Chondrocyte terminal differentiation, apoptosis, and type X collagen expression are downregulated by parathyroid hormone

Genome-Wide Association Studies for Body Conformation Traits in Korean Holstein Population

The objective of this study was to identify quantitative trait loci (QTL) and nearby candidate genes that influence body conformation traits. Phenotypic data for 24 body conformation traits were collected from a population of 2329 Korean Holstein cattle, and all animals were genotyped using the 50 K Illumina bovine SNP chip. A total of 24 genome-wide significant SNPs associated with 24 body conformation traits were identified by genome-wide association analysis. The selection of the most promising candidate genes was based on gene ontology (GO) terms and the previously identified functions that influence various body conformation traits as determined in our study. These genes include KCNA1, RYBP, PTH1R, TMIE, and GNAI3 for body traits; ANGPT1 for rump traits; MALRD1, INHBA, and HOXA13 for feet and leg traits; and CDK1, RHOBTB1, and SLC17A1 for udder traits, respectively. These findings contribute to our understanding of the genetic basis of body conformation traits in this population and pave the way for future breeding strategies aimed at enhancing desirable traits in dairy cattle.

A Novel Heterozygous Missense Variant in Parathyroid Hormone 1 is Related to the Occurrence of Developmental Dysplasia of the Hip

Introduction: Developmental dysplasia of the hip (DDH) is one of the most common diseases in the pediatric orthopedics, with an incidence of 1-5%. Genetic factors are the bases of the pathogenesis of DDH, but the pathogenic variants and pathogenesis of DDH are still unknown. There are no key accurate diagnostic or prognostic molecular markers for DDH. The purpose of our study was to screen for genetic variant associated with DDH and explore its pathogenesis. Materials and Methods: The genetic variation of DDH was tested by variant NGS-based exome analyses, verified by the Sanger sequencing. Results: A four-generation family in which DDH was present in three generations was recruited. A novel heterozygous missense variant c.629C>T (p.(Ala210Val)) in exon 7/8 of the parathyroid hormone 1 receptor (PTH1R) gene was identified through screening of two affected and one unaffected family members. The candidate variant was validated in all available family members with all three affected members being positive for the PTH1R variant. Conclusion: Our results are highly supportive of PTH1R as a novel candidate gene for DDH and demonstrated that the combination of pedigree information and next-generation sequencing is an effective method for identifying pathogenic variants associated with DDH.

An updated view on Temporomandibular Joint degeneration: insights from the cell subsets of mandibular condylar cartilage

The high prevalence of temporomandibular joint osteoarthritis (TMJOA), which causes joint dysfunction, indicates the need for more effective methods for treatment and repair. Mandibular condylar cartilage (MCC), a typical fibrocartilage that experiences degenerative changes during the development of TMJOA, has become a research focus and therapeutic target in recent years. MCC is composed of four zones of cells at various stages of differentiation. The cell subsets in MCC exhibit different physiological and pathological characteristics during development and in TMJOA. Most studies of TMJOA are mainly concerned with gene regulation of pathological changes. The corresponding treatment targets with specific cell subsets in MCC may provide more accurate and reliable results for cartilage repair and TMJOA treatment. In this review, we summarized the current research progress on the cell subsets of MCC from the perspective of MCC development and degeneration. We hope to provide a reference for further exploration of the pathological process of TMJOA and improvement of TMJOA treatment.

3D bio-printed biphasic scaffolds with dual modification of silk fibroin for the integrated repair of osteochondral defects

