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Updated: Feb 19, 2026
Three-dimensional Confocal Analysis of Microglia/macrophage Markers of Polarization in Experimental Brain Injury
Published on: September 4, 2013
Osteopontin Augments M2 Microglia Response and Separates M1- and M2-Polarized Microglial Activation in Permanent
Anne Ladwig1, Helene Luise Walter1, Jörg Hucklenbroich1
1Department of Neurology, University Hospital of Cologne, Cologne, Germany.
Background:
Focal cerebral ischemia induces distinct neuroinflammatory processes. We recently reported the extracellular phosphor-glyco-protein osteopontin (OPN) to directly affect primary microglia in vitro, promoting survival while shifting their inflammatory profile towards a more neutral phenotype. We here assessed the effects of OPN on microglia after stroke in vivo, with focus on infarct demarcation.
Methods:
Animals underwent focal photothrombotic stroke and were injected intracerebroventricularly with 500 μg OPN or vehicle. Immunohistochemistry assessed neuronal damage and infarct volume, neovascularisation, glial scar formation, microglial activation, and M1 and M2 polarisation.
Results:
After photothrombotic stroke, areas covered by M1 and M2 microglia substantially overlapped. OPN treatment reduced that overlap, with microglia appearing more spread out and additionally covering the infarct core. OPN additionally modulated the quantity of microglia subpopulations, reducing iNOS+ M1 cells while increasing M2 microglia, shifting the M1/M2 balance towards an M2 phenotype. Moreover, OPN polarized astrocytes towards the infarct.
Conclusion:
Microglial activation and M1 and M2 polarization have distinct but overlapping spatial patterns in permanent focal ischemia. Data suggest that OPN is involved in separating M1 and M2 subpopulations, as well as in shifting microglia polarization towards the M2 phenotype modulating beneficially inflammatory responses after focal infarction.
Insights
Osteopontin (OPN) shifts microglia towards a beneficial M2 phenotype after stroke, reducing inflammatory M1 cells and improving infarct demarcation. This neuroprotective effect aids in modulating inflammatory responses post-focal infarction.
Area of Science:
- Neuroscience
- Immunology
- Pathology
Background:
- Focal cerebral ischemia triggers specific neuroinflammatory responses.
- Osteopontin (OPN) is an extracellular glycoprotein influencing microglial survival and inflammatory profiles.
- Previous in vitro studies showed OPN promotes microglial survival and a neutral inflammatory phenotype.
Purpose of the Study:
- To investigate the in vivo effects of OPN on microglia following focal cerebral ischemia.
- To determine OPN's role in infarct demarcation and microglial polarization after stroke.
Main Methods:
- Focal photothrombotic stroke was induced in animals.
- Osteopontin (OPN) or vehicle was administered intracerebroventricularly.
- Immunohistochemistry was used to assess neuronal damage, infarct volume, neovascularization, glial scar formation, and microglial M1/M2 polarization.
Main Results:
- OPN treatment reduced the overlap between M1 and M2 microglia subpopulations, promoting a more spread-out distribution.
- OPN modulated microglial subpopulations, decreasing iNOS+ M1 cells and increasing M2 microglia, thus shifting the M1/M2 balance towards M2.
- OPN influenced astrocyte polarization towards the infarct area.
Conclusions:
- Microglial activation and M1/M2 polarization exhibit distinct spatial patterns in focal ischemia.
- OPN appears to separate M1 and M2 microglial subpopulations and promote M2 polarization.
- OPN beneficially modulates inflammatory responses after focal infarction by shifting microglia towards an M2 phenotype.
