Modulation of ERK 1/2 and p38 MAPK signaling pathways by ATP in osteoblasts: involvement of mechanical stress-activated calcium influx, PKC and Src activation

Role of ESCCAL-1 in regulating exocytosis of AuNPs in human esophageal squamous carcinoma cells

Exocytosis is a critical factor for designing efficient nanocarriers and determining cytotoxicity. However, the research on the exocytosis mechanism of nanoparticles, especially the role of long non-coding RNAs (lncRNAs), has not been reported. In this study, the exocytosis of AuNPs in the KYSE70 cells and the involved molecular pathways of exocytosis are analyzed. It demonstrates that nanoparticles underwent time-dependent release from the cells by exocytosis, and the release of β-hexosaminidase confirms that AuNPs are excreted through lysosomes. Mechanistic studies reveal that lncRNA ESCCAL-1 plays a vital role in controlling the exocytosis of AuNPs through activation of the MAPK pathway, including the phosphorylation of ERK and JNK. The study implies that the ESCCAL-1-mediated pathway plays an important role in the exocytosis of AuNPs in KYSE70 cells. This finding has implications for the role of ESCCAL-1 on the drug resistance of esophagus cancer by controlling lysosome-mediated exocytosis.

Study of Active Phytochemicals and Mechanisms of Cnidii Fructus in Treating Osteoporosis Based on HPLC-Q-TOF-MS/MS and Network Pharmacology

INTRODUCTION

This study aimed to clarify the anti-osteoporosis mechanism of Cnidii Fructus (CF) via network pharmacology and experimental verification.

METHODS

HPLC fingerprints combined with HPLC-Q-TOF-MS/MS analysis confirmed common components (CCS) of CF. Then, network pharmacology was used to investigate the anti-OP mechanism of CF, including potential anti-OP phytochemicals, potential targets, and related signalling pathway. Molecular docking analysis was carried on investigating the protein-ligand interactions. Finally, in vitro experiments were performed to verify anti-OP mechanism of CF.

RESULTS

In this study, 17 compounds from CF were identified by HPLC-Q-TOF-MS/MS and HPLC fingerprints and then were further screened key compounds and potential targets by PPI analysis, ingredient-target network and hub network. The key compounds were SCZ10 (Diosmin), SCZ16 (Pabulenol), SCZ6 (Osthenol), SCZ8 (Bergaptol) and SCZ4 (Xanthotoxol). The potential targets were SRC, MAPK1, PIK3CA, AKT1 and HSP90AA1. Molecular docking further analysis indicated that the five key compounds have a good binding affinity with related proteins. CCK8 assays, TRAP staining experiments, and ALP activity assays concluded that osthenol and bergaptol inhibited osteoclast formation and promoted osteoblast bone formation to improve osteoporosis.

CONCLUSION

Based on network pharmacology and in vitro experiments analysis, this study revealed that CF possessed an anti-OP effect, and its potential therapeutic effect may be involved with osthenol and bergaptol from CF.

Src kinase partially mediates cytokine-induced endothelial dysfunction

OBJECTIVES

Endothelial dysfunction is known to be a key characteristic of preeclampsia (PE) and can contribute to progression of symptoms and injury to multiple organ systems. Delivery is the only treatment for progression of PE, but development of an endothelial-based therapy for PE presents a promising strategy. Growth factors and cytokines are dysregulated in PE and can impact endothelial function, manifesting changes in Ca2+ signaling and interruptions in monolayer barrier function that contribute to symptoms of hypertension, proteinuria, and edema. In this study, we highlight Src kinase as a partial mediator of growth factor and cytokine mediated endothelial dysfunction.

STUDY DESIGN

Fura-2 Ca2+ imaging and Electrical Cell Impedance Sensing (ECIS) assays are performed on growth factor or cytokine exposed human umbilical vein endothelial cells (HUVECs). Inhibitors to MEK/ERK (U0126) or Src (PP2) are used to determine the contribution of kinase signaling pathways.

MAIN OUTCOME MEASURES

Decreases in HUVEC Ca2+ signaling or monolayer resistance measure endothelial dysfunction. Reversal of endothelial dysfunction by kinase inhibitors reveals the respective contibutions of MEK/ERK and Src kinase.

RESULTS

We show that Src inhibition protects Ca2+ signaling responses against insults induced by VEGF165, bFGF, PlGF, TNFα, and IL-1β. Additionally, we show that Src inhibition protects the endothelial monolayer from the full impact of TNFα insult. Further, we find that MEK/ERK inhibition does not offer protection from growth factor-mediated endothelial dysfunction.

CONCLUSIONS

The results of this study suggest cytokine and growth factor-stimulated Src kinase plays a partial role on promoting endothelial dysfunction in HUVECs.

Dkk-1-TNF-α crosstalk regulates MC3T3E1 pre-osteoblast proliferation and differentiation under mechanical stress through the ERK signaling pathway

The study aims to explore the role of the ERK signaling pathway in the crosstalk between Dkk-1 and TNF-α in MC3T3E1 pre-osteoblasts under cyclic tensile/compressive stress. A forced four-point bending system was used to apply cyclic uniaxial tensile/compressive strain (2000 μ, 0.5 Hz) to MC3T3E1 cells. Dkk-1 and TNF-α expression were upregulated in MC3T3E1 cells under compressive strain. Cell proliferation, the cell cycle, osteogenesis-related gene (Wnt5a, Runx2, Osterix) expression, β-catenin expression, and the p-ERK/ERK ratio were significantly enhanced, whereas apoptosis, the RANKL/OPG ratio, and TNF-α expression were significantly attenuated, by Dkk-1 silencing. Dkk-1 expression increased and the effects of Dkk-1 silencing were reversed when exogenous TNF-α was added. Mechanically, TNF-α crosstalked with Dkk-1 through ERK signaling in MC3T3E1 cells. ERK signaling blockade impaired Dkk-1-induced TNF-α expression and TNF-α-mediated Dkk-1 expression. Dkk-1 and TNF-α crosstalked, partially through ERK signaling, in MC3T3E1 cells under compressive/tensile strain, synergistically modulating various biological behaviors of the cells. These findings not only provide mechanical insight into the cellular events and molecular regulation of orthodontic tooth movement (OTM), but also aid the development of novel strategies to accelerate OTM.

Identification of GRIN2D as a novel therapeutic target in pancreatic ductal adenocarcinoma

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) is a devastating disease with a dismal prognosis, and despite significant advances in our understanding of its genetic drivers, like KRAS, TP53, CDKN2A, and SMAD4, effective therapies remain limited. Here, we identified a new therapeutic target GRIN2D and then explored its functions and mechanisms in PDAC progression.

METHODS

We performed a genome-wide RNAi screen in a PDAC xenograft model and identified GRIN2D, which encodes the GluN2D subunit of N-methyl-D-aspartate receptors (NMDARs), as a potential oncogene. Western blot, immunohistochemistry, and analysis on Gene Expression Omnibus were used for detecting the expression of GRIN2D in PDAC. Cellular experiments were conducted for exploring the functions of GRIN2D in vitro while subcutaneous and orthotopic injections were used in in vivo study. To clarify the mechanism, we used RNA sequencing and cellular experiments to identify the related signaling pathway. Cellular assays, RT-qPCR, and western blot helped identify the impacts of the NMDAR antagonist memantine.

RESULTS

We demonstrated that GRIN2D was highly expressed in PDAC cells, and further promoted oncogenic functions. Mechanistically, transcriptome profiling identified GRIN2D-regulated genes in PDAC cells. We found that GRIN2D promoted PDAC progression by activating the p38 MAPK signaling pathway and transcription factor CREB, which in turn promoted the expression of HMGA2 and IL20RB. The upregulated GRIN2D could effectively promote tumor growth and liver metastasis in PDAC. We also investigated the therapeutic potential of NMDAR antagonism in PDAC and found that memantine reduced the expression of GRIN2D and inhibited PDAC progression.

CONCLUSION

Our results suggested that NMDA receptor GRIN2D plays important oncogenic roles in PDAC and represents a novel therapeutic target.

