SF3B1 encodes a core component of the U2 snRNP spliceosome, the molecular machine that recognizes branch points in pre-messenger RNA and defines where introns are removed. Mutations in SF3B1 are among the most frequent genetic lesions in myelodysplastic syndromes, a group of clonal blood disorders in which the bone marrow produces immature cells that fail to mature properly, and they are particularly associated with ring sideroblasts and aberrant erythropoiesis. Patients with SF3B1-mutant disease suffer from anemia that often becomes transfusion-dependent, yet strategies to restore terminal erythroid maturation in this setting remain limited. Luspatercept, a fusion protein that traps TGF-beta family ligands, has offered partial benefit, but the search for accessible, mechanism-defining interventions continues.

To model the disease, the team used a zebrafish sf3b1 knockdown system. Zebrafish embryos are transparent, develop rapidly, and carry erythroid reporter lines that allow researchers to watch red blood cell formation in real time. In the morphants, erythroid reporter expression collapsed and hemoglobinization was severely impaired, recapitulating the ineffective erythropoiesis characteristic of SF3B1-linked disease. When the researchers treated these embryos with As2S2, erythroid reporter expression returned and hemoglobinization was reinstated. The rescue was partial but persistent at later developmental stages, indicating that the compound does not merely mask the defect but partially reinstates the maturation program that sf3b1 deficiency disrupts.

The mechanism emerged from integrated transcriptomic and proteomic analyses. As2S2 remodels metabolic and translational programs in the deficient embryos, reshaping the cellular economy of developing red blood cells. More notably, the compound attenuates TGF-beta pathway activity, and the single most prominent change is the induction of smad7. Smad7 is an inhibitory Smad, a negative feedback regulator that blocks receptor-mediated phosphorylation of the canonical Smad2 and Smad3 signaling cascade. By upregulating smad7, As2S2 effectively applies a brake to hyperactive TGF-beta signaling, a pathway whose excessive activity is known to suppress terminal erythroid maturation.

To validate that this Smad7-dependent mechanism is genuinely therapeutic rather than incidental, the researchers performed comparative analysis with pharmacologic TGF-beta inhibition. The two interventions share an overlapping therapeutic axis, converging on the same TGF-beta-modulating mechanism. This convergence validates the Smad7-dependent pathway and reveals that As2S2 acts as an in vivo chemical probe, a small molecule that counteracts sf3b1-dependent erythroid failure through a defined molecular route. The team also notes that As2S2 shares a convergent TGF-beta-modulating mechanism with luspatercept, the clinically approved erythroid maturation agent, suggesting that the compound and the biologic rescue erythropoiesis through a common regulatory node.

The study is notable for its experimental design. Zebrafish have become an increasingly important model for hematologic disorders because their erythroid development is highly conserved with that of humans and their optical transparency permits quantitative imaging of blood cell formation. By combining a genetic knockdown model with reporter lines, transcriptomics, proteomics, and pharmacologic comparison, the researchers built a multi-layered evidence chain that links a clinical compound to a specific molecular mediator. The integrated omics approach revealed that As2S2 does not simply correct splicing, the primary defect caused by sf3b1 loss, but instead bypasses it by modulating downstream signaling, a strategy that may prove more tractable than attempting to restore spliceosome function directly.

Smad7 has long been recognized as a rheostat of TGF-beta biology, but its role in erythroid maturation has been underappreciated. The new findings highlight Smad7 as a candidate for therapeutic modulation in SF3B1-associated ineffective erythropoiesis. If Smad7 upregulation can be achieved safely in patients, whether through As2S2 or through other means, it may offer a way to counteract the TGF-beta-driven suppression of red cell maturation that contributes to anemia in myelodysplastic syndromes. The convergence with luspatercept suggests that Smad7 sits within the same regulatory circuit that biologic agents already exploit clinically.

Arsenic disulfide is distinct from arsenic trioxide, the form of arsenic that has already earned regulatory approval for acute promyelocytic leukemia. As2S2 is a mineral compound with a long history in traditional Chinese medicine and has been investigated in hematologic malignancies, but its application to spliceosome-mutant anemia represents a new therapeutic direction. The zebrafish model provides an efficient platform for testing such compounds in vivo, and the partial persistence of rescue at later developmental stages suggests that the effect is not merely transient. Further work will be needed to determine whether As2S2 can achieve similar erythroid maturation rescue in mammalian models and ultimately in patients with SF3B1-mutant myelodysplastic syndromes.

The findings carry broader implications for how researchers approach spliceosome-driven disease. Rather than attempting to repair the mutated spliceosome itself, an enormously difficult task given that SF3B1 is a core component of a large molecular machine, the As2S2 strategy identifies a downstream signaling pathway that can be modulated pharmacologically. This bypass approach may be applicable to other spliceosome-mutant disorders, and the identification of Smad7 as a mediator opens a concrete molecular target. The study also underscores the value of zebrafish as a discovery platform, allowing rapid in vivo screening of compounds that would be difficult to evaluate in cell culture alone.

