Melatonin signaling dysfunction in adolescent idiopathic scoliosis

Understanding genetic factors in idiopathic scoliosis, a complex disease of childhood

Idiopathic scoliosis (AIS) is the most common pediatric spinal deformity, affecting ~3% of children worldwide. AIS significantly impacts national health in the U. S. alone, creating disfigurement and disability for over 10% of patients and costing billions of dollars annually for treatment. Despite many investigations, the underlying etiology of IS is poorly understood. Twin studies and observations of familial aggregation reveal significant genetic contributions to IS. Several features of the disease including potentially strong genetic effects, the early onset of disease, and standardized diagnostic criteria make IS ideal for genomic approaches to finding risk factors. Here we comprehensively review the genetic contributions to IS and compare those findings to other well-described complex diseases such as Crohn's disease, type 1 diabetes, psoriasis, and rheumatoid arthritis. We also summarize candidate gene studies and evaluate them in the context of possible disease aetiology. Finally, we provide study designs that apply emerging genomic technologies to this disease. Existing genetic data provide testable hypotheses regarding IS etiology, and also provide proof of principle for applying high-density genome-wide methods to finding susceptibility genes and disease modifiers.

[Etiopathogenesis of adolescent idiopathic scoliosis and new molecular concepts]

Adolescent idiopathic scoliosis (AIS) is the most common form of scoliosis that affects a significant number of young teenagers, mainly females (0.2-6 % of the population). Historically, several hypothesis were postulated to explain the aetiology of AIS, including genetic factors, biochemical factors, mechanics, neurological, muscular factors and hormonal factors. The neuroendocrine hypothesis involving a melatonin deficiency as the source for AIS has generated great interest. This hypothesis stems from the fact that experimental pinealectomy in chicken, and more recently in rats maintained in a bipedal mode, produces a scoliosis. The biological relevance of melatonin in idiopathic scoliosis is controversial since no significant decrease in circulating melatonin level has been observed in a majority of studies. Analysis of melatonin signal transduction in musculoskeletal tissues of AIS patients demonstrated for the first time a defect occurring in a cell autonomous manner in different cell types isolated from AIS patients suffering of the most severe form of that disease. These results have led to a classification of AIS patients in three different functional groups depending on their response to melatonin, suggesting that the cause of AIS involves several genes. Molecular analysis showed that melatonin signaling dysfunction is triggered by an increased phosphorylation of Gi proteins inactivating their function. This discovery has led to development of a first scoliosis screening assay. This test, using blood sample, is currently in clinical validation process in Canada and could be used for screening children at high risk of developing AIS.

Idiopathic scoliosis and pineal lesions in Australian children

PURPOSE

To determine whether treatment of pineal lesions in children is associated with development of idiopathic scoliosis.

METHODS

38 boys and 10 girls with pineal lesions were identified. Their mean age at presentation was 10 years. The pineal pathology varied from cysts and epidermoid to teratoma, germinoma, pineocytoma, and glioblastoma. Treatment ranged from biopsy/extirpation to radiotherapy.

RESULTS

12 patients died. No scoliosis was found in any females or any of the deceased. Two boys had scoliosis: one had a 12-degree right upper thoracic curve with 32-degree kyphosis and the other had a 60-degree right thoracolumbar idiopathic curve, requiring a 2-stage arthrodesis.

CONCLUSION

Pineal ablation is not related to the development of idiopathic scoliosis in humans.

Biomechanical simulations of the scoliotic deformation process in the pinealectomized chicken: a preliminary study

BACKGROUND

The basic mechanisms whereby mechanical factors modulate the metabolism of the growing spine remain poorly understood, especially the role of growth adaptation in spinal disorders like in adolescent idiopathic scoliosis (AIS). This paper presents a finite element model (FEM) that was developed to simulate early stages of scoliotic deformities progression using a pinealectomized chicken as animal model.

METHODS

The FEM includes basic growth and growth modulation created by the muscle force imbalance. The experimental data were used to adapt a FEM previously developed to simulate the scoliosis deformation process in human. The simulations of the spine deformation process are compared with the results of an experimental study including a group of pinealectomized chickens.

