Id4, a new candidate gene for senile osteoporosis, acts as a molecular switch promoting osteoblast differentiation

Gene Expression Analyses in Models of Rosiglitazone-Induced Physiological and Pathological Mineralization Identify Novel Targets to Improve Bone and Vascular Health

Clinical studies revealed detrimental skeletal and vascular effects of the insulin sensitizer rosiglitazone. We have shown earlier that rosiglitazone accelerates osteoblast differentiation from human mesenchymal stem cells (hMSC) at the expense of increased oxidative stress and cell death. In calcifying human vascular cells, rosiglitazone stimulates pathological mineralization, an effect diminished by the antioxidant resveratrol. Here, we aimed to elucidate transcriptional networks underlying the rosiglitazone-enhanced mineralization phenotype. We performed genome-wide transcriptional profiling of osteogenic hMSCs treated with rosiglitazone for short-term periods of 1 up to 48 h during the first two days of differentiation, a phase that we show is sufficient for rosiglitazone stimulation of mineralization. Microarray-based mRNA expression analysis revealed 190 probes that were differently expressed in at least one condition compared to vehicle-treated control. This rosiglitazone gene signature contained well-known primary PPAR targets and was also endogenously regulated during osteogenic hMSC differentiation and osteoblast-like differentiation of vascular smooth muscle cells (VSMCs) into calcifying vascular cells (CVCs). Comparative analysis revealed rosiglitazone targets that were commonly enriched in osteoblasts and CVCs or specifically enriched in either osteoblasts or CVCs. Finally, we compared expression patterns of CVC-specific genes with patient expression data from carotid plaque versus intact adjacent tissue, and identified five rosiglitazone targets to be differentially regulated in CVCs and carotid plaque but not osteoblasts when compared to their non-mineralizing counterparts. These targets, i.e., PDK4, SDC4, SPRY4, TCF4 and DACT1, may specifically control extracellular matrix mineralization in vascular cells, and hence provide target candidates for further investigations to improve vascular health.

Id4 modulates salivary gland homeostasis and its expression is downregulated in IgG4-related disease via miR-486-5p

Salivary glands are physiologically orchestrated by the coordinated balance between cell differentiation, proliferation, apoptosis, and interactions between epithelial, mesenchymal endothelial, and neuronal cells, and they are frequent sites of manifestations of Sjögren's syndrome (SS) or IgG4-related disease (IgG4-RD). However, little is known about salivary gland homeostasis and its involvement in those diseases. Inhibitor of DNA binding/differentiation 4 (Id4) is an Id protein involved in the transcriptional control of many biological events, including differentiation. Studies of Id4-deficient mice revealed that Id4-deficient submandibular glands were smaller and exhibited accelerated differentiation, compared with those from wild-type littermates. In addition, dry mouth symptoms and Th17 expansion in splenocytes were also observed in the absence of Id4. Furthermore, Id4 levels in the salivary glands of patients with IgG4-RD, but not SS, were significantly decreased compared with those of healthy controls. miRNA-mRNA integrated analysis demonstrated that miR-486-5p was upregulated in IgG4-RD patients and that it might regulate Id4 in the lesion sites. Together, these results provide evidence for the inhibitory role of Id4 in salivary differentiation, and a critical association between Id4 downregulation and IgG4-RD.

Inhibition of miR338 rescues cleidocranial dysplasia in Runx2 mutant mice partially via the Hif1a-Vegfa axis

Haploinsufficiency of Runt-related transcription factor-2 (RUNX2) is responsible for cleidocranial dysplasia (CCD), a rare hereditary disease with a range of defects, including delayed closure of the cranial sutures and short stature. Symptom-based treatments, such as a combined surgical-orthodontic approach, are commonly used to treat CCD patients. However, there have been few reports of treatments based on Runx2-specific regulation targeting dwarfism symptoms. Previously, we found that the miR338 cluster, a potential diagnostic and therapeutic target for postmenopausal osteoporosis, could directly target Runx2 during osteoblast differentiation in vitro. Here, we generated miR338^-/-;Runx2^+/- mice to investigate whether inhibition of miR338 could rescue CCD defects caused by Runx2 mutation in vivo. We found that the dwarfism phenotype caused by Runx2 haploinsufficiency was recovered in miR338^-/-;Runx2^+/- mice, with complete bone density restoration and quicker closure of fontanels. Single-cell RNA-seq analysis revealed that knockout of miR338 specifically rescued the osteoblast lineage priming ability of bone marrow stromal cells in Runx2^+/- femurs, which was further confirmed by Osterix-specific conditional knockout of miR338 in Runx2^+/- mice (OsxCre; miR338 ^fl/fl;Runx2^+/-). Mechanistically, ablation of the miR338 cluster in Runx2^+/- femurs directly rescued the Hif1a-Vegfa pathway in Runx2^+/- osteoblasts, as proven by gene expression profiles and ChIP and Re-ChIP assays. Collectively, our data revealed the genetic interaction between Runx2 and the miR338 cluster during osteoblast differentiation and implied that the miR338 cluster could be a potential therapeutic target for CCD.

Skeletal Class III Malocclusion Is Associated with ADAMTS2 Variants and Reduced Expression in a Familial Case

Skeletal Class III malocclusion with maxillary deficiency is a severe maxillofacial disease with unclear pathogenic mechanisms. We recruited a Han Chinese family who was clinically diagnosed with skeletal Class III malocclusion and maxillary deficiency. Using whole exome sequencing, a missense variant in ADAMTS2 (NM_014244: c.3506G>T: p.G1169V) was identified and predicted as deleterious by in silico tools. We also found ADAMTS2 variants associated with deficient maxillary development in a cohort. ADAMTS2 expression in HEK293 cells showed significant decrease due to the variant, which was also consistent in dental pulp stem cells from the proband and a healthy control. In the adamts2-knockdown zebrafish model, the length and width of the ethmoid plate, as well as the length of the palatoquadrate became significantly shorter than the control group (p < 0.001), while there was no significant difference in the length and width of the mandible. The expression of Sox3, which was required in early embryonic craniofacial development, was significantly downregulated in the adamts2-knockdown zebrafish embryos. Bioinformatic and cellular studies showed that the decreased expression of ADAMTS2 may inhibit downstream ErbB signaling pathway transduction and restrain subsequent osteogenesis in human adult mesenchymal stromal cells. Collectively, these data showed that ADAMTS2 (c.3506G>T: p.G1169V) may confer susceptibility to risk of skeletal Class III malocclusion with maxillary deficiency.

Let-7 as a Promising Target in Aging and Aging-Related Diseases: A Promise or a Pledge

The abnormal regulation and expression of microRNA (miRNA) are closely related to the aging process and the occurrence and development of aging-related diseases. Lethal-7 (let-7) was discovered in Caenorhabditis elegans (C. elegans) and plays an important role in development by regulating cell fate regulators. Accumulating evidence has shown that let-7 is elevated in aging tissues and participates in multiple pathways that regulate the aging process, including affecting tissue stem cell function, body metabolism, and various aging-related diseases (ARDs). Moreover, recent studies have found that let-7 plays an important role in the senescence of B cells, suggesting that let-7 may also participate in the aging process by regulating immune function. Therefore, these studies show the diversity and complexity of let-7 expression and regulatory functions during aging. In this review, we provide a detailed overview of let-7 expression regulation as well as its role in different tissue aging and aging-related diseases, which may provide new ideas for enriching the complex expression regulation mechanism and pathobiological function of let-7 in aging and related diseases and ultimately provide help for the development of new therapeutic strategies.

The role of CDK8 in mesenchymal stem cells in controlling osteoclastogenesis and bone homeostasis

Bone marrow mesenchymal stem cells (MSCs) are critical regulators of postnatal bone homeostasis. Osteoporosis is characterized by bone volume and strength deterioration, partly due to MSC dysfunction. Cyclin-dependent kinase 8 (CDK8) belongs to the transcription-related CDK family. Here, CDK8 in MSCs was identified as important for bone homeostasis. CDK8 level was increased in aged MSCs along with the association with aging-related signals. Mouse genetic studies revealed that CDK8 in MSCs plays a crucial role in bone resorption and homeostasis. Mechanistically, CDK8 in MSCs extrinsically controls osteoclastogenesis through the signal transducer and transcription 1 (STAT1)-receptor activator of the nuclear factor κ Β ligand (RANKL) axis. Moreover, aged MSCs have high osteoclastogenesis-supporting activity, partly through a CDK8-dependent manner. Finally, pharmacological inhibition of CDK8 effectively repressed MSC-dependent osteoclastogenesis and prevented ovariectomy-induced osteoclastic activation and bone loss. These findings highlight that the CDK8-STAT1-RANKL axis in MSCs could play a crucial role in bone resorption and homeostasis.

