Stellate cells are specialized cells found primarily in the liver and pancreas, named for their star-shaped appearance. They play a central role in storing vitamin A, maintaining tissue structure, and, when things go wrong, driving the scarring process known as fibrosis. The term also applies to a distinct group of star-shaped neurons in the brain, though these share only the name and shape, not the function.
Where Stellate Cells Sit in the Liver
Hepatic stellate cells live in a thin gap called the Space of Disse, wedged between the liver’s main working cells (hepatocytes) and the cells lining its tiny blood vessels. From this position, they extend long projections that wrap around the blood vessels, giving them the star-like shape that earned their name. They make up a relatively small fraction of total liver cells, but their location puts them in direct contact with both the bloodstream and the liver’s core machinery, making them uniquely positioned to sense and respond to injury.
Vitamin A Storage
In a healthy liver, stellate cells serve as the body’s main warehouse for vitamin A. They absorb retinol from the blood, convert it into a storage form called retinyl esters, and pack it into large fat droplets inside the cell. These lipid droplets are one of the defining features of a resting, or “quiescent,” stellate cell. The liver as a whole holds the majority of the body’s vitamin A reserves, and stellate cells are the specific cells responsible for that stockpile.
What Happens When Stellate Cells Activate
When the liver is injured, whether by chronic alcohol use, viral hepatitis, fatty liver disease, or other insults, stellate cells undergo a dramatic transformation. They shed their vitamin A-filled fat droplets, change shape, and begin behaving like a completely different cell type called a myofibroblast. In this activated state, they multiply rapidly, become mobile, and start producing large quantities of structural proteins, particularly collagen types I, III, and IV.
This collagen is the raw material of scar tissue. In small amounts after a single injury, it helps the liver repair itself. But when the injury is ongoing, activated stellate cells keep churning out collagen faster than the body can break it down. The result is fibrosis: stiff, non-functional scar tissue that gradually replaces healthy liver tissue. If fibrosis progresses far enough, it becomes cirrhosis.
The activation process is triggered by a cascade of inflammatory signals, oxidative stress, and shifts in how the cells generate energy. Activated stellate cells ramp up their use of sugar for fuel in a pattern similar to what cancer cells do, relying on a high-speed but inefficient energy pathway. Blocking that metabolic shift in laboratory experiments can actually push the cells back toward their resting state.
Can Activation Be Reversed?
For years, scientists believed the only way to get rid of activated stellate cells was for them to die through a process called apoptosis (programmed cell death). That is part of the story: when liver injury stops, many activated stellate cells do self-destruct, allowing fibrosis to gradually resolve. But research in mice has revealed a second pathway. Tracking individual stellate cells through liver recovery showed that roughly 40 to 45 percent of previously activated cells survived and reverted to a quiescent-like state rather than dying off.
There is a catch. These reverted cells carry a kind of molecular memory. When exposed to a new round of injury, they reactivate faster and more aggressively than cells that were never activated in the first place. This helps explain why people with a history of liver damage can develop fibrosis more quickly if the injury returns.
Stellate Cells in the Pancreas
The pancreas contains its own version of stellate cells, called pancreatic stellate cells. In a healthy pancreas, they help maintain the organ’s structure, support its blood vessels, and contribute to the basement membrane that holds tissue together. Like their liver counterparts, pancreatic stellate cells can activate into a myofibroblast-like state when the organ is injured.
In chronic pancreatitis, this activation drives progressive scarring of the pancreas, much like hepatic stellate cells do in the liver. In pancreatic cancer, their role is even more concerning. Activated pancreatic stellate cells engage in extensive cross-talk with tumor cells, helping create a dense, fibrous barrier around the tumor known as the stroma. This stroma does more than just provide physical scaffolding. It promotes tumor growth and spread, reduces oxygen supply to the tumor (which paradoxically helps certain cancer cells thrive), helps the tumor evade the immune system, and makes cancer cells more resistant to both chemotherapy and radiation.
Stellate Neurons in the Brain
The term “stellate cell” also refers to a family of star-shaped neurons scattered across several brain regions. These are entirely unrelated to the stellate cells of the liver and pancreas, sharing only the characteristic radiating shape, with a round cell body and dendrites branching outward in multiple directions.
Brain stellate cells come in both excitatory and inhibitory varieties, and they serve different roles depending on where they sit. In the cerebral cortex, excitatory spiny stellate cells cluster in layer IV of sensory areas like the visual and touch-processing cortices. They act as high-fidelity translators of incoming signals from the thalamus, the brain’s sensory relay station, and pass that information to other layers of the cortex while maintaining precise spatial organization. Their dendrites and axons stay mostly local, connecting within a single cortical column rather than projecting to distant brain regions.
In the cerebellum, stellate cells play an inhibitory role. Located in the molecular layer, they use the neurotransmitter GABA to dampen the activity of Purkinje cells, the large neurons responsible for coordinating movement. Stellate cells also appear in the auditory brainstem, where both excitatory and inhibitory types help process sound, and in the entorhinal cortex, where they project to the hippocampus and contribute to memory and spatial navigation.
Why Stellate Cells Matter for Treatment
Because hepatic and pancreatic stellate cells are the primary drivers of organ fibrosis, they have become a major focus for drug development. The challenge is delivering treatments specifically to these cells without affecting the rest of the organ. Researchers have developed approaches that exploit unique receptors on the surface of activated stellate cells. One strategy uses a small cyclic peptide that binds to a growth factor receptor found predominantly on activated stellate cells, delivering anti-fibrotic compounds directly to them and inhibiting their activation. Another approach packages drugs inside tiny particles coated with molecules that recognize proteins on the stellate cell surface, reducing collagen production in laboratory experiments.
No approved drugs yet target stellate cells specifically in humans, but the ability to identify these cells through protein markers is well established. Resting stellate cells produce a structural protein called GFAP, which is also found in brain cells. As stellate cells activate, they begin producing alpha-smooth muscle actin, a reliable marker of the activated, scar-producing state. GFAP appears to mark the earliest stages of activation, while alpha-smooth muscle actin becomes prominent as activation progresses, giving researchers and pathologists a way to gauge how far along the fibrotic process has gone in a tissue sample.