Growth hormone and IGF-I stimulate cell function in distinct zones of the rat epiphyseal growth plate

Promotion of Joint Degeneration and Chondrocyte Metabolic Dysfunction by Excessive Growth Hormone in Mice

OBJECTIVE

Many patients with acromegaly, a hormonal disorder with excessive growth hormone (GH) production, report pain in joints. We undertook this study to characterize the joint pathology of mice with overexpression of bovine GH (bGH) or a GH receptor antagonist (GHa) and to investigate the effect of GH on regulation of chondrocyte cellular metabolism.

METHODS

Knee joints from mice overexpressing bGH or GHa and wild-type (WT) control mice were examined using histology and micro-computed tomography for osteoarthritic (OA) pathologies. Additionally, cartilage from bGH mice was used for metabolomics analysis. Mouse primary chondrocytes from bGH and WT mice, with or without pegvisomant treatment, were used for quantitative polymerase chain reaction and Seahorse respirometry analyses.

RESULTS

Both male and female bGH mice at ~13 months of age had increased knee joint degeneration, which was characterized by loss of cartilage structure, expansion of hypertrophic chondrocytes, synovitis, and subchondral plate thinning. The joint pathologies were also demonstrated by significantly higher Osteoarthritis Research Society International and Mankin scores in bGH mice compared to WT control mice. Metabolomics analysis revealed changes in a wide range of metabolic pathways in bGH mice, including beta-alanine metabolism, tryptophan metabolism, lysine degradation, and ascorbate and aldarate metabolism. Also, bGH chondrocytes up-regulated fatty acid oxidation and increased expression of Col10a. Joints of GHa mice were remarkably protected from developing age-associated joint degeneration, with smooth articular joint surface.

CONCLUSION

This study showed that an excessive amount of GH promotes joint degeneration in mice, which was associated with chondrocyte metabolic dysfunction and hypertrophic changes, whereas antagonizing GH action through a GHa protects mice from OA development.

Short and Long-Term Effects of Growth Hormone in Children and Adolescents With GH Deficiency

The syndrome of impaired GH secretion (GH deficiency) in childhood and adolescence had been identified at the end of the 19th century. Its non-acquired variant (naGHD) is, at childhood onset, a rare syndrome of multiple etiologies, predominantly characterized by severe and permanent growth failure culminating in short stature. It is still difficult to diagnose GHD and, in particular, to ascertain impaired GH secretion in comparison to levels in normally-growing children. The debate on what constitutes an optimal diagnostic process continues. Treatment of the GH deficit via replacement with cadaveric pituitary human GH (pit-hGH) had first been demonstrated in 1958, and opened an era of therapeutic possibilities, albeit for a limited number of patients. In 1985, the era of recombinant hGH (r-hGH) began: unlimited supply meant that substantial long-term experience could be gained, with greater focus on efficacy, safety and costs. However, even today, the results of current treatment regimes indicate that there is still a substantial fraction of children who do not achieve adult height within the normal range. Renewed evaluation of height outcomes in childhood-onset naGHD is required for a better understanding of the underlying causes, whereby the role of various factors - diagnostics, treatment modalities, mode of treatment evaluation - during the important phases of child growth - infancy, childhood and puberty - are further explored.

Effects of GH/IGF axis on bone and cartilage

Growth hormone (GH) and its mediator, the insulin-like growth factor-1 (IGF-1) regulate somatic growth, metabolism and many aspects of aging. As such, actions of GH/IGF have been studied in many tissues and organs over decades. GH and IGF-1 are part of the hypothalamic/pituitary somatotrophic axis that consists of many other regulatory hormones, receptors, binding proteins, and proteases. In humans, GH/IGF actions peak during pubertal growth and regulate skeletal acquisition through stimulation of extracellular matrix production and increases in bone mineral density. During aging the activity of these hormones declines, a state called somatopaguss, which associates with deleterious effects on the musculoskeletal system. In this review, we will focus on GH/IGF-1 action in bone and cartilage. We will cover many studies that have utilized congenital ablation or overexpression of members of this axis, as well as cell-specific gene-targeting approaches used to unravel the nature of the GH/IGF-1 actions in the skeleton in vivo.

