Inhibition of JAK2/STAT3 signaling suppresses bone marrow stromal cells proliferation and osteogenic differentiation, and impairs bone defect healing

LIF regulates the expression of miR-27a-3p and HOXA10 in bovine endometrial epithelial cells via STAT3 pathway

LIF is crucial in regulating embryo implantation, while HOXA10 is a marker gene for uterine receptivity. However, the specific mechanism of LIF regulating HOXA10 during cow embryo implantation has not been fully understood. To address this knowledge gap, the experiment involved treating bovine endometrial epithelial cells (BEECs) with LIF to investigate the relationship between LIF, miRNA, and HOXA10. The experimental findings revealed that applying LIF resulted in a substantial increase in the proliferation of endometrial epithelial cells. Moreover, the expressions of PI3K, AKT, HOXA10, CDK4, cyclinD1, and cyclinE1 were significantly elevated. Conversely, the expression of p21Cipl was significantly reduced. In the group that received a combination of LIF and a STAT3 inhibitor, the expression of PI3K/AKT remained significantly increased, but there was no significant change in the expression of HOXA10. When miRNA-27a-3p was overexpressed, it resulted in a decrease in both the RNA and protein expression of HOXA10. Conversely, inhibiting miRNA-27a-3p increased the RNA and protein expression of HOXA10. In the presence of LIF treatment, the expression of miRNA-27a-3p was reduced, while the expression of HOXA10 was increased. However, when LIF and a STAT3 inhibitor were combined, there was no significant change in the expression of miRNA-27a-3p or HOXA10. Consequently, LIF facilitated cell proliferation by activating the PI3K/AKT pathway. LIF controlled the expression of miRNA-27a-3p and HOXA10 in endometrial epithelial cells through STAT3, with miRNA-27a-3p negatively regulating the expression of HOXA10.

Cyclic mechanical stretch pre-stimulated bone marrow mesenchymal stem cells promote the healing of infected bone defect in a mouse model

Cyclic mechanical stretch (CMS) is an effective method to accelerate mesenchymal stem cells (MSCs) differentiation. Here, CMS pre-stimulated bone marrow MSCs (CMS-BMSCs) was investigated, characterized and evaluated the therapeutic potential of CMS-BMSCs on the treatment of infected bone defect in mouse model. BMSCs were obtained from C57BL/6J mice and then subjected to CMS. The osteogenic differentiation capacity of BMSCs was evaluated by alkaline phosphatase (ALP) assay, Alizarin Red staining, qRT-PCR, and Western blot. The pre-stimulated BMSCs were transplanted into infected bone defect mice, osteogenesis, antibacterial effects, and inflammatory responses were examined. CMS significantly increased ALP activity and the expression of osteoblastic genes (col1a1, runx2, and bmp7) and enhanced osteogenic differentiation and nrf2 expression of BMSCs. Transplantation of CMS pre-stimulated BMSCs promoted the healing of infected bone defect in mice, enhanced antibacterial effects, and reduced inflammatory responses in the mid-sagittal section of the fracture callus. CMS pre-stimulated BMSCs enhance the healing of infected bone defects in a mouse model, suggesting a potential therapeutic strategy for treating infected bone defects.

Signal transducer and activator of transcription 3 positively regulates osteoblastic differentiation in MC3T3-E1 cells

BACKGROUND

Signal transducer and activator of transcription 3 (STAT3) plays a pivotal role in osteoblastic differentiation. However, the exact role of STAT3 in osteogenic differentiation of the pre-osteoblastic cell line MC3T3-E1 is still controversial.

METHODS

In this study, we demonstrated that eradication of STAT3 signaling by the inhibitors cryptotanshinone (CPT, a STAT3-specific inhibitor) or STAT3 siRNA both suppressed osteogenic differentiation of MC3T3-E1 cells, with a decrease in alkaline phosphatase (ALP) activity, protein expressions of the osteogenic differentiation markers Collagen I (ColI), ALP, and osteocalcin (OCN), and reduced matrix mineralization capacity at the terminal stage of osteogenic differentiation. However, the inhibition of STAT3 by CPT did not affect MC3T3-E1 cell proliferation. To further clarify the effect of STAT3 on osteogenic differentiation of MC3T3-E1 cells, we forced STAT3 expression and found that this ameliorated osteogenic differentiation.

RESULTS

Thus, our results confirmed that STAT3 is a likely positive regulator of osteogenic differentiation in MC3T3-E1 cells.

CONCLUSIONS

These findings may provide a basis for the development of more efficient and controllable protocols for osteoblastic differentiation and facilitate their use in regenerative medicine. In addition, our results provide novel insights into the effect of the STAT3 antagonist CPT on modulation of osteogenesis.

Osteoclast-Derived Exosomal miR-5134-5p Interferes with Alveolar Bone Homeostasis by Targeting the JAK2/STAT3 Axis

Background

In chronic periodontitis, exosomes transport various informative substances between osteoclasts and osteoblasts in alveolar bone. Herein, we aimed to investigate the effect of exosomal micro-ribonucleic acid (miRNA/miR)-5134-5p derived from osteoclasts on osteoblastic proliferation and differentiation and the development of periodontitis in vivo and in vitro.

Methods

The effects of OC-Exos on the proliferation and differentiation of osteoblasts were identified by Real-time quantitative reverse polymerase chain reaction (qRT-PCR), Western blot(WB), alkaline phosphatase(ALP) staining, etc. Exosomal miRNA expression was analyzed by sequencing. The sites of miRNA action were predicted through TargetScan and tested by double luciferase assay. After transfecting miR-5134-5p mimic/inhibitor into osteoblasts, we measured the proliferation and differentiation of osteoblasts by ALP staining and WB, etc. Furthermore, OC-Exos were injected into the gingival sulcus at the ligation site. Inflammation was observed by Hematoxylin-eosin (H&E) staining, the expression of inflammatory factors were detected by qRT-PCR, the resorption of alveolar bone was observed by Micro CT.