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Aging increases CDK8 expression level in MSCs and their progeny

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CDK8 in MSCs plays a crucial role in bone resorption and homeostasis

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CDK8 in MSCs extrinsically controls osteoclastogenesis through STAT1/RANKL axis

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CDK8 inhibitor prevents ovariectomy-induced osteoclastic activation and bone loss

Targeting Sirt1, AMPK, Nrf2, CK2, and Soluble Guanylate Cyclase with Nutraceuticals: A Practical Strategy for Preserving Bone Mass

There is a vast pre-clinical literature suggesting that certain nutraceuticals have the potential to aid the preservation of bone mass in the context of estrogen withdrawal, glucocorticoid treatment, chronic inflammation, or aging. In an effort to bring some logical clarity to these findings, the signaling pathways regulating osteoblast, osteocyte, and osteoclast induction, activity, and survival are briefly reviewed in the present study. The focus is placed on the following factors: the mechanisms that induce and activate the RUNX2 transcription factor, a key driver of osteoblast differentiation and function; the promotion of autophagy and prevention of apoptosis in osteoblasts/osteoclasts; and the induction and activation of NFATc1, which promotes the expression of many proteins required for osteoclast-mediated osteolysis. This analysis suggests that the activation of sirtuin 1 (Sirt1), AMP-activated protein kinase (AMPK), the Nrf2 transcription factor, and soluble guanylate cyclase (sGC) can be expected to aid the maintenance of bone mass, whereas the inhibition of the serine kinase CK2 should also be protective in this regard. Fortuitously, nutraceuticals are available to address each of these targets. Sirt1 activation can be promoted with ferulic acid, N1-methylnicotinamide, melatonin, nicotinamide riboside, glucosamine, and thymoquinone. Berberine, such as the drug metformin, is a clinically useful activator of AMPK. Many agents, including lipoic acid, melatonin, thymoquinone, astaxanthin, and crucifera-derived sulforaphane, can promote Nrf2 activity. Pharmacological doses of biotin can directly stimulate sGC. Additionally, certain flavonols, notably quercetin, can inhibit CK2 in high nanomolar concentrations that may be clinically relevant. Many, though not all, of these agents have shown favorable effects on bone density and structure in rodent models of bone loss. Complex nutraceutical regimens providing a selection of these nutraceuticals in clinically meaningful doses may have an important potential for preserving bone health. Concurrent supplementation with taurine, N-acetylcysteine, vitamins D and K2, and minerals, including magnesium, zinc, and manganese, plus a diet naturally high in potassium, may also be helpful in this regard.

The Potential Use of Mesenchymal Stem Cells and Their Derived Exosomes for Orthopedic Diseases Treatment

Musculoskeletal disorders (MSDs) are conditions that can affect muscles, bones, and joints. These disorders are very painful and severely limit patients' mobility and are more common in the elderly. MSCs are multipotent stem cells isolated from embryonic (such as the umbilical cord) and mature sources (such as adipose tissue and bone marrow). These cells can differentiate into various cells such as osteoblasts, adipocytes, chondrocytes, NP-like cells, Etc. Due to MSC characteristics such as immunomodulatory properties, ability to migrate to the site of injury, recruitment of cells involved in repair, production of growth factors, and large amount production of extracellular vesicles, these cells have been used in many regenerative-related medicine studies. Also, MSCs produce different types of EVs, such as exosomes, to the extracellular environment. Exosomes reflect MSCs' characteristics and do not have cell therapy-associated problems because they are cell-free. These vesicles carry proteins, nucleic acids, and lipids to the host cell and change their function. This review focuses on MSCs and MSCs exosomes' role in repairing dense connective tissues such as tendons, cartilage, invertebrate disc, bone fracture, and osteoporosis treatment.

Serum Amyloid A Correlates With the Osteonecrosis of Femoral Head by Affecting Bone Metabolism

Osteonecrosis of femoral head (ONFH) is a progressive hip joint disease without disease-modifying treatment. Lacking understanding of the pathophysiological process of ONFH has become the humper to develop therapeutic approach. Serum amyloid A (SAA) is an acute phase lipophilic protein during inflammation and we found that SAA is increased for the first time in the serum of ONFH patients through proteomic studies and quantitatively verified by ELISA. Treating rBMSCs with SAA inhibited the osteogenic differentiation via Wnt/β-catenin signaling pathway deactivation and enhanced the adipogenic differentiation via MAPK/PPARγ signaling pathway activation. Finally, bilateral critical-sized calvarial-defect rat model which received SAA treated rBMSCs demonstrated reduction of bone formation when compared to untreated rBMSCs implantation control. Hence, SAA is a vital protein in the physiological process of ONFH and can act as a potential therapeutic target to treat ONFH.

Comparison Study of Stem Cell-Derived Extracellular Vesicles for Enhanced Osteogenic Differentiation

Stem cell-derived extracellular vesicles (EVs) have shown great promise in the field of regenerative medicine and tissue engineering. Recently, human bone marrow-derived mesenchymal stem cell (BMSC)-derived EVs have been considered for bone tissue engineering applications. In this study, we evaluated the osteogenic capability of placental stem cell (PSC)-derived EVs and compared them to the well-characterized BMSC-derived EVs. EVs were extracted from three designated time points (0, 7, and 21 days) after osteogenic differentiation. The results showed that the PSC-derived EVs had much higher protein and lipid concentrations than EVs derived from BMSCs. The extracted EVs were characterized by observing their morphology and size distribution before utilizing next-generation sequencing to determine their microRNA (miRNA) profiles. A total of 306 miRNAs within the EVs were identified, of which 64 were significantly expressed in PSC-derived EVs that related to osteogenic differentiation. In vitro osteogenic differentiation study indicated the late-stage (21-day extracted)-derived EVs higher osteogenic enhancing capability when compared with the early stage-derived EVs. We demonstrated that EVs derived from PSCs could be a new source of EVs for bone tissue engineering applications.

Vertebral Bone Marrow-Derived Mesenchymal Stromal Cells from Osteoporotic and Healthy Patients Possess Similar Differentiation Properties In Vitro

Osteoporosis is a disease characterized by low bone mass and an increased risk of fractures. Although several cellular players leading to osteoporosis have been identified, the role of mesenchymal stromal cells (MSC) is still not fully elaborated. The aim of this study was, therefore, to isolate and characterize MSCs from vertebral body of healthy non-osteoporotic and osteoporotic patients, with a particular focus on their osteogenic differentiation potential. Isolated MSCs were characterized by their osteogenic, adipogenic, and chondrogenic differentiation, as well as surface marker expression, proliferation behavior, and immunomodulatory capacity. The mineralization process was confirmed using Alizarin Red S and alkaline phosphatase (ALP) stains and further evaluated by determining ALP activity, mineral deposition, and free phosphate ion release. MSCs from both healthy and osteoporotic patients showed common fibroblast-like morphology and similar proliferation behavior. They expressed the typical MSC surface markers and possessed immunomodulatory capacity. Both groups demonstrated solid trilineage differentiation potential; osteogenic differentiation was further confirmed by increased ALP activity, deposition of inorganic crystals, phosphate ion release, and expression of osteoblast marker genes. Overall, MSCs from osteoporotic and non-osteoporotic patients showed neither a difference in general MSC features nor in the detailed analysis regarding osteogenic differentiation. These data suggest that vertebral body MSCs from osteoporotic patients were not impaired; rather, they possessed full osteogenic potential compared to MSCs from non-osteoporotic patients.

