A Novel Mechanism for GlycoRNA Regulating VEGF Signaling
Scientists have discovered a class of RNA modified with sugar molecules (GlycoRNA) on the cell surface. These RNAs act like "molecular sponges," adsorbing the pro-angiogenic factor VEGF-A and thus precisely controlling blood vessel development. This discovery rewrites our understanding of extracellular RNA function, opening up new avenues for treating cancer and cardiovascular diseases.
Imagine each cell wears a delicate sugar coating—this is the glycocalyx. Traditionally, this coating is mainly composed of proteins and carbohydrates, responsible for important functions such as cell recognition and signal transduction.
However, in recent years, scientists have discovered a surprising secret within this coating: RNA is also localized to the cell surface.
In 2019, Professor Carolyn Bertozzi's team at Stanford University first reported GlycoRNA—a class of small RNAs modified with sialic acid and fucose. They are like RNA dressed in a sugar coating, quietly lying on the cell surface, waiting to be discovered. However, how do these GlycoRNAs attach to the cell surface? What exactly do they do? These have remained a mystery.
On January 28, 2026, Ryan A. Flynn's team from Harvard University published a study in Nature titled "GlycoRNA complexed with heparan sulfate regulates VEGF-A signalling." This study reveals a novel mechanism by which heparan sulfate negatively regulates VEGF-A signaling and angiogenesis by recruiting glycosylated RNA to form a ribonucleoprotein complex on the cell surface.
Ryan A. Flynn's team, through Genome-Wide CRISPR Screening, identified the key code for GlycoRNA localization on the cell surface: heparan sulfate (HS)—a negatively charged long-chain sugar molecule—which is precisely the "scaffold" of GlycoRNA!
The research team conducted a series of gene knockout experiments to verify this discovery. Knocking out EXT1 or EXT2 (these two enzymes are crucial for HS chain synthesis) completely eliminated GlycoRNA signaling. Treatment of cells with heparinase to degrade existing HS chains also rapidly reduced GlycoRNA signaling. More interestingly, knocking out NDST1 (responsible for N-sulfation modification of HS) reduced GlycoRNA by 75%; knocking out HS6ST1 (responsible for 6-O-sulfation modification) reduced GlycoRNA by 70%. These results clearly demonstrate that specific chemical modifications of the HS chain are crucial for recruiting and stabilizing GlycoRNA.
The research team also observed a dynamic process: after treating cells with Heparinase to remove HS, GlycoRNA gradually recovered within 3 hours as new HS chains were synthesized. This indicates that the HS chain acts like a "base of a magnet," continuously recruiting new GlycoRNA to form cell surface ribonucleoprotein particles (csRNPs). These csRNPs not only contain GlycoRNA but also various RNA-binding proteins such as DDX21 and hnRNP-U, which together constitute a sophisticated nanoscale signal regulatory unit.
The research team chose vascular endothelial growth factor A (VEGF-A165), a star molecule in angiogenesis, as their research subject. This is because it possesses a positively charged heparin-binding domain (rich in arginine), which promotes vascular endothelial cell proliferation and migration, and its interaction with Heparan Sulfate is crucial to its activity.
Using UV cross-linked immunoprecipitation and micro-thermophoresis, the research team confirmed a surprising fact: VEGF-A165 can directly bind small RNAs (including snRNA, rRNA, tRNA, etc.), while the short isoform VEGF-A121, lacking the heparin-binding domain, cannot bind RNA. More importantly, Sialylated GlycoRNAs bind more strongly to VEGF-A165, indicating that glycosylation plays a vital role in regulating this interaction.
Functional experiments revealed the true role of RNA—it acts as a "brake" rather than an "accelerator." When human umbilical vein endothelial cells (HUVECs) were treated with RNase to degrade cell surface RNA, VEGF-A165-induced ERK phosphorylation levels increased threefold, and the amount of VEGF-A165 bound to the cell surface also increased twofold. This indicates that GlycoRNA acts like a "molecular sponge," adsorbing VEGF-A165 and preventing it from binding to its receptor VEGFR2, thereby inhibiting the activation of the downstream ERK signaling pathway.
