Transforming Growth Factor β1/Smad4 Signaling Affects Osteoclast Differentiation via Regulation of miR-155 Expression

Molecular Signaling Pathways and MicroRNAs in Bone Remodeling: A Narrative Review

Bone remodeling is an intricate process executed throughout one's whole life via the cross-talk of several cellular events, progenitor cells and signaling pathways. It is an imperative mechanism for regaining bone loss, recovering damaged tissue and repairing fractures. To achieve this, molecular signaling pathways play a central role in regulating pathological and causal mechanisms in different diseases. Similarly, microRNAs (miRNAs) have shown promising results in disease management by mediating mRNA targeted gene expression and post-transcriptional gene function. However, the role and relevance of these miRNAs in signaling processes, which regulate the delicate balance between bone formation and bone resorption, are unclear. This review aims to summarize current knowledge of bone remodeling from two perspectives: firstly, we outline the modus operandi of five major molecular signaling pathways, i.e.,the receptor activator of nuclear factor kappa-B (RANK)-osteoprotegrin (OPG) and RANK ligand (RANK-OPG-RANKL), macrophage colony-stimulating factor (M-CSF), Wnt/β-catenin, Jagged/Notch and bone morphogenetic protein (BMP) pathways in regards to bone cell formation and function; and secondly, the miRNAs that participate in these pathways are introduced. Probing the miRNA-mediated regulation of these pathways may help in preparing the foundation for developing targeted strategies in bone remodeling, repair and regeneration.

The role of circulating miRNAs in the diagnosis of osteoporosis miRNAs in osteoporosis

OBJECTIVE

Osteoporosis, defined as a systemic skeletal disease, is characterized by increased bone fragility and fracture risk. Studies have shown that dysregulation of the functions of miRNAs or the mechanisms they mediate may be an important pathological factor in bone degeneration. Therefore, the aim of the study was to determine the role of miRNAs, which are thought to play a role in bone metabolism, in osteoporosis.

METHODS

The study included 48 patients who were diagnosed with osteoporosis according to the results of a bone mineral density assessment by quantitative computed tomography and 36 healthy individuals. MiRNAs from plasma samples obtained from blood samples taken into ethylenediaminetetraacetic acid (EDTA) tubes were isolated with the miRNA isolation kit and converted to cDNA. Expression analysis of miR-21-5p, miR-34a-5p, miR-210, miR-122-5p, miR-125b-5p, miR-133a, miR-143-3p, miR-146a, miR-155-5p, and miR-223 was performed on the real-time PCR (RT-PCR) device.

RESULTS

When miRNA expression levels in the patient group were compared with the control group, all miRNAs were found to be downregulated in the patients. When fold changes in expression levels in the patient group were examined, significant differences were found in miR-21-5p, miR-133a, mir143-3p, miR-210, and miR-223. In the receiver operating curve analysis, area under the curve=0.882 for the combination of miR-34, miR-125, miR-133, and miR-210.

CONCLUSION

In this study, it was determined that the combined effects of miRNAs, as well as their single effects, were effective in the development of osteoporosis. Therefore, a miRNA panel to be created can make a significant contribution to the development of novel diagnostic and treatment approaches for this disease.

The impact and mechanism of nerve injury on bone metabolism

With an increasing understanding of the mechanisms of fracture healing, it has been found that nerve injury plays a crucial role in the process, but the specific mechanism is yet to be completely revealed. To address this issue and provide novel insights for fracture treatment, we compiled this review. This review aims to study the impact of nerve injury on fracture healing, exploring the role of neurotrophic factors in the healing process. We first revisited the effects of the central nervous system (CNS) and the peripheral nervous system (PNS) on the skeletal system, and further explained the phenomenon of significantly accelerated fracture healing under nerve injury conditions. Then, from the perspective of neurotrophic factors, we delved into the physiological functions and mechanisms of neurotrophic factors, such as nerve growth factor (NGF), Neuropeptides (NPs), and Brain-derived neurotrophic factor (BDNF), in bone metabolism. These effects include direct actions on bone cells, improvement of local blood supply, regulation of bone growth factors, control of cellular signaling pathways, promotion of callus formation and bone regeneration, and synergistic or antagonistic effects with other endocrine factors, such as Sema3A and Transforming Growth Factor β (TGF-β). Finally, we discussed the treatments of fractures with nerve injuries and the future research directions in this review, suggesting that the relationship between nerve injury and fracture healing, as well as the role of nerve injury in other skeletal diseases.

TGF-β1 Inhibits Osteoclast Differentiation and Abnormal Angiogenesis in Intervertebral Disc Degeneration: Evidence from RNA Sequencing and Animal Studies

OBJECTIVE

Mechanisms involved in developing intervertebral disc degeneration (IDD) are poorly understood, thus making developing effective therapies difficult. This study aimed to suggest a possible molecular mechanism, based on transcriptome sequencing-identified transforming growth factor (TGF-β), underlying the effects on bone homeostasis in IDD.

METHODS

A mouse model for IDD was established. Transcriptome sequencing of nucleus pulposus tissue from mice (n = 3) identified differentially expressed mRNAs and key genes impacting bone homeostasis. A protein-protein interaction network pinpointed core genes. GO and KEGG analysis revealed gene functions. Expression levels of TGF-β1, tartrate-resistant acid phosphatase (TRAP), and cathepsin K (CTSK) were measured. Micro-CT evaluated vertebral structures and vascular imaging. Western Blot measured expression levels of Vegf, Opn, MMP3, and MMP13. Safranin O-Fast Green and TRAP staining were performed on intervertebral discs and endplates.

