Orcinol glucoside targeted p38 as an agonist to promote osteogenesis and protect glucocorticoid-induced osteoporosis.

BACKGROUND: Glucocorticoids (GC)-induced osteoporosis (GIOP) is the most common cause of secondary osteoporosis, which leads to an increased risk of fracture in patients. The inhibition of the osteoblast effect is one of the main pathological characteristics of GIOP, but without effective drugs on treatment. PURPOSE: The aim of this study was to investigate the potential effects of orcinol glucoside (OG) on osteoblast cells and GIOP mice, as well as the mechanism of the underlying molecular target protein of OG both in vitro osteoblast cell and in vivo GIOP mice model. METHODS: GIOP mice were used to determine the effect of OG on bone density and bone formation. Then, a cellular thermal shift assay coupled with mass spectrometry (CETSA-MS) method was used to identify the target of OG. Surface plasmon resonance (SPR), enzyme activity assay, molecular docking, and molecular dynamics were used to detect the affinity, activity, and binding site between OG and its target, respectively. Finally, the anti-osteoporosis effect of OG through the target signal pathway was investigated in vitro osteoblast cell and in vivo GIOP mice model. RESULTS: OG treatment increased bone mineral density (BMD) in GIOP mice and effectively promoted osteoblast proliferation, osteogenic differentiation, and mineralization in vitro. The CETSA-MS result showed that the target of OG acting on the osteoblast is the p38 protein. SPR, molecular docking assay and enzyme activity assay showed that OG could direct bind to the p38 protein and is a p38 agonist. The cellular study found that OG could promote p38 phosphorylation and upregulate the proteins expression of its downstream osteogenic (Runx2, Osx, Collagen Ⅰ, Dlx5). Meanwhile, it could also inhibit the nuclear transport of GR by increasing the phosphorylation site at GR226 in osteoblast cell. In vivo GIOP mice experiment further confirmed that OG could prevent bone loss in the GIOP mice model through promoting p38 activity as well as its downstream proteins expression and activity. CONCLUSIONS: This study has established that OG could promote osteoblast activity and revise the bone loss in GIOP mice by direct binding to the p38 protein and is a p38 agonist to improve its downstream signaling, which has great potential in GIOP treatment for targeting p38. This is the first report to identify OG anti-osteoporosis targets using a label-free strategy (CETSA-MS).

Jintiange proteins promote osteogenesis and inhibit apoptosis of osteoblasts by enhancing autophagy via PI3K/AKT and ER stress pathways.

ETHNOPHARMACOLOGICAL RELEVANCE: Tiger bone, which had long been used in traditional Chinese medicine, had the action of removing wind and alleviating pain, strengthening the sinews and bones, and often used to treat bone impediment, and atrophic debility of bones in TCM clinical practice. As a substitute of natural bone tiger, artificial tiger bone Jintiange (JTG), has been approved by the State Food and Drug Administration of China for relief the symptom of osteoporosis, such as lumbago and back pain, lassitude in loin and legs, flaccidity and weakness legs, and walk with difficulty based on TCM theory. JTG has similar chemical profile to natural tiger bone, and contains mineral substance, peptides and proteins, and has been shown to protect bone loss in ovariectomized mice and exert the regulatory effects on osteoblast and osteoclast activities. But how the peptides and proteins in JTG modulate bone formation remains unclear. AIM: To investigate the stimulating effects of JTG proteins on osteogenesis and explore the possible underlying mechanisms. MATERIALS AND METHODS: JTG proteins were prepared from JTG Capsules by extracting calcium, phosphorus and other inorganic elements using SEP-PaktC18 desalting column. MC3T3-E1 cells were treated with JTG proteins to evaluate their effects and explore the underlying mechanisms. Osteoblast proliferation was detected by CCK-8 method. ALP activity was detected using a relevant assay kit, and bone mineralized nodules were stained with alizarin red-Tris-HCl solution. Cell apoptosis was analyzed by flow cytometry. Autophagy was observed by MDC staining, and autophagosomes were observed by TEM. Nuclear translocations of LC3 and CHOP were detected by immunofluorescence and observed under a laser confocal microscope. The expression of key proteins related to osteogenesis, apoptosis, autophagy and PI3K/AKT and ER stress pathways was analyzed by Western Blot analysis. RESULTS: JTG proteins improved osteogenesis as evidenced by the alteration of proliferation, differentiation and mineralization of MC3T3-E1 osteoblasts, inhibited their apoptosis, and enhanced autophagosome formation and autophagy. They also regulated the expression of key proteins of PI3K/AKT and ER stress pathways. In addition, PI3K/AKT and ER stress pathway inhibitors could reverse the regulatory effects of JTG proteins on osteogenesis, apoptosis, autophagy and PI3K/AKT and ER stress pathways. CONCLUSION: JTG proteins increased the osteogenesis and inhibited osteoblast apoptosis by enhancing autophagy via PI3K/AKT and ER stress signaling pathways.

Connectivity Map Analysis Identifies Fisetin as a Treatment Compound for Osteoporosis Through Activating the PI3K-AKT Signaling Pathway in Mouse Pre-osteoblastic MC3T3-E1 Cells.

AIMS: This research aimed at exploring potential new compounds to be used in the treatment of osteoporosis by Connectivity Map (CMap) and determining the role of fisetin in osteoporosis according to its effects on the PI3K-AKT signaling pathway in MC3T3-E1 pre-osteoblastic cells. METHODS: Microarray analysis was used to obtain the differentially expressed genes in published gene expression data. Potent compounds for osteoporosis therapy were discovered by CMap analysis. DAVID and Gene Set Enrichment Analysis (GSEA) were used to discover signaling pathways that connected to osteoporosis disease. Cell viability was evaluated by a CCK-8 assay. Quantitative realtime Polymerase Chain Reaction (qRT-PCR) and western blot analysis were used to test the mRNA and protein expressions related to the PI3K-AKT signaling pathway in MC3T3-E1 cells, respectively. RESULTS: CMap analysis identified fisetin as a promising compound for anti-osteoporosis treatment. DAVID and GSEA analysis showed that the PI3K-AKT signaling pathway was inactivated in osteoporosis. Cell experiments revealed that fisetin caused an elevation of cell viability, up-regulated the mRNA levels of the Runt-related transcription factor-2 (Runx2), Osterix (Osx), collagen type I 1 (Col1a1) and Osteoprotegerin (OPG) while down-regulated the nuclear factor-κB ligand (RANKL) mRNA level. DISCUSSION: The protein levels of Runx2, Col1a1 and Osteocalcin (OCN) were also increased by fisetin. Furthermore, fisetin activated the phosphoinositide-3-kinase/protein kinase B (PI3K-AKT) signaling pathway, and blocking this pathway by the inhibitor LY-294002 could impair fisetin's functions on proliferation, differentiation and OPG/RANKL expression ratio in the MC3T3-E1 cells. CONCLUSION: Our results demonstrated that fisetin could promote MC3T3-E1 cell proliferation, differentiation and increase OPG/RANKL expression ratio through activating the PI3K-AKT pathway, which has potential for the treatment of osteoporosis.