Key regulators of vascular calcification in chronic kidney disease: Hyperphosphatemia, BMP2, and RUNX2.

Vascular calcification is quite common in patients with end-stage chronic kidney disease and is a major trigger for cardiovascular complications in these patients. These complications significantly impact the survival rate and long-term prognosis of individuals with chronic kidney disease. Numerous studies have demonstrated that the development of vascular calcification involves various pathophysiological mechanisms, with the osteogenic transdifferentiation of vascular smooth muscle cells (VSMCs) being of utmost importance. High phosphate levels, bone morphogenetic protein 2 (BMP2), and runt-related transcription factor 2 (RUNX2) play crucial roles in the osteogenic transdifferentiation process of VSMCs. This article primarily reviews the molecular mechanisms by which high phosphate, BMP2, and RUNX2 regulate vascular calcification secondary to chronic kidney disease, and discusses the complex interactions among these factors and their impact on the progression of vascular calcification. The insights provided here aim to offer new perspectives for future research on the phenotypic switching and osteogenic transdifferentiation of VSMCs, as well as to aid in optimizing clinical treatment strategies for this condition, bearing significant clinical and scientific implications.

Cell sheet produced from periodontal ligament stem cells activated by PAR1 improves osteogenic differentiation.

Periodontal regeneration is a challenge, and tissue engineering based on periodontal ligament stem cells (PDLSCs) has been shown to be a promising alternative to this process. However, the need for scaffolds has limited the therapeutic use of PDLSCs. In this context, scaffold-free tissue engineering using the cell sheet (CS) technique has been developed as an alternative approach to improve tissue regeneration. Previously, we showed that Protease-activated receptor-1 (PAR1) can regulate PDLSCs. Herein, we evaluate whether PAR1 influences osteogenesis in CSs produced from PDLSCs, without the use of scaffolds. PDLSCs were isolated and immunophenotyped. Then, CSs were obtained by supplementing the culture medium with ascorbic acid (50 µg/mL), and PAR1 was activated through its agonist peptide (100 nM). Scaffold-free 3D CSs were successfully produced from PDLSCs, and they showed higher proliferation potential than isolated PDLSCs. Also, PAR1 activation decreased senescence and improved osteogenic differentiation of CSs by increasing mineralized nodule deposition and alkaline phosphatase concentration; PAR1 also modulated osteogenic markers at the gene and protein levels. We further demonstrated that this effect was regulated by Wnt, TGF-ßI, MEK, p38 MAPK, and FGF/VEGF signaling pathways in PDLSCs (p < 0.05%). Overall, PAR1 activation increased osteogenic activity in CSs, emerging as a promising scaffold-free therapeutic approach for periodontal regeneration.

SCUBE3 promotes osteogenic differentiation and mitophagy in human bone marrow mesenchymal stem cells through the BMP2/TGF-ß signaling pathway.

In clinical settings, addressing large bone defects remains a significant challenge for orthopedic surgeons. The use of genetically modified bone marrow mesenchymal stem cells (BMSCs) has emerged as a highly promising approach for these treatments. Signal peptide-CUB-EGF domain-containing protein 3 (SCUBE3) is a multifunctional secreted glycoprotein, the role of which remains unclear in human hBMSCs. This study used various experimental methods to elucidate the potential mechanism by which SCUBE3 influences osteogenic differentiation of hBMSCs in vitro. Additionally, the therapeutic efficacy of SCUBE3, in conjunction with porous GeLMA microspheres, was evaluated in vivo using a mouse bone defect model. Our findings indicate that SCUBE3 levels increase significantly during early osteogenic differentiation of hBMSCs, and that reducing SCUBE3 levels can hinder this differentiation. Overexpressing SCUBE3 elevated osteogenesis gene and protein levels and enhanced calcium deposition. Furthermore, treatment with recombinant human SCUBE3 (rhSCUBE3) protein boosted BMP2 and TGF-ß expression, activated mitophagy in hBMSCs, ameliorated oxidative stress, and restored osteogenic function through SMAD phosphorylation. In vivo, GELMA/OE treatment effectively accelerated bone healing in mice. In conclusion, SCUBE3 fosters osteogenic differentiation and mitophagy in hBMSCs by activating the BMP2/TGF-ß signaling pathway. When combined with engineered hydrogel cell therapy, it could offer valuable guidance for the clinical management of extensive bone defects.