RESULTS

Transcriptomic analysis found 1790 differentially expressed mRNAs in IDD mice. Twenty-eight genes related to bone homeostasis in IDD were identified. TGF-β1 was confirmed as the core gene. GO and KEGG showed TGF-β1 regulates osteoclast markers like CTSK and TRAP through pathways including NF-κB and MAPK. Experimental validation revealed lower TGF-β1 expression in IDD mice than controls, and increased TRAP and CTSK expression. Micro-CT showed decreased bone mass and intervertebral disc space in IDD mice. Vascular imaging showed increased vascular volume in IDD cartilaginous endplates. Western blot displayed increased VEGF and OPN levels, but decreased MMP3 and MMP13 in IDD mice. Safranin O-fast green staining revealed severe IDD degeneration. However, TGF-β1 injection improved bone parameters in IDD mice. In vitro experiments confirmed TGF-β1 inhibits bone marrow macrophages differentiation into osteoclasts.

CONCLUSION

From our data, we conclude that TGF-β1 repressed osteoclast differentiation and aberrant bone-associated angiogenesis in cartilage endplates (EPs) to alleviate IDD, which may be instrumental for the therapeutic targeting of IDD.

MicroRNA based combinatorial therapy against TKIs resistant CML by inactivating the PI3K/Akt/mTOR pathway: a review

Chronic myeloid leukemia (CML) is characterized by presence of Philadelphia chromosome, which harbors BCR-ABL oncogene responsible for encoding BCR-ABL oncoprotein. This oncoprotein interferes with cellular signaling pathways, resulting in tumor progression. Among these pathways, PI3K/Akt/mTOR pathway is significantly upregulated in CML. Tyrosine kinase inhibitors (TKIs) are current standard therapy for CML, and they have shown remarkable efficacy. However, emergence of TKIs drug resistance has necessitated investigation of novel therapeutic approaches. Components of PI3K/Akt/mTOR pathway have emerged as attractive targets in this context, as this pathway is known to be activated in TKIs-resistant CML cells/patients. Inhibiting this pathway may provide a complementary approach to improving TKIs' efficacy and treatment outcomes. Given previous research indicating that miRNAs play an inhibitory role in cancer, current study used computational tools to identify miRNAs that specifically target pathway's core components. A comprehensive analysis was performed, resulting in identification of 111 miRNAs that potentially target PI3K/Akt/mTOR pathway. From this extensive list, 7 miRNAs was selected for further investigation based on their consistent downregulation across leukemia subtypes. Except for hsa-miR-199a-3p, remaining six miRNAs have been extensively studied in acute myeloid leukemia (AML). Given high similarity between AML and CML, it is believed that six miRNAs which are not studied in context of CML may also be advantageous for curing chemoresistance in CML. Building upon this knowledge, it is reasonable to speculate that a combination therapy approach involving use of miRNAs alongside TKIs may offer improved therapy for TKIs-resistant CML compared to TKIs monotherapy alone.

The Role of miR-155 in Antitumor Immunity

MicroRNAs belong to a group of short non-coding RNA molecules that are involved in the regulation of gene expression at multiple levels. Their function was described two decades ago, and, since then, microRNAs have become a rapidly developing field of research. Their participation in the regulation of cellular processes, such as proliferation, apoptosis, cell growth, and migration, made microRNAs attractive for cancer research. Moreover, as a single microRNA can simultaneously target multiple molecules, microRNAs offer a unique advantage in regulating multiple cellular processes in different cell types. Many of these cell types are tumor cells and the cells of the immune system. One of the most studied microRNAs in the context of cancer and the immune system is miR-155. MiR-155 plays a role in modulating innate and adaptive immune mechanisms in distinct immune cell types. As such, miR-155 can be part of the communication between the tumor and immune cells and thus impact the process of tumor immunoediting. Several studies have already revealed its effect on antitumor immune responses, and the targeting of this molecule is increasingly implemented in cancer immunotherapy. In this review, we discuss the current knowledge of miR-155 in the regulation of antitumor immunity and the shaping of the tumor microenvironment, and the plausible implementation of miR-155 targeting in cancer therapy.

MicroRNAs: emerging biomarkers and therapeutic targets of bone fragility in chronic kidney disease

Bone fragility is highly prevalent, yet underdiagnosed in patients with chronic kidney disease. Incomplete understanding of the pathophysiology and limitations of current diagnostics contribute to therapeutic hesitation, if not nihilism. This narrative review addresses the question of whether microRNAs (miRNAs) may improve therapeutic decision making in osteoporosis and renal osteodystrophy. miRNAs are key epigenetic regulators of bone homeostasis and show promise as both therapeutic targets and as biomarkers, primarily of bone turnover. Experimental studies show that miRNAs are involved in several osteogenic pathways. Clinical studies exploring the usefulness of circulating miRNAs for fracture risk stratification and for guiding and monitoring therapy are few and, so far, provide inconclusive results. Likely, (pre)analytical heterogeneity contributes to these equivocal results. In conclusion, miRNAs are promising in metabolic bone disease, both as a diagnostic tool and as therapeutic targets, but not yet ready for clinical prime time.

