Expression of leukemia inhibitory factor (LIF)/interleukin-6 family cytokines and receptors during in vitro osteogenesis: differential regulation by dexamethasone and LIF

Spatial Organization of Osteoclastic Coupling Factors and Their Receptors at Human Bone Remodeling Sites

The strictly regulated bone remodeling process ensures that osteoblastic bone formation is coupled to osteoclastic bone resorption. This coupling is regulated by a panel of coupling factors, including clastokines promoting the recruitment, expansion, and differentiation of osteoprogenitor cells within the eroded cavity. The osteoprogenitor cells on eroded surfaces are called reversal cells. They are intermixed with osteoclasts and become bone-forming osteoblast when reaching a critical density and maturity. Several coupling factors have been proposed in the literature, but their effects and expression pattern vary between studies depending on species and experimental setup. In this study, we investigated the mRNA levels of proposed secreted and membrane-bound coupling factors and their receptors in cortical bone remodeling events within the femur of healthy adolescent human controls using high-sensitivity RNA in situ hybridization. Of the proposed coupling factors, human osteoclasts showed mRNA-presence of LIF, PDGFB, SEMA4D, but no presence of EFNB2, and OSM. On the other hand, the osteoblastic reversal cells proximate to osteoclasts presented with LIFR, PDGFRA and PLXNB1, but not PDGFRB, which are all known receptors of the proposed coupling factors. Although EFNB2 was not present in mature osteoclasts, the mRNA of the ligand-receptor pair EFNB2:EPHB4 were abundant near the central blood vessels within intracortical pores with active remodeling. EPHB4 and SEMA4D were also abundant in mature bone-forming osteoblasts. This study highlights that especially LIF:LIFR, PDGFB:PDGFRA, SEMA4D:PLXNB1 may play a critical role in the osteoclast-osteoblast coupling in human remodeling events, as they are expressed within the critical cells.

gp130 Cytokines Activate Novel Signaling Pathways and Alter Bone Dissemination in ER+ Breast Cancer Cells

Breast cancer cells frequently home to the bone marrow, where they encounter signals that promote survival and quiescence or stimulate their proliferation. The interleukin-6 (IL-6) cytokines signal through the co-receptor glycoprotein130 (gp130) and are abundantly secreted within the bone microenvironment. Breast cancer cell expression of leukemia inhibitory factor (LIF) receptor (LIFR)/STAT3 signaling promotes tumor dormancy in the bone, but it is unclear which, if any of the cytokines that signal through LIFR, including LIF, oncostatin M (OSM), and ciliary neurotrophic factor (CNTF), promote tumor dormancy and which signaling pathways are induced. We first confirmed that LIF, OSM, and CNTF and their receptor components were expressed across a panel of breast cancer cell lines, although expression was lower in estrogen receptor-negative (ER^- ) bone metastatic clones compared with parental cell lines. In estrogen receptor-positive (ER⁺ ) cells, OSM robustly stimulated phosphorylation of known gp130 signaling targets STAT3, ERK, and AKT, while CNTF activated STAT3 signaling. In ER^- breast cancer cells, OSM alone stimulated AKT and ERK signaling. Overexpression of OSM, but not CNTF, reduced dormancy gene expression and increased ER⁺ breast cancer bone dissemination. Reverse-phase protein array revealed distinct and overlapping pathways stimulated by OSM, LIF, and CNTF with known roles in breast cancer progression and metastasis. In breast cancer patients, downregulation of the cytokines or receptors was associated with reduced relapse-free survival, but OSM was significantly elevated in patients with invasive disease and distant metastasis. Together these data indicate that the gp130 cytokines induce multiple signaling cascades in breast cancer cells, with a potential pro-tumorigenic role for OSM and pro-dormancy role for CNTF. © 2021 American Society for Bone and Mineral Research (ASBMR).

Influences of the IL-6 cytokine family on bone structure and function

The IL-6 family of cytokines comprises a large group of cytokines that all act via the formation of a signaling complex that includes the glycoprotein 130 (gp130) receptor. Despite this, many of these cytokines have unique roles that regulate the activity of bone forming osteoblasts, bone resorbing osteoclasts, bone-resident osteocytes, and cartilage cells (chondrocytes). These include specific functions in craniofacial development, longitudinal bone growth, and the maintenance of trabecular and cortical bone structure, and have been implicated in musculoskeletal pathologies such as craniosynostosis, osteoporosis, rheumatoid arthritis, osteoarthritis, and heterotopic ossifications. This review will work systematically through each member of this family and provide an overview and an update on the expression patterns and functions of each of these cytokines in the skeleton, as well as their negative feedback pathways, particularly suppressor of cytokine signaling 3 (SOCS3). The specific cytokines described are interleukin 6 (IL-6), interleukin 11 (IL-11), oncostatin M (OSM), leukemia inhibitory factor (LIF), cardiotrophin 1 (CT-1), ciliary neurotrophic factor (CNTF), cardiotrophin-like cytokine factor 1 (CLCF1), neuropoietin, humanin and interleukin 27 (IL-27).