Repair of osteochondral defects is still a challenge, especially the regeneration of hyaline cartilage. Parathyroid hormone (PTH) can inhibit the hypertrophy of chondrocytes to maintain the phenotype of hyaline cartilage. Here, we aimed to construct a bio-printed biphasic scaffold with a mechanical gradient based on dual modification of silk fibroin (SF) for the integrated repair of osteochondral defects. Briefly, SF was grafted with PTH (SF-PTH) and covalently immobilized with methacrylic anhydride (SF-MA), respectively. Next, gelatin methacryloyl (GM) mixed with SF-PTH or SF-MA was used as a bio-ink for articular cartilage and subchondral bone regeneration. Finally, the GM + SF-PTH/GM + SF-MA osteochondral biphasic scaffold was constructed using 3D bioprinting technology, and implanted in a rabbit osteochondral defect model. In this study, the SF-PTH bio-ink was synthesized for the first time. In vitro results indicated that the GM + SF-MA bio-ink had good mechanical properties, while the GM + SF-PTH bio-ink inhibited the hypertrophy of chondrocytes and was beneficial for the production of hyaline cartilage extracellular matrix. Importantly, an integrated GM + SF-PTH/GM + SF-MA biphasic scaffold with a mechanical gradient was successfully constructed. The results in vivo demonstrated that the GM + SF-PTH/GM + SF-MA scaffold could promote the regeneration of osteochondral defects and maintain the phenotype of hyaline cartilage to a large extent. Collectively, our results indicate that the integrated GM + SF-PTH/GM + SF-MA biphasic scaffold constructed by 3D bioprinting is expected to become a new strategy for the treatment of osteochondral defects.

PPAR-δ Agonist With Mesenchymal Stem Cells Induces Type II Collagen-Producing Chondrocytes in Human Arthritic Synovial Fluid

Osteoarthritis (OA) is an inflammatory joint disease characterized by degeneration of articular cartilage within synovial joints. An estimated 27 million Americans suffer from OA, and the population is expected to reach 67 million in the United States by 2030. Thus, it is urgent to find an effective treatment for OA. Traditional OA treatments have no disease-modifying effect, while regenerative OA therapies such as autologous chondrocyte implantation show some promise. Nonetheless, current regenerative therapies do not overcome synovial inflammation that suppresses the differentiation of mesenchymal stem cells (MSCs) to chondrocytes and the expression of type II collagen, the major constituent of functional cartilage. We discovered a synergistic combination that overcame synovial inflammation to form type II collagen-producing chondrocytes. The combination consists of peroxisome proliferator–activated receptor (PPAR) δ agonist, human bone marrow (hBM)-derived MSCs, and hyaluronic acid (HA) gel. Interestingly, those individual components showed their own strong enhancing effects on chondrogenesis. GW0742, a PPAR-δ agonist, greatly enhanced MSC chondrogenesis and the expression of type II collagen and glycosaminoglycan (GAG) in hBM-MSC-derived chondrocytes. GW0742 also increased the expression of transforming growth factor β that enhances chondrogenesis and suppresses cartilage fibrillation, ossification, and inflammation. HA gel also increased MSC chondrogenesis and GAG production. However, neither GW0742 nor HA gel could enhance the formation of type II collagen-producing chondrocytes from hBM-MSCs within human OA synovial fluid. Our data demonstrated that the combination of hBM-MSCs, PPAR-δ agonist, and HA gel significantly enhanced the formation of type II collagen-producing chondrocytes within OA synovial fluid from 3 different donors. In other words, the novel combination of PPAR-δ agonist, hBM-MSCs, and HA gel can overcome synovial inflammation to form type II collagen cartilage within human OA synovial fluid. This novel articularly injectable formula could improve OA treatment in the future clinical application.

Polymorphisms in ten candidate genes are associated with conformational and locomotive traits in Spanish Purebred horses

The Spanish Purebred horses, also known as Andalusian horses, compete to the highest standards in international dressage events. Gait and conformation could be used as early selection criteria to detect young horses with promising dressage ability. Although the genetic background of equine size variation has been recently uncovered, the genetic basis of horse conformational and locomotive traits is not known, hampered by the complex genetic architecture underlying quantitative traits and the lack of phenotypic data. The aim of this study was to validate the loci associated with size in 144 Spanish Purebred horses, and to seek novel associations between loci previously associated with the development of osteochondrosis (OC) lesions and 20 conformational and locomotive traits. Ten loci were associated with different conformational and locomotive traits (LCORL/NCAPG, HMGA2, USP31, MECR, COL24A1, MGP, FAM184B, PTH1R, KLF3 and SGK1), and the LCORL/NCAPG association with size in the Spanish Purebred horse was validated. Except for HMGA2, all polymorphisms seem to influence both the prevalence of OC lesions and morphological characters, supporting the link between conformation and OC. Also, the implication of most genes in either immune and inflammatory responses and cellular growth, or ossification processes, reinforces the role that these mechanisms have in the aetiology of OC, as well as their reflection on the general conformation of the individual. These polymorphisms could be used in marker-assisted selection (MAS) programmes to improve desirable conformational traits, but taking into account their possible detrimental effect on OC prevalence.