Differential expression profile of plasma exosomal microRNAs in acute type A aortic dissection with acute lung injury

MicroRNAs (miRNAs) packaged into exosomes mediate cell communication and contribute to the pathogenesis of acute type A aortic dissection (ATAAD) with acute lung injury (ALI). The expression profile of plasma exosomal miRNAs in ATAAD patients with ALI hasn’t been identified. We performed a miRNA-sequencing to analyze the differentially expressed miRNAs (DE-miRNAs) of circulating exosomes in ATAAD patients with ALI compared to patients without ALI, founding 283 specific miRNAs in two groups. We respectively selected the top 10 downregulated and upregulated DE-miRNAs for further studies. The predicted transcription factors (TFs) of these DE-miRNAs were SMAD2, SRSF1, USF1, etc. The Gene Ontology (GO) and Kyoto Encyclopedia Genes and Genomes (KEGG) analysis predicted their target genes mainly involved acute inflammatory response, cell junction, cytoskeleton, NF-κB signaling pathway, etc. Construction and analysis of the PPI network revealed that RHOA and INSR were considered hub genes with the highest connectivity degrees. Moreover, we confirmed two exosomal miRNAs (hsa-miR-485-5p and hsa-miR-206) by real-time quantitative polymerase chain reaction (RT-qPCR) in a validation cohort. Our study identified a plasma exosomal miRNAs signature related to ATAAD with ALI. Certain DE-miRNAs may contribute to the progression of this disease, which help us better understand the pathogenesis of ATAAD with ALI.

Regulation of osteoclast-mediated bone resorption by microRNA

Osteoclast-mediated bone resorption is responsible for bone metabolic diseases, negatively impacting people's health and life. It has been demonstrated that microRNA influences the differentiation of osteoclasts by regulating the signaling pathways during osteoclast-mediated bone resorption. So far, the involved mechanisms have not been fully elucidated. This review introduced the pathways involved in osteoclastogenesis and summarized the related microRNAs binding to their specific targets to mediate the downstream pathways in osteoclast-mediated bone resorption. We also discuss the clinical potential of targeting microRNAs to treat osteoclast-mediated bone resorption as well as the challenges of avoiding potential side effects and producing efficient delivery methods.

Role of Exosomal Non-Coding RNAs in Bone-Related Diseases

Bone-related diseases seriously affect the lives of patients and carry a heavy economic burden on society. Treatment methods cannot meet the diverse clinical needs of affected patients. Exosomes participate in the occurrence and development of many diseases through intercellular communication, including bone-related diseases. Studies have shown that exosomes can take-up and “package” non-coding RNAs and “deliver” them to recipient cells, thereby regulating the function of recipient cells. The exosomal non-coding RNAs secreted by osteoblasts, osteoclasts, chondrocytes, and other cells are involved in the regulation of bone-related diseases by inhibiting osteoclasts, enhancing chondrocyte activity and promoting angiogenesis. Here, we summarize the role and therapeutic potential of exosomal non-coding RNAs in the bone-related diseases osteoporosis, osteoarthritis, and bone-fracture healing, and discuss the clinical application of exosomes in patients with bone-related diseases.

microRNA-155 Expression and Butyrylcholinesterase Activity in the Liver Tissue of Mice Infected with Toxoplasma gondii (Avirulent and Virulent Strains)

PURPOSE

Toxoplasma gondii is an apicomplexan parasite that exhibits distinct strain-related virulence patterns in mice. It can induce hepatic inflammation. The present study investigated MicroRNA-155 (miRNA-155) expression and butyrylcholinesterase (BChE) activity in the liver tissue of mice infected with virulent and avirulent strains of T. gondii.

METHODS

Mice groups included: Group (A), uninfected controls; Group (B), infected with T. gondii avirulent strain (ME-49) and euthanized 7, 27, 47, or 67 days post-infection (pi); Group (C), infected by T. gondii virulent strain (RH) and euthanized 7 days pi; and Group (D), infected by T. gondii virulent strain (RH), treated 24 h pi with sulfamethoxazole-trimethoprim (150 mg/Kg/day and 30 mg/Kg/day, respectively) and euthanized 5, 10, or 20 days pi. miRNA-155 expression was estimated in the liver tissue using the reverse transcription real-time polymerase chain reaction and the ΔΔC_t method. BChE activity was estimated in liver homogenates by Ellman's colorimetric method. Liver sections were examined histopathologically.

RESULTS

revealed a significant elevation in miRNA-155 expression and a significant reduction of BChE activity in all the infected untreated groups compared to the uninfected mice. In group B, the maximum upregulation of miRNA-155 expression and the least reduction in BChE activity were detected 7 days pi. In group D, complete restoration of normal levels occurred 20 days pi. Liver sections showed distinct histopathological patterns with detection of intracellular tachyzoites in group B.

CONCLUSION

miRNA-155 and BChE play a role in regulating host-parasite interaction in toxoplasmosis and may contribute to the pathogenesis of T. gondii induced hepatic damage.

