The pivotal role of microRNA-21 in osteoclastogenesis inhibition by anthracycline glycoside aloin.

Osteopenic disorders such as osteoporosis and rheumatoid arthritis are characterized by excessive bone resorption by osteoclasts relative to bone formation by osteoblasts. MicroRNAs are emerging as key players in bone remodeling, modulating the functions of both osteoblasts and osteoclasts. Among them, miR-21 is highly expressed in osteoclast precursors and is known to regulate genesis, differentiation, and apoptosis of osteoclasts. The pro-osteoclastogenic nature of miR-21 makes it a potential candidate as a therapeutic target to treat bone disorders. We had previously demonstrated that anthroglycoside aloin derived from Aloe vera was effective in promoting osteoblastogenesis and inhibiting osteoclastogenesis. The present study investigated the role of miR-21 in aloin's inhibitory effect on osteoclast differentiation. Aloin effectively suppressed receptor activator of nuclear factor kappa-B (NFĸB) ligand (RankL)-induced miR-21 expression via repression of NFĸB activation. MiR-21 suppression resulted in upregulation of osteoclast suppressor programmed cell death protein 4 (PDCD4), and downregulation of osteoclast marker cathepsin K. Knockdown or gain-of-function studies revealed that miR-21 was pivotal to aloin's inhibitory effect on osteoclastogenesis. This study also highlights the dynamic potential of aloin as a therapeutic agent to treat osteopenic disorders.

NF-κB pathway inhibition by anthrocyclic glycoside aloin is key event in preventing osteoclastogenesis in RAW264.7 cells.

BACKGROUND: Osteoporosis is a bone pathology leading to increased fracture risk and challenging the quality of life. As current treatments can exhibit deleterious side effects, the use of phyto-compounds with therapeutic and preventive activities against orthopaedic related problems represents a promising alternative. PURPOSE: We investigated the effect of aloin, an anthrocyclic compound, on inhibition of osteoclastogenesis using receptor of the nuclear factor κB (NF-κB) ligand (RANKL)-induced RAW264.7 macrophage cells. STUDY DESIGN/METHODS: The inhibitory effect of aloin on in vitro osteoclastogenesis was evaluated by reduction in tartrate-resistant acid phosphatase (TRAP) content and expression levels of osteoclast-specific gene, cathepsin K. Multinuclear formation of osteoclast was assessed with haematoxylin and eosin staining. F4/80 content the marker of the murine monocyte/macrophage cells, was evaluated by immunocytochemistry. The underlining mechanisms were assessed by Western blots and EMSA. Effect of aloin on generation of intracellular reactive oxygen species (ROS) was estimated by dichlorofluorescein diacetate (DCFH-DA). Bone degradation effect was evaluated by bone pit assay. The bone pit culture supernatant was studied by Fluorescein assay. RESULTS: We demonstrated that aloin reduced TRAP content and levels of osteoclast-specific gene and protein, cathepsin K. Treatment with aloin (0.75 µM) prevented multinuclear formation (haematoxylin and eosin staining), reduced intracellular TRAP content (TRAP Staining) and increased F4/80 content (F4/80 immunohistochemistry) in RANKL (20 ng/ml) treated RAW cells. Treatment of the RAW cells with aloin suppressed RANKL-induced NF-κB pathway components like IKKα, IKKß, Phospho.IKK α/ß, NF-κB-p65, Phospho NF-κB-p65 and IκBα. EMSA studies showed aloin dose dependently reduced DNA binding activity of NF-κB. Additionally, in vitro bone pit assay revealed that aloin prevented bone degradation and also decreased the fluorescence content in cells, thus confirming the role of aloin in inhibition of osteoclastogenesis . CONCLUSION: Collectively, this study identifies aloin as a potent inhibitor of osteoclastogenesis and bone resorption. The action of aloin was in par with alendronate sodium trihydrate and may provide evidence for its therapeutic potential to treat diseases involving abnormal bone lysis.