Prostaglandins and Bone

Exploring an innovative augmentation strategy in spinal fusion: A novel selective prostaglandin EP4 receptor agonist as a potential osteopromotive factor to enhance lumbar posterolateral fusion

BACKGROUND

On-site delivery of bioactive agents facilitates enhancing the effectiveness of spinal fusion. However, the FDA-approved agents currently used in clinical practice are limited by side effects and cost issues, urging exploration of new alternatives.

AIM

This study aimed to investigate the effectiveness of KMN-159, a novel selective prostaglandin EP4 receptor agonist with osteopromotive properties, in spinal posterolateral fusion (PLF) surgery.

METHODS

Various doses of KMN-159 were delivered locally using a mineralized collagen matrix (MCM) scaffold, and its efficacy results were compared with FDA-approved recombinant human bone morphogenetic protein-2 (rhBMP-2) in a rat lumbar PLF model. 192 male Wistar rats, aged 10 weeks, were randomized into 8 groups: 1) SHAM, 2) MCM, 3) MCM +10 μg rhBMP-2 (per scaffold), 4-8) MCM + 0.1, 1, 10, 100 or 1000 μg KMN-159 (per scaffold). PLF surgery was performed at the L4-5 level, and animals were euthanized after 3 and 6 weeks for spinal fusion evaluation.

RESULTS

KMN-159 exhibited dose-dependent osteopromotive effects on osteoblasts, osteoclasts, and vascular ingrowth within MCM carriers, resulting in new bone formation in a dose-dependent manner. The mid- and high-dose KMN-159 (10, 100, and 1000 μg) groups significantly enhanced PLF with biomechanical improvement, while low-dose (0.1 and 1 μg) groups were insufficient to achieve lumbar fusion.

CONCLUSION

KMN-159 emerges as a novel osteopromotive factor, coupled with its functionalized MCM scaffold presents a potential bioactive material for enhancing PLF surgery outcomes.

COX-2 inhibition as a therapeutic strategy for bone loss in Staphylococcus aureus osteomyelitis

Bone loss in Staphylococcus aureus (S. aureus) osteomyelitis poses a serious challenge to orthopedic treatment, but the underlying mechanism of systemic osteoporosis caused by chronic infection is not completely clear. In this study, γ-irradiation-killed S. aureus (IKSA) was applied to simulate the inflammation and explore the mechanism of systemic bone loss caused by it. In this study, we found that the systemic application of IKSA caused bone loss in mice through increasing osteoclasts and decreasing osteoblasts. An immune response profile with up-regulated COX-2 is identified based on our transcriptional data from IKSA mice bone marrow cells. COX-2 expression is widely up-regulated in bone marrow immune cells, such as myeloid-derived suppressor cells (MDSCs), neutrophils and macrophages in the IKSA-treated mice. Mechanistically, COX-2 stimulated the increasing proportion of MDSCs and neutrophils and the inflammatory response of the bone marrow immune cells, that may regulate bone metabolism. Importantly, COX-2 inhibitor, celecoxib could rescue the bone loss induced by IKSA, which may reason from decrease of inflammatory gene expression in MDSCs, neutrophils and macrophages. Excitingly, COX-2 expression is also increased in bone marrow from mice and patients with S. aureus osteomyelitis. These findings suggested a therapeutic potential for inhibiting COX-2 in combating bone loss in S. aureus osteomyelitis.

Recent advances in the application and biological mechanism of silicon nitride osteogenic properties: a review

