Stroke Brain miR-223-3p Rise Driven by Immune Infiltration

A new study published in Cellular and Molecular Neurobiology demonstrates that the significant increase of this molecule in brain tissue following a stroke is primarily caused by the infiltration of peripheral immune cells rather than an intrinsic upregulation of the microRNA within the brain’s resident cells. This finding challenges previous bulk tissue analyses that suggested miR-223-3p was actively produced at higher rates by the brain itself in response to ischemia.

Ischemic stroke triggers a rapid and profound immune response, characterized by the infiltration of immune cells into the brain parenchyma. This process reshapes the cellular composition of the brain tissue, which can confound the analysis of molecules that are enriched in specific immune cell types. MicroRNAs, including miR-223-3p, act as powerful regulators by fine-tuning messenger RNA expression, thereby modulating cell-type-specific responses to the ischemic injury. While several previous bulk tissue analyses indicated elevated levels of this anti-inflammatory microRNA in ischemic stroke, the pathological relevance of this deregulation remained unclear due to the lack of single-cell resolution in those studies.

The study team, led by researchers including Nea Korvenlaita and Tarja Malm, utilized a multi-species approach to dissect the source of the miR-223-3p elevation. They observed that miR-223-3p is acutely increased in the blood of ischemic stroke patients and is selectively expressed in myeloid cells in mice. Because of this myeloid specificity, the microRNA appears massively elevated in bulk ischemic brain lysates. However, the research reveals that this elevation primarily reflects the increased abundance of myeloid cells in the brain rather than a per-cell upregulation of the microRNA within the brain tissue itself.

A striking finding from the investigation is that brain-infiltrating macrophages exhibited acutely reduced levels of miR-223-3p. The researchers hypothesize that these infiltrating macrophages initially acquire a more proinflammatory phenotype compared to the brain-resident macrophages. This shift in phenotype is supported by a re-analysis of single-cell transcriptomics data from the dataset GSE234052, which further indicated a proinflammatory macrophage phenotype after acute cerebral ischemia.

In healthy brain tissue, miR-223-3p is expressed by microglia and resident macrophages. When ischemia occurs, it causes the infiltration of miR-223-3p-rich peripheral myeloid cells into the brain. This influx of cells increases the overall level of miR-223-3p in tissue lysates, creating the illusion of intrinsic upregulation. In contrast, within the ischemic macrophages themselves, the levels of miR-223-3p were decreased, while no significant deregulation was found in microglia. This distinction highlights the importance of distinguishing between cell-type-specific expression changes and changes in cell population abundance.

The study exemplifies the inherent limitations of bulk tissue analyses in neuroimmunology. By relying on tissue-level data, previous studies may have drawn incorrect conclusions about the regulatory mechanisms of microRNAs in stroke. The current findings underscore the need to revisit these conclusions, especially when immune cell infiltration and the enrichment of a specific molecule are suspected. The technical challenges of integrated spatial miRNA and mRNA detection at single-cell resolution remain significant, but overcoming them is essential to accurately dissect the regulatory mechanisms underlying ischemic stroke pathology.

Understanding the precise cellular sources of microRNA changes is crucial for the development of effective immunomodulatory therapies.

By clarifying the source of miR-223-3p elevation, the study helps to refine the interpretation of bulk tissue data and encourages the use of single-cell technologies in future research. The findings highlight the complexity of the brain’s response to ischemia and the importance of considering cellular heterogeneity when analyzing molecular changes in disease states.

Subject of Research: Elevated Brain Tissue miR-223-3p After Ischemic Stroke Reflects Immune Infiltration Rather Than Intrinsic Upregulation

Article Title: Elevated Brain Tissue miR-223-3p After Ischemic Stroke Reflects Immune Infiltration Rather Than Intrinsic Upregulation

Article References: Korvenlaita, N., Gómez-Budia, M., Pistono, C., Scoyni, F., Jäntti, H., Ohtonen, S., Fazaludeen, M. F., de Sande, A. H., Bouvy-Liivrand, M., Heinäniemi, M., Kaikkonen, M. U., Lehtonen, Š., Koistinaho, J., Narkilahti, S., Ramiro, L., Penalba, A., Montaner, J., Batkova, T., Mikulik, R., … Malm, T. (2026). Elevated Brain Tissue miR-223-3p After Ischemic Stroke Reflects Immune Infiltration Rather Than Intrinsic Upregulation. Cellular and Molecular Neurobiology. https://doi.org/10.1007/s10571-026-01797-5

Image Credits: AI Generated

DOI: 10.1007/s10571-026-01797-5

Keywords: Elevated, Brain, Tissue, miR-223-3p, Ischemic, Stroke, Reflects, Immune, Infiltration, Rather, Than, Intrinsic