Complement involvement in bone homeostasis and bone disorders

Copper Complexes with New Glycyl-l-histidyl-l-lysine-Hyaluronan Conjugates Show Antioxidant Properties and Osteogenic and Angiogenic Synergistic Effects

In recent years, hyaluronic acid (HA) and the natural tripeptide glycyl-l-histidyl-l-lysine (GHK), especially its copper(II) complex (GHK-Cu), individually have been shown to exert helpful properties for bone protection and regeneration. However, they are not strong enough to handle oxidative stress, hydrolytic attack, or environmental conditions. Being aware that conjugation chemistry has recently emerged as an appealing approach for generating new molecular entities capable of preserving the molecular integrity of their moieties or delaying their degradation, herein we present the synthesis of conjugates of HA with GHK (GHK-HA), at different loadings of the tripeptide. GHK-HA binds copper(II) ions and potentiates the chemical and biological properties of the two components in in vitro assays. The results highlight copper's role in promoting the expression and release of certain trophic, angiogenic, and osteogenic factors, including brain-derived neurotrophic factor (BDNF), vascular endothelial growth factor (VEGF), as well as bone morphogenetic protein-2 (BMP-2). The protective and regenerative activities of the metal ion are related to the translocation of its intracellular chaperones Copper Chaperone for Superoxide Dismutase (CCS) and Antioxidant-1 (Atox1) to the nucleus where they act as transcription factors.

Bone impairment in atypical hemolytic and uremic syndrome treated by long-term eculizumab

Atypical hemolytic uremic syndrome (aHUS) is a thrombotic microangiopathy, related to complement dysregulation, including Factor H deficiency (FH) treated by lifelong eculizumab therapy. Its long-term tolerance is not yet fully described. We report two patients with genetic FH deficiency receiving long-term eculizumab and displaying a peculiar bone phenotype. First case is a 13-year-old girl, presenting with bone pains, arthritis, and deformities, for which X-rays and MRI described multifocal osteochondritis. Bone biopsy revealed an active remodeling bone (many areas of bone formation and resorption) and C3c accumulation on immunohistochemical staining. The second patient is an 11-year-old girl, displaying mechanical bone pains, for which bone scintigraphy found hypofixation of wrists and ankles. These findings could be consistent with a side effect of eculizumab, as C3c accumulation may result from the downstream C5-blockade. Alternatively, bone alterations could be due to the absence of FH, as described in murine models. Further investigations are required to characterize bone disease in aHUS.

Multi-omics analyses reveal aberrant differentiation trajectory with WNT1 loss-of-function in type XV osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a group of severe genetic bone disorders characterized by congenital low bone mass, deformity, and frequent fractures. Type XV OI is a moderate to severe form of skeletal dysplasia caused by WNT1 variants. In this cohort study from southern China, we summarized the clinical phenotypes of patients with WNT1 variants and found that the proportion of type XV patients was around 10.3% (25 out of 243) with a diverse spectrum of phenotypes. Functional assays indicated that variants of WNT1 significantly impaired its secretion and effective activity, leading to moderate to severe clinical manifestations, porous bone structure, and enhanced osteoclastic activities. Analysis of proteomic data from human skeleton indicated that the expression of SOST (sclerostin) was dramatically reduced in type XV patients compared to patients with COL1A1 quantitative variants. Single-cell transcriptome data generated from human tibia samples of patients diagnosed with type XV OI and leg-length discrepancy, respectively, revealed aberrant differentiation trajectories of skeletal progenitors and impaired maturation of osteocytes with loss of WNT1, resulting in excessive CXCL12+ progenitors, fewer mature osteocytes, and the existence of abnormal cell populations with adipogenic characteristics. The integration of multi-omics data from human skeleton delineates how WNT1 regulates the differentiation and maturation of skeletal progenitors, which will provide a new direction for the treatment strategy of type XV OI and relative low bone mass diseases such as early onset osteoporosis.

Brain-Bone Crosstalk in a Murine Polytrauma Model Promotes Bone Remodeling but Impairs Neuromotor Recovery and Anxiety-Related Behavior

Traumatic brain injury (TBI) and long bone fractures are a common injury pattern in polytrauma patients and modulate each other's healing process. As only a limited number of studies have investigated both traumatic sites, we tested the hypothesis that brain-bone polytrauma mutually impacts neuro- and osteopathological outcomes. Adult female C57BL/6N mice were subjected to controlled cortical impact (CCI), and/or osteosynthetic stabilized femoral fracture (FF), or sham surgery. Neuromotor and behavioral impairments were assessed by neurological severity score, open field test, rotarod test, and elevated plus maze test. Brain and bone tissues were processed 42 days after trauma. CCI+FF polytrauma mice had increased bone formation as compared to FF mice and increased mRNA expression of bone sialoprotein (BSP). Bone fractures did not aggravate neuropathology or neuroinflammation assessed by cerebral lesion size, hippocampal integrity, astrocyte and microglia activation, and gene expression. Behavioral assessments demonstrated an overall impaired recovery of neuromotor function and persistent abnormalities in anxiety-related behavior in polytrauma mice. This study shows enhanced bone healing, impaired neuromotor recovery and anxiety-like behavior in a brain-bone polytrauma model. However, bone fractures did not aggravate TBI-evoked neuropathology, suggesting the existence of outcome-relevant mechanisms independent of the extent of brain structural damage and neuroinflammation.

Effects of interleukin-10 treated macrophages on bone marrow mesenchymal stem cells via signal transducer and activator of transcription 3 pathway

BACKGROUND

Alveolar bone defects caused by inflammation are an urgent issue in oral implant surgery that must be solved. Regulating the various phenotypes of macrophages to enhance the inflammatory environment can significantly affect the progression of diseases and tissue engineering repair process.

AIM

To assess the influence of interleukin-10 (IL-10) on the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) following their interaction with macrophages in an inflammatory environment.

METHODS

IL-10 modulates the differentiation of peritoneal macrophages in Wistar rats in an inflammatory environment. In this study, we investigated its impact on the proliferation, migration, and osteogenesis of BMSCs. The expression levels of signal transducer and activator of transcription 3 (STAT3) and its activated form, phosphorylated-STAT3, were examined in IL-10-stimulated macrophages. Subsequently, a specific STAT3 signaling inhibitor was used to impede STAT3 signal activation to further investigate the role of STAT3 signaling.

RESULTS

IL-10-stimulated macrophages underwent polarization to the M2 type through substitution, and these M2 macrophages actively facilitated the osteogenic differentiation of BMSCs. Mechanistically, STAT3 signaling plays a crucial role in the process by which IL-10 influences macrophages. Specifically, IL-10 stimulated the activation of the STAT3 signaling pathway and reduced the macrophage inflammatory response, as evidenced by its diminished impact on the osteogenic differentiation of BMSCs.

CONCLUSION

Stimulating macrophages with IL-10 proved effective in improving the inflammatory environment and promoting the osteogenic differentiation of BMSCs. The IL-10/STAT3 signaling pathway has emerged as a key regulator in the macrophage-mediated control of BMSCs' osteogenic differentiation.

Gene expression supports a single origin of horns and antlers in hoofed mammals

Horns, antlers, and other bony cranial appendages of even-toed hoofed mammals (ruminant artiodactyls) challenge traditional morphological homology assessments. Cranial appendages all share a permanent bone portion with family-specific integument coverings, but homology determination depends on whether the integument covering is an essential component or a secondary elaboration of each structure. To enhance morphological homology assessments, we tested whether juvenile cattle horn bud transcriptomes share homologous gene expression patterns with deer antlers relative to pig outgroup tissues, treating the integument covering as a secondary elaboration. We uncovered differentially expressed genes that support horn and antler homology, potentially distinguish them from non-cranial-appendage bone and other tissues, and highlight the importance of phylogenetic outgroups in homology assessments. Furthermore, we found differentially expressed genes that could support a shared cranial neural crest origin for horns and antlers and expression patterns that refine our understanding of the timing of horn and antler differentiation.

Fracture haematoma proteomics

Aims

The aim of this study was to determine the fracture haematoma (fxH) proteome after multiple trauma using label-free proteomics, comparing two different fracture treatment strategies.

Methods

A porcine multiple trauma model was used in which two fracture treatment strategies were compared: early total care (ETC) and damage control orthopaedics (DCO). fxH was harvested and analyzed using liquid chromatography-tandem mass spectrometry. Per group, discriminating proteins were identified and protein interaction analyses were performed to further elucidate key biomolecular pathways in the early fracture healing phase.

Results

The early fxH proteome was characterized by immunomodulatory and osteogenic proteins, and proteins involved in the coagulation cascade. Treatment-specific proteome alterations were observed. The fxH proteome of the ETC group showed increased expression of pro-inflammatory proteins related to, among others, activation of the complement system, neutrophil functioning, and macrophage activation, while showing decreased expression of proteins related to osteogenesis and tissue remodelling. Conversely, the fxH proteome of the DCO group contained various upregulated or exclusively detected proteins related to tissue regeneration and remodelling, and proteins related to anti-inflammatory and osteogenic processes.

Conclusion

The early fxH proteome of the ETC group was characterized by the expression of immunomodulatory, mainly pro-inflammatory, proteins, whereas the early fxH proteome of the DCO group was more regenerative and osteogenic in nature. These findings match clinical observations, in which enhanced surgical trauma after multiple trauma causes dysbalanced inflammation, potentially leading to reduced tissue regeneration, and gained insights into regulatory mechanisms of fracture healing after severe trauma.

