IRF2 enhances RANKL-induced osteoclast differentiation via regulating NF-κB/NFATc1 signaling

Hepatocyte growth factor is protective in early stage but bone-destructive in late stage of experimental periodontitis

BACKGROUND AND OBJECTIVE

Clinical studies found high levels of hepatocyte growth factor (HGF) expression in patients with periodontitis. Studies suggest that HGF plays an important role in periodontitis, is involved in inflammation, and modulates alveolar bone integrity in periodontitis. This study aims to investigate the effects and mechanisms of HGF in the progression of experimental periodontitis.

METHODS

We used silk thread ligation to induce periodontitis in HGF-overexpressing transgenic (HGF-Tg) and wild-type C57BL/6J mice. The effects of HGF overexpression on alveolar bone destruction were assessed by microcomputed tomography imaging at baseline and on days 7, 14, 21, and 28. We analyzed the cytokines (IL-6 and TNF-α) and lymphocytes in periodontitis tissues by enzyme-linked immunosorbent assay and flow cytometry. The effects of HGF on alveolar bone destruction were further tested by quantifying the systemic bone metabolism markers CTXI and PINP and by RNA sequencing for the signaling pathways involved in bone destruction. Western blotting and immunohistochemistry were performed to further elucidate the involved signaling pathways.

RESULTS

We found that experimental periodontitis increased HGF production in periodontitis tissues; however, the effects of HGF overexpression were inconsistent with disease progression. In the early stage of periodontitis, periodontal inflammation and alveolar bone destruction were significantly lower in HGF-Tg mice than in wild-type mice. In the late stage, HGF-Tg mice showed higher inflammatory responses and progressively aggravated bone destruction with continued stimulation of inflammation. We identified the IL-17/RANKL/TRAF6 pathway as a signaling pathway involved in the HGF effects on the progression of periodontitis.

CONCLUSION

HGF plays divergent effects in the progression of experimental periodontitis and accelerates osteoclastic activity and bone destruction in the late stage of inflammation.

Corynoline Suppresses Osteoclastogenesis and Attenuates ROS Activities by Regulating NF-κB/MAPKs and Nrf2 Signaling Pathways

Declining estrogen production in postmenopausal females causes osteoporosis in which the resorption of bone exceeds the increase in bone formation. Although clinical drugs are currently available for the treatment of osteoporosis, sustained medication use is accompanied by serious side effects. Corydalis bungeana Herba, a famous traditional Chinese herb listed in the Chinese Pharmacopoeia Commission, constitutes various traditional Chinese Medicine prescriptions, which date back to thousands of years. One of the primary active components of C. bungeana Turcz. is Corynoline (Cor), a plant isoquinoline alkaloid derived from the Corydalis species, which possesses bone metabolism disease therapeutic potential. The study aimed at exploring the effects as well as mechanisms of Cor on osteoclast formation and bone resorption. TRAcP staining, F-actin belt formation, and pit formation were employed for assessing the osteoclast function. Western blot, qPCR, network pharmacology, and docking analyses were used for analyzing the expression of osteoclast-associated genes and related signaling pathways. The study focused on investigating how Cor affected OVX-induced trabecular bone loss by using a mouse model. Cor could weaken osteoclast formation and function by affecting the biological receptor activators of NF-κB and its ligand at various concentrations. Mechanistically, Cor inhibited the NF-κB activation, and the MAPKs pathway stimulated by RANKL. Besides, Cor enhanced the protein stability of the Nrf2, which effectively abolished the RANKL-stimulated ROS generation. According to an OVX mouse model, Cor functions in restoring bone mass, improving microarchitecture, and reducing the ROS levels in the distal femurs, which corroborated with its in vitro antiosteoclastogenic effect. The present study indicates that Cor may restrain osteoclast formation and bone loss by modulating NF-κB/MAPKs and Nrf2 signaling pathways. Cor was shown to be a potential drug candidate that can be utilized for the treatment of osteoporosis.

Suppression of IRF9 Promotes Osteoclast Differentiation by Decreased Ferroptosis via STAT3 Activation

Osteoporosis is a chronic disease that endangers the health of the elderly. Inhibiting osteoclast hyperactivity is a key aspect of osteoporosis prevention and treatment. Several studies have shown that interferon regulatory factor 9 (IRF9) not only regulates innate and adaptive immune responses but also plays an important role in inflammation, antiviral response, and cell development. However, the exact role of IRF9 in osteoclasts has not been reported. To elucidate the role of IRF9 in osteoclast differentiation, we established the ovariectomized mouse model of postmenopausal osteoporosis and found that IRF9 expression was reduced in ovariectomized mice with overactive osteoclasts. Furthermore, knockdown of IRF9 expression enhanced osteoclast differentiation in vitro. Using RNA sequencing, we identified that the differentially expressed genes enriched by IRF9 knockdown were related to ferroptosis. We observed that IRF9 knockdown promoted osteoclast differentiation via decreased ferroptosis in vitro and further verified that IRF9 knockdown reduced ferroptosis by activating signal transducer and activator of transcription 3 (STAT3) to promote osteoclastogenesis. In conclusion, we identified an essential role of IRF9 in the regulation of osteoclastogenesis in osteoporosis and its underlying mechanism.

