Endochondral Bone Growth Research Articles

FGFR3 promotes synchondrosis closure and fusion of ossification centers through the MAPK pathway

Activating mutations in FGFR3 cause achondroplasia and thanatophoric dysplasia, the most common human skeletal dysplasias. In these disorders, spinal canal and foramen magnum stenosis can cause serious neurologic complications. Here, we provide evidence that FGFR3 and MAPK signaling in chondrocytes promote synchondrosis closure and fusion of ossification centers. We observed premature synchondrosis closure in the spine and cranial base in human cases of homozygous achondroplasia and thanatophoric dysplasia as well as in mouse models of achondroplasia. In both species, premature synchondrosis closure was associated with increased bone formation. Chondrocyte-specific activation of Fgfr3 in mice induced premature synchondrosis closure and enhanced osteoblast differentiation around synchondroses. FGF signaling in chondrocytes increases Bmp ligand mRNA expression and decreases Bmp antagonist mRNA expression in a MAPK-dependent manner, suggesting a role for Bmp signaling in the increased bone formation. The enhanced bone formation would accelerate the fusion of ossification centers and limit the endochondral bone growth. Spinal canal and foramen magnum stenosis in heterozygous achondroplasia patients, therefore, may occur through premature synchondrosis closure. If this is the case, then any growth-promoting treatment for these complications of achondroplasia must precede the timing of the synchondrosis closure.

Rac1/iNos/nitric oxide signaling is required for chondrocyte proliferation and endochondral bone growth

Rac1/iNos/nitric oxide signaling is required for chondrocyte proliferation and endochondral bone growth

Growth and vitamin D deficiency in a population from 19th century Birmingham, England

AbstractThe West Midlands of England were the cradle of the Industrial Revolution. The 19th century AD skeletal remains from St Martin's Church, Birmingham, West Midlands, provided an important opportunity to assess the health of an urban, working‐class population at this key point in British history. The purpose of this study is to investigate the effect of rickets on growth in this population. Modern clinical data suggest that those with vitamin D deficiency may be retarded in growth, but this has, to our knowledge, yet to be demonstrated in an archaeological population. We investigate the hypothesis that in Birmingham, subadults with rickets showed deficient growth compared with those lacking bony signs of the disease. Age at death was estimated using dental calcification; long‐bone lengths were used as measures of endochondral bone growth. Results showed that for subadults aged 2–6 years, bones in those with signs of rickets tended to be short for their ages, and the deficit in bone length was more marked toward the upper end of the 2–6 year age group. Analysis of the data indicated that deficiency in bone length in rickets primarily reflects deficiency of endochondral bone growth, but for the femur, bending deformity was probably an additional factor reducing the overall length in rickets compared with those without the disease. It was previously suggested (Mays et al., 2006) that in this population rickets may have been a recurrent disease, probably on a seasonal (winter) basis. If this is accepted, a reason why older children with rickets show a greater deficit in long‐bone growth than younger ones is that they are more likely to have had multiple episodic vitamin D deficiency than younger children who have experienced fewer vitamin D deficient winter seasons. Multiple episodes or prolonged vitamin D deficiency disease may be necessary to cause growth deficit sufficient to be detectable in skeletal samples. Copyright © 2008 John Wiley & Sons, Ltd.

Endochondral bone formation in toothless (osteopetrotic) rats: failures of chondrocyte patterning and type X collagen expression.

