Targeting endothelial PDGFR-ß facilitates angiogenesis-associated bone formation through the PAK1/NICD axis.

The intricate orchestration of osteoporosis (OP) pathogenesis remains elusive. Mounting evidence suggests that angiogenesis-driven osteogenesis serves as a crucial foundation for maintaining bone homeostasis. This study aimed to explore the potential of the endothelial platelet-derived growth factor receptor-ß (PDGFR-ß) in mitigating bone loss through its facilitation of H-type vessel formation. Our findings demonstrate that the expression level of endothelial PDGFR-ß is reduced in samples obtained from individuals suffering from OP, as well as in ovariectomy mice. Depletion of PDGFR-ß in endothelial cells ameliorates angiogenesis-mediated bone formation in mice. The regulatory influence of endothelial PDGFR-ß on H-type vessels is mediated through the PDGFRß-P21-activated kinase 1-Notch1 intracellular domain signaling cascade. In particular, the endothelium-specific enhancement of PDGFR-ß facilitates H-type vessels and their associated bone formation in OP. Hence, the strategic targeting of endothelial PDGFR-ß emerges as a promising therapeutic approach for the management of OP in the near future.

Bone-derived PDGF-BB enhances hippocampal non-specific transcytosis through microglia-endothelial crosstalk in HFD-induced metabolic syndrome.

BACKGROUND: It is well known that high-fat diet (HFD)-induced metabolic syndrome plays a crucial role in cognitive decline and brain-blood barrier (BBB) breakdown. However, whether the bone-brain axis participates in this pathological process remains unknown. Here, we report that platelet-derived growth factor-BB (PDGF-BB) secretion by preosteoclasts in the bone accelerates neuroinflammation. The expression of alkaline phosphatase (ALPL), a nonspecific transcytosis marker, was upregulated during HFD challenge. MAIN BODY: Preosteoclast-specific Pdgfb transgenic mice with high PDGF-BB concentrations in the circulation recapitulated the HFD-induced neuroinflammation and transcytosis shift. Preosteoclast-specific Pdgfb knockout mice were partially rescued from hippocampal neuroinflammation and transcytosis shifts in HFD-challenged mice. HFD-induced PDGF-BB elevation aggravated microglia-associated neuroinflammation and interleukin-1ß (IL-1ß) secretion, which increased ALPL expression and transcytosis shift through enhancing protein 1 (SP1) translocation in endothelial cells. CONCLUSION: Our findings confirm the role of bone-secreted PDGF-BB in neuroinflammation and the transcytosis shift in the hippocampal region during HFD challenge and identify a novel mechanism of microglia-endothelial crosstalk in HFD-induced metabolic syndrome.

The role of EGFR signaling in age-related osteoporosis in mouse cortical bone.

So far, there has been no effective cure for osteoporotic cortical bone, the most significant change in long bone structure during aging and the main cause of bone fragility fractures, because its underlying molecular and cellular mechanisms remain largely unknown. We used 3- and 15-mo-old mice as well as 15-mo-old mice treated with vehicle and gefitinib to evaluate structural, cellular, and molecular changes in cortical bone. We found that the senescence of osteoprogenitors was increased, whereas the expression of phosphorylated epidermal growth factor receptor (EGFR) on the endosteal surface of cortical bone down-regulated in middle-aged 15-mo-old mice compared with young 3-mo-old mice. Further decreasing EGFR signaling by gefitinib treatment in middle-aged mice resulted in promoted senescence of osteoprogenitors and accelerated cortical bone degeneration. Moreover, inhibiting EGFR signaling suppressed the expression of enhancer of zeste homolog 2 (Ezh2), the repressor of cell senescence-inducer genes, through ERK1/2 pathway, thereby promoting senescence in osteoprogenitors. Down-regulated EGFR signaling plays a physiologically significant role during aging by reducing Ezh2 expression, leading to the senescence of osteoprogenitors and the decline in bone formation on the endosteal surface of cortical bone.-Liu, G., Xie, Y., Su, J., Qin, H., Wu, H., Li, K., Yu, B., Zhang, X. The role of EGFR signaling in age-related osteoporosis in mouse cortical bone.