Regulation of Osteoclastogenesis and Bone Resorption by miRNAs

Osteoclasts are specialized bone-resorbing cells that contribute to physiological bone development and remodeling in bone metabolism throughout life. Abnormal production and activation of osteoclasts lead to excessive bone resorption in pathological conditions, such as in osteoporosis and in arthritic diseases with bone destruction. Recent epigenetic studies have shed novel insight into the dogma of the regulation of gene expression. microRNAs belong to a category of epigenetic regulators, which post-transcriptionally regulate and silence target gene expression, and thereby control a variety of biological events. In this review, we discuss miRNA biogenesis, the mechanisms utilized by miRNAs, several miRNAs that play important roles in osteoclast differentiation, function, survival and osteoblast-to-osteoclast communication, and their translational potential and challenges in bone biology and skeletal diseases.

The underestimated role of the microphthalmia-associated transcription factor (MiTF) in normal and pathological haematopoiesis

Haematopoiesis, the process by which a restrained population of stem cells terminally differentiates into specific types of blood cells, depends on the tightly regulated temporospatial activity of several transcription factors (TFs). The deregulation of their activity or expression is a main cause of pathological haematopoiesis, leading to bone marrow failure (BMF), anaemia and leukaemia. TFs can be induced and/or activated by different stimuli, to which they respond by regulating the expression of genes and gene networks. Most TFs are highly pleiotropic; i.e., they are capable of influencing two or more apparently unrelated phenotypic traits, and the action of a single TF in a specific setting often depends on its interaction with other TFs and signalling pathway components. The microphthalmia-associated TF (MiTF) is a prototype TF in multiple situations. MiTF has been described extensively as a key regulator of melanocyte and melanoma development because it acts mainly as an oncogene. Mitf-mutated mice show a plethora of pleiotropic phenotypes, such as microphthalmia, deafness, abnormal pigmentation, retinal degeneration, reduced mast cell numbers and osteopetrosis, revealing a greater requirement for MiTF activity in cells and tissue. A growing amount of evidence has led to the delineation of key roles for MiTF in haematopoiesis and/or in cells of haematopoietic origin, including haematopoietic stem cells, mast cells, NK cells, basophiles, B cells and osteoclasts. This review summarizes several roles of MiTF in cells of the haematopoietic system and how MiTFs can impact BM development.

Roles of MicroRNAs in Bone Destruction of Rheumatoid Arthritis

As an important pathological result of rheumatoid arthritis (RA), bone destruction will lead to joint injury and dysfunction. The imbalance of bone metabolism caused by increased osteoclast activities and decreased osteoblast activities is the main cause of bone destruction in RA. MicroRNAs (MiRNAs) play an important role in regulating bone metabolic network. Recent studies have shown that miRNAs play indispensable roles in the occurrence and development of bone-related diseases including RA. In this paper, the role of miRNAs in regulating bone destruction of RA in recent years, especially the differentiation and activities of osteoclast and osteoblast, is reviewed. Our results will not only help provide ideas for further studies on miRNAs’ roles in regulating bone destruction, but give candidate targets for miRNAs-based drugs research in bone destruction therapy of RA as well.

miR‑155‑5p downregulation inhibits epithelial‑to‑mesenchymal transition by targeting SIRT1 in human nasal epithelial cells

Epithelial-to-mesenchymal transition (EMT) in nasal epithelial cells is involved with tissue remodeling of nasal polyps. The present study investigated the molecular mechanisms through which miR-155-5p regulated EMT in chronic rhinosinusitis (CRS). Patients were divided into the following groups: CRSsNP, CRS without nasal polyposis group, CRSwNP, CRS with nasal polyposis and controls. The expression of transforming growth factor (TGF)-β1, EMT markers, sirtuin 1 (SIRT1) and miR-155-5p were determined by western blotting and reverse transcription-quantitative PCR. Cell morphology following TGF-β1 treatment in the presence of miR-155-5p inhibitors or controls was observed under a microscope. Target genes and potential binding sites between miR-155-5p and SIRT1 were predicted by TargetScan and confirmed using dual-luciferase reporter assay. In patients with CRS, the expression levels of E-cadherin were downregulated and the expression levels of TGF-β1, mesenchymal markers and miR-155-5p were upregulated. Additionally, these changes in expression levels were reduced or increased to a greater extent in the CRSwNP group compared with the CRSsNP group. Furthermore, TGF-β1 expression promoted EMT in human nasal epithelial cells (HNEpCs) and upregulated miR-155-5p expression. These effects were reversed by miR-155-5p inhibitors. Additionally, SIRT1 was predicted as a target gene of miR-155-5p. Downregulation of miR-155-5p upregulated epithelial marker expression and downregulated mesenchymal marker expression by regulating SIRT1. Therefore, the downregulation of miR-155-5p inhibited EMT in HNEpCs by targeting SIRT1.

