Recent research on the growth plate: Recent insights into the regulation of the growth plate

Inadequate linear catch-up growth in children born small for gestational age: Influencing factors and underlying mechanisms

A minority of children born small for gestational age (SGA) may experience catch-up growth failure and remain short in adulthood. However, the underlying causes and mechanisms of this phenomenon are not yet fully comprehended. We reviewed the present state of research concerning the growth hormone-insulin-like growth factor axis and growth plate in SGA children who fail to achieve catch-up growth. Additionally, we explored the factors influencing catch-up growth in SGA children and potential molecular mechanisms involved. Furthermore, we considered the potential benefits of supplementary nutrition, specific dietary patterns, probiotics and drug therapy in facilitating catch-up growth.

Maternal F-53B exposure during pregnancy and lactation affects bone growth and development in male offspring

6:2 Chlorinated polyfluoroalkyl ether sulfonate (F-53B) is a new type of perfluorinated and polyfluoroalkyl substance (PFAS) that is used extensively in industry and manufacturing. F-53B causes damage to multiple mammalian organs. However, the impacts of F-53B on bone are unknown. Maternal exposure to F-53B is of particular concern because of the vulnerability of the developing fetus and newborn to contaminants from the mother. The goal of this study was to examine the impacts of maternal F-53B exposure on bone growth and development in offspring and to explore its underlying mechanisms. Herein, C57BL/6 J mice were given free access to deionized water containing 0, 0.57, or 5.7 mg/L F-53B during pregnancy and lactation. F-53B exposure resulted in impaired liver function, decreased IGF-1 secretion, dysregulation of bone metabolism and disruption of the dynamic balance between osteoblasts and osteoclasts in male offspring. F-53B inhibits longitudinal bone growth and development and causes osteoporosis in male offspring. F-53B may affect the growth and development of offspring bone via the IGF-1/OPG/RANKL/CTSK signaling pathway. This study provides new insights for the study of short stature and bone injury caused by F-53B.

Clinical profiles and molecular genetic analyses of 98 Chinese children with short statures

Background

Short stature is one of the most prevalent endocrine disorders in children, and its genetic basis is a complex and actively researched subject. Currently, there is limited genetic research on exome sequencing for short stature, and more large-scale studies are necessary for further exploration.

Methods

The retrospective study entailed investigation of 98 Chinese children with short statures (height SDS ≤ -2.5) of unknown etiologies recruited between 2017 and 2021. Whole-exome sequencing (WES) was performed on these patients to identify the potential genetic etiologies. The clinical data were reviewed retrospectively to assess the pathogenicity of the identified mutations. Additionally, 31 patients consented to and received recombinant human growth hormone (rhGH) therapy for 12 months. The short-term effects of rhGH treatment were evaluated across different etiologies of patients with short statures.

Results

The WES results were used to identify 31 different variants in 18 genes among 24 (24.5%) patients. Individuals with more severe short statures were more likely to have underlying genetic etiologies. Short stature accompanied by other phenotypes had significantly higher diagnostic yields than simple severe short stature. The rhGH therapy demonstrated efficacy in most children. Nevertheless, the treatment response was suboptimal in a boy diagnosed with 3M syndrome.

Conclusion

WES is an important approach for confirming genetic disorders in patients with severe short statures of unknown etiologies, suggesting that it could be used as a primary diagnostic strategy. The administration of rhGH may not be suitable for all children with short statures, and the identification of the genetic cause of short stature by WES has significant guidance value for rhGH treatment.

Polystyrene microplastic-induced endoplasmic reticulum stress contributes to growth plate endochondral ossification disorder in young rat

BACKGROUND

Previous studies on the effects of microplastics (MPs) on bone in early development are limited. This study aimed to investigate the adverse effects of MPs on bone in young rats and the potential mechanism.

METHODS

Three-week-old female rats were orally administered MPs for 28 days, and endoplasmic reticulum (ER) stress inhibitor salubrinal (SAL) and ER stress agonist tunicamycin (TM) were added to evaluate the effect of ER stress on toxicity of MPs. The indicators of growth and plasma markers of bone turnover were evaluated. Tibias were analyzed using micro-computed tomography (micro-CT). Histomorphological staining of growth plates was performed, and related gene expression of growth plate chondrocytes was tested.

RESULTS

After exposure of MPs, the rats had decreased growth, shortened tibial length, and altered blood calcium and phosphorus metabolism. Trabecular bone was sparse according to micro-CT inspection. In the growth plate, the thickness of proliferative zone substantial reduced while the thickness of hypertrophic zone increased significantly, and the chondrocytes were scarce and irregularly arranged according to tibial histological staining. The transcription of the ER stress-related genes BIP, PERK, ATF4, and CHOP dramatically increased, and the transcription factors involved in chondrocyte proliferation, differentiation, apoptosis, and matrix secretion were aberrant according to RT-qPCR and western blotting. Moreover, the addition of TM showed higher percentage of chondrocyte death. Administration of SAL alleviated all of the MPs-induced symptoms.

CONCLUSION

These results indicated that MPs could induce growth retardation and longitudinal bone damage in early development. The toxicity of MPs may attribute to induced ER stress and impaired essential processes of the endochondral ossification after MPs exposure.

Early puberty suppression and gender-affirming hormones do not alter final height in transgender adolescents

BACKGROUND

Early puberty suppression (ePS; Tanner stages 2 and 3) through gonadotropin-releasing hormone agonists (GnRHas) and gender-affirming hormones (GAHs) interferes with growth and may impact final height (FH).

AIM

To investigate the impact of ePS and GAH on FH in trans boys and trans girls.

METHODS

Retrospective study, including 10 trans boys and 22 trans girls at FH. Bone age (BA) was determined at the start of ePS and at the start of GAH according to Greulich and Pyle; predicted adult height (PAH) was calculated according to Bayley and Pinneau's tables; target height (TH) was calculated as adjusted mean of maternal and paternal height. Target height, PAH, and BA were determined according to sex registered at birth (SRAB) and experienced gender (EG).

RESULTS

The age at the start of PS was 12.37 ± 0.74 years in trans boys and 13.10 ± 1.12 years in trans girls. Total height gain since the start of ePS in trans boys was 14.62 ± 4.08 cm, with 70% achieved before the start of GAH. In trans girls, it was 20.68 ± 7.66 cm, with 61% achieved before GAH. Target height for SRAB was the most accurate predictor for FH in both trans boys and girls: the difference with FH was 1.57 cm ± 3.1 (P = .168) and -0.98 cm ± 4.17 (P = .319), respectively. Also the difference between FH and PAH at the start of PS for SRAB was nonsignificant in both trans boys and girls (2.62 cm ± 3.79, P = .056 and -2.35 cm ± 5.2, P = .051, respectively).

CONCLUSION

Early puberty suppression and GAH do not impact FH, supporting the safety of the treatment; however, trans adolescents achieve a FH in line with SRAB, rather than EG.

Nutritional Strategies for the Prevention and Management of Cow's Milk Allergy in the Pediatric Age

Cow's milk allergy (CMA) is one of the most common pediatric food allergies. The prevalence and severity of CMA have increased dramatically in the last decades, under the pressure of environmental factors in genetically predisposed individuals. Among the environmental influences, nutritional factors play a crucial role. Diet is the most modifiable factor, representing a potential target for the prevention and treatment of CMA. In this review, we report the most scientific-based nutritional strategies for preventing and managing pediatric CMA. In addition, we propose the most complete supplement of compounds able to prevent nutrient deficiencies in CMA pediatric patients and to positively influence the disease course.

Nutrient-regulated dynamics of chondroprogenitors in the postnatal murine growth plate

Longitudinal bone growth relies on endochondral ossification in the cartilaginous growth plate, where chondrocytes accumulate and synthesize the matrix scaffold that is replaced by bone. The chondroprogenitors in the resting zone maintain the continuous turnover of chondrocytes in the growth plate. Malnutrition is a leading cause of growth retardation in children; however, after recovery from nutrient deprivation, bone growth is accelerated beyond the normal rate, a phenomenon termed catch-up growth. Although nutritional status is a known regulator of long bone growth, it is largely unknown whether and how chondroprogenitor cells respond to deviations in nutrient availability. Here, using fate-mapping analysis in Axin2CreERT2 mice, we showed that dietary restriction increased the number of Axin2+ chondroprogenitors in the resting zone and simultaneously inhibited their differentiation. Once nutrient deficiency was resolved, the accumulated chondroprogenitor cells immediately restarted differentiation and formed chondrocyte columns, contributing to accelerated growth. Furthermore, we showed that nutrient deprivation reduced the level of phosphorylated Akt in the resting zone and that exogenous IGF-1 restored the phosphorylated Akt level and stimulated differentiation of the pooled chondroprogenitors, decreasing their numbers. Our study of Axin2CreERT2 revealed that nutrient availability regulates the balance between accumulation and differentiation of chondroprogenitors in the growth plate and further demonstrated that IGF-1 partially mediates this regulation by promoting the committed differentiation of chondroprogenitor cells.

