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

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.

Splicing factor YBX1 regulates bone marrow stromal cell fate during aging.

Senescence and altered differentiation potential of bone marrow stromal cells (BMSCs) lead to age-related bone loss. As an important posttranscriptional regulatory pathway, alternative splicing (AS) regulates the diversity of gene expression and has been linked to induction of cellular senescence. However, the role of splicing factors in BMSCs during aging remains poorly defined. Herein, we found that the expression of the splicing factor Y-box binding protein 1 (YBX1) in BMSCs decreased with aging in mice and humans. YBX1 deficiency resulted in mis-splicing in genes linked to BMSC osteogenic differentiation and senescence, such as Fn1, Nrp2, Sirt2, Sp7, and Spp1, thus contributing to BMSC senescence and differentiation shift during aging. Deletion of Ybx1 in BMSCs accelerated bone loss in mice, while its overexpression stimulated bone formation. Finally, we identified a small compound, sciadopitysin, which attenuated the degradation of YBX1 and bone loss in old mice. Our study demonstrated that YBX1 governs cell fate of BMSCs via fine control of RNA splicing and provides a potential therapeutic target for age-related osteoporosis.

Betulinic acid impairs metastasis and reduces immunosuppressive cells in breast cancer models.

Breast cancer is the most common female cancer with considerable metastatic potential, explaining the need for new candidates that inhibit tumor metastasis. In our study, betulinic acid (BA), a kind of pentacyclic triterpenoid compound derived from birch trees, was evaluated for its anti-metastasis activity in vitro and in vivo. BA decreased the viability of three breast cancer cell lines and markedly impaired cell migration and invasion. In addition, BA could inhibit the activation of stat3 and FAK which resulted in a reduction of matrix metalloproteinases (MMPs), and increase of the MMPs inhibitor (TIMP-2) expression. Moreover, in our animal experiment, intraperitoneal administration of 10 mg/kg/day BA suppressed 4T1 tumor growth and blocked formation of pulmonary metastases without obvious side effects. Furthermore, histological and immunohistochemical analyses showed a decrease in MMP-9 positive cells, MMP-2 positive cells and Ki-67 positive cells and an increase in cleaved caspase-3 positive cells upon BA administration. Notably, BA reduced the number of myeloid-derived suppressor cells (MDSCs) in the lungs and tumors. Interestingly, in our caudal vein model, BA also obviously suppressed 4T1 tumor pulmonary metastases. These findings suggested that BA might be a potential agent for inhibiting the growth and metastasis of breast cancer.

[Effects of FGF-21 on Osteogenic Differentiation of Human Bone Marrow Mesenchymal Stem Cells in High Glucose Environment].

OBJECTIVES: To determine the effect of fibroblast growth factor-21(FGF-21)on the osteogenic differention of human bone mesenchymal stem cells (hBMSCs) exposed to a hyperglycemia condition in vitro. METHODS: hBMSCs were isolated from adult bone marrows, and identified by Alizarin red and oil red O staining. The expressions of immunophenotype were analysed using flow cytometry (CD105, CD90, CD73, CD44).HBMSCs were divided into control group[glucose (Glu) concentration of 5.5 mmol/L], Glu A, B, C groups(Glu 16.5, 25, 40 mmol/L), FGF-21 group (Glu 5.5mmol/ L+ FGF-21 ),Glu B+ FGF-21 group, and Glu B +FGF-21+cell mitogen activated protein kinase (MAPK) blocker (PD98059, SP600125 ,and SB203580) groups. The effect of FGF-21 on the differentiation of hBMSCs was detected using indicators as follows: alkaline phosphatase(ALP)on day 14, mRNA expressions ofALP, osteocalcin(OCN)and Runx2, protein expressions and phosphorylation of extracellular signal regulated kinase (ERK), mitogen-activated protein kinase(P38) and c-Jun N-terminal kinases(JNK) on day 21. RESULTS: hBMSCs differentiated into osteoblast cells and lipocyte. The hBMSCs were identified by flow cytometry.Compared with control group, significant increases of ALP mRNA, OCN mRNA and Runx2mRNA levels, as well as phosphorylation of ERK, P38 and JNK were observed in Glu A, B, C groups.Compared with Glu B group, ALP, OCN and Runx2 mRNA levels, and phosphorylation of ERK, P38 and JNK were decreased in Glu B+FGF-21 group .Compared with Glu B+FGF-21 group, ALP and Runx2 mRNA levels, and phosphorylation of ERK, JNK and P38 were decreased in Glu B +FGF-21 +MAPK blocker groups. CONCLUSIONS: High glucose could promote the biomineralization of hBMSCs. FGF-21 in high glucose environment could inhibit the osteogenic differentiation of hBMSCs.