Mst2 Controls Bone Homeostasis by Regulating Osteoclast and Osteoblast Differentiation

The Hippo signalling pathway in bone homeostasis: Under the regulation of mechanics and aging

The Hippo signalling pathway is a conserved kinase cascade that orchestrates diverse cellular processes, such as proliferation, apoptosis, lineage commitment and stemness. With the onset of society ages, research on skeletal aging-mechanics-bone homeostasis has exploded. In recent years, aging and mechanical force in the skeletal system have gained groundbreaking research progress. Under the regulation of mechanics and aging, the Hippo signalling pathway has a crucial role in the development and homeostasis of bone. We synthesize the current knowledge on the role of the Hippo signalling pathway, particularly its downstream effectors yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ), in bone homeostasis. We discuss the regulation of the lineage specification and function of different skeletal cell types by the Hippo signalling pathway. The interactions of the Hippo signalling pathway with other pathways, such as Wnt, transforming growth factor beta and nuclear factor kappa-B, are also mentioned because of their importance for modulating bone homeostasis. Furthermore, YAP/TAZ have been extensively studied as mechanotransducers. Due to space limitations, we focus on reviewing how mechanical forces and aging influence cell fate, communications and homeostasis through a dysregulated Hippo signalling pathway.

Distinct and overlapping functions of YAP and TAZ in tooth development and periodontal homeostasis

Orthodontic tooth movement (OTM) involves mechanical-biochemical signal transduction, which results in tissue remodeling of the tooth-periodontium complex and the movement of orthodontic teeth. The dynamic regulation of osteogenesis and osteoclastogenesis serves as the biological basis for remodeling of the periodontium, and more importantly, the prerequisite for establishing periodontal homeostasis. Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are key effectors of the Hippo signaling pathway, which actively respond to mechanical stimuli during tooth movement. Specifically, they participate in translating mechanical into biochemical signals, thereby regulating periodontal homeostasis, periodontal remodeling, and tooth development. YAP and TAZ have widely been considered as key factors to prevent dental dysplasia, accelerate orthodontic tooth movement, and shorten treatment time. In this review, we summarize the functions of YAP and TAZ in regulating tooth development and periodontal remodeling, with the aim to gain a better understanding of their mechanisms of action and provide insights into maintaining proper tooth development and establishing a healthy periodontal and alveolar bone environment. Our findings offer novel perspectives and directions for targeted clinical treatments. Moreover, considering the similarities and differences in the development, structure, and physiology between YAP and TAZ, these molecules may exhibit functional variations in specific regulatory processes. Hence, we pay special attention to their distinct roles in specific regulatory functions to gain a comprehensive and profound understanding of their contributions.

Identification of topoisomerase 2A as a novel bone metastasis-related gene in liver hepatocellular carcinoma

BACKGROUND

Bone is the second most frequent site of metastasis for Liver hepatocellular carcinoma (LIHC), which leads to an extremely poor prognosis. Identifying novel biomarkers and therapeutic targets for LIHC patients with bone metastasis is urgently needed.

METHODS

In this study, we used multiple databases for comprehensive bioinformatics analysis, including TCGA, GEO, ICGC, GTEx, TISIDB, and TIMER, to identify key genes related to bone metastasis of LIHC. Clinical tissues and tissue microarray were adopted to assess the expression of TOP2A through qRT-PCR and immunohistochemistry analyses in LIHC. Gene enrichment analysis, DNA methylation, gene mutation, prognosis, and tumor immunity associated with TOP2A in LIHC were investigated. In vitro and in vivo experiments were performed to explore the functional role of TOP2A in LIHC bone metastasis.

RESULTS

We identified that TOP2A was involved in LIHC bone metastasis. Clinically, TOP2A was highly expressed in LIHC tumoral specimens, with the highest level in the bone metastasis lesions. TOP2A was an independent prognostic factor that higher expression of TOP2A was markedly associated with poorer prognosis in LIHC. Moreover, the abnormal expression of TOP2A might be related to DNA hypomethylation, often accompanied by TP53 mutation, immune escape and immunotherapy failure. Enrichment analysis and validation experiments unveiled that TOP2A stimulated the Hippo-YAP signaling pathway in LIHC. Functional assays confirmed that TOP2A could promote bone-specific metastatic potential and tumor-induced osteolysis in LIHC.

