Differentiation syndrome occurs when ATRA and ATO, which work by forcing the immature leukemic cells of APL to mature and eventually die, trigger a violent inflammatory reaction in the process. Patients can develop fever, fluid accumulation in the lungs, low blood pressure, and kidney failure. In severe cases, the syndrome can be fatal. Despite decades of clinical experience, the biological mechanisms underlying the condition have remained poorly understood, and doctors currently have no reliable way to predict which patients will develop it. The new research, led by Giulia Falconi, Luca Guarnera, and Maria Teresa Voso of the University of Rome Tor Vergata, together with colleagues across Italy, set out to change that by examining the clinical, molecular, and cellular fingerprints of the syndrome.

The team analyzed two independent groups of APL patients. The first was a real-life cohort of 34 patients treated at multiple Italian centers, reflecting the diversity of everyday clinical practice. The second comprised 18 patients enrolled in the landmark APL0406 clinical trial, the study that established the ATRA-ATO combination as the standard of care. From each patient, the researchers collected blood samples at baseline and at sequential time points during treatment, allowing them to track molecular changes as therapy unfolded. Crucially, the analysis included both patients who developed differentiation syndrome and those who did not, providing a natural comparison group.

The most striking clinical finding concerned transfusions. Patients who went on to develop differentiation syndrome required a median of nine units of red blood cells during the induction phase of treatment, compared with just three units in patients who did not develop the syndrome—a difference that was highly statistically significant. Even after adjusting for other clinical variables in a multivariable analysis, the transfusion burden retained its independent association with the syndrome. In other words, patients whose disease demanded more blood support early in treatment were markedly more likely to experience the complication later on.

Why would transfusion requirements track so closely with differentiation syndrome? The answer, the researchers suggest, lies in the biology of erythroid maturation—the process by which red blood cell precursors develop into mature cells. When the team performed RNA sequencing on the patients’ blood samples, they identified 93 genes that were differentially expressed in patients who developed the syndrome. When these gene signatures were mapped onto known biological pathways, they showed striking enrichment for processes related to hematopoietic stem cell differentiation and erythroid maturation. This suggests that the same differentiation programs that ATRA and ATO deliberately activate in leukemic cells may also be perturbing normal blood cell development, particularly the red cell lineage, in susceptible patients.

The molecular data were complemented by measurements of inflammatory signaling molecules. Cytokine profiling of the blood samples revealed elevated levels of interleukin-6, a potent inflammatory messenger, with a trend toward even higher concentrations at the moment the syndrome declared itself. Interleukin-6 is a well-known driver of systemic inflammation and has been implicated in cytokine release syndromes seen with other cancer therapies, including CAR-T cell treatment. Its presence here reinforces the picture of differentiation syndrome as an inflammatory storm, one that unfolds in a molecular environment already primed by disordered blood cell maturation.

But the study did not stop at the leukemic cells themselves. One of its most provocative contributions concerns the endothelium—the delicate layer of cells that lines blood vessels and controls what passes between the bloodstream and surrounding tissues. The researchers grew human pulmonary microvascular endothelial cells, or HPMECs, in the laboratory and exposed them to ATRA and ATO. The drugs induced marked morphological changes in these cells and significantly increased their permeability, allowing fluid and molecules to leak across the endothelial barrier. This laboratory phenomenon closely mirrors the capillary leak that characterizes differentiation syndrome in patients, in which fluid escapes from blood vessels into the lungs and other organs, causing potentially deadly swelling and respiratory distress.

Encouragingly, the researchers found a way to blunt this endothelial damage. When dexamethasone, a corticosteroid commonly used to prevent and treat differentiation syndrome, was added to the cell cultures alongside ATRA and ATO, the increased permeability was significantly attenuated. The finding provides a mechanistic explanation for a clinical practice that has existed for years: steroids work, at least in part, by stabilizing the endothelial barrier against the leak-inducing effects of the leukemia drugs. It also suggests that the laboratory model could be used to test other protective agents in the future.

Taken together, the results support a new model of differentiation syndrome as a three-part process. First, erythroid dysregulation—the same maturation programs triggered in leukemic cells—disrupts normal red cell development, driving the anemia that necessitates transfusions. Second, ATRA and ATO directly injure the endothelial lining of blood vessels, creating a capillary leak phenotype. Third, an inflammatory environment rich in interleukin-6 amplifies the damage. Each element feeds the others, and the transfusion burden emerges as a visible downstream marker of the earliest, hidden phase of the cascade.

