The inhibition effects of insulin on BMP2-induced muscle heterotopic ossification

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.

Suppression of Overactive Insulin-Like Growth Factor 1 Attenuates Trauma-Induced Heterotopic Ossification in Mice

Heterotopic ossification (HO) is the ectopic bone formation in soft tissues. Aside from hereditary HO, traumatic HO is common after orthopedic surgery, combat-related injuries, severe burns, or neurologic injuries. Recently, mammalian target of rapamycin (mTOR) was demonstrated to be involved in the chondrogenic and osteogenic processes of HO formation. However, its upstream signaling mechanism remains unknown. The current study used an Achilles tendon puncture-induced HO model to show that overactive insulin-like growth factor 1 (IGF-1) was involved in the progression of HO in mice. Micro-computed tomography imaging showed that IGF-1 not only accelerated the rate of osteogenesis and increased ectopic bone volume but also induced spontaneous ectopic bone formation in undamaged Achilles tendons. Blocking IGF-1 activity with IGF-1 antibody or IGF-1 receptor inhibitor picropodophyllin significantly inhibited HO formation. Mechanistically, IGF-1/IGF-1 receptor activates phosphatidylinositol 3-kinase (PI3K)/Akt signaling to promote the phosphorylation of mTOR, resulting in the chondrogenic and osteogenic differentiation of tendon-derived stem cells into chondrocytes and osteoblasts in vitro and in vivo. Inhibitors of PI3K (LY294002) and mTOR (rapamycin) both suppressed the IGF-1-stimulated mTOR signal and mitigated the formation of ectopic bones significantly. In conclusion, these results indicate that IGF-1 mediated the progression of traumatic HO through PI3K/Akt/mTOR signaling, and suppressing IGF-1 signaling cascades attenuated HO formation, providing a promising therapeutic strategy targeting HO.

The roles and regulatory mechanisms of TGF-β and BMP signaling in bone and cartilage development, homeostasis and disease

Transforming growth factor-βs (TGF-βs) and bone morphometric proteins (BMPs) belong to the TGF-β superfamily and perform essential functions during osteoblast and chondrocyte lineage commitment and differentiation, skeletal development, and homeostasis. TGF-βs and BMPs transduce signals through SMAD-dependent and -independent pathways; specifically, they recruit different receptor heterotetramers and R-Smad complexes, resulting in unique biological readouts. BMPs promote osteogenesis, osteoclastogenesis, and chondrogenesis at all differentiation stages, while TGF-βs play different roles in a stage-dependent manner. BMPs and TGF-β have opposite functions in articular cartilage homeostasis. Moreover, TGF-β has a specific role in maintaining the osteocyte network. The precise activation of BMP and TGF-β signaling requires regulatory machinery at multiple levels, including latency control in the matrix, extracellular antagonists, ubiquitination and phosphorylation in the cytoplasm, nucleus-cytoplasm transportation, and transcriptional co-regulation in the nuclei. This review weaves the background information with the latest advances in the signaling facilitated by TGF-βs and BMPs, and the advanced understanding of their diverse physiological functions and regulations. This review also summarizes the human diseases and mouse models associated with disordered TGF-β and BMP signaling. A more precise understanding of the BMP and TGF-β signaling could facilitate the development of bona fide clinical applications in treating bone and cartilage disorders.

Recent progress in bone-repair strategies in diabetic conditions

Bone regeneration following trauma, tumor resection, infection, or congenital disease is challenging. Diabetes mellitus (DM) is a metabolic disease characterized by hyperglycemia. It can result in complications affecting multiple systems including the musculoskeletal system. The increased number of diabetes-related fractures poses a great challenge to clinical specialties, particularly orthopedics and dentistry. Various pathological factors underlying DM may directly impair the process of bone regeneration, leading to delayed or even non-union of fractures. This review summarizes the mechanisms by which DM hampers bone regeneration, including immune abnormalities, inflammation, reactive oxygen species (ROS) accumulation, vascular system damage, insulin/insulin-like growth factor (IGF) deficiency, hyperglycemia, and the production of advanced glycation end products (AGEs). Based on published data, it also summarizes bone repair strategies in diabetic conditions, which include immune regulation, inhibition of inflammation, reduction of oxidative stress, promotion of angiogenesis, restoration of stem cell mobilization, and promotion of osteogenic differentiation, in addition to the challenges and future prospects of such approaches.