G-CSF partially mediates bone loss induced by Staphylococcus aureus infection in mice.

Bone loss in Staphylococcus aureus (S. aureus) osteomyelitis poses a serious challenge to orthopedic treatment. The present study aimed to elucidate how S. aureus infection in bone might induce bone loss. The C57BL/6 mice were injected with S. aureus (106 CFU/ml, 100 µl) or with the same amount of vehicle (control) via the tail vein. Microcomputed tomography (microCT) analysis showed bone loss progressing from week 1 to week 5 after infection, accompanied by a decreased number of osteocalcin-positive stained osteoblasts and the suppressed mRNA expression of Runx2 and osteocalcin. Transcriptome profiles of GSE30119 were downloaded and analyzed to determine the differences in expression of inflammatory factors between patients with S. aureus infected osteomyelitis and healthy controls, the data showed significantly higher mRNA expression of granulocyte colony-stimulating factor (G-CSF) in the whole blood from patients with S. aureus infection. Enzyme-linked immunosorbent assay (ELISA) analysis confirmed an increased level of G-CSF in the bone marrow and serum from S. aureus infected mice, which might have been due to the increased amount of F4/80+ macrophages. Interestingly, G-CSF neutralizing antibody treatment significantly rescued the bone loss after S. aureus infection, as evidenced by its roles in improving BV/TV and preserving osteocalcin- and osterix-positive stained cells. Importantly, we found that G-CSF level was significantly up-regulated in the serum from osteomyelitis patients infected by S. aureus Together, S. aureus infection might suppress the function of osteoblastic cells and induce progressive bone loss by up-regulating the level G-CSF, suggesting a therapeutic potential for G-CSF neutralization in combating bone loss in S. aureus osteomyelitis.

Effects of Staphylococcus aureus on stem cells and potential targeted treatment of inflammatory disorders.

Due to the advanced studies on stem cells in developmental biology, the roles of stem cells in the body and their phenotypes in related diseases have not been covered clearly. Meanwhile, with the intensive research on the mechanisms of stem cells in regulating various diseases, stem cell therapy is increasingly being attention because of its effectiveness and safety. As one of the most widely used stem cell in stem cell therapies, hematopoietic stem cell transplantation shows huge advantage in treatment of leukemia and other blood-malignant diseases. Besides, due to the effect of anti-inflammatory and immunomodulatory, mesenchymal stem cells could be a potential therapeutic strategy for variety infectious diseases. In this review, we summarized the effects of Staphylococcus aureus (S. aureus) and its components on different types of adult stem cells and their downstream signaling pathways. Also, we reviewed the roles of different kinds of stem cells in various disease models caused by S. aureus, providing new insights for applying stem cell therapy to treat infectious diseases.

Lipoteichoic acid restrains macrophage senescence via ß-catenin/FOXO1/REDD1 pathway in age-related osteoporosis.

Osteoporosis and its related fractures are common causes of morbidity and mortality in older adults, but its underlying molecular and cellular mechanisms remain largely unknown. In this study, we found that lipoteichoic acid (LTA) treatment could ameliorate age-related bone degeneration and attenuate intramedullary macrophage senescence. FOXO1 signaling, which was downregulated and deactivated in aging macrophages, played a key role in the process. Blocking FOXO1 signaling caused decreased REDD1 expression and increased phosphorylation level of mTOR, a major driver of aging, as well as aggravated bone loss and deteriorated macrophage senescence. Moreover, LTA elevated FOXO1 signaling through ß-catenin pathway while ß-catenin inhibition significantly suppressed FOXO1 signaling, promoted senescence-related protein expression, and accelerated bone degeneration and macrophage senescence. Our findings indicated that ß-catenin/FOXO1/REDD1 signaling plays a physiologically significant role that protecting macrophages from senescence during aging.

Single nucleotide polymorphisms in the development of osteomyelitis and prosthetic joint infection: a narrative review.