GP130 Cytokines in Breast Cancer and Bone

Breast cancer cells have a high predilection for skeletal homing, where they may either induce osteolytic bone destruction or enter a latency period in which they remain quiescent. Breast cancer cells produce and encounter autocrine and paracrine cytokine signals in the bone microenvironment, which can influence their behavior in multiple ways. For example, these signals can promote the survival and dormancy of bone-disseminated cancer cells or stimulate proliferation. The interleukin-6 (IL-6) cytokine family, defined by its use of the glycoprotein 130 (gp130) co-receptor, includes interleukin-11 (IL-11), leukemia inhibitory factor (LIF), oncostatin M (OSM), ciliary neurotrophic factor (CNTF), and cardiotrophin-1 (CT-1), among others. These cytokines are known to have overlapping pleiotropic functions in different cell types and are important for cross-talk between bone-resident cells. IL-6 cytokines have also been implicated in the progression and metastasis of breast, prostate, lung, and cervical cancer, highlighting the importance of these cytokines in the tumor–bone microenvironment. This review will describe the role of these cytokines in skeletal remodeling and cancer progression both within and outside of the bone microenvironment.

The effect of fludrocortisone on the uterine receptivity partially mediated by ERK1/2-mTOR pathway

Implantation of embryos needs endometrial receptivity. Mineralocorticoids is one of the causes influencing the implantation window. This study targeted to evaluation fludrocortisone different properties on endometrial receptivity. The objective of this study was to assess whether treatment with fludrocortisone could impact the expression of diverse genes and proteins that are involved in uterine receptivity in mice. In this study, 40 female adult BALB/c mice were used. The samples were allocated to four groups of ten. Control group (C) received: vehicle; fludrocortisone group (FCA): received 1.5 mg/kg fludrocortisone; PP242 group (PP242): received 30 mg/kg PP242; fludrocortisone+PP242 group (FCA+PP242): received fludrocortisone and PP242. Mice were killed on window implantation day after mating and confirmed pregnancy. The endometrial epithelium of mouse was collected to assess mRNA expression of leukemia inhibitory factor (LIF), mucin-1 (MUC1), heparin-binding epidermal growth factor (HB-EGF), (Msx.1), miRNA Let-7a, and miRNA 223-3p as well as protein expression of extracellular signal-regulated kinase 1/2 (ERK1/2), mammalian target of rapamycin (mTOR), and eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) in the uterine using real-time PCR and western blot, respectively. In comparison with the control group, fludrocortisone administration upregulated the expression of LIF, HB-EGF, Msx.1, miRNA Let-7a, ERK1/2, and mTOR in the epithelial endometrium. The PP242-treated group demonstrated a significant rise in the expression of MUC1, miRNA 223-3p and a remarkable decline in ERK1/2 and p-4E-BP1 levels in comparison with the control group. Combination therapy of (FCA+PP242) resulted in a remarkable rise in LIF, Msx-1, HB-EGF, ERK1/2, and mTOR levels, in comparison with the PP242 group. Furthermore, combination therapy of (FCA+PP242) downregulated the expression of MUC1 in comparison with the PP242-treated group. According to the results, fludrocortisone affected uterine receptivity possibly by means of modulating the expression of genes involved in the uterine receptivity and activation of the ERK1/2-mTOR pathway.

Bone corticalization requires local SOCS3 activity and is promoted by androgen action via interleukin-6

Long bone strength is determined by its outer shell (cortical bone), which forms by coalescence of thin trabeculae at the metaphysis (corticalization), but the factors that control this process are unknown. Here we show that SOCS3-dependent cytokine expression regulates bone corticalization. Young male and female Dmp1Cre.Socs3 ^f/f mice, in which SOCS3 has been ablated in osteocytes, have high trabecular bone volume and poorly defined metaphyseal cortices. After puberty, male mice recover, but female corticalization is still impaired, leading to a lasting defect in bone strength. The phenotype depends on sex-steroid hormones: dihydrotestosterone treatment of gonadectomized female Dmp1Cre.Socs3 ^f/f mice restores normal cortical morphology, whereas in males, estradiol treatment, or IL-6 deletion, recapitulates the female phenotype. This suggests that androgen action promotes metaphyseal corticalization, at least in part, via IL-6 signaling.The strength of long bones is determined by coalescence of trabeculae during corticalization. Here the authors show that this process is regulated by SOCS3 via a mechanism dependent on IL-6 and expression of sex hormones.

Dental Pulp Cells Isolated from Teeth with Superficial Caries Retain an Inflammatory Phenotype and Display an Enhanced Matrix Mineralization Potential

We have isolated dental pulp cells (DPCs) from three healthy (hDPCs) and three carious (cDPCs) donors and shown that compared to hDPCs cells isolated from superficial carious lesions show higher clonogenic potential; show an equivalent proportion of cells with putative stem cell surface markers; show enhanced matrix mineralization capability; have enhanced angiogenic marker expression and retain the inflammatory phenotype in vitro characteristic of superficial caries lesions in vivo. Our findings suggest that cDPCs may be used for further investigation of the cross talk between inflammatory, angiogenic and mineralization pathways in repair of carious pulp. In addition cells derived from carious pulps (almost always discarded) may have potential for future applications in mineralized tissue repair and regeneration.

Design of Tissue-engineered Nanoscaffold Through Self-assembly of Peptide Amphiphile

In order to mimic in vivo topography of the native tissue created by extracellular matrix (ECM) components, which make up all soft tissues, the surface features of each biomaterial should be considered as a nanodimensional structure. In this study, an artificial ECM was designed to mimic the nanostructured topography created by ECM components in native tissue. The proliferation and differentiation of mesenchymal stem cells (MSCs) was investigated in a three dimensional (3-D) network of nanofibers formed by the self-assembly of peptide amphiphile (PA) molecules. PA was synthesized by standard solid phase chemistry that ends with the alkylation of the NH2 terminus of the peptide. The sequence of arginine-glycine-aspartic acid (RGD) was included in peptide design as well. A 3-D network of nanofibers was formed by mixing MSC suspensions in a media with dilute aqueous solution of PA. The attachment, proliferation and osteogenic differentiation of MSCs were influenced by the self-assembled PA nanofibers as the cell scaffold and the values were significantly high compared with those in the static culture (2-D tissue culture plate).