Higher BMP Expression in Tendon Stem/Progenitor Cells Contributes to the Increased Heterotopic Ossification in Achilles Tendon With Aging

Although the mineralization in tendon tissue has been reported in a series of aging and disease models, the underlying mechanisms remain unknown. This study aimed to describe the appearance of heterotopic ossification in rat Achilles tendon and further verify whether this tissue metaplasia is related to the enhanced osteogenic differentiation of tendon stem/progenitor cells (TSPCs) owing to the higher expression of bone morphogenetic proteins (BMP-2/4/7) with aging. The male SD rats, aged 4, 8, and 20 months (M), were used. The analyses of ossification and BMP expression in tendon were tested by radiological view (X-ray and CT), histological staining [hematoxylin and eosin (HE), Alcian blue, and Alizarin red], immunohistochemistry, and Western blot. The osteogenic differentiation potential and BMP expression of TSPCs were examined by Alizarin red S staining and real-time PCR. TSPCs were treated with BMP-2 or noggin, and the osteogenic differentiation potential was also examined. X-ray and CT showed the appearance of heterotopic ossification in tendon, and the volume and density of ossification was increased with aging. Histological staining showed the appearance of calcified region surrounded by chondrocyte-like cells and the increased osteogenesis-related gene and BMP expression in ossified tendon with aging. Moreover, the osteogenic differentiation potential and BMP expression in TSPCs isolated from ossified tendon were increased with aging. Additionally, BMP-2 increased the calcium nodule formation and osteogenesis-related gene expression in TSPCs. The addition of noggin inhibited BMP-induced enhancement of osteogenic differentiation. Thus, these findings suggested that the enhanced osteogenic differentiation of TSPCs contributes to the increased heterotopic ossification in aged tendon, which might be induced by the higher expression of BMPs with aging.

Identification of biological pathways and genes associated with neurogenic heterotopic ossification by text mining

Background

Neurogenic heterotopic ossification is a disorder of aberrant bone formation affecting one in five patients sustaining a spinal cord injury or traumatic brain injury (SCI-TBI-HO). However, the underlying mechanisms of SCI-TBI-HO have proven difficult to elucidate. The aim of the present study is to identify the most promising candidate genes and biological pathways for SCI-TBI-HO.

Methods

In this study, we used text mining to generate potential explanations for SCI-TBI-HO. Moreover, we employed several additional datasets, including gene expression profile data, drug data and tissue-specific gene expression data, to explore promising genes that associated with SCI-TBI-HO.

Results

We identified four SCI-TBI-HO-associated genes, including GDF15, LDLR, CCL2, and CLU. Finally, using enrichment analysis, we identified several pathways, including integrin signaling, insulin pathway, internalization of ErbB1, urokinase-type plasminogen activator and uPAR-mediated signaling, PDGFR-beta signaling pathway, EGF receptor (ErbB1) signaling pathway, and class I PI3K signaling events, which may be associated with SCI-TBI-HO.

Conclusions

These results enhance our understanding of the molecular mechanisms of SCI-TBI-HO and offer new leads for researchers and innovative therapeutic strategies.

Osteogenesis activity of isocoumarin a through the activation of the PI3K-Akt/Erk cascade-activated BMP/RUNX2 signaling pathway

Bone formation refers to a series of complex events related to the activities of osteoblasts. In this study, we evaluated the osteogenesis activity of a natural compound named isocoumarin A that was isolated from the rhizomes of Polygonum amplexicaule on the non-transformed preosteoblastic cell line MC3T3-E1 for an in vitro study, and the results revealed that it increased the proliferation and promoted the mineralization of the extracellular matrix of MC3T3-E1 cells after treatment for 3 d in a dose-dependent manner. The cell metabolic activity peaked at 169% at 10 μM, and the activity of alkaline phosphatase (ALP) tripled to 15.94 U/mg compared with the control group. The protein levels of morphogenetic protein 2 (BMP-2), runt-related transcription factor 2 (RUNX2), ALP, and the mRNA levels of ALP, type I collagen (COL-1), and osteocalcin (OCN) were also upregulated after isocoumarin A administration. The mechanism investigation revealed that these effects were associated with the activation of the p-Akt/p-Erk1/2-activated BMP/RUNX2 signaling pathway. Subsequently, the in vivo investigation on the zebrafish embryos model demonstrated that isocoumarin A (0.30 mM) increased the number of vertebrae (5.38 ± 2.07 pcs) and the vertebral area (433.25 ± 111.77 μm²) in the development process of zebrafish embryos after a 7-day postfertilization (dpf) culture compared with the control group (2.50 ± 1.16 pcs and 209.75 ± 86.40 μm²). Together, these results indicated that isocoumarin A could be viewed as a promising candidate in early drug discovery and development to promote the healing of fractures and postmenopausal osteoporosis.