Currently, despite advancements in diagnostic and therapeutic modalities, osteomyelitis and prosthetic joint infection (PJI) continue to pose significant challenges for orthopaedic surgeons. These challenges are primarily attributed to the high degree of heterogeneity exhibited by these disorders, which are influenced by a combination of environmental and host factors. Recent research efforts have delved into the pathogenesis of osteomyelitis and PJI by investigating single nucleotide polymorphisms (SNPs). This review comprehensively summarizes the current evidence regarding the associations between SNPs and the predisposition to osteomyelitis and PJI across diverse populations. The findings suggest potential linkages between SNPs in genes such as IL-1, IL-6, IFN-γ, TNF-α, VDR, tPA, CTSG, COX-2, MMP1, SLC11A1, Bax, NOS2, and NLRP3 with the development of osteomyelitis. Furthermore, SNPs in genes like IL-1, IL-6, TNF-α, MBL, OPG, RANK, and GCSFR are implicated in susceptibility to PJI. However, it is noted that most of these studies are single-center reports, lacking in-depth mechanistic research. To gain a more profound understanding of the roles played by various SNPs in the development of osteomyelitis and PJI, future multi-center studies and fundamental investigations are deemed necessary.

Clinical characteristics, treatment and efficacy of calcaneal osteomyelitis: A systematic review with synthesis analysis 1118 reported cases.

BACKGROUND: Calcaneal osteomyelitis (CO) still poses great challenges to orthopaedic surgeons due to unique anatomic and functional features of the calcaneus. This study summarized the current data regarding clinical characteristics, treatment and efficacy of CO, based on an analysis of literature-reported cases. MATERIALS AND METHODS: We searched the PubMed, Embase, and Cochrane Library databases to find English and Chinese studies reporting on CO patients between 2000 and 2021, with available data for synthesis analysis. The quality of the included studies was evaluated by the National Institutes of Health (NIH) assessment scale. Effective data were extracted and pooled for analysis. RESULTS: Altogether 198 studies involving 1118 patients were included, with a male-to-female ratio of 2.3 (724 males and 310 females). The median age at CO diagnosis was 46 years, with a median symptom duration of 3 months. Injury-related infections (524 cases) and diabetic foot infections (336 cases) were the two most common causes, with ulcer (468 cases) and wound sinus or exudation (209 cases) being the predominant symptoms. The overall positive culture rate was 80.2%, with polymicrobial infections accounting for 18.1%. Staphylococcus aureus was the most frequently detected pathogen (42.7%), with fungal-related infections isolated in 17 cases. Although most patients received surgical interventions (96.9%), the recurrence rate was 20.1%. The incidence of infection relapse following partial calcanectomy, total calcanectomy, debridement with implantation of local antibiotics, and debridement with or without flap or skin coverage were 31.7%, 45.0%, 16.8%, and 15.1%, respectively. The overall incidence of limb amputation was 12.4%, with all-cause and CO-related mortalities of 2.8% and 0.2%, separately. CONCLUSIONS: CO shared similar characteristics with extremity chronic osteomyelitis, primarily affecting young males, with trauma and diabetic foot as the leading causes and Staphylococcus aureus as the most frequently detected pathogen. Despite surgery being the primary treatment modality, clinical outcomes remained unsatisfactory, marked by high rates of infection recurrence and limb amputation.

The CD163/TWEAK/Fn14 axis: A potential therapeutic target for alleviating inflammatory bone loss.

