BMP signalling in skeletal development, disease and repair

Structural extracellular matrix-mediated molecular signaling in wound repair and tissue regeneration

The extracellular matrix (ECM) is a complex, non-cellular network of molecules that offers structural support for cells and tissues. The ECM is composed of various structural components, including collagen, fibronectin, laminin, perlecan, nidogen, tenascin, and fibulin, which are capable of binding to each other and to cell-to-adhesion receptors, endowing the ECM with unique physical and biochemical properties that are essential for its function in maintaining health and managing disease. Over the past three decades, extensive research has shown that the core of the ECM can significantly impact cellular events at the molecular level. Structural modifications have also been strongly associated with tissue repair. Through interactions with cells, matrix proteins regulate critical processes such as cell proliferation and differentiation, migration, and apoptosis, essential for maintaining tissue homeostasis, formation, and regeneration. This review emphasizes the interlocking networks of ECM macromolecules and their primary roles in tissue regeneration and wound repair. Through studying ECM dynamics, researchers have discovered molecular signaling pathways that demonstrate how the ECM influences protein patterns and open up more possibilities for developing therapeutics that target the ECM to enhance wound repair and tissue regeneration.

Nanoclay gels attenuate BMP2-associated inflammation and promote chondrogenesis to enhance BMP2-spinal fusion

Bone morphogenetic protein 2 (BMP2) is clinically applied for treating intractable fractures and promoting spinal fusion because of its osteogenic potency. However, adverse effects following the release of supraphysiological doses of BMP2 from collagen carriers are widely reported. Nanoclay gel (NC) is attracting attention as a biomaterial, given the potential for localized efficacy of administered agents. However, the efficacy and mechanism of action of NC/BMP2 remain unclear. This study explored the efficacy of NC as a BMP2 carrier in bone regeneration and the enhancement mechanism. Subfascial implantation of NC containing BMP2 elicited superior bone formation compared with collagen sponge (CS). Cartilage was uniformly formed inside the NC, whereas CS formed cartilage only on the perimeter. Additionally, CS induced a dose-dependent inflammatory response around the implantation site, whereas NC induced a minor response, and inflammatory cells were observed inside the NC. In a rat spinal fusion model, NC promoted high-quality bony fusion compared to CS. In vitro, NC enhanced chondrogenic and osteogenic differentiation of hBMSCs and ATDC5 cells while inhibiting osteoclastogenesis. Overall, NC/BMP2 facilitates spatially controlled, high-quality endochondral bone formation without BMP2-induced inflammation and promotes high-density new bone, functioning as a next-generation BMP2 carrier.

Polydopamine grafting polyether ether ketone to stabilize growth factor for efficient osteonecrosis repair

This study examines the biocompatibility, osteogenic potential, and effectiveness of polyether ether ketone (PEEK) composites for treating osteonecrosis, seeking to establish a theoretical basis for clinical application. A range of PEEK composite materials, including sulfonated polyether ether ketone (SPEEK), polydopamine-sulfonated polyether ether ketone (SPEEK-PDA), bone-forming peptide-poly-dopamine-sulfonated polyether ether ketone (SPEEK-PDA-BFP), and vascular endothelial growth factor-poly-dopamine-sulfonated polyether ether ketone (SPEEK-PDA-VEGF), were constructed by concentrated sulfuric acid sulfonation, polydopamine modification and grafting of bioactive factors. The experiments involved adult male New Zealand rabbits aged 24-28 weeks and weighing 2.6-4 kg. The SPEEK-PDA-BFP possesses the smallest water contact angle, indicating the highest hydrophilicity, with its surface characterized by a rich density of clustered BFP particles. The SPEEK-PDA-BFP exhibits superior adhesion, proliferation, and differentiation capabilities, along with pronounced bacteriostatic effects, which are attributed to its dense particle clusters. The SPEEK-PDA-BFP facilitates the formation of regular and dense bone trabeculae. Comparative study on treating osteonecrosis with SPEEK-PDA-VEGF and SPEEK-PDA-BFP highlighted the superior formation of mature bone trabeculae and angiogenic protein CD31 around SPEEK-PDA-VEGF. The PEEK composite materials have good biocompatibility, osteogenic activity and bone repair activity. In particular, SPEEK-PDA-VEGF composite materials have the best effect on bone repair.

Osteogenic Effects of Bioactive Compounds Found in Fruits on Mesenchymal Stem Cells: A Review

Phytochemicals, which are bioactive compounds contained in fruits, vegetables, and teas, have a positive effect on human health by having anti-inflammatory, antioxidant, and anticarcinogenic effects. Several studies have highlighted the ability of bioactive compounds to activate key cellular enzymes associated with important signaling pathways related to cell division and proliferation, as well as their role in inflammatory and immunological responses. Some phytochemicals are associated with increased proliferation, differentiation, and expression of markers related to osteogenesis, bone formation, and mineralization by activating various signaling pathways. The objective of this study was to clarify which bioactive compounds present in fruits have osteogenic effects on mesenchymal stem cells and the possible associated mechanisms. A literature search was conducted in the LILACS, MEDLINE, and PubMed databases for pertinent articles published between 2014 and 2024. This review included 34 articles that report the osteogenic effects of various bioactive compounds found in different fruits. All the articles reported that phytochemicals play a role in enhancing the regenerative properties of mesenchymal cells, such as proliferation, osteogenic differentiation, secretion of angiogenic factors, and extracellular matrix formation. This review highlights the potential of these phytochemicals in the prevention and treatment of bone diseases. However, more studies are recommended to identify and quantify the therapeutic dose of phytochemicals, investigate their mechanisms in humans, and ensure their safety and effectiveness for health, particularly for bone health.

Hierarchy Reproduction: Multiphasic Strategies for Tendon/Ligament-Bone Junction Repair

Tendon/ligament-bone junctions (T/LBJs) are susceptible to damage during exercise, resulting in anterior cruciate ligament rupture or rotator cuff tear; however, their intricate hierarchical structure hinders self-regeneration. Multiphasic strategies have been explored to fuel heterogeneous tissue regeneration and integration. This review summarizes current multiphasic approaches for rejuvenating functional gradients in T/LBJ healing. Synthetic, natural, and organism-derived materials are available for in vivo validation. Both discrete and gradient layouts serve as sources of inspiration for organizing specific cues, based on the theories of biomaterial topology, biochemistry, mechanobiology, and in situ delivery therapy, which form interconnected network within the design. Novel engineering can be constructed by electrospinning, 3-dimensional printing, bioprinting, textiling, and other techniques. Despite these efforts being limited at present stage, multiphasic scaffolds show great potential for precise reproduction of native T/LBJs and offer promising solutions for clinical dilemmas.

Phlorofucofuroeckol-A: A Natural Compound with Potential to Attenuate Inflammatory Diseases Caused by Airborne Fine Dust

Background and Objectives: Persistent exposure to airborne fine dust (FD) particles contributing to air pollution has been linked to various human health issues, including respiratory inflammation, allergies, and skin diseases. We aimed to identify potential seaweed anti-inflammatory bioactive reagents and determine their effects on systemic inflammatory responses induced by FD particles. Materials and Methods: While exploring anti-inflammatory bioactive reagents, we purified compounds with potential anti-inflammatory effects from the seaweed extracts of Ecklonia cava, Ecklonia stolonifera, and Codium fragile. Structural analyses of the purified compounds siphonaxanthin (Sx), fucoxanthin (Fx), dieckol (Dk), and phlorofucofuroeckol-A (PFF-A) were performed using NMR and LC-MS/MS. Results: Notably, these compounds, especially PFF-A, showed significant protective effects against FD-induced inflammatory responses in RAW 264.7 cells without cytotoxicity. Further investigation of inflammatory-associated signaling demonstrated that PFF-A inhibited IL-1β expression by modulating the NF-κB/MAPK signal pathway in FD-induced RAW 264.7 cells. Additionally, gene profiling revealed the early activation of various signature genes involved in the production of inflammatory cytokines and chemokines using gene profiling. Treatment with PFF-A markedly reduced the expression levels of pro-inflammatory and apoptosis-related genes and even elevated the Bmp gene families. Conclusions: These results suggested that PFF-A is a potential natural therapeutic candidate for managing FD-induced inflammatory response.

Developing a ceRNA-based lncRNA-miRNA-mRNA regulatory network to uncover roles in skeletal muscle development

The precise role of lncRNAs in skeletal muscle development and atrophy remain elusive. We conducted a bioinformatic analysis of 26 GEO datasets from mouse studies, encompassing embryonic development, postnatal growth, regeneration, cell proliferation, and differentiation, using R and relevant packages (limma et al.). LncRNA-miRNA relationships were predicted using miRcode and lncBaseV2, with miRNA-mRNA pairs identified via miRcode, miRDB, and Targetscan7. Based on the ceRNA theory, we constructed and visualized the lncRNA-miRNA-mRNA regulatory network using ggalluvial among other R packages. GO, Reactome, KEGG, and GSEA explored interactions in muscle development and regeneration. We identified five candidate lncRNAs (Xist, Gas5, Pvt1, Airn, and Meg3) as potential mediators in these processes and microgravity-induced muscle wasting. Additionally, we created a detailed lncRNA-miRNA-mRNA regulatory network, including interactions such as lncRNA Xist/miR-126/IRS1, lncRNA Xist/miR-486-5p/GAB2, lncRNA Pvt1/miR-148/RAB34, and lncRNA Gas5/miR-455-5p/SOCS3. Significant signaling pathway changes (PI3K/Akt, MAPK, NF-κB, cell cycle, AMPK, Hippo, and cAMP) were observed during muscle development, regeneration, and atrophy. Despite bioinformatics challenges, our research underscores the significant roles of lncRNAs in muscle protein synthesis, degradation, cell proliferation, differentiation, function, and metabolism under both normal and microgravity conditions. This study offers new insights into the molecular mechanisms governing skeletal muscle development and regeneration.