Silicon nitride, an emerging bioceramic material, is highly sought after in the biomedical industry due to its osteogenesis-promoting properties, which are a result of its unique surface chemistry and excellent mechanical properties. Currently, it is used in clinics as an orthopedic implant material. The osteogenesis-promoting properties of silicon nitride are manifested in its contribution to the formation of a local osteogenic microenvironment, wherein silicon nitride and its hydrolysis products influence osteogenesis by modulating the biological behaviors of the constituents of the osteogenic microenvironment. In particular, silicon nitride regulates redox signaling, cellular autophagy, glycolysis, and bone mineralization in cells involved in bone formation via several mechanisms. Moreover, it may also promote osteogenesis by influencing immune regulation and angiogenesis. In addition, the wettability, surface morphology, and charge of silicon nitride play crucial roles in regulating its osteogenesis-promoting properties. However, as a bioceramic material, the molding process of silicon nitride needs to be optimized, and its osteogenic mechanism must be further investigated. Herein, we summarize the impact of the molding process of silicon nitride on its osteogenic properties and clinical applications. In addition, the mechanisms of silicon nitride in promoting osteogenesis are discussed, followed by a summary of the current gaps in silicon nitride mechanism research. This review, therefore, aims to provide novel ideas for the future development and applications of silicon nitride.

Immune System Acts on Orthodontic Tooth Movement: Cellular and Molecular Mechanisms

Orthodontic tooth movement (OTM) is a tissue remodeling process based on orthodontic force loading. Compressed periodontal tissues have a complicated aseptic inflammatory cascade, which are considered the initial factor of alveolar bone remodeling. Since skeletal and immune systems shared a wide variety of molecules, osteoimmunology has been generally accepted as an interdisciplinary field to investigate their interactions. Unsurprisingly, OTM is considered a good mirror of osteoimmunology since it involves immune reaction and bone remolding. In fact, besides bone remodeling, OTM involves cementum resorption, soft tissue remodeling, orthodontic pain, and relapse, all correlated with immune cells and/or immunologically active substance. The aim of this paper is to review the interaction of immune system with orthodontic tooth movement, which helps gain insights into mechanisms of OTM and search novel method to short treatment period and control complications.

PEG2-Induced Pyroptosis Regulates the Expression of HMGB1 and Promotes hEM15A Migration in Endometriosis

Endometriosis (EMS) is a common gynecological disease. Prostaglandin E2 (PGE2), which induces chronic pelvic inflammation and cell pyroptosis, a form of programmed cell death based on inflammasome activation, are involved in EMS, but the extent of their involvement and roles remain unclear. The present study aimed to evaluate PGE2-induced pyroptosis in EMS and the influence of PGE2 in EMS progression. Using western blotting, it was found that the expressions of PGE2 and pyroptosis-related proteins (NLRP3, cleaved caspase-1, interleukin (IL)-1β and IL-18) were higher in EMS tissues than in normal endometrial tissues. The levels of PGE2, IL-1β, and IL-18 in the serum of patients with EMS and cell culture fluids were also detected. Using the transwell assay, we verified that PGE2 promoted hEM15A migration via the NLRP3/caspase-1 pyroptotic pathway, and PGE2-induced pyroptosis upregulated the expressions of high mobility group box 1 (HMGB1), E-cadherin, and vimentin. Immunohistochemistry analysis confirmed that PGE2-induced pyroptosis contributed to EMS invasion. These results suggest that PGE2-induced pyroptosis affects the progression of EMS by changing the migration ability of pyroptotic cells and upregulating the expression of HMGB1, E-cadherin, and vimentin. Our findings provide crucial evidence for new treatment pathways and use of anti-inflammatory drugs in EMS.

Senescent preosteoclast secretome promotes metabolic syndrome associated osteoarthritis through cyclooxygenase 2

Background

Metabolic syndrome-associated osteoarthritis (MetS-OA) is a distinct osteoarthritis phenotype defined by the coexistence of MetS or its individual components. Despite the high prevalence of MetS-OA, its pathogenic mechanisms are unclear. The aim of this study was to determine the role of cellular senescence in the development of MetS-OA.

Methods

Analysis of the human osteoarthritis initiative (OAI) dataset was conducted to investigate the MRI subchondral bone features of MetS-human OA participants. Joint phenotype and senescent cells were evaluated in two MetS-OA mouse models: high-fat diet (HFD)-challenged mice and STR/Ort mice. In addition, the molecular mechanisms by which preosteoclasts become senescent as well as how the senescent preosteoclasts impair subchondral bone microenvironment were characterized using in vitro preosteoclast culture system.