High-resolution genome screen for bone mineral density in heterogeneous stock rat

We previously demonstrated that skeletal mass, structure, and biomechanical properties vary considerably in heterogeneous stock (HS) rat strains. In addition, we observed strong heritability for several of these skeletal phenotypes in the HS rat model, suggesting that it represents a unique genetic resource for dissecting the complex genetics underlying bone fragility. The purpose of this study was to identify and localize genes associated with bone mineral density in HS rats. We measured bone phenotypes from 1524 adult male and female HS rats between 17 and 20 weeks of age. Phenotypes included dual-energy X-ray absorptiometry (DXA) measurements for bone mineral content and areal bone mineral density (aBMD) for femur and lumbar spine (L3-L5), and volumetric BMD measurements by CT for the midshaft and distal femur, femur neck, and fifth lumbar vertebra (L5). A total of 70,000 polymorphic single-nucleotide polymorphisms (SNPs) distributed throughout the genome were selected from genotypes obtained from the Affymetrix rat custom SNPs array for the HS rat population. These SNPs spanned the HS rat genome with a mean linkage disequilibrium coefficient between neighboring SNPs of 0.95. Haplotypes were estimated across the entire genome for each rat using a multipoint haplotype reconstruction method, which calculates the probability of descent for each genotyped locus from each of the eight founder HS strains. The haplotypes were tested for association with each bone density phenotype via a mixed model with covariate adjustment. We identified quantitative trait loci (QTLs) for BMD phenotypes on chromosomes 2, 9, 10, and 13 meeting a conservative genomewide empiric significance threshold (false discovery rate [FDR] = 5%; p < 3 × 10(-6)). Importantly, most QTLs were localized to very small genomic regions (1-3 megabases [Mb]), allowing us to identify a narrow set of potential candidate genes including both novel genes and genes previously shown to have roles in skeletal development and homeostasis.

The primary function of gp130 signaling in osteoblasts is to maintain bone formation and strength, rather than promote osteoclast formation

Interleukin-6 (IL-6) family cytokines act via gp130 in the osteoblast lineage to stimulate the formation of osteoclasts (bone resorbing cells) and the activity of osteoblasts (bone forming cells), and to inhibit expression of the osteocyte protein, sclerostin. We report here that a profound reduction in trabecular bone mass occurs both when gp130 is deleted in the entire osteoblast lineage (Osx1Cre gp130 f/f) and when this deletion is restricted to osteocytes (DMP1Cre gp130 f/f). This was caused not by an alteration in osteoclastogenesis, but by a low level of bone formation specific to the trabecular compartment. In contrast, cortical diameter increased to maintain ultimate bone strength, despite a reduction in collagen type 1 production. We conclude that osteocytic gp130 signaling is required for normal trabecular bone mass and proper cortical bone composition.

The enigmatic cytokine oncostatin m and roles in disease

Oncostatin M is a secreted cytokine involved in homeostasis and in diseases involving chronic inflammation. It is a member of the gp130 family of cytokines that have pleiotropic functions in differentiation, cell proliferation, and hematopoetic, immunologic, and inflammatory networks. However, Oncostatin M also has activities novel to mediators of this cytokine family and others and may have fundamental roles in mechanisms of inflammation in pathology. Studies have explored Oncostatin M functions in cancer, bone metabolism, liver regeneration, and conditions with chronic inflammation including rheumatoid arthritis, lung and skin inflammatory disease, atherosclerosis, and cardiovascular disease. This paper will review Oncostatin M biology in a historical fashion and focus on its unique activities, in vitro and in vivo, that differentiate it from other cytokines and inspire further study or consideration in therapeutic approaches.

Fuzzy clustering analysis of osteosarcoma related genes

Osteosarcoma is the most common malignant bone-tumor with a peak manifestation during the second and third decade of life. In order to explore the influence of genetic factors on the mechanism of osteosarcoma by analyzing the inter relationship between osteosarcoma and its related genes, and then provide potential genetic references for the prevention, diagnosis and treatment of osteosarcoma, we collected osteosarcoma related gene sequences in Genebank of National Center for Biotechnology Information (NCBI) and local alignment analysis for a pair of sequences was carried out to identify the measurement association among related sequences. Then fuzzy clustering method was used for clustering analysis so as to contact the unknown genes through the consistent osteosarcoma related genes in one class. From the result of fuzzy clustering analysis, we could classify the osteosarcoma related genes into two groups and deduced that the genes clustered into one group had similar function. Based on this knowledge, we found more genes related to the pathogenesis of osteosarcoma and these genes could exert similar function as Runx2, a risk factor confirmed in osteosarcoma, this study may help better understand the genetic mechanism and provide new molecular markers and therapies for osteosarcoma.

Cold induced sweating syndrome with urinary system anomaly association

Mutation in the cytokine receptor-like factor 1 and the cardiotrophin-like cytokine (CRLF1 or CLCF1 genes) phenotypically presents as cold induced sweating syndrome (CISS), which is a rare autosomal recessive disorder. The syndrome is characterized by paradoxical sweating in cold weather, dysmorphic facial features, musculoskeletal deformities, difficulty in feeding, and unexplained recurrent episodes of high-grade fever. We are presenting the first case of CISS with urinary system anomaly, which might relate to CRLF1/CLCF1 complex role in the embryonal nephrogenesis.