Comparative transcriptome analysis identifies CARM1 and DNMT3A as genes associated with osteoporosis

To identify new candidate genes in osteoporosis, mainly involved in epigenetic mechanisms, we compared whole gene-expression in osteoblasts (OBs) obtained from women undergoing hip replacement surgery due to fragility fracture and severe osteoarthritis. Then, we analyzed the association of several SNPs with BMD in 1028 women. Microarray analysis yielded 2542 differentially expressed transcripts belonging to 1798 annotated genes, of which 45.6% (819) were overexpressed, and 54.4% (979) underexpressed (fold-change between - 7.45 and 4.0). Among the most represented pathways indicated by transcriptome analysis were chondrocyte development, positive regulation of bone mineralization, BMP signaling pathway, skeletal system development and Wnt signaling pathway. In the translational stage we genotyped 4 SNPs in DOT1L, HEY2, CARM1 and DNMT3A genes. Raw data analyzed against inheritance patterns showed a statistically significant association between a SNP of DNMT3A and femoral neck-(FN) sBMD and primarily a SNP of CARM1 was correlated with both FN and lumbar spine-(LS) sBMD. Most of these associations remained statistically significant after adjusting for confounders. In analysis with anthropometric and clinical variables, the SNP of CARM1 unexpectedly revealed a close association with BMI (p = 0.000082), insulin (p = 0.000085), and HOMA-IR (p = 0.000078). In conclusion, SNPs of the DNMT3A and CARM1 genes are associated with BMD, in the latter case probably owing to a strong correlation with obesity and fasting insulin levels.

Novel transplant of combined platelet-rich fibrin Releasate and bone marrow stem cells prevent bone loss in Ovariectomized osteoporotic mice

BACKGROUND

Osteoporosis is a metabolic bone disorder characterized by deterioration in the quantity and quality of bone tissue, with a consequent increase susceptibility to fracture.

METHODS

In this study, we sought to determine the efficacy of platelet-rich fibrin releasates (PRFr) in augmenting the therapeutic effects of stem cell-based therapy in treating osteoporotic bone disorder. An osteoporosis mouse model was established through bilateral ovariectomy on 12-week-old female ICR (Institute of Cancer Research) mice. Eight weeks postoperatively, the ovariectomized (OVX) mice were left untreated (control) or injected with PRFr, bone marrow stem cells (BMSCs), or the combination of BMSCs and PRFr. Two different injection (single versus quadruple) dosages were tested to investigate the accumulative effects of BMSCS and PRFr on bone quality. Eight weeks after injection, the changes in tibial microstructural profiles included the percentage of bone volume versus total tissue volume (BV/TV, %), bone mineral density (BMD, g/cm3), trabecular number (Tb.N, number/mm), and trabecular separation (Tb.Sp, mm) and bony histology were analyzed.

RESULTS

Postmenopausal osteoporosis model was successfully established in OVX mice, evidenced by reduced BMD, decreased BV/TV, lower Tb.N but increased Tb.Sp. Eight weeks after injection, there was no significant change to BMD and bone trabeculae could be detected in mice that received single-injection regimen. In contrast, in mice which received 4 doses of combined PRFr and BMSCs, the BMD, BV/TV, and TB.N increased, and the TB.Sp decreased significantly compared to untreated OVX mice. Moreover, the histological analysis showed the trabecular spacing become narrower in OVX-mice treated with quadruple injection of BMSCs and combined PRFr and BMSCs than untreated control.

CONCLUSION

The systemic administration of combined BMSCs and PRFr protected against OVX-induced bone mass loss in mice. Moreover, the improvement of bony profile scores in quadruple-injection group is better than the single-injection group, probably through the increase in effect size of cells and growth factors. Our data also revealed the combination therapy of BMSCs and PRFr has better effect in enhancing osteogenesis, which may provide insight for the development of a novel therapeutic strategy in osteoporosis treatment.

Muscle transcriptome analysis identifies genes involved in ciliogenesis and the molecular cascade associated with intramuscular fat content in Large White heavy pigs

Intramuscular fat content (IMF) is a complex trait influencing the technological and sensorial features of meat products and determining pork quality. Thus, we aimed at analyzing through RNA-sequencing the Semimembranosus muscle transcriptome of Italian Large White pigs to study the gene networks associated with IMF deposition. Two groups of samples were used; each one was composed of six unrelated pigs with extreme and divergent IMF content (0.67 ± 0.09% in low IMF vs. 6.81 ± 1.17% in high IMF groups) that were chosen from 950 purebred individuals. Paired-end RNA sequences were aligned to Sus scrofa genome assembly 11.1 and gene counts were analyzed using WGCNA and DeSeq2 packages in R environment. Interestingly, among the 58 differentially expressed genes (DEGs), several were related to primary cilia organelles (such as Lebercilin 5 gene), in addition to the genes involved in the regulation of cell differentiation, in the control of RNA-processing, and G-protein and ERK signaling pathways. Together with cilia-related genes, we also found in high IMF pigs an over-expression of the Fibroblast Growth Factor 2 (FGF2) gene, which in other animal species was found to be a regulator of ciliogenesis. Four WGCNA gene modules resulted significantly associated with IMF deposition: grey60 (P = 0.003), darkturquoise (P = 0.022), skyblue1 (P = 0.022), and lavenderblush3 (P = 0.030). The genes in the significant modules confirmed the results obtained for the DEGs, and the analysis with “cytoHubba” indicated genes controlling RNA splicing and cell differentiation as hub genes. Among the complex molecular processes affecting muscle fat depots, genes involved in primary cilia may have an important role, and the transcriptional reprogramming observed in high IMF pigs may be related to an FGF-related molecular cascade and to ciliogenesis, which in the literature have been associated with fibro-adipogenic precursor differentiation.

TRAF3, a Target of MicroRNA-363-3p, Suppresses Senescence and Regulates the Balance Between Osteoblastic and Adipocytic Differentiation of Rat Bone Marrow-Derived Mesenchymal Stem Cells

Bone marrow-derived mesenchymal stem cells (BMSCs) have the potential to differentiate into osteoblasts or adipocytes, and an imbalance between adipogenesis and osteogenesis causes age-related bone loss. In this study, we determined the influence of tumor necrosis factor receptor-associated factor 3 (TRAF3) on senescence and osteoblastic and adipocytic differentiation of rat BMSCs. TRAF3 expression increased during osteogenic differentiation but decreased during adipocytic differentiation of rat BMSCs, and compared with day 0 cultures, on day 14, the differences were significant. Overexpression of TRAF3 significantly promoted BMSC osteogenic differentiation and suppressed adipogenic differentiation and senescence. Furthermore, Traf3 was determined to be a target gene of miR-363-3p in BMSCs, and TRAF3 expression in BMSCs was reduced by miR-363-3p overexpression. This overexpression attenuated the effects of TRAF3 on BMSC adipogenic differentiation, osteogenic differentiation, and senescence. Taken together, these results uncovered the mechanism by which TRAF3 promotes BMSC osteogenic differentiation and suppresses adipogenic differentiation and senescence, indicating that the miR-363-3p-TRAF3 axis might be a novel therapeutic target for BMSC-based bone tissue engineering in osteoporosis.

Deciphering GRINA/Lifeguard1: Nuclear Location, Ca2+ Homeostasis and Vesicle Transport

The Glutamate Receptor Ionotropic NMDA-Associated Protein 1 (GRINA) belongs to the Lifeguard family and is involved in calcium homeostasis, which governs key processes, such as cell survival or the release of neurotransmitters. GRINA is mainly associated with membranes of the endoplasmic reticulum, Golgi, endosome, and the cell surface, but its presence in the nucleus has not been explained yet. Here we dissect, with the help of different software tools, the potential roles of GRINA in the cell and how they may be altered in diseases, such as schizophrenia or celiac disease. We describe for the first time that the cytoplasmic N-terminal half of GRINA (which spans a Proline-rich domain) contains a potential DNA-binding sequence, in addition to cleavage target sites and probable PY-nuclear localization sequences, that may enable it to be released from the rest of the protein and enter the nucleus under suitable conditions, where it could participate in the transcription, alternative splicing, and mRNA export of a subset of genes likely involved in lipid and sterol synthesis, ribosome biogenesis, or cell cycle progression. To support these findings, we include additional evidence based on an exhaustive review of the literature and our preliminary data of the protein–protein interaction network of GRINA.

