Nuclear Factor-κB p65 Facilitates Longitudinal Bone Growth by Inducing Growth Plate Chondrocyte Proliferation and Differentiation and by Preventing Apoptosis

IĸB Protein BCL3 as a Controller of Osteogenesis and Bone Health

OBJECTIVE

IĸB protein B cell lymphoma 3-encoded protein (BCL3) is a regulator of the NF-κB family of transcription factors. NF-κB signaling fundamentally influences the fate of bone-forming osteoblasts and bone-resorbing osteoclasts, but the role of BCL3 in bone biology has not been investigated. The objective of this study was to evaluate BCL3 in skeletal development, maintenance, and osteoarthritic pathology.

METHODS

To assess the contribution of BCL3 to skeletal homeostasis, neonatal mice (n = 6-14) lacking BCL3 (Bcl3-/- ) and wild-type (WT) controls were characterized for bone phenotype and density. To reveal the contribution to bone phenotype by the osteoblast compartment in Bcl3-/- mice, transcriptomic analysis of early osteogenic differentiation and cellular function (n = 3-7) were assessed. Osteoclast differentiation and function in Bcl3-/- mice (n = 3-5) was assessed. Adult 20-week Bcl3-/- and WT mice bone phenotype, strength, and turnover were assessed. A destabilization of the medial meniscus model of osteoarthritic osteophytogenesis was used to understand adult bone formation in Bcl3-/- mice (n = 11-13).

RESULTS

Evaluation of Bcl3-/- mice revealed congenitally increased bone density, long bone dwarfism, increased bone biomechanical strength, and altered bone turnover. Molecular and cellular characterization of mesenchymal precursors showed that Bcl3-/- cells displayed an accelerated osteogenic transcriptional profile that led to enhanced differentiation into osteoblasts with increased functional activity, which could be reversed with a mimetic peptide. In a model of osteoarthritis-induced osteophytogenesis, Bcl3-/- mice exhibited decreased pathological osteophyte formation (P < 0.05).

CONCLUSION

Cumulatively, these findings demonstrate that BCL3 controls developmental mineralization to enable appropriate bone formation, whereas in a pathological setting, it contributes to skeletal pathology.

A synthetic mechanogenetic gene circuit for autonomous drug delivery in engineered tissues

Mechanobiologic signals regulate cellular responses under physiologic and pathologic conditions. Using synthetic biology and tissue engineering, we developed a mechanically responsive bioartificial tissue that responds to mechanical loading to produce a preprogrammed therapeutic biologic drug. By deconstructing the signaling networks induced by activation of the mechanically sensitive ion channel transient receptor potential vanilloid 4 (TRPV4), we created synthetic TRPV4-responsive genetic circuits in chondrocytes. We engineered these cells into living tissues that respond to mechanical loading by producing the anti-inflammatory biologic drug interleukin-1 receptor antagonist. Chondrocyte TRPV4 is activated by osmotic loading and not by direct cellular deformation, suggesting that tissue loading is transduced into an osmotic signal that activates TRPV4. Either osmotic or mechanical loading of tissues transduced with TRPV4-responsive circuits protected constructs from inflammatory degradation by interleukin-1α. This synthetic mechanobiology approach was used to develop a mechanogenetic system to enable long-term, autonomously regulated drug delivery driven by physiologically relevant loading.

Innovative Three-Dimensional Microscopic Analysis of Uremic Growth Plate Discloses Alterations in the Process of Chondrocyte Hypertrophy: Effects of Growth Hormone Treatment

Chronic kidney disease (CKD) alters the morphology and function of the growth plate (GP) of long bones by disturbing chondrocyte maturation. GP chondrocytes were analyzed in growth-retarded young rats with CKD induced by adenine intake (AD), control rats fed ad libitum (C) or pair-fed with the AD group (PF), and CKD rats treated with growth hormone (ADGH). In order to study the alterations in the process of GP maturation, we applied a procedure recently described by our group to obtain high-quality three-dimensional images of whole chondrocytes that can be used to analyze quantitative parameters like cytoplasm density, cell volume, and shape. The final chondrocyte volume was found to be decreased in AD rats, but GH treatment was able to normalize it. The pattern of variation in the cell cytoplasm density suggests that uremia could be causing a delay to the beginning of the chondrocyte hypertrophy process. Growth hormone treatment appears to be able to compensate for this disturbance by triggering an early chondrocyte enlargement that may be mediated by Nkcc1 action, an important membrane cotransporter in the GP chondrocyte enlargement.

The effect of bone inhibitors on periosteum-guided cartilage regeneration

The regeneration capacity of knee cartilage can be enhanced by applying periosteal grafts, but this effect varies depending on the different sources of the periosteal grafts applied for cartilage formation. Tibia periosteum can be used to enhance cartilage repair. However, long-term analysis has not been conducted. The endochondral ossification capacity of tibia periosteum during cartilage repair also needs to be investigated. In this study, both vascularized and non-vascularized tibia periosteum grafts were studied to understand the relationship between tissue perfusion of the periosteum graft and the effects on cartilage regeneration and bone formation. Furthermore, anti-ossification reagents were added to evaluate the efficacy of the prevention of bone formation along with cartilage regeneration. A critical-size cartilage defect (4 × 4 mm) was created and was covered with an autologous tibia vascularized periosteal flap or with a non-vascularized tibia periosteum patch on the knee in the rabbit model. A portion of the vascularized periosteum group was also treated with the anti-osteogenic reagents Fulvestrant and IL1β to inhibit unwanted bone formation. Our results indicated that the vascularized periosteum significantly enhanced cartilage regeneration in the cartilage defect region in long-term treatment compared to the non-vascularized group. Furthermore, the addition of anti-osteogenic reagents to the vascularized periosteum group suppressed bone formation but also reduced the cartilage regeneration rate. Our study using vascularized autologous tissue to repair cartilage defects of the knee may lead to the modification of current treatment in regard to osteoarthritis knee repair.

The Transcription Factor-microRNA Regulatory Network during hESC-chondrogenesis

Human embryonic stem cells (ESCs) offer a promising therapeutic approach for osteoarthritis (OA). The unlimited source of cells capable of differentiating to chondrocytes has potential for repairing damaged cartilage or to generate disease models via gene editing. However their use is limited by the efficiency of chondrogenic differentiation. An improved understanding of the transcriptional and post-transcriptional regulation of chondrogenesis will enable us to improve hESC chondrogenic differentiation protocols. Small RNA-seq and whole transcriptome sequencing was performed on distinct stages of hESC-directed chondrogenesis. This revealed significant changes in the expression of several microRNAs including upregulation of known cartilage associated microRNAs and those transcribed from the Hox complexes, and the downregulation of pluripotency associated microRNAs. Integration of miRomes and transcriptomes generated during hESC-directed chondrogenesis identified key functionally related clusters of co-expressed microRNAs and protein coding genes, associated with pluripotency, primitive streak, limb development and extracellular matrix. Analysis identified regulators of hESC-directed chondrogenesis such as miR-29c-3p with 10 of its established targets identified as co-regulated 'ECM organisation' genes and miR-22-3p which is highly co-expressed with ECM genes and may regulate these genes indirectly by targeting the chondrogenic regulators SP1 and HDAC4. We identified several upregulated transcription factors including HOXA9/A10/D13 involved in limb patterning and RELA, JUN and NFAT5, which have targets enriched with ECM associated genes. We have developed an unbiased approach for integrating transcriptome and miRome using protein-protein interactions, transcription factor regulation and miRNA target interactions and identified key regulatory networks prominent in hESC chondrogenesis.

Nerve growth factor promotes ASIC1a expression via the NF-κB pathway and enhances acid-induced chondrocyte apoptosis

Nerve growth factor (NGF) is a neurotrophic factor that is thought to have a broad role in the nervous system and tumors, and has recently been described as a mediator of inflammation. It is not clear whether or not NGF participates in apoptosis of articular chondrocytes. In this study, we determined if NGF affects ASIC1a expression and NF-κB P65 activation in rat chondrocytes, and measured the effectiveness of NGF on apoptotic protein expression in acid-induced chondrocytes. NGF was shown to up-regulate the level of ASIC1a in a dose- and time-dependent fashion. Simultaneously, NGF activated NF-κB P65 in chondrocytes. Additionally, the elevated ASIC1a expression induced by NGF was eliminated by the NF-κB inhibitor (PDTC) in chondrocytes. Moreover, NGF reduced cell viability and induced LDH release under the premise of acid-induced articular chondrocytes. Furthermore, NGF could enhance cleaved-caspase 9 and cleaved-PARP expression in acid-pretreated chondrocytes, and which could be inhibited by using psalmotoxin 1(PcTX1) or PDTC. Together, these results indicated that NGF may up-regulate ASIC1a expression through the NF-κB signaling pathway, and further promote acid-induced apoptosis of chondrocytes.