Results

Osteoblastic proliferation and differentiation were negatively regulated by OC-Exos in vitro. miRNA sequencing analysis revealed that miR-5134-5p expression was significantly elevated in OC-Exos, which also increased in osteoblasts following OC-Exo intervention. The dual-luciferase assay revealed that miR-5134-5p and Janus kinase 2 (JAK2) had binding sites. miR-5134-5p-mimics could upregulate miR-5134-5p expression in osteoblasts while downregulating Runt-related transcription factor 2(Runx2), phosphorylated-JAK2 (p-JAK2), and phosphorylated-signal transducer and activator of transcription 3 (p-STAT3) expression and inhibited osteogenic differentiation. However, miR-5134-5p-inhibitor had the opposite effect. In vivo, the OC-Exo group demonstrated morphological disruption of periodontal tissue, massive inflammatory cell infiltration, upregulation of inflammatory factors mRNA expression, a significant decrease in BV/TV, and an increase in the cementoenamel junction and alveolar bone crest distance.

Conclusion

Osteoclast-derived exosomal miR-5134-5p inhibits osteoblastic proliferation and differentiation via the JAK2/STAT3 pathway. OC-Exos exacerbate periodontal tissue inflammation and accelerate alveolar bone resorption in mice with experimental periodontitis.

JAK/STAT as a Potential Therapeutic Target for Osteolytic Diseases

Several cytokines with major biological functions in inflammatory diseases exert their functions through the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signal transduction pathway. JAKs phosphorylate the cytoplasmic domain of the receptor, inducing the activation of its substrates, mainly the proteins known as STATs. STATs bind to these phosphorylated tyrosine residues and translocate from the cytoplasm to the nucleus, further regulating the transcription of several genes that regulate the inflammatory response. The JAK/STAT signaling pathway plays a critical role in the pathogenesis of inflammatory diseases. There is also increasing evidence indicating that the persistent activation of the JAK/STAT signaling pathway is related to several inflammatory bone (osteolytic) diseases. However, the specific mechanism remains to be clarified. JAK/STAT signaling pathway inhibitors have gained major scientific interest to explore their potential in the prevention of the destruction of mineralized tissues in osteolytic diseases. Here, our review highlights the importance of the JAK/STAT signaling pathway in inflammation-induced bone resorption and presents the results of clinical studies and experimental models of JAK inhibitors in osteolytic diseases.

Suppressing STAT3 activation impairs bone formation during maxillary expansion and relapse

OBJECTIVES

The mid-palatal expansion technique is commonly used to correct maxillary constriction in dental clinics. However, there is a tendency for it to relapse, and the key molecules responsible for modulating bone formation remain elusive. Thus, this study aimed to investigate whether signal transducer and activator of transcription 3 (STAT3) activation contributes to osteoblast-mediated bone formation during palatal expansion and relapse.

METHODOLOGY

In total, 30 male Wistar rats were randomly allocated into Ctrl (control), E (expansion only), and E+Stattic (expansion plus STAT3-inhibitor, Stattic) groups. Micro-computed tomography, micromorphology staining, and immunohistochemistry of the mid-palatal suture were performed on days 7 and 14. In vitro cyclic tensile stress (10% magnitude, 0.5 Hz frequency, and 24 h duration) was applied to rat primary osteoblasts and Stattic was administered for STAT3 inhibition. The role of STAT3 in mechanical loading-induced osteoblasts was confirmed by alkaline phosphatase (ALP), alizarin red staining, and western blots.

RESULTS

The E group showed greater arch width than the E+Stattic group after expansion. The differences between the two groups remained significant after relapse. We found active bone formation in the E group with increased expression of ALP, COL-I, and Runx2, although the expression of osteogenesis-related factors was downregulated in the E+stattic group. After STAT3 inhibition, expansive force-induced bone resorption was attenuated, as TRAP staining demonstrated. Furthermore, the administration of Stattic in vitro partially suppressed tensile stress-enhanced osteogenic markers in osteoblasts.

CONCLUSIONS

STAT3 inactivation reduced osteoblast-mediated bone formation during palatal expansion and post-expansion relapse, thus it may be a potential therapeutic target to treat force-induced bone formation.

Osteoblastic STAT3 Is Crucial for Orthodontic Force Driving Alveolar Bone Remodeling and Tooth Movement

Mechanical force is essential to shape the internal architecture and external form of the skeleton by regulating the bone remodeling process. However, the underlying mechanism of how the bone responds to mechanical force remains elusive. Here, we generated both orthodontic tooth movement (OTM) model in vivo and a cyclic stretch-loading model in vitro to investigate biomechanical regulation of the alveolar bone. In this study, signal transducer and activator of transcription 3 (STAT3) was screened as one of the mechanosensitive proteins by protein array analysis of cyclic stretch-loaded bone mesenchymal stem cells (BMSCs) and was also proven to be activated in osteoblasts in response to the mechanical force during OTM. With an inducible osteoblast linage-specific Stat3 knockout model, we found that Stat3 deletion decelerated the OTM rate and reduced orthodontic force-induced bone remodeling, as indicated by both decreased bone resorption and formation. Both genetic deletion and pharmacological inhibition of STAT3 in BMSCs directly inhibited mechanical force-induced osteoblast differentiation and impaired osteoclast formation via osteoblast-osteoclast cross-talk under mechanical force loading. According to RNA-seq analysis of Stat3-deleted BMSCs under mechanical force, matrix metalloproteinase 3 (Mmp3) was screened and predicted to be a downstream target of STAT3. The luciferase and ChIP assays identified that Stat3 could bind to the Mmp3 promotor and upregulate its transcription activity. Furthermore, STAT3-inhibitor decelerated tooth movement through inhibition of the bone resorption activity, as well as MMP3 expression. In summary, our study identified the mechanosensitive characteristics of STAT3 in osteoblasts and highlighted its critical role in force-induced bone remodeling during orthodontic tooth movement via osteoblast-osteoclast cross-talk. © 2022 American Society for Bone and Mineral Research (ASBMR).

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

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

Oxalate induces the ossification of RTECs by activating the JAK2/STAT3 signaling pathway and participates in the formation of kidney stones

BACKGROUND

The ossification of renal tubular epithelial cells (RTECs) plays an important initial role in the formation of kidney stones, but its specific mechanism is still unclear. The JAK2/STAT3 signaling pathway is important for bone cell differentiation. Accordingly, we explored the role and mechanism of the JAK2/STAT3 signaling pathway in the ossification of RTECs.