LncRNA Hoxaas3 promotes lung fibroblast activation and fibrosis by targeting miR-450b-5p to regulate Runx1

Long noncoding RNAs (lncRNAs) participate in organ fibrosis and various pulmonary diseases, but its role in idiopathic pulmonary fibrosis (IPF) is not fully understood. In this study, we found lncRNA Hoxaas3 (Hoxaas3) was up-regulated in the mice model of BLM-induced PF and TGF-β1-induced fibrogenesis in lung fibroblasts (LF). Overexpression of Hoxaas3 promoted fibrogenesis, whereas Hoxaas3 inhibition attenuated lung fibrosis both in vitro and in vivo, through regulation of miR-450b-5p. Furthermore, miR-450b-5p inhibition stimulated fibrogenesis by regulating runt-related transcription factor 1 (Runx1), whereas up-regulation of miR-450b-5p alleviated fibrogenesis in LF. Mechanistically, our study showed that Hoxaas3 regulated lung fibroblast activation and fibrogenesis by acting as a competing endogenous RNA for miR-450b-5p: Hoxaas3 decreased the expression of miR-450b-5p to stimulate level and activity of Runx1 and induced fibrotic LF, whereas Runx1 inhibition alleviated the pro-fibrotic effect of Hoxaas3. In addition, Hoxaas3 was regulated by TGF-β1/Smad4 pathway as its transcriptional target. In conclusion, our study showed the role and mechanism of the TGF-β1/Smad4- Hoxaas3–miR-450b-5p–Runx1 axis for a better understanding of PF, demonstrated Hoxaas3 maybe a new diagnostic biomarker or potential therapeutic target for IPF.

Involvement of Noncoding RNAs in the Differentiation of Osteoclasts

As the most important bone-resorbing cells, osteoclasts play fundamental roles in bone remodeling and skeletal health. Much effort has been focused on identifying the regulators of osteoclast metabolism. Noncoding RNAs (ncRNAs) reportedly regulate osteoclast formation, differentiation, survival, and bone-resorbing activity to participate in bone physiology and pathology. The present review intends to provide a general framework for how ncRNAs and their targets regulate osteoclast differentiation and the important events of osteoclastogenesis they are involved in, including osteoclast precursor generation, early differentiation, mononuclear osteoclast fusion, and multinucleated osteoclast function and survival. This framework is beneficial for understanding bone biology and for identifying the potential biomarkers or therapeutic targets of bone diseases. The review also summarizes the results of in vivo experiments and classic experiment methods for osteoclast-related researches.

A microRNA Approach to Discriminate Cortical Low Bone Turnover in Renal Osteodystrophy

A main obstacle to diagnose and manage renal osteodystrophy (ROD) is the identification of intracortical bone turnover type (low, normal, high). The gold standard, tetracycline‐labeled transiliac crest bone biopsy, is impractical to obtain in most patients. The Kidney Disease Improving Global Outcomes Guidelines recommend PTH and bone‐specific alkaline phosphatase (BSAP) for the diagnosis of turnover type. However, PTH and BSAP have insufficient diagnostic accuracy to differentiate low from non‐low turnover and were validated for trabecular turnover. We hypothesized that four circulating microRNAs (miRNAs) that regulate osteoblast (miRNA‐30b, 30c, 125b) and osteoclast development (miRNA‐155) would provide superior discrimination of low from non‐low turnover than biomarkers in clinical use. In 23 patients with CKD 3‐5D, we obtained tetracycline‐labeled transiliac crest bone biopsy and measured circulating levels of intact PTH, BSAP, and miRNA‐30b, 30c, 125b, and 155. Spearman correlations assessed relationships between miRNAs and histomorphometry and PTH and BSAP. Diagnostic test characteristics for discriminating low from non‐low intracortical turnover were determined by receiver operator curve analysis; areas under the curve (AUC) were compared by χ² test. In CKD rat models of low and high turnover ROD, we performed histomorphometry and determined the expression of bone tissue miRNAs. Circulating miRNAs moderately correlated with bone formation rate and adjusted apposition rate at the endo‐ and intracortical envelopes (ρ = 0.43 to 0.51; p < 0.05). Discrimination of low versus non‐low turnover was 0.866, 0.813, 0.813, and 0.723 for miRNA‐30b, 30c, 125b, and 155, respectively, and 0.509 and 0.589 for PTH and BSAP, respectively. For all four miRNAs combined, the AUC was 0.929, which was superior to that of PTH and BSAP alone and together (p < 0.05). In CKD rats, bone tissue levels of the four miRNAs reflected the findings in human serum. These data suggest that a panel of circulating miRNAs provide accurate noninvasive identification of bone turnover in ROD. © 2020 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

TGFβ1 Regulates Human RANKL-Induced Osteoclastogenesis via Suppression of NFATc1 Expression

Osteoclasts are multinucleated giant cells responsible for bone resorption. Various mediators involved in osteoclast differentiation have been investigated as possible therapeutic targets for osteoporosis and rheumatoid arthritis (RA). Although transforming growth factor beta1 (TGFβ1) has been described as one such multifunctional cytokine essential for bone remodeling, its effect on osteoclastogenesis remains controversial. Therefore, we sought to examine the effect of TGFβ1 on osteoclast generation induced by receptor activator of nuclear factor (NF)-κB ligand (RANKL) in humans. Peripheral blood monocytes, isolated using magnetic bead sorting, were cultured with macrophage-colony stimulating factor (M-CSF) or RANKL with or without TGFβ1. Tartrate-resistant acid phosphatase (TRAP) staining, as well as bone resorption assays, revealed that TGFβ1 suppressed RANKL-mediated human osteoclast development. Real-time reverse transcription PCR and Western blotting revealed that TGFβ1 reduced the gene and protein expression of nuclear factor of activated T cells, cytoplasmic 1 (NFATc1), the master regulator of osteoclast differentiation, respectively. Luciferase assays indicated that TGFβ1 inhibited the NF-κB p65-stimulated promoter activity of NFATc1. Immunofluorescence analysis demonstrated that TGFβ1 abrogated RANKL-induced nuclear translocation of p65. Thus, TGFβ1 regulates human RANKL-induced osteoclastogenesis via downregulation of NFATc1 by blocking nuclear translocation of NF-κB, suggesting that TGFβ1 may be a potential therapeutic target for RA.