Radial Extracorporeal Shock Wave Treatment Promotes Bone Growth and Chondrogenesis in Cultured Fetal Rat Metatarsal Bones

BACKGROUND

Substantial evidence exists to show the positive effects of radialextracorporeal shock wave therapy (ESWT) on bone formation. However, it is unknown whether rESWT can act locally at the growth plate level to stimulate linear bone growth. One way to achieve this is to stimulate chondrogenesis in the growth plate without depending on circulating systemic growth factors. We wished to see whether rESWT would stimulate metatarsal rat growth plates in the absence of vascularity and associated systemic growth factors.

QUESTIONS/PURPOSES

To study the direct effects of rESWT on growth plate chondrogenesis, we asked: (1) Does rESWT stimulate longitudinal bone growth of ex vivo cultured bones? (2) Does rESWT cause any morphological changes in the growth plate? (3) Does rESWT locally activate proteins specific to growth plate chondrogenesis?

METHODS

Metatarsal bones from rat fetuses were untreated (controls: n = 15) or exposed to a single application of rESWT at a low dose (500 impulses, 5 Hz, 90 mJ; n = 15), mid-dose (500 impulses, 5 Hz, 120 mJ; n = 14) or high dose (500 impulses, 10 Hz, 180 mJ; n = 34) and cultured for 14 days. Bone lengths were measured on Days 0, 4, 7, and 14. After 14 days of culturing, growth plate morphology was assessed with a histomorphometric analysis in which hypertrophic cell size (> 7 µm) and hypertrophic zone height were measured (n = 6 bones each). Immunostaining for specific regulatory proteins involved in chondrogenesis and corresponding staining were quantitated digitally by a single observer using the automated threshold method in ImageJ software (n = 6 bones per group). A p value < 0.05 indicated a significant difference.

RESULTS

The bone length in the high-dose rESWT group was increased compared with that in untreated controls (4.46 mm ± 0.75 mm; 95% confidence interval, 3.28-3.71 and control: 3.50 mm ± 0.38 mm; 95% CI, 4.19-4.72; p = 0.01). Mechanistic studies of the growth plate's cartilage revealed that high-dose rESWT increased the number of proliferative chondrocytes compared with untreated control bones (1363 ± 393 immunopositive cells per bone and 500 ± 413 immunopositive cells per bone, respectively; p = 0.04) and increased the diameter of hypertrophic chondrocytes (18 ± 3 µm and 13 ± 3 µm, respectively; p < 0.001). This was accompanied by activation of insulin-like growth factor-1 (1015 ± 322 immunopositive cells per bone and 270 ± 121 immunopositive cells per bone, respectively; p = 0.043) and nuclear factor-kappa beta signaling (1029 ± 262 immunopositive cells per bone and 350 ± 60 immunopositive cells per bone, respectively; p = 0.01) and increased levels of the anti-apoptotic proteins B-cell lymphoma 2 (718 ± 86 immunopositive cells per bone and 35 ± 11 immunopositive cells per bone, respectively; p < 0.001) and B-cell lymphoma-extra-large (107 ± 7 immunopositive cells per bone and 34 ± 6 immunopositive cells per bone, respectively; p < 0.001).

CONCLUSION

In a model of cultured fetal rat metatarsals, rESWT increased longitudinal bone growth by locally inducing chondrogenesis. To verify whether rESWT can also stimulate bone growth in the presence of systemic circulatory factors, further studies are needed.

CLINICAL RELEVANCE

This preclinical proof-of-concept study shows that high-dose rESWT can stimulate longitudinal bone growth and growth plate chondrogenesis in cultured fetal rat metatarsal bones. A confirmatory in vivo study in skeletally immature animals must be performed before any clinical studies.

RelA promotes proliferation but inhibits osteogenic and chondrogenic differentiation of mesenchymal stem cells

NF-κB is known to be implicated in skeletal development and related diseases. Previous studies have shown that RelA, a key subunit of NF-κB, is involved in osteoblast and chondrocyte survival and differentiation. Yet, the physiological roles of RelA in mesenchymal stem cells (MSCs), which give rise to both chondrocytes and osteoblasts, are still poorly understood. Here, we generated Prrx1-Cre;RelA^f/f mice to delete RelA in Prrx1⁺ bone marrow MSCs and found that RelA deletion led to decreased MSC proliferation and altered differentiation, with increased osteogenic and chondrogenic differentiation but decreased adipogenic differentiation. Bone size and mass were not significantly changed in the mutant mice, although they developed moderate osteoarthritis-like phenotypes. Thus, our studies reveal important but discordant functions of RelA in MSC proliferation and differentiation, and provide an explanation why MSC-specific RelA knockout mice only develop minor skeletal phenotypes.

1q21.1 deletion and a rare functional polymorphism in siblings with thrombocytopenia-absent radius-like phenotypes

Thrombocytopenia-absent radii (TAR) syndrome, characterized by neonatal thrombocytopenia and bilateral radial aplasia with thumbs present, is typically caused by the inheritance of a 1q21.1 deletion and a single-nucelotide polymorphism in RBM8A on the nondeleted allele. We evaluated two siblings with TAR-like dysmorphology but lacking thrombocytopenia in infancy. Family NCI-107 participated in an IRB-approved cohort study and underwent comprehensive clinical and genomic evaluations, including aCGH, whole-exome, whole-genome, and targeted sequencing. Gene expression assays and electromobility shift assays (EMSAs) were performed to evaluate the variant of interest. The previously identified TAR-associated 1q21.1 deletion was present in the affected siblings and one healthy parent. Multiple sequencing approaches did not identify previously described TAR-associated SNPs or mutations in relevant genes. We discovered rs61746197 A > G heterozygosity in the parent without the deletion and apparent hemizygosity in both siblings. rs61746197 A > G overlaps a RelA–p65 binding motif, and EMSAs indicate the A allele has higher transcription factor binding efficiency than the G allele. Stimulation of K562 cells to induce megakaryocyte differentiation abrogated the shift of both reference and alternative probes. The 1q21.1 TAR-associated deletion in combination with the G variant of rs61746197 on the nondeleted allele is associated with a TAR-like phenotype. rs61746197 G could be a functional enhancer/repressor element, but more studies are required to identify the specific factor(s) responsible. Overall, our findings suggest a role of rs61746197 A > G and human disease in the setting of a 1q21.1 deletion on the other chromosome.

NF-κB Signaling Regulates Physiological and Pathological Chondrogenesis

The nuclear factor-κB (NF-κB) is a transcription factor that regulates the expression of genes that control cell proliferation and apoptosis, as well as genes that respond to inflammation and immune responses. There are two means of NF-κB activation: the classical pathway, which involves the degradation of the inhibitor of κBα (IκBα), and the alternative pathway, which involves the NF-κB-inducing kinase (NIK, also known as MAP3K14). The mouse growth plate consists of the resting zone, proliferative zone, prehypertrophic zone, and hypertrophic zone. The p65 (RelA), which plays a central role in the classical pathway, is expressed throughout the cartilage layer, from the resting zone to the hypertrophic zone. Inhibiting the classical NF-κB signaling pathway blocks growth hormone (GH) or insulin-like growth factor (IGF-1) signaling, suppresses cell proliferation, and suppresses bone morphogenetic protein 2 (BMP2) expression, thereby promoting apoptosis. Since the production of autoantibodies and inflammatory cytokines, such as tumor necrosis factor-α (TNFα), interleukin (IL)-1β, IL-6, and IL-17, are regulated by the classical pathways and are increased in rheumatoid arthritis (RA), NF-κB inhibitors are used to suppress inflammation and joint destruction in RA models. In osteoarthritis (OA) models, the strength of NF-κB-activation is found to regulate the facilitation or suppression of OA. On the other hand, RelB is involved in the alternative pathway, and is expressed in the periarticular zone during the embryonic period of development. The alternative pathway is involved in the generation of chondrocytes in the proliferative zone during physiological conditions, and in the development of RA and OA during pathological conditions. Thus, NF-κB is an important molecule that controls normal development and the pathological destruction of cartilage.

