YBX1 promotes type H vessel–dependent bone formation in an m5C-dependent manner
Yu-Jue Li, Qi Guo, Ming-Sheng Ye, GuangPing Cai, Wen-Feng Xiao, Sheng Deng, Ye Xiao
Yu-Jue Li, Qi Guo, Ming-Sheng Ye, GuangPing Cai, Wen-Feng Xiao, Sheng Deng, Ye Xiao
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Research Article Angiogenesis Bone biology

YBX1 promotes type H vessel–dependent bone formation in an m5C-dependent manner

Abstract

RNA-binding proteins (RBPs) interact with RNA and ubiquitously regulate RNA transcripts during their life cycle, playing a fundamental role in the progression of angiogenesis-related diseases. In the skeletal system, endothelium-dependent angiogenesis is indispensable for bone formation. However, the role of RBPs in endothelium-dependent bone formation is unclear. Here, we show that RBP–Y-box-binding protein 1 (YBX1) was strongly reduced in the bone vasculature of ovariectomy (OVX) mice. Endothelial cell–specific deletion of Ybx1 impaired CD31-high, endomucin-high (CD31hiEMCNhi) endothelium morphology and resulted in low bone mass whereas Ybx1 overexpression promoted angiogenesis-dependent osteogenesis and ameliorated bone loss. Mechanistically, YBX1 deletion disrupted CD31, EMCN, and bone morphogenetic protein 4 (BMP4) stability in an m5C-dependent manner and blocked endothelium-derived BMP4 release, thereby inhibiting osteogenic differentiation of bone mesenchymal stromal cells. Administration of recombinant BMP4 protein restored impaired bone formation in Ybx1 deletion mice. Tail vein injection of CD31-modified polyethylene glycol–poly (lactic-co-glycolic acid) carrying sciadopitysin, a natural YBX1 agonist, pharmacologically partially reversed CD31hiEMCNhi vessels’ decline and improved bone mass in both OVX and aging animals. These findings demonstrated the role of RBP-YBX1 in angiogenesis-dependent bone formation and provided a therapeutic approach for ameliorating osteoporosis.

Authors

Yu-Jue Li, Qi Guo, Ming-Sheng Ye, GuangPing Cai, Wen-Feng Xiao, Sheng Deng, Ye Xiao

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Figure 2

Endothelial Ybx1 deletion impairs CD31hiEMCNhi endothelium formation and bone formation.

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Endothelial Ybx1 deletion impairs CD31hiEMCNhi endothelium formation and...
(A and B) RT-qPCR analysis of Ybx1 expression in CD31hiEMCNhi ECs (A) and BMSCs (B) from EC-specific Ybx1-knockout female mice (Ybx1iΔEC) and their littermate controls (Ybx1fl/fl). (C) FACS analysis dot plot of CD31hiEMCNhi ECs in each group. (D) Quantification of type H (left) and L (right) ECs from in each group. (E and F) Representative images (E) and quantitation (F) of CD31 (green) and EMCN (red) immunostained, 4-week-old Ybx1iΔEC and Ybx1fl/fl femora. (G) ELISA analysis of estradiol levels in each group. (H) Representative images (left) and quantitation (right) of VEGFA (red) immunostained in each group. (I and J) Representative μCT images (I) and quantitative μCT analysis (J) of trabecular bone microarchitecture of 4-week-old Ybx1iΔEC and Ybx1fl/fl mice. (K) Representative images (left) and quantitation (right) of Osterix+ (green) immunostained in each group. (L) Representative images (left) and quantitation (right) of COL1 (green) immunostained in each group. (M and N) Representative fluorescence images (M) and quantification (N) of bone histomorphometric parameters (MAR and BFR/BS) in each group. (O) Immunohistochemical staining (left) and quantification (right) of Ocn+ cells (brown) in trabecular bone surfaces of each group. (P) Representative images (left) and quantification (right) of TRAP+ cells in trabecular bone surfaces of each group. n = 8 mice in each group. n = 2 independent experiments. Data are shown as the mean ± SEM. Scale bar, 50 μm and 100 μm. *P < 0.05; **P < 0.01; ***P < 0.001 by Student’s t test. Tb. BV/TV, trabecular bone volume per tissue volume; Tb. N, trabecular number; Tb. Sp, trabecular separation; Tb. Th, trabecular thickness; MAR, mineral apposition rate; BFR/BS, bone formation rate.