CONCLUSIONS

These findings unveil that TOP2A might be a novel prognostic biomarker and therapeutic target for LIHC bone metastasis.

Hippo-YAP/TAZ signaling in osteogenesis and macrophage polarization: Therapeutic implications in bone defect repair

Bone defects caused by diseases or surgery are a common clinical problem. Researchers are devoted to finding biological mechanisms that accelerate bone defect repair, which is a complex and continuous process controlled by many factors. As members of transcriptional costimulatory molecules, Yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ) play an important regulatory role in osteogenesis, and they affect cell function by regulating the expression of osteogenic genes in osteogenesis-related cells. Macrophages are an important group of cells whose function is regulated by YAP/TAZ. Currently, the relationship between YAP/TAZ and macrophage polarization has attracted increasing attention. In bone tissue, YAP/TAZ can realize diverse osteogenic regulation by mediating macrophage polarization. Macrophages polarize into M1 and M2 phenotypes under different stimuli. M1 macrophages dominate the inflammatory response by releasing a number of inflammatory mediators in the early phase of bone defect repair, while massive aggregation of M2 macrophages is beneficial for inflammation resolution and tissue repair, as they secrete many anti-inflammatory and osteogenesis-related cytokines. The mechanism of YAP/TAZ-mediated macrophage polarization during osteogenesis warrants further study and it is likely to be a promising strategy for bone defect repair. In this article, we review the effect of Hippo-YAP/TAZ signaling and macrophage polarization on bone defect repair, and highlight the regulation of macrophage polarization by YAP/TAZ.

The relationship between the Hippo signaling pathway and bone metastasis of breast cancer

Bone is the most common site of metastasis from breast cancer, which is the most prevalent cancer affecting women globally. Bone metastasis from breast cancer severely affects the quality of life of patients and increases mortality. The molecular mechanisms of metastasis, colonization, and proliferation of breast cancer cells in bone are complex and involve the interaction between breast cancer cells and the bone microenvironment. However, the precise mechanism is not clear at present. In recent years, the Hippo signaling pathway has attracted much attention due to its important role in regulating the expression of major effector molecules during tumor development. In particular, studies have found that the mutation and aberrant expression of the core components of the Hippo signaling pathway affect breast cancer cell migration and invasion, indicating that this pathway plays a role in bone metastasis, although the molecular mechanism of this pathway in breast cancer metastasis has not been fully elucidated. In this review, we discuss the function of the Hippo signaling pathway, introducing its role in breast cancer metastasis, especially bone metastasis of breast cancer, so as to lay a solid theoretical foundation for further research and for the development of effective targeted therapeutic agents.

Possible Future Avenues for Rheumatoid Arthritis Therapeutics: Hippo Pathway

Rheumatoid arthritis (RA) is a persistent systemic autoimmune disease with the hallmarks of swelling of the joint, joint tenderness, and progressive joint destruction, which may cause synovial inflammation and pannus as a basic pathological change, resulting in joint malformations and serious disorders. At present, the precise etiology and mechanism of pathogenesis of RA are unknown. The imbalance of immune homeostasis is the origin of RA. Hippo pathway is widely expressed in a range of cell lineages and plays a fundamental role in maintaining the immune steady state and may be involved in the pathogenic mechanism of RA. This study reviews the progress of Hippo pathway and its main members in the pathogenesis of RA from three aspects: regulating the maintenance of autoimmune homeostasis, promoting the pathogenicity of synovial fibroblasts and regulating the differentiation of osteoclasts. The study also presents a new way to recognize the pathogenesis of rheumatoid arthritis, which is favorable for finding a new way for treating the rheumatoid arthritis.