Integrated GelMA and liposome composite hydrogel with effective coupling of angiogenesis and osteogenesis for promoting bone regeneration

In clinical scenarios, bone defects stemming from trauma, infections, degenerative diseases, or hereditary conditions necessitate considerable bone grafts. Researchers ardently focus on creating diverse biomaterials to expedite and enhance these intricate restorative processes. These biomaterials play a pivotal role in aiding osteogenesis and angiogenesis factors for reconstructing stable, fully developed bone tissue. We observed the utilization of Desferoxamine (DFO) facilitated angiogenesis, thereby enabling Kartogenin (KGN) to activate the β-catenin/Runx-2 pathway. Our study introduces a composite hydrogel loaded with KGN and DFO via liposomes to enhance the coupling of angiogenesis and osteogenesis. Within this composite hydrogel system, KGN and DFO undergo effective release. This controlled release substantially promotes a conducive microenvironment for angiogenesis and osteogenesis. Our in vitro studies provide compelling evidence of the synergistic impact between KGN and DFO on osteogenic processes. Moreover, the composite hydrogel exhibits the capability to enhance the expression of proteins and genes associated with both angiogenesis and osteogenesis. In rat skull defect model, the composite hydrogel notably stimulates vascularization and osteogenic differentiation without infection or mortality. In summary, results underscore the potential of this composite hydrogel as an alternative to autografts for bone defect repair, offering a promising approach for future clinical and regenerative applications.

Multifunctional electrospinning periosteum: Development status and prospect

In the repair of large bone defects, loss of the periosteum can result in diminished osteoinductive activity, nonunion, and incomplete regeneration of the bone structure, ultimately compromising the efficiency of bone regeneration. Therefore, the research and development of tissue-engineered periosteum which can replace the periosteum function has become the focus of current research. The functionalized electrospinning periosteum is expected to mimic the natural periosteum and enhance bone repair processes more effectively. This review explores the construction strategies for functionalized electrospun periosteum from the following perspectives: ⅰ) bioactive factor modification (bone morphogenetic protein-2 (BMP-2), vascular endothelial growth factor (VEGF) etc.), ⅱ) inorganic compound modification, ⅲ) drug modification, ⅳ) artificial periosteum in response to physical stimuli. Furthermore, the construction of artificial periosteum through electrospinning, in conjunction with other strategies, is also analyzed. Finally, the current challenges and prospects for the development of electrospinning periosteum are also discussed.

Discoidin domain receptor 2 is an important modulator of BMP signaling during heterotopic bone formation

Bone morphogenetic proteins are essential for bone regeneration/fracture healing but can also induce heterotopic ossification (HO). Understanding accessory factors modulating BMP signaling would provide both a means of enhancing BMP-dependent regeneration while preventing HO. This study focuses on the ability of the collagen receptor, discoidin domain receptor 2 (DDR2), to regulate BMP activity. As will be shown, induction of bone formation by subcutaneous BMP2 implants is severely compromised in Ddr2-deficient mice. In addition, Ddr2 deficiency attenuates HO in mice expressing the ACVR1 mutation associated with human fibrodysplasia ossificans progressiva. In cells migrating into BMP2 implants, DDR2 is co-expressed with GLI1, a skeletal stem cell marker, and DDR2/GLI1-positive cells participate in BMP2-induced bone formation where they contribute to chondrogenic and osteogenic lineages. Consistent with this distribution, conditional knockout of Ddr2 in Gli1-expressing cells inhibited bone formation to the same extent seen in globally Ddr2-deficient animals. This response was explained by selective inhibition of Gli1+ cell proliferation without changes in apoptosis. The basis for this DDR2 requirement was explored further using bone marrow stromal cells. Although Ddr2 deficiency inhibited BMP2-dependent chondrocyte and osteoblast differentiation and in vivo, bone formation, early BMP responses including SMAD phosphorylation remained largely intact. Instead, Ddr2 deficiency reduced the nuclear/cytoplasmic ratio of the Hippo pathway intermediates, YAP and TAZ. This suggests that DDR2 regulates Hippo pathway-mediated responses to the collagen matrix, which subsequently affect BMP responsiveness. In summary, DDR2 is an important modulator of BMP signaling and a potential therapeutic target both for enhancing regeneration and treating HO.

Palovarotene (Sohonos), a synthetic retinoid for reducing new heterotopic ossification in fibrodysplasia ossificans progressiva: history, present, and future

Retinoids are metabolic derivatives of vitamin A and play crucial roles in the regulation of various tissues and organs during prenatal and postnatal development. Active retinoids, like all-trans-retinoic acid, are synthesized in the cytoplasm and subsequently interact with nuclear retinoic acid receptors (RARα, RARβ, and RARγ) to enhance transcription of specific genes. In the absence of retinoids, RARs can still bind to response elements of target genes but repress their transcription. Chondrogenic cell differentiation and cartilage maturation in the growth plate require the absence of retinoid signaling and transcriptional repression by unliganded RARs. This led to the hypothesis that synthetic retinoid agonists may be pharmacological agents to inhibit those cellular processes and counter the excessive formation of cartilage and bone in conditions like heterotopic ossification (HO). HO can be instigated by diverse culprits including trauma, invasive surgeries, inflammatory disorders, or genetic conditions. One such genetic disease is fibrodysplasia ossificans progressiva (FOP), a rare disorder driven by activating mutations in the ACVR1 gene. Patients with FOP have severe and progressive HO formation in soft tissues, leading to extensive permanent loss of mobility and increased mortality. Synthetic retinoid agonists selective for RARα or RARγ showed efficacy against injury-induced and genetic HO in mouse models. The RARγ agonists showed the highest effectiveness, with palovarotene being selected for clinical trials in patients with FOP. Post hoc analyses of phase II and phase III clinical trials showed that palovarotene has significant disease-modifying effects for FOP, but with significant risks such as premature growth plate closure in some younger subjects. This review provides an overview of retinoid and RAR roles in skeletal development and discusses the identification of palovarotene as a potential FOP therapy, the clinical data supporting its regulatory approval in some countries, and the potential applications of this drug for other relevant disorders besides FOP.

Advances in meniscus tissue engineering: Towards bridging the gaps from bench to bedside

Meniscus is vital for maintaining the anatomical and functional integrity of knee. Injuries to meniscus, commonly caused by trauma or degenerative processes, can result in knee joint dysfunction and secondary osteoarthritis, while current conservative and surgical interventions for meniscus injuries bear suboptimal outcomes. In the past decade, there has been a significant focus on advancing meniscus tissue engineering, encompassing isolated scaffold strategies, biological augmentation, physical stimulus, and meniscus organoids, to improve the prognosis of meniscus injuries. Despite noteworthy promising preclinical results, translational gaps and inconsistencies in the therapeutic efficiency between preclinical and clinical studies exist. This review comprehensively outlines the developments in meniscus tissue engineering over the past decade (Scheme 1). Reasons for the discordant results between preclinical and clinical trials, as well as potential strategies to expedite the translation of bench-to-bedside approaches are analyzed and discussed.

Exploring the role of peripheral nerves in trauma-induced heterotopic ossification

Recent studies have linked pain and the resultant nociception-induced neural inflammation (NINI) to trauma-induced heterotopic ossification (THO). It is postulated that nociception at the injury site stimulates the transient receptor potential vanilloid-1 (the transient receptor potential cation channel subfamily V member 1) receptors on sensory nerves within the injured tissues resulting in the expression of neuroinflammatory peptides, substance P (SP), and calcitonin gene-related peptide (CGRP). Additionally, BMP-2 released from fractured bones and soft tissue injury also selectively activates TRVP1 receptors, resulting in the release of SP and CGRP and causing neuroinflammation and degranulation of mast cells causing the breakdown the blood-nerve barrier (BNB), leading to release of neural crest derived progenitor cells (NCDPCs) into the injured tissue. Parallel to this process BMP-2 initiates the NCDPCs toward osteogenic differentiation. CGRP has direct osteogenic effects on osteoprogenitor cells/mesenchymal stem cells, by activating BMP-2 via canonical Wnt/β-catenin signaling and cAMP-cAMP-response element binding protein signaling. BMP-2 binds to TGF-βRI and activates TGF-β-activated kinase 1 (TAK1) leading to phosphorylation of SMAD1/5/8, which binds to the co-activator SMAD4 and translocates to the nucleus to serve as transcription factor for BMP responsive genes critical in osteogenesis such as Runx2 and others. Thus, NINI phenotypes, and specifically CGRP induction, play a crucial role in THO initiation and progression through the activation of the BMP pathway, breakdown of the BNB, leading to the escape of NCDPCs, and the osteogenic differentiation of the latter.