LINC01133 promotes the osteogenic differentiation of bone marrow mesenchymal stem cells by upregulating CTNNB1 by acting as a sponge for miR-214-3p.

BACKGROUND: Osteoporosis results from decreased bone mass and disturbed bone structure. Human bone marrow mesenchymal stem cells (hBMSCs) demonstrate robust osteogenic differentiation, a critical process for bone formation. This research was designed to examine the functions of LINC01133 in osteogenic differentiation. METHODS: Differentially expressed lncRNAs affecting osteogenic differentiation in hBMSCs were identified from the GEO database. A total of 74 osteoporosis patients and 70 controls were enrolled. hBMSCs were stimulated to undergo osteogenic differentiation using an osteogenic differentiation medium (OM). RT-qPCR was performed to evaluate LINC01133 levels and osteogenesis-related genes such as osteocalcin, osteopontin, and RUNX2. An alkaline phosphates (ALP) activity assay was conducted to assess osteogenic differentiation. Cell apoptosis was detected using flow cytometry. Dual luciferase reporter assay and RIP assay were employed to investigate the association between miR-214-3p and LINC01133 or CTNNB1. Loss or gain of function assays were conducted to elucidate the impact of LINC01133 and miR-214-3p on osteogenic differentiation of hBMSCs. RESULTS: LINC01133 and CTNNB1 expression decreased in osteoporotic patients but increased in OM-cultured hBMSCs, whereas miR-214-3p showed an opposite trend. Depletion of LINC01133 suppressed the expression of genes associated with bone formation and ALP activity triggered by OM in hBMSCs, leading to increased cell apoptosis. Nevertheless, this suppression was partially counteracted by the reduced miR-214-3p levels. Mechanistically, LINC01133 and CTNNB1 were identified as direct targets of miR-214-3p. CONCLUSIONS: Our study highlights the role of LINC01133 in positively regulating CTNNB1 expression by inhibiting miR-214-3p, thereby promoting osteogenic differentiation of BMSCs. These findings may provide valuable insights into bone regeneration in osteoporosis.

Role of oxytocin in bone.

Oxytocin (OT) is a posterior pituitary hormone that, in addition to its role in regulating childbirth and lactation, also exerts direct regulatory effects on the skeleton through peripheral OT and oxytocin receptor (OTR). Bone marrow mesenchymal stem cells (BMSCs), osteoblasts (OB), osteoclasts (OC), chondrocytes, and adipocytes all express OT and OTR. OT upregulates RUNX2, BMP2, ALP, and OCN, thereby enhancing the activity of BMSCs and promoting their differentiation towards OB rather than adipocytes. OT also directly regulates OPG/RANKL to inhibit adipocyte generation, increase the expression of SOX9 and COMP, and enhance chondrocyte differentiation. OB can secrete OT, exerting influence on the surrounding environment through autocrine and paracrine mechanisms. OT directly increases OC formation through the NκB/MAP kinase signaling pathway, inhibits osteoclast proliferation by triggering cytoplasmic Ca2+ release and nitric oxide synthesis, and has a dual regulatory effect on OCs. Under the stimulation of estrogen, OB synthesizes OT, amplifying the biological effects of estrogen and OT. Mediated by estrogen, the OT/OTR forms a feedforward loop with OB. Apart from estrogen, OT also interacts with arginine vasopressin (AVP), prostaglandins (PGE2), leptin, and adiponectin to regulate bone metabolism. This review summarizes recent research on the regulation of bone metabolism by OT and OTR, aiming to provide insights into their clinical applications and further research.