Stem cells in Osteoporosis: From Biology to New Therapeutic Approaches

Osteoporosis is a systemic disease that affects the skeleton, causing reduction of bone density and mass, resulting in destruction of bone microstructure and increased risk of bone fractures. Since osteoporosis is a disease affecting the elderly and the aging of the world's population is constantly increasing, it is expected that the incidence of osteoporosis and its financial burden on the insurance systems will increase continuously and there is a need for more understanding this condition in order to prevent and/or treat it. At present, available drug therapy for osteoporosis primarily targets the inhibition of bone resorption and agents that promote bone mineralization, designed to slow disease progression. Safe and predictable pharmaceutical means to increase bone formation have been elusive. Stem cell therapy of osteoporosis, as a therapeutic strategy, offers the promise of an increase in osteoblast differentiation and thus reversing the shift towards bone resorption in osteoporosis. This review is focused on the current views regarding the implication of the stem cells in the cellular and physiologic mechanisms of osteoporosis and discusses data obtained from stem cell-based therapies of osteoporosis in experimental animal models and the possibility of their future application in clinical trials.

Medical Treatment for Osteoporosis: From Molecular to Clinical Opinions

Osteoporosis is a major concern all over the world. With aging, a gradual loss of bone mass results in osteopenia and osteoporosis. Heritable factors account for 60–80% of optimal bone mineralization. Modifiable factors, such as weight-bearing exercise, nutrition, body mass, and hormonal milieu, play an important role in the development of osteopenia and osteoporosis in adulthood. Currently, anti-resorptive agents, including estrogen, bisphosphonates, and selective estrogen receptor modulators (SERMs), are the drugs of choice for osteoporosis. Other treatments include parathyroid hormone (PTH) as well as the nutritional support of calcium and vitamin D. New treatments such as tissue-selective estrogen receptor complexes (TSECs) are currently in use too. This review, which is based on a systematic appraisal of the current literature, provides current molecular and genetic opinions on osteoporosis and its medical treatment. It offers evidence-based information to help researchers and clinicians with osteoporosis assessment. However, many issues regarding osteoporosis and its treatment remain unknown or controversial and warrant future investigation.

JNK inactivation suppresses osteogenic differentiation, but robustly induces osteopontin expression in osteoblasts through the induction of inhibitor of DNA binding 4 (Id4)

Osteoblasts are versatile cells involved in multiple whole-body processes, including bone formation and immune response. Secretory amounts and patterns of osteoblast-derived proteins such as osteopontin (OPN) and osteocalcin (OCN) modulate osteoblast function. However, the regulatory mechanism of OPN and OCN expression remains unknown. Here, we demonstrate that p54/p46 c-jun N-terminal kinase (JNK) inhibition suppresses matrix mineralization and OCN expression but increases OPN expression in MC3T3-E1 cells and primary osteoblasts treated with differentiation inducers, including ascorbic acid, bone morphogenic protein-2, or fibroblast growth factor 2. Preinhibition of JNK before the onset of differentiation increased the number of osteoblasts that highly express OPN but not OCN (OPN-OBs), indicating that JNK affects OPN secretory phenotype at the early stage of osteogenic differentiation. Additionally, we identified JNK2 isoform as being critically involved in OPN-OB differentiation. Microarray analysis revealed that OPN-OBs express characteristic transcription factors, cell surface markers, and cytokines, including glycoprotein hormone α2 and endothelial cell-specific molecule 1. Moreover, we found that inhibitor of DNA binding 4 is an important regulator of OPN-OB differentiation and that dual-specificity phosphatase 16, a JNK-specific phosphatase, functions as an endogenous regulator of OPN-OB induction. OPN-OB phenotype was also observed following LPS from Porphyromonas gingivalis stimulation during osteogenic differentiation. Collectively, these results suggest that the JNK-Id4 signaling axis is crucial in the control of OPN and OCN expression during osteoblastic differentiation.-Kusuyama, J., Amir, M. S., Albertson, B. G., Bandow, K., Ohnishi, T., Nakamura, T., Noguchi, K., Shima, K., Semba, I., Matsuguchi, T. JNK inactivation suppresses osteogenic differentiation, but robustly induces osteopontin expression in osteoblasts through the induction of inhibitor of DNA binding 4 (Id4).

Mouse polycomb group gene Cbx2 promotes osteoblastic but suppresses adipogenic differentiation in postnatal long bones

A set of key developmental genes is essential for skeletal growth from multipotent progenitor cells at weaning. Polycomb group proteins, which regulate such genes contributes to the cell lineage commitment and subsequent differentiation via epigenetic chromatin modification and remodeling. However, it is unclear which cell lineage and gene sets are targeted by polycomb proteins during skeletal growth. We now report that mice deficient in a polycomb group gene Cbx2^cterm/cterm exhibited skeletal hypoplasia in the tibia, femur, and cranium. Long bone cavities in these mice contained fewer multipotent mesenchymal stromal cells. RNA-sequencing of bone marrow cells showed downregulation and upregulation of osteoblastic and adipogenic genes, respectively. Furthermore, the expression levels of genes specifically expressed in B-cell precursors were decreased. Forced expression of Cbx2 in Cbx2^cterm/cterm bone marrow stromal cell recovered fibroblastic colony formation and suppressed adipogenic differentiation. Collectively, our results suggest that Cbx2 controls the maintenance and adipogenic differentiation of mesenchymal stromal cells in the bone marrow.

Epigenetic regulation of ID4 in breast cancer: tumor suppressor or oncogene?

Background

Inhibitor of differentiation protein 4 (ID4) is a dominant negative regulator of the basic helix-loop-helix (bHLH) family of transcription factors. During tumorigenesis, ID4 may act as a tumor suppressor or as an oncogene in different tumor types. However, the role of ID4 in breast cancer is not clear where both an oncogenic and a tumor suppressor function have been attributed. Here, we hypothesize that ID4 behaves as both, but its role in breast differs according to the estrogen receptor (ER) status of the tumor.

Methods

ID4 expression was retrieved from TCGA database using UCSC Xena. Association between overall survival (OS) and ID4 was assessed using Kaplan–Meier plotter. Correlation between methylation and expression was analyzed using the MEXPRESS tool. In vitro experiments involved ectopic expression of ID4 in MCF-7, T47D, and MDA-MB231 breast cancer cell lines. Migration and colony formation capacity were assessed after transfection treatments. Gene expression was analyzed by ddPCR and methylation by MSP, MS-MLPA, or ddMSP.

Results

Data mining analysis revealed that ID4 expression is significantly lower in ER+ tumors with respect to ER− tumors or normal tissue. We also demonstrate that ID4 is significantly methylated in ER+ tumors. Kaplan–Meier analysis indicated that low ID4 expression levels were associated with poor overall survival in patients with ER+ tumors. In silico expression analysis indicated that ID4 was associated with the expression of key genes of the ER pathway only in ER+ tumors. In vitro experiments revealed that ID4 overexpression in ER+ cell lines resulted in decreased migration capacity and reduced number of colonies. ID4 overexpression induced a reduction in ER levels in ER+ cell lines, while estrogen deprivation with fulvestrant did not induce changes neither in ID4 methylation nor in ID4 expression.

Conclusions

We propose that ID4 is frequently silenced by promoter methylation in ER+ breast cancers and functions as a tumor suppressor gene in these tumors, probably due to its interaction with key genes of the ER pathway. Our present study contributes to the knowledge of the role of ID4 in breast cancer.

Electronic supplementary material

The online version of this article (10.1186/s13148-018-0542-8) contains supplementary material, which is available to authorized users.

