Growth hormone directly and indirectly stimulates articular chondrocyte cell growth

Excess Growth Hormone Triggers Inflammation-Associated Arthropathy, Subchondral Bone Loss, and Arthralgia

Growth hormone (GH) is a key mediator of skeletal growth. In humans, excess GH secretion due to pituitary adenoma, seen in patients with acromegaly, results in severe arthropathies. This study investigated the effects of long-term excess GH on the knee joint tissues. One year-old wild-type (WT) and bovine GH (bGH) transgenic mice were used as a model for excess GH. bGH mice showed increased sensitivity to mechanical and thermal stimuli, compared with WT mice. Micro-computed tomography analyses of the distal femur subchondral bone revealed significant reductions in trabecular thickness and significantly reduced bone mineral density of the tibial subchondral bone-plate that were associated with increased osteoclast activity in both male and female bGH compared with WT mice. bGH mice showed severe loss of matrix from the articular cartilage, osteophytosis, synovitis, and ectopic chondrogenesis. Articular cartilage loss in the bGH mice was associated with elevated markers of inflammation and chondrocyte hypertrophy. Finally, hyperplasia of synovial cells was associated with increased expression of Ki-67 and diminished p53 levels in the synovium of bGH mice. Unlike the low-grade inflammation seen in primary osteoarthritis, arthropathy caused by excess GH affects all joint tissues and triggers severe inflammatory response. Data of this study suggest that treatment of acromegalic arthropathy should involve inhibition of ectopic chondrogenesis and chondrocyte hypertrophy.

Proteomic, mechanical, and biochemical characterization of cartilage development

The objective of this work is to examine the development of porcine cartilage by analyzing its mechanical properties, biochemical content, and proteomics at different developmental stages. Cartilage from the knees of fetal, neonatal, juvenile, and mature pigs was analyzed using histology, mechanical testing, biochemical assays, fluorophore-assisted carbohydrate electrophoresis, and bottom-up proteomics. Mature cartilage has 2.2-times the collagen per dry weight of fetal cartilage, and fetal cartilage has 2.1-times and 17.9-times the glycosaminoglycan and DNA per dry weight of mature cartilage, respectively. Tensile and compressive properties peak in the juvenile stage, with a tensile modulus 4.7-times that of neonatal. Proteomics analysis reveals increases in collagen types II and III, while collagen types IX, XI, and XIV, and aggrecan decrease with age. For example, collagen types IX and XI decrease 9.4-times and 5.1-times, respectively from fetal to mature. Mechanical and biochemical measurements have their greatest developmental changes between the neonatal and juvenile stages, where mechanotransduction plays a major role. Bottom-up proteomics serves as a powerful tool for tissue characterization, showing results beyond those of routine biochemical analysis. For example, proteomic analysis shows significant drops in collagen types IX, XI, and XIV throughout development, which shows insight into the permanence of cartilage's matrix. Changes in overall glycosaminoglycan content compared to aggrecan and link protein indicate non-enzymatic degradation of aggrecan structures or hyaluronan in mature cartilage. In addition to tissue characterization, bottom-up proteomics techniques are critical in tissue engineering efforts toward repair or regeneration of cartilage in animal models. STATEMENT OF SIGNIFICANCE: In this study, the development of porcine articular cartilage is interrogated through biomechanical, biochemical, and proteomic techniques, to determine how mechanics and extracellular matrix composition change from fetal to mature cartilage. For the first time, a bottom-up proteomics approach is used to reveal a wide variety of protein changes through aging; for example, the collagen subtype composition of the cartilage increases in collagen types II and III, and decreases in collagen types IX, XI, and XIV. This analysis shows that bottom-up proteomics is a critical tool in tissue characterization, especially toward developing a deeper understanding of matrix composition and development in tissue engineering studies.

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.