Electrosprayed Particles Loaded with Kartogenin as a Potential Osteochondral Repair Implant

The restoration of cartilage damage is a slow and not always successful process. Kartogenin (KGN) has significant potential in this space-it is able to induce the chondrogenic differentiation of stem cells and protect articular chondrocytes. In this work, a series of poly(lactic-co-glycolic acid) (PLGA)-based particles loaded with KGN were successfully electrosprayed. In this family of materials, PLGA was blended with a hydrophilic polymer (either polyethyleneglycol (PEG) or polyvinylpyrrolidone (PVP)) to control the release rate. Spherical particles with sizes in the range of 2.4-4.1 µm were fabricated. They were found to comprise amorphous solid dispersions, with high entrapment efficiencies of >93%. The various blends of polymers had a range of release profiles. The PLGA-KGN particles displayed the slowest release rate, and blending with PVP or PEG led to faster release profiles, with most systems giving a high burst release in the first 24 h. The range of release profiles observed offers the potential to provide a precisely tailored profile via preparing physical mixtures of the materials. The formulations are highly cytocompatible with primary human osteoblasts.

Nutrient-regulated dynamics of chondroprogenitors in the postnatal murine growth plate

Longitudinal bone growth relies on endochondral ossification in the cartilaginous growth plate where chondrocytes accumulate and synthesize the matrix scaffold that is replaced by bone. The chondroprogenitors in the resting zone maintain the continuous turnover of chondrocytes in the growth plate. Malnutrition is a leading cause of growth retardation in children; however, after recovery from nutrient deprivation, bone growth is accelerated beyond the normal rate, a phenomenon termed catch-up growth. Though nutritional status is a known regulator of long bone growth, it is largely unknown if and how chondroprogenitor cells respond to deviations in nutrient availability. Here, using fate-mapping analysis in Axin2Cre ^ERT2 mice, we showed that dietary restriction increased the number of Axin2+ chondroprogenitors in the resting zone and simultaneously inhibited their differentiation. Once nutrient deficiency was resolved, the accumulated chondroprogenitor cells immediately restarted differentiation and formed chondrocyte columns, contributing to accelerated growth. Furthermore, we showed that nutrient deprivation reduced the level of phosphorylated Akt in the resting zone, and that exogenous IGF-1 canceled this reduction and stimulated differentiation of the pooled chondroprogenitors, decreasing their numbers. Our study of Axin2Cre ^ERT2 revealed that nutrient availability regulates the balance between accumulation and differentiation of chondroprogenitors in the growth plate, and further demonstrated that IGF-1 partially mediates this regulation by promoting the committed differentiation of the chondroprogenitor cells.

Idiopathic Short Stature: What to Expect from Genomic Investigations

Short stature is a common concern for physicians caring for children. In traditional investigations, about 70% of children are healthy, without producing clinical and laboratory findings that justify their growth disorder, being classified as having constitutional short stature or idiopathic short stature (ISS). In such scenarios, the genetic approach has emerged as a great potential method to understand ISS. Over the last 30 years, several genes have been identified as being responsible for isolated short stature, with almost all of them being inherited in an autosomal-dominant pattern. Most of these defects are in genes related to the growth plate, followed by genes related to the growth hormone (GH)–insulin-like growth factor 1 (IGF1) axis and RAS-MAPK pathway. These patients usually do not have a specific phenotype, which hinders the use of a candidate gene approach. Through multigene sequencing analyses, it has been possible to provide an answer for short stature in 10–30% of these cases, with great impacts on treatment and follow-up, allowing the application of the concept of precision medicine in patients with ISS. This review highlights the historic aspects and provides an update on the monogenic causes of idiopathic short stature and suggests what to expect from genomic investigations in this field.

No pubertal growth spurt, rapid bone maturation, and menarche post GnRHa treatment in girls with precocious puberty

OBJECTIVES

To study total growth, rate of bone maturation, and menarche after discontinuation of Gonadotropin releasing hormone agonist (GnRHa) treatment for central precocious puberty (CPP).

METHODS

Twenty girls with CPP on treatment with GnRHa were followed from discontinuation of treatment to final height (FH). Height, height velocity (HV), and bone age were measured every 6 months. Age at menarche was collected.

RESULTS

Once treatment is discontinued, rate of bone maturation (bone age [BA]/chronological [CA]) accelerated from 0.7 ± 0.3 at end of treatment to 1.2 ± 0.8 post treatment, similar to BA/CA prior to treatment. BA at treatment discontinuation ranged from 11-14 years. On average, treatment was stopped when CA was within 9 months of BA. All girls continued to grow from end of treatment to menarche averaging an increase of 4.7 ± 3.7 cm, with HV 3.2 ± 2.0 cm/year. Post-menarche they grew an additional 4.6 ± 2.1 cm, with HV 2.4 ± 1.9 cm/year. Acceleration of HV was not seen post treatment. The younger the BA at initiation or completion of treatment, the longer time to menarche. No one had menarche prior to a BA of 12.5 year.

CONCLUSIONS

A pubertal growth spurt does not usually occur after treatment with GnRHa in girls with CPP. Rate of bone maturation accelerates post treatment. These factors are important in assessing optimal height outcome and decisions regarding cessation of treatment. This study will help clinicians give patients and families better estimates of growth and onset of menarche post treatment.

Growing Pains: The Need for Engineered Platforms to Study Growth Plate Biology

Growth plates, or physis, are highly specialized cartilage tissues responsible for longitudinal bone growth in children and adolescents. Chondrocytes that reside in growth plates are organized into three distinct zones essential for proper function. Modeling key features of growth plates may provide an avenue to develop advanced tissue engineering strategies and perspectives for cartilage and bone regenerative medicine applications and a platform to study processes linked to disease progression. In this review, a brief introduction of the growth plates and their role in skeletal development is first provided. Injuries and diseases of the growth plates as well as physiological and pathological mechanisms associated with remodeling and disease progression are discussed. Growth plate biology, namely, its architecture and extracellular matrix organization, resident cell types, and growth factor signaling are then focused. Next, opportunities and challenges for developing 3D biomaterial models to study aspects of growth plate biology and disease in vitro are discussed. Finally, opportunities for increasingly sophisticated in vitro biomaterial models of the growth plate to study spatiotemporal aspects of growth plate remodeling, to investigate multicellular signaling underlying growth plate biology, and to develop platforms that address key roadblocks to in vivo musculoskeletal tissue engineering applications are described.

Experimental Exposure to Bisphenol A Has Minimal Effects on Bone Tissue in Growing Rams—A Preliminary Study

Simple Summary

Bisphenol A (BPA) is a well-known synthetic compound that belongs to the group of chemicals that disrupt the endocrine system in humans and animals. Although bones represent a potential target for these compounds, studies investigating BPA-related effects in bones in large farm animals are limited. We exposed young rams aged 9–12 months to BPA through feed for 64 days and investigated the effects of BPA on bone length, mass, microscopic structure, mineral content, strength, and serum bone parameters. We discovered that BPA had no significant effects on most of the parameters studied. Only manganese was decreased, and copper increased in the femurs of the BPA-exposed rams. These results suggest that a 2-month, low-dose exposure to BPA in growing rams did not affect the macro- and microstructure, metabolism, and biomechanical behavior of femur bones; however, it did affect the composition of microelements in bone, which could affect the bone in the long term.

Abstract

Bisphenol A (BPA) is a well-known synthetic compound that belongs to the group of endocrine-disrupting chemicals. Although bone tissue is a target for these compounds, studies on BPA-related effects on bone morphology in farm animals are limited. In this preliminary study, we investigated the effects of short-term dietary BPA exposure on femoral morphology, metabolism, mineral content, and biomechanical behavior in rams aged 9–12 months. Fourteen rams of the Istrian Pramenka breed were randomly divided into a BPA group and a control group (seven rams/group) and exposed to 25 µg BPA/kg bw for 64 days in feed. Blood was collected for determination of bone turnover markers (procollagen N-terminal propeptide, C-terminal telopeptide), and femurs were assessed via computed tomography, histomorphometry, three-point bending test, and mineral analysis. BPA had no significant effects on most of the parameters studied. Only mineral analysis showed decreased manganese (50%; p ≤ 0.05) and increased copper content (25%; p ≤ 0.05) in the femurs of BPA-exposed rams. These results suggest that a 2-month, low-dose exposure to BPA in growing rams did not affect the histomorphology, metabolism, and biomechanical behavior of femurs; however, it affected the composition of microelements, which could affect the histometric and biophysical properties of bone in the long term.