The complement factor H-related protein-5 (CFHR5) exacerbates pathological bone formation in ankylosing spondylitis

Ankylosing spondylitis (AS) is a chronic inflammatory disease, characterized by excessive new bone formation. We previously reported that the complement factor H-related protein-5 (CFHR5), a member of the human factor H protein family, is significantly elevated in patients with AS compared to other rheumatic diseases. However, the pathophysiological mechanism underlying new bone formation by CFHR5 is not fully understood. In this study, we revealed that CFHR5 and proinflammatory cytokines (TNF, IL-6, IL-17A, and IL-23) were elevated in the AS group compared to the HC group. Correlation analysis revealed that CFHR5 levels were not significantly associated with proinflammatory cytokines, while CFHR5 levels in AS were only positively correlated with the high CRP group. Notably, treatment with soluble CFHR5 has no effect on clinical arthritis scores and thickness at hind paw in curdlan-injected SKG, but significantly increased the ectopic bone formation at the calcaneus and tibia bones of the ankle as revealed by micro-CT image and quantification. Basal CFHR5 expression was upregulated in AS-osteoprogenitors compared to control cells. Also, treatment with CFHR5 remarkedly induced bone mineralization status of AS-osteoprogenitors during osteogenic differentiation accompanied by MMP13 expression. We provide the first evidence demonstrating that CFHR5 can exacerbate the pathological bone formation of AS. Therapeutic modulation of CFHR5 could be promising for future treatment of AS. KEY MESSAGES: Serum level of CFHR5 is elevated and positively correlated with high CRP group of AS patients. Recombinant CFHR5 protein contributes to pathological bone formation in in vivo model of AS. CFHR5 is highly expressed in AS-osteoprogenitors compared to disease control. Recombinant CFHR5 protein increased bone mineralization accompanied by MMP13 in vitro model of AS.

Association of neutrophil to lymphocyte ratio with bone mineral density in post-menopausal women: a systematic review and meta-analysis

BACKGROUND

We conducted a systematic review and meta-analysis to compare the neutrophil lymphocyte ratio (NLR) levels between women with post-menopausal osteopenia or osteoporosis to those with normal bone mineral density (BMD).

METHODS

We used Web of Science, PubMed, and Scopus to conduct a systematic search for relevant publications published before June 19, 2022, only in English language. We reported standardized mean difference (SMD) with a 95% confidence interval (CI). Because a significant level of heterogeneity was found, we used the random-effects model to calculate pooled effects. We used the Newcastle-Ottawa scale for quality assessment.

RESULTS

Overall, eight articles were included in the analysis. Post-menopausal women with osteoporosis had elevated levels of NLR compared to those without osteoporosis (SMD = 1.03, 95% CI = 0.18 to 1.88, p = 0.017, I2 = 98%). In addition, there was no difference between post-menopausal women with osteopenia and those without osteopenia in neutrophil lymphocyte ratio (NLR) levels (SMD = 0.58, 95% CI=-0.08 to 1.25, p = 0.085, I2 = 96.8%). However, there was no difference between post-menopausal women with osteoporosis and those with osteopenia in NLR levels (SMD = 0.75, 95% CI=-0.01 to 1.51, p = 0.05, I2 = 97.5%, random-effect model).

CONCLUSION

The results of this study point to NLR as a potential biomarker that may be easily introduced into clinical settings to help predict and prevent post-menopausal osteoporosis.

The role of the complement system in disc degeneration and Modic changes

Disc degeneration and vertebral endplate bone marrow lesions called Modic changes are prevalent spinal pathologies found in chronic low back pain patients. Their pathomechanisms are complex and not fully understood. Recent studies have revealed that complement system proteins and interactors are dysregulated in disc degeneration and Modic changes. The complement system is part of the innate immune system and plays a critical role in tissue homeostasis. However, its dysregulation has also been associated with various pathological conditions such as rheumatoid arthritis and osteoarthritis. Here, we review the evidence for the involvement of the complement system in intervertebral disc degeneration and Modic changes. We found that only a handful of studies reported on complement factors in Modic changes and disc degeneration. Therefore, the level of evidence for the involvement of the complement system is currently low. Nevertheless, the complement system is tightly intertwined with processes known to occur during disc degeneration and Modic changes, such as increased cell death, autoantibody production, bacterial defense processes, neutrophil activation, and osteoclast formation, indicating a contribution of the complement system to these spinal pathologies. Based on these mechanisms, we propose a model how the complement system could contribute to the vicious cycle of tissue damage and chronic inflammation in disc degeneration and Modic changes. With this review, we aim to highlight a currently understudied but potentially important inflammatory pathomechanism of disc degeneration and Modic changes that may be a novel therapeutic target.

Transcriptional reprogramming during human osteoclast differentiation identifies regulators of osteoclast activity

Enhanced osteoclastogenesis and osteoclast activity contribute to the development of osteoporosis, which is characterized by increased bone resorption and inadequate bone formation. As novel antiosteoporotic therapeutics are needed, understanding the genetic regulation of human osteoclastogenesis could help identify potential treatment targets. This study aimed to provide an overview of transcriptional reprogramming during human osteoclast differentiation. Osteoclasts were differentiated from CD14+ monocytes from eight female donors. RNA sequencing during differentiation revealed 8 980 differentially expressed genes grouped into eight temporal patterns conserved across donors. These patterns revealed distinct molecular functions associated with postmenopausal osteoporosis susceptibility genes based on RNA from iliac crest biopsies and bone mineral density SNPs. Network analyses revealed mutual dependencies between temporal expression patterns and provided insight into subtype-specific transcriptional networks. The donor-specific expression patterns revealed genes at the monocyte stage, such as filamin B (FLNB) and oxidized low-density lipoprotein receptor 1 (OLR1, encoding LOX-1), that are predictive of the resorptive activity of mature osteoclasts. The expression of differentially expressed G-protein coupled receptors was strong during osteoclast differentiation, and these receptors are associated with bone mineral density SNPs, suggesting that they play a pivotal role in osteoclast differentiation and activity. The regulatory effects of three differentially expressed G-protein coupled receptors were exemplified by in vitro pharmacological modulation of complement 5 A receptor 1 (C5AR1), somatostatin receptor 2 (SSTR2), and free fatty acid receptor 4 (FFAR4/GPR120). Activating C5AR1 enhanced osteoclast formation, while activating SSTR2 decreased the resorptive activity of mature osteoclasts, and activating FFAR4 decreased both the number and resorptive activity of mature osteoclasts. In conclusion, we report the occurrence of transcriptional reprogramming during human osteoclast differentiation and identified SSTR2 and FFAR4 as antiresorptive G-protein coupled receptors and FLNB and LOX-1 as potential molecular markers of osteoclast activity. These data can help future investigations identify molecular regulators of osteoclast differentiation and activity and provide the basis for novel antiosteoporotic targets.

Trichostatin A enhances the titanium rods osseointegration in osteoporotic rats by the inhibition of oxidative stress through activating the AKT/Nrf2 pathway

The use of titanium implants as fixed supports following fractures in patients with OP can often result in sterile loosening and poor osseointegration. Oxidative stress has been shown to play a particularly important role in this process. While TSA has been reported to facilitate in vivo osteogenesis, the underlying mechanisms remain to be clarified. It also remains unclear whether TSA can improve the osseointegration of titanium implants. This study investigated whether TSA could enhance the osseointegration of titanium rods by activating AKT/Nrf2 pathway signaling, thereby suppressing oxidative stress. MC3T3-E1 cells treated with CCCP to induce oxidative stress served as an in vitro model, while an OVX-induced OP rat model was employed for in vivo analysis of titanium rod implantation. In vitro, TSA treatment of CCCP-treated MC3T3-E1 cells resulted in the upregulation of osteogenic proteins together with increased AKT, total Nrf2, nuclear Nrf2, HO-1, and NQO1 expression, enhanced mitochondrial functionality, and decreased oxidative damage. Notably, the PI3K/AKT inhibitor LY294002 reversed these effects. In vivo, TSA effectively enhanced the microstructural characteristics of distal femur trabecular bone, increased BMSCs mineralization capacity, promoted bone formation, and improved the binding of titanium implants to the surrounding tissue. Finally, our results showed that TSA could reverse oxidative stress-induced cell damage while promoting bone healing and improving titanium rods' osseointegration through AKT/Nrf2 pathway activation.

Ribosome biogenesis controls cranial suture MSC fate via the complement pathway in mouse and human iPSC models

Disruption of global ribosome biogenesis selectively affects craniofacial tissues with unclear mechanisms. Craniosynostosis is a congenital craniofacial disorder characterized by premature fusion of cranial suture(s) with loss of suture mesenchymal stem cells (MSCs). Here we focused on ribosomopathy disease gene Snord118, which encodes a small nucleolar RNA (snoRNA), to genetically disturb ribosome biogenesis in suture MSCs using mouse and human induced pluripotent stem cell (iPSC) models. Snord118 depletion exhibited p53 activation, increased cell death, reduced proliferation, and premature osteogenic differentiation of MSCs, leading to suture growth and craniosynostosis defects. Mechanistically, Snord118 deficiency causes translational dysregulation of ribosomal proteins and downregulation of complement pathway genes. Further complement pathway disruption by knockout of complement C3a receptor 1 (C3ar1) exacerbated MSC and suture defects in mutant mice, whereas activating the complement pathway rescued MSC cell fate and suture growth defects. Thus, ribosome biogenesis controls MSC fate via the complement pathway to prevent craniosynostosis.

Staphylococcus aureus enhances osteoclast differentiation and bone resorption by stimulating the NLRP3 inflammasome pathway

BACKGROUND

Osteomyelitis is one of the most challenging infectious diseases and is mainly caused by Staphylococcus aureus (S. aureus). In this study, we analyzed the effect of S. aureus on osteoclast differentiation and its possible molecular mechanism.