Results

Humans and mice with MetS are more likely to develop osteoarthritis-related subchondral bone alterations than those without MetS. MetS-OA mice exhibited a rapid increase in joint subchondral bone plate and trabecular thickness before articular cartilage degeneration. Subchondral preosteoclasts undergo senescence at the pre- or early-osteoarthritis stage and acquire a unique secretome to stimulate osteoblast differentiation and inhibit osteoclast differentiation. Antagonizing preosteoclast senescence markedly mitigates pathological subchondral alterations and osteoarthritis progression in MetS-OA mice. At the molecular level, preosteoclast secretome activates COX2-PGE2, resulting in stimulated differentiation of osteoblast progenitors for subchondral bone formation. Administration of a selective COX2 inhibitor attenuated subchondral bone alteration and osteoarthritis progression in MetS-OA mice. Longitudinal analyses of the human Osteoarthritis Initiative (OAI) cohort dataset also revealed that COX2 inhibitor use, relative to non-selective nonsteroidal antiinflammatory drug use, is associated with less progression of osteoarthritis and subchondral bone marrow lesion worsening in participants with MetS-OA.

Conclusions

Our findings suggest a central role of a senescent preosteoclast secretome-COX2/PGE2 axis in the pathogenesis of MetS-OA, in which selective COX2 inhibitors may have disease-modifying potential.

Funding

This work was supported by the National Institutes of Health grant R01AG068226 and R01AG072090 to MW, R01AR079620 to SD, and P01AG066603 to XC.

Endosomal TLR3 signaling in stromal osteoblasts induces prostaglandin E2-mediated inflammatory periodontal bone resorption

Toll-like receptors (TLRs) are pattern recognition receptors that play a critical role in innate immune diseases. TLR3, which is localized in the endosomal compartments of hematopoietic immune cells, is able to recognize double-stranded RNA (dsRNA) derived from viruses and bacteria and thereby induce innate immune responses. Inflammatory periodontal bone resorption is caused by bacterial infections, which initially is regulated by innate immunity; however, the roles of TLR3 signaling in bone resorption are still not known. We examined the roles of TLR3 signaling in bone resorption using poly(I:C), a synthetic dsRNA analog. In cocultures of mouse bone marrow cells and stromal osteoblasts, poly(I:C) clearly induced osteoclast differentiation. In osteoblasts, poly(I:C) increased PGE2 production and upregulated the mRNA expression of PGE2-related genes, Ptgs2 and Ptges, as well as that of a gene related to osteoclast differentiation, Tnfsf11. In addition, we found that indomethacin (a COX-2 inhibitor) or an antagonist of the PGE2 receptor EP4 attenuated the poly(I:C)-induced PGE2 production and subsequent Tnfsf11 expression. Poly(I:C) also prolonged the survival of the mature osteoclasts associated with the increased mRNA expression of osteoclast marker genes, Nfatc1 and Ctsk. In ex vivo organ cultures of periodontal alveolar bone, poly(I:C) induced bone-resorbing activity in a dose-dependent manner, which was attenuated by the simultaneous administration of either indomethacin or an EP4 antagonist. These data suggest that TLR3 signaling in osteoblasts controls PGE2 production and induces the subsequent differentiation and survival of mature osteoclasts. Endogenous TLR3 in stromal osteoblasts and osteoclasts synergistically induces inflammatory alveolar bone resorption in periodontitis.

Periodontitis and diabetes mellitus co-morbidity: A molecular dialogue

BACKGROUND

Type 2 diabetes mellitus (T2DM) and periodontitis are two biologically linked diseases that often coexist in complex interaction. While periodontitis may lead to insulin receptor desensitization, diabetes may increase the expression of inflammatory cytokines, such as Tumor Necrosis Factor-α (TNF-α) and Interleukin 6 (IL-6), in the gingival crevicular fluid and activate osteoclasts via Receptor activator of nuclear factor kappa-Β ligand (RANK-L) production, leading to bone resorption. However, the association between the two diseases processes, where one may exacerbate the progression of the other, is unclear. In addition, both diseases have similar mechanistic themes, such as chronic inflammation and oxidative stress. This review aimed to investigate the pathophysiological and molecular mechanisms underlying T2DM and periodontitis.