Leukemia inhibitory factor: a paracrine mediator of bone metabolism

Leukemia inhibitory factor (LIF) is a soluble interleukin-6 family cytokine that regulates a number of physiologic functions, including normal skeletal remodeling. LIF signals through the cytokine co-receptor glycoprotein-130 in complex with its cytokine-specific receptor [LIF receptor (LIFR)] to activate signaling cascades in cells of the skeletal system, including stromal cells, chondrocytes, osteoblasts, osteocytes, adipocytes, and synovial fibroblasts. LIF action on skeletal cells is cell-type specific, and frequently dependent on the state of cell differentiation. This review describes the expression patterns of LIF and LIFR in bone, their regulation by physiological and inflammatory agents, as well as cell-specific influences of LIF on osteoblast, osteoclast, chondrocyte, and adipocyte differentiation. The actions of LIF in normal skeletal growth and maintenance, in pathological states (e.g. autocrine tumor cell signaling and growth in bone) and inflammatory conditions (e.g. arthritis) will be discussed, as well as the signaling pathways activated by LIF and their importance in bone formation and resorption.

The enhancement of osteogenesis through the use of dental pulp pluripotent stem cells in 3D

The potential for osteogenic differentiation of dental pulp mesenchymal stem cells (DPMSCs) in vitro and in vivo has been well documented in a variety of studies. Previously, we obtained a population of cells from human dental pulp called dental pulp pluripotent stem cells (DPPSCs) that could differentiate into mesodermal, ectodermal and endodermal progenies. We compared the osteogenic capacity of DPPSCs and DPMSCs that had been isolated from the same donors (N=5) and cultivated in the same osteogenic medium in 3D (three dimensions) Cell Carrier glass scaffolds. We also compared the architecture of bone-like tissue obtained from DPPSCs and human maxillary bone tissue. Differentiation was evaluated by scanning electron microscopy, whereas the expression of bone markers such as ALP, Osteocalcin, COLL1 and Osteonectin was investigated by quantitative real time polymerase chain reaction (qRT-PCR). We also used calcium quantification, Alizarin red staining and alkaline phosphatase (ALP) activity to compare the two cell types. New bone tissue formed by DPPSCs was in perfect continuity with the trabecular host bone structure, and the restored bone network demonstrated high interconnectivity. Significant differences between DPPSCs and DPMSCs were observed for the expression of bone markers, calcium deposition and ALP activity during osteogenic differentiation; these criteria were higher for DPPSCs than DPMSCs. Both DPPSCs and differentiated tissue showed normal chromosomal dosage after being cultured in vitro and analysed using short-chromosome genomic hybridisation (short-CGH). This study demonstrates the stability and potential for the use of DPPSCs in bone tissue engineering applications.

GP130 cytokines and bone remodelling in health and disease

Cytokines that bind to and signal through the gp130 co-receptor subunit include interleukin (IL)-6, IL-11, oncostatin M (OSM), leukemia inhibitory factor (LIF), cardiotrophin-1 (CT-1), and ciliary neutrophic factor (CNTF). Apart from contributing to inflammation, gp130 signalling cytokines also function in the maintenance of bone homeostasis. Expression of each of these cytokines and their ligand-specific receptors is observed in bone and joint cells, and bone-active hormones and inflammatory cytokines regulate their expression. gp130 signalling cytokines have been shown to regulate the differentiation and activity of osteoblasts, osteoclasts and chondrocytes. Furthermore, cytokine and receptor specific gene-knockout mouse models have identified distinct roles for each of these cytokines in regulating bone resorption, bone formation and bone growth. This review will discuss the current models of paracrine and endocrine actions of gp130-signalling cytokines in bone remodelling and growth, as well as their impact in pathologic bone remodelling evident in periodontal disease, rheumatoid arthritis, spondylarthropathies and osteoarthritis.

Ciliary neurotrophic factor inhibits bone formation and plays a sex-specific role in bone growth and remodeling

Ciliary neurotrophic factor (CNTF) receptor (CNTFR) expression has been described in osteoblast-like cells, suggesting a role for CNTF in bone metabolism. When bound to CNTF, neuropoietin (NP), or cardiotrophin-like-cytokine (CLC), CNTFR forms a signaling complex with gp130 and the leukemia inhibitory factor receptor, which both play critical roles in bone cell biology. This study aimed to determine the role of CNTFR-signaling cytokines in bone. Immunohistochemistry detected CNTF in osteoblasts, osteocytes, osteoclasts, and proliferating chondrocytes. CNTFR mRNA was detected in primary calvarial osteoblasts and was upregulated during osteoblast differentiation. Treatment of osteoblasts with CNTF or CLC, but not NP, significantly inhibited mineralization and osterix mRNA levels. Twelve-week-old male CNTF ( -/- ) mice demonstrated reduced femoral length, cortical thickness, and periosteal circumference; but femoral trabecular bone mineral density (Tb.BMD) and tibial trabecular bone volume (BV/TV) were not significantly different from wild-type, indicating a unique role for CNTF in bone growth in male mice. In contrast, female CNTF ( -/- ) femora were of normal width, but femoral Tb.BMD, tibial BV/TV, trabecular number, and trabecular thickness were all increased. Female CNTF ( -/- ) tibiae also demonstrated high osteoblast number and mineral apposition rate compared to wild-type littermates, and this was intrinsic to the osteoblast lineage. CNTF is expressed locally in bone and plays a unique role in female mice as an inhibitor of trabecular bone formation and in male mice as a stimulus of cortical growth.