Mechanoresponsive regulation of tissue regeneration during distraction osteogenesis.

Distraction osteogenesis is widely used for bone tissue engineering. Mechanical stimulation plays a central role in the massive tissue regeneration observed during distraction osteogenesis. Although distraction osteogenesis has been a boon for patients with bone defects, we still have limited knowledge about the intrinsic mechanotransduction that converts physical forces into biochemical signals capable of inducing cell behavior changes and new tissue formation. In this review, we summarize the findings for mechanoresponsive factors, including cells, genes, and signaling pathways, during the distraction osteogenesis different phases. These elements function for coupling of osteogenesis and angiogenesis via the Integrin-FAK, TGF-ß/BMP, Wnt/ß-catenin, Hippo, MAPK, PI3K/Akt, and HIF-1α signaling pathways in a mechanoresponsive niche. The available evidence further suggests the existence of a balance between the epithelial-mesenchymal transition and mesenchymal-epithelial transition under hypoxic stress. We also briefly summarize the current in silico simulation algorithms and propose several future research directions that may advance understanding of distraction osteogenesis in the era of bioinformation, particularly the integration of artificial intelligence models with reliable single-cell RNA sequencing datasets. The objective of this review is to utilize established knowledge to further optimize existing distraction protocols and to identify potential therapeutic targets.

Composite bioink incorporating cell-laden liver decellularized extracellular matrix for bioprinting of scaffolds for bone tissue engineering.

The field of bone tissue engineering (BTE) has witnessed a revolutionary breakthrough with the advent of three-dimensional (3D) bioprinting technology, which is considered an ideal choice for constructing scaffolds for bone regeneration. The key to realizing scaffold biofunctions is the selection and design of an appropriate bioink, and existing bioinks have significant limitations. In this study, a composite bioink based on natural polymers (gelatin and alginate) and liver decellularized extracellular matrix (LdECM) was developed and used to fabricate scaffolds for BTE using 3D bioprinting. Through in vitro studies, the concentration of LdECM incorporated into the bioink was optimized to achieve printability and stability and to improve the proliferation and osteogenic differentiation of loaded rat bone mesenchymal stem cells (rBMSCs). Furthermore, in vivo experiments were conducted using a Sprague Dawley rat model of critical-sized calvarial defects. The proposed rBMSC-laden LdECM-gelatin-alginate scaffold, bioprinted layer-by-layer, was implanted in the rat calvarial defect and the development of new bone growth was studied for four weeks. The findings showed that the proposed bioactive scaffolds facilitated angiogenesis and osteogenesis at the defect site. The findings of this study suggest that the developed rBMSC-laden LdECM-gelatin-alginate bioink has great potential for clinical translation and application in solving bone regeneration problems.

Modulation of osteoblastogenesis by NRF2: NRF2 activation suppresses osteogenic differentiation and enhances mineralization in human bone marrow-derived mesenchymal stromal cells.

Mesenchymal stromal stem cells (MSCs) or skeletal stem cells (SSCs) play a major role in tissue repair due to their robust ability to differentiate into osteoblasts, chondrocytes, and adipocytes. Complex cell signaling cascades tightly regulate this differentiation. In osteogenic differentiation, Runt-related transcription factor 2 (RUNX2) and ALP activity are essential. Furthermore, during the latter stages of osteogenic differentiation, mineral formation mediated by the osteoblast occurs with the secretion of a collagenous extracellular matrix and calcium deposition. Activation of nuclear factor erythroid 2-related factor 2 (NRF2), an important transcription factor against oxidative stress, inhibits osteogenic differentiation and mineralization via modulation of RUNX2 function; however, the exact role of NRF2 in osteoblastogenesis remains unclear. Here, we demonstrate that NRF2 activation in human bone marrow-derived stromal cells (HBMSCs) suppressed osteogenic differentiation. NRF2 activation increased the expression of STRO-1 and KITLG (stem cell markers), indicating NRF2 protects HBMSCs stemness against osteogenic differentiation. In contrast, NRF2 activation enhanced mineralization, which is typically linked to osteogenic differentiation. We determined that these divergent results were due in part to the modulation of cellular calcium flux genes by NRF2 activation. The current findings demonstrate a dual role for NRF2 as a HBMSC maintenance factor as well as a central factor in mineralization, with implications therein for elucidation of bone formation and cellular Ca2+ kinetics, dystrophic calcification and, potentially, application in the modulation of bone formation.