Objective: Osteoclast (OC) over-activation is an important cause of bone loss that is strongly correlated with inflammation. Although the CD163/TWEAK/Fn14 axis has been implicated in several inflammatory pathologies, its contributions to inflammatory bone loss remain poorly understood. This study aimed to evaluate the interaction of the CD163/TWEAK/Fn14 axis with OC in inflammatory bone loss. Methods: To assess the role of CD163 in bone homeostasis, we characterized the bone phenotypes of CD163-deficient mice and their wild-type littermates. CD163 and TWEAK levels were evaluated in the bone marrow of mice with LPS-induced bone loss and individuals with rheumatoid arthritis (RA). Bone mass changes were assessed using uCT and histology following supplementation with recombinant mouse CD163 protein (rCD163) or blockade of TWEAK/Fn14 signaling in CD163-deficient mice and mice with LPS-induced bone loss. The impact of CD163/TWEAK on OC differentiation and bone resorption capacity was analyzed in vitro. Results: CD163 deficiency caused decreased bone mass and increased OC abundance. Lower CD163 expression and higher TWEAK expression were observed in the bone marrow of mice with LPS-induced bone loss and individuals with RA. TWEAK, mainly derived from CD68+ macrophages, was responsible for bone loss, and supplementing rCD163 or blocking TWEAK/Fn14 signaling contributed to rescue bone loss. TWEAK/Fn14 synergistically promoted RANKL-dependent OC differentiation and bone resorption capability through downstream mitogen-activated protein kinases (MAPK) signaling, while the pro-osteoclastic effect of TWEAK was suppressed by CD163. Conclusion: Our findings suggest that the CD163/TWEAK/Fn14 axis is a potential therapeutic target for inflammatory bone loss by regulating osteoclastogenesis.

The effect of Staphylococcus aureus on innate and adaptive immunity and potential immunotherapy for S. aureus-induced osteomyelitis.

Osteomyelitis is a chronic inflammatory bone disease caused by infection of open fractures or post-operative implants. Particularly in patients with open fractures, the risk of osteomyelitis is greatly increased as the soft tissue damage and bacterial infection are often more severe. Staphylococcus aureus, one of the most common pathogens of osteomyelitis, disrupts the immune response through multiple mechanisms, such as biofilm formation, virulence factor secretion, and metabolic pattern alteration, which attenuates the effectiveness of antibiotics and surgical debridement toward osteomyelitis. In osteomyelitis, immune cells such as neutrophils, macrophages and T cells are activated in response to pathogenic bacteria invasion with excessive inflammatory factor secretion, immune checkpoint overexpression, and downregulation of immune pathway transcription factors, which enhances osteoclastogenesis and results in bone destruction. Therefore, the study of the mechanisms of abnormal immunity will be a new breakthrough in the treatment of osteomyelitis.

Bone-derived PDGF-BB drives brain vascular calcification in male mice.

Brain vascular calcification is a prevalent age-related condition often accompanying neurodegenerative and neuroinflammatory diseases. The pathogenesis of large-vessel calcifications in peripheral tissue is well studied, but microvascular calcification in the brain remains poorly understood. Here, we report that elevated platelet-derived growth factor BB (PDGF-BB) from bone preosteoclasts contributed to cerebrovascular calcification in male mice. Aged male mice had higher serum PDGF-BB levels and a higher incidence of brain calcification compared with young mice, mainly in the thalamus. Transgenic mice with preosteoclast-specific Pdgfb overexpression exhibited elevated serum PDGF-BB levels and recapitulated age-associated thalamic calcification. Conversely, mice with preosteoclast-specific Pdgfb deletion displayed diminished age-associated thalamic calcification. In an ex vivo cerebral microvascular culture system, PDGF-BB dose-dependently promoted vascular calcification. Analysis of osteogenic gene array and single-cell RNA-Seq (scRNA-Seq) revealed that PDGF-BB upregulated multiple osteogenic differentiation genes and the phosphate transporter Slc20a1 in cerebral microvessels. Mechanistically, PDGF-BB stimulated the phosphorylation of its receptor PDGFRß (p-PDGFRß) and ERK (p-ERK), leading to the activation of RUNX2. This activation, in turn, induced the transcription of osteoblast differentiation genes in PCs and upregulated Slc20a1 in astrocytes. Thus, bone-derived PDGF-BB induced brain vascular calcification by activating the p-PDGFRß/p-ERK/RUNX2 signaling cascade in cerebrovascular cells.

Similarities and Differences Between Diabetes-Related and Trauma-Related Calcaneal Osteomyelitis: Comparisons Based on 681 Reported Cases.