Limb Mesoderm and Head Ectomesenchyme Both Express a Core Transcriptional Program During Chondrocyte Differentiation

To explain how cartilage appeared in different parts of the vertebrate body at discrete times during evolution, we hypothesize that different embryonic populations co-opted expression of a core gene regulatory network (GRN) driving chondrocyte differentiation. To test this hypothesis, laser-capture microdissection coupled with RNA-seq was used to reveal chondrocyte transcriptomes in the developing chick humerus and ceratobranchial, which are mesoderm- and neural crest-derived, respectively. During endochondral ossification, two general types of chondrocytes differentiate. Immature chondrocytes (IMM) represent the early stages of cartilage differentiation, while mature chondrocytes (MAT) undergo additional stages of differentiation, including hypertrophy and stimulating matrix mineralization and degradation. Venn diagram analyses generally revealed a high degree of conservation between chondrocyte transcriptomes of the limb and head, including SOX9, COL2A1, and ACAN expression. Typical maturation genes, such as COL10A1, IBSP, and SPP1, were upregulated in MAT compared to IMM in both limb and head chondrocytes. Gene co-expression network (GCN) analyses of limb and head chondrocyte transcriptomes estimated the core GRN governing cartilage differentiation. Two discrete portions of the GCN contained genes that were differentially expressed in limb or head chondrocytes, but these genes were enriched for biological processes related to limb/forelimb morphogenesis or neural crest-dependent processes, respectively, perhaps simply reflecting the embryonic origin of the cells. A core GRN driving cartilage differentiation in limb and head was revealed that included typical chondrocyte differentiation and maturation markers, as well as putative novel “chondrocyte” genes. Conservation of a core transcriptional program during chondrocyte differentiation in both the limb and head suggest that the same core GRN was co-opted when cartilage appeared in different regions of the skeleton during vertebrate evolution.

ERα/β/DMP1 axis promotes trans-differentiation of chondrocytes to bone cells through GSK-3β/β-catenin pathway

Estrogen-induced premature closing of the growth plate in the long bones is a major cause of short stature after premature puberty. Recent studies have found that chondrocytes can directly trans-differentiate into osteoblasts in the process of endochondral bone formation, which indicates that cartilage formation and osteogenesis may be a continuous biological process. However, whether estrogen promotes the direct trans-differentiation of chondrocytes into osteoblasts remains largely unknown. Chondrocytes were treated with different concentrations of 17β-estradiol, and Alizarin Red staining and alkaline phosphatase activity assay were used to detected osteogenesis. Specific short hairpin RNA and tamoxifen were used to block the estrogen receptor (ER) pathway and osteogenic marker genes and downstream gene expression were detected using real-time quantitative polymerase chain reaction, western blot, and immunohistochemistry staining. The findings showed that 17β-estradiol promoted the chondrocyte osteogenesis in vitro, even at high concentrations. In addition, blocking of the ERα/β pathway inhibited the trans-differentiation of chondrocytes into osteogenic cells. Furthermore, we found that dentin matrix protein 1 (DMP1), which is a direct downstream molecular of ER, was involved in 17β-estradiol/ER pathway-regulated osteogenesis. As well, glycogen synthase kinase-3 beta (GSK-3β)/β-catenin signal pathway also participates in ERα/β/DMP1-regulated chondrocyte osteogenesis. The GSK-3β/β-catenin signal pathway was involved in ERα/β/DMP1-regulated chondrocyte osteogenesis. These findings suggest that ER/DMP1/GSK-3β/β-catenin plays a vital role in estrogen regulation of chondrocyte osteogenesis and provide a therapeutic target for short stature caused by epiphyseal fusion.

Total Flavonoids of Rhizoma Drynariae Ameliorate Bone Growth in Experimentally Induced Tibial Dyschondroplasia in Chickens via Regulation of OPG/RANKL Axis

Background:Rhizoma Drynariae, traditional Chinese herb, is widely used to treat and prevent bone disorders. However, experimental evidence on the use of Rhizoma Drynariae extract, total flavonoids of Rhizoma Drynariae (TFRD) to treat tibial dyschondroplasia (TD) in chickens and its underlying mechanisms have not been investigated.

Purpose: To evaluate the therapeutic effect of TFRD on leg disease caused by TD and elucidate its mechanisms in modulating the bone status.

Methods: Thiram-induced chicken TD model has been established. The tibia status was evaluated by analyzing tibia-related parameters including tibial weight, tibial length and its growth plate width and by performing histopathological examination. The expression of tibial bone development-related genes and proteins was confirmed by western blotting and qRT-PCR.

Results: The results showed that administration of TFRD mitigated lameness, increased body weight, recuperated growth plate width in broilers affected by TD and the increase of tibia weight and tibia length is significantly positively correlated with body weight. Compared with the TD group broilers, 500 mg/kg TFRD evidently reduced the damage width of the growth plate and improved its blood vessel distribution by elevating the gene expression levels of BMP-2 and Runx2 and OPG/RANKL ratio. Furthermore, correlation analysis found that the damage width of the growth plate was negatively correlated with the expression levels of BMP-2 and OPG.

Conclusion: The present study revealed that TFRD could promote the bone growth via upregulating OPG/RANKL ratio, suggesting that TFRD might be a potential novel drug in the treatment of TD in chickens.

Impaired proliferation of growth plate chondrocytes in a model of osteogenesis imperfecta

Short stature is the second conspicuous characteristic of osteogenesis imperfecta (OI), but the etiological mechanism is unclear. The proliferation of growth plate chondrocytes (GPCs) plays an essential role in longitudinal bone growth, and chondrocyte division deficiency can cause shortened limbs. However, few studies have reported the abnormal changes of growth plate and GPCs in OI. In this study, the cell proliferative performance of GPCs in heterozygous Col1a2^oim/+ mice were studied and the underlying mechanism was explored by RNA-Sequencing. The results indicated that chondrocytes of Col1a2^oim/+ background displayed impaired cell division when compared with cells of wild-type littermates. A group of differentially expressed genes involving chondrocyte proliferation related pathways including cell cycle, TGF-β signaling pathway and Hedgehog signaling pathway were identified. These dysregulated genes and pathways in GPCs of Col1a2^oim/+ mice are likely to play an important role in their shortened long bones. Further investigations to reveal the effect of these genes on bone elongation not only facilitate the understanding of OI short stature, but also contribute to developing new treatments.

Clinical Profiles and Genetic Spectra of 814 Chinese Children With Short Stature

CONTEXT

Data and studies based on exome sequencing for the genetic evaluation of short stature are limited, and more large-scale studies are warranted. Some factors increase the likelihood of a monogenic cause of short stature, including skeletal dysplasia, severe short stature, and small for gestational age (SGA) without catch-up growth. However, whether these factors can serve as predictors of molecular diagnosis remains unknown.

OBJECTIVE

We aimed to explore the diagnostic efficiency of the associated risk factors and their exome sequences for screening.

METHODS

We defined and applied factors that increased the likelihood of monogenic causes of short stature in diagnostic genetic tests based on next-generation sequencing (NGS) in 814 patients with short stature and at least 1 other factor.

RESULTS

Pathogenic/likely pathogenic (P/LP) variants in genes, copy number variations, and chromosomal abnormalities were identified in 361 patients. We found P/LP variants among 111 genes, and RASopathies comprised the most important etiology. Short stature combined with other phenotypes significantly increased the likelihood of a monogenic cause, including skeletal dysplasia, facial dysmorphism, and intellectual disability, compared with simple severe short stature (<-3 SD scores). We report novel candidate pathogenic genes, KMT2C for unequivocal growth hormone insensitivity and GATA6 for SGA.

CONCLUSION

Our study identified the diagnostic characteristics of NGS in short stature with different risk factors. Our study provides novel insights into the current understanding of the etiology of short stature in patients with different phenotypes.

Temperature, heat shock proteins and growth regulation of the bone tissue

Ambient heat modulates the elongation of bones in mammals, and the mechanism of such a plasticity has not been studied completely. The influence of heat on growth and development of bone depends on its values. Five zones of temperature influence on the bone tissue with different biological effects have been distinguished : a) under-threshold thermal zone < 36.6 ºС, insufficient amount of heat is a limiting factor for osteogenesis; b) normal temperature zone 36.6‒37.5 ºС, the processes of breakdown and development of bone in this temperature range is balanced; b) zone of mild thermal shock 39‒41 ºС, the processes of functioning of osteoblasts, osteocytes and formation of the bone tissue intensify; d) the zone of sublethal thermal shock > 42 ºС, growth of bone slows; e) zone of non-critical shock > 50 ºС, bone tissue cells die. We propose a model of the mechanism of influence of heat shock on bone growth. Mild heat shock is a type of stress to which membrane enzymes adenylyl cyclase and cAMP-protein kinase react. Protein kinase A phosphorylates the gene factors of thermal shock proteins, stress proteins and enzymes of energy-generating processes – glycolysis and lipolysis. Heat shock protein HSP70 activates alkaline phosphatase and promotes the process of mineralization of the bone tissue. In the cells, there is intensification in syntheses of insulin-like growth factor-I, factors of mitogenic action, signals of intensification of blood circulation (NO) and synthesis of somatotropin. The affinity between insulin-like growth factor I and its acid-labile subunit decreases, leading to increased free and active insulin-like growth factor I. Against the background of acceleration of the capillarization process, energy generation and the level of stimulators of growth of bone tissue, mitotic and functional activities of producer cells of the bone – osteoblasts and osteocytes – activate. The generally known Allen’s rule has been developed and expanded: “Warm-blooded animals of different species have longer distal body parts (tails) if after birth the young have developed in the conditions of higher temperature”. The indicated tendency is realized through increased biosynthesis of heat shock proteins and other stimulators of growth processes in the bone tissue.