HIGHLIGHT

Uncontrolled diabetes is often associated with severe periodontitis, measured by clinical attachment loss. Alteration in the oral microbiome composition, which may activate the host inflammatory response and lead to irreversible oxidative stress, is a common finding in both diseases. An understanding of the molecular crosstalk between the two disease processes is crucial for developing therapeutic targets that inhibit bone resorption and halt the progression of periodontitis in patients with diabetes.

CONCLUSION

The Oral microbiome composition in T2DM and periodontitis shifts toward dysbiosis, favoring bacterial pathogens, such as Fusobacteria and Porphyromonas species. Both conditions are marked by pro-inflammatory immune activity via the activation of Interleukin 17 (IL-17), Interleukin 1 (IL-1), TNF-α, and Nuclear Factor Kappa Beta (NF-κB). Common molecular crosstalk signaling appears to involve advanced glycation end products (AGEs) and oxidative stress. Thus, future drug targets are multifactorial, ranging from modulatory of host inflammatory response to preventing the accumulation of AGEs and oxidative free radicals.

Dietary Intake of Flaxseed Oil since Early Stages of Life Promotes Femur Quality in Male Rats

BACKGROUND

Flaxseed oil (FO) is an alpha linolenic acid source important for growth and body development. However, there is little literature on the role of FO in critical stages of bone development and formation.

OBJECTIVE

This study evaluated the influence of a diet containing FO on rat femurs.

METHODS

After birth, mothers and pups were divided into control and flaxseed groups (n = 6 pups each) fed diets containing 7% soybean oil (C) or 7% FO. At 21 days, pups were weaned and separated from the mothers, and control or experimental diets were continued. At 67 days, the following were analyzed: osteocalcin and osteoprotegerin (OPG) levels, bone mineral density (BMD) and content, and bone area; the dimension, BMD, head radiodensity, and biomechanical proprieties of the right femur; and histomorphometric parameters of the left femur.

RESULTS

Compared to the C group, the FO group presented (p < 0.05) a lower body mass (-3.7%) and medullary area (-10.1%) and higher osteocalcin (+36.7%), OPG (+52.5%), femur width (+3.8%), absolute mass (+2.3%), femur BMD (+3.6%), head radiodensity (+6.1%), maximum force (+7.4%), breaking strength (+17.3), and cortical thickness (+7.0).

CONCLUSION

The FO diet contributed to femur quality in healthy male Wistar rats.

Role and Regulation of Mechanotransductive HIF-1α Stabilisation in Periodontal Ligament Fibroblasts

Orthodontic tooth movement (OTM) creates compressive and tensile strain in the periodontal ligament, causing circulation disorders. Hypoxia-inducible factor 1α (HIF-1α) has been shown to be primarily stabilised by compression, but not hypoxia in periodontal ligament fibroblasts (PDLF) during mechanical strain, which are key regulators of OTM. This study aimed to elucidate the role of heparan sulfate integrin interaction and downstream kinase phosphorylation for HIF-1α stabilisation under compressive and tensile strain and to which extent downstream synthesis of VEGF and prostaglandins is HIF-1α-dependent in a model of simulated OTM in PDLF. PDLF were subjected to compressive or tensile strain for 48 h. In various setups HIF-1α was experimentally stabilised (DMOG) or destabilised (YC-1) and mechanotransduction was inhibited by surfen and genistein. We found that HIF-1α was not stabilised by tensile, but rather by compressive strain. HIF-1α stabilisation had an inductive effect on prostaglandin and VEGF synthesis. As expected, HIF-1α destabilisation reduced VEGF expression, whereas prostaglandin synthesis was increased. Inhibition of integrin mechanotransduction via surfen or genistein prevented stabilisation of HIF-1α. A decrease in VEGF expression was observed, but not in prostaglandin synthesis. Stabilisation of HIF-1α via integrin mechanotransduction and downstream phosphorylation of kinases seems to be essential for the induction of VEGF, but not prostaglandin synthesis by PDLF during compressive (but not tensile) orthodontic strain.