Fibrosis may not be as irreversible as once believed
For generations, idiopathic pulmonary fibrosis has been understood as a sentence without appeal — a slow hardening of the lungs that medicine could slow but never undo. Now, researchers at National Jewish Health have traced the persistence of that scarring to a single molecular signal, a protein called BCL-2 that keeps the cells responsible for fibrosis alive long past their purpose. The discovery, confirmed in human tissue and tested with an already-approved drug, raises a possibility that has long seemed out of reach: that even established lung scarring might one day be reversed.
- IPF kills most patients within three to five years, and until now no treatment could do more than slow the disease's relentless advance.
- A protein called BCL-2 was found to block the natural death of fibroblasts — the repair cells that, when they refuse to disappear, keep producing scar tissue and locking the lungs in a state of permanent damage.
- These lingering fibroblasts also turn senescent, becoming toxic bystanders that flood surrounding tissue with inflammatory signals and prevent the lungs from ever shifting into a healing mode.
- Researchers tested Venetoclax — already FDA-approved for blood cancers — on mice with established fibrosis, and found that fibroblast numbers fell, collagen decreased, and lung function measurably improved.
- Because the drug exists and is approved, the path to human clinical trials is shorter than it would be for any newly developed compound, giving patients and physicians a rare reason for urgency rather than patience.
Inside the lungs of someone with idiopathic pulmonary fibrosis, the body's repair system has turned against itself. Air sacs that should remain supple have grown rigid and scarred, oxygen exchange falters, and a simple flight of stairs becomes an exhausting ordeal. Most patients survive only three to five years after diagnosis.
For decades, scientists knew that cells called fibroblasts were at the center of the problem. Normally, these cells arrive after injury, rebuild tissue, and then die off through a process called apoptosis — the body's natural cleanup. In pulmonary fibrosis, something prevents that death. The fibroblasts linger, keep producing collagen, and the lungs harden permanently.
Researchers at National Jewish Health have now identified the mechanism behind that failure. A protein called BCL-2 acts as a survival signal, keeping fibroblasts alive when they should be clearing out. Working with genetically modified mice that had elevated BCL-2 in their fibroblasts, the team found that while normal mice developed and then resolved lung scarring, the BCL-2 mice showed fibroblasts that remained elevated for up to twelve weeks, with persistent scarring and structural damage that closely mirrored what is seen in human patients.
The problem ran deeper still. These fibroblasts weren't merely surviving — they were becoming senescent, a state in which cells stop dividing but continue releasing inflammatory molecules that damage surrounding tissue. Gene sequencing showed that healthy fibroblasts eventually shifted toward repair; the BCL-2 fibroblasts never made that transition. To confirm the finding extended beyond mice, researchers used spatial transcriptomics to analyze lung tissue from actual IPF patients. The results matched: fibrotic regions in human lungs showed fibroblasts with high BCL-2 expression and strong senescence signatures.
The most consequential test came next. Using Venetoclax — an FDA-approved drug for certain blood cancers that works by inhibiting BCL-2 — researchers treated mice after fibrosis was already well established. Fibroblast numbers fell sharply, collagen levels dropped, lung oxygenation improved, and imaging showed more tissue capable of exchanging oxygen. Scar tissue had lessened and air sacs had reopened, while other support cells appeared unharmed.
Current IPF therapies can only slow progression; they cannot undo damage. This research points toward a fundamentally different strategy — clearing the cells that refuse to die and allowing the lungs' own repair processes to resume. Because Venetoclax already exists as an approved medication, the timeline toward clinical trials could be meaningfully compressed. Researchers caution that long-term safety and patient selection still require study, but for those living with a disease that steadily steals breath, the prospect that advanced scarring might not be irreversible marks a significant turning point.
Inside the lungs of a person with idiopathic pulmonary fibrosis, something has gone terribly wrong with the body's own repair system. Millions of tiny air sacs that should remain soft and flexible have turned rigid and scarred. Oxygen can barely cross into the bloodstream. A walk up the stairs becomes an ordeal. Most patients live only three to five years after diagnosis.
For decades, doctors knew that cells called fibroblasts were driving this damage. These cells normally appear after injury, rebuild tissue, and then die off through a natural process called apoptosis—the body's way of cleaning up after itself. But in pulmonary fibrosis, something stops them from dying. They linger. They keep producing collagen and scar tissue long after the original injury has healed. The lungs harden. The disease becomes permanent.