Impaired cell cycle regulation of the osteoblast-related heterodimeric transcription factor Runx2-Cbfbeta in osteosarcoma cells

Bone formation and osteoblast differentiation require the functional expression of the Runx2/Cbfbeta heterodimeric transcription factor complex. Runx2 is also a suppressor of proliferation in osteoblasts by attenuating cell cycle progression in G(1). Runx2 levels are modulated during the cell cycle, which are maximal in G(1) and minimal beyond the G(1)/S phase transition (S, G(2), and M phases). It is not known whether Cbfbeta gene expression is cell cycle controlled in preosteoblasts nor how Runx2 or Cbfbeta are regulated during the cell cycle in bone cancer cells. We investigated Runx2 and Cbfbeta gene expression during cell cycle progression in MC3T3-E1 osteoblasts, as well as ROS17/2.8 and SaOS-2 osteosarcoma cells. Runx2 protein levels are reduced as expected in MC3T3-E1 cells arrested in late G(1) (by mimosine) or M phase (by nocodazole), but not in cell cycle arrested osteosarcoma cells. Cbfbeta protein levels are cell cycle independent in both osteoblasts and osteosarcoma cells. In synchronized MC3T3-E1 osteoblasts progressing from late G1 or mitosis, Runx2 levels but not Cbfbeta levels are cell cycle regulated. However, both factors are constitutively elevated throughout the cell cycle in osteosarcoma cells. Proteasome inhibition by MG132 stabilizes Runx2 protein levels in late G(1) and S in MC3T3-E1 cells, but not in ROS17/2.8 and SaOS-2 osteosarcoma cells. Thus, proteasomal degradation of Runx2 is deregulated in osteosarcoma cells. We propose that cell cycle control of Runx2 gene expression is impaired in osteosarcomas and that this deregulation may contribute to the pathogenesis of osteosarcoma.

gp130 signaling in bone cell biology: multiple roles revealed by analysis of genetically altered mice

The receptor subunit gp130 is utilized by a wide range of cytokines, many of which have critical functions in regulating the actions of osteoclasts and osteoblasts. In vitro studies have revealed remarkably consistent effects of many of these family members, specifically, actions on receptors in the osteoblast lineage that stimulate osteoblast differentiation and stimulate production of RANKL, thereby increasing the formation of osteoclasts. In contrast to this simple model of gp130 action on bone, deletion of cytokines or receptors that interact with gp130 reveal a range of bone phenotypes implicating critical roles for gp130 signaling in longitudinal bone growth, bone resorption and bone formation. In most cases, deletion of gp130, ligands or ligand-specific receptors interacting with gp130 causes a low level of bone formation; a high level of bone formation was only observed in gp130(Y757F/Y757F) mice, gp130 signaling mutants, where it is caused by a cell-lineage autonomous increase in osteoclast formation and an IL-6-dependent coupling pathway. On the other hand, the range of gene knockouts may cause either a reduction or an increase in osteoclast formation, and in many cases alterations in osteoclast size and ability to resorb bone. Since some knockouts are neonatal lethal, interpretation of ex vivo analyses and the contribution of each component to bone remodeling are not clearly defined, and there is still much work to be done before these questions can be resolved. Taken together these results indicate multiple roles for gp130 cytokines in controlling osteoblasts and osteoclast function, including paracrine roles to mediate signaling between these two cell types.

Mechanism of shortened bones in mucopolysaccharidosis VII

Mucopolysaccharidosis VII (MPS VII) is a lysosomal storage disease in which deficiency in beta-glucuronidase results in glycosaminoglycan (GAG) accumulation in and around cells, causing shortened long bones through mechanisms that remain largely unclear. We demonstrate here that MPS VII mice accumulate massive amounts of the GAG chondroitin-4-sulfate (C4S) in their growth plates, the cartilaginous region near the ends of long bones responsible for growth. MPS VII mice also have only 60% of the normal number of chondrocytes in the growth plate and 55% of normal chondrocyte proliferation at 3weeks of age. We hypothesized that this reduction in proliferation was due to C4S-mediated overactivation of fibroblast growth factor receptor 3 (FGFR3). However, MPS VII mice that were FGFR3-deficient still had shortened bones, suggesting that FGFR3 is not required for the bone defect. Further study revealed that MPS VII growth plates had reduced tyrosine phosphorylation of STAT3, a pro-proliferative transcription factor. This was accompanied by a decrease in expression of leukemia inhibitory factor (LIF) and other interleukin 6 family cytokines, and a reduction in phosphorylated tyrosine kinase 2 (TYK2), Janus kinase 1 (JAK1), and JAK2, known activators of STAT3 phosphorylation. Intriguingly, loss of function mutations in LIF and its receptor leads to shortened bones. This suggests that accumulation of C4S in the growth plate leads to reduced expression of LIF and reduced STAT3 tyrosine phosphorylation, which results in reduced chondrocyte proliferation and ultimately shortened bones.