Ageing and Osteoarthritis

The increase in global lifespan has in turn increased the prevalence of osteoarthritis which is now the most common type of arthritis. Cartilage tissue located on articular joints erodes during osteoarthritis which causes pain and may lead to a crippling loss of function in patients. The pathophysiology of osteoarthritis has been understudied and currently no disease modifying treatments exist. The only current end-point treatment remains joint replacement surgery. The primary risk factor for osteoarthritis is age. Clinical and basic research is now focused on understanding the ageing process of cartilage and its role in osteoarthritis. This chapter will outline the physiology of cartilage tissue, the clinical presentation and treatment options for the disease and the cellular ageing processes which are involved in the pathophysiology of the disease.

Gene Expression Profiling of Mouse Condylar Cartilage during Mastication by Means of Laser Microdissection and cDNA Array

Little is known about the mechanisms of mandibular condylar growth. In this study, gene expression in the mandibular condylar cartilage of young post-natal mice was monitored by means of a cDNA microarray, real-time PCR, and laser microdissection before and after the initiation of mastication (newborn, 7 days, 21 days, initiation of mastication, and 35 days). Insulin-like growth factor-1 (IGF-I), transforming-growth-factor-beta-2 (TGFbeta2), and aggrecan mRNAs were clearly expressed at 21 days, while the expression of osteopontin mRNAs was most clear at 35 days. Parathyroid-hormone-related protein (PTHrP), Indian-hedgehog (Ihh), and insulin-like growth factor-2 (IGF-2) mRNAs were clearly expressed during lactation (newborn and 7 days). Heat-shock-protein 84 (HSP-84) and heat-shock-protein 86 (HSP-86) were clearly expressed at 35 days. These results revealed that gene expression changed during mandibular condylar cartilage growth, and that, interestingly, these changes coincided with the initiation of mastication.

Cellular ageing mechanisms in osteoarthritis

Age is the strongest independent risk factor for the development of osteoarthritis (OA) and for many years this was assumed to be due to repetitive microtrauma of the joint surface over time, the so-called 'wear and tear' arthritis. As our understanding of OA pathogenesis has become more refined, it has changed our appreciation of the role of ageing on disease. Cartilage breakdown in disease is not a passive process but one involving induction and activation of specific matrix-degrading enzymes; chondrocytes are exquisitely sensitive to changes in the mechanical, inflammatory and metabolic environment of the joint; cartilage is continuously adapting to these changes by altering its matrix. Ageing influences all of these processes. In this review, we will discuss how ageing affects tissue structure, joint use and the cellular metabolism. We describe what is known about pathways implicated in ageing in other model systems and discuss the potential value of targeting these pathways in OA.

Age-independent effects of hyaluronan amide derivative and growth hormone on human osteoarthritic chondrocytes

AIM

Increased age is the most prominent risk factor for the initiation and progression of osteoarthritis (OA). The effects of human growth hormone (hGH) combined or not with hyaluronan amide derivative (HAD) were evaluated on human OA chondrocytes, to define their biological action and potentiality in OA treatment.

MATERIAL AND METHODS

Cell viability, metabolic activity, gene expression and factors released were tested at different time points on chondrocytes treated with different concentrations of hGH (0.01-10 μg/ml) alone or in combination with HAD (1 mg/ml).

RESULTS

We found that OA chondrocytes express GH receptor and that the different doses of hGH tested did not affect cell viability, metabolic activity or the expression of collagen type 2, 1, or 10 nor did it induce the release of IGF-1 or FGF-2. Conversely, hGH treatment increased the expression of hyaluronan receptor CD44. HAD combined with hGH reduced metabolic activity, IL6 release and gene expression, but not the suppressor of cytokine signaling 2 (SOCS2), which was significantly induced and translocated into the nucleus. The parameters analyzed, independently of the treatments used proportionally decreased with increasing age of the patients.