The clinical implications could be significant. Red blood cell transfusion counts are recorded routinely for every APL patient, making them an early, inexpensive, and universally accessible biomarker. Patients requiring frequent transfusions during induction could be flagged for closer monitoring, earlier steroid intervention, or enrollment in prospective studies of preventive strategies. The researchers caution that their findings, while compelling, come from a combined cohort of 52 patients, and validation in larger, independent populations will be essential before transfusion burden is adopted into formal risk stratification. Still, in a complication that has long defied prediction, the idea that a number already written in every patient’s chart might reveal who is at highest risk is a rare and welcome piece of good news—one that could help make the cure for acute promyelocytic leukemia not just effective, but safer.

Subject of Research: Differentiation syndrome pathogenesis in acute promyelocytic leukemia

Article Title: Transcriptomic profile and endothelial changes during differentiation syndrome in acute promyelocytic leukemia

Article References: Falconi, G., Guarnera, L., Lazzaroni, F., Galossi, E., Ottone, T., Attardi, E., Piazza, R., Lumia, E., Silvestrini, G., Travaglini, S., Divona, M., Fabiani, E., Curti, A., Martini, V., Mazzone, C., La Barbera, E. O., Sica, S., Mannelli, F., Gurnari, C., … Voso, M. T. (2026). Transcriptomic profile and endothelial changes during differentiation syndrome in acute promyelocytic leukemia. Annals of Hematology. https://doi.org/10.1007/s00277-026-07180-0

Image Credits: AI Generated

DOI: 10.1007/s00277-026-07180-0

Keywords: acute promyelocytic leukemia, differentiation syndrome, all-trans retinoic acid, arsenic trioxide, transcriptomics, endothelial permeability, interleukin-6, red blood cell transfusion, erythroid maturation, dexamethasone, biomarker, hematology

The research, led by Yingying Zhu, Chun Jiang, Xiuhui He, Xiang Gao, and corresponding author Zhengxuan Jiang of the Department of Ophthalmology at The Second Affiliated Hospital of Anhui Medical University, describes a previously underappreciated signaling chain that connects the metabolic chaos of diabetes to the physical collapse of the retinal endothelial barrier. At the heart of the discovery is histone lactylation, a relatively recently identified epigenetic mark in which lactate-derived lactyl groups are chemically attached to lysine residues on histone tails. Rather than being an inert byproduct of metabolism, lactate in this context acts as a signaling molecule that reshapes which genes are switched on inside retinal blood vessel cells.

To dissect the mechanism, the team assembled evidence from multiple complementary systems. They examined human epiretinal membranes and fibrovascular membranes obtained from patients with proliferative diabetic retinopathy, retinal tissue from diabetic rats, and retinal endothelial cells grown under diabetic-like conditions. Across all of these models, a consistent pattern emerged: where lactate accumulated, protein lactylation rose, and one particular mark—lactylation at lysine 9 of histone H3, abbreviated H3K9la—stood out as prominently elevated under diabetic conditions. This convergence across human tissue, animal models, and cultured cells gave the finding a robustness that single-model studies often lack.

The critical question was what H3K9 lactylation actually does inside these endothelial cells. Histone modifications of this kind generally work by altering the physical state of chromatin, the complex of DNA and protein that packages the genome. When specific histone residues are acetylated or lactylated, the chromatin at nearby genes tends to loosen, granting the transcriptional machinery access and boosting gene expression. The researchers found that lactate-driven H3K9la became enriched at the promoter region of the PTK2 gene, which encodes focal adhesion kinase, a well-known regulator of cell adhesion, migration, and survival. With the promoter epigenetically opened up, PTK2 transcription increased, and levels of the phosphorylated, active form of the kinase climbed in parallel.

From there, the story moves from the nucleus to the cytoskeleton. Activated PTK2 was found to associate with FMNL2, a formin-family protein that governs the assembly of actin filaments, and this association was linked to increased tyrosine phosphorylation of FMNL2 itself. The consequence was a cascade of cytoskeletal remodeling inside the endothelial cells: the internal scaffolding of the cells reorganized in a way that destabilized VE-cadherin, the adhesive molecule that stitching neighboring endothelial cells together at adherens junctions. When VE-cadherin junctions falter, the endothelial sheet loses its seals, permeability rises, and fluid and proteins leak across the barrier. In the retina, that leakage translates directly into macular edema and progressive vision impairment.

