| First Author | Chen HR | Year | 2022 |
| Journal | Theranostics | Volume | 12 |
| Issue | 2 | Pages | 512-529 |
| PubMed ID | 34976198 | Mgi Jnum | J:317435 |
| Mgi Id | MGI:6854144 | Doi | 10.7150/thno.64033 |
| Citation | Chen HR, et al. (2022) Monocytes promote acute neuroinflammation and become pathological microglia in neonatal hypoxic-ischemic brain injury. Theranostics 12(2):512-529 |
| abstractText | Rationale: Monocytes belong to the mononuclear phagocyte system and are immune responders to tissue injury and infection. There were also reports of monocytes transforming to microglia-like cells. Here we explore the roles of monocytes in microglia ontogeny and the pathogenesis of neonatal cerebral hypoxic-ischemic (HI) brain injury in mice. Methods: We used three genetic methods to track the development of monocytes, including CX3CR1(GFP/+); CCR2(RFP/+) reporter mice, adoptive transfer of GFP(+) monocytes, and fate-mapping with CCR2-CreER mice, in neonatal mouse brains with or without lipopolysaccharide (LPS, 0.3 mg/kg)-sensitized Vannucci HI. We also used genetic (CCR2(RFP/ RFP), CCR2 knockout) and pharmacological methods (RS102895, a CCR2 antagonist) to test the roles of monocytic influx in LPS/HI brain injury. Results: CCR2(+) monocytes entered the late-embryonic brains via choroid plexus, but rapidly became CX3CR1(+) amoeboid microglial cells (AMCs). The influx of CCR2(+) monocytes declined after birth, but recurred after HI or LPS-sensitized HI (LPS/HI) brain injury, particularly in the hippocampus. The CCR2-CreER-based fate-mapping showed that CCR2(+) monocytes became CD68(+) TNFalpha(+) macrophages within 4 d after LPS/HI, and maintained as TNFalpha(+) MHCII(+) macrophages or persisted as Tmem119(+) Sall1(+) P2RY12(+) ramified microglia for at least five months after injury. Genetic deletion of the chemokine receptor CCR2 markedly diminished monocytic influx, the expression of pro- and anti-inflammatory cytokines, and brain damage. Post-LPS/HI application of RS102895 also reduced inflammatory responses and brain damage, leading to better cognitive functions. Conclusion: These results suggest that monocytes promote acute inflammatory responses and may become pathological microglia long after the neonatal LPS/HI insult. Further, blocking the influx of monocytes may be a potential therapy for neonatal brain injury. |
