Euphoesulatin A prevents osteoclast differentiation and bone loss via inhibiting RANKL-induced ROS production and NF-κB and MAPK signal pathways

RANKL promotes MT2 degradation and ROS production in osteoclast precursors through Beclin1-dependent autophagy

ROS produced under oxidative stress are crucial for osteoclast differentiation. Metallothionein (MT) is a ROS-scavenging molecule. As a member of MT family, MT2 can clear ROS in osteoclast precursors (OCPs) and contributes to osteoclast differentiation. RANKL can promote OCP autophagy. Given the molecular-degrading effect of autophagy, the relationship between RANKL-dependent autophagy, MT2 and ROS during osteoclast differentiation is worth exploring. We depended in vitro RANKL administration and RANKL-overexpressing (Tg-RANKL) mice to observe the effects of RANKL on ROS production, MT2 protein expression, Beclin1 expression and autophagic activity in OCPs. Spautin1 was used to investigate the relationship between Beclin1-dependent autophagy and RANKL-regulated MT2 expression. Osteoclast-targeting MT2-cDNA-AAVs were applied to assess the therapeutic effect of MT2 on Tg-RANKL-related bone loss. The results showed that RANKL promoted ROS production but reduced MT2 protein expression in OCPs. RANKL also enhanced Beclin1 expression and LC3-puncta abundance. Decreased Beclin1 expression with spautin1 blocked RANKL-increased ROS production and osteoclast differentiation and recovered RANKL-decreased MT2 expression. MT2 selective overexpression with CD11b-promoter-MT2-cDNA-AAVs attenuated ROS production and osteoclastogenesis in Tg-RANKL mice and improved bone loss. Overall, RANKL can reduce MT2 protein expression through Beclin1-dependent autophagy, thereby promoting ROS production and osteoclast differentiation; this suggests that MT2-overexpressing small molecule drugs have the potential to treat RANKL-related bone loss.

Echinococcus granulosus promotes MAPK pathway-mediated osteoclast differentiation by inhibiting Nrf2 in osseous echinococcosis

Osseous echinococcosis causes severe "osteolytic" changes in the bone tissue of Echinococcus granulosus (E. granulosus) infection sites by promoting the over-differentiation of osteoclasts at the site. Nrf2 is a key regulator of osteoclast differentiation and formation, and this study investigated the regulatory mechanism by which Nrf2 promotes osteoclast differentiation after E. granulosus infection. In vitro, our study revealed that PSC intervention suppressed the expression levels of intracellular Nrf2 and its downstream effector, heme oxygenase-1 (HO-1), while increasing the content of intracellular reactive oxygen species (ROS), thereby promoting osteoclast differentiation. Next, we treated bone marrow mononuclear cells (BMMCs) with protoscoleces (PSC) and found that Nrf2 knockdown significantly promoted osteoclast formation, whereas Nrf2 activation had the opposite effect. We also verified that phosphorylation of the MAPK pathway was promoted after PSC intervention. In vivo, we established an osseous CE model and reported that Nrf2 knockout mice presented more pronounced bone destruction and more active osteoclast differentiation in infected bone tissue. In this study, we demonstrated that Nrf2 plays an important regulatory role in echinococcosis of the bone caused by E. granulosus infection both in vitro and in vivo. E. granulosus infection inhibits the expression of Nrf2 in cells, which leads to increased osteoclast differentiation and active bone resorption. This study provides not only a direction for more precise mechanistic research but also a new molecular target for the drug treatment of osseous echinococcosis.

Astragaloside IV attenuates glucocorticoid-induced osteoclastogenesis and bone loss via the MAPK/NF-κB pathway

BACKGROUND

Astragaloside IV (AS-IV) is a bioactive saponin extracted from Radix Astragali, and it is reported to promote osteoblast differentiation while inhibiting osteoclastogenesis. However, the mechanism of AS-IV in glucocorticoid-induced osteoclastogenesis (GIO) remains undetermined. Herein, we examined the influence of AS-IV on GIO and bone loss.