Spirulina Enhances Bone Modeling in Growing Male Rats by Regulating Growth-Related Hormones

In recent years, growth hormone deficiency in children has been treated with hormone therapy despite the possible significant side effects. Therefore, it was deemed beneficial to develop functional foods or dietary supplements for safely improving children's growth. Spirulina platensis is known for its high antioxidant, anti-aging, anti-cancer, and immunity-enhancing properties, as well as its high digestibility and high protein content, but little has been reported about its influence on bone development in children with a normal supply of protein. In this study, we evaluated the effects of spirulina on the bone metabolism and antioxidant profiles of three-week-old growing male rats. The animals were divided into four groups (n = 17 per group) and were fed AIN93G diets with 0% (control), 30% (SP30), 50% (SP50), and 70% (SP70) of casein protein replaced by spirulina, respectively, for seven weeks. We observed that spirulina enhanced bone growth and bone strength by stimulating parathyroid hormone and growth hormone activities, as well its increased antioxidant activity. These results indicate that spirulina provides a suitable dietary supplement and alternative protein source with antioxidant benefits for growth improvement in early developmental stages.

Bioactive IGF-1 release from collagen-GAG scaffold to enhance cartilage repair in vitro

Tissue engineering is a promising technique for cartilage repair. Toward this goal, a porous collagen-glycosaminoglycan (CG) scaffold was loaded with different concentrations of insulin-like growth factor-1 (IGF-1) and evaluated as a growth factor delivery device. The biological response was assessed by monitoring the amount of type II collagen and proteoglycan synthesised by the chondrocytes seeded within the scaffolds. IGF-1 release was dependent on the IGF-1 loading concentration used to adsorb IGF-1 onto the CG scaffolds and the amount of IGF-1 released into the media was highest at day 4. This initial IGF-1 release could be modelled using linear regression analysis. Osteoarthritic (OA) chondrocytes seeded within scaffolds containing adsorbed IGF-1 deposited decorin and type II collagen in a dose dependent manner and the highest type II collagen deposition was achieved via loading the scaffold with 50 μg/ml IGF-1. Cells seeded within the IGF-1 loaded scaffolds also deposited more extracellular matrix than the no growth factor control group thus the IGF-1 released from the scaffold remained bioactive and exerted an anabolic effect on OA chondrocytes. The effectiveness of adsorbing IGF-1 onto the scaffold may be due to protection of the molecule from proteolytic digestion allowing a more sustained release of IGF-1 over time compared to adding multiple doses of exogenous growth factor. Incorporating IGF-1 into the CG scaffold provided an initial therapeutic burst release of IGF-1 which is beneficial in initiating ECM deposition and repair in this in vitro model and shows potential for developing this delivery device in vivo.

Fibroblast growth factor receptor 3 effects on proliferation and telomerase activity in sheep growth plate chondrocytes

BACKGROUND

Fibroblast growth factor receptor 3 (FGFR3) inhibits growth-plate chondrocyte proliferation and limits bone elongation. Gain-of-function FGFR3 mutations cause dwarfism, reduced telomerase activity and shorter telomeres in growth plate chondroyctes suggesting that FGFR3 reduces proliferative capacity, inhibits telomerase, and enhances senescence. Thyroid hormone (T3) plays a role in cellular maturation of growth plate chondrocytes and a known target of T3 is FGFR3. The present study addressed whether reduced FGFR3 expression enhanced telomerase activity, mRNA expression of telomerase reverse transcriptase (TERT) and RNA component of telomerase (TR), and chondrocyte proliferation, and whether the stimulation of FGFR3 by T3 evoked the opposite response.