METHODS

We cultured RAW 264.7 cells with live S. aureus for 5 days. We assessed cell viability and the formation of resorption pits. We tested the NLRP3 inflammasome signaling pathways and measured the mRNA expression levels of osteoclastspecific genes, including TRAP, MMP9, cathepsin K, calcitonin receptor and ATP6V0d2. Furthermore, we analyzed the protein expression levels of the protein in the NF-κB and p38 MAPK signaling pathways to clarify the signaling pathways by which S. aureus promotes osteoclast differentiation.

RESULTS

Staphylococcus aureus induced NLRP3 inflammasome activation. S. aureus promoted bone resorption and enhanced the expression of osteoclastspecific genes, such as TRAP, MMP9, cathepsin K, calcitonin receptor and ATP6V0d2. MCC950 was used to inhibit NLRP3 inflammasome activity. Osteoclast differentiation and the expression of osteoclastspecific genes induced by S. aureus were inhibited by MCC950 pretreatment. The degradation of IκBα and phosphorylation of P65 were increased under the induction of S. aureus, but proteins in the p38 MAPK signaling pathway did not change significantly.

CONCLUSION

Staphylococcus aureus induces osteoclast differentiation and promotes bone resorption in vitro, and the NLRP3 inflammasome signaling pathway plays a significant role in this process. S. aureus-induced NLRP3 inflammasome activation was mainly dependent on the NF-κB signaling pathway during osteoclastogenesis.

Ambient PM2.5 Exposure and Bone Homeostasis: Analysis of UK Biobank Data and Experimental Studies in Mice and in Vitro

BACKGROUND

Previous evidence has identified exposure to fine ambient particulate matter (PM 2.5 ) as a leading risk factor for adverse health outcomes. However, to date, only a few studies have examined the potential association between long-term exposure to PM 2.5 and bone homeostasis.

OBJECTIVE

We sought to examine the relationship between long-term PM 2.5 exposure and bone health and explore its potential mechanism.

METHODS

This research included both observational and experimental studies. First, based on human data from UK Biobank, linear regression was used to explore the associations between long-term exposure to PM 2.5 (i.e., annual average PM 2.5 concentration for 2010) and bone mineral density [BMD; i.e., heel BMD (n = 37,440 ) and femur neck and lumbar spine BMD (n = 29,766 )], which were measured during 2014-2020. For the experimental animal study, C57BL/6 male mice were assigned to ambient PM 2.5 or filtered air for 6 months via a whole-body exposure system. Micro-computed tomography analyses were applied to measure BMD and bone microstructures. Biomarkers for bone turnover and inflammation were examined with histological staining, immunohistochemistry staining, and enzyme-linked immunosorbent assay. We also performed tartrate-resistant acid phosphatase (TRAP) staining and bone resorption assay to determine the effect of PM 2.5 exposure on osteoclast activity in vitro. In addition, the potential downstream regulators were assessed by real-time polymerase chain reaction and western blot.

RESULTS

We observed that long-term exposure to PM 2.5 was significantly associated with lower BMD at different anatomical sites, according to the analysis of UK Biobank data. In experimental study, mice exposed long-term to PM 2.5 exhibited excessive osteoclastogenesis, dysregulated osteogenesis, higher tumor necrosis factor-alpha (TNF- α ) expression, and shorter femur length than control mice, but they demonstrated no significant differences in femur structure or BMD. In vitro, cells stimulated with conditional medium of PM 2.5 -stimulated macrophages had aberrant osteoclastogenesis and differences in the protein/mRNA expression of members of the TNF- α / Traf 6 / c -Fos pathway, which could be partially rescued by TNF- α inhibition.

DISCUSSION

Our prospective observational evidence suggested that long-term exposure to PM 2.5 is associated with lower BMD and further experimental results demonstrated exposure to PM 2.5 could disrupt bone homeostasis, which may be mediated by inflammation-induced osteoclastogenesis. https://doi.org/10.1289/EHP11646.

Changes in the components of salivary exosomes due to initial periodontal therapy

PURPOSE

Exosomes are membrane vesicles that are present in body fluids and contain proteins, lipids, and microRNA (miRNA). Periodontal tissue examinations assess the degree of periodontal tissue destruction according to the probing depth (PD), clinical attachment loss (CAL), bleeding on probing, and X-ray examinations. However, the accurate evaluation of the prognosis of periodontitis is limited. In this study, we collected saliva from patients before and after initial periodontal therapy (IPT) and compared changes in the clinical parameters of periodontitis with changes in the components of salivary exosomes.

METHODS

Saliva was collected from patients with stage III and IV periodontitis at the first visit and post-IPT. Exosomes were purified from the saliva, and total protein and RNA were extracted. Changes in expression levels of C6, CD81, TSG101, HSP70, and 6 kinds of miRNA were analyzed by western blots and real-time polymerase chain reaction.

RESULTS

Patients with increased C6 expression after IPT had significantly higher levels of periodontal inflamed surface area (PISA), miR-142, and miR-144 before and after IPT than patients with decreased C6 expression after IPT. Patients with decreased and unchanged CD81 expression after IPT showed significantly higher PD, CAL, and PISA before IPT than after IPT. Patients with decreased and unchanged TSG101 expression after IPT had significantly higher PD before IPT than after IPT. Patients with increased HSP70 expression after IPT had significantly higher PD and PISA before and after IPT than patients with unchanged HSP70 after IPT. The expression levels of miR-142, miR-144, miR-200b, and miR-223 changed with changes in the levels of C6, CD81, TSG101, and HSP70 in the salivary exosomes of periodontitis patients before and after IPT.

CONCLUSIONS

The expression levels of proteins and miRNAs in salivary exosomes significantly changed after IPT in periodontitis patients, suggesting that the components of exosomes could serve as biomarkers for periodontitis.

Notch1 is a marker for in situ resting osteocytes in a 3-dimensional gel culture model

PURPOSE

Osteocytes in vivo exhibit different functional states, but no specific marker to distinguish these is currently available.

MATERIALS AND METHODS

To simulate the differentiation process of pre-osteoblasts to osteocytes in vitro, MC3T3-E1 cells were cultured on type I collagen gel and a three-dimensional (3D) culture system was established. The Notch expression of osteocyte-like cells in 3D culture system was compared with that of in situ osteocytes in bone tissues.

RESULTS

Immunohistochemistry demonstrated that Notch1 was not detected in "resting" in situ osteocytes, but was detected in normal cultured osteocyte-like cell line MLO-Y4. Osteocytes obtained from conventional osteogenic-induced osteoblasts and long-term cultured MLO-Y4 cells could not replicate the Notch1 expression pattern from in situ osteocytes. From day 14-35 of osteogenic induction, osteoblasts in 3D culture system gradually migrated into the gel to form canaliculus-like structures similar to bone canaliculus. On day 35, stellate-shaped osteocyte-like cells were observed, and expression of DMP1 and SOST, but not Runx2, was detected. Notch1 was not detected by immunohistochemistry, and Notch1 mRNA level was not significantly different from that of in situ osteocytes. In MC3T3-E1 cells, down-regulation of Notch2 increased Notch1, Notch downstream genes (β-catenin and Nfatc1), and Dmp1. In MLO-Y4 cells, Notch2 decreased after Notch1 siRNA transfection. Downregulation of Notch1 or Notch2 decreased Nfatc1, β-catenin, and Dmp1, and increased Sost.

CONCLUSIONS

We established "resting state" osteocytes using an in vitro 3D model. Notch1 can be a useful marker to help differentiate the functional states of osteocytes (activated vs. resting state).

Inhibition of C5AR1 impairs osteoclast mobilization and prevents bone loss

Age-related and chemotherapy-induced bone loss depends on cellular senescence and the cell secretory phenotype. However, the factors secreted in the senescent microenvironment that contribute to bone loss remain elusive. Here, we report a central role for the inflammatory alternative complement system in skeletal bone loss. Through transcriptomic analysis of bone samples, we identified complement factor D, a rate-limiting factor of the alternative pathway of complement, which is among the most responsive factors to chemotherapy or estrogen deficiency. We show that osteoblasts and osteocytes are major inducers of complement activation, while monocytes and osteoclasts are their primary targets. Genetic deletion of C5ar1, the receptor of the anaphylatoxin C5a, or treatment with a C5AR1 inhibitor reduced monocyte chemotaxis and osteoclast differentiation. Moreover, genetic deficiency or inhibition of C5AR1 partially prevented bone loss and osteoclastogenesis upon chemotherapy or ovariectomy. Altogether, these lines of evidence support the idea that inhibition of alternative complement pathways may have some therapeutic benefit in osteopenic disorders.

Evaluation of C4 Gene Copy Number in Pediatric Acute Neuropsychiatric Syndrome

Pediatric acute-onset neuropsychiatric syndrome (PANS) is an abrupt-onset neuropsychiatric disorder. PANS patients have an increased prevalence of comorbid autoimmune illness, most commonly arthritis. In addition, an estimated one-third of PANS patients present with low serum C4 protein, suggesting decreased production or increased consumption of C4 protein. To test the possibility that copy number (CN) variation contributes to risk of PANS illness, we compared mean total C4A and total C4B CN in ethnically matched subjects from PANS DNA samples and controls (192 cases and 182 controls). Longitudinal data from the Stanford PANS cohort (n = 121) were used to assess whether the time to juvenile idiopathic arthritis (JIA) or autoimmune disease (AI) onset was a function of total C4A or C4B CN. Lastly, we performed several hypothesis-generating analyses to explore the correlation between individual C4 gene variants, sex, specific genotypes, and age of PANS onset. Although the mean total C4A or C4B CN did not differ in PANS compared to controls, PANS patients with low C4B CN were at increased risk for subsequent JIA diagnosis (hazard ratio = 2.7, p value = 0.004). We also observed a possible increase in risk for AI in PANS patients and a possible correlation between lower C4B and PANS age of onset. An association between rheumatoid arthritis and low C4B CN has been reported previously. However, patients with PANS develop different types of JIA: enthesitis-related arthritis, spondyloarthritis, and psoriatic arthritis. This suggests that C4B plays a role that spans these arthritis types.