METHODS

We used oxalate or ethylene glycol to construct kidney stone models in vitro and in vivo, and investigated the expression of osteogenic-specific genes, osteogenesis ability, and JAK2/STAT3 signaling in the kidney stone models by western blotting, qRT-PCR, immunofluorescence, and immunohistochemistry. Then, genetic engineering or drugs were used to inhibit the expression or activation of JAK2, and the expression of osteogenic-specific genes and the osteogenic ability of the RTECs were determined again.

RESULTS

In the in vitro and in vivo kidney stone models, the expression of osteogenic specific genes in the RTECs was significantly upregulated, the osteogenic capacity was significantly increased, and the expression of p-JAK2 (phospho-JAK2) and p-STAT3 (phospho-STAT3) was significantly increased. When the expression or activation of JAK2 was inhibited, the ossification of RTECs and the formation of kidney stones was reversed.

CONCLUSIONS

During the formation of kidney stones, RTECs undergo obvious ossification, and the JAK2/STAT3 signaling pathway plays a key positive regulatory role in this process.

Stat3 Signaling Pathway: A Future Therapeutic Target for Bone-Related Diseases

Signal transducer and activator of transcription 3 (Stat3) is activated by phosphorylation and translocated to the nucleus to participate in the transcriptional regulation of DNA. Increasing evidences point that aberrant activation or deletion of the Stat3 plays a critical role in a broad range of pathological processes including immune escape, tumorigenesis, and inflammation. In the bone microenvironment, Stat3 acts as a common downstream response protein for multiple cytokines and is engaged in the modulation of cellular proliferation and intercellular interactions. Stat3 has direct impacts on disease progression by regulating mesenchymal stem cells differentiation, osteoclast activation, macrophage polarization, angiogenesis, and cartilage degradation. Here, we describe the theoretical basis and key roles of Stat3 in different bone-related diseases in combination with in vitro experiments and animal models. Then, we summarize and categorize the drugs that target Stat3, providing potential therapeutic strategies for their use in bone-related diseases. In conclusion, Stat3 could be a future target for bone-related diseases.

The Interleukin-6 trans-signaling promotes progesterone production in human granulosa-lutein cells

As a critical paracrine regulator of multiple reproductive functions, the cytokine interleukin-6 (IL-6) is expressed in human granulosa cells and can be detected in follicular fluid. At present, the functional role of IL-6 in the regulation of ovarian steroidogenesis is controversial. Moreover, the detailed molecular mechanisms by which IL-6 regulates the production of progesterone in human granulosa cells remain to be elucidated. In the present study, we used primary and immortalized human granulosa-lutein (hGL) cells to investigate the effects of IL-6 on progesterone synthesis and the underlying molecular mechanisms. We found that IL-6 trans-signaling by the combined addition of IL-6 and soluble IL-6 receptor (sIL-6Rα) induced StAR expression and progesterone production in hGL cells. Additionally, IL-6/sIL-6Rα activated the phosphorylation of Janus activated kinase 2 (JAK2) and signal transducer and activator of transcription 3 (STAT3), and the cellular effects were abolished by AG490 (JAK2 inhibitor), C188–9 (STAT3 inhibitor), or siRNA-mediated knockdown of STAT3. IL-6 trans-signaling-induced activation of JAK2/STAT3 also upregulated the expression of suppressor of cytokine signaling 3 (SOCS3), which, in turn, negatively regulated the JAK2/STAT3 pathway by suppressing STAT3 activation and its downstream effects. Our findings provide insight into the molecular mechanisms by which IL-6 trans-signaling modulates steroidogenesis in hGL cells.

Advances in mesenchymal stem cell conditioned medium-mediated periodontal tissue regeneration

Periodontitis is a chronic inflammatory disease that leads to the destruction of both soft and hard periodontal tissues. Complete periodontal regeneration in clinics using the currently available treatment approaches is still a challenge. Mesenchymal stem cells (MSCs) have shown promising potential to regenerate periodontal tissue in various preclinical and clinical studies. The poor survival rate of MSCs during in vivo transplantation and host immunogenic reaction towards MSCs are the main drawbacks of direct use of MSCs in periodontal tissue regeneration. Autologous MSCs have limited sources and possess patient morbidity during harvesting. Direct use of allogenic MSCs could induce host immune reaction. Therefore, the MSC-based indirect treatment approach could be beneficial for periodontal regeneration in clinics. MSC culture conditioned medium (CM) contains secretomes that had shown immunomodulatory and tissue regenerative potential in pre-clinical and clinical studies. MSC-CM contains a cocktail of growth factors, cytokines, chemokines, enzymes, and exosomes, extracellular vesicles, etc. MSC-CM-based indirect treatment has the potential to eliminate the drawbacks of direct use of MSCs for periodontal tissue regeneration. MSC-CM holds the tremendous potential of bench-to-bed translation in periodontal regeneration applications. This review focuses on the accumulating evidence indicating the therapeutic potential of the MSC-CM in periodontal regeneration-related pre-clinical and clinical studies. Recent advances on MSC-CM-based periodontal regeneration, existing challenges, and prospects are well summarized as guidance to improve the effectiveness of MSC-CM on periodontal regeneration in clinics.

Biological Functions of Let-7e-5p in Promoting the Differentiation of MC3T3-E1 Cells

MicroRNAs let-7c and let-7f, two members of the let-7 family, were involved in regulating osteoblast differentiation and have an important role in bone formation. Let-7e-5p, which also belonged to the let-7 family, presented in the differentiation of adipose-derived stem cells and mouse embryonic stem cells. However, the role of let-7e-5p in osteoblast differentiation was unclear. Thus, this study aimed to elucidate the function of let-7e-5p in osteoblast differentiation and its mechanism. Firstly, we found that the let-7e-5p mimic promoted osteoblast differentiation but not the proliferation of MC3T3-E1 cells by positively regulating the expression levels of osteogenic-associated genes (RUNX2, OCN, OPN, and OSX), the activity of ALP, and formation of mineralized nodules. Moreover, we ascertained that the let-7e-5p mimic downregulated the post-transcriptional expression of SOCS1 by specifically binding to the 3′ untranslated region of SOCS1 mRNA. Also, let-7e-5p-induced SOCS1 downregulation increased the protein levels of p-STAT5 and IGF-1, which were both modulated by SOCS1 molecules. Furthermore, let-7e-5p abrogated the inhibition of osteogenic differentiation mediated by SOCS1 overexpression. Therefore, these results suggested that let-7e-5p regulated the differentiation of MC3T3-E1 cells through the JAK2/STAT5 pathway to upregulate IGF-1 gene expression by inhibiting SOCS1. These findings may provide a new insight into the regulatory role of let-7e-5p in osteogenic differentiation and imply the existence of a novel mechanism underlying let-7e-5p-mediated osteogenic differentiation.

