In a landmark discovery that resolves a biological enigma spanning more than three decades, researchers at Memorial Sloan Kettering Cancer Center (MSK) have unveiled a sophisticated, dual-purpose mechanism within the human immune system. The study, published in the October 7 edition of Nature, demonstrates that a chemical signaling molecule long known for summoning immune cells to fight infections serves a secondary, equally critical role: it acts as a protective shield, shielding healthy tissue from the collateral damage often caused by the body’s own inflammatory defenses.
This breakthrough not only redefines our understanding of how the body manages inflammation but also opens promising new avenues for treating complex conditions such as inflammatory bowel disease (IBD), asthma, and various forms of cancer.
The Genesis of a Mystery (1992–2024)
The scientific quest began in 1992, when researchers at McGill University identified a mysterious fatty signaling molecule, 5-oxoETE (5-oxo-6,8,11,14-eicosatetraenoic acid). This molecule acts as a biological "flare," alerting the immune system to the presence of pathogens and directing white blood cells—specifically neutrophils—to the site of an infection.
At the time, scientists observed an enzyme capable of both producing and degrading this signaling molecule. However, the genetic identity of this enzyme remained elusive. Without knowing which gene encoded the protein, researchers were effectively blindfolded; they could not manipulate the gene to observe its function or investigate how its failure might contribute to human pathology. For over 30 years, this "missing enzyme" remained a significant gap in the molecular map of human immunity.
The breakthrough arrived through the meticulous work of Yanan Ma, PhD, a postdoctoral researcher at the Sloan Kettering Institute. By employing a systematic genetic screening process in cultured human cells, Dr. Ma identified the culprit: the gene DHRS7. When this gene was disabled, the enzyme’s activity ceased, confirming that DHRS7 was the elusive genetic key that had baffled the scientific community for a generation.
The Zebrafish Advantage: A Shift in Methodology
The identification of DHRS7 was made possible only by abandoning traditional animal models. For decades, biomedical research has relied heavily on mice and rats due to their mammalian genetic overlap with humans. However, as Dr. Ma noted, mice lack a crucial receptor necessary to recognize the 5-oxoETE signal. Consequently, the entire signaling pathway is essentially "dark" in rodents, making them unsuitable for this specific line of inquiry.
"Mice and rats are the primary model used in biomedical research," explains Dr. Ma, a 2023 Marie-Josée Kravis WISE Fellow. "It makes sense—they’re mammals, and there’s about an 80% overlap between their genes and ours. But the pathway is intact in zebrafish. Picking the right alternative model was critical to advancing our understanding of how the human body truly responds."
By pivoting to zebrafish, the MSK team was able to observe the signaling pathway in a living organism where the biological machinery remained fully functional. This decision proved to be the catalyst for uncovering a function that had remained hidden for decades: the realization that the immune system’s "alarm" is also its "shield."
The Paradox of Inflammation
The research team, led by cell biologist Philipp Niethammer, PhD, has spent years investigating the molecular intricacies of inflammation. The traditional view of the immune response is relatively linear: pathogens enter, chemical signals are released, immune cells arrive, and "chemical warfare" is unleashed to destroy the invaders.
"They flood the site with toxic substances to kill the bacteria," Dr. Niethammer explains. "But this can cause damage to healthy cells if it gets out of control."
The breakthrough study emerged from the convergence of two seemingly separate projects within the Niethammer lab. While Dr. Ma was identifying the DHRS7 gene, postdoctoral researcher Miklos Lengyel, MD, PhD, was studying colitis in zebrafish. When Dr. Lengyel disabled the receptor for 5-oxoETE (the zebrafish equivalent of the human OXER1 gene), he expected to see a reduction in inflammation. Instead, he observed the opposite: the zebrafish developed severe intestinal inflammation spontaneously, even in the absence of infection.
When the team disabled DHRS7 as well, they witnessed the same outcome. The inflammation paradoxically increased, suggesting that the 5-oxoETE pathway was not merely an inflammatory trigger but a necessary component for tissue integrity.
The Mechanism: A Molecular Shield
Through further investigation, the researchers identified that the 5-oxoETE pathway works in concert with a group of proteins known as NUDIX hydrolases. These enzymes perform essential "housekeeping," clearing away damaged DNA building blocks that would otherwise interfere with cellular function.
When the 5-oxoETE pathway is active, it signals cells to ramp up their protective defenses. If this signal is lost, intestinal cells lose their resilience, becoming highly susceptible to the routine metabolic stress caused by the gut’s own microbiome. These stressed cells then die, triggering a secondary wave of inflammation that the body perceives as an infection, even when none exists.
"As it turns out, this signal isn’t just an alarm, it’s also a shield," Dr. Niethammer notes. "These immune cells unleash chemical warfare against a pathogen, and organisms have evolved an elegant way of protecting healthy cells at the same time."
Clinical Implications: Cancer, IBD, and Beyond
The discovery has immediate implications for the treatment of inflammatory diseases and oncology. In human patients, mutations in DHRS7 and OXER1 have already been linked to various gastrointestinal and uterine cancers. Furthermore, research suggests that low levels of 5-oxoETE are correlated with poor outcomes in patients suffering from colorectal, pancreatic, and kidney cancers.
Potential Therapeutic Pathways
- Radiation and Chemotherapy: By activating this newly discovered pathway, clinicians may one day be able to increase the "resilience" of healthy gut tissue. This could potentially mitigate the severe intestinal damage often caused by radiation therapy and chemotherapy.
- Inflammatory Bowel Disease (IBD): Because the pathway is essential for maintaining the integrity of mucosal linings, restoring or augmenting 5-oxoETE signaling could offer a novel way to manage the chronic inflammation seen in patients with Crohn’s disease or ulcerative colitis.
- Asthma Management: Independent studies on primates have shown that blocking the OXER1 receptor—while effective at suppressing acute immune responses—led to the disappearance of protective mucus-producing cells in the airways. This confirms that broad-spectrum anti-inflammatory treatments may inadvertently strip away the body’s natural protective barriers.
Integration of Stress: A New Model of Immunity
The research also highlights a fascinating integration of physical and metabolic stress. Doctoral student Zaza Gelashvili, a co-author of the study, demonstrated that physical injury initiates the release of arachidonic acid, the precursor to 5-oxoETE.
"You can think of it as the first step in a chain reaction: Physical stress unlocks the raw material, oxidative stress drives the conversion, and DHRS7 amplifies the signal," says Gelashvili, whose related work on mechanical stress was recently published in Nature Communications.
This suggests that the human body does not treat physical trauma and bacterial infection as isolated events. Instead, it uses the 5-oxoETE pathway to integrate information from multiple stressors, coordinating a response that balances the need for defense with the necessity of tissue survival.
Conclusion
The work of the MSK team—supported by the National Institutes of Health, the Starr Foundation, and the Crohn’s Colitis Foundation—represents a shift in paradigm. By revealing that the immune system’s inflammatory signals double as protective shields, the researchers have fundamentally altered our understanding of the body’s self-regulatory mechanisms.
As the scientific community moves toward developing therapies that target this pathway, the focus will shift from simply "stopping" inflammation to "modulating" it. By reinforcing the natural shield identified by Dr. Ma and Dr. Lengyel, future treatments may be able to fight disease more effectively while sparing the healthy tissues that current therapies often leave in their wake.
The 30-year mystery of the missing enzyme has been solved, but in its place, a much larger, more hopeful question has emerged: how can we harness this dual-action system to build a more resilient human body?