In 3D microfluidic chip experiments, RNase-treated vascular endothelial cells exhibited stronger migration capabilities, forming longer lumen-like structures and displaying a more active angiogenesis phenotype. This further confirms that cell surface GlycoRNA is an important negative regulator for maintaining angiogenesis homeostasis.
To validate this mechanism in vivo, the research team designed a sophisticated mutant: mutating all eight arginine residues in the heparin-binding domain of VEGF-A165 to lysine, creating the VEGF-A165 HS(R/K) mutant. This design retained the ability to bind to heparan sulfate (because the total positive charge remained unchanged), but lost the ability to bind to RNA (because arginine is a key amino acid for RNA recognition).
In a mouse retinal angiogenesis model, injection of wild-type VEGF-A165 increased blood vessel density, while injection of the HS(R/K) mutant led to a further increase in blood vessel density, resulting in significant hypervascularization. In a zebrafish embryonic development model, injection of mRNA encoding the HS(R/K) mutant caused defects in intersegmental vessels and excessive angiogenesis, perfectly mimicking the phenotype of "RNA brake failure."
The research team also conducted Wnt3a fusion protein experiments, fusing the heparin-binding domain of VEGF-A165 to the Wnt3a signaling protein. The results showed that the wild-type fusion protein inhibited Wnt signaling, maintaining normal embryonic axis length; while the HS(R/K) fusion protein led to excessive activation of Wnt signaling, resulting in embryonic axis shortening. This demonstrates that the RNA binding capacity of the heparin-binding domain is a universal mechanism for limiting growth factor activity.
Fig. 1 Schematic of HS–RNP complex regulation of VEGF-A signalling and angiogenesis. (Chai, et al. 2026)
This study reveals a novel cell surface regulatory axis: the heparan sulfate chain, as a negatively charged glycan backbone, plays two roles simultaneously. On the one hand, it recruits negatively charged GlycoRNAs and their bound RNA-binding proteins (such as DDX21 and hnRNP-U) to form cell surface ribonucleoprotein granule (csRNP) clusters; on the other hand, it binds to the heparin-binding domain of VEGF-A165 through electrostatic interactions.
Under normal physiological conditions, VEGF-A165 is trapped within csRNP clusters, unable to effectively activate its receptor VEGFR2, ERK signaling is suppressed, and angiogenesis is controlled. When cell surface RNA is degraded by RNase, or when the RNA-binding-deficient HS(R/K) mutant is used, VEGF-A165 is released from the csRNP clusters, leading to robust activation of VEGFR2, excessive ERK signaling activation and pathological angiogenesis.
This means that cells can fine-tune the activity of growth factors by regulating the abundance and composition of csRNAs, achieving precise responses to external signal stimuli. This regulatory mechanism is both rapid (without requiring changes in gene expression) and reversible (RNA can be dynamically exchanged), making it an ideal mechanism for cells to adapt to changes in the microenvironment.
This study represents a theoretical breakthrough on multiple levels. It is the first to demonstrate that GlycoRNAs anchor to the cell surface via heparan sulfate, forming functional complexes and revealing that RNA plays an active signaling regulatory role in the extracellular environment, rather than merely being metabolic waste or passive messengers. The research establishes a new paradigm of the "RNA-Glycoprotein" ternary interaction network, closely linking glycobiology, RNA biology, and signal transduction biology.
From a disease treatment perspective, this discovery provides novel targets for various vascular-related diseases. In cancer treatment, tumor angiogenesis is abnormally active; targeting csRNPs may starve tumors by enhancing the "RNA brake" function. In pathological angiogenesis diseases such as diabetic retinopathy, enhancing csRNP function may inhibit harmful angiogenesis. Conversely, in ischemic diseases such as coronary artery disease or peripheral vascular disease, local degradation of csRNAs can enhance the efficacy of VEGF and promote therapeutic angiogenesis. In tissue engineering, this mechanism can be used to optimize the vascularization of the stem cell microenvironment.
In drug development, this research opens up several new avenues of thought. We can develop RNase analogs to locally degrade csRNA and enhance the efficacy of VEGF therapy; we can also design GlycoRNA mimics to competitively bind to VEGF and inhibit pathological angiogenesis; and we can also indirectly regulate the assembly and function of csRNP by modulating HS sulfation modification.
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