Glucocorticoid-induced leucine zipper may play an important role in icariin by suppressing osteogenesis inhibition induced by glucocorticoids in osteoblasts

Inhibition of Fin Regeneration in Fathead Minnow (Pimephales promelas) by a Potent Synthetic Glucocorticoid and Development of Adverse Outcome Pathway 334

Despite structural and functional conservation across vertebrate species, the glucocorticoid receptor has been minimally studied in comparison to other biological targets for endocrine-disrupting compounds in aquatic systems. Because prolonged use of pharmaceutical glucocorticoids in humans has been linked to osteoporosis and impaired bone growth, we hypothesized that the ability of teleost fish to regenerate fins following damage may be inhibited by exposure to synthetic glucocorticoids in the environment. In the present study, we examined fin regeneration following a 7 days waterborne exposure of juvenile fathead minnows (Pimephales promelas) to the synthetic glucocorticoids, fluticasone propionate and dexamethasone. Expression of several biologically relevant gene products (sgk1, tdgf1, runx2a, lef1, shha, and tsc22d3) was measured in paired caudal fin and whole-body tissues. Fluticasone propionate and dexamethasone significantly impaired fin regeneration at measured water concentrations of 2.62 μg/L and 4.62 mg/L, respectively. Changes in gene expression indicated disruption of intercellular communication in the Wnt/β-catenin and bone morphogenetic protein (BMP) signaling pathways after exposure to 4.86 μg/L fluticasone propionate. Upregulation of tsc22d3, a transcription factor responsible for suppression of anti-inflammatory response, may be the plausible cause of repressed cellular signaling. These findings advance the development of adverse outcome pathway 334─Glucocorticoid Receptor Activation Leads to Impaired Fin Regeneration─and elucidate both the mechanistic relationship between activation of the glucocorticoid receptor by fluticasone propionate and inhibition of fin regeneration, which could plausibly reduce individual fitness in aquatic systems.

Icariin suppresses osteogenic differentiation and promotes bone regeneration in Porphyromonas gingivalis-infected conditions through EphA2-RhoA signaling pathway

Periodontitis is associated with multiple systemic diseases and can cause bone loss. Porphyromonas gingivalis (P. gingivalis) is one of the most virulent periodontal pathogens. Icariin is a flavonoid extracted from the traditional Chinese herbal medicine Herba Epimedii, and can regulate bone metabolism. However, its effects on promoting bone metabolism have not been fully elucidated. In this experiment, we infected MC3T3-E1 cells with P. gingivalis. Flow cytometry results show that persistent bacterial infection does not affect cell proliferative activity. Western blotting, ALP activity detection, mineral content determination, and immunofluorescence blotting confirmed that icariin improved osteogenic differentiation in the inflammatory state, and this effect may be more obvious in the early stage of osteogenic differentiation. The antibacterial assays, ROS and MMP fluorescence assays demonstrated that icariin exerted a significant inhibitory effect on bacterial growth and attenuated the inflammatory response in bacterial-infected conditions. The results of in vivo experiments in animals further validated the excellent properties exerted by icariin in the repair of bone defects. Additionally, in the P. gingivalis-infected state, icariin exert a regulatory effect on EphA2-RhoA signaling pathway to augment osteogenic differentiation. These exciting findings suggest that icariin holds significant potential for therapeutic application in the management of periodontal bone loss.

Activation of cannabinoid receptor 2 alleviates glucocorticoid-induced osteonecrosis of femoral head with osteogenesis and maintenance of blood supply

In glucocorticoid (GC)-induced osteonecrosis of the femoral head (ONFH), downregulated osteogenic ability and damaged blood supply are two key pathogenic mechanisms. Studies suggested that cannabinoid receptor 2 (CB2) is expressed in bone tissue and it plays a positive role in osteogenesis. However, whether CB2 could enhance bone formation and blood supply in GC-induced ONFH remains unknown. In this study, we focused on the effect of CB2 in GC-induced ONFH and possible mechanisms in vitro and in vivo. By using GC-induced ONFH rat model, rat-bone mesenchymal stem cells (BMSCs) and human umbilical vein endothelial cells (HUVECs) to address the interaction of CB2 in vitro and in vivo, we evaluate the osteogenic and angiogenic effect variation and possible mechanisms. Micro-CT, histological staining, angiography, calcein labeling, Alizarin red staining (ARS), alkaline phosphatase (ALP), tartrate-resistant acid phosphatase (TRAP) staining, TUNEL staining, migration assay, scratch assay, and tube formation were applied in this study. Our results showed that selective activation of CB2 alleviates GC-induced ONFH. The activation of CB2 strengthened the osteogenic activity of BMSCs under the influence of GCs by promotion of GSK-3β/β-catenin signaling pathway. Furthermore, CB2 promoted HUVECs migration and tube-forming capacities. Our findings indicated that CB2 may serve as a rational new treatment strategy against GC-induced ONFH by osteogenesis activation and maintenance of blood supply.

Promoting Effect of Pinostrobin on the Proliferation, Differentiation, and Mineralization of Murine Pre-osteoblastic MC3T3-E1 Cells

Pinostrobin (PI), a natural flavonoid found in a variety of plants, is well known for its rich pharmacological activities. However, its osteogenic function remains unclear. The aim of this study is to evaluate the effect of PI on the proliferation, differentiation, and mineralization of murine pre-osteoblastic MC3T3-E1 cells in vitro using MTT, alkaline phosphatase (ALP) activity, the synthesis of collagen I (Col I) assay, and Von-Kossa staining, respectively. The expression of osteocalcin (OCN) mRNA in cells was detected by real-time PCR. The effect of PI on the differentiation of dexamethasone (DEX)-suppressed cells was also investigated. The results showed that PI greatly promoted the proliferation of MC3T3-E1 cells at 5–80 μg/mL (p < 0.05 or p < 0.01), and caused a significant elevation of ALP activity, Col I content, and mineralization of osteoblasts at 10–40 μg/mL (p < 0.05 or p < 0.01), and the expression levels of OCN gene were greatly upregulated after PI treatment (p < 0.01). Furthermore, PI could rescue the inhibition effect of cell differentiation induced by DEX. Taken together, these results indicated that PI could directly promote proliferation, differentiation, and mineralization of MC3T3-E1 cells and has potential for use as a natural treatment for osteoporosis.