CONCLUSIONS

hGH only induced CD44 receptor on OA chondrocytes but did not affect other parameters, such as chondrocytic gene markers or IGF-1 or FGF-2 release. HAD reduced all the effects induced by hGH partially through a significant induction of SOCS2. These data show that GH or HAD treatment does not influence the response of the OA chondrocytes, thus the modulation of cellular response is age-independent.

REPAIR OF ARTICULAR CARTILAGE INJURY

Articular cartilage defects heal poorly and lead to consequences as osteoarthritis. Clinical experience has indicated that no existing medication would substantially promote the healing process, and the cartilage defect requires surgical replacement. Allograft decays quickly for multiple reasons including the preparation process and immune reaction, and the outcome is disappointing. The extreme shortage of sparing in articular cartilage has much discouraged the use of autograft, which requires modification. The concept that constructs a chondral or osteochondral construct for the replacement of injured native tissue introduces that of tissue engineering. Limited number of cells are expanded either in vitro or in vivo, and resided temporally on a scaffold of biomaterial, which also acts as a vehicle to transfer the cells to the recipient site. Three core elements constitute this technique: the cell, a biodegradable scaffold, and an environment suitable for cells to present their proposed activity. Modern researches have kept updating those elements for a better performance of such cultivation of living tissue.

Repair of articular cartilage defects: review and perspectives

Articular cartilage defects heal poorly and lead to catastrophic degenerative arthritis. Clinical experience has indicated that no existing medication substantially promotes the healing process and the cartilage defect requires surgical replacement, preferably with an autograft. However, there is a shortage of articular cartilage that can be donated for autografting. A review of previous unsuccessful experiences reveals the reason for the current strategy to graft cartilage defects with regenerated cartilage. Autologous cartilage regeneration is a cell-based therapy in which autogenous chondrocytes or other chondrogenic cells are cultured to constitute cartilaginous tissue according to the principles of tissue engineering. Current studies are concentrating on improving such techniques from the three elements of tissue engineering, namely the cells, biomaterial scaffolds, and culture conditions. Some models of articular cartilage regeneration have yielded good repair of cartilage defects, in animal models and clinical settings, but the overall results suggest that there is room for improvement of this technique before its routine clinical application. Autologous cartilage regeneration remains the mainstay for repairing articular cartilage defects but more studies are required to optimize the efficacy of regeneration. A more abundant supply of more stable cells, i.e. capable of maintaining the phenotype of chondrogenesis, has to be identified. Porous scaffolds of biocompatible, biodegradable materials that maintain and support the presentation of the chondrogenic cells need to be fabricated. If the cells are not implanted early to allow their in vivo constitution of cartilage, a suitable in vitro cultivation method has to be devised for a consistent yield of regenerative cartilage.

Joint injury and osteoarthritis: soluble mediators in the course and treatment of cartilage pathology

Osteoarthritis is a disabling disease of the aging generation, which results in loss of quality of life and increased healthcare costs. Cytokines appear to play an important role in the cartilaginous degeneration characterizing the pathological process. Increasing experience is being gained with cytokine-modulating therapies aimed at interfering with effects of chondrodegradative cytokines in the synovial fluid. Although in vitro and in vivo effectiveness of several of these therapies has been demonstrated, clinical effectiveness remains disputable, which may be related to the low levels of inflammatory cytokines found in osteoarthritic joints. By contrast, directly after joint trauma, which has been shown to predipose to early osteoarthritis, synovial fluid cytokine levels are strongly increased. Cytokine-modulating therapies, however, have hardly been considered for this indication. Increased knowledge of intra-articular soluble mediators correlating with cartilage pathology will lead to further development of cytokine-modulating products and, eventually, to effective inhibition of cartilage degeneration, in both the osteoarthritic as well as injured joints.