Examining Mechanisms for Voltage-Sensitive Calcium Channel-Mediated Secretion Events in Bone Cells

In addition to their well-described functions in cell excitability, voltage-sensitive calcium channels (VSCCs) serve a critical role in calcium (Ca2+)-mediated secretion of pleiotropic paracrine and endocrine factors, including those produced in bone. Influx of Ca2+ through VSCCs activates intracellular signaling pathways to modulate a variety of cellular processes that include cell proliferation, differentiation, and bone adaptation in response to mechanical stimuli. Less well understood is the role of VSCCs in the control of bone and calcium homeostasis mediated through secreted factors. In this review, we discuss the various functions of VSCCs in skeletal cells as regulators of Ca2+ dynamics and detail how these channels might control the release of bioactive factors from bone cells. Because VSCCs are druggable, a better understanding of the multiple functions of these channels in the skeleton offers the opportunity for developing new therapies to enhance and maintain bone and to improve systemic health.

Could hypoxia rehabilitate the osteochondral diseased interface? Lessons from the interplay of hypoxia and purinergic signals elsewhere

The osteochondral unit comprises the articular cartilage (90%), subchondral bone (5%) and calcified cartilage (5%). All cells present at the osteochondral unit that is ultimately responsible for matrix production and osteochondral homeostasis, such as chondrocytes, osteoblasts, osteoclasts and osteocytes, can release adenine and/or uracil nucleotides to the local microenvironment. Nucleotides are released by these cells either constitutively or upon plasma membrane damage, mechanical stress or hypoxia conditions. Once in the extracellular space, endogenously released nucleotides can activate membrane-bound purinoceptors. Activation of these receptors is fine-tuning regulated by nucleotides' breakdown by enzymes of the ecto-nucleotidase cascade. Depending on the pathophysiological conditions, both the avascular cartilage and the subchondral bone subsist to significant changes in oxygen tension, which has a tremendous impact on tissue homeostasis. Cell stress due to hypoxic conditions directly influences the expression and activity of several purinergic signalling players, namely nucleotide release channels (e.g. Cx43), NTPDase enzymes and purinoceptors. This review gathers experimental evidence concerning the interplay between hypoxia and the purinergic signalling cascade contributing to osteochondral unit homeostasis. Reporting deviations to this relationship resulting from pathological alterations of articular joints may ultimately unravel novel therapeutic targets for osteochondral rehabilitation. At this point, one can only hypothesize how hypoxia mimetic conditions can be beneficial to the ex vivo expansion and differentiation of osteo- and chondro-progenitors for auto-transplantation and tissue regenerative purposes.

Gap Junctions and Connexins in Microglia-Related Oxidative Stress and Neuroinflammation: Perspectives for Drug Discovery

Microglia represent the immune system of the brain. Their role is central in two phenomena, neuroinflammation and oxidative stress, which are at the roots of different pathologies related to the central nervous system (CNS). In order to maintain the homeostasis of the brain and re-establish the equilibrium after a threatening imbalance, microglia communicate with each other and other cells within the CNS by receiving specific signals through membrane-bound receptors and then releasing neurotrophic factors into either the extracellular milieu or directly into the cytoplasm of nearby cells, such as astrocytes and neurons. These last two mechanisms rely on the activity of protein structures that enable the formation of channels in the membrane, namely, connexins and pannexins, that group and form gap junctions, hemichannels, and pannexons. These channels allow the release of gliotransmitters, such as adenosine triphosphate (ATP) and glutamate, together with calcium ion (Ca2+), that seem to play a pivotal role in inter-cellular communication. The aim of the present review is focused on the physiology of channel protein complexes and their contribution to neuroinflammatory and oxidative stress-related phenomena, which play a central role in neurodegenerative disorders. We will then discuss how pharmacological modulation of these channels can impact neuroinflammatory phenomena and hypothesize that currently available nutraceuticals, such as carnosine and N-acetylcysteine, can modulate the activity of connexins and pannexins in microglial cells and reduce oxidative stress in neurodegenerative disorders.

Casein kinase 1α mediates eryptosis: a review

Eryptosis is a coordinated non-lytic cell death of erythrocytes characterized by cell shrinkage, cell membrane scrambling, Ca²⁺ influx, ceramide accumulation, oxidative stress, activation of calpain and caspases. Physiologically, it aims at removing damaged or aged erythrocytes from circulation. A plethora of diseases are associated with enhanced eryptosis, including metabolic diseases, cardiovascular pathology, renal and hepatic diseases, hematological disorders, systemic autoimmune pathology, and cancer. This makes eryptosis and eryptosis-regulating signaling pathways a target for therapeutic interventions. This review highlights the eryptotic signaling machinery containing several protein kinases and its small molecular inhibitors with a special emphasis on casein kinase 1α (CK1α), a serine/threonine protein kinase with a broad spectrum of activity. In this review article, we provide a critical analysis of the regulatory role of CK1α in eryptosis, highlight triggers of CK1α-mediated suicidal death of red blood cells, cover the knowledge gaps in understanding CK1α-driven eryptosis and discover the opportunity of CK1α-targeted pharmacological modulation of eryptosis. Moreover, we discuss the directions of future research focusing on uncovering crosstalks between CK1α and other eryptosis-regulating kinases and pathways.

Injury-induced MAPK activation triggers body axis formation in Hydra by default Wnt signaling

Hydra's almost unlimited regenerative potential is based on Wnt signaling, but so far it is unknown how the injury stimulus is transmitted to discrete patterning fates in head and foot regenerates. We previously identified mitogen-activated protein kinases (MAPKs) among the earliest injury response molecules in Hydra head regeneration. Here, we show that three MAPKs-p38, c-Jun N-terminal kinases (JNKs), and extracellular signal-regulated kinases (ERKs)-are essential to initiate regeneration in Hydra, independent of the wound position. Their activation occurs in response to any injury and requires calcium and reactive oxygen species (ROS) signaling. Phosphorylated MAPKs hereby exhibit cross talk with mutual antagonism between the ERK pathway and stress-induced MAPKs, orchestrating a balance between cell survival and apoptosis. Importantly, Wnt3 and Wnt9/10c, which are induced by MAPK signaling, can partially rescue regeneration in tissues treated with MAPK inhibitors. Also, foot regenerates can be reverted to form head tissue by a pharmacological increase of β-catenin signaling or the application of recombinant Wnts. We propose a model in which a β-catenin-based stable gradient of head-forming capacity along the primary body axis, by differentially integrating an indiscriminate injury response, determines the fate of the regenerating tissue. Hereby, Wnt signaling acquires sustained activation in the head regenerate, while it is transient in the presumptive foot tissue. Given the high level of evolutionary conservation of MAPKs and Wnts, we assume that this mechanism is deeply embedded in our genome.

Analysis of ceRNA networks during mechanical tension-induced osteogenic differentiation of periodontal ligament stem cells

The molecular mechanisms underlying osteogenic differentiation of periodontal ligament stem cells (PDLSCs) under mechanical tension remain unclear. This study aimed to identify a potential long non-coding ribonucleic acids (lncRNAs)/circular RNAs (circRNAs)-microRNAs (miRNAs)-messenger RNAs (mRNAs) network in mechanical tension-induced osteogenic differentiation of PDLSCs. PDLSCs were isolated from the healthy human periodontal ligament, identified, cultured, and exposed to tensile force. The expression of osteogenic markers was examined, and whole transcriptome sequencing was performed to identify the expression patterns of lncRNA, circRNA, miRNAs, and mRNAs. Enrichment analyses were also performed. Candidate targets of differentially expressed non-coding RNAs (ncRNAs) were predicted, and potential competitive endogenous RNA (ceRNA) networks were constructed by Cytoscape. We found that the osteogenic differentiation of PDLSCs was significantly enhanced under dynamic tension (magnitude: 12%, frequency: 0.7 Hz). Overall, 344 lncRNAs, 57 miRNAs, 41 circRNAs, and 70 mRNAs were differentially expressed in the tension group and the control group. Functional enrichment analysis showed that differentially expressed mRNAs were mainly enriched in osteogenesis-related and mechanical stress-related biological processes and signal transduction pathways (e.g., tumor necrosis factor [TNF] and Hippo signaling pathways). The lncRNA/circRNA-miRNA-mRNA networks were depicted, and potential key ceRNA networks were identified. Our findings may help to further explore the underlying regulatory mechanism of osteogenic differentiation of PDLSCs under mechanical tensile stress.

Effect of Tensile Frequency on the Osteogenic Differentiation of Periodontal Ligament Stem Cells

Purpose

The role of periodontal ligament stem cells (PDLSCs) in mediating osteogenesis involved in orthodontic tooth movement (OTM) is well established. However, various relevant in vitro studies vary in the frequency of tension. The effect of tensile frequency on the mechanotransduction of PDLSCs is not clear. The current study aimed to determine the effect of different tensile frequencies on the osteogenic differentiation of PDLSCs and to identify important mechano-sensitivity genes.