Background: Current information were still limited regarding clinical characteristics, diagnosis, and treatment efficacy of calcaneal osteomyelitis (CO). The present study summarized similarities and differences between diabetes-related CO (DRCO) and trauma-related CO (TRCO) based on synthesis analysis of literature-reported cases. Methods: We searched the PubMed, Embase, and Cochrane Library databases to find English studies reporting DRCO and TRCO published between January 2000 and December 2021. Effective data were extracted and synthesized for comparisons. Results: Altogether 108 studies with 278 DRCO and 403 TRCO patients were analyzed. The ratio of females among the DRCO patients was significantly higher than that of the TRCO patients (37.4% vs 24.3%, P < 0.001). The median age at diagnosis of the DRCO patients was statistically older than the TRCO patients (56 vs 44 years, P < 0.001). The median symptom duration of the DRCO patients was longer than the TRCO patients (4 vs 2 months, P = 0.136), with ulcer and sinus as the top symptoms for the DRCO and TRCO patients, respectively. The positive rate of pathogen culture for the DRCO patients was significantly higher than that for the TRCO patients (94.8% vs 69.5%, P < 0.001). The DRCO patients had higher risks of infection relapse (32.3% vs 16.3%, P < 0.001) and amputation (24.8% vs 1.4%, P < 0.001), and a higher all-cause mortality (4.9% vs 1.3%, P = 0.03) than the TRCO patients. Conclusion: DRCO and TRCO shared similar and different clinical features and diagnostic issues. However, compared with TRCO, the clinical efficacy and prognosis of DRCO were worse.

TWIST1 rescue calcium overload and apoptosis induced by inflammatory microenvironment in S. aureus-induced osteomyelitis.

Currently, there is no effective therapy for Staphylococcus aureus-induced osteomyelitis. It is widely recognized that the inflammatory microenvironment around abscess plays an essential role in protracting the course of S. aureus-induced osteomyelitis. In this study, we found TWIST1 was highly expressed in macrophages around abscesses but less related to local S. aureus in the later stages of Staphylococcus aureus-infected osteomyelitis. Mouse bone marrow macrophages show apoptosis and elevated TWIST1 expression when treated with the inflammatory medium. Knockdown of TWIST1 induced macrophage apoptosis, impaired the bacteria phagocytosis/killing abilities, and promoted cell apoptosis markers expression in inflammatory microenvironment stimulation. Furthermore, inflammatory microenvironments were responsible for inducing calcium overload in macrophage mitochondrial while calcium overload inhibition significantly rescued macrophage apoptosis, bacteria phagocytosis/killing abilities and improved the mice's antimicrobial ability. Our findings indicated that TWIST1 is a crucial molecule that protects macrophages from calcium overload induced by inflammatory microenvironments.

Effects of Dopamine on stem cells and its potential roles in the treatment of inflammatory disorders: a narrative review.

Inflammation is the host's protective response against harmful external stimulation that helps tissue repair and remodeling. However, excessive inflammation seriously threatens the patient's life. Due to anti-inflammatory effects, corticosteroids, immunosuppressants, and monoclonal antibodies are used to treat various inflammatory diseases, but drug resistance, non-responsiveness, and severe side effect limit their development and application. Therefore, developing other alternative therapies has become essential in anti-inflammatory therapy. In recent years, the in-depth study of stem cells has made them a promising alternative drug for the treatment of inflammatory diseases, and the function of stem cells is regulated by a variety of signals, of which dopamine signaling is one of the main influencing factors. In this review, we review the effects of dopamine on various adult stem cells (neural stem cells, mesenchymal stromal cells, hematopoietic stem cells, and cancer stem cells) and their signaling pathways, as well as the application of some critical dopamine receptor agonists/antagonists. Besides, we also review the role of various adult stem cells in inflammatory diseases and discuss the potential anti-inflammation function of dopamine receptors, which provides a new therapeutic target for regenerative medicine in inflammatory diseases.

Elevated PDGF-BB from Bone Impairs Hippocampal Vasculature by Inducing PDGFRß Shedding from Pericytes.