Role and Regulation of Transcription Factors in Osteoclastogenesis

Bones serve mechanical and defensive functions, as well as regulating the balance of calcium ions and housing bone marrow.. The qualities of bones do not remain constant. Instead, they fluctuate throughout life, with functions increasing in some situations while deteriorating in others. The synchronization of osteoblast-mediated bone formation and osteoclast-mediated bone resorption is critical for maintaining bone mass and microstructure integrity in a steady state. This equilibrium, however, can be disrupted by a variety of bone pathologies. Excessive osteoclast differentiation can result in osteoporosis, Paget's disease, osteolytic bone metastases, and rheumatoid arthritis, all of which can adversely affect people's health. Osteoclast differentiation is regulated by transcription factors NFATc1, MITF, C/EBPα, PU.1, NF-κB, and c-Fos. The transcriptional activity of osteoclasts is largely influenced by developmental and environmental signals with the involvement of co-factors, RNAs, epigenetics, systemic factors, and the microenvironment. In this paper, we review these themes in regard to transcriptional regulation in osteoclastogenesis.

Aikeqing, a kidney- and spleen-tonifying compound Chinese medicine granule, prevented ovariectomy-induced bone loss in rats via the suppression of osteoclastogenesis

Postmenopausal women are prone to osteoporosis due to increased osteoclast activation and bone resorption caused by oestrogen deficiency. In Traditional Chinese Medicine theory, medicines with spleen- and kidney-nourishing effects are commonly used in postmenopausal osteoporosis (PMOP) treatment. Aikeqing (AKQ) is a compound Chinese medicinal granule with spleen- and kidney-nourishing effects. Herein, we investigate the in vitro and in vivo anti-osteoporotic effects of AKQ, its underlying mechanisms and pharmacodynamic basis. In vitro antiosteoporotic effects of AKQ were assessed by its ability to promote osteoblastogenesis in MC3T3-E1 and/or inhibit RANKL-induced osteoclastogenesis in murine bone marrow monocytes (BMMs). The protective effect of AKQ on bone loss induced by oestrogen deficiency was evaluated in ovariectomized rats. The underlying mechanisms were studied in BMMs by detecting the effects of AKQ on the RANKL-induced expression of genes and proteins involved in the regulation of osteoclastogenesis. The main chemical constituents of AKQ in the granule were analyzed by UPLC-QTOF-MS. Our findings show that AKQ did not affect osteoblastogenesis, but it inhibited RANKL-induced osteoclastogenesis. In the ovariectomized rats, oral administration of AKQ (4 g/kg/d) for 90 d effectively prevented oestrogen deficiency-induced bone loss. Mechanistic studies in BMMs revealed that AKQ inhibited RNAKL-induced activation of NF-κB (p65) and MAPKs (p38 and JNK) via blocking the RANK-TRAF6 interaction, subsequently suppressing the translocation and expression of NFATc1 and c-Fos. UPLC-QTOF-MS analysis quantified the 123 main components of AKQ. Taken together, AKQ was demonstrated for the first time as a novel alternative therapy for osteoclast-associated bone diseases.

Cholesterol sulfate inhibits osteoclast differentiation and survival by regulating the AMPK-Sirt1-NF-κB pathway

Cholesterol sulfate (CS) is an activator of retinoic acid-related orphan receptor α (RORα). CS treatment or RORα overexpression attenuates osteoclastogenesis in a collagen-induced arthritis mouse model. However, the mechanism by which CS and RORα regulate osteoclast differentiation remains largely unknown. Thus, we aimed to investigate the role of CS and RORα in osteoclastogenesis and their underlying mechanism. CS inhibited osteoclast differentiation, but RORα deficiency did not affect osteoclast differentiation and CS-mediated inhibition of osteoclastogenesis. CS enhanced adenosine monophosphate-activated protein kinase (AMPK) phosphorylation and sirtuin1 (Sirt1) activity, leading to nuclear factor-κB (NF-κB) inhibition by decreasing acetylation at Lys310 of p65. The NF-κB inhibition was restored by AMPK inhibitor, but the effects of CS on AMPK and NF-κB were not altered by RORα deficiency. CS also induced osteoclast apoptosis, which may be due to sustained AMPK activation and consequent NF-κB inhibition, and the effects of CS were significantly reversed by interleukin-1β treatment. Collectively, these results indicate that CS inhibits osteoclast differentiation and survival by suppressing NF-κB via the AMPK-Sirt1 axis in a RORα-independent manner. Furthermore, CS protects against bone destruction in lipopolysaccharide- and ovariectomy-mediated bone loss mouse models, suggesting that CS is a useful therapeutic candidate for treating inflammation-induced bone diseases and postmenopausal osteoporosis.