Astragaloside IV Improves Tibial Defect in Rats and Promotes Proliferation and Osteogenic Differentiation of hBMSCs through MiR-124-3p.1/STAT3 Axis

Astragaloside IV (AST-IV) facilitates the proliferation and migration of osteoblast-like cells. We sought to explore the effect and potential mechanism of AST-IV on regeneration of tibial defects. To reveal the effect of AST-IV on regeneration of tibial defects in rat, HE staining and microcomputed tomography (μCT) were performed on tibial bone. The binding relationship between miR-124-3p.1 and STAT3 was analyzed by TargetScan V7.2 and a dual-luciferase reporter assay. Human bone marrow mesenchymal stromal/stem cells (hBMSCs) were identified by morphological observation and flow-cytometric analysis. To reveal the effect and mechanism of AST-IV on phenotypes of hBMSCs, hBMSCs were treated with AST-IV, miR-124-3p.1 mimic, and pcDNA-STAT3, and cell viability, cell cycle, ALP activity, and calcium deposition of hBMSCs in vitro were determined by MTT, flow-cytometric analysis, ELISA, and Alizarin red staining, respectively. The expressions of osteoblast marker molecules (RUNX2, OCN, Smad4), miR-124-3p.1, and STAT3 were indicated by RT-qPCR and Western blot. AST-IV decreased miR-124-3p.1 expression, increased STAT3 expression in tibial bone defects, and promoted regeneration of tibial bone defects in a concentration-dependent manner. The hBMSCs appeared spindle-shaped and were positive for CD105, but negative for CD34. MiR-124-3p.1 negatively regulated STAT3 expression in hBMSCs under osteogenic conditions. AST-IV promoted viability, cell cycle, ALP activity, and osteogenic differentiation of hBMSCs along with increased expressions of osteoblast marker molecules, which was partially reversed by miR-124-3p.1 overexpression. However, the effect of miR-124-3p.1 overexpression on hBMSCs was also partially reversed by STAT3 overexpression. AST-IV improves tibial defects in rats and promotes proliferation and osteogenic differentiation of hBMSCs through the miR-124-3p.1/STAT3 axis.

STAT3 activation by catalpol promotes osteogenesis-angiogenesis coupling, thus accelerating osteoporotic bone repair

BACKGROUND

Bone fracture repair has gained a lot of attention due to the high incidence of delayed union or even nonunion especially in osteoporotic patients, resulting in a dreadful impact on the quality of life. However, current therapies involve the costly expense and hence become unaffordable strategies for fracture recovery. Herein, developing new strategies for better bone repair is essential and urgent. Catalpol treatment has been reported to attenuate bone loss and promote bone formation. However, the mechanisms underlying its effects remain unraveled.

METHODS

Rat bone marrow mesenchymal stem cells (BMSCs) were isolated from rat femurs. BMSC osteogenic ability was assessed using ALP and ARS staining, immunofluorescence, and western blot analysis. BMSC-mediated angiogenic potentials were determined using the western blot analysis, ELISA testing, scratch wound assay, transwell migration assay, and tube formation assay. To investigate the molecular mechanism, the lentivirus transfection was used. Ovariectomized and sham-operated rats with calvaria defect were analyzed using micro-CT, H&E staining, Masson's trichrome staining, microfil perfusion, sequential fluorescent labeling, and immunohistochemistry assessment after administrated with/without catalpol.

RESULTS

Our results manifested that catalpol enhanced BMSC osteoblastic differentiation and promoted BMSC-mediated angiogenesis in vitro. More importantly, this was conducted via the JAK2/STAT3 pathway, as knockdown of STAT3 partially abolished beneficial effects in BMSCs. Besides, catalpol administration facilitated bone regeneration as well as vessel formation in an OVX-induced osteoporosis calvarial defect rat model.

CONCLUSIONS

The data above showed that catalpol could promote osteogenic ability of BMSC and BMSC-dependent angiogenesis through activation of the JAK2/STAT3 axis, suggesting it may be an ideal therapeutic agent for clinical medication of osteoporotic bone fracture.

MEK1/2 Inhibitor (GDC0623) Promotes Osteogenic Differentiation of Primary Osteoblasts Inhibited by IL-1β through the MEK-Erk1/2 and Jak/Stat3 Pathways

OBJECTIVE

We evaluated the effects and mechanisms of GDC0623 on osteogenic differentiation of osteoblasts induced by IL-1β. Methodology. Osteoblasts were treated with 20 ng/ml IL-1β and 0.1 µM GDC0623. Cell proliferation levels were evaluated by the cell counting kit 8 (CCK8), EdU assay, and western blotting [proliferating cell nuclear antigen (PCNA) and Cyclin D1]. Osteoblasts were cultured in an osteogenic induction medium for 1-3 weeks after which their differentiations were assessed by alkaline phosphatase (ALP) staining, Alizarin Red staining, calcium concentration, immunocytochemistry staining, real-time quantitative PCR (RT-qPCR), and immunofluorescence staining. The osteogenesis-associated mechanisms were further evaluated by western blotting using appropriate antibodies.

RESULTS

Relative to the control group, IL-1β induced the rapid proliferation of osteoblasts and suppressed their osteogenic differentiations by upregulating the activities of MEK-Erk1/2 as well as Jak-Stat3 pathways and by elevating MMP13 and MMP9 levels. However, blocking of the MEK-Erk1/2 signaling pathway by GDC0623 treatment reversed these effects.

CONCLUSION

Inhibition of Jak-Stat3 pathway by C188-9 downregulated the expression levels of MMP9 and MMP13, activated MEK-Erk1/2 pathway, and inhibited osteogenic differentiation.