Evidence suggests a unique association between bone aging and neurodegenerative/cerebrovascular disorders. However, the mechanisms underlying bone-brain interplay remain elusive. Here platelet-derived growth factor-BB (PDGF-BB) produced by preosteoclasts in bone is reported to promote age-associated hippocampal vascular impairment. Aberrantly elevated circulating PDGF-BB in aged mice and high-fat diet (HFD)-challenged mice correlates with capillary reduction, pericyte loss, and increased blood-brain barrier (BBB) permeability in their hippocampus. Preosteoclast-specific Pdgfb transgenic mice with markedly high plasma PDGF-BB concentration faithfully recapitulate the age-associated hippocampal BBB impairment and cognitive decline. Conversely, preosteoclast-specific Pdgfb knockout mice have attenuated hippocampal BBB impairment in aged mice or HFD-challenged mice. Persistent exposure of brain pericytes to high concentrations of PDGF-BB upregulates matrix metalloproteinase 14 (MMP14), which promotes ectodomain shedding of PDGF receptor ß (PDGFRß) from pericyte surface. MMP inhibitor treatment alleviates hippocampal pericyte loss and capillary reduction in the conditional Pdgfb transgenic mice and antagonizes BBB leakage in aged mice. The findings establish the role of bone-derived PDGF-BB in mediating hippocampal BBB disruption and identify the ligand-induced PDGFRß shedding as a feedback mechanism for age-associated PDGFRß downregulation and the consequent pericyte loss.

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.

Serum Calcium Level Combined with Platelet Count May Be Useful Indicators for Assisted Diagnosis of Extremity Posttraumatic Osteomyelitis: A Comparative Analysis.

BACKGROUND: A previous study had reported that patients with osteomyelitis (OM) appeared to be more likely to develop hypocalcemia before and after surgery. Calcium sulfate (CS) is frequently used as a local antibiotic vehicle in the treatment of OM, which may also affect serum calcium level. However, whether changes of serum calcium level are caused by OM and/or local use of calcium sulfate remains unclear. Also, platelet (PLT) count plays a crucial predictive role in periprosthetic joint infections (PJIs), but its role in assisted diagnosis of OM is largely unknown. The purpose of this study was to determine whether serum calcium level and PLT count may be helpful in assisted diagnosis of PTOM. METHODS: Between January 2013 and December 2018, we analyzed 468 consecutive patients (392 males and 76 females), including 170 patients with posttraumatic OM (PTOM), 130 patients with aseptic bone nonunion (ABN), and 168 patients recovered from fractures with requirement of implant removal set as controls. Preoperative serological levels of calcium, phosphorus, and PLT were detected, and comparisons were conducted among the above three groups. Additionally, correlations and receiver operating characteristic (ROC) curves were displayed to test whether calcium level and PLT can differentiate patients with ABN and PTOM. RESULTS: Outcomes showed that the incidences of asymptomatic hypocalcemia (PTOM vs. ABN vs. controls = 22.94% vs. 6.92% vs. 8.82%, χ 2 = 21.098, P < 0.001) and thrombocytosis (PTOM vs. ABN vs. controls = 35.3% vs. 13.84% vs. 12.35%, χ 2 = 28.512, P < 0.001) were highest in PTOM patients. Besides, the mean serological levels of phosphorus in PTOM and ABN patients were significantly higher than those in the controls (P = 0.007). The Area Under the Curve (AUC) of the ROC curve outcomes revealed that, with the combination of serum calcium level with PLT count, the predictive role was acceptable (AUC 0.730, P < 0.001, 95% CI 0.681-0.780). Also, serological levels of calcium of 2.225 mmol/L and PLT count of 246.5 × 109/L were identified as the optimal cut-off values to distinguish patients with and without PTOM. However, age- and gender-related differences in serum calcium levels (age, P = 0.056; gender, P = 0.978) and PLT count (age, P = 0.363; gender, P = 0.799) were not found to be statistically significant in any groups. In addition, no significant correlations were identified between serum calcium level and PLT count (R = 0.010, P = 0.839). CONCLUSIONS: Asymptomatic hypocalcemia and thrombocytosis appeared to be more frequent in this cohort with PTOM. Serological levels of calcium and PLT count may be useful biomarkers in screening patients suspected of PTOM.

Osteoclasts protect bone blood vessels against senescence through the angiogenin/plexin-B2 axis.