Effects of corticosterone on the metabolic activity of cultured chicken chondrocytes

Background

Corticosterone is one of the most crucial glucocorticoids (GCs) in poultry. Our previous study shows that corticosterone can retard the longitudinal growth of bones by depressing the proliferation and differentiation of chondrocytes in broilers. The present study was designed to investigate whether corticosterone affect the development of chondrocytes and the synthesis of collagen in vitro. The chondrocytes were isolated from proximal tibial growth plates of 6-week-old broiler chickens and cultured with different doses of corticosterone for 48 h. Then the cell viability, alkaline phosphatase (ALP) activity and the expression of parathyroid hormone-related peptide (PTHrP) and type X collagen (Col X) were detected.

Results

At 10⁻⁹-10⁻⁶ M concentration, corticosterone significantly inhibited the viability and differentiation of chondrocytes, as indicated by decreases in ALP and type X collagen expression. Conversely, there was completely opposite effect at 10⁻¹⁰ M. In addition, the expression of PTHrP was significantly downregulated at 10⁻⁶ M and 10⁻⁸ M, and was upregulated at 10⁻¹⁰ M.

Conclusions

The results suggested that corticosterone regulated chicken chondrocytes performance depending on its concentration with high concentrations inhibiting the viability and differentiation of chondrocytes and light concentrations promoting them, and these roles of corticosterone may be in part mediated through PTHrP.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-015-0398-5) contains supplementary material, which is available to authorized users.

Emerging genetic basis of osteochondritis dissecans

Genome-wide association studies (GWAS) provide an unbiased approach in the identification of genes that increase the risk for osteochondritis dissecans (OCD). Recent GWAS in humans, horses, and pigs are reviewed and genes identified. The identified genes tended to cluster with respect to function and biologic processes. GWAS in humans are a critical next step in the effort to provide a better understanding of the causes of OCD, which will, in turn, allow preventive strategies for treatment of adolescents and young adults who are at risk for the development of degenerative joint disease due to the effects of OCD.

KRT8, FAF1 and PTH1R gene polymorphisms are associated with leg weakness traits in pigs

The liability to lesions of dysfunctions of bone and joints in pigs, summarized as leg weakness and mostly expressed as osteochondrosis, is an animal welfare and economic issue in pig production. The objective of this study was to identify polymorphisms in the functional and positional candidate genes keratin 8 (KRT8), Fas-associated factor 1 (FAF1) and parathyroid hormone type I receptor (PTH1R) and to evaluate their association with leg weakness traits. Therefore, osteochondrosis lesions were scored in animals of a Duroc × Pietrain F2 population (DuPi; n = 310) and commercial herds of the breed Large White (n = 298). In addition, bone mineralization traits were observed in DuPi population. SNPs were identified in genes KRT8 (g.8,039G > A), FAF1 (g.380,914T > C) and PTH1R (c.1,672C > T). KRT8 showed significant association with bone mineral density and content (P ≤ 0.05). FAF1 was association with OC lesions score of all joints inspected (P ≤ 0.05). PTH1R showed significant dominance effects on OC lesion scores of the distal femur articular cartilage (P = 0.01) and epiphysis of the distal ulna (P = 0.05) as well as sums of scores of all joints (OCsum, P = 0.04) and assignment to groups of either severely or gently affected animals (OCcat, P = 0.01). This study reveals clear genetic-statistical evidence for a link of KRT8, FAF1 and PTH1R with some of leg weakness related traits in pigs.