3'-UTR Polymorphisms of MTHFR and TS Associated with Osteoporotic Vertebral Compression Fracture Susceptibility in Postmenopausal Women

Postmenopausal osteoporosis is one of the most prominent diseases in postmenopausal women and it is increasing in prevalence with the aging population. Furthermore, osteoporosis and osteoporotic vertebral compression fractures (OVCFs) are related to mortality and decreased quality of life. Therefore, searching for biomarkers that are able to identify postmenopausal women who are at high risk of developing OVCFs is an effective strategy for improving the quality of life of patients and alleviating social and economic burdens. In this study, we investigated methylenetetrahydrofolate reductase (MTHFR) and thymidylate synthase (TS) gene polymorphisms in postmenopausal women with OVCF. We recruited 301 postmenopausal women and performed genotyping for the presence of MTHFR 2572C>A, 4869C>G and TS 1100C>T, 1170A>G. Genotyping was analyzed using the polymerization chain reaction restriction fragment length polymorphism assay. MTHFR 2572C>A and TS 1100C>T were associated with the prevalence of osteoporosis (MTHFR 2572CC versus CA+AA: odd ratio [OR] adjusted age, hypertention [HTN], and diabetes mellitus [DM] = 0.49, p = 0.012) and the occurrence of OVCFs (MTHFR 2572CC versus CA+AA: OR adjusted age, HTN, and DM = 0.38, p = 0.013; TS 1100CC versus CT+TT: OR adjusted age, HTN, and DM = 0.46, p = 0.02). Our novel finding is the identification of MTHFR and TS genetic variants that decrease susceptibility to OVCFs. Our findings suggest that polymorphisms in the MTHFR and TS genes are associated with susceptibility to osteoporosis and OVCFs in postmenopausal women.

HEY2, a target of miR-137, indicates poor outcomes and promotes cell proliferation and migration in hepatocellular carcinoma

HEY2, a bHLH transcription factor, has been implicated in the progression of human cancers. Here, we showed that HEY2 expression was markedly increased in HCC, compared with the adjacent nontumorous tissues. High HEY2 expression was closely correlated with tumor multiplicity, tumor differentiation and TNM stage. Kaplan-Meier analyses revealed that HEY2 expression was significantly associated with poor overall and disease-free survival in a training cohort of 361 patients with HCC. The prognostic implication of HEY2 was validated in another cohort of 169 HCC patients. Multivariate Cox regression model indicated HEY2 as an independent factor for overall survival in HCC (Hazard ratio = 1.645, 95% confident interval: 1.309-2.067, P<0.001). We also demonstrated that HEY2 expression was inhibited by miR-137. In clinical samples, HEY2 expression was reversely associated to miR-137 expression. Furthermore, overexpression of HEY2 increased cell viabilities, colony formation and cell migration, whereas knockdown of HEY2 resulted in the opposite phenotypes. Collectively, our data suggest HEY2 as a promising biomarker for unfavorable outcomes and a novel therapeutic target for the clinical management of HCC.

Disease implication of hyper-Hippo signalling

The Hippo signalling pathway regulates cellular proliferation, apoptosis and differentiation, thus exerting profound effects on cellular homeostasis. Inhibition of Hippo signalling has been frequently implicated in human cancers, indicating a well-known tumour suppressor function of the Hippo pathway. However, it is less certain whether and how hyperactivation of the Hippo pathway affects biological outcome in living cells. This review describes current knowledge of the regulatory mechanisms of the Hippo pathway, mainly focusing on hyperactivation of the Hippo signalling nexus. The disease implications of hyperactivated Hippo signalling have also been discussed, including arrhythmogenic cardiomyopathy, Sveinsson's chorioretinal atrophy, Alzheimer's disease, amyotrophic lateral sclerosis and diabetes. By highlighting the significance of disease-relevant Hippo signalling activation, this review can offer exciting prospects to address the onset and potential reversal of Hippo-related disorders.

IL15RA is required for osteoblast function and bone mineralization

Interleukin-15 receptor alpha (IL15RA) is an important component of interleukin-15 (IL15) pro-inflammatory signaling. In addition, IL15 and IL15RA are present in the circulation and are detected in a variety of tissues where they influence physiological functions such as muscle contractility and overall metabolism. In the skeletal system, IL15RA was previously shown to be important for osteoclastogenesis. Little is known, however, about its role in osteoblast function and bone mineralization. In this study, we evaluated bone structural and mechanical properties of an Il15ra whole-body knockout mouse (Il15ra^-/-) and used in vitro and bioinformatic analyses to understand the role IL15/IL15RA signaling on osteoblast function. We show that lack of IL15RA decreased bone mineralization in vivo and in isolated primary osteogenic cultures, suggesting a cell-autonomous effect. Il15ra^-/- osteogenic cultures also had reduced Rankl/Opg mRNA ratio, indicating defective osteoblast/osteoclast coupling. We analyzed the transcriptome of primary pre-osteoblasts from normal and Il15ra^-/- mice and identified 1150 genes that were differentially expressed at a FDR of 5%. Of these, 844 transcripts were upregulated and 306 were downregulated in Il15ra^-/- cells. The largest functional clusters, highlighted using DAVID analysis, were related to metabolism, immune response, bone mineralization and morphogenesis. The transcriptome analysis was validated by qPCR of some of the most significant hits. Using bioinformatic approaches, we identified candidate genes, including Cd200 and Enpp1, that could contribute to the reduced mineralization. Silencing Il15ra using shRNA in the calvarial osteoblast MC3T3-E1 cell line decreased ENPP1 activity. Taken together, these data support that IL15RA plays a cell-autonomous role in osteoblast function and bone mineralization.

Loss of Rictor with aging in osteoblasts promotes age-related bone loss

Osteoblast dysfunction is a major cause of age-related bone loss, but the mechanisms underlying changes in osteoblast function with aging are poorly understood. This study demonstrates that osteoblasts in aged mice exhibit markedly impaired adhesion to the bone formation surface and reduced mineralization in vivo and in vitro. Rictor, a specific component of the mechanistic target of rapamycin complex 2 (mTORC2) that controls cytoskeletal organization and cell survival, is downregulated with aging in osteoblasts. Mechanistically, we found that an increased level of reactive oxygen species with aging stimulates the expression of miR-218, which directly targets Rictor and reduces osteoblast bone surface adhesion and survival, resulting in a decreased number of functional osteoblasts and accelerated bone loss in aged mice. Our findings reveal a novel functional pathway important for age-related bone loss and support for miR-218 and Rictor as potential targets for therapeutic intervention for age-related osteoporosis treatment.

Induction of Lumen Formation in a Three-dimensional Model of Mammary Morphogenesis by Transcriptional Regulator ID4: ROLE OF CaMK2D IN THE EPIGENETIC REGULATION OF ID4 GENE EXPRESSION

Concomitant loss of lumen formation and cell adhesion protein CEACAM1 is a hallmark feature of breast cancer. In a three-dimensional culture model, transfection of CEACAM1 into MCF7 breast cells can restore lumen formation by an unknown mechanism. ID4, a transcriptional regulator lacking a DNA binding domain, is highly up-regulated in CEACAM1-transfected MCF7 cells, and when down-regulated with RNAi, abrogates lumen formation. Conversely, when MCF7 cells, which fail to form lumena in a three-dimensional culture, are transfected with ID4, lumen formation is restored, demonstrating that ID4 may substitute for CEACAM1. After showing the ID4 promoter is hypermethylated in MCF7 cells but hypomethylated in MCF/CEACAM1 cells, ID4 expression was induced in MCF7 cells by agents affecting chromatin remodeling and methylation. Mechanistically, CaMK2D was up-regulated in CEACAM1-transfected cells, effecting phosphorylation of HDAC4 and its sequestration in the cytoplasm by the adaptor protein 14-3-3. CaMK2D also phosphorylates CEACAM1 on its cytoplasmic domain and mutation of these phosphorylation sites abrogates lumen formation. Thus, CEACAM1 is able to maintain the active transcription of ID4 by an epigenetic mechanism involving HDAC4 and CaMK2D, and the same kinase enables lumen formation by CEACAM1. Because ID4 can replace CEACAM1 in parental MCF7 cells, it must act downstream from CEACAM1 by inhibiting the activity of other transcription factors that would otherwise prevent lumen formation. This overall mechanism may be operative in other cancers, such as colon and prostate, where the down-regulation of CEACAM1 is observed.

Cell Fate and Differentiation of Bone Marrow Mesenchymal Stem Cells

Osteoblasts and bone marrow adipocytes originate from bone marrow mesenchymal stem cells (BMMSCs) and there appears to be a reciprocal relationship between adipogenesis and osteoblastogenesis. Alterations in the balance between adipogenesis and osteoblastogenesis in BMMSCs wherein adipogenesis is increased relative to osteoblastogenesis are associated with decreased bone quality and quantity. Several proteins have been reported to regulate this reciprocal relationship but the exact nature of the signals regulating the balance between osteoblast and adipocyte formation within the bone marrow space remains to be determined. In this review, we focus on the role of Transducin-Like Enhancer of Split 3 (TLE3), which was recently reported to regulate the balance between osteoblast and adipocyte formation from BMMSCs. We also discuss evidence implicating canonical Wnt signalling, which plays important roles in both adipogenesis and osteoblastogenesis, in regulating TLE3 expression. Currently, there is demand for new effective therapies that target the stimulation of osteoblast differentiation to enhance bone formation. We speculate that reducing TLE3 expression or activity in BMMSCs could be a useful approach towards increasing osteoblast numbers and reducing adipogenesis in the bone marrow environment.

