Inflammatory stimulation reshapes microglial vesicle miRNA cargo and modestly alters recipient cells

Neuroinflammation is a hallmark of neurodegenerative diseases and contributes to progressive neuronal dysfunction, and microglia—the resident immune cells of the central nervous system—orchestrate inflammatory responses and can transmit activation signals through extracellular vesicles. These vesicles carry bioactive molecules, including microRNAs, that may influence the phenotypes of recipient cells. In an in vitro study published in Cellular and Molecular Neurobiology, researchers investigated whether extracellular-vesicle-associated inflamma-miRNAs derived from classically activated microglia contribute to the propagation of inflammatory responses, and their findings reveal both a role for two specific microRNAs in donor cells and the limits of targeting them to block inflammatory communication.

Microglial cells were stimulated with lipopolysaccharide (LPS) or ATP, two well-established inflammatory triggers. Extracellular vesicles were then isolated from the conditioned medium and characterized using nanoparticle tracking analysis and western blot, standard techniques for confirming vesicle size distribution and marker protein content. Naïve microglia—cells that had not been stimulated—were subsequently exposed either to the conditioned medium or to the isolated vesicles, and the researchers measured inflammatory markers and microRNA expression in the recipient cells.

The results showed a clear remodeling of the microRNA cargo. LPS stimulation induced a pro-inflammatory phenotype in donor microglia, characterized by increased iNOS expression and significant enrichment of miR-155, a microRNA widely associated with inflammatory activation. miR-34a, another microRNA implicated in neurodegenerative pathways, showed an increasing trend in the donor cells. A similar increase in both microRNAs was observed in the extracellular vesicles released by the activated cells, although in the vesicles this enrichment did not reach statistical significance—a nuance the authors emphasize rather than overstate.

To probe whether these microRNAs causally contribute to the inflammatory state, the team used inhibition approaches. Blocking miR-155 partially attenuated LPS-induced iNOS expression in donor microglia, supporting its involvement in the inflammatory pathway. Conversely, inhibiting miR-34a partially increased TREM2 levels, a receptor associated with microglial homeostasis, suggesting that miR-34a participates in regulating the balance between inflammatory and homeostatic states. These partial effects indicate that neither microRNA acts alone; each contributes to a broader regulatory network rather than serving as a single master switch.

The critical test came when the researchers examined whether the vesicle cargo could transmit inflammation to recipient cells. Extracellular vesicles derived from activated microglia did induce modest inflammatory changes in naïve recipient microglia, confirming that the vesicles carry some bioactive capacity. However, when the researchers inhibited individual microRNAs in the donor cells before vesicle release, this manipulation had no effect on the vesicle-mediated propagation of inflammatory signals to the recipient cells.

This null result is scientifically meaningful. It suggests that extracellular-vesicle-mediated inflammatory communication is likely regulated by multiple factors beyond individual microRNAs. Targeting a single microRNA within the donor cell, even one as prominently enriched as miR-155, was insufficient to disrupt the overall inflammatory message carried by the vesicles.

The authors conclude that their findings support a role for miR-155 and miR-34a in the inflammatory response of donor microglia, while suggesting that vesicle-mediated inflammatory communication depends on a more complex set of molecular determinants. The limited impact of microRNA inhibition on vesicle-mediated propagation, they note, highlights the complexity of extracellular-vesicle signaling mechanisms—a caution against assuming that abundant cargo molecules are necessarily the functional drivers of intercellular communication.

Because this was an in vitro study using cultured microglial cells, the findings apply to isolated cell systems rather than living brain tissue, and the modest inflammatory changes observed in recipient cells should be interpreted within that scope. The work does, however, provide a mechanistic foundation for future investigations into how microglial vesicle cargo is remodeled during inflammation and which components beyond individual microRNAs sustain the propagation of inflammatory signals between immune cells of the central nervous system.

Subject of Research: How inflammatory stimulation changes the miRNA cargo of microglial extracellular vesicles and its effects on recipient microglia in vitro.

Article Title: Inflammatory stimulation remodels microglial extracellular vesicle miRNA cargo and selectively modulates recipient microglial responses

Article References: Francesca, D. C., Francesca, M., Sabrina, P., D’Silva, C., Libotte, M. E. C., Eleonora, P., Giorgia, B., Giampaolo, Z., & Barbara, M. (2026). Inflammatory stimulation remodels microglial extracellular vesicle miRNA cargo and selectively modulates recipient microglial responses. Cellular and Molecular Neurobiology. https://doi.org/10.1007/s10571-026-01823-6

Image Credits: AI Generated

DOI: 10.1007/s10571-026-01823-6

Keywords: microglia, extracellular vesicles, microRNA, miR-155, miR-34a, neuroinflammation, lipopolysaccharide, iNOS, TREM2, in vitro study, cell culture, neurodegenerative disease