The effect of type II collagen coating of chitosan fibrous scaffolds on mesenchymal stem cell adhesion and chondrogenesis

The biocompatibility of chitosan and its similarity to glycosaminoglycans (GAG) make it attractive for cartilage tissue engineering. We have previously reported improved chondrogenesis but limited cell adhesion on chitosan scaffolds. Our objectives were to produce chitosan scaffolds coated with different densities of type II collagen and to evaluate the effect of this coating on mesenchymal stem cell (MSC) adhesion and chondrogenesis. Chitosan fibrous scaffolds were obtained by a wet spinning method and coated with type II collagen at two different densities. A polyglycolic acid mesh served as a reference group. The scaffolds were characterized by Fourier-transform infrared spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and type II collagen content. Constructs were analyzed after MSCs seeding via live/dead assay, weight and DNA evaluations, SEM, and TEM. Constructs were cultured in chondrogenic medium for 21 days prior to quantitative analysis (weight, DNA, and GAG), SEM, TEM, histology, immunohistochemistry, and quantitative real time polymerase chain reaction. The cell attachment and distribution after seeding correlated with the density of type II collagen. The cell number, the matrix production, and the expression of genes specific for chondrogenesis were improved after culture in collagen coated chitosan constructs. These findings encourage the use of type II collagen for coating chitosan scaffolds to improve MSCs adhesion and chondrogenesis, and confirm the importance of biomimetic scaffolds for tissue engineering.

Effect of parathyroid hormone on type X and type II collagen expression in mesenchymal stem cells from osteoarthritic patients

A major drawback of current cartilage and intervertebral disc tissue engineering is that human mesenchymal stem cells (MSCs) from osteoarthritic (OA) patients express type X collagen (COL10), a marker of late-stage chondrocyte hypertrophy (associated with endochondral ossification). Parathyroid hormone (PTH) regulates endochondral ossification by inhibiting chondrocyte differentiation toward hypertrophy. In this study, we investigated the effect of PTH on expression of COL10 in MSCs from OA patients and analyzed the potential mechanisms related to its effect. MSCs were obtained from aspirates from the intramedullary canal of donors undergoing total hip replacement for OA. Expanded cells were then incubated for 0-48  h without (control) or with 100  nM PTH (1-34). Protein expression and phosphorylation were measured by Western blot. Results showed that PTH (1-34) inhibited expression of COL10 in MSCs from OA patients in a time-dependent manner. In parallel, PTH (1-34) stimulated expression of COL2, a marker of chondrogenic differentiation. Results also showed that PTH (1-34) inhibited in a sustained manner the phosphorylation of p38 and AKT protein kinase signaling pathways. Interestingly, the modulation of COL2 and COL10 gene expression was significant as rapidly as after 1  h in the presence of PTH (1-34); changes in the phosphorylation of p38 and AKT were significant only after 6  h. This suggests that while p38 and AKT protein kinase signaling pathways may not be required to initiate the regulation of expression of COL2 and COL10 by PTH (1-34), these pathways may modulate later events necessary for preventing precocious MSC hypertrophy.

Decrease in the expression of the type 1 PTH/PTHrP receptor (PTH1R) on chondrocytes in animals with osteoarthritis

BACKGROUND

To evaluate the expression of the type 1 PTH/PTHrP receptor (PTH1R) on chondrocytes from hyaline cartilage over the course of osteoarthritis (OA).

METHODS

In 12 NZW rabbits, the anterior cruciate ligament (ACL) was resected to create anterior instability of the knee. In 12 control rabbits, only a sham operation, without resection of the ACL, was performed. Four animals from each group were killed at 3, 6, and 12 weeks. After opening the knee joint, OA was macroscopically graded and hyaline cartilage of the load-bearing area was evaluated histologically according to the Mankin scale and by immunostaining for PTH1R.

RESULTS

There was a positive linear correlation between the time after surgery and the macroscopic and histologic OA scores. The scores in the control group were constant over the time course. Immunostaining showed significantly less expression of PTH1R in the experimental compared to the control group after 6 (P < 0.05) and 12 weeks (P < 0.01). In the experimental group, a negative linear correlation between PTH1R expression and macroscopic and histologic grades was found.