An overview of recent progress in the molecular mechanisms and key biological macromolecules involved in limb regeneration of decapods

Understanding the molecular mechanisms of limb regeneration in decapods can significantly enhance aquaculture production by improving survival and growth, as well as facilitating the development of lab-grown crustacean meat as a sustainable protein source. This review explores the molecular mechanisms of decapod limb regeneration, focusing on the key signaling pathways, genes, and proteins involved in this process. The initial stages of regeneration involve immune response and hemolymph coagulation, which are regulated via signaling pathways such as Toll, MAPK, IMD, and JAK/STAT. Subsequent stages, including blastema formation and limb growth, are regulated by signaling pathways such as Wnt, Hippo, Hedgehog, Ecdysteroid, TGF-β, Notch, Insulin-like, Fibroblast Growth Factor, Epidermal Growth Factor, and BMP. This review also discusses the interplay among environmental factors, nutrition, and hormonal signaling in regeneration and how these elements influence regenerative capability. Furthermore, this review highlights existing research gaps in decapod regeneration and suggests future research directions. This review aims to bridge existing gaps in decapod regeneration research and guide future studies toward potential breakthroughs in aquaculture practices.

Hydrolyzed egg yolk peptide alleviates ovariectomy-induced osteoporosis by regulating lipid metabolism

Osteoporosis is a systemic, progressive bone disease that causes metabolic disorders. Previous study identified the preventive effects of hydrolyzed egg yolk peptide (YPEP) on osteoporosis. However, the underlying antiosteoporosis mechanism remains unclear. Herein, 30 female rats were randomly divided into 5 groups (n = 6), including the sham, OVX, E2 (25 μg/kg/d 17β-estradiol), LYPEP (10 mg/kg/d YPEP), and HYPEP (40 mg/kg/d YPEP) groups. YPEP treatment significantly changed bone turnover marker levels and prevented the deterioration of bone structure and strength caused by ovariectomy. YPEP supplementation significantly changed endogenous metabolites related to lipid metabolism in the serum of ovariectomized rats, identifying 46 metabolites closely linked to bone biomarkers. Additionally, YPEP reduced the expression of the lipid metabolism-related protein peroxisome proliferator-activated receptor PPARγ and increased the expression of bone formation proteins BMP2 and RUNX2. Collectively, these results elucidated that YPEP improves osteoporosis by inhibiting lipogenesis to promote bone formation. This study provides novel evidence for the use of YPEP in treating osteoporosis.

Comprehensive Overview of Interface Strategies in Implant Osseointegration

With the improvement of implant design and the expansion of application scenarios, orthopedic implants have become a common surgical option for treating fractures and end‐stage osteoarthritis. Their common goal is rapidly forming and long‐term stable osseointegration. However, this fixation effect is limited by implant surface characteristics and peri‐implant bone tissue activity. Therefore, this review summarizes the strategies of interface engineering (osteogenic peptides, growth factors, and metal ions) and treatment methods (porous nanotubes, hydrogel embedding, and other load‐release systems) through research on its biological mechanism, paving the way to achieve the adaptation of both and coordination between different strategies. With the transition of the osseointegration stage, interface engineering strategies have demonstrated varying therapeutic effects. Especially, the activity of osteoblasts runs almost through the entire process of osseointegration, and their physiological activities play a dominant role in bone formation. Furthermore, diseases impacting bone metabolism exacerbate the difficulty of achieving osseointegration. This review aims to assist future research on osseointegration engineering strategies to improve implant‐bone fixation, promote fracture healing, and enhance post‐implantation recovery.

ARF alters PAF1 complex integrity to selectively repress oncogenic transcription programs upon p53 loss

The polymerase associated factor 1 (PAF1) complex (PAF1c) promotes RNA polymerase II (RNA Pol II) transcription at the elongation step; however, how PAF1c transcription activity is selectively regulated during cell fate transitions remains poorly understood. Here, we reveal that the alternative reading frame (ARF) tumor suppressor operates at two levels to restrain PAF1c-dependent oncogenic transcriptional programs upon p53 loss in mouse cells. First, ARF assembles into homo-oligomers to bind the PAF1 subunit to promote PAF1c disassembly, consequently dampening PAF1c interaction with RNA Pol II and PAF1c-dependent transcription. Second, ARF targets the RUNX family transcription factor 1 (RUNX1) to selectively tune gene transcription. Consistently, ARF loss triggers RUNX1- and PAF1c-dependent transcriptional activation of pro-growth ligands (growth differentiation factor/bone morphogenetic protein [GDF/BMP]), promoting a cell-intrinsic GDF/BMP-Smad1/5 axis that aberrantly induce cell growth. Notably, pharmacologic inactivation of GDF/BMP signaling and genetic perturbation of RUNX1 significantly attenuate cell proliferation mediated by dual p53 and ARF loss, offering therapeutic utility. Our data underscore the significance of selective ARF-mediated tumor-suppressive functions through a universal transcriptional regulator.

Concrete-Inspired Bionic Bone Glue Repairs Osteoporotic Bone Defects by Gluing and Remodeling Aging Macrophages

Osteoporotic fractures are characterized by abnormal inflammation, deterioration of the bone microenvironment, weakened mechanical properties, and difficulties in osteogenic differentiation. The chronic inflammatory state characterized by aging macrophages leads to delayed or non-healing of the fracture or even the formation of bone defects. The current bottleneck in clinical treatment is to achieve strong fixation of the comminuted bone fragments and effective regulation of the complex microenvironment of aging macrophages. Inspired by cement and gravel in concrete infrastructure, a biomimetic bone glue with poly(lactic-co-glycolic acid) microspheres is developed and levodopa/oxidized chitosan hydrogel stabilized on an organic-inorganic framework of nanohydroxyapatite, named DOPM. DOPM is characterized via morphological and mechanical characterization techniques, in vitro experiments with bone marrow mesenchymal stromal cells, and in vivo experiments with an aged SD rat model exhibiting osteoporotic bone defects. DOPM exhibited excellent adhesion properties, good biocompatibility, and significant osteogenic differentiation. Transcriptomic analysis revealed that DOPM improved the inflammatory microenvironment by inhibiting the NF-κB signaling pathway and promoting aging macrophage polarization toward M2 macrophages, thus significantly accelerating bone defect repair and regeneration. This biomimetic bone glue, which enhances osteointegration and reestablishes the homeostasis of aging macrophages, has potential applications in the treatment of osteoporotic bone defects.

Association of serum alkaline phosphatase levels with bone mineral density, osteoporosis prevalence, and mortality in US adults with osteoporosis: evidence from NHANES 2005-2018

This study examined the association of serum total alkaline phosphatase (T-ALP) with bone mineral density (BMD) and osteoporosis prevalence in the general population, and investigated its association with mortality in individuals with osteoporosis, using data from the National Health and Nutrition Examination Survey (NHANES) between 2005 and 2018. Elevated serum T-ALP levels were significantly associated with both reduced BMD and an increased risk of osteoporosis in all participants. Moreover, elevated T-ALP levels were linked to higher all-cause mortality among individuals with osteoporosis during this period.

INTRODUCTION

The evidence regarding the association between serum T-ALP, BMD and osteoporosis prevalence in general population is incomplete, and limited evidence is available concerning its association with mortality among individuals with osteoporosis. The study investigated the association of serum T-ALP with BMD and osteoporosis prevalence in the general population, and examined its association with mortality in individuals with osteoporosis.

METHODS

All participants were adults from the NHANES (2005-2018), and mortality data were obtained from the National Death Index up to December 31, 2019. Firstly, the association of serum T-ALP with BMD and osteoporosis risk was assessed using linear regression model, subgroup analysis, analysis of covariance and weighted logistic regression model, respectively. Secondly, survival analysis including Kaplan-Meier curves, Cox proportional hazards models, and restricted cubic spline regression models were utilized to analyze the relationship between serum T-ALP levels and mortality risk.

RESULTS

The study included 13,724 participants aged 18 to 85 years, and 944 were diagnosed with osteoporosis, among whom 221 died during a median of 133 months follow-up. Totally, elevated serum T-ALP was significantly associated with low BMD in femoral neck and lumbar spine, and the results exhibited consistency across diverse age, genders, races, and BMI subgroups. Moreover, for each 1 SD increase in T-ALP, there was a 0.5% increase in the prevalence of osteoporosis [OR (95%CI): 1.005 (1.005, 1.005), p < 0.001]. Among individuals with osteoporosis, for every 1 SD increase in T-ALP, the all-cause mortality increased by 0.4% [HR (95%CI):1.004 (1.002, 1.006), p < 0.001]. Meanwhile, comparing participants with highest serum T-ALP levels (> 79 IU/L) to those with lowest levels (< 53 IU/L) further raised the prevalence of osteoporosis [OR (95%CI):1.292 (1.021, 1.636), p = 0.033] and all-cause mortality [HR (95% CI):1.232 (1.041, 1.459), p = 0.015].

CONCLUSIONS

Based on a representative sample of US adults, elevated serum T-ALP levels were found to be significantly associated with both reduced BMD and an increased risk of osteoporosis across all participants, as well as with a higher all-cause mortality in individuals with osteoporosis.