Maresin1: A multifunctional regulator in inflammatory bone diseases

Inflammation plays a crucial role in the physical response to danger signals, the elimination of toxic stimuli, and the restoration of homeostasis. However, dysregulated inflammatory responses lead to tissue damage, and chronic inflammation can disrupt osteogenic-osteoclastic homeostasis, ultimately leading to bone loss. Maresin1 (MaR1), a member of the specialized pro-resolving mediators (SPMs) family, has been found to possess significant anti-inflammatory, anti-allergic, pro-hemolytic, pro-healing, and pain-relieving properties. MaR1 is synthesized by macrophages (Mφs) and omega-3 fatty acids, and it may have the potential to promote bone homeostasis and treat inflammatory bone diseases. MaR1 has been found to stimulate osteoblast proliferation through leucine-rich repeat G protein-coupled receptor 6 (LGR6). It also activates Mφ phagocytosis and M2-type polarization, which helps to control the immune system. MaR1 can regulate T cells to exert anti-inflammatory effects and inhibit neutrophil infiltration and recruitment. In addition, MaR1 is involved in antioxidant signaling, including nuclear factor erythroid 2-related factor 2 (NRF2). It has also been found to promote the autophagic behavior of periodontal ligament stem cells, stimulate Mφs against pathogenic bacteria, and regulate tissue regeneration and repair. In summary, this review provides new information and a comprehensive overview of the critical roles of MaR1 in inflammatory bone diseases, indicating its potential as a therapeutic approach for managing skeletal metabolism and inflammatory bone diseases.

The anaphylatoxin C5a: Structure, function, signaling, physiology, disease, and therapeutics

The complement system is one of the oldest known tightly regulated host defense systems evolved for efficiently functioning cell-based immune systems and antibodies. Essentially, the complement system acts as a pivot between the innate and adaptive arms of the immune system. The complement system collectively represents a cocktail of ∼50 cell-bound/soluble glycoproteins directly involved in controlling infection and inflammation. Activation of the complement cascade generates complement fragments like C3a, C4a, and C5a as anaphylatoxins. C5a is the most potent proinflammatory anaphylatoxin, which is involved in inflammatory signaling in a myriad of tissues. This review provides a comprehensive overview of human C5a in the context of its structure and signaling under several pathophysiological conditions, including the current and future therapeutic applications targeting C5a.

Review of Recurrently Mutated Genes in Craniosynostosis Supports Expansion of Diagnostic Gene Panels

Craniosynostosis, the premature fusion of the cranial sutures, affects ~1 in 2000 children. Although many patients with a genetically determined cause harbor a variant in one of just seven genes or have a chromosomal abnormality, over 60 genes are known to be recurrently mutated, thus comprising a long tail of rarer diagnoses. Genome sequencing for the diagnosis of rare diseases is increasingly used in clinical settings, but analysis of the data is labor intensive and involves a trade-off between achieving high sensitivity or high precision. PanelApp, a crowd-sourced disease-focused set of gene panels, was designed to enable prioritization of variants in known disease genes for a given pathology, allowing enhanced identification of true-positives. For heterogeneous disorders like craniosynostosis, these panels must be regularly updated to ensure that diagnoses are not being missed. We provide a systematic review of genetic literature on craniosynostosis over the last 5 years, including additional results from resequencing a 42-gene panel in 617 affected individuals. We identify 16 genes (representing a 25% uplift) that should be added to the list of bona fide craniosynostosis disease genes and discuss the insights that these new genes provide into pathophysiological mechanisms of craniosynostosis.

A multi-omics study to characterize the transdifferentiation of human dermal fibroblasts to osteoblast-like cells

Background: Various skeletal disorders display defects in osteoblast development and function. An in vitro model can help to understand underlying disease mechanisms. Currently, access to appropriate starting material for in vitro osteoblastic studies is limited. Native osteoblasts and their progenitors, the bone marrow mesenchymal stem cells, (MSCs) are problematic to isolate from affected patients and challenging to expand in vitro. Human dermal fibroblasts in vitro are a promising substitute source of cells. Method: We developed an in vitro culturing technique to transdifferentiate fibroblasts into osteoblast-like cells. We obtained human fibroblasts from forearm skin biopsy and differentiated them into osteoblast-like cells with ß-glycerophosphate, ascorbic acid, and dexamethasone treatment. Osteoblastic phenotype was confirmed by staining for alkaline phosphatase (ALP), calcium and phosphate deposits (Alizarin Red, Von Kossa) and by a multi-omics approach (transcriptomic, proteomic, and phosphoproteomic analyses). Result: After 14 days of treatment, both fibroblasts and MSCs (reference cells) stained positive for ALP together with a significant increase in bone specific ALP (p = 0.04 and 0.004, respectively) compared to untreated cells. At a later time point, both cell types deposited minerals, indicating mineralization. In addition, fibroblasts and MSCs showed elevated expression of several osteogenic genes (e.g. ALPL, RUNX2, BMPs and SMADs), and decreased expression of SOX9. Ingenuity Pathways Analysis of RNA sequencing data from fibroblasts and MSCs showed that the osteoarthritis pathway was activated in both cell types (p_adj. = 0.003 and 0.004, respectively). Discussion: These data indicate that our in vitro treatment induces osteoblast-like differentiation in fibroblasts and MSCs, producing an in vitro osteoblastic cell system. This culturing system provides an alternative tool for bone biology research and skeletal tissue engineering.

Proteomics Profiling of Osteoporosis and Osteopenia Patients and Associated Network Analysis

Bone mass reduction due to an imbalance in osteogenesis and osteolysis is characterized by low bone mineral density (LBMD) and is clinically classified as osteopenia (ON) or osteoporosis (OP), which is more severe. Multiple biomarkers for diagnosing OP and its progression have been reported; however, most of these lack specificity. This cohort study aimed to investigate sensitive and specific LBMD-associated protein biomarkers in patients diagnosed with ON and OP. A label-free liquid chromatography-mass spectrometry (LC-MS) proteomics approach was used to analyze serum samples. Patients’ proteomics profiles were filtered for potential confounding effects, such as age, sex, chronic diseases, and medication. A distinctive proteomics profile between the control, ON, and OP groups (Q² = 0.7295, R² = 0.9180) was identified, and significant dysregulation in a panel of proteins (n = 20) was common among the three groups. A comparison of these proteins showed that the levels of eight proteins were upregulated in ON, compared to those in the control and the OP groups, while the levels of eleven proteins were downregulated in the ON group compared to those in the control group. Interestingly, only one protein, myosin heavy chain 14 (MYH14), showed a linear increase from the control to the ON group, with the highest abundance in the OP group. A significant separation in the proteomics profile between the ON and OP groups (Q² = 0.8760, R² = 0.991) was also noted. Furthermore, a total of twenty-six proteins were found to be dysregulated between the ON and the OP groups, with fourteen upregulated and twelve downregulated proteins in the OP, compared to that in the ON group. Most of the identified dysregulated proteins were immunoglobulins, complement proteins, cytoskeletal proteins, coagulation factors, and various enzymes. Of these identified proteins, the highest area under the curve (AUC) in the receiver operating characteristic (ROC) analysis was related to three proteins (immunoglobulin Lambda constant 1 (IGLC1), RNA binding protein (MEX3B), and fibulin 1 (FBLN1)). Multiple reaction monitoring (MRM), LC-MS, was used to validate some of the identified proteins. A network pathway analysis of the differentially abundant proteins demonstrated dysregulation of inflammatory signaling pathways in the LBMD patients, including the tumor necrosis factor (TNF), toll-like receptor (TL4), and interferon-γ (IFNG) signaling pathways. These results reveal the existence of potentially sensitive protein biomarkers that could be used in further investigations of bone health and OP progression.

The role of C5a-C5aR1 axis in bone pathophysiology: A mini-review

Bone remodeling is a physiological, dynamic process that mainly depends on the functions of 2 cell types: osteoblasts and osteoclasts. Emerging evidence suggests that complement system is crucially involved in the regulation of functions of these cells, especially during inflammatory states. In this context, complement component 5a (C5a), a powerful pro-inflammatory anaphylatoxin that binds the receptor C5aR1, is known to regulate osteoclast formation and osteoblast inflammatory responses, and has thus been proposed as potential therapeutic target for the treatment of inflammatory bone diseases. In this review, we will analyze the role of C5a-C5aR1 axis in bone physiology and pathophysiology, describing its involvement in the pathogenesis of some of the most frequent inflammatory bone diseases such as rheumatoid arthritis, and also in osteoporosis and bone cancer and metastasis. Moreover, we will examine C5aR1-based pharmacological approaches that are available and have been tested so far for the treatment of these conditions. Given the growing interest of the scientific community on osteoimmunology, and the scarcity of data regarding the role of C5a-C5aR1 axis in bone pathophysiology, we will highlight the importance of this axis in mediating the interactions between skeletal and immune systems and its potential use as a therapeutic target.