Published as an open-access research article in Annals of Hematology, the study was supported by the National Natural Science Foundation of China, the Zhejiang Provincial Natural Science Foundation, and multiple Shanghai municipal programs. The authors declare no competing interests. As research continues into the molecular mechanisms of ineffective erythropoiesis, the convergence of an ancient mineral compound, a modern genetic model, and a defined signaling mediator offers a compelling example of how traditional pharmacology and contemporary molecular biology can illuminate each other. Whether As2S2 will translate into clinical benefit for patients with SF3B1-mutant myelodysplastic syndromes remains to be determined, but the identification of Smad7 as a pharmacologically tractable mediator provides a clear path forward.

Subject of Research: As2S2 restores erythroid maturation in sf3b1-deficient zebrafish by upregulating smad7

Article Title: As2S2 restores erythroid maturation in sf3b1-deficient zebrafish by upregulating smad7

Article References: Wu, F., Cai, S., Luo, Q., Li, H., Tao, Y., Li, J., Chen, Y., Wang, Y., Xu, H., Hu, K., Ding, N., Ni, R., Jin, R., Liu, M., Shi, Y., Yu, L., & Lu, J. (2026). As2S2 restores erythroid maturation in sf3b1-deficient zebrafish by upregulating smad7. Annals of Hematology. https://doi.org/10.1007/s00277-026-07324-2

Image Credits: AI Generated

DOI: 10.1007/s00277-026-07324-2

Keywords: As2S2, restores, erythroid, maturation, sf3b1-deficient, zebrafish, upregulating, smad7, scientific research

The study, led by Shuhong Guan, Xiaoqin Zhu, Yunqi Ge, Deyue Cui and corresponding author Jun Zhou of the Department of Respiratory and Critical Care Medicine at The First People’s Hospital of Changzhou, focused on macrophages, the versatile immune cells that patrol lung tissue. Macrophages are not a single entity but a spectrum of functional states. At one pole sit the M1-like cells, which mount inflammatory, microbe-killing responses; at the other pole sit the M2-like cells, which are classically associated with tissue repair, wound healing and, crucially, the resolution phase of inflammation. In the context of chronic injury, however, M2-like macrophages have increasingly been implicated in pathological scarring, and the new work helps explain how they communicate their pro-fibrotic message to neighboring cells.

The messengers in question are exosomes, nanoscale vesicles roughly 30 to 150 nanometers in diameter that cells release into their surroundings. Far from being cellular debris, exosomes are now recognized as sophisticated intercellular communication vehicles, packed with proteins, lipids and nucleic acids, including microRNAs, which are short regulatory RNA molecules that fine-tune gene expression after transcription. When an exosome is taken up by a recipient cell, its microRNA cargo can silence specific target messenger RNAs, effectively reprogramming the recipient’s behavior. To establish their experimental system, the researchers isolated exosomes from both resting M0 macrophages and M2-polarized macrophages, using two sources: the RAW264.7 mouse monocyte-macrophage cell line and primary macrophages derived from mouse bone marrow. The team verified the identity and purity of their vesicle preparations using transmission electron microscopy to visualize the characteristic cup-shaped morphology, nanoparticle tracking analysis to profile size distribution, and immunoblotting for canonical exosome markers such as CD9, CD63 and CD81, while confirming the absence of contaminants like the endoplasmic reticulum protein calnexin and the Golgi protein GM130.

With the vesicles characterized, the researchers turned to a mouse model of pulmonary fibrosis induced by bleomycin, a chemotherapy agent whose pulmonary toxicity produces scarring that closely mirrors the human disease. When M2-derived exosomes were administered to these mice, the fibrotic process was notably exacerbated compared with animals receiving exosomes from resting M0 macrophages. In other words, the cargo of the M2 macrophage vesicles was not benign; it actively accelerated the deposition of scar tissue in the injured lung. Fluorescently labeled exosomes injected into the tail vein were tracked in vivo and ex vivo, revealing that the vesicles homed to the lung among the major organs, and time-course experiments showed that exosomal microRNA content accumulated in recipient lung cells over hours of exposure.

Comprehensive microRNA sequencing of the exosomes from M0 and M2 macrophages revealed a candidate culprit: miR-350-5p, a microRNA that was markedly enriched in the M2-derived vesicles. Functional assays then demonstrated that this microRNA could be delivered into two key recipient cell types, lung fibroblasts and alveolar epithelial cells, the very populations whose misbehavior defines pulmonary fibrosis. Fibroblasts are the cells responsible for producing collagen and other extracellular matrix components, and in fibrosis they become activated into myofibroblasts, hypersecretory cells that lay down matrix far in excess of what tissue repair requires. Alveolar epithelial cells, meanwhile, can undergo epithelial-mesenchymal transition, or EMT, a developmental program in which epithelial cells lose their adhesive, barrier-maintaining character and acquire migratory, matrix-producing traits. Both processes were significantly promoted when cells were exposed to M2-derived exosomes in vitro.