Pregnancy-Associated Plasma Protein (PAPP)-A2 in Physiology and Disease

The growth hormone (GH)/insulin-like growth factor (IGF) axis plays fundamental roles during development, maturation, and aging. Members of this axis, composed of various ligands, receptors, and binding proteins, are regulated in a tissue- and time-specific manner that requires precise control that is not completely understood. Some of the most recent advances in understanding the implications of this axis in human growth are derived from the identifications of new mutations in the gene encoding the pregnancy-associated plasma protein PAPP-A2 protease that liberates IGFs from their carrier proteins in a selective manner to allow binding to the IGF receptor 1. The identification of three nonrelated families with mutations in the PAPP-A2 gene has shed light on how this protease affects human physiology. This review summarizes our understanding of the implications of PAPP-A2 in growth physiology, obtained from studies in genetically modified animal models and the PAPP-A2 deficient patients known to date.

Analysis of Association between Morphometric Parameters of Growth Plate and Bone Growth of Tibia in Mice and Humans

OBJECTIVE

The purposes of this study are to evaluate which growth plate parameters are associated with bone growth in mice and to compare the mouse results with those in humans.

DESIGN

The sagittal sections of the proximal growth plate of the mouse tibia from neonate to young adult stages were subjected to histomorphometric and functional analyses. The radiographic images of tibias of human patients until puberty were analyzed to obtain the tibia length and the proximal growth plate height. It was found that a linear correlation best modeled the relationship between the growth plate variables with the tibia growth rate and length.

RESULTS

In mice, total height, resting zone height, combined height of the proliferation and prehypertrophic zones, proliferation activity, and the total width of tibia growth plate showed high linear correlation with tibia bone length and bone growth rate, but the hypertrophic zone height and the growth plate area did not. In both mice and humans, the total growth plate width of tibia was found to have the strongest correlation with tibia length and growth rate.

CONCLUSIONS

The results validated that growth plate total height, the height of the resting zone and cell proliferation activity are appropriate parameters to evaluate the balance between growth plate activity and bone growth in mice, consistent with previous reports. The study also provided a new growth plate parameter candidate, growth plate width for growth plate activity evaluation in both mouse and human tibia bone.

Manganese deficiency induces avian tibial dyschondroplasia by inhibiting chondrocyte proliferation and differentiation

Manganese (Mn) is an essential trace element for bone growth, and its deficiency has been shown to increase the incidence of leg abnormalities in fast-growing broilers, such as tibial dyschondroplasia (TD). Proliferation and differentiation of growth plate chondrocyte are critical for tibia development, but their roles in Mn deficiency-induced TD remains to be elucidated. Thirty 1-day-old Arbor Acres chicks were randomly divided into two groups and fed with control diet (60 mg Mn/kg diet) and Mn-deficiency diet (22 mg Mn/kg diet) for 42 days, respectively. Mn deficiency-induced TD model was successfully established and samples from proximal tibia metaphysis and growth plate were collected for assays. Pathological observation showed that Mn deficiency induced morphological abnormality and irregular arrangement of chondrocytes in proliferative and hypertrophic zone of tibial growth plate. Also, Mn deficiency decreased mRNA and protein expression levels of type II collagen and type X collagen in tibial growth plate, indicating the impairment of proliferating and hypertrophic chondrocytes. Moreover, down-regulated gene expression levels of Sox9, Tgf-β, Ihh, Runx2, Mef2c and Bmp-2 were shown in tibial growth plate of Mn-deficiency group, demonstrating that Mn deficiency inhibited the transcription levels of key regulators to disrupt chondrocyte proliferation and differentiation. Collectively, these findings confirmed that Mn deficiency affected the proliferation and differentiation of chondrocytes in tibial growth plate via inhibiting related regulatory factors, leading to TD in broilers.

Wasting and Stunting in Infants and Young Children as Risk Factors for Subsequent Stunting or Mortality: Longitudinal Analysis of Data from Malawi, South Africa, and Pakistan

BACKGROUND

Few studies have had sufficient longitudinal data to track how different malnourished states relate to mortality at different ages and interrelate over time.

OBJECTIVES

This study aims to describe the RRs and proportions of mortality associated with wasting and stunting and the pathways into and out of these nutritional states.

METHODS

Longitudinal growth data sets collected for children ages 0-24 months from Malawi, South Africa, and Pakistan were combined (n = 5088). Children were classified as deceased, wasted (weight for height < -2 SD; 1-4%), stunted (length < -2SD; 20-47%), or wasted and stunted (WaSt; 2-5%) at ages 3, 6, 9, 12, 18, and 24 months. Mixed-effects Cox models were used to study the association between nutritional status and mortality.

RESULTS

By age 3 months, 20% of children were already stunted, rising to 49% by 24 months, while wasting (4.2% and 2.2% at 3 months, respectively) and WaSt (0.9% and 3.7% at 24 months, respectively) were less common. The HR for mortality in WaSt was 9.5 (95% CI, 5.9-15), but 60% of WaSt-associated mortality occurred at 3-6 months. Wasting or WaSt was associated with 10-23% of deaths beyond 6 months, but in the second year over half of deaths occurred in stunted, nonwasted children. Stunting persisted in 82% of children and wasting persisted in 44%. Wasted children were more likely than nonwasted, nonstunted children to become stunted (RR, 1.93; 95% CI, 1.7-2.2), but 94% of children who progressed to stunting had not been wasted in the prior period.

CONCLUSIONS

WaSt greatly increased the risk of death, particularly in very young infants, but more deaths overall were associated with stunting. Most stunting appeared to be either intrauterine in origin or arose in children without prior wasting. Either stunting and wasting represent alternative responses to restricted nutrition, or stunting also has other, nonnutritional causes.

Enlightenment of Growth Plate Regeneration Based on Cartilage Repair Theory: A Review

The growth plate (GP) is a cartilaginous region situated between the epiphysis and metaphysis at the end of the immature long bone, which is susceptible to mechanical damage because of its vulnerable structure. Due to the limited regeneration ability of the GP, current clinical treatment strategies (e.g., bone bridge resection and fat engraftment) always result in bone bridge formation, which will cause length discrepancy and angular deformity, thus making satisfactory outcomes difficult to achieve. The introduction of cartilage repair theory and cartilage tissue engineering technology may encourage novel therapeutic approaches for GP repair using tissue engineered GPs, including biocompatible scaffolds incorporated with appropriate seed cells and growth factors. In this review, we summarize the physiological structure of GPs, the pathological process, and repair phases of GP injuries, placing greater emphasis on advanced tissue engineering strategies for GP repair. Furthermore, we also propose that three-dimensional printing technology will play a significant role in this field in the future given its advantage of bionic replication of complex structures. We predict that tissue engineering strategies will offer a significant alternative to the management of GP injuries.

Growth, growth potential, and influences on adult height in the transgender and gender-diverse population

The sexually dimorphic trait of height is one aspect of the experience of transgender and gender‐diverse (TGD) individuals that may influence their gender dysphoria and satisfaction with their transition. In this article, we have reviewed the current knowledge of the factors that contribute to one's final adult height and how it might be affected in TGD youth who have not experienced their gonadal puberty in the setting of receiving gonadotropin‐releasing hormone analog (GnRHa) and gender‐affirming hormonal treatment. Additional research is needed to characterize the influence of growth and final adult height on the lived experience of TGD youth and adults and how to best assess their growth, predict their final adult height, and how medical transition can be potentially modified to help them meet their goals.

