Hypoxia-inducible protein 2 mediates metabolic adaptation of Ly6ChighLy6Glow monocytes after stroke.

Ly6ChighLy6Glow monocytes represent a distinct subset infiltrating the stroke brain with anti-inflammatory properties distinct from classical Ly6Chigh monocytes.

• Single-cell transcriptomic profiling was used to characterize monocyte heterogeneity in the stroke brain.
• Ly6ChighLy6Glow monocyte-derived macrophages were identified as having an anti-inflammatory phenotype in the ischemic brain.
• This subset was identified by combining analysis of stroke patient samples with in vivo and in vitro murine studies.

HIG2 (Hilpda/hypoxia-inducible lipid droplet-associated protein) was identified as a critical mediator of the anti-inflammatory property of Ly6ChighLy6Glow monocyte-derived macrophages in the stroke brain.

• HIG2 was identified through combined analysis of stroke patient samples, in vivo and in vitro murine studies, and single-cell transcriptomic profiling.
• HIG2 expression was associated with the anti-inflammatory phenotype of this specific monocyte-derived macrophage subset.
• HIG2 is also known as hypoxia-inducible lipid droplet-associated protein (Hilpda).

HIG2 promotes phosphatidylcholine synthesis through Hif1α-dependent transcriptional regulation of choline kinase α.

• HIG2 mechanistically initiates lipid metabolism reprogramming that underpins the anti-inflammatory phenotype of Ly6ChighLy6Glow monocyte-derived macrophages.
• The pathway involves Hif1α-dependent transcriptional regulation of choline kinase α as a key downstream effector.
• Phosphatidylcholine synthesis was identified as a critical metabolic output linking HIG2 activity to anti-inflammatory macrophage polarization in the ischemic brain.

Intranasal delivery of recombinant HIG2 protein improves neurological outcomes after stroke.

• Recombinant HIG2 protein was administered via intranasal delivery as a therapeutic intervention.
• This treatment approach resulted in improved neurological outcomes after stroke in the murine model.
• The finding suggests that targeting HIG2 may represent a novel immunometabolic strategy to mitigate poststroke neuroinflammation.

Ly6Chigh monocytes play critical roles in secondary neuroinflammation in the stroke brain and show increased infiltration with substantial heterogeneity.

• Growing evidence reveals increased infiltration of myeloid cells with substantial heterogeneity in the stroke brain.
• Ly6Chigh monocytes were previously recognized as a pro-inflammatory subset but demonstrate functional heterogeneity in the ischemic environment.
• The study addressed the question of how Ly6Chigh monocyte-derived macrophages adapt to the ischemic environment in the stroke brain.