Methods

Human PDLSCs were isolated, identified, and subjected to cyclic equibiaxial tensile strain of 12% at different frequencies of 0.1 Hz, 0.5 Hz, 0.7 Hz, or static cultures. Osteogenic differentiation of PDLSCs was assessed by using Western blotting. High-throughput sequencing was used to identify differential mRNA expression. Short time-series expression miner (STEM) was utilized to describe the frequency patterns of the mRNAs. The functions and enriched pathways were identified, and the hub genes were identified and validated.

Results

We found that the osteoblastic differentiation capacity of PDLSCs increased with tensile frequency in the range of 0.1–0.7 Hz. Eight frequency-tendency gene expression profiles were identified to be statistically significant. Tensile frequency-specific expressed genes, such as SALL1 and EYA1, which decreased with the increase in tensile frequency, were found.

Conclusion

The osteoblastic differentiation of PDLSCs under mechanical tensile force is frequency dependent. EYA1 and SALL1 were identified as potential important tensile frequency-sensitive genes, which may contribute to the cyclic tension-induced osteogenic differentiation of PDLSCs in a frequency-dependent manner.

Enhancement of Bone Regeneration Through the Converse Piezoelectric Effect, A Novel Approach for Applying Mechanical Stimulation

Serious bone injuries have devastating effects on the lives of patients including limiting working ability and high cost. Orthopedic implants can aid in healing injuries to an extent that exceeds the natural regenerative capabilities of bone to repair fractures or large bone defects. Autografts and allografts are the standard implants used, but disadvantages such as donor site complications, a limited quantity of transplantable bone, and high costs have led to an increased demand for synthetic bone graft substitutes. However, replicating the complex physiological properties of biological bone, much less recapitulating its complex tissue functions, is challenging. Extensive efforts to design biocompatible implants that mimic the natural healing processes in bone have led to the investigation of piezoelectric smart materials because the bone has natural piezoelectric properties. Piezoelectric materials facilitate bone regeneration either by accumulating electric charge in response to mechanical stress, which mimics bioelectric signals through the direct piezoelectric effect or by providing mechanical stimulation in response to electrical stimulation through the converse piezoelectric effect. Although both effects are beneficial, the converse piezoelectric effect can address bone atrophy from stress shielding and immobility by improving the mechanical response of a healing defect. Mechanical stimulation has a positive impact on bone regeneration by activating cellular pathways that increase bone formation and decrease bone resorption. This review will highlight the potential of the converse piezoelectric effect to enhance bone regeneration by discussing the activation of beneficial cellular pathways, the properties of piezoelectric biomaterials, and the potential for the more effective administration of the converse piezoelectric effect using wireless control.

The Anti-diabetic Drug Gliquidone Modulates Lipopolysaccharide-Mediated Microglial Neuroinflammatory Responses by Inhibiting the NLRP3 Inflammasome

The sulfonylurea drug gliquidone is FDA approved for the treatment of type 2 diabetes. Binding of gliquidone to ATP-sensitive potassium channels (SUR1, Kir6 subunit) in pancreatic β-cells increases insulin release to regulate blood glucose levels. Diabetes has been associated with increased levels of neuroinflammation, and therefore the potential effects of gliquidone on micro- and astroglial neuroinflammatory responses in the brain are of interest. Here, we found that gliquidone suppressed LPS-mediated microgliosis, microglial hypertrophy, and proinflammatory cytokine COX-2 and IL-6 levels in wild-type mice, with smaller effects on astrogliosis. Importantly, gliquidone downregulated the LPS-induced microglial NLRP3 inflammasome and peripheral inflammation in wild-type mice. An investigation of the molecular mechanism of the effects of gliquidone on LPS-stimulated proinflammatory responses showed that in BV2 microglial cells, gliquidone significantly decreased LPS-induced proinflammatory cytokine levels and inhibited ERK/STAT3/NF-κB phosphorylation by altering NLRP3 inflammasome activation. In primary astrocytes, gliquidone selectively affected LPS-mediated proinflammatory cytokine expression and decreased STAT3/NF-κB signaling in an NLRP3-independent manner. These results indicate that gliquidone differentially modulates LPS-induced microglial and astroglial neuroinflammation in BV2 microglial cells, primary astrocytes, and a model of neuroinflammatory disease.

Skeletal Functions of Voltage Sensitive Calcium Channels

Voltage-sensitive calcium channels (VSCCs) are ubiquitous multimeric protein complexes that are necessary for the regulation of numerous physiological processes. VSCCs regulate calcium influx and various intracellular processes including muscle contraction, neurotransmission, hormone secretion, and gene transcription, with function specificity defined by the channel's subunits and tissue location. The functions of VSCCs in bone are often overlooked since bone is not considered an electrically excitable tissue. However, skeletal homeostasis and adaptation relies heavily on VSCCs. Inhibition or deletion of VSCCs decreases osteogenesis, impairs skeletal structure, and impedes anabolic responses to mechanical loading. RECENT FINDINGS: While the functions of VSCCs in osteoclasts are less clear, VSCCs have distinct but complementary functions in osteoblasts and osteocytes. PURPOSE OF REVIEW: This review details the structure, function, and nomenclature of VSCCs, followed by a comprehensive description of the known functions of VSCCs in bone cells and their regulation of bone development, bone formation, and mechanotransduction.

Extracellular purines and bone homeostasis

Maintenance of a healthy skeleton is highly dependent on an intricate regulation of bone metabolism, as changes in the balance between bone formation and bone resorption leads to bone loss, bone fragility and ultimately bone fractures. During the last three decades it has become increasingly evident that physiological release of purines in the extracellular space is imperative for bone homeostasis and is orchestrated via the network of purinoceptors. Adenosine derivatives are released locally in the skeleton either by the bone forming osteoblasts or the bone degrading osteoclasts actioned directly by processes like mechanical loading and indirectly by systemic hormones. Adenosine derivatives directly affect the bone cells by their action on the membranal receptors or have co-stimulatory actions with bone active hormones such as parathyroid hormone or the gut hormones. Any deviations leading to increased levels of extracellular adenosine derivatives in the bone tissue such as in pathologic situations, trigger complex pathways with opposing effects on tissue health as presented by studies involving a range of model organisms. Pathological conditions where skeletal purinergic signaling is affected are following tissue injury like microdamage and macroscopic fractures; and during inflammatory processes where nucleotides and nucleosides play an important part in the pathophysiological skeletal response. Moreover, adenosine derivatives also play an important role in the interaction between malignant cells and bone cells in several types of cancers involving the skeleton, such as but not limited to multiple myeloma and bone osteolysis. Much knowledge has been gained over the last decades. The net- resulting phenotype of adenosine derivatives in bone (including the ratio of ATP to Adenosine) is highly dependent on CD39 and CD73 enzymes together with the expression and activity of the specific receptors. Thus, each component is important in the physiological and pathophysiological processes in bone. Promising perspectives await in the future in treating skeletal disorders with medications targeting the individual components of the purinergic signaling pathway.

P2Y Receptors in Bone - Anabolic, Catabolic, or Both?

P2Y receptors, including eight subtypes, are G protein-coupled receptors that can be activated by extracellular nucleotides. Nearly all P2Y receptors are expressed in bone cells, suggesting their involvements in bone physiology and pathology. However, their exact roles in bone homeostasis are not entirely clear. Therefore, this mini review summarizes new research developments regarding individual P2Y receptors and their roles in bone biology, particularly detailing those which execute both anabolic and catabolic functions. This dual function has highlighted the conundrum of pharmacologically targeting these P2Y receptors in bone-wasting diseases. Further research in finding more precise targeting strategy, such as promoting anabolic effects via combining with physical exercise, should be prioritized.