RESULTS

The comparison of the simulation results of the spine deformation process (Cobb angle of 37 degrees ) is in agreement with experimental scoliotic deformities of two representative cases (Cobb angle of 41 degrees and 30 degrees ). For the vertebral wedging, a good agreement is also observed between the calculated (28 degrees ) and the observed (25 degrees - 30 degrees ) values.

CONCLUSION

The proposed biomechanical model presents a novel approach to realistically simulate the scoliotic deformation process in pinealectomized chickens and investigate different parameters influencing the progression of scoliosis.

Molecular determinants of melatonin signaling dysfunction in adolescent idiopathic scoliosis

Presently, the genetic cause of adolescent idiopathic scoliosis (AIS), the most common form of scoliosis, remains unclear. Among many hypotheses, the neuroendocrine hypothesis involving a melatonin deficiency as the source for AIS generated the greatest interest and controversy since no decrease in circulating melatonin level has been observed in a majority of studies. Previously, we have reconciled the role of melatonin in AIS by demonstrating a melatonin signaling dysfunction occurring in osteoblasts derived from AIS patients, which contrasted with similar cells isolated from healthy subjects. We found that this difference is caused in AIS cells by increased phosphorylation of serine residues affecting the activity of G inhibitory proteins normally associated with melatonin cell surface receptors. Here we propose a preliminary molecular classification of patients with AIS based on the cellular response to the melatonin (cAMP) and distinct protein-protein interactions. These interactions include those between protein kinase C delta (PKCdelta) and MT2 melatonin receptors or PKCdelta and the receptor for activated protein C kinase 1. This finding could help in future molecular classification of patients with AIS.

Expression of the melatonin receptor (MT) 1 in benign and malignant human bone tumors

The beneficial effects of melatonin on bone homeostasis have been shown in various diseases. As this indoleamine causes dose-dependent modulation of bone-forming osteoblast and bone-resorbing osteoclast activities by receptor-independent and -dependent pathways, we investigated the expression of G-protein-coupled melatonin receptors (MTs) in malignant and non-malignant human bone lesions. By TaqMan polymerase chain reaction (PCR), we analyzed 30 specimens from osteosarcoma and 11 from benign bone tumors for MT1-mRNA expression. Furthermore, we determined mRNA expression levels of the osteoclast activity-stimulating receptor activator of nuclear factor-kappa B ligand (RANKL) and its counterpart osteoprotegerin (OPG). Although mean MT1-mRNA levels were similar (P = 0.596) in malignant (4.39 +/- 4.98-fold) and benign samples (4.64 +/- 6.81-fold), the highest MT1-mRNA levels (up to 27-fold) were observed in individual osteosarcomas, particularly, in two specimens of patients with local recurrence of the tumor. Moreover, mean RANKL- and OPG-mRNA levels were similar in malignant and benign specimens (RANKL: 7.38 +/- 9.61-fold versus 3.57 +/- 3.11-fold, P = 0.207; OPG: 23.45 +/- 32.76 versus 8.07 +/- 7.23-fold, P = 0.133). Again, highest RANKL- and OPG-mRNA levels (up to 41- and 160-fold, respectively) were observed in individual osteosarcomas. Expression of MT1-mRNA was confirmed in two human osteosarcoma cell lines (HOS, MG63). High expression levels of MT1-mRNA together with low OPG-mRNA were found in both osteosarcoma cell lines, while in normal human osteoblasts and bone marrow stromal cells, high OPG-mRNA levels were associated with low MT1-mRNA levels. These data on the abundant expression of MT1-mRNA in human bone tumors and osteosarcoma cells lines suggest an important role for MT1 in bone pathology.