What makes this axis scientifically compelling is that it forges a direct line from metabolism to cell structure through epigenetics. Diabetic tissue is known to be lactate-rich, a product of altered glucose metabolism and hypoxic stress. The study shows that this excess lactate does not merely fuel inflammation or oxidative damage indirectly; it physically marks the chromatin of barrier-regulating genes, amplifies a kinase–formin signaling module, and dismantles the junctions that hold the retinal vasculature together. In effect, a metabolic byproduct of diabetes becomes an epigenetic instruction that tells blood vessel cells to let go of each other.

Just as importantly, the research demonstrates that the damage is not irreversible in experimental settings. The team showed that pharmacologically reducing lactate production, inhibiting the catalytic activity of CBP/p300—the histone acetyltransferase enzymes responsible for writing lactylation marks—blocking PTK2 activity, or knocking down FMNL2 all attenuated endothelial barrier defects and reduced retinal vascular leakage. Each of these interventions targets a different rung on the same ladder, and the fact that several independent points of disruption produce protective effects strengthens the causal interpretation of the pathway and opens multiple potential angles for therapy.

The therapeutic implications are considerable. Existing treatments for diabetic retinopathy, such as anti-VEGF injections and laser photocoagulation, address downstream consequences of vascular dysfunction rather than the metabolic and epigenetic drivers of barrier failure. If the lactate–H3K9la–PTK2–FMNL2 axis can be safely modulated in patients—for example, by limiting lactate accumulation, tuning histone lactylation, or inhibiting focal adhesion kinase signaling locally in the eye—clinicians might one day intervene earlier in the disease process, before irreversible vascular damage takes hold. PTK2 inhibitors already exist in oncology research, and CBP/p300 catalytic inhibitors are under active investigation in multiple fields, meaning that repurposing strategies could accelerate translation.

The study also adds to a fast-growing body of literature on lactylation as a regulatory modification. Since histone lactylation was first described as a link between cellular metabolism and gene regulation, researchers have implicated it in macrophage polarization, tumor biology, fibrosis, and neural inflammation. The new work extends this framework to the vascular endothelium of the eye, suggesting that lactylation may be a general mechanism by which metabolically stressed tissues lose barrier integrity. Given that barrier failure is central to conditions ranging from sepsis to diabetic kidney disease, the conceptual reach of these findings may extend well beyond ophthalmology.

Caveats remain, as they always do at this stage of research. The pharmacological interventions were tested in experimental and preclinical systems, and the leap from rat retinas and cultured endothelial cells to human therapy will require careful validation, dosing studies, and safety assessment. Human tissue samples from proliferative diabetic retinopathy show the molecular signature, but they represent an advanced stage of disease; whether earlier interventions along this axis prevent progression is a question for future longitudinal work. Still, the identification of a defined metabolic–epigenetic–signaling pathway underlying inner blood–retinal barrier breakdown represents a genuine conceptual advance, one that reframes diabetic retinopathy not simply as a disease of damaged vessels, but as a disease of miswritten chromatin in the cells that guard the eye.

Subject of Research: Lactate-induced H3K9 histone lactylation disrupting the inner blood–retinal barrier via the PTK2–FMNL2 axis in diabetic retinopathy

Article Title: Lactate-induced H3K9 lactylation disrupts the inner blood–retinal barrier by activating the PTK2–FMNL2 axis in diabetic retinopathy

Article References: Zhu, Y., Jiang, C., He, X., Gao, X., & Jiang, Z. (2026). Lactate-induced H3K9 lactylation disrupts the inner blood–retinal barrier by activating the PTK2–FMNL2 axis in diabetic retinopathy. Cellular and Molecular Life Sciences. https://doi.org/10.1007/s00018-026-06448-y

Image Credits: AI Generated

DOI: 10.1007/s00018-026-06448-y

Keywords: diabetic retinopathy, inner blood–retinal barrier, histone lactylation, H3K9la, lactate, PTK2, FMNL2, VE-cadherin, endothelial permeability, focal adhesion signaling, epigenetics, retinal vascular leakage