The pacemaker of endochondral bone growth is cell division and hypertrophy of chondrocytes. The developmental stages of chondrocytes, characterized by the expression of collagen types II and X, are arranged in arrays across the growth zone. Mutations in collagen II and X genes as well as the absence of their gene products lead to different, altered patterns of chondrocyte stages which remain aligned across the growth plate (GP). Here we analyze GP of rats bearing the mutation toothless (tl) which, apart from bone defects, develop a progressive, severe chondrodystrophy during postnatal weeks 3 to 6. Mutant GP exhibited disorganized, non-aligned chondrocytes and mineralized metaphyseal bone but without cartilage mineralization or cartilaginous extensions into the metaphysis. Expression of mRNA coding for collagen types II (Col II) and X (Col X) was examined in the tibial GP by in situ hybridization. Mutant rats at 2 weeks exhibited Col II RNA expression and some hypertrophied chondrocytes (HC) but no Col X RNA was detected. By 3rd week, HC had largely disappeared from the central part of the mutant GP and Col II RNA expression was present but weak and in 2 separate bands. Peripherally the GP contained HC but without Col X RNA expression. This abnormal pattern was exacerbated by the fourth week. Bone mineralized but cartilage in the GP did not. These data suggest that the tl mutation involves a regulatory function for chondrocyte maturation, including Col X RNA synthesis and mineralization, and that the GP abnormalities are related to the Col X deficiency. The differences in patterning in the tl rat GP compared to direct Col X mutations may be explained by compensatory effects.

Transcriptional regulators of chondrocyte hypertrophy

Coordinated transition from proliferation to terminal differentiation and hypertrophy of growth plate chondrocytes is required for normal growth of endochondral bones and thus determines final height in humans. Over the last decades, transcription factors of the Sox and Runx families have been shown to be the central regulators of this process. More recently, numerous additional transcription factors have been identified as positive or negative regulators of chondrocyte hypertrophy, such as Shox/Shox2, Dlx5, and MEF2C. These factors do not only control skeletal development and growth, but might also participate in ectopic chondrocyte hypertrophy during the pathogenesis of osteoarthritis. This review focuses on recent advances in our understanding of the transcriptional regulation of chondrocyte hypertrophy, with particular attention to genes that have only recently been implicated in cartilage development or received little attention so far.

Identification of Quantitative Trait Loci Affecting Murine Long Bone Length in a Two-Generation Intercross of LG/J and SM/J Mice

Study of mutations with large phenotypic effects has allowed the identification of key players in skeletal development. However, the molecular nature of variation in large, phenotypically normal populations tends to be characterized by smaller phenotypic effects that remain undefined. We use interval mapping and quantitative trait locus (QTL) mapping techniques in the combined F2-F3 populations (n = 2111) of an LG/J x SM/J mouse intercross to detect QTLs associated with the lengths of the humerus, ulna, femur, and tibia. Seventy individual trait QTLs affecting long bone lengths were detected, with several chromosomes harboring multiple QTLs. The genetic architecture suggests mainly small, additive effects on long bone length, with roughly one third of the QTLs displaying dominance. Sex interactions were common, and four sex-specific QTLs were observed. Pleiotropy could not be rejected for most of the QTLs identified. Thirty-one epistatic interactions were detected, almost all affecting regions including or immediately adjacent to QTLs. A complex regulatory network with many gene interactions modulates bone growth, possibly with integrated skeletal modules that allow fine-tuning of developmental processes present. Candidate genes in the QTL CIs include many genes known to affect endochondral bone growth and genes that have not yet been associated with bone growth or body size but have a strong potential to influence these traits.

The PI3K pathway regulates endochondral bone growth through control of hypertrophic chondrocyte differentiation

BackgroundThe majority of our bones develop through the process of endochondral ossification that involves chondrocyte proliferation and hypertrophic differentiation in the cartilage growth plate. A large number of growth factors and hormones have been implicated in the regulation of growth plate biology, however, less is known about the intracellular signaling pathways involved. PI3K/Akt has been identified as a major regulator of cellular proliferation, differentiation and death in multiple cell types.Results and DiscussionEmploying an organ culture system of embryonic mouse tibiae and LY294002, a pharmacological inhibitor of PI3K, we show that inhibition of the pathway results in significant growth reduction, demonstrating that PI3K is required for normal endochondral bone growth in vitro. PI3K inhibition reduces the length of the proliferating and particularly of the hypertrophic zone. Studies with organ cultures and primary chondrocytes in micromass culture show delayed hypertrophic differentiation of chondrocytes and increased apoptosis in the presence of LY294002. Surprisingly, PI3K inhibition had no strong effect on IGF1-induced bone growth, but partially blocked the anabolic effects of C-type natriuretic peptide.ConclusionOur data demonstrate an essential role of PI3K signaling in chondrocyte differentiation and as a consequence of this, in the endochondral bone growth process.

