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 3

Local s.c. treatment with 1,25(OH)2D at the proinflammatory stage suppressed M1 macrophage differentiation but augmented M2 macrophage differentiation at fracture sites.

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Local s.c. treatment with 1,25(OH)2D at the proinflammatory stage suppre...
(A) B6 mice received femoral fracture surgery (Fx). Immediately after the fracture surgery, the animals received one of the following daily s.c. treatments (Tx) at fracture sites: a) vehicle control (VC), b) 100 ng/kg/mouse 1,25 (OH)2D (VD ), or c) 1,000 ng/kg/mouse 1,25(OH)2D (VD). Additionally, a group of normal healthy mice was included as a control (intact bones). At days 1, 4, and 7 after the treatments, intact and fractured bones were collected, and cells were isolated as described in Methods. The cells were then analyzed by FACS. (B) Gating strategy shows that the cells are gated on viable CD11b+/F4/80+ macrophages for the FACS analysis. (C) Representative FACS plots show the expression of IL-1β (left panel) and IL-12 (right panel) in CD11b+F4/80+ macrophages at day 1 after the treatments. (D) Cumulative data of the mean fluorescent intensities (MFIs) of IL-1β (upper panels) and IL-12 (lower panels) expressions in CD11b+F4/80+ macrophages at day 1. (E) Cumulative data of the percent of IL-1βhi and IL-12hi cells among CD11b+F4/80+ macrophages at day 1. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001, ANOVA test, n = 3. (F) B6 mice were subjected to fracture surgery and, immediately after the fracture surgery, received a dose of either VC or 100 ng/kg 1,25(OH)2D (VD). At days 4 and 7, fractured bones were collected. Paraffin embedded sections from day 4 were stained for iNOS and those from day 7 were stained for ARG1 by 3,3′-Diaminobenzidine (DAB) staining. Arrows indicate positively stained cells. Representative images are shown.