The effect of NR4A1 in hMSCs. Orphan nuclear receptor NR4A1 regulates both osteoblastogenesis and adipogenesis in human mesenchymal stem cells

The Ingenuity Pathway Analysis (IPA) previously showed that the nuclear receptor subfamily 4 group A member 1 gene (NR4A1) is associated with both osteoporosis and adipogenesis. Here, we investigated the effects of modulation of NR4A1 expression on the differentiation of human bone marrow–derived mesenchymal stem cells (BMD-MSCs) into osteoblasts and adipocytes. Control BMD-MSCs and NR4A1-overexpressing cells were also treated with the NR4A1 antagonist DIM-C-pPhOH. Total RNA was isolated from control BMD-MSCs, NR4A1-overexpressing BMD-MSCs, and BMD-MSCs treated with NR4A1 siRNA. Differentially expressed genes were extracted from the next-generation RNA sequencing data. IPA was used to determine the role of NR4A1 in osteoblastogenesis and adipogenesis. NR4A1 knockdown enhanced calcification, whereas NR4A1 overexpression decreased calcification and significantly increased adipogenesis. Treatments of BMD-MSCs with DIM-C-pPhOH and NR4A1 siRNA showed similar results. RNA-seq and IPA of the three groups of cells (control, NR4A1 knockdown, and NR4A1 overexpression) indicated that Notch signaling mediated the effects of NR4A1 in osteoblastogenesis and adipogenesis. We conclude that NR4A1 suppresses osteoblastogenesis and promotes adipogenesis. NR4A1 may also play a role in the progression of osteoporosis and adipogenesis by modulating the Notch signaling cascade.