Eucommia ulmoides Oliver polysaccharide alleviates glucocorticoid-induced osteoporosis by stimulating bone formation via ERK/BMP-2/SMAD signaling

Osteoporosis (OP) is a metabolic disease characterized by low bone mineral mass owing to osteoblast dysfunction. Eucommia ulmoides Oliver (EuO) is a Chinese herbal medicine traditionally used to treat OP. Here, a polysaccharide purified from the EuO cortex (EuOCP3) was administered to OP mice constructed with dexamethasone (Dex) to investigate its anti-OP activity. EuOCP3 significantly improved Dex-induced bone microarchitecture destruction, increased osteoblast numbers and surface, and stimulated an increase in the expression of osteoblast differentiation markers in the femurs of OP mice. Furthermore, EuOCP3 was applied to MC3T3-E1 cells to further explore its effects on osteoblast differentiation. EuOCP3 significantly promoted osteoblast differentiation and increased the level of phosphorylated extracellular signal-regulated kinase1/2 (ERK1/2) and SMAD1/5/8. The EuOCP3-mediated enhancement of osteoblast differentiation-related proteins and phosphorylated SMAD1/5/8 expression levels was strongly suppressed by an ERK inhibitor (PD98059), which confirmed the critical role of ERK signaling in EuOCP3-induced osteoblast differentiation. In summary, EuOCP3 can stimulate bone formation by improving osteoblast differentiation via ERK/BMP-2/SMAD signaling, indicating the potential use of EuOCP3 as a functional ingredient in food products for anti-OP treatment.

3D-printed biomimetic scaffolds loaded with ADSCs and BMP-2 for enhanced rotator cuff repair

Rotator cuff tear repair poses significant challenges due to the complex gradient interface structure. In the face of disease-related disruptions in the tendon-bone interface (TBI), the strategy of constructing a biomimetic scaffold is a promising avenue. A novel 3D-printed rotator cuff scaffold loaded adipose stem cells (ADSCs), bone morphogenetic protein-2 (BMP-2), and collagen type I (COL I). The efficiency of the slow-release BMP-2 design depended on the dopamine-hyaluronic acid (HAD) and BMP-2 reaction. The cumulative release of BMP-2 was 44.97 ± 5.45% at 4 weeks. The 3D-printed bilayer scaffold, incorporating COL I and BMP-2, effectively promoted the differentiation of ADSCs into osteogenic, tenogenic, and chondrogenic lineages in vitro. The combination of 3D-printed bioactive scaffolds and ADSCs demonstrated a superior repair effect on rotator cuff injuries in vivo. Therefore, these findings indicates that the 3D-printed biomimetic scaffold loaded with ADSCs and BMP-2 holds potential as a promising graft for TBI healing.

Interaction of high lipogenic states with titanium on osteogenesis

As obesity rates continue to rise, the prevalence of metabolic dysfunction and alcohol-associated steatotic liver disease (MetALD), a new term for Nonalcoholic Fatty Liver Disease (NAFLD), also increases. In an aging population, it is crucial to understand the interplay between metabolic disorders, such as MetALD, and bone health. This understanding becomes particularly significant in the context of implant osseointegration. This study introduces an in vitro model simulating high lipogenesis through the use of human Mesenchymal Stroma Cells-derived adipocytes, 3D intrahepatic cholangiocyte organoids (ICO), and Huh7 hepatocytes, to evaluate the endocrine influence on osteoblasts interacting with titanium. We observed a significant increase in intracellular fat accumulation in all three cell types, along with a corresponding elevation in metabolic gene expression compared to the control groups. Notably, osteoblasts undergoing mineralization in this high-lipogenesis environment also displayed lipid vesicle accumulation. The study further revealed that titanium surfaces modulate osteogenic gene expression and impact cell cycle progression, cell survival, and extracellular matrix remodeling under lipogenic conditions. These findings provide new insights into the challenges of implant integration in patients with obesity and MetALD, offering a deeper understanding of the metabolic influences on bone regeneration and implant success.

Mechanisms of Bone Morphogenetic Protein 2 in Respiratory Diseases

PURPOSE OF REVIEW

Bone morphogenetic protein 2 (BMP2) belongs to the transforming growth factor-β (TGF-β) superfamily and plays an important role in regulating embryonic development, angiogenesis, osteogenic differentiation, tissue homeostasis, and cancer invasion. Increasing studies suggest BMP2 is involved in several respiratory diseases. This study aimed to review the role and mechanisms of BMP2 in respiratory diseases.

RECENT FINDINGS

BMP2 signaling pathway includes the canonical and non-canonical signaling pathway. The canonical signaling pathway is the BMP2-SMAD pathway, and the non-canonical signaling pathway includes mitogen-activated protein kinase (MAPK) pathway and phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) pathway. The BMP2 is related to pulmonary hypertension (PH), lung cancer, pulmonary fibrosis (PF), asthma, and chronic obstructive pulmonary disease (COPD). BMP2 inhibits the proliferation of pulmonary artery smooth muscle cells (PASMCs), promotes the apoptosis of PASMCs to reduce pulmonary vascular remodeling in PH, which is closely related to the canonical and non-canonical pathway. In addition, BMP2 stimulates the proliferation and migration of cells to promote the occurrence, colonization, and metastasis of lung cancer through the canonical and the non-canonical pathway. Meanwhile, BMP2 exert anti-fibrotic function in PF through canonical signaling pathway. Moreover, BMP2 inhibits airway inflammation to maintain airway homeostasis in asthma. However, the signaling pathways involved in asthma are poorly understood. BMP2 inhibits the expression of ciliary protein and promotes squamous metaplasia of airway epithelial cells to accelerate the development of COPD. In conclusion, BMP2 may be a therapeutic target for several respiratory diseases.

BMP3b regulates bone mass by inhibiting BMP signaling

Bone morphogenetic protein 3b (BMP3b), also known as growth differentiation factor 10 (GDF10), is a non-osteogenic BMP highly expressed in the skeleton. Although in vitro studies have shown that BMP3b suppresses osteoblast differentiation, the physiological role of BMP3b in regulating bone mass in vivo remains unknown. Here, we show that BMP3b deletion in mice leads to a high bone mass phenotype via an unexpected novel mechanism involving de-repression of canonical BMP/Smad signaling. BMP3b null mice were viable, and exhibited no significant difference in body size compared to wildtype control. Trabecular bone parameters assessed by histomorphometry and μCT, revealed a significant increase in bone volume and bone mineral density. Expression of osteoblast-differentiation genes were elevated in bone tissue of BMP3b null mice, whereas expression of osteoclast-related genes remained unchanged. Consistent with this, Bmp3b was highly expressed in osteoblasts relative to osteoclast cells. Ex-vivo culture of primary bone marrow mesenchymal stem cells (BMSCs) and primary bone marrow-derived osteoclasts revealed that inactivation of BMP3b enhances osteogenesis without affecting osteoclastogenesis. Mechanistically, we found that BMP3b suppressed BMP4-induced Smad1/5 phosphorylation and inhibited the activity of a BMP4-driven Id-1 luciferase reporter. Protein-protein interaction assays revealed that BMP3b competitively interfered with the association of BMP4 and BMP type I receptors. These findings suggest that BMP3b regulates bone mass by acting as a BMP receptor antagonist. Thus, maintenance of bone mass involves antagonism of canonical BMP/Smad signaling by a member of the BMP family.

Polystyrene nanoplastics mediate skeletal toxicity through oxidative stress and the BMP pathway in zebrafish (Danio rerio)

The widespread presence of micro(nano)plastics (MNPs) has generated public concern. Studies have indicated that MNPs can accumulate in mammalian bones; however, research on the skeletal toxicity and underlying molecular mechanisms of MNPs in aquatic organisms remains limited. We subjected zebrafish embryos to three varying levels (1, 10, 100 μg/mL) of polystyrene nanoplastics (PSNPs) exposure over a period of 7 days in our research. The results revealed that PSNPs significantly reduced the body length and hatching rate of zebrafish, leading to skeletal deformities. mRNA level analysis showed significant upregulation of sp7, sparc, and smad1 genes transcription by PSNPs. Moreover, PSNPs markedly downregulated the mRNA levels associated with runx2a, bmp2a, and bmp4. Further investigations demonstrated that PSNPs dramatically increased ROS levels in zebrafish larvae, with significant downregulation of transcription levels of sod1 and cat genes, resulting in a sharp increase in transcription levels of apoptosis-related regulatory genes bcl-2 and bax. Furthermore, PSNPs led to a marked rise in Caspase 3 activity in zebrafish larvae, suggesting the initiation of apoptosis. PSNPs also notably inhibited alkaline phosphatase (AKP) activity. Compared to a 4-day exposure, a 7-day exposure to PSNPs intensified abnormalities across multiple indicators. In summary, our research indicates that PSNPs cause significant oxidative stress in zebrafish larvae, resulting in apoptosis. Moreover, PSNPs disrupt the transcription of genes related to skeletal development through the bone morphogenetic protein (BMP) pathway, further disrupting skeletal development processes and ultimately resulting in skeletal deformities in zebrafish larvae. This study provides new insights into the skeletal toxicity of MNPs.