To test whether miR-350-5p was truly the active ingredient, the researchers inhibited the microRNA inside M2 macrophages before collecting their exosomes. The result was striking: exosomes depleted of miR-350-5p lost much of their ability to drive fibroblast activation and EMT in cell culture. Moving back into the animal model, mice treated with exosomes from miR-350-5p-inhibited M2 macrophages showed significantly attenuated pulmonary fibrosis and reduced collagen deposition compared with mice receiving normal M2 exosomes. This gain-of-function and loss-of-function pairing, in which adding the microRNA worsens disease and removing it improves it, provides strong causal evidence that the microRNA is not merely a passenger but an active pro-fibrotic agent.

The mechanistic heart of the paper lies in the identification of the microRNA’s target. Using complementary approaches, the team showed that miR-350-5p directly binds to and suppresses Smad7, a well-characterized inhibitory molecule in the transforming growth factor beta signaling pathway. TGF-beta is the master cytokine of fibrosis, and its intracellular Smad signaling cascade drives the transcription of collagen genes, alpha-smooth muscle actin and other markers of the myofibroblast phenotype. Smad7 acts as a built-in brake on this pathway, providing negative feedback that keeps TGF-beta responses in check. By silencing Smad7, exosomal miR-350-5p effectively removes that brake, amplifying TGF-beta/Smad signaling in both fibroblasts and alveolar epithelial cells and pushing them toward fibrotic phenotypes. The elegance of this mechanism is that it allows immune cells to influence the fibrotic program of structural cells without direct cell-to-cell contact, using a soluble, packaged RNA message that survives in the extracellular space.

The clinical implications are considerable. Current antifibrotic drugs for idiopathic pulmonary fibrosis, nintedanib and pirfenidone, target downstream pathways of fibrogenesis but do not reverse established scarring, and the search for upstream, disease-modifying targets remains intense. The miR-350-5p/Smad7 axis identified here offers two potential intervention points. Antisense oligonucleotide technologies, including locked nucleic acid inhibitors and antagomirs, have matured to the point where microRNA inhibition in the lung is a plausible therapeutic strategy, and several microRNA-targeting drugs are already in clinical trials for other indications. Alternatively, strategies that bolster Smad7 expression or mimic its braking function could restore equilibrium to TGF-beta signaling in fibrotic lungs. Because the exosomal delivery mechanism concentrates the microRNA in recipient lung cells, intercepting the vesicles themselves, for example by blocking uptake pathways, represents a third possible approach.

As with any preclinical study, important caveats apply. The work was performed in mouse models and mouse cell lines, and miR-350-5p is a rodent microRNA whose human counterpart and target repertoire would need to be validated before the findings can be translated. Bleomycin-induced fibrosis, while widely used, captures only part of the pathology of idiopathic pulmonary fibrosis, which develops over decades rather than weeks and involves repeated microinjuries, aging-related changes and genetic susceptibility. The authors also note that inhibiting miR-350-5p in M2 macrophages only partially improved fibroblast activation and EMT in vitro, indicating that other cargo molecules within M2 exosomes likely contribute to the pro-fibrotic signal. Nonetheless, the study adds a compelling new layer to the understanding of how macrophages orchestrate fibrosis, and it underscores a broader theme in modern cell biology: that the vesicles cells shed are not waste but potent packages of regulatory information. If the miR-350-5p/Smad7 axis holds up in human tissue and translational models, it could open a genuinely new front in the fight against a disease that medicine has long been losing.

Subject of Research: The role of M2 macrophage-derived exosomal miR-350-5p in targeting Smad7 to drive pulmonary fibrosis

Article Title: M2 macrophage-derived exosomal miR-350-5p facilitates pulmonary fibrosis through targeting Smad7 in lung fibroblasts and alveolar epithelial cells

Article References: Guan, S., Zhu, X., Ge, Y., Cui, D., & Zhou, J. (2026). M2 macrophage-derived exosomal miR-350-5p facilitates pulmonary fibrosis through targeting Smad7 in lung fibroblasts and alveolar epithelial cells. Cellular and Molecular Life Sciences. https://doi.org/10.1007/s00018-026-06400-0

Image Credits: AI Generated

DOI: 10.1007/s00018-026-06400-0

Keywords: pulmonary fibrosis, M2 macrophages, exosomes, miR-350-5p, Smad7, TGF-beta signaling, epithelial-mesenchymal transition, fibroblast activation, microRNA, idiopathic pulmonary fibrosis, collagen deposition, lung fibrosis