Researchers at National Jewish Health may have finally found why. A protein called BCL-2, which acts as a cellular survival signal, was keeping these fibroblasts alive when they should have been disappearing. The discovery, published in Nature Communications, came from work with genetically modified mice that had elevated BCL-2 specifically in their fibroblasts. When scientists exposed these mice to bleomycin—a chemical that triggers lung scarring—something striking happened. Normal mice developed fibrosis that peaked and then gradually resolved as fibroblasts died and collagen levels dropped. The BCL-2 mice took a different path. Their fibroblasts remained elevated for up to twelve weeks. Scarring persisted. Lung tissue became distorted, with collapsed air sacs and cyst-like damage that mirrored what researchers see in human patients.
The team uncovered another layer to the problem. The fibroblasts that refused to die weren't simply staying active—they were becoming senescent, a state of cellular aging in which cells stop dividing but continue pumping out inflammatory molecules that damage surrounding tissue. Gene sequencing showed that healthy fibroblasts eventually shifted toward repair programs. The BCL-2 fibroblasts never made that transition. They remained locked in a pro-fibrotic state, with genes linked to senescence—p16, p21, and others—staying highly active. To confirm this wasn't just a mouse phenomenon, researchers analyzed lung tissue from actual IPF patients using spatial transcriptomics, a technique that maps gene activity inside tissue samples. The results matched. Fibrotic regions in human lungs contained fibroblasts expressing high levels of BCL-2, and these same cells carried strong senescence signatures.
Then came the test that mattered most. Could blocking BCL-2 actually reverse established fibrosis? The researchers used Venetoclax, a drug already approved by the FDA for certain blood cancers because it inhibits BCL-2. They waited until fibrosis was well established in their mouse models, then began treatment. The results were striking. Fibroblast numbers dropped sharply. Collagen levels decreased. Lung oxygenation improved. Imaging showed more lung tissue capable of exchanging oxygen. Under the microscope, scar tissue had lessened and air sacs had reopened. The therapy appeared to specifically target harmful fibroblasts while leaving other support cells intact.
The implications are substantial. Current IPF treatments mainly slow the disease's progression—they cannot reverse scarring. This work suggests a fundamentally different approach: removing the cells that refuse to die, allowing the lungs' natural repair processes to restart. Because Venetoclax already exists as an approved medication, researchers may move more quickly toward testing it in actual IPF patients than would be possible with a drug developed from scratch. The findings also hint at something broader. Senescent cells appear in many age-related diseases—heart disease, kidney fibrosis, chronic inflammatory conditions. Understanding how to clear them could reshape treatment across multiple fields.
Scientists emphasize that more work lies ahead. Long-term safety must be confirmed. Researchers need to determine which patients might benefit most. But for people living with a disease that steadily steals breath and energy, the possibility that even advanced scarring might not be permanent carries weight. The work marks a major step forward in understanding why fibrosis persists and how it might one day be reversed.
Notable Quotes
BCL-2 plays a central role in allowing harmful fibroblasts to survive and sustain fibrosis. By therapeutically inhibiting this pathway, we were able to promote the clearance of these cells and restore key aspects of normal lung architecture.— David Riches, PhD, senior author and head of the Division of Cell Biology at National Jewish Health
Resistance to cell death and the development of senescence are tightly linked in driving persistent fibrosis. Targeting BCL-2 not only addresses fibroblast survival but also helps disrupt the underlying biology that sustains disease progression.— Elizabeth Redente, PhD, professor of medicine at National Jewish Health and first author of the study
The Hearth Conversation Another angle on the story
Why does the body fail to clean up these fibroblasts in the first place? What breaks the apoptosis system?
That's the core mystery the study doesn't fully answer. The researchers showed that BCL-2 is blocking the death signal, but they didn't identify what causes BCL-2 to stay elevated in fibrotic lungs. It's like finding the brake is stuck without knowing why someone pressed it.
So this is really about one protein doing all that damage?
BCL-2 is the linchpin, but it's not acting alone. The fibroblasts also become senescent—they're aging in place, constantly signaling damage to nearby tissue. Blocking BCL-2 helps them die, but it also seems to interrupt that senescence state. It's a two-part problem with one solution.
The drug they tested—Venetoclax—it's already being used for cancer. Why would it work differently in the lungs?
BCL-2 is BCL-2, whether it's in a cancer cell or a fibroblast. The difference is context. In blood cancers, you want those cells dead. In fibrosis, you want the fibroblasts dead so the lungs can heal. Same mechanism, different disease.
What worries you about moving this to human trials?
Safety is the obvious one. You're asking the immune system to clear a lot of dead cells at once. You need to know that won't trigger inflammation that makes things worse. And you need to find the right dose—enough to clear the fibroblasts, not so much that you damage healthy cells.
If this works in people, how quickly could it change treatment?
That depends on the trials. But because the drug exists, you're not waiting for FDA approval of a new compound. You're testing a known drug in a new disease. That could compress years off the timeline. For a disease where patients live three to five years, speed matters enormously.