Association of neurocan and microglial functional state following intracerebral hemorrhage

Intracerebral hemorrhage (ICH) triggers a robust inflammatory response characterized by microglial activation and the recruitment of macrophages. Neurocan, a major chondroitin sulfate proteoglycan, is enriched in injured brain tissue, but its temporal profile after ICH and its relationship with microglia/macrophage (M/M) function remains unclear. This study aimed to investigate the temporal pattern of neurocan after ICH, examine its association with (M/M) responses in vivo, and assess whether neurocan enhances nicotinamide adenine dinucleotide phosphate oxidase 2 (NOX2)-related microglial responses in vitro. A total of 48 C57BL/6J mice were injected intracerebrally with collagenase to induce ICH. Brain samples were collected 3, 7, 10, and 14 days after. Expression of neurocan and several M/M markers were evaluated by immunofluorescence microscopy. In vitro , primary microglia were treated with recombinant neurocan alone or together with hemin, interferon-gamma (IFN-γ), and interleukin-1 beta (IL-1β). NOX2 expression was then assessed as an indicator of microglial activation. Neurocan expression changed dynamically after ICH, with lesion-associated elevation from the early stage and a peak around day 7. Ionized calcium-binding adapter molecule 1 (IBA1)-positive M/M and neurocan were both enriched in the injured hemisphere compared with the contralateral side, but their regional patterns were not entirely consistent. IBA1 showed significant differences between the perihematomal region and lesion core, whereas neurocan did not differ significantly between these two lesion-associated regions. Additional phenotypic analyses showed distinct temporal patterns among inflammatory, oxidative, disease-associated, and repair-related M/M markers after ICH. In vitro , recombinant neurocan increased NOX2 expression in primary microglia, and this effect was more evident under ICH-mimicking inflammatory conditions. Neurocan exhibits dynamic lesion-associated changes after ICH and is associated with M/M responses in the injured brain. The in vitro findings further suggest that neurocan may enhance pro-inflammatory and oxidative microglial activation. Together, these results identify neurocan as a potentially important mediator of the post-ICH inflammatory microenvironment and a potential therapeutic target in hemorrhagic stroke. • Neurocan shows time-dependent changes after intracerebral hemorrhage (ICH) • Neurocan and myeloid activity corresponds in perihematoma but not lesion core • Pro-inflammatory microglia/macrophage activation is prominent after ICH • In vitro, hemin and cytokines mimic NOX2 elevation in ICH • Neurocan increases NOX2 in primary microglia under these ICH-mimicking conditions