Strontium Ranelate Inhibits Osteoclastogenesis through NF-κB-Pathway-Dependent Autophagy

Strontium ranelate (SR) is a pharmaceutical agent used for the prevention and treatment of osteoporosis and fragility fracture. However, little attention has been paid to the effect of SR on alveolar bone remodeling during orthodontic tooth movement and its underlying mechanism. Here, we investigated the influence of SR on orthodontic tooth movement and tooth resorption in Sprague–Dawley rats and the relationship between the nuclear factor–kappa B (NF-κB) pathway, autophagy, and osteoclastogenesis after the administration of SR in vitro and in vivo. In this study, it was found that SR reduced the expression of autophagy-related proteins at the pressure side of the first molars during orthodontic tooth movement. Similarly, the expression of these autophagy-related proteins and the size and number of autophagosomes were downregulated by SR in vitro. The results also showed that SR reduced the number of osteoclasts and suppressed orthodontic tooth movement and root resorption in rats, which could be partially restored using rapamycin, an autophagy inducer. Autophagy was attenuated after pre-osteoclasts were treated with Bay 11-7082, an NF-κB pathway inhibitor, while SR reduced the expression of the proteins central to the NF-κB pathway. Collectively, this study revealed that SR might suppress osteoclastogenesis through NF-κB-pathway-dependent autophagy, resulting in the inhibition of orthodontic tooth movement and root resorption in rats, which might offer a new insight into the treatment of malocclusion and bone metabolic diseases.

Phosphatidyl Inositol 3-Kinase (PI3K)-Inhibitor CDZ173 protects against LPS-induced osteolysis

A major complication of a joint replacement is prosthesis loosening caused by inflammatory osteolysis, leading to the revision of the operation. This is due to the abnormal activation of osteoclast differentiation and function caused by periprosthetic infection. Therefore, targeting abnormally activated osteoclasts is still effective for treating osteolytic inflammatory diseases. CDZ173 is a selective PI3K inhibitor widely used in autoimmune-related diseases and inflammatory diseases and is currently under clinical development. However, the role and mechanism of CDZ173 in osteoclast-related bone metabolism remain unclear. The possibility for treating aseptic prosthesis loosening brought on by inflammatory osteolysis illness can be assessed using an LPS-induced mouse cranial calcium osteolysis model. In this study, we report for the first time that CDZ173 has a protective effect on LPS-induced osteolysis. The data show that this protective effect is due to CDZ173 inhibiting the activation of osteoclasts in vivo. Meanwhile, our result demonstrated that CDZ173 had a significant inhibitory effect on RANKL-induced osteoclasts. Furthermore, using the hydroxyapatite resorption pit assay and podosol actin belt staining, respectively, the inhibitory impact of CDZ173 on bone resorption and osteoclast fusion of pre-OC was determined. In addition, staining with alkaline phosphatase (ALP) and alizarin red (AR) revealed that CDZ173 had no effect on osteoblast development in vitro. Lastly, CDZ173 inhibited the differentiation and function of osteoclasts by weakening the signal axis of PI3K-AKT/MAPK-NFATc1 in osteoclasts. In conclusion, our results highlight the potential pharmacological role of CDZ173 in preventing osteoclast-mediated inflammatory osteolysis and its potential clinical application.

Anti-Osteoporotic Effect of Lactobacillus brevis AR281 in an Ovariectomized Mouse Model Mediated by Inhibition of Osteoclast Differentiation

Osteoporosis is a global disease characterized by weakened bone microarchitecture, leading to osteoporotic fractures. Estrogen replacement therapy is the traditional treatment for osteoporosis but carries with it an increased risk of cardiac events. In search of a safe and effective treatment, we used Lactobacillus brevis AR281, which has anti-inflammatory properties, to conduct a 7-week experiment, investigating its inhibitory effects on osteoporosis in an ovariectomized (ovx) mouse model. The results demonstrated that AR281 significantly improved bone microarchitecture and biomechanical strength in ovx mice by attenuating bone resorption. AR281 significantly decreased the critical osteoclast activator, the ratio of the receptor activator for nuclear factor kappa B (NF-κB) ligand (RANKL) to osteoprotegerin, and pro-inflammatory osteoclastogenic mediators, such as IL-1, IL-6, and IL-17, which can increase the RANKL expression. Moreover, AR281 modulated intestinal microbiota in ovx mice increased the abundance of Akkermansia, which is responsible for the improvement of gut epithelial barrier integrity. In an in vitro trial, AR281 suppressed the number of osteoclasts differentiated from the osteoclast precursor RAW264.7 cells caused by RANKL through the tumor necrosis factor (TNF) receptor-associated factor 6 (TRAF6)/NF-κB/nuclear factor of activated T cells c1 (NFATc1) pathway. Therefore, AR281 may be a natural alternative for combating osteoporosis.