New Study Identifies Unique Type of Microglia Associated with Stroke in the I/R Injured Brain

Abstract
Ischemic stroke is the leading cause of immortal disability and death worldwide. For treatment in the acute phase, it is necessary to control excessive reactive oxygen species (ROS) damage during ischemia/reperfusion (I/R). Microglia are well known to be closely associated with excessive ROS response in the early stage of I/R. However, the precise roles of microglia associated with mitigating ROS damage, and molecular markers of heterogenetic microglia in the I/R damaged brain has not been clarified. Here, we identified a new type of microglia associated with stroke in the I/R injured brain. Single-cell RNA sequencing (scRNA-seq) was used to assess transcriptional changes of microglia and immune cells in the contralateral (CL) and ipsilateral (IL) hemispheres after transient middle cerebral artery occlusion (tMCAO) surgery to mimic ischemic stroke. We classified a unique type of microglia with enhanced antioxidant function and markers similar to those of disease-associated microglia (DAM), designated them as stroke-associated microglia (SAM). The representative antioxidant enzyme, Peroxiredoxin-1 (Prdx1), was predominantly expressed in SAM and mediated ROS defense genes, including Txn1, Srx1, Mt1, and Mt2. In the Prdx1−/− I/R damaged brain, we observed significantly increased infarction, as assessed by TTC staining, and FACS analysis detected severe microglial cell death. Importantly, scRNA transcriptomics data showed that the SAM population was specifically decreased in Prdx1−/− mice and that these mice exhibited decreased ROS damage resistance. Inflammatory responses which were detected by ELISA and qPCR, were also increased in Prdx1−/− IL hemispheres. Finally, Prdx1-dependent antioxidative SAM were found to be essential for increasing the transcription levels of stroke-protective molecules, such as osteopontin and ferritin. A novel microglia type (SAM) is specifically activated in response to stroke I/R injury, and that Prdx1 expression is required for the activation and enhanced antioxidant function of SAM.

A research team, affiliated with UNIST has identified a new type of microglia associated with stroke in the ischemia/reperfusion (I/R) injured brain. This breakthrough has been led by Professor Sung Ho Park and his research team in the Department of Biological Sciences at UNIST, in collaboration with a research team, led by Professor Goo Taeg Oh from Ewha Womans University.

Microglia, the primary immune cells in the central nervous system (CNS), are known to eliminate unwanted germs and debris and remove dying neurons. In this study, the research team classified a new type of microglia with enhanced antioxidant function and markers similar to those of disease-associated microglia (DAM), designated them as stroke-associated microglia (SAM).

Through animal experiments, the research team demonstrated that the presence of the typical antioxidant gene, Peroxiredoxin-1 (Prdx1), protects against acute I/R injury and is required for SAM activation and the consequent reduction of microglial cell death and inflammatory responses.

In addition, after performing transient middle cerebral artery occlusion (tMCAO) surgery to induce ischemic stroke in mice, the research team found that Prdx1−/− mice were more severely injured by acute I/R injury, as confirmed by TTC staining, neurological deficit scores, motor tests, and the survival rate, indicating that Prdx1 has a protective function.

Figure 1. Peroxiredoxin1 (Prdx1) is essential for SAM activation after stroke damage. (Left) UMAP plots showing clusters and annotations of cells identified in Prdx1+/+ and Prdx1−/− IL hemispheres after tMCAO. (Right) Representative images of TTC stained brain slices of Prdx1+/+ (n = 18) and Prdx1−/− (n = 22) mice.

“In this study, we have, for the first time, identified a specialized and distinctive type of microglia with enhanced antioxidant function in stroke mice,” says Professor Park. “Prdx1-dependent SAM may be a potential biomarker and therapeutic target for protecting microglial function and treating brain I/R injury,” He adds, “Although this new cluster will require further study, our findings provide a new perspective that Prdx1-mediated microglial heterogeneity is important in ischemic stroke.”

This study has been jointly participated by Wonhyo Lee, a doctoral researcher within the Department of Biological Sciences at UNIST and Sinai Kim, a doctoral researcher within the Department of Life Sciences at Ewha Womans University, as first authors.
Their findings have been published in the August 2022 issue of Redox Biology, a renowned journal in the areas of both health and disease. This study was carried out with the support of the National Research Foundation of Korea (NRF).

Journal Reference
Sinai Kim, Wonhyo Lee, Huiju Jo, et al., “The antioxidant enzyme Peroxiredoxin-1 controls stroke-associated microglia against acute ischemic stroke,” Redox Biology, (2022).