Upregulation of miR-664a-3p Ameliorates Calcific Aortic Valve Disease by Inhibiting the BMP2 Signaling Pathway

The development of calcific aortic valve disease (CAVD) is a complex process of ectopic calcification involving various factors that lead to aortic valve stenosis, hemodynamic changes, and, in severe cases, even sudden death. Currently, aortic valve replacement is the only effective method. The osteogenic differentiation of aortic valve interstitial cells (AVICs) is one of the key factors of valve calcification. Emerging evidence suggests that bone morphogenetic protein 2 (BMP2) can induce the proosteogenic activation of AVICs. However, the regulatory mechanism underlying this activation in AVICs is unclear. In the present study, we elucidated through high-throughput RNA sequencing and RT-qPCR that miR-664a-3p was evidently downregulated in the calcific aortic valve. We also proved that miR-664a-3p was involved in regulating osteogenic differentiation in AVICs. Target prediction analysis and dual-luciferase reporter gene assay confirmed that miR-664a-3p is preferentially bound to BMP2. Furthermore, the effect of the miR-664a-3p/BMP2 axis on osteogenic differentiation in AVICs was examined using the gain- and loss-of-function approach. Finally, we constructed a mouse CAVD model and verified the effect of the miR-664a-3p/BMP2 axis on the aortic valve calcification leaflets in vivo. In conclusion, miR-664a-3p regulates osteogenic differentiation in AVICs through negative regulation of BMP2, highlighting that miR-664a-3p may be a potential therapeutic target for CAVD.

Immuno-hippo: Research progress of the hippo pathway in autoimmune disease

Extensive research in Drosophila and mammals has identified the core components of Hippo signaling, which controls gene expression. Studies of Drosophila have demonstrated the highly conserved Hippo pathway controls tissue homeostasis and organ size by regulating the balance between cell proliferation and apoptosis. Recent work has indicated a potential role of the Hippo pathway in regulating the immune system, which is the key player in autoimmune disease (AID). Therefore, the Hippo pathway may become a novel target for curing AID. Although the pivotal role of both the Hippo pathway in tumorigenesis has been thoroughly investigated, the role of it in AID is still poorly understood. Elucidating the role of Hippo signaling pathways in the activation and expression of specific molecules involved in immune regulation is important for understanding the pathogenesis of AID and exploring novel therapeutic targets. To aid in further research, this review describes the relationship between the Hippo pathway and inflammatory signals such as NF-κB and JAK-STAT, the function of the Hippo pathway in the formation and differentiation of immune cells, and the regulatory role of the Hippo pathway in AID.

Role of Hippo-YAP Signaling in Osseointegration by Regulating Osteogenesis, Angiogenesis, and Osteoimmunology

The social demand for dental implantation is growing at a rapid rate, while dentists are faced with the dilemma of implantation failures associated with unfavorable osseointegration. Clinical-friendly osteogenesis, angiogenesis and osteoimmunology around dental implants play a pivotal role in a desirable osseointegration and it's increasingly appreciated that Hippo-YAP signaling pathway is implicated in those biological processes both in vitro and in vivo in a variety of study. In this article we review the multiple effects of Hippo-YAP signaling in osseointegration of dental implants by regulating osteogenesis, angiogenesis and osteoimmunology in peri-implant tissue, as well as highlight prospective future directions of relevant investigation.

The novel role of Hippo-YAP/TAZ in immunity at the mammalian maternal-fetal interface: Opportunities, challenges

The Hippo-Yes-associated protein (YAP)/transcriptional co-activator with PDZ-binding motif (TAZ), originally identified as a regulator of tissue generation and tumorigenesis, has been proven to have a pivotal position in immunity. Its multi-faceted roles in regulating immunity cover both intrinsic mechanism of immune cells and the crosstalk with non-immune cells. Survival of the allogeneic embryo in the maternal uterine environment depends on immune tolerance, supported by the highly orchestrated cooperation between decidual immune cells, decidual stromal cells and trophoblasts at the maternal-fetal interface. The abnormal maternal-fetal dialogue is believed to be associated with adverse pregnancy outcomes such as spontaneous pregnancy loss. Recent breakthroughs shed light on the how the Hippo-YAP/TAZ manipulate the decidualization and trophoblast invasion, while further research is needed to integrate and reconcile existing findings of the Hippo-YAP/TAZ in immunity and to extend them at the context of pregnancy. In this review, we summarized the Hippo-YAP/TAZ pathways, detailed the effects of YAP/TAZ on immune cells, and discussed the role of YAP/TAZ at the maternal-fetal interface and the potential of YAP/TAZ on immunity regulation at the context of pregnancy. Given the remarkable effect of therapeutic intervention of YAP/TAZ in cancer and autoimmune diseases, it is worthy to explore the response to YAP/TAZ inhibition in the maternal-fetal immunity. This may provide a new valuable target for therapy of pregnancy loss, or potentially other pregnancy complications.

