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SIK3-mKO Enhances Myelin Debris Phagocytosis via CD11c Complement Pathway for White Matter Protection Poststroke
Leilei Mao1, Chenran Wang1, Ke Wang1
1Medical Research and Innovation Center of Shanghai Pudong Hospital, State Key Laboratory of Brain Function and Disorders, MOE Frontiers Center for Brain Science, and Institutes of Brain Science, Fudan University, China (L.M., C.W., K.W., C.Z., Z. Shi, Y.Y., J.Z., J.W., M.H., Y.G.).
Background:
White matter preservation is a rate-limiting factor in neurological recovery after ischemic stroke and depends on efficient clearance of myelin debris by microglia/macrophages. Our prior work demonstrated that microglia/macrophage-specific SIK3 (salt-inducible kinase) knockout (SIK3-mKO) promotes an anti-inflammatory subset, enhances myelin phagocytosis, and limits white matter injury, yet the downstream molecular mechanisms remain undefined. Here, we elucidate a previously unrecognized signaling axis underlying these protective effects.
Methods:
SIK3-mKO mice (SIK3Flox+/+;CX3CR1CreER) were generated via tamoxifen-induced Cre recombination. Transient focal cerebral ischemia was induced by 60-minute transient middle cerebral artery occlusion. Neurological outcomes were assessed via Garcia, rotarod, foot-fault, and adhesive-removal tests. Immunofluorescence, flow cytometry, single-cell RNA sequencing, real-time quantitative polymerase chain reaction, ex vivo myelin phagocytosis assay, magnetic resonance imaging, and compound action potential recordings were used to characterize microglia/macrophage polarization, myelin phagocytic capacity, white matter integrity, and nerve conduction function.
Results:
In the acute phase poststroke, SIK3-mKO selectively upregulated CD11c and its upstream complement initiator component 1q in anti-inflammatory microglia/macrophage subsets. Within the 400 to 800 µm peri-infarct zone, SIK3-mKO elevated the proportion of CD11c+ microglia/macrophage by 15.1% and C1q+ microglia/macrophage by 15.8% relative to wild-type controls. This CD11c-component 1q axis enhanced myelin debris clearance by 19.0% while constraining pathological engulfment of intact myelin, representing a balanced functional switch that mitigates severe demyelination. Conversely, myeloid-CD11c silencing using AAV-Itgax shRNA partially reversed SIK3-mKO-conferred protection. CD11c knockdown reduced anti-inflammatory microglia/macrophage proportions by 9.7%, attenuated physiological phagocytosis and lowered debris clearance efficiency by 7.5%, reduced MBP (myelin basic protein)-positive myelin preservation by 10.0%, and ultimately impaired white matter preservation and neurological recovery.
Conclusions:
We identify the SIK3-CD11c-component 1q axis as a novel pathway that orchestrates microglia/macrophage phagocytic homeostasis and preserves white matter integrity after ischemic stroke. These findings clarify SIK3 signaling in microglia/macrophage and highlight the CD11c-centered complement cascade as a promising therapeutic target for restoring white matter integrity in poststroke neurorepair.