E Proteins and ID Proteins: Helix-Loop-Helix Partners in Development and Disease

The basic Helix-Loop-Helix (bHLH) proteins represent a well-known class of transcriptional regulators. Many bHLH proteins act as heterodimers with members of a class of ubiquitous partners, the E proteins. A widely expressed class of inhibitory heterodimer partners-the Inhibitor of DNA-binding (ID) proteins-also exists. Genetic and molecular analyses in humans and in knockout mice implicate E proteins and ID proteins in a wide variety of diseases, belying the notion that they are non-specific partner proteins. Here, we explore relationships of E proteins and ID proteins to a variety of disease processes and highlight gaps in knowledge of disease mechanisms.

Id4 functions downstream of Bmp signaling to restrict TCF function in endocardial cells during atrioventricular valve development

The atrioventricular canal (AVC) connects the atrial and ventricular chambers of the heart and its formation is critical for the development of the cardiac valves, chamber septation and formation of the cardiac conduction system. Consequently, problems in AVC formation can lead to congenital defects ranging from cardiac arrhythmia to incomplete cardiac septation. While our knowledge about early heart tube formation is relatively comprehensive, much remains to be investigated about the genes that regulate AVC formation. Here we identify a new role for the basic helix-loop-helix factor Id4 in zebrafish AVC valve development and function. id4 is first expressed in the AVC endocardium and later becomes more highly expressed in the atrial chamber. TALEN induced inactivation of id4 causes retrograde blood flow at the AV canal under heat induced stress conditions, indicating defects in AV valve function. At the molecular level, we found that id4 inactivation causes misexpression of several genes important for AVC and AV valve formation including bmp4 and spp1. We further show that id4 appears to control the number of endocardial cells that contribute to the AV valves by regulating Wnt signaling in the developing AVC endocardium.

A Comprehensive Genomic Analysis Reveals the Genetic Landscape of Mitochondrial Respiratory Chain Complex Deficiencies

Mitochondrial disorders have the highest incidence among congenital metabolic disorders characterized by biochemical respiratory chain complex deficiencies. It occurs at a rate of 1 in 5,000 births, and has phenotypic and genetic heterogeneity. Mutations in about 1,500 nuclear encoded mitochondrial proteins may cause mitochondrial dysfunction of energy production and mitochondrial disorders. More than 250 genes that cause mitochondrial disorders have been reported to date. However exact genetic diagnosis for patients still remained largely unknown. To reveal this heterogeneity, we performed comprehensive genomic analyses for 142 patients with childhood-onset mitochondrial respiratory chain complex deficiencies. The approach includes whole mtDNA and exome analyses using high-throughput sequencing, and chromosomal aberration analyses using high-density oligonucleotide arrays. We identified 37 novel mutations in known mitochondrial disease genes and 3 mitochondria-related genes (MRPS23, QRSL1, and PNPLA4) as novel causative genes. We also identified 2 genes known to cause monogenic diseases (MECP2 and TNNI3) and 3 chromosomal aberrations (6q24.3-q25.1, 17p12, and 22q11.21) as causes in this cohort. Our approaches enhance the ability to identify pathogenic gene mutations in patients with biochemically defined mitochondrial respiratory chain complex deficiencies in clinical settings. They also underscore clinical and genetic heterogeneity and will improve patient care of this complex disorder.

Mitochondria play a crucial role in ATP biosynthesis and comprise proteins encoded in both the nuclear and mitochondrial genomes. Although more than 250 mitochondrial disease-causing genes have been reported, the exact genetic causes in patients remain largely unknown. Here, we aimed to provide further insights into the pathogenic mechanisms of mitochondrial disorders. We investigated the genes encoded in the nuclear and mitochondrial genomes using comprehensive genomic analysis in 142 patients with mitochondrial respiratory chain complex deficiencies. We identified 3 novel disease-causing mitochondria-related genes (MRPS23, QRSL1, and PNPLA4) as well as other disease-causing genes and novel pathogenic mutations in known mitochondrial disease-causing genes. All pathogenic mutations in this study are validated by genetic and/or functional evidence. Our findings, including the achievement of firm genetic diagnoses for 49 of 142 patients (34.5%), were higher than the general diagnosis rate of approximately 25% and demonstrated the value of comprehensive genomic analysis. Accordingly, we have shed light on the genetic heterogeneity underlying mitochondrial disorders.

Transcription Factors in Craniofacial Development: From Receptor Signaling to Transcriptional and Epigenetic Regulation

Craniofacial morphogenesis is driven by spatial-temporal terrains of gene expression, which give rise to stereotypical pattern formation. Transcription factors are key cellular components that control these gene expressions. They are information hubs that integrate inputs from extracellular factors and environmental cues, direct epigenetic modifications, and define transcriptional status. These activities allow transcription factors to confer specificity and potency to transcription regulation during development.

Inhibitor of differentiation 4 (ID4) acts as an inhibitor of ID-1, -2 and -3 and promotes basic helix loop helix (bHLH) E47 DNA binding and transcriptional activity

The four known ID proteins (ID1-4, Inhibitor of Differentiation) share a homologous helix loop helix (HLH) domain and act as dominant negative regulators of basic-HLH transcription factors. ID proteins also interact with many non-bHLH proteins in complex networks. The expression of ID proteins is increasingly observed in many cancers. Whereas ID-1, ID-2 and ID-3, are generally considered as tumor promoters, ID4 on the contrary has emerged as a tumor suppressor. In this study we demonstrate that ID4 heterodimerizes with ID-1, -2 and -3 and promote bHLH DNA binding, essentially acting as an inhibitor of inhibitors of differentiation proteins. Interaction of ID4 was observed with ID1, ID2 and ID3 that was dependent on intact HLH domain of ID4. Interaction with bHLH protein E47 required almost 3 fold higher concentration of ID4 as compared to ID1. Furthermore, inhibition of E47 DNA binding by ID1 was restored by ID4 in an EMSA binding assay. ID4 and ID1 were also colocalized in prostate cancer cell line LNCaP. The alpha helix forming alanine stretch N-terminal, unique to HLH ID4 domain was required for optimum interaction. Ectopic expression of ID4 in DU145 prostate cancer line promoted E47 dependent expression of CDKNI p21. Thus counteracting the biological activities of ID-1, -2 and -3 by forming inactive heterodimers appears to be a novel mechanism of action of ID4. These results could have far reaching consequences in developing strategies to target ID proteins for cancer therapy and understanding biologically relevant ID-interactions.

Acoustic-frequency vibratory stimulation regulates the balance between osteogenesis and adipogenesis of human bone marrow-derived mesenchymal stem cells

Osteoporosis can be associated with the disordered balance between osteogenesis and adipogenesis of bone marrow-derived mesenchymal stem cells (BM-MSCs). Although low-frequency mechanical vibration has been demonstrated to promote osteogenesis, little is known about the influence of acoustic-frequency vibratory stimulation (AFVS). BM-MSCs were subjected to AFVS at frequencies of 0, 30, 400, and 800 Hz and induced toward osteogenic or adipogenic-specific lineage. Extracellular matrix mineralization was determined by Alizarin Red S staining and lipid accumulation was assessed by Oil Red O staining. Transcript levels of osteogenic and adipogenic marker genes were evaluated by real-time reverse transcription-polymerase chain reaction. Cell proliferation of BM-MSCs was promoted following exposure to AFVS at 800 Hz. Vibration at 800 Hz induced the highest level of calcium deposition and significantly increased mRNA expression of COL1A1, ALP, RUNX2, and SPP1. The 800 Hz group downregulated lipid accumulation and levels of adipogenic genes, including FABP4, CEBPA, PPARG, and LEP, while vibration at 30 Hz supported adipogenesis. BM-MSCs showed a frequency-dependent response to acoustic vibration. AFVS at 800 Hz was the most favorable for osteogenic differentiation and simultaneously suppressed adipogenesis. Thus, acoustic vibration could potentially become a novel means to prevent and treat osteoporosis.