Accelerated hypertrophic chondrocyte kinetics in GDF‐7 deficient murine tibial growth plates

The Growth/Differentiation Factors (GDFs) are a subgroup of the Bone Morphogenetic Proteins (BMPs) well known for their role in joint formation and chondrogenesis. Mice deficient in one of these signaling molecules, GDF-5, have recently been shown to exhibit a decreased rate of endochondral bone growth in the proximal tibia due to a significantly longer hypertrophic phase duration. GDF-7 is a related family member, which exhibits a high degree of sequence identity with GDF-5. The purpose of the present study was to determine whether GDF-7 deficiency also alters the endochondral bone growth rate in mice and, if so, how this is achieved. Stereologic and cell kinetic parameters in proximal tibial growth plates from 5-week-old female GDF-7 -/- mice and wild type control littermates were examined. GDF-7 deficiency resulted in a statistically significant increase in growth rate (+26%; p = 0.0084) and rate of cell loss at the chondrosseous junction (+25%; p = 0.0217). Cells from GDF-7 deficient mice also exhibited a significantly shorter hypertrophic phase duration compared to wild type controls (-27%; p = 0.0326). These data demonstrate that, in the absence of GDF-7, the rate of endochondral bone growth is affected through the modulation of hypertrophic phase duration in growth plate chondrocytes. These findings further support a growing body of evidence implicating the GDFs in the formation, maturation, and maintenance of healthy cartilage.

Enhanced Type X Collagen Expression in the Extruded Nucleus Pulposus of the Chondrodystrophoid Dog

The causes of early degeneration and calcification of the nucleus pulposus in the chondrodystrophoid dog are poorly understood, and the underlying molecular mechanism of this process has not yet been clearly defined. Type X collagen is one of the key molecules in endochondral bone growth and development, especially matrix calcification. The relationship between type X collagen and disc degeneration and calcification in chondrodystrophoid dogs has not yet been studied. We analyzed the expression of type X collagen in degeneration and calcification of the intervertebral disc in chondrodystrophoid dogs, using type X collagen immunohistochemistry. Control intervertebral discs were collected from five dogs (4 female, 1 male, average age 1.3 years, beagle breed). Degenerated intervertebral discs were surgically removed from 11 canine patients with intervertebral disc extrusion (1 female, 10 male, average age 5.1 years, dachshund breed) in Nippon Veterinary and Animal Science University. All extruded disc samples showed hypertrophic changes and clustering of cells, typical features observed in the degenerated nucleus pulposus. The relative expression of type X collagen in the degenerated nucleus pulposus (84.3 +/- 11.0%) was significantly increased compared to the control nucleus pulposus (5.4 +/- 5.4%). Our findings suggest that type X collagen might contribute to the development of degeneration or calcification in the nucleus pulposus of the chondrodystrophoid dog.

Developmental basis of limb length in rodents: evidence for multiple divisions of labor in mechanisms of endochondral bone growth

Mammals are remarkably diverse in limb lengths and proportions, but the number and kind of developmental mechanisms that contribute to length differences between limb bones remain largely unknown. Intra- and interspecific differences in bone length could result from variations in the cellular processes of endochondral bone growth, creating differences in rates of chondrocyte proliferation or hypertrophy, variation in the shape and size of chondrocytes, differences in the number of chondrocytes in precursor populations and throughout growth, or a combination of these mechanisms. To address these questions, this study compared cellular mechanisms of endochondral bone growth in cross-sectional ontogenetic series of the appendicular skeleton of two rodent species: the mouse (Mus musculus) and Mongolian gerbil (Meriones unguiculatus). Results indicate that multiple cellular processes of endochondral bone growth contribute to phenotypic differences in limb bone length. The data also suggest that separate developmental processes contribute to intraspecific length differences in proximal versus distal limb bones, and that these proximo-distal mechanisms are distinct from mechanisms that contribute to interspecific differences in limb bone length related to body size. These developmental "divisions of labor" are hypothesized to be important features of vertebrate limb development that allow (1) morphology in the autopods to evolve independently of the proximal limb skeleton, and (2) adaptive changes in limb proportions related to locomotion to evolve independently of evolutionary changes in body size.

