved protection against liver injury and MASH.
Lead author Xiaoxue Qiu, who previously worked in the Lin lab and now leads her own lab at the University of Minnesota, noted that manipulating this specific subtype of disease-associated hepatocytes can have a major impact on how the disease progresses.
Looking Ahead: A New Target for Therapy
This discovery shifts the understanding of how the liver responds to metabolic stress. By identifying THEMIS as a key regulator of hepatocyte senescence, researchers now have a concrete starting point to identify other drivers of liver damage.
Professor Lin believes these findings could pave the way for new therapeutic targets, potentially allowing doctors to manipulate the THEMIS pathway to protect patients from the progression of MASH.
Key Takeaways: The THEMIS Discovery
- New Cell Type: Researchers found a unique cluster of hepatocytes that only exist in MASH livers.
- The Senescence Link: These cells are “senescent,” meaning they’ve stopped dividing and contribute to inflammation.
- Protective Protein: The protein THEMIS, usually found in immune cells, is activated in MASH hepatocytes to help the liver adapt to stress.
- Clinical Impact: Increasing THEMIS levels protects the liver, while removing it accelerates damage, suggesting a new pathway for MASH treatments.
Frequently Asked Questions
What is the difference between MASLD and MASH?
MASLD (metabolic dysfunction-associated steatotic liver disease) is the broader term for fatty liver disease associated with metabolic issues. MASH (metabolic dysfunction-associated steatohepatitis) is a more severe form characterized by inflammation and liver cell damage, which can lead to cirrhosis.
What is cellular senescence?
Cellular senescence is a state where a cell permanently stops dividing. While this can prevent damaged cells from becoming cancerous, the accumulation of senescent cells in tissues often leads to chronic inflammation and organ dysfunction.
How was this research funded?
The study was supported by the American Heart Association, the National Institutes of Health (NIH), and the University of Michigan Diabetes Research Center.