Synthesis and Antiosteoporotic Characterization of Diselenyl Maleimides: Discovery of a Potent Agent for the Treatment of Osteoporosis by Targeting RANKL

To discover new osteoclast-targeting antiosteoporosis agents, we identified forty-six diselenyl maleimides, which were efficiently prepared using a novel, simple, and metal-free method at room temperature in a short reaction time. Among them, 3k showed the most marked inhibition of osteoclast differentiation with an IC50 value of 0.36 ± 0.03 μM. Moreover, 3k significantly suppressed RANKL-induced osteoclast formation, bone resorption, and osteoclast-specific genes expression in vitro. Mechanistic studies revealed that 3k remarkably blocked the RANKL-induced mitogen-activated protein kinase (MAPK) and NF-κB signaling pathways. In ovariectomized mice, intragastric administration of 3k significantly alleviated bone loss, exhibiting an effect similar to that of alendronate. Surface plasmon resonance assay and microscale thermophoresis assay results suggested that RANKL might be a potential molecular target for 3k. Collectively, the findings presented above provided a novel candidate for further development of bone antiresorptive drugs that target RANKL.

Causal Association of Telomere Length and Loss of Bone: a Directional Mendelian Randomization Study of Multi-Outcomes

This study employed a genome-wide association study (GWAS) to investigate the relationship between telomere length and marginal bone loss (MBL), a marker of bone health and aging. Telomere length, a biological indicator of aging, was analyzed alongside several serum markers of bone loss. Following a screen for appropriate instrumental variables, telomere length was designated as the exposure variable. We conducted the main analysis using random-effects inverse variance weighting (IVW) and supplemented it with MR Egger, weighted median, simple mode, and weighted mode analyses, employing a total of five methods. Positive outcomes underwent scrutiny through heterogeneity analysis, horizontal multiplicity analysis, and leave-one-out plot. Subsequently, the effective gene locus was chosen for a reverse MR analysis, with positive results serving as the exposure variable. We found a causal relationship between telomere length and the expression of osteocalcin (OC), matrix metalloproteinase-3 (MMP-3), and matrix metalloproteinase-12 (MMP-12), key markers of bone metabolism. Our findings suggest that telomere wear and shortening may contribute to increased activity of OC, MMP-3, and MMP-12, thus affecting bone metabolism. However, reverse Mendelian randomization analysis did not indicate a significant impact of OC, MMP-3, and MMP-12 on telomere length, implying a unidirectional relationship. Overall, this meta-analysis underscores the association between telomere length and bone loss, highlighting the importance of timing and duration of telomere wear and shortening in influencing bone metabolism.

Functional modularity and mechanical stress shape plastic responses during fish development

The adaptive potential of plastic phenotypes relies on combined developmental responses. We investigated how manipulation of developmental conditions related to foraging mode in the fish Megaleporinus macrocephalus induces plastic responses at different levels: (a) functional modularity of skull bones, (b) biomechanical properties of the chondrocranium using finite element models, (c) bmp4 expression levels, used as a proxy for molecular pathways involved in bone responses to mechanical load. We identified new modules in experimental groups, suggesting increased integration in specific head bone elements associated with the development of subterminal and upturned mouths, which are major features of Megaleporinus plastic morphotypes released in the lab. Plastic responses in head shape involved differences in the magnitude of mechanical stress, which seem restricted to certain chondrocranium regions. Three bones represent a "mechanical unit" related to changes in mouth position induced by foraging mode, suggesting that functional modularity might be enhanced by the way specific regions respond to mechanical load. Differences in bmp4 expression levels between plastic morphotypes indicate associations between molecular signaling pathways and biomechanical responses to load. Our results offer a multilevel perspective of epigenetic factors involved in plastic responses, expanding our knowledge about mechanisms of developmental plasticity that originate novel complex phenotypes.

Mechanical heterogeneity in a soft biomaterial niche controls BMP2 signaling

The extracellular matrix is known to impact cell function during regeneration by modulating growth factor signaling. However, how the mechanical properties and structure of biomaterials can be used to optimize the cellular response to growth factors is widely neglected. Here, we engineered a macroporous biomaterial to study cellular signaling in environments that mimic the mechanical stiffness but also the mechanical heterogeneity of native extracellular matrix. We found that the mechanical interaction of cells with the heterogeneous and non-linear deformation properties of soft matrices (E < 5 kPa) enhances BMP-2 growth factor signaling with high relevance for tissue regeneration. In contrast, this effect is absent in homogeneous hydrogels that are often used to study cell responses to mechanical cues. Live cell imaging and in silico finite element modeling further revealed that a subpopulation of highly active, fast migrating cells is responsible for most of the material deformation, while a second, less active population experiences this deformation as an extrinsic mechanical stimulation. At an overall low cell density, the active cell population dominates the process, suggesting that it plays a particularly important role in early tissue healing scenarios where cells invade tissue defects or implanted biomaterials. Taken together, our findings demonstrate that the mechanical heterogeneity of the natural extracellular matrix environment plays an important role in triggering regeneration by endogenously acting growth factors. This suggests the inclusion of such mechanical complexity as a design parameter in future biomaterials, in addition to established parameters such as mechanical stiffness and stress relaxation.

Analysis of the causal relationship between gut microbiota and bone remodeling growth factor from the gene association

BACKGROUND

A growing body of evidence indicates a close association between the gut microbiota (GM) and the bone remodeling (BR) process, raising suspicions that the GM may actively participate in BR by modulating the levels of growth factors. However, the precise causal relationship between them remains unclear. Due to many confounding factors, many microorganisms related to BR growth factors have not been identified. We aimed to elucidate the causal relationship between the GM and BR growth factors.

METHODS

We evaluated the genome-wide association study (GWAS) summary statistics for GM and five common growth factors associated with BR: namely, bone morphogenetic proteins (BMP), transforming growth factors(TGF), insulin growth factors (IGFs), epidermal growth factors (EGFs), and fibroblast growth factors (FGF). The causal relationship between the GM and BR growth factors was studied by double-sample Mendelian randomized analysis. We used five Mendelian randomization (MR) methods, including inverse variance-weighted (IVW), MR-Egger, simple mode, weighted median, and weighted model methods.

RESULTS

Through MR analysis, a total of 56 bacterial genera were co-identified as associated with BMP, TGF, IGF, EGF, and FGF. Among them, eight genera were found to have a causal relationship with multiple growth factors: Marvinbryantia was causally associated with BMP-6 (P = 0.018, OR = 1.355) and TGF-β2 (P = 0.002, OR = 1.475); Lachnoclostridium, BMP-7 (P = 0.021, OR = 0.73) and IGF-1 (P = 0.046, OR = 0.804); Terrisporobacter, TGF-β (P = 0.02, OR = 1.726) and FGF-23 levels (P = 0.016, OR = 1.76); Ruminiclostridium5, TGF-β levels (P = 0.024, OR = 0.525) and FGFR-2 (P = 0.003, OR = 0.681); Erysipelatoclostridium, TGF-β2 (P = 0.001, OR = 0.739) and EGF and its receptor (EGFR) (P = 0.012, OR = 0.795); Eubacterium_brachy_group, FGFR-2 (P = 0.045, OR = 1.153) and EGF (P = 0.013, OR = 0.7); Prevotella9 with EGFR (P = 0.022, OR = 0.818) and FGFR-2 (P = 0.011, OR = 1.233) and Faecalibacterium with FGF-23 (P = 0.02, OR = 2.053) and IGF-1 (P = 0.005, OR = 0.843).

CONCLUSION

We confirmed the causal relationship between the GM and growth factors related to BR, which provides a new perspective for the study of BR, through targeted regulation of specific bacteria to prevent and treat diseases and growth factor-mediated BR disorders.

Clinical management and innovation in fracture non-union

INTRODUCTION

With the introduction and continuous improvement in operative fracture fixation, even the most severe bone fractures can be treated with a high rate of successful healing. However, healing complications can occur and when healing fails over prolonged time, the outcome is termed a fracture non-union. Non-union is generally believed to develop due to inadequate fixation, underlying host-related factors, or infection. Despite the advancements in fracture fixation and infection management, there is still a clear need for earlier diagnosis, improved prediction of healing outcomes and innovation in the treatment of non-union.

AREAS COVERED

This review provides a detailed description of non-union from a clinical perspective, including the state of the art in diagnosis, treatment, and currently available biomaterials and orthobiologics.Subsequently, recent translational development from the biological, mechanical, and infection research fields are presented, including the latest in smart implants, osteoinductive materials, and in silico modeling.

EXPERT OPINION

The first challenge for future innovations is to refine and to identify new clinical factors for the proper definition, diagnosis, and treatment of non-union. However, integration of in vitro, in vivo, and in silico research will enable a comprehensive understanding of non-union causes and correlations, leading to the development of more effective treatments.

New insights into the function of the NLRP3 inflammasome in sarcopenia: mechanism and therapeutic strategies

Sarcopenia is one of the most common skeletal muscle disorders and is characterized by infirmity and disability. While extensive research has focused on elucidating the mechanisms underlying the progression of sarcopenia, further comprehensive insights into its pathogenesis are necessary to identify new preventive and therapeutic approaches. The involvement of inflammasomes in sarcopenia is widely recognized, with particular emphasis on the NLRP3 (NLR family pyrin domain containing 3) inflammasome. In this review, we aim to elucidate the underlying mechanisms of the NLRP3 inflammasome and its relevance in sarcopenia of various etiologies. Furthermore, we highlight interventions targeting the NLRP3 inflammasome in the context of sarcopenia and discuss the current limitations of our knowledge in this area.

