Background: Enhancing hematoma clearance through phagocytosis may reduce brain injury after intracerebral hemorrhage (ICH). In the current study, we investigated the role of CD47 in regulating erythrophagocytosis and brain injury after ICH in nude mice.
Methods: This study was in two parts. First, male adult nude mice had an intracaudate injection of 30μl saline, blood from male adult wild type (WT) mice or blood from CD47 knockout (CD47 KO) mice. Second, mice had an intracaudate injection of 30μl CD47 KO blood with clodronate or control liposomes. Clodronate liposomes were also tested in saline-injected mice. All mice then had magnetic resonance imaging to measure hematoma size and brain swelling. Brains were used for immunohistochemistry and Western blot.
Results: Erythrophagocytosis occurred in and around the hematoma. Injection of CD47 KO blood resulted in quicker clot resolution. Hematoma volume (assessed by T2* lesion volume) showed no difference between two groups at day 1 (14.3 ± 2.9 vs. 14.4 ± 3.2 mm3, p>0.05). However, when ICH was induced with CD47 KO blood, MRI T2* volumes were significantly smaller compared to WT blood at day 3 (7.8 ± 1.7 vs.11.8 ± 4.3 mm3, p<0.01). CD47 KO blood also resulted in less brain swelling, and less neurological deficits compared to WT blood. Higher brain heme oxygenase-1 levels and more microglial activation (mostly M2 polarized microglia) were found after CD47 KO blood injection at day-3. Co-injection of clodronate liposomes, to deplete phagocytes, caused more severe brain swelling (day 3: 7.1 ± 4.1 vs. 2.0 ± 2.0% in the control liposome group, p<0.05) and less clot resolution (day 3: 10.9 ± 2.3 vs. 7.7 ± 1.8 mm3 in control liposome group, p<0.05).
Conclusion: These results indicated CD47 has a key role in hematoma clearance after ICH.