The IRF2BP2-KLF2 axis regulates osteoclast and osteoblast differentiation

Kruppel-like factor 2 (KLF2) has been implicated in the regulation of cell proliferation, differentiation, and survival in a variety of cells. Recently, it has been reported that KLF2 regulates the p65-mediated transactivation of NF-κB. Although the NF-κB pathway plays an important role in the differentiation of osteoclasts and osteoblasts, the role of KLF2 in these bone cells has not yet been fully elucidated. In this study, we demonstrated that KLF2 regulates osteoclast and osteoblast differentiation. The overexpression of KLF2 in osteoclast precursor cells inhibited osteoclast differentiation by downregulating c-Fos, NFATc1, and TRAP expression, while KLF2 overexpression in osteoblasts enhanced osteoblast differentiation and function by upregulating Runx2, ALP, and BSP expression. Conversely, the downregulation of KLF2 with KLF2-specific siRNA increased osteoclast differentiation and inhibited osteoblast differentiation. Moreover, the overexpression of interferon regulatory protein 2-binding protein 2 (IRF2BP2), a regulator of KLF2, suppressed osteoclast differentiation and enhanced osteoblast differentiation and function. These effects were reversed by downregulating KLF2. Collectively, our data provide new insights and evidence to suggest that the IRF2BP2/KLF2 axis mediates osteoclast and osteoblast differentiation, thereby affecting bone homeostasis.

Phosphoproteomic profiling reveals a defined genetic program for osteoblastic lineage commitment of human bone marrow-derived stromal stem cells

Bone marrow-derived mesenchymal stem cells (MSCs) differentiate into osteoblasts upon stimulation by signals present in their niche. Because the global signaling cascades involved in the early phases of MSCs osteoblast (OB) differentiation are not well-defined, we used quantitative mass spectrometry to delineate changes in human MSCs proteome and phosphoproteome during the first 24 h of their OB lineage commitment. The temporal profiles of 6252 proteins and 15,059 phosphorylation sites suggested at least two distinct signaling waves: one peaking within 30 to 60 min after stimulation and a second upsurge after 24 h. In addition to providing a comprehensive view of the proteome and phosphoproteome dynamics during early MSCs differentiation, our analyses identified a key role of serine/threonine protein kinase D1 (PRKD1) in OB commitment. At the onset of OB differentiation, PRKD1 initiates activation of the pro-osteogenic transcription factor RUNX2 by triggering phosphorylation and nuclear exclusion of the histone deacetylase HDAC7.

Microtubule actin crosslinking factor 1 (MACF1) knockdown inhibits RANKL-induced osteoclastogenesis via Akt/GSK3β/NFATc1 signalling pathway

Osteoclasts are responsible for bone resorption and play essential roles in causing bone diseases such as osteoporosis. Microtubule actin crosslinking factor 1 (MACF1) is a large spectraplakin protein that has been implicated in regulating cytoskeletal distribution, cell migration, cell survival and cell differentiation. However, whether MACF1 regulates the differentiation of osteoclasts has not been elucidated. In this study, we found that the expression of MACF1 was increased in primary bone marrow-derived monocytes (BMMs) of osteoporotic mice and was downregulated during receptor activator of nuclear factor kappa-B ligand (RANKL)-induced osteoclastogenesis of pre-osteoclast cell lines RAW264.7 cells. RAW264.7 cells were transfected with shMACF1 using a lentiviral vector to study the role of MACF1 in osteoclastogenic differentiation. Knockdown of MACF1 in RAW264.7 cells inhibited the formation of multinucleated osteoclasts and decreased the expression of osteoclast-marker genes (Ctsk, Acp5, Mmp9 and Oscar) during RANKL-induced osteoclastogenesis. Additionally, knockdown of MACF1 disrupted actin ring formation in osteoclasts and further blocked the bone resorption activity of osteoclasts by reducing the area and depth of pits. Knockdown of MACF1 had no effect on the survival of pre-osteoclasts and mature osteoclasts. We further established that knockdown of MACF1 attenuated the phosphorylation of Akt and GSK3β and inhibited the expression of its downstream target NFATc1. Akt activator rescued the inhibition of osteoclast differentiation by MACF1 knockdown. These data demonstrate that MACF1 positively regulates osteoclast differentiation via the Akt/GSK3β/NFATc1 signalling pathway, suggesting that targeting MACF1 may be a novel therapeutic approach against osteoporosis.