Long term oncostatin M treatment induces an osteocyte-like differentiation on osteosarcoma and calvaria cells

Previous in vitro studies on primary osteoblastic and osteosarcoma cells (normal and transformed osteoblasts) have shown that oncostatin M (OSM), a member of the interleukin-6 family, possesses cytostatic and pro-apoptotic effects in association with complex and poorly understood activities on osteoblast differentiation. In this study, we use rat osteosarcoma cells transduced with lentiviral particles encoding OSM (lvOSM) to stably produce this cytokine. We show that after several weeks of culture, transduced OSRGA and ROS 17/2.8 cells are growth inhibited and sensitized to apoptosis induced by the kinase inhibitor Staurosporine (Sts). Moreover, this long term OSM treatment induces (i) a decrease in osteoblastic markers, (ii) morphological changes leading to an elongated and/or stellate shape and (iii) an increase in osteocytic markers (sclerostin and/or E11), suggesting an osteocyte-like differentiation. We also show that non transformed rat calvaria cells transduced with lvOSM differentiate into stellate shaped cells expressing sclerostin, E11, Phex and functional hemichannels. Together, these results indicate that osteosarcoma cells stably producing OSM do not develop resistance to this cytokine and thus could be a valuable new tool to study the anti-cancer effect of OSM in vivo. Moreover, OSM-over-expressing osteoblastic cells differentiate into osteocyte-like cells, the major cellular contingent in bone, providing new culture conditions for this cell type which is difficult to obtain in vitro.

Leukemia inhibitory factor secretion is a predictor and indicator of early progenitor status in adult bone marrow stromal cells

Bone marrow-derived stromal cells (BMSCs) are defined by their ability to self-renew and differentiate into at least three mesenchymal cell types (bone, adipose, and cartilage). The inability to isolate a reliably efficacious and homogeneous population of early progenitor cells has limited efforts to increase their therapeutic potential. In this study, we focused on identifying protein markers that may be employed to predict the efficacy of a cultured BMSC population. Markers of progenitor status were identified by comparing BMSCs at early and late passage, donor-matched skin fibroblasts, and commercially available dermal fibroblast cell lines. Differentiation potential was determined according to in vitro assays of osteogenesis, adipogenesis, and chondrogenesis. Early-passage BMSCs differentiated into all three lineages, whereas late-passage BMSCs and both fibroblast preparations did not. To identify novel markers of early progenitors, microarray transcript analysis between early-passage BMSCs and fibroblasts was performed. Messenger RNA encoding the cytokine leukemia inhibitory factor (LIF) was identified as differentially expressed. Enzyme-linked immunosorbent assay on conditioned media confirmed that LIF secretion was much higher from early progenitor BMSCs than donor-matched or commercial lines of fibroblasts and dropped with extensive expansion or induction of differentiation. In clonally expanded BMSCs, colonies that retained progenitor status expressed significantly higher levels of LIF than those that failed to differentiate. Our results indicate that LIF expression may represent a marker to quantify the differentiation potential of BMSCs and may be especially suited for the rapid, noninvasive quality control of clinical preparations.

Cardiotrophin-1 is an osteoclast-derived stimulus of bone formation required for normal bone remodeling

Cardiotrophin (CT-1) signals through gp130 and the LIF receptor (LIFR) and plays a major role in cardiac, neurological, and liver biology. We report here that CT-1 is also expressed within bone in osteoclasts and that CT-1 is capable of increasing osteoblast activity and mineralization both in vitro and in vivo. Furthermore, CT-1 stimulated CAAT/enhancer-binding protein-delta (C/EBP delta) expression and runt-related transcription factor 2 (runx2) activation. In neonate CT-1(-/-) mice, we detected low bone mass associated with reduced osteoblasts and many large osteoclasts, but increased cartilage remnants within the bone, suggesting impaired resorption. Cultured bone marrow (BM) from CT-1(-/-) mice generated many oversized osteoclasts and mineralized poorly compared with wildtype BM. As the CT-1(-/-) mice aged, the reduced osteoblast surface (ObS/BS) was no longer detected, but impaired bone resorption continued resulting in an osteopetrotic phenotype in adult bone. CT-1 may now be classed as an essential osteoclast-derived stimulus of both bone formation and resorption.

Leukemia inhibitory factor influences the fate choice of mesenchymal progenitor cells

Osteoblasts and adipocytes derive from a common mesenchymal precursor, and in at least some circumstances, differentiation along these two lineages is inversely related. For example, we have recently observed that concomitant with inhibition of osteoblast differentiation and bone nodule formation, leukemia inhibitory factor (LIF) induces genes regulating lipid metabolism in fetal rat calvaria (RC) cell cultures. In this study, we further investigated the adipogenic capacity of LIF-treated RC cells. Quantitative analyses revealed that LIF increased the adipocyte differentiation induced by the peroxisome proliferator-activated receptor gamma agonist BRL49653 (BRL) in RC cell populations. Gene expression profiling of individual RC cell colonies in untreated cells or cells treated with LIF, BRL, or combined LIF-BRL suggested that some adipocytes arose from bipotential or other primitive precursors, including osteoprogenitors, since many colonies co-expressed osteoblast and adipocyte differentiation markers, whereas some arose from other cell pools, most likely committed preadipocytes present in the population. These analyses further suggested that LIF and BRL do not act at the same stages of the mesenchymal hierarchy, but rather that LIF modifies differentiation of precursor cells, whereas BRL acts later to favor adipocyte differentiation. Taken together, our data suggest that LIF increased adipocyte differentiation at least in part by altering the fate of osteoblastic cells and their precursors.

Molecular genetic studies of gene identification for osteoporosis: a 2004 update

This review summarizes comprehensively the most important and representative molecular genetics studies of gene identification for osteoporosis published up to the end of December 2004. It is intended to constitute a sequential update of our previously published review covering the available data up to the end of 2002. Evidence from candidate gene association studies and genome-wide linkage studies in humans, as well as quantitative trait locus mapping animal models are reviewed separately. Studies of transgenic and knockout mice models relevant to osteoporosis are summarized. An important extension of this update is incorporation of functional genomic studies (including DNA microarrays and proteomics) on osteogenesis and osteoporosis, in light of the rapid advances and the promising prospects of the field. Comments are made on the most notable findings and representative studies for their potential influence and implications on our present understanding of genetics of osteoporosis. The format adopted by this review should be ideal for accommodating future new advances and studies.