The Molecular Mechanism of Vitamin E as a Bone-Protecting Agent: A Review on Current Evidence

Bone remodelling is a tightly-coordinated and lifelong process of replacing old damaged bone with newly-synthesized healthy bone. In the bone remodelling cycle, bone resorption is coupled with bone formation to maintain the bone volume and microarchitecture. This process is a result of communication between bone cells (osteoclasts, osteoblasts, and osteocytes) with paracrine and endocrine regulators, such as cytokines, reactive oxygen species, growth factors, and hormones. The essential signalling pathways responsible for osteoclastic bone resorption and osteoblastic bone formation include the receptor activator of nuclear factor kappa-B (RANK)/receptor activator of nuclear factor kappa-B ligand (RANKL)/osteoprotegerin (OPG), Wnt/β-catenin, and oxidative stress signalling. The imbalance between bone formation and degradation, in favour of resorption, leads to the occurrence of osteoporosis. Intriguingly, vitamin E has been extensively reported for its anti-osteoporotic properties using various male and female animal models. Thus, understanding the underlying cellular and molecular mechanisms contributing to the skeletal action of vitamin E is vital to promote its use as a potential bone-protecting agent. This review aims to summarize the current evidence elucidating the molecular actions of vitamin E in regulating the bone remodelling cycle.

MicroRNAs: Key Regulators to Understand Osteoclast Differentiation?

MicroRNAs (miRNAs) are small non-coding single-stranded RNAs that represent important posttranscriptional regulators of protein-encoding genes. In particular, miRNAs play key roles in regulating cellular processes such as proliferation, migration, and cell differentiation. Recently, miRNAs emerged as critical regulators of osteoclasts (OCs) biology and have been involved in OCs pathogenic role in several disorders. OCs are multinucleated cells generated from myeloid precursors in the bone marrow, specialized in bone resorption. While there is a growing number of information on the cytokines and signaling pathways that are critical to control the differentiation of osteoclast precursors (OCPs) into mature OCs, the connection between OC differentiation steps and miRNAs is less well-understood. The present review will first summarize our current understanding of the miRNA-regulated pathways in the sequential steps required for OC formation, from the motility and migration of OCPs to the cell-cell fusion and the final formation of the actin ring and ruffled border in the functionally resorbing multinucleated OCs. Then, considering the difficulty of working on primary OCs and on the generation of robust data we will give an update on the most recent advances in the detection technologies for miRNAs quantification and how these are of particular interest for the understanding of OC biology and their use as potential biomarkers.

Analysis of the promoter region of the human miR-32 gene in colorectal cancer

The pathogenesis of colorectal cancer (CRC) is poorly understood. MicroRNA (miR)-32 upregulation in CRC tissues was previously reported, where it increased the proliferation, migration and invasion, and reduced apoptosis of CRC cells by inhibiting the expression of phosphatase and tensin homolog (PTEN). However, the mechanism underlying miR-32 upregulation remains unknown. miR-32 is an intronic miRNA located within intron 14 of the transmembrane protein 245 gene (TMEM245). The present study aimed to elucidate the biological pathways underlying miR-32 regulation in CRC. A truncated promoter containing the 5′-flanking region of TMEM245/miR-32 gene was constructed. The promoter region was analyzed by dual luciferase reporter assay in CRC cells. DNA pull-down assay and mass spectrometry (MS) were used to identify proteins binding to the core promoter. Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) and transcription factor (TF) analyses were used to identify the binding proteins. The −320 to −1 bp fragment of the 5′-flanking region exhibited the highest luciferase activity. The regions spanning −606 to −320 bp exhibited a significant decrease in luciferase activity, compared with the −320 to −1 bp fragment. DNA pull-down assay and MS revealed 403 potential miR-32 promoter binding proteins. GO and KEGG pathway analysis indicated that these proteins were involved in numerous physiological and biochemical processes, including ‘structural molecule activity’, ‘RNA binding’, ‘small molecule metabolic process’ and ‘biogenesis’. Furthermore, TF analysis revealed 10 potential interacting TFs, including SMAD family member 1 (SMAD1), signal transducer and activator of transcription 1 (STAT1) and forkhead box K1 (Foxk1). These results suggested that the core promoter region may be located within-320 to −1 bp of the 5′-flanking region of TMEM245/miR-32 gene, while the region from −606 to −320 bp may harbor repressive regulatory elements. The TFs SMAD1, STAT1 and Foxk1 may be involved in the transcriptional regulation of miR-32.