Three-dimensional printed calcium phosphate scaffolds emulate bone microstructure to promote bone regrowth and repair.

The interconnected structures in a 3D scaffold allows the movement of cells and nutrients. Therefore, this study aimed to investigate the in-vivo bioactivity of 3D-printed ß-tricalcium phosphate (ß-TCP) and hydroxyapatite (HAP) scaffolds that replicate biological bone. This study included 24-week-old male New Zealand white rabbits. A cylindrical bone defect with a diameter of 4.5 mm and a depth of 8 mm was created in the lateral aspect of the distal femur. A 3D-printed scaffold was implanted in the right femur (experimental side), whereas the left femur was kept free of implantation (control side). Micro-CT analysis and histological observations of the bone defect site were conducted at 4, 8, and 12 weeks postoperatively to track the bone repair progress. No evidence of new bone tissue formation was found in the medullary cavity of the bone defect on the control side. In contrast, on the experimental side, the 3D scaffold demonstrated sufficient bioactivity, leading to the growth of new bone tissue. Over time, new bone tissue gradually extended from the periphery toward the center, a phenomenon evident in both micro-CT images and biopsy staining. In the current study, we observed that the cells involved in bone metabolism adhered, spread, and proliferated on our newly designed 3D-printed scaffold with a bone microstructure. Therefore, it is suggested that this scaffold has sufficient bioactivity to induce new bone formation and could be expected to be a more useful artificial bone than the existing version.

CB1 Promotes Osteogenic Differentiation Potential of Periodontal Ligament Stem Cells by Enhancing Mitochondrial Transfer of Bone Marrow Mesenchymal Stem Cells.

OBJECTIVE: To reveal the role and mechanism of cannabinoid receptor 1 (CB1) and mitochondria in promoting osteogenic differentiation of periodontal ligament stem cells (PDLSCs) in the inflammatory microenvironment. METHODS: Bidirectional mitochondrial transfer was performed in bone mesenchymal stem cells (BMSCs) and PDLSCs. Laser confocal microscopy and quantitative flow cytometry were used to observe the mitochondrial transfer and quantitative mitochondrial transfer efficiency. Realtime reverse transcription polymerase chain reaction (RT-PCR) was employed to detect gene expression. Alkaline phosphatase (ALP) activity, alizarin red staining (ARS) and quantitative calcium ion analysis were used to evaluate the degree of osteogenic differentiation of PDLSCs. RESULTS: Bidirectional mitochondrial transfer was observed between BMSCs and PDLSCs. The indirect co-culture system could simulate intercellular mitochondrial transfer. Compared with the conditioned medium (CM) for BMSCs, that for HA-CB1 BMSCs could significantly enhance the mineralisation ability of PDLSCs. The mineralisation ability of PDLSCs could not be enhanced after removing the mitochondria in CM for HA-CB1 BMSCs. The expression level of HO-1, PGC-1α, NRF-1, ND1 and HK2 was significantly increased in HA-CB1 BMSCs. CONCLUSION: CM for HA-CB1 BMSCs could significantly enhance the damaged osteogenic differentiation ability of PDLSCs in the inflammatory microenvironment, and the mitochondria of CM played an important role. CB1 was related to the activation of the HO-1/PGC-1α/NRF-1 mitochondrial biogenesis pathway, and significantly increased the mitochondrial content in BMSCs.

Thecal and Epithecal Ossifications of the Turtle Shell: Ontogenetic And Phylogenetic Aspects.