Genetic association study of growth hormone receptor and idiopathic scoliosis

Although the etiology of scoliosis is multifactorial, genetic factors play an important role. Recent linkage studies on familial idiopathic scoliosis revealed multiple putative predisposition loci. A genetic association study is complementary to linkage studies in defining the genetic basis of complex traits of diseases like idiopathic scoliosis. The onset and progression of adolescent idiopathic scoliosis is a manifestation of aberrant growth in the spine. Meanwhile, a high proportion of patients with adolescent idiopathic scoliosis have additional phenotypes, which suggest systemic growth dys-regulation during puberty. The growth hormone-insulin-like growth factor axis plays the principle role in skeletal growth regulation. Because growth hormone receptor alleles were associated with body stature and response to growth hormone treatment, we hypothesized the growth hormone receptor is a candidate predisposing and disease modifier gene for adolescent idiopathic scoliosis. Five hundred ten girls with adolescent idiopathic scoliosis and 363 normal subjects were recruited. Curve severity, arm span, and bone mineral densities were recorded. Five polymorphisms were studied by polymerase chain reaction-restriction fragment length polymorphism. All the genotype and allele frequencies were comparable between groups. The Cobb angles among patients of different genotypes were similar. The growth hormone receptor did not appear to be a predisposing gene or disease modifier gene of adolescent idiopathic scoliosis.

Melatonin receptor 1B (MTNR1B) gene polymorphism is associated with the occurrence of adolescent idiopathic scoliosis

STUDY DESIGN

A genetic association study to comprehensively investigate variations of melatonin receptor 1B gene polymorphism by a set of tagging single nucleotide polymorphisms (tagSNPs) derived from the International Hapmap project.

OBJECTIVES

To determine whether melatonin receptor 1B (MTNR1B) gene polymorphisms are associated with the predisposition and/or disease severity of adolescent idiopathic scoliosis (AIS).

SUMMARY OF BACKGROUND DATA

Linkage studies suggested a genetic predisposition for AIS. In addition, evidence showed that AIS might be related to melatonin deficiency and dysfunction of melatonin signaling pathway. Locating in one of the chromosomal regions linked to AIS, MTNR1B gene is a potential candidate gene for AIS.

METHODS

This study was carried out in 2-stage case-control analysis: 1) initial screening (472 cases and 304 controls) and 2) separate replication test (342 cases and 347 controls) to confirm results in the screening. In the first screening stage, 5 tagSNPs were selected to cover most of the genetic variation in the MTNR1B gene. In the second stage, SNPs showing association in the screening stage were studied in a separate replication sample set to confirm the association. Genotyping was performed by PCR-RFLP.

RESULTS

The first stage showed a putative association between rs4753426 and AIS, which was confirmed in the replication sample set. By meta-analysis, the frequency of C allele of this SNP locating in the promoter was significantly higher in the cases than controls (P = 0.006 aftermeta-analysis). Subjects with the CC genotype had an odds ratio of 1.29 for AIS. Another SNP rs741837 in promoter region, being moderate linkage disequilibrium with rs4753426, was also marginally associated with AIS.

CONCLUSION

Polymorphisms of the promoter of MTNR1B gene were associated with AIS, but not with the curve severity in AIS patients. This suggested that MTNR1B was an AIS predisposition gene.

Recent advances in the aetiology of adolescent idiopathic scoliosis

The aetiology of adolescent idiopathic scoliosis (AIS) is still unknown despite many years of research effort. Theories on AIS's aetiology have included mechanical, hormonal, metabolic, neuromuscular, growth, and genetic abnormalities. Amongst these, some factors may be epiphenomena rather than the cause itself. Other factors may even contribute to curve progression, rather than curve initiation. Current views maintain that AIS is a multifactorial disease with genetic predisposing factors [Lowe et al. in J Bone Joint Surg [Am] 82:1157-1168, 2000]. With improvements in diagnostic methods, imaging and genomics, there has been considerable recent work on aetiology. This review aims to bring readers up-to-date with the latest developments in scoliosis research.