Platelet Lysate Induces in Human Osteoblasts Resumption of Cell Proliferation and Activation of Pathways Relevant for Revascularization and Regeneration of Damaged Bone

To understand the regenerative effect of platelet-released molecules in bone repair one should investigate the cascade of events involving the resident osteoblast population during the reconstructive process. Here the in vitro response of human osteoblasts to a platelet lysate (PL) stimulus is reported. Quiescent or very slow dividing osteoblasts showed a burst of proliferation after PL stimulation and returned to a none or very slow dividing condition when the PL was removed. PL stimulated osteoblasts maintained a differentiation capability in vitro and in vivo when tested in absence of PL. Since angiogenesis plays a crucial role in the bone healing process, we investigated in PL stimulated osteoblasts the activation of hypoxia-inducible factor 1-alpha (HIF-1α) and signal transducer and activator of transcription 3 (STAT3) pathways, involved in both angiogenesis and bone regeneration. We observed phosphorylation of STAT3 and a strong induction, nuclear translocation and DNA binding of HIF-1α. In agreement with the induction of HIF-1α an enhanced secretion of vascular endothelial growth factor (VEGF) occurred. The double effect of the PL on quiescent osteoblasts, i.e., resumption of proliferation and activation of pathways promoting both angiogenesis and bone formation, provides a rationale to the application of PL as therapeutic agent in post-traumatic bone repair.

Tensile force-induced PDGF-BB/PDGFRβ signals in periodontal ligament fibroblasts activate JAK2/STAT3 for orthodontic tooth movement

Orthodontic force-induced osteogenic differentiation and bone formation at tension side play a pivotal role in orthodontic tooth movement (OTM). Platelet-derived growth factor-BB (PDGF-BB) is a clinically proven growth factor during bone regeneration process with unclear mechanisms. Fibroblasts in periodontal ligament (PDL) are considered to be mechanosensitive under orthodontic force. Thus, we established OTM model to investigate the correlation between PDGF-BB and fibroblasts during bone regeneration at tension side. We confirmed that tensile force stimulated PDL cells to induce osteogenic differentiation via Runx-2, OCN up-regulation, and to accelerate new bone deposition along the periodontium and the alveolar bone interface. Interestingly, PDGF-BB level was remarkably enhanced at tension side during OTM in parallel with up-regulated PDGFRβ+/α-SMA+ fibroblasts in PDL by immunohistochemistry. Moreover, orthodontic force-treated primary fibroblasts from PDL were isolated and, cultured in vitro, which showed similar morphology and phenotype with control fibroblasts without OTM treatment. PDGFRβ expression was confirmed to be increased in orthodontic force-treated fibroblasts by immunofluorescence and flow cytometry. Bioinformatics analysis identified that PDGF-BB/PDGFRβ signals were relevant to the activation of JAK/STAT3 signals. The protein expression of JAK2 and STAT3 was elevated in PDL of tension side. Importantly, in vivo, the treatment of the inhibitors (imatinib and AG490) for PDGFRβ and JAK-STAT signals were capable of attenuating the tooth movement. The osteogenic differentiation and bone regeneration in tension side were down-regulated upon the treatment of inhibitors during OTM. Meanwhile, the expressions of PDGFRβ, JAK2 and STAT3 were inhibited by imatinib and AG490. Thus, we concluded that tensile force-induced PDGF-BB activated JAK2/STAT3 signals in PDGFRβ⁺ fibroblasts in bone formation during OTM.

Mmu_circ_003795 regulates osteoblast differentiation and mineralization in MC3T3‑E1 and MDPC23 by targeting COL15A1

Circular RNAs (circRNAs) are a class of non-coding RNAs that exhibit important regulatory roles in various biological processes. However, the role of circRNAs and their potential role in osteoblast differentiation and mineralization is unclear. The aim of the present study was to investigate the expression of mmu_circ_003795 and its effect on collagen type XV α 1 chain (COL15A1). First, it was identified that the expression levels of mmu_circ_003795 and osteopontin (OPN) were upregulated in the induced cells. Silencing of mmu_circ_003795 reduced the gene and protein levels of COL15A1 and OPN, whereas the expression level of mmu-microRNA (miR)-1249-5p was upregulated. In addition, after 7 or 14 days of induction, alkaline phosphatase and Alizarin Red-S staining were decreased in the mmu_circRNA_003795 inhibitory group compared with the negative control group. In conclusion, mmu_circ_003795 may regulate osteoblast differentiation and mineralization in MC3T3-E1 and MDPC23 cells via mmu-miR-1249-5p by targeting COL15A1.

The potential function of miR-135b-mediated JAK2/STAT3 signaling pathway during osteoblast differentiation

MC3T3-E1 cells were divided into Blank, miR-135b mimics, miR-135b inhibitors, AG490, and miR-135b inhibitors + AG490 groups. Cell viability was determined by MTT, alkaline phosphatase (ALP) activity by the corresponding kit, and mineralization by alizarin red staining. Furthermore, miR-135b, osteoblast-specific genes, and JAK2/STAT3 were detected through quantitative real-time polymerase chain reaction and Western blotting. MiR-135b downregulation was identified with increased JAK2 during osteoblast differentiation. JAK2 was confirmed as a target gene of miR-135b by dual-luciferase reporter assay. MC3T3-E1 cells in both miR-135b mimics and AG490 groups manifested decrease in cell viability, ALP activity, and mineralized nodes, as well as reductions in osteoblast-specific genes and proteins of JAK2, p-JAK2, and p-STAT3, but increase in cell apoptosis. However, opposite changes of the above factors were shown in cells from miR-135b inhibitors group. Notably, AG490 could reverse promotion effects of miR-135b inhibitors on osteoblast differentiation. Inhibiting miR-135b could activate the JAK2/STAT3 signaling pathway, thereby improving the cell viability and promoting the osteoblast differentiation.