METHODS

RAW264.7 cells were incubated with dexamethasone (Dex) alone or Dex and receptor activator of nuclear factor-B ligand (RANKL) (Dex and RANKL) for 2 days, and then treated with Dex or Dex and RANKL through AS-IV for the timeframes indicated. Following, mice were intraperitoneally administered with an intermediate-acting glucocorticoid, methylprednisolone (MP), or MP and AS-IV for 6 weeks.

RESULTS

AS-IV significantly decreased Dex-induced osteoclast nucleus and area, however, it did not impact the number of Dex-induced osteoclasts in RAW264.7 cells. AS-IV also significantly decreased the osteoclastic marker protein expressions in Dex-induced RAW264.7 cells with concentration of dose dependent fashion. Additionally, AS-IV promoted p38 phosphorylation (p-) and p-p65 translocation to the nucleus, while inhibiting phosphorylation of extracellular signal-regulated kinase (ERK) (p-ERK) and inhibitor of Nuclear factor κB (NF-κB) (p-IκB) levels. However, the AS-IV-mediated action on p-MAPK, p-NF-κB, and osteoclastic marker expressions were reversed by MAPK or IκB inhibitor in Dex-induced RAW264.7 cells. Furthermore, our in vivo evaluation revealed that AS-IV also attenuated the MP-mediated bone loss, and suppressed osteoclastogenesis.

CONCLUSIONS

This study demonstrates that AS-IV inhibits GIO and attenuates bone loss via the MAPK/NF-κB pathway. This also suggested that AS-IV could be a potential promising therapeutic agent for glucocorticoid-triggered bone loss.

Mechanisms of Nrf2 suppression and Camkk1 upregulation in Echinococcus granulosus-induced bone loss

Osteoclast differentiation is essential for maintaining bone metabolism, and its dysregulation, particularly in the context of Echinococcus granulosus (CE) infection, can lead to severe bone loss. This study explores a novel mechanism by which CE protoscolices (PSC) drive osteoclast differentiation through the inhibition of Nrf2, followed by the upregulation of Camkk1. Transcriptome sequencing revealed a significant down-regulation of Nrf2 in cells treated with PSC. This was confirmed by Western blot and Q-PCR assays showing reduced Nrf2 protein and gene levels. In vivo studies with Nrf2 knockout mice demonstrated that the absence of Nrf2 exacerbates bone loss induced by PSC in both the spine and lower limbs, as observed through Micro-CT imaging and TRAP staining.Further investigations identified Camkk1 as a key downstream target of Nrf2. Using high-throughput sequencing and CO-IP experiments, we established that Nrf2 directly interacts with and regulates Camkk1. Functional assays indicated that PSC-induced upregulation of Camkk1 is significantly enhanced by Nrf2 knockdown, while silencing Camkk1 alone inhibits osteoclast differentiation.The therapeutic potential of this pathway was evaluated by screening small molecule inhibitors of Camkk1, with Crenolani emerging as a potent compound. In vivo administration of Crenolani in PSC-treated mice significantly alleviated bone loss in a dose-dependent manner.These findings elucidate a crucial molecular mechanism in osteoclast differentiation driven by CE infection and propose a promising therapeutic strategy for combating CE-induced bone destruction. This study advances our understanding of bone.

Role of immune dysregulation in peri-implantitis

Peri-implantitis, a complex condition that can lead to dental implant failure, is characterized by inflammatory destruction resulting from immune dysregulation. Oral microbial dysbiosis and foreign body stimulation are the main factors contributing to such dysregulation, impairing immune cell function and triggering an inflammatory response. Immune dysregulation plays a critical role in the pathophysiology of peri-implantitis, impacting the balance of T cell subsets, the production of inflammatory factors, and immune-related molecular signaling pathways. Understanding the relationship between immune dysregulation and peri-implantitis is crucial for developing targeted strategies for clinical diagnosis and individualized treatment planning. This review explores the similarities and differences in the immune microenvironment of oral bacterial infections and foreign body rejection, analyzes the relevant molecular signaling pathways, and identifies new key targets for developing innovative immunotherapeutic drugs and effective and personalized treatment modalities for peri-implantitis. Additionally, it addresses the challenges and potential directions for translating immunotherapy into clinical practice for peri-implantitis, offering insights that bridge the gaps in current literature and pave the way for future research.