Melatonin the "light of night" in human biology and adolescent idiopathic scoliosis

Melatonin "the light of night" is secreted from the pineal gland principally at night. The hormone is involved in sleep regulation, as well as in a number of other cyclical bodily activities and circadian rhythm in humans. Melatonin is exclusively involved in signalling the 'time of day' and 'time of year' (hence considered to help both clock and calendar functions) to all tissues and is thus considered to be the body's chronological pacemaker or 'Zeitgeber'. The last decades melatonin has been used as a therapeutic chemical in a large spectrum of diseases, mainly in sleep disturbances and tumours and may play a role in the biologic regulation of mood, affective disorders, cardiovascular system, reproduction and aging. There are few papers regarding melatonin and its role in adolescent idiopathic scoliosis (AIS). Melatonin may play a role in the pathogenesis of scoliosis (neuroendocrine hypothesis) but at present, the data available cannot clearly support this hypothesis. Uncertainties and doubts still surround the role of melatonin in human physiology and pathophysiology and future research is needed.

Therapeutic treatments potentially mediated by melatonin receptors: potential clinical uses in the prevention of osteoporosis, cancer and as an adjuvant therapy

Melatonin's therapeutic potential is grossly underestimated because its functional roles are diverse and its mechanism(s) of action are complex and varied. Melatonin produces cellular effects via a variety of mechanisms in a receptor independent and dependent manner. In addition, melatonin is a chronobiotic agent secreted from the pineal gland during the hours of darkness. This diurnal release of melatonin impacts the sensitivity of melatonin receptors throughout a 24-hr period. This changing sensitivity probably contributes to the narrow therapeutic window for use of melatonin in treating sleep disorders, that is, at the light-to-dark (dusk) or dark-to-light (dawn) transition states. In addition to the cyclic changes in melatonin receptors, many genes cycle over the 24-hr period, independent or dependent upon the light/dark cycle. Interestingly, many of these genes support a role for melatonin in modulating metabolic and cardiovascular physiology as well as bone metabolism and immune function and detoxification of chemical agents and cancer reduction. Melatonin also enhances the actions of a variety of drugs or hormones; however, the role of melatonin receptors in modulating these processes is not known. The goal of this review is to summarize the evidence related to the utility of melatonin as a therapeutic agent by focusing on its other potential uses besides sleep disorders. In particular, its use in cancer prevention, osteoporosis and, as an adjuvant to other therapies are discussed. Also, the role that melatonin and, particularly, its receptors play in these processes are highlighted.

Biomechanical spinal growth modulation and progressive adolescent scoliosis--a test of the 'vicious cycle' pathogenetic hypothesis: summary of an electronic focus group debate of the IBSE

There is no generally accepted scientific theory for the causes of adolescent idiopathic scoliosis (AIS). As part of its mission to widen understanding of scoliosis etiology, the International Federated Body on Scoliosis Etiology (IBSE) introduced the electronic focus group (EFG) as a means of increasing debate on knowledge of important topics. This has been designated as an on-line Delphi discussion. The text for this debate was written by Dr Ian A Stokes. It evaluates the hypothesis that in progressive scoliosis vertebral body wedging during adolescent growth results from asymmetric muscular loading in a "vicious cycle" (vicious cycle hypothesis of pathogenesis) by affecting vertebral body growth plates (endplate physes). A frontal plane mathematical simulation tested whether the calculated loading asymmetry created by muscles in a scoliotic spine could explain the observed rate of scoliosis increase by measuring the vertebral growth modulation by altered compression. The model deals only with vertebral (not disc) wedging. It assumes that a pre-existing scoliosis curve initiates the mechanically-modulated alteration of vertebral body growth that in turn causes worsening of the scoliosis, while everything else is anatomically and physiologically 'normal' The results provide quantitative data consistent with the vicious cycle hypothesis. Dr Stokes' biomechanical research engenders controversy. A new speculative concept is proposed of vertebral symphyseal dysplasia with implications for Dr Stokes' research and the etiology of AIS. What is not controversial is the need to test this hypothesis using additional factors in his current model and in three-dimensional quantitative models that incorporate intervertebral discs and simulate thoracic as well as lumbar scoliosis. The growth modulation process in the vertebral body can be viewed as one type of the biologic phenomenon of mechanotransduction. In certain connective tissues this involves the effects of mechanical strain on chondrocytic metabolism a possible target for novel therapeutic intervention.