Involvement of complement peptides C3a and C5a in osteoarthritis pathology

Osteoarthritis (OA) affects more than 500 million people worldwide and is among the five diseases in Germany causing the highest suffering of the patients and cost for the society. The quality of life of OA patients is severely compromised, and adequate therapy is lacking owing to a knowledge gap that acts as a major barrier to finding safe and effective solutions. Chronic, low-grade inflammation plays a central role in OA pathogenesis and is associated with both OA pain and disease progression. Innate immune pathways, such as the complement- and pattern-recognition receptor pathways, are pivotal to the inflammation in OA and key components of the innate immune system implicated in OA include DAMP-TLR signaling, the complement system, carboxypeptidase B (CPB), and mononuclear cells. Anaphylatoxins C3a and C5a are small polypeptides (77 and 74 amino acids, respectively) which are released by proteolytic cleavage of the complement components C3 and C5. The alternative complement pathway seems to play a crucial role in OA pathogenesis as these complement components, mostly C3 and its activation peptide C3a, were detected at high levels in osteoarthritic cartilage, synovial membrane, and cultured chondrocytes. Targeting the complement system by using anti-complement drugs as a therapeutic option bears the risk of major side effects such as increasing the risk of infection, interfering with cell regeneration and metabolism, and suppressing the clearance of immune complexes. Despite those adverse effects, several synthetic complement peptide antagonists show promising effects in ameliorating inflammatory cell responses also in joint tissues.

Complement C3-α and C3-β Levels in Synovial Fluid But Not in Blood Correlate With the Severity of Osteoarthritis Research Society International Histopathological Grades in Primary Knee Osteoarthritis

BACKGROUND

Primary osteoarthritis (OA) is the most common cause of knee arthritis worldwide. The knee synovial fluid complement C3-β chain levels have been shown to correlate with clinical symptoms of knee OA. It is not known whether the complement C3 in the synovial fluid is derived from the circulation or is produced locally in the knee.

METHODS

Fifty primary OA patients undergoing a total knee arthroplasty procedure were evaluated for biochemical analyses of C3-α and C3-β chains in the synovial fluid and blood plasma. These levels were corelated with the severity of corresponding knee OA based on the Osteoarthritis Research Society International (OARSI) grade.

RESULTS

Both synovial C3-α and C3-β levels correlated significantly with the severity of OA. Neither plasma C3-α levels nor C3-β levels significantly correlated with OARSI grading. Neither synovial C3-α levels nor C3-β correlated significantly with plasma C3-α or C3-β levels, respectively. Synovial C3-α chain and C3-β chain levels were significantly higher in the grade >6 group. In plasma, neither C3-α chain levels nor C3-β chain levels were significantly different between the groups. Neither synovial C3-α nor C3-β levels significantly correlated with plasma erythrocyte sedimentation rate or C-reactive protein levels.

CONCLUSION

In knee primary OA, C3 seems to be produced and released locally into the synovial fluid instead of being derived from blood in the circulation. Synovial C3 levels, but not blood plasma C3, correlate with the histopathological severity of primary OA in the knee. Synovial C3 may be an important factor in the pathogenesis of primary OA clinical symptoms and a potential target for therapeutic intervention.

Identification of Genes with Altered Methylation in Osteoclast Differentiation and Its Roles in Osteoporosis

Osteoporosis is one of the most common metabolic skeletal diseases, which affects more than 200 million people worldwide, especially elderly and postmenopausal women. One of the main processes of osteoporosis is attenuated bone formation. Abundant evidence has confirmed that overactivated osteoclasts are responsible for the attenuated bone formation. This study aims at identifying novel methylation-associated biomarkers and therapeutic targets in osteoclasts by integrally analyzing methylation profiles and gene expression data. DNA methylation profile and gene expression data were obtained from the Gene Expression Omnibus (GEO) database. Subsequently, we integrated the two sets of data to screen for differentially expressed genes with differential methylation level (DM-DEGs) between osteoclasts and CD14⁺ monocytes from donors. Then, Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were performed to uncover the enriched functions and pathways of identified DM-DEGs. In addition, by combining protein-protein interaction analysis and receiver-operator characteristic analysis, we finally identified four hub DM-DEGs. Gene Set Enrichment Analysis was utilized to validate and investigate the potential biological functions of the four hub DM-DEGs. Finally, Real-time quantitative PCR (QPCR) was performed to validate the mRNA expression level of the four identified hub DM-DEGs during osteoclast differentiation. CCRL2, CCL18, C1QB, and SELL were highly correlated with osteoclastic differentiation and osteoporosis phenotype. QPCR revealed that the expression of CCRL2, CCL18, and C1QB was increased during osteoclast differentiation, whereas the expression of SELL was decreased. The present study indicated a connection between gene expression and DNA methylation during osteoclast differentiation and that four hub DM-DEGs in osteoclastogenesis and osteoporosis pathogenesis might be potential candidates for intensive research and therapeutic targets for the treatment of osteoporosis.

Electrochemical deposition of lithium coating on titanium implant with enhanced early stage osseointegration

Recently, a large number of studies have reported that lithium (Li) displayed a positive effect on osteogenesis. However, only a few studies have investigated the Li-incorporated surfaces through electrochemical deposition. In this study, electrochemical deposition was conducted on a CHI600E electrochemical workstation. The characterization of electrochemical deposition (ECD) and ECD-Li surfaces were detected by field-emission scanning electron microscopy with energy-dispersive spectrometer. rBMSCs were cultured on two surfaces for subsequent adhesion, proliferation and live/dead assay. To evaluate the effects of Li-incorporated implants by electrochemical deposition on osseointegration in vivo, teeth extraction of two premolars and one first molar in bilateral mandible were performed on six male beagle dogs. After 3 months, ZDI and ZDI-Li implants were inserted into the bilateral mandible of each beagle dog. Micro Computed Tomography (Micro-CT) and hard tissue sectioning analysis were carried out to evaluate the osseointegration at 4- and 8-weeks post-implantation. Results showed that ECD-Li surface promoted adhesion and proliferation of BMSCs in the early stage. More importantly, through micro-CT analysis, the values of bone volume/total volume (BV/TV) (0.374 ± 0.015), bone-implant contact (BIC) (0.831 ± 0.025), and Tb.Th (0.412 ± 0.007) in ZDI-Li group was significantly higher than those of ZDI group (0.302 ± 0.009, 0.700 ± 0.023, 0.353 ± 0.001, p < .01) at 4 weeks. Similarly, ZDI-Li group manifested more bone contact with the implant surfaces at 4 weeks based on hard tissue sectioning analysis, whereas no significant difference was detected between two groups at 8 weeks. Therefore, incorporating Li into implant surface through ECD could enhance early osseointegration in vivo.

Hormone sensitive lipase ablation promotes bone regeneration

There is an inverse relationship between the differentiation of mesenchymal stem cells (MSCs) along either an adipocyte or osteoblast lineage, with lineage differentiation known to be mediated by transcription factors PPARγ and Runx2, respectively. Endogenous ligands for PPARγ are generated during the hydrolysis of triacylglycerols to fatty acids through the actions of lipases such as hormone sensitive lipase (HSL). To examine whether reduced production of endogenous PPARγ ligands would influence bone regeneration, we examined the effects of HSL knockout on fracture repair in mice using a tibial mono-cortical defect as a model. We found an improved rate of fracture repair in HSL-ko mice documented by serial μCT and bone histomorphometry compared to wild-type (WT) mice. Similarly, accelerated rates of bone regeneration were observed with a calvarial model where implantation of bone grafts from HSL-ko mice accelerated bone regeneration at the injury site. Further analysis revealed improved MSC differentiation down osteoblast and chondrocyte lineage with inhibition of HSL. MSC recruitment to the injury site was greater in HSL-ko mice than WT. Finally, we used single cell RNAseq to understand the osteoimmunological differences between WT and HSL-ko mice and found changes in the pre-osteoclast population. Our study shows HSL-ko mice as an interesting model to study improvements to bone injury repair. Furthermore, our study highlights the potential importance of pre-osteoclasts and osteoclasts in bone repair.

The Yin and Yang of Immunity in Stem Cell Decision Guidance in Tissue Ecologies: An Infection Independent Perspective

The impact of immune system and inflammation on organ homeostasis and tissue stem cell niches in the absence of pathogen invasion has long remained a conundrum in the field of regenerative medicine. The paradoxical role of immune components in promoting tissue injury as well as resolving tissue damage has complicated therapeutic targeting of inflammation as a means to attain tissue homeostasis in degenerative disease contexts. This confound could be resolved by an integrated intricate assessment of cross-talk between inflammatory components and micro- and macro-environmental factors existing in tissues during health and disease. Prudent fate choice decisions of stem cells and their differentiated progeny are key to maintain tissue integrity and function. Stem cells have to exercise this fate choice in consultation with other tissue components. With this respect tissue immune components, danger/damage sensing molecules driving sterile inflammatory signaling cascades and barrier cells having immune-surveillance functions play pivotal roles in supervising stem cell decisions in their niches. Stem cells learn from their previous damage encounters, either endogenous or exogenous, or adapt to persistent micro-environmental changes to orchestrate their decisions. Thus understanding the communication networks between stem cells and immune system components is essential to comprehend stem cell decisions in endogenous tissue niches. Further the systemic interactions between tissue niches integrated through immune networks serve as patrolling systems to establish communication links and orchestrate micro-immune ecologies to better organismal response to injury and promote regeneration. Understanding these communication links is key to devise immune-centric regenerative therapies. Thus the present review is an integrated attempt to provide a unified purview of how inflammation and immune cells provide guidance to stem cells for tissue sculpting during development, organismal aging and tissue crisis based on the current knowledge in the field.