Interactions between Growth of Muscle and Stature: Mechanisms Involved and Their Nutritional Sensitivity to Dietary Protein: The Protein-Stat Revisited

Childhood growth and its sensitivity to dietary protein is reviewed within a Protein-Stat model of growth regulation. The coordination of growth of muscle and stature is a combination of genetic programming, and of two-way mechanical interactions involving the mechanotransduction of muscle growth through stretching by bone length growth, the core Protein-Stat feature, and the strengthening of bone through muscle contraction via the mechanostat. Thus, growth in bone length is the initiating event and this is always observed. Endocrine and cellular mechanisms of growth in stature are reviewed in terms of the growth hormone-insulin like growth factor-1 (GH-IGF-1) and thyroid axes and the sex hormones, which together mediate endochondral ossification in the growth plate and bone lengthening. Cellular mechanisms of muscle growth during development are then reviewed identifying (a) the difficulties posed by the need to maintain its ultrastructure during myofibre hypertrophy within the extracellular matrix and the concept of muscle as concentric "bags" allowing growth to be conceived as bag enlargement and filling, (b) the cellular and molecular mechanisms involved in the mechanotransduction of satellite and mesenchymal stromal cells, to enable both connective tissue remodelling and provision of new myonuclei to aid myofibre hypertrophy and (c) the implications of myofibre hypertrophy for protein turnover within the myonuclear domain. Experimental data from rodent and avian animal models illustrate likely changes in DNA domain size and protein turnover during developmental and stretch-induced muscle growth and between different muscle fibre types. Growth of muscle in male rats during adulthood suggests that "bag enlargement" is achieved mainly through the action of mesenchymal stromal cells. Current understanding of the nutritional regulation of protein deposition in muscle, deriving from experimental studies in animals and human adults, is reviewed, identifying regulation by amino acids, insulin and myofibre volume changes acting to increase both ribosomal capacity and efficiency of muscle protein synthesis via the mechanistic target of rapamycin complex 1 (mTORC1) and the phenomenon of a "bag-full" inhibitory signal has been identified in human skeletal muscle. The final section deals with the nutritional sensitivity of growth of muscle and stature to dietary protein in children. Growth in length/height as a function of dietary protein intake is described in the context of the breastfed child as the normative growth model, and the "Early Protein Hypothesis" linking high protein intakes in infancy to later adiposity. The extensive paediatric studies on serum IGF-1 and child growth are reviewed but their clinical relevance is of limited value for understanding growth regulation; a role in energy metabolism and homeostasis, acting with insulin to mediate adiposity, is probably more important. Information on the influence of dietary protein on muscle mass per se as opposed to lean body mass is limited but suggests that increased protein intake in children is unable to promote muscle growth in excess of that linked to genotypic growth in length/height. One possible exception is milk protein intake, which cohort and cross-cultural studies suggest can increase height and associated muscle growth, although such effects have yet to be demonstrated by randomised controlled trials.

Bone tissue and histological and molecular events during development of the long bones

The bones are of mesenchymal or ectomesenchymal origin, form the skeleton of most vertebrates, and are essential for locomotion and organ protection. As a living tissue they are highly vascularized and remodelled throughout life to maintain intact. Bones consist of osteocytes entrapped in a mineralized extracellular matrix, and via their elaborated network of cytoplasmic processes they do not only communicate with each other but also with the cells on the bone surface (bone lining cells). Bone tissue develops through a series of fine-tuned processes, and there are two modes of bone formation, referred to either as intramembranous or endochondral ossification. In intramembranous ossification, bones develop directly from condensations of mesenchymal cells, and the flat bones of the skull, the clavicles and the perichondral bone cuff develop via this process. The bones of the axial (ribs and vertebrae) and the appendicular skeleton (e.g. upper and lower limbs) form through endochondral ossification where mesenchyme turns into a cartilaginous intermediate with the shape of the future skeletal element that is gradually replaced by bone. Endochondral ossification occurs in all vertebrate taxa and its onset involves differentiation of the chondrocytes, mineralization of the extracellular cartilage matrix and vascularization of the intermediate, followed by disintegration and resorption of the cartilage, bone formation, and finally - after complete ossification of the cartilage model - the establishment of an avascular articular cartilage. The epiphyseal growth plate regulates the longitudinal growth of the bones, achieved by a balanced proliferation and elimination of chondrocytes, and the question whether the late hypertrophic chondrocytes die or transform into osteogenic cells is still being hotly debated. The complex processes leading to endochondral ossification have been studied for over a century, and this review aims to give an overview of the histological and molecular events, arising from the long bones' (e.g. femur, tibia) development. The fate of the hypertrophic chondrocytes will be discussed in the light of new findings obtained from cell tracking studies.

Physiological regulation of bone length and skeletal proportion in mammals

NEW FINDINGS

What is the topic of this review? Mechanisms regulating bone length and skeletal proportions What advances does it highlight? The study of differential bone length between leg and finger bones, metatarsals of the Egyptian jerboa and genomic analysis of giraffes.

ABSTRACT

Among mammalian species, skeletal structures vary greatly in size and shape, leading to a dramatic variety of body sizes and proportions. How different bones grow to different lengths, whether among different species, different individuals of the same species, or even in different anatomical parts of our the body, has always been a fascinating subject of research in biology and physiology. In the current review, we focus on some of the recent advances in the field and discuss how these provided important new insights into the mechanisms regulating bone length and skeletal proportions.

Laser Capture Microdissection of Mouse Growth Plate Cartilage

The ability to identify, isolate, and study pure populations of cells is critical for understanding normal physiology in organs and tissues, which involves spatial regulation of signaling pathways and interactions between cells with different functions, expression profiles, and lineages. Here, we focus on assessing the growth plate cartilage, composed of multiple functionally and histologically distinct zones, to investigate temporally and spatially dependent gene expression differences. In this chapter, we describe the method of laser capture microdissection to isolate chondrocytes from different zones of differentiation in the mouse growth plate cartilage for RNA isolation, and subsequent downstream applications, such as RNA-sequencing and quantitative real-time PCR. We also provide an assessment of different factors contributing to the integrity of the isolated RNA, such as staining methods and procedures in RNA isolation.

Bone tissue morphology of rat offspring lactationally exposed to polychlorinated biphenyl 169 and 155

Polychlorinated biphenyls (PCBs) are ubiquitous, persistent, organic pollutants also considered endocrine-disrupting chemicals. Our study examined the effects of lactational exposure to nondioxin-like PCB-155 and/or dioxin-like PCB-169 on longitudinal femur growth at the distal epiphyseal growth plate (EGP) in young rats at three different ages [postnatal days (PNDs) 9, 22, and 42]. After delivery, lactating rats were divided into four groups (PCB-169, PCB-155, PCB-155 + 169, and control) and administered PCBs intraperitoneally. The femurs of offspring were used to estimate growth rate (µm/day), and histomorphometric analysis on the distal femur included the thickness of the EGP and zones of proliferation and hypertrophy with calcification. Stereometry was used to determine trabecular bone volume density. In the PCB-169 and PCB-155 + 169 groups, PCB-169 affected longitudinal bone growth in the early postnatal period by interfering with chondrocytes in the EGP zone of proliferation and, to a lesser extent, the zone of hypertrophy. Morphometric alterations in EGP structure diminished until puberty. A slow growth rate persisted in the PCB-169 group until PND 42, while in the PCB-155 group, a fast growth rate between PNDs 9 to 22 was significantly reduced between PNDs 22 to 42. Sterometric assessment showed decreased trabecular bone volume in the PCB-155 + 169 group compared with that in the control on PND 9 and increased in the PCB-169 group compared with that in the PCB-155 group on PND 42. To summarize, studied PCB congeners exerted congener- and age-dependent effects on femur growth rate and its histomorphometric characteristics.

Short Stature is Progressive in Patients with Heterozygous NPR2 Mutations

BACKGROUND

NPR2 encodes atrial natriuretic peptide receptor B (ANPRB), a regulator of skeletal growth. Biallelic loss-of-function mutations in NPR2 result in acromesomelic dysplasia Maroteaux type (AMDM; OMIM 602875), while heterozygous mutations may account for 2% to 6% of idiopathic short stature (ISS).

OBJECTIVE

Describe the physical proportions and growth characteristics of an extended family with novel NPR2 mutations including members with AMDM, ISS, or normal stature.

DESIGN AND PARTICIPANTS

We performed whole exome sequencing in 2 healthy parents and 2 children with AMDM. Detailed genotyping and phenotyping were performed on members of a multigenerational family in an academic medical center. We expressed mutant proteins in mammalian cells and characterized expression and function.

RESULTS

The sisters with AMDM were compound heterozygotes for missense mutations in the NPR2 gene, a novel p.P93S (maternal) and the previously reported p.R989L (paternal). Both mutant ANPRB proteins were normally expressed in HEK293T cells and exhibited dominant negative effects on wild-type ANPRB catalytic activity. Heterozygous relatives had proportionate short stature (height z-scores -2.06 ± 0.97, median ± SD) compared with their wild-type siblings (-1.37 ± 0.59). Height z-scores progressively and significantly decreased as NPR2-heterozygous children matured, while remaining constant in their wild-type siblings.