Heme oxygenase-1 attenuates the inhibitory effect of bortezomib against the APRIL-NF-κB-CCL3 signaling pathways in multiple myeloma cells: Corelated with bortezomib tolerance in multiple myeloma

Osteoclasts (OCs) play an essential role in bone destruction in patients with multiple myeloma (MM). Bortezomib can ameliorate bone destruction in patients with MM, but advanced MM often resists bortezomib. We studied the molecular mechanisms of bortezomib tolerance in MM. The expression of the MM-related genes in newly diagnosed patients with MM and normal donors were studied. C-C motif chemokine ligand 3 (CCL3) is a cytokine involved in the differentiation of OCs, and its expression is closely related to APRIL (a proliferation-inducing ligand). We found that bortezomib treatment inhibited APRIL and CCL3. But the heme oxygenase-1 (HO-1) activator hemin attenuated the inhibitory effects of bortezomib on APRIL and CCL3. We induced mononuclear cells to differentiate into OCs, and the enzyme-linked immunosorbent assay showed that the more OCs differentiated, the higher the levels CCL3 secretions detected. Animal experiments showed that hemin promoted MM cell infiltration in mice. The weight and survival rate of tumor mice were associated with HO-1 expression. Immunohistochemical staining showed that HO-1, APRIL, and CCL3 staining were positively stained in the tumor infiltrating sites. Then, MM cells were transfected with L-HO-1/si-HO-1 expression vectors and cultured with an nuclear factor (NF)-kappa B (κB) pathway inhibitor, QNZ. The results showed that HO-1 was the upstream gene of APRIL, NF-κB, and CCL3. We showed that HO-1 could attenuate the inhibitory effect of bortezomib against the APRIL-NF-κB-CCL3 signaling pathways in MM cells, and the tolerance of MM cells to bortezomib and the promotion of bone destruction are related to HO-1.

Auranofin Inhibits RANKL-Induced Osteoclastogenesis by Suppressing Inhibitors of κB Kinase and Inflammasome-Mediated Interleukin-1β Secretion

Osteoporosis is a degenerative metabolic disease caused by an imbalance between osteogenesis and osteoclastogenesis. Increased levels of proinflammatory cytokines combined with decreased estrogen levels, which are commonly seen in postmenopausal women, can lead to overactivation of osteoclasts. Therefore, targeting osteoclast maturation may represent a novel strategy for both treating and preventing osteoporosis. Auranofin is a gold-based compound first approved in 1985 for the treatment of rheumatic diseases. Here, we examined whether auranofin suppresses osteoclast differentiation in vitro and in vivo. Auranofin was shown to suppress receptor activator of NF-κB ligand- (RANKL-) induced osteoclastogenesis in mouse bone marrow macrophages (BMMs) and Raw264.7 macrophages. Cotreatment of macrophages with auranofin blocked the RANKL-induced inhibitors of κB kinase (IKK) phosphorylation, resulting in inhibition of nuclear translocation of p65. The pan-caspase inhibitor nivocasan potently reduced not only inflammasome-mediated interleukin-1β (IL-1β) secretion but also osteoclast differentiation in BMMs. Auranofin suppressed inflammasome activation, as evidenced by decreased production of cleaved IL-1β in both bone marrow-derived macrophages (BMDMs) and J774.A1 cells. Loss of both bone mass in ovariectomized mice was significantly recovered by oral administration of auranofin. Taken together, these data strongly support the use of auranofin for the prevention of osteoclast-related osteoporosis.