Chitosan-based biomaterials promote bone regeneration by regulating macrophage fate

The development of various osteogenic biomaterials has not only promoted the development of bone tissue engineering but also provided more possibilities for bone defect repair. However, most previous studies have focused on the interaction of biomaterials on endogenous or exogenous stem cells involved in the bone regeneration process while neglecting the effect of changes in the immune microenvironment of bone defect sites on bone regeneration after biomaterial implantation into the host. With the development of bone immunology, the role of various immune cells, especially macrophages, in bone regeneration has gradually attracted the attention of researchers. An increasing number of studies have begun to target macrophages to better promote bone regeneration by modulating the fate of macrophages in a spatiotemporally ordered manner to mimic the changes in the immune microenvironment of bone defect sites during the natural repair process of bone tissue. Chitosan is one of the most abundant natural polysaccharides in the world. In recent years, various chitosan-based biomaterials have been widely used in macrophage fate modulation and bone regeneration. In this review, we review the interaction between macrophages and scaffold materials, general information about chitosan, the modulation of macrophage fate by chitosan-based biomaterials, and their application in bone regeneration.

CA1 Modulates the Osteogenic Differentiation of Dental Follicle Stem Cells by Activating the BMP Signaling Pathway In Vitro

BACKGROUND

Carbonic anhydrase 1 (CA1) has been found to be involved in osteogenesis and osteoclast in various human diseases, but the molecular mechanisms are not completely understood. In this study, we aim to use siRNA and lentivirus to reduce or increase the expression of CA1 in Dental follicle stem cells (DFSCs), in order to further elucidate the role and mechanism of CA1 in osteogenesis, and provide better osteogenic growth factors and stem cell selection for the application of bone tissue engineering in alveolar bone fracture transplantation.

METHODS

The study used RNA interference and lentiviral vectors to manipulate the expression of the CA1 gene in DFSCs during in vitro osteogenic induction. The expression of osteogenic marker genes was evaluated and changes in CA1, alkaline phosphatase (ALP), Runt-related transcription factor 2 (RUNX2), and Bone morphogenetic proteins (BMP2) were measured using quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting (WB). The osteogenic effect was assessed through Alizarin Red staining.

RESULTS

The mRNA and protein expression levels of CA1, ALP, RUNX2, and BMP2 decreased distinctly in the si-CA1 group than other groups (p < 0.05). In the Lentivirus-CA1 (LV-CA1) group, the mRNA and protein expressions of CA1, ALP, RUNX2, and BMP2 were amplified to varying degrees than other groups (p < 0.05). Apart from CA1, BMP2 (43.01%) and ALP (36.69%) showed significant upregulation (p < 0.05). Alizarin red staining indicated that the LV-CA1 group produced more calcified nodules than other groups, with a higher optical density (p < 0.05), and the osteogenic effect was superior.

CONCLUSIONS

CA1 can impact osteogenic differentiation via BMP related signaling pathways, positioning itself upstream in osteogenic signaling pathways, and closely linked to osteoblast calcification and ossification processes.

Podocyte Pathogenic Bone Morphogenetic Protein-2 Pathway and Immune Cell Behaviors in Primary Membranous Nephropathy

Primary membranous nephropathy (PMN) is one of the leading causes of end-stage renal disease, and the most frequent cause of massive proteinuria in nondiabetic adults, resulting in fatal complications. However, the underlying pathomechanisms of PMN remain largely unclear. Here, single-cell RNA sequencing is employed to analyze kidney biopsies from eleven PMN patients and seven healthy subjects. Profiling 44 060 cells from patients allowed us to characterize the cellular composition and cell-type-specific gene expression in the PMN kidney. The complement-induced BMP2/pSMAD1/COL4 pathway is identified as the pathogenic pathway in podocytes, bridging two key events, i.e., complement system activation and glomerular basement membrane thickening in PMN. Augmented infiltration and activation of myeloid leukocytes and B lymphocytes are found, profiling delicate crosstalk of immune cells in PMN kidneys. Overall, these results provide valuable insights into the roles of podocytes and immune cells in PMN, and comprehensive resources toward the complete understanding of PMN pathophysiology.

A Narrative Review on Recombinant Human Bone Morphogenetic Protein 2: Where Are We Now?

Spinal fusion is a prevalent surgical intervention for degenerative spinal diseases, with increasing demand driven by ageing populations. The coexistence of multiple chronic conditions, termed multimorbidity, often complicates surgical outcomes, making advanced bone grafts crucial for successful fusions. This paper reviews the development, clinical application, and controversies surrounding the use of recombinant human bone morphogenetic protein-2 (rhBMP-2) in spinal fusion surgeries. A comprehensive narrative review was conducted, focusing on literature from January 1980 to January 2024, sourced from PubMed and Google Scholar. Studies included those examining rhBMP-2 specifically in spinal fusion contexts, excluding other bone morphogenetic proteins (BMPs) and non-spinal applications. This review presents an overarching synopsis of rhBMP-2, its development history and clinical efficacy, the emergence of side effects, and evolving patterns of clinical use. As discussed in this review, clinical practice has adjusted usage and dosages to mitigate adverse effects, yet the need for safer delivery mechanisms persists. rhBMP-2 remains a potent osteoinductive agent with comparable fusion success, as measured by radiographic fusion and good clinical outcomes, to autologous grafts but poses unique risks. This review sets out how further research is essential to optimise the delivery of rhBMP-2 to reduce side effects. Enhanced understanding and innovation of spatio-temporal presentation relative to endogenous BMP could significantly improve patient outcomes in spinal fusion surgeries. The review contributes to the growing body of literature on the use of rhBMP-2 in spine surgery and discusses changing patterns of clinical use over time.

In Vitro Biocompatibility Assessment of Bioengineered PLA-Hydrogel Core-Shell Scaffolds with Mesenchymal Stromal Cells for Bone Regeneration

Human mesenchymal stromal cells (hMSCs), whether used alone or together with three-dimensional scaffolds, are the best-studied postnatal stem cells in regenerative medicine. In this study, innovative composite scaffolds consisting of a core-shell architecture were seeded with bone-marrow-derived hMSCs (BM-hMSCs) and tested for their biocompatibility and remarkable capacity to promote and support bone regeneration and mineralization. The scaffolds were prepared by grafting three different amounts of gelatin-chitosan (CH) hydrogel into a 3D-printed polylactic acid (PLA) core (PLA-CH), and the mechanical and degradation properties were analyzed. The BM-hMSCs were cultured in the scaffolds with the presence of growth medium (GM) or osteogenic medium (OM) with differentiation stimuli in combination with fetal bovine serum (FBS) or human platelet lysate (hPL). The primary objective was to determine the viability, proliferation, morphology, and spreading capacity of BM-hMSCs within the scaffolds, thereby confirming their biocompatibility. Secondly, the BM-hMSCs were shown to differentiate into osteoblasts and to facilitate scaffold mineralization. This was evinced by a positive Von Kossa result, the modulation of differentiation markers (osteocalcin and osteopontin), an expression of a marker of extracellular matrix remodeling (bone morphogenetic protein-2), and collagen I. The results of the energy-dispersive X-ray analysis (EDS) clearly demonstrate the presence of calcium and phosphorus in the samples that were incubated in OM, in the presence of FBS and hPL, but not in GM. The chemical distribution maps of calcium and phosphorus indicate that these elements are co-localized in the same areas of the sections, demonstrating the formation of hydroxyapatite. In conclusion, our findings show that the combination of BM-hMSCs and PLA-CH, regardless of the amount of hydrogel content, in the presence of differentiation stimuli, can provide a construct with enhanced osteogenicity for clinically relevant bone regeneration.

Enhanced effects of slowly co-released TGF-β3 and BMP-2 from biomimetic calcium phosphate-coated silk fibroin scaffolds in the repair of osteochondral defects

Bioactive agents have demonstrated regenerative potential for cell-free bone tissue engineering. Nevertheless, certain challenges persist, including ineffective delivery methods and confined therapeutic potency. Here, we demonstrated that the biomimetic calcium phosphate coating system (BioCaP) could effectively uptake and slowly release the incorporated bioactive agents compared to the surface absorption system via osteoclast-mediated degradation of BioCaP coatings. The release kinetics were determined as a function of time. The release rate was stable without remarkable burst release during the first 1 day, followed by a sustained release from day 7 to day 19. Then, we developed the bi-functional BioCaP-coated silk fibroin scaffolds enabling the effective co-delivery of TGF-β3 and BMP-2 (SFI-T/SFI-B) and the corresponding slow release of TGF-β3 and BMP-2 exhibited superior potential in promoting chondrogenesis and osteogenesis without impairing cell vitality in vitro. The SFI-T/SFI-B scaffolds could improve cartilage and bone regeneration in 5 × 4 mm rabbit osteochondral (OC) defect. These findings indicate that the biomimetic calcium-phosphate coated silk fibroin scaffolds with slowly co-released TGF-β3 and BMP-2 effectively promote the repair of OC defects, hence facilitating the future clinical translation of controlled drug delivery in tissue engineering.