Changes in melatonin receptors in relation to the development of scoliosis in pinealectomized chickens

STUDY DESIGN

The 2[125I]iodomelatonin binding assay was used to investigate the involvement of melatonin receptors in the development of scoliosis in pinealectomized chickens.

OBJECTIVE

To compare the binding properties of melatonin receptors in the thoracic spinal cord between pinealectomized chickens that had scoliosis develop and those that did not.

SUMMARY OF BACKGROUND DATA

Surgical pinealectomy in young chickens induced scoliosis with a reported incidence of 50% to 100%. The factors regulating the development of scoliosis in this animal model are unclear. Melatonin receptors have been shown in the spinal cord of chickens, but their functions are still unknown. This study addresses the question as to whether spinal cord melatonin receptors are related to the pathogenesis of scoliosis in pinealectomized chickens.

METHOD

Control and pinealectomized chickens were kept under controlled lighting conditions and monitored for scoliosis development. At 9-11 weeks after pinealectomy, thoracic spinal cords were removed for 2[125I]iodomelatonin binding assay, and blood was collected for serum melatonin assay at either the middle of the light period or middle of the dark period.

RESULTS

Pinealectomy in young chickens produced: (1) loss of diurnal variations in serum melatonin levels, (2) 50% incidence of scoliosis, and (3) attenuation in the diurnal variations in the receptor affinity to melatonin. No differences were detected in the serum melatonin levels or binding of spinal cord melatonin receptors between the pinealectomized chickens that had scoliosis develop and those that did not.

CONCLUSION

Changes are detected in melatonin receptor binding after pinealectomy. However, these changes cannot account for the reason why scoliosis develops in some chickens after pinealectomy, while it does not in others. Neither low melatonin serum level nor changes in spinal cord melatonin binding can be a sole etiologic factor in the pathogenesis of scoliosis in pinealectomized chickens.

Melatonin enhances alkaline phosphatase activity in differentiating human adult mesenchymal stem cells grown in osteogenic medium via MT2 melatonin receptors and the MEK/ERK (1/2) signaling cascade

The goals of this study were to determine (a) if melatonin enhances human adult mesenchymal stem cell (hAMSC) differentiation into osteoblasts as assessed by measuring alkaline phosphatase (ALP) enzyme activity, and (b) identify potential signal transduction pathways that mediate this process. ALP activity significantly increased in hAMSCs following a 10-day incubation in osteogenic medium, relative to hAMSCs incubated in basal growth medium alone. Melatonin (50 nm), added in combination with the osteogenic medium, significantly increased ALP activity relative to osteogenic medium alone. Co-exposure of hAMSCs to osteogenic medium supplemented with melatonin and either pertussis toxin or the melatonin receptor antagonists, luzindole or 4P-PDOT (MT2 receptor selective), inhibited the melatonin-induced increase in ALP activity, indicating the involvement of melatonin receptors, in particular, MT2 receptors. Assessment of melatonin receptor function following exposure to osteogenic medium containing either vehicle or melatonin produced dichotomous results. That is, if the differentiation of hAMSCs into an osteoblast was induced by osteogenic medium alone, then 2-[125I]-iodomelatonin binding and melatonin receptor function increased. However, examination of melatonin receptor function following chronic melatonin exposure, an exposure that resulted in a 50% enhancement in ALP activity, revealed that these receptors were desensitized. This was reflected by a complete loss in specific 2-[125I]-iodomelatonin binding as well as melatonin efficacy to inhibit forskolin-induced cAMP accumulation. Further characterization of the mechanisms underlying melatonin's effects on these differentiation processes revealed that MEK (1/2) and ERK (1/2), epidermal growth factor receptors, metalloproteinase and clathrin-mediated endocytosis were essential while PKA was not. Our results are consistent with a role for melatonin in osteoblast differentiation. If so, then, the decrease in plasma melatonin levels observed in humans during late adulthood may further enhance susceptibility to osteoporosis.