Normalization strategies differently affect circulating miRNA profile associated with the training status

MicroRNAs are fine regulators of the whole-body adaptive response but their use as biomarkers is limited by the lack of standardized pre- and post-analytical procedures. This work aimed to compare different normalization approaches for RT-qPCR data analyses, in order to identify the most reliable and reproducible method to analyze circulating miRNA expression profiles in sedentary and highly-trained subjects. As the physically active status is known to affect miRNA expression, they could be effective biomarkers of the homeostatic response. Following RNA extraction from plasma, a panel of 179 miRNAs was assayed by RT-qPCR and quantified by applying different normalization strategies based on endogenous miRNAs and exogenous oligonucleotides. hsa-miR-320d was found as the most appropriate reference miRNA in reducing the technical variability among the experimental replicates and, hence, in highlighting the inter-cohorts differences. Our data showed an association between the physically active status and specific skeletal muscle- and bone-associated circulating miRNAs profiles, revealing that established epigenetic modifications affect the baseline physiological status of these tissues. Since different normalization strategies led to different outputs, in order to avoid misleading interpretation of data, we remark the importance of the accurate choice of the most reliable normalization method in every experimental setting.

MicroRNAs are Critical Regulators of Osteoclast Differentiation

PURPOSE OF REVIEW

Our goal is to comprehensively review the most recent reports of microRNA (miRNA) regulation of osteoclastogenesis. We highlight validated miRNA-target interactions and their place in the signaling networks controlling osteoclast differentiation and function.

RECENT FINDINGS

Using unbiased approaches to identify miRNAs of interest and reporter-3'UTR assays to validate interactions, recent studies have elucidated the impact of specific miRNA-mRNA interactions during in vitro osteoclastogenesis. There has been a focus on signaling mediators downstream of the RANK and CSF1R signaling, and genes essential for differentiation and function. For example, several miRNAs directly and indirectly target the master osteoclast transcription factor, Nfatc1 (e.g. miR-124 and miR-214) and Rho-GTPases, Cdc42 and Rac1 (e.g. miR-29 family).

SUMMARY

Validating miRNA expression patterns, targets, and impact in osteoclasts and other skeletal cells is critical for understanding basic bone biology and for fulfilling the therapeutic potential of miRNA-based strategies in the treatment bone diseases.

Identification of new therapeutic targets for osteoarthritis through genome-wide analyses of UK Biobank data

Osteoarthritis is the most common musculoskeletal disease and the leading cause of disability globally. Here, we perform a genome-wide association study for osteoarthritis (77,052 cases and 378,169 controls), analysing 4 phenotypes: knee osteoarthritis, hip osteoarthritis, knee and/or hip osteoarthritis, and any osteoarthritis. We discover 64 signals, 52 of them novel, more than doubling the number of established disease loci. Six signals fine map to a single variant. We identify putative effector genes by integrating eQTL colocalization, fine-mapping, human rare disease, animal model, and osteoarthritis tissue expression data. We find enrichment for genes underlying monogenic forms of bone development diseases, and for the collagen formation and extracellular matrix organisation biological pathways. Ten of the likely effector genes, including TGFB1, FGF18, CTSK and IL11 have therapeutics approved or in clinical trials, with mechanisms of action supportive of evaluation for efficacy in osteoarthritis.

MicroRNA‑100‑5p inhibits osteoclastogenesis and bone resorption by regulating fibroblast growth factor 21

MicroRNAs (miRNAs/miRs) are post‑transcriptional regulators that serve important roles in osteoclastogenesis and bone metabolism; however, the roles of miRNAs have not been completely clarified. The present study aimed to investigate the effects of miR‑100‑5p on the mechanism of liver‑bone endocrine metabolism. A miRNA microarray analysis was conducted to evaluate the miRNA expression profile during receptor activator of nuclear factor‑κB ligand‑stimulated osteoclastogenesis. Hematoxylin and eosin and tartrate‑resistant acid phosphatase staining were performed to analyze the trabecular bone microstructure and osteoclast differentiation. The mRNA and protein expression levels were assessed by reverse transcription‑quantitative polymerase chain reaction and western blotting, respectively. The results revealed that in vitro osteoclast differentiation and in vivo bone resorption were suppressed by miR‑100‑5p overexpression. In vivo, a decrease in miR‑100‑5p and an increase in FGF21 were simultaneously observed in mice following ovariectomy (OVX). Bioinformatics analysis and experimental data confirmed that FGF21 was a direct target of miR‑100‑5p. Conversely, augmentation of miR‑100‑5p using a specific agomir in OVX‑operated mice decreased the levels of FGF21 in the serum and liver, and prevented osteoclastogenesis and bone loss. The present study revealed that FGF21 may be a signal molecule associated with the mechanism of liver‑bone endocrine metabolism and may be targeted by miR‑100‑5p. In addition, miR‑100‑5p may serve an important role in protecting against OVX‑induced osteoporosis.

The emerging role of microRNAs in bone remodeling and its therapeutic implications for osteoporosis

Osteoporosis, a common and multifactorial disease, is influenced by genetic factors and environments. However, the pathogenesis of osteoporosis has not been fully elucidated yet. Recently, emerging evidence suggests that epigenetic modifications may be the underlying mechanisms that link genetic and environmental factors with increased risks of osteoporosis and bone fracture. MicroRNA (miRNA), a major category of small noncoding RNA with 20–22 bases in length, is recognized as one important epigenetic modification. It can mediate post-transcriptional regulation of target genes with cell differentiation and apoptosis. In this review, we aimed to profile the role of miRNA in bone remodeling and its therapeutic implications for osteoporosis. A deeper insight into the role of miRNA in bone remodeling and osteoporosis can provide unique opportunities to develop a novel diagnostic and therapeutic approach of osteoporosis.