Primary cilia mediate skeletogenic BMP and Hedgehog signaling in heterotopic ossification

Heterotopic ossification (HO), defined as the formation of extraskeletal bone in muscle and soft tissues, is a diverse pathological process caused by either genetic mutations or inciting trauma. Fibrodysplasia ossificans progressiva (FOP) is a genetic form of HO caused by mutations in the bone morphogenetic protein (BMP) type I receptor gene activin A receptor type 1 (ACVR1). These mutations make ACVR1 hypersensitive to BMP and responsive to activin A. Hedgehog (Hh) signaling also contributes to HO development. However, the exact pathophysiology of how skeletogenic cells contribute to endochondral ossification in FOP remains unknown. Here, we showed that the wild-type or FOP-mutant ACVR1 localized in the cilia of stem cells from human exfoliated deciduous teeth with key FOP signaling components, including activin A receptor type 2A/2B, SMAD family member 1/5, and FK506-binding protein 12kD. Cilia suppression by deletion of intraflagellar transport 88 or ADP ribosylation factor like GTPase 3 effectively inhibited pathological BMP and Hh signaling, subdued aberrant chondro-osteogenic differentiation in primary mouse or human FOP cells, and diminished in vivo extraskeletal ossification in Acvr1Q207D, Sox2-Cre; Acvr1R206H/+ FOP mice and in burn tenotomy-treated wild-type mice. Our results provide a rationale for early and localized suppression of cilia in affected tissues after injury as a therapeutic strategy against either genetic or acquired HO.

BRCC3 Regulation of ALK2 in Vascular Smooth Muscle Cells: Implication in Pulmonary Hypertension

BACKGROUND

An imbalance of antiproliferative BMP (bone morphogenetic protein) signaling and proliferative TGF-β (transforming growth factor-β) signaling is implicated in the development of pulmonary arterial hypertension (PAH). The posttranslational modification (eg, phosphorylation and ubiquitination) of TGF-β family receptors, including BMPR2 (bone morphogenetic protein type 2 receptor)/ALK2 (activin receptor-like kinase-2) and TGF-βR2/R1, and receptor-regulated Smads significantly affects their activity and thus regulates the target cell fate. BRCC3 modifies the activity and stability of its substrate proteins through K63-dependent deubiquitination. By modulating the posttranslational modifications of the BMP/TGF-β-PPARγ pathway, BRCC3 may play a role in pulmonary vascular remodeling, hence the pathogenesis of PAH.

METHODS

Bioinformatic analyses were used to explore the mechanism by which BRCC3 deubiquitinates ALK2. Cultured pulmonary artery smooth muscle cells (PASMCs), mouse models, and specimens from patients with idiopathic PAH were used to investigate the rebalance between BMP and TGF-β signaling in regulating ALK2 phosphorylation and ubiquitination in the context of pulmonary hypertension.

RESULTS

BRCC3 was significantly downregulated in PASMCs from patients with PAH and animals with experimental pulmonary hypertension. BRCC3, by de-ubiquitinating ALK2 at Lys-472 and Lys-475, activated receptor-regulated Smad1/5/9, which resulted in transcriptional activation of BMP-regulated PPARγ, p53, and Id1. Overexpression of BRCC3 also attenuated TGF-β signaling by downregulating TGF-β expression and inhibiting phosphorylation of Smad3. Experiments in vitro indicated that overexpression of BRCC3 or the de-ubiquitin-mimetic ALK2-K472/475R attenuated PASMC proliferation and migration and enhanced PASMC apoptosis. In SM22α-BRCC3-Tg mice, pulmonary hypertension was ameliorated because of activation of the ALK2-Smad1/5-PPARγ axis in PASMCs. In contrast, Brcc3-/- mice showed increased susceptibility of experimental pulmonary hypertension because of inhibition of the ALK2-Smad1/5 signaling.

CONCLUSIONS

These results suggest a pivotal role of BRCC3 in sustaining pulmonary vascular homeostasis by maintaining the integrity of the BMP signaling (ie, the ALK2-Smad1/5-PPARγ axis) while suppressing TGF-β signaling in PASMCs. Such rebalance of BMP/TGF-β pathways is translationally important for PAH alleviation.

Cortactin controls bone homeostasis through regulating the differentiation of osteoblasts and osteoclasts

Cortactin (CTTN), a cytoskeletal protein and substrate of Src kinase, is implicated in tumor aggressiveness. However, its role in bone cell differentiation remains unknown. The current study revealed that CTTN was upregulated during osteoblast and adipocyte differentiation. Functional experiments demonstrated that CTTN promoted the in vitro differentiation of mesenchymal stem/progenitor cells into osteogenic and adipogenic lineages. Mechanistically, CTTN was able to stabilize the protein level of mechanistic target of rapamycin kinase (mTOR), leading to the activation of mTOR signaling. In-depth investigation revealed that CTTN could bind with casitas B lineage lymphoma-c (c-CBL) and counteract the function of c-CBL, a known E3 ubiquitin ligase responsible for the proteasomal degradation of mTOR. Silencing c-Cbl alleviated the impaired differentiation of osteoblasts and adipocytes caused by CTTN siRNA, while silencing mTOR mitigated the stimulation of osteoblast and adipocyte differentiation induced by CTTN overexpression. Notably, transplantation of CTTN-silenced bone marrow stromal cells (BMSCs) into the marrow of mice led to a reduction in trabecular bone mass, accompanied by a decrease in osteoblasts and an increase in osteoclasts. Furthermore, CTTN-silenced BMSCs expressed higher levels of receptor activator of nuclear factor κB ligand (RANKL) than control BMSCs did and promoted osteoclast differentiation when cocultured with bone marrow-derived osteoclast precursor cells. This study provides evidence that CTTN favors osteoblast differentiation by counteracting the c-CBL-induced degradation of mTOR and inhibits osteoclast differentiation by downregulating the expression of RANKL. It also suggests that maintaining an appropriate level of CTTN expression may be advantageous for maintaining bone homeostasis.

Ovarian fibrosis: molecular mechanisms and potential therapeutic targets

Ovarian fibrosis, characterized by the excessive proliferation of ovarian fibroblasts and the accumulation of extracellular matrix (ECM), serves as one of the primary causes of ovarian dysfunction. Despite the critical role of ovarian fibrosis in maintaining the normal physiological function of the mammalian ovaries, research on this condition has been greatly underestimated, which leads to a lack of clinical treatment options for ovarian dysfunction caused by fibrosis. This review synthesizes recent research on the molecular mechanisms of ovarian fibrosis, encompassing TGF-β, extracellular matrix, inflammation, and other profibrotic factors contributing to abnormal ovarian fibrosis. Additionally, we summarize current treatment approaches for ovarian dysfunction targeting ovarian fibrosis, including antifibrotic drugs, stem cell transplantation, and exosomal therapies. The purpose of this review is to summarize the research progress on ovarian fibrosis and to propose potential therapeutic strategies targeting ovarian fibrosis for the treatment of ovarian dysfunction.

The Role of Neuromodulation and Potential Mechanism in Regulating Heterotopic Ossification

Heterotopic ossification (HO) is a pathological process characterized by the aberrant formation of bone in muscles and soft tissues. It is commonly triggered by traumatic brain injury, spinal cord injury, and burns. Despite a wide range of evidence underscoring the significance of neurogenic signals in proper bone remodeling, a clear understanding of HO induced by nerve injury remains rudimentary. Recent studies suggest that injury to the nervous system can activate various signaling pathways, such as TGF-β, leading to neurogenic HO through the release of neurotrophins. These pathophysiological changes lay a robust groundwork for the prevention and treatment of HO. In this review, we collected evidence to elucidate the mechanisms underlying the pathogenesis of HO related to nerve injury, aiming to enhance our understanding of how neurological repair processes can culminate in HO.

miR-20a: a key regulator of orthodontic tooth movement via BMP2 signaling pathway modulation

AIM

In this study, we aimed to establish a rat tooth movement model to assess miR-20's ability in enhancing the BMP2 signaling pathway and facilitate alveolar bone remodeling.

METHOD

60 male SD rats had nickel titanium spring devices placed between their left upper first molars and incisors, with the right side serving as the control. Forces were applied at varying durations (18h, 24h, 30h, 36h, 42h, 1d, 3d, 5d, 7d, 14d), and their bilateral maxillary molars and surrounding alveolar bones were retrieved for analysis. Fluorescent quantitative PCR was conducted to assess miR-20a, BMP2, Runx2, Bambi and Smad6 gene expression in alveolar bone, and western blot was performed to determine the protein levels of BMP2, Runx2, Bambi, and Smad6 after mechanical loading.

RESULT

We successfully established an orthodontic tooth movement model in SD rats and revealed upregulated miR-20a expression and significantly increased BMP2 and Runx2 gene expression and protein synthesis in alveolar bone during molar tooth movement. Although Bambi and Smad6 gene expression did not significantly increase, their protein synthesis was found to decrease significantly.

