Cedars-Sinai team identifies the liver enzyme that decides when fatty disease becomes MASH

Roughly 100 million Americans carry fatty liver disease. About one in five of them will progress to the more dangerous form: the inflammatory, scarring stage called MASH (metabolic dysfunction-associated steatohepatitis). For MASH there is still no cure and only one approved drug.

A multicenter study published this week in Nature Metabolism and co-led by Ekihiro Seki, MD, PhD at Cedars-Sinai names the molecular switch that decides when a liver cell tips from coping to self-destructing. The switch is an enzyme called UBE2N, which helps the cell clear out damaged energy-producing parts (mitochondria) and break down excess fat. When researchers restored UBE2N in mice fed a fatty Western diet, liver damage eased. The Cedars-Sinai release calls UBE2N the deciding lever. The underlying paper shows why.

A liver cell is constantly recycling its own parts. UBE2N attaches a chemical tag called ubiquitin to a recycling protein called p62, marking damaged mitochondria for destruction. When UBE2N is abundant, the cell's garbage service works. When UBE2N falls, as it does in MASH, damaged mitochondria pile up, p62 accumulates, and the cell's stress response runs hot. That stress response, in turn, drives a particular kind of inflammatory cell death. The paper shows this is what destroys liver tissue in the disease.

The mechanism has a name, PANoptosis, and an on/off switch. The switch is a transcription factor called THAP11. In healthy liver cells, THAP11 keeps UBE2N levels steady. As fatty acids accumulate, THAP11 ramps up and silences the UBE2N gene, removing the brake on the disease.

They knocked out UBE2N in liver cells and watched MASH get worse. They put UBE2N back and watched the disease ease. When they simultaneously knocked out p62, the protein UBE2N is supposed to clear, the Ube2n-knockout mice were rescued. That is the test that pins the harm to p62 accumulation specifically, not to some other effect of UBE2N. The Bioengineer.org writeup walks through each step.

To check the human side, the team ran single-nucleus RNA sequencing and digital spatial transcriptomics on tissue from MASH patients. Hepatocytes, the working cells of the liver, showed the same UBE2N downregulation that the mice did, with the same p62 pile-up downstream.

The field currently has one approved MASH drug: resmetirom, sold as Rezdiffra, which targets a thyroid hormone receptor in the liver. UBE2N is a different kind of target. It is not a fat-burner but a cell-housekeeping enzyme. The new axis is the cell's garbage service, not its metabolism.

In the Cedars-Sinai release, Seki says: "The UBE2N enzyme appears to protect the liver from the inflammation and damage associated with MASH by helping remove damaged mitochondria and supporting the breakdown of fat." The verb appears is doing real work in that sentence.

The paper does not announce a drug, a clinical trial, or a timeline. It announces a defined molecular target and a hypothesis: that restoring or mimicking UBE2N, or blocking the THAP11 repressor, could become a way to slow or stop MASH before it reaches cirrhosis. The ScienceDaily coverage reprints the institutional release. The underlying signal is the Nature Metabolism paper and the Cedars-Sinai team that produced it.

The study is mice plus human tissue, not a human trial. The only outside discussant cited in the release is Shelly Lu, a Cedars-Sinai colleague. Broader field consensus on THAP11 as the master switch, and on UBE2N as a viable drug target, has not yet been tested outside the lab that proposed it.

THAP11 silences UBE2N, UBE2N tags p62 for mitophagy, and the failure of that garbage service drives the cell-death cascade. When p62 is removed at the same time as UBE2N, the mice are rescued, pinning the harm to a specific step. The same direction of change shows up in human MASH tissue, not just in mice.

For a disease with roughly 100 million American patients and one approved drug, a second, mechanistically distinct axis is a real expansion of the map. The next move is whether any group, academic or industry, can build a molecule that restores UBE2N, blocks THAP11, or otherwise makes the cell's garbage service run again. The paper has not promised a therapy. It has named the place to look.