Freeze-dried chitosan-platelet-rich plasma implants improve supraspinatus tendon attachment in a transosseous rotator cuff repair model in the rabbit

Rotator cuff tears result in shoulder pain, stiffness, weakness and loss of motion. After surgical repair, high failure rates have been reported based on objective imaging and it is recognized that current surgical treatments need improvement. The aim of the study was to assess whether implants composed of freeze-dried chitosan (CS) solubilized in autologous platelet-rich plasma (PRP) can improve rotator cuff repair in a rabbit model. Complete tears were created bilaterally in the supraspinatus tendon of New Zealand White rabbits ( n = 4 in a pilot feasibility study followed by n = 13 in a larger efficacy study), which were repaired using transosseous suturing. On the treated side, CS-PRP implants were injected into the transosseous tunnels and the tendon itself, and healing was assessed histologically at time points ranging from one day to two months post-surgery. CS-PRP implants were resident within transosseous tunnels and adhered to tendon surfaces at one day post-surgery and induced recruitment of polymorphonuclear cells from 1 to 14 days. CS-PRP implants improved attachment of the supraspinatus tendon to the humeral head through increased bone remodelling at the greater tuberosity and also inhibited heterotopic ossification of the supraspinatus tendon at two months. In addition, the implants did not induce any detectable deleterious effects. This preliminary study provides the first evidence that CS-PRP implants could be effective in improving rotator cuff tendon attachment in a small animal model.

MiR-378 and BMP-Smad can influence the proliferation of sheep myoblast

MicroRNA (miRNA) is a sort of endogenous ~20-25 nt non-coding RNAs, and it can regulate a variety of biological events. We found the miR-378 may involve in regulating the muscle development of sheep during our previous research. However, the molecular mechanism of miR-378 regulating myoblast proliferation is still unclear. In this research, we predicted that BMP2 (Bone morphogenetic protein 2) was the target gene of miR-378 and the BMP-Smad signal pathway that BMP2 participated in playing an important role in the muscle development. Therefore, we tried to determine whether miR-378 influence myoblast proliferation of sheep through the BMP-Smad signal pathway. The results indicated that inhibit BMP-Smad signal pathway by interfering Smad4 to promote proliferation of sheep myoblasts; promote BMP-Smad signal pathway by interfering Smad7 to inhibit proliferation of sheep myoblasts; over-expression miR-378 promotes BMP-Smad signal pathway and myoblast proliferation in sheep; interfering miR-378 inhibits BMP-Smad signal pathway and myoblast proliferation in sheep. However, when both of which functioned at the myoblast, miR-378 could not fully depend on BMP-Smad signal pathway to regulate myoblast proliferation. In sum, both miR-378 and BMP-Smad can influence the proliferation of myoblast, but miR-378 does not target the 3' UTR of sheep BMP2.

Insulin antagonises pigment epithelium-derived factor (PEDF)-induced modulation of lineage commitment of myocytes and heterotrophic ossification

Extensive bone defects arising as a result of trauma, infection and tumour resection and other bone pathologies necessitates the identification of effective strategies in the form of tissue engineering, gene therapy and osteoinductive agents to enhance the bone repair process. PEDF is a multifunctional glycoprotein which plays an important role in regulating osteoblastic differentiation and bone formation. PEDF treatment of mice and human skeletal myocytes at physiological concentration inhibited myogenic differentiation and activated Erk1/2 MAPK- dependent osteogenic transdifferentiation of myocytes. In mice, insulin, a promoter of bone regeneration, attenuated PEDF-induced expression of osteogenic markers such as osteocalcin, alkaline phosphatase and mineralisation for bone formation in the muscle and surrounding adipose tissue. These results provide new insights into the molecular aspects of the antagonising effect of insulin on PEDF-dependent modulation of the differentiation commitment of musculoskeletal environment into osteogenesis, and suggest that PEDF may be developed as an effective clinical therapy for bone regeneration as its heterotopic ossification can be controlled via co-administration of insulin.