Vertebral Rounding Deformity in Pediatric Spondylolisthesis Occurs Due to Deficient of Endochondral Ossification of the Growth Plate

A study using rat spondylolisthesis models. To clarify pathomechanism of vertebral rounding deformity in pediatric spondylolisthesis. For high-grade slippage, rounding of sacrum surface associated with L5 spondylolisthesis is reported to be the most responsible risk factor. However, the exact pathomechanism of the rounding deformity is yet to be clarified. Spondylolisthesis rat model (4-week-old) was used. Radiographs were taken weekly for 5 weeks after the surgery. The lumbar spines were harvested for histology. Hematoxylin and eosin, alcian blue staining, and tartrate-resistant acid phosphatase staining were used. Immunohistochemically, the growth plate cartilage was studied for type II and X collagen. A modified bone histomorphometric analysis was also performed. Radiographs showed slippage 1 week after surgery. Rounding deformity was obvious 2 weeks after surgery. The rounding deformity progressed with time. Three weeks after surgery, the specific columns of growth plate were unclear at the anterior corner, which corresponded to the rounding surface observed on radiographs. Instead, a huge mass of cartilage was observed at that site. Tartrate-resistant acid phosphatase-positive cells were observed in the vicinity of the growth plate except in relation with the anterior corner. The growth plate and cartilage mass at the anterior corner stained positive for type II collagen. Chondrocytes in the hypertrophied layer stained positively for type X collagen; however, staining was faint at the anterior corner. The results suggested that the chondrocytes at the anterior did not form, morphologically and functionally, the normal growth plate. From histomorphometrical analysis, the normal posterior growth plate made endochondral bone growth in 510 +/- 20 microm for a week, whereas the anterior corner in 200 +/- 15 microm. Deficient endochondral ossification of the growth plate in the anterior upper corner of the vertebra could be the pathomechanism of the rounding deformity of the sacrum.

Plasma Amino-Terminal Pro C-Type Natriuretic Peptide in the Neonate: Relation to Gestational Age and Postnatal Linear Growth

C-type natriuretic peptide (CNP) plays an essential role in endochondral bone growth. Insight into CNP's paracrine actions is possible using plasma measurements of the amino-terminal pro C-type natriuretic peptide (NTproCNP). Whether correlations of NTproCNP with linear growth, as found in children and lambs, apply in neonates is unknown. Our objective was to determine the effects of prematurity, gender, and antenatal steroids on plasma NTproCNP at birth, and serial changes in hormone concentrations, linear growth, and markers of bone turnover in the first month of postnatal life. This is a prospective study of newborn infants admitted to an intensive care unit. A total of 48 infants (four gestation groups) were enrolled. Umbilical cord samples were also obtained from 39 healthy term infants. Plasma NTproCNP and CNP were measured in cord plasma. In enrolled neonates, serial measurements of hormone concentrations and markers of bone turnover were related to tibial growth velocity as measured by knemometry. Cord plasma NTproCNP was inversely related to gestational age (r = -0.35; P = 0.003) and was higher in males (P < 0.001). Plasma NTproCNP (P = 0.016) and CNP (P < 0.001) increased within the first week of life, the increase relating inversely to gestational age (r = -0.64; P < 0.001). Plasma NTproCNP at 1 wk was strongly correlated with linear growth velocity (r = 0.49; P < 0.001), and also at 2-4 wk, the relation being stronger than observed between bone turnover markers and growth velocity. In neonates with diverse disorders affecting growth and nutrition, plasma NTproCNP was strongly correlated with linear growth during the first 4 wk of postnatal life and may prove to be a novel marker of growth plate activity in neonates.