TRIM38 regulates NF-κB activation through TAB2 degradation in osteoclast and osteoblast differentiation

The tripartite motif protein 38 (TRIM38), a member of the TRIM family, is involved in various cellular processes such as cell proliferation, differentiation, apoptosis, and antiviral defense. However, the role of TRIM38 in osteoclast and osteoblast differentiation is not yet known. In this study, we report the involvement of TRIM38 in osteoclast and osteoblast differentiation. Overexpression of TRIM38, in osteoclast precursor cells, attenuated receptor activator of nuclear factor kappa B ligand (RANKL)-induced osteoclast formation, RANKL-triggered NF-κB activation, and expression of osteoclast marker genes, such as NFATc1, osteoclast-associated receptor (OSCAR), and tartrate-resistant acid phosphatase (TRAP); and down-regulation of TRIM38 expression showed the opposite effects. Ectopic expression of TRIM38 in osteoblast precursors induced increased osteoblast differentiation and function. Elevated expression of alkaline phosphatase (ALP), bone sialoprotein (BSP), and osteocalcin was also observed due to blockade of NF-κB activation. Conversely, knockdown of TRIM38 showed the opposite effects. TRIM38 also induced degradation of lysosome-dependent transforming growth factor beta-activated kinase 1 and MAP3K7-binding protein 2 (TAB2), further blocking NF-κB activation. Taken together, our data suggest that TRIM38 plays a critical role in bone remodeling as a negative regulator of NF-κB in both osteoclast and osteoblast differentiation.

The versatile hippo pathway in oral-maxillofacial development and bone remodeling

The Hippo signaling pathway is implicated in key aspects of cell proliferation, control of organ size, stem cell functions and tumor suppression. Its functions are primarily mediated either through direct effects on transcription factors to influence target gene expression or through crosstalk with other signaling pathways that regulate multiple physiological activities. Studies are revealing Hippo pathway involvement in diverse functions including renewal of intestinal epithelium, promotion of myocardial cell proliferation, cancer suppression, etc. In this review we discuss Hippo pathway signaling in oral-maxillofacial development and bone remodeling under normal and pathological conditions and highlight promising future research directions.

YAP1 is essential for osteoclastogenesis through a TEADs-dependent mechanism

Yes-associated protein 1 (YAP1), the core effector of the Hippo signaling pathway, has been identified as a key regulator of tissue homeostasis and organ development by controlling cell proliferation and differentiation. Previous studies have shown that YAP1 regulates multiple steps during skeletal development and bone remodeling, including the self-renewal and differentiation of mesenchymal stem cells (MSCs). However, its role in osteoclastogenesis remains largely unknown. Here, we report that YAP1 is an essential regulator for osteoclast differentiation and activity. Both mRNA and protein levels of YAP1 were downregulated during RANKL-induced osteoclastogenesis. Short hairpin RNA-mediated knockdown of YAP1 in bone marrow-derived macrophages (BMM) prevented the formation and function of multinucleated osteoclasts, and markedly abrogated the expression of osteoclast marker genes. Furthermore, the suppression of osteoclastogenesis and bone resorption activity were also observed in the BMM treated with verteporfin, a small molecule that inhibits the association of YAP1 with the transcriptional enhancer-associated domain (TEAD) family of transcription factors, the major partner of YAP1. Mechanistically, the interaction of YAP1/TEADs with AP-1 and cooperation on downstream gene transcription were confirmed, and RANKL-induced NF-κB signaling was also impaired in the YAP1-inhibited condition. Our results revealed the essential role of YAP1 and the YAP1-TEADs complex in regulating osteoclastogenesis and related gene expression.