Inhibitor of differentiation 4 (ID4): From development to cancer

Highly conserved Inhibitors of DNA-Binding (ID1-ID4) genes encode multi-functional proteins whose transcriptional activity is based on dominant negative inhibition of basic helix-loop-helix (bHLH) transcription factors. Initial animal models indicated a degree of compensatory overlap between ID genes such that deletion of multiple ID genes was required to generate easily recognizable phenotypes. More recently, new model systems have revealed alterations in mice harboring deletions in single ID genes suggesting complex gene and tissue specific functions for members of the ID gene family. Because ID genes are highly expressed during development and their function is associated with a primitive, proliferative cellular phenotype there has been significant interest in understanding their potential roles in neoplasia. Indeed, numerous studies indicate an oncogenic function for ID1, ID2 and ID3. In contrast, the inhibitor of differentiation 4 (ID4) presents a paradigm shift in context of well-established role of ID1, ID2 and ID3 in development and cancer. Apart from some degree of functional redundancy such as HLH dependent interactions with bHLH protein E2A, many of the functions of ID4 are distinct from ID1, ID2 and ID3: ID4 proteins a) regulate distinct developmental processes and tissue expression in the adult, b) promote stem cell survival, differentiation and/or timing of differentiation, c) epigenetic inactivation/loss of expression in several advanced stage cancers and d) increased expression in some cancers such as those arising in the breast and ovary. Thus, in spite of sharing the conserved HLH domain, ID4 defies the established model of ID protein function and expression. The underlying molecular mechanism responsible for the unique role of ID4 as compared to other ID proteins still remains largely un-explored. This review will focus on the current understanding of ID4 in context of development and cancer.

Identification of endoglin-dependent BMP-2-induced genes in the murine periodontal ligament cell line PDL-L2

Background

The periodontal ligament (PDL), connective tissue located between the cementum of teeth and alveolar bone of the mandibula, plays an important role in the maintenance and regeneration of periodontal tissues. We reported previously that endoglin was involved in the BMP-2-induced osteogenic differentiation of mouse PDL cells, which is associated with Smad-2 phosphorylation but not Smad-1/5/8 phosphorylation. In this study, to elucidate the detailed mechanism underlying the BMP-2 signalling pathway unique to PDL cells, we performed a microarray analysis to identify BMP-2-inducible genes in PDL-L2 cells, a mouse PDL-derived cell line, with or without endoglin knockdown.

Findings

Sixty-four genes were upregulated more than twofold by BMP-2 in PDL-L2 cells. Of these genes, 11 were endoglin-dependent, including Id4, which encodes ID4, a helix-loop-helix transcription factor closely associated with TGF-β signaling and osteoblast differentiation. The endoglin-dependent induction of ID4 by BMP-2 was also verified at a protein level.

Conclusion

Our findings indicate that ID4 could be a signal mediator involved in the BMP-2-induced endoglin-dependent osteogenic differentiation of PDL cells.

Id transcriptional regulators in adipogenesis and adipose tissue metabolism

Id proteins (Id1-Id4) are helix-loop-helix (HLH) transcriptional regulators that lack a basic DNA binding domain. They act as negative regulators of basic helix-loop-helix (bHLH) transcription factors by forming heterodimers and inhibit their DNA binding and transcriptional activity. Id proteins are implicated in the regulation of various cellular mechanisms such as cell proliferation, cellular differentiation, cell fate determination, angiogenesis and tumorigenesis. A handful of recent studies also disclosed that Id proteins have critical functions in adipocyte differentiation and adipose tissue metabolism. Here, we reviewed the progress made thus far in understanding the specific functions of Id proteins in adipose tissue differentiation and metabolism. In addition to reviewing the known mechanisms of action, we also discuss possible additional mechanisms in which Id proteins might participate in regulating adipogenic and metabolic pathways.

let-7 enhances osteogenesis and bone formation while repressing adipogenesis of human stromal/mesenchymal stem cells by regulating HMGA2

Bone and fat cells share a common progenitor, stromal/mesenchymal stem cells (MSCs), that can differentiate into osteoblasts or adipocytes. Osteogenesis and adipogenesis of MSCs maintain homeostasis under physiological conditions. The disruption of this homeostasis leads to bone-related metabolic diseases. For instance, reduction in bone formation, which is usually accompanied by an increase in bone marrow adipogenesis, occurs with aging, immobility, or osteoporosis. Thus, it is crucial to gain an understanding of how osteogenic and adipogenic lineages of MSCs are regulated. Here, we present evidence that let-7 is a positive regulator of bone development. Using gain- and loss-of-function approaches, we demonstrate that let-7 markedly promotes osteogenesis and suppresses adipogenesis of MSCs in vitro. Moreover, let-7 could promote ectopic bone formation of MSCs in vivo. Subsequent studies further demonstrated that let-7's effects are mediated through the repression of high-mobility group AT-hook 2 (HMGA2) expression. RNAi depletion of HMGA2 could also enhance osteogenesis and repress adipogenesis. Overall, we found a novel role of let-7/HMGA2 axis in regulating the balance of osteogenesis and adipogenesis of MSCs. Thus, let-7 can be used as a novel therapeutic target for disorders that are associated with bone loss and adipocyte accumulation.

Hey bHLH transcription factors

Hey bHLH transcription factors are direct targets of canonical Notch signaling. The three mammalian Hey proteins are closely related to Hes proteins and they primarily repress target genes by either directly binding to core promoters or by inhibiting other transcriptional activators. Individual candidate gene approaches and systematic screens identified a number of Hey target genes, which often encode other transcription factors involved in various developmental processes. Here, we review data on interaction partners and target genes and conclude with a model for Hey target gene regulation. Furthermore, we discuss how expression of Hey proteins affects processes like cell fate decisions and differentiation, e.g., in cardiovascular, skeletal, and neural development or oncogenesis and how this relates to the observed developmental defects and phenotypes observed in various knockout mice.

Id4 dependent acetylation restores mutant-p53 transcriptional activity

Background

The mechanisms that can restore biological activity of mutant p53 are an area of high interest given that mutant p53 expression is observed in one third of prostate cancer. Here we demonstrate that Id4, an HLH transcriptional regulator and a tumor suppressor, can restore the mutant p53 transcriptional activity in prostate cancer cells.

Methods

Id4 was over-expressed in prostate cancer cell line DU145 harboring mutant p53 (P223L and V274F) and silenced in LNCaP cells with wild type p53. The cells were used to quantitate apoptosis, p53 localization, p53 DNA binding and transcriptional activity. Immuno-precipitation/-blot studies were performed to demonstrate interactions between Id4, p53 and CBP/p300 and acetylation of specific lysine residues within p53.

Results

Ectopic expression of Id4 in DU145 cells resulted in increased apoptosis and expression of BAX, PUMA and p21, the transcriptional targets of p53. Mutant p53 gained DNA binding and transcriptional activity in the presence of Id4 in DU145 cells. Conversely, loss of Id4 in LNCaP cells abrogated wild type p53 DNA binding and transactivation potential. Gain of Id4 resulted in increased acetylation of mutant p53 whereas loss of Id4 lead to decreased acetylation in DU145 and LNCaP cells respectively. Id4 dependent acetylation of p53 was in part due to a physical interaction between Id4, p53 and acetyl-transferase CBP/p300.

Conclusions

Taken together, our results suggest that Id4 regulates the activity of wild type and mutant p53. Id4 promoted the assembly of a macromolecular complex involving CBP/P300 that resulted in acetylation of p53 at K373, a critical post-translational modification required for its biological activity.