RESULTS

Sheep growth-plate proliferative zone chondrocytes were cultured and transfected with siRNA to reduce FGFR3 expression; FGFR3 siRNA reduced chondrocyte FGFR3 mRNA and protein resulting in greater proliferation and increased TERT mRNA expression and telomerase activity (p < 0.05). Chondrocytes treated with T3 significantly enhanced FGFR3 mRNA and protein expression and reduced telomerase activity (p < 0.05); TERT and TR were not significantly reduced. The action of T3 at the growth plate may be partially mediated through the FGFR3 pathway.

CONCLUSIONS

The results suggest that FGFR3 inhibits chondrocyte proliferation by down-regulating TERT expression and reducing telomerase activity indicating an important role for telomerase in sustaining chondrocyte proliferative capacity during bone elongation.

Growth cartilage expression of growth hormone/insulin-like growth factor I axis in spontaneous and growth hormone induced catch-up growth

INTRODUCTION

Catch-up growth following the cessation of a growth inhibiting cause occurs in humans and animals. Although its underlying regulatory mechanisms are not well understood, current hypothesis confer an increasing importance to local factors intrinsic to the long bones' growth plate (GP).

AIM

The present study was designed to analyze the growth-hormone (GH)-insulin-like growth factor I (IGF-I) axis in the epiphyseal cartilage of young rats exhibiting catch-up growth as well as to evaluate the effect of GH treatment on this process.

MATERIAL AND METHODS

Female Sprague-Dawley rats were randomly grouped: controls (group C), 50% diet restriction for 3 days+refeeding (group CR); 50% diet restriction for 3 days+refeeding & GH treatment (group CRGH). Analysis of GH receptor (GHR), IGF-I, IGF-I receptor (IGF-IR) and IGF binding protein 5 (IGFBP5) expressions by real-time PCR was performed in tibial growth plates extracted at the time of catch-up growth, identified by osseous front advance greater than that of C animals.

RESULTS

In the absence of GH treatment, catch-up growth was associated with increased IGF-I and IGFBP5 mRNA levels, without changes in GHR or IGF-IR. GH treatment maintained the overexpression of IGF-I mRNA and induced an important increase in IGF-IR expression.

CONCLUSIONS

Catch-up growth that happens after diet restriction might be related with a dual stimulating local effect of IGF-I in growth plate resulting from overexpression and increased bioavailability of IGF-I. GH treatment further enhanced expression of IGF-IR which likely resulted in a potentiation of local IGF-I actions. These findings point out to an important role of growth cartilage GH/IGF-I axis regulation in a rat model of catch-up growth.

Binding and release characteristics of insulin-like growth factor-1 from a collagen-glycosaminoglycan scaffold

Tissue engineering is a promising technique for cartilage repair, but to optimize novel scaffolds before clinical trials, it is necessary to determine their characteristics for binding and release of growth factors. Toward this goal, a novel, porous collagen-glycosaminoglycan scaffold was loaded with a range of concentrations of insulin-like growth factor-1 (IGF-1) to evaluate its potential as a controlled delivery device. The kinetics of IGF-1 adsorption and release from the scaffold was demonstrated using radiolabeled IGF-1. Adsorption was rapid, and was approximately proportional to the loading concentration. Ionic bonding contributed to this interaction. IGF-1 release was studied over 14 days to compare the release profiles from different loading groups. Two distinct phases occurred: first, a burst release of up to 44% was noted within the first 24 h; then, a slow, sustained release (13%-16%) was observed from day 1 to 14. When the burst release was subtracted, the relative percentage of remaining IGF-1 released was similar for all loading groups and broadly followed t(½) kinetics until approximately day 6. Scaffold cross-linking using dehydrothermal treatment did not affect IGF-1 adsorption or release. Bioactivity of released IGF-1 was confirmed by seeding scaffolds (preadsorbed with unlabeled IGF-1) with human osteoarthritic chondrocytes and demonstrating increased proteoglycan production in vitro.