Heterotopic ossification vs. fracture healing: Extracellular vesicle cargo proteins shed new light on bone formation

Fibrodysplasia ossificans progressiva (FOP) is an extremely rare disease in which bone tissue forms in extraskeletal sites, which is known as heterotopic ossification (HO). Extracellular vesicles (EVs) are small phospholipid-enclosed particles released by various cells which have an emerging, but not completely understood role in various (patho)physiological processes. In order to further study the pathophysiology of FOP we conducted a small observational study comparing the proteomic profiles of EV cargo, derived from pooled plasma of four patient groups: FOP patient (N = 1) during active disease phase (flare-up), FOP patients during remission (N = 2), patients after long bone fracture (N = 20) and healthy controls (N = 10). After isolation of EVs – their protein cargo was determined using liquid chromatography / mass spectrometry, after which a functional gene enrichment analysis was performed. Our results show a sizeable difference of the proteomics profiles in which EVs from the bone fracture group show significant activity of integrin interactions, Wnt, VEGF, IGF-1 and PDGF pathways; conversely, FOP patients' EVs indicate that HO occurs via processes of innate immunity and the Ephrin B signaling pathway. We hypothesize that the Ephrin B signaling (expressed in EVs) contributes to HO by aiding in mesenchymal stem cell recruitment and osteogenic differentiation, as well as by contributing to the inflammatory response, including macrophage chemotaxis and activation. This is, to our knowledge, the first published analysis of EV protein cargo in FOP.

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Proteomics-based analysis of extracellular vesicles’ protein cargo in FOP patients, bone fracture healing and controls.

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Marked differences in signaling pathways expressed in extracellular vesicles in FOP vs. patients with bone fractures.

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Ephrin B signaling pathway expressed in extracellular vesicles identified as a likely cogwheel in heterotopic ossification.

Complement receptor C5aR1 on osteoblasts regulates osteoclastogenesis in experimental postmenopausal osteoporosis

In recent years, evidence has accumulated that the complement system, an integral part of innate immunity, may be involved in the regulation of bone homeostasis as well as inflammatory bone loss, for example, in rheumatoid arthritis and periodontitis. Complement may also contribute to osteoporosis development, but investigation of the mechanism is limited. Using mice with a conditional deletion of the complement anaphylatoxin receptor C5aR1, we here demonstrated that C5aR1 in osteoblasts (C5aR1 ^Runx2-Cre mice) or osteoclasts (C5aR1 ^LysM-Cre mice) did not affect physiological bone turnover or age-related bone loss in either sex, as confirmed by micro-computed tomography, histomorphometry, and biomechanical analyses of the bone and by the measurement of bone turnover markers in the blood serum. When female mice were subjected to ovariectomy (OVX), a common model for postmenopausal osteoporosis, significant bone loss was induced in C5aR1 ^fl/fl and C5aR1 ^LysM-Cre mice, as demonstrated by a significantly reduced bone volume fraction, trabecular number and thickness as well as an increased trabecular separation in the trabecular bone compartment. Confirming this, the osteoclast number and the receptor activator of nuclear factor k-B (RANK) ligand (RANKL) serum level were significantly elevated in these mouse lines. By contrast, C5aR1 ^Runx2-Cre mice were protected from bone loss after OVX and the serum RANKL concentration was not increased after OVX. These data suggested that bone cell-specific C5aR1 may be redundant in bone homeostasis regulation under physiological conditions. However, C5aR1 on osteoblasts was crucial for the induction of bone resorption under osteoporotic conditions by stimulating RANKL release, whereas C5aR1 on osteoclasts did not regulate OVX-induced bone loss. Therefore, our results implicate C5aR1 on osteoblasts as a potential target for treating postmenopausal osteoporosis.

Maturation of biomimetic hydroxyapatite in physiological fluids: a physicochemical and proteomic study

Biomimetic calcium-deficient hydroxyapatite (CDHA) as a bioactive material exhibits exceptional intrinsic osteoinductive and osteogenic properties because of its nanostructure and composition, which promote a favorable microenvironment. Its high reactivity has been hypothesized to play a relevant role in the in vivo performance, mediated by the interaction with the biological fluids, which is amplified by its high specific surface area. Paradoxically, this high reactivity is also behind the in vitro cytotoxicity of this material, especially pronounced in static conditions. The present work explores the structural and physicochemical changes that CDHA undergoes in contact with physiological fluids and to investigate its interaction with proteins. Calcium-deficient hydroxyapatite discs with different micro/nanostructures, coarse (C) and fine (F), were exposed to cell-free complete culture medium over extended periods of time: 1, 7, 14, 21, 28, and 50 days. Precipitate formation was not observed in any of the materials in contact with the physiological fluid, which would indicate that the ionic exchanges were linked to incorporation into the crystal structure of CDHA or in the hydrated layer. In fact, CDHA experienced a maturation process, with a progressive increase in crystallinity and the Ca/P ratio, accompanied by an uptake of Mg and a B-type carbonation process, with a gradual propagation into the core of the samples. However, the reactivity of biomimetic hydroxyapatite was highly dependent on the specific surface area and was amplified in nanosized needle-like crystal structures (F), whereas in coarse specimens the ionic exchanges were restricted to the surface, with low penetration in the material bulk. In addition to showing a higher protein adsorption on F substrates, the proteomics study revealed the existence of protein selectivity toward F or C microstructures, as well as the capability of CDHA, and more remarkably of F-CDHA, to concentrate specific proteins from the culture medium. Finally, a substantial improvement in the material's ability to support cell proliferation was observed after the CDHA maturation process.

C3-targeted therapy in periodontal disease: moving closer to the clinic

Complement plays a key role in immunosurveillance and homeostasis. When dysregulated or overactivated, complement can become a pathological effector, as seen in several inflammatory disorders, including periodontal disease. Recently, clinical correlative studies and preclinical mechanistic investigations have collectively demonstrated that complement is hyperactivated during periodontitis and that targeting its central component (C3) provides therapeutic benefit in nonhuman primates (NHPs). The preclinical efficacy of a C3-targeted drug candidate combined with excellent safety and pharmacokinetic profiles supported its use in a recent Phase IIa clinical study in which C3 inhibition resolved gingival inflammation in patients with periodontal disease. We posit that C3-targeted intervention might represent a novel and transformative host-modulation therapy meriting further investigation in Phase III clinical trials for the treatment of periodontitis.

Application of hydroxyapatite/collagen composite material for maxillary sinus floor augmentation

The aim of this study was to clarify whether hydroxyapatite/collagen composite material (HAp/Col) could be useful as a graft material for maxillary sinus floor augmentation (MSFA). MSFA and implant placement were performed simultaneously. When the lateral approach was employed, 3 out of 19 implants failed in 3 maxillary sinuses (success rate; 84.2%), and in these cases the alveolar bone heights, cortical bone thicknesses and values of the implant stability quotient were smaller. If alveolar the bone height, cortical bone thickness, and healing period are optimized, HAp/Col can be a useful graft material for MSFA.

The effect of aging on the bone healing properties of blood plasma

OBJECTIVES

Age-related changes in blood composition have been found to affect overall health. Thus, this study aimed to understand the effect of these changes on bone healing by assessing how plasma derived from young and old rats affect bone healing using a rat model.

METHODS

. Blood plasma was collected from 6-month and 24-month old rats. Differences in elemental composition and metabolome were assessed using optical emission spectrometry and liquid mass spectrometry, respectively. Bilateral tibial bone defects were created in eight rats. Young plasma was randomly applied to one defect, while aged plasma was applied to the contralateral one. Rats were euthanized after two weeks, and their tibiae were analyzed using micro-CT and histology. The proteome of bone marrow was analyzed in an additional group of three rats.

RESULTS

Bone-defects treated with aged-plasma were significantly bigger in size and presented lower bone volume/tissue volume compared to defects treated with young-plasma. Histomorphometric analysis showed fewer mast cells, macrophages, and lymphocytes in defects treated with old versus young plasma. The proteome analysis showed that young plasma upregulated pathways required for bone healing (e.g. RUNX2, platelet signaling, and crosslinking of collagen fibrils) whereas old plasma upregulated pathways, involved in disease and inflammation (e.g. IL-7, IL-15, IL-20, and GM-CSF signaling). Plasma derived from old rats presented higher concentrations of iron, phosphorous, and nucleotide metabolites as well as lower concentrations of platelets, citric acid cycle, and pentose phosphate pathway metabolites compared to plasma derived from young rats.

CONCLUSION

bone defects treated with plasma-derived from young rats showed better healing compared to defects treated with plasma-derived from old rats. The application of young and old plasmas has different effects on the proteome of bone defects.

The emerging role of Interleukin 37 in bone homeostasis and inflammatory bone diseases

Interleukin 37 (IL-37) is a newly identified cytokine that belongs to the IL-1 family. Unlike other members of the IL-1 family, it has been demonstrated that IL-37 possesses anti-inflammatory characteristics in both innate and acquired immune responses. Recently, significant progress has been made in understanding the role of IL-37 in inflammatory signaling pathways. Meanwhile, IL-37 has also attracted more and more attention in bone homeostasis and inflammatory bone diseases. The latest studies have revealed that IL-37 palys an essential role in the regulation of osteoclastogenesis and osteoblastogenesis. The levels of IL-37 are abnormal in patients with inflammatory bone diseases such as rheumatoid arthritis (RA), osteoarthritis (OA), ankylosing spondylitis (AS), and periodontitis. In addition, in vivo studies have further confirmed that recombinant IL-37 treatment displayed therapeutic potential in these diseases. The present review article aims to provide an overview describing the biological functions of IL-37 in bone homeostasis and inflammatory bone diseases, thus shedding new light on a novel therapeutic strategy in the future.