Homozygous Loss-of-Function Mutations in CCDC134 Are Responsible for a Severe Form of Osteogenesis Imperfecta

Osteogenesis imperfecta (OI) is a primary bone fragility disorder with an estimated prevalence of 1 in 15,000 births. The majority of OI cases are inherited in an autosomal-dominant manner, while 5% to 10% have recessive or X-linked inheritance. Up to now, approximately 5% of OI cases remain without mutation demonstrated, supporting the involvement of other genes in the disease spectrum. By whole-exome sequencing, we identified a homozygous variant (c.2T>C) in CCDC134 gene in three patients from two unrelated families with severe bone fragility that did not respond to bisphosphonate treatment, short stature, and gracile long bones with pseudarthroses but no dentinogenesis imperfecta. CCDC134 encodes a secreted protein widely expressed and implicated in the regulation of some mitogen-activated protein kinases (MAPK) signaling pathway. Western blot and immunofluorescence analyses confirmed the absence of CCDC134 protein in patient cells compared with controls. Furthermore, we demonstrated that CCDC134 mutations are associated with increased Erk1/2 phosphorylation, decreased OPN mRNA and COL1A1 expression and reduced mineralization in patient osteoblasts compared with controls. These data support that CCDC134 is a new gene involved in severe progressive deforming recessive osteogenesis imperfecta (type III). © 2020 American Society for Bone and Mineral Research.

HSP90 inhibitors strengthen extracellular ATP-stimulated synthesis of interleukin-6 in osteoblasts: Amplification of p38 MAP kinase

Heat shock protein 90 (HSP90) is expressed ubiquitously in a variety of cell types including osteoblasts. HSP90 acts as a key driver of proteostasis under pathophysiological conditions. Here, we investigated the involvement of HSP90 in extracellular ATP-stimulated interleukin (IL)-6 synthesis and HSP90 downstream signalling in osteoblast-like MC3T3-E1 cells. In osteoblasts, extracellular ATP stimulates the synthesis of IL-6, a bone-remodelling agent. Geldanamycin, 17-allylamino-17-demethoxy-geldanamycin (17-AAG) and onalespib, three different HSP90 inhibitors, amplified the ATP-stimulated IL-6 release. Geldanamycin increased IL-6 mRNA expression elicited by ATP. ATP enhanced the triiodothyronine-induced osteocalcin release, but HSP90 inhibitors suppressed the release. Extracellular ATP induced the phosphorylation of p44/p42 mitogen-activated protein kinase (MAPK), p38 MAPK, c-Jun N-terminal kinase (JNK), p70 S6 kinase, Akt, and myosin phosphatase-targeting subunit (MYPT), a Rho-kinase substrate. SB203580, an inhibitor of p38 MAPK, suppressed ATP-stimulated IL-6 release. Inhibitors of MEK1/2 (PD98059), JNK (SP600125), upstream kinase of p70 S6 kinase (rapamycin) and Akt (deguelin), all increased IL-6 release. Y27632, a Rho-kinase inhibitor, failed to affect the IL-6 release stimulated by ATP. Geldanamycin and 17-AAG both amplified ATP-induced p38 MAPK phosphorylation, although geldanamycin inhibited the phosphorylation of Akt induced by ATP. In addition, SB203580 significantly reduced the amplification by geldanamycin of the IL-6 release. Taken together, our results strongly suggest that HSP90 inhibitors up-regulate extracellular ATP-stimulated IL-6 synthesis via amplification of p38 MAPK activation in osteoblasts. SIGNIFICANCE OF THE STUDY: Heat shock protein 90 (HSP90) acts as a key driver of proteostasis under pathophysiological conditions in a variety of cell types. We have previously shown that HSP90 is expressed at high levels in osteoblast-like MC3T3-E1 cells, even in their quiescent state, consistent with HSP90 performing an important physiological function in osteoblasts. In the present study, we investigated whether HSP90 is implicated in extracellular ATP-induced interleukin (IL)-6 synthesis in osteoblast-like MC3T3-E1 cells. Our results strongly suggest that HSP90 inhibitors up-regulate extracellular ATP-stimulated IL-6 synthesis via amplification of p38 mitogen-activated protein kinase activation in osteoblasts.

Age-related osteogenesis on lateral force application to rat incisor – Part I: Premaxilla suture remodeling

Objectives:

The suture is a fibrous tissue intervening two adjacent bone segments, existing only in the craniofacial region. In spite of wide use of palatal expansion in various ages, the age-dependent cellular mechanism for osteogenesis is largely unknown. The aim of this study was to examine the proliferation and differentiation pattern of the suture cells on lateral expansion in rats depending on the ages.

Materials and Methods:

Calibrated lateral tensile stress of 50 g was given to the male Sprague-Dawley rat incisors using a double helix in 30 young (10 weeks) and another 30 aged (52 weeks) group, respectively. Each group was subdivided into control, 1, 3, 7, 14, and 21 days, with five animals in each group. Premaxilla area was retrieved from each animal for further histologic analyses including H and E, Masson’s trichrome, and immunohistochemical staining using antibodies against phospho-extracellular signal-regulated kinase, proliferating cell nuclear antigen (PCNA), and fibroblast growth factor receptor-2 (FGFR2). Positive cell counts in the region of interest were conducted.

Results:

Gross suture separation and subsequent bone formation on the sutural side bone surface were observed in both groups, characterized as active collagen turnover, remarkable woven bone projection toward the sutural mesenchyme and subsequent maturation in 3 weeks. Increase in PCNA- and FGFR2-postive cell proportions were comparable in both groups, indicating similar time- and area-specific proliferation and osteogenic differentiation patterns in the stretched suture regardless of the age groups.

Conclusion:

According to the results, it can be implicated that the tensile stress applied to the suture in the adult group may induce active bone formation similar to that in young group, in associated with FGFR2 and Erk signaling cascade. Mesenchymal cells in the premaxillary suture appear to retain remarkable potential for further proliferation and differentiation even in aged subjects.

IDH2 deficiency increases bone mass with reduced osteoclastogenesis by limiting RANKL expression in osteoblasts

Mitochondria are not only responsible for cellular energy production but are also involved in signaling, cellular differentiation, cell death, and aging. Mitochondrial NADP⁺-dependent isocitrate dehydrogenase (IDH2) catalyzes the decarboxylation of isocitrate to α-ketoglutarate, accompanied by NADPH production. IDH2 plays a central role in mitochondrial function in multiple cell types and various organs, including the heart, kidneys, and brain. However, the function of IDH2 in bone tissue is yet to be elucidated. Here, we report that disruption of IDH2 in mice results in high bone mass due to decreased osteoclast number and resorption activity. Although IDH2 played no cell-intrinsic role in osteoclasts, IDH2-deficient animals showed decreased serum markers of osteoclast activity and bone resorption. Bone marrow stromal cells/osteoblasts from Idh2 knockout mice were defective in promoting osteoclastogenesis due to a reduced expression of a key osteoclastogenic factor, receptor activator of nuclear factor-κB ligand (RANKL), in osteoblasts in vivo and in vitro through the attenuation of ATF4-NFATc1 signaling. Our findings suggest that IDH2 is a novel regulator of osteoblast-to-osteoclast communication and bone metabolism, acting via the ATF4-NFATc1-RANKL signaling axis in osteoblasts, and they provide a rationale for further study of IDH2 as a potential therapeutic target for the prevention of bone loss.

20(S)-hydroxycholesterol and simvastatin synergistically enhance osteogenic differentiation of marrow stromal cells and bone regeneration by initiation of Raf/MEK/ERK signaling

Previous studies have demonstrated the significant roles of simvastatin (SVA) and oxysterols in the osteogenesis process. In this study, we evaluate the effect of a combination of SVA and 20(S)-hydroxycholesterol (20(S)OHC) on the cell viability and osteogenic differentiation of bone marrow stromal cells (BMSCs). After treatment with a control vehicle, SVA (0.025, 0.10, 0.25 or 1.0 μM), 20(S)OHC (5 μM), or a combination of both (0.25 μM SVA + 5 μM 20(S)OHC), the proliferation, apoptosis, ALP activity, mineralization, osteogenesis-related gene expression and Raf/MEK/ERK signaling activity in BMSCs were measured. Our results showed that high concentrations of SVA (0.25 and 1.0 μM) enhanced osteogenesis-related genes expression while attenuating cell viability. The addition of 5 μM 20(S)OHC induced significantly higher proliferative activity, which neutralized the inhibitory effect of SVA on the viability of BMSCs. Moreover, compared to supplementation with only one of the additives, combined supplementation with both SVA and 20(S)OHC induced significantly enhanced ALP activity, calcium sedimentation, osteogenesis-related genes (ALP, OCN and BMP-2) expression and Raf/MEK/ERK signaling activity in BMSCs; these enhancements were attenuated by treatment with the inhibitor U0126, indicating a significant role of Raf/MEK/ERK signaling in mediating the synergistically enhanced osteogenic differentiation of BMSCs by combined SVA and 20(S)OHC treatment. Additionally, histological examination confirmed a synergistic effect of SVA and 20(S)OHC on enhancing bone regeneration in a rabbit calvarial defect model. This newly developed SVA/20(S)OHC formulation may be used as an osteoinductive drug to enhance bone healing.