The problem of the origin of the bony shell in turtles has a two-century history and still has not lost its relevance. First, this concerns the issues of the homology, the sources of formation and the ratio of bones of different nature, that is, thecal and epithecal, in particular. This article analyzes various views on the nature of the shell elements, and proposes their typification, based on modern data on developmental biology. It is proposed that the defining characteristic of the types of shell ossifications is not the level of their anlage in the dermis (thecality or epithecality), but, first of all, the primary sources of their formation: (1) neural crest (nuchal and plastral plates); (2) vertebral and rib periosteum (neural and costal plates); and (3) dermal mesenchyme (peripheral, suprapygal and pygal plates, as well as epithecal elements). In addition, there is complete correspondence between these types of ossifications and the sequence of their appearance in the turtle ontogenesis. The data show fundamental coincidence of the modifications of the ontogenetic development and evolutionary formation of the shell ossifications and are in agreement with a stepwise model for the origin of the turtle body plan. Particular attention is paid to the origin of the epithecal elements of the turtle shell, which correspond to the additional or supernumerary ossifications and seem to have wider distribution among turtles, than previously thought.

Bone Regeneration Revolution: Pulsed Electromagnetic Field Modulates Macrophage-Derived Exosomes to Attenuate Osteoclastogenesis.

Introduction: In the process of bone regeneration, a prominent role is played by macrophages involved in both the initial inflammation and the regeneration/vascularization phases, due to their M2 anti-inflammatory phenotype. Together with osteoclasts, they participate in the degradation of the bone matrix if the inflammatory process does not end. In this complex scenario, recently, much attention has been paid to extracellular communication mediated by nanometer-sized vesicles, with high information content, called exosomes (EVs). Considering these considerations, the purpose of the present work is to demonstrate how the presence of a pulsed electromagnetic field (PEMF) can positively affect communication through EVs. Methods: To this aim, macrophages and osteoclasts were treated in vitro with PEMF and analyzed through molecular biology analysis and by electron microscopy. Moreover, EVs produced by macrophages were characterized and used to verify their activity onto osteoclasts. Results: The results confirmed that PEMF not only reduces the inflammatory activity of macrophages and the degradative activity of osteoclasts but that the EVS produced by macrophages, obtained from PEMF treatment, positively affect osteoclasts by reducing their activity. Discussion: The co-treatment of PEMF with M2 macrophage-derived EVs (M2-EVs) decreased osteoclastogenesis to a greater degree than separate treatments.

Mir-381-3p aggravates ovariectomy-induced osteoporosis by inhibiting osteogenic differentiation through targeting KLF5/Wnt/ß-catenin signaling pathway.

BACKGROUND: Increasing evidence shows the pivotal significance of miRNAs in the pathogenesis of osteoporosis. miR-381-3p has been identified as an inhibitor of osteogenesis. This study explored the role and mechanism of miR-381-3p in postmenopausal osteoporosis (PMOP), the most common type of osteoporosis. METHODS: Bilateral ovariectomy (OVX) rat model was established and miR-381-3p antagomir was administrated through the tail vein in vivo. The pathological changes in rats were assessed through the evaluation of serum bone turnover markers (BALP, PINP, and CTX-1), hematoxylin and eosin (H&E) staining, as well as the expression of osteoblast differentiation biomarkers. Moreover, isolated bone marrow mesenchymal stem cells from OVX-induced rats (OVX-BMMSCs) were utilized to explore the impact of miR-381-3p on osteoblast differentiation. In addition, the target gene and downstream pathway of miR-381-3p were further investigated both in vivo and in vitro. RESULTS: miR-381-3p expression was elevated, whereas KLF5 was suppressed in OVX rats. miR-381-3p antagomir decreased serum levels of bone turnover markers, improved trabecular separation, promoted osteoblast differentiation biomarker expression in OVX rats. ALP activity and mineralization were suppressed, and levels of osteoblast differentiation biomarkers were impeded after miR-381-3p overexpression during osteoblast differentiation of OVX-BMMSCs. While contrasting results were found after inhibition of miR-381-3p. miR-381-3p targets KLF5, negatively affecting its expression as well as its downstream Wnt/ß-catenin pathway, both in vivo and in vitro. Silencing of KLF5 restored Wnt/ß-catenin activation induced by miR-381-3p antagomir. CONCLUSION: miR-381-3p aggravates PMOP by inhibiting osteogenic differentiation through targeting KLF5/Wnt/ß-catenin pathway. miR-381-3p appears to be a promising candidate for therapeutic intervention in PMOP.

