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Updated: Nov 8, 2025
Depletion and Reconstitution of Macrophages in Mice
Published on: August 1, 2012
Alpha defensin-1 attenuates surgically induced osteoarthritis in association with promoting M1 to M2 macrophage
1Department of Orthopaedic Surgery, Laboratory of Endocrinology and Metabolism, National Clinical Research Center for Geriatrics, West China Hospital, West China Medical School, SiChuan University, ChengDu, SiChuan Province, People's Republic of China.
Objective:
Macrophages play an important part in the pathogenesis of osteoarthritis (OA). Our objective was to determine the effects of α-defensin-1 on macrophage polarization and consequently OA.
Methods:
OA synovial tissue and synovial fluid were assessed for the presence of M1 (CD68+CD16+CD206-) and M2 (CD68+CD206+CD16-) macrophages by flow cytometry. M0, M1, and M2 macrophages were co-cultured with OA chondrocytes to determine their influence on chondrogenic phenotype. Polarization of THP-1 activated monocytes from M1 to M2 in response to α-defensin-1 was evaluated by flow cytometry, RT-PCR and RNA sequencing. Effects of intra-articular α-defensin-1 in vivo were evaluated in a rat meniscal/ligamentous injury (MLI) model.
Results:
The quantity of M1 exceeded M2 polarized macrophages in human OA synovial tissue (mean difference 26.1% [13.6-38.6%], P < 0.001) and fluid (mean difference 10.5% [5.0-16.1%], P = 0.003). M1 to M2 polarization in vitro was most effectively promoted with 10 ng/mL α-defensin-1. Compared with untreated macrophages, the α-defensin-1 polarized macrophages modified co-cultured OA chondrocytes from a pro-catabolic state to a pro-anabolic (regenerative-like) state based on expression of COL2A1, ACN, MMP3, MMP13 and ADAMTS5. Intra-articular α-defensin-1 decreased severity of cartilage damage and synovitis in the MLI rat model. RNAseq analyses suggested insulin and Toll-like receptor signaling pathways in the chondroprotective α-defensin-1 mechanism of action.
Conclusion:
α-defensin-1 promotes M1 to M2 macrophage polarization in vitro, has beneficial effects on chondrocytes indirectly via M2 macrophage polarization, and attenuates the severity of OA in vivo, suggesting it might be a candidate treatment for OA.
Insights
Alpha-defensin-1 shifts macrophages from M1 to M2, promoting a regenerative state in osteoarthritis (OA) chondrocytes. This peptide reduces cartilage damage and synovitis in vivo, suggesting potential as an OA therapeutic.
Area of Science:
- Immunology
- Biochemistry
- Orthopedics
Background:
- Macrophages are key players in osteoarthritis (OA) pathogenesis.
- M1 macrophages are pro-inflammatory, while M2 macrophages are associated with tissue repair.
Purpose of the Study:
- To investigate the effect of alpha-defensin-1 on macrophage polarization.
- To determine the impact of alpha-defensin-1-modulated macrophages on OA chondrocytes.
- To evaluate the therapeutic potential of alpha-defensin-1 in an OA model.
Main Methods:
- Assessed M1 and M2 macrophage populations in human OA synovial tissue and fluid via flow cytometry.
- Co-cultured OA chondrocytes with M0, M1, and M2 macrophages.
- Induced M1 to M2 polarization using alpha-defensin-1 in vitro and evaluated changes via flow cytometry, RT-PCR, and RNA sequencing.
- Administered intra-articular alpha-defensin-1 in a rat meniscal/ligamentous injury (MLI) model.
Main Results:
- M1 macrophages were significantly more abundant than M2 macrophages in human OA samples.
- Alpha-defensin-1 (10 ng/mL) effectively promoted M1 to M2 polarization in vitro.
- Alpha-defensin-1-polarized macrophages shifted OA chondrocytes from a pro-catabolic to a pro-anabolic state.
- Intra-articular alpha-defensin-1 reduced cartilage damage and synovitis in the MLI rat model.
- RNA sequencing indicated insulin and Toll-like receptor signaling pathways are involved in alpha-defensin-1's mechanism.
Conclusions:
- Alpha-defensin-1 promotes M1 to M2 macrophage polarization.
- This polarization indirectly benefits chondrocytes, promoting a regenerative phenotype.
- Alpha-defensin-1 attenuates OA severity in vivo, showing promise as a potential OA treatment.