CONCLUSIONS

The results show an in vivo decrease in the expression of PTH1R on chondrocytes over the time course of OA. Further studies are needed to evaluate whether new treatment approaches could evolve from this knowledge.

PTH stimulated growth and decreased Col-X deposition are phosphotidylinositol-3,4,5 triphosphate kinase and mitogen activating protein kinase dependent in avian sterna

Type X collagen (Col-X) deposition is a marker of terminal differentiation during chondrogenesis, in addition to appositional growth and apoptosis. The parathyroid hormone/parathyroid hormone related peptide (PTH/PTHrP) receptor, or PPR, is a G-Protein coupled receptor (GPCR), which activates several downstream pathways, moderating chondrocyte differentiation, including suppression of Col-X deposition. An Avian sterna model was used to analyze the PPR GPCR downstream kinase role in growth rate and extracellular matrix (ECM) including Col-II, IX, and X. Phosphatidylinositol kinase (PI3K), mitogen activating protein kinase (MAPK) and protein kinase A (PKA) were inhibited with specific established inhibitors LY294002, PD98059, and H89, respectively to test the hypothesis that they could reverse/inhibit the PTH/PTHrP pathway. Excised E14 chick sterna were PTH treated with or without an inhibitor and compared to controls. Sternal length was measured every 24 hr. Cultured sterna were immuno-stained using specific antibodies for Col-II, IX, or X and examined via confocal microscopy. Increased growth in PTH-treated sterna was MAPK, PI3K, and PKA dose dependent, suggesting growth was regulated through multiple pathways. Col-X deposition was rescued in PTH-treated sterna in the presence of PI3K or MAPK inhibitors, but not with the PKA inhibitor. All three inhibitors moderately disrupted Col-II and Col-IX deposition. These results suggest that PTH can activate multiple pathways during chondrocyte differentiation.

Transcriptomic analysis identifies Foxo3A as a novel transcription factor regulating mesenchymal stem cell chrondrogenic differentiation

Multipotent mesenchymal stromal cells (MSC) are progenitor cells able to differentiate into several lineages including chondrocytes, and thus represent a suitable source of cells for cartilage engineering. However, the control of MSC differentiation to hypertrophy is a crucial step for the clinical application of MSC in cartilage repair where a stable chondrogenic phenotype without transition to terminal differentiation is the goal to achieve. This study aims at identifying new factors that may regulate this process. Using microarrays, we compared the transcriptional profiles of human MSC and MSC-derived chondrocytes obtained after culture in micropellets. After chondrogenesis induction, 676 genes were upregulated, among which five transcription factors not yet associated with chondrocyte differentiation of adult stem cells. These factors, in particular Foxo3A, are strongly expressed at day 21 and in mature chondrocytes. We investigated the role of Foxo3A using RNA interference. Our results revealed an important role of Foxo3A in the differentiation process of MSC toward chondrogenic fate, both in early and late stages. Indeed, stable Foxo3A knockdown tends to increase cell survival and decrease apoptosis, mainly in early stages of chondrogenesis. Importantly, we show that the loss of Foxo3A in MSC results in an increased expression level of markers specific for mature (aggrecan, collagen II) and hypertrophic (collagen X) chondrocytes. Therefore, our findings suggest that upregulation of Foxo3A over the course of chondrogenic differentiation plays a dual role, mainly inhibiting the differentiation process toward hypertrophy and promoting cell apoptosis.