Interaction between bone and immune cells: Implications for postmenopausal osteoporosis

Postmenopausal osteoporosis is a systemic disease characterized by the loss of bone mass and increased bone fracture risk largely resulting from significantly reduced levels of the hormone estrogen after menopause. Besides the direct negative effects of estrogen-deficiency on bone, indirect effects of altered immune status in postmenopausal women might contribute to ongoing bone destruction, as postmenopausal women often display a chronic low-grade inflammatory phenotype with altered cytokine expression and immune cell profile. In this context, it was previously shown that various immune cells interact with osteoblasts and osteoclasts either via direct cell-cell contact, or more likely via paracrine mechanisms. For example, specific subtypes of T lymphocytes express TNFα, which was shown to increase osteoblast apoptosis and to indirectly stimulate osteoclastogenesis via B cell-produced receptor-activator of NF-κB ligand (RANKL), thereby triggering bone loss during postmenopausal osteoporosis. T_h17 cells release interleukin-17 (IL-17), which directs mesenchymal stem cell differentiation towards the osteogenic lineage, but also indirectly increases osteoclast differentiation. B lymphocytes are a major regulator of osteoclast formation via granulocyte colony-stimulating factor secretion and the RANKL/osteoprotegerin system under estrogen-deficient conditions. Macrophages might act differently on bone cells dependent on their polarization profile and their secreted paracrine factors, which might have implications for the development of postmenopausal osteoporosis, because macrophage polarization is altered during disease progression. Likewise, neutrophils play an important role during bone homeostasis, but their over-activation under estrogen-deficient conditions contributes to osteoblast apoptosis via the release of reactive oxygen species and increased osteoclastogenesis via RANKL signaling. Furthermore, mast cells might be involved in the development of postmenopausal osteoporosis, because they store high levels of osteoclastic mediators, including IL-6 and RANKL, in their granules and their numbers are greatly increased in osteoporotic bone. Additionally, bone fracture healing is altered under estrogen-deficient conditions with the increased presence of pro-inflammatory cytokines, including IL-6 and Midkine, which might contribute to healing disturbances. Consequently, in addition to the direct negative influence of estrogen-deficiency on bone, immune cell alterations contribute to the pathogenesis of postmenopausal osteoporosis.

Complement C3a activates osteoclasts by regulating the PI3K/PDK1/SGK3 pathway in patients with multiple myeloma

OBJECTIVE

Myeloma bone disease (MBD) is the most common complication of multiple myeloma (MM). Our previous study showed that the serum levels of C3/C4 in MM patients were significantly positively correlated with the severity of bone disease. However, the mechanism of C3a/C4a in osteoclasts MM patients remains unclear.

METHODS

The formation and function of osteoclasts were analyzed after adding C3a/C4a in vitro. RNA-seq analysis was used to screen the potential pathways affecting osteoclasts, and the results were verified by Western blot, qRT-PCR, and pathway inhibitors.

RESULTS

The osteoclast area per view induced by 1 μg/mL (mean ± SD: 50.828 ± 12.984%) and 10 μg/mL (53.663 ± 12.685%) of C3a was significantly increased compared to the control group (0 μg/mL) (34.635 ± 8.916%) (P < 0.001 and P < 0.001, respectively). The relative mRNA expressions of genes, OSCAR/TRAP/RANKL/cathepsin K, induced by 1 μg/mL (median: 5.041, 3.726, 1.638, and 4.752, respectively) and 10 μg/mL (median: 5.140, 3.702, 2.250, and 5.172, respectively) of C3a was significantly increased compared to the control group (median: 3.137, 2.004, 0.573, and 2.257, respectively) (1 μg/mL P = 0.001, P = 0.003, P < 0.001, and P = 0.008, respectively; 10 μg/mL: P < 0.001, P = 0.019, P < 0.001, and P = 0.002, respectively). The absorption areas of the osteoclast resorption pits per view induced by 1 μg/mL (mean ± SD: 51.464 ± 11.983%) and 10 μg/mL (50.219 ± 12.067%) of C3a was also significantly increased (33.845 ± 8.331%) (P < 0.001 and P < 0.001, respectively) compared to the control. There was no difference between the C4a and control groups. RNA-seq analysis showed that C3a promoted the proliferation of osteoclasts using the phosphoinositide 3-kinase (PI3K) signaling pathway. The relative expressions of PIK3CA/phosphoinositide dependent kinase-1 (PDK1)/serum and glucocorticoid inducible protein kinases (SGK3) genes and PI3K/PDK1/p-SGK3 protein in the C3a group were significantly higher than in the control group. The activation role of C3a in osteoclasts of MM patients was reduced by the SGK inhibitor (EMD638683).

CONCLUSIONS

C3a activated osteoclasts by regulating the PI3K/PDK1/SGK3 pathways in MM patients, which was reduced using a SGK inhibitor. Overall, our results identified potential therapeutic targets and strategies for MBD patients.

Increased Presence of Complement Factors and Mast Cells in Alveolar Bone and Tooth Resorption

Periodontitis is the inflammatory destruction of the tooth-surrounding and -supporting tissue, resulting at worst in tooth loss. Another locally aggressive disease of the oral cavity is tooth resorption (TR). This is associated with the destruction of the dental mineralized tissue. However, the underlying pathomechanisms remain unknown. The complement system, as well as mast cells (MCs), are known to be involved in osteoclastogenesis and bone loss. The complement factors C3 and C5 were previously identified as key players in periodontal disease. Therefore, we hypothesize that complement factors and MCs might play a role in alveolar bone and tooth resorption. To investigate this, we used the cat as a model because of the naturally occurring high prevalence of both these disorders in this species. Teeth, gingiva samples and serum were collected from domestic cats, which had an appointment for dental treatment under anesthesia, as well as from healthy cats. Histological analyses, immunohistochemical staining and the CH-50 and AH-50 assays revealed increased numbers of osteoclasts and MCs, as well as complement activity in cats with TR. Calcifications score in the gingiva was highest in animals that suffer from TR. This indicates that MCs and the complement system are involved in the destruction of the mineralized tissue in this condition.

Ubiquitin-specific protease 53 promotes osteogenic differentiation of human bone marrow-derived mesenchymal stem cells

The ubiquitin protease pathway plays important role in human bone marrow-derived mesenchymal stem cell (hBMSC) differentiation, including osteogenesis. However, the function of deubiquitinating enzymes in osteogenic differentiation of hBMSCs remains poorly understood. In this study, we aimed to investigate the role of ubiquitin-specific protease 53 (USP53) in the osteogenic differentiation of hBMSCs. Based on re-analysis of the Gene Expression Omnibus database, USP53 was selected as a positive regulator of osteogenic differentiation in hBMSCs. Overexpression of USP53 by lentivirus enhanced osteogenesis in hBMSCs, whereas knockdown of USP53 by lentivirus inhibited osteogenesis in hBMSCs. In addition, USP53 overexpression increased the level of active β-catenin and enhanced the osteogenic differentiation of hBMSCs. This effect was reversed by the Wnt/β-catenin inhibitor DKK1. Mass spectrometry showed that USP53 interacted with F-box only protein 31 (FBXO31) to promote proteasomal degradation of β-catenin. Inhibition of the osteogenic differentiation of hBMSCs by FBXO31 was partially rescued by USP53 overexpression. Animal studies showed that hBMSCs with USP53 overexpression significantly promoted bone regeneration in mice with calvarial defects. These results suggested that USP53 may be a target for gene therapy for bone regeneration.

Complement Has Brains-Do Intracellular Complement and Immunometabolism Cooperate in Tissue Homeostasis and Behavior?

The classical liver-derived and serum-effective complement system is well appreciated as a key mediator of host protection via instruction of innate and adaptive immunity. However, recent studies have discovered an intracellularly active complement system, the complosome, which has emerged as a central regulator of the core metabolic pathways fueling human immune cell activity. Induction of expression of components of the complosome, particularly complement component C3, during transmigration from the circulation into peripheral tissues is a defining characteristic of monocytes and T cells in tissues. Intracellular complement activity is required to induce metabolic reprogramming of immune cells, including increased glycolytic flux and OXPHOS, which drive the production of the pro-inflammatory cytokine IFN-γ. Consequently, reduced complosome activity translates into defects in normal monocyte activation, faulty Th1 and cytotoxic T lymphocyte responses and loss of protective tissue immunity. Intriguingly, neurological research has identified an unexpected connection between the physiological presence of innate and adaptive immune cells and certain cytokines, including IFN-γ, in and around the brain and normal brain function. In this opinion piece, we will first review the current state of research regarding complement driven metabolic reprogramming in the context of immune cell tissue entry and residency. We will then discuss how published work on the role of IFN-γ and T cells in the brain support a hypothesis that an evolutionarily conserved cooperation between the complosome, cell metabolism and IFN-γ regulates organismal behavior, as well as immunity.