Identification of novel RANKL inhibitors through in silico analysis

Receptor activator of nuclear factor-κB ligand (RANKL) is considered the principal regulator of osteoclast differentiation. Therefore, strategies interfering with the RANKL-RANK signaling pathway may effectively inhibit osteoclast differentiation and mitigate bone resorption. Consequently, RANKL has become a promising target for new drug design strategies. Despite extensive research on specific drugs and antibodies, only a few have shown efficacy in treating osteoporosis. To address this challenge, we aimed to explore new approaches for designing drugs for osteoporosis. In this study, a 3D quantitative structure-activity relationship (QSAR) pharmacophore model was built for RANKL with reference to known inhibitor IC50 values. The optimal pharmacophore model was then employed as a 3D query to screen databases for novel lead compounds. The obtained compounds were subjected to ADMET and TOPKAT analyses to predict drug pharmacokinetics and toxicity. Molecular docking and de novo evolution approaches were applied to verify the docking binding affinities of the compounds. Five candidate compounds were subjected to further in vitro analyses to assess their anti-osteoporotic effects, among which compound 4 demonstrated significant inhibitory activity, achieving an inhibitory rate of 92.6 % on osteoclastogenesis at a concentration of 10 μM. Subsequent molecular dynamics (MD) simulations to assess the stability and behavior of compound 4 and its evolved variant, ZINC00059014397_Evo, within the RANKL binding site revealed that the variant is a potential therapeutic agent for targeting osteoclasts. This study offers valuable insights for developing next generation RANKL inhibitors for osteoporosis treatments.

Nanoparticulate bioceramic putty suppresses osteoclastogenesis and inflammatory bone loss in mice via inhibition of TRAF6-mediated signalling pathways: A laboratory investigation

AIM

This study aimed to determine the effects of iRoot BP Plus on receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclastogenesis in vitro and inflammation-mediated bone resorption in vivo and investigated the underlying molecular mechanisms.

METHODOLOGY

CCK-8 was performed to test cell viability in RANKL-induced RAW 264.7 cells and BMDMs in response to iRoot BP Plus. The effect of iRoot BP Plus on osteoclastogenesis was determined using TRAP staining and phalloidin staining, respectively. Pit formation assay was conducted to measure osteoclast resorptive capacity. Western blot and qPCR were performed to examine osteoclast-related proteins and gene expression, respectively. Western blot was also used to investigate the signalling pathways involved. For in vivo experiments, an LPS-induced mouse calvarial bone resorption model was established to analyse the effect of iRoot BP Plus on bone resorption (n = 6 per group). At 7 days, mouse calvaria were collected and prepared for histological analysis.

RESULTS

We identified that iRoot BP Plus extracts significantly attenuated RANKL-induced osteoclastogenesis, reduced sealing zone formation, restrained osteolytic capacity and decreased osteoclast-specific gene expression (p < .01). Mechanistically, iRoot BP Plus extracts reduced TRAF6 via proteasomal degradation, then suppressed the phosphorylation of mitogen-activated protein kinases (MAPKs), blocked the nuclear translocation of c-Fos and diminished nuclear factor-κB (NF-κB) p65 and NFATc1 accumulation. Consistent with the in vitro results, iRoot BP Plus extracts attenuated osteoclast activity thus protecting against inflammatory bone resorption in vivo (p < .05), which was accompanied by a suppression of TRAF6, c-Fos, NFATc1 and cathepsin K expression.