Mustn1 is expressed during chondrogenesis and is necessary for chondrocyte proliferation and differentiation in vitro

Mustn1 encodes a small nuclear protein expressed specifically in the musculoskeletal system that was originally identified as a strongly up-regulated gene during bone regeneration, especially in fracture callus proliferating chondrocytes. Further experiments were undertaken to investigate its expression and role during chondrogenesis. Initially, whole mount mouse in situ hybridization was carried out and revealed Mustn1 expression in areas of active chondrogenesis that included limb buds, branchial arches and tail bud. To elucidate its function, experiments were carried out to perturb Mustn1 by overexpression and silencing in the pre-chondrocytic RCJ3.1C5.18 (RCJ) cell line. In these cells, Mustn1 is normally differentially regulated, with a spike in expression 2 days after induction of differentiation. Further, Mustn1 was successfully overexpressed in multiple RCJ cell lines by approximately 2-6 fold, and reduced to approximately 32-52% in silenced cell lines as compared to parental Mustn1 levels. Overexpressing, silenced, control, and parental RCJ cell lines were assayed for proliferation and differentiation. No statistically significant changes were observed in either proliferation or proteoglycan production when Mustn1 overexpressing lines were compared to parental and control. By contrast, both proliferation rate and differentiation were significantly reduced in Mustn1 silenced cell lines. Specifically, RNAi silenced cell lines showed reductions in populations of approximately 55-75%, and also approximately 34-40% less matrix (proteoglycan) production as compared to parental and random control lines. Further, this reduction in matrix production was accompanied by significant downregulation of chondrogenic marker genes, such as Sox9, Collagen type II (Col II), and Collagen type X (Col X). Lastly, reintroduction of Mustn1 into a silenced cell line rescued this phenotype, returning proliferation rate, matrix production, and chondrogenic marker gene expression back to parental levels. Taken together these data suggest that Mustn1 is a necessary regulator of chondrocyte function.

In vitro regulation of proliferation and differentiation within a postnatal growth plate of the cranial base by parathyroid hormone-related peptide (PTHrP)

Parathyroid hormone-related peptide (PTHrP) is known to be an important regulator of chondrocyte differentiation in embryonic growth plates, but little is known of its role in postnatal growth plates. The present study explores the role of PTHrP in regulating postnatal chondrocyte differentiation using a novel in vitro organ culture model based on the ethmoidal growth plate of the cranial base taken from the postnatal day 10 mouse. In vitro the ethmoidal growth plate continued to mineralize and the chondrocytes progressed to hypertrophy, as observed in vivo, but the proliferative zone was not maintained. Treatment with PTHrP inhibited mineralization and reduced alkaline phosphatase (ALP) activity in the hypertrophic zone in the ethmoidal growth plates grown ex vivo, and also increased the proliferation of non-hypertrophic chondrocytes. In addition, exogenous PTHrP reduced the expression of genes associated with terminal differentiation: type X collagen, Runx2, and ALP, as well as the PTH/PTHrP receptor (PPR). Activation of the protein kinase A pathway using 8-Br-cAMP mimicked some of these pro-proliferative/anti-differentiative effects of PTHrP. PTHrP and PPR were found to be expressed within the ethmoidal growth plate using semi-quantitative PCR, and in other cranial growth plates such as the spheno-occipital and pre-sphenoidal synchondroses. These results provide the first functional evidence that PTHrP regulates proliferation and differentiation within the postnatal, cranial growth plate. J. Cell. Physiol. 219: 688-697, 2009. (c) 2009 Wiley-Liss, Inc.

Peptide hormones as developmental growth and differentiation factors

Peptide hormones, usually considered to be endocrine factors responsible for communication between tissues remotely located from each other, are increasingly being found to be synthesized in developing tissues, where they act locally. Several hormones are now known to be produced in developing tissues that are unrelated to the endocrine gland of origin in the adult. These hormones are synthesized locally, and are active as differentiation and survival factors, before the developing adult endocrine tissue becomes functional. There is increasing evidence for paracrine and/or autocrine actions for these factors during development, thus, placing them among the conventional growth and differentiation factors. We review the evidence for the view that thyroid hormones, growth hormone, prolactin, insulin, and parathyroid hormone-related protein are developmental growth and differentiation factors.