The lncRNA MCF2L-AS1 controls osteogenic differentiation by regulating miR-33a

Bone homeostasis is maintained by balanced osteoblast-mediated tissue production and osteoclast-mediated tissue destruction, and is disrupted in pathological conditions such as osteoporosis. The mechanisms underlying osteogenic differentiation of bone marrow mesenchymal stem cells, which is critical to bone homeostasis, are not completely clear, despite extensively studies. Long noncoding RNAs (lncRNAs) have recently emerged as novel therapeutic targets in various diseases. However, the expression pattern and biological function of lncRNAs in osteogenic differentiation remain unclear. In this study, we aimed to determine the role of lncRNAs in osteogenic differentiation of human bone marrow mesenchymal stem cells. We found high lncRNA MCF2L-AS1 expression in human bone marrow mesenchymal stem cells, and used bioinformatics analysis to analyze its function. MCF2L-AS1 knockdown induced inhibition of osteoblast differentiation. Silencing of MCF2L-AS1 increased the expression of miR-33a and subsequently inhibited Runx2 expression at the post-transcriptional level. Moreover, MCF2L-AS1 directly interacted with miR-33a, and downregulation of miR-33a efficiently reversed the suppression of Runx2 induced by MCF2L-AS1 short hairpin RNA (shRNA). Thus, MCF2L-AS1 positively regulated the expression of Runx2 by sponging miR-33a, and promoted osteogenic differentiation in BMSCs. Our results indicated that the lncRNA MCF2L-AS1 plays a critical role in the osteogenic differentiation of BMSCs, and targeting lncRNA MCF2L-AS1 could be a promising strategy to promote osteogenic differentiation.

RAI3 knockdown enhances osteogenic differentiation of bone marrow mesenchymal stem cells via STAT3 signaling pathway

Bone marrow mesenchymal stem cells (BMSCs), which have multipotential differentiation and self-renewal ability, have been becoming an attractive source of seed cells for bone tissue engineering. Nonetheless, the precise underlying mechanisms of osteogenesis of BMSCs have not been fully understood. Retinoic acid-induced gene 3 (RAI3) has been found to play important roles in mesenchymal stem cells (MSCs) adipogenesis in our previous study. However, its function in the osteogenic differentiation of BMSCs remains unknown. In this study, we found that RAI3 was significantly reduced in osteogenically differentiated BMSCs; RAI3 knockdown promoted osteogenesis of BMSCs both in vitro and in vivo. Moreover, we found RAI3 knockdown significantly upregulated the expression level of phosphorylated signal transducer and activator of transcription 3 (p-STAT3), and AG-490 which can inhibit the STAT3 signaling reversed the enhancing effect of RAI3 knockdown on the osteogenic differentiation of BMSCs. These results suggest that RAI3 plays important roles in BMSCs osteogenesis with an involvement of the STAT3 signaling, which might open a new avenue to explore BMSCs osteogenesis for the application of BMSCs in bone regeneration.

Nuclear accumulation of pyruvate kinase M2 promotes liver regeneration via activation of signal transducer and activator of transcription 3

AIMS

Pyruvate kinase M2 (PKM2), a unique isoform of the pyruvate kinases, not only acts as a crucial metabolic enzyme when it locates in the cytoplasm, but also plays important roles in tumor formation and growth when it accumulates in the nuclei. Our aim was to investigate the potential role of PKM2 in liver regeneration in mice insulted with carbon tetrachloride (CCl₄).

MATERIAL AND METHODS

The liver regeneration model was established by intraperitoneal injection of CCl₄ for 48 h in male BALB/c mice. The expression of PKM2, phospho-STAT3, STAT3, proliferating cell nuclear antigen (PCNA) and Cyclin D1 were evaluated by western blot. The distribution of PKM2 was verified by immunofluorescence staining. The degree of injured region was assessed by hematoxylin and eosin (HE) staining. The proliferation of liver cells was tested by Immunohistochemistry.

KEY FINDINGS

The nuclear accumulation of PKM2 increased in the liver treated with CCl₄, but treatment with ML-265 significantly suppressed CCl₄-induced nuclear accumulation of PKM2. In addition, treatment with ML-265 suppressed the level of cyclin D1 and proliferating cell nuclear antigen (PCNA), reduced the count of Ki67-positive hepatocytes, and expanded the damaged region in histological examination. Meanwhile, treatment with ML-265 suppressed the phosphorylation of nuclear signal transducer and activator of transcription 3 (STAT3). Inhibition of STAT3 by stattic made the same effects as ML-265.

SIGNIFICANCE

These data uncovered the role of nuclear PKM2 in liver regeneration and the pro-proliferation effects of nuclear PKM2 may be through targeting its downstream transcription factor STAT3.

Chronic Hypoxia-Induced Microvessel Proliferation and Basal Membrane Degradation in the Bone Marrow of Rats Regulated through the IL-6/JAK2/STAT3/MMP-9 Pathway

Chronic hypoxia (CH) is characterized by long-term hypoxia that is associated with microvessel proliferation and basal membrane (BM) degradation in tissues. The IL-6/JAK2/STAT3/MMP-9 pathway has been described in a variety of human cancers and plays an essential role in microvessel proliferation and BM degradation. Therefore, this study investigated the role of the IL-6/JAK2/STAT3/MMP-9 pathway in hypoxia-mediated microvessel proliferation and BM degradation in the rat bone marrow. Eighty pathogen-free Sprague Dawley male rats were randomly divided into four groups (20 per group)—control group, CH group (exposed to hypoxia in a hypobaric chamber at a simulated altitude of 5000 m for 28 d), CH + STAT3 inhibitor group (7.5 mg/kg/d), and CH + DMSO group. Microvessel density (MVD) and BM degradation in the bone marrow were determined by immunofluorescence staining and transmission electron microscopy. Serum IL-6 levels were assessed by enzyme-linked immunosorbent assay (ELISA), and the levels of P-JAK2, P-STAT3, and MMP-9 were assessed by western blot analysis and real-time reverse transcription PCR (RT-PCR). Hypoxia increased serum IL-6 levels, which in turn increased JAK2 and STAT3 phosphorylation, which subsequently upregulated MMP-9. Overexpression of MMP-9 significantly promoted the elevation of MVD and BM degradation. Inhibition of STAT3 using an inhibitor, SH-4-54, significantly downregulated MMP-9 expression and decreased MVD and BM degradation. Surprisingly, STAT3 inhibition also decreased serum IL-6 levels and JAK2 phosphorylation. Our results suggest that the IL-6/JAK2/STAT3/MMP-9 pathway might be related to CH-induced microvessel proliferation and BM degradation in the bone marrow.

miR-21 may Act as a Potential Mediator Between Inflammation and Abnormal Bone Formation in Ankylosing Spondylitis Based on TNF-α Concentration-Dependent Manner Through the JAK2/STAT3 Pathway

Objective:

To explore the role of microRNA (miR-21) in new bone formation in ankylosing spondylitis (AS) as mediated by different concentration of tumor necrosis factor-α (TNF-α).