Dexamethasone-functionalized gels induce osteogenic differentiation of encapsulated hMSCs

Synthetic hydrogels represent highly controlled environments for three-dimensional culture of human mesenchymal stem cells (hMSCs). Encapsulated hMSCs are presented with a "blank" environment, and this environment can be closely controlled in order to elicit an osteogenic response. In vitro, dexamethasone is an efficient and reliable factor that leads to the osteogenic differentiation of human mesenchymal stem cells (hMSCs). The aim of this work was to develop a dexamethasone-releasing poly(ethylene glycol) (PEG)-based hydrogel scaffold to deliver dexamethasone to encapsulated cells in a sustained manner. To accomplish this goal, dexamethasone was covalently linked to a photoreactive mono-acrylated PEG molecule through a degradable lactide bond, and this molecule was covalently incorporated into the PEG hydrogel during photopolymerization. Over time, hydrolysis of the ester bonds resulted in dexamethasone release from the gel. The biological activity of the released dexamethasone was verified in monolayer cell culture and in three-dimensional culture (i.e., in the gel) by the ability of hMSCs to express osteogenic genes, including alkaline phosphatase, osteopontin, and core binding factor alpha 1, as measured using real-time reverse transcription polymerase chain reaction (RT-PCR). These studies indicate that encapsulated hMSCs are capable of osteogenic differentiation in response to released dexamethasone.

The neuropeptide VIP potentiates IL-6 production induced by proinflammatory osteotropic cytokines in calvarial osteoblasts and the osteoblastic cell line MC3T3-E1

Skeletal turnover is orchestrated by a complex network of regulatory factors. Lately, regulation of bone metabolism through neuro-osteological interactions has been proposed. Here, we address the question whether IL-6 production can be affected by interactions between the neuropeptide VIP and proinflammatory, bone-resorbing cytokines. By using calvarial osteoblasts, we showed that IL-1beta increased IL-6 production time- and concentration-dependently, and that these effects were potentiated by VIP. Furthermore, IL-1beta stimulated IL-6 promoter activity in the osteoblastic cell line MC3T3-E1 stably transfected with a human IL-6 promoter/luciferase construct, and both VIP, and the related neuropeptide PACAP-38, increased the effect of IL-1beta in a synergistic manner. The IL-6 protein release from calvarial osteoblasts was also stimulated by the osteoclastogenic, proinflammatory cytokines IL-11, LIF, OSM, IL-17, TGF-beta, and TNF-alpha. All effects, except for that of TNF-alpha, were synergistically potentiated by VIP. These findings further support the role of neuropeptides, and the presence of neuro-immunological interactions, in bone metabolism.

GP130/OSMR is the only LIF/IL-6 family receptor complex to promote osteoblast differentiation of calvaria progenitors

Leukemia inhibitory factor (LIF) and its receptor (LIFR) are "twins" of Oncostatin M (OSM) and OSMR, respectively, likely having arisen through gene duplications. We compared their effects in a bone nodule-forming model of in vitro osteogenesis, rat calvaria (RC) cell cultures. Using a dominant-negative LIF mutant (hLIF-05), we showed that in RC cell cultures mouse OSM (mOSM) activates exclusively glycoprotein 130 (gp130)/OSMR. In treatments starting at early nodule formation stage, LIF, mOSM, IL-11, and IL-6 + sIL-6R inhibit bone nodule formation, that is, osteoprogenitor differentiation. Treatment with mOSM, and no other cytokine of the family, in early cultures (day 1-3 or 1-4) increases bone colony numbers. hLIF-05 also dose dependently stimulates bone nodule formation, confirming the inhibitory action of gp130/LIFR on osteogenesis. In pulse treatments at successive stages of bone nodule formation and maturation, LIF blocks osteocalcin (OCN) expression by differentiated osteoblasts, but has no effect on bone sialoprotein (BSP) expression. Mouse OSM inhibits OCN and BSP expression in preconfluent cultures with no or progressively reduced effects at later stages, reflecting the disruption of early nodules, possibly due to the strong apoptotic action of mOSM in RC cell cultures. In summary, LIFR and OSMR display differential effects on differentiation and phenotypic expression of osteogenic cells, most likely through different signal transduction pathways. In particular, gp130/OSMR is the only receptor complex of the family to stimulate osteoprogenitor differentiation in the RC cell culture model.

Estrogen regulation of growth hormone action

GH plays a pivotal role in regulating body growth and development, which is modulated by sex steroids. A close interplay between estrogen and GH leads to attainment of gender-specific body composition during puberty. The physiological basis of the interaction is not well understood. Most previous studies have focused on the effects of estrogen on GH secretion. There is also strong evidence that estrogen modulates GH action independent of secretion. Oral but not transdermal administration of estrogen impairs the metabolic action of GH in the liver, causing a fall in IGF-I production and fat oxidation. This results in a loss of lean tissue and a gain of body fat in postmenopausal women and an impairment of GH effect in hypopituitary women on GH replacement. The negative metabolic sequelae are potentially important because of the widespread use of oral estrogen and estrogen-related compounds. Estrogen affects GH action at the level of receptor expression and signaling. More recently, estrogen has been shown to inhibit Janus kinase/signal transducer and activator of transcription signaling by GH via the induction of suppressor of cytokine signaling-2, a protein inhibitor for cytokine signaling. This represents a novel paradigm of steroid regulation of cytokine receptors and is likely to have significance for a diverse range of cytokine function.