Major biological obstacles for persistent cell-based regeneration of articular cartilage

Hyaline articular cartilage, the load-bearing tissue of the joint, has very limited repair and regeneration capacities. The lack of efficient treatment modalities for large chondral defects has motivated attempts to engineer cartilage constructs in vitro by combining cells, scaffold materials and environmental factors, including growth factors, signaling molecules, and physical influences. Despite promising experimental approaches, however, none of the current cartilage repair strategies has generated long lasting hyaline cartilage replacement tissue that meets the functional demands placed upon this tissue in vivo. The reasons for this are diverse and can ultimately result in matrix degradation, differentiation or integration insufficiencies, or loss of the transplanted cells and tissues. This article aims to systematically review the different causes that lead to these impairments, including the lack of appropriate differentiation factors, hypertrophy, senescence, apoptosis, necrosis, inflammation, and mechanical stress. The current conceptual basis of the major biological obstacles for persistent cell-based regeneration of articular cartilage is discussed, as well as future trends to overcome these limitations.

[Joint cartilage differentiation and osteoarthritis]

During skeletal development, the mechanisms of formation, differentiation and maturation of the cartilage are important steps in the skeleton morphogenesis; these mechanisms regulate growth of long bones and joint formation. Although cartilage in the growth plate and articular cartilage are very similar, they have some differences in the differentiation mechanisms. Growth plate cartilage regulates the growth of long bones by cartilage substitution of bone, while articular cartilage is maintained by delay of chondrocyte maturation and hypertrophy. Maybe, the mechanism of cartilage maturation is activated and increased during osteoarthritis, resulting in loss of the biomechanical properties required by the joints to resist the impact required by the skeleton to move.

PTHrP regulates growth plate chondrocyte differentiation and proliferation in a Gli3 dependent manner utilizing hedgehog ligand dependent and independent mechanisms

Growth plate chondrocytes undergo a tightly regulated process of differentiation, allowing for the longitudinal growth of bones. Although it is known that parathyroid hormone related protein (PTHrP) and Indian hedgehog regulate the differentiation of growth plate chondrocytes, how these pathways interact to regulate chondrocyte development is not fully elucidated. We examined how the interaction between PTHrP and the hedgehog activated transcription factors, Gli2 and Gli3, regulates growth plate chondrocyte differentiation and proliferation. Analysis of fetal limbs showed that Gli2 is a negative regulator and Gli3 a positive regulator of type X collagen expression. Limb explant cultures showed that PTHrP treatment inhibited type X collagen expression and increased chondrocyte proliferation. This effect was substantially enhanced in Gli2-/- limbs, was blocked in Gli3-/- limbs, and was only partially inhibited by hedgehog ligand blockade. PTHrP negatively regulated Gli mediated transcription in cell cultures, and regulated the level of the repressor form of Gli3 in a PKA dependent manner. These results show that PTHrP regulates growth plate chondrocyte proliferation and differentiation in part through the activity of Gli3, suggesting a crucial role for Gli3 in growth plate chondrocyte development.

Parathyroid hormone/parathyroid hormone-related peptide modulates growth of avian sternal cartilage via chondrocytic proliferation

Parathyroid hormone (PTH; 10(-7) to 10(-15) M) decreased terminal chondrogenesis in the avian sterna. During the first half of an 8-day culture, 100 nM PTH (1-34) significantly increased sternal length and downregulated the deposition of type X collagen and its mRNA expression. However, it remains unclear how PTH increased cartilaginous growth. In this study, we examined growth by both cell proliferation and analysis of cyclin d1 and collagen mRNA. Types II, IX, and X collagens and cyclin d1 mRNA were quantified through real-time RT-PCR, while Ki-67 was used as an immunohistochemical proliferation marker. Extracellular matrix content was measured through mRNA quantification of types II, IX, and X collagen and observing deposition of the same collagens. PTH significantly increased the proliferation marker Ki-67 in the sternal cephalic region. There was less type II and X collagen in PTH-treated sterna with concomitant decreases in mRNA production, suggesting that proliferation was the major contributor to cartilage growth in the presence of PTH/PTH-related peptide receptor activation. In conclusion, these experiments demonstrated that PTH increased cartilage growth by upregulating cell proliferation or other extracellular matrix components.