Transcriptional components of anteroposterior positional information during zebrafish fin regeneration

Many fish and salamander species regenerate amputated fins or limbs, restoring the size and shape of the original appendage. Regeneration requires that spared cells retain or recall information encoding pattern, a phenomenon termed positional memory. Few factors have been implicated in positional memory during vertebrate appendage regeneration. Here, we investigated potential regulators of anteroposterior (AP) pattern during fin regeneration in adult zebrafish. Sequence-based profiling from tissues along the AP axis of uninjured pectoral fins identified many genes with region-specific expression, several of which encoded transcription factors with known AP-specific expression or function in developing embryonic pectoral appendages. Transgenic reporter strains revealed that regulatory sequences of the transcription factor gene alx4a activated expression in fibroblasts and osteoblasts within anterior fin rays, whereas hand2 regulatory sequences activated expression in these same cell types within posterior rays. Transgenic overexpression of hand2 in all pectoral fin rays did not affect formation of the proliferative regeneration blastema, yet modified the lengths and widths of regenerating bones. Hand2 influenced the character of regenerated rays in part by elevation of the vitamin D-inactivating enzyme encoded by cyp24a1, contributing to region-specific regulation of bone metabolism. Systemic administration of vitamin D during regeneration partially rescued bone defects resulting from hand2 overexpression. Thus, bone-forming cells in a regenerating appendage maintain expression throughout life of transcription factor genes that can influence AP pattern, and differ across the AP axis in their expression signatures of these and other genes. These findings have implications for mechanisms of positional memory in vertebrate tissues.

Osteoblast-adipocyte lineage plasticity in tissue development, maintenance and pathology

Osteoblasts and adipocytes share a common precursor in adult bone marrow and there is a degree of plasticity between the two cell lineages. This has important implications for the etiology of not only osteoporosis but also several other diseases involving an imbalance between osteoblasts and adipocytes. Understanding the process of differentiation of osteoblasts and adipocytes and their trans-differentiation is crucial in order to identify genes and other factors that may contribute to the pathophysiology of such diseases. Several transcriptional regulators have been shown to control osteoblast and adipocyte differentiation and function. Regulation of cell commitment occurs at the level of the progenitor cell through cross talk between complex signaling pathways and epigenetic mechanisms such as DNA methylation, chromatin remodeling, and microRNAs. Here we review the complex precursor cell microenvironment controlling osteoblastogenesis and adipogenesis during tissue development, maintenance, and pathology.

TLE3, transducing-like enhancer of split 3, suppresses osteoblast differentiation of bone marrow stromal cells

In senile osteoporosis the balance of adipogenesis and osteoblastogenesis in bone marrow stromal cells (BMSCs) is disrupted so that adipogenesis is increased with respect to osteoblastogenesis, and as a result, bone mass is decreased. While the molecular mechanisms controlling the balance between osteoblastogenesis and adipogenesis are of great interest, the exact nature of the signals regulating this process remains to be determined. In general, adipogenesis is a reciprocal relationship with osteoblastogenesis in BMSCs. Recently transducin-like enhancer of split 3 (TLE3), was reported to enhance adipogenesis in pre adipocytes. However, the effect of TLE3 on osteoblast differentiation of BMSCs is completely unknown. Here we report that TLE3 not only enhances adipocyte differentiation in BMSCs but also suppresses osteoblast differentiation. Firstly we examined the expression and localization of TLE3. We found that TLE3 is expressed in the nucleus of bone marrow stromal cells and that over-expression of TLE3 induced adipocyte differentiation and suppressed ALP activity induced by treatment with BMP2 in these cells. In contrast, adipocyte differentiation was decreased and ALP activity increased when endogenous TLE3 was knocked down by shRNA in BMSCs. To examine the mechanism by which TLE3 is able to suppress osteoblast differentiation, we focused on Runx2, a transcription factor essential for osteoblast differentiation. We found that TLE3 strongly suppressed ALP activity and OSE2-luciferase activity induced by Runx2 and this repression of Runx2 by TLE3 occurs via HDACs because treatment with TSA, a class I and II HDAC inhibitor, rescued this repression. In conclusion, we identify TLE3 as a suppressor of BMSC differentiation in osteoblast lineage cells in vitro. Our data suggest that TLE3 activity may be a key in balancing adipocyte and osteoblast differentiation in the adult bone marrow microenvironment.

Id4 deficiency attenuates prostate development and promotes PIN-like lesions by regulating androgen receptor activity and expression of NKX3.1 and PTEN

Background

Inhibitor of differentiation 4 (Id4), a member of the helix-loop-helix family of transcriptional regulators has emerged as a tumor suppressor in prostate cancer. Id4 is expressed in the normal prostate where its expression is also regulated by androgens. In this study we investigated the effect of loss of Id4 (Id4-/-) on adult prostate morphology.

Methods

Histological analysis was performed on prostates from 6-8 weeks old Id4-/-, Id4+/- and Id4+/+ mice. Expression of Id1, Sox9, Myc, androgen receptor, Akt, p-Akt, Pten and Nkx3.1 was investigated by immunohistochemistry. Androgen receptor binding on NKX3.1 promoter was studied by chromatin immuno-precipitation. Id4 was either over-expressed or silenced in prostate cancer cell lines DU145 and LNCaP respectively followed by analysis of PTEN, NKX3.1 and Sox9 expression.

Results

Id4-/- mice had smaller prostates with fewer tubules, smaller tubule diameters and subtle mPIN like lesions. Levels of androgen receptor were similar between wild type and Id4-/- prostate. Decreased NKX3.1 expression was in part due to decreased androgen receptor binding on NKX3.1 promoter in Id4-/- mice. The increase in the expression of Myc, Sox9, Id1, Ki67 and decrease in the expression of PTEN, Akt and phospho-AKT was associated with subtle mPIN like lesions in Id4-/- prostates. Finally, prostate cancer cell line models in which Id4 was either silenced or over-expressed confirmed that Id4 regulates NKX3.1, Sox9 and PTEN.

Conclusions

Our results suggest that loss of Id4 attenuates normal prostate development and promotes hyperplasia/dysplasia with subtle mPIN like lesions characterized by gain of Myc and Id1 and loss of Nkx3.1 and Pten expression. One of the mechanisms by which Id4 may regulate normal prostate development is through regulating androgen receptor binding to respective response elements such as those on NKX3.1 promoter. In spite of these complex alterations, large neoplastic lesions in Id4-/- prostates were not observed suggesting the possibility of mechanisms/pathways such as loss of Akt that could restrain the formation of significant pre-cancerous lesions.

Gene Expression Regulation underlying Osteo-, Adipo-, and Chondro-Genic Lineage Commitment of Human Mesenchymal Stem Cells

Human mesenchymal stem cells have a high potential in regenerative medicine. They can be isolated from a variety of adult tissues, including bone marrow, and can be differentiated into multiple cell types of the mesodermal lineage, including adipocytes, osteocytes, and chondrocytes. Stem cell differentiation is controlled by a process of interacting lineage-specific and multipotent genes. In this chapter, the authors use full genome microarrays to explore gene expression profiles in the process of Osteo-, Adipo-, and Chondro-Genic lineage commitment of human mesenchymal stem cells.

Fam57b (family with sequence similarity 57, member B), a novel peroxisome proliferator-activated receptor γ target gene that regulates adipogenesis through ceramide synthesis

This report identifies a novel gene encoding Fam57b (family with sequence similarity 57, member B) as a novel peroxisome proliferator-activated receptor γ (PPARγ)-responsive transmembrane gene that is related to obesity. The gene was identified based on an integrated bioinformatics analysis of the following three expression profiling data sets: adipocyte differentiation of mouse stromal cells (ST2 cells), adipose tissues from obesity mice, and siRNA-mediated knockdown of Pparγ using ST2 cells. Fam57b consists of three variants expressed from different promoters and contains a Tram-Lag1-CLN8 domain that is related to ceramide synthase. Reporter and ChIP assays showed that Fam57b variant 2 is a bona fide PPARγ target gene in ST2 cells. Fam57b was up-regulated during adipocyte differentiation, suggesting that FAM57B is involved in this process. Surprisingly, FAM57B overexpression inhibited adipogenesis, and siRNA-mediated knockdown promoted adipocyte differentiation. Analysis of the ceramide content by lipid assay found that ceramides were in fact augmented in FAM57B-overexpressing ST2 cells. We also confirmed that ceramide inhibits adipogenesis. Therefore, the aforementioned results of FAM57B overexpression and siRNA experiments are reconciled by ceramide synthesis. In summary, we present in vitro evidence showing that PPARγ regulates Fam57b transcription during the adipogenesis of ST2 cells. In addition, our results suggest that PPARγ activation contributes to the regulation of ceramide metabolism during adipogenesis via FAM57B.