The emerging role of Hippo signaling pathway in regulating osteoclast formation

A delicate balance between osteoblastic bone formation and osteoclastic bone resorption is crucial for bone homeostasis. This process is regulated by the Hippo signaling pathway including key regulatory molecules RASSF2, NF2, MST1/2, SAV1, LATS1/2, MOB1, YAP, and TAZ. It is well established that the Hippo signaling pathway plays an important part in regulating osteoblast differentiation, but its role in osteoclast formation and activation remains poorly understood. In this review, we discuss the emerging role of Hippo-signaling pathway in osteoclast formation and bone homeostasis. It is revealed that specific molecules of the Hippo-signaling pathway take part in a stage specific regulation in pre-osteoclast proliferation, osteoclast differentiation and osteoclast apoptosis and survival. Upon activation, MST and LAST, transcriptional co-activators YAP and TAZ bind to the members of the TEA domain (TEAD) family transcription factors, and influence osteoclast differentiation via regulating the expression of downstream target genes such as connective tissue growth factor (CTGF/CCN2) and cysteine-rich protein 61 (CYR61/CCN1). In addition, through interacting or cross talking with RANKL-mediated signaling cascades including NF-κB, MAPKs, AP1, and NFATc1, Hippo-signaling molecules such as YAP/TAZ/TEAD complex, RASSF2, MST2, and Ajuba could also potentially modulate osteoclast differentiation and function. Elucidating the roles of the Hippo-signaling pathway in osteoclast development and specific molecules involved is important for understanding the mechanism of bone homeostasis and diseases.

MiR-30a attenuates osteoclastogenesis via targeting DC-STAMP-c-Fos-NFATc1 signaling

Osteoclast is a kind of unique cells which is responsible for bone matrix absorption. It was widely reported that microRNAs (miRNAs) could regulate several physiological processes, including osteoclastogenesis. In our study, microarray analysis showed that miR-30a was down-regulated during osteoclastogenesis after RANKL (receptor activator of nuclear factor κB ligand) stimulation. Osteoclasts and actin-ring formation as well as bone resorption were inhibited when miR-30a was overexpressed in osteoclast precursor cells. Meantime, when miR-30a was inhibited in osteoclast precursor cells, osteoclasts and actin-ring formation as well as bone resorption were promoted. Furthermore, we discovered that miR-30a overexpression inhibited the protein levels of DC-STAMP, c-Fos and NFATc1. However, when DC-STAMP was inhibited by using a DC-STAMP siRNA, we could not detect the inhibition effect of osteoclastogenesis and bone resorption induced by miR-30a. In conclusion, miR-30a attenuated osteoclastogenesis via suppression of DC-STAMP-c-Fos-NFATc1 signaling pathway. On these grounds, this study may reveal a new promising target for the treatment of osteoporosis and other osteopenic disorders.

Systematic morphological profiling of human gene and allele function via Cell Painting

We hypothesized that human genes and disease-associated alleles might be systematically functionally annotated using morphological profiling of cDNA constructs, via a microscopy-based Cell Painting assay. Indeed, 50% of the 220 tested genes yielded detectable morphological profiles, which grouped into biologically meaningful gene clusters consistent with known functional annotation (e.g., the RAS-RAF-MEK-ERK cascade). We used novel subpopulation-based visualization methods to interpret the morphological changes for specific clusters. This unbiased morphologic map of gene function revealed TRAF2/c-REL negative regulation of YAP1/WWTR1-responsive pathways. We confirmed this discovery of functional connectivity between the NF-κB pathway and Hippo pathway effectors at the transcriptional level, thereby expanding knowledge of these two signaling pathways that critically regulate tumor initiation and progression. We make the images and raw data publicly available, providing an initial morphological map of major biological pathways for future study.

DOI:http://dx.doi.org/10.7554/eLife.24060.001

Many human diseases are caused by particular changes, called mutations, in patients’ DNA. A genome is the complete DNA set of an organism, which contains all the information to build the body and keep it working. This information is stored as a code made up of four chemicals called bases. Humans have about 30,000 genes built from DNA, which contain specific sequences of bases. Genome sequencing can determine the exact order of these bases, and has revealed a long list of mutations in genes that could cause particular diseases. However, over 30% of genes in the human body do not have a known role. Genes can serve multiple roles, some of which are not yet discovered, and even when a gene’s purpose is known, the impact of each particular mutation in a given gene is largely uncatalogued. Therefore, new methods need to be developed to identify the biological roles of both normal and abnormal gene sequences.