The ATP-binding protein FgArb1 is essential for penetration, infectious and normal growth of Fusarium graminearum

ATP-binding cassette (ABC) transporters act mainly to transport compounds across cellular membranes and are important for diverse biological processes. However, their roles in pathogenesis have not been well-characterized in Fusarium graminearum. Sixty F. graminearum ABC protein genes were functionally characterized. Among them, FgArb1 regulates normal growth and importantly is essential for pathogenicity. Thus, the regulatory mechanisms of FgArb1 in pathogenicity were analyzed in this study. FgArb1 interacts with the mitogen-activated protein kinase (MAPK) FgSte7, and partially modulates plant penetration by regulating the phosphorylation of FgGpmk1 (the downstream kinase of FgSte7). The FgArb1 mutant exhibited dramatically reduced infective growth within wounded host tissues, likely resulting from its increased sensitivity to oxidative stresses, defective cell wall integrity and reduced deoxynivalenol (DON) production. FgArb1 also is important for the production of sexual and asexual spores that are important propagules for plant infection. In addition, FgArb1 is involved in the regulation of protein biosynthesis through impeding nuclear export of small ribosomal subunit. Finally, acetylation modification at sites K28, K65, K341 and K525 in FgArb1 is required for its biological functions. Taken together, results of this study provide a novel insight into functions of the ABC transporter in fungal pathogenesis.

Involvement of GSK3/β-catenin in the action of extracellular ATP on differentiation of primary cultures from rat calvaria into osteoblasts

Modulation of purinergic receptors play an important role in the regulation of osteoblasts differentiation and bone formation. In this study, we investigated the involvement of the GSK3/βcatenin signaling in the action of ATPγ-S on osteogenic differentiation of primary cell cultures from rat calvaria. Our results indicate that the cell treatment with 10 or 100 µM ATPγ-S for 96 h increase the cytoplasmic levels of β-catenin and its translocation to nucleus respect to control. A similar effect was observed after cell treatment with the GSK3 inhibitor LiCl (10 mM). Cell treatments with 4-10 mM LiCl significantly stimulated ALP activity respect to control at 4 and 7 days, suggesting that inhibition of GSK-3 mediates osteoblastic differentiation of rat calvarial cells. Effects comparison between ATP and LiCl shown that ALP activity was significantly increased by 10 µM ATPγ-S and decreased by 10 mM LiCl at 10 day of treatment, respect to control, suggesting that the effect of ATPγ-S was less potent but more persistent than of LiCl in stimulating this osteogenic marker in calvarial cells. Cell culture mineralization was significantly increased by treatment with 10 µM ATPγ-S and decreased by 10 mM LiCl, respect to control. In together, these results suggest that GSK3 inhibition is involved in ATPγ-S action on rat calvarial cell differentiation into osteoblasts at early steadies. In addition such inhibition by LiCl appear promote osteoblasts differentiation at beginning but has a deleterious effect on its function at later steadies as the extracellular matrix mineralization.

The role of transient receptor potential polycystin channels in bone diseases

Transient receptor potential (TRP) channels are cation channels which act as molecular sensors that enable cells to detect and respond to a plethora of mechanical and environmental cues. TRPs are involved in various physiological processes, such as mechanosensation, non-inception and thermosensation, while mutations in genes encoding them can lead to pathological conditions, called "channelopathies". The subfamily of transient receptor potential polycystins (TRPPs), Polycystin 1 (PC1, TRPP1) and Polycystin 2 (PC2, TRPP2), act as mechanoreceptors, sensing external mechanical forces, including strain, stretch and fluid shear stress, triggering a cascade of signaling pathways involved in osteoblastogenesis and ultimately bone formation. Both in vitro studies and research on animal models have already identified their implications in bone homeostasis. However, uncertainty veiling the role of polycystins (PCs) in bone disease urges studies to elucidate further their role in this field. Mutations in TRPPs have been related to autosomal polycystic kidney disease (ADKPD) and research groups try to identify their role beyond their well-established contribution in kidney disease. Such an elucidation would be beneficial for identifying signaling pathways where polycystins are involved in bone diseases related to exertion of mechanical forces such as osteoporosis, osteopenia and craniosynostosis. A better understanding of the implications of TRPPs in bone diseases would possibly lay the cornerstone for effective therapeutic schemes.

[Effect of endomorphin-1 postconditioning against myocardial ischemia-reperfusion injury in rats and the role of Erk1/2 signaling pathway]

OBJECTIVE

To investigate the effect of postischemic treatment with endomorphin-1 (EM-1) against myocardial ischemia/reperfusion (IR) injury in rats and on extracellular signal regulated kinase 1/2 (Erk1/2)-dependent signaling pathway.

METHODS

Sprague-Dawley rats were randomly divided into 5 groups, namely the sham-operated group, IR group, EM-1 post-treatment group (EM50 group), EM-1 post-treatment group with PD98059 treatment (EM50+PD group), and PD98059 post-treatment group (PD group). The hemodynamic indexes of the rats were recorded. After reperfusion, CK-MB, LDH, CTnI, MDA, IL-6, TNF-α, and SOD activities or contents were measured, the infarct size was determined, and the expression levels of Erk1/2, P-Erk1/2 and cleaved caspase-3 were detected using Western blotting.

RESULTS

Compared with the sham group, the IR group showed significantly decreased heart rate and mean arterial pressure (P<0.05), which were increased obviously by EM-1 post-treatment (P<0.05). EM-1 post-treatment also resulted in significantly decreased LDH, CK-MB, CTnI, MDA, IL-6, and TNF-α activities or contents (P<0.05), increased SOD activity (P<0.05), reduced the infarct size (P<0.05), and increased the expression level of P-Erk protein (P<0.05). Compared with EM50 group, EM50+PD group showed significantly decreased heart rate and mean arterial pressure (P<0.05), increased LDH, CK-MB, CTnI, MDA, IL-6, and TNF-α activities or contents (P<0.05), decreased SOD activity, increased infarct size (P<0.05), and lowered expression of P-Erk protein (P<0.05).

CONCLUSION

Postischemic treatment with EM-1 protects the heart against IR injury by improving the cardiac function, inhibiting inflammation, and inhibiting oxidative stress and myocardial apoptosis, and Erk1/2 signaling pathway may be involved in this process.

Inhibitory effect of JAK inhibitor on mechanical stress-induced protease expression by human articular chondrocytes

OBJECTIVE

To investigate whether janus kinase (JAK) inhibitor exhibits a chondro-protective effect against mechanical stress-induced expression of a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) and matrix metalloproteinase (MMPs) in human chondrocytes.

MATERIALS AND METHODS

Normal human articular chondrocytes were seeded onto stretch chambers and incubated with or without tofacitinib (1000 nM) for 12 h before mechanical stimulation or cytokine stimulation. Uni-axial cyclic tensile strain (CTS) (0.5 Hz, 10% elongation, 30 min) was applied and the gene expression levels of type II collagen α1 chain (COL2A1), aggrecan (ACAN), ADAMTS4, ADAMTS5, MMP13, and runt-related transcription factor 2 (RUNX-2) were examined by real-time polymerase chain reaction. Nuclear translocation of RUNX-2 and nuclear factor-κB (NF-κB) was examined by immunocytochemistry, and phosphorylation of mitogen-activated protein kinase (MAPK) and signaling transducer and activator of transcription (STAT) 3 was examined by western blotting. The concentration of interleukin (IL)-1β, IL-6, and tumor necrosis factor-α in the supernatant was examined by enzyme-linked immunosorbent assay.

RESULTS

COL2A1 and ACAN gene expression levels were decreased by CTS, but these catabolic effects were canceled by tofacitinib. Tofacitinib significantly down-regulated CTS-induced expression of ADAMTS4, ADAMTS5, MMP13, and RUNX2, and the release of IL-6 in supernatant by chondrocytes. Tofacitinib also reduced CTS-induced nuclear translocation of RUNX-2 and NF-κB, and phosphorylation of MAPK and STAT3.

CONCLUSION

Tofacitinib suppressed mechanical stress-induced expression of ADAMTS4, ADAMTS5, and MMP13 by human chondrocytes through inhibition of the JAK/STAT and MAPK cascades.

