Journal
JOURNAL OF ORTHOPAEDIC RESEARCH
Volume 38, Issue 8, Pages 1703-1709Publisher
WILEY
DOI: 10.1002/jor.24590
Keywords
intervertebral disk; macrophage; recruitment inflammation
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Funding
- JSPS KAKENHI [17K16700]
- Grants-in-Aid for Scientific Research [17K16700] Funding Source: KAKEN
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Macrophages, particularly M1 macrophages, produce proinflammatory cytokines and contribute to the degenerative process in injured intervertebral disks (IVDs). We previously showed that macrophages in both intact and injured IVDs increased following IVD injury. Resident macrophages and macrophages recruited from the peripheral blood have distinct roles in tissue. However, it remains to be determined whether increased macrophages derive from resident or recruited macrophages. We investigated the origin of M1 macrophages in injured IVDs using green fluorescent protein (GFP) transgenic bone marrow chimeric mice. The M1 macrophage marker, CD86, increased in both disk-derived resident macrophages and bone marrow-derived macrophages (BMMs) after lipopolysaccharide/interferon gamma stimulation in vitro. Following IVD injury, the proportion of cells positive for the CD86 ligand, the F4/80 antigen, and the surface glycoprotein CD11b (CD86+ CD11b+ F4/80+) significantly increased in GFP+ populations at days 3, 7, and 14. In contrast, CD86+ CD11b+ F4/80+ cells in GFP- populations significantly increased on day 3, and thereafter decreased on days 7 and 14. The proportion of CD86+ CD11b+ F4/80+ cells in the GFP+ populations was significantly higher than that in the GFP- populations at days 1, 3, 7, and 14. Monocyte chemoattractant protein-1 expression in disk-derived macrophages, but not in BMMs, increased following interleukin-1 beta stimulation. Our results suggest M1 macrophages following IVD injury originate from recruited macrophages. Resident macrophages may behave differently in IVD injury. The role of resident macrophages needs to be clarified. Further investigation is needed.
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