Background: Hematoma clearance has been a proposed therapeutic strategy for hemorrhagic stroke. This study investigated the impact of CX3CR1 (CX3C chemokine receptor 1) activation mediated by r-FKN (recombinant fractalkine) on hematoma resolution, neuroinflammation, and the underlying mechanisms involving AMPK (AMP-activated protein kinase)/PPARγ (peroxisome proliferator-activated receptor gamma) pathway after experimental germinal matrix hemorrhage (GMH).
Methods: A total of 313 postnatal day 7 Sprague Dawley rat pups were used. GMH was induced using bacterial collagenase by a stereotactically guided infusion. r-FKN was administered intranasally at 1, 25, and 49 hours after GMH for short-term neurological evaluation. Long-term neurobehavioral tests (water maze, rotarod, and foot-fault test) were performed 24 to 28 days after GMH with the treatment of r-FKN once daily for 7 days. To elucidate the underlying mechanism, CX3CR1 CRISPR, or selective CX3CR1 inhibitor AZD8797, was administered intracerebroventricularly 24 hours preinduction of GMH. Selective inhibition of AMPK/PPARγ signaling in microglia via intracerebroventricularly delivery of liposome-encapsulated specific AMPK (Lipo-Dorsomorphin), PPARγ (Lipo-GW9662) inhibitor. Western blot, Immunofluorescence staining, Nissl staining, Hemoglobin assay, and ELISA assay were performed.
Results: The brain expression of FKN and CX3CR1 were elevated after GMH. FKN was expressed on both neurons and microglia, whereas CX3CR1 was mainly expressed on microglia after GMH. Intranasal administration of r-FKN improved the short- and long-term neurobehavioral deficits and promoted M2 microglia polarization, thereby attenuating neuroinflammation and enhancing hematoma clearance, which was accompanied by an increased ratio of p-AMPK (phosphorylation of AMPK)/AMPK, Nrf2 (nuclear factor erythroid 2-related factor 2), PPARγ, CD36 (cluster of differentiation 36), CD163 (hemoglobin scavenger receptor), CD206 (the mannose receptor), and IL (interleukin)-10 expression, and decreased CD68 (cluster of differentiation 68), IL-1β, and TNF (tumor necrosis factor) α expression. The administration of CX3CR1 CRISPR or CX3CR1 inhibitor (AZD8797) abolished the protective effect of FKN. Furthermore, selective inhibition of microglial AMPK/PPARγ signaling abrogated the anti-inflammation effects of r-FKN after GMH.
Conclusions: CX3CR1 activation by r-FKN promoted hematoma resolution, attenuated neuroinflammation, and neurological deficits partially through the AMPK/PPARγ signaling pathway, which promoted M1/M2 microglial polarization. Activating CX3CR1 by r-FKN may provide a promising therapeutic approach for treating patients with GMH.
Keywords: CX3C chemokine receptor 1; fractalkine; hematoma; hemorrhage; microglia.