A team led by chemical engineer S. Patrick Walton at Michigan State University reports a fast, scalable way to purify “exomeres”—protein-rich, nonvesicular nanoparticles that ferry microRNAs (miRNAs) between cells—and shows that the particles’ RNA cargo resists enzymatic destruction even under harsh conditions. The findings, posted as a bioRxiv preprint, position exomeres as intriguing, potentially more durable alternatives to extracellular vesicles (EVs) for RNA-based therapeutics and diagnostics.
Cells broadcast molecular messages using a mixed fleet of EVs, which are membrane-bound bubbles that have dominated the delivery conversation for years. Exomeres, discovered more recently, are smaller (roughly 35–50 nm), lack lipid membranes, and are packed with RNA-interference (RNAi) machinery, such as the Argonaute protein AGO2. That biochemical signature hints that the particles’ core job is to move miRNAs and silence genes in recipient cells.
Until now, isolating exomeres at a useful scale has been a chokepoint. Techniques like asymmetric flow field-flow fractionation and ultracentrifugation can work but are time-consuming, equipment-intensive, and hard to translate into bioprocessing. Instead, Walton’s group adapted tangential flow filtration (TFF)—a staple of biotech manufacturing that separates by size as fluids sweep along semipermeable hollow fibers.
The researchers designed a “tandem TFF” cascade that first clarifies cell-culture media, then sequentially enriches particle classes using 0.05-micrometer and 500, 300, and 100 kilodalton cutoffs. Fractions corresponding to EVs and to exomeres were collected within hours, not days. Western blots showed the exomere fraction—termed F4—was depleted of canonical EV markers (CD9, CD63, FLOT1) and enriched for AGO2 and HSP90AB1—features also seen in exomeres isolated by ultracentrifugation, but with less contamination.
Crenated edges
Electron microscopy revealed approximately 40–50 nm particles with crenated edges; immunogold labeling placed AGO2 and sialylated glycans at their perimeters, consistent with prior reports that exomeres are studded with glycoproteins, such as LGALS3BP.
The shocker came from stress-testing the cargo. When the team treated EVs with RNase plus the membrane-disrupting detergent Triton X-100, small RNAs were chewed up as expected. Exomere RNA, in contrast, shrugged off RNase even when the samples were pre-treated with either protease or detergent. Control experiments confirmed the enzymes were active. The result points to a highly stable, non-membranous complex that shelters miRNAs—an attractive trait for circulating therapies that must survive nuclease-rich blood.
Small-RNA sequencing mapped reads to 812 mature miRNAs and uncovered distinct loading preferences. Several miRNAs were significantly enriched in exomeres; notably, miR-30a-3p appeared only in the exomere fraction across replicates. Two widely expressed miRNAs—miR-24-3p and miR-222-3p—looked stable across particle types, suggesting practical internal controls for future assays.
The work doesn’t yet solve every puzzle. Other nanoparticle species of similar size exist in biofluids, and the precise architecture of the exomere—possibly ring-like glycoprotein assemblies cradling RNAi proteins—remains to be nailed down. Still, by converting a manufacturing-friendly filtration platform into an exomere enricher, the study removes a key barrier to scale. If validated in animal models and patient samples, TFF-purified exomeres could accelerate two frontiers at once: robust, off-the-shelf carriers for therapeutic RNAs and a new class of stable biomarkers for disease monitoring.