Determinants of height in adolescent girls with anorexia nervosa

BACKGROUND

Anorexia nervosa, a condition characterized by marked caloric restriction and low insulin like growth factor-1 levels, would be expected to cause short stature. However, this disorder is also associated with hypogonadotropic hypogonadism and high growth hormone levels. Delays in growth-plate closure from associated hypogonadism may result in a longer period of time available for statural growth with protective effects on stature. In addition, growth hormone may have direct effects on the growth plate independent of insulin-like growth factor 1 to increase statural growth.

OBJECTIVES AND METHODS

To determine the impact of undernutrition, hypogonadism, and acquired growth hormone resistance on height in adolescents with anorexia nervosa (aged 12-18 years), we examined 208 girls: 110 with anorexia nervosa and 98 controls of comparable chronological age. Sixty-three girls with anorexia nervosa and 79 controls were followed prospectively over 1 year. Mean duration of illness was 11.6 +/- 13.2 months. In a subset, overnight growth hormone sampling was performed every 30 minutes for 12 hours, and fasting insulin-like growth factor 1 levels were obtained.

RESULTS

The difference between height and target height and between predicted adult height and target height did not differ between the groups, indicating preservation of height potential. The groups had comparable bone age, but bone age was lower than chronological age in girls with anorexia nervosa. Girls with anorexia nervosa had lower insulin-like growth factor 1 levels and higher nadir growth hormone levels than those of controls. Nadir growth hormone levels predicted height SD scores and predicted adult-height SD scores in controls but not in the girls with anorexia nervosa. In girls with anorexia nervosa, insulin-like growth factor 1 and duration of illness predicted height measures. Height SD scores of <0 were more likely after 32 months of illness and at insulin-like growth factor 1 levels of <134 ng/mL. Delayed baseline bone age predicted subsequent increases in height SD scores in immature girls with anorexia nervosa.

CONCLUSIONS

Our data suggest that preservation of height potential in this cohort of girls with anorexia nervosa may be a consequence of delayed bone age. Hypogonadism may negate the deleterious effects of undernutrition on stature by allowing for a longer duration of growth.

Systemic administration of IGF-I enhances healing in collagenous extracellular matrices: evaluation of loaded and unloaded ligaments

BACKGROUND

Insulin-like growth factor-I (IGF-I) plays a crucial role in wound healing and tissue repair. We tested the hypotheses that systemic administration of IGF-I, or growth hormone (GH), or both (GH+IGF-I) would improve healing in collagenous connective tissue, such as ligament. These hypotheses were examined in rats that were allowed unrestricted activity after injury and in animals that were subjected to hindlimb disuse. Male rats were assigned to three groups: ambulatory sham-control, ambulatory-healing, and hindlimb unloaded-healing. Ambulatory and hindlimb unloaded animals underwent surgical disruption of their knee medial collateral ligaments (MCLs), while sham surgeries were performed on control animals. Healing animals subcutaneously received systemic doses of either saline, GH, IGF-I, or GH+IGF-I. After 3 weeks, mechanical properties, cell and matrix morphology, and biochemical composition were examined in control and healing ligaments.

RESULTS

Tissues from ambulatory animals receiving only saline had significantly greater strength than tissue from saline receiving hindlimb unloaded animals. Addition of IGF-I significantly improved maximum force and ultimate stress in tissues from both ambulatory and hindlimb unloaded animals with significant increases in matrix organization and type-I collagen expression. Addition of GH alone did not have a significant effect on either group, while addition of GH+IGF-I significantly improved force, stress, and modulus values in MCLs from hindlimb unloaded animals. Force, stress, and modulus values in tissues from hindlimb unloaded animals receiving IGF-I or GH+IGF-I exceeded (or were equivalent to) values in tissues from ambulatory animals receiving only saline with greatly improved structural organization and significantly increased type-I collagen expression. Furthermore, levels of IGF-receptor were significantly increased in tissues from hindlimb unloaded animals treated with IGF-I.