USP36 regulates the proliferation, survival, and differentiation of hFOB1.19 osteoblast.

BACKGROUND: Effective bone formation relies on osteoblast differentiation, a process subject to intricate post-translational regulation. Ubiquitin-specific proteases (USPs) repress protein degradation mediated by the ubiquitin-proteasome pathway. Several USPs have been documented to regulate osteoblast differentiation, but whether other USPs are involved in this process remains elusive. METHODS: In this study, we conducted a comparative analysis of 48 USPs in differentiated and undifferentiated hFOB1.19 osteoblasts, identifying significantly upregulated USPs. Subsequently, we generated USP knockdown hFOB1.19 cells and evaluated their osteogenic differentiation using Alizarin red staining. We also assessed cell viability, cell cycle progression, and apoptosis through MTT, 7-aminoactinomycin D staining, and Annexin V/PI staining assays, respectively. Quantitative PCR and Western blotting were employed to measure the expression levels of osteogenic differentiation markers. Additionally, we investigated the interaction between the USP and its target protein using co-immunoprecipitation (co-IP). Furthermore, we depleted the USP in hFOB1.19 cells to examine its effect on the ubiquitination and stability of the target protein using immunoprecipitation (IP) and Western blotting. Finally, we overexpressed the target protein in USP-deficient hFOB1.19 cells and evaluated its impact on their osteogenic differentiation using Alizarin red staining. RESULTS: USP36 is the most markedly upregulated USP in differentiated hFOB1.19 osteoblasts. Knockdown of USP36 leads to reduced viability, cell cycle arrest, heightened apoptosis, and impaired osteogenic differentiation in hFOB1.19 cells. USP36 interacts with WD repeat-containing protein 5 (WDR5), and the knockdown of USP36 causes an increased level of WDR5 ubiquitination and accelerated degradation of WDR5. Excessive WDR5 improved the impaired osteogenic differentiation of USP36-deficient hFOB1.19 cells. CONCLUSIONS: These observations suggested that USP36 may function as a key regulator of osteoblast differentiation, and its regulatory mechanism may be related to the stabilization of WDR5.

Autophagy Regulates Age-Related Jawbone Loss via LepR+ Stromal Cells.

Bone aging and decreased autophagic activity are related but poorly explored in the jawbone. This study aimed to characterize the aging jawbones and jawbone-derived stromal cells (JBSCs) and determine the role of autophagy in jawbone mass decline. We observed that the jawbones of older individuals and mice exhibited similar age-related bone loss. Furthermore, leptin receptor (LepR)-lineage cells served as the primary source for in vitro cultured and expanded JBSCs, referred to as LepR-Cre+/JBSCs. RNA-sequencing data from the jawbones and LepR-Cre+/JBSCs showed the upregulated expression of the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) pathway during aging. Through single-cell transcriptomics, we identified a decrease in the proportion of osteogenic lineage cells and the activation of the PI3K/AKT pathway in LepR-lineage cells in aging bone tissues. Reduced basal autophagic activity, diminished autophagic flux, and decreased osteogenesis occurred in the jawbones and LepR-Cre+/JBSCs from older mice (O-mice; O-JBSCs). Pharmacologic and constitutive autophagy activation alleviated the impaired osteogenesis in O-JBSCs. In addition, the suppression of mTOR-induced autophagy improved the aging phenotype of O-JBSCs. The activation of autophagy in LepR-Cre+/JBSCs using chemical autophagic activators reduced the alveolar bone resorption in O-mice. Therefore, our study demonstrated that ATG molecules and pathways are crucial in jawbone aging, providing novel approaches to understanding age-related jawbone loss.