Regulation of Cytokine Receptor Signaling by Nuclear Hormone Receptors: A New Paradigm for Receptor Interaction

Cytokine receptors act through a complex signaling network involving Janus kinases (JAKs) and the signal transducers and activators of transcription (STATs) to regulate diverse biological processes controlling growth, development, homeostasis, and immune function. JAK/STAT signaling is terminated by negative regulators including the suppressors of cytokine signaling (SOCSs), protein tyrosine phosphatases, and protein inhibitors of activated STAT. There is a wealth of evidence that nuclear hormone receptors (NHRs) are important regulators of cytokine action. The molecular mechanisms underlying NHR regulation are incompletely understood, but may include control of cytokine production and modulation of the expression and signaling of cytokine receptors. NHRs regulate cytokine receptor signaling by affecting STAT expression and by acting as coregulators of STAT transcriptional action. More recently, NHRs have been shown to exert regulatory effects indirectly through SOCSs, which is a novel mechanism for receptor crosstalk. Better understanding of the regulatory interaction between these two classes of receptors potentially leads to new drug design and/or therapeutic strategies for treatment of cytokine-related diseases.

Runx2 control of organization, assembly and activity of the regulatory machinery for skeletal gene expression

We present an overview of Runx involvement in regulatory mechanisms that are requisite for fidelity of bone cell growth and differentiation, as well as for skeletal homeostasis and the structural and functional integrity of skeletal tissue. Runx-mediated control is addressed from the perspective of support for biological parameters of skeletal gene expression. We review recent findings that are consistent with an active role for Runx proteins as scaffolds for integration, organization and combinatorial assembly of nucleic acids and regulatory factors within the three-dimensional context of nuclear architecture.

Null leukemia inhibitory factor receptor (LIFR) mutations in Stuve-Wiedemann/Schwartz-Jampel type 2 syndrome

Stuve-Wiedemann syndrome (SWS) is a severe autosomal recessive condition characterized by bowing of the long bones, with cortical thickening, flared metaphyses with coarsened trabecular pattern, camptodactyly, respiratory distress, feeding difficulties, and hyperthermic episodes responsible for early lethality. Clinical overlap with Schwartz-Jampel type 2 syndrome (SJS2) has suggested that SWS and SJS2 could be allelic disorders. Through studying a series of 19 families with SWS/SJS2, we have mapped the disease gene to chromosome 5p13.1 at locus D5S418 (Zmax=10.66 at theta =0) and have identified null mutations in the leukemia inhibitory factor receptor (LIFR or gp190 chain) gene. A total of 14 distinct mutations were identified in the 19 families. An identical frameshift insertion (653_654insT) was identified in families from the United Arab Emirates, suggesting a founder effect in that region. It is interesting that 12/14 mutations predicted premature termination of translation. Functional studies indicated that these mutations alter the stability of LIFR messenger RNA transcripts, resulting in the absence of the LIFR protein and in the impairment of the JAK/STAT3 signaling pathway in patient cells. We conclude, therefore, that SWS and SJS2 represent a single clinically and genetically homogeneous condition due to null mutations in the LIFR gene on chromosome 5p13.

Prostaglandin E2 receptors in abdominal aortic aneurysm and human aortic smooth muscle cells

BACKGROUND

Prostaglandin (PG) E(2) (PGE(2)) appears to have a role in stimulating production of interleukin-6 (IL-6) and apoptosis of smooth muscle cells in diseased aortic tissue. These actions are mediated by cellular receptors for PGE(2) EP receptors.

OBJECTIVE

This study was undertaken to identify EP receptors associated with production of IL-6 by aortic explants.

METHODS

Biopsy specimens of abdominal aortic aneurysm were used for explant culture and preparation of messenger RNA. The presence of EP1, EP2, EP3, and EP4 receptors in tissue and cells was investigated with reverse-transcriptase polymerase chain reaction. IL-6 and cyclic adenosine monophosphate were measured with an enzyme-linked immunosorbent assay.

RESULTS

PGE(2) or 11-deoxy-PGE(1) (EP 2/3/4 agonist) reversed partially the indomethacin suppression of IL-6 secretion from explant cultures, whereas butaprost (EP2 receptor agonist) and sulprostone (EP 1/3 receptor agonist) had no effect. Aortic biopsy specimens expressed EP2, EP3-III, and EP4 receptors. Aortic smooth muscle cells expressed EP2 receptor and four variants of EP3 receptor, ie, EP3-Ib, EP3-II, EP3-III, and EP3-IV, but PGE(2) did not stimulate secretion of IL-6. In contrast, PGE(2) or 11-deoxy-PGE(1) stimulated secretion of IL-6 from aortic macrophages.

CONCLUSIONS

In aortic explants, PGE(2) stimulates IL-6 secretion by activation of EP4 receptors, present in macrophages.

Adult mesenchymal stem cells and cell-based tissue engineering

The identification of multipotential mesenchymal stem cells (MSCs) derived from adult human tissues, including bone marrow stroma and a number of connective tissues, has provided exciting prospects for cell-based tissue engineering and regeneration. This review focuses on the biology of MSCs, including their differentiation potentials in vitro and in vivo, and the application of MSCs in tissue engineering. Our current understanding of MSCs lags behind that of other stem cell types, such as hematopoietic stem cells. Future research should aim to define the cellular and molecular fingerprints of MSCs and elucidate their endogenous role(s) in normal and abnormal tissue functions.