Adenosine triphosphate induces P2Y2 activation and interleukin-8 release in human esophageal epithelial cells

BACKGROUND AND AIM

Immune-mediated mucosal inflammation characterized by the release of interleukin (IL)-8 is associated with gastroesophageal reflux disease. ATP released by human esophageal epithelial cells (HEECs) mediates the release of cytokines through P2 nucleotide receptors that are present on various cells, including HEECs. This study characterized and identified human esophageal epithelial P2 receptors that are responsible for ATP-mediated release of IL-8 by using a human esophageal stratified squamous epithelial model.

METHODS

Primary HEECs were cultured with the use of an air-liquid interface (ALI) system. The ATP analogue adenosine 5'-O-3-thiotriphosphate (ATP-γ-S) was added to the basolateral compartment, and IL-8 release was measured. Involvement of the P2Y2 receptor was assessed with the use of selective and non-selective receptor antagonists and a P2Y2 receptor agonist. Expression of the P2Y2 receptor was assessed using western blotting and immunohistochemistry.

RESULTS

Adenosine triphosphate-γ-S induced IL-8 release through the P2Y2 receptor. A P2Y2 receptor antagonist but not a P2X3 receptor antagonist or a P2Y1 receptor antagonist blocked ATP-γ-S-mediated IL-8 release. Conversely, a P2Y2 receptor agonist induced IL-8 release. Western blotting and immunohistochemistry of the P2Y2 receptor showed strong expression of the P2Y2 receptor on ALI-cultured HEECs and in human esophagus. Inhibition of extracellular signal-regulated kinase but not of protein kinase C blocked the ATP-mediated release of IL-8. ATP-γ-S induced phosphorylation of extracellular signal-regulated kinase, and a P2Y2 receptor antagonist blocked this phosphorylation.

CONCLUSIONS

Interleukin-8 release after purinergic stimulation in ALI-cultured HEECs is mediated through P2Y2 receptor activation. ATP-induced IL-8 release maybe involved in the pathogenesis of refractory gastroesophageal reflux disease.

Activation of the P2Y2 receptor regulates bone cell function by enhancing ATP release

Bone cells constitutively release ATP into the extracellular environment where it acts locally via P2 receptors to regulate bone cell function. Whilst P2Y2 receptor stimulation regulates bone mineralisation, the functional effects of this receptor in osteoclasts remain unknown. This investigation used the P2Y2 receptor knockout (P2Y2R-/- ) mouse model to investigate the role of this receptor in bone. MicroCT analysis of P2Y2R-/- mice demonstrated age-related increases in trabecular bone volume (≤48%), number (≤30%) and thickness (≤17%). In vitro P2Y2R-/- osteoblasts displayed a 3-fold increase in bone formation and alkaline phosphatase activity, whilst P2Y2R-/- osteoclasts exhibited a 65% reduction in resorptive activity. Serum cross-linked C-telopeptide levels (CTX, resorption marker) were also decreased (≤35%). The resorption defect in P2Y2R-/- osteoclasts was rescued by the addition of exogenous ATP, suggesting that an ATP deficit could be a key factor in the reduced function of these cells. In agreement, we found that basal ATP release was reduced up to 53% in P2Y2R-/- osteoclasts. The P2Y2 receptor agonists, UTP and 2-thioUTP, increased osteoclast activity and ATP release in wild-type but not in P2Y2R-/- cells. This indicates that the P2Y2 receptor may regulate osteoclast function indirectly by promoting ATP release. UTP and 2-thioUTP also stimulate ATP release from osteoblasts suggesting that the P2Y2 receptor exerts a similar function in these cells. Taken together, our findings are consistent with the notion that the primary action of P2Y2 receptor signalling in bone is to regulate extracellular ATP levels.

Pannexin hemichannels: A novel promising therapy target for oxidative stress related diseases

Pannexins, which contain three subtypes: pannexin-1, -2, and -3, are vertebrate glycoproteins that form non-junctional plasma membrane intracellular hemichannels via oligomerization. Oxidative stress refers to an imbalance of the generation and elimination of reactive oxygen species (ROS). Studies have shown that elevated ROS levels are pivotal in the development of a variety of diseases. Recent studies indicate that the occurrence of these oxidative stress related diseases is associated with pannexin hemichannels. It is also reported that pannexins regulate the production of ROS which in turn may increase the opening of pannexin hemichannels. In this paper, we review recent researches about the important role of pannexin hemichannels in oxidative stress related diseases. Thus, pannexin hemichannels, novel therapeutic targets, hold promise in managing oxidative stress related diseases such as the tumor, inflammatory bowel diseases (IBD), pulmonary fibrosis, chronic obstructive pulmonary disease (COPD), cardiovascular disease, insulin resistance (IR), and neural degeneration diseases.

FBXO25 regulates MAPK signaling pathway through inhibition of ERK1/2 phosphorylation

The FBXO25 mediates degradation of ELK-1 and thus inhibits transcriptional activation of immediate early genes (iEG). Here we show that FBXO25 regulates yet another node of this signaling pathway, by decreasing MAPK/ERK activity. We show that induction of FBXO25 reduced ERK1/2 phosphorylation independently of MEK1/2. Accordingly, in HAP1 FBXO25 knockout cells (FBXO25^KO), we observed that upon PMA treatment ERK1/2 was more active than in parental cells. An increase in cell proliferation under receptor mediated activation of the ERK signaling pathway in FBXO25^KO cells was also observed. Taken together we show that FBXO25 functions as a negative regulator of MAPK signaling though the reduction of ERK1/2 activation.

Differential roles of PKC isoforms (PKCs) and Ca2+ in GnRH and phorbol 12-myristate 13-acetate (PMA) stimulation of p38MAPK phosphorylation in immortalized gonadotrope cells

We examined the role of PKCs and Ca²⁺ in GnRH-stimulated p38MAPK phosphorylation in the gonadotrope derived αT3-1 and LβT2 cell lines. GnRH induced a slow and rapid increase in p38MAPK phosphorylation in αT3-1 and LβT2 cells respectively, while PMA gave a slow response. The use of dominant negatives for PKCs and peptide inhibitors for the receptors for activated C kinase (RACKs), has revealed differential role for PKCα, PKCβII, PKCδ and PKCε in p38MAPK phosphorylation in a ligand-and cell context-dependent manner. The paradoxical findings that PKCs activated by GnRH and PMA play a differential role in p38MAPK phosphorylation may be explained by differential localization of the PKCs. Basal, GnRH- and PMA- stimulation of p38MAPK phosphorylation in αT3-1 cells is mediated by Ca²⁺ influx via voltage-gated Ca²⁺ channels and Ca²⁺ mobilization, while in the differentiated LβT2 gonadotrope cells it is mediated only by Ca²⁺ mobilization. p38MAPK resides in the cell membrane and is relocated to the nucleus by GnRH (∼5 min). Thus, we have identified the PKCs and the Ca²⁺ pools involved in GnRH stimulated p38MAPK phosphorylation.

Src-family tyrosine kinases and the Ca2+ signal

In this review, we shall describe the rich crosstalk between non-receptor Src-family kinases (SFKs) and the Ca²⁺ transient generated in activated cells by a variety of extracellular and intracellular stimuli, resulting in diverse signaling events. The exchange of information between SFKs and Ca²⁺ is reciprocal, as it flows in both directions. These kinases are main actors in pathways leading to the generation of the Ca²⁺ signal, and reciprocally, the Ca²⁺ signal modulates SFKs activity and functions. We will cover how SFKs participate in the generation of the cytosolic Ca²⁺ rise upon activation of a series of receptors and the mechanism of clearance of this Ca²⁺ signal. The role of SFKs modulating Ca²⁺-translocating channels participating in these events will be amply discussed. Finally, the role of the Ca²⁺ sensor protein calmodulin on the activity of c-Src, and potentially on other SFKs, will be outlined as well. This article is part of a Special Issue entitled: ECS Meeting edited by Claus Heizmann, Joachim Krebs and Jacques Haiech.