Age- and site-specific decline in insulin-like growth factor-I receptor expression is correlated with differential growth plate activity in the mouse hindlimb

The proximal and distal growth plates of the principal long bones do not contribute equally to longitudinal growth. Most forelimb elongation occurs at the shoulder and wrist, while most hindlimb growth occurs at the knee. This study examined whether insulin-like growth factor-I (IGF-I), a potent growth regulator, could underlie this variation via differential receptor expression. The spatiotemporal distribution of the IGF-I receptor (IGF-IR) was mapped in hindlimb growth plates (overall and within regional zones) from immature mice using immunohistochemistry. Growth activity was assessed by size/morphology of the growth plate and proliferating cell nuclear antigen (PCNA) expression. Both IGF-IR and PCNA staining declined considerably with age in the proximal femur and distal tibia (hip and ankle), but expression remained high in the more active distal femur and proximal tibia (knee) throughout growth. Growth plate size decreased with age in all sites, but the absolute and relative decline in IGF-IR in the hips and ankles of older mice indicated a site-specific loss of IGF-I sensitivity in these less active regions. These results suggest that regulation of the IGF-IR may at least partially mediate differential long bone growth, thereby providing a local mechanism for altering skeletal proportions absent modification of systemic hormone levels.

Enhanced repair of extensive articular defects by insulin-like growth factor-I-laden fibrin composites

Stem cells indigenous to the cancellous spaces of the bone bed in an acute injury provide an important source of pluripotent cells for cartilage repair. Insulin-like growth factor-I facilitates chondrogenesis of bone marrow-derived stem cells in long-term culture and may enhance chondrogenesis in healing cartilage lesions in vivo. This study examined the impact of insulin-like growth factor-I, gradually released from fibrin clots polymerized in situ, on the recruitable stem-cell pool in a full-thickness critical cartilage defect model. Twelve full-thickness 15-mm cartilage lesions in the femoropatellar articulations of six young mature horses were repaired by an injection of autogenous fibrin containing 25 microg of human recombinant insulin-like growth factor-I or, in control joints, fibrin without the growth factor. All horses were killed at 6 months, and cartilage repair tissue and surrounding cartilage were assessed by histology, histochemistry, types I and II collagen immunohistochemistry, types I and II collagen in situ hybridization, and matrix biochemical determinations. White tissue filled grafted and control lesions, with the growth factor-treated defects being more completely filled and securely attached to the subchondral bone. A moderately improved chondrocyte population, more columnar cellular organization, and better attachment to the underlying bone were evident on histological evaluation of growth factor-treated defects. Type-II procollagen mRNA was abundantly present in the deeper half of the treated sections compared with moderate message expression in control tissues. Immunolocalization of type-II collagen showed a preponderance of the collagen in growth factor-treated lesions, confirming translation of type-II message to protein. Composite histologic healing scores for treated defects were significantly improved over those for control defects. DNA content in the cartilage defects was similar in treated and control joints. Matrix proteoglycan content was similar in treated and control defects and lower in the defects than in the intact surrounding and remote cartilage of the treated and control joints. The proportion of type-II collagen significantly increased in growth factor-treated tissues. Fibrin polymers laden with insulin-like growth factor-I improved the histologic appearance and the proportion of type-II collagen in healing, full-thickness cartilage lesions. However, none of the biochemical or morphologic features were consistent with those of normal articular cartilage.

Identification and cloning of a novel phosphatase expressed at high levels in differentiating growth plate chondrocytes

Growth plate chondrocytes progress through a proliferative phase before acquiring a terminally-differentiated phenotype. In this study we used Percoll density gradients to separate chick growth plate chondrocytes into populations of different maturational phenotype. By applying agarose gel differential display to these populations we cloned a cDNA encoding a novel 268 amino acid protein (3X11A). 3X11A contains two peptide motifs that are conserved in a recently identified superfamily of phosphotransferases. It is likely that 3X11A is a phosphatase, but its substrate specificity remains uncertain. 3X11A expression is upregulated 5-fold during chondrocyte terminal differentiation and its expression is approximately 100-fold higher in hypertrophic chondrocytes than in non-chondrogenic tissues. This suggests that 3X11A participates in a biochemical pathway that is particularly active in differentiating chondrocytes.