Therapeutic and Preventive Effects of Osteoclastogenesis Inhibitory Factor on Osteolysis, Proliferation of Mammary Tumor Cell and Induction of Cancer Stem Cells in the Bone Microenvironment

Background: We examined the effects of recombinant human osteoclastogenesis inhibitory factor (hOCIF) on osteolysis, proliferation of mammary tumor cells, and induction of cancer stem cells (CSCs) in the tumor-bone and tumor-subcutaneous microenvironments (TB- and TS-microE). Methods: Mouse mammary tumor cells were transplanted onto the calvaria or into a subcutaneous lesion of female mice, creating a TB-microE and a TS-microE, and the mice were then treated with hOCIF. To investigate the preventive effects of hOCIF, mice were treated with hOCIF before tumor cell implantation onto the calvaria (Pre), after (Post), and both before and after (Whole). The number of CSCs and cytokine levels were evaluated by IHC and ELISA assay, respectively. Results: hOCIF suppressed osteolysis, and growth of mammary tumors in the TB-microE, but not in the TS-microE. In the Pre, Post, and Whole groups, hOCIF suppressed osteolysis, and cell proliferation. hOCIF increased mouse osteoprotegrin (mOPG) levels in vivo, which suppressed mammary tumor cell proliferation in vitro. These preventive effects were observed in the dose-dependent. hOCIF did not affect the induction of CSCs in either microenvironment. Conclusion: While receptor activator of NF-κB ligand (RANKL) targeting therapy may not affect the induction of CSCs, RANKL is a potential target for prevention as well as treatment of breast cancer bone metastasis.

Expression and function of immune ligand-receptor pairs in NK cells and cancer stem cells: therapeutic implications

BACKGROUND

The interplay between the immune system and cancer cells has come to the forefront of cancer therapeutics, with novel immune blockade inhibitors being approved for the treatment of an increasing list of cancers. However, the majority of cancer patients still display or develop resistance to these promising drugs. It is possible that cancer stem cells (CSCs) are contributing to this therapeutic resistance. Although CSCs usually represent a small percentage of the total number of cancer cells, they are endowed with the ability of self-renewal and to produce differentiated progeny. Additionally, they have shown the capacity to establish tumors after transplantation to animals, even in small numbers. CSCs have also been found to be resistant to various anti-cancer therapies, including chemotherapy, radiation therapy and, more recently, immunotherapy. This is true despite the sensitivity of CSCs to lysis in vitro by natural killer (NK) cells, the main effector cells of the innate immune system. In this paper the expression of ligands specific for NK cells on CSCs, the intracellular network responsible for the expression of the NK cytotoxicity receptors, and the status of activation of NK cells in the tumor micro-environment are reviewed. The aim of this review is to highlight potential strategies for overcoming CSC immune resistance, thereby enhancing the efficacy of current and future anti-cancer therapies.

THERAPEUTIC IMPLICATIONS

NK cell activation in the tumor micro-environment through drugs neutralizing inhibitory immune receptors, and combined with other drugs harnessing the potential of the adaptive immune system, could be the most effective approach for attacking both stem cell and non-stem cell cancer populations.

Glucagon-like peptide 2 decreases osteoclasts by stimulating apoptosis dependent on nitric oxide synthase

OBJECTIVES

Glucagon-like peptide 2 (GLP2) is involved in the regulation of energy absorption and metabolism. Despite the importance of the GLP2 signalling mechanisms on osteoclast, little has been studied on how GLP2 works during osteoclastogenesis.

MATERIALS AND METHODS

RAW264.7 cells were infected with rLV-Green-GLP2. The induction of osteoclasts was performed by RANKL. TRAP were detected by RT-PCR, Western blotting and staining. Total nitric oxide and total NOS activity were measured. Cells apoptosis was detected by Hoest33258 and Annix V staining. Animal test, chromatin immunoprecipitation (CHIP), co-immunoprecipitation(IP) and luciferase reporter assay were also performed.

RESULTS

We indicate that GLP2 is associated with osteoporosis-related factors in aged rats, including BALP, TRAP, IL6, TNFα, Nitric Oxide (NO), iNOS, calcitonin and occludin. Moreover, GLP2 is demonstrated to result in negative action during proliferation of tartrate-resistant acid phosphatase-positive (TRAP+) osteoclasts. Furthermore, GLP2 decreases osteoclasts induced from monocyte/macrophage cells RAW264.7 as well as the serum TRAP activity in aged rats. Mechanistic investigations reveal GLP2 enhances the expression of iNOS through stimulating the activity of TGFβ-Smad2/3 signalling in osteoclasts. In particular, inhibition of TGFβ fully abrogates this function of GLP2 in osteoclasts. Strikingly, overexpression of GLP2 significantly increases the product of nitric oxide via iNOS which promotes apoptosis of osteoclasts by decreasing bcl2 or increasing caspase3. Thereby, the ability of GLP2 to regulate apoptosis depends on TGFβ-Smad2/3-iNOS-NO signalling pathway since total NOS inhibitor L-NMMA specifically inhibits the actions by GLP2.

CONCLUSIONS

GLP2 induces apoptosis via TGFβ-Smad2/3 signalling, which contributes to the inhibition of the proliferation of osteoclasts and which may provide potential therapeutic targets for the treatment of osteoporosis.