Methods:

Fibroblasts isolated from the hips of patients with AS were induced to osteogenesis. These cells were then stimulated with varying concentrations of TNF-α. MicroRNA-21 expressions were evaluated using reverse transcription–polymerase chain reaction (RT-PCR) and osteogenesis was detected via Alizarin Red S (ARS) staining and measurement of alkaline phosphatase (ALP) activity. Relative expressions of p-STAT3, Nuclear STAT3, cytoplasm STAT3, Runx2, BMP2, osteopontin, osteocalcin, and LC3B in AS fibroblasts were measured after exposure to different concentrations of TNF-α. The STAT3-inhibiting small interfering RNA allowed further exploration on its impact on miR-21 and primary miR-21 expressions. A proteoglycan-induced arthritis (PGIA) Balb/c mouse model was established in order to monitor sacroiliac joint (SIJ) inflammation and subsequent damage through magnetic resonance image. Serum miR-21 and TNF-α expressions were evaluated using RT-PCR and enzyme-linked immunosorbent assay. At week 16, mice models were transfected intravenously with miR-21 overexpressing agomir and miR-21 inhibiting antagomir for 7 successive days. The rate of abnormal bone formation at SIJ was evaluated using microcomputed tomography and hematoxylin and eosin staining at week 24. Western blot analysis enabled quantification of STAT-3, JAK-2, and interleukin (IL)-17A expressions present in the SIJ.

Results:

The in vitro miR-21 expression and osteogenesis activity were noted to be augmented in the setting of low TNF-α concentrations (0.01-0.1 ng/mL) while they were depressed in settings with higher TNF-α concentrations (1-10 ng/mL). Samples with the most distinct ARS manifestation and ALP activity as well as the highest miR-21 expressions were those who received 0.1 ng/mL of TNF-α. Primary miR-21 was found to be notable raised by Si-STAT3, while the converse effect was seen in mature miR-21 expressions. Intravenous injection of exogenous miR-21 contributed to new bone formation and significantly elevated expressions of STAT3, JAK2, and IL-17 in PGIA mice.

Conclusions:

The results revealed that miR-21 may act as a potential mediator between new bone formation and inflammation in AS.

Dicalcium silicate microparticles modulate the differential expression of circRNAs and mRNAs in BMSCs and promote osteogenesis via circ_1983–miR-6931–Gas7 interaction

Among C₂S-induced differentially expressed circRNAs, circ_1983 is involved in osteogenesis via circ_1983–miR-6931–Gas7 ceRNA interaction-mediated Runx2 upregulation.

Cellular hypoxia promotes osteogenic differentiation of mesenchymal stem cells and bone defect healing via STAT3 signaling

Background

Hypoxia in the vicinity of bone defects triggers the osteogenic differentiation of precursor cells and promotes healing. The activation of STAT3 signaling in mesenchymal stem cells (MSCs) has similarly been reported to mediate bone regeneration. However, the interaction between hypoxia and STAT3 signaling in the osteogenic differentiation of precursor cells during bone defect healing is still unknown.

Methods

In this study, we assessed the impact of different durations of CoCl₂-induced cellular hypoxia on the osteogenic differentiation of MSCs. Role of STAT3 signaling on hypoxia induced osteogenic differentiation was analyzed both in vitro and in vivo. The interaction between cellular hypoxia and STAT3 signaling in vivo was investigated in a mouse femoral bone defect model.

Results

The peak osteogenic differentiation and expression of vascular endothelial growth factor (VEGF) occurred after 3 days of hypoxia. Inhibiting STAT3 reversed this effect. Hypoxia enhanced the expression of hypoxia-inducible factor 1-alpha (HIF-1α) and STAT3 phosphorylation in MSCs. Histology and μ-CT results showed that CoCl₂ treatment enhanced bone defect healing. Inhibiting STAT3 reduced this effect. Immunohistochemistry results showed that CoCl₂ treatment enhanced Hif-1α, ALP and pSTAT3 expression in cells present in the bone defect area and that inhibiting STAT3 reduced this effect.

Conclusions

The in vitro study revealed that the duration of hypoxia is crucial for osteogenic differentiation of precursor cells. The results from both the in vitro and in vivo studies show the role of STAT3 signaling in hypoxia-induced osteogenic differentiation of precursor cells and bone defect healing.

The inhibition of miR‑101a‑3p alleviates H/R injury in H9C2 cells by regulating the JAK2/STAT3 pathway

Hypoxia/reoxygenation (H/R) is used as an in vivo model of ischemia/reperfusion injury, and myocardial ischemia can lead to heart disease. Therefore, it is necessary to prevent myocardial H/R injury to avoid the risk of heart disease. The aim of the present study was to investigate whether inhibiting microRNA (miR)-101a-3p attenuated H9C2 cell H/R injury, apoptosis mechanisms and key target proteins. Cell viability and apoptosis were determined by Cell Counting Kit-8 assays and flow cytometry using a cell apoptosis kit, respectively. The contents of creatine kinase (CK) and lactate dehydrogenase (LDH) were detected using colorimetric assays. Dual luciferase assays were carried out to determine if miR-101a-3p inhibited Janus kinase (JAK)2. Western blot analysis and reverse transcription-quantitative PCR were used to determine proteins levels and mRNAs expression. It was found that the inhibition of miR-101a-3p increased the growth of H9C2 cells and decreased H9C2 cell apoptosis during H/R injury. The inhibition of miR-101a-3p reduced the amounts of CK and LDH in H/R model H9C2 cells. The inhibition of miR-101a-3p lowered the levels of Bax, interleukin-6 and tumor necrosis factor-α, but raised the levels of phosphorylated (p)-STAT3 and p-JAK2 in H9C2 cells subjected to H/R injury treatment. miR-101a-3p mimic was found to inhibit H9C2 cell viability, raise p-JAK2 level and slightly increase p-STAT3 during H/R injury. AG490 induced H9C2 cell apoptosis, and decreased the levels of p-JAK2 and p-STAT3 during H/R injury. The data indicated that inhibiting miR-101a-3p reduced H/R damage in H9C2 cells and decreased apoptosis via Bax/Bcl-2 signaling during H/R injury. In addition, it was suggested that the inhibition of miR-101a-3p decreased H/R injury in H9C2 cell by regulating the JAK2/STAT3 signaling pathway.