Bone growth during daily or intermittent calcitriol treatment during renal failure with advanced secondary hyperparathyroidism

Calcitriol is a standard therapy for secondary hyperparathyroidism in chronic renal failure. We evaluated whether the effect of daily or intermittent calcitriol administration is more efficient in enhancing bone growth in renal failure with advanced secondary hyperparathyroidism in weanling 5/6 nephrectomized rats loaded with phosphorus to induce severe secondary hyperparathyroidism. The animals were treated daily or three times weekly with calcitriol for 4 weeks but the total weekly dose of calcitriol was the same. Although calcitriol increased the serum calcium, it did not lower parathyroid hormone (PTH) or improve tibia and body length. Animals with renal failure and advanced secondary hyperparathyroidism had decreased PTH/PTHrP, which was accompanied by an increase in the cyclin kinase inhibitor p57(Kip2). Calcitriol treatment upregulated the PTH/PTHrP receptor but also increased inhibitors of cell proliferation such as p21(Waf1/Cip1), IGFBP3, and FGFR3. Calcitriol also enhanced markers of chondrocyte differentiation, such as IGF1, Vitamin D receptor, FGF23, and bone morphogenetic protein-7. Receptor activator of nuclear factor-kappabeta ligand levels improved with calcitriol treatment but without changes in osteoprotegerin suggesting an enhancement of osteo/chondroclastogenesis and mineralization. Overall, both daily and intermittent calcitriol had similar effects on endochondral bone growth in phosphorus-loaded rats with renal failure.

C-Type Natriuretic Peptide Regulates Cellular Condensation and Glycosaminoglycan Synthesis during Chondrogenesis

C-type natriuretic peptide (CNP) has recently been identified as a key anabolic regulator of endochondral bone growth, but the cellular and molecular mechanisms involved are incompletely understood. Although CNP has been shown to stimulate proliferation and hypertrophic differentiation of growth plate chondrocytes, it is unknown whether CNP affects the earliest stages of endochondral bone development, condensation of mesenchymal precursor cells, and chondrogenesis. Here we demonstrate that CNP increases the number of chondrogenic condensations of mouse embryonic limb bud cells in micromass culture. This is accompanied by increased expression of the cell adhesion molecule N-cadherin. In addition, CNP stimulates glycosaminoglycan synthesis as indicated by increased Alcian blue staining. However, expression of the chondrogenic transcription factors Sox9, -5, and -6 or of the main extracellular matrix genes encoding collagen II and aggrecan is not affected by CNP. Instead, we show that CNP increases expression of enzymes involved in chondroitin sulfate synthesis, a required step in the production of cartilage glycosaminoglycans. In summary, we demonstrate a novel role of CNP in promoting chondrogenesis by stimulating expression of molecules involved in cell adhesion molecules and glycosaminoglycan synthesis.

C-Type Natriuretic Peptide Forms in the Ovine Fetal and Maternal Circulations: Evidence for Independent Regulation and Reciprocal Response to Undernutrition

C-type natriuretic peptide (CNP) has a crucial role in postnatal endochondral bone growth and is rapidly responsive to changes in nutrition. Although CNP is expressed in the placenta, little is known about the regulation and role of CNP in fetal-maternal health. We hypothesized that CNP may be similarly responsive to undernutrition in the growing fetus, in which maternal nutrition is crucial to normal growth and development. We therefore studied maternal and fetal CNP and the aminoterminal (bioinactive) fragment of proCNP (NTproCNP) in 39 chronically catheterized pregnant sheep before and after a 3-d maternal fast from 121 d gestation. Maternal CNP and NTproCNP levels were higher than in the fetus (CNP 12-fold, NTproCNP 1.5-fold, both P < 0.001). The ratio of NTproCNP to CNP was higher in the fetus than the mother (53 +/- 3 vs. 8.7 +/- 0.6, P < 0.001), suggesting enhanced synthesis and/or degradation of CNP in the fetus. As in postnatal lambs, fetal plasma CNP forms fell promptly during maternal fasting. In contrast, maternal levels exhibited reciprocal and contemporaneous increase, which was reversed by refeeding. Uteroplacental production of CNP was suggested by a high venoarterial concentration gradient across the gravid uterus, and a correlation between maternal NTproCNP levels and placental weight (r(2) = 0.26, P = 0.01). These studies provide the first evidence that CNP is regulated independently in the fetus. Reciprocal increases in maternal CNP forms may reflect the response of the uteroplacental unit to substrate deficiency. CNP may have a role in maintaining fetal welfare and provides a possible marker of uteroplacental nutrient supply.