CONCLUSION

These findings provide valuable insights into the signalling mechanisms underlying nanoparticulate bioceramic putty-mediated bone homeostasis.

VSIG4 inhibits RANKL-induced osteoclastogenesis by enhancing Nrf2-dependent antioxidant response against reactive oxygen species production

Osteoporosis is a prevalent systemic skeletal disorder, particularly affecting postmenopausal women, primarily due to excessive production and activation of osteoclasts. However, the current anti-osteoporotic drugs utilized in clinical practice may lead to certain side effects. Therefore, it is necessary to further unravel the potential mechanisms regulating the osteoclast differentiation and to identify novel targets for osteoporosis treatment. This study revealed the most significant decline in VSIG4 expression among the VSIG family members. VSIG4 overexpression significantly inhibited RANKL-induced osteoclastogenesis and bone resorption function. Mechanistically, both western blot and immunofluorescence assay results demonstrated that VSIG4 overexpression attenuated the expression of osteoclast marker genes and dampened the activation of MAPK and NF-κB signaling pathways. Furthermore, VSIG4 overexpression could inhibit the generation of reactive oxygen species (ROS) and stimulate the expression of Nrf2 along with its downstream antioxidant enzymes via interaction with Keap1. Notably, a potent Nrf2 inhibitor, ML385, could reverse the inhibitory effect of VSIG4 on osteoclast differentiation. In line with these findings, VSIG4 overexpression also mitigated bone loss induced by OVX and attenuated the activation of osteoclasts in vivo. In conclusion, our results suggest that VSIG4 holds promise as a novel target for addressing postmenopausal osteoporosis. This is achieved by suppressing osteoclast formation via enhancing Nrf2-dependent antioxidant response against reactive oxygen species production.

Pirfenidone Inhibits Alveolar Bone Loss in Ligature-Induced Periodontitis by Suppressing the NF-κB Signaling Pathway in Mice

There has been increasing interest in adjunctive use of anti-inflammatory drugs to control periodontitis. This study was performed to examine the effects of pirfenidone (PFD) on alveolar bone loss in ligature-induced periodontitis in mice and identify the relevant mechanisms. Experimental periodontitis was established by ligating the unilateral maxillary second molar for 7 days in mice (n = 8 per group), and PFD was administered daily via intraperitoneal injection. The micro-computed tomography and histology analyses were performed to determine changes in the alveolar bone following the PFD administration. For in vitro analysis, bone marrow macrophages (BMMs) were isolated from mice and cultured with PFD in the presence of RANKL or LPS. The effectiveness of PFD on osteoclastogenesis, inflammatory cytokine expression, and NF-κB activation was determined with RT-PCR, Western blot, and immunofluorescence analyses. PFD treatment significantly inhibited the ligature-induced alveolar bone loss, with decreases in TRAP-positive osteoclasts and expression of inflammatory cytokines in mice. In cultured BMM cells, PFD also inhibited RANKL-induced osteoclast differentiation and LPS-induced proinflammatory cytokine (IL-1β, IL-6, TNF-a) expression via suppressing the NF-κB signal pathway. These results suggest that PFD can suppress periodontitis progression by inhibiting osteoclastogenesis and inflammatory cytokine production via inhibiting the NF-κB signal pathway, and it may be a promising candidate for controlling periodontitis.

Euphorbia diterpenoids: isolation, structure, bioactivity, biosynthesis, and synthesis (2013-2021)

Covering: 2013 to 2021As the characteristic metabolites of Euphorbia plants, Euphorbia diterpenoids have always been a hot topic in related science communities due to their intriguing structures and broad bioactivities. In this review, we intent to provide an in-depth and extensive coverage of Euphorbia diterpenoids reported from 2013 to the end of 2021, including 997 new Euphorbia diterpenoids and 78 known ones with latest progress. Multiple aspects will be summarized, including their occurrences, chemical structures, bioactivities, and syntheses, in which the structure-activity relationship and biosynthesis of this class will be discussed for the first time.