Overexpression of Gα11 in Osteoblast Lineage Cells Suppresses the Osteoanabolic Response to Intermittent PTH and Exercise

Intermittent parathyroid hormone (iPTH) treatment and mechanical loading are osteoanabolic stimuli that are partially mediated through actions on G protein-coupled receptors (GPCRs). GPCR signaling can be altered by heterotrimeric G protein Gα subunits levels, which can therefore lead to altered responses to such stimuli. Previous studies have suggested that enhanced signaling through the Gαq/11 pathway inhibits the osteoanabolic actions of PTH. The influence of Gαq/11 signaling on mechanotransduction, however, has not been reported in vivo. Using transgenic mice that specifically overexpress Gα11 in osteoblast lineage cells (G11-Tg mice), we investigated the skeletal effects of elevated Gα11 levels on iPTH and mechanical loading by treadmill exercise. Both regimens increased trabecular and cortical bone in Wild-Type (WT) mice as a result of increased bone formation. In G11-Tg mice, there was no change in trabecular or cortical bone and no increase in bone formation in response to iPTH or exercise. While exercise reduced osteoclast parameters in WT mice, these changes were diminished in G11-Tg mice as expression of M-csf and Trap remained increased. Collectively, our results suggest that osteoblastic upregulation of Gα11 is inhibitory to osteoanabolic actions of both PTH and exercise, and that its suppression may be a promising target for treating bone loss.

Decoding the intervertebral disc: Unravelling the complexities of cell phenotypes and pathways associated with degeneration and mechanotransduction

Back pain is the most common cause of pain and disability worldwide. While its etiology remains unknown, it is typically associated with intervertebral disc (IVD) degeneration. Despite the prevalence of back pain, relatively little is known about the specific cellular pathways and mechanisms that contribute to the development, function and degeneration of the IVD. Consequently, current treatments for back pain are largely limited to symptomatic interventions. However, major progress is being made in multiple research directions to unravel the biology and pathology of the IVD, raising hope that effective disease-modifying interventions will soon be developed. In this review, we will discuss our current knowledge and gaps in knowledge on the developmental origin of the IVD, the phenotype of the distinct cell types found within the IVD tissues, molecular targets in IVD degeneration identified using bioinformatics strategies, and mechanotransduction pathways that influence IVD cell fate and function.

Cytosolic malate dehydrogenase regulates RANKL-mediated osteoclastogenesis via AMPK/c-Fos/NFATc1 signaling

Cytosolic malate dehydrogenase (malate dehydrogenase 1, MDH1) plays pivotal roles in the malate/aspartate shuttle that might modulate metabolism between the cytosol and mitochondria. In this study, we investigated the role of MDH1 in osteoclast differentiation and formation. MDH1 expression was induced by receptor activator of nuclear factor kappa-B ligand (RANKL) treatment. Knockdown of MDH1 by infection with retrovirus containing MDH1-specific shRNA (shMDH1) reduced mature osteoclast formation and bone resorption activity. Moreover, the expression of marker genes associated with osteoclast differentiation was downregulated by shMDH1 treatment, suggesting a role of MDH1 in osteoclast differentiation. In addition, intracellular ATP production was reduced following the activation of adenosine 5' monophosphate-activated protein kinase (AMPK), a cellular energy sensor and negative regulator of RANKL-induced osteoclast differentiation, in shMDH1-infected osteoclasts compared to control cells. In addition, the expression of c-Fos and nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1), a critical transcription factor of osteoclastogenesis, was decreased with MDH1 knockdown during RANKL-mediated osteoclast differentiation. These findings provide strong evidence that MDH1 plays a critical role in osteoclast differentiation and function via modulation of the intracellular energy status, which might affect AMPK activity and NFATc1 expression.

Effect of Combined Action of Extracellular ATP and Elevated Calcium on Osteogenic Differentiation of Primary Cultures From Rat Calvaria

The in vitro osteogenic differentiation has been intensively studied. However, it is not yet clear precisely how osteogenesis can be optimized. Changes in extracellular Ca(2+) concentration ([Ca(2+) ]e ), as well as modulation of purinergic receptors play an important role in the regulation of osteoblasts differentiation and bone formation. In this study, we investigated the effects of a combined treatment of ATPγ-S and high [Ca(2+) ]e (5.35 mM) on osteogenic differentiation and function of primary cell cultures from rat calvaria. Our results indicate that ATPγ-S stimulates cell transition from the G0 to S phase of cell cycle, involving the PI3K signaling pathway. Treatment with 10 or 100 µM ATPγ-S and [Ca(2+) ]e (ATP-[Ca(2+) ]e ) for 48 h increases cell number significantly above the control. ATPγ-S treatment in osteogenic medium containing [Ca(2+) ]e stimulates the gene expression of BMP-4, BMP-5, and OPN at 16, 48, and 72 h, respectively, above control. In same conditions, treatment for 6 days with 10 µM UTP or 100 µM UDP significantly increased the ALP activity respect to control. Cells grown in osteogenic medium showed a statistically significant increase in calcium deposits at 15 and 18 days, for 10 µM ATPγ-S treatment, and at 18 and 22 days, for [Ca(2+) ]e treatment, respect to control but ATP-[Ca(2+) ]e treatment shown a significant greater mineralization at 15 days respect to ATPγ-S, and at 18 days respect to both agonists. In conclusion, we demonstrated that an osteogenic medium containing 10 µM ATPγ-S and 5.35 mM [Ca(2+) ]e enhance osteogenesis and mineralization by rat primary calvarial cells cultures. J. Cell. Biochem. 117: 2658-2668, 2016. © 2016 Wiley Periodicals, Inc.

Mesenchymal Stem Cells Ageing: Targeting the "Purinome" to Promote Osteogenic Differentiation and Bone Repair

Mesenchymal stem cells (MSCs) are multipotent cells that can differentiate into bone forming cells. Such ability is compromised in elderly individuals resulting in bone disorders such as osteoporosis, also limiting their clinical usage for cell transplantation and bone tissue engineering strategies. In bone marrow niches, adenine and uracil nucleotides are important local regulators of osteogenic differentiation of MSCs. Nucleotides can be released to the extracellular milieu under both physiological and pathological conditions via (1) membrane cell damage, (2) vesicle exocytosis, (3) ATP-binding cassette transporters, and/or (4) facilitated diffusion through maxi-anion channels, hemichannels or ligand-gated receptor pores. Nucleotides and their derivatives act via adenosine P1 (A1 , A2A , A2B , and A3 ) and nucleotide-sensitive P2 purinoceptors comprising ionotropic P2X and G-protein-coupled P2Y receptors. Purinoceptors activation is terminated by membrane-bound ecto-nucleotidases and other ecto-phosphatases, which rapidly hydrolyse extracellular nucleotides to their respective nucleoside 5'-di- and mono-phosphates, nucleosides and free phosphates, or pyrophosphates. Current knowledge suggests that different players of the "purinome" cascade, namely nucleotide release sites, ecto-nucleotidases and purinoceptors, orchestrate to fine-tuning regulate the activity of MSCs in the bone microenvironment. Increasing studies, using osteoprogenitor cell lines, animal models and, more recently, non-modified MSCs from postmenopausal women, raised the possibility to target chief components of the purinergic signaling pathway to regenerate the ability of aged MSCs to differentiate into functional osteoblasts. This review summarizes the main findings of those studies, prompting for novel therapeutic strategies to control ageing disorders where bone destruction exceeds bone formation, like osteoporosis, rheumatoid arthritis, and fracture mal-union. J. Cell. Physiol. 231: 1852-1861, 2016. © 2016 Wiley Periodicals, Inc.

Regulation of the osteogenic and adipogenic differentiation of bone marrow-derived stromal cells by extracellular uridine triphosphate: The role of P2Y2 receptor and ERK1/2 signaling

An imbalance in the osteogenesis and adipogenesis of bone marrow-derived stromal cells (BMSCs) is a crucial pathological factor in the development of osteoporosis. Growing evidence suggests that extracellular nucleotide signaling involving the P2 receptors plays a significant role in bone metabolism. The aim of the present study was to investigate the effects of uridine triphosphate (UTP) on the osteogenic and adipogenic differentiation of BMSCs, and to elucidate the underlying mechanisms. The differentiation of the BMSCs was determined by measuring the mRNA and protein expression levels of osteogenic- and adipogenic-related markers, alkaline phosphatase (ALP) staining, alizarin red staining and Oil Red O staining. The effects of UTP on BMSC differentiation were assayed using selective P2Y receptor antagonists, small interfering RNA (siRNA) and an intracellular signaling inhibitor. The incubation of the BMSCs with UTP resulted in a dose-dependent decrease in osteogenesis and an increase in adipogenesis, without affecting cell proliferation. Significantly, siRNA targeting the P2Y2 receptor prevented the effects of UTP, whereas the P2Y6 receptor antagonist (MRS2578) and siRNA targeting the P2Y4 receptor had little effect. The activation of P2Y receptors by UTP transduced to the extracellular signal-regulated kinase 1/2 (ERK1/2) signaling pathway. This transduction was prevented by the mitogen-activated protein kinase inhibitor (U0126) and siRNA targeting the P2Y2 receptor. U0126 prevented the effects of UTP on osteogenic- and adipogenic-related gene expression after 24 h of culture, as opposed to 3 to 7 days of culture. Thus, our data suggest that UTP suppresses the osteogenic and enhances the adipogenic differentiation of BMSCs by activating the P2Y2 receptor. The ERK1/2 signaling pathway mediates the early stages of this process.