Sequential transfection of RUNX2/SP7 and ATF4 coated onto dexamethasone-loaded nanospheresenhances osteogenesis

The timing of gene transfection greatly influences stem cell differentiation. Sequential transfection is crucial for regulation of cell behavior. When transfected several days after differentiation initiation, genes expressed at the late stage of differentiation can regulate cell behaviors and functions. To determine the optimal timing of key gene delivery, we sequentially transfected human mesenchymal stem cells (hMSCs). This method can easily control osteogenesis of stem cells. hMSCs were first transfected with RUNX2 and SP7 using poly(lactic-co-glycolic acid) nanoparticles to induce osteogenesis, and then with ATF4 after 5, 7, and 14 days. Prior to transfecting hMSCs with all three genes, each gene was individually transfected and its expression was monitored. Transfection of these genes was confirmed by RT-PCR, Western blotting, and confocal microscopy. The pDNAs entered the nuclei of hMSCs, and RUNX2 and SP7 proteins were translated and triggered osteogenesis. Second, the ATF4 gene was delivered when cells were at the pre-osteoblasts stage. To induce the osteogenesis of hMSCs, the optimal timing of ATF4 gene delivery was 14 days after RUNX2/SP7 transfection. Experiments in 2- and 3-dimensional culture systems confirmed that transfection of ATF4 at 14 days after RUNX2/SP7 promoted osteogenic differentiation of hMSCs.

Microenvironmental factors that regulate mesenchymal stem cells: lessons learned from the study of heterotopic ossification

Bone marrow contains a non-hematopoietic, clonogenic, multipotent population of stromal cells that are later called mesenchymal stem cells (MSC). Similar cells that share many common features with MSC are also found in other organs, which are thought to contribute both to normal tissue regeneration and to pathological processes such as heterotopic ossification (HO), the formation of ectopic bone in soft tissue. Understanding the microenvironmental factors that regulate MSC in vivo is essential both for understanding the biology of the stem cells and for effective translational applications of MSC. Unfortunately, this important aspect has been largely underappreciated. This review tries to raise the attention and highlight this critical issue by updating the relevant literature along with discussions of the key issues in the area.

Icaritin, a novel plant-derived osteoinductive agent, enhances the osteogenic differentiation of human bone marrow- and human adipose tissue-derived mesenchymal stem cells

For the treatment of diseases affecting bones using bone regenerative medicine, there is an urgent need to develop safe, inexpensive drugs that can strongly induce bone formation. In the present study, we systematically investigated the effects of icaritin, a metabolic product of icariin, on the osteogenic differentiation of human bone marrow‑derived mesenchymal stem cells (hBMSCs) and human adipose tissue‑derived stem cells (hADSCs) in vitro. After treatment with icaritin at concentrations of 10‑8-10‑5 M, hBMSCs and hADSCs were examined for alkaline phosphatase activity, osteocalcin (OC) secretion, matrix mineralization and expression levels of bone‑related mRNA and proteins. Data showed that icaritin at concentrations 10‑7-10‑5 M significantly increased alkaline phosphatase activity, OC secretion at different time points, and calcium deposition at day 21. In addition, icaritin upregulated the mRNA expression of genes for bone morphogenetic proteins (BMP‑2, ‑4 and ‑7), bone transcription factors (Runx2 and Dlx5) and bone matrix proteins (ALP, OC and Col‑1). Moreover, icaritin increased the protein levels of BMPs, Runx2 and OC, as detected by western blot analysis. These findings suggest that icaritin enhances the osteogenic differentiation of hBMSCS and hADSCs. Icaritin exerts its potent osteogenic effect possibly by directly stimulating the production of BMPs. Although the osteogenic activity of icaritin in vitro was inferior to that of rhBMP‑2, icaritin displayed better results than icariin. Moreover, the low cost, simple extraction procedure, and an abundance of icaritin make it appealing as a bone regenerative medicine.

Fabrication of Core-Shell PEI/pBMP2-PLGA Electrospun Scaffold for Gene Delivery to Periodontal Ligament Stem Cells

Bone tissue engineering is the most promising technology for enhancing bone regeneration. Scaffolds loaded with osteogenic factors improve the therapeutic effect. In this study, the bioactive PEI (polyethylenimine)/pBMP2- (bone morphogenetic protein-2 plasmid-) PLGA (poly(D, L-lactic-co-glycolic acid)) core-shell scaffolds were prepared using coaxial electrospinning for a controlled gene delivery to hPDLSCs (human periodontal ligament stem cells). The pBMP2 was encapsulated in the PEI phase as a core and PLGA was employed to control pBMP2 release as a shell. First, the scaffold characterization and mechanical properties were evaluated. Then the gene release behavior was analyzed. Our results showed that pBMP2 was released at high levels in the first few days, with a continuous release behavior in the next 28 days. At the same time, PEI/pBMP2 showed high transfection efficiency. Moreover, the core-shell electrospun scaffold showed BMP2 expression for a much longer time (more than 28 days) compared with the single axial electrospun scaffold, as evaluated by qRT-PCR and western blot after culturing with hPDLSCs. These results suggested that the core-shell PEI/pBMP2-PLGA scaffold fabricated by coaxial electrospinning had a good gene release behavior and showed a prolonged expression time with a high transfection efficiency.