CONCLUSION

MiR-20a was found to be involved in rat tooth movement model alveolar bone remodeling, wherein it promoted remodeling by reducing Bambi and Smad6 protein synthesis through the BMP2 signaling pathway.

mTORC1 and BMP-Smad1/5 regulation of serum-stimulated myotube hypertrophy: a role for autophagy

Protein synthesis regulation is critical for skeletal muscle hypertrophy, yet other established cellular processes are necessary for growth-related cellular remodeling. Autophagy has a well-acknowledged role in muscle quality control, but evidence for its role in myofiber hypertrophy remains equivocal. Both mammalian target of rapamycin complex I (mTORC1) and bone morphogenetic protein (BMP)-Smad1/5 (Sma and Mad proteins from Caenorhabditis elegans and Drosophila, respectively) signaling are reported regulators of myofiber hypertrophy; however, gaps remain in our understanding of how this regulation is integrated with growth processes and autophagy regulation. Therefore, we investigated the mTORC1 and Smad1/5 regulation of protein synthesis and autophagy flux during serum-stimulated myotube growth. Chronic serum stimulation experiments were performed on day 5 differentiated C2C12 myotubes incubated in differentiation medium [2% horse serum (HS)] or growth medium [5% fetal bovine serum (FBS)] for 48 h. Rapamycin or LDN193189 was dosed for 48 h to inhibit mTORC1 and BMP-Smad1/5 signaling, respectively. Acute serum stimulation was examined in day 7 differentiated myotubes. Protein synthesis was measured by puromycin incorporation. Bafilomycin A1 and immunoblotting for LC3B were used to assess autophagy flux. Chronic serum stimulation increased myotube diameter 22%, total protein 21%, total RNA 100%, and Smad1/5 phosphorylation 404% and suppressed autophagy flux. Rapamycin, but not LDN193189, blocked serum-induced myotube hypertrophy and the increase in total RNA. Acute serum stimulation increased protein synthesis 111%, Smad1/5 phosphorylation 559%, and rpS6 phosphorylation 117% and suppressed autophagy flux. Rapamycin increased autophagy flux during acute serum stimulation. These results provide evidence for mTORC1, but not BMP-Smad1/5, signaling being required for serum-induced myotube hypertrophy and autophagy flux by measuring LC3BII/I expression. Further investigation is warranted to examine the role of autophagy flux in myotube hypertrophy.NEW & NOTEWORTHY The present study demonstrates that myotube hypertrophy caused by chronic serum stimulation requires mammalian target of rapamycin complex 1 (mTORC1) signaling but not bone morphogenetic protein (BMP)-Smad1/5 signaling. The suppression of autophagy flux was associated with serum-induced myotube hypertrophy and mTORC1 regulation of autophagy flux by measuring LC3BII/I expression. Rapamycin is widely investigated for beneficial effects in aging skeletal muscle and sarcopenia; our results provide evidence that rapamycin can regulate autophagy-related signaling during myotube growth, which could benefit skeletal muscle functional and metabolic health.

In-silico identification of deleterious non-synonymous SNPs of TBX1 gene: Functional and structural impact towards 22q11.2DS

The TBX1 gene plays a critical role in the development of 22q11.2 deletion syndrome (22q11.2DS), a complex genetic disorder associated with various phenotypic manifestations. In this study, we performed in-silico analysis to identify potentially deleterious non-synonymous single nucleotide polymorphisms (nsSNPs) within the TBX1 gene and evaluate their functional and structural impact on 22q11.2DS. A comprehensive analysis pipeline involving multiple computational tools was employed to predict the pathogenicity of nsSNPs. This study assessed protein stability and explored potential alterations in protein-protein interactions. The results revealed the rs751339103(C>A), rs780800634(G>A), rs1936727304(T>C), rs1223320618(G>A), rs1248532217(T>C), rs1294927055 (C>T), rs1331240435 (A>G, rs1601289406 (A>C), rs1936726164 (G>A), and rs911796187(G>A) with a high-risk potential for affecting protein function and stability. These nsSNPs were further analyzed for their impact on post-translational modifications and structural characteristics, indicating their potential disruption of molecular pathways associated with TBX1 and its interacting partners. These findings provide a foundation for further experimental studies and elucidation of potential therapeutic targets and personalized treatment approaches for individuals affected by 22q11.2DS.

GREM2 inactivation increases trabecular bone mass in mice

Osteoporosis is a common skeletal disease affecting millions of individuals world-wide, with an increased risk of fracture, and a decreased quality of life. Despite its well-known consequences, the etiology of osteoporosis and optimal treatment methods are not fully understood. Human genetic studies have identified genetic variants within the FMN2/GREM2 locus to be associated with trabecular volumetric bone mineral density (vBMD) and vertebral and forearm fractures, but not with cortical bone parameters. GREM2 is a bone morphogenetic protein (BMP) antagonist. In this study, we employed Grem2-deficient mice to investigate whether GREM2 serves as the plausible causal gene for the fracture signal at the FMN2/GREM2 locus. We observed that Grem2 is moderately expressed in bone tissue and particularly in osteoblasts. Complete Grem2 gene deletion impacted mouse survival and body growth. Partial Grem2 inactivation in Grem2+/- female mice led to increased trabecular BMD of femur and increased trabecular bone mass in tibia due to increased trabecular thickness, with an unchanged cortical thickness, as compared with wildtype littermates. Furthermore, Grem2 inactivation stimulated osteoblast differentiation, as evidenced by higher alkaline phosphatase (Alp), osteocalcin (Bglap), and osterix (Sp7) mRNA expression after BMP-2 stimulation in calvarial osteoblasts and osteoblasts from the long bones of Grem2-/- mice compared to wildtype littermates. These findings suggest that GREM2 is a possible target for novel osteoporotic treatments, to increase trabecular bone mass and prevent osteoporotic fractures.

Lead Decreases Bone Morphogenetic Protein-7 (BMP-7) Expression and Increases Renal Cell Carcinoma Growth in a Sex-Divergent Manner

Both tissue and blood lead levels are elevated in renal cell carcinoma (RCC) patients. These studies assessed the impact of the subchronic lead challenge on the progression of RCC in vitro and in vivo. Lead challenge of Renca cells with 0.5 μM lead acetate for 10 consecutive passages decreased E-cadherin expression and cell aggregation. Proliferation, colony formation, and wound healing were increased. When lead-challenged cells were injected into mice, tumor size at day 21 was increased; interestingly, this increase was seen in male but not female mice. When mice were challenged with 32 ppm lead in drinking water for 20 weeks prior to tumor cell injection, there was an increase in tumor size in male, but not female, mice at day 21. To investigate the mechanism underlying the sex differences, the expression of sex hormone receptors in Renca cells was examined. Control Renca cells expressed estrogen receptor (ER) alpha but not ER beta or androgen receptor (AR), as assessed by qPCR, and the expression of ERα was increased in tumors in both sexes. In tumor samples harvested from lead-challenged cells, both ERα and AR were detected by qPCR, yet there was a significant decrease in AR seen in lead-challenged tumor cells from male mice only. This was paralleled by a plate-based array demonstrating the same sex difference in BMP-7 gene expression, which was also significantly decreased in tumors harvested from male but not female mice; this finding was validated by immunohistochemistry. A similar expression pattern was seen in tumors harvested from the mice challenged with lead in the drinking water. These data suggest that lead promotes RCC progression in a sex-dependent via a mechanism that may involve sex-divergent changes in BMP-7 expression.

Challenges of mesenchymal stem cells in the clinical treatment of COVID-19

The 2019 coronavirus disease (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has brought an enormous public health burden to the global society. The duration of the epidemic, the number of infected people, and the widespread of the epidemic are extremely rare in modern society. In the initial stage of infection, people generally show fever, cough, and dyspnea, which can lead to pneumonia, acute respiratory syndrome, kidney failure, and even death in severe cases. The strong infectivity and pathogenicity of SARS-CoV-2 make it more urgent to find an effective treatment. Mesenchymal stem cells (MSCs) are a kind of pluripotent stem cells with the potential for self-renewal and multi-directional differentiation. They are widely used in clinical experiments because of their low immunogenicity and immunomodulatory function. Mesenchymal stem cell-derived exosomes (MSC-Exo) can play a physiological role similar to that of stem cells. Since the COVID-19 pandemic, a series of clinical trials based on MSC therapy have been carried out. The results show that MSCs are safe and can significantly improve patients' respiratory function and prognosis of COVID-19. Here, the effects of MSCs and MSC-Exo in the treatment of COVID-19 are reviewed, and the clinical challenges that may be faced in the future are clarified.

Exosomes: A New Hope for Angiogenesis-Mediated Bone Regeneration

Bone is a metabolically dynamic structure that is generally remodeled throughout the lifetime of an individual but often causes problems with increasing age. A key player for bone development and homeostasis, but also under pathological conditions, is the bone vasculature. This complex system of arteries, veins, and capillaries forms distinct structures where each subset of endothelial cells has important functions. Starting with the basic process of angiogenesis and bone-specific blood vessel formation, coupled with initial bone formation, the importance of different vascular structures is highlighted with respect to how these structures are maintained or changed during homeostasis, aging, and pathological conditions. After exemplifying the current knowledge on bone vasculature, this review will move on to exosomes, a novel hotspot of scientific research. Exosomes will be introduced starting from their discovery via current isolation procedures and state-of-the-art characterization to their role in bone vascular development, homeostasis, and bone regeneration and repair while summarizing the underlying signal transduction pathways. With respect to their role in these processes, especially mesenchymal stem cell-derived extracellular vesicles are of interest, which leads to a discussion on patented applications and an update on ongoing clinical trials. Taken together, this review provides an overview of bone vasculature and bone regeneration, with a major focus on how exosomes influence this intricate system, as they might be useful for therapeutic purposes in the near future.