The role of purinergic signalling in the musculoskeletal system

Accumulating evidence now suggests that purinergic signalling exerts significant regulatory effects in the musculoskeletal system. In particular, it has emerged that extracellular nucleotides are key regulators of bone cell differentiation, survival and function. This review discusses our current understanding of the direct effects of purinergic signalling in bone, cartilage and muscle.

Proteomic analysis of the effect of extracellular calcium ions on human mesenchymal stem cells: Implications for bone tissue engineering

Human mesenchymal stem cells-bone marrow (BM-hMSCs) are considered as the most suitable seed cells for bone tissue engineering. Calcium ions (Ca(2+)) forms an important component of a number of commercial bone substitutes and support materials. For efficient bone tissue engineering, it is crucial to explore the effect of extracellular Ca(2+) on the growth and differentiation of BM-hMSCs, and to understand their molecular mechanisms. Therefore, in the present study, BM-hMSCs were cultivated in serum free growth medium or serum free growth medium with additional 4 or 6mM Ca(2+) for 3weeks, following which, the proliferation and osteoblastic differentiation of these cells were evaluated. Differentially expressed proteins were established using iTRAQ labeling coupled with nano-LC-MS/MS. Our data revealed that Ca(2+) significantly promoted the proliferation of BM-hMSCs in the early stage. Furthermore, Ca(2+) showed osteoinduction properties. MAPKs signaling pathway might participate in the osteogenic differentiation of BM-hMSCs caused by Ca(2+). Certain newly found proteins could be potentially important for the osteogenic differentiation of BM-hMSCs and may be associated with osteogenesis.

Shock wave treatment enhances cell proliferation and improves wound healing by ATP release-coupled extracellular signal-regulated kinase (ERK) activation

Shock wave treatment accelerates impaired wound healing in diverse clinical situations. However, the mechanisms underlying the beneficial effects of shock waves have not yet been fully revealed. Because cell proliferation is a major requirement in the wound healing cascade, we used in vitro studies and an in vivo wound healing model to study whether shock wave treatment influences proliferation by altering major extracellular factors and signaling pathways involved in cell proliferation. We identified extracellular ATP, released in an energy- and pulse number-dependent manner, as a trigger of the biological effects of shock wave treatment. Shock wave treatment induced ATP release, increased Erk1/2 and p38 MAPK activation, and enhanced proliferation in three different cell types (C3H10T1/2 murine mesenchymal progenitor cells, primary human adipose tissue-derived stem cells, and a human Jurkat T cell line) in vitro. Purinergic signaling-induced Erk1/2 activation was found to be essential for this proliferative effect, which was further confirmed by in vivo studies in a rat wound healing model where shock wave treatment induced proliferation and increased wound healing in an Erk1/2-dependent fashion. In summary, this report demonstrates that shock wave treatment triggers release of cellular ATP, which subsequently activates purinergic receptors and finally enhances proliferation in vitro and in vivo via downstream Erk1/2 signaling. In conclusion, our findings shed further light on the molecular mechanisms by which shock wave treatment exerts its beneficial effects. These findings could help to improve the clinical use of shock wave treatment for wound healing.

Involvement of ILK/ERK1/2 and ILK/p38 pathways in mediating the enhanced osteoblast differentiation by micro/nanotopography

The hierarchical micro/nanotextured topography (MNT) on titanium (Ti) implant surface significantly enhances osteoblast differentiation. We have demonstrated that integrin-linked kinase (ILK) is a key underlying signal molecule and β-catenin is one of its downstream mediators in MNT-regulated osteoblast behavior. Here we propose that mitogen-activated protein kinases (MAPKs), including extracellular signal-regulated kinase 1/2 (ERK1/2), p38 and c-Jun NH2-terminal kinase (JNK), are other mediators downstream of ILK, and this study aims to confirm this. Firstly, the levels of ILK and MAPK activity in MG63 cells on MNT are examined by Western blot analysis. The ILK, ERK1/2 and p38 signals are significantly up-regulated by MNT, whereas the JNK activity is undetectable by Western blot. The MG63 cell morphology, proliferation and differentiation are studied in the absence and presence of the MAPK subgroup inhibitors to confirm their roles in cell functions on the Ti surface. The MAPK subgroup inhibitors obviously change the cell shape and depress cell proliferation. Blocking the ERK1/2 or p38 signaling, but not the JNK signaling, significantly down-regulates the cell osteogenesis-related gene expression, ALP production, collagen secretion and matrix mineralization. Afterwards, the ILK expression is down-regulated using ILK-specific siRNA (ILKsi) and then the MAPK activity is determined. ILKsi significantly attenuates the phosphorylated ERK1/2 and p38 levels on MNT, explicitly demonstrating that the ERK1/2 and p38 signalings are downstream effectors of ILK. In conclusion, these data demonstrate that both ILK/ERK1/2 and ILK/p38 pathways are involved in the mechanisms mediating the enhanced osteoblast differentiation by biomaterial surface topography, hopefully directing the biomaterial modification and biofunctionalization.

Inserted rest period resensitizes MC3T3-E1 cells to fluid shear stress in a time-dependent manner via F-actin-regulated mechanosensitive channel(s)

The underlying cellular mechanism of anabolic effect recovered by inserting rest is not fully understood. In this work, we studied the role of F-actin regulated mechanosensitive channel(s) re-activation in mechanosensitivity modulation in vitro. Results showed that steady fluid shear stress (sFSS) stimulation with 30-min rest period was more potential in increasing alkalinephosphatase (ALP) activity than 10 and 0-min rest periods, and insertion of 30 min, but not 0 or 10 min, recovered the [Ca(2+)]i transient and contribution of the mechanosensitive channel(s). During the rest period, F-actin experienced polymerization (0-10 min), followed by depolymerization (10-30 min); inhibition of F-actin polymerization/depolymerization significantly increased/decreased the [Ca(2+)]i transient, as well as the contribution of the mechanosensitive channel(s) in subsequent sFSS stimulation. Our results demonstrated that the long rest period between sFSS loadings recruited [Ca(2+)]i transient via F-actin depolymerization-induced reactivation of mechanosensitive channel(s), suggesting that F-actin-regulated cellular stiffness could account for the decreased anabolic response during continuous mechanical loading in bone cells.

Shockwaves induce osteogenic differentiation of human mesenchymal stem cells through ATP release and activation of P2X7 receptors

Shockwave treatment promotes bone healing of nonunion fractures. In this study, we investigated whether this effect could be due to adenosine 5'-triphosphate (ATP) release-induced differentiation of human mesenchymal stem cells (hMSCs) into osteoprogenitor cells. Cultured bone marrow-derived hMSCs were subjected to shockwave treatment and ATP release was assessed. Osteogenic differentiation and mineralization of hMSCs were evaluated by examining alkaline phosphatase activity, osteocalcin production, and calcium nodule formation. Expression of P2X7 receptors and c-fos and c-jun mRNA was determined with real-time reverse transcription polymerase chain reaction and Western blotting. P2X7-siRNA, apyrase, P2 receptor antagonists, and p38 MAPK inhibitors were used to evaluate the roles of ATP release, P2X7 receptors, and p38 MAPK signaling in shockwave-induced osteogenic hMSCs differentiation. Shockwave treatment released significant amounts (≈ 7 μM) of ATP from hMSCs. Shockwaves and exogenous ATP induced c-fos and c-jun mRNA transcription, p38 MAPK activation, and hMSC differentiation. Removal of ATP with apyrase, targeting of P2X7 receptors with P2X7-siRNA or selective antagonists, or blockade of p38 MAPK with SB203580 prevented osteogenic differentiation of hMSCs. Our findings indicate that shockwaves release cellular ATP that activates P2X7 receptors and downstream signaling events that caused osteogenic differentiation of hMSCs. We conclude that shockwave therapy promotes bone healing through P2X7 receptor signaling, which contributes to hMSC differentiation.