KAT6A/YAP/TEAD4 pathway modulates osteoclastogenesis by regulating the RANKL/OPG ratio on the compression side during orthodontic tooth movement.

BACKGROUND: Orthodontic tooth movement (OTM) is a dynamic equilibrium of bone remodeling, involving the osteogenesis of new bone and the osteoclastogenesis of old bone, which is mediated by mechanical force. Periodontal ligament stem cells (PDLCSs) in the periodontal ligament (PDL) space can transmit mechanical signals and regulate osteoclastogenesis during OTM. KAT6A is a histone acetyltransferase that plays a part in the differentiation of stem cells. However, whether KAT6A is involved in the regulation of osteoclastogenesis by PDLSCs remains unclear. RESULTS: In this study, we used the force-induced OTM model and observed that KAT6A was increased on the compression side of PDL during OTM, and also increased in PDLSCs under compression force in vitro. Repression of KAT6A by WM1119, a KAT6A inhibitor, markedly decreased the distance of OTM. Knockdown of KAT6A in PDLSCs decreased the RANKL/OPG ratio and osteoclastogenesis of THP-1. Mechanistically, KAT6A promoted osteoclastogenesis by binding and acetylating YAP, simultaneously regulating the YAP/TEAD axis and increasing the RANKL/OPG ratio in PDLSCs. TED-347, a YAP-TEAD4 interaction inhibitor, partly attenuated the elevation of the RANKL/OPG ratio induced by mechanical force. CONCLUSION: Our study showed that the PDLSCs modulated osteoclastogenesis and increased the RANKL/OPG ratio under mechanical force through the KAT6A/YAP/TEAD4 pathway. KAT6A might be a novel target to accelerate OTM.

Bone and entheseal targets for growth factors in diffuse idiopathic skeletal hyperostosis.

INTRODUCTION: Diffuse idiopathic skeletal hyperostosis (DISH) is a common condition of the adult skeleton where new bone growth occurs in entheseal and bony regions. The cause for the new bone growth is unclear but many lines of evidence point to a role for growth factors linked to abnormal metabolism in these patients. The bone targets for these presumed growth factors are poorly defined. This review summarises the clinical evidence relevant to the sites of origin of new bone formation in DISH to better define potential cellular targets for bone growth in DISH. METHODS: This is a narrative review of relevant papers identified from searches of PubMed and online journals. RESULTS: Sites of new bone growth in the enthesis were identified in patients with DISH, with likely cellular targets for growth factors being mesenchymal stem cells in the outer part of the enthesis. Similar undifferentiated skeletal stem cells are present in the outer annulus fibrosis and in the bony eminences of vertebral bodies and other bones, with the potential for response to growth factors. CONCLUSION: Mesenchymal stem cells are present in specific entheseal and bony locations that are likely responsive to putative growth factors leading to new bone formation characteristic of DISH. Further study of these regions in the context of metabolic abnormalities in DISH will allow for better understanding of the pathophysiology of this common condition.

A new insight for investigating the prenatal and postnatal ossification centers of pelvic and femur bones in white New Zealand rabbits (Oryctolagus cuniculus) using 3D CT, double stain technique, and morphometry.