CONCLUSION

These results support two of our hypotheses that systemic administration of IGF-I or GH+IGF-I improve healing in collagenous tissue. Systemic administration of IGF-I improves healing in collagenous extracellular matrices from loaded and unloaded tissues. Growth hormone alone did not result in any significant improvement contrary to our hypothesis, while GH + IGF-I produced remarkable improvement in hindlimb unloaded animals.

Effect of growth factors on cell proliferation, matrix deposition, and morphology of human nasal septal chondrocytes cultured in monolayer

OBJECTIVES

Tissue engineering of septal cartilage provides ex vivo growth of cartilage from a patient's own septal chondrocytes for use in craniofacial reconstruction. To become clinically applicable, it is necessary to rapidly expand a limited population of donor chondrocytes and then stimulate the production of extracellular matrix on a biocompatible scaffold. The objective of this study was to determine favorable serum-free culture conditions for proliferation of human septal chondrocytes using various concentrations and combinations of four growth factors.

STUDY DESIGN

Prospective, randomized, controlled study.

METHODS

Nasal septal chondrocytes from six patient donors were isolated by enzymatic digestion and expanded in monolayer culture in both serum-free media (SFM) and 2% fetal bovine serum (FBS). Both of these groups were exposed to varying concentrations and combinations of transforming growth factor (TGF)-beta1, basic fibroblast growth factor (FGF)-2 both at 1, 5, and 25 ng/mL, and bone morphogenetic protein (BMP)-2 and insulin-like growth factor (IGF)-1, both at 5, 25, and 125 ng/mL in the medium during the expansion phase. Cell morphology was assessed throughout the culture duration. After 7 days of monolayer growth, cultures were assessed for cellularity and glycosaminoglycan (GAG) content.

RESULTS

The addition of low-dose FBS in culture media consistently led to significantly greater cell proliferation and matrix deposition than the SFM cell cultures. FGF-2 and TGF-beta1 both alone and in combination led to the greatest proliferative effect compared with the other growth factors. In contrast, BMP-2 and IGF-1 led to the least cell proliferation although was most effective in retaining chondrocyte cell morphology.

CONCLUSIONS

With the addition of TGF-beta1 and FGF-2 to culture media, the concentration of serum can be greatly decreased and possibly eliminated altogether without jeopardizing cell proliferation.

Directing stem cell differentiation into the chondrogenic lineage in vitro

A major area in regenerative medicine is the application of stem cells in cartilage tissue engineering and reconstructive surgery. This requires well-defined and efficient protocols for directing the differentiation of stem cells into the chondrogenic lineage, followed by their selective purification and proliferation in vitro. The development of such protocols would reduce the likelihood of spontaneous differentiation of stem cells into divergent lineages upon transplantation, as well as reduce the risk of teratoma formation in the case of embryonic stem cells. Additionally, such protocols could provide useful in vitro models for studying chondrogenesis and cartilaginous tissue biology. The development of pharmacokinetic and cytotoxicity/genotoxicity screening tests for cartilage-related biomaterials and drugs could also utilize protocols developed for the chondrogenic differentiation of stem cells. Hence, this review critically examines the various strategies that could be used to direct the differentiation of stem cells into the chondrogenic lineage in vitro.

Growth hormone as an early embryonic growth and differentiation factor

In this review we consider the evidence that growth hormone (GH) acts in the embryo as a local growth, differentiation, and cell survival factor. Because both GH and its receptors are present in the early embryo before the functional differentiation of pituitary somatotrophs and before the establishment of a functioning circulatory system, the conditions are such that GH may be a member of the large battery of autocrine/paracrine growth factors that control embryonic development. It has been clearly established that GH is able to exert direct effects, independent of insulin-like growth factor-I (IGF-I), on the differentiation, proliferation, and survival of cells in a wide variety of tissues in the embryo, fetus, and adult. The signaling pathways behind these effects of GH are now beginning to be determined, establishing early extrapituitary GH as a bona fide developmental growth factor.