CONCLUSIONS

Biallelic NPR2 mutations cause severe skeletal dysplasia (AMDM), whereas heterozygous mutations lead to a subtler phenotype characterized by progressive short stature with by increasing loss of height potential with age.

Größenwachstum und Knochengesundheit bei Erkrankungen der Wachstumsfuge und des Knochens: Möglichkeiten und Grenzen einer GH-Therapie

Hintergrund

Genetische, parakrine und endokrine Faktoren beeinflussen das Größenwachstum und die Knochenmineralisation.

Fragestellung

Wie sind spontanes Größenwachstum und Knochengesundheit von Patienten mit seltenen Knochenerkrankungen? Kann man Wachstum und Knochengesundheit bei diesen Erkrankungen mit Wachstumshormon („growth hormone“ [GH]) verbessern?

Material und Methoden

Ergebnisse eines Expertentreffens mit Literaturrecherche zur Knochengesundheit von mit Kleinwuchs assoziierten ossären Erkrankungen und deren Therapieoptionen.

Ergebnisse

Viele Patienten mit einer Osteogenesis imperfecta sind kleinwüchsig. Eine zusätzliche Gabe von GH hat keinen Einfluss auf die Erwachsenengröße und wird derzeit nicht angewendet. Patienten mit unzureichendem Größenwachstum bei Pseudohypoparathyreoidismus (PHP) können bei Nachweis eines GH-Mangels mit GH behandelt werden und von der Therapie profitieren. Kinder mit X‑chromosomal vererbter hypophosphatämischer Rachitis haben unter der bisherigen Therapie mit Phosphat und Calcitriol einen disproportionierten Kleinwuchs. Randomisierte Therapiestudien mit GH führten zwar zu einer vorübergehenden Verbesserung der Körperhöhe, aber zu keiner signifikanten Verbesserung der Erwachsenenkörpergröße. Bei SHOX-Defizienz ist eine GH-Therapie zugelassen und hinsichtlich Köpergrößenzunahme vergleichbar effektiv wie bei Mädchen mit Ullrich-Turner-Syndrom (UTS). Zusätzlich legen Beobachtungsstudien nahe, dass eine GH-Therapie das bei UTS erhöhte Frakturrisiko reduzieren kann. Entzündung, verminderte körperliche Aktivität und Malnutrition führen bei Patienten mit juveniler idiopathischer Arthritis (JIA) zu einem Kleinwuchs mit Verlust an Muskel- und Knochenmasse. Studien konnten einen positiven Effekt von GH auf Längenwachstum, Dichte, Geometrie und Metabolismus des Knochens sowie auf die Muskelmasse zeigen. Die Therapie mit GH ist bei den Patienten mit JIA nicht zugelassen.

Schlussfolgerungen

Bei den genannten Knochenerkrankungen muss jede Wachstumsstörung individuell betrachtet werden. Neben dem Größenwachstum kann sich die GH-Therapie je nach Indikation positiv auf Stoffwechsel, Mineralsalzgehalt und Knochendichte auswirken. Zugelassene Indiktionen für eine GH-Therapie liegen bei PHP nur bei einem GH-Mangel und bei Patienten mit intrauterinem Kleinwuchs (SGA) und UTS/SHOX-Mangel vor. Neben einer Zunahme des Wachstums sollte eine Verbesserung der Knochengesundheit im Kindes- und Jugendalter als Zielparameter einer GH-Therapie diskutiert werden.

Evaluation and management of a child with short stature

Growth monitoring is a fundamental approach to evaluate a child's health and it is part of preventive programs to timely identify and treat a possible disease. Height and weight measurements, calculation of height velocity over time are main instruments to discover pathological deviations. Short stature is defined as a height that is greater than or equal 2 standard deviations (SDS) below the mean height for reference children comparable for sex and age. According to the International Classification of Pediatric Endocrine Diagnosis (ICPED) the possible causes of short stature could be divided into three groups: primary growth disorders (intrinsic diseases of the growth plate), secondary growth disorders (diseases that interfere on the growth plate setting) and the idiopathic short stature in which no possible cause is identified. The etiology of short stature is not always a disease, but it could be a variant of normal growth. Furthermore, to date there are new advances in the genetic causes of short stature. A detailed evaluation of a child with growth impairment should include an accurate history, a standardize physical examination, general and specific laboratory evaluations, radiologic investigations and genetic testing. Short stature could represent an important threat for physical and psychological health in a child, so a prompt identification of abnormal growth deviations offers the possibility to early treat the possible cause of shortness. This review aimed to discuss a practical approach to a child with short stature on the bases of the most recent scientific evidence.

The Actions of IGF-1 in the Growth Plate and Its Role in Postnatal Bone Elongation

PURPOSE OF REVIEW

Bone elongation is a complex process driven by multiple intrinsic (hormones, growth factors) and extrinsic (nutrition, environment) variables. Bones grow in length by endochondral ossification in cartilaginous growth plates at ends of developing long bones. This review provides an updated overview of the important factors that influence this process.

RECENT FINDINGS

Insulin-like growth factor-1 (IGF-1) is the major hormone required for growth and a drug for treating pediatric skeletal disorders. Temperature is an underrecognized environmental variable that also impacts linear growth. This paper reviews the current state of knowledge regarding the interaction of IGF-1 and environmental factors on bone elongation. Understanding how internal and external variables regulate bone lengthening is essential for developing and improving treatments for an array of bone elongation disorders. Future studies may benefit from understanding how these unique relationships could offer realistic new approaches for increasing bone length in different growth-limiting conditions.

Mapping of developmental dysplasia of the hip to two novel regions at 8q23-q24 and 12p12

Developmental dysplasia of the hip (DDH), previously known as congenital hip dislocation, is a frequently disabling condition characterized by premature arthritis later in life. Genetic factors play a key role in the aetiology of DDH. In the present study, a genome-wide linkage scan with the Affymetrix 10K GeneChip was performed on a four-generation Chinese family, which included 19 healthy members and 5 patients. Parametric and non-parametric multipoint linkage analyses were carried out with Genespring GT v.2.0 software, and the logarithm of odds (LOD) score and nonparametric linkage (NPL) score were calculated. Parametric linkage analysis was performed, assuming an autosomal recessive trait with full penetrance and Affymetrix 'Asian' allele frequencies. The strongest evidence for linkage was found on chromosome 8q23-24, with a peak LOD score of 2.658 (θ=0), covering 2.377 Mb from single nucleotide polymorphisms (SNPs) rs724717 to rs720132. This interval included nine additional successive SNPs: rs1566071, rs1902121, rs756404, rs702768, rs777813, rs2033995, rs147959, rs2884367 and rs1898287. The same region also yielded the highest NPL score of 2.883 (P=0.0156) from the non-parametric multipoint linkage analysis. Additionally, the second highest NPL score of 2.727 (P=0.0156) and LOD score of 2.528 (θ=0) were obtained on chromosome 12p12 for three consecutive markers (rs1919980, rs763853 and rs725124). This region overlapped a narrow distance of 0.642 Mb. Notably, in addition to these two regions; no significant linkage was identified for other chromosomal regions (with LOD and NPL scores >2.0). For the first time, at least for this pedigree, the evidence in the present study showed that DDH is mapped to two novel regions at 8q23-q24 and 12p12.

Exposure to the RXR Agonist SR11237 in Early Life Causes Disturbed Skeletal Morphogenesis in a Rat Model

Longitudinal bone growth occurs through endochondral ossification (EO), controlled by various signaling molecules. Retinoid X Receptor (RXR) is a nuclear receptor with important roles in cell death, development, and metabolism. However, little is known about its role in EO. In this study, the agonist SR11237 was used to evaluate RXR activation in EO. Rats given SR11237 from post-natal day 5 to post-natal day 15 were harvested for micro-computed tomography (microCT) scanning and histology. In parallel, newborn CD1 mouse tibiae were cultured with increasing concentrations of SR11237 for histological and whole-mount evaluation. RXR agonist-treated rats had shorter long bones than the controls and developed dysmorphia of the growth plate. Cells invading the calcified and dysmorphic growth plate appeared pre-hypertrophic in size and shape, in correspondence with p57 immunostaining. Additionally, SOX9-positive cells were found surrounding the calcified tissue. The epiphysis of SR11237-treated bones showed increased TRAP staining and additional TUNEL staining at the osteo-chondral junction. MicroCT revealed morphological disorganization in the long bones of the treated animals. This study suggests that stimulation of RXR causes irregular ossification, premature closure of the growth plate, and disrupted long bone growth in rodent models

CREB activation in hypertrophic chondrocytes is involved in the skeletal overgrowth in epiphyseal chondrodysplasia Miura type caused by activating mutations of natriuretic peptide receptor B