Synthetic glucocorticoids (GCs), one of the most effective treatments for chronic inflammatory and autoimmune conditions in children, have adverse effects on the growing skeleton. GCs inhibit angiogenesis in growing bone, but the underlying mechanisms remain unclear. Here, we show that GC treatment in young mice induces vascular endothelial cell senescence in metaphysis of long bone, and that inhibition of endothelial cell senescence improves GC-impaired bone angiogenesis with coupled osteogenesis. We identify angiogenin (ANG), a ribonuclease with pro-angiogenic activity, secreted by osteoclasts as a key factor for protecting the neighboring vascular cells against senescence. ANG maintains the proliferative activity of endothelial cells through plexin-B2 (PLXNB2)-mediated transcription of ribosomal RNA (rRNA). GC treatment inhibits ANG production by suppressing osteoclast formation in metaphysis, resulting in impaired endothelial cell rRNA transcription and subsequent cellular senescence. These findings reveal the role of metaphyseal blood vessel senescence in mediating the action of GCs on growing skeleton and establish the ANG/PLXNB2 axis as a molecular basis for the osteoclast-vascular interplay in skeletal angiogenesis.

Skeleton-secreted PDGF-BB mediates arterial stiffening.

Evidence links osteoporosis and cardiovascular disease but the cellular and molecular mechanisms are unclear. Here we identify skeleton-secreted platelet-derived growth factor-BB (PDGF-BB) as a key mediator of arterial stiffening in response to aging and metabolic stress. Aged mice and those fed high-fat diet (HFD), relative to young mice and those fed normal chow food diet, respectively, had higher serum PDGF-BB and developed bone loss and arterial stiffening. Bone/bone marrow preosteoclasts in aged mice and HFD mice secrete an excessive amount of PDGF-BB, contributing to the elevated PDGF-BB in blood circulation. Conditioned medium prepared from preosteoclasts stimulated proliferation and migration of the vascular smooth muscle cells. Conditional transgenic mice, in which PDGF-BB is overexpressed in preosteoclasts, had 3-fold higher serum PDGF-BB concentration and developed simultaneous bone loss and arterial stiffening spontaneously at a young age. Conversely, in conditional knockout mice, in which PDGF-BB is deleted selectively in preosteoclasts, HFD did not affect serum PDGF-BB concentration; as a result, HFD-induced bone loss and arterial stiffening were attenuated. These studies confirm that preosteoclasts are a main source of excessive PDGF-BB in blood circulation during aging and metabolic stress and establish the role of skeleton-derived PDGF-BB as an important mediator of vascular stiffening.

α-Hemolysin suppresses osteogenesis by inducing lipid rafts accumulation in bone marrow stromal cells.

α-hemolysin (Hla) is considered an essential virulent factor for Staphylococcus aureus (S. aureus) toxicity, the mechanism by which Hla affect bone metabolism is poorly understood. In this study, 2-month-old C57BL/6 mice were treated with Hla (40 µg/kg, i.p.) or S. aureus (1 × 106 CFU/ml, 100 µl, i.v.) with the presence or absence of methyl-ß-cyclodextrin (MßCD) (300 mg/kg, i.p.). MicroCT analysis showed progressive bone loss from week 2 to week 4 after Hla treatment, accompanied by a decreased osteoblasts and increased osteoclasts in femoral metaphysis in mice. Further, Hla stimulated the expression of Caveolin-1 in vivo and in vitro, activated lipid rafts accumulation in cell membrane of bone marrow stromal cells (BMSCs), and suppressed osteogenesis of BMSCs. Destruction of lipid rafts with MßCD or inhibition of Caveolin-1 with Daidzein blocked the detrimental effect of Hla on osteogenesis of BMSCs. Importantly, treating mice with MßCD rescued the loss of osteoblasts and increased osteoclastogenesis induced by Hla as well as the bone loss induced by S. aureus infection. Together, we demonstrate that Hla induces bone destruction directly by suppressing osteogenesis and indirectly by stimulating osteoclastogenesis, and that lipid rafts may mediate the detrimental effect of Hla and S. aureus on osteogenesis and bone formation.