Inhibition of miR-337-3p involved in the protection of CoCl2 -induced injury in PC12 cells via activating JAK2/STAT3 signaling pathway

OBJECTIVE

To investigate the possibility of microRNA (miR)-337-3p in the protection of hypoxia-induced injury in PC12 cells via modulating the JAK2/STAT3 signaling pathway.

METHODS

Dual-luciferase reporter assay analyzed the relationship between the miR-337-3p and JAK2. PC12 cells were divided into normal, CoCl₂ , CoCl2 + NC, CoCl2 + inhibitors, CoCl2 + JAK2, and CoCl2 + mimics + JAK2 groups. Then, PC12 cell viability and apoptosis were measured by the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) and Annexin-V-fluorescein isothiocyanate/propidium iodide methods. Quantitative real-time polymerase chain reaction and Western blot analysis were used to determine expressions. Besides, the intracellular reactive oxygen species (ROS) was examined by dichloro-dihydro-fluorescein diacetate (DCFH-DA) while the mitochondrial membrane potential (MMP) by using JC-1.

RESULTS

The negative targeting relationship between miR-337-3p and JAK2 was confirmed. When compared with the normal group, miR-337-3p was increased while JAK2 and STAT3 were decreased in CoCl₂ -induced PC12 cells, with decreased cell viability. Moreover, either miR-337-3p inhibitor or JAK2 overexpression could partially reverse CoCl₂ -induced decrease in PC12 cell viability. Besides, CoCl₂ could also trigger PC12 cell apoptosis by increasing cleaved caspase 3 and Bax but decreasing Bcl-2 and Bcl-XL, which, however, were abolished with the transfection of miR-337-3p inhibitors or lentivirus transfection to activate JAK2. Compared with the CoCl₂ group, the average of fluorescent signals of ROS in the CoCl2 + inhibitors group and the CoCl2 + JAK2 group was lower, while the activities of superoxide dismutase, catalase, glutathione peroxidase, and total anti-oxidative capacity were higher, together with an increase in MMP.

CONCLUSION

Inhibiting miR-337-3p could activate the JAK2/STAT3 signaling pathway to suppress CoCl ₂ -induced cytotoxicity and apoptosis and ameliorate oxidative stress and MMP in PC12 cells.

HIF-1α facilitates osteocyte-mediated osteoclastogenesis by activating JAK2/STAT3 pathway in vitro

Osteocytes, entrapped within the mineralized bone matrix, has been found to have numerous functions such as acting as an orchestrator of bone remodeling through regulation of both osteoclast and osteoblast activity and also functioning as an endocrine cell. Due to a specialized morphology and surrounding structure, osteocytes are more tolerant to hypoxia during osteoporosis, fracture, osteoarthritis, and orthodontic-orthognathic combination therapy. Hypoxia-inducible factor-1α (HIF-1α) is one of the master regulators of hypoxia reactions, playing an important role in bone modeling, remodeling, and homeostasis. This study aimed to investigate the pivotal functional role of HIF-1α in osteocytes initiating of bone remodeling under hypoxia. In the present study, the osteoclasts formation induced by RAW264.7 was significantly promoted in conditioned media (CM) from osteocytic MLO-Y4 exposed to hypoxia in vitro. Therefore, hypoxic MLO-Y4 cells simulated by 100 μmol/L CoCl₂ or 2% O₂ stably expressed HIF-1α proteins and upregulated the expression of receptor activator of nuclear factor-κB ligand (RANKL) at both the messenger RNA (mRNA) and protein level. Furthermore, with the Knockdown of HIF-1α, the expression of RANKL mRNA and protein decreased after transient transfection. In addition, the phosphorylation of Janus kinase 2 (JAK2) and signal transducer and activator of transcription (STAT3) was also correlated with HIF-1α and RANKL levels under hypoxia. Then AG490, a JAK2 inhibitor, inhibited p-JAK2, p-STAT3 and RANKL expression. It was possible that AG490 disturbed the contact of HIF-1α and RANKL by JAK2/STAT3 pathway, influencing osteoclastogenesis. Our findings suggested that HIF-1α promoted the expression of RANKL by activating JAK2/STAT3 pathway in MLO-Y4 cells, and enhanced osteocyte-mediated osteoclastic differentiation in vitro.

RIPK1 suppresses apoptosis mediated by TNF and caspase-3 in intervertebral discs

BACKGROUND

Low back pain has become a serious social and economic burden and the leading cause of disability worldwide. Among a variety of pathophysiological triggers, intervertebral disc (IVD) degeneration plays a primary underlying role in causing such pain. Specifically, multiple independent endplate changes have been implicated in the initiation and progression of IVD degeneration.

METHODS

In this study, we built a signaling network comprising both well-characterized IVD pathology-associated proteins as well as some potentially correlated proteins that have been associated with one or more of the currently known pathology-associated proteins. We then screened for the potential IVD degeneration-associated proteins using patients' normal and degenerative endplate specimens. Short hairpin RNAs for receptor interacting serine/threonine kinase 1 (RIPK1) were constructed to examine the effects of RIPK1 knockdown in primary chondrocyte cells and in animal models of caudal vertebra intervertebral disc degeneration in vivo.

RESULTS

RIPK1 was identified as a potential IVD degeneration-associated protein based on IVD pathology-associated signaling networks and the patients' degenerated endplate specimens. Construction of the short hairpin RNAs was successful, with short-term RIPK1 knockdown triggering inflammation in the primary chondrocytes, while long-term knockdown triggered apoptosis through cleavage of the caspase 3 pathway, down-regulated NF-κB and mitogen-activating protein kinase (MAPK)s cascades, and decreased cell survival and inflammation. Animal models of caudal vertebra intervertebral disc degeneration further demonstrated that apoptosis was induced by up-regulation of tumor necrosis factor (TNF) accompanied by down-regulation of NF-κB and MAPKs cascades that are dependent on caspase and RIPK1.

CONCLUSIONS

These results provide proof-of-concept for developing novel therapies to combat IVD degeneration through interfering with RIPK1-mediated apoptosis signaling pathways especially in patients with RIPK1 abnormality.