Natriuretic peptide receptor B (NPRB) produces cyclic guanosine monophosphate (cGMP) when bound by C-type natriuretic peptide (CNP). Activating mutations in NPRB cause a skeletal overgrowth disorder, which has been named epiphyseal chondrodysplasia, Miura type (ECDM; OMIM #615923). Here we explored the cellular and molecular mechanisms for the skeletal overgrowth in ECDM using a mouse model in which an activating mutant NPRB is specifically expressed in chondrocytes. The mutant mice (NPRB[p.V883M]-Tg) exhibited postnatal skeletal overgrowth and increased cGMP in cartilage. Both endogenous and transgene-derived NPRB proteins were localized at the plasma membrane of hypertrophic chondrocytes. The hypertrophic zone of growth plate was thickened in NPRB[p.V883M]-Tg. An in vivo BrdU-labeling assay suggested that some of the hypertrophic chondrocytes in NPRB[p.V883M]-Tg mice continued to proliferate, although wild-type (WT) chondrocytes stopped proliferating after they became hypertrophic. In vitro cell studies revealed that NPRB activation increased the phosphorylation of cyclic AMP-responsive element binding protein (CREB) and expression of cyclin D1 in matured chondrocytes. Treatment with cell-permeable cGMP also enhanced the CREB phosphorylation. Inhibition of cyclic adenosine monophosphate (cAMP)/protein kinase A pathway had no effects on the CREB phosphorylation induced by NPRB activation. In immunostaining of the growth plates for the proliferation marker Ki67, phosphorylated CREB and cyclin D1, most signals were similarly observed in the proliferating zone in both genotypes, but some cells in the hypertrophic zone of NPRB[p.V883M]-Tg were also positively stained. These results suggest that NPRB activation evokes its signal in hypertrophic chondrocytes to induce CREB phosphorylation and make them continue to proliferate, leading to the skeletal overgrowth in ECDM.

Inducible knockout of CHUK/IKKα in adult chondrocytes reduces progression of cartilage degradation in a surgical model of osteoarthritis

CHUK/IKKα contributes to collagenase-driven extracellular matrix remodeling and chondrocyte hypertrophic differentiation in vitro, in a kinase-independent manner. These processes contribute to osteoarthritis (OA), where chondrocytes experience a phenotypic shift towards hypertrophy concomitant with abnormal matrix remodeling. Here we investigated the contribution of IKKα to OA in vivo. To this end, we induced specific IKKα knockout in adult chondrocytes in AcanCreER^T2/+; IKKα^f/f mice treated with tamoxifen (cKO). Vehicle-treated littermates were used as wild type controls (WT). At 12 weeks of age, WT and cKO mice were subjected to the destabilization of medial meniscus (DMM) model of post-traumatic OA. The cKO mice showed reduced cartilage degradation and collagenase activity and fewer hypertrophy-like features at 12 weeks after DMM. Interestingly, in spite of the protection from structural articular cartilage damage, the postnatal growth plates of IKKα cKO mice after DMM displayed abnormal architecture and composition associated with increased chondrocyte apoptosis, which were not as evident in the articular chondrocytes of the same animals. Together, our results provide evidence of a novel in vivo functional role for IKKα in cartilage degradation in post-traumatic OA, and also suggest intrinsic, cell-autonomous effects of IKKα in chondrocytes that control chondrocyte phenotype and impact on cell survival, matrix homeostasis, and remodeling.

Possible Contribution of Wnt-Responsive Chondroprogenitors to the Postnatal Murine Growth Plate

Active cell proliferation and turnover in the growth plate is essential for embryonic and postnatal bone growth. We performed a lineage tracing of Wnt/β-catenin signaling responsive cells (Wnt-responsive cells) using Axin2^CreERT2 ;Rosa26ZsGreen mice and found a novel cell population that resides in the outermost layer of the growth plate facing the Ranvier's groove (RG; the perichondrium adjacent to growth plate). These Wnt-responsive cells rapidly expanded and contributed to formation of the outer growth plate from the neonatal to the growing stage but stopped expanding at the young adult stage when bone longitudinal growth ceases. In addition, a second Wnt-responsive sporadic cell population was localized within the resting zone of the central part of the growth plate during the postnatal growth phase. While it induced ectopic chondrogenesis in the RG, ablation of β-catenin in the Wnt-responsive cells strongly inhibited expansion of their descendants toward the growth plate. These findings indicate that the Wnt-responsive cell population in the outermost layer of the growth plate is a unique cell source of chondroprogenitors involving lateral growth of the growth plate and suggest that Wnt/β-catenin signaling regulates function of skeletal progenitors in a site- and stage-specific manner. © 2019 American Society for Bone and Mineral Research.

Limb- and tendon-specific Adamtsl2 deletion identifies a role for ADAMTSL2 in tendon growth in a mouse model for geleophysic dysplasia

Geleophysic dysplasia is a rare, frequently lethal condition characterized by severe short stature with progressive joint contractures, cardiac, pulmonary, and skin anomalies. Geleophysic dysplasia results from dominant fibrillin-1 (FBN1) or recessive ADAMTSL2 mutations, suggesting a functional link between ADAMTSL2 and fibrillin microfibrils. Mice lacking ADAMTSL2 die at birth, which has precluded analysis of postnatal limb development and mechanisms underlying the skeletal anomalies of geleophysic dysplasia. Here, detailed expression analysis of Adamtsl2 using an intragenic lacZ reporter shows strong Adamtsl2 expression in limb tendons. Expression in developing and growing bones is present in regions that are destined to become articular cartilage but is absent in growth plate cartilage. Consistent with strong tendon expression, Adamtsl2 conditional deletion in limb mesenchyme using Prx1-Cre led to tendon anomalies, albeit with normal collagen fibrils, and distal limb shortening, providing a mouse model for geleophysic dysplasia. Unexpectedly, conditional Adamtsl2 deletion using Scx-Cre, a tendon-specific Cre-deleter strain, which does not delete in cartilage, also impaired skeletal growth. Recombinant ADAMTSL2 is shown here to colocalize with fibrillin microfibrils in vitro, and enhanced staining of fibrillin-1 microfibrils was observed in Prx1-Cre Adamtsl2 tendons. The findings show that ADAMTSL2 specifically regulates microfibril assembly in tendons and that proper microfibril composition in tendons is necessary for tendon growth. We speculate that reduced bone growth in geleophysic dysplasia may result from external tethering by short tendons rather than intrinsic growth plate anomalies. Taken together with previous work, we suggest that GD results from abnormal microfibril assembly in tissues, and that ADAMTSL2 may limit the assembly of fibrillin microfibrils.

Undernutrition and growth in the developing world

PURPOSE OF REVIEW

Despite targeted interventions, an estimated 150.8 million children under 5 years globally are still stunted, of which more than half live in Asia and more than one-third live in Africa. This review summarizes our current knowledge regarding how longitudinal bone growth is regulated by nutritional intake in the developing world. Dietary macronutrients and micronutrients necessary for growth are also briefly reviewed.

RECENT FINDINGS

Recent advances include investigations of nutritionally sensitive regulators of growth as well as prospective evaluations of the role of specific dietary components on growth in order to better assess their impact.

SUMMARY

Further investigation is required to understand how nutrition impacts growth, the mechanisms underlying stunting and to optimize therapeutic strategies for children who are at risk for growth attenuation or are stunted in low and middle-income countries (LMICs).

Retinoic Receptor Signaling Regulates Hypertrophic Chondrocyte-specific Gene Expression

BACKGROUND/AIM

Retinoid signaling is important for the maturation of growth-plate chondrocytes. The effect of retinoid receptor gamma (RARγ) signaling on the expression of genes in hypertrophic chondrocytes is unclear. This study investigated the role of RARγ signaling in regulation of hypertrophic chondrocyte-specific genes.

MATERIALS AND METHODS

The gene expression in mouse E17.5 tibial cartilage was examined by in situ hybridization analysis. Real-time reverse transcription-polymerase chain reaction (RT-PCR) and immunoblotting were used for analysis of mRNA and phosphorylated mitogen-activated protein kinase (MAPK).

RESULTS

mRNA expression of Rarg and connective tissue growth factor (Ccn2) was detected in maturing chondrocytes throughout the cartilaginous skeletal elements. In chondrogenic ATDC5 cells, an RARγ agonist induced the gene expression of type-X collagen (Col10A1), transglutaminase-2 (Tg2), matrix metalloproteinase-13 (Mmp13), and Ccn2 mRNA, whereas a retinoic acid pan-agonist suppressed RARγ agonist-stimulated gene expression. Phosphorylated extracellular signal regulated-kinases (pERK1/2), p-p38, and phosphorylated c-Jun N-terminal kinase (pJNK) MAPK were time-dependently increased by RARγ agonist treatment. Experimental p38 inhibition led to a severe drop in the RARγ agonist-stimulated expressions of Col10A1, Tg2, Mmp13, and Ccn2 mRNA.

CONCLUSION

RARγ signaling is required for the differentiation of hypertrophic chondrocytes, with differential cooperation with p38 MAPK.

