Your liver doesn't become fatty in a day; it builds gradually, quietly, cell by cell, usually with zero symptoms for years. Since it happens quietly, it is more dangerous than you expect it to be. Furthermore, there is a new study on a little-known enzyme called RPN11, which might generate a lot of interest for people who love reading about health.
For most of human existence, nobody figured out the inner workings of the liver properly. Today, researchers are able to trace fat buildup down to individual molecules and observe how a single enzyme can cause a chain reaction that turns your healthy liver cell into a fat-storing one. This is why the new research about RPN11 is must-know.
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A Disease That Hides in Plain Sight
To understand the inner workings of the liver, researchers are exploring MASLD (metabolic dysfunction-associated steatotic liver disease). Conventionally, it was called NAFLD, and its aggressive form was NASH, but today it is known as MASH. So, why did this name change occured? MASLD or MASH is tightly related to metabolic issues inside the body, such as unhealthy fat levels, insulin resistance and high blood sugar levels.
The Lancet Gastroenterology & Hepatology journal in 2023 reports that around 38 percent of adults in the world are affected by MASLD. And this number is not guesswork. Researchers measure it through MRI, ultrasound, or other tools, and it also depends on which people they choose for the study. Numbers may vary, but nothing can deny that MASLD is one of the most common chronic liver conditions on the planet.
If you have a fatty liver, you are unlikely to develop anything worse. However, for some of us, it can progress. The fat buildup triggers inflammation and injures liver cells. Over time, it can cause fibrosis, and in more severe cases, it can even advance to cirrhosis or worse. Since it is so widespread, even a small progression could be a massive public health issue. But what decides whether your liver cell handles extra fat safely, or spirals into stress, inflammation, and injury?
How researchers hunt down RPN11
Researchers were searching for enzymes called deubiquitylating enzymes (DUBs), as implied in a 2024 Cell Metabolism article. However, to understand DUBs, one should know their function. In simpler words, DUBs are a kind of molecular editors. Here, a cell tags proteins with a marker called ubiquitin. The ubiquitin flags proteins for destruction by the cell's internal recycling system. And that's where DUBs act like protagonists by removing those tags and rescuing the proteins from being broken down.
Researchers screened liver tissue in obese mice and checked around 100 known DUBs, out of which only one enzyme behaved strangely. This enzyme was RPN11, also known as PSMD14. Surprisingly, it was not only the mice that had elevated RPN11 levels, but also the NAFLD patients. In simpler terms, RPN11 matters for both lab animals and people.
So, what's that thing that switches RPN11 on? The answer is that certain saturated fats, including palmitate, trigger a sharp rise in RPN11 inside liver cells. Here, what happens is that shorter-chain fats do not cause the same reaction; rather, RPN11 responds only to a particular type of fat stress instead of fat in general.
When they explored further, the researchers found a protein called ATF3. The mechanism is such that when the liver is exposed to palmitate, ATF3 gets attached to the RPN11 gene, which turns production on. So, when you lower ATF 3 levels, a fat-triggered rise in RPN11 disappears. The gist is that fat stress activates ATF3, and ATF3 activates RPN11.
They couldn't outright confirm if RPN11 was actually the driving factor, so researchers bred mice with RPN11 removed from liver cells. They found that if mice consumed a high-fat diet, they were largely protected and stored less fat in the liver, which kept lower blood triglyceride levels and lower liver-to-body weight ratios than average mice on the same diet. It implies that RPN11 is not solely responsible, but genetics, insulin resistance and diet also play a critical role.
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What happened after the chain reaction
Based on all the research, it was confirmed that RPN11 was not a small player, but a crucial enzyme. Investigators tried to find what real role it plays inside the cell and how it works. As a result, they found that it's a process where RPN11 targets a protein called METTL3, removes a tag from METTL3 and protects it from being broken down. Consequently, more METTL3 builds up, and higher METTL3 levels imply an increase in ACSS3 gene expression.
Unfortunately, ACSS3 is responsible for an enzyme that turns fatty acids into the propionyl-CoA molecule. The molecule is responsible for a chemical change inside the cell's nucleus called histone propionylation. Histone propionylation eventually turns on a set of genes involved in fat production. Let's understand the flow of this process. The dietary lipid overload turns on RPN11; RPN11 protects METTL3; METTL3 promotes ACSS3; and ACSS3 fuels a nuclear reaction that switches on fat-making genes, and the liver gets fatty.
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Capzimin: A Compound Worth Watching
Once the pathway was mapped, researchers experimented to see whether blocking it could be helpful or not. And that's how you get to know a compound called Capzimin. It is not like old drugs that finish or shut down the entire protein-recycling system, but it targets RPN11's specific activity, which makes it an ideal and precise research candidate. However, safety and effectiveness are not guaranteed.
When they tested Capzimin on animals, it reduced fat and lowered ALT and AST, which are the two markers used by doctors to check for liver damage. Moreover, it also showed better insulin sensitivity and lower blood glucose levels without the mice losing weight or appetite. This implies that Capzimin is working efficiently and directly on liver metabolism, and not through appetite changes.
Furthermore, Capzimin was also tested by researchers on human liver cells grown in the lab, including 3D models that mimic real liver tissue. What makes it interesting is that fat content dropped there too, showing that the idea might work apart from animals. However, lab-grown cells can not fully replicate a living human body, and there is always a margin of error, which makes the safety questionable.
So, what do we have now? RPN11 is a genuine driver of liver fat buildup, as supported by the studies. With the RPN11 pathway, we understand how fat-related stress pushes the liver into making more fat. However, you can't deny that Capzimin showed some real promise in the early testing phase.
In the end, it is still early-stage science, untested in humans, and there is no assurance that it will become an approved treatment. However, modern-day researchers have much clearer maps of the liver's fat-control switches, and an early tool that seems able to flip it off. In short, a solution may not have arrived, but it's almost on the way.