C-type natriuretic peptide regulates endochondral bone growth through p38 MAP kinase-dependent and -independent pathways.

BackgroundC-type natriuretic peptide (CNP) has recently been identified as an important anabolic regulator of endochondral bone growth, but the molecular mechanisms mediating its effects are not completely understood.ResultsWe demonstrate in a tibia organ culture system that pharmacological inhibition of p38 blocks the anabolic effects of CNP. We further show that CNP stimulates endochondral bone growth largely through expansion of the hypertrophic zone of the growth plate, while delaying mineralization. Both effects are reversed by p38 inhibition. We also performed Affymetrix microarray analyses on micro-dissected tibiae to identify CNP target genes. These studies confirmed that hypertrophic chondrocytes are the main targets of CNP signaling in the growth plate, since many more genes were regulated by CNP in this zone than in the others. While CNP receptors are expressed at similar levels in all three zones, cGMP-dependent kinases I and II, important transducers of CNP signaling, are expressed at much higher levels in hypertrophic cells than in other areas of the tibia, providing a potential explanation for the spatial distribution of CNP effects. In addition, our data show that CNP induces the expression of NPR3, a decoy receptor for natriuretic peptides, suggesting the existence of a feedback loop to limit CNP signaling. Finally, detailed analyses of our microarray data showed that CNP regulates numerous genes involved in BMP signaling and cell adhesion.ConclusionOur data identify novel target genes of CNP and demonstrate that the p38 pathway is a novel, essential mediator of CNP effects on endochondral bone growth, with potential implications for understanding and treatment of numerous skeletal diseases.

Overexpression of the C-type natriuretic peptide (CNP) is associated with overgrowth and bone anomalies in an individual with balanced t(2;7) translocation

Longitudinal bone growth is determined by the process of endochondral ossification in the cartilaginous growth plate, which is located at both ends of vertebrae and long bones and involves many systemic hormones and local regulators. We report the molecular characterization of a de novo balanced t(2;7)(q37.1;q21.3) translocation in a young female with Marfanoid habitus and skeletal anomalies. The translocation was characterized by fluorescence in situ hybridization (FISH), checked for other abnormalities by array-comparative genomic hybridization (CGH), and finally, the breakpoints were cloned, sequenced, and compared. Biochemical dosage was applied to study the possible mechanisms that may cause the proposita's phenotype. The breakpoint on chromosome 2 disrupts the hypothetical gene MGC42174 (HUGO-approved symbol DIS3L2) and is located in the proximity of the NPPC gene coding for C-type natriuretic peptide (CNP), a molecule that regulates endochondral bone growth. CNP plasma concentration was doubled in the proband compared to five normal controls, while NPPC was substantially overexpressed in her fibroblasts. A transgenic mouse generated to target NPPC overexpression in bone showed a phenotype highly reminiscent of the patient's phenotype. The breakpoint on chromosome 7 is localized proximally at about 75 kb from the COL1A2 gene. The COL1A2 allele on the derivative chromosome was strongly underexpressed in fibroblasts, but total collagen was not significantly different from controls. Several evidences support the conclusion that the proband's abnormal phenotype is associated with C-type natriuretic peptide overexpression.