For hundreds of years, biologists have used microscopy to study how living cells work. Rohban et al. have now asked whether modern software that extracts data from microscopy images could create a fingerprint-like profile of a cell that would reflect how its genes affect its role and appearance. While some genes do not necessarily carry a code with instructions of what a cell should look like, they can indirectly modify the structure of the cell. The resulting changes in the shape of the cell can then be captured in images. The idea was that two cells with matching profiles would indicate that their combinations of genes had matching biological roles too.

Rohban et al. tested their approach with human cells grown in the laboratory. In each sample of cells, they ‘turned on’ one of a few hundred relatively well-known human genes, some of which were known to have similar roles. The cells were then stained via a technique called ‘Cell Painting’ to reveal eight specific components of each cell, including its DNA and its surface membrane. The stained cells were imaged under a microscope and the resulting microscopy images analyzed to create a profile of each type of cell. Rohban et al. confirmed that turning on genes known to perform similar biological roles lead to similar-looking cells. The analysis also revealed a previously unknown interaction between two major pathways in the cell that control how cancer starts and develops.

In the future, this approach could predict the biological roles of less-understood genes by looking for profiles that match those of well-known genes. Applying this strategy to every human gene, and mutations in genes that are linked to diseases, could help to answer many mysteries about how genes build the human body and keep it working.

DOI:http://dx.doi.org/10.7554/eLife.24060.002

RCANs regulate the convergent roles of NFATc1 in bone homeostasis

Activation of calcineurin-dependent nuclear factor of activated T cells c1 (NFATc1) is convergent for normal bone homeostasis. NFATc1 regulates both osteoclastogenesis and osteoblastogenesis. Here we investigated the roles of regulator of calcineurin (RCAN) genes in bone homeostasis. RCANs function as potent physiological inhibitors of calcineurin. Overexpression of RCANs in osteoclast precursor cells attenuated osteoclast differentiation, while their overexpression in osteoblasts enhanced osteoblast differentiation and function. Intriguingly, opposing effects of RCANs in both cell types were shown by blocking activation of the calcineurin-NFATc1 pathway. Moreover, the disruption of RCAN1 or RCAN2 in mice resulted in reduced bone mass, which is associated with strongly increased osteoclast function and mildly reduced osteoblast function. Taken together, RCANs play critical roles in bone homeostasis by regulating both osteoclastogenesis and osteoblastogenesis, and they serve as inhibitors for calcineurin-NFATc1 signaling both in vivo and in vitro.

miR-218 is involved in the negative regulation of osteoclastogenesis and bone resorption by partial suppression of p38MAPK-c-Fos-NFATc1 signaling: Potential role for osteopenic diseases

The increased osteoclastic activity accounts for pathological bone loss in diseases including osteoporosis. MicroRNAs are widely accepted to be involved in the regulation of osteopenic diseases. Recently, the low expression of miR-218 was demonstrated in CD14(+) peripheral blood mononuclear cells (PBMCs) from patients with postmenopausal osteoporosis. However, its role and the underlying mechanism in osteoporosis are still undefined. Here, an obvious decrease in miR-218 expression was observed during osteoclastogenesis under receptor activator of nuclear factor κB ligand (RANKL) stimulation, in both osteoclast precursors of bone marrow macrophages (BMMs) and RAW 264.7. Further analysis confirmed that overexpression of miR-218 obviously attenuated the formation of multinuclear mature osteoclasts, concomitant with the decrease in Trap and Cathepsin K levels, both the master regulators of osteoclastogenesis. Moreover, miR-218 up-regulation dramatically inhibited osteoclast precursor migration, actin ring formation and bone resorption. Mechanism assay demonstrated that miR-218 overexpression attenuated the expression of p38MAPK, c-Fos and NFATc1 signaling molecules. Following preconditioning with P79350, an agonist of p38MAPK, the inhibitor effect of miR-218 on osteoclastogenesis and bone-resorbing activity was strikingly ameliorated. Together, this study revealed a crucial role of miR-218 as a negative regulator for osteoclastogenesis and bone resorption by suppressing the p38MAPK-c-Fos-NFATc1 pathway. Accordingly, this research will provide a promising therapeutic agent against osteopenic diseases including osteoporosis.