Osteoclast differentiation and formation induced by titanium implantation through complement C3a

Titanium implantation is widely used for dental replacement with advantages of excellent mechanical strength, corrosion resistance, chemical stability and biocompatibility. Some patients, however, are subject to the failure of implantation due to bone resorption, which closely related to the inflammatory responses without clear mechanisms. In this study, first we found that there were inflammatory responses and increases of osteoclasts in the surrounding tissues near by the titanium implant. Further, data revealed that the C3 was increased in the serum and surrounding tissues near by the titanium implant, and activated by classical and alternative pathways. Next, we recognized that the C3a/C3aR, no C3b played an important role in stimulating secretions of pro-inflammatory cytokines of TNF-α and MMP9 via transcription factors NF-kB and NFATc1. This cascade of responses to titanium implant leaded the differentiation and proliferation of osteoclasts in vivo and in vitro, bone resorption of surrounding tissues of Ti implant. These suggest that the cleaved C3a fragment plays predominant roles in the activation of osteoclast. Therefore, the blocking C3a activation should provide potential to prevent bone resorption and prolong the survival of biomaterial implants.

The Dramatic Role of IFN Family in Aberrant Inflammatory Osteolysis

Skeletal system has been considered a highly dynamic system, in which bone-forming osteoblasts and bone-resorbing osteoclasts go through a continuous remodeling cycle to maintain homeostasis of bone matrix. It has been well acknowledged that interferons (IFNs), acting as a subgroup of cytokines, not only have crucial effects on regulating immunology but also could modulate the dynamic balance of bone matrix. In the light of different isoforms, IFNs have been divided into three major categories in terms of amino acid sequences, recognition of specific receptors and biological activities. Currently, type I IFNs consist of a multi-gene family with several subtypes, of which IFN-α exerts pro-osteoblastogenic effects to activate osteoblast differentiation and inhibits osteoclast fusion to maintain bone matrix integrity. Meanwhile, IFN-β suppresses osteoblast-mediated bone remodeling as well as exhibits inhibitory effects on osteoclast differentiation to attenuate bone resorption. Type II IFN constitutes the only type, IFN-γ, which exerts regulatory effects on osteoclastic bone resorption and osteoblastic bone formation by biphasic ways. Interestingly, type III IFNs are regarded as new members of IFN family composed of four members, including IFN-λ1 (IL-29), IFN-λ2 (IL-28A), IFN-λ3 (IL-28B) and IFN-λ4, which have been certified to participate in bone destruction. However, the direct regulatory mechanisms underlying how type III IFNs modulate the metabolic balance of bone matrix, remains poorly elucidated. In this review, we have summarized functions of IFN family during physiological and pathological conditions and described the mechanisms by which IFNs maintain bone matrix homeostasis via affecting the osteoclast-osteoblast crosstalk. In addition, the potential therapeutic effects of IFNs on inflammatory bone destruction diseases such as rheumatoid arthritis (RA), osteoarthritis (OA) and infectious bone diseases are also well displayed, which are based on the predominant role of IFNs in modulating the dynamic equilibrium of bone matrix.

ROS signaling cascades: dual regulations for osteoclast and osteoblast

Accumulating evidence indicates that intracellular reactive oxygen species (ROS) production is highly involved in bone homeostasis by intervening osteoclast or osteoblast differentiation. Interestingly, ROS that are known as oxidizing agents exert dose-dependent biphasic properties in bone remodeling, including preventing osteoblast activity but accelerating osteoclast resorption. ROS mainly composed of superoxide anion radical, hydroxyl radical, nitric oxide, and two-electron reduction product hydrogen peroxide, which are important components to regulate bone cell metabolism and function in mammal skeleton. These free radicals can be partly produced in bone and boosted in an inflammation state. Although numerous researches have emphasized the impacts of ROS on bone cell biology and verified the mechanism of ROS signaling cascades, the recapitulatory commentary is necessary. In this review article, we particularly focus on the regulation of the intracellular ROS and its potential mechanism impacting on cell-signaling transduction in osteoclast and osteoblast differentiation for preferable understanding the pathogenesis and searching for novel therapeutic protocols for human bone diseases.

Complement activation links inflammation to dental tissue regeneration

OBJECTIVES

Complement is an efficient plasma immune surveillance system. It initiates inflammation by inducing vascular modifications and attracting immune cells expressing Complement receptors. Investigating Complement receptors in non-immune cells pointed out Complement implication in the regeneration of tissue such as liver, skin, or bone. This review will shed the light on Complement implication in the initial steps of dental tissue regeneration.

MATERIALS AND METHODS

Review of literature was conducted on Complement local expression and implication in oral tissue regeneration in vivo and in vitro.

RESULTS

Recent data reported expression of Complement receptors and soluble proteins in dental tissues. Cultured pulp fibroblasts secrete all Complement components. Complement C3b and MAC have been shown to control bacteria growth in the dental pulp while C3a and C5a are involved in the initial steps of pulp regeneration. Indeed, C3a induces pulp stem cell/fibroblast proliferation, and fibroblast recruitment, while C5a induces neurite growth, guides stem cell recruitment, and odontoblastic differentiation. Similarly, cultured periodontal ligament cells produce C5a which induces bone marrow mesenchymal stem cell recruitment.

CONCLUSIONS

Overall, this review highlights that local Complement synthesis in dental tissues plays a major role, not only in eliminating bacteria but also in the initial steps of dental tissue regeneration, thus providing a link between dental tissue inflammation and regeneration.

CLINICAL RELEVANCE

Complement provides an explanation for understanding why inflammation preceeds regeneration. This may also provide a biological rational for understanding the reported success conservative management of mature permanent teeth with carious pulp exposure.

Evaluation of global gene expression in regenerate tissues during Masquelet treatment

The Masquelet induced-membrane (IM) technique is indicated for large segmental bone defects. Attributes of the IM and local milieu that contribute to graft-to-bone union are unknown. Using a rat model, we compared global gene expression profiles in critically sized femoral osteotomies managed using a cement spacer as per Masquelet to those left empty. At the end of the experiment, IM and bone adjacent to the spacer were collected from the Masquelet side. Nonunion tissue in the defect and bone next to the empty defect were collected from the contralateral side. Tissues were subjected to RNA isolation, sequencing, and differential expression analysis. Cell type enrichment analysis suggested the IM and the bone next to the polymethylmethacrylate (PMMA) spacer were comparatively enriched for osteoblastic genes. The nonunion environment was comparatively enriched for innate and adaptive immune cell markers, but only macrophages were evident in the Masquelet context. iPathwayGuide was utilized to identify cell signaling pathways and protein interaction networks enriched in the Masquelet environment. For IM vs nonunion false-discovery rate correction of P values rendered overall pathway differences nonsignificant, and so only protein interaction networks are presented. For the bone comparison, substantial enrichment of pathways and networks known to contribute to osteogenic mechanisms was revealed. Our results suggest that the PMMA spacer affects the cut bone ends that are in contact with it and at the same time induces the foreign body reaction and formation of the IM. B cells in the empty defect suggest a chronic inflammatory response to a large segmental osteotomy.

Identification of osteoporosis markers through bioinformatic functional analysis of serum proteome

Osteoporosis is a severe chronic skeletal disorder that increases the risks of disability and mortality; however, the mechanism of this disease and the protein markers for prognosis of osteoporosis have not been well characterized. This study aims to characterize the imbalanced serum proteostasis, the disturbed pathways, and potential serum markers in osteoporosis by using a set of bioinformatic analyses. In the present study, the large-scale proteomics datasets (PXD006464) were adopted from the Proteome Xchange database and processed with MaxQuant. The differentially expressed serum proteins were identified. The biological process and molecular function were analyzed. The protein-protein interactions and subnetwork modules were constructed. The signaling pathways were enriched. We identified 209 upregulated and 230 downregulated serum proteins. The bioinformatic analyses revealed a highly overlapped functional protein classification and the gene ontology terms between the upregulated and downregulated protein groups. Protein-protein interactions and pathway analyses showed a high enrichment in protein synthesis, inflammation, and immune response in the upregulated proteins, and cell adhesion and cytoskeleton regulation in the downregulated proteins. Our findings greatly expand the current view of the roles of serum proteins in osteoporosis and shed light on the understanding of its underlying mechanisms and the discovery of serum proteins as potential markers for the prognosis of osteoporosis.

Dysfunction of MiR-148a-NRP1 Functional Axis Suppresses Osteogenic Differentiation of Periodontal Ligament Stem Cells Under Inflammatory Microenvironment

Periodontitis is a chronic inflammatory disease that can lead to the loss of periodontal bone tissue. The osteogenic potential of periodontal ligament stem cells (PDLSCs) is significantly decreased in periodontitis microenvironment. However, the mechanism is still unclear. We used Porphyromonas gingivalis lipopolysaccharide (LPS) as a stimulator of PDLSCs to mimic the periodontal inflammatory environment. The mineralization capability was restrained in LPS-stimulated PDLSCs, and the level of miR-148a increased, while the level of Neuropilin 1 (NRP1) decreased. Downregulation of miR-148a could reverse the osteogenesis deficiency of PDLSCs under LPS treatment. In addition, the expression of miR-148a in PDLSCs was negatively correlated with the expression of NRP1. Furthermore, overexpression of NRP1 upregulated the osteogenesis ability of LPS-stimulated PDLSCs, while inhibition of NRP1 eliminated the stimulative effect of miR-148a inhibitor on osteogenic differentiation. These data illustrated that the inflammatory environment mimicked by LPS inhibits osteogenesis by upregulation of miR-148a and subsequent downregulation of NRP1. We also found, compared to healthy periodontal tissues, miR-148a level increased, while NRP1 level decreased in periodontitis tissues. These two phenomena also exist in PDLSCs that come from the upper two types of tissues. To summarize, the decline of osteogenic potential of PDLSCs under inflammatory condition of periodontitis is related to miR-148a/NRP1 functional axis. This study may provide a novel strategy in the molecular aspect for the therapy of periodontitis.