1,25-Dihydroxyvitamin D suppresses M1 macrophages and promotes M2 differentiation at bone injury sites
Samiksha Wasnik, … , Kin-Hing William Lau, Xiaolei Tang
Samiksha Wasnik, … , Kin-Hing William Lau, Xiaolei Tang
Published September 6, 2018
Citation Information: JCI Insight. 2018;3(17):e98773. https://doi.org/10.1172/jci.insight.98773.
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Research Article Bone biology

1,25-Dihydroxyvitamin D suppresses M1 macrophages and promotes M2 differentiation at bone injury sites

Abstract

An indispensable role of macrophages in bone repair has been well recognized. Previous data have demonstrated the copresence of M1 macrophages and mesenchymal stem cells (MSCs) during the proinflammatory stage of bone repair. However, the exact role of M1 macrophages in MSC function and bone repair is unknown. This study aimed to define the role of M1 macrophages at bone injury sites via the function of 1,25-Dihydroxyvitamin D (1,25[OH]2D) in suppressing M1 but promoting M2 differentiation. We showed that 1,25(OH)2D suppressed M1 macrophage–mediated enhancement of MSC migration. Additionally, 1,25(OH)2D inhibited M1 macrophage secretion of osteogenic proteins (i.e., Oncostatin M, TNF-α, and IL-6). Importantly, the 1,25(OH)2D-mediated suppression of osteogenic function in M1 macrophages at the proinflammatory stage was associated with 1,25(OH)2D-mediated reduction of MSC abundance, compromised osteogenic potential of MSCs, and impairment of fracture repair. Furthermore, outside the proinflammatory stage, 1,25(OH)2D treatment did not suppress fracture repair. Accordingly, our data support 2 conclusions: (a) M1 macrophages are important for the recruitment and osteogenic priming of MSCs and, hence, are necessary for fracture repair, and (b) under vitamin D–sufficient conditions, 1,25(OH)2D treatment is unnecessary and can be detrimental if provided during the proinflammatory stage of fracture healing.

Authors

Samiksha Wasnik, Charles H. Rundle, David J. Baylink, Mohammad Safaie Yazdi, Edmundo E. Carreon, Yi Xu, Xuezhong Qin, Kin-Hing William Lau, Xiaolei Tang

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Figure 4

M1 macrophages enhanced the migration of MSCs, which was dose-dependently suppressed by 1,25(OH)2D.

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M1 macrophages enhanced the migration of MSCs, which was dose-dependentl...
(A) In a transwell culture system, the lower chambers were added with medium, RAW 264.7 cells, or RAW 264.7 cells + LPS + IFN-γ (M1 differentiation condition). Additionally, the wells, which contained RAW 264.7 cells + LPS + IFN-γ, were also added with vehicle control (VC), 10 nM 1,25(OH)2D (10 nM VD), or 100 nM 1,25(OH)2D (100 nM VD). Twenty-four hours later, BM-derived MSCs were added into upper chambers, and the cells were cultured. Twenty-four hours after that, the membranes were stained with crystal blue for the enumeration of migrated MSCs. (B) Representative microscopic images show the migration of MSCs in the membranes. Blue color indicates migrated cells. Magnification, 20×. (C) Cumulative data show migrated MSCs (average number of 3 different microscopic fields). (D and E) The same experiment was performed using BM-derived primary macrophages. Magnification, 10×. **P < 0.01, ***P < 0.001, ****P < 0.0001, ANOVA, n = 3.