Arthropathy of neonatal onset multisystem inflammatory disease (NOMID/CINCA)

Neonatal onset multisystem inflammatory disease (NOMID), an autoinflammatory disease, is characterized by fever, chronic urticarial rash, CNS manifestations, and arthropathy. Approximately 50% of patients with NOMID have de novo missense mutations in CIAS1, which is associated with modulation of the IL-1b and apoptotic pathways. Approximately 60% of NOMID patients have prominent arthropathy, most commonly involving the knees, the cause of which remains poorly understood. To more fully describe the findings of NOMID arthropathy on MRI and radiography and to provide a better understanding of the origin of the bony lesions. We imaged 20 patients with NOMID to further investigate NOMID-associated bony lesions. Bony abnormalities were seen in the knees of 11/20 patients. The knee findings included enlarged, deformed femora and patellae in all and tibiae in the majority, without evidence of synovitis. Some patients had other joint involvement. Most had short stature and valgus or varus knee deformities. No association was noted between bony abnormalities and CIAS1 mutations. The abnormalities appeared to be the result of a mass-producing process. The resulting heterogeneously calcified masses appeared to originate in the physis and deformed the adjacent metaphysis and epiphysis. These findings suggest that the arthropathy of NOMID is the result of abnormal endochondral bone growth. Further investigation is needed to determine whether this deformity is triggered by inflammation early in development or by CIAS1 mutations causing abnormal chondrocyte apoptosis.

Dexamethasone stimulates expression of C-type Natriuretic Peptide in chondrocytes

BackgroundGrowth of endochondral bones is regulated through the activity of cartilaginous growth plates. Disruption of the physiological patterns of chondrocyte proliferation and differentiation – such as in endocrine disorders or in many different genetic diseases (e.g. chondrodysplasias) – generally results in dwarfism and skeletal defects. For example, glucocorticoid administration in children inhibits endochondral bone growth, but the molecular targets of these hormones in chondrocytes remain largely unknown. In contrast, recent studies have shown that C-type Natriuretic Peptide (CNP) is an important anabolic regulator of cartilage growth, and loss-of-function mutations in the human CNP receptor gene cause dwarfism. We asked whether glucocorticoids could exert their activities by interfering with the expression of CNP or its downstream signaling components.MethodsPrimary mouse chondrocytes in monolayer where incubated with the synthetic glucocorticoid Dexamethasone (DEX) for 12 to 72 hours. Cell numbers were determined by counting, and real-time PCR was performed to examine regulation of genes in the CNP signaling pathway by DEX.ResultsWe show that DEX does influence expression of key genes in the CNP pathway. Most importantly, DEX significantly increases RNA expression of the gene encoding CNP itself (Nppc). In addition, DEX stimulates expression of Prkg2 (encoding cGMP-dependent protein kinase II) and Npr3 (natriuretic peptide decoy receptor) genes. Conversely, DEX was found to down-regulate the expression of the gene encoding its receptor, Nr3c1 (glucocorticoid receptor), as well as the Npr2 gene (encoding the CNP receptor).ConclusionOur data suggest that the growth-suppressive activities of DEX are not due to blockade of CNP signaling. This study reveals a novel, unanticipated relationship between glucocorticoid and CNP signaling and provides the first evidence that CNP expression in chondrocytes is regulated by endocrine factors.

A Novel Mutation in FGFR3 Causes Camptodactyly, Tall Stature, and Hearing Loss (CATSHL) Syndrome

Activating mutations of FGFR3, a negative regulator of bone growth, are well known to cause a variety of short-limbed bone dysplasias and craniosynostosis syndromes. We mapped the locus causing a novel disorder characterized by camptodactyly, tall stature, scoliosis, and hearing loss (CATSHL syndrome) to chromosome 4p. Because this syndrome recapitulated the phenotype of the Fgfr3 knockout mouse, we screened FGFR3 and subsequently identified a heterozygous missense mutation that is predicted to cause a p.R621H substitution in the tyrosine kinase domain and partial loss of FGFR3 function. These findings indicate that abnormal FGFR3 signaling can cause human anomalies by promoting as well as inhibiting endochondral bone growth.