BACKGROUND: The ossification centers in rabbit limbs are related to fetal age and bone maturation. OBJECTIVE: To address the limited studies on ossification in the hind limbs of New Zealand rabbits, we investigated the prenatal and postnatal development of the pelvic and femur bones. METHODS: Double staining with Alcian Blue and Alizarin Red, computed tomography (CT), and 3D reconstruction were employed to visualize and analyze ossification centers in detail. RESULTS: Using double staining, we observed these patterns: At prenatal days 18 and 21, ossification centers appeared in the ilium. By prenatal days 23 and 25, ossification began in the ischium. On postnatal day 1, ilium ossification centers spread across most of the ilium wings, except for the iliac crest, and new centers appeared in the pubis and cotyloid bones. Most bones had ossified by the third week and one month postnatal, except for the iliac crest and ischial tuberosity. At 1.5 months, both were fully ossified. On day 18 post coitum, an ossification center was visible in the middle of the femur shaft. By day 28 post coitum, ossification extended through the shaft, and postnatally, new ossification spots appeared at the extremities by day one and week one. By the third week, complete ossification of the femur head, lesser trochanter, third trochanter, medial condyle, and lateral condyle was observed. At 1.5 months, the entire proximal extremity was ossified. CONCLUSION: 3D CT provided clear imaging of ossification progression in the pelvic and femur bones. This study enhances our understanding of vertebrate skeletal development.

CCKR signaling map, G-Protein bindings, hormonal regulation, and neural mechanisms may influence the osteogenic/cementogenic differentiation potential of hPDLSCs.

OBJECTIVE: Periodontal regeneration poses challenges due to the periodontium's complexity, relying on mesenchymal cells from the periodontal ligament (hPDLSCs) to regenerate hard tissues like bone and cementum. While some hPDLSCs have high regeneration potential (HOP-hPDLSCs), most are low potential (LOP-hPDLSCs). This study analyzed hPDLSCs from a single donor to minimize inter-individual variability and focus on key differences in differentiation potentials. DESIGN: This study used RNA-seq, genomic databases, and bioinformatics tools to explore signaling pathways (SPs), biological processes (BPs), and molecular functions (MFs) guiding HOP cells to mineralized matrix production. It also investigated limitations of LOP cells and strategies for enhancing their osteo/cementogenesis. RESULTS: In basal conditions, HOP exhibited a multifunctional gene network with higher expression of genes related to osteo/cementogenesis, cell differentiation, immune modulation, stress response, and hormonal regulation. In contrast, LOP focused on steroid hormone biosynthesis and nucleic acid maintenance. During osteo/cementogenic induction, HOP showed strong modulation of genes related to angiogenesis, cell division, mesenchymal differentiation, and extracellular matrix production. LOP demonstrated neural synaptic-related processes and preserved cellular cytoskeleton integrity. CCKR map signaling and G-protein receptor bindings gained significance during osteo/cementogenesis in HOP-hPDLSCs. Both HOP and LOP shared common BPs related to gastrointestinal and reproductive system development. CONCLUSION: The osteo/cementogenic differentiation of HOP cells may be regulated by CCKR signaling, G-protein bindings, and specific hormonal regulation. LOP cells seem committed to neural mechanisms. This study sheds light on hPDLSCs' complex characteristics, offering a deeper understanding of their differentiation potential for future periodontal regeneration research and therapies.

Developing long bones respond to surrounding tissues by trans-pairing of periosteal osteoclasts and endocortical osteoblasts.

Developing long bones alter their shape while maintaining uniform cortical thickness via coordinated activity of bone-forming osteoblasts and bone-resorbing osteoclasts at periosteal and endosteal surfaces, a process we designate trans-pairing. Two types of trans-pairing shift cortical bone in opposite orientations: peri-forming trans-pairing (peri-t-p) increases bone marrow space and endo-forming trans-pairing (endo-t-p) decreases it, via paired activity of bone resorption and formation across the cortex. Here, we focused on endo-t-p in growing bones. Analysis of endo-t-p activity in the cortex of mouse fibulae revealed osteoclasts under the periosteum compressed by muscles, and expression of RANKL in periosteal cells of the cambium layer. Furthermore, mature osteoblasts were localized on the endosteum, while preosteoblasts were at the periosteum and within cortical canals. X-ray tomographic microscopy revealed the presence of cortical canals more closely associated with endo- than with peri-t-p. Sciatic nerve transection followed by muscle atrophy and unloading induced circumferential endo-t-p with concomitant spread of cortical canals. Such canals likely supply the endosteum with preosteoblasts from the periosteum under endo-t-p, allowing bone shape to change in response to mechanical stress or nerve injury.