Scientists Find a Hidden Brake on Cholesterol Clearance

Key takeaways

• In experiments involving mice and human cells, researchers identified a pathway that reduces the liver’s ability to remove LDL cholesterol from the bloodstream.

• High dietary cholesterol activated a protein called Ral, triggering a process that depleted the receptors liver cells use to capture LDL.

• Blocking an enzyme involved in that process stabilized the receptors and substantially lowered circulating LDL cholesterol in mice.

• An experimental drug targeting the enzyme has already completed early human safety testing, but it has not been shown to lower cholesterol in people.

Cholesterol clearance has a bottleneck

Cholesterol levels depend partly on what the body removes—not just what it produces or absorbs.

Liver cells help manage that balance using LDL receptors, structures on their surface that capture circulating LDL particles and bring them inside for processing. When fewer receptors are available, the liver has less capacity to clear LDL from the blood.

Researchers at the University of California San Diego have identified a previously unrecognized pathway that interferes with this system. Their findings help explain how high dietary cholesterol can weaken the machinery responsible for removing cholesterol from circulation.

A signal that removes the receptors

The process begins with Ral, a protein involved in cellular signaling.

In the experiments, high dietary cholesterol activated Ral, setting off a sequence that increased LDL receptor turnover. An enzyme called cathepsin A, or CTSA, helped drive that loss.

The result was fewer receptors available to capture LDL.

That distinction matters: the problem was not simply more cholesterol entering the system. It was also a reduction in the liver’s ability to take it back out.

Blocking the breakdown

When researchers used a small-molecule inhibitor to block CTSA, LDL receptors became more stable and circulating LDL cholesterol fell substantially in mice.

The finding points to preservation as a potential strategy: protect the liver’s existing clearance machinery rather than allow it to be depleted.

The researchers report that this pathway differs from those targeted by current cholesterol-lowering medications. That raises the possibility of another treatment approach, although the study does not establish whether it would work better than—or add to—existing options in people.

A head start, not a finished treatment

An experimental CTSA inhibitor had previously completed a Phase 1 human trial during development for another purpose.

That earlier testing could shorten the path to a trial examining cholesterol-lowering effects. It does not mean the drug is approved, proven effective, or established as safe for long-term use in this setting.

The central unanswered question remains straightforward: will blocking this pathway lower LDL cholesterol in people at a tolerable dose?

Mouse results and experiments in human cells cannot settle that.

What this means for healthy aging

This is a mechanistic study, not a dietary trial. It does not establish a human dietary cholesterol threshold, identify a particular food to avoid, or justify changing an existing treatment plan.

Its value is in revealing another control point in cholesterol regulation—and a possible way to intervene when the liver’s clearance system is underperforming.

The takeaway

Researchers have identified a pathway that accelerates the loss of LDL receptors and shown that blocking it can lower circulating LDL cholesterol in mice.

The next step is human testing to determine whether protecting those receptors translates into a useful, durable treatment.

References:

1. Xue Feng, Shuo Zhang, Yuqi Wang, Twisha Kurlagunda, Allyssa Sit, Priyadarshini Jaishankar, Pusu Yang, Sadatsugu Sakane, Se Yong Park, Churaibhon Wisessaowapak, Kaylee Nguyen, Jamie Yan, Himani Pothulu, Catherine Dinh, Felicia Chu, Yuyao Ren, Bichen Zhang, Patrick Secrest, Linmeng Han, Chao-Wei Hung, Preethi Veeragandham, Yuliya Skorobogatko, Tatiana Kisseleva, Philip L.S.M. Gordts, Adam R. Renslo, Peng Zhao, Amit R. Majithia, Alan R. Saltiel. Dietary cholesterol activates a Ral-dependent pathway driving LDLR turnover. Nature, 2026; 656 (8127): 452 DOI: 10.1038/s41586-026-10697-z