Pathogenic gene screening in 91 Chinese patients with short stature of unknown etiology with a targeted next-generation sequencing panel

Background

Dwarfism is a common severe growth disorder, but the etiology is unclear in the majority of cases. Recombinant human growth hormone may be a treatment option, but it has limited efficacy. The currently known laboratory assays do not meet the precision requirements for clinical diagnosis. Here, we have constructed a targeted next-generation sequencing (NGS) panel of selected genes that are suspected to be associated with dwarfism for genetic screening.

Methods

Genetic screening of 91 children with short stature of unknown etiology was performed with the help of the NGS panel. All the coding regions and exon-intron boundaries of 166 genes were included in the panel. To clarify the pathogenicity of these mutations, their clinical data were reviewed and analyzed.

Results

The assay identified p.A72G, p.I282V, and p.P491S variants of the PTPN11 gene and a p.I437T variant of the SOS1 gene in 4 cases with Noonan syndrome. A frameshift mutation (p.D2407fs) of the ACAN gene was identified in a case of idiopathic short stature with moderately advanced bone age. A p.R904C variant of the COL2A1 gene was found in a patient, who was accordingly diagnosed with Stickler syndrome. Severe short stature without limb deformity was associated with a p.G11A variant of HOXD13. In addition, we evaluated evidence that a p.D401N variant of the COMP gene may cause multiple epiphyseal dysplasia.

Conclusions

Our findings suggest that syndromes, particularly Noonan syndrome, may be overlooked due to atypical clinical features. This gene panel has been verified to be effective for the rapid screening of genetic etiologies associated with short stature and for guiding precision medicine-based clinical management.

Transcriptomic characterization elucidates a signaling network that controls antler growth

Deer antlers are amazing appendages with the fastest growth rate among mammalian organs. Antler growth is driven by the growth center through a modified endochondral ossification process. Thus, identification of signaling pathways functioning in antler growth center would help us to uncover the underlying molecular mechanism of rapid antler growth. Furthermore, exploring and dissecting the molecular mechanism that regulates antler growth is extremely important and helpful for identifying methods to enhance long bone growth and treat cartilage- and bone-related diseases. In this study, we build a comprehensive intercellular signaling network in antler growth centers from both the slow growth stage and rapid growth stage using a state-of-art RNA-Seq approach. This network includes differentially expressed genes that regulate the activation of multiple signaling pathways, including the regulation of actin cytoskeleton, calcium signaling, and adherens junction. These signaling pathways coordinately control multiple biological processes, including chondrocyte proliferation and differentiation, matrix homeostasis, mechanobiology, and aging processes, during antler growth in a comprehensive and efficient manner. Therefore, our study provides novel insights into the molecular mechanisms regulating antler growth and provides valuable and powerful insight for medical research on therapeutic strategies targeting skeletal disorders and related cartilage and bone diseases.

Mapping molecular landmarks of human skeletal ontogeny and pluripotent stem cell-derived articular chondrocytes

Tissue-specific gene expression defines cellular identity and function, but knowledge of early human development is limited, hampering application of cell-based therapies. Here we profiled 5 distinct cell types at a single fetal stage, as well as chondrocytes at 4 stages in vivo and 2 stages during in vitro differentiation. Network analysis delineated five tissue-specific gene modules; these modules and chromatin state analysis defined broad similarities in gene expression during cartilage specification and maturation in vitro and in vivo, including early expression and progressive silencing of muscle- and bone-specific genes. Finally, ontogenetic analysis of freshly isolated and pluripotent stem cell-derived articular chondrocytes identified that integrin alpha 4 defines 2 subsets of functionally and molecularly distinct chondrocytes characterized by their gene expression, osteochondral potential in vitro and proliferative signature in vivo. These analyses provide new insight into human musculoskeletal development and provide an essential comparative resource for disease modeling and regenerative medicine.

Differential aging of growth plate cartilage underlies differences in bone length and thus helps determine skeletal proportions

Bones at different anatomical locations vary dramatically in size. For example, human femurs are 20-fold longer than the phalanges in the fingers and toes. The mechanisms responsible for these size differences are poorly understood. Bone elongation occurs at the growth plates and advances rapidly in early life but then progressively slows due to a developmental program termed “growth plate senescence.” This developmental program includes declines in cell proliferation and hypertrophy, depletion of cells in all growth plate zones, and extensive underlying changes in the expression of growth-regulating genes. Here, we show evidence that these functional, structural, and molecular senescent changes occur earlier in the growth plates of smaller bones (metacarpals, phalanges) than in the growth plates of larger bones (femurs, tibias) and that this differential aging contributes to the disparities in bone length. We also show evidence that the molecular mechanisms that underlie the differential aging between different bones involve modulation of critical paracrine regulatory pathways, including insulin-like growth factor (Igf), bone morphogenetic protein (Bmp), and Wingless and Int-1 (Wnt) signaling. Taken together, the findings reveal that the striking disparities in the lengths of different bones, which characterize normal mammalian skeletal proportions, is achieved in part by modulating the progression of growth plate senescence.

The various bones found in human extremities vary dramatically in size. For example, the femur in the thigh is approximately 20 times longer than the phalanges of the toes. The mechanisms that regulate how much a particular bone grows to attain the skeletal proportions of each animal remain mostly unknown. In this study, we sought to uncover these mechanisms and found that this scaling in skeletal size is achieved in part by modulating the rate of aging of growth plates in different bones. Bone elongation occurs at the cartilaginous growth plates and proceeds rapidly in early life but slows and eventually stops due to a developmental program termed “growth plate senescence,” which is used to describe the gradual decline in growth plate function with age. We discovered that this developmental program is more advanced in shorter bones than in longer bones and that this differential aging contributes to the disparities in bone growth. We show that the molecular mechanisms that underlie this differential aging between bones involve differential expression of specific local signaling pathways, which regulate cell proliferation and differentiation in the growth plate. Taken together, we conclude that the striking disparities in the lengths of different bones—characteristic of normal mammalian skeletal proportions—are achieved in part by modulating the progression of aging in the growth plates.

Mechano-growth factor protects against mechanical overload induced damage and promotes migration of growth plate chondrocytes through RhoA/YAP pathway

Epiphyseal growth plate is highly dynamic tissue which is controlled by a variety of endocrine, paracrine hormones, and by complex local signaling loops and mechanical loading. Mechano growth factor (MGF), the splice variant of the IGF-I gene, has been discovered to play important roles in tissue growth and repair. However, the effect of MGF on the growth plate remains unclear. In the present study, we found that MGF mRNA expression of growth plate chondrocytes was upregulated in response to mechanical stimuli. Treatment of MGF had no effect on growth plate chondrocytes proliferation and differentiation. But it could inhibit growth plate chondrocytes apoptosis and inflammation under mechanical overload. Moreover, both wound healing and transwell assay indicated that MGF could significantly enhance growth plate chondrocytes migration which was accompanied with YAP activation and nucleus translocation. Knockdown of YAP with YAP siRNA suppressed migration induced by MGF, indicating the essential role of YAP in MGF promoting growth plate chondrocytes migration. Furthermore, MGF promoted YAP activation through RhoA GTPase mediated cytoskeleton reorganization, RhoA inhibition using C3 toxin abrogated MGF induced YAP activation. Importantly, we found that MGF promoted focal adhesion(FA) formation and knockdown of YAP with YAP siRNA partially suppressed the activation of FA kinase, implying that YAP is associated with FA formation. In conclusion, MGF is an autocrine growth factor which is regulated by mechanical stimuli. MGF could not only protect growth plate chondrocytes against damage by mechanical overload, but also promote migration through activation of RhoA/YAP signaling axis. Most importantly, our findings indicate that MGF promote cell migration through YAP mediated FA formation to determine the FA-cytoskeleton remodeling.

Thyroid Hormone Signaling in the Development of the Endochondral Skeleton

Thyroid hormone (TH) is an established regulator of skeletal growth and maintenance both in clinical studies and in laboratory models. The clinical consequences of altered thyroid status on the skeleton during development and in adulthood are well known, and genetic mouse models in which elements of the TH signaling axis have been manipulated illuminate the mechanisms which underlie TH regulation of the skeleton. TH is involved in the regulation of the balance between proliferation and differentiation in several skeletal cell types including chondrocytes, osteoblasts, and osteoclasts. The effects of TH are mediated primarily via the thyroid hormone receptors (TRs) α and β, ligand-inducible nuclear receptors which act as transcription factors to regulate target gene expression. Both TRα and TRβ signaling are important for different stages of skeletal development. The molecular mechanisms of TH action in bone are complex and include interaction with a number of growth factor signaling pathways. This review provides an overview of the regulation and mechanisms of TH action in bone, focusing particularly on the role of TH in endochondral bone formation during postnatal growth.