Constitutive activation of the alternative NF-κB pathway disturbs endochondral ossification

Endochondral ossification is important for skeletal development. Recent findings indicate that the p65 (RelA) subunit, a main subunit of the classical nuclear factor-κB (NF-κB) pathway, plays essential roles in chondrocyte differentiation. Although several groups have reported that the alternative NF-κB pathway also regulates bone homeostasis, the role of the alternative NF-κB pathway in chondrocyte development is still unclear. Here, we analyzed the in vivo function of the alternative pathway on endochondral ossification using p100-deficient (p100^-/-) mice, which carry a homozygous deletion of the COOH-terminal ankyrin repeats of p100 but still express functional p52 protein. The alternative pathway was activated during the periarticular stage in wild-type mice. p100^-/- mice exhibited dwarfism, and histological analysis of the growth plate revealed abnormal arrangement of chondrocyte columns and a narrowed hypertrophic zone. Consistent with these observations, the expression of hypertrophic chondrocyte markers, type X collagen (ColX) or matrix metalloproteinase 13, but not early chondrogenic markers, such as Col II or aggrecan, was suppressed in p100^-/- mice. An in vivo BrdU tracing assay clearly demonstrated less proliferative activity in chondrocytes in p100^-/- mice. These defects were partly rescued when the RelB gene was deleted in p100^-/- mice. Taken together, the alternative NF-κB pathway may regulate chondrocyte proliferation and differentiation to maintain endochondral ossification.

Redox control of chondrocyte differentiation and chondrogenesis

Chondrogenesis involves the recruitment and migration of mesenchymal cells, mesenchymal condensation, and chondrocyte differentiation and hypertrophy. Multiple factors precisely regulate chondrogenesis. Recent studies have demonstrated that the redox status of chondrocytes plays an essential role in the regulation of chondrocyte differentiation and chondrogenesis. Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are important factors that change the intracellular redox status. Physiological levels of ROS/RNS act as intracellular signals in chondrocytes, and oxidative stress impairs the metabolism of chondrocytes. Under physiological conditions, the balance between ROS/RNS production and elimination ensures that redox-sensitive signalling proteins function correctly. The redox homeostasis of chondrocytes ensures that they respond appropriately to endogenous and exogenous stimuli. This review focuses on the redox regulation of key signalling pathways and transcription factors that control chondrogenesis and chondrocyte differentiation. Additionally, the mechanism by which ROS/RNS regulate signalling proteins and transcription factors in chondrocytes is also reviewed.

Differential Effects of the Antioxidants N-Acetylcysteine and Pyrrolidine Dithiocarbamate on Mesenchymal Stem Cell Chondrogenesis

Introduction

Mesenchymal stem cell (MSC) chondrogenesis is associated with increases in intracellular reactive oxygen species (ROS), which may result in oxidative stress that is detrimental to cartilage regeneration. This study evaluated the ability of the antioxidants N-acetylcysteine (NAC) or pyrrolidine dithiocarbamate (PDTC) to reduce intracellular ROS, and their effect on MSC chondrogenesis and maturation of cartilage-like extracellular matrix.

Methods

Equine bone marrow MSCs were cultured in serum-supplemented chondrogenic medium with or without NAC or PDTC. ROS was quantified in monolayer after 8 and 72 h of culture. MSCs were seeded into agarose, cultured for 15 days, and analyzed for viable cell density, glycosaminoglycan (GAG) and hydroxyproline accumulation, and collagen gene expression. PDTC cultures were evaluated for oxidative damage by protein carbonylation, and mechanical properties via compressive testing.

Results

NAC significantly lowered levels of ROS after 8 but not 72 h, and suppressed GAG accumulation (70%). In secondary experiments using serum-free medium, NAC significantly increased levels of ROS at 72 h, and lowered cell viability and extracellular matrix accumulation. PDTC significantly reduced levels of ROS (~ 30%) and protein carbonylation (27%), and enhanced GAG accumulation (20%). However, the compressive modulus for PDTC-treated samples was significantly lower (40%) than controls. Gene expression was largely unaffected by the antioxidants.

Conclusions

NAC demonstrated a limited ability to reduce intracellular ROS in chondrogenic culture, and generally suppressed accumulation of extracellular matrix. Conversely, PDTC was an effective antioxidant that enhanced GAG accumulation, although the concomitant reduction in compressive properties is a significant limitation for cartilage repair.

Effect of Hemiepiphysiodesis on the Growth Plate: The Histopathological Changes and Mechanism Exploration of Recurrence in Mini Pig Model

PURPOSE

Hemiepiphysiodesis has been widely used to correct angular deformity of long bone in immature patients. However, there is a limited knowledge about the biomechanical effect of this technique on the histopathological changes of the growth plate and the mechanism of recurrence of malformation after implant removal. We aimed to evaluate the biomechanical effect of hemiepiphysiodesis on the histopathological changes of the growth plate and the mechanism of recurrence of malformation after implant removal in Bama miniature pigs, and to explore the role of asymmetric stress during this procedure.

METHODS

Eight 3-month-old male Bama miniature pigs sustained surgeries on the bilateral medial hind leg proximal tibia as the intervention group (n=16), and four pigs sustained bilateral sham surgeries as the control (n=8). In the 18th week after surgeries, hardware was removed in the unilateral leg of each animal in the intervention group. In the 24th week of the study, all animals were euthanized. A total of 24 samples were obtained and stained with H&E, TUNEL, and immunohistochemistry. Sixteen samples in the intervention group were divided into two subgroups. The tibias without an implant were included in the implant removal group (IR group), while the tibias with an implant were included in the implant persist group (IP group). The proximal tibia specimens were divided into 3 equidistant parts from medial to lateral, named as area A, area B, and area C, respectively. The change of thickness of growth plates, chondral apoptosis index, and the expression of Caspase-3, Caspase-9, CHOP, and P65 were compared.

RESULTS

H&E staining showed the thickness of growth plate to be varied in different areas. In the IP group, the thickness of growth plate in areas A and B was statistically significantly thinner than that in area C (p<0.05). In the IR group, the thickness of growth plate in areas A and B was statistically significantly thicker than that in area C (p<0.05). TUNEL staining showed that the apoptosis rate increased significantly after hemiepiphysiodesis and declined after implant removal (p<0.05). Immunohistochemical staining suggested that the expression of Caspase-3, Caspase-9, P65, and CHOP protein was upregulated in the experimental group and downregulated after implant removal.

CONCLUSION

The thickness parameter of the growth plate changes with asymmetric pressure. When the pressure is relieved, the recurrence of malformation is related to the thickening of the growth plate.

Effect of Nutrition on Statural Growth

In children, proper growth and development are often regarded as a surrogate marker for good health. A complex system controls the initiation, rate, and cessation of growth, and thus gives a wonderful example of the interactions between genetics, epigenetics, and environmental factors (especially stress and nutrition). Malnutrition is considered a leading cause of growth attenuation in children. This review summarizes our current knowledge regarding the mechanisms linking nutrition and skeletal growth, including systemic factors, such as insulin, growth hormone, insulin-like growth factor-1, fibroblast growth factor-21, etc., and local mechanisms, including mTOR, miRNAs, and epigenetics. Studying the molecular mechanisms regulating skeletal growth may lead to the establishment of better nutritional and therapeutic regimens for more effective linear growth in children with malnutrition and growth abnormalities. 
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Runx2 mediated Induction of Novel Targets ST2 and Runx3 Leads to Cooperative Regulation of Hypertrophic Differentiation in ATDC5 Chondrocytes

Knowledge concerning expression and function of Suppression of Tumorigenicity 2 (ST2) in chondrocytes is at present, limited. Analysis of murine growth plates and ATDC5 chondrocytes indicated peak expression of the ST2 transmembrane receptor (ST2L) and soluble (sST2) isoforms during the hypertrophic differentiation concomitant with the expression of the hypertrophic markers Collagen X (Col X), Runx2 and MMP-13. Gain- and loss-of-function experiments in ATDC5 and primary human growth plate chondrocytes (PHCs), confirmed regulation of ST2 by the key transcription factor Runx2, indicating ST2 to be a novel Runx2 target. ST2 knock-out mice (ST2−/−) exhibited noticeable hypertrophic zone (HZ) reduction in murine growth plates, accompanied by lower expression of Col X and Osteocalcin (OSC) compared to wild-type (WT) mice. Likewise, ST2 knockdown resulted in decreased Col X expression and downregulation of OSC and Vascular Endothelial Growth Factor (VEGF) in ATDC5 cells. The ST2 suppression was also associated with upregulation of the proliferative stage markers Sox9 and Collagen II (Col II), indicating ST2 to be a new regulator of ATDC5 chondrocyte differentiation. Runx3 was, furthermore, identified as a novel Runx2 target in chondrocytes. This study suggests that Runx2 mediates ST2 and Runx3 induction to cooperatively regulate hypertrophic differentiation of ATDC5 chondrocytes.

Cancer growth regulation by 4-hydroxynonenal

While reactive oxygen species (ROS) gain their carcinogenic effects by DNA mutations, if generated in the vicinity of genome, lipid peroxidation products, notably 4-hydroxynonenal (HNE), have much more complex modes of activities. Namely, while ROS are short living and have short efficiency distance range (in nm or µm) HNE has strong binding affinity for proteins, thus forming relatively stable adducts. Hence, HNE can diffuse from the site or origin changing structure and function of respective proteins. Consequently HNE can influence proliferation, differentiation and apoptosis of cancer cells on one hand, while on the other it can affect genome functionality, too. Although HNE is considered to be important factor of carcinogenesis due to its ability to covalently bind to DNA, it might also be cytotoxic for cancer cells, as well as it can modulate their growth. In addition to direct cytotoxicity, HNE is also involved in activity mechanisms by which several cytostatic drugs and radiotherapy exhibit their anticancer effects. Complementary to that, the metabolic pathway for HNE detoxification through RLIP76, which is enhanced in cancer, may be a target for anti-cancer treatments. In addition, some cancer cells can undergo apoptosis or necrosis, if exposed to supraphysiological HNE levels in the cancer microenvironment, especially if challenged additionally by pro-oxidative cytostatics and/or inflammation. These findings could explain previously observed disappearance of HNE from invading cancer cells, which is associated with the increase of HNE in non-malignant cells close to invading cancer utilizing cardiolipin as the source of cancer-inhibiting HNE.

Inflammatory Diseases and Growth: Effects on the GH-IGF Axis and on Growth Plate

This review briefly describes the most common chronic inflammatory diseases in childhood, such as cystic fibrosis (CF), inflammatory bowel diseases (IBDs), juvenile idiopathic arthritis (JIA), and intrauterine growth restriction (IUGR) that can be considered, as such, for the changes reported in the placenta and cord blood of these subjects. Changes in growth hormone (GH) secretion, GH resistance, and changes in the insulin-like growth factor (IGF) system are described mainly in relationship with the increase in nuclear factor-κB (NF-κB) and pro-inflammatory cytokines. Changes in the growth plate are also reported as well as a potential role for microRNAs (miRNAs) and thus epigenetic changes in chronic inflammation. Many mechanisms leading to growth failure are currently known; however, it is clear that further research in the field is still warranted.

Indomethacin induces differential effects on in vitro endochondral ossification depending on the chondrocyte's differentiation stage

Heterotopic ossification (HO) is the abnormal formation of bone in soft tissues and is a frequent complication of hip replacement surgery. Heterotopic ossifications are described to develop via endochondral ossification and standard treatment is administration of indomethacin. It is currently unknown how indomethacin influences heterotopic ossification on a molecular level; therefore, we aimed to determine whether indomethacin might influence heterotopic ossification via impairing the chondrogenic phase of endochondral ossification. Progenitor cell models differentiating in the chondrogenic lineage (ATDC5, primary human bone marrow stem cells and ex vivo periosteal agarose cultures) were treated with increasing concentrations of indomethacin and a decrease in gene- and protein expression of chondrogenic and hypertrophic markers (measured by RT-qPCR and immunoblotting) as well as decreased glycosamino-glycan content (by alcian blue histochemistry) was observed. Even when hypertrophic differentiation was provoked, the addition of indomethacin resulted in decreased hypertrophic marker expression. Interestingly, when mature chondrocytes were treated with indomethacin, a clear increase in collagen type 2 expression was observed. Similarly, when ATDC5 cells and bone marrow stem cells were pre-differentiated to obtain a chondrocyte phenotype and indomethacin was added from this time point onward, low concentrations of indomethacin also resulted in increased chondrogenic differentiation. Indomethacin induces differential effects on in vitro endochondral ossification, depending on the chondrocyte's differentiation stage, with complete inhibition of chondrogenic differentiation as the most pronounced action. This observation may provide a rational behind the elusive mode of action of indomethacin in the treatment of heterotopic ossifications. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:847-857, 2017.

Insulin-Like Growth Factor-Independent Effects of Growth Hormone on Growth Plate Chondrogenesis and Longitudinal Bone Growth

GH stimulates growth plate chondrogenesis and longitudinal bone growth directly at the growth plate. However, it is not clear yet whether these effects are entirely mediated by the local expression and action of IGF-1 and IGF-2. To determine whether GH has any IGF-independent growth-promoting effects, we generated (TamCart)Igf1r(flox/flox) mice. The systemic injection of tamoxifen in these mice postnatally resulted in the excision of the IGF-1 receptor (Igf1r) gene exclusively in the growth plate. (TamCart)Igf1r(flox/flox) tamoxifen-treated mice [knockout (KO) mice] and their Igf1r(flox/flox) control littermates (C mice) were injected for 4 weeks with GH. At the end of the 4-week period, the tibial growth and growth plate height of GH-treated KO mice were greater than those of untreated C or untreated KO mice. The systemic injection of GH increased the phosphorylation of Janus kinase 2 and signal transducer and activator of transcription 5B in the tibial growth plate of the C and KO mice. In addition, GH increased the mRNA expression of bone morphogenetic protein-2 and the mRNA expression and protein phosphorylation of nuclear factor-κB p65 in both C and KO mice. In cultured chondrocytes transfected with Igf1r small interfering RNA, the addition of GH in the culture medium significantly induced thymidine incorporation and collagen X mRNA expression. In conclusion, our findings demonstrate that GH can promote growth plate chondrogenesis and longitudinal bone growth directly at the growth plate, even when the local effects of IGF-1 and IGF-2 are prevented. Further studies are warranted to elucidate the intracellular molecular mechanisms mediating the IGF-independent, growth-promoting GH effects.

CXC chemokine ligand 12a enhances chondrocyte proliferation and maturation during endochondral bone formation

OBJECTIVE

We investigated the roles of CXC chemokine ligand 12a (CXCL12a), also known as stromal cell-derived factor-1α (SDF-1α), in endochondral bone growth, which can give us important clues to understand the role of CXCL12a in osteoarthritis (OA).

METHODS

Primary chondrocytes and tibial explants from embryonic 15.5 day-old mice were cultured with recombinant mouse CXCL12a. To assess the role of CXCL12a in chondrogenic differentiation, we conducted mesenchymal cell micromass culture.

RESULTS

In tibia organ cultures, CXCL12a increased total bone length in a dose-dependent manner through proportional effects on cartilage and bone. In accordance with increased length, CXCL12a increased the protein level of proliferation markers, such as cyclin D1 and proliferating cell nuclear antigen (PCNA), in primary chondrocytes as well as in tibia organ culture. In addition, CXCL12a increased the expression of Runx2, Col10 and MMP13 in primary chondrocytes and tibia organ culture system, implying a role of CXCL12a in chondrocyte maturation. Micromass cultures of limb-bud mesenchymal progenitor cells (MPCs) revealed that CXCL12a has a limited effect on early chondrogenesis, but significantly promoted maturation of chondrocytes. CXCL12a induced the phosphorylation of p38 and Erk1/2 MAP kinases and IκB. The increased expression of cyclin D1 by CXCL12a was significantly attenuated by inhibitors of MEK1 and NF-κB. On the other hand, p38 and Erk1/2 MAP kinase and NF-κB signaling were associated with CXCL12a-induced expression of Runx2 and MMP13, the marker of chondrocyte maturation.

CONCLUSION

CXCL12a promoted the proliferation and maturation of chondrocytes, which strongly suggest that CXCL12a may have a negative effect on articular cartilage and contribute to OA progression.

Novel role for cyclophilin A in regulation of chondrogenic commitment and endochondral ossification

Recent studies showed that cyclophilin A (CypA) promotes NF-κB/p65 nuclear translocation, resulting in enhanced NF-κB activity and altered expression of its target genes, such as the Sox9 transcriptional factor, which plays a critical role in chondrogenic differentiation and endochondral ossification. In this report, we unveil the role of CypA in signal-induced chondrogenic differentiation and endochondral ossification. Expression levels of the chondrogenic differentiation markers and transcriptional regulators Sox9 and Runx2 were all significantly lower in CypA knockdown chondrogenic cells than in wild-type cells, indicating that CypA plays a functional role in chondrogenic differentiation. In vitro differentiation studies using micromass cultures of mouse limb bud cells further supported the conclusion that CypA is needed for chondrogenic differentiation. Newborn CypA-deficient pups double stained with alcian blue and alizarin red exhibited generalized, pronounced skeletal defects, while high-resolution micro-computed tomography (microCT) analyses of the femurs and lumbar vertebrae revealed delayed or incomplete endochondral ossification. Comparative histology and immunohistochemistry (IHC) analyses further verified the effects of CypA deficiency on chondrogenic differentiation. Our results provide evidence for the important contribution of CypA as a pertinent component acting through NF-κB-Sox9 in regulation of chondrogenesis signaling. These findings are important to better understand signal-induced chondrogenesis of chondrogenic progenitors in physiological and pathophysiological contexts.

Identification and characterization of the novel Col10a1 regulatory mechanism during chondrocyte hypertrophic differentiation

The majority of human skeleton develops through the endochondral pathway, in which cartilage-forming chondrocytes proliferate and enlarge into hypertrophic chondrocytes that eventually undergo apoptosis and are replaced by bone. Although at a terminal differentiation stage, hypertrophic chondrocytes have been implicated as the principal engine of bone growth. Abnormal chondrocyte hypertrophy has been seen in many skeletal dysplasia and osteoarthritis. Meanwhile, as a specific marker of hypertrophic chondrocytes, the type X collagen gene (COL10A1) is also critical for endochondral bone formation, as mutation and altered COL10A1 expression are often accompanied by abnormal chondrocyte hypertrophy in many skeletal diseases. However, how the type X collagen gene is regulated during chondrocyte hypertrophy has not been fully elucidated. We have recently demonstrated that Runx2 interaction with a 150-bp mouse Col10a1 cis-enhancer is required but not sufficient for its hypertrophic chondrocyte-specific reporter expression in transgenic mice, suggesting requirement of additional Col10a1 regulators. In this study, we report in silico sequence analysis of this 150-bp enhancer and identification of its multiple binding factors, including AP1, MEF2, NFAT, Runx1 and TBX5. Using this enhancer as bait, we performed yeast one-hybrid assay and identified multiple candidate Col10a1-interacting genes, including cyclooxygenase 1 (Cox-1) and Cox-2. We have also performed mass spectrometry analysis and detected EF1-alpha, Fus, GdF7 and Runx3 as components of the specific complex formed by the cis-enhancer and nuclear extracts from hypertrophic MCT (mouse chondrocytes immortalized with large T antigen) cells that express Col10a1 abundantly. Notably, some of the candidate genes are differentially expressed in hypertrophic MCT cells and have been associated with chondrocyte hypertrophy and Runx2, an indispensible Col10a1 regulator. Intriguingly, we detected high-level Cox-2 expression in hypertrophic MCT cells. Electrophoretic mobility shift assay and chromatin immunoprecipitation assays confirmed the interaction between Cox-2 and Col10a1 cis-enhancer, supporting its role as a candidate Col10a1 regulator. Together, our data support a Cox-2-containing, Runx2-centered Col10a1 regulatory mechanism, during chondrocyte hypertrophic differentiation.

The involvement of SIRT1 and transcription factor NF-κB (p50/p65) in regulation of porcine ovarian cell function

The role of either mTOR system/enzyme sirtuin1 (SIRT1) or transcription factor NF-κB in the direct control of ovarian function has not been estabished. The aim of our in vitro experiments was to examine the involvement of SIRT1 and the p65 and p50 subunits of NFκB in control of porcine ovarian granulosa cell functions and the interrelationships between SIRT1, NFκB (p65, p50) 30 and FSH in the ovary. Monolayers of primary granulosa cells were transfected with gene constructs encoding either SIRT1 or p65 and p50, and thereafter cultured with, or without, addition of FSH. The accumulation of markers of proliferation (cyclin B1 and cyclin-dependent protein kinase Cdc2/p34) and proteins p50, p65 and SIRT1 in the cells was detected by using SDS-PAGE/Western immunoblotting and immunocytochemistry. The secretion of progesterone (P4) and insulin-like growth factor I (IGF-I) was measured by using radioimmunoassay. It was observed that transfection of cells with a SIRT1 gene construct promoted accumulation of proliferation markers, Cdc2/p34, cyclin B1, decreased accumulation of p50 and p65 and stimulated release of P4 and IGF-I. Co-transfection of cells with cDNA p50 and cDNA p65 enhanced the accumulation of SIRT1 and the release of P4 but did not influence the release of IGF-I. Adding FSH to the culture medium stimulated accumulation of both subunits of NF-κB, as well as accumulation of Cdc2/p34, cyclin B1 and release of both P4 and IGF-I. The ability of FSH to promote NF-κB accumulation, the similarity of the main effects of FSH, SIRT1 and NF-κB, as well as the inability of NF-κB to substantially modify the the majority of FSH effects suggest that SIRT1/NF-κB system could be a mediator of FSH action on ovarian cell functions. On the other hand, SIRT1 was able to inhibit NF-κB and to change stimulatory the effect of FSH on NF-κB from stimulatory to inhibitory. This could suggest the existence of negative feedback control of FSH/NF-κB system by high amounts of SIRT1. Our observations (1) confirm the previous data on proliferation, P4 and IGF-I release in ovarian cells and their up-regulation by FSH, (2) demonstrate the presence of SIRT1, NF-κB/p50 and NF-κB/p65 in these cells, (3) show for the first time the involvement of SIRT1 and NF-κB in direct control of proliferation and secretory activity of ovarian cells, (4) represent the first data on interrelationships between FSH, SIRT1 and NF-κB within the ovary.

CCN2/CTGF is required for matrix organization and to protect growth plate chondrocytes from cellular stress

CCN2 (connective tissue growth factor (CTGF/CCN2)) is a matricellular protein that utilizes integrins to regulate cell proliferation, migration and survival. The loss of CCN2 leads to perinatal lethality resulting from a severe chondrodysplasia. Upon closer inspection of Ccn2 mutant mice, we observed defects in extracellular matrix (ECM) organization and hypothesized that the severe chondrodysplasia caused by loss of CCN2 might be associated with defective chondrocyte survival. Ccn2 mutant growth plate chondrocytes exhibited enlarged endoplasmic reticula (ER), suggesting cellular stress. Immunofluorescence analysis confirmed elevated stress in Ccn2 mutants, with reduced stress observed in Ccn2 overexpressing transgenic mice. In vitro studies revealed that Ccn2 is a stress responsive gene in chondrocytes. The elevated stress observed in Ccn2−/− chondrocytes is direct and mediated in part through integrin α5. The expression of the survival marker NFκB and components of the autophagy pathway were decreased in Ccn2 mutant growth plates, suggesting that CCN2 may be involved in mediating chondrocyte survival. These data demonstrate that absence of a matricellular protein can result in increased cellular stress and highlight a novel protective role for CCN2 in chondrocyte survival. The severe chondrodysplasia caused by the loss of CCN2 may be due to increased chondrocyte stress and defective activation of autophagy pathways, leading to decreased cellular survival. These effects may be mediated through nuclear factor κB (NFκB) as part of a CCN2/integrin/NFκB signaling cascade.

Differential response of chondrocytes and chondrogenic-induced mesenchymal stem cells to C1-OH tributanoylated N-acetylhexosamines

Articular cartilage has a limited ability to self-repair because of its avascular nature and the low mitotic activity of the residing chondrocytes. There remains a significant need to develop therapeutic strategies to increase the regenerative capacity of cells that could repair cartilage. Multiple cell types, including chondrocytes and mesenchymal stem cells, have roles in articular cartilage regeneration. In this study, we evaluated a platform technology of multiple functionalized hexosamines, namely 3,4,6-O-tributanoylated-N-acetylgalactosamine (3,4,6-O-Bu₃GalNAc), 3,4,6-O-tributanoylated-N-acetylmannosamine (3,4,6-O-Bu₃ManNAc) and 3,4,6-O-Bu₃GlcNAc, with the potential ability to reduce NFκB activity. Exposure of IL-1β-stimulated chondrocytes to the hexosamine analogs resulted in increased expression of ECM molecules and a corresponding improvement in cartilage-specific ECM accumulation. The greatest ECM accumulation was observed with 3,4,6-O-Bu₃GalNAc. In contrast, mesenchymal stem cells (MSCs) exposed to 3,4,6-O-Bu₃GalNAc exhibited a dose dependent decrease in chondrogenic differentation as indicated by decreased ECM accumulation. These studies established the disease modification potential of a hexosamine analog platform on IL-1β-stimulated chondrocytes. We determined that the modified hexosamine with the greatest potential for disease modification is 3,4,6-O-Bu₃GalNAc. This effect was distinctly different with 3,4,6-O-Bu₃GalNAc exposure to chondrogenic-induced MSCs, where a decrease in ECM accumulation and differentiation was observed. Furthermore, these studies suggest that NFκB pathway plays a complex role cartilage repair.

GSK-3α and GSK-3β proteins are involved in early stages of chondrocyte differentiation with functional redundancy through RelA protein phosphorylation

Here we examine the roles of two isoforms of glycogen synthase kinase-3 (GSK-3), GSK-3α and GSK-3β, in skeletal development. Both isoforms were unphosphorylated and active in chondrocyte differentiation stages during SOX9 and type II collagen (COL2A1) expression. Although knock-out of both alleles of Gsk3a (Gsk3a(-/-)) or a single allele of Gsk3b (Gsk3b(+/-)) in mice did not significantly affect skeletal development, compound knock-out (Gsk3a(-/-);Gsk3b(+/-)) caused dwarfism with impairment of chondrocyte differentiation. GSK-3α and GSK-3β induced differentiation of cultured chondrocytes with functional redundancy in a cell-autonomous fashion, independently of the Wnt/β-catenin signal. Computational predictions followed by SOX9 and COL2A1 transcriptional assays identified RelA (NF-κB p65) as a key phosphorylation target of GSK-3. Among several phosphorylation residues in RelA, Thr-254 was identified as the critical phosphorylation site for GSK-3 that modulated chondrocyte differentiation. In conclusion, redundant functions of GSK-3α and GSK-3β through phosphorylation of RelA at Thr-254 play a crucial role in early stages of chondrocyte differentiation.

Activation of NF-κB/p65 facilitates early chondrogenic differentiation during endochondral ossification

BACKGROUND

NF-κB/p65 has been reported to be involved in regulation of chondrogenic differentiation. However, its function in relation to key chondrogenic factor Sox9 and onset of chondrogenesis during endochondral ossification is poorly understood. We hypothesized that the early onset of chondrogenic differentiation is initiated by transient NF-κB/p65 signaling.

METHODOLOGY/PRINCIPAL FINDINGS

The role of NF-κB/p65 in early chondrogenesis was investigated in different in vitro, ex vivo and in vivo endochondral models: ATDC5 cells, hBMSCs, chicken periosteal explants and growth plates of 6 weeks old mice. NF-κB/p65 activation was manipulated using pharmacological inhibitors, RNAi and activating agents. Gene expression and protein expression analysis, and (immuno)histochemical stainings were employed to determine the role of NF-κB/p65 in the chondrogenic phase of endochondral development. Our data show that chondrogenic differentiation is facilitated by early transient activation of NF-κB/p65. NF-κB/p65-mediated signaling determines early expression of Sox9 and facilitates the subsequent chondrogenic differentiation programming by signaling through key chondrogenic pathways.

CONCLUSIONS/SIGNIFICANCE

The presented data demonstrate that NF-κB/p65 signaling, as well as its intensity and timing, represents one of the transcriptional regulatory mechanisms of the chondrogenic developmental program of chondroprogenitor cells during endochondral ossification. Importantly, these results provide novel possibilities to improve the success of cartilage and bone regenerative techniques.

Exogenous signal-independent nuclear IkappaB kinase activation triggered by Nkx3.2 enables constitutive nuclear degradation of IkappaB-alpha in chondrocytes

NF-κB is a multifunctional transcription factor involved in diverse biological processes. It has been well documented that NF-κB can be activated in response to various stimuli. While signal-inducible NF-κB activation mechanisms have been extensively characterized, exogenous signal-independent intrinsic NF-κB activation processes remain poorly understood. Here we show that IκB kinase β (IKKβ) can be intrinsically activated in the nucleus by a homeobox protein termed Nkx3.2 in the absence of exogenous IKK-activating signals. We found that ubiquitin chain-dependent, but persistent, interactions between Nkx3.2 and NEMO (also known as IKKγ) can give rise to constitutive IKKβ activation in the nucleus. Once the Nkx3.2-NEMO-IKKβ complex is formed in the nucleus, IKKβ-induced Nkx3.2 phosphorylation at Ser148 and Ser168 allows βTrCP to be engaged to cause IκB-α ubiquitination independent of IκB-α phosphorylation at Ser32 and Ser36. Taken together, our results provide a novel molecular explanation as to how an intracellular factor such as Nkx3.2 can accomplish persistent nuclear IKK activation to enable intrinsic and constitutive degradation of IκB in the nucleus in the absence of exogenous NF-κB-activating signals, which, in turn, plays a role in chondrocyte viability maintenance.

Nuclear factor-kappaB (NF-kappaB) p65 interacts with Stat5b in growth plate chondrocytes and mediates the effects of growth hormone on chondrogenesis and on the expression of insulin-like growth factor-1 and bone morphogenetic protein-2

Growth hormone (GH) stimulates growth plate chondrogenesis and longitudinal bone growth with its stimulatory effects primarily mediated by insulin-like growth factor-1 (IGF-1) both systemically and locally in the growth plate. It has been shown that the transcription factor Stat5b mediates the GH promoting effect on IGF-1 expression and on chondrogenesis, yet it is not known whether other signaling molecules are activated by GH in growth plate chondrocytes. We have previously demonstrated that nuclear factor-κB p65 is a transcription factor expressed in growth plate chondrocytes where it facilitates chondrogenesis. We have also shown that fibroblasts isolated from a patient with growth failure and a heterozygous mutation of inhibitor-κBα (IκB; component of the nuclear factor-κB (NF-κB) signaling pathway) exhibit GH insensitivity. In this study, we cultured rat metatarsal bones in the presence of GH and/or pyrrolidine dithiocarbamate (PDTC), a known NF-κB inhibitor. The GH-mediated stimulation of metatarsal longitudinal growth and growth plate chondrogenesis was neutralized by PDTC. In cultured chondrocytes isolated from rat metatarsal growth plates, GH induced NF-κB-DNA binding and chondrocyte proliferation and differentiation and prevented chondrocyte apoptosis. The inhibition of NF-κB p65 expression and activity (by NF-κB p65 siRNA and PDTC, respectively) in chondrocytes reversed the GH-mediated effects on chondrocyte proliferation, differentiation, and apoptosis. Lastly, the inhibition of Stat5b expression in chondrocytes prevented the GH promoting effects on NF-κB-DNA binding, whereas the inhibition of NF-κB p65 expression or activity prevented the GH-dependent activation of IGF-1 and bone morphogenetic protein-2 expression.

Proepithelin stimulates growth plate chondrogenesis via nuclear factor-kappaB-p65-dependent mechanisms

Proepithelin, a previously unrecognized growth factor in cartilage, has recently emerged as an important regulator for cartilage formation and function. In the present study, we provide several lines of evidences in proepithelin-mediated induction of cell proliferation, differentiation, and apoptosis in the metatarsal growth plate. Proepithelin-mediated stimulation of metatarsal growth and growth plate chondrogenesis was neutralized by pyrrolidine dithiocarbamate, a known NF-κB inhibitor. In rat growth plate chondrocytes, proepithelin induced NF-κB-p65 nuclear translocation, and nuclear NF-κB-p65 initiated its target gene cyclin D1 to regulate chondrocyte functions. The inhibition of NF-κB-p65 expression and activity (by p65 short interfering RNA (siRNA) and pyrrolidine dithiocarbamate, respectively) in chondrocytes reversed the proepithelin-mediated induction of cell proliferation and differentiation and the proepithelin-mediated prevention of cell apoptosis. Moreover, the inhibition of the phosphatidylinositol 3-kinase and Akt abolished the effects of proepithelin on NF-κB activation. Finally, using siRNA and antisense strategies, we demonstrated that endogenously produced proepithelin by chondrocytes is important for chondrocyte growth in serum-deprived conditions. These results support the hypothesis that the induction of NF-κB activity of in growth plate chondrocytes is critical in proepithelin-mediated growth plate chondrogenesis and longitudinal bone growth.

The epigenetic effect of glucosamine and a nuclear factor-kappa B (NF-kB) inhibitor on primary human chondrocytes--implications for osteoarthritis

OBJECTIVE

Idiopathic osteoarthritis is the most common form of osteoarthritis (OA) world-wide and remains the leading cause of disability and the associated socio-economic burden in an increasing aging population. Traditionally, OA has been viewed as a degenerative joint disease characterized by progressive destruction of the articular cartilage and changes in the subchondral bone culminating in joint failure. However, the etiology of OA is multifactorial involving genetic, mechanical and environmental factors. Treatment modalities include analgesia, joint injection with steroids or hyaluronic acid, oral supplements including glucosamine and chondroitin sulfate, as well as physiotherapy. Thus, there is significant interest in the discovery of disease modifying agents. One such agent, glucosamine (GlcN) is commonly prescribed even though the therapeutic efficacy and mechanism of action remain controversial. Inflammatory cytokines, including IL-1β, and proteinases such as MMP-13 have been implicated in the pathogenesis and progression of OA together with an associated CpG demethylation in their promoters. We have investigated the potential of GlcN to modulate NF-kB activity and cytokine-induced abnormal gene expression in articular chondrocytes and, critically, whether this is associated with an epigenetic process.

METHOD

Human chondrocytes were isolated from the articular cartilage of femoral heads, obtained with ethical permission, following fractured neck of femur surgery. Chondrocytes were cultured for 5 weeks in six separate groups; (i) control culture, (ii) cultured with a mixture of 2.5 ng/ml IL-1β and 2.5 ng/ml oncostatin M (OSM), (iii) cultured with 2mM N-acetyl GlcN (Sigma-Aldrich), (iv) cultured with a mixture of 2.5 ng/ml IL-1β, 2.5 ng/ml OSM and 2mM GlcN, (v) cultured with 1.0 μM BAY 11-7082 (BAY; NF-kB inhibitor: Calbiochem, Darmstadt, Germany) and, (vi) cultured with a mixture of 2.5 ng/ml IL-1β, 2.5 ng/ml OSM and 1.0 μM BAY. The levels of IL1B and MMP13 mRNA were examined using qRT-PCR. The percentage DNA methylation in the CpG sites of the IL1β and MMP13 proximal promoter were quantified by pyrosequencing.

RESULT

IL1β expression was enhanced over 580-fold in articular chondrocytes treated with IL-1β and OSM. GlcN dramatically ameliorated the cytokine-induced expression by 4-fold. BAY alone increased IL1β expression by 3-fold. In the presence of BAY, IL-1β induced IL1B mRNA levels were decreased by 6-fold. The observed average percentage methylation of the -256 CpG site in the IL1β promoter was 65% in control cultures and decreased to 36% in the presence of IL-1β/OSM. GlcN and BAY alone had a negligible effect on the methylation status of the IL1B promoter. The cytokine-induced loss of methylation status in the IL1B promoter was ameliorated by both GlcN and BAY to 44% and 53%, respectively. IL-1β/OSM treatment increased MMP13 mRNA levels independently of either GlcN or BAY and no change in the methylation status of the MMP13 promoter was observed.

CONCLUSION

We demonstrate for the first time that GlcN and BAY can prevent cytokine-induced demethylation of a specific CpG site in the IL1β promoter and this was associated with decreased expression of IL1β. These studies provide a potential mechanism of action for OA disease modifying agents via NF-kB and, critically, demonstrate the need for further studies to elucidate the role that NF-kB may play in DNA demethylation in human chondrocytes.

Tumor necrosis factor-α accelerates the calcification of human aortic valve interstitial cells obtained from patients with calcific aortic valve stenosis via the BMP2-Dlx5 pathway

Calcific aortic valve stenosis (CAS) is the most frequent heart valve disease in the elderly, accompanied by valve calcification. Tumor necrosis factor-α (TNF-α), a pleiotropic cytokine secreted mainly from macrophages, has been detected in human calcified valves. However, the role of TNF-α in valve calcification remains unclear. To clarify whether TNF-α accelerates the calcification of aortic valves, we investigated the effect of TNF-α on human aortic valve interstitial cells (HAVICs) obtained from patients with CAS (CAS group) and with aortic regurgitation or aortic dissection having a noncalcified aortic valve (control group). HAVICs (2 × 10(4)) were cultured in a 12-well dish in Dulbecco's modified Eagle's medium with 10% fetal bovine serum. The medium containing TNF-α (30 ng/ml) was replenished every 3 days after the cells reached confluence. TNF-α significantly accelerated the calcification and alkaline phosphatase (ALP) activity of HAVICs from CAS but not the control group after 12 days of culture. Furthermore, gene expression of calcigenic markers, ALP, bone morphogenetic protein 2 (BMP2), and distal-less homeobox 5 (Dlx5) were significantly increased after 6 days of TNF-α treatment in the CAS group but not the control group. Dorsomorphin, an inhibitor of mothers against decapentaplegic homologs (Smads) 1/5/8 phosphorylation, significantly inhibited the enhancement of TNF-α-induced calcification, ALP activity, Smad phosphorylation, and Dlx5 gene expression of HAVICs from the CAS group. These results suggest that HAVICs from the CAS group have greater sensitivity to TNF-α, which accelerates the calcification of aortic valves via the BMP2-Dlx5 pathway.

Role of NF-κB in the skeleton

Since the discovery that deletion of the NF-κB subunits p50 and p52 causes osteopetrosis in mice, there has been considerable interest in the role of NF-κB signaling in bone. NF-κB controls the differentiation or activity of the major skeletal cell types - osteoclasts, osteoblasts, osteocytes and chondrocytes. However, with five NF-κB subunits and two distinct activation pathways, not all NF-κB signals lead to the same physiologic responses. In this review, we will describe the roles of various NF-κB proteins in basal bone homeostasis and disease states, and explore how NF-κB inhibition might be utilized therapeutically.

Perturbation of adhesion molecule-mediated chondrocyte-matrix interactions by 4-hydroxynonenal binding: implication in osteoarthritis pathogenesis

Introduction

Objectives were to investigate whether interactions between human osteoarthritic chondrocytes and 4-hydroxynonenal (HNE)-modified type II collagen (Col II) affect cell phenotype and functions and to determine the protective role of carnosine (CAR) treatment in preventing these effects.

Methods

Human Col II was treated with HNE at different molar ratios (MR) (1:20 to 1:200; Col II:HNE). Articular chondrocytes were seeded in HNE/Col II adduct-coated plates and incubated for 48 hours. Cell morphology was studied by phase-contrast and confocal microscopy. Adhesion molecules such as intercellular adhesion molecule-1 (ICAM-1) and α1β1 integrin at protein and mRNA levels were quantified by Western blotting, flow cytometry and real-time reverse transcription-polymerase chain reaction. Cell death, caspases activity, prostaglandin E2 (PGE₂), metalloproteinase-13 (MMP-13), mitogen-activated protein kinases (MAPKs) and nuclear factor-kappa B (NF-κB) were assessed by commercial kits. Col II, cyclooxygenase-2 (COX-2), MAPK, NF-κB-p65 levels were analyzed by Western blotting. The formation of α1β1 integrin-focal adhesion kinase (FAK) complex was revealed by immunoprecipitation.

Results

Col II modification by HNE at MR approximately 1:20, strongly induced ICAM-1, α1β1 integrin and MMP-13 expression as well as extracellular signal-regulated kinases 1 and 2 (ERK^1/2) and NF-κB-p65 phosphorylation without impacting cell adhesion and viability or Col II expression. However, Col II modification with HNE at MR approximately 1:200, altered chondrocyte adhesion by evoking cell death and caspase-3 activity. It inhibited α1β1 integrin and Col II expression as well as ERK^1/2 and NF-κB-p65 phosphorylation, but, in contrast, markedly elicited PGE₂ release, COX-2 expression and p38 MAPK phosphorylation. Immunoprecipitation assay revealed the involvement of FAK in cell-matrix interactions through the formation of α1β1 integrin-FAK complex. Moreover, the modification of Col II by HNE at a 1:20 or approximately 1:200 MR affects parameters of the cell shape. All these effects were prevented by CAR, an HNE-trapping drug.

Conclusions

Our novel findings indicate that HNE-binding to Col II results in multiple abnormalities of chondrocyte phenotype and function, suggesting its contribution in osteoarthritis development. CAR was shown to be an efficient HNE-snaring agent capable of counteracting these outcomes.

Growth hormone and insulin-like growth factor I insensitivity of fibroblasts isolated from a patient with an I{kappa}B{alpha} mutation

CONTEXT

NF-kappaB is a family of transcription factors involved in cell proliferation, differentiation, and apoptosis.

OBJECTIVE

We have recently demonstrated that NF-kappaB is expressed in the growth plate and it mediates the growth-promoting effects of IGF-I on chondrogenesis and longitudinal bone growth. Humans with defects of the NF-kappaB pathway exhibit growth failure, which suggests a possible regulatory role for NF-kappaB in statural growth. We have previously reported a child with ectodermal dysplasia, immunodeficiency, and growth retardation, harboring a heterozygous mutation of IkappaBalpha, an essential component of the NF-kappaB pathway. Since he was found with low IGF-l and IGFBP-3, and elevated GH secretion, an IGF-l generation test was carried out: baseline IGF-l was low and only responded to a high dose of GH. Thus, the diagnosis of GH resistance was made.

RESULTS

To assess the underlying mechanisms of his GH resistance, we cultured the patient's skin fibroblasts with GH and/or IGF-I. While both GH and IGF-l induced cell proliferation and NF-kappaB activity in controls' fibroblasts, they had no effect on the patient's fibroblasts. In the fibroblasts of the patient's father (who displays mosaicism for the IkappaBalpha mutation), GH and IGF-l elicited an attenuated stimulatory effect. In addition, GH stimulated STAT5 phosphorylation and IGF-l mRNA expression in controls ' and the father's fibroblasts, while IGF-l induced PI3K activity and mRNA and protein expression of TDAG51, a target gene for IGF-I. In contrast, none of these effects was elicited by GH or IGF-l in the patient's fibroblasts.

CONCLUSION

Our findings suggest that this patient's IkappaBalpha mutation caused GH and IGF-l resistance which, in turn, contributed to his growth failure.

New insight on FGFR3-related chondrodysplasias molecular physiopathology revealed by human chondrocyte gene expression profiling

Endochondral ossification is the process by which the appendicular skeleton, facial bones, vertebrae and medial clavicles are formed and relies on the tight control of chondrocyte maturation. Fibroblast growth factor receptor (FGFR)3 plays a role in bone development and maintenance and belongs to a family of proteins which differ in their ligand affinities and tissue distribution. Activating mutations of the FGFR3 gene lead to craniosynostosis and multiple types of skeletal dysplasia with varying degrees of severity: thanatophoric dysplasia (TD), achondroplasia and hypochondroplasia. Despite progress in the characterization of FGFR3-mediated regulation of cartilage development, many aspects remain unclear. The aim and the novelty of our study was to examine whole gene expression differences occurring in primary human chondrocytes isolated from normal cartilage or pathological cartilage from TD-affected fetuses, using Affymetrix technology. The phenotype of the primary cells was confirmed by the high expression of chondrocytic markers. Altered expression of genes associated with many cellular processes was observed, including cell growth and proliferation, cell cycle, cell adhesion, cell motility, metabolic pathways, signal transduction, cell cycle process and cell signaling. Most of the cell cycle process genes were down-regulated and consisted of genes involved in cell cycle progression, DNA biosynthesis, spindle dynamics and cytokinesis. About eight percent of all modulated genes were found to impact extracellular matrix (ECM) structure and turnover, especially glycosaminoglycan (GAG) and proteoglycan biosynthesis and sulfation. Altogether, the gene expression analyses provide new insight into the consequences of FGFR3 mutations in cell cycle regulation, onset of pre-hypertrophic differentiation and concomitant metabolism changes. Moreover, impaired motility and ECM properties may also provide clues about growth plate disorganization. These results also suggest that many signaling pathways may be directly or indirectly altered by FGFR3 and confirm the crucial role of FGFR3 in the control of growth plate development.

Independent and cooperative roles of tumor necrosis factor-alpha, nuclear factor-kappaB, and bone morphogenetic protein-2 in regulation of metastasis and osteomimicry of prostate cancer cells and differentiation and mineralization of MC3T3-E1 osteoblast-like cells

The molecular mechanisms involved in prostate cancer (PC) metastasis and bone remodeling are poorly understood. We recently reported that phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) mediates transcriptional regulation and activation of bone morphogenetic protein (BMP)-2 signaling by nuclear factor (NF)-kappaB in bone metastatic prostate cancer cells. In the present study, we demonstrate that NF-kappaB, whether activated by recombinant human tumor necrosis factor (TNF)-alpha or by ectopic expression of the p65 subunit, is involved in extracellular matrix adhesion and invasion of osteotropic PC-3 and C4-2B, but not LNCaP, cells. The enhanced metastatic potential was associated with transcriptional upregulation of osteopontin, osteocalcin, and collagen IA1 in osteotropic PC cells, suggesting their role in osteomimicry of PC cells. Unlike BMP-4, BMP-2 protein enhanced the invasive properties of C4-2B cells, but not in LNCaP cells. Also, this effect was nullified by Noggin. In addition, BMP-2 mediates TNF-alpha-induced invasion of C4-2B cells in a NF-kappaB-dependent fashion. TNF-alpha or conditioned media (CM) of TNF-alpha-stimulated C4-2B cells upregulated BMP-2 and BMP-dependent Smad transcripts and inhibited receptor activator of NF-kappaB ligand transcripts in RAW 264.7 preosteoclast cells, respectively, implying that this factor may contribute to suppression of osteoclastogenesis via direct and paracrine mechanisms. In contrast, CM of TNF-alpha-stimulate or BMP2-stimulated C4-2B cells induced in vitro mineralization of MC3T3-E1 osteoblast cells in a BMP-2-dependent and NF-kappaB-dependent manner, respectively. Taken together, the results suggest that mutual interactions between these factors may be pivotal not only in enhancing the osteomimicry and metastatic potential of PC cells, but also in bone remodeling and in shifting the balance from osteoclastogenesis towards osteoblastogenesis.

TNFalpha promotes osteogenic differentiation of human mesenchymal stem cells by triggering the NF-kappaB signaling pathway

Mesenchymal stem cells are multipotent cells able to differentiate into different mesenchymal lineages. Studies in the past had suggested that two of these mesenchymal differentiation directions, the chondrogenic and the myogenic differentiation, are negatively regulated by the transcription factor NF-kappaB. Although osteogenic differentiation has been extensively studied, the influence of NF-kappaB on this differentiation lineage was not subject of detailed analyses in the past. We have analyzed the consequences of TNF-alpha treatment and genetic manipulation of the NF-kappaB pathway for osteogenic differentiation of hMSCs. Treatment of hMSCs during differentiation with TNF-alpha activates NF-kappaB and this results in enhanced expression of osteogenetic proteins like bone morphogenetic protein2 (BMP-2) and alkaline phosphatase (ALP). In addition, enhanced matrix mineralization was observed. The direct contribution of the NF-kappaB pathway was confirmed in cells that express a constitutively active version of the NF-kappaB-inducing kinase IKK2 (CA-IKK2). The IKK2/NF-kappaB-induced BMP-2 up-regulation results in the enhancement of RUNX2 and Osterix expression, two critical regulators of the osteogenic differentiation program. Interestingly, a genetic block of the NF-kappaB pathway did not interfere with osteogenic differentiation. We conclude that TNFalpha mediated NF-kappaB activation, although not absolutely required for BMP-2 expression and matrix mineralization nevertheless supports osteogenic differentiation and matrix mineralization by increasing BMP-2 expression. Our results therefore suggest that NF-kappaB activation may function in lineage selection during differentiation of hMSCs by fostering osteogenic differentiation at the expense of other differentiation lineages.

A TLR2 ligand suppresses inflammation by modulation of chemokine receptors and redirection of leukocyte migration

Toll-like receptors orchestrate rapid local protective innate-immune responses to invading pathogens and optimize leukocyte priming of subsequent adaptive responses. Paradoxically, systemic excess of the TLR2 ligand, bacterial lipoprotein (BLP), suppresses peripheral inflammatory responses. Here, we demonstrate that this phenomenon is regulated via the TLR2-dependent, cell-autonomous down-regulation of inflammatory chemokine receptor expression on a variety of leukocyte subsets. Remarkably, BLP mediated no effect on constitutive chemokine receptor expression. By tracking adoptively transferred wild-type and TLR2(-/-) leukocytes in vivo, we observed that BLP mediated chemokine receptor switching directed leukocytes away from inflamed sites toward secondary lymphoid organs. These data highlight a novel role for TLR ligands, such as BLP, in regulating leukocyte retention and migration away from innate immune lesions via discrete constitutive and inflammatory chemokine receptor regulation.

Stimulatory effects of insulin-like growth factor-I on growth plate chondrogenesis are mediated by nuclear factor-kappaB p65

Insulin-like growth factor-I (IGF-I) is an important regulator of endochondral ossification. However, little is known about the signaling pathways activated by IGF-I in growth plate chondrocytes. We have previously shown that NF-kappaB-p65 facilitates growth plate chondrogenesis. In this study, we first cultured rat metatarsal bones with IGF-I and/or pyrrolidine dithiocarbamate (PDTC), a known NF-kappaB inhibitor. The IGF-I-mediated stimulation of metatarsal growth and growth plate chondrogenesis was neutralized by PDTC. In rat growth plate chondrocytes, IGF-I induced NF-kappaB-p65 nuclear translocation. The inhibition of NF-kappaB-p65 expression and activity (by p65 short interfering RNA and PDTC, respectively) in chondrocytes reversed the IGF-I-mediated induction of cell proliferation and differentiation and the IGF-I-mediated prevention of cell apoptosis. Moreover, the inhibition of the phosphatidylinositol 3-kinase and Akt abolished the effects of IGF-I on NF-kappaB activation. In conclusion, our findings indicate that IGF-I stimulates growth